Preliminary Study on Curing of Thick Rubber Article

In this study, several batches of natural rubber (SMR L) were compounded with three different types of accelerators, which were N-cyclohexylbenzothiazole-2-sulphenamide (CBS), diphenylguanidine (DPG) and zinc diethyldithiocarbamate (ZDEC). ZDEC is known as an ultrafast accelerator. The rubber compounds were cured at 140°C, 130°C, 120°C, 110°C and 100°C in accordance with the temperature gradients observed within the thick rubber block. The main aim of this study is to cure the rubber at each temperature region to the same cure time as that of the outermost region (20 minutes at 140°C). The amount of sulfur and accelerator were adjusted accordingly at each curing temperature to match the state of cure at 140°C. The state of cure of of the vulcanized rubbers were measured using hardness and tensile strength. The same state of cure is achieved if the hardness and tensile strength value are within ±2 IRHD and ±3 MPa, respectively with that of the control vulcanized rubber (hardness and tensile strength cured at 140°C). The results shows that the hardness and tensile strength of the vulcanized rubber at each temperature region are within the expected margins. The results clearly indicated that the type and amount of accelerators, and the amount of sulfur were correctly chosen at each temperature.