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Thermo-mechanical and morphological characterization of needle punched non-woven banana fiber reinforced polymer composites
Journal Pre-proof Thermo-mechanical and morphological characterization of needle punched nonwoven banana fiber reinforced polymer composites Jack J. Kenned, K. Sankaranarayanasamy, J.S. Binoj, C. Suresh Kumar PII:
S0266-3538(19)31611-2
DOI:
https://doi.org/10.1016/j.compscitech.2019.107890
Reference:
CSTE 107890
To appear in:
Composites Science and Technology
Received Date: 8 June 2019 Revised Date:
16 October 2019
Accepted Date: 25 October 2019
Please cite this article as: Kenned JJ, Sankaranarayanasamy K, Binoj JS, Kumar CS, Thermomechanical and morphological characterization of needle punched non-woven banana fiber reinforced polymer composites, Composites Science and Technology (2019), doi: https://doi.org/10.1016/ j.compscitech.2019.107890. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier Ltd.
Thermo-mechanical and morphological characterization of needle punched nonwoven banana fiber reinforced polymer composites Jack J Kenned a*, K. Sankaranarayanasamy a, b, J. S. Binoj c, C. Suresh Kumar d a
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli- 620015, Tamil Nadu, India b
Department of Mechanical Engineering, National Institute of Technology, Puducherry-609609, Puducherry, India
c
Department of Mechanical Engineering, SreeVidyanikethan Engineering College, Tirupati - 517102, Andhra Pradesh, India d
Department of Aeronautical Engineering, Bharath Institute of Higher Education and Research, Selaiyur, Chennai-600073, Tamilnadu, India
Abstract The purpose of this study is to employ a novel technique for the fabrication of natural fiber reinforced polymer composites that could stand toe to toe with glass fiber composites in terms of thermo-mechanical properties without any chemical treatment. The reinforcement fibers were extracted from the pseudostem of the nendran banana plant. Later a non-woven fabric composite consisting of banana fibers reinforced with unsaturated polyester (UPE) matrix was fabricated using the needle punching technique. Composite specimens were subjected to tensile, flexural, hardness, quasi-static indentation (QSI) and dynamic mechanical analysis (DMA) test for evaluating mechanical properties. However, the optimal properties was achieved at 40 wt.% fiber content with an increase in tensile and flexural strength of 36% and 33% for needle-punched banana fiber composites (NPBFC) compared with random banana fiber composites (RBFC) respectively. It was also evidenced from the load bearing capacity and hardness of NPBFC having 2420 N and 87 HRRW, proves its superiority over RBFC and comparable with RGFC. Further, the viscoelastic properties of UPE and NPBFC were analysed. Subsequently, the characteristic bonds of cellulose were represented through infra-red spectroscopy and the crystallinity index was exposed through X-ray diffraction analysis. In addition, thermal analysis was done and the stability of the optimized NPBFC witnessed was upto 260°C. Also, morphology-properties correlation was established. Finally, the experimental results were validated using theoretical models. This study concludes that the synthesized novel NPBFC endorses its potentiality as a probable reinforcement in industrial safety helmet, automotive door panel and light weight structural applications. Keywords: Banana fiber; Needle-punch; Polymer composites; Thermo-mechanical properties; Morphological properties. * Corresponding author. Tel: + 91 9443695891, E-mail: [email protected]
1. Introduction Any natural or man-made materials capable of being processed into a fabric can be defined as a fiber. Natural fibers are those which are not synthetic or man-made but could be sourced from animals or plants [1]. Realizing the insalubrious nature of synthetic fibers, researchers are currently gingerly turning away from them and focusing on the alternative, natural fiber composites (NFCs) [2-4]. Products made using these fibers have seamlessly made their way into the industry in a multitude forms [5-10]. Moreover, low density, high specific strength and stiffness, low cost, less absorption of CO2, less hazardous manufacturing processes, good electrical resistance, acoustic insulation, low emissions and less abrasive damage to processing equipment by NFCs compared to synthetic fiber composites are the advantages that have further kindled this change [11-13]. However, NFCs are not exactly problem-free as they pose issues of moisture absorption, lower strength, greater variation of properties and lower durability [14-16]. Despite these setbacks, biodegradability and the environmental benefit characteristics have made natural fibers a popular reinforcement in polymer matrix which can potentially replace traditional aramid fiber, carbon fiber and glass fiber composites [17, 18]. Various plant fibers that have been explored as a potential reinforcement include oil palm, areca, coir, jute, flax, hemp, ramie, kenaf, coconut, banana, sisal, and pineapple [19, 20]. Out of these, banana fibers have been studied extensively [21, 22]. India and Brazil are the largest producers of banana fibers. Production of banana in India during 2016-2017 had reached around 29.16 million tones, being cultivated in an area of 858 hectares [23]. Such a large production results in a similar magnitude of bio-waste and the banana fibers used in the composite fabrication are extracted from the pseudostem of the banana plant (Musa sapientum), which is supported by its abundant supply and at no additional cost [21]. Considerable research has been done on the subject of improvement of the properties of lignocellulosic fiber composites, which banana fiber composites fall under. Structural constituents, relative concentrations, various fiber parameters like length, distribution, diameter and orientation strongly influence the properties of the composite [24]. However, handling of an effective load transfer between the fiber and matrix requires that the interfacial interactions of the constituents should be strong [25]. The chemical modifications were adopted for overcoming this issue and to enable impactful influence on the properties of the composite. For banana fiber composites, the chemical treatments performed include alkaline, acetylation treatment [26], silane treatment [27], permanganate, benzoylation treatment [28] and maleated coupling reagents [29]. However, all these chemical treatments have their own limitations. Though it improves the interfacial bonding these are highly toxic, time consuming, costly and polluting the environment this prompted to study about an alternate method which would eliminate the above said hassles. Hence the objective of this study is to
fabricate a novel needle punched banana fiber reinforced polymer composites as a potential and alternate replacement for the existing carcinogenic composites. However, there is no report seen in literature on the study of untreated needle punched non-woven banana fiber composites. In this study, banana fibers extracted from the Nendran variety of banana plants were needle-punched to form a non-woven fabric, thereby bonded with an unsaturated polyester matrix forming a novel NPBFC. The investigated thermal, mechanical and morphological properties of NPBFC express its potentiality as a probable reinforcement in industrial safety helmet, automotive door panel, garden railing and light weight structural applications. 2.Materials and Methods 2.1. Raw fiber extraction from the banana plant Different varieties of banana plants including Red banana, Nendran, Rasthaly, Morris and Poovan were analyzed for their physico-chemical properties by Kiruthika and Veluraja [30]. The present investigation deals with the nendran variety of banana plant and the selection for this is on two grounds, is its excellent strength ( ≈ 450 MPa) and better economy compared to the other variety of bananas. The pseudostem was removed from the mature banana plant; nine days post its harvesting. From the pseudostem, the cortex region was extracted and fed into the retting machine to extract the fibers. Subsequently, the extracted fibers were sun dried for a period of 7 to 9 days to reduce the moisture content. Later, these dried fibers were kept in the oven at temperatures ranging from 50°C to 60°C for a period of 12 to 16 hrs for removal of the entire moisture content. These dried fibers were further subjected to a mechanical scutching process for easy removal of fibers from any hurds adhering to the fiber bundles using turbine blades. Fig.1 represents the process flow diagram of composite from the plant origin. 2.2. Chemical and physical properties of raw banana fiber The quantity of holo-cellulose was quantified by D Addico, Wise and Murphy method. Lignin and α cellulose content were determined by using TAPPI standards T 222OM-06 and T 203 respectively [31]. Hemicellulose was calculated by using the following relation Hemicellulose = (quantity of holo-cellulose - quantity of α cellulose) The chemical and physical properties of raw banana fiber are listed in Tables 1 and 2 respectively. 2.3. Botanical properties of raw banana fiber Narrow and wide banana sheath fibers were individually inspected by micro technique for the purpose of investigating its interior structure. The sheath of banana plant was sliced into small pieces and immersed in FAA solution (Maleic acid 5 ml + Formaldehyde 5 ml + 70% ethyl alcohol of 90 ml) for duration of 24 hrs for specimen preservation. Later, they
were dried out using tertiarybutyl alcohol and implanted in paraffin blocks. Further, the blocks were partitioned into a size of 10-12 m pieces by a rotary microtome that revolved in the right-handed direction. The prepared samples were then fixed to a glass slide stained with safranine and toluidine blue for improvement in image visibility. Finally, the specimens were observed with the help of a polarized light micrograph for examining the fiber structure. 2.4. Needle punching technique Needle-punching technique was used for mechanical entanglement of webs or batts of 30 mm long fibers to produce the fabric. This was accomplished through the action of reciprocating barbed (felting) needles which interlocked the fibers. The consolidated structure maintained its integrity through inter-fiber friction. A triangular barbed needle of regular barb spacing which implied an evenly spacing 9 barbs on a blade of ≈ 30 mm in length was used with an optimized penetration depth of 8 mm and a punch density of 100 punches/cm2. 3. Composite preparations and testing Unsaturated polyester resin, Methyl Ethyl Ketone Peroxide (MEKP) and accelerator cobalt naphthalene were procured from LEO Enterprises, Nagercoil. Unsaturated polyester was selected as the matrix material, due to its excellent process ability and cross-linking tendency. Later, the matrix was mixed with catalyst Methyl Ethyl Ketone Peroxide (MEKP) and accelerator cobalt naphthalene in a ratio of 98:1:1. The characteristics of the pure resin were tested for physical and mechanical properties are listed as in Table.3. A mild steel mold of dimensions 300 x 150 x 3 mm3 was used for the preparation of the composites with different fiber wt. %. The NPBF were impregnated with the prepared resin in the mold and compressed with a lid to form a sheet using the hand lay-up technique. In order to maintain homogeneity in the mixture, a mechanical stirrer was used and a continuous stirring process was performed. During this process, extreme care was taken to avoid clumbing and tangling during mixing. Later, the matrix was degassed by hand with the help of a roller and allowed to settle down by applying a compression load of 350 kN. The entire process was carried out at ambient temperature ( ≈ 27°C) with a relative humidity of about 65%. Silicon spray was applied over the mold for removing the cured NPBFC. Similarly, procedure was adopted for fabrication of 30 mm RBFC as well as RGFC specimens. 3.1
Mechanical testing The fabricated composite specimens were tested for tensile, flexural and hardness
properties as per ASTM standards. Tensile and flexural tests were carried out using UK made Tinius Olsen universal testing machine (UTM) having a 50 kN load cell and a cross head speed of 0.5 mm/min adhering to ASTM-D3039 and ASTM-D790 standards respectively. In addition, QSI tests were also performed on the same UTM using hemispherical indenter with 12.7 mm diameter for evaluating indentation damage resistance of the specimens. Meanwhile, hardness of the composite samples was tested following the ASTM-D785-98
standard using a data acquisition system embedded in a Rockwell hardness testing machine. In each case, five samples were tested and considered for calculating standard deviation. 3.2
Thermal analysis of NPBFC Thermal stability of the optimized NPBFC was analyzed by Thermo-Gravimetric
Analysis (TGA) Model 4000 (Germany made). An amount of 6- 8 mg of the pulverized composite specimen was placed in an alumina crucible for testing and the process was carried out in an inert atmosphere with Nitrogen flowing in at a rate of 20 ml/min. The temperature was increased in steps of 10°C/min from 35 to 850°C. 3.3
Dynamic mechanical analysis (DMA) DMA test was carried out to analyse the viscoelastic properties of UPE and NPBFC
specimens (10 wt. % to 50 wt. %) as per ASTM D 4065-01 standard using DMA Q800 V 7.4 (TA instruments, USA) set up. Single cantilever clamp, temperature sweep mode was employed to characterize the specimens. The specimens were applied with sinusoidal stress of 1 Hz frequency and strain amplitude of 25 µm. The experimentation was conducted in the temperature range of 25oC to 170oC with the heating rate of 2oC/min. 3.4
Fourier-transform infrared (FTIR) spectroscopy of NPBFC The Optimized NPBFC sample was dried, ground to powder and then pelletized with
KBr. Four scans were taken at a resolution of 4 and the infrared spectrum for the optimized NPBFC sample was obtained using a PerkinElmer Spectrum 2 series 93947 of version 10.03.09 for the wavelength ranging from 400 cm-1 to 4000 cm-1. 3.5
Structural characterization of NPBFC Optimized NPBFC was pulverized to obtain a fine powder and compacted at a
pressure of 110MPa. The compacted powder was then held in a standard disk of the Rigaku Ultima III X-ray Diffractometer for a continuous scanning mode at a scan speed of 2°/min and temperature of 300K. The step size adopted for this procedure was 0.02° (2θ) in the angular range of 10° - 80°. The sealed-tube of Cu-Kα radiation was operated at 40 kV and 32 o
mA at a wavelength of 1.54 A for deriving the X-ray Diffraction (XRD) patterns of optimized NPBFC. 3.6
Morphological analysis Composite specimens subjected to tensile and flexural testing were analyzed for
surface fracture and fiber matrix inter-relations using FESEM images taken by Carl Zeiss Microscope of Model SIGMA, with the X Flash detector energy resolution above 126eV and an acceleration voltage range of 0.21-30 kV. The fractured RBFC, RGFC and NPBFC samples having dimensions 5 mm x 5 mm x 3 mm were taken and mounted on a specimen stub. Prior to being subjected to imaging, the samples went through vacuum sputter coating where they were coated with an ultrathin layer of gold for making the surface conductive in order to avoid electron charge accumulation.
4. Results and Discussion 4.1.
Anatomical analysis of banana pseudo stem The banana leaf sheath consists of an outer ad axial thick portion and an inner ab axial
thin portion with wide air chambers in between the outer and the inner portions as shown in Figs.2 (a, b). The wide median chamber is divided by thick vertical partitions. The vertical partitions have isolated vascular strands and circular masses of fibers. The vascular strands have wide circular vessels associated with phloem and fibers surrounding the vascular strands. In the ad axial and ab axial segments, the leaf sheaths are larger and smaller with discrete circular fiber bundles (Figs.2 - c, d, e & f) embedded in the walled compact ground parenchyma cells, whereas the fiber bundles differ in their distribution. The fibers are libri forms type and have thin lignified walls and wide lumen. The cell lumen of the fiber wall is 5µm in wide and 2µm in thick. However, when the fiber bundle is macerated, the fibers are either in thick solid bundle or separated into individual fibers of two types, one as narrow fibers with thin narrow and gradually tapering towards the ends, and the other as fibers wide with wide lumen and long tapering towards the ends as shown in Fig.2 (g, h). The anatomical analysis, it ensured the promotion of better bonding characteristics by the presence of the fiber bundles with vascular strands around the cell lumen of the banana leaf sheath when employed as reinforcement with the polymer matrix during composite fabrication. Figs.3 (a, b) show the narrow and wide fibers with a bundle of fiber extracts embedded in them. The structure of a cell wall consists of four components, namely, primary wall, secondary wall; middle lamellae and cell lumen. These are depicted in Figs.3 (c to h). The measurement of cell wall was done using the image processing technique through Image J software. Details are tabulated in Table.4. The primary wall had cellulose which provides a boost to the strength of the fiber, whereas the secondary wall had lignin resulting in hardness to the fiber. Moreover, the middle lamellae is an intercellular layer joining the adjacent cells are made up of hemicellulose and lignin, whereas the middle part of each cell comprises free space for storage of water, referred to as lumens. 4.2. Estimation of tensile and flexural strength Embedding the fibers in the matrix improves the tensile properties of the composite due to superior inherent strength compared to the matrix [32]. Fig.4 (a) shows the tensile strength of the UPE, RBFC, RGFC and NPBFC. When the fibers were embedded in the matrix, a shift in nature from brittle to ductile was observed. As the fiber wt. % of the RBFC, RGFC and NPBFC increased from 10 to 40 wt. %, an increase in strength was noticed. Also, when the fiber content was increased beyond 40 wt. %, an abrupt reduction in strength was observed. Significantly the NPBFC proved its superiority over the RBFC with values approaching those of the RGFC
The strength of the pure resin is low due to its brittle nature. At 10 wt. % fiber content, the failure observed was predominantly brittle in nature which was the result of the presence of higher amount of matrix hence low strength of the composites. Between 20 and 30 wt. % fiber content, the tensile strength is marginally increased due to a minute improvement in the interfacial bonding between the composite constituents, whereas the occurrence of failure arising as a result of the brittle failure of the matrix and a ductile fiber pull-out. However, at 40 wt. % fiber content the best performance was revealed due to optimal interfacial bonding. The nature of failure occurred was very little brittle failure largely associated with ductile fiber pull-out as well as fiber-matrix debonding. This proves the enhanced stress transfer between the matrix and fiber. Beyond 40 wt. %, a decreasing trend in the tensile strength was observed. This was due to fiber agglomeration factor which leads to inefficient stress transfer from matrix to fiber. The superiority of the NPBFC might be attributed due to the needle-punching action that might have roughened up the fiber’s surface, possibly removing unwanted residues like wax from the fibers and enhancing the interfacial bonding through mechanical interlocking. Generally, the tensile load applied to a composite is transferred to the fibers by means of shearing mechanism. A homogeneous mass per unit area (GSM) was obtained by needle punching technique for all fiber wt. % of NPBFC samples, due to the possession of a uniform fiber laying pattern, which led to a smoother stress transfer along the entire specimens unlike what was observed for RBFC and RGFC. The resin uptake of the NPBFC increases by the use of an optimum needling density (100 punches/cm2), leading to a better peg formation and, as a consequence, increase in strength, making the packing of fiber assembly in an array and thus more compact in nature [33]. When the punch density is below the optimized level, the fibers are poorly entangled, if it is above due to the severe action of the barbs fiber breakage were visible. Similarly, an increase in the mass per unit area (GSM) from 10 to 40 wt. % fiber resulting in enhanced wetting and resin holding capacity due to better resin uptake [34]. Increasing the mass per unit area beyond 40 wt. % (i.e. 50 wt.%), the high packing factor hinders the penetration of resin into fibers, leading to a lower resin uptake, which leads to inefficient interfacial bonding, thereby reduction in strength was noticed [35]. On the other hand, the optimized depth of penetration (8 mm) paves the way for the matrix to effectively penetrate into the fibers, thereby enhancing its strength. When the penetration depth is below the optimized level the fiber entanglement will become puffy, if it is more than optimized, fiber breakages were observed. Hence it can be concluded that the optimized value of the NPBFC was found as 40 wt. % fiber content. Similar to the trend representing the tensile strength, the flexural strength of pure resin is low owing to its brittle nature as shown in Fig.4 (b). As the fiber content is increased from
10 to 40 wt. % for RBFC and RGFC, the flexural strength also increased due to a better embodiment of the reinforcement and higher degree of orientation along with the matrix. However, beyond 40 wt. %, a decreasing trend in the flexural strength was observed. This was due to inferior interfacial bonding. Moreover, in case of NPBFC, an intermediate flexural strength between the RBFC and RGFC was noticed. This was closer to that of RGFC. The increasing trend in flexural strength was observed for an increment in mass per unit area from 10 to 40 wt. %. This could be attributed to higher wettability, uniform laying pattern, higher mass per unit area and a higher resin uptake as a result of optimized needle penetration and punch density [34]. Nevertheless, beyond 40 wt. % fiber content a reduction in the resin uptake was observed. This was the result of poor penetration of matrix into the fiber. Hence at 50 wt % the flexural strength is abruptly reduced. 4.3. Evaluation of indentation damage resistance The quasi-static indentation study of the prepared composite specimens which includes the analysis of peak force, dent depth, linear stiffness and absorbed energy are shown in Fig.5 (a-f). The slope of the peak force deformation curve prior to the initial load drop provides linear stiffness [36] of the quasi-anisotropic RBF, RGF and NPBF composites. Moreover, the inference from the graph was that the stiffness of the optimized NPBF composite specimen was much higher than the 40 wt. % RBFC, almost identical with that of 40 wt. % RGFC as indicated in Fig.5 (e). The maximum load bearing capacity for 40 wt. % RGFC and NPBFC are similar and is evident by same amount of dent depth and absorbed energy for 40 wt. % NPBFC are depicted in Fig.5 (d, f). After the removal of the intender, the dent depth or residual displacement observed was comparably low for 40 wt.% NPBFC and 40 wt.% RGFC. A low dent depth indicative of higher load carrying capacity was recorded for tested 40 wt. % NPBFC and 40wt. % RGFC. On the other hand, the remaining fiber percentages of NPBFC and 40 wt. % RBFC resulted in higher dent depths, indicative of lower load bearing strength. 4.4. Measurement of hardness Hardness is the measure of resistance offered by the composite to indentation, penetration, abrasion and denting. It is gauged by the Rockwell ‘R’ scale. The higher the value on the scale, higher is the hardness. Low values were observed for pure resin and, when the fiber weight percentage increased from 10 wt. % to 40 wt. % for RBFC and RGFC, an increasing trend in the hardness was found. The maximum hardness was measured at 40 wt. %. However, beyond 40 wt. % fiber content, the hardness was found to decline due to poor interfacial bonding as seen in Fig.6. A similar trend was noticed for the NPBFC specimen for an increase in mass per unit area. However, the peak hardness value was almost at par with
that of RGFC owing to an optimal interfacial bonding achieved by enhanced wettability, matrix uptake and penetration. 4.5. Thermal analysis of NPBFC The thermo gravimetric (TG) and differential thermo gravimetric (DTG) analysis of the optimized NPBFC specimen are depicted in Fig.7 (a). Three pertinent ranges in the analysis were observed; initial range was noted between the room temperature and 100°C, where only a minor weight loss was witnessed owing to loss in moisture content (evaporation) from the hydrophilic cellulose. This moisture content could have arisen in the form of non-freezing bound water, freezing bound water and free water [37-39]. The most visible range and the major weight loss occurred in the temperature range from 260°C to 380°C. This major peak observed could be due to the degradation in alpha cellulose and hemicellulose. The final range of the disintegration of the chemical elements was at 420°C, where the ultimate deprivation of sample happened. This may be attributed to the dilapidation of the most difficult macro-component present in the sample to decompose, viz. lignin [40] and volatization of the matrix. However, the residues may remain stable upto 800°C since it requires higher temperatures for degradation. The conclusion from the analysis was that the optimized NPBFC has appreciable thermal stability upto 260°C and opens up avenues for it in a wide range application. 4.6. DMA analysis of UPE and NPBFC Fig.8 (a) shows the storage modulus (E’) as a function of temperature for UPE and NPBFC specimens. It can be inferred that in all the cases, when the temperature increases the storage modulus keep on decreasing. When the fibers are impregnated in the matrix, E’ curves reveal enhanced storage modulus as the weight percentage of fiber is increased from 10 wt. % to 40 wt. % which occurs predominantly in the transition region. This is due to modulus incompatibility between fiber and matrix and producing superior interfacial bonding [41]. However, increasing the fiber content beyond 40 wt. % due to agglomeration factor reduction in storage modulus was observed owing to inferior bonding between the composite constituents [42]. Interestingly it can be observed that E’ has the tendency to move towards right when the fibers are impregnated in the matrix and covers large area both rubbery and glassy region due to tightly packed constituents. The amount of energy lost as heat due to viscous flow in UPE and NPBFC specimens are shown in Fig.8 (b). The plotted E” curves as a function of temperature in the DMA test replicate similar trend as that of E’ plot. It can be stated that all the tested specimen attains peak value due to dissipation of higher amount of mechanical energy and keep on decreasing while increasing the temperature. The dissipation of energy causes polymeric material to be soft with greater chain mobility. It was observed that reinforcement of fibers in UPE results in peak broadening of E” curves due to more chain segment and more free volume [43]
The damping factor of UPE and NPBFC specimens are shown in Fig.8 (c). It might be emphasized that tan δ value is keep on increasing as the temperature is increased from 25oC it reaches its peak value in the transition zone. However, further increasing the temperature tan δ value decreases which is in the rubbery zone. The increase in the glass transition temperature (Tg) of the NPBFC specimen can be observed from the compiled curves. Significantly all the NPBFC specimens exhibited lower damping factor than the UPE. This is attributed due to unfrozen chain mobility of the polymer. 4.7. FTIR analysis of NPBFC The infrared spectrum of optimized NPBFC is obtained as shown in Fig.7 (b). Alkenes, esters, aromatics, ketenes and alcohol, with different oxygen-containing functional groups are the main constituents of biomass [44]. The pivotal spectrum exhibited around 3346.7 cm-1 for O-H stretching absorption, around 2920 cm-1 for C–H stretching absorption of aliphatic methylene group, around 2246 cm-1 for C=O stretching absorption, around 1724.2 cm-1 for C=C benzene stretching ring, around 1370 cm-1 for COO axisymmetric stretching, bending of CH, CH2 and CH3 groups, around 1053.3 cm-1 for C–O–C stretching absorption at the beta- (1-4)- glycosidic linkage in cellulose and around 650-715 cm-1 for C-O in-plane carbonate bending and S-O sulphate bending [45]. The spectrum bands at 1595 cm1
and 1105 cm-1 are due to the presence of lignin and cellulose respectively [30]. Hence, the
present study confirms the availability of chemical constituents and functional groups in the fiber which in turn have boosted the specific mechanical properties of the fabricated composites. 4.8. Structural analysis of NPBFC The XRD pattern of the optimized NPBFC is displayed in Fig.7 (c). The major peak noted at 2θ=22.66° in the diffractogram clearly indicates the crystalline features of cellulose. The cellulose standard profile was evident from International Centre for Diffraction Data [46]. Apart from this, the existence of one more phase was seen, i.e the amorphous phase of lignin, which is revealed by the broad straight line. This is evident of a healthy cellulose content, which duly increases the mechanical properties. The Crystallinity index was found as 55%. The crystallinity fraction indicates the lateral packing of cellulose chain molecules as high in order, which, in turn, exhibits the superior tensile strength of the NPBFC [30]. 4.9. Microstructural analysis The interface can be regarded as the three-dimensional boundary between the fiber and matrix. It is highly critical in controlling composite properties, since fiber-matrix interaction occurs through this interface. This interaction can be possible through three mechanisms: mechanical coupling or micromechanical interlocking, physical coupling such as Vander Waals or electrostatic interaction and chemical bonding out of these chemical bonding plays vital role. This is schematically represented in Fig.9.
The fractured interface of FESEM analysis of the experimented tensile, flexural of RBFC, RGFC and NPBFC specimen for various fiber weight percentages are shown in Figs.10 and 11. At 10 wt. % fiber content, the micrograph reveals (Fig.10-a, f, k), mostly matrix pores and peeling. This shows that the failure of the composite specimens was dominated by matrix failure; hence the strength of the composite specimens was low. However, when the fiber content was increased from 10 to 30 wt.% (Fig.10-b, c, g, h, l, m), due to minute enhancement in interfacial bonding, the failure was mainly in form of fiber pullout confirming marginal stress transfer from matrix to fiber. This results in slight increase in strength of the composite specimens. Meanwhile, at 40 wt. % fiber content (Fig.10-d, i, n) the matrix failure was observed to be very meager and debonding is slightly lower than 30 wt. %. Moreover, it is associated with high dominant fiber pull-out. This phenomenon resulted in superior strength among all wt. % due to optimal interfacial bonding. Beyond 40 wt. % fiber content (i.e. at 50 wt. %), Fig.10 (e, j, o) depicted very little matrix failure along with high interfacial debonding associated with fiber pull-out which is less than 40 wt. % and more than 30 wt. %. This resulted abrupt reduction in strength due to fiber to fiber contact. However the dominancy of matrix failure observed in micrograph of NPBFC reveals, as the fiber wt. % is increased from 10 to 40 wt. % is keep on reducing and much lower than RGFC and RBFC. Moreover, in such cases the failure was dominated by fiber pull-out which was higher than RGFC and RBFC. This proves that the stress was transferred from matrix to fiber smoothly than RGFC and RBFC. Thus NPBFC offered superior in strength. Similarly, FESEM images of flexural composite specimens of RGFC, RBFC and NPBFC are displayed in Fig.11 (a-o). The micrograph revealed similar trend as that of fractured tensile composite specimens. The predominant failure such as fiber pullout, fiber breakage, matrix fracture, fiber fracture, matrix peeling, matrix crack, matrix pores, fibermatrix debonding and broken fibers was observed in Fig.11 (a, b, c, f, g, h, k, l, m). However, at 40 wt. % fiber content, a honey comb structure was witnessed even after the fracture. This proves excellent bonding of fiber with matrix that resulted superior strength. Meanwhile, when the fiber content arises from 40 to 50 wt. %, matrix pores were seen. This was the result of a less amount of matrix and the agglomeration formation. Hence the strength was reduced. 5. Theoretical Modeling of composite Various theoretical models have been proposed by renowned scientists for the prediction of the randomly oriented short fiber polymer composite [47]. Among the various projected models, two pertinent models and their empirical relation were employed for finding the tensile properties well before start of the manufacture of the composite material, based on fiber and matrix properties.
(i)
Series model: (1)
(ii)
Hirsch’s model: (2)
where
-Volume fraction of fiber,
matrix (N/m2),
-Volume fraction of matrix ,
-Tensile strength of the composite (N/m2),
-Tensile strength of
-Tensile strength of fiber
(N/m2), x- Parameter constant having values between 0 and 1. Analytical comparison of the predicted tensile strength of RBFC, RGFC and NPBFC with the factual experimental data was made for the validation of the above models. The model results were correlated with experimental values. The correlation done was in the range upto optimum fiber content range. The term ‘X’ denotes the volume fraction of the fiber and ‘x’ is a factor which denotes the stress transfer between matrix and the fiber. Results attained were found to be better when x=0.1 which was applied for the fabricated composites [21]. The empirical as well as theoretical models regression equations for the manufactured composite can be stated as below.
(i)
Experimental Results RBFC, σc
= 0.154X + 36.48
-
(3)
RGFC, σc
= 0.642X + 40.61
-
(4)
NPBFC, σc
= 0.521X + 35.92
-
(5)
RBFC, σc
= 0.676X + 32.38
-
(6)
RGFC, σc
= 0.817X + 39.29
-
(7)
-
(8)
(ii) Series Model
NPBFC, σc (iii)
= 0.751X + 36.15
Hirsch’s Model RBFC, σc
= 0.981X + 32.84
-
(9)
RGFC, σc
= 1.198X + 39.06
-
(10)
NPBFC, σc
= 1.099X + 36.23
-
(11)
Experimentally, addition of fiber beyond the optimum fiber content (i.e. 40 wt. %) makes the composite strength inferior. This could be attributed to poor interfacial bonding between the fiber and the matrix, which is reflected in the experimental curve. However, this phenomenon does not figure in the two models since they have their own limitation, namely applicability only for perfectly bonded materials as depicted in Fig.12 (a-c). The conclusion
is that the Hirsch’s model is more correlated with the experimental values with better correlation factor (R2) values for the fabricated composites. 6. Conclusions The fabricated NPBFC laminate exhibited excellent mechanical properties at 40 wt. % fiber content. This is much superior than RBFC and comparable with RGFC. The superior properties were attributed due to optimized needle punching parameters such as depth of penetration 8 mm and
punch density of 100 punches/cm2. Similarly, the uniform GSM obtained through the needle punching technique enables smooth transfer of stress from matrix to fiber, thereby improving the mechanical properties of NPBFC. The TGA revealed optimized NPBFC has excellent thermal stability upto 260°C, permitting its use in automotive industry, safety equipment etc. QSI experimentation confirms the high load bearing capacity of the NPBFC composites. These were endorsed by the morphological analysis. Hence NPBFC can be a potential and alternate replacement for existing carcinogenic RGFC in relation to its thermo-mechanical properties. This needle punching technique obviates the traditional use of chemicals to enhance the interfacial bonding of natural fiber composites, keeping the working environment safe from the ill effects of these hazardous chemicals leading the way to a greener environment.
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Table Captions Table.1: Bio-chemical properties of raw banana fiber Property Cellulose (%) Hemicellulose (%) Lignin (%) Moisture (%)
Quantity 71.08 12.61 7.67 6.73
Table.2: Physical properties of raw banana fiber Property Diameter (µm) Density (g/cm3) Tensile Strength (MPa) Elongation at break (%) Microfibril angle (°) Lumen size (µm)
Quantity 138±0.0671 1.28 412.5±46.7 27.89 11 6
Table.3: Properties of unsaturated polyester (liquid and cured) resin. Liquid Resin Density 1.18 g/cm3 Appearance Slightly yellow viscous liquid Acid value 22 ± 3 mg KOH/g Specific gravity at 25° C 1.25 ± 0.04 Viscosity at 25°C 220-280 centipoise Volatile content 35 ± 1 wt.% Cured Resin Tensile strength 36.0 ± 2 MPa Tensile modulus 1.23 ± 0.2 GPa Elongation at break 1.32 ± 0.25% Flexural strength 42.10 ± 2.51 MPa Flexural modulus 1.71 ± 0.21 GPa Shear strength 4.5 ± 0.54 MPa Impact strength 0.62 ± 0.03 J/cm2 Rockwell hardness 61 ± 2 HRRW
Table.4: Cell wall dimensions of narrow and wide banana leaf sheath fiber Description Banana Stem Wide Fiber Middle part of the fiber Total thickness of the fiber Total middle lamella Total primary wall Total secondary wall
Dimensions (µm)
25 5 5 5
Total cell lumen Tapering part of the fiber Thickness of the fiber Cell lumen Primary Secondary wall Middle lamella Banana Stem Narrow fiber Middle part of the fiber Fiber total thickness Cell lumen Primary wall Secondary wall Middle lamella Tapering part of the fiber Fiber total thickness Cell lumen Primary wall Secondary wall Middle lamella
10 14 8 2 3 1
25 15 3 5 2 15 8 2 3 2
Figure Captions
Fig.1: Flow diagram of composite from plant origin (a) Banana plant (b) Pseudo stem (c) Extracted raw fiber (d) Needle punching machine, (e) Needle punched fiber roll and (f) NPBFC
Fig.2: Anatomical micrographs of banana plant pseudo stem: (a) - Transverse section of banana sheath showing upper horizontal portion and vertical partition, (b) - Transverse section of leaf sheath showing lower horizontal portion and vertical partition, (c) - Fiber bundles of leaf sheath, (d) - Fiber bundles
enlarged, (e) - Larger fiber bundles enlarged and (f) - Smaller fiber bundles along the epidermal region. [AC - Air Chamber, AbS - Abaxial Side, Fi- Fiber, Pa - Parenchyma, Ph- Phloem, Ve- vessel, VaSt & VSt - Vascular Strand, VePa - Vessel Parenchyma, AdE - Adaxial Epidermis, FiB - Fiber Bundle, GPa & GP- Ground Parenchyma, Hd- Hypodermis, AbE – Abaxial Epidermis]
Fig.3: Optical micrographs of banana plant pseudo stem: (a) - Fibers separated showing Narrow Fibers and Wide Fibers, (b) - A bundle of Fibers intact, (c) - Wide Fiber Tapering part, (d) - Wide FiberMiddle part, (e) - Wide Fiber showing Tapering end portion, (f) - Wide Fiber - Middle part, (g) - Narrow Fiber - Tapering end part and (h) - Narrow Fiber - Middle part [FiB - Fiber Bundle, NFi - Narrow Fiber, WFi - Wide Fiber, CL - Cell Lumen, FiE - Fiber End, ML - Middle Lamella, MP - Middle part, PW Primary Wall, SW - Secondary Wall, Ep- Epidermis]
Fig.4: (a) Tensile strength Vs Fiber wt. in % (b) Flexural strength Vs Fiber wt. in % of composites
Fig.5: Indentation damage resistance of (a) Peak force Vs indentation displacement for RBFC (b) Peak force Vs indentation displacement for NPBFC (c) Peak force Vs indentation displacement for RGFC (d) Dent depth Vs Fiber wt.% (e) Linear stiffness Vs Fiber wt.% (f) Absorbed energy Vs Fiber wt.% of composites
Fig.6: Hardness measurement of RBFC, RGFC & NPBFC
Fig.7: (a) TG and DTG analysis (b) FTIR spectrum (c) XRD pattern of NPBFC at optimum fiber content
Fig.8: DMA test results showing viscoelastic behavior of UPE and NPBFC (a) Storage modulus (E’) (b) Loss modulus (E’’) and (c) tan δ
Fig.9: Schematic representation of chemical bonding at fiber/matrix interface
Fig.10: FESEM of fractured tensile specimens: RBFC (a, b, c, d & e @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%), RGFC (f, g, h, i& j @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%) and NPBFC (k, l, m, n & o @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%)
Fig.11: FESEM of fractured flexural specimens: RBFC (a, b, c, d & e @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%), RGFC (f, g, h, i& j @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%) and NPBFC (k, l, m, n & o @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%)
Fig.12: Tensile strength prediction of (a) RBFC (b) RGFC &(c) NPBFC using Series and Hirsch’s models
Conflict of Interest The authors declared the following conflict of interest statement: (i).
All authors have participated in (a) analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.
(ii). This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue. (iii). The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript.
Yours sincerely, Jack J. Kenned Research Scholar, Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli – 620015, Tamil Nadu India.
S0266-3538(19)31611-2
DOI:
https://doi.org/10.1016/j.compscitech.2019.107890
Reference:
CSTE 107890
To appear in:
Composites Science and Technology
Received Date: 8 June 2019 Revised Date:
16 October 2019
Accepted Date: 25 October 2019
Please cite this article as: Kenned JJ, Sankaranarayanasamy K, Binoj JS, Kumar CS, Thermomechanical and morphological characterization of needle punched non-woven banana fiber reinforced polymer composites, Composites Science and Technology (2019), doi: https://doi.org/10.1016/ j.compscitech.2019.107890. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. 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. © 2019 Published by Elsevier Ltd.
Thermo-mechanical and morphological characterization of needle punched nonwoven banana fiber reinforced polymer composites Jack J Kenned a*, K. Sankaranarayanasamy a, b, J. S. Binoj c, C. Suresh Kumar d a
Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli- 620015, Tamil Nadu, India b
Department of Mechanical Engineering, National Institute of Technology, Puducherry-609609, Puducherry, India
c
Department of Mechanical Engineering, SreeVidyanikethan Engineering College, Tirupati - 517102, Andhra Pradesh, India d
Department of Aeronautical Engineering, Bharath Institute of Higher Education and Research, Selaiyur, Chennai-600073, Tamilnadu, India
Abstract The purpose of this study is to employ a novel technique for the fabrication of natural fiber reinforced polymer composites that could stand toe to toe with glass fiber composites in terms of thermo-mechanical properties without any chemical treatment. The reinforcement fibers were extracted from the pseudostem of the nendran banana plant. Later a non-woven fabric composite consisting of banana fibers reinforced with unsaturated polyester (UPE) matrix was fabricated using the needle punching technique. Composite specimens were subjected to tensile, flexural, hardness, quasi-static indentation (QSI) and dynamic mechanical analysis (DMA) test for evaluating mechanical properties. However, the optimal properties was achieved at 40 wt.% fiber content with an increase in tensile and flexural strength of 36% and 33% for needle-punched banana fiber composites (NPBFC) compared with random banana fiber composites (RBFC) respectively. It was also evidenced from the load bearing capacity and hardness of NPBFC having 2420 N and 87 HRRW, proves its superiority over RBFC and comparable with RGFC. Further, the viscoelastic properties of UPE and NPBFC were analysed. Subsequently, the characteristic bonds of cellulose were represented through infra-red spectroscopy and the crystallinity index was exposed through X-ray diffraction analysis. In addition, thermal analysis was done and the stability of the optimized NPBFC witnessed was upto 260°C. Also, morphology-properties correlation was established. Finally, the experimental results were validated using theoretical models. This study concludes that the synthesized novel NPBFC endorses its potentiality as a probable reinforcement in industrial safety helmet, automotive door panel and light weight structural applications. Keywords: Banana fiber; Needle-punch; Polymer composites; Thermo-mechanical properties; Morphological properties. * Corresponding author. Tel: + 91 9443695891, E-mail: [email protected]
1. Introduction Any natural or man-made materials capable of being processed into a fabric can be defined as a fiber. Natural fibers are those which are not synthetic or man-made but could be sourced from animals or plants [1]. Realizing the insalubrious nature of synthetic fibers, researchers are currently gingerly turning away from them and focusing on the alternative, natural fiber composites (NFCs) [2-4]. Products made using these fibers have seamlessly made their way into the industry in a multitude forms [5-10]. Moreover, low density, high specific strength and stiffness, low cost, less absorption of CO2, less hazardous manufacturing processes, good electrical resistance, acoustic insulation, low emissions and less abrasive damage to processing equipment by NFCs compared to synthetic fiber composites are the advantages that have further kindled this change [11-13]. However, NFCs are not exactly problem-free as they pose issues of moisture absorption, lower strength, greater variation of properties and lower durability [14-16]. Despite these setbacks, biodegradability and the environmental benefit characteristics have made natural fibers a popular reinforcement in polymer matrix which can potentially replace traditional aramid fiber, carbon fiber and glass fiber composites [17, 18]. Various plant fibers that have been explored as a potential reinforcement include oil palm, areca, coir, jute, flax, hemp, ramie, kenaf, coconut, banana, sisal, and pineapple [19, 20]. Out of these, banana fibers have been studied extensively [21, 22]. India and Brazil are the largest producers of banana fibers. Production of banana in India during 2016-2017 had reached around 29.16 million tones, being cultivated in an area of 858 hectares [23]. Such a large production results in a similar magnitude of bio-waste and the banana fibers used in the composite fabrication are extracted from the pseudostem of the banana plant (Musa sapientum), which is supported by its abundant supply and at no additional cost [21]. Considerable research has been done on the subject of improvement of the properties of lignocellulosic fiber composites, which banana fiber composites fall under. Structural constituents, relative concentrations, various fiber parameters like length, distribution, diameter and orientation strongly influence the properties of the composite [24]. However, handling of an effective load transfer between the fiber and matrix requires that the interfacial interactions of the constituents should be strong [25]. The chemical modifications were adopted for overcoming this issue and to enable impactful influence on the properties of the composite. For banana fiber composites, the chemical treatments performed include alkaline, acetylation treatment [26], silane treatment [27], permanganate, benzoylation treatment [28] and maleated coupling reagents [29]. However, all these chemical treatments have their own limitations. Though it improves the interfacial bonding these are highly toxic, time consuming, costly and polluting the environment this prompted to study about an alternate method which would eliminate the above said hassles. Hence the objective of this study is to
fabricate a novel needle punched banana fiber reinforced polymer composites as a potential and alternate replacement for the existing carcinogenic composites. However, there is no report seen in literature on the study of untreated needle punched non-woven banana fiber composites. In this study, banana fibers extracted from the Nendran variety of banana plants were needle-punched to form a non-woven fabric, thereby bonded with an unsaturated polyester matrix forming a novel NPBFC. The investigated thermal, mechanical and morphological properties of NPBFC express its potentiality as a probable reinforcement in industrial safety helmet, automotive door panel, garden railing and light weight structural applications. 2.Materials and Methods 2.1. Raw fiber extraction from the banana plant Different varieties of banana plants including Red banana, Nendran, Rasthaly, Morris and Poovan were analyzed for their physico-chemical properties by Kiruthika and Veluraja [30]. The present investigation deals with the nendran variety of banana plant and the selection for this is on two grounds, is its excellent strength ( ≈ 450 MPa) and better economy compared to the other variety of bananas. The pseudostem was removed from the mature banana plant; nine days post its harvesting. From the pseudostem, the cortex region was extracted and fed into the retting machine to extract the fibers. Subsequently, the extracted fibers were sun dried for a period of 7 to 9 days to reduce the moisture content. Later, these dried fibers were kept in the oven at temperatures ranging from 50°C to 60°C for a period of 12 to 16 hrs for removal of the entire moisture content. These dried fibers were further subjected to a mechanical scutching process for easy removal of fibers from any hurds adhering to the fiber bundles using turbine blades. Fig.1 represents the process flow diagram of composite from the plant origin. 2.2. Chemical and physical properties of raw banana fiber The quantity of holo-cellulose was quantified by D Addico, Wise and Murphy method. Lignin and α cellulose content were determined by using TAPPI standards T 222OM-06 and T 203 respectively [31]. Hemicellulose was calculated by using the following relation Hemicellulose = (quantity of holo-cellulose - quantity of α cellulose) The chemical and physical properties of raw banana fiber are listed in Tables 1 and 2 respectively. 2.3. Botanical properties of raw banana fiber Narrow and wide banana sheath fibers were individually inspected by micro technique for the purpose of investigating its interior structure. The sheath of banana plant was sliced into small pieces and immersed in FAA solution (Maleic acid 5 ml + Formaldehyde 5 ml + 70% ethyl alcohol of 90 ml) for duration of 24 hrs for specimen preservation. Later, they
were dried out using tertiarybutyl alcohol and implanted in paraffin blocks. Further, the blocks were partitioned into a size of 10-12 m pieces by a rotary microtome that revolved in the right-handed direction. The prepared samples were then fixed to a glass slide stained with safranine and toluidine blue for improvement in image visibility. Finally, the specimens were observed with the help of a polarized light micrograph for examining the fiber structure. 2.4. Needle punching technique Needle-punching technique was used for mechanical entanglement of webs or batts of 30 mm long fibers to produce the fabric. This was accomplished through the action of reciprocating barbed (felting) needles which interlocked the fibers. The consolidated structure maintained its integrity through inter-fiber friction. A triangular barbed needle of regular barb spacing which implied an evenly spacing 9 barbs on a blade of ≈ 30 mm in length was used with an optimized penetration depth of 8 mm and a punch density of 100 punches/cm2. 3. Composite preparations and testing Unsaturated polyester resin, Methyl Ethyl Ketone Peroxide (MEKP) and accelerator cobalt naphthalene were procured from LEO Enterprises, Nagercoil. Unsaturated polyester was selected as the matrix material, due to its excellent process ability and cross-linking tendency. Later, the matrix was mixed with catalyst Methyl Ethyl Ketone Peroxide (MEKP) and accelerator cobalt naphthalene in a ratio of 98:1:1. The characteristics of the pure resin were tested for physical and mechanical properties are listed as in Table.3. A mild steel mold of dimensions 300 x 150 x 3 mm3 was used for the preparation of the composites with different fiber wt. %. The NPBF were impregnated with the prepared resin in the mold and compressed with a lid to form a sheet using the hand lay-up technique. In order to maintain homogeneity in the mixture, a mechanical stirrer was used and a continuous stirring process was performed. During this process, extreme care was taken to avoid clumbing and tangling during mixing. Later, the matrix was degassed by hand with the help of a roller and allowed to settle down by applying a compression load of 350 kN. The entire process was carried out at ambient temperature ( ≈ 27°C) with a relative humidity of about 65%. Silicon spray was applied over the mold for removing the cured NPBFC. Similarly, procedure was adopted for fabrication of 30 mm RBFC as well as RGFC specimens. 3.1
Mechanical testing The fabricated composite specimens were tested for tensile, flexural and hardness
properties as per ASTM standards. Tensile and flexural tests were carried out using UK made Tinius Olsen universal testing machine (UTM) having a 50 kN load cell and a cross head speed of 0.5 mm/min adhering to ASTM-D3039 and ASTM-D790 standards respectively. In addition, QSI tests were also performed on the same UTM using hemispherical indenter with 12.7 mm diameter for evaluating indentation damage resistance of the specimens. Meanwhile, hardness of the composite samples was tested following the ASTM-D785-98
standard using a data acquisition system embedded in a Rockwell hardness testing machine. In each case, five samples were tested and considered for calculating standard deviation. 3.2
Thermal analysis of NPBFC Thermal stability of the optimized NPBFC was analyzed by Thermo-Gravimetric
Analysis (TGA) Model 4000 (Germany made). An amount of 6- 8 mg of the pulverized composite specimen was placed in an alumina crucible for testing and the process was carried out in an inert atmosphere with Nitrogen flowing in at a rate of 20 ml/min. The temperature was increased in steps of 10°C/min from 35 to 850°C. 3.3
Dynamic mechanical analysis (DMA) DMA test was carried out to analyse the viscoelastic properties of UPE and NPBFC
specimens (10 wt. % to 50 wt. %) as per ASTM D 4065-01 standard using DMA Q800 V 7.4 (TA instruments, USA) set up. Single cantilever clamp, temperature sweep mode was employed to characterize the specimens. The specimens were applied with sinusoidal stress of 1 Hz frequency and strain amplitude of 25 µm. The experimentation was conducted in the temperature range of 25oC to 170oC with the heating rate of 2oC/min. 3.4
Fourier-transform infrared (FTIR) spectroscopy of NPBFC The Optimized NPBFC sample was dried, ground to powder and then pelletized with
KBr. Four scans were taken at a resolution of 4 and the infrared spectrum for the optimized NPBFC sample was obtained using a PerkinElmer Spectrum 2 series 93947 of version 10.03.09 for the wavelength ranging from 400 cm-1 to 4000 cm-1. 3.5
Structural characterization of NPBFC Optimized NPBFC was pulverized to obtain a fine powder and compacted at a
pressure of 110MPa. The compacted powder was then held in a standard disk of the Rigaku Ultima III X-ray Diffractometer for a continuous scanning mode at a scan speed of 2°/min and temperature of 300K. The step size adopted for this procedure was 0.02° (2θ) in the angular range of 10° - 80°. The sealed-tube of Cu-Kα radiation was operated at 40 kV and 32 o
mA at a wavelength of 1.54 A for deriving the X-ray Diffraction (XRD) patterns of optimized NPBFC. 3.6
Morphological analysis Composite specimens subjected to tensile and flexural testing were analyzed for
surface fracture and fiber matrix inter-relations using FESEM images taken by Carl Zeiss Microscope of Model SIGMA, with the X Flash detector energy resolution above 126eV and an acceleration voltage range of 0.21-30 kV. The fractured RBFC, RGFC and NPBFC samples having dimensions 5 mm x 5 mm x 3 mm were taken and mounted on a specimen stub. Prior to being subjected to imaging, the samples went through vacuum sputter coating where they were coated with an ultrathin layer of gold for making the surface conductive in order to avoid electron charge accumulation.
4. Results and Discussion 4.1.
Anatomical analysis of banana pseudo stem The banana leaf sheath consists of an outer ad axial thick portion and an inner ab axial
thin portion with wide air chambers in between the outer and the inner portions as shown in Figs.2 (a, b). The wide median chamber is divided by thick vertical partitions. The vertical partitions have isolated vascular strands and circular masses of fibers. The vascular strands have wide circular vessels associated with phloem and fibers surrounding the vascular strands. In the ad axial and ab axial segments, the leaf sheaths are larger and smaller with discrete circular fiber bundles (Figs.2 - c, d, e & f) embedded in the walled compact ground parenchyma cells, whereas the fiber bundles differ in their distribution. The fibers are libri forms type and have thin lignified walls and wide lumen. The cell lumen of the fiber wall is 5µm in wide and 2µm in thick. However, when the fiber bundle is macerated, the fibers are either in thick solid bundle or separated into individual fibers of two types, one as narrow fibers with thin narrow and gradually tapering towards the ends, and the other as fibers wide with wide lumen and long tapering towards the ends as shown in Fig.2 (g, h). The anatomical analysis, it ensured the promotion of better bonding characteristics by the presence of the fiber bundles with vascular strands around the cell lumen of the banana leaf sheath when employed as reinforcement with the polymer matrix during composite fabrication. Figs.3 (a, b) show the narrow and wide fibers with a bundle of fiber extracts embedded in them. The structure of a cell wall consists of four components, namely, primary wall, secondary wall; middle lamellae and cell lumen. These are depicted in Figs.3 (c to h). The measurement of cell wall was done using the image processing technique through Image J software. Details are tabulated in Table.4. The primary wall had cellulose which provides a boost to the strength of the fiber, whereas the secondary wall had lignin resulting in hardness to the fiber. Moreover, the middle lamellae is an intercellular layer joining the adjacent cells are made up of hemicellulose and lignin, whereas the middle part of each cell comprises free space for storage of water, referred to as lumens. 4.2. Estimation of tensile and flexural strength Embedding the fibers in the matrix improves the tensile properties of the composite due to superior inherent strength compared to the matrix [32]. Fig.4 (a) shows the tensile strength of the UPE, RBFC, RGFC and NPBFC. When the fibers were embedded in the matrix, a shift in nature from brittle to ductile was observed. As the fiber wt. % of the RBFC, RGFC and NPBFC increased from 10 to 40 wt. %, an increase in strength was noticed. Also, when the fiber content was increased beyond 40 wt. %, an abrupt reduction in strength was observed. Significantly the NPBFC proved its superiority over the RBFC with values approaching those of the RGFC
The strength of the pure resin is low due to its brittle nature. At 10 wt. % fiber content, the failure observed was predominantly brittle in nature which was the result of the presence of higher amount of matrix hence low strength of the composites. Between 20 and 30 wt. % fiber content, the tensile strength is marginally increased due to a minute improvement in the interfacial bonding between the composite constituents, whereas the occurrence of failure arising as a result of the brittle failure of the matrix and a ductile fiber pull-out. However, at 40 wt. % fiber content the best performance was revealed due to optimal interfacial bonding. The nature of failure occurred was very little brittle failure largely associated with ductile fiber pull-out as well as fiber-matrix debonding. This proves the enhanced stress transfer between the matrix and fiber. Beyond 40 wt. %, a decreasing trend in the tensile strength was observed. This was due to fiber agglomeration factor which leads to inefficient stress transfer from matrix to fiber. The superiority of the NPBFC might be attributed due to the needle-punching action that might have roughened up the fiber’s surface, possibly removing unwanted residues like wax from the fibers and enhancing the interfacial bonding through mechanical interlocking. Generally, the tensile load applied to a composite is transferred to the fibers by means of shearing mechanism. A homogeneous mass per unit area (GSM) was obtained by needle punching technique for all fiber wt. % of NPBFC samples, due to the possession of a uniform fiber laying pattern, which led to a smoother stress transfer along the entire specimens unlike what was observed for RBFC and RGFC. The resin uptake of the NPBFC increases by the use of an optimum needling density (100 punches/cm2), leading to a better peg formation and, as a consequence, increase in strength, making the packing of fiber assembly in an array and thus more compact in nature [33]. When the punch density is below the optimized level, the fibers are poorly entangled, if it is above due to the severe action of the barbs fiber breakage were visible. Similarly, an increase in the mass per unit area (GSM) from 10 to 40 wt. % fiber resulting in enhanced wetting and resin holding capacity due to better resin uptake [34]. Increasing the mass per unit area beyond 40 wt. % (i.e. 50 wt.%), the high packing factor hinders the penetration of resin into fibers, leading to a lower resin uptake, which leads to inefficient interfacial bonding, thereby reduction in strength was noticed [35]. On the other hand, the optimized depth of penetration (8 mm) paves the way for the matrix to effectively penetrate into the fibers, thereby enhancing its strength. When the penetration depth is below the optimized level the fiber entanglement will become puffy, if it is more than optimized, fiber breakages were observed. Hence it can be concluded that the optimized value of the NPBFC was found as 40 wt. % fiber content. Similar to the trend representing the tensile strength, the flexural strength of pure resin is low owing to its brittle nature as shown in Fig.4 (b). As the fiber content is increased from
10 to 40 wt. % for RBFC and RGFC, the flexural strength also increased due to a better embodiment of the reinforcement and higher degree of orientation along with the matrix. However, beyond 40 wt. %, a decreasing trend in the flexural strength was observed. This was due to inferior interfacial bonding. Moreover, in case of NPBFC, an intermediate flexural strength between the RBFC and RGFC was noticed. This was closer to that of RGFC. The increasing trend in flexural strength was observed for an increment in mass per unit area from 10 to 40 wt. %. This could be attributed to higher wettability, uniform laying pattern, higher mass per unit area and a higher resin uptake as a result of optimized needle penetration and punch density [34]. Nevertheless, beyond 40 wt. % fiber content a reduction in the resin uptake was observed. This was the result of poor penetration of matrix into the fiber. Hence at 50 wt % the flexural strength is abruptly reduced. 4.3. Evaluation of indentation damage resistance The quasi-static indentation study of the prepared composite specimens which includes the analysis of peak force, dent depth, linear stiffness and absorbed energy are shown in Fig.5 (a-f). The slope of the peak force deformation curve prior to the initial load drop provides linear stiffness [36] of the quasi-anisotropic RBF, RGF and NPBF composites. Moreover, the inference from the graph was that the stiffness of the optimized NPBF composite specimen was much higher than the 40 wt. % RBFC, almost identical with that of 40 wt. % RGFC as indicated in Fig.5 (e). The maximum load bearing capacity for 40 wt. % RGFC and NPBFC are similar and is evident by same amount of dent depth and absorbed energy for 40 wt. % NPBFC are depicted in Fig.5 (d, f). After the removal of the intender, the dent depth or residual displacement observed was comparably low for 40 wt.% NPBFC and 40 wt.% RGFC. A low dent depth indicative of higher load carrying capacity was recorded for tested 40 wt. % NPBFC and 40wt. % RGFC. On the other hand, the remaining fiber percentages of NPBFC and 40 wt. % RBFC resulted in higher dent depths, indicative of lower load bearing strength. 4.4. Measurement of hardness Hardness is the measure of resistance offered by the composite to indentation, penetration, abrasion and denting. It is gauged by the Rockwell ‘R’ scale. The higher the value on the scale, higher is the hardness. Low values were observed for pure resin and, when the fiber weight percentage increased from 10 wt. % to 40 wt. % for RBFC and RGFC, an increasing trend in the hardness was found. The maximum hardness was measured at 40 wt. %. However, beyond 40 wt. % fiber content, the hardness was found to decline due to poor interfacial bonding as seen in Fig.6. A similar trend was noticed for the NPBFC specimen for an increase in mass per unit area. However, the peak hardness value was almost at par with
that of RGFC owing to an optimal interfacial bonding achieved by enhanced wettability, matrix uptake and penetration. 4.5. Thermal analysis of NPBFC The thermo gravimetric (TG) and differential thermo gravimetric (DTG) analysis of the optimized NPBFC specimen are depicted in Fig.7 (a). Three pertinent ranges in the analysis were observed; initial range was noted between the room temperature and 100°C, where only a minor weight loss was witnessed owing to loss in moisture content (evaporation) from the hydrophilic cellulose. This moisture content could have arisen in the form of non-freezing bound water, freezing bound water and free water [37-39]. The most visible range and the major weight loss occurred in the temperature range from 260°C to 380°C. This major peak observed could be due to the degradation in alpha cellulose and hemicellulose. The final range of the disintegration of the chemical elements was at 420°C, where the ultimate deprivation of sample happened. This may be attributed to the dilapidation of the most difficult macro-component present in the sample to decompose, viz. lignin [40] and volatization of the matrix. However, the residues may remain stable upto 800°C since it requires higher temperatures for degradation. The conclusion from the analysis was that the optimized NPBFC has appreciable thermal stability upto 260°C and opens up avenues for it in a wide range application. 4.6. DMA analysis of UPE and NPBFC Fig.8 (a) shows the storage modulus (E’) as a function of temperature for UPE and NPBFC specimens. It can be inferred that in all the cases, when the temperature increases the storage modulus keep on decreasing. When the fibers are impregnated in the matrix, E’ curves reveal enhanced storage modulus as the weight percentage of fiber is increased from 10 wt. % to 40 wt. % which occurs predominantly in the transition region. This is due to modulus incompatibility between fiber and matrix and producing superior interfacial bonding [41]. However, increasing the fiber content beyond 40 wt. % due to agglomeration factor reduction in storage modulus was observed owing to inferior bonding between the composite constituents [42]. Interestingly it can be observed that E’ has the tendency to move towards right when the fibers are impregnated in the matrix and covers large area both rubbery and glassy region due to tightly packed constituents. The amount of energy lost as heat due to viscous flow in UPE and NPBFC specimens are shown in Fig.8 (b). The plotted E” curves as a function of temperature in the DMA test replicate similar trend as that of E’ plot. It can be stated that all the tested specimen attains peak value due to dissipation of higher amount of mechanical energy and keep on decreasing while increasing the temperature. The dissipation of energy causes polymeric material to be soft with greater chain mobility. It was observed that reinforcement of fibers in UPE results in peak broadening of E” curves due to more chain segment and more free volume [43]
The damping factor of UPE and NPBFC specimens are shown in Fig.8 (c). It might be emphasized that tan δ value is keep on increasing as the temperature is increased from 25oC it reaches its peak value in the transition zone. However, further increasing the temperature tan δ value decreases which is in the rubbery zone. The increase in the glass transition temperature (Tg) of the NPBFC specimen can be observed from the compiled curves. Significantly all the NPBFC specimens exhibited lower damping factor than the UPE. This is attributed due to unfrozen chain mobility of the polymer. 4.7. FTIR analysis of NPBFC The infrared spectrum of optimized NPBFC is obtained as shown in Fig.7 (b). Alkenes, esters, aromatics, ketenes and alcohol, with different oxygen-containing functional groups are the main constituents of biomass [44]. The pivotal spectrum exhibited around 3346.7 cm-1 for O-H stretching absorption, around 2920 cm-1 for C–H stretching absorption of aliphatic methylene group, around 2246 cm-1 for C=O stretching absorption, around 1724.2 cm-1 for C=C benzene stretching ring, around 1370 cm-1 for COO axisymmetric stretching, bending of CH, CH2 and CH3 groups, around 1053.3 cm-1 for C–O–C stretching absorption at the beta- (1-4)- glycosidic linkage in cellulose and around 650-715 cm-1 for C-O in-plane carbonate bending and S-O sulphate bending [45]. The spectrum bands at 1595 cm1
and 1105 cm-1 are due to the presence of lignin and cellulose respectively [30]. Hence, the
present study confirms the availability of chemical constituents and functional groups in the fiber which in turn have boosted the specific mechanical properties of the fabricated composites. 4.8. Structural analysis of NPBFC The XRD pattern of the optimized NPBFC is displayed in Fig.7 (c). The major peak noted at 2θ=22.66° in the diffractogram clearly indicates the crystalline features of cellulose. The cellulose standard profile was evident from International Centre for Diffraction Data [46]. Apart from this, the existence of one more phase was seen, i.e the amorphous phase of lignin, which is revealed by the broad straight line. This is evident of a healthy cellulose content, which duly increases the mechanical properties. The Crystallinity index was found as 55%. The crystallinity fraction indicates the lateral packing of cellulose chain molecules as high in order, which, in turn, exhibits the superior tensile strength of the NPBFC [30]. 4.9. Microstructural analysis The interface can be regarded as the three-dimensional boundary between the fiber and matrix. It is highly critical in controlling composite properties, since fiber-matrix interaction occurs through this interface. This interaction can be possible through three mechanisms: mechanical coupling or micromechanical interlocking, physical coupling such as Vander Waals or electrostatic interaction and chemical bonding out of these chemical bonding plays vital role. This is schematically represented in Fig.9.
The fractured interface of FESEM analysis of the experimented tensile, flexural of RBFC, RGFC and NPBFC specimen for various fiber weight percentages are shown in Figs.10 and 11. At 10 wt. % fiber content, the micrograph reveals (Fig.10-a, f, k), mostly matrix pores and peeling. This shows that the failure of the composite specimens was dominated by matrix failure; hence the strength of the composite specimens was low. However, when the fiber content was increased from 10 to 30 wt.% (Fig.10-b, c, g, h, l, m), due to minute enhancement in interfacial bonding, the failure was mainly in form of fiber pullout confirming marginal stress transfer from matrix to fiber. This results in slight increase in strength of the composite specimens. Meanwhile, at 40 wt. % fiber content (Fig.10-d, i, n) the matrix failure was observed to be very meager and debonding is slightly lower than 30 wt. %. Moreover, it is associated with high dominant fiber pull-out. This phenomenon resulted in superior strength among all wt. % due to optimal interfacial bonding. Beyond 40 wt. % fiber content (i.e. at 50 wt. %), Fig.10 (e, j, o) depicted very little matrix failure along with high interfacial debonding associated with fiber pull-out which is less than 40 wt. % and more than 30 wt. %. This resulted abrupt reduction in strength due to fiber to fiber contact. However the dominancy of matrix failure observed in micrograph of NPBFC reveals, as the fiber wt. % is increased from 10 to 40 wt. % is keep on reducing and much lower than RGFC and RBFC. Moreover, in such cases the failure was dominated by fiber pull-out which was higher than RGFC and RBFC. This proves that the stress was transferred from matrix to fiber smoothly than RGFC and RBFC. Thus NPBFC offered superior in strength. Similarly, FESEM images of flexural composite specimens of RGFC, RBFC and NPBFC are displayed in Fig.11 (a-o). The micrograph revealed similar trend as that of fractured tensile composite specimens. The predominant failure such as fiber pullout, fiber breakage, matrix fracture, fiber fracture, matrix peeling, matrix crack, matrix pores, fibermatrix debonding and broken fibers was observed in Fig.11 (a, b, c, f, g, h, k, l, m). However, at 40 wt. % fiber content, a honey comb structure was witnessed even after the fracture. This proves excellent bonding of fiber with matrix that resulted superior strength. Meanwhile, when the fiber content arises from 40 to 50 wt. %, matrix pores were seen. This was the result of a less amount of matrix and the agglomeration formation. Hence the strength was reduced. 5. Theoretical Modeling of composite Various theoretical models have been proposed by renowned scientists for the prediction of the randomly oriented short fiber polymer composite [47]. Among the various projected models, two pertinent models and their empirical relation were employed for finding the tensile properties well before start of the manufacture of the composite material, based on fiber and matrix properties.
(i)
Series model: (1)
(ii)
Hirsch’s model: (2)
where
-Volume fraction of fiber,
matrix (N/m2),
-Volume fraction of matrix ,
-Tensile strength of the composite (N/m2),
-Tensile strength of
-Tensile strength of fiber
(N/m2), x- Parameter constant having values between 0 and 1. Analytical comparison of the predicted tensile strength of RBFC, RGFC and NPBFC with the factual experimental data was made for the validation of the above models. The model results were correlated with experimental values. The correlation done was in the range upto optimum fiber content range. The term ‘X’ denotes the volume fraction of the fiber and ‘x’ is a factor which denotes the stress transfer between matrix and the fiber. Results attained were found to be better when x=0.1 which was applied for the fabricated composites [21]. The empirical as well as theoretical models regression equations for the manufactured composite can be stated as below.
(i)
Experimental Results RBFC, σc
= 0.154X + 36.48
-
(3)
RGFC, σc
= 0.642X + 40.61
-
(4)
NPBFC, σc
= 0.521X + 35.92
-
(5)
RBFC, σc
= 0.676X + 32.38
-
(6)
RGFC, σc
= 0.817X + 39.29
-
(7)
-
(8)
(ii) Series Model
NPBFC, σc (iii)
= 0.751X + 36.15
Hirsch’s Model RBFC, σc
= 0.981X + 32.84
-
(9)
RGFC, σc
= 1.198X + 39.06
-
(10)
NPBFC, σc
= 1.099X + 36.23
-
(11)
Experimentally, addition of fiber beyond the optimum fiber content (i.e. 40 wt. %) makes the composite strength inferior. This could be attributed to poor interfacial bonding between the fiber and the matrix, which is reflected in the experimental curve. However, this phenomenon does not figure in the two models since they have their own limitation, namely applicability only for perfectly bonded materials as depicted in Fig.12 (a-c). The conclusion
is that the Hirsch’s model is more correlated with the experimental values with better correlation factor (R2) values for the fabricated composites. 6. Conclusions The fabricated NPBFC laminate exhibited excellent mechanical properties at 40 wt. % fiber content. This is much superior than RBFC and comparable with RGFC. The superior properties were attributed due to optimized needle punching parameters such as depth of penetration 8 mm and
punch density of 100 punches/cm2. Similarly, the uniform GSM obtained through the needle punching technique enables smooth transfer of stress from matrix to fiber, thereby improving the mechanical properties of NPBFC. The TGA revealed optimized NPBFC has excellent thermal stability upto 260°C, permitting its use in automotive industry, safety equipment etc. QSI experimentation confirms the high load bearing capacity of the NPBFC composites. These were endorsed by the morphological analysis. Hence NPBFC can be a potential and alternate replacement for existing carcinogenic RGFC in relation to its thermo-mechanical properties. This needle punching technique obviates the traditional use of chemicals to enhance the interfacial bonding of natural fiber composites, keeping the working environment safe from the ill effects of these hazardous chemicals leading the way to a greener environment.
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Table Captions Table.1: Bio-chemical properties of raw banana fiber Property Cellulose (%) Hemicellulose (%) Lignin (%) Moisture (%)
Quantity 71.08 12.61 7.67 6.73
Table.2: Physical properties of raw banana fiber Property Diameter (µm) Density (g/cm3) Tensile Strength (MPa) Elongation at break (%) Microfibril angle (°) Lumen size (µm)
Quantity 138±0.0671 1.28 412.5±46.7 27.89 11 6
Table.3: Properties of unsaturated polyester (liquid and cured) resin. Liquid Resin Density 1.18 g/cm3 Appearance Slightly yellow viscous liquid Acid value 22 ± 3 mg KOH/g Specific gravity at 25° C 1.25 ± 0.04 Viscosity at 25°C 220-280 centipoise Volatile content 35 ± 1 wt.% Cured Resin Tensile strength 36.0 ± 2 MPa Tensile modulus 1.23 ± 0.2 GPa Elongation at break 1.32 ± 0.25% Flexural strength 42.10 ± 2.51 MPa Flexural modulus 1.71 ± 0.21 GPa Shear strength 4.5 ± 0.54 MPa Impact strength 0.62 ± 0.03 J/cm2 Rockwell hardness 61 ± 2 HRRW
Table.4: Cell wall dimensions of narrow and wide banana leaf sheath fiber Description Banana Stem Wide Fiber Middle part of the fiber Total thickness of the fiber Total middle lamella Total primary wall Total secondary wall
Dimensions (µm)
25 5 5 5
Total cell lumen Tapering part of the fiber Thickness of the fiber Cell lumen Primary Secondary wall Middle lamella Banana Stem Narrow fiber Middle part of the fiber Fiber total thickness Cell lumen Primary wall Secondary wall Middle lamella Tapering part of the fiber Fiber total thickness Cell lumen Primary wall Secondary wall Middle lamella
10 14 8 2 3 1
25 15 3 5 2 15 8 2 3 2
Figure Captions
Fig.1: Flow diagram of composite from plant origin (a) Banana plant (b) Pseudo stem (c) Extracted raw fiber (d) Needle punching machine, (e) Needle punched fiber roll and (f) NPBFC
Fig.2: Anatomical micrographs of banana plant pseudo stem: (a) - Transverse section of banana sheath showing upper horizontal portion and vertical partition, (b) - Transverse section of leaf sheath showing lower horizontal portion and vertical partition, (c) - Fiber bundles of leaf sheath, (d) - Fiber bundles
enlarged, (e) - Larger fiber bundles enlarged and (f) - Smaller fiber bundles along the epidermal region. [AC - Air Chamber, AbS - Abaxial Side, Fi- Fiber, Pa - Parenchyma, Ph- Phloem, Ve- vessel, VaSt & VSt - Vascular Strand, VePa - Vessel Parenchyma, AdE - Adaxial Epidermis, FiB - Fiber Bundle, GPa & GP- Ground Parenchyma, Hd- Hypodermis, AbE – Abaxial Epidermis]
Fig.3: Optical micrographs of banana plant pseudo stem: (a) - Fibers separated showing Narrow Fibers and Wide Fibers, (b) - A bundle of Fibers intact, (c) - Wide Fiber Tapering part, (d) - Wide FiberMiddle part, (e) - Wide Fiber showing Tapering end portion, (f) - Wide Fiber - Middle part, (g) - Narrow Fiber - Tapering end part and (h) - Narrow Fiber - Middle part [FiB - Fiber Bundle, NFi - Narrow Fiber, WFi - Wide Fiber, CL - Cell Lumen, FiE - Fiber End, ML - Middle Lamella, MP - Middle part, PW Primary Wall, SW - Secondary Wall, Ep- Epidermis]
Fig.4: (a) Tensile strength Vs Fiber wt. in % (b) Flexural strength Vs Fiber wt. in % of composites
Fig.5: Indentation damage resistance of (a) Peak force Vs indentation displacement for RBFC (b) Peak force Vs indentation displacement for NPBFC (c) Peak force Vs indentation displacement for RGFC (d) Dent depth Vs Fiber wt.% (e) Linear stiffness Vs Fiber wt.% (f) Absorbed energy Vs Fiber wt.% of composites
Fig.6: Hardness measurement of RBFC, RGFC & NPBFC
Fig.7: (a) TG and DTG analysis (b) FTIR spectrum (c) XRD pattern of NPBFC at optimum fiber content
Fig.8: DMA test results showing viscoelastic behavior of UPE and NPBFC (a) Storage modulus (E’) (b) Loss modulus (E’’) and (c) tan δ
Fig.9: Schematic representation of chemical bonding at fiber/matrix interface
Fig.10: FESEM of fractured tensile specimens: RBFC (a, b, c, d & e @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%), RGFC (f, g, h, i& j @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%) and NPBFC (k, l, m, n & o @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%)
Fig.11: FESEM of fractured flexural specimens: RBFC (a, b, c, d & e @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%), RGFC (f, g, h, i& j @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%) and NPBFC (k, l, m, n & o @ 10 wt.%, 20 wt.%, 30 wt.%, 40 wt.% & 50 wt.%)
Fig.12: Tensile strength prediction of (a) RBFC (b) RGFC &(c) NPBFC using Series and Hirsch’s models
Conflict of Interest The authors declared the following conflict of interest statement: (i).
All authors have participated in (a) analysis and interpretation of the data; (b) drafting the article or revising it critically for important intellectual content; and (c) approval of the final version.
(ii). This manuscript has not been submitted to, nor is under review at, another journal or other publishing venue. (iii). The authors have no affiliation with any organization with a direct or indirect financial interest in the subject matter discussed in the manuscript.
Yours sincerely, Jack J. Kenned Research Scholar, Department of Mechanical Engineering, National Institute of Technology, Tiruchirappalli – 620015, Tamil Nadu India.