Phase transformation and thermomechanical characteristics of stretched polyvinylidene fluoride

Phase transformation and thermomechanical characteristics of the polyvinylidene fluoride (PVDF) are investigated using a microtesting machine and a thermomechanical analyzer. The phase transformation from the α- to β-phase of the PVDF resulted from increased PVDF chain length caused by the stretching procedure. The results show that the phase transformation changed due to increased stretching ratios with smaller changes for stretching ratios over 4. Young's modulus along the stretching direction was higher than that along the transverse of stretching. The thermomechanical curve variation can be divided into two parts: one part is a gradual slope before about 50 °C, and the other is similar to exponential growth. Thermomechanical change, thermal elongation, and expansion greatly influence the stretching ratios of 5 in the stretching direction. The higher stretching ratio easily causes the shrink influence of the material due to the higher cohesion of the amorphous regions. Therefore, the observed results can provide useful information to optimize for piezoelectric or pyroelectric PVDF applications.