Influence of thermal treatment on the electrical and electromechanical properties of Cellular Polypropylene ferroelectrets

Cellular Polypropylene (PP) ferroelectrets combine high piezoelectric activity with high mechanical flexibility and compliance. Therefore, they have attracted considerable interest in scientific research and industrial development.Morphological modifications are suspected to yield a better thermal performance by improving the thermal stability of the crystalline phase. PP is available in isotactic (iPP), syndiotactic (sPP) and atactic (aPP) chain conformations. Isotactic PP has the highest melting point (188 °C), while syndiotactic PP melts earlier (161 °C) [4]. Atactic PP does crystallize because of the lack of stereoregularity. Isotactic PP adopts four different chiralities in the crystalline state, which gives iPP the possibility of crystallizing into different polymorphs depending on its thermo-mechanical history.The α-crystal form is thermodynamically favored and is prone to form under normal crystallization conditions. The β crystal form occurs in high proportions only under specific crystallization conditions, and usually coexists with α polymorphs due to its low nucleation rate.