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Nanocelluloses from jute fibers and their nanocomposites with natural rubber: Preparation and characterization
Accepted Manuscript Title: Nanocelluloses from jute fibres and their nanocomposites with natural rubber: preparation and characterisation Author: Martin George Thomas Eldho Abraham Jyotishkumar P L.A. Pothan Hanna J. Maria Sabu Thomas PII: DOI: Reference:
S0141-8130(15)00600-5 http://dx.doi.org/doi:10.1016/j.ijbiomac.2015.08.053 BIOMAC 5321
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
2-6-2015 21-8-2015 24-8-2015
Please cite this article as: M.G. Thomas, E. Abraham, J. P, L.A. Pothan, H.J. Maria, S. Thomas, Nanocelluloses from jute fibres and their nanocomposites with natural rubber: preparation and characterisation, International Journal of Biological Macromolecules (2015), http://dx.doi.org/10.1016/j.ijbiomac.2015.08.053 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract
Abstract: Nanocellulose fibres having an average diameter of 50 nm were isolated from raw jute fibres by steam explosion process. The isolation of nanocellulose from jute fibres by this extraction process is proved by SEM, XRD, FTIR, birefringence and TEM characterizations. This
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nanocellulose was used as the reinforcing agent in natural rubber (NR) latex along with cross linking agents to prepare crosslinked nanocomposite films. The effects of nanocellulose loading analysed.
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on the morphology and mechanics of the nanocomposites have been carefully
Significant improvements in the Young’s modulus and tensile strength of the nanocomposite
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were observed because of the reinforcing ability of the nanocellulose in the rubber matrix. A mechanism is suggested for the formation of the Zn-cellulose complex. The three dimensional
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network of cellulose nano fibers (cellulose/celullose net work and Zn/cellulose net work) in the
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te
d
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NR matrix plays a major role in improving the properties of the crosslinked nanocomposites.
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*Manuscript
Nanocelluloses from jute fibres and their nanocomposites with natural rubber: preparation and characterisation Martin George Thomas,1 Eldho Abraham 2,5,Jyotishkumar P1,L.A.Pothan2,Hanna J Maria3, Sabu Thomas* 3,4 1
Technology,Cochin University P.O, Cochin- 682 022, Kerala, India. 2
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Department of Polymer Science and Rubber Technology, Cochin Universiy of Science and
Research Department of Chemistry, CMS College, Kottayam-690 110, Kerala, India.
3
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International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi
University, Kottayam-686 560, Kerala, India. 4
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School of Chemical Sciences, Mahatma Gandhi University, Kottayam-686 560, Kerala, India.
5
R.H. Smith Institute of Plant Sciences and Genetics, Hebrew University of Jerusalem, Israel, 76100
M
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Corresponding email: [email protected] and [email protected]
Abstract:
Nanocellulose fibres having an average diameter of 50 nm were isolated from raw jute fibres
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by steam explosion process. The isolation of nanocellulose from jute fibres by this extraction process is proved by SEM, XRD, FTIR, birefringence and TEM characterizations. This
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nanocellulose was used as the reinforcing agent in natural rubber (NR) latex along with cross linking agents to prepare crosslinked nanocomposite films. The effects of nanocellulose loading on the morphology and mechanics of the nanocomposites have been carefully analysed. Significant improvements in the Young’s modulus and tensile strength of the nanocomposite were observed because of the reinforcing ability of the nanocellulose in the
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rubber matrix. A mechanism is suggested for the formation of the Zn-cellulose complex. The three dimensional network of cellulose nano fibers (cellulose/celullose net work and Zn/cellulose net work) in the NR matrix plays a major role in improving the properties of the crosslinked nanocomposites.
Key words: Bionanocomposites; fibre/matrix bond; natural rubber; nanocellulose; Zn/cellulose complex
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1. Introduction Natural fibers are composed of cellulose nanofibres which is the most abundant and renewable biomaterial on earth and is totally biodegradable. Natural fiber reinforced polymer composites have attracted substantial interest as a potential structural material as well as in
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other applications in the past decades. The attractive features of natural fibers like jute, sisal, coir, cotton, flax and banana are their low cost, light weight, high specific modulus, renewability and biodegradability. Out of these fibres, jute fibre is one of the major under-
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utilized agricultural raw materials which has a cellulose content with 70% of its dry weight. Its annual production is around 3000000 tons/year especially from the central part of Asia[1].
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Jute fibre can be planted in river flats, depressions, and saline-alkali soils, which are unavailable to plant cotton and most food corps, and no pesticides and fertilizer are needed
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during the growth of jute, so it is a kind of ‘‘pure green’’ agro-product. Due to its heterogeneity and crystallinity, however, direct utilization of the biomass is extremely low. Not more than 20 per cent of the jute husks is utilised in the jute industry, the remaining
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being used either as fuel in rural areas or underutilized. Production in the cooperative fold is not more than 20 to 25 per cent. Efforts are going on for exploring wider export markets for
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jute and jute products but still most of the raw jute fibre remained underutilized. Judged from the increase in production and employment, the progress has been rather slow and exports in
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physical terms have remained more or less static. In the present work, ultra fine nanocellulose from jute fibres have been prepared by steam explosion method. The extraction processes of the nanocellulose from natural sources are reported by various researchers [2-4]. The characteristics of nanocellulose depend on the origin of the fibers and the isolation conditions which must be adjusted depending on the substrate to be hydrolyzed. We have reported the
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isolation of the nanocelluloses from various sources by steam explosion technique [5]. The preparation of nanocellulose by this technique will give additional advantages over earlier ones by the yield and the isolation of the nanofibre as embedded in the raw fibre entity. The nanocellulose will then be used for the preparation of biodegradable nanocomposites with NR which is discussed in the later part of this paper. The studied nanocomposites are expected to have superior mechanical, electrical and dielectric properties as compared to their micro and macro counterparts. Production of ‘green composites’ based on raw materials derived from natural sources of plant or animal origin are of great interest both in the academic and industrial fields. In the
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past decades, research has been focused on the development of replacing reinforcing elements like carbon black, silica and glass fibres in polymer composites since they are potentially toxic. In the context of both biomass valorization and nanocomposite materials development, cellulose nanofibres (nanocellulose) used as filler in a green matrix appear to be an interesting reinforcing agent [6,7]. Green chemistry coupled with nanotechnology would be the much attracted area of research all over the world because of the environmental
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and technological concerns. When compared with glass fibers, silica and carbon black, nanocellulose as reinforcing filler in composites has many advantages. The combination of
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high surface area, high aspect ratio, environment benefits and low cost, as well as the exceptional mechanical properties, have made the nanocellulose attractive to use as a filler in
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bionanocomposite[8,9].Due to the high surface to volume ratio, green nanocomposites exhibit unique mechanical, electrical and thermal properties in addition to its environmental
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safety.
Nanocelluloses have been incorporated as reinforcing fillers into a wide range of polymer matrixes [10,11] including segmented polyurethanes [12] due to their appealing intrinsic
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properties. Being a bio-based polymer, the use of bio-nano reinforcements in NR is beneficial in the development of biobased green nanocomposites. Furthermore, most of the bio-based
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nano reinforcements are usually available as liquid suspensions to retain their dimensional stability as in the case of the aqueous suspension of nanocellulose. Hence, the blending of the nanocellulose and NR latex both in aqueous suspension provides a viable route to disperse
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nano reinforcements in the latex matrix. NR-based nanocomposites with bio-based nano reinforcements like chitin whiskers, starch nanocrystals, cellulose whiskers extracted from Syngonanthus nitens (Capim Dourado), rachis of palm tree, sisal and bagasse are reported in the literature [13-15]. When compared with platelet like morphology of nanocrystals
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extracted from other sources like starch and potato, nanocelluloses present the originality to have a rod like morphology having very high aspect ratio which gives exceptional characteristics to the nanofibres [3,4]. Furthermore, it can be seen that most of these studies use latex blending technique without vulcanization, for the bionanocomposite preparation. Our group already reported on the nanocomposites of NR reinforced by nanocellulose which is extracted from banana fibres[16]. Nanocomposite materials of natural rubber filled with cellulose fibres were reported by earlier researchers [8,29]. Here we are reporting the effective utilization of jute fibres by isolating the nanocellulose and finding application of this nanocellulose in NR latex matrix for the preparation of bionanocomposites. More over the crosslinking agents like Zinc dithiocarbomate (ZDC), Zinc mercapto benzothiozole 3 Page 4 of 41
(ZMBT), Zinc oxide (ZnO) and sulfur were used during the processing stage to improve the mechanical properties.
2. Materials and methods 2.1.
Materials
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Raw jute fibres for the nanocellulose extraction were obtained from YMCA Marthandom, Tamil Nadu, India. Centrifuged latex of natural rubber was kindly supplied by Rubber Board, Kottayam, Kerala, India. It contained spherical rubber particles with a dry rubber content
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(DRC) of 60% and it contains more than 98% of cis-1,4-polyisoprene. The various chemicals used for extraction of fibre and the preparation of nanocellulose and nanocomposite are
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NaOH, acetic acid, NaClO2, oxalic acid, sulfur, zinc dithiocarbamate (ZDC), zinc mercaptobenzothiozole (ZMBT), zinc oxide (ZnO), KOH etc. and all are from Nice
Experimental steps for the isolation of nanocellulose from raw jute fibres
2.2.1 Alkali treatment of the fibre
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2.2.
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Chemicals, Cochin, India. All reagents used were of analytical grade.
The jute bast fibres were cut it into pieces and subjected for alkali treatment by soaking it in
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2% caustic soda for 2 hours at room temperature. 2.2.2 Alkali treatment followed by steam explosion
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Steam explosion technique was applied on the alkali treated jute fibre for one hour. Steam pre-treatment was performed by loading the alkali soaked jute fibre directly into the steam gun and treating it with high pressure steam (20 lbs) at temperatures within 100 to 150oC for 2 hours followed by sudden release of pressure. 2.2.3 Sodium chlorite bleaching of the steam exploded fibre
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After the successive alkali followed by steam treatments, the bleaching treatment with sodium chlorite (NaClO2) solution (pH 2.3) for 1 h at 50oC was performed to remove the remaining lignin. In the bleaching step, the absence of elemental chlorine is accomplished by using NaClO2 as the bleaching agent. The bleached fibres were pure white in color. 2.2.4 Oxalic acid treatment followed by steam explosion The bleached fibre was subjected to mild acid hydrolysis by treating it with 5% oxalic acid. The second step of steam explosion for one hour was carried out after the acid treatment. The fibres were then centrifuged repeatedly with water and then subjected to mechanical stirring
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followed by sonication. The pH of the nanocellulose were neutralised with 0.1% NaOH solution. 2.3
Nanocomposite preparation
The extracted nanocellulose was mixed with the NR latex along with other cross linking components as described in the Table 1 formulation. The composite films were prepared from prevulcanised latex by casting on a glass plate followed by drying at ambient temperature.
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The prevulcanization of the compounded latex was conducted at 70oC for 2 h using water bath with constant gentle stirring. The sample numbers 0, 1, 2 and 3 indicate the weight
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[ Table 1 here]
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percentage of nanocellulose used.
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The aqueous suspension of the various proportions of nanocellulose, latex and the crosslinking agents were mixed by ball milling followed by ultra sonication. The ball milling process was conducted for two hours in water medium with ceramic balls (1.5 cm diameter)
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in stainless steel container (1 lit). The speed of the mill was 300 rotations per minute. It is then subjected to ultra-sonication for 10 minutes in 50% amplitude with an ice bath
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temperature. The mixed aqueous suspension of the nanocomposites poured in to glass plates and dried for 24 hours at oven with a temperature of 50-60oC in order to obtain dry films of 1 mm to 2 mm thick depending on the test and with weight fractions of nanocellulose within
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the NR matrix ranging from 0 to 3 wt %. Resulting films were conditioned at room temperature in desiccators containing phosphorous pentoxide (P2O5) until tested. 2.4 Scanning electron microscopy (SEM) SEM analysis of the fibres were done by an Analytical Scanning electron microscope (A-
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SEM), ZEISS EVO 60. The microscope works with tungsten filament and maximum acceleration voltage of 20 kV. The samples were mounted on aluminium stabs and goldcoated with a sputter coater. 2.5 Transmission electron microscopy (TEM) The size of the nanocellulose fibres and their distribution and dispersion in NR matrix were characterized by transmission electron microscopy (TEM) with a CM 12 PHILIPS HRTEM. For the evaluation of the dispersion of nanofibres on the dried NR matrix, cryo cutting method was adopted. The cryo cutting of the nanocomposites were done by a thin section of about 100 nm was cut with a diamond knife at -100oC (Tg of NR is ~ -73OC) to observe the dispersion of nanocellulose inside the rubber matrix. 5 Page 6 of 41
2.6 Fourier transforms infrared spectroscopy (FTIR) Fourier Transform- Infra Red spectroscopy (FTIR) spectra of the fibers were recorded by a Shimadzu IR-470 IR spectrophotometer. 2.7. X-ray diffraction analysis (XRD) X-ray diffraction of the fibres and the nanocomposites were performed using a Bruker AXS X-ray diffractometer equipped with a filtered Cu-Kα radiation source (λ = 0.1542 nm) at the
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operating voltage and current of 45 kV and 40 mA, respectively and a 2D detector. 2.8. Mechanical testing
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Tests for measuring the tensile strength were carried out according to ASTM designation D 412-98 using dumb-bell specimens. Rate of separation of power-actuated grip was 500
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mm/min, which was maintained throughout the experiment. Averages of three samples were tested for a particular composition.
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2.9. Thermo gravimetric analysis (TGA)
TGA was carried out on a TGA Q50 (TA Instruments, DE, U.S.A.) following the ASTM D3850-94 standard. An approximate 10- 20 mg of the specimen was loaded in the open
constant heating rates of 10°C/min.
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3. Results and discussion
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platinum pan. The samples were heated from 25 to 500°C under nitrogen atmosphere at
3.1 Extraction of nanocellulose from jute fibres
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3.1.1. Morphological analysis by SEM and TEM Raw jute fibre contains about 70 wt% of cellulose and 15 and 10 wt% of hemicellulose and lignin components, respectively. The Fig. 1 represents the SEM of jute fibres at different processing stages (Fig. 1 (A) raw jute fibre, (B) alkali treated fibre, (C) bleached fibre and
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(D) acid hydrolysed fibre). It was possible to verify the presence of lignin and hemicellulose using SEM images of the raw and alkali treated fibres. It is worth noting that the washing out and dissolving of lignin and hemicellulose starts at the alkali treatment (2% NaOH) and its complete removal was possible at the bleaching stage. The alkali treatment allows the exposure of the raw fibres and the inner parts of the fibers were exposed to chemicals by the steam explosion process. During the chemical treatment (alkalization) most of the lignin and hemicellulose were removed. Mechanical treatment (steam explosion) further removed the amorphous materials (lignin, hemicellulose etc) from the inner part of the fibre via depolymerisation and defibrillation. Scanning electron micrographs show changes in the morphology of the fibers in terms of size and level of smoothnes after acid hydrolysis. Lignin 6 Page 7 of 41
is rapidly oxidized by chlorine. Lignin oxidation leads to lignin degradation and leads to the formation of hydroxyl, carbonyl and carboxylic groups, which facilitate the lignin solubilization in an alkaline medium. Thus cellulose macrofibrils of the original fibres were separated from each other to produce microfibrils with diameters around 5–30 µm, Fig.1 (C). Acid coupled steam treatment after bleaching process helps to disintegrate the fibrils further. Fig. 1 (D) shows the SEM photographs of the individualized nanofibrils after acid treatment.
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It can be seen from the SEM that the size of the jute fibre is reduced from 5-30 μm to about 50 nm. Thus acid coupled steam explosion helps in defibrillating the fibre diameter to nano
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range.
The analysis of the final nanocellulose by TEM is also carried out and is shown in Fig. 2. It
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also supports the evidence for the isolation of individual nanofibres of jute fibres by steam explosion process coupled with mild alkali and acid treatment. The average size of the
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individual nanocellulose fibres are in the range of 50 nm diameters with a length of few micrometers. Aspect ratio of the extracted cellulose nanofibres were estimated from transmission electron micrographs. The aspect ratio (fibril length to the diameter ratio) is one
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of the most important parameters in determining reinforcing capability of the nanofibres for composite application. From the visible portion of the TEM with statistical analysis it is
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calculated that the aspect ratio falls in the range of 100nm.
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[Fig.1: here]
[Fig. 2 here]
3.1.2. Fourier Transform Infrared (FTIR) Analysis
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To investigate the structural changes on the jute fibres during the alkali treatment, steam explosion, bleaching and the acid hydrolysis; FT-IR spectroscopy was used. FTIR spectra of the untreated, steam exploded, bleached and acid hydrolysed jute cellulose fibres are shown in Fig. 3. The raw jute sample gives a very low intensity absorbance at 3330 and 1630 cm -1. These peaks are responsible for the OH-bending and OH-stretching frequencies respectively. In the raw fibre, the hydroxyl groups are bound by other cementing materials like lignin, waxes and hemicelluloses and hence its peaks are not exposed in the FTIR spectrum. The absorption band located at 2895 cm−1 is related to CH2 groups [5,] and its intensity increased with treatments. The percentage of the pure cellulose is increased with various treatments thereby increasing the intensity of the CH2- group in the β-glucosides rings of the cellulose 7 Page 8 of 41
molecules. The absorption band at 1725cm−1 is associated with the aromatic ring vibration due to the presence of lignin and acetyl or uronic ester groups of hemicelluloses normally appear in the region 1700–1740cm−1 [17]. The absence of this corresponding peak in the bleached and acid hydrolysed fibres indicates the complete removal of lignin [5,17] and hemicelluloses by the various processing steps. But two strong absorption bands at 3320 and 1631 cm−1 of bleached and acid hydrolysed jute fibres indicate that the hydroxyl groups of
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the cellulose molecules are exposed and it absorbs water from the moisture through hydrogen bonding [18]. The absorption band at 1163cm−1 corresponds to C-O-C stretching, and the
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peak at 896cm−1 is associated with the C-H rock vibration of cellulose (anomeric vibration, specific for β-glucosides). These peaks show an increasing tendency with treatments and
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steam explosion indicating the removal of tightly bound cementing materials and exposure of the pure cellulosic fibres. Similar results have been observed by Jahan et al.[19] during
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production of MCC from jute fibers and Fahma et al.[20] when isolating nanofibers from oil palm fruit bunch. Thus the alkali treatment coupled with steam explosion followed by
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bleaching removes the lignin, hemicelluloses and other cementing materials.
[Fig. 3 here]
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From the FTIR analysis it has been concluded that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peak at 1725 cm-1and 1250 cm-1. These peaks are chiefly
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responsible for the hemicellulose and lignin components. These characteristic peaks are completely absent in the final bleached cellulose fibre. The increase in the intensity of the peaks at 3320 cm-1 and 1631 cm-1 of final bleached fibre is responsible for the increased
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(free) cellulose content.
3.1.3. X-ray diffraction (XRD) analysis The crystallinity of untreated jute fibres, alkaline treated followed by steam exploded jute, bleached and acid hydrolysed jute fibres has been analyzed by X-ray diffractometry. It can be noted from Fig. 4 that the fibres show increasing orientation along a particular axis as the amorphous zones are dissolved. The gradual removal of non-crystalline materials especially lignin and the hemicelluloses changed the nature of
fiber to more crystalline which is
confirmed from the XRD (Fig 4) , where the intensity of crystalline peaks were found to be increased for the treated fibers. These changes during each processing stages is due to the removal of these noncrystalline materials resulting in the loss of the disordered regions [21]. 8 Page 9 of 41
[Fig. 4 here]
From the X-ray diffraction patterns (Fig 4) the percent crystallinity of the raw jute, steam exploded jute, bleached jute and acid hydrolysed jute was calculated using the equation given below [22,23 ] X a = Ia / (Ic + Ia)…………………… (3)
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Xc = Ic / (Ic + Ia)……………………(2) where Ic and Ia represent the integrated intensities corresponding to the crystalline and
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amorphous phases, respectively, i.e. the areas under the respective curves. The percentage
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[Table 2 here].
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crystallinity values Xc and amorphous portion value Xa are given in Table 2.
The changes in crystallinity is due to the removal of water soluble hemicelluloses and alkali
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soluble lignin as lignin chlorides in the NaOCl2 bleaching step.
It can also be found that the XRD pattern of all the jute fibres exhibits a sharp high peak at ◦
◦
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2θ=23.2 , and a weaker diffraction peak at 2θ=15.3 which are assigned to cellulose I. The mild alkali treatment (2%) is not able to make a lattice transformation from cellulose I to
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cellulose II which is clear from all the diffraction patterns. In most lignified plant cells lignin and hemicellulose are deposited between the micro fibrils to give an interrupted lamellar structure and without the removal of these noncellulosic components, the cellulose I to cellulose II transformation will be restricted. With the treatment of NaOH and bleaching agents, the lignin is removed and in this case also the degree of crystallinity goes on
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increasing. This may be due to the removal of lignin which acts as a cementing material and on delignification, an ordered arrangement of the crystalline cellulose in the structure takes place. SEM given in Fig.1 shows individualized and uniform fibers, which correlates with the spectroscopic evidence for the removal of cementing material around the fiber bundles; namely hemicelluloses, and lignin. The high crystalline jute nanocellulose fibres could be more effective in providing better reinforcement for rubber composite materials because of its high Young’s modulus (138GPa) of the crystalline regions along the longitudinal direction.
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3.1.4. Birefringence analysis Optical surface morphology and the birefringence properties of jute nanocelluloses were investigated. Birefringence was used to confirm the presence of isolated nanocrystals in an aqueous paste. It can also be used as a good dispersibility criterion in suspension [24]. This birefringence results originated from the structural anisotropy of the nanocellulose and the
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flow anisotropy resulting from the alignment of the nanocrystals under flow, generally operated before observation. Aqueous nanocellulose films with 4% cellulose fibre viewed
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[Fig. 5 here]
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through crossed polarizers to note the birefringence of the crystalline nanocellulose.
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Fig. 5 shows the size of the crystalline nanocellulose, by birefringence under crossed polarizers. The nanofibres were sonicated for 20-30 minutes and therefore the nanocelluloses lost its fibrous nature and turned to crystalline character in this process and possesed some
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liquid crystalline properties. Without proper sonication the nanocelluloses are in fibrous state and are unable to give any birefringence. The sonication of the nanocellulose changed their
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fibre property to a liquid crystalline in nature. The nanocellulose film presented smooth surface and dark view with crystalline reflection under cross polarization. After sonication a well-dispersed birefringence occurred (Fig. 5), exhibiting colour spots for the formation of
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crystal domains. These results indicated that the sonicated suspensions exhibited strong shear birefringence, highlighting the ability of the crystalline nanocellulose to form a chiral nematic liquid crystalline phase in equilibrium with the isotropic phase. The birefringence of the aqueous nanocrystals proved their good dispersion in water suggesting that the suspension
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contained a large number of single cellulose crystals, highlighting the success of the proposed isolation process.
3.2. Characterisation of NR/ jute nanocellulose composite 3.2.1. Morphological analysis by TEM The morphology of NR/nanocellulose materials and the distribution level of the filler within the matrix were evaluated by observing the cryo-cut TEM images of the nanocomposites. Fig. 6 shows the cryo-cut TEM of the inner part of the NR/nanocellulose composite; (A) neat matrix, (B) 1% nanocomposite, (C) 2% nanocomposite and (D) 3% nanocomposite. By comparing with the micrographs showing the cryo-cut surface of the nanocomposites, it is 10 Page 11 of 41
easy to identify the contribution from the filler. Jute nanocellulose appears are dispersed in a homogenous nanolevel and the cloudiness of the filler particles increases with its concentration. The TEM of the neat NR gives a clear appearance showing the absence of fillers. We can observe that the distribution of the filler among the matrix is homogeneous for all the compositions. While in 2% loading a network formation could be observed. At 2% nanofiber loading, nanoscopic fibers make a network by H-bonding interaction as reported
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previously by Dufrense et al [25-28] and Cintil et al [29]. This could be understood from TEM micrograph. In all scientific literature related nanocelullose composites, the network
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formation of nanofibers has been well documented. This can be explained to be due to the interaction between nanofibers through H-bonding. This network structure of the nanofibers
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restricts the mobility of polymer chains trapped between the nano fiber network. These immoblised polymers chains contribute to the high mechanical properties of the
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nanocomposites.
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[Fig. 6 here]
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The black spots in the TEM of the nanocomposites can be due to the unreacted crosslinking agents [30,31]. It is not possible to see the individual nanocelluloses even though the scales are in 200 nm which proves the nanomeric homogenous dispersion of filler. Furthermore, our
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group already reported about the existence of Zn/cellulose complex in NR/nanocellulose crosslinked composite system [32]. The vulcanising agents used for the crosslinking of the NR matrix play a major role in the formation of this Zn/cellulose complex. This complex formation also helps for the better dispersion of
the nano fibers in the NR matrix.
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Furthermore, no particular sedimentation phenomenon of nanocellulose within the thickness of the films was observed.
3.2.2. X-ray diffraction analysis (XRD) XRD analysis of the nanocomposites was also carried out in order to verify the crystalline nature of the nanocellulose after the reinforcement and to know the dispersion of nanocellulose in NR matrix (Fig. 7). The diffractograms of unfilled NR and reinforced nanocellulose were added as references. The diffraction pattern recorded for a film of nanocellulose displays typical peaks of A-type amylose allomorph of cellulose I crystalline form [33]. It is characterized by a strong peak at 2θ = 17.9° and a very strong peak at 25.07°. 11 Page 12 of 41
The natural rubber film displays a typical behavior of an amorphous polymer. It is characterized by a broad hump located around 2θ = 19°.
[Fig. 7 here]
It is interesting to note that none of the X-ray diffraction pattern of the studied
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nanocomposites gives additional peak for the presence of crystalline nanocellulose in the NR matrix. The peaks corresponding to the A-type amylose allomorph of the reinforced
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nanocellulose is completely absent in whole of the studied NR composites which is unexpected. NR is amorphous in nature if it is not stretched. Another interesting observation
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is the decrease in the intensity of the broad hump peak of the NR with increasing nanocellulose content. This reduction in the intensity of the corresponding broad hump peak
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of nanocomposites gives clear evidence about the formation of the Zn/cellulose network in between the layers of NR matrix. This in turn increases the interlayer distances between the rubber molecules and the diffraction rays travels a longer path than the pure NR matrix. Thus,
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the nanocellulose diffraction signals at 17.9° and 25.07◦ are masked by the NR matrix because of the nanomeric dispersion of nanocellulose in between the layers of NR which
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leads to the formation of Zn/cellulose network. It is reported that cellulose and starch nanocrystals grafted with PCL by ring opening polymerization present similar behavior and no signal of nanoparticle crystals was detected due to the high crystallinity of PCL [34, 35].
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The filler and the crosslinking agents were added together during the vulcanizing step and the sulfur molecules will facilitate the breaking of the double bonds of the NR back bone by entering in between the chains of natural rubber and make new bonds with each other. The entering of sulfur molecule in between the chains of NR makes more room to accommodate
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the nanocellulose in between the layers of NR latex. The filler and the crosslinking agents enter in between the molecular chains of natural rubber and makes new bond with each other. The breaking of the double bond in the natural rubber backbone makes two active sites and a cross linking network between sulfur and natural rubber. In addition to that cross linking network, cellulose molecules will make a complex with zinc metal which is clearly discussed and reported in our earlier work [24]. This complex formation will lead to the loss of crystallinity of the cross linked nanocomposites. In summary, the absence of crystalline peak in the nanocomposite could
due to the formation of Zn-cellulose complex. However,
possible dilution effect (very low content of nanocelulose in the NR matrix) can not be negleted. 12 Page 13 of 41
3.2.3. Mechanical properties of the nanocomposites The tensile properties of NR nanocomposites at room temperature with different nanocellulose loading are shown in Fig. 8. Stress vs. strain curves show that the nanocomposites present higher initial modulus and better tensile strengths than NR. The addition of the filler is expected to increase the modulus of composites that results from the
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inclusion of rigid crystalline filler particles into the rubber matrix [36,37]. When crystalline nanocellulose is reinforced with amorphous matrix, crystallization of composite surface
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probably dominates over its bulk nature, giving higher modulus to the resulting composites. The modulus of elasticity of the nanocomposite is increased steadily with the addition of
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nanofibres and improved from 1.3 MPa to 3.8 MPa with the increase in nanocellulose content from 0 to 3 wt.%. Vulcanized NR inherently possesses good strength because of strain-
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induced crystallization. The strain-induced crystallization of NR is not affected by the addition of nanocellulose fibres, as is evident from the increase in stress above 400% strain. The increased tensile strength and modulus observed with increasing nanocellulose content is
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attributed to the possible restriction of polymer chain mobility in the vicinity of crosslinked Zn/cellulose and cellulose-cellulose three dimensional network. Despite the moderate
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increase in tensile strength and modulus, the behavior of the stress- strain curve is not changed by the addition of nanocellulose indicating that the effect due to crosslinking of NR predominates over the reinforcing effect of nanofibres. An increase in the nanocellulose
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content decreases the micro spaces between the nanofibre and the matrix and thereby decreasing the extent of Zn/cellulose network, which will also strengthen the filler–matrix interfacial adhesion. The specific surface area of the filler in contact with the matrix is also increased. As a result, the values of tensile strength show an increasing trend with increasing
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nanofibre content in the composite.
[Fig. 8 here]
[Table 3 here] Siqueira et al. [38] as well as Bras et al.[39] have reported tensile strength and modulus in the range of 0.5 MPa for NR matrix phase. The higher tensile strength and the modulus of the matrix material in the current paper are due to the vulcanization (crosslinking) of NR as well as the processing method used.The crosslink density values were calculated using equation (1) and is shown in Table 3. 13 Page 14 of 41
Cx= E/6RT ………….(1) Where Cx is the crosslink density (moles per unit volume), R = molar gas constant = 8.31 J.mol-1.K-1,T is the absolute temperature and E is the Young’s modulus.With the increase of nanocellulose loading the crosslink density is found to be increasing.This is associated with the filler (nanocellulose)-polymer interactions. Furthermore, studies on
ip t
vulcanized NR based clay nanocomposites prepared by latex blending and melt compounding showed limited improvement in properties compared to the matrix material [40,41] which
cr
suggest that the percentage improvement in mechanical properties with the addition of nano
us
reinforcements depend significantly on the properties of the matrix.
The presence of hydroxyl groups in the nanocellulose is responsible for its inherent hydrophilic nature.The network formation by the nanocellulose in the NR matrix gives rise to
an
good mechanical properties to the sytem (Table 3). Of the three hydroxyl groups present in cellulose, a hydroglucose unit, one is primary hydroxyl group at C6, while the other two are
M
secondary hydroxyl groups at C2 and C3 positions. A three dimensional network of Zn/cellulose and cellulose/cellulose is formed within the composite entity and these hydroxyl groups have a major contribution in the formation of this network. Due to this three
ed
dimensional network, the interfacial bonding and mechanical interlocking between the nanofibre and matrix is increased dramatically in the resultant composite.Infact the natural
ce pt
rubber chains are immobilized by the netwok.(Fig .6E) This in turn increases the tensile strength and modulus of the composites at all mixing ratios compared to that of neat NR (Table 3).. The enhanced interfacial bonding will increase stress transfer efficiency from the matrix to the filler with a consequent improvement in the mechanical properties of the
Ac
composites. Elongation at break of the nanocomposites decreased gradually with increase in nanocellulose content and this was an expected behavior because of the immobilization of the polymer chains by the net work.
The percentage of elongation for the neat NR film
percentage is 884% but is 415% in nanocomposites with a 3 wt.% nanocellulose. Thus the incorporation of fibre into the polymer matrix reduces the matrix mobility, resulting in stiffness of the composite. As a result, Young’s modulus increased with increasing the filler content of the composites and the percentage of the elongation is regularly decreased with increasing the cellulose content. Overall, rubber-rubber, rubber-cellulose, cellulose / cellulose and NR/Zn/cellulose interactions together make the nanocomposites with good mechanical properties. 14 Page 15 of 41
3.2.4. Thermogravimetric analysis (TGA) of the nanocomposites The thermal degradation of the NR nanocomposites has been investigated by TGA in terms of percentage weight loss with temperature. Fig. 9 is the TGA curves of the nanocellulose, NR and their nanocomposites. The nanocellulose shows a peak at 60oC for the evaporation of water. The other main degradation concentrated in between 250-400oC and is related to the
ip t
pyrolysis of the cellulose components. The initial thermal stability of nanocellulose is much lower than that of NR however, their residual char is ~10 wt. % which is thrice the value of
cr
NR and its composites (~3 wt. %). In filled composite system, the decomposition mechanism is rather complex because of the homogenous distribution of fillers into latex phase and due
us
to the presence of Zn/cellulose complex network. At higher filler percentage, the composite systems are not homogenous because of the agglomeration and also due to the difference in
an
polarity of individual components.
Interesting observation is the increased thermal stability of the nanocomposites with lower filler content. It can be seen from the Fig. 9 that the decomposition temperature of 1%
M
nanocomposite is slightly higher than the pristine NR matrix and then it is shifted to lower temperature with increasing the nanocellulose percentage. Thermal stability of the
ed
nanocomposites shows a reduced value except for 1% composite. At lower filler percentage the Zn/cellulose complex and the percolation network plays for
the increased thermal
stability even though the nanocellulose possess lower thermal characteristics. The decreased
ce pt
thermal stability at higher filler percentage is due to the critical volume fraction and the percolation threshold value in addition to the agglomeration of the fillers at higher concentration. The agglomeration of fillers in NR latex is further clear from the TEM shown in Fig. 6. The degradation temperature of the nanocellulose is comparatively lower than NR
Ac
matrix which also causes the reduced thermal stability at higher filler percentage. The high surface polarity of nanocellulose due to hydroxyl groups lead to the agglomeration of filler particles at higher weight percentage. Moreover the presence of oxygen in the cellulose backbone and its side chain will make favorable atmosphere for the early thermal degradation of the nanocomposite. With increasing the percentage of the nanocellulose, the tendency of the rubber particles to create active centers for interaction with filler is diminishing because of the greater filler-filler interaction. Moreover, the existence of only one degradation step in the composite again confirmed the uniformity of the system and proves the existence of the interconnected three dimensional network of NR-nanocellulose complex. The thermal degradation results for the neat matrix show that the main degradation will be the degradation 15 Page 16 of 41
of isoprene units (~368oC). In other words, in the composite degradation, the absence of peaks at lower temperatures can be attributed to the presence of homogenous three dimensional Zn/cellulose complex networks. We can summarize the whole degradation of the composite in two step process. In the first stage of the degradation, the deterioration of polymer chain and the cross linking network into simple products and in the second stage of the decomposition the volatilization of the products formed in the first step. With increased
ip t
filler percentage, the residual char increased in proportion to its nanocellulose content which has a higher residual char than the NR. When comparing with the thermal stability of the
cr
nanocellulose and NR matrix, we can conclude that the thermal stability can be improved to some extent at the lower filler percentage. We have a substantial improvement by
us
incorporating nanocellulose in the natural rubber matrix. Even though the thermal degradation of cellulose starts at 327oC, its degradation in the composite (when it is
an
reinforced in the NR matrix) will start at ~360oC. Thus the use temperature range of nanocellulose can be improved by reinforcing the nanocellulose in the natural rubber matrix.
4.
M
[Fig. 9 here]
Conclusions
ed
Steam explosion combined with acid hydrolysis has been found to be successful in obtaining fibres in the nano dimension from jute fibres. A homogenous nanocellulose fibrils with a
ce pt
average diameter of 50 nm is obtained by this process. Nanocomposite materials were obtained by casting and evaporating a mixture of NR latex and aqueous suspension of cellulose nanofibrils which is obtained from jute fibre by steam explosion. The filler was evenly distributed in the composite structure which is evident from their TEM and XRD analysis.. The increase of nanocellulose content in the NR matrix causes a drastic increase in
Ac
the mechanical properties of the composite. The Young’s modulus and tensile strength of material increased, but elongation at break decreased.The increased mechanical performance is due to the network formation by the nanocellulose in the NR matrix.The composite also shared good thermal properties. Finally it is important to add that nanocellulose obtained from jute is a good candidate as reinforcement for NR type nanocomposites.
16 Page 17 of 41
References: [1]. K.G. Satyanarayana,.G.G.C. Arizaga, and F. Wypych, Biodegradable composites based
ip t
on lignocellulosic fibers—An overview Prog. Polym. Sci. 34,(2009) 982–1021 [2]H. Kargarzadeh Á I. Ahmad (&) Á I. Abdullah Á. S. Y. Zainudin, Effects of hydrolysis
extracted from kenaf bastfibers,Cellulose 19, (2012) 855–866.
cr
conditions on the morphology, crystallinity, and thermal stability of cellulose nanocrystals
us
[3]. J.L. Putaux, S. Molina-Boisseau, T. Momaur, and A. Dufresne, Platelet nanocrystals resulting from the disruption of waxy maize starch granules by acid hydrolysis
an
Biomacromolecules,45 (2003), 1198-1202,
[4].Y Habibi, LA Lucia, OJ Rojas, Cellulose nanocrystals: chemistry, self-assembly, and
M
applications Chem Rev.,110 (2010),: 3479–3500
[5].E. Abraham, B. Deepa, L.A. Pothen, J. Cintil, S. Thomas, M.J. John, R. Anandjiwala, S.S. Narine, Carbohyd. Polym.92 (2013), 1477.
ed
[6]. H. Angellier, J.L. Putaux, S. Molina-Boisseau, D. Dupeyre, and A. Dufresne, Starch Nanocrystal Fillers in an Acrylic Polymer Matrix Macromol Symp., 221 (2005) 95-104
ce pt
[7]. H.P.S. Abdul Khalil, A.H. Bhat, A.F. Ireana Yusra, Green composites from sustainable cellulose nanofibrils Carbohyd. Polym.. 87(2012) 963-979 [8].
G. Siqueira, J. Bras, A. Dufresne, Cellulosic bionanocomposites: a review of
preparation, properties and applications. Polymers 2 (2010) 728-765.
Ac
[9]. S. S. Ray, Polylactide-based bionanocomposites: a promising class of hybrid materials Chem Res 45 (2012) 1710-1720 [10]. S. A. Paralikar, J. Simonsen, and J. Lombardi, Poly(vinyl alcohol)/cellulose nanocrystal barrier membranes J Membrane Sci.,320 (2008) 248-258
17 Page 18 of 41
[11]. M.A.S. Azizi Samir, F. Alloin, J.Y. Sanchez, and A. Dufresne, Cellulose nanocrystals reinforced poly(oxyethylene) Polymer 45 (2004) 4149-4157 [12]. M. Floros, L Hojabri, E Abraham, J Jose, S Thomas, L Pothan, AL Leao, S Narine, Enhancement of thermal stability, strength and extensibility of lipid-based polyurethanes with cellulose-based nanofibers Polym. Degrad. Stab.97 (2012) 1970–1978
NR-based nanocomposite Appl Polym Sci., 119(2): (2011) 855–62
ip t
[13]. S. Khanlari, M. Kokabi, J Thermal stability, aging properties, and flame resistance of
cr
[14]. K. G. Nair and A. Dufresne, Crab shells chitin whiskers reinforced natural rubber
us
nanocomposites Biomacromolecules 4 (2003) 666–74
[15]. H. Angellier, S. Molina-Boisseau, L. Lebrun and A. Dufresne, and structural properties of waxy maize starch nanocrystals reinforced natural rubber. Macromolecules 38 (2005)
an
3783–91
[16]. E. Abraham, B. Deepa, L.A. Pothan, M. Jacob, S. Thomas, R. Anandjiwala and. S.S.
M
Narine, Physico-mechanical properties of green nanocomposites based on cellulose nanofibre and natural rubber latex. Cellulose. 20 (2013) 417-427
ed
[17]. M. Nuruddin,, A. Chowdhury,, S. A. Haque, M. Rahman,, S. F. Farhad,, M. Sarwar Jahan, et al, Extraction and characterization of cellulose microfibrils from agricultural wastes
ce pt
in an integrated biorefinery initiative. Cell. Chem. Technol. 45 (2011).347–354. [18]. S. Ifuku, M. Nogi, K. Abe, M. Yoshioka, M. Morimoto, H. Saimoto and H. Yano, Synthesis of silver nanoparticles templated by TEMPO-mediated oxidized bacterial cellulose nanofibers Biomacromolecules, 10(9), (2009) 2714–2717.
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[19]. M. S. Jahan, A. Saeed, Z. He, and Y. Ni, Jute as raw material for the preparation of microcrystalline cellulose Cellulose, 18 (2011).451–459. [20]. F. Fahma, S. Iwamoto, N. Hori, T. Iwata, and A. Takemura, Isolation, preparation, and characterization of nanofibers from oil palm empty-fruit-bunch (OPEFB) Cellulose,17 (2010). 977–985. [21] T. Saito,, & A Isogai, TEMPO-mediated oxidation of native cellulose: The effect of oxidation conditions on chemical and crystal structures of the water insoluble fractions Biomacromolecules, 5(5) (2004). 1983–1989
18 Page 19 of 41
[22] A., Thygesen, J. Oddershede, H., Lilholt, A. B. Thomsen,
K Ståhl., On the
determination of crystallinity and cellulose content in plant fibres. Cellulose, 12, (2005). 563– 576 [23 ] A.T. Koshy, B. Kuriakose, S. Thomas and S. Varghese~ Studies on the effect of blend ratio and
ip t
crosslinking system on thermal, X-ray and dynamic mechanical properties of blends of natural rubber and ethylene-vinyl acetate copolymer Polymer, 34 (16) , 1993, 3428-3436
A. Alemdar, & M. Sain, Isolation and characterization of nanofibers from agricultural residues–Wheat straw and soy hulls. Bioresource technology,99(6), (2008) 1664-1671.
cr
[24].
us
[25] N., Lin, & A. Dufresne, Physical and/or chemical compatibilization of extruded cellulose nanocrystal reinforced polystyrene nanocomposites. Macromolecules, 46(14),
an
(2013). 5570-5583.
[26]S. Boufi,, H., Kaddami,, & A. Dufresne, Mechanical performance and transparency of reinforced
polymer
nanocomposites.
Engineering, 299(5), (2014). 560-568.
Macromolecular
Materials
and
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nanocellulose
[27 ] D., Dufresne A.: Mechanical properties of natural rubbernanocomposites reinforced
ed
with cellulosic nano -particles obtained from combined mechanical shearing,and enzymatic and acid hydrolysis of sisal fibers.Cellulose, 18, (2011),.57–65 [28] A. Dufresne, Nanocellulose: A new ageless bionanomaterial 16(6),( 2013), 220–227
ce pt
[29] C. J. Chirayil,, J. Joy , L. Mathew, J. Koetz, & S. Thomas, Nanofibril reinforced unsaturated polyester nanocomposites: Morphology, mechanical and barrier properties, viscoelastic behavior and polymer chain confinement. (2014). Industrial Crops and Products, 56, 246-254.
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[30] R. Rajasekar, G.C. Nayak, A. Malas, C.K. Das, Development of compatibilized SBR and EPR nanocomposites containing dual filler system,Materials & Design, 35, (2012),878– 885
[31] K.R. Rajisha, H.J. Maria, L.A. Pothan, Zakiah Ahmad, S. Thomas, Preparation and characterization of potato starch nanocrystal reinforced natural rubber nanocomposites, International Journal of Biological Macromolecules 67 (2014) 147–153 [32]. E. Abraham, P.A. Elbi, B. Deepa,, P. Jyotishkukar, L.A. Pothen,, S. Thomas, S.S. Narine, X-ray diffraction and biodegradation analysis of green nanocomposites of natural rubber/nanocellulose Poly. Degra. and Sta. 97 (2012) 2378-2387.
19 Page 20 of 41
[33].D. Bondeson, A. P. Mathew, & K. Oksman, Optimization of the isolation of nanocrystals from microcrystalline cellulose by acid hydrolysis Cellulose, 13(2) (2006). 171– 180 [34]. N. Lin, G. Chen, J. Huang, A. Dufresne,, & P. R, Effects of polymer grafted natural nanocrystals on the structure and mechanical properties of poly(lactic acid): A case of
ip t
cellulose whisker-graft-polycaprolactone Chang, J. Appl. Polym Sci., 113(5) (2009). 3417– 3425
cr
[35]. J. H. Yu, F. J. Ai, A. Dufresne, , S. J. Gao, J. Huang, & P. R. Chang, Structure and mechanical properties of poly(lactic acid) filled with (starch nanocrystal)-graftpoly(epsilon-
us
caprolactone) Macromol. Mater. Eng, 293(9) (2008). 763–770.
[36]. H. Ismail, M, Edyhan, B. Wirjosentono, Bamboo fiber filled natural rubber composites:
an
the effects of filler loading and bonding agent. Polym Test., 21(2) (2002) 139–44. [37]. A. Karmakar, S. S. Chauhan, J. M. Modak and M. Chanda, Mechanical properties of
M
wood–fiber reinforced polypropylene composites: effect of a novel compatibilizer with isocyanate functional group Composites A 38 (2007) 227–33 [38]. G. Siqueira, S. Tapin-Lingua, J. Bras, D.S. Perez, A. Dufresne, Mechanical properties
ed
of natural rubber nanocomposites reinforced with cellulosic nanoparticles obtained from combined mechanical shearing, and enzymatic and acid hydrolysis of sisal fibers Cellulose
ce pt
18 (2011) 57–65.
[39]. J.Bras, M. L. Hassan, C.Bruzesse, E. A. Hassan, N. A. El-Wakil, A. Dufresne, Mechanical, barrier, and biodegradability properties of bagasse cellulose whiskers reinforced natural rubber nanocomposites Ind Crops Prod., 32(3) (2010) 627–33.
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[40]. S Varghese, J Karger-Kocsis, Natural rubber based nanocomposites by latex compounding with layered silicates. Polymer 44 (2003) 4921–7 [41]. S Varghese, J Karger-Kocsis, Melt compounded natural rubber nanocomposites wuth pristine and organophilic layered silicates of natural and synthetic origin J. Appl. Polym Sci., 91 (2004) 813–9.
20 Page 21 of 41
ip t cr us
List of tables
Table 1 Formulation of the cross linked NR/nanocellulose composite
1% Nano
2%Nano
3% Nano
Natural rubber latex (Centrifuged)
96.5
95.5
94.5
93.5
Jute nanocellulose dispersion
0
1
2
3
1.5
1.5
1.5
0.75
0.75
0.75
0.75
ed
M
Neat NR
an
Weight % in the nanocomposite
1.5
ZMBT dispersion
0.6
0.6
0.6
0.6
Zinc oxide dispersion
0.3
0.3
0.3
0.3
KOH solution
0.35
0.35
0.35
0.35
Sulphur dispersion
Ac
ce pt
ZDC dispersion
Table 2 The crystallinity of the jute fibres at different processing stages Sample
Xc %
Xa%
1.
Raw jute fibre
46.32
53.68
2.
Steam exploded
62.54
37.46
3.
Bleached fibre
77.54
22.45
4.
Acid hydrolysed fibre
82.22
17.77
No
21 Page 22 of 41
Table 3: The tensile test data of the nanocomposites Sample
Tensile
Elongation
Stress at
Stress at
Crosslink
strength
at break
100%
200%
density
(MPa)
(%)
(MPa)
(MPa)
(moles/L)
3.52
860
1.90
2.05
2. 1% Nanocomposite
3.81
750
2.20
2.30
3. 2% Nanocomposite
4.15
620
2.60
2.60
4. 3% Nanocomposite
4.25
410
3.05
cr
1. Natural rubber
1.39x10-3
ip t
No
1.91x10-3 2.2 x10-3
an
us
3.40
1.61x10-3
M
Figure captions:
Fig. 1: SEM of jute fibres at different processing stages (A): Raw jute fibre; (B) Alkali treated fibre; (C): Steam exploded followed by bleached fibre; (D): Acid hydrolysed fibre
ed
Fig. 2: TEM images of jute nanofibres
Fig. 3: FTIR spectrum of jute fibre during various treatments
ce pt
Fig. 4: XRD spectrum of jute fibre during various treatments Fig. 5: Birefringence analysis of jute nanofibres
Ac
Fig. 6 : Cryo-TEM of the inner part of the NR/nanocellulose composite (A): Neat matrix; (B) 1% nanocomposite; (C): 2% nanocomposite; (D): 3% nanocomposite (E) Schematic represention showing the possible interation between nanocellulose through H-bonding creating a netwok structure . Fig. 7 : XRD analysis of the NR/nanocellulose composites Fig. 8 : Tensile properties of nanocellulose/NR composite Fig. 9 : Thermo gravimetric (TGA) properties of nanocellulose/NR composite
22 Page 23 of 41
cr
ip t Ac
ce pt
ed
M
an
us
Figures
Figure. 1
23 Page 24 of 41
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Figure. 2
24 Page 25 of 41
ip t cr us an M Ac
ce pt
ed
Figure. 3
Figure. 4
25 Page 26 of 41
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Ac
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ed
M
an
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cr
Figure. 5
Figure. 6 26 Page 27 of 41
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Ac
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ed
Figure 7
Figure. 8
27 Page 28 of 41
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Ac
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ed
Figure. 9
28 Page 29 of 41
Table(s)
Table 1 Formulation of the cross linked NR/nanocellulose composite Weight % in the nanocomposite 1% Nano
2%Nano
3% Nano
Natural rubber latex (Centrifuged)
96.5
95.5
94.5
93.5
Jute nanocellulose dispersion
0
1
2
Sulphur dispersion
1.5
1.5
ZDC dispersion
0.75
0.75
ZMBT dispersion
0.6
0.6
Zinc oxide dispersion
0.3
KOH solution
0.35
ip t
Neat NR
cr
3
1.5
0.75
0.75
0.6
0.6
0.3
0.3
0.3
0.35
0.35
0.35
Ac ce p
te
d
M
an
us
1.5
Page 30 of 41
Table(s)
Table 2 The crystallinity of the jute fibres at different processing stages Xc %
Xa%
1.
Raw jute fibre
46.32
53.68
2.
Steam exploded
62.54
37.46
3.
Bleached fibre
77.54
22.45
4.
Acid hydrolysed fibre
82.22
17.77
Ac
ce pt
ed
M
an
us
cr
ip t
Sample
No
Page 31 of 41
Table(s)
Table 3: The tensile test data of the nanocomposites Sample
Tensile
Elongatio
Stress at
Stress at
Crosslink
strength
n at
100%
200%
density
(MPa)
break
(MPa)
(MPa)
(moles/L)
1. Natural rubber
3.52
(%) 860
2. 1% Nanocomposite
3.81
750
2.20
2.30
3. 2% Nanocomposite
4.15
620
2.60
2.60
4. 3% Nanocomposite
4.25
410
3.05
3.40
1.90
2.05
1.39x10-3 1.61x10-3
ip t
No
1.91x10-3
Ac
ce pt
ed
M
an
us
cr
2.2 x10-3
Page 32 of 41
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 33 of 41
Ac ce p
te
d
M
an
us
cr
ip t
Figure(s)
Page 34 of 41
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 35 of 41
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 36 of 41
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 37 of 41
Ac ce p
te
d
M
an
us
cr
ip t
Figure(s)
Page 38 of 41
Ac
ce
pt
ed
M
an
us
cr
i
Figure(s)
Page 39 of 41
Ac
ce
pt
ed
M
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Figure(s)
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Figure(s)
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S0141-8130(15)00600-5 http://dx.doi.org/doi:10.1016/j.ijbiomac.2015.08.053 BIOMAC 5321
To appear in:
International Journal of Biological Macromolecules
Received date: Revised date: Accepted date:
2-6-2015 21-8-2015 24-8-2015
Please cite this article as: M.G. Thomas, E. Abraham, J. P, L.A. Pothan, H.J. Maria, S. Thomas, Nanocelluloses from jute fibres and their nanocomposites with natural rubber: preparation and characterisation, International Journal of Biological Macromolecules (2015), http://dx.doi.org/10.1016/j.ijbiomac.2015.08.053 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Abstract
Abstract: Nanocellulose fibres having an average diameter of 50 nm were isolated from raw jute fibres by steam explosion process. The isolation of nanocellulose from jute fibres by this extraction process is proved by SEM, XRD, FTIR, birefringence and TEM characterizations. This
ip t
nanocellulose was used as the reinforcing agent in natural rubber (NR) latex along with cross linking agents to prepare crosslinked nanocomposite films. The effects of nanocellulose loading analysed.
cr
on the morphology and mechanics of the nanocomposites have been carefully
Significant improvements in the Young’s modulus and tensile strength of the nanocomposite
us
were observed because of the reinforcing ability of the nanocellulose in the rubber matrix. A mechanism is suggested for the formation of the Zn-cellulose complex. The three dimensional
an
network of cellulose nano fibers (cellulose/celullose net work and Zn/cellulose net work) in the
Ac ce p
te
d
M
NR matrix plays a major role in improving the properties of the crosslinked nanocomposites.
Page 1 of 41
*Manuscript
Nanocelluloses from jute fibres and their nanocomposites with natural rubber: preparation and characterisation Martin George Thomas,1 Eldho Abraham 2,5,Jyotishkumar P1,L.A.Pothan2,Hanna J Maria3, Sabu Thomas* 3,4 1
Technology,Cochin University P.O, Cochin- 682 022, Kerala, India. 2
ip t
Department of Polymer Science and Rubber Technology, Cochin Universiy of Science and
Research Department of Chemistry, CMS College, Kottayam-690 110, Kerala, India.
3
cr
International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi
University, Kottayam-686 560, Kerala, India. 4
us
School of Chemical Sciences, Mahatma Gandhi University, Kottayam-686 560, Kerala, India.
5
R.H. Smith Institute of Plant Sciences and Genetics, Hebrew University of Jerusalem, Israel, 76100
M
an
Corresponding email: [email protected] and [email protected]
Abstract:
Nanocellulose fibres having an average diameter of 50 nm were isolated from raw jute fibres
ed
by steam explosion process. The isolation of nanocellulose from jute fibres by this extraction process is proved by SEM, XRD, FTIR, birefringence and TEM characterizations. This
ce pt
nanocellulose was used as the reinforcing agent in natural rubber (NR) latex along with cross linking agents to prepare crosslinked nanocomposite films. The effects of nanocellulose loading on the morphology and mechanics of the nanocomposites have been carefully analysed. Significant improvements in the Young’s modulus and tensile strength of the nanocomposite were observed because of the reinforcing ability of the nanocellulose in the
Ac
rubber matrix. A mechanism is suggested for the formation of the Zn-cellulose complex. The three dimensional network of cellulose nano fibers (cellulose/celullose net work and Zn/cellulose net work) in the NR matrix plays a major role in improving the properties of the crosslinked nanocomposites.
Key words: Bionanocomposites; fibre/matrix bond; natural rubber; nanocellulose; Zn/cellulose complex
1 Page 2 of 41
1. Introduction Natural fibers are composed of cellulose nanofibres which is the most abundant and renewable biomaterial on earth and is totally biodegradable. Natural fiber reinforced polymer composites have attracted substantial interest as a potential structural material as well as in
ip t
other applications in the past decades. The attractive features of natural fibers like jute, sisal, coir, cotton, flax and banana are their low cost, light weight, high specific modulus, renewability and biodegradability. Out of these fibres, jute fibre is one of the major under-
cr
utilized agricultural raw materials which has a cellulose content with 70% of its dry weight. Its annual production is around 3000000 tons/year especially from the central part of Asia[1].
us
Jute fibre can be planted in river flats, depressions, and saline-alkali soils, which are unavailable to plant cotton and most food corps, and no pesticides and fertilizer are needed
an
during the growth of jute, so it is a kind of ‘‘pure green’’ agro-product. Due to its heterogeneity and crystallinity, however, direct utilization of the biomass is extremely low. Not more than 20 per cent of the jute husks is utilised in the jute industry, the remaining
M
being used either as fuel in rural areas or underutilized. Production in the cooperative fold is not more than 20 to 25 per cent. Efforts are going on for exploring wider export markets for
ed
jute and jute products but still most of the raw jute fibre remained underutilized. Judged from the increase in production and employment, the progress has been rather slow and exports in
ce pt
physical terms have remained more or less static. In the present work, ultra fine nanocellulose from jute fibres have been prepared by steam explosion method. The extraction processes of the nanocellulose from natural sources are reported by various researchers [2-4]. The characteristics of nanocellulose depend on the origin of the fibers and the isolation conditions which must be adjusted depending on the substrate to be hydrolyzed. We have reported the
Ac
isolation of the nanocelluloses from various sources by steam explosion technique [5]. The preparation of nanocellulose by this technique will give additional advantages over earlier ones by the yield and the isolation of the nanofibre as embedded in the raw fibre entity. The nanocellulose will then be used for the preparation of biodegradable nanocomposites with NR which is discussed in the later part of this paper. The studied nanocomposites are expected to have superior mechanical, electrical and dielectric properties as compared to their micro and macro counterparts. Production of ‘green composites’ based on raw materials derived from natural sources of plant or animal origin are of great interest both in the academic and industrial fields. In the
2 Page 3 of 41
past decades, research has been focused on the development of replacing reinforcing elements like carbon black, silica and glass fibres in polymer composites since they are potentially toxic. In the context of both biomass valorization and nanocomposite materials development, cellulose nanofibres (nanocellulose) used as filler in a green matrix appear to be an interesting reinforcing agent [6,7]. Green chemistry coupled with nanotechnology would be the much attracted area of research all over the world because of the environmental
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and technological concerns. When compared with glass fibers, silica and carbon black, nanocellulose as reinforcing filler in composites has many advantages. The combination of
cr
high surface area, high aspect ratio, environment benefits and low cost, as well as the exceptional mechanical properties, have made the nanocellulose attractive to use as a filler in
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bionanocomposite[8,9].Due to the high surface to volume ratio, green nanocomposites exhibit unique mechanical, electrical and thermal properties in addition to its environmental
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safety.
Nanocelluloses have been incorporated as reinforcing fillers into a wide range of polymer matrixes [10,11] including segmented polyurethanes [12] due to their appealing intrinsic
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properties. Being a bio-based polymer, the use of bio-nano reinforcements in NR is beneficial in the development of biobased green nanocomposites. Furthermore, most of the bio-based
ed
nano reinforcements are usually available as liquid suspensions to retain their dimensional stability as in the case of the aqueous suspension of nanocellulose. Hence, the blending of the nanocellulose and NR latex both in aqueous suspension provides a viable route to disperse
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nano reinforcements in the latex matrix. NR-based nanocomposites with bio-based nano reinforcements like chitin whiskers, starch nanocrystals, cellulose whiskers extracted from Syngonanthus nitens (Capim Dourado), rachis of palm tree, sisal and bagasse are reported in the literature [13-15]. When compared with platelet like morphology of nanocrystals
Ac
extracted from other sources like starch and potato, nanocelluloses present the originality to have a rod like morphology having very high aspect ratio which gives exceptional characteristics to the nanofibres [3,4]. Furthermore, it can be seen that most of these studies use latex blending technique without vulcanization, for the bionanocomposite preparation. Our group already reported on the nanocomposites of NR reinforced by nanocellulose which is extracted from banana fibres[16]. Nanocomposite materials of natural rubber filled with cellulose fibres were reported by earlier researchers [8,29]. Here we are reporting the effective utilization of jute fibres by isolating the nanocellulose and finding application of this nanocellulose in NR latex matrix for the preparation of bionanocomposites. More over the crosslinking agents like Zinc dithiocarbomate (ZDC), Zinc mercapto benzothiozole 3 Page 4 of 41
(ZMBT), Zinc oxide (ZnO) and sulfur were used during the processing stage to improve the mechanical properties.
2. Materials and methods 2.1.
Materials
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Raw jute fibres for the nanocellulose extraction were obtained from YMCA Marthandom, Tamil Nadu, India. Centrifuged latex of natural rubber was kindly supplied by Rubber Board, Kottayam, Kerala, India. It contained spherical rubber particles with a dry rubber content
cr
(DRC) of 60% and it contains more than 98% of cis-1,4-polyisoprene. The various chemicals used for extraction of fibre and the preparation of nanocellulose and nanocomposite are
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NaOH, acetic acid, NaClO2, oxalic acid, sulfur, zinc dithiocarbamate (ZDC), zinc mercaptobenzothiozole (ZMBT), zinc oxide (ZnO), KOH etc. and all are from Nice
Experimental steps for the isolation of nanocellulose from raw jute fibres
2.2.1 Alkali treatment of the fibre
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2.2.
an
Chemicals, Cochin, India. All reagents used were of analytical grade.
The jute bast fibres were cut it into pieces and subjected for alkali treatment by soaking it in
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2% caustic soda for 2 hours at room temperature. 2.2.2 Alkali treatment followed by steam explosion
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Steam explosion technique was applied on the alkali treated jute fibre for one hour. Steam pre-treatment was performed by loading the alkali soaked jute fibre directly into the steam gun and treating it with high pressure steam (20 lbs) at temperatures within 100 to 150oC for 2 hours followed by sudden release of pressure. 2.2.3 Sodium chlorite bleaching of the steam exploded fibre
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After the successive alkali followed by steam treatments, the bleaching treatment with sodium chlorite (NaClO2) solution (pH 2.3) for 1 h at 50oC was performed to remove the remaining lignin. In the bleaching step, the absence of elemental chlorine is accomplished by using NaClO2 as the bleaching agent. The bleached fibres were pure white in color. 2.2.4 Oxalic acid treatment followed by steam explosion The bleached fibre was subjected to mild acid hydrolysis by treating it with 5% oxalic acid. The second step of steam explosion for one hour was carried out after the acid treatment. The fibres were then centrifuged repeatedly with water and then subjected to mechanical stirring
4 Page 5 of 41
followed by sonication. The pH of the nanocellulose were neutralised with 0.1% NaOH solution. 2.3
Nanocomposite preparation
The extracted nanocellulose was mixed with the NR latex along with other cross linking components as described in the Table 1 formulation. The composite films were prepared from prevulcanised latex by casting on a glass plate followed by drying at ambient temperature.
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The prevulcanization of the compounded latex was conducted at 70oC for 2 h using water bath with constant gentle stirring. The sample numbers 0, 1, 2 and 3 indicate the weight
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[ Table 1 here]
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percentage of nanocellulose used.
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The aqueous suspension of the various proportions of nanocellulose, latex and the crosslinking agents were mixed by ball milling followed by ultra sonication. The ball milling process was conducted for two hours in water medium with ceramic balls (1.5 cm diameter)
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in stainless steel container (1 lit). The speed of the mill was 300 rotations per minute. It is then subjected to ultra-sonication for 10 minutes in 50% amplitude with an ice bath
ed
temperature. The mixed aqueous suspension of the nanocomposites poured in to glass plates and dried for 24 hours at oven with a temperature of 50-60oC in order to obtain dry films of 1 mm to 2 mm thick depending on the test and with weight fractions of nanocellulose within
ce pt
the NR matrix ranging from 0 to 3 wt %. Resulting films were conditioned at room temperature in desiccators containing phosphorous pentoxide (P2O5) until tested. 2.4 Scanning electron microscopy (SEM) SEM analysis of the fibres were done by an Analytical Scanning electron microscope (A-
Ac
SEM), ZEISS EVO 60. The microscope works with tungsten filament and maximum acceleration voltage of 20 kV. The samples were mounted on aluminium stabs and goldcoated with a sputter coater. 2.5 Transmission electron microscopy (TEM) The size of the nanocellulose fibres and their distribution and dispersion in NR matrix were characterized by transmission electron microscopy (TEM) with a CM 12 PHILIPS HRTEM. For the evaluation of the dispersion of nanofibres on the dried NR matrix, cryo cutting method was adopted. The cryo cutting of the nanocomposites were done by a thin section of about 100 nm was cut with a diamond knife at -100oC (Tg of NR is ~ -73OC) to observe the dispersion of nanocellulose inside the rubber matrix. 5 Page 6 of 41
2.6 Fourier transforms infrared spectroscopy (FTIR) Fourier Transform- Infra Red spectroscopy (FTIR) spectra of the fibers were recorded by a Shimadzu IR-470 IR spectrophotometer. 2.7. X-ray diffraction analysis (XRD) X-ray diffraction of the fibres and the nanocomposites were performed using a Bruker AXS X-ray diffractometer equipped with a filtered Cu-Kα radiation source (λ = 0.1542 nm) at the
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operating voltage and current of 45 kV and 40 mA, respectively and a 2D detector. 2.8. Mechanical testing
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Tests for measuring the tensile strength were carried out according to ASTM designation D 412-98 using dumb-bell specimens. Rate of separation of power-actuated grip was 500
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mm/min, which was maintained throughout the experiment. Averages of three samples were tested for a particular composition.
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2.9. Thermo gravimetric analysis (TGA)
TGA was carried out on a TGA Q50 (TA Instruments, DE, U.S.A.) following the ASTM D3850-94 standard. An approximate 10- 20 mg of the specimen was loaded in the open
constant heating rates of 10°C/min.
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3. Results and discussion
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platinum pan. The samples were heated from 25 to 500°C under nitrogen atmosphere at
3.1 Extraction of nanocellulose from jute fibres
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3.1.1. Morphological analysis by SEM and TEM Raw jute fibre contains about 70 wt% of cellulose and 15 and 10 wt% of hemicellulose and lignin components, respectively. The Fig. 1 represents the SEM of jute fibres at different processing stages (Fig. 1 (A) raw jute fibre, (B) alkali treated fibre, (C) bleached fibre and
Ac
(D) acid hydrolysed fibre). It was possible to verify the presence of lignin and hemicellulose using SEM images of the raw and alkali treated fibres. It is worth noting that the washing out and dissolving of lignin and hemicellulose starts at the alkali treatment (2% NaOH) and its complete removal was possible at the bleaching stage. The alkali treatment allows the exposure of the raw fibres and the inner parts of the fibers were exposed to chemicals by the steam explosion process. During the chemical treatment (alkalization) most of the lignin and hemicellulose were removed. Mechanical treatment (steam explosion) further removed the amorphous materials (lignin, hemicellulose etc) from the inner part of the fibre via depolymerisation and defibrillation. Scanning electron micrographs show changes in the morphology of the fibers in terms of size and level of smoothnes after acid hydrolysis. Lignin 6 Page 7 of 41
is rapidly oxidized by chlorine. Lignin oxidation leads to lignin degradation and leads to the formation of hydroxyl, carbonyl and carboxylic groups, which facilitate the lignin solubilization in an alkaline medium. Thus cellulose macrofibrils of the original fibres were separated from each other to produce microfibrils with diameters around 5–30 µm, Fig.1 (C). Acid coupled steam treatment after bleaching process helps to disintegrate the fibrils further. Fig. 1 (D) shows the SEM photographs of the individualized nanofibrils after acid treatment.
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It can be seen from the SEM that the size of the jute fibre is reduced from 5-30 μm to about 50 nm. Thus acid coupled steam explosion helps in defibrillating the fibre diameter to nano
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range.
The analysis of the final nanocellulose by TEM is also carried out and is shown in Fig. 2. It
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also supports the evidence for the isolation of individual nanofibres of jute fibres by steam explosion process coupled with mild alkali and acid treatment. The average size of the
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individual nanocellulose fibres are in the range of 50 nm diameters with a length of few micrometers. Aspect ratio of the extracted cellulose nanofibres were estimated from transmission electron micrographs. The aspect ratio (fibril length to the diameter ratio) is one
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of the most important parameters in determining reinforcing capability of the nanofibres for composite application. From the visible portion of the TEM with statistical analysis it is
ed
calculated that the aspect ratio falls in the range of 100nm.
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[Fig.1: here]
[Fig. 2 here]
3.1.2. Fourier Transform Infrared (FTIR) Analysis
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To investigate the structural changes on the jute fibres during the alkali treatment, steam explosion, bleaching and the acid hydrolysis; FT-IR spectroscopy was used. FTIR spectra of the untreated, steam exploded, bleached and acid hydrolysed jute cellulose fibres are shown in Fig. 3. The raw jute sample gives a very low intensity absorbance at 3330 and 1630 cm -1. These peaks are responsible for the OH-bending and OH-stretching frequencies respectively. In the raw fibre, the hydroxyl groups are bound by other cementing materials like lignin, waxes and hemicelluloses and hence its peaks are not exposed in the FTIR spectrum. The absorption band located at 2895 cm−1 is related to CH2 groups [5,] and its intensity increased with treatments. The percentage of the pure cellulose is increased with various treatments thereby increasing the intensity of the CH2- group in the β-glucosides rings of the cellulose 7 Page 8 of 41
molecules. The absorption band at 1725cm−1 is associated with the aromatic ring vibration due to the presence of lignin and acetyl or uronic ester groups of hemicelluloses normally appear in the region 1700–1740cm−1 [17]. The absence of this corresponding peak in the bleached and acid hydrolysed fibres indicates the complete removal of lignin [5,17] and hemicelluloses by the various processing steps. But two strong absorption bands at 3320 and 1631 cm−1 of bleached and acid hydrolysed jute fibres indicate that the hydroxyl groups of
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the cellulose molecules are exposed and it absorbs water from the moisture through hydrogen bonding [18]. The absorption band at 1163cm−1 corresponds to C-O-C stretching, and the
cr
peak at 896cm−1 is associated with the C-H rock vibration of cellulose (anomeric vibration, specific for β-glucosides). These peaks show an increasing tendency with treatments and
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steam explosion indicating the removal of tightly bound cementing materials and exposure of the pure cellulosic fibres. Similar results have been observed by Jahan et al.[19] during
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production of MCC from jute fibers and Fahma et al.[20] when isolating nanofibers from oil palm fruit bunch. Thus the alkali treatment coupled with steam explosion followed by
M
bleaching removes the lignin, hemicelluloses and other cementing materials.
[Fig. 3 here]
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From the FTIR analysis it has been concluded that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peak at 1725 cm-1and 1250 cm-1. These peaks are chiefly
ce pt
responsible for the hemicellulose and lignin components. These characteristic peaks are completely absent in the final bleached cellulose fibre. The increase in the intensity of the peaks at 3320 cm-1 and 1631 cm-1 of final bleached fibre is responsible for the increased
Ac
(free) cellulose content.
3.1.3. X-ray diffraction (XRD) analysis The crystallinity of untreated jute fibres, alkaline treated followed by steam exploded jute, bleached and acid hydrolysed jute fibres has been analyzed by X-ray diffractometry. It can be noted from Fig. 4 that the fibres show increasing orientation along a particular axis as the amorphous zones are dissolved. The gradual removal of non-crystalline materials especially lignin and the hemicelluloses changed the nature of
fiber to more crystalline which is
confirmed from the XRD (Fig 4) , where the intensity of crystalline peaks were found to be increased for the treated fibers. These changes during each processing stages is due to the removal of these noncrystalline materials resulting in the loss of the disordered regions [21]. 8 Page 9 of 41
[Fig. 4 here]
From the X-ray diffraction patterns (Fig 4) the percent crystallinity of the raw jute, steam exploded jute, bleached jute and acid hydrolysed jute was calculated using the equation given below [22,23 ] X a = Ia / (Ic + Ia)…………………… (3)
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Xc = Ic / (Ic + Ia)……………………(2) where Ic and Ia represent the integrated intensities corresponding to the crystalline and
cr
amorphous phases, respectively, i.e. the areas under the respective curves. The percentage
an
[Table 2 here].
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crystallinity values Xc and amorphous portion value Xa are given in Table 2.
The changes in crystallinity is due to the removal of water soluble hemicelluloses and alkali
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soluble lignin as lignin chlorides in the NaOCl2 bleaching step.
It can also be found that the XRD pattern of all the jute fibres exhibits a sharp high peak at ◦
◦
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2θ=23.2 , and a weaker diffraction peak at 2θ=15.3 which are assigned to cellulose I. The mild alkali treatment (2%) is not able to make a lattice transformation from cellulose I to
ce pt
cellulose II which is clear from all the diffraction patterns. In most lignified plant cells lignin and hemicellulose are deposited between the micro fibrils to give an interrupted lamellar structure and without the removal of these noncellulosic components, the cellulose I to cellulose II transformation will be restricted. With the treatment of NaOH and bleaching agents, the lignin is removed and in this case also the degree of crystallinity goes on
Ac
increasing. This may be due to the removal of lignin which acts as a cementing material and on delignification, an ordered arrangement of the crystalline cellulose in the structure takes place. SEM given in Fig.1 shows individualized and uniform fibers, which correlates with the spectroscopic evidence for the removal of cementing material around the fiber bundles; namely hemicelluloses, and lignin. The high crystalline jute nanocellulose fibres could be more effective in providing better reinforcement for rubber composite materials because of its high Young’s modulus (138GPa) of the crystalline regions along the longitudinal direction.
9 Page 10 of 41
3.1.4. Birefringence analysis Optical surface morphology and the birefringence properties of jute nanocelluloses were investigated. Birefringence was used to confirm the presence of isolated nanocrystals in an aqueous paste. It can also be used as a good dispersibility criterion in suspension [24]. This birefringence results originated from the structural anisotropy of the nanocellulose and the
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flow anisotropy resulting from the alignment of the nanocrystals under flow, generally operated before observation. Aqueous nanocellulose films with 4% cellulose fibre viewed
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[Fig. 5 here]
cr
through crossed polarizers to note the birefringence of the crystalline nanocellulose.
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Fig. 5 shows the size of the crystalline nanocellulose, by birefringence under crossed polarizers. The nanofibres were sonicated for 20-30 minutes and therefore the nanocelluloses lost its fibrous nature and turned to crystalline character in this process and possesed some
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liquid crystalline properties. Without proper sonication the nanocelluloses are in fibrous state and are unable to give any birefringence. The sonication of the nanocellulose changed their
ed
fibre property to a liquid crystalline in nature. The nanocellulose film presented smooth surface and dark view with crystalline reflection under cross polarization. After sonication a well-dispersed birefringence occurred (Fig. 5), exhibiting colour spots for the formation of
ce pt
crystal domains. These results indicated that the sonicated suspensions exhibited strong shear birefringence, highlighting the ability of the crystalline nanocellulose to form a chiral nematic liquid crystalline phase in equilibrium with the isotropic phase. The birefringence of the aqueous nanocrystals proved their good dispersion in water suggesting that the suspension
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contained a large number of single cellulose crystals, highlighting the success of the proposed isolation process.
3.2. Characterisation of NR/ jute nanocellulose composite 3.2.1. Morphological analysis by TEM The morphology of NR/nanocellulose materials and the distribution level of the filler within the matrix were evaluated by observing the cryo-cut TEM images of the nanocomposites. Fig. 6 shows the cryo-cut TEM of the inner part of the NR/nanocellulose composite; (A) neat matrix, (B) 1% nanocomposite, (C) 2% nanocomposite and (D) 3% nanocomposite. By comparing with the micrographs showing the cryo-cut surface of the nanocomposites, it is 10 Page 11 of 41
easy to identify the contribution from the filler. Jute nanocellulose appears are dispersed in a homogenous nanolevel and the cloudiness of the filler particles increases with its concentration. The TEM of the neat NR gives a clear appearance showing the absence of fillers. We can observe that the distribution of the filler among the matrix is homogeneous for all the compositions. While in 2% loading a network formation could be observed. At 2% nanofiber loading, nanoscopic fibers make a network by H-bonding interaction as reported
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previously by Dufrense et al [25-28] and Cintil et al [29]. This could be understood from TEM micrograph. In all scientific literature related nanocelullose composites, the network
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formation of nanofibers has been well documented. This can be explained to be due to the interaction between nanofibers through H-bonding. This network structure of the nanofibers
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restricts the mobility of polymer chains trapped between the nano fiber network. These immoblised polymers chains contribute to the high mechanical properties of the
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nanocomposites.
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[Fig. 6 here]
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The black spots in the TEM of the nanocomposites can be due to the unreacted crosslinking agents [30,31]. It is not possible to see the individual nanocelluloses even though the scales are in 200 nm which proves the nanomeric homogenous dispersion of filler. Furthermore, our
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group already reported about the existence of Zn/cellulose complex in NR/nanocellulose crosslinked composite system [32]. The vulcanising agents used for the crosslinking of the NR matrix play a major role in the formation of this Zn/cellulose complex. This complex formation also helps for the better dispersion of
the nano fibers in the NR matrix.
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Furthermore, no particular sedimentation phenomenon of nanocellulose within the thickness of the films was observed.
3.2.2. X-ray diffraction analysis (XRD) XRD analysis of the nanocomposites was also carried out in order to verify the crystalline nature of the nanocellulose after the reinforcement and to know the dispersion of nanocellulose in NR matrix (Fig. 7). The diffractograms of unfilled NR and reinforced nanocellulose were added as references. The diffraction pattern recorded for a film of nanocellulose displays typical peaks of A-type amylose allomorph of cellulose I crystalline form [33]. It is characterized by a strong peak at 2θ = 17.9° and a very strong peak at 25.07°. 11 Page 12 of 41
The natural rubber film displays a typical behavior of an amorphous polymer. It is characterized by a broad hump located around 2θ = 19°.
[Fig. 7 here]
It is interesting to note that none of the X-ray diffraction pattern of the studied
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nanocomposites gives additional peak for the presence of crystalline nanocellulose in the NR matrix. The peaks corresponding to the A-type amylose allomorph of the reinforced
cr
nanocellulose is completely absent in whole of the studied NR composites which is unexpected. NR is amorphous in nature if it is not stretched. Another interesting observation
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is the decrease in the intensity of the broad hump peak of the NR with increasing nanocellulose content. This reduction in the intensity of the corresponding broad hump peak
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of nanocomposites gives clear evidence about the formation of the Zn/cellulose network in between the layers of NR matrix. This in turn increases the interlayer distances between the rubber molecules and the diffraction rays travels a longer path than the pure NR matrix. Thus,
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the nanocellulose diffraction signals at 17.9° and 25.07◦ are masked by the NR matrix because of the nanomeric dispersion of nanocellulose in between the layers of NR which
ed
leads to the formation of Zn/cellulose network. It is reported that cellulose and starch nanocrystals grafted with PCL by ring opening polymerization present similar behavior and no signal of nanoparticle crystals was detected due to the high crystallinity of PCL [34, 35].
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The filler and the crosslinking agents were added together during the vulcanizing step and the sulfur molecules will facilitate the breaking of the double bonds of the NR back bone by entering in between the chains of natural rubber and make new bonds with each other. The entering of sulfur molecule in between the chains of NR makes more room to accommodate
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the nanocellulose in between the layers of NR latex. The filler and the crosslinking agents enter in between the molecular chains of natural rubber and makes new bond with each other. The breaking of the double bond in the natural rubber backbone makes two active sites and a cross linking network between sulfur and natural rubber. In addition to that cross linking network, cellulose molecules will make a complex with zinc metal which is clearly discussed and reported in our earlier work [24]. This complex formation will lead to the loss of crystallinity of the cross linked nanocomposites. In summary, the absence of crystalline peak in the nanocomposite could
due to the formation of Zn-cellulose complex. However,
possible dilution effect (very low content of nanocelulose in the NR matrix) can not be negleted. 12 Page 13 of 41
3.2.3. Mechanical properties of the nanocomposites The tensile properties of NR nanocomposites at room temperature with different nanocellulose loading are shown in Fig. 8. Stress vs. strain curves show that the nanocomposites present higher initial modulus and better tensile strengths than NR. The addition of the filler is expected to increase the modulus of composites that results from the
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inclusion of rigid crystalline filler particles into the rubber matrix [36,37]. When crystalline nanocellulose is reinforced with amorphous matrix, crystallization of composite surface
cr
probably dominates over its bulk nature, giving higher modulus to the resulting composites. The modulus of elasticity of the nanocomposite is increased steadily with the addition of
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nanofibres and improved from 1.3 MPa to 3.8 MPa with the increase in nanocellulose content from 0 to 3 wt.%. Vulcanized NR inherently possesses good strength because of strain-
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induced crystallization. The strain-induced crystallization of NR is not affected by the addition of nanocellulose fibres, as is evident from the increase in stress above 400% strain. The increased tensile strength and modulus observed with increasing nanocellulose content is
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attributed to the possible restriction of polymer chain mobility in the vicinity of crosslinked Zn/cellulose and cellulose-cellulose three dimensional network. Despite the moderate
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increase in tensile strength and modulus, the behavior of the stress- strain curve is not changed by the addition of nanocellulose indicating that the effect due to crosslinking of NR predominates over the reinforcing effect of nanofibres. An increase in the nanocellulose
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content decreases the micro spaces between the nanofibre and the matrix and thereby decreasing the extent of Zn/cellulose network, which will also strengthen the filler–matrix interfacial adhesion. The specific surface area of the filler in contact with the matrix is also increased. As a result, the values of tensile strength show an increasing trend with increasing
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nanofibre content in the composite.
[Fig. 8 here]
[Table 3 here] Siqueira et al. [38] as well as Bras et al.[39] have reported tensile strength and modulus in the range of 0.5 MPa for NR matrix phase. The higher tensile strength and the modulus of the matrix material in the current paper are due to the vulcanization (crosslinking) of NR as well as the processing method used.The crosslink density values were calculated using equation (1) and is shown in Table 3. 13 Page 14 of 41
Cx= E/6RT ………….(1) Where Cx is the crosslink density (moles per unit volume), R = molar gas constant = 8.31 J.mol-1.K-1,T is the absolute temperature and E is the Young’s modulus.With the increase of nanocellulose loading the crosslink density is found to be increasing.This is associated with the filler (nanocellulose)-polymer interactions. Furthermore, studies on
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vulcanized NR based clay nanocomposites prepared by latex blending and melt compounding showed limited improvement in properties compared to the matrix material [40,41] which
cr
suggest that the percentage improvement in mechanical properties with the addition of nano
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reinforcements depend significantly on the properties of the matrix.
The presence of hydroxyl groups in the nanocellulose is responsible for its inherent hydrophilic nature.The network formation by the nanocellulose in the NR matrix gives rise to
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good mechanical properties to the sytem (Table 3). Of the three hydroxyl groups present in cellulose, a hydroglucose unit, one is primary hydroxyl group at C6, while the other two are
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secondary hydroxyl groups at C2 and C3 positions. A three dimensional network of Zn/cellulose and cellulose/cellulose is formed within the composite entity and these hydroxyl groups have a major contribution in the formation of this network. Due to this three
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dimensional network, the interfacial bonding and mechanical interlocking between the nanofibre and matrix is increased dramatically in the resultant composite.Infact the natural
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rubber chains are immobilized by the netwok.(Fig .6E) This in turn increases the tensile strength and modulus of the composites at all mixing ratios compared to that of neat NR (Table 3).. The enhanced interfacial bonding will increase stress transfer efficiency from the matrix to the filler with a consequent improvement in the mechanical properties of the
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composites. Elongation at break of the nanocomposites decreased gradually with increase in nanocellulose content and this was an expected behavior because of the immobilization of the polymer chains by the net work.
The percentage of elongation for the neat NR film
percentage is 884% but is 415% in nanocomposites with a 3 wt.% nanocellulose. Thus the incorporation of fibre into the polymer matrix reduces the matrix mobility, resulting in stiffness of the composite. As a result, Young’s modulus increased with increasing the filler content of the composites and the percentage of the elongation is regularly decreased with increasing the cellulose content. Overall, rubber-rubber, rubber-cellulose, cellulose / cellulose and NR/Zn/cellulose interactions together make the nanocomposites with good mechanical properties. 14 Page 15 of 41
3.2.4. Thermogravimetric analysis (TGA) of the nanocomposites The thermal degradation of the NR nanocomposites has been investigated by TGA in terms of percentage weight loss with temperature. Fig. 9 is the TGA curves of the nanocellulose, NR and their nanocomposites. The nanocellulose shows a peak at 60oC for the evaporation of water. The other main degradation concentrated in between 250-400oC and is related to the
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pyrolysis of the cellulose components. The initial thermal stability of nanocellulose is much lower than that of NR however, their residual char is ~10 wt. % which is thrice the value of
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NR and its composites (~3 wt. %). In filled composite system, the decomposition mechanism is rather complex because of the homogenous distribution of fillers into latex phase and due
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to the presence of Zn/cellulose complex network. At higher filler percentage, the composite systems are not homogenous because of the agglomeration and also due to the difference in
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polarity of individual components.
Interesting observation is the increased thermal stability of the nanocomposites with lower filler content. It can be seen from the Fig. 9 that the decomposition temperature of 1%
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nanocomposite is slightly higher than the pristine NR matrix and then it is shifted to lower temperature with increasing the nanocellulose percentage. Thermal stability of the
ed
nanocomposites shows a reduced value except for 1% composite. At lower filler percentage the Zn/cellulose complex and the percolation network plays for
the increased thermal
stability even though the nanocellulose possess lower thermal characteristics. The decreased
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thermal stability at higher filler percentage is due to the critical volume fraction and the percolation threshold value in addition to the agglomeration of the fillers at higher concentration. The agglomeration of fillers in NR latex is further clear from the TEM shown in Fig. 6. The degradation temperature of the nanocellulose is comparatively lower than NR
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matrix which also causes the reduced thermal stability at higher filler percentage. The high surface polarity of nanocellulose due to hydroxyl groups lead to the agglomeration of filler particles at higher weight percentage. Moreover the presence of oxygen in the cellulose backbone and its side chain will make favorable atmosphere for the early thermal degradation of the nanocomposite. With increasing the percentage of the nanocellulose, the tendency of the rubber particles to create active centers for interaction with filler is diminishing because of the greater filler-filler interaction. Moreover, the existence of only one degradation step in the composite again confirmed the uniformity of the system and proves the existence of the interconnected three dimensional network of NR-nanocellulose complex. The thermal degradation results for the neat matrix show that the main degradation will be the degradation 15 Page 16 of 41
of isoprene units (~368oC). In other words, in the composite degradation, the absence of peaks at lower temperatures can be attributed to the presence of homogenous three dimensional Zn/cellulose complex networks. We can summarize the whole degradation of the composite in two step process. In the first stage of the degradation, the deterioration of polymer chain and the cross linking network into simple products and in the second stage of the decomposition the volatilization of the products formed in the first step. With increased
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filler percentage, the residual char increased in proportion to its nanocellulose content which has a higher residual char than the NR. When comparing with the thermal stability of the
cr
nanocellulose and NR matrix, we can conclude that the thermal stability can be improved to some extent at the lower filler percentage. We have a substantial improvement by
us
incorporating nanocellulose in the natural rubber matrix. Even though the thermal degradation of cellulose starts at 327oC, its degradation in the composite (when it is
an
reinforced in the NR matrix) will start at ~360oC. Thus the use temperature range of nanocellulose can be improved by reinforcing the nanocellulose in the natural rubber matrix.
4.
M
[Fig. 9 here]
Conclusions
ed
Steam explosion combined with acid hydrolysis has been found to be successful in obtaining fibres in the nano dimension from jute fibres. A homogenous nanocellulose fibrils with a
ce pt
average diameter of 50 nm is obtained by this process. Nanocomposite materials were obtained by casting and evaporating a mixture of NR latex and aqueous suspension of cellulose nanofibrils which is obtained from jute fibre by steam explosion. The filler was evenly distributed in the composite structure which is evident from their TEM and XRD analysis.. The increase of nanocellulose content in the NR matrix causes a drastic increase in
Ac
the mechanical properties of the composite. The Young’s modulus and tensile strength of material increased, but elongation at break decreased.The increased mechanical performance is due to the network formation by the nanocellulose in the NR matrix.The composite also shared good thermal properties. Finally it is important to add that nanocellulose obtained from jute is a good candidate as reinforcement for NR type nanocomposites.
16 Page 17 of 41
References: [1]. K.G. Satyanarayana,.G.G.C. Arizaga, and F. Wypych, Biodegradable composites based
ip t
on lignocellulosic fibers—An overview Prog. Polym. Sci. 34,(2009) 982–1021 [2]H. Kargarzadeh Á I. Ahmad (&) Á I. Abdullah Á. S. Y. Zainudin, Effects of hydrolysis
extracted from kenaf bastfibers,Cellulose 19, (2012) 855–866.
cr
conditions on the morphology, crystallinity, and thermal stability of cellulose nanocrystals
us
[3]. J.L. Putaux, S. Molina-Boisseau, T. Momaur, and A. Dufresne, Platelet nanocrystals resulting from the disruption of waxy maize starch granules by acid hydrolysis
an
Biomacromolecules,45 (2003), 1198-1202,
[4].Y Habibi, LA Lucia, OJ Rojas, Cellulose nanocrystals: chemistry, self-assembly, and
M
applications Chem Rev.,110 (2010),: 3479–3500
[5].E. Abraham, B. Deepa, L.A. Pothen, J. Cintil, S. Thomas, M.J. John, R. Anandjiwala, S.S. Narine, Carbohyd. Polym.92 (2013), 1477.
ed
[6]. H. Angellier, J.L. Putaux, S. Molina-Boisseau, D. Dupeyre, and A. Dufresne, Starch Nanocrystal Fillers in an Acrylic Polymer Matrix Macromol Symp., 221 (2005) 95-104
ce pt
[7]. H.P.S. Abdul Khalil, A.H. Bhat, A.F. Ireana Yusra, Green composites from sustainable cellulose nanofibrils Carbohyd. Polym.. 87(2012) 963-979 [8].
G. Siqueira, J. Bras, A. Dufresne, Cellulosic bionanocomposites: a review of
preparation, properties and applications. Polymers 2 (2010) 728-765.
Ac
[9]. S. S. Ray, Polylactide-based bionanocomposites: a promising class of hybrid materials Chem Res 45 (2012) 1710-1720 [10]. S. A. Paralikar, J. Simonsen, and J. Lombardi, Poly(vinyl alcohol)/cellulose nanocrystal barrier membranes J Membrane Sci.,320 (2008) 248-258
17 Page 18 of 41
[11]. M.A.S. Azizi Samir, F. Alloin, J.Y. Sanchez, and A. Dufresne, Cellulose nanocrystals reinforced poly(oxyethylene) Polymer 45 (2004) 4149-4157 [12]. M. Floros, L Hojabri, E Abraham, J Jose, S Thomas, L Pothan, AL Leao, S Narine, Enhancement of thermal stability, strength and extensibility of lipid-based polyurethanes with cellulose-based nanofibers Polym. Degrad. Stab.97 (2012) 1970–1978
NR-based nanocomposite Appl Polym Sci., 119(2): (2011) 855–62
ip t
[13]. S. Khanlari, M. Kokabi, J Thermal stability, aging properties, and flame resistance of
cr
[14]. K. G. Nair and A. Dufresne, Crab shells chitin whiskers reinforced natural rubber
us
nanocomposites Biomacromolecules 4 (2003) 666–74
[15]. H. Angellier, S. Molina-Boisseau, L. Lebrun and A. Dufresne, and structural properties of waxy maize starch nanocrystals reinforced natural rubber. Macromolecules 38 (2005)
an
3783–91
[16]. E. Abraham, B. Deepa, L.A. Pothan, M. Jacob, S. Thomas, R. Anandjiwala and. S.S.
M
Narine, Physico-mechanical properties of green nanocomposites based on cellulose nanofibre and natural rubber latex. Cellulose. 20 (2013) 417-427
ed
[17]. M. Nuruddin,, A. Chowdhury,, S. A. Haque, M. Rahman,, S. F. Farhad,, M. Sarwar Jahan, et al, Extraction and characterization of cellulose microfibrils from agricultural wastes
ce pt
in an integrated biorefinery initiative. Cell. Chem. Technol. 45 (2011).347–354. [18]. S. Ifuku, M. Nogi, K. Abe, M. Yoshioka, M. Morimoto, H. Saimoto and H. Yano, Synthesis of silver nanoparticles templated by TEMPO-mediated oxidized bacterial cellulose nanofibers Biomacromolecules, 10(9), (2009) 2714–2717.
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[19]. M. S. Jahan, A. Saeed, Z. He, and Y. Ni, Jute as raw material for the preparation of microcrystalline cellulose Cellulose, 18 (2011).451–459. [20]. F. Fahma, S. Iwamoto, N. Hori, T. Iwata, and A. Takemura, Isolation, preparation, and characterization of nanofibers from oil palm empty-fruit-bunch (OPEFB) Cellulose,17 (2010). 977–985. [21] T. Saito,, & A Isogai, TEMPO-mediated oxidation of native cellulose: The effect of oxidation conditions on chemical and crystal structures of the water insoluble fractions Biomacromolecules, 5(5) (2004). 1983–1989
18 Page 19 of 41
[22] A., Thygesen, J. Oddershede, H., Lilholt, A. B. Thomsen,
K Ståhl., On the
determination of crystallinity and cellulose content in plant fibres. Cellulose, 12, (2005). 563– 576 [23 ] A.T. Koshy, B. Kuriakose, S. Thomas and S. Varghese~ Studies on the effect of blend ratio and
ip t
crosslinking system on thermal, X-ray and dynamic mechanical properties of blends of natural rubber and ethylene-vinyl acetate copolymer Polymer, 34 (16) , 1993, 3428-3436
A. Alemdar, & M. Sain, Isolation and characterization of nanofibers from agricultural residues–Wheat straw and soy hulls. Bioresource technology,99(6), (2008) 1664-1671.
cr
[24].
us
[25] N., Lin, & A. Dufresne, Physical and/or chemical compatibilization of extruded cellulose nanocrystal reinforced polystyrene nanocomposites. Macromolecules, 46(14),
an
(2013). 5570-5583.
[26]S. Boufi,, H., Kaddami,, & A. Dufresne, Mechanical performance and transparency of reinforced
polymer
nanocomposites.
Engineering, 299(5), (2014). 560-568.
Macromolecular
Materials
and
M
nanocellulose
[27 ] D., Dufresne A.: Mechanical properties of natural rubbernanocomposites reinforced
ed
with cellulosic nano -particles obtained from combined mechanical shearing,and enzymatic and acid hydrolysis of sisal fibers.Cellulose, 18, (2011),.57–65 [28] A. Dufresne, Nanocellulose: A new ageless bionanomaterial 16(6),( 2013), 220–227
ce pt
[29] C. J. Chirayil,, J. Joy , L. Mathew, J. Koetz, & S. Thomas, Nanofibril reinforced unsaturated polyester nanocomposites: Morphology, mechanical and barrier properties, viscoelastic behavior and polymer chain confinement. (2014). Industrial Crops and Products, 56, 246-254.
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[30] R. Rajasekar, G.C. Nayak, A. Malas, C.K. Das, Development of compatibilized SBR and EPR nanocomposites containing dual filler system,Materials & Design, 35, (2012),878– 885
[31] K.R. Rajisha, H.J. Maria, L.A. Pothan, Zakiah Ahmad, S. Thomas, Preparation and characterization of potato starch nanocrystal reinforced natural rubber nanocomposites, International Journal of Biological Macromolecules 67 (2014) 147–153 [32]. E. Abraham, P.A. Elbi, B. Deepa,, P. Jyotishkukar, L.A. Pothen,, S. Thomas, S.S. Narine, X-ray diffraction and biodegradation analysis of green nanocomposites of natural rubber/nanocellulose Poly. Degra. and Sta. 97 (2012) 2378-2387.
19 Page 20 of 41
[33].D. Bondeson, A. P. Mathew, & K. Oksman, Optimization of the isolation of nanocrystals from microcrystalline cellulose by acid hydrolysis Cellulose, 13(2) (2006). 171– 180 [34]. N. Lin, G. Chen, J. Huang, A. Dufresne,, & P. R, Effects of polymer grafted natural nanocrystals on the structure and mechanical properties of poly(lactic acid): A case of
ip t
cellulose whisker-graft-polycaprolactone Chang, J. Appl. Polym Sci., 113(5) (2009). 3417– 3425
cr
[35]. J. H. Yu, F. J. Ai, A. Dufresne, , S. J. Gao, J. Huang, & P. R. Chang, Structure and mechanical properties of poly(lactic acid) filled with (starch nanocrystal)-graftpoly(epsilon-
us
caprolactone) Macromol. Mater. Eng, 293(9) (2008). 763–770.
[36]. H. Ismail, M, Edyhan, B. Wirjosentono, Bamboo fiber filled natural rubber composites:
an
the effects of filler loading and bonding agent. Polym Test., 21(2) (2002) 139–44. [37]. A. Karmakar, S. S. Chauhan, J. M. Modak and M. Chanda, Mechanical properties of
M
wood–fiber reinforced polypropylene composites: effect of a novel compatibilizer with isocyanate functional group Composites A 38 (2007) 227–33 [38]. G. Siqueira, S. Tapin-Lingua, J. Bras, D.S. Perez, A. Dufresne, Mechanical properties
ed
of natural rubber nanocomposites reinforced with cellulosic nanoparticles obtained from combined mechanical shearing, and enzymatic and acid hydrolysis of sisal fibers Cellulose
ce pt
18 (2011) 57–65.
[39]. J.Bras, M. L. Hassan, C.Bruzesse, E. A. Hassan, N. A. El-Wakil, A. Dufresne, Mechanical, barrier, and biodegradability properties of bagasse cellulose whiskers reinforced natural rubber nanocomposites Ind Crops Prod., 32(3) (2010) 627–33.
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[40]. S Varghese, J Karger-Kocsis, Natural rubber based nanocomposites by latex compounding with layered silicates. Polymer 44 (2003) 4921–7 [41]. S Varghese, J Karger-Kocsis, Melt compounded natural rubber nanocomposites wuth pristine and organophilic layered silicates of natural and synthetic origin J. Appl. Polym Sci., 91 (2004) 813–9.
20 Page 21 of 41
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List of tables
Table 1 Formulation of the cross linked NR/nanocellulose composite
1% Nano
2%Nano
3% Nano
Natural rubber latex (Centrifuged)
96.5
95.5
94.5
93.5
Jute nanocellulose dispersion
0
1
2
3
1.5
1.5
1.5
0.75
0.75
0.75
0.75
ed
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Neat NR
an
Weight % in the nanocomposite
1.5
ZMBT dispersion
0.6
0.6
0.6
0.6
Zinc oxide dispersion
0.3
0.3
0.3
0.3
KOH solution
0.35
0.35
0.35
0.35
Sulphur dispersion
Ac
ce pt
ZDC dispersion
Table 2 The crystallinity of the jute fibres at different processing stages Sample
Xc %
Xa%
1.
Raw jute fibre
46.32
53.68
2.
Steam exploded
62.54
37.46
3.
Bleached fibre
77.54
22.45
4.
Acid hydrolysed fibre
82.22
17.77
No
21 Page 22 of 41
Table 3: The tensile test data of the nanocomposites Sample
Tensile
Elongation
Stress at
Stress at
Crosslink
strength
at break
100%
200%
density
(MPa)
(%)
(MPa)
(MPa)
(moles/L)
3.52
860
1.90
2.05
2. 1% Nanocomposite
3.81
750
2.20
2.30
3. 2% Nanocomposite
4.15
620
2.60
2.60
4. 3% Nanocomposite
4.25
410
3.05
cr
1. Natural rubber
1.39x10-3
ip t
No
1.91x10-3 2.2 x10-3
an
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3.40
1.61x10-3
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Figure captions:
Fig. 1: SEM of jute fibres at different processing stages (A): Raw jute fibre; (B) Alkali treated fibre; (C): Steam exploded followed by bleached fibre; (D): Acid hydrolysed fibre
ed
Fig. 2: TEM images of jute nanofibres
Fig. 3: FTIR spectrum of jute fibre during various treatments
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Fig. 4: XRD spectrum of jute fibre during various treatments Fig. 5: Birefringence analysis of jute nanofibres
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Fig. 6 : Cryo-TEM of the inner part of the NR/nanocellulose composite (A): Neat matrix; (B) 1% nanocomposite; (C): 2% nanocomposite; (D): 3% nanocomposite (E) Schematic represention showing the possible interation between nanocellulose through H-bonding creating a netwok structure . Fig. 7 : XRD analysis of the NR/nanocellulose composites Fig. 8 : Tensile properties of nanocellulose/NR composite Fig. 9 : Thermo gravimetric (TGA) properties of nanocellulose/NR composite
22 Page 23 of 41
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Figures
Figure. 1
23 Page 24 of 41
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Figure. 2
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Figure. 3
Figure. 4
25 Page 26 of 41
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Figure. 5
Figure. 6 26 Page 27 of 41
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Figure 7
Figure. 8
27 Page 28 of 41
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Figure. 9
28 Page 29 of 41
Table(s)
Table 1 Formulation of the cross linked NR/nanocellulose composite Weight % in the nanocomposite 1% Nano
2%Nano
3% Nano
Natural rubber latex (Centrifuged)
96.5
95.5
94.5
93.5
Jute nanocellulose dispersion
0
1
2
Sulphur dispersion
1.5
1.5
ZDC dispersion
0.75
0.75
ZMBT dispersion
0.6
0.6
Zinc oxide dispersion
0.3
KOH solution
0.35
ip t
Neat NR
cr
3
1.5
0.75
0.75
0.6
0.6
0.3
0.3
0.3
0.35
0.35
0.35
Ac ce p
te
d
M
an
us
1.5
Page 30 of 41
Table(s)
Table 2 The crystallinity of the jute fibres at different processing stages Xc %
Xa%
1.
Raw jute fibre
46.32
53.68
2.
Steam exploded
62.54
37.46
3.
Bleached fibre
77.54
22.45
4.
Acid hydrolysed fibre
82.22
17.77
Ac
ce pt
ed
M
an
us
cr
ip t
Sample
No
Page 31 of 41
Table(s)
Table 3: The tensile test data of the nanocomposites Sample
Tensile
Elongatio
Stress at
Stress at
Crosslink
strength
n at
100%
200%
density
(MPa)
break
(MPa)
(MPa)
(moles/L)
1. Natural rubber
3.52
(%) 860
2. 1% Nanocomposite
3.81
750
2.20
2.30
3. 2% Nanocomposite
4.15
620
2.60
2.60
4. 3% Nanocomposite
4.25
410
3.05
3.40
1.90
2.05
1.39x10-3 1.61x10-3
ip t
No
1.91x10-3
Ac
ce pt
ed
M
an
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cr
2.2 x10-3
Page 32 of 41
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M
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Figure(s)
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M
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Figure(s)
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M
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Figure(s)
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M
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Figure(s)
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M
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Figure(s)
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M
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Figure(s)
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M
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Figure(s)
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Figure(s)
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Figure(s)
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