Evaluation on Thermal Stability of Hybrid Bamboo/Sisal Fibre Reinforced Polymer Composites

Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

Evaluation on Thermal Stability of Hybrid Bamboo/sisal fibre reinforced polymer composites

A.P.S.V.R.Subrahmanyam1, P.S.V.Pradeep2,G. Babitha2, B.S. Karthik roshan2, G. Ratan kumar2, K. Jyothi shanmukhi2

1Assistant Professor, Dept. of Mechanical Engineering, ANITS, Visakhapatnam-531162, A.P., India

B.Tech Students, Dept. of Mechanical Engineering, ANITS, Visakhapatnam-531162, A.P., India

Abstract The natural fibre industry has drawn much attention of world after experiencing the disasters that synthetic fibres had produced. The investigation was carried to evaluate the effect of fibre loading of sisal and bamboo into the epoxy resin. In this study, the composites were prepared by hand layup technique. The bamboo (B) and sisal (S) fibre composites were fabricated with different volume ratios B/S 30/0, B/S 0/30, B/S 20/10, B/S 10/20, B/S 15/15 and pure epoxy. The hybridization effects were studied by Fourier-transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA), which states that incorporation of natural fibres had significantly lowered the thermal stability of the epoxy matrix. The above mentioned tests were performed according to ASTM standards. The sample with highest bamboo content has proven to be superior among all other hybrid composites in thermal stability. Keywords: hybrid composite, TGA, FTIR, thermal stability.

1. Introduction The growing environmental issues have encouraged the researchers to investigate the enhancement of properties of natural fibers reinforced polymer composites. A great demand has risen for replacing the synthetic fibres with natural fibres due to their ill effects on the environment. The composites have raised from single fiber composites to hybrid composites ie., incorporating two different fibres(natural or synthetic) into a polymer, due to their better mechanical and thermal properties compared to virgin matrix. Sisal is one of the most widely used natural fibres. It requires less investment and maintenance for cultivation. It is mostly grown in wastelands and helps in soil conservation. It is superior to other natural fibres due to poor crimp property, higher strength, large staple length, bright shiny colour. It is used in traditional uses like making ropes, mats, carpets, handicrafts etc., Sisal has proven to be a potential reinforcing material in various applications like automobiles, railways, geo-textiles, building materials, defence and in the packaging industry. Thermal stability is an important variable that affects the physical properties of the lignocelluloses fibres. It refers to maintaining the mechanical properties like strength, elasticity, toughness at a given temperature. The lignocellulosic fibres mainly consist of components such

Volume XII, Issue IV, 2020 Page No: 4077 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

as cellulose, hemicellulose, lignin and partially stable constituents like waxes, pectin and water soluble components [1].The thermal degradation of natural fibres consists of three stages .The initial weight loss can be ascribed to evaporation of water in the fibres with a maximum weight loss of 10% below 200°C temperature [2]. The first stage can be attributed to depolymerization of hemicellulose and breakage of glycoside linkages of celluloses [3]. The lignin and other earlier decomposition products further decompose in the second stage .According to Yi et al. [4] lignin decomposes in a broad range of temperature 60°C - 450°C. However, the effects of these components will be limited by their amount. Nabi Sahed and Jog [5] stated that thermal degradation of natural fibres produce volatile products resulting in porous material with inferior mechanical properties. Surface modifications also improve mechanical and thermal properties of fibre reinforced composites among which mercerization i.e., alkaline treatment is frequently used to improve the properties [1, 5, 6, 7]. These treatments enhance fibre/matrix adhesion by removing the impurities like lignin, pectin and waxes. These impurities are responsible for the hydrophilicity of the fibres and absorbing more and more water. Alkaline treatment results in fibrillation, which causes breaking of composite fibre bundle into smaller fibres. It results in greater surface roughness and leads to better mechanical interlocking [8, 9]. Gonzalez et al. [9.5] worked on effects of incorporating wood flour into a polymer matrix and concluded that mechanical properties deteriorate with increasing temperature. Joseph et al. [10] investigated the thermal behavior by thermogravimetric analysis, carried at a heating rate of 10°C/min in inert atmosphere, of polypropylene (PP) composites reinforced with sisal fibers that were both untreated as well as treated with urethane derivative of PP glycol (PPG/TDi) and maleic anhydride modified PP (MAPP) in order to improve the fiber/matrix interfacial adhesion. The authors found that the treated fiber composites show superior thermal stability comparing with the untreated fiber composites as well as the neat PP and the pure sisal fiber.[10] .Ganan et al showed that TG/DTG curves for epoxy(DGEBA/TETA) composites reinforced with composites reinforced with 30 wt% of sisal fibers that were both untreated or mercerized, silanized, or silanized with previous mercerization. The authors indicated that treated fibres showed better thermal stability than the untreated fibre composites. The shoulder peak around 310°C of the untreated fibres shifted to 330°C with treatment. Gupta and Srivastav studied the effects of different fibre loadings (15, 20, 25 & 30) of sisal in epoxy matrix and concluded that the increase in sisal fibre loading increased the thermal, mechanical and water absorption properties [11]. Influence of atmospheres on thermal decomposition is another point worth discussing. The onset of thermogravimetric degradation in a natural fiber composite is a complex process. It depends not only on the comparative thermal stability of fiber vs. matrix but also on the experiment atmosphere. Gases conduct heat at different rates. In general, two atmospheres namely inert (nitrogen, helium, argon) and oxidative atmospheres are used in thermogravimetric analysis. In inert atmosphere, the composites undergo single degradation but in presence of oxygen, the fibres decompose in a different manner. Stevulova reported that cellulose depolymerization occurs in three processes- thermo oxidation, dehydration, and depolymerization. Depolymerization results in glycosane formation .The thermo-oxidation and dehydration are driven by diffusion of oxygen [12] .They run mainly in amorphous phases of polysaccharides. Concurrently, depolymerization of cellulose leads to decrease in average polymerization degree. Under air atmosphere, heating of cellulose causes oxidation of hydroxyl groups in cellulose molecules and number of carbonyl groups increase. Zhang et al[13] reported that oxygen breaks the epoxy chain by introducing carbon double bond oxygen to the tertiary

Volume XII, Issue IV, 2020 Page No: 4078 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

carbon attached to oxygen and results in earlier generation of by products like CO2, H2O etc. The peak degradation temperature of all composites shifted to lower temperatures as compared to measurement under nitrogen atmosphere. An attempt has been made to explore thermal stability of Bamboo/ Sisal hybrid natural fibre polymer matrix composite using Fourier transform Infrared spectrometry (FTIR) and Thermogravimetric analysis (TGA). Since, there is a possibility of using this natural fibre hybrid composite in the manufacturing of structural and shielding components used in aerospace and automobiles industries.

2. Experimental procedure

2.1 Materials The reinforcements used in this study were bamboo fibre, sisal fibre and mixture of epoxy resin LY556 and hardener HY 917 was used as matrix. The bamboo fibre was procured from Vruksha fibres (Guntur) while epoxy resin and hardener and sisal fibres from Go Green Products (Chennai).The tools required were purchased from a local resource.

Table 1.Chemical Composition of Bamboo fibre

Constituents Percentage Hemicelluloses 11.6 Cellulose 72.6 Lignin 9.5

Table 2 .Chemical composition of Sisal fibre

Constituents Percentage % Hemicelluloses 22 Cellulose 65 Lignin 9.9 Waxes 2

2.2 Preparation of composites The composites were fabricated by the hand layup process. The Fig. 1 shows the fibres soaked in 2% NaOH solution .They were washed with distilled water to remove traces of NaOH and dried in sun light. The dried fibres were chopped into several strands and combed. The fibre loading in the composite was restricted to be 30%. Composites were made in different volume ratios such as B/S 20/10, B/S 10/20 and B/S 15/15. A clean plastic sheet was laid on an even horizontal surface. The calculated amount of bamboo & sial fibres was spread in bilateral pattern in an area of 150*150 mm2 as shown in Fig.2. The epoxy resin mixed with hardener in the ratio 10:1 was used to wet the bamboo fibres followed by overlaying them by sisal fibres .The whole stack was wetted by the epoxy mixture making to a thickness of 2mm. The air bubbles trapped in between the fibres were removed using a roller. The composites were in left in open

Volume XII, Issue IV, 2020 Page No: 4079 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

atmosphere to cure for 12 hrs. The cured composites were cut in desired dimensions using an angle grinder.

a) b)

Fig.1 Fibres immersed in 2 % NaOH a) Bamboo b) Sisal

Fig.2 Fibres chopped and combed Table 3. Sample Designation

Samples Matrix (%) Bamboo (%) Sisal (%) Total fibre (%) EPOXY 100 0 0 0 Bamboo/epoxy 70 30 0 30 Sisal /epoxy 70 0 30 30 A 70 20 10 30 B 70 10 20 30 C 70 15 15 30

Volume XII, Issue IV, 2020 Page No: 4080 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

3. Methodology 3.1 Thermogravimetric analysis The thermal decomposition of samples was analyzed by NETZSCH STA 449 F3 Jupiter shown in Fig.3. The thermal analysis was carried out on 8mg sample from a temperature range of 25 0C to 8000C at a heating rate of 100C/min in nitrogen atmosphere with a flow rate of 20 ml/min. The analysis was performing by placing the sample in Alumina Al2O3 crucible .Nitrogen was used for good heat transfer efficiency and removal of volatiles from the sample. The graphs were plotted with weight loss against temperature.

Fig.3 TGA Equipment. 3.2 Fourier-transform infrared spectroscopy The infrared spectra of the samples were measured using Perkin Elmer Spectrum FTIR/ATR shown in Fig.4.The transmittance was measured over the range of ATR IR 4000cm-1 to 600 cm-1. The unique spectral fingerprints were obtained representing the unique chemical structure. The results were obtained showing "Transmittance vs Wave number".

Fig.4 FTIR Spectrometer

4. Results and discussion

4.1 TGA Analysis The TGA curves obtained in the TG-DSC instrument are plotted in the Fig..6. The temperatures corresponding to the initial weight loss, weight loss to 75% are tabulated in the table 2. The thermal degradation of sample A was single step degradation which was similar to the bamboo fibres while that of sample B and C were similar to that of sisal fibre. The degradation of the samples B and C took place in three distinct steps of weight loss. The initial

Volume XII, Issue IV, 2020 Page No: 4081 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

weight loss can be ascribed to loss of moisture in the fibre or physically absorbed water in the fibres. The initial loss occurred in the temperature range of 200- 340°C [14]. The first stage of degradation is the region which represents the major weight loss of the sample. The major loss can be attributed to decomposition of hemicelluloses and celluloses .Celluloses decomposes by depolymerization which are more thermally stable than hemicelluloses. Cellulose contain more crystalline chains than amorphous form [15].The temperatures corresponding to the major loss follow the order Epoxy> Bamboo/epoxy >sisal/epoxy >A>C>B. The peak (main) temperature decreased with the amount of sisal in the hybrid composites. The second stage of degradation can be attributed to decomposition of lignin and earlier decomposed products. The lignin decomposes at a higher temperature due to its complex three- dimensional amorphous polymer with the presence of aromatic rings with various possible branches [16, 17]. With the increase in sisal content in the composite the single step degradation turned into two well defined peaks.

Table 4. Initial and major weight loss of epoxy and hybrid composites

SAMPLE Initial weight loss (5%) Major weight loss (75%)

EPOXY 330 450 Bamboo/epoxy 206 409 Sisal/epoxy 279 508 A 317 419 B 320 521 C 250 472

Table 5. TGA results of epoxy and hybrid composites

First stage degradation

Sample T onset(°C) T peak(°C) T exit(°C)

Epoxy 295 390 490

Bamboo/epoxy 277 387 470

Sisal/epoxy 273 382 476

A 266 369 478

B 262 352 455

C 243 355 483

Volume XII, Issue IV, 2020 Page No: 4082 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

Fig. 5 Variation of weight loss (%) with temperature of epoxy and hybrid composites.

The epoxy shows the better thermal stability compared to all other samples with Tonset=295°C, Tpeak=390°C and Texit=490°C followed by bamboo /epoxy with Tonset=277°C, Tpeak=387°C, Texit=470°C. The lower degradation temperature of natural fibres is responsible for decrease of thermal stability of the bamboo/epoxy over pure epoxy sample. Bamboo /epoxy sample reveals better thermal stability compared to sisal /epoxy sample due to less cellulose content of sisal fibres compared to bamboo fibre..The sample A has higher peak temperature among the hybrid composites. The peak temperature decreased with decrease in bamboo content. The thermal stability follows the order Epoxy>bamboo/epoxy sisal/epoxy >A>C>B. With the increase in sisal content in the composite the single step degradation turned into two well defined peaks. The onset temperature, peak temperature and exit temperature of the first stage degradation are tabulated in Table 5.

4.2 FTIR Analysis Fig.6, Fig.7, Fig.8 shows the FTIR composition of natural fibre hybrid composite of bamboo and sisal of different ratios. The natural fibre hybrid composite (bamboo and sisal) of different ratios were having similar peak intensity. Both bamboo and sisal fibre consist of cellulose, hemicelluloses, and lignin; therefore the hybrid composite peak intensities obtained are identical. However, there were still differences among pure bamboo fibre and pure sisal fibre −1 peak. The peaks at regions 1368-1365 cm were attributed to the CH2 bending and OH bending. Both sisal and bamboo fibres show peak at 1742 and 1733cm−1 represent acids of hemicelluloses. The absence of this peak was observed in hybrid composites of bamboo and sisal, indicating the removal of most of the hemicellulose. The peak at 1247-1240cm−1 regions is due to the stretching of phenolic hydroxyl groups in lignin. Total disappear of this peak in sisal and bamboo cellulose samples revealed that lignin was removed. On the other hand, all cellulose samples

Volume XII, Issue IV, 2020 Page No: 4083 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

show peak at 1166–1160cm−1 region assigned as C–O–C stretching attributed to the β-(1→4)- glycosidic linkage in cellulose . Fig.6, Fig.7, Fig.8 also shows all cellulose with broad peak intensity band at 3343– 3295cm−1 attributed to O–H stretching vibration. The peaks at 2923–2900cm−1 and 1324– −1 1310cm regions were characteristics of C–H stretching and –CH2bending respectively. The peak at 1651–1645cm−1 is attributed to the H–O–H stretching vibration of absorbed water in −1 carbohydrate. The peaks at 830–825cm region are related to glycosidic –C1–H deformation, a ring vibration, and –O–H bending. These characters imply the β-glycosidic linkages between the anhydroglucose units in cellulose. The rise of intensity peaks at 1021–1015cm−1 regions confirms that the cellulose content increases due to chemical treatment. All the hybrid composite ratios show identical peaks compared to commercial cellulose. This further confirms that hemicelluloses and lignin in both sisal and bamboo fibre were well removed during the chemical treatment.

100

Transmittance [%] Transmittance

3331.64

2913.88

2355.99

2080.24

1990.65 1947.16

1645.44 1573.72 1507.21 1422.59 1365.88

1246.70

1154.04 1103.69 1021.54

829.43

703.75 662.05 575.41 517.26

3500 3000 2500 2000 1500 1000 500 Wavenumber cm-1

E:\USERS DATA\EXTERNAL\EXT 2020\JANUARY\PADALAFig.6 SAI FTIR PRADEEP\FTIR graphs C.0 of Sample FTIR C A Instrument type and / or accessory 23-01-2020

Page 1/1

Volume XII, Issue IV, 2020 Page No: 4084 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

100

Transmittance [%] Transmittance

3295.34

2913.09

2329.05

2186.80

2053.59

1880.33

1595.59

1505.94

1421.71

1367.85

1310.30

1240.63

1152.97

1102.81

1018.03

826.01

661.66

581.48

541.88

3500 3000 2500 2000 1500 1000 500 Wavenumber cm-1

Fig.7 FTIR graphs of sample B E:\USERS DATA\EXTERNAL\EXT 2020\JANUARY\PADALA SAI PRADEEP\FTIR B.0 FTIR B.. Instrument type and / or accessory 23-01-2020

100 Page 1/1

Transmittance [%] Transmittance

3326.08

2913.81

2103.99 2001.73 1927.81

1646.48 1508.01 1422.45 1366.59 1320.57 1243.74 1152.70 1101.51 1015.97

827.08 659.74 608.90 541.48 521.47

3500 3000 2500 2000 1500 1000 500 Wavenumber cm-1

Fig.8 FTIR graphs of sample C E:\USERS DATA\EXTERNAL\EXT 2020\JANUARY\PADALA SAI PRADEEP\FTIR A.1 FTIR A.. Instrument type and / or accessory 23-01-2020

Page 1/1

Volume XII, Issue IV, 2020 Page No: 4085 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

5. Conclusions  Although the mechanical properties increase with the increase in fibre content in the virgin matrix, there is a necessity of evaluation of degradation temperature of the material to satisfy the requirements of the industry.  The FTIR results stated that the mercerization of the fibres with NaOH lead to removal of hydrophilic hydroxyl groups in hemicelluloses,celluloses,lignin. It therefore resulted in good adhesion between fibre and matrix.  It is evident from the thermal tests that the higher content of cellulose and lignin in bamboo fibres resulted in higher thermal stability among the composites. Due to incorporation of less thermally resistant natural fibres into epoxy resin lowered the thermal stability of the composite.  Although the sisal fibre reinforced hybrid composites revealed the second stage degradation, it is clear from Monteiro et al. [14] that the second stage of degradation is not helpful in engineering applications.

Acknowledgement The authors would like to thank Head of Sophisticated Analytical Instruments Facility (SAIF) and supporting staff at Indian Institute of Technology, Madras for providing facility and allowing us to perform the tests.

References

[1] A.K. Bledzki, J. Gassan. Composites Reinforced With Cellulose‐Based Fibers. Prog. Polym. Sci. 1999; 4:221–274. [2] Monteiro SN, Calado V, Rodriguez RJS, Margem FM. Thermo-gravimetric behavior of natural fibers reinforced polymer composites—an overview. Mater Sci Eng A. 2012; 557:17–28. [3] Mohini Saxena, Asokan Pappu, Ruhi Haque, and Anusha Sharma. Sisal Fiber Based Polymer Composites and Their Applications. Cellulose fibers: Bio-and nano-polymer composites 2011; 589-659, [4] Yi C, Tian L, Tang F, Luoxiin Wang, Hantao Zou and Weilin Xu. Crystalline transition behavior of sisal in cycle process. Polymer Composites 2009; 31(5):933-938. [5] D. Nabi Sahed, J.P. Jog. Natural fiber polymer composites: a review. Adv. Polym. Technol. 1999; 18:351-363. [6] A.K. Mohanty, M. Misra, G. Hinrichsen, Macromol. Biofibres, biodegradable polymers and biocomposites: An overview. Mater. Eng.2000; 276: 1-24. [7] A.K. Mohanty, M. Misra, L.T. Drzal, J. Polym. Sustainable bio-composites from renewable resources: opportunities and challenges in the green materials world. Journal of polymers and the Environment 2002;10:19-26. [8] Mishra S, Misra M, Tripathy SS et alGraft copolymerization of acrylonitrile on chemically modified sisal fibers. Macromol. Mater. Eng. 2001; 286:107-113.– [9] Mishra S, M.Misra, S.S. Tripathy, S.K. Nayak and A.K. Mohanty. Potentiality of pineapple leaf fiber as reinforcement in PALF polyester composite surface modification

Volume XII, Issue IV, 2020 Page No: 4086 Journal of Xi'an University of Architecture & Technology ISSN No : 1006-7930

and mechanical performance. Journal of Reinforced Plastics and Composites 2001; 20(4):321-334. [9] C. Gonzalez, G.E. Myers,Thermal Degradation of Wood Fillers at the Melt-Processing Temperatures of Wood-Plastic Composites: Effects on Wood Mechanical Properties and Production of Voiatiles. International Journal of Polymeric Materials 1993; 23:67-85. [10] P.V. Joseph, K. Joseph, S. Thoas, C.K.S. Pillai, V.S. Prasad G. Groeninckx, M. Sarkissova. The thermal and crystallisation studies of short sisal fibre reinforced polypropylene composites.Composites A 2003; 34: 253-266 [11] M K Gupta &R K Srivastava. Properties of sisal reinforced epoxy composites. Indian Journal of Fibre & Textile Research 2016; 41: 235-241. [12] Stevulova N, Estokova A, Cigasova J, Schwarzova I, Kacik F, Geffert A. Thermal degradation of natural and treated hemp hurds under air and nitrogen atmosphere. J Therm Anal Calorim. 2017; 128:1649-1660. [13] Zhang X, Wu Y, Wen H, Hu G, Yang Z, Tao J. The influence of oxygen on thermal decomposition characteristics of epoxy resins cured by anhydride. Polym Degrad Stab. 2018; 156:125-131. [14] Monteiro SN, Calado V, Rodriguez RJS, Margem FM. Thermo gravimetric behavior of natural fibers reinforced polymer composites—an overview.Mater.Sci.Eng A. 2012;557:17-28. [15] Ishak MR, Sapuan SM, Leman Z, Rahman MZA, Anwar UMK. Characterization of sugar palm (Arenga pinnata) fibres. J Therm Anal Calorim. 2012;109:981-989. [16] Vanholme R, Demedts B, Morreel K, Ralph J, Boerjan W. Lignin biosynthesis and structure. Plant Physiol. 2010; 153: 895-905. [17] Collard FX, Blin J. A review on pyrolysis of biomass constituents: mechanisms and composition of the products obtained from the conversion of cellulose, hemicelluloses and lignin. Renew Sustain Energy Rev. 2014; 38:594-608.

Volume XII, Issue IV, 2020 Page No: 4087