Department of Chemistry, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia 3

Transcription

1 The Effect of Compatibilising Agent and Surface Modifi cation on the Physical Properties of Short Pineapple Leaf Fibre (PALF) Reinforced High Impact Polystyrene (HIPS) Composites The Effect of Compatibilising Agent and Surface Modification on the Physical Properties of Short Pineapple Leaf Fibre (PALF) Reinforced High Impact Polystyrene (HIPS) Composites J.P. Siregar 1, S. M. Sapuan 1*, M.Z.A. Rahman 2 and H.M.D.K. Zaman 3 1 Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia 2 Department of Chemistry, Universiti Putra Malaysia, UPM Serdang, Selangor, Malaysia 3 Radiation Processing Technology Division, Malaysia Nuclear Agency, Bangi Kajang, Selangor, Malaysia Received: 19 May 2008, Accepted: 14 October 2008 SUMMARY The aim of this study was to investigate the effects of compatibilising agent and surface modification of short pineapple leaf fibre on physical properties of short pineapple leaf fibre reinforced high impact polystyrene (HIPS) composites. The purpose of using the compatibilising agents in this study was to modify the HIPS which include the polystyrene-block-poly(ethylene-ran-butylene)-block-poly(styrene-graft-maleic anhydride) and poly(styreneco-maleic anhydride). Meanwhile, the alkali treatment was also used to modify the natural fibre surface of short PALF. The results have shown that adding compatibilising agent has improved the physical properties of the composites more effectively than by only using alkali treatment to modify the natural fibre surface. INTRODUCTION Recently, using natural fibre or lignocellulosic fillers and reinforcements for polymer thermoplastics has gradually gained acceptance in plastics-based industrial applications 1. The use of natural fibres in polymer thermoplastics to reduce costs and to improve their mechanical properties is not very new; actually there have already been numerous published papers about this topic. It has been proven that composite products formed from natural fibres such as sugar palm, oil palm, hemp, jute, flax, henequen, kenaf, banana, pineapple leaf (PALF), coir, abaca and mixed with plastics have good mechanical properties with low specific mass. This is why the above natural fibres can be offered as alternative materials to replace glass-fibre reinforced plastics. However, their high level of moisture Smithers Rapra Technology, 2009 absorption and the poor wettability of non-polar plastics have resulted in an insufficient adhesion between untreated fibres and the polymer matrix, which can lead to debonding with age 2,3. The inherent incompatibility of hydrophilic natural fibres with hydrophobic thermoplastic polymers usually can yield poor interfacial adhesion, which results in the deterioration of the mechanical and physical properties of the composites in the final products. Previous researchers have conducted studies to increase the efficiency of transfer of stress from the matrix to the fibres to improve the interfacial adhesion, which included physical and chemical methods 4,5. In this paper, the effect of surface modification of short PALF with *Corresponding author (sapuan@eng.upm.edu.my). Tel: , Fax: alkali treatment and modifying the HIPS matrix by using various concentrations of polystyrene-blockpoly(ethylene-ran-butylene)-blockpoly(styrene-graft-maleic anhydride) and poly(styrene-co-maleic anhydride) as compatibilisers on the physical properties of short pineapple leaf fibrereinforced high impact polystyrene (HIPS) composites is presented. EXPERIMENTAL AND METHOD Materials The pineapple leaf fibre (Ananas comosus) was obtained from, Pemalang, Central of Java, Indonesia. The size of pineapple leaf fibre that was used in this research was mesh. The high impact polystyrene (HIPS) used as the polymer matrix was Idemitsu PS HT 50, supplied by the Petrochemical (M) Sdn Bhd, Pasir Gudang, Johor, Malaysia. There are two types of compatibilising agent that were used in this research, which are polystyrene-block-poly(ethylene-ran- Polymers & Polymer Composites, Vol. 17, No. 6,

2 J.P. Siregar, S. M. Sapuan, M.Z.A. Rahman and H.M.D.K. Zaman butylene)-block-poly(styrene-graftmaleic anhydride) and poly(styrene-comaleic anhydride). Sodium hydroxide (NaOH) that was also used to treat the pineapple leaf fibres was supplied by Aldrich Chemical Company, Malaysia. Table 1 gives physical properties of HIPS and compatibilising agents in this study. Compatibilising Agent There were three different weight concentrations (2%, 4%, and 6%) of compatibilising agent that were applied for both types of compatibiliser. The weight of the short PALF, which was 50% of the total formulation, was kept constant while the ratio of HIPS and compatibilising agent were varied (Table 2). Preparation of Composite Alkali (NaOH) Treatment The short pineapple leaf fibre was soaked in two different concentrations (2% and 4%) of NaOH solution in a water bath for 1 hour at room temperature. The ratio of the fibres to the solution was 1:20 (w/v). After treatment, the fibres were washed, rinsed several times with distilled water and then dried in an oven at 80 C for 24 hours. Compounding Compounding was carried out using a melt mixer (a Brabender Plasticorder intensive mixer, model PL2000-6). The mixing temperature and screw speed were set at 165 C and 50 rpm. HIPS were charged in the chamber and after melting (3 minutes), the dried SPALFs were added. The mixing process of SPALF and HIPS took place for about 15 minutes. Compression Moulding The melt compounded mixture obtained from the previous process was placed in the compression mould (Carver hot press) at a temperature of 165 C and endured the process of preheating for 5 minutes and fully press-heating for 5 minutes. This was Table 1. Physical properties of HIPS and compatibilising agents Material Specific MFI Water Code Gravity (g/10 min) Absorption (%) High Impact Polystyrene <0.1 HIPS Polystyrene-block-poly(ethylene-ranbutylene)-block-poly(styrene-graft-maleic PSgMA anhydride) Poly(styrene-co-maleic anhydride) PScoMA Table 2. Denotation of sample composites Sample Material UF50 Untreated fibre with size mesh CFA2 50% fibre+48%hips+2% of PSgMA CFA4 50% fibre+46%hips+4% of PSgMA CFA6 50% fibre+44%hips+6% of PSgMA CFB2 50% fibre+48%hips+2% of PScoMA CFB4 50% fibre+46%hips+4% of PScoMA CFB6 50% fibre+44%hips+6% of PScoMA TFA2 Treated fibre with 2% NaOH (50% fibre+50% HIPS) TFA4 Treated fibre with 4% NaOH (50% fibre+50% HIPS) followed by cooling for 5 minutes and finally the composites were formed into sheets. The specimens for the physical tests were obtained from these composite sheets. Testing Procedure Water Absorption Samples were cut from the prepared composites sheets and were immersed in distilled water at room temperature for 24 h. Then they were removed from the bath and carefully dried with absorbent paper before being put on the scale. The percentage of weight change due to the water absorption was calculated by using the following formula: MA = M M t M 0 where M 0 is the mass of the dried specimen and M t is the mass of the specimen as a function of immersed time. Thickness Swelling The samples for the thickness swelling had similar size and the same immersion procedure as the samples used in the water absorption experiment. Initially three thickness measurements were taken for each specimen before it was immersed in the distilled water. The calculation of thickness swelling is based on the following equation: TS = T t = T T 0 where T 0 is the thickness of the composite specimen before immersion (mm) and T t is the thickness of the specimen after immersion. Melt Flow Index (MFI) The MFI test was carried out according to ASTM 1238, using a Toyoseiki Melt Indexer model SO1. The melt flow index was determined by performing 380 Polymers & Polymer Composites, Vol. 17, No. 6, 2009

3 The Effect of Compatibilising Agent and Surface Modifi cation on the Physical Properties of Short Pineapple Leaf Fibre (PALF) Reinforced High Impact Polystyrene (HIPS) Composites an extrusion process for 10 minutes at a temperature of 200 C with 5 kg total load of piston. The sample materials were heated for four minutes before the MFI measurement. A cutter was used to automatically cut off extrude at every 30 seconds. The calculations of MFI were based on the following formula: MFI = 600xm T where: MFI = melt flow index (g/min) m = average mass of cut sample (g) T = sample cutting time for measuring mass, (s) 600 = number of seconds in 10 minutes Specific Gravity Determination The specific gravity of the composites was measured using the Archimedes principle, which involves the immersion of a known weight of composite into distilled water. The specific gravity was calculated according to the following formula: W fa = 0 W fa W fb where: ρ = specific gravity of composites ρ o = specific gravity of water W fa = the weight of composites in air (g) W fb = the weight of composites in the water (g) RESULTS AND DISCUSSION Table 3 shows the effect of using compatibilising agents and surface modification on the physical properties of short PALF/HIPS composites such as water absorption, thickness swelling, melt flow index (MFI), and specific gravity. Water Absorption Water absorption of composites indicates their capability to absorb water after immersion in distilled water for 24 hours. Basically, the addition of natural fibre to a reinforced polymer matrix causes an increase of water absorption by the composite because the natural fibre is hydrophilic in nature with an abundance of hydroxyl groups that are not compatible with a hydrophobic matrix; the moisture content can reach 3-13% 6-8. Figure 1 shows the effect of modified HIPS using compatibilisers and natural fibre surface modification with alkali treatment on water absorption of short PALF/HIPS composites. The addition of 2% by weight of the compatibilisers (PSgMA and PScoMA) to modify the HIPS increased the water absorption of composites to 4.480% and 4.195% respectively. It is supposed that the water absorption of the composites will increase if there is poor interfacial adhesion between natural fibre and modified matrix. An increase in concentration of both compatibilising agents up to 6 wt.% reduced the water absorption of the composites. This was attributed to the formation of covalent bonds between the functional groups of maleic anhydride and the hydroxyl groups at the natural fibre surface 9. In order to get strong adhesion between natural fibres and polymer matrix in MAPP compatibilised composites, the fibres Qiu et al. 10 fully encapsulated the fibres within the matrix, which prevented the water molecules from penetrating into the cellulose. In the present work, the alkali treatment of short PALF with 2% and 4% concentrations of NaOH slightly improved the water absorption of the composites. Thickness Swelling High moisture absorption by natural fibres has previously been found to cause swelling and a plasticising effect, resulting in dimensional instability and poor mechanical properties of Table 3. Effect of compatibilising agents and alkali treatment on physical properties of short PALF/HIPS composites Sample Physical Properties Water Absorption (%) UF (0.169) CFA (0.227) CFA (0.146) CFA (0.154) CFB (0.034) CFB (0.160) CFB (0.062) TFA (0.167) TFA (0.195) Thickness Swelling (%) (0.227) (0.433) (0.382) (0.336) (0.104) (0.297) (0.171) (0.269) (0.243) Note: Values are average of fi ve samples determinations Values in italic parentheses are standard deviations Melt Flow Index (MFI) (g/10 minute) (0.024) (0.018) (0.054) (0.039) (0.019) (0.063) (0.019) (0.011) (0.006) Specific gravity (0.007) (0.008) (0.008) (0.010) (0.006) (0.007) (0.009) (0.009) (0.008) Polymers & Polymer Composites, Vol. 17, No. 6,

4 J.P. Siregar, S. M. Sapuan, M.Z.A. Rahman and H.M.D.K. Zaman Figure 1. Water absorption of short PALF/HIPS composites Figure 2. Thickness swelling of short PALF/HIPS composites Figure 3. Melt flow index (MFI) of short PALF/HIPS composites composites 11. In this work, the effects of using modified HIPS and alkali-treated short PALF on the thickness swelling of short PALF/HIPS composites after being immersed in distilled water for 24 h are shown in Figure 2. The modification of HIPS with a compatibilising agent and surface modifications of the natural fibre have been successfully used to improve the moisture resistance of composites; it greatly reduced the swelling in thickness after immersion in distilled water for 24 hours compared with ones that had been treated with alkali only. It can be concluded that the modified HIPS with compatibilising agent is more effective compared to surface modification with alkali treatment alone. Melt Flow Index (MFI) Figure 3 depicts the melt flow index (MFI) of short PALF/HIPS composites with modified HIPS and surface modification of short PALF. The result of untreated fibre reinforced HIPS composites show the lower MFI value (0.32 g/10 min) compared to the result of modified HIPS with compatibilisers and surface modification of natural fibre. It is indicated that the presence of a high content of natural fibre (50%) will affect the agglomeration of natural fibre, resulting in poor dispersion of the composites 12. The modification of HIPS with compatibiliser and surface modification of short PALF with alkali have improved the MFI value of short PALF/HIPS composites. The addition of PSgMA and PScoMA from 2% up to 6% weight content produced significantly better flow behaviour compared to the short PALF with alkali treatment. The MFI value decreased with the increase of PSgMA and PScoMA concentrations. It can be seen that the MFIs of 2 wt.% PSgMA and PScoMA were only g/10 min and g/10 min respectively, and with an increase to 6 wt.% PSgMA and PScoMA, the MFI decreased to g/10 min and g/10 min respectively. The MFI of composites with alkali-treated fibre (2% and 4%) 382 Polymers & Polymer Composites, Vol. 17, No. 6, 2009

5 The Effect of Compatibilising Agent and Surface Modifi cation on the Physical Properties of Short Pineapple Leaf Fibre (PALF) Reinforced High Impact Polystyrene (HIPS) Composites were g/10 min and 4.89 g/10 min respectively. Specific Gravity Figure 4 shows the influence of the modification of HIPS with compatibilising agents and surface modification of natural fibre on the specific gravity of short PALF/HIPS composites. The presence of PSgMA slightly reduced the specific gravity of composites because the specific gravity of PSgMA was lower than HIPS. The PSgMA that was used as a compatibiliser had a specific gravity of approximately 0.91, while the specific gravity of the HIPS was Furthermore, the increase of PSgMA concentration from 2 wt.% to 6 wt.% has decreased the specific gravity of the composites. A result contrary to the above was found in the case where the addition of compatibilising agent (PScoMA) from to 2 wt.% to 6 wt.% has increased the specific gravity of composites because the specific gravity of PScoMA was higher (1.1 g/cm 3 ) than HIPS. CONCLUSIONS The effect of modification of the HIPS matrix using compatibilising agents and of surface modification of the natural fibre with alkali treatment on the physical properties of short PALF/ HIPS composites has been studied. Both modifications successfully improved the physical properties of short PALF/HIPS composites. The improvement of fibre-matrix adhesion can reduce the hygroscopicity of natural fibre based materials, resulting in reduction of the water absorption and thickness swelling of composites. The present work has shown that modification of the HIPS with compatibilising agents results in better performance than the surface modification of the natural fibre by alkali treatment. ACKNOWLEDGMENTS The authors wish to thank the Ministry of Higher Education Malaysia for funding the research through Fundamental Research Grant Scheme (FRGS) grant number Thanks are also due to the staff of the Malaysia Nuclear Agency, Selangor, Malaysia for their support to carry out this research. REFERENCES Figure 4. Specific gravity of short PALF/HIPS composites 1. Rowell R.M., Claufield D.F., Chen G., Ellis D., Jacobson R.E., Lange S.E. et al., In: Proceedings of the Second International Symposium on Natural Polymers and Composites, Embrapa Agricultural Instrumentation, Brazil, 1998, p Gassan J., A study of fibre and interface parameters affecting the fatigue behaviour of natural fibre composites. Composites Part A: Applied Sci. and Manufacturing, 33 (2002) Doan T.T.L., Gao S.L., and Mäder E., Jute/polypropylene composites I. Effect of matrix modification. Composites Sci. and Technol., 66 (2006) Bledzki A.K. and Gassan J., Composites reinforced with cellulose based fibres. Progress in Polym. Sci., 24 (1999), Nabi, S. D., Jog, J.P., Natural fiber polymer composites: a review. Advances in Polym. Technol., 18 (1999) George J., Bhagawan S.S., and Thomas S., Effects of environment on properties of low density polyethylene composites reinforced with pineapple leaf fibre. Composites Sci. Technol., 58 (1998) Khalil H.P.S.A., Issam A.M., Shakri M.T.A., Suriani R., and Awang A.Y., Conventional agro-composites from chemically modified fibres. Industrial Crops and Products, 26 (2007) Rout J., Misra M., Tripathy S.S., Nayak S.K., Mohanty A.K., The influence of fibre treatment on the performance of coir-polyester composites. Composites Sci. Technol., 61 (2001) Tserki V., Matzinos P., and Panayiotou C., Novel biodegradable composites based treated lignocellulosic waste flour as filler: part II, development of biodegradable composites using treated and compatibilized waste flour. Composites Part A: Applied Sci. and Manufacturing, 37 (2006) Qiu W., Endo T., and Hirotsu T., Structure and properties of composites of highly crystalline cellulose with polypropylene: Effect of polypropylene molecular weight. European Polym. J., 42 (2006) Polymers & Polymer Composites, Vol. 17, No. 6,

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