Study On Recrystallization Behavior Of Polypropylene And The Mold Foaming Process

Polymer foamed materials has excellent mechanical properties and plays an important role in packaging,construction,automobile and other industries.Adopting supercritical CO2 foaming has the advantages of short forming period,low requirement to equipment and environment-friendly,but it also has the obvious problem of low production efficiency.Therefore,a secondary depressurization foaming process was proposed to improve the foaming efficiency of polymers.The foaming of the semi-crystalline polymer PPB-M02 and the amorphous polymer COC5013F under the secondary depressurization process were studied respectively.The basic data of them under the condition of one step depressurization foaming were tested respectively,and the foaming ratio under different holding time,temperature and holding pressure was obtained.For the crystalline polymer polypropylene,it was found that the expansion ratio decreases with the increase of the holding time,the DSC test shows that the recrystallization behavior of PP during the heat preservation stage affects the foaming process;through its secondary decompression foaming experiment,it was found that it is difficult to obtain a higher expansion ratio than the primary expansion,and the internal cell structure has not been significantly improved,indicating that the secondary decompression foaming process is not applicable.The application of secondary depressurization foaming to COC has a significant effect.Under the same holding time,its foaming ratio is significantly improved than that of primary pressure-reducing foaming.This shows that secondary depressurization foaming is feasible for COC-type amorphous polymers.Furthermore,the effect of foaming pressure and holding temperature on polypropylene samples was studied by using the high temperature melting peak values obtained from different recrystallization behaviors of polypropylene measured in the DSC.The calculation formulas between foaming pressure,holding temperature and melting peak value in melting state were obtained.