Critical role of depressurization and effects of saturation conditions in the formation of β‐Crystal during isotactic polypropylene foaming with supercritical CO2

The melting behavior and crystalline forms of isotactic polypropylene (iPP) samples crystallized under different conditions of pressure and temperature were investigated using differential scanning calorimeter (DSC) and wide‐angle X‐ray diffraction (WAXD), respectively. When treated with dynamic supercritical CO2(Sc‐CO2), iPP samples undergo the formation of β‐crystal that does not occur on the treatment with atmospheric pressure and static supercritical CO2(Sc‐CO2) pressure. In addition, the relative content of β‐crystal has deep dependence on melt state and depressurization rate. Depressurization plays very critical role in the formation of β‐crystal by means of imposing three‐dimensional tensile field during cell growth. The tensile field induced α‐row nuclei where the formation of β‐crystal occurred. This finding will provide one new method to induce β‐crystal in iPP parts. POLYM. ENG. SCI. 56:980–986, 2016.