Thesis (M.Sc.)--Chulalongkorn University, 2009

Field natural rubber latex was concentrated by creaming method via addition of creaming agents, namely carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC) and hydroxypropyl methyl cellulose (HPMC). The effects of creaming agent concentration, creaming time and temperature on dry rubber content (DRC) were studied to determine the optimum condition for latex creaming process. Creamed latex was cured by vulcanization in a stirred reactor with sulfur elements and tetramethylthiuram disulfide as curing agent. Free-vulcanized latex obtained from the reaction with varying temperature, cure time and curing agent concentration were made into films and dried at room temperature. Tensile properties, elongation at break, hardness of the film products were measured. Crosslink density, chloroform number and swelling index of latex were also investigated. It was found that optimum condition for latex concentrate was using HPMC as creaming agent at 0.6% concentration, at room temperature, for 24 hours. For vulcanization of creamed latex, the maximum tensile strength was obtained from TMTD 2 phr at vulcanization temperature of 50 °C and cured time of 3 hours. At lower vulcanization temperatures, longer cured time was required. Chloroform number and swelling index showed that the latex compounds were not completely vulcanized