Kaolin reinforcement of some rubbers with novel sulfur cure systems

2018-03-08T13:14:35Z (GMT) by Ali Ansarifar Saad H. Sheikh
A large amount of kaolin (China clay) was used to reinforce the hardness, tensile strength, elongation at break, stored energy density at break, tear resistance, and Young’s modulus of some sulfur-cured NR, BR and EPDM. The kaolin surface had been pre-treated with 3-mercaptopropyltrimethoxysilane (MPTS) to reduce its polarity and prevent it from adsorbing moisture which could have been detrimental to the cure of the rubbers. For NR, the hardness and Young’s modulus improved, tensile strength and tear resistance were unchanged and the remaining properties deteriorated when kaolin was added. The viscosity increased and the scorch and optimum cure times decreased with kaolin. The highest cure rate ever reported for a sulfur-cured NR-based compound was achieved when kaolin was mixed with the rubber. For BR and EPDM, most of the properties including the viscosity gained significantly from the presence of kaolin in the rubbers. It was concluded that kaolin was an extending or non-reinforcing filler for NR, and highly reinforcing for BR and EPDM. Notably, the scorch and optimum cure times and cure rate of BR benefited so much, whereas with the exception of the scorch time, the optimum cure time and cure rate of EPDM were adversely affected by kaolin. The addition of kaolin increased the crosslink density of NR but had a detrimental effect on the crosslink density of BR and EPDM. The early indications are that kaolin is a viable alternative to carbon black and silica/silane systems in rubber reinforcement.