LAUSR

The effects of temperature on the nonlinear mechanical behaviors of hard-elastic isotactic polypropylene films are systematically studied with in-situ ultrafast synchrotron radiation small- and wide-angle X-ray scattering techniques (SAXS/WAXS) during uniaxial tensile deformation at temperatures from 30 to 160 °C. Based on the mechanical behaviors and structural evolutions in strain–temperature two-dimensional space, three temperature regions (I, II, and III) are clearly defined with the α relaxation temperature (Tα ≈ 80 °C) and the onset of melting temperature (Tonset ≈ 135 °C) as boundaries, where different mechanisms dominate the nonlinear deformations after yield. In region I, microstrain in lamellar stacks em obtains an accelerated increase after yield and reaches a value significantly larger than corresponding macrostrain e, during which neither slipping, melting, nor cavitation occurs. We propose stress-induced microphase separation of interlamellar amorphous to be responsible to the hyperelastic b...