Solid‐phase rheology of an anisotropic polymer (vectra A)

The solid‐phase rheology of a thermotropic polyester which is liquid crystalline in the melt (Vectra A) was studied for one‐dimensional finite‐amplitude deformations, including step‐strain and recovery, step‐stress and recovery, and step‐strain followed by small‐amplitude oscillations. The rheology is complex, and cannot be described by existing models. Below a critical strain, which is history‐dependent, Vectra A deforms as a linear viscoelastic solid. Above the critical strain the deformation is both viscoplastic and viscoelastic. There appears to be a maximum recoverable strain of about 0.03, beyond which all deformation is nonrecoverable. A large number of relaxation modes is required to describe the stress, and one time scale is inadequate to describe the time‐dependence of yielding and plastic flow.