Abstract:
In this research, gypsum from waste plaster molds were reutilized as filler in natural rubber in comparison with a commercial gypsum as well as calcium carbonate, a general filler used in natural rubber. Effects of epoxidized natural rubber as a coupling agent were also studied so as to improve compatibility between rubber and filler. Natural rubber was mixed with vulcanizing chemicals and fillers in an internal mixer and a two-roll mill, respectively. Rubber compounds were examined for their curing characteristics using a moving dierheometer and were then cured in a compression molding machine. The vulcanizates were tested fortheir tensile properties and tear strength. The results indicated that gypsum from waste plaster molds can effectively be used as an inert filler in natural rubber. Mechanical properties of waste gypsum filled rubbers were comparable to those filled with the commercial gypsum and calcium carbonate. However, when the amount of filler was higher than 40 part per hundred rubbers (phr), the tensile strength decreased significantly. The tear strength also dropped when the amount of filler was higher than 10 phr. The decrease in these mechanical properties was due to filler agglomeration. When epoxidized natural rubber was used as a coupling agent, the dynamic mechanical propertiesclearly illustrated the enhancement of interaction between rubber and filler. However, as gypsum acted as an inert filler, the mechanical properties were almost similar to those without epoxidized natural rubber.