长链支化聚丙烯结晶行为及发泡性能研究

The Investigation on Crystallization Behavior and Foamability of Long Chain Branched Polypropylene

通过广角X射线衍射(WAXD)、示差扫描量热(DSC)和偏光显微镜(POM)研究了长链支化聚丙烯(LCBPP)和线性等规聚丙烯(PP)的结晶行为.WAXD和DSC的结果显示LCBPP样品有利于β结晶,出现了少量β晶.DSC和POM的结果显示在等温结晶过程中长链支化结构起到促进异相成核和细化晶粒的作用,LCBPP样品的结晶温度提高,结晶速度增大,球晶尺寸显著减小.采用间歇釜式超临界二氧化碳发泡法对LCBPP和线性PP样品进行发泡,由于LCBPP结晶温度高,结晶速率更快,有利于泡孔的固化定型,可以提高发泡温度,研究结果表明在相同的发泡压力下LCBPP样品发泡温度窗口较宽,为5 K左右,而线性PP样品的发泡温度窗口较窄,仅为2 K左右,同时在相同的发泡条件下LCBPP样品的发泡倍率较大.

The crystallization behavior of long chain branched polypropylene （LCBPP） and linear isotactic polypropylene （PP） was studied by DSC,WAXD and POM. The results of WXAD and DSC showed that the LCB structure was conductive to β-crystal crystallization,a little of β-crystal appeared in LCBPP samples. The results of POM and DSC verified that the LCB structure can perform the function of promoting heterogeneous nucleation and decreasing crystal size. Compared with pure PP, the crystallization temperature and crystallization rate of LCBPP increased. The crystal size of LCBPP decreased with the increased branching content. The higher crystallization temperature and faster crystallization rate of LCBPP were in favor of bubble curing and increased the maximum foaming temperature. In addition, because of the higher melt strength of LCBPP,the LCBPP showed bigger expanding ratio than linear PP at the same foaming condition. The results of batch foaming with supercritical CO2 as blowing agent at 18 MPa showed that the LCBPP displayed a better foamability than linear PP. The LCBPP exhibited a wide foaming temperature window （ about 5 K） while linear PP exhibited a very narrow foaming temperature window （about 2 K） and the maximum expantion ratio of LCBPP was 25.8 while the maximum expantion ratio of linear PP was only 18.6.