Deformation-Induced Phase Transitions of Polyamide 12 at Different Temperatures: An in Situ Wide-Angle X-ray Scattering Study

Abstract

Deformation-induced phase transition of polyamide 12 (PA 12) was studied with in situ wide-angle X-ray scattering (WAXS) at temperatures below and above glass transition temperature. Irrespective to the testing temperature, a transient α′′ phase occurred in the early plastic deformation stage, whose lifetime is decreasing with the increase of temperature. At temperature below glass transition temperature, the transient α′′ phase further transforms into a mesomorphic state with increasing the strain, while high temperature promotes the transient α′′ phase transforming into γ′ phase. The different final states at temperatures below and above glass transition temperature is due to the competition and coupling between external work and thermal activation. External work from tensile deformation is responsible for the appearance of the transient α′′ phase and the final mesomorphic state at temperature below glass transition temperature, while thermal activation drives the transition from the transient α′′ phase to γ′ phase. All these phase transitions occur in the plastic deformation region, which shows a close correlation between the mechanical response and the structural evolution during tensile deformation.