苯乙烯对高密度聚乙烯的扩散聚合行为研究

Diffusion and Polymerization Behavior of Styrene in High Density Polyethylene Pellets

针对苯乙烯（St）对高密度聚乙烯（HDPE）的扩散聚合行为,及其产物粒子中聚苯乙烯（PS）的分布和形态特征进行了研究.结果表明：在70～90℃的扩散温度条件下,St对HDPE的扩散行为符合Fickian扩散的特征,且在90℃下当引发剂的过氧化苯甲酰（BPO）添加量在St的0.5 wt%～1 wt%之间时,HDPE粒料中PS含量将达到11 wt%,而当BPO大过量添加至5 wt%时PS的含量将达到16 wt%左右的最大值;无论BPO的添加量如何改变,HDPE粒料中的PS分布曲线均呈＂M＂形的形态,其峰值出现在距粒料表面200μm附近的区域且和HDPE粒料的结晶结构有关,但在HDPE粒料中生成的所有PS分散相的平均尺寸均小于100 nm;BPO添加量为0.5 wt%的体系即使在熔融挤出后,其PS分散相也仅略微发生聚集而不发生显著的聚并,呈现出一种类似于糍米团的复合结构,且其尺度分布在数十至200 nm的范围内;在BPO添加量为0.5 wt%的体系中,PS分散相和HDPE基体之间存在着良好的相互作用,不仅在其伸长率达到600%时仍未断裂,而且在各点上的拉伸应力值均大于纯HDPE,对制备HDPE/PS纳米合金或其他HDPE改性材料应为较理想的条件，

Diffusion and polymerization behaviour of styrene（St） in commercially-available high density polyethylene（HDPE） pellets were studied and HDPE/PS nanoblend pellets were synthesized. Both the diffusion and polymerization steps were carried out in water medium. At 70-90 ℃,diffusion behaviour of St towards HDPE pellets showed features of Fickian Diffusion. The saturation values of diffused St were different at different diffusion temperatures,and higher diffusion temperature meant higher saturation value,higher diffusion rate and shorter time to reach the saturation value. The amount of the initiator BPO was important in view of PS content in the pellets. With 0. 5 wt%-1 wt% BPO,PS content was 11 wt% when diffusion and polymerization were carried out at 90 ℃,while the PS content increased to about 16 wt% when excess amount of BPO（5 wt%） was used. The diametrical distribution of PS was investigated by Micro Fourier Transform Infrared Spectroscopy,showing that PS appeared throughout the HDPE pellets. PS distributions along the diameters of the pellets showed similar ＂M ＂shape curves for HDPE/PS pellets synthesized with different amounts of BPO. The peaks of the curves appeared at 200 μm area to the surface and were related to crystalline structure of HDPE pellets. The phase morphology of PS in the blend pellets were characterized by field emission scanning electron microscopy. Typical sea-island morphology was revealed with an average particle size of less than 100 nm. The HDPE/PS blend pellets were melt-processed into cylindrical bars. PS phases in the extrusion bars of the blend pellets synthesized with 0. 5 wt% BPO showed Ci Rice morphology,reflecting that PS particles were aggregating instead of coalescing during processing,and particle sizes were from tens of nm to 200 nm. The disperse PS phase and HDPE matrix had good interaction and the HDPE/PS bars did not break with elongation of 600% and showed higher tensile stress than pure HDPE bars,which meant that 0. 5 wt% BPO was fairly good condition for preparing HDPE/PS nanoblends or other modified HDPE materials.