Micromechanical analysis of molecular orientation in high-temperature creep of polycarbonate

Abstract The molecular orientation of bisphenol-A polycarbonate (PC) was determined by the in-situ wide-angle X-ray diffraction (WAXD) measurement during high-temperature creep. The resulting creep and WAXD data were used to analyze the coupled deformation of macro-continuum and micro-structure. A four elements viscoelastic model was introduced to fit the creep results and describe the time-dependent orientation in creep. The delayed elastic stress was regarded as an assessment of molecular orientation, and two dashpots in the model were used to analyze the physical meanings of retardation time, which helped to understand the mechanism of molecular orientation and the role of free volume and stress on the viscoelastic parameters. A threshold range of free volume was proposed to interpret the change regularity of retardation time, delayed elastic modulus and coefficient C. The delayed elastic stress can be successfully used in assessing the orientation. Our work provides a deeper insight into the evolution of molecular orientation induced by high-temperature creep.