Network defects in vulcanised rubber

Abstract

The molecular weight of natural rubber is very high and must be reduced by mastication so that it has sufficient plasticity to enable the incorporation of compounding ingredients. Such a reduction in molecular weight increases the number of elastically ineffective chain ends which reduces the physical properties of vulcanisate. This thesis describes an attempt made to decrease the number of free chain ends by combining them with radical acceptors that will form vulcanisable end groups. These will form cross-links during the vulcanisation process and tie the free chain ends into the network. Such vulcanisates produce significantly better physical properties. A method to quantitatively assess the reduction in free chain ends has been developed. It is necessary to carry out the mastication process under nitrogen as competition from oxygen, which acts as a powerful radical acceptor, reduces the yield of reactive end groups. This improves a serious practical limitation on the method.