稀土氧化物对PP-g-MAH结晶行为的影响

Effect of Rare Earth Oxides on Crystallization Behavior of PP-g-MAH

用反应挤出的方法制备了PPgMAH,采用DSC、PLM和WAXD等测试技术研究了纯PP、PPgMAH及添加稀土氧化物Nd2O3和CeO2的PPgMAH等4种样品的结晶行为。DSC结果表明,PPgMAH的结晶速率比纯PP的大,而稀土氧化物的加入则使其进一步增大,当加入CeO2时样品的的结晶速率最大;PPgMAH的结晶活化能比纯PP的低,而且加入CeO2后下降更多;加入稀土氧化物粉体后,PPgMAH的Avrami指数n变化不大,即稀土氧化物的加入并没有显著改变PP的成核机理和生长方式。计算发现,加入稀土氧化物提高了PP的平衡熔点和熔融热焓。DSC实验和PLM观察结果均表明,稀土氧化物是PP的有效成核剂。分析结果表明,加入稀土氧化物后,异相成核成为PPgMAH结晶过程的控制因素,它降低了结晶活化能,使接枝产物的结晶速率增大。WAXD测试发现,与PP相比,PPgMAH的微晶尺寸增大,晶胞参数变化不大。

Isotactic polypropylene grafted with maleic anhydride(PP-g-MAH) and PP-g-MAH filled with Nd_2O_3 or CeO_2(REOs) were prepared by means of reactive extrusion. The crystallization behavior and crystal structure of PP, PP-g-MAH and PP-g-MAH filled with REOs were studied by DSC, PLM and WAXD techniques. The results show that the crystallization rate of the grafted polypropylene is higher than that of blank polypropylene. Furthermore, the addition of the REO can accelerate the crystallization rate of the grafted polypropylene. After introducing the REO into PP-g-MAH, the heterogeneous nucleation dominates the process of crystallization, and the low active energy for crystallization increases the crystallization rate. In particular, PP-g-MAH filled with CeO_2 has the lowest active energy and the highest crystallization rate. The addition of REOs does not influence notably the nucleation mechanism and growth mode of the crystallization of i-PP, whereas it enhances the equilibrium melting point and equilibrium melting enthalpy of PP-g-MAH. The WAXD analysis indicates that the addition of the REO can increase the crystallite size of the α-form crystal.