Comprehensive characterization of natural cellulosic fiber from Coccinia grandis stem

Accepted Manuscript Title: Comprehensive characterization of natural cellulosic fiber from Coccinia grandis stem Authors: S. Garette Jebadurai, R. Edwin Raj, V.S. Sreenivasan, J.S. Binoj PII: DOI: Reference:

S0144-8617(18)31461-9 https://doi.org/10.1016/j.carbpol.2018.12.027 CARP 14381

To appear in: Received date: Revised date: Accepted date:

17 June 2018 21 November 2018 10 December 2018

Please cite this article as: Jebadurai SG, Raj RE, Sreenivasan VS, Binoj JS, Comprehensive characterization of natural cellulosic fiber from Coccinia grandis stem, Carbohydrate Polymers (2018), https://doi.org/10.1016/j.carbpol.2018.12.027 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.

Comprehensive characterization of natural cellulosic fiber from Coccinia grandis stem

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S. Garette Jebadurai a, R. Edwin Raj b,*, V. S. Sreenivasan a, J. S. Binoj c

Department of Mechanical Engineering, V V College of Engineering, Tisaiyanvilai - 627657,

Tamilnadu, India. b

Department of Mechanical Engineering, St. Xavier’s Catholic College of Engineering,

Nagercoil - 629003, Tamilnadu, India.

Micromachining Research Centre, Department of Mechanical Engineering, Sree Vidyanikethan

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Engineering College (Autonomous), Tirupati - 517102, Andhra Pradesh, India.

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* Corresponding author. Tel.: +91 09442054535; fax: +91 04652 233982.

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Highlights:

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E-mail address: [email protected] (R. Edwin Raj).

Anatomical, thermal and tensile properties of Coccinia grandis fiber (CGF) studied.

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High cellulose content (63.22%) of CGF provides good mechanical strength.

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XRD and FTIR analyses exhibit the presence of Iβ cellulose in CGF.

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TGA established the thermal stability to withstand polymerization temperature.

Abstract 1

The anatomical, physico-chemical, mechanical, thermal and surface characteristics of Coccinia grandis fiber (CGF) was studied for a potential substitute to the harmful synthetic fibers. The anatomical analysis of Coccinia grandis stem reveals the presence of high strength

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xylem fibers. Polarized light microscopy and scanning electron microscopy of CGF shows a hierarchical cell structure composed of a primary and a secondary cell wall, cell lumen and the middle lamellae. The average cross-sectional area and density of the CGF was 0.0111 mm2 and 1.5175±0.005 g/cm3 respectively. The x-ray diffraction and Fourier transform infrared analysis of the fiber indicates the presence of cellulose Iβ with a crystallinity index of 46.09%. The mean

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young’s modulus and tensile strength of the CGF was 124 GPa and 775 MPa respectively, which

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is sufficient enough for the reinforcement in polymer composites. The thermogravimetric

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analysis confirms the thermal stability of CGF up to 250°C, which is well within the

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polymerization process temperature.

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Keywords: Coccinia grandis; Natural fiber; Physico-chemical analysis; Mechanical analysis;

1. Introduction

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Surface analysis; Thermal analysis.

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Man-made fibers are stronger, more durable, cheaper and less sensitive to temperature and moisture than natural fibers [1]. The benefits of natural fiber should attract industries to

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adopt them in many products due to its eco-friendly characteristics such as biodegradability and

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safety to the end users [2]. Since strict environmental regulations are being enforced in many countries, there is an increased interest in the use of such resources, which has led to a positive change in composite industries for natural fiber market [3]. Today, a revolution in the use of natural fibers as a reinforcements for synthetic fiber is taking place, primarily in the automobile industry. Natural fibers such as flax and hemp are being used in the production of door panels 2

and automobile roofs [3]. Large quantities of natural fibers are needed to substitute artificial fibers and the current production level of such fibers does not meet today’s demand. New potential plant fibers are to be identified along with easy and cost effective technological

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development is needed to extract fibers. Such potential fibers are to be characterized to determine the microstructural, physico-chemical, thermal and mechanical properties [4]. Natural fibers are generally extracted from stems, leaves, roots, fruits and seeds of plants, and some of them possess high specific mechanical properties. The general application of plant fiber includes ropes, strings, cords, cables, canvas, textiles, hats, mats, fancy articles and brushes etc. [6].

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In this study the stem of a plant, Coccinia grandis (CG), which belongs to the family

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cucurbitaceae was selected for fiber extraction and potential estimation as a reinforcement in

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composite [7]. CG also known as ivy gourd, tendli and tindora is available in plenty in India.

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They have both medicinal value and rich fiber content. CG is a dioecious, perennial, herbaceous vine that can grow between 9 and 28 m high. It has glabrous stems with pentagonal cross-section

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having internodes of 1.5 - 1.9 cm wide and 10 - 15 cm long (Fig. 1a) [8]. The coccinia grandis

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fiber was not characterized comprehensively until today to assess its potentiality to substitute

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artificial fiber for polymer composite reinforcement.

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Fig. 1. (a) Coccinia grandis plant with glabrous stems and (b) Extracted CGFs The present work aims to analyze the potential of its usage as a reinforcement in polymeric matrix composite. The microstructural, physical, chemical, thermal and mechanical

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properties of the fiber were analyzed and compared with that of the other natural fibers. The degree of roughness on CGF surface was also determined using three-dimensional non-contact surface roughness tester to ascertain its bonding characteristics. The chemical analysis was conducted to know the lignin, cellulose, wax, moisture and ash content along with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The microstructural

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examination was done along with mechanical testing to assess its mechanical properties. The

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thermal degradation properties of CGF was also analyzed by using thermo gravimetric analysis

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(TGA), to confirm its stability to withstand polymerization temperature.

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2.1. Materials

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2. Experimental

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CG stems were collected from farms around the village, called Tisaiyanvilai in Tirunelveli District, Tamilnadu, India and the fibers were extracted using microbial degradation

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technique [9]. The extracted CGFs were then sun dried for a week to remove the moisture content and machine combed for separation. The separated CGFs is shown in Fig. 1b.

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2.2. Characterization of CGFs 2.2.1. Anatomical analysis of CG stem and fibers A healthy CG stem was sliced into small pieces (10 mm × 10 mm) and held in FAA solution (5 ml formaldehyde + 5 ml acetic acid + 90 ml of 70% ethyl alcohol), for 24 h. They

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were dehydrated through a graded tertiary-butyl alcohol series and embedded in paraffin to section them of 10-12 µm thick using a rotary microtome [10]. The sectioned slices were affixed in glass slide and stained with a mixture of toluidine blue, safranine, fast green and Lugo’s iodine

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solution [11]. For normal observations, bright field imaging was used and for the crystal (starch grains and lignified cells) studies, polarized light was employed.

CG stem and fibers were examined in both transverse and longitudinal position at different magnification in FE-SEM ZEISS SIGMA model microscope. Prior to the analysis, the samples were coated with gold (layer thickness ~ 30 nm) to avoid charging of samples under

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electron beam.

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2.2.2. Physical characterization of CGFs

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The fiber cross-sections were irregular and to nullify the variability in measurement, a 40

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mm long fiber was cut into four sections of 10 mm each and photographed. The images were then post-processed using ImageJ software. A contour line was drawn to delineate fiber cross-

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section, and the average cross-sectional area was determined.

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The dimensions of different microscopic features of CGF such as middle lamellae,

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primary wall, secondary wall and fiber lumen were calculated from the SEM images using ImageJ software. The porosity of the fiber was computed as the ratio between the total surface

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area of the fiber lumens to the raw cross-sectional area of the fiber [12]. The density of CGF was determined using a pycnometer with toluene as the immersion liquid [12]. The fibers were

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dehydrated for 96 h in a desiccator containing silica before doing the measurement. The density of CGF was calculated using the expression: (1)

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where

is the density of CGF (g/cm3),

is the density of toluene (g/cm3), m1 is the

mass of the empty pycnometer (kg), m2 is the mass of the pycnometer filled with chopped fibers (kg), m3 is the mass of the pycnometer filled with toluene (kg) and m4 is mass of the pycnometer

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filled with chopped fibers and toluene (kg). The fineness of CGF was measured in terms of linear density in accordance with ASTM D 1577-92 [4] in Tex and denier. 2.2.3. Chemical characterization

The lignin content was determined by klason method where the samples were crushed and extracted with dichloromethane before being hydrolysed in 72% solution of sulphuric acid

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and quantified [13]. The cellulose content was calculated following Kurshner and Hoffer

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method, where the crushed samples were extracted with dichloromethane, and then in a mixture

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of ethanol and 95% nitric acid [14].

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The wax content of CGF was determined with soxlet extraction using ethanol for 6 h

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[15]. The solution was then transferred to a separator funnel, and chloroform was added to

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extract the wax. Purified water was then added, and chloroform and alcohol separate into two layers. The chloroform evaporates from the solution leaving the waxy residue, which were dried

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and weighed to determine the wax content. To determine the moisture content, the samples were dried in an oven at 104°C for 4 h to

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measure the weight loss using the expression:

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% moisture =

×100

(2)

X-ray spectra (scan range (2θ) = 10° - 80°; θ = diffraction angle; scan speed = 5.0

deg/min) of CGF samples were obtained with Rigaku X-ray diffractometer D/Max Ultima III with an X-ray tube producing monochromatic Cu Kα radiation. The integrated intensities of the Bragg peaks in the spectrum was identified to estimate the crystallinity indices. 6

FTIR spectra of CGF was recorded using a Perkin Elmer spectrum RXI FTIR spectrometer in a KBr matrix with a scan rate of 32 scans per minute and a resolution of 2 cm -1 in the wave number region from 400 to 4000 cm-1. CGF samples were grounded to fine powder

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using a mortar and pestle. This powder was mixed with KBr and pelletized by pressurization to record FTIR spectra under standard conditions. 2.2.4. Mechanical properties

The dried CGFs were tested for tensile strength at various gauge lengths (GL) of 10, 20, 30, 40 and 50 mm in Instron universal testing machine of type 5500R according to ASTM D

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3822-01 standard [4], with a cross head speed of 0.1 mm/min. Pneumatic grips were used to

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clamp the fibers at a pressure of 0.4 MPa. The average strain rates were in the order of 0.6 s-1 and

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0.15 s-1 for the GLs of 10 mm and 50 mm respectively. 20 samples were examined at each GL,

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and the average values were reported. Testings were performed at an ambient temperature of ~

2.2.5. Thermal analysis

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21°C and at a relative humidity of about 65%.

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The thermal stability of CGF was evaluated by thermo gravimetric (TG and DTG)

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analysis using Jupiter simultaneous thermal analyzer (Model STA 449 F3, NETZSCH, Germany) in nitrogen atmosphere at a flow rate of 20 ml/min to prevent oxidation effects. 10 mg

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of crushed CGF was kept in an alumina crucible, which was instrumented with thermocouple to measure the variation in temperature. The heating rate was maintained at 10°C/min and the

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samples were tested from 28°C to 500°C. 2.2.6. Surface morphology study

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A non-contact 3D profiler (Talsurf CCI MP, UK) was used to estimate the surface roughness of CGFs. 50 mm length CGFs were used to determine the surface roughness along the length of the fiber.

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3. Results and discussion 3.1. Anatomical analysis of CG stem and fibers

The transverse sections of CG stem show that it is deeply grooved in five regions. The wide segments of CG stem are united in the middle part (Fig. 2a) whereas the segments in the outer region are fan shaped and are separated from each other by parenchymatous tissue. Phloem

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semicircular mass is present at the outer end of each segment. Two or three thin layered periderm

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and wide parenchymatous cortex are seen in the outer periphery of stem (Fig. 2b). Irregular

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shape sclerenchyma cells are randomly distributed in the cortical zone. sclerenchyma cells are

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sclereids with thick lignified secondary walls and wide lumen (Fig. 2b). Each segment has four or five straight uniseriate lines of xylem, which are surrounded by parenchymatous xylem rays

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(Fig. 2b).

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The long radial rows of xylem consist of radial chains with wide circular thin walled

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vessels which are ensheathed by thick layer of fibers (Fig. 2c). Similar to other natural fibers, CGFs possess a hierarchical structure. The polygonal shape fibers have wide lumen, thick layer

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of lignin and thin primary wall. The width of fiber ranges from 15 to 30 µm. The cell walls of the fibers are 8 µm thick approximately (Fig. 2d & 2e). Xylem fibers are separated from each other

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by maceration fluid which consists of 10% chromic acid and 10% nitric acid.

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Fig. 2. (a) Transverse section of a CG stem showing grooved stem with thick holes. (10X).

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(b) An enlarged CG stem segment exhibiting secondary phloem and xylem (30X). (c) Magnified view of secondary xylem displaying vessels ensheathed by fibers. (160X). (d)

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Expanded view of xylem fibers revealing primary walls, secondary walls and lumens (560X) (e) Transverse sections of CGFs (600X) Fig. 3 shows the SEM images of CGF in transverse section, where it shows the cell lumen, primary wall, secondary wall and middle lamellae. This porous structure encourages good penetration when used as a reinforcement for polymer composite preparation.

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Fig. 3. SEM view of CGF in transverse section – (a) 213X and (b) 822X

Fig. 4a shows the longitudinal view of CGF where narrow, oblique slit like pits are seen

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in the lateral walls. The pits occur in row and are 30 - 40 µm long. SEM image of longitudinal

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views of CGFs are shown in Fig. 4b-4d in different magnifications. It is evident from SEM

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images (Fig. 4b-4d) that rough lateral surface of CGF contains pits and voids. These surface

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irregularities will enhance interface bonding between CGF and the resin during composite

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fabrication.

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Fig. 4. (a) Longitudinal view of CGF (polarized light micrograph; 40X), (b) SEM images of

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longitudinal view of CGF – 117X, (c) 248X, (d) 504X and (e) 2890X 3.2. Physico-chemical analysis

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Fig. 5. Comparison of physico-chemical properties of CGF with other natural and synthetic

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fibers [4,5,16,17,18 & 19]

The physico-chemical properties of CGF are collated with those of other natural and

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synthetic fibers and is shown in Fig. 5. The cross-sectional area of natural fiber varies according to the source and the growth rate of the plant. The sectional area of the fiber influences the

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modulus and the strength of the fiber and are normally inversely proportional [20-22]. Fig. 2d and 3a shows the irregularity in the cross-section area of 40 mm long CGF sample which measures as 0.011, 0.0115, 0.0108 and 0.0111 mm2 [4]. The porosity fraction was determined by image analysis and it varies from 42% to 46%. The high porous fraction enables impregnation of resin during composite fabrication. The 12

microstructural features of CGF is reported in Table 1. The primary wall thickness is twice as that of secondary wall and the lumen thickness (17426±9261 nm) is high enough to accommodate enough porosity on the CGF surface for good bonding. The density of CGF is

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1.5175±0.005 g/cm3 which is approximately same as that of cotton, ramie, sisal, flax and hemp fibers but less than that of artificial fibers such as carbon and glass fibers. The fineness of the fiber is 130.9 tex or 1178.1 denier. Table 1 Physical properties of CGFs

Average values for CGF

Primary wall thickness (nm)

3226 ± 835

Secondary wall thickness (nm)

1824 ± 687

Middle lamellae thickness (nm)

2302 ± 505

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Physical parameter

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Fineness of CGF (tex)

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Diameter of CGF (µm) Colour of CGF

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Density of CGF (g/cm3)

543-621 White 130.9 1.5175 42-46

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Porosity of CGF (%)

17426 ± 9261

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Cell lumen thickness (nm)

The chemical composition of fiber influences its properties, and in many ways, the fiber

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themselves can be considered as fibrous composite materials. Cellulose and lignin contents in the natural fibers act as reinforcement and matrix, respectively. Generally cellulose has four basic types classified as cellulose I, II, III and IV. The physico-chemical and the mechanical properties of the natural fibers largely depend on its cellulose type, because each type of cellulose has its own cell geometry. As cellulose is the strongest (reinforcement) material in natural fibers, their 13

content has significant influence on its mechanical properties. In general, fiber strength increases with increasing cellulose content [23]. As reported in Fig. 5, CGFs contain 63.22% cellulose, which is ~ 47% greater than that of coir fiber, one of a strong natural fiber. The lignin content

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also influences favorably the structural properties of the fiber [24] and CGF has 24.42%. Lignin fills the spaces in the cell wall between cellulose, hemicellulose, and pectin components, especially the vascular and support tissues. It is covalently linked to cellulose and therefore cross-links different plant polysaccharides, conferring mechanical strength to the cell wall [25]. Plant waxes exist on the surface of plant fibers to control evaporation, wet-ability and hydration

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[26]. They reduce the adhesive property of the fibers with the resins while making composite

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materials with it. CGF contains only 0.32% wax, and the moisture content is only 9.14% which

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are very negligible quantity to influence the bond quality.

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3.2.1. XRD analysis

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The X-ray spectrum of the CGF is shown in Fig. 6a, where two well-defined diffraction

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peaks appear along with minor peaks, which signifies the semi-crystalline nature of CGF. In corroboration with other researcher [27, 28, 29], the two major peaks at 16.4° and 22.56° belongs

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to cellulose I and IV of a monoclinic structure [28-30]. Similar peak pattern was reported by

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Senthamaraikannan and Kathiresan on CGF [31].

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Fig. 6. (a) X-ray spectra of CGF, (b) FTIR spectra of CGF

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0) crystallographic

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The peaks at 16.4° and 22.56° are attributed to the (2 0 0) and (1

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46.09% based on reference datum,

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planes [28, 32-34] and the crystallinity index (CI) was calculated using the equation (3) as

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(3)

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where H22.5 is the height of the peak at 2θ = 22.5° and H18.5 is the diffraction intensity at 2θ =

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18.5° [33, 35]. This CI value is higher than that of Juncus effuses (33.4%), oil palm fruit (34.1%), Date palm (38.5%), Wrighitia tinctoria (40.6%), Grewia tilifolia (41.7%), Coconut

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(41.9%) and Artisdita hystrix (44.85%) and smaller than that for Tamarindus indica fruit fibers (55%), Areca fruit husk (55.5%), saharan aloe vera (56.5%), cissus quadrangularis root (56.6%),

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ramie (58%), sansevieria cylindrica (60%), cotton (60%), sisal (71%), jute (71%), flax (80%) and hemp fibers (88%). Moreover, this CI value is approximately equal to that of Prosopis juliflora bark (46%), Lygeum spartum (46.19%), Cissus quadrangularis stem (47.15%) and Ferula communis fibers (48.1%) [4, 5, 29, 31, 33-35, 36, 37]. This higher CI value (46.09%) indicates CGF

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crystallites are orderly in nature. The crystallite size (L) was calculated using scherrer’s formula [34] as 1.91 nm. (4)

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where k = 0.89 the Scherrer’s constant, β is the peak’s full width half maximum (FWHM) and λ is the wavelength of the radiation [28, 30, 38]. The crystallite size of CGF (1.91 nm) is smaller than that of ramie fibers (16 nm), tamarindus indica fruit fibers (5.73 nm), cotton fibers (5.5 nm), corn stalk fibers (3.8 nm) and flax fibers (2.8 nm) and greater than that of ferula communis (1.6 nm) and carbon fibers (0.669 nm) [33, 36, 37, 38, 39]. The larger crystallite size (L = 1.91 nm)

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reduces chemical reactivity and water absorption capacity of CGF when reinforced in matrix

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medium.

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3.2.2. FTIR analysis

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The FTIR spectrum shown in Fig. 6b. The band positions of natural fibers vary based on

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their origin [40]. Recent work on the same fiber by other researchers have reported peaks at

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3336, 2919, 2346, 1733, 1644, 1546, 1426, 1249, 1179 and 1031 cm−1, which was quite similar to this FTIR findings [31]. The bands at 3400 cm-1 (3345.85 in Fig. 6b) and 760 cm-1(770.55 in

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Fig. 6b) are attributed to cellulose Iβ [29, 30, 39]. The bands at 1740 cm-1(1750.11 in Fig. 6b), 1455.14 cm-1 and 1510 cm-1(1506.41 in Fig. 6b) are attributed to lignin [30]. The bands at

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2919.15 cm-1and 2850.77 cm-1 indicate reduction of C-H stretch of alkyl and methylene group in

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CGF [5]. The bands at 1423.1 cm-1 and 1368.42 cm-1 represents the existence of C-H bond in CGF [41, 42]. The C-O stretch of acetyl group of lignin at 1236.21 cm-1 is present in the spectrum [42]. The existence of saline in CGF was confirmed by the bands at 770.55 cm-1 and 897.6 cm-1 [4]. The bands at 1019.26 cm-1 and 1153.17 cm-1 represent the presence of strong and broad C-OH stretching of cellulose in CGF [5]. 16

The presence of Hydrogen bonds and O-H stretching is manifested by the peek at 3670.61 cm-1 and that of hemicellulose is expressed at 1634.35 cm-1 [4, 16]. The bands at 1538.48 cm-1 and 2137.68 cm-1 indicate the presence of C≡C alkynes group and the availability

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of C-H stretching of phenols and esters is indicated by the peek at 1331.83 cm-1 [16]. 3.3. Tensile characteristics

The tensile characteristics of CGF tested under different gauge length (GL) is tabulated in Table 2, where no significant correlation exists with respect to GL. The tensile characteristics of CGF is also dependent on its plant source, age, mechanism of fiber extraction and fiber

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microstructure, where the crack initiate from the bigger flaw leading to fiber failure. As the GL

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increases, more flaws exist and they link with each other for sudden failure at higher GL (50

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mm).

length Tensile strength Young’s (MPa)

10

424.242

30

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50

area (mm²)

26.515

16

0.0132

84.07

7.6

0.0126

774.642

110.663

7.0

0. 0112

728.723

123.51

5.9

0.0094

553.956

98.920

5.6

0.0091

638.968

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(%)

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Strain to failure Cross sectional

modulus (GPa)

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(mm)

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Gauge

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Table 2 Tensile characteristics of CGF

The young’s modulus of CGF increases with increasing GL and as expected for the

natural fiber, the strain to failure decreases with increasing GL due to the probability of the distribution of flaws in the volume of the fiber and their size.

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Table 3 Comparison of tensile properties of CGF with major synthetic fibers Mechanical properties Fiber

Tensile (MPa)

CGF

424 - 775

26.51 – 123.51

5.6 - 16

E-glass

2000 - 3500

70

2.5

Carbon

2400 - 4000

230 - 400

1.4 – 1.8

[36]

Aramid

3000 - 3150

63 – 67

3.3 – 3.7

[36]

S-glass

4570

86

2.8

[36]

Young’s modulus (GPa) Strain to failure (%)

References _

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strength

[36]

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The tensile properties of CGFs are compared with that of major synthetic fibers and

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tabulated in Table 3. The tensile strength of CGFs is low when compared with that of synthetic

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fibers such as E-glass, carbon and aramid. The CGF is more ductile than the synthetic fibers to

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3.4. Thermo gravimetric analysis

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provide more toughness for structural materials.

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Fig. 7a depicts a typical TGA and DTG curves of the powdered CGF sample. The removal of moisture is evident from the DTG curve (Fig. 7a) where the weight loss begins at

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80°C and continues till 105ºC with a weight loss of 8.63%. There is no significant weight loss till

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250°C, which indicates a good thermal stability for reinforcement application in CGF/polymer composite. Depolymerisation and degradation of hemicellulose and cellulose occur between

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250°C and 350°C, with a reported weight loss of 62% [43, 44], which is quite similar to the one reported for CGF earlier [31]. This is indicated by a sudden fall in DTG curve which corresponds to the thermal decomposition of hemicelluloses and glycosidic links of cellulose [42]. The drop at 320°C in DTG curve indicates the possible flinch of thermal decomposition of cellulose I and complete decomposition of α-cellulose [3]. Similar drops were observed for bamboo, hemp, jute, 18

kenaf and cissus quadrangularis root fibers at 321°C, 308.2°C, 298.2°C, 307.2°C and 328.9°C

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respectively [9].

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Fig. 7. (a) TG and DTG curve of CGF, (b) Broido’s plot of CGF

(5)

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]] = - (

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using the Broido’s equation [45].

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The kinetic activation energy (Ea) was calculated to find out the kinematic parameter of CGF

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where R is the universal gas constant (8.314 J/mol K), T is the temperature in Kelvin, y is the normalized weight (wt/w0), wt is the weight of the sample at any time t, w0 is the initial sample

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weight and k is the Boltzman constant (1.3806 10-23 J/K). The kinetic activation energy was and

(Fig. 7b). The kinetic activation

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computed from the Broido’s plot drawn between

energy (Ea) of CGFs was 82.3 kJ/mol, which is within the specified range (60 - 170 kJ/mol) for

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natural materials [3], which ensures thermal stability to withstand polymerization process temperature during composite fabrication.

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Table 4 Comparison of degradation temperature of CGF with major synthetic fibers Percentage weight loss and the corresponding temperature in °C 5% 25% 50% 75% 75°C 295°C 335°C 495°C CGF Glass* 586°C ------Carbon 542°C 641°C 695°C 738°C Aramid 344°C 577°C 596°C --* Ultimate fiber weight loss was 1.6%.

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Fiber

The degradation temperature of CGF is compared with that of other synthetic fibers and is tabulated in Table 4. Even though the degradation temperature of CGFs is low in comparison with other synthetic fibers, this value is high enough to withstand polymerization temperature

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encountered during polymer composite fabrication.

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3.5. Surface roughness analysis

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Fig. 8a shows the surface texture of CGF in 3D view and 8b shows the 2D line diagram of the same. The 2D line diagram indicates the variation in surface roughness of CGF along the

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length. The variation in peak value indicates the non-uniform nature of the surface. The mean

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roughness (Ra) of CGF is 0.613±0.014 µm which is high enough to enable good interfacial bond

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between the CGF and the matrix.

Fig. 8. (a) 3D surface texture of CGF, (b) 2D line diagram of CGF 20

4. Conclusions Comprehensive characterization of a natural fiber, Coccinia grandis was done to assess its potentiality for reinforcement in polymer composite fabrication. The presence of sufficient

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content of cellulose and lignin ensures high specific strength of the fiber in tensile test. The microscopic image analysis reveals the presence of porous fraction on the fiber surface along with surface irregularities enables good bonding while reinforcing it in polymer composite. The thermal stability up to 250°C enables the fiber to withstand polymerization process temperature. In conclusion the anatomical, physico-chemical, mechanical and thermal characteristics exhibits

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by the CGF, confirms the suitability of this fiber to replace harmful synthetic fibers.

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References

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[1] Pramendra kumar bajpai, Inderdeep singh, Jitendra madaan. Tribological behavior of natural

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fiber reinforced PLA composites. Wear, 2013, 297, 829-840. [2] Chen qin W, Nattakan soykeabkae, Ni xiuywan, Ton paijs. The effect of fibre volume

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2008, 71, 458 -467.

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Table 1 Physical properties of CGFs Physical parameter

Average values for CGF 3226 ± 835

Secondary wall thickness (nm)

1824 ± 687

Middle lamellae thickness (nm)

2302 ± 505

Cell lumen thickness (nm)

17426 ± 9261

Diameter of CGF (µm)

543-621

Colour of CGF

White

Fineness of CGF (tex)

130.9

Density of CGF (g/cm3)

1.5175

Porosity of CGF (%)

42-46

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TE

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M

A

N

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Primary wall thickness (nm)

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Table 2 Tensile characteristics of CGF

strength (MPa)

Young’s

Strain to

Cross sectional

modulus (GPa)

failure (%)

area (mm²)

424.242

26.515

20

638.968

84.07

30

774.642

110.663

40

728.723

123.51

50

553.956

98.920

16

0.0132

7.6

0.0126

7.0

0. 0112

5.9

0.0094

5.6

0.0091

A

CC

EP

TE

D

M

A

N

10

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(mm)

Tensile

U

Gauge length

28

Mechanical properties Fiber CGF

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Table 3 Comparison of tensile properties of CGF with major synthetic fibers

Tensile strength Young’s modulus (GPa) Strain to failure (%) (MPa) 424 - 775 26.51 – 123.51 5.6 - 16 2000 - 3500

70

Carbon

2400 - 4000

230 - 400

Aramid

3000 - 3150

63 – 67

S-glass

4570

86

_

2.5

[39]

1.4 – 1.8

[39]

3.3 – 3.7

[39]

2.8

[39]

A

CC

EP

TE

D

M

A

N

U

E-glass

References

29

Table 4 Comparison of degradation temperature of CGF with major synthetic fibers Percentage weight loss and the corresponding temperature in °C 5% 25% 50% 75% CGF 75°C 295°C 335°C 495°C Glass* 586°C ------Carbon 542°C 641°C 695°C 738°C Aramid 344°C 577°C 596°C --* Ultimate fiber weight loss was 1.6%.

A

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EP

TE

D

M

A

N

U

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Fiber

30