Whitening Generation in PVDF Under Cyclic Loading

Whitening is defined as the change in the opacity of a polymeric material due to microvoid nucleation and/or grow, resulting in volume increase and possible modification of the mechanical properties. Its formation may arise from processing conditions or mechanical stresses acting in the polymers. The understanding of the whitening phenomenon and its effect on mechanical behavior is of great importance for engineering application; for instance, poly (vinylidene fluoride) (PVDF) is widely used as pressure barrier in flexible raisers, where high pressure and aggressive media are presents and the presence of whitening may increase the gas permeation rate.The present study, cyclic loading experiments were performed on PVDF to generate whitening in a controlled manner. Subsequently, the whitening effect on the mechanical properties were evaluated using tensile tests and the structure was evaluated using X-ray diffraction, while the fracture surface was analyzed via scanning electron microscopy. It was observed that cyclic load was able to nucleated the voids and there was an increase in the crystallinity and in the mechanical properties of the material.Copyright © 2015 by ASME