不同分子量的高密度聚乙烯与茂金属线型低密度聚乙烯的相容性

采用动态流变学测试和结晶动力学的方法研究了两种分子量的高密度聚乙烯(HDPE)与茂金属线型低密度聚乙烯(m-LLDPE)共混体系的相容性.流变学研究表明,HDPE/m-LLDPE共混物在低ω区域lgG′-lgω关系曲线偏离线性规律,在熔融态为非均相体系.DSC分析发现HDPE/m-LLDPE共混物体系中HDPE的熔点随着m-LLDPE含量的增多而逐渐下降,说明HDPE与m-LLDPE二者具有机械相容性.当HDPE在m-LLDPE的熔体中等温结晶,分子量较高的HDPE结晶速率与纯HDPE相近,m-LLDPE的含量变化对Avrami指数n的影响不大;分子量较低的HDPE指数n和半结晶时间t1/2随m-LLDPE含量的增加逐渐增大,结晶速率随着m-LLDPE含量的增加逐渐下降,表明熔融态的m-LLDPE和HDPE存在着较强的分子间相互作用,二者具有一定的相容性.

MELT COMPATIBILITY OF METALLOCENE LINEAR LOW-DENSITY POLYETHYLENE AND HIGH-DENSITY POLYETHYLENE BLENDS

The compatibility between m-LLDPE and two sorts of HDPE with different molecular weights in the melt state was investigated with rheological methods,nonisothermal and isothermal crystallization dynamics.The rheological measurements suggested that HDPE and m-LLDPE blends were heterogeneous systems at 190℃ based on the relationship of lgG' and lgω in the low ω region that deviated the linear model.The DSC results showed that with an increase in the content of m-LLDPE,the melting peak of HDPE shifted to lower temperature,suggesting that HDPE and m-LLDPE may be partially compatible.When the blends were cooled from the melt to temperatures where HDPE could crystallize,but the m-LLDPE couldn't,the Avrami exponent n of high-Mw HDPE increased slightly compared to that of pure HDPE,and the content of m-LLDPE had littleeffect on the vales of n.Meanwhile,the crystallization half-time(or crystallization rate) of high-Mw HDPE was very similar to that of pure HDPE.However,the Avrami exponent and the crystallization rate of the low-Mw HDPE decreased with an increase in the content of m-LLDPE,indicating that the m-LLDPE retarded crystallization of HDPE,possibly due to the reasons including the dilution of HDPE by m-LLDPE(m-LLDPE as a solvent in molten state),hindrance of viscous m-LLDPE to the HDPE crystallization front,and decreased supercooling degree because of the compatibility between the m-LLDPE and low-Mw HDPE.This provided further evidence that the compatibility of the low-Mw HDPE with m-LLDPE was better than that with the highMw HDPE.