In this work

structural evolution of uniaxially oriented poly(3-hydroxybutyrate-

co

-3-hydroxyvalerate) (PHBV) films during stretching and subsequent heating was studied. The mechanism for generating

β

-form crystals during the second drawing and the transformation of

β

-form during heating were investigated

via in situ

synchrotron wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR)

together with the measurement of stress-strain curves. It was found that relative contents

orientation and size of

β

-form crystals increased with the increase of strain

while the crystallinity

orientation and crystal size of

α

-form decreased. These results revealed that the packing states of molecular chains in α-form lamellar crystals must be disordered for generating the

β

form chains. In the following heating process

crystallinity

orientation and crystal size of

α

-form crystals increased with the increase of temperature

and the

β

-form crystals gradually disappeared. This was mainly owing to the transformation of the

β

-form into the

α

-form with higher orientation. The melting temperature of the

β

-crystals ranges from 65 ℃ to 135 ℃. This work provides new insight into the structural evolution of PHBV films

which will provide a theoretical basis for the processing and property control of bio-based polyester films.