The effect of water absorption on stretch-induced crystallization of poly (ethylene terephthalate): An in-situ synchrotron radiation wide angle X-ray scattering study

The structural evolution of poly (ethylene terephthalate) (PET) with distinct water absorption during uniaxial deformation slightly above glass transition temperature (T-g) were investigated by in-situ synchrotron radiation wide angle X-ray scattering (WAXS). Results show that the locally ordered structures are not conducive to stretch-induced crystallization (SIC) although the corresponding entropy is more close to crystals compared to random chains, which is due to the limited chain mobility therein. The frozen orders should be destroyed to achieve the critical chain mobility required by SIC even with the presence of water as plasticizer. Unexpectedly, absorption of water does not enhance but suppresses SIC though it does promote the chain mobility, originating from lower stress level with higher water contents. Stress and chain mobility directly correlate with chain stretch and orientation in positive and negative manners, respectively, demonstrating that chain stretch and orientation also play important role in SIC around T-g.