Natural rubber–cassava starch foam by compression moulding

Abstract

The foaming processes of mixtures of cassava starch–water and cassava starch–natural rubber latex blends have been carried out by compression moulding. The appropriate conditions under which to produce expanded foam are as follows: a temperature of 150°C, 10·8 MPa pressure, and a 2 min moulding 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 with natural rubber, the natural rubber could not be dispersed in the gelatinised starch when blended at a temperature of 70°C. 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 storage modulus of the foam obtained increased (42–233%) with increasing natural rubber content owing to the high elasticity of the natural rubber and its 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 of the natural rubber. Furthermore, an addition of 15–30% of calcium carbonate by weight of the dry starch of the blends was found to increase the compressive stress and storage modulus of the foams (69–148%) and the hardness and brittleness of the foams.