Natural rubber-cassava starch foam by compression moulding

The foaming processes of mixtures of cassava starch-water and cassava starc h natural rubber latex blends have been carried out by compression moulding . The appropriate conditions under which to produce expanded foam are as fo llows: a temperature of 150 degreesC, 10.8 MPa pressure, and a 2 min mouldi ng time. For the foam from the cassava starch with water as a blowing agent , it was found that water levels in the range of 150-200% by weight of the dry starch gave good conditions for foaming. The resulting foamed material has a uniform closed cell structure. Regarding blending of cassava starch w ith natural rubber, the natural rubber could not be dispersed in the gelati nised starch when blended at a temperature of 70 degreesC. To stabilise and prevent the coagulation of natural rubber in the blending process, Nonidet P40. a nonionic surfactant, was used. A suitable amount of Nonidet P40 was 1.5% by weight of natural rubber latex. The compressive stress and the sto rage modulus of the foam obtained increased (42-233%) with increasing natur al rubber content owing to the high elasticity of the natural rubber and it s promotion of more elasticity to the foams. When 2-5% of benzoyl peroxide by weight of natural rubber was added to the rubber latex, the compressive stress of the foam was further increased (20-118%) owing to vulcanisation o f the natural rubber. Furthermore, an addition of 15-30% of calcium carbona te by weight of the dry starch of the blends was found to increase the comp ressive stress and storage modulus of the foams (69-148%) and the hardness and brittleness of the foams. (C) 2001 IoM Communications Ltd.