聚丙烯“催化合金”组成对结晶行为的影响

用示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯“催化合金”(PP-cats)组成对等温结晶行为与动力学的影响,并与等规聚丙烯(iPP)进行比较.结果表明,与纯PP相比较,PP-cats的平衡熔融温度明显下降,表明PP-cats中作为主要组分的丙烯均聚物和乙丙无规共聚物之间存在较强的相互作用.PP-cats的结晶初期动力学可用Avrami模型很好地描述,结晶过程均为预先成核和三维生长方式.PP-cats的结晶速率随体系中乙丙共聚物含量的增加而增大,而PP-cats的晶体生长速率随体系中乙丙共聚物含量的增加而减小.由于PP-cats熔体的粘度远高于纯PP,使得PP-cats中PP分子链运动能力降低,导致了PP-cats较低的晶体生长速率.此外,与纯PP相比,PP-cats的成核密度大幅度提高,被认为是PP-cats具有快的结晶速率的主要原因.

EFFECT OF COMPOSITION ON CRYSTALLIZATION BEHAVIOR FOR POLYPROPYLENE CATALLOYS

Effect of composition on crystallization behavior for polypropylene catalloys (PP-cats)was studied by using differential scanning calorimetry (DSC)and polarized optical microscopy (POM).The decrease of melting point for PP-cats indicates the existence of stronger interaction between the propylene homopolymer and the ethylene-propylene random copolymer (EPR)in PP-cats.The isothermal crystallization kinetics of PP-cats in the early stage could be described by the Avrami model, and a comparison with that of pure iPP was carried out.It is found that the crystallization of PP-cats proceeds with instantaneous nucleation and three-dimensional growth.The overall crystallization rate of PP-cats is higher than that of pure iPP and increases with the increase of the EPR content.However,the spherulite growth rate of PP-cats appears slower than that of pure iPP and decrease with the increase of the EPR content,which is ascribed to the difficulty in moving of propylene chains due to the higher viscosity of PP-cats melt.Furthermore,the results of morphology observation reveal that the nucleation density of PP-cats is rather higher than that of pure iPP.It is suggested that the higher overall crystallization rate of PP-cats is a result of the nucleation effect of the EP content.