聚丙烯催化合金(PP-c)的晶体结构及其影响因素

用差示扫描量热法(DSC)和广角X射线衍射(WAXD)研究了两种乙烯含量不同的聚丙烯反应合金(PP-c)等温结晶下的晶体结构及PPβ晶含量的影响因素.结果表明,在通常的等温结晶条件下,乙烯含量较高的试样(PEP40)的熔融曲线出现双熔融峰.WAXD分析证明,其熔融双峰分别代表均聚聚丙烯(PP)的α晶和β晶.计算结果表明,PEP40中β晶含量与结晶温度有关,124℃结晶时β晶含量最高.在220℃对PP-c熔体进行热处理可显著提高PEP40中β晶的含量;在相同温度下热处理后,较低乙烯含量的试样(PEP20)也出现晶型异构.比较200℃与220℃下热处理对PEP20等温结晶的结晶形态的影响,发现后者使微晶尺寸明显变小,并呈现较完善的β球晶形态.

Crystalline Structure of Polypropylene Catalloys and Related Influence Factors

Crystalline structures of two types of polypropylene catalloys(PP-c) containing different ethylene contents were investigated by differential scanning calorimeter(DSC) and wide-angle X-ray diffraction(WAXD).When the PEP40 containing higher ethylene content crystallizes isothermally in the temperature range investigated,double melting peaks appear in each endotherm region.WAXD measurement evidences that the behavior results from the coexistence of α-form and β-form of PP crystals.The calculated results show that the β-crystal content in PEP40 depends on the crystallization temperature and the β-crystal content of them crystallized at 124 ℃ approaches the maximum.In addition,the thermal treatment at 220 ℃ greatly increases the β-crystal content in PEP40 samples and induces the existence of β-crystal in PEP20 samples.Compared with those being treated thermally at 200 ℃,the PEP20 samples crystallized isothermally at 124 ℃ after being treated thermally at 220 ℃ for 30 min exhibit smaller crystalline size and clear morphology of β-spherulite.