Transient microstructure in long alkane segment polyamide: Deformation mechanism and its temperature dependence

Abstract

Deformation-induced microstructure evolution of Polyamide 1012, with an emphasis on lamella development, polymorphism transition and molecular orientation, is investigated. When deformed above Tg (100 °C), a series of complex SAXS patterns are continuously identified at intermediate strain including four-point pattern, figure-8 pattern and X-shaped pattern, accompanied with two-bar pattern on the meridian, which corresponds to the transient microstructure. Such particular structure is resulted from the approach of tilted lamellae along the drawing direction, the insertion and the orientation of new lamellae. To investigate the temperature dependence, the microstructure developments at 30 °C (below Tg), 60 °C (close to Tg) and 100 °C (above Tg) are compared. Considering 38% enhancement of the fracture stress with elevated temperature (from 60 °C to 100 °C), the temperature dependence of particular SAXS patterns further suggests that the elongation above Tg favors higher level of stretching-induced crystallization and better aligned microfibrillar structure, which competes with thermal-induced increased chain mobility. Based on the comprehensive results, the correlation between microstructure and mechanical response has been successfully established, which is featured by the synchronous occurrence of transient structure with slight strain hardening.