Structural Evolution and Mechanical Properties in New TPE during Uniaxial Deformation by in-situ Synchrotron X-Ray Scattering (Paper No. 10)

摘要

In-situ structural changes during uniaxial stretching and subsequent retraction of a new type of thermoplastic elastomer (TPE) based on the propylene dominant ethylene-propylene (EP) copolymer were studied. Simultaneous measurements of stress-strain relationship and time-resolved synchrotron small-angle X-ray scattering (SAXS) revealed the relationship between structural formation and stress evolution during deformation, which can be described as follows. In the initial stages of stretching, the crystalline lamellar structure is realigned along the stretching direction and simultaneously undergoes a "destruction" process. At strains larger than 100%, strain-induced crystallites begin to form and the corresponding stress increases with strain. During retraction, the strain-induced lamellar structure decreases its long range order. However, after complete retraction to zero stress, the TPE sample still possesses some long range structures and exhibits an elastic behavior in subsequent extension and retraction cycles, similar to that of vulcanized natural rubber. Scattering results clearly showed that during the 2nd cycle of extension and retraction, the strain-induced crystals formed during the first cycle behave as the macroscopic network points responsible for the elasticity.