Properties of Rice Husk
Recent interest on the environmental impact of polymer-based materials has lead to the development of new products prepared with recycled polymers and/or containing biodegradable materials. Lignocellulosic plastic composites constitute an important set within this kind of materials showing several advantages over traditional mineral-filled plastic composites: low density, low production costs, biodegradability, renewability, etc. Stiffness, hardness and dimensional stability of plastics have also been improved by incorporation of lignocellulosic fillers .
However, the use of agro-fibers shows some drawbacks such as degradation at relatively low temperature due to the presence of cellulose and hemicellulose. This early thermal degradation limits the allowed processing temperature to less than 200 ºC and restricts the type of thermoplastics that can be used with agro-fibres to some commodity plastics such as PE, PP, PVC and PS[3]. Natural fiber/PP composites have been used in automotive applications and recently they have been investigated for using in construction, such as building profiles, decking, railing products, etc.1,4.
Other factors should be taken into account when designing composites made of lignocellulosic fibers for specific applications, among them its poor resistance to moisture5. Outdoor applications have raised the interest on this property since moisture absorbed by the composite led to dimensional changes and to decreasing mechanical performance4. These negative effects can be reduced if the fibers are encapsulated in the plastic with good adhesion between the fibers and the matrix. The addition of a compatibilizer has been a useful tool for achieving such adhesion. Maleic anhydride-grafted PP (MAPP) is the most common compatibilizer used to improve interfacial adhesion for bio-fillers/apolar thermoplastic matrices even so new alternatives are being currently studied.
Rice husk (RH) is one of the major agricultural residues produced as a by-product during rice processing. Usually it has been a problem for rice farmers due to its resistance to decomposition in the ground, difficult digestion and low nutritional value for animals8. According to Marti-Ferrer the lignin and hemicellulose contents of rice husk are lower than wood whereas the cellulose content is similar. For this reason RHF can be processed at higher temperatures than wood. Therefore, the use of rice husk in the manufacture of polymer composites is attracting much attention.
The group of Kim, in Korea, has published many studies dealing with PP-rice husk composites9-14. They observed that tensile and impact strengths (notched and unnotched specimens) decreased with increasing filler loading while the elastic modulus increased9,11. The thickness swelling and the absorption of water were shown to slightly increase as the filler loading increased, but this was to a negligible extent as compared with wood-based composites. Despite the low properties of the composites the researchers concluded that rice husk flour could be utilized as a biodegradable filler to minimize environmental pollution9. Addition of PPMA as coupling agent improved the water absorption properties10. In other studies the researchers verified improvements in thermal stability, dynamic mechanical properties, tensile properties and crystallinity with addition of MAPP.
Despite of the great interest on lightweight materials few studies have focused on determining the density of natural fibers-filled polymer composites. In the present study we used a thermoplastic polymer as matrix (PP) and rice husk flour (RHF) as filler to prepare composites. PP modified with maleic anhydride (MAPP) was used as coupling agent. The objective of the work was to explore the effect of RHF loading and the presence of MAPP on the density, mechanical properties and water absorption behavior of the composites.
For more information please visit website: www.scielo.br
Recent interest on the environmental impact of polymer-based materials has lead to the development of new products prepared with recycled polymers and/or containing biodegradable materials. Lignocellulosic plastic composites constitute an important set within this kind of materials showing several advantages over traditional mineral-filled plastic composites: low density, low production costs, biodegradability, renewability, etc. Stiffness, hardness and dimensional stability of plastics have also been improved by incorporation of lignocellulosic fillers .
However, the use of agro-fibers shows some drawbacks such as degradation at relatively low temperature due to the presence of cellulose and hemicellulose. This early thermal degradation limits the allowed processing temperature to less than 200 ºC and restricts the type of thermoplastics that can be used with agro-fibres to some commodity plastics such as PE, PP, PVC and PS[3]. Natural fiber/PP composites have been used in automotive applications and recently they have been investigated for using in construction, such as building profiles, decking, railing products, etc.1,4.
Other factors should be taken into account when designing composites made of lignocellulosic fibers for specific applications, among them its poor resistance to moisture5. Outdoor applications have raised the interest on this property since moisture absorbed by the composite led to dimensional changes and to decreasing mechanical performance4. These negative effects can be reduced if the fibers are encapsulated in the plastic with good adhesion between the fibers and the matrix. The addition of a compatibilizer has been a useful tool for achieving such adhesion. Maleic anhydride-grafted PP (MAPP) is the most common compatibilizer used to improve interfacial adhesion for bio-fillers/apolar thermoplastic matrices even so new alternatives are being currently studied.
Rice husk (RH) is one of the major agricultural residues produced as a by-product during rice processing. Usually it has been a problem for rice farmers due to its resistance to decomposition in the ground, difficult digestion and low nutritional value for animals8. According to Marti-Ferrer the lignin and hemicellulose contents of rice husk are lower than wood whereas the cellulose content is similar. For this reason RHF can be processed at higher temperatures than wood. Therefore, the use of rice husk in the manufacture of polymer composites is attracting much attention.
The group of Kim, in Korea, has published many studies dealing with PP-rice husk composites9-14. They observed that tensile and impact strengths (notched and unnotched specimens) decreased with increasing filler loading while the elastic modulus increased9,11. The thickness swelling and the absorption of water were shown to slightly increase as the filler loading increased, but this was to a negligible extent as compared with wood-based composites. Despite the low properties of the composites the researchers concluded that rice husk flour could be utilized as a biodegradable filler to minimize environmental pollution9. Addition of PPMA as coupling agent improved the water absorption properties10. In other studies the researchers verified improvements in thermal stability, dynamic mechanical properties, tensile properties and crystallinity with addition of MAPP.
Despite of the great interest on lightweight materials few studies have focused on determining the density of natural fibers-filled polymer composites. In the present study we used a thermoplastic polymer as matrix (PP) and rice husk flour (RHF) as filler to prepare composites. PP modified with maleic anhydride (MAPP) was used as coupling agent. The objective of the work was to explore the effect of RHF loading and the presence of MAPP on the density, mechanical properties and water absorption behavior of the composites.
For more information please visit website: www.scielo.br
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