Density and Water Absorption of Sugarcane Bagasse-Filled Poly(vinyl chloride) Composites

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1 Density and Water Absorption of Sugarcane Bagasse-Filled Poly(vinyl chloride) Composites Density and Water Absorption of Sugarcane Bagasse-Filled Poly(vinyl chloride) Composites Riza Wirawan, SM Sapuan, Robiah Yunus, and Khalina Abdan Faculty of Engineering, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia Received: 23 February 2011, Accepted: 20 February 2012 SUMMARY Sugarcane bagasse is divided into two main components, pith and rind, with pith representing the inner part of the sugarcane bagasse and rind the outer part. In this study, both part of bagasse and were used separately as a filler in poly(vinyl chloride) to construct a natural fibre thermoplastic composite. The bagasse incorporated in poly(vinyl chloride) using internal mixer followed by hot-pressing to obtain a plate of sugarcane bagasse/ PVC composite with various filler loading (10%, 20%, 30%, and 40% in weight). Density of the composites was determined and the composites were subjected to water immersion tests in order to study the effect of filler loading and fibre source on the density and water absorption behaviour. It was observed that the physical properties were influenced significantly by both fibre source and fibre content. Keywords: Bagasse, Composite, Water absorption, Thickness swelling, Density 1. INTRODUCTION Recently, the use of natural fibres as fillers in thermoplastic polymer composite materials has received a great deal of attention from researchers due to their environmentally friendliness, comparable properties to synthetic fillers and stock reliability as a renewable resource 1-3. Sugarcane bagasse, a natural fibre material, is an abundant agricultural waste produced as a by-product of sugarcane milling process. According to FAO statistical data in 2007, the annual world sugarcane stalks production is over 1,400 million tonnes, of which 30% is wasted as bagasse. Therefore, the use of sugarcane bagasse in the production of thermoplastic based composites may contribute to the waste reduction, which is a benefit not only economically but also environmentally. wirawan@mutiara.upm.edu.my Smithers Rapra Technology, 2012 Poly(vinyl chloride) is an inexpensive thermoplastic polymer which is widely used in a broad range of applications. This material, widely known as PVC, is easy to fabricate, can last for a long time and has an outstanding chemical resistance to wide range of corrosive fluids. PVC is also available in many forms, from rigid to flexible products, due to its unique response to various functional additives 4,5. PVC, however, is also suspected as a contaminant material. When it is processed, or when it decomposes, it produces chemical substances that can harm the atmosphere, for example hydrogen chloride and dioxins. This has provoked environmental groups to criticize its mass utilization. Mixing PVC with natural fibres is an alternative win-win solution. Introducing natural fibre composite as substitute materials for some PVC products may reduce the use of PVC, while conserving the advantages of the composites 6. Sugarcane bagasse is a residue of sugarcane (Saccharum officinarum) milling. During the milling process, the sugarcane stalk is crushed to extract the sucrose. This procedure produces a large volume of residue, bagasse, containing both crushed rind and pith fibres 7,8. Rind is material on the surface layer while pith is the inner part of the sugarcane. The chemical contents of bagasse fibres are cellulose (40%), natural rubber (24.4%), lignin (15.0%), sucrose (14%), ash (5%), protein (1.8%), glucose (1.4%), oils (0.6%), and acid (0.6%) 8. The main current use of sugarcane bagasse is as a combustible in the sugarcane industry. However, due to low calorimetric value of the bagasse, alternative fuels are preferred and the availability of sugarcane bagasse, as a waste, will probably increase in the near future 8. Utilisation of sugarcane bagasse as a filler and reinforcement for polymeric material is an approach to converting bagasse into more value-added industrial products. With its adequate tensile strength ( MPa) and modulus of elasticity Polymers & Polymer Composites, Vol. 20, No. 7,

2 Riza Wirawan, SM Sapuan, Robiah Yunus, and Khalina Abdan (15-19 GPa) there is a potential of the bagasse to be used as a reinforcing agent in natural fibre composite 7,9. In this study, the density, water absorption and thickness swelling of such composites with various fibre contents and different fibre sources (pith and rind) were observed, to study the effect of fibre content and fibre source on the physical properties of sugar cane-bagasse/pvc composites. 2. MATERIALS AND METHODS 2.1 Materials The studied matrix was unplasticised poly(vinyl chloride) compound (PVC) IR045A supplied by Polymer Resources Sdn. Bhd., Kelang, Selangor, Malaysia, and the studied sugarcane bagasse was a residue of the sugarcane milling process obtained from sugarcane juice makers in Malaysia. 2.2 Methods Preparation of Composites Both pith and rind of sugarcane bagasse were sun-dried for 2 x 12 hour periods before they were fed into a ring knife flaker separately to obtain short fibres (below 3 cm in length). The fibres were then sieved to obtain more homogeneous dimensions, followed by an oven-drying process at 80 C for 24 hours. The mesh (300 mm 425 mm) of fibres were used in this study. A thermal mixing process was carried out using a Haake Polydrive R600 internal mixer at a temperature of 170 C and rotor speed of 50 rpm. PVC pellets were fed into the chamber and mixed for five minutes, followed by feeding of the fibres. The total mixing time was 15 minutes. In this study, 10%, 20%, 30%, and 40% weight fractions of pith and rind fibres were prepared. The final stage of the composite preparation process in this study was hot-pressing. Hot pressing was carried out at a temperature of 170 C for 12.5 minutes, and the mixture was then cooled under pressure to room temperature. The final products were in the form of plates with dimensions of 15 cm x 15 cm x 3 mm. The plates were then cut into a rectangular shape with dimensions of 1 cm x 1 cm x 3 mm for density, water absorption and thickness swelling measurements Density Determination The density determination was performed using an AND GR-200 analytical balance with density measurement kit. It was performed by means of Archimedes principle, also called the buoyancy method. A body immersed in a fluid apparently loses weight by an amount equal to the weight of the fluid it displaces. Hence, density can be determined by measuring the weight of a sample when it is placed in the air (W a ) and its weight when it is fully immersed in distilled water (W b ) at temperature of 25 C. The following formula was used to calculate the density, ρ in g/cm 3 : ρ = W a ( 0.997) W a W b (1) where is the density of distilled water at 25 C in g/cm Water Absorption Determination Specimens were oven-dried at 80 C for 24 hours. The weights of dried specimens were measured and recorded as W 0. The samples were then immersed in distilled water at ambient temperature. After a certain time, the specimens were removed from the bath and carefully dried with absorbent paper before weighing. The weight of the specimens after immersion was recorded as W t. The weight gain, WG, due to water absorption was calculated as follows: WG = ( W t W 0 W 0 ) 100% (2) Thickness Swelling Determination As a complement to water absorption testing, thickness swelling was determined for the same specimens. The thicknesses of the dried specimens were recorded as T 0, while thicknesses of immersed specimens were recorded as T t. The thickness swelling, TS, was calculated by using Equation (3). TS = ( T t T 0 T 0 ) 100% 3. RESULTS AND DISCUSSION (3) 3.1 Density Figure 1 shows the results of density determination of the pith/pvc and the rind/pvc composites, while the density of unfilled PVC, pith and rind was found to be ± g/ cm 3, ± g/cm 3 and ± 0.009, respectively. It is observed that the density of both rind/pvc and pith/pvc composites were lower than that of untreated PVC and decreased linearly with the increase of fibre content. The densities of all composites were in between the density of PVC and the sugarcane bagasse. It is interesting that, although the difference in density of pith and rind was not significant, the rind/pvc composites showed higher density compared to pith/pvc composites at the same content, indicating the effect of the intrinsic properties of the filler on the properties of composites due to a difference in morphology of pith and rind components. Lee and Mariatti 10 reported that there was a difference in shape and size between pith and rind components. The size of the hollow cavity, called the lumen, in the cells of the rind component is smaller than that of the pith component. Moreover, Rasul et al. 11 reported that the particle density of the rind was higher than that of the pith (0.550 ± 0.02 g/cm 3 and ± 0.01 g/cm 3, respectively). Particle density was defined as the ratio of the mass of to the volume covered 660 Polymers & Polymer Composites, Vol. 20, No. 7, 2012

3 Density and Water Absorption of Sugarcane Bagasse-Filled Poly(vinyl chloride) Composites by the outer surface of the material, including the cavity volume within the material. The lower particle density of pith indicates a higher lumen volume inside the pith component than inside the rind component. When sugarcane bagasse was incorporated into PVC, the lumen would be covered by the matrix, creating cavities inside the composite. Since the lumen volume of pith is higher than that in the rind, the volume of cavities inside the pith/ PVC composites was higher, resulting in lower density compared to rind/pvc composites. 3.2 Water Absorption and Thickness Swelling Water absorption test results are presented in Figure 3. In general, the weight gains due to water absorption of the composites linearly increased with the square root of the immersion time, and then tended to be more constant after a prolonged time, following a Fickian diffusion process 12,13. On the other hand, higher fibre loading resulted in higher water absorption. It seems that the hygroscopic property of natural fibre was responsible to the increase of the weight gain due to water absorption. The cell walls of natural fibres contain hydroxyl and other oxygen-containing groups that attract water through hydrogen bonding 12. Table 1 summarises the initial rate of absorption (k), maximum water absorption (M), and diffusion coefficient (D) of each studied composite. The determination of k was conducted by calculating the slope of the initial plot using linear regression, while D was calculated using Equation (4): Figure 1. Density of sugarcane bagasse/pvc composites Figure 2. Water absorption curve of (a) pith/pvc composites and (b) rind/pvc composites (a) (b) Figure 3. Weight gain due to water absorption of sugarcane bagasse/pvc composites after 24 hours of immersion D = kh 4M 2 (4) where h is the thickness of the sample. The diffusion coefficient is the important parameter in Fick s model which represents the ability of water Polymers & Polymer Composites, Vol. 20, No. 7,

4 Riza Wirawan, SM Sapuan, Robiah Yunus, and Khalina Abdan Table 1. Water absorption parameters of sugarcane bagasse/pvc composites Material k (%/h 1/2 ) M (%) D (m 2 /s) PVC x Pith 10% x Pith 20% x Pith 30% x Pith 40% x Rind 10% x Rind 20% x Rind 30% x Rind 40% x Figure 4. Thickness swelling curve of (a) pith/pvc composites and (b) rind/pvc composites (a) (b) molecules to penetrate inside the composite structure 13. Furthermore, Figure 3 shows the comparison of water absorption between pith/pvc and rind/pvc composites after 24 hours of immersion, which reveals the same trend with the diffusion coefficient shown in Table 1. It is interesting to observe that at low fibre content (10%), the rind/pvc performed higher water absorption than pith/pvc composites at the same fibre content. However, the increasing rate of rind/pvc weight gain due to the increase of fibre loading, represented by the slope of the regression line, is lower than that of pith/pvc. When the weight gain of pith/pvc increased at a high rate with the increase of fibre loading, the weight gain of rind/pvc was increasing at a lower rate. As a result the weight gain of pith/pvc with high fibre content (30% and 40%) was higher than that of rind/ PVC composites with the same fibre content, in contrast to the weight gain at low fibre content. Vilay et al. 9 stated that water absorption is influenced by temperature, fibre content, orientation, permeability, surface protection, exposed surface area and diffusivity. In this study, temperature and fibre content was controlled, while the fibre orientation of pith/pvc and rind/ PVC was assumed to be identical due to the same processing parameters. The difference in permeability between pith and rind may explain the difference in their water absorption. The higher slope of the regression line of pith/pvc as compared to rind/pvc composites indicates that pith is of better permeability than rind. However, it fails to explain why the rind/pvc composites showed higher water absorption compared to pith/pvc composites at low fibre content. The remaining factors that may possibly explain the phenomena are fibre surface protection and exposed surface area, which are related to the fibre-matrix interfacial adhesion. It seems that the pith/pvc composites are of better fibre-matrix interfacial adhesion as compared to rind/pvc composites. A gap may lie between the fibre and matrix when the fibre-matrix interfacial adhesion is poor. A high gap volume means low fibre surface protection and high exposed surface area and, as a result, high water absorption. It seems that at low fibre content, the effect of fibre surface protection and exposed surfaces area was more dominant compared to the fibre permeability and diffusivity, resulting higher water absorption of rind/pvc composites. Finally, Figures 4 and 5 show the thickness swelling of both pith/ PVC and rind/pvc composites. It is observed that the trend was similar to that of the weight gain, indicating the correlation between thickness swelling and weight gain due to water absorption. The penetration of water inside a composite may swell the cell wall of cellulosic fibre, resulting in thickness swelling of the composite structure 12, Polymers & Polymer Composites, Vol. 20, No. 7, 2012

5 Density and Water Absorption of Sugarcane Bagasse-Filled Poly(vinyl chloride) Composites Figure 5. Thickness swelling due to water absorption of sugarcane bagasse/pvc composites after 24 hours of immersion 4. CONCLUSIONS The density of both pith/pvc and rind/ PVC composites decreased linearly with the increase of fibre content. The rind/pvc composites obtained higher density as compared to pith/ PVC with the same fibre content due to the smaller volume of lumen existing in the unit cell. Furthermore, weight gain and thickness swelling due to water absorption increased linearly with the increase of fibre content. Beside the fibre properties, such as fibre permeability and diffusivity, surface protection and exposed surfaces area and diffusivity of the fibre were also responsible in the moisture content of composites. 5. ACKNOWLEDGEMENT The authors wish to thank Universiti Putra Malaysia for financial support of this study and fellowship funding for the main author through the Research University Grant Scheme (RUGS; Project no: 05/01/07/0190RU) and Graduate Research Fellowship (GRF). REFERENCES 1. George J., Sreekala M.S., and Thomas S., A review on interface modification and characterization of natural fiber reinforced plastic composites. Polymer Engineering & Science, 41 (2001) Saheb D.N. and Jog J.P., Natural fiber polymer composites: A review. Advances in Polymer Technology, 18 (1999) Satyanarayana K.G., Arizaga G.G.C., and Wypych F., Biodegradable composites based on lignocellulosic fibers--an overview. Progress in Polymer Science, 34 (2009) Willoughby D., Plastic Piping Handbook. New York: McGraw-Hill; Nass L., Encyclopedia of PVC. New York: Marcel Dekker; Ayora M., Ríos R., Quijano J., and Márquez A., Evaluation by torque-rheometer of suspensions of semi-rigid and flexible natural fibers in a matrix of poly(vinyl chloride). Polymer Composites, 18 (1997) Reis J.M.L., Fracture and flexural characterization of natural fiberreinforced polymer concrete. Construction and Building Materials, 20 (2006) Vazquez A., Dominguez V.A., and Kenny J.M., Bagasse Fiber- Polypropylene Based Composites. Journal of Thermoplastic Composite Materials, 12 (1999) Vilay V., Mariatti M., Mat Taib R., and Todo M., Effect of fiber surface treatment and fiber loading on the properties of bagasse fiber-reinforced unsaturated polyester composites. Composites Science and Technology, 68 (2008) Lee S.C. and Mariatti M., The effect of bagasse fibers obtained (from rind and pith component) on the properties of unsaturated polyester composites. Materials Letters, 62 (2008) Rasul M.G., Rudolph V., and Carsky M., Physical properties of bagasse. Fuel, 78 (1999) Das S., Saha A.K., Choudhury P.K., Basak R.K., Mitra B.C., Todd T., et al. Effect of steam pretreatment of jute fiber on dimensional stability of jute composite. Journal of Applied Polymer Science, 76 (2000) Espert A., Vilaplana F., and Karlsson S., Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties. Composites Part A: Applied Science and Manufacturing, 35 (2004) Polymers & Polymer Composites, Vol. 20, No. 7,

6 Riza Wirawan, SM Sapuan, Robiah Yunus, and Khalina Abdan 664 Polymers & Polymer Composites, Vol. 20, No. 7, 2012