长支化聚丙烯结晶性对低温釜式发泡行为的影响

Effects of Crystal Status on the Solid-State Foaming Process of Long Chain Branched Polypropylene

以自制的长支化聚丙烯(LCB PP)为原料,进行不同热历史处理,研究了LCB PP结晶状态与低温固相发泡行为之间的关系。由于自制的LCB PP带有较多的支化结构,在结晶过程中可以起到异相成核的作用,因此在较高降温速率下,可以制得微晶尺寸较小,晶区不完善的LCB PP。结果表明,结晶度、晶区完善程度和微晶尺寸对自制LCB PP熔点以下的低温固相发泡行为有着显著影响,三者之间存在协同作用:随LCB PP结晶度降低,晶区不完善度增加,微晶尺寸减小,CO2在LCB PP基体中的溶解度和扩散系数显著提高,且LCB PP发泡后的泡孔结构明显改善;同时,低结晶度、小微晶尺寸,晶区完善度较低的LCB PP在固相发泡时有更宽的可发泡温度区间和更高的发泡倍率。

Three kinds of self-made long chains branching polypropylene（ LCB PP） samples with different crystal statuses were prepared by different thermo-history. The influence of crystal status on the solid-state foaming process of the LCB PP was investigated. Smaller crystal size and higher crystal defect could be obtained by cooling at the fast rate and the abundant LCBs in the LCB PP sample may act as heterogeneous nucleation during crystallization. The results indicate that the solid-state forming process of the LCB PP is closely related to its crystallinity,crystal defect,and microcrystal size. The solubility and diffusion coefficient of CO2 into LCB PP obviously increase with decrease of the crystallinity and micro-crystal size,and increase of the crystal defect. Therefore,the cellular structure of the foamed PP is optimized. Furthermore,a widened foaming temperature zone and a high foaming expansion ratio could be achieved for the LCB PP with lower crystallinity,smaller micro-crystal size and higher crystal defect.