Structure Evolution of Polyamide 1212 during the Uniaxial Stretching Process: In Situ Synchrotron Wide-Angle X-ray Diffraction and Small-Angle X-ray Scattering Analysis

Structure evolution of polyamide 1212 (PA1212) during the uniaxial stretching process at room temperature was investigated by in situ synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. Variation mechanism of polymorphic phase and long spacing dacwas discussed in depth. Deformation induced crystal-crystal transition in PA1212 from triclinic α-form to mesomorphic phase was observed by WAXD analysis, and it could be ascribed to the lamellar slippage mechanism. From 2D-WAXD patterns, crystal transition in PA1212 took place earlier in meridian direction (parallel to stretching direction) than equatorial direction. It could be explained by the fact that the lamellae with the normal perpendicular to the stretching direction tended to experience lamellar slippage and fragmentation, where polymer chains in (010) lattice plane consisting of sheets of hydrogen bonds were easy to experience conformational transformation. This new crystal transition behavior from α-form to mesomorphic phase would further enrich the research area of crystal transition in semicrystalline polymers.