结构因素对聚丙烯热变形温度的影响

Effect of structural factors on the heat deformation temperature of polypropylene

按ISO 75-2规定的聚丙烯热变形温度测试方法,对4种聚丙烯分别进行平放样条和侧放样条实验方式的国内外比对实验。实验结果表明,侧放样条的热变形温度偏差一般都在标准规定的5℃范围内,数据分散度较好;而平放样条的热变形温度实验偏差在2.3～22.6℃,远超过标准规定范围。采用DSC,POM,2D-WAXD等方法研究了聚丙烯平行试样间的结构差异以及平放方式数据偏差较大的原因。表征结果显示,通过注塑成型的聚丙烯样条,芯层的结晶度高于皮层,但皮层的取向度高于芯层,皮层厚度也不同;结晶度越高,取向度越大,皮层越厚,则热变形温度越高。该结论对于修订标准具有一定意义。

The heat deformation temperature(HDT) of 4 kinds of polypropylene in the flatwise and edgewise orientations were measured at home and abroad according to ISO 75-2 standard. The results showed that the HDT deviations of edgewise samples were generally within the specified range of 5 ℃, with good data dispersion,while the HDT experimental data deviations for flatwise samples were in the range of 2.3 ℃ to 22.6 ℃ and far beyond the standard range. DSC,POM and 2D-WAXD methods were used to study the structural differences between parallel samples of polypropylene and the reasons for the large deviation of data in flatwise mode. The results showed that crystallinity of the core layer of polypropylene splines formed by injection molding is higher than that of the skin layer,but the orientation degree of skin layer is higher than that of the core layer and the skin layers had different thicknesses. The higher the crystallinity,the greater the orientation,and the thicker the skin layer, the higher the HDT. This is of guiding significance to the revision of standards.