Thesis (M.Sc.)--Chulalongkorn University, 2000

Natural rubber blends were prepared by mixing natural rubber latex with 18% W/V cassava starch paste, before dividing the mixture into two pasts for the rubber/starch mix sheet production and rubber/starch mix de-foamed sheet production. This is to study the effect of cassava starch content on physical properties of natural rubber blends. In the rubber/starch mix sheet production, the mixture was stirred at 1.3 revolution per second before pouring into a stainless steel tray and dried at 60 degree celsius in a vented air oven. Similarly, in the rubber/starch mix de-foamed sheet production, the mixture was stirred with sodium bicarbonate added then placed in a plastic box. It was heated and dried, using a microwave oven set at medium-high level for 3,000 seconds, foam was formed at the same time. The mass was de-foamed and homogenized using a two-roll mill. It was found that cassava starch affects the physical properties for both processes. In the rubber/starch mix sheet production, plasticity retention index, Mooney viscosity, optimum cure time, density, hardness and %elongation at break increase with the increase of cassava starch content while both tensile and tear strengths decrease. In the rubber/starch mix de-foamed sheet production, optimum cure time, density before and after vulcanization and compression deflection increase with the increasing of cassava starch content whereas density before compounding decreases. However, %elongation at break and tensile strength exhibit high values at starch contents between 20-30% indicating it being a reinforcing filler.