硅氧烷液晶共聚物作为β晶成核剂对等规聚丙烯结晶结构与形态的影响

采用广角X射线衍射(WAXD)与偏光显微镜(POM)等手段研究了硅氧烷液晶共聚物(LCP-O2)作为新型成核剂对聚丙烯(PP)共混样品结晶结构与形态的影响.结果表明,低浓度的LCP-O2在PP共混体系中起到异相成核的作用,使PP的晶核数目增多,球晶细化,并提高了结晶速度,同时也诱导出了β晶的形成.LCP-O2的成核效果主要依赖于其在PP中的相对含量、液晶的分子结构与结晶的热处理过程,且随着结晶温度或成核剂含量的增加,对应PP试样的β晶含量(Kβ)呈现先增加,后降低的趋势.当LCP-O2质量分数为1.0%,在130℃等温结晶1h,对应PP试样的Kβ最大,为58%.此外,属于单斜晶的α球晶呈现黑白颜色,晶束呈放射状生长,边界清晰;而属于三方晶的β球晶亮度要高于α球晶,其颜色艳丽多彩,束状晶片聚集体呈支化生长,内部排列比α晶疏散,边界相对模糊,且β晶与α晶的形态分别在157和171℃完全消失.

Influence of Liquid Crystalline Copolysiloxane as a β-Form Nucleator on Crystallization Structure and Morphology of Isotactic Polypropylene

The influence of liquid crystalline copolysiloxane (LCP-O2) as a new nucleator on crystallization structure and morphology of isotactic polypropylene (PP) has been investigated by means of wide angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). The experimental results showed that LCP-O2 with low concentration in PP played a role in the heterogeneous nucleation effect, enhanced the crystallization velocity, and the spherulites became smaller and more homogeneous. Moreover, β-phase was induced in PP. The nucleating activity of LCP-O2 mainly depended on its concentration, molecular structure of liquid crystalline, and thermal history of processing. The relative content of β-form (K_β) increased with increasing crystallization temperature or LCP-O2 concentration, reached a maximum value, and then decreased as the temperature or LCP-O2 concentration further increased. K_β was 58% when the mass fraction of LCP-O2 was 1.0%, and the crystalline temperature and time were 130 ℃ and 1 h, respectively. The trigonal β spherulite with the sheaflike grain growth is bright and colorful compared with the black and white monoclinic α one with the cross-hatched radial grain growth. In addition, the rotundity of α-spherulites was clear, while that of β-spherulites was relative obscure. With increasing temperature, the morphology of β and α spherulite disappeared at 157 and 171 ℃, respectively.