Cassava starch-natural rubber blends as shock absorbing foam / Piyawan Surunchanajirasakul

The foaming process of the mixtures of cassava starch-water and cassava starch-natural rubber latex blends was carried out by compression molding. The appropriate condition to produce an expanded-foam is as follows: a temperature within a range of 130-150℃, 50-110 kgf cm-2 pressure and the 2 min molding time. For the foam from the cassava starch and water it was found that the level of water in the range of 150-200% by weight of the dry starch could give a good condition of foaming. The resulting foamed material has a uniform closed cell structure. Considering the blending of cassava starch-natural rubber, the natural rubber could not be dispersed in the gelatinized starch when blending at the temperature 70℃. To stabilize and prevent the coagulation of natural rubber in the blending process, Nonidet P40, a non-ionic surfactant, was used. 1 he suitable amount of Nonidet P40 was 1.5% by weight of natural rubber latex. The compressive strength and the storage modulus of the foam obtained increased with increasing natural rubber content due 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 is added to the rubber latex, the compressive strength of the foam are further increased due to the vulcanization of the rubber. Furthermore, addition of 5-30% calcium carbonate by weight of the dry starch of the blends are also study. It was found that the compressive strength and storage modulus of the foams increased with increasing content of calcium carbonate when its content was higher than 5%. Likewise, the hardness and brittleness of the foams also increased.