影响聚丙烯发泡倍率和泡孔结构的主要工艺参数研究

The Processing Factors of Effect on Expansion Ratio and Cell Structure of PP Foam

以自行研制的高熔体强度聚丙烯为原料,在同向双螺杆挤出机-熔体泵发泡系统上,采用超临界二氧化碳为发泡剂,分析研究了影响聚丙烯发泡倍率和泡孔结构的主要因素。结果表明:随发泡剂注入量增大,聚丙烯发泡倍率提高,但发泡剂注入量应控制在一定的范围内,小于气体在聚丙烯熔体中的溶解度,否则,泡孔容易破裂、合并,发泡倍率降低;熔体温度是影响聚丙烯发泡倍率的关键因素,随熔体温度降低,聚丙烯发泡倍率增大,控制熔体温度在聚丙烯树脂结晶温度以上5℃左右内,能够得到发泡倍率高,泡孔结构好的聚丙烯发泡体;聚丙烯泡孔结构参数与机头压力和熔体温度密切相关,提高机头压力有利于气泡成核,降低熔体温度有利于减少气泡合并和破裂,得到泡孔尺寸小且均匀、泡孔密度高的聚丙烯发泡制品。

The processing factors of effect on expansion ratio and cell structure of PP foam were analysized based on a great deal of PP foaming experiments, which were carried out on self-developed super-critical liquid foaming equipment by using melt modified high melt strength PP as matrix and SCCO2 as foam agent. The results showed that the expansion ratio of PP foam could be increased by increasing the CO： concentration,but should be kept under the solubility of CO2 in PP melt. Otherwise the cell was ruptured, coalesced or not expanded. The melt temperature of PP in the die was crucial for obtaining high expansion ratio of PP foam. The expansion ratio was increased by decreasing the melt temperature until it was close to the crystallization temperature of PP resin. The PP foam with high expansion ratio and fine cell could be obtained by controlling the melt temperature above the crystallization temperature around 5 ℃. The cell structure was also related with the die pressure and melt temperature. Increasing die pressure could benefit cell nucleation. Decreasing melt temperature could benefit the reduction of cell rupture and coalescent.