Shear-Modification of Rubber

Flow of entangled polymers causes chain disentanglement, with a consequent reduction in the viscosity and elasticity (e.g., die swell). Interestingly, the time for recovery of the entanglements is significantly longer than the linear relaxation time. This is surprising, since less entangled chains are expected to diffuse and recover their structure more rapidly. The practical significance is that such flow-induced modification of rubber can offer a means to improve the processability of rubber without affecting the cured properties. (Other methods, such as reducing the molecular weight or using plasticizers, reduce the strength of elastomers.) This talk describes our recent investigation of shear modification and reentanglement in polyisobutylene.