Vibration‐induced change of crystal structure in isotactic polypropylene and its improved mechanical properties

In order to understand the formation of different crystal structures and improve the mechanical properties of isotactic polypropylene (iPP), melt vibration technology, which generally includes shear vibration and hydrostatic pressure vibration, was used to induce the change of crystal structure of iPP. iPP forms α crystal structure in traditional injection molding. Through melt vibration, crystal orientated and its size became smaller, and a change of crystal structure of iPP from α form to β form and γ form was achieved. Therefore, the mechanical properties of iPP were improved. At high melting temperature (230 °C), only β form can be induced. At low melting temperature (190 °C), either β form or γ form can be induced, depending on the combination of frequency and vibration pressure.