Composites of Rice Husk/Wheat Straw with Pmdi Resin and Polypropylene

Abstract

The application of agricultural fibers for making particleboards has been studied in two types of composites: (i) type I particleboards were composites of wheat straw and rice husk fibers with polymeric methylene di-phenyl diisocyanate resin (pMDI) as a binder made by compression moulding; (ii) type II particleboards were composites of rice husk and polypropylene made by extrusion and injection moulding. In type I particleboards, the effects of varying the resin content and various combinations of wheat straw/rice husk fibers were investigated and characterised in terms of physical and mechanical properties of particle boards such as modulus of rupture, modulus of elasticity, compression strength, density, dimensional stability and water absorption. Results indicated that with increasing binder content, the physical and mechanical properties were improved until an optimum level of binder content was reached. Particleboards made of wheat straw blended with 6% pMDI showed a maximum MOE. Dimensional stability and water absorption of particle-boards made by combining wheat straw and rice husks were superior to those made only from wheat straw. In type II particleboards, the non-polar polypropylene had poor affinity with rice husk, which resulted in weak interfacial adhesion and low mechanical properties. Tri-methoxy vinyl silane as coupling agent and maleic anhydride-grafted polypropylene (MAPP) as compatibiliser were used to obtain improved interfacial adhesion. The interface-treated composites were characterised by measuring tensile strength, tensile modulus, impact strength and optical microscopy. The combination of silane and MAPP proved effective in improving interfacial adhesion between polypropylene and rice husk. The improved interface allowed effective transfer of mechanical stress through boundary regions as verified by better mechanical properties. The latter was confirmed by the improved interface morphology of composites. The best impact strength result was obtained at a combination of 1.5 wt.% silane and 5 wt.% MAPP in all rice husk composites.