乙烯含量对抗冲丙烯共聚物等温结晶行为的影响

利用DSC研究了乙烯含量不同的4种抗冲丙烯共聚物的等温结晶动力学.结果表明4种样品在考察的温度范围内(126~130℃)的等温结晶动力学完全符合Avrami方程,并得到了不同结晶温度下Avrami方程的结晶动力学参数k,n和t1/2,随着样品中乙烯含量的增加,Avrami指数(n)随温度变化不大,样品的结晶过程可能属于三维扩散控制的成核增长,4种样品的结晶活化能ΔE在279.5~343.1 kJ/mol范围内,且随乙烯含量增加,结晶活化能增大,充分说明样品中的乙烯含量是影响其结晶活化能的主要因素.结晶分级分析测试结果显示,随着乙烯含量的增加,聚丙烯均聚物部分链结构规整性提高,结构规整、可结晶的长序列含量在减少,可见乙烯含量的变化规律直接决定上述参数的变化规律.

THE EFFECT OF ETHYLENE CONTENT ON THE ISOTHERMAL CRYSTALLIZATION BEHAVIOR OF IMPACT PROPYLENE COPOLYMER

The isothermal crystallization kinetics for four impact propylene copolymers with different ethylene contents at different crystallization temperatures were investigated by employing differential scanning calorimetry(DSC).The results indicated that the kinetics of isothermal crystallization for all the samples was fitted quite well by the Avrami equation within the selected crystallization temperature range(126～130℃).With the increase of ethylene content in impact propylene copolymers,the Avrami exponent(n) did not vary significantly with temperature.The crystallization of impact propylene copolymer may involve heterogeneous nucleation with the controlled 3-dimensional diffusion.Crystallization activation energy(ΔE) of four impact propylene copolymers ranged from about 279.5 to around 343.1 kJ/mol.As the ethylene content increased,the crystallization activation energy increased.The results clearly indicate the significant influence of the ethylene content on the crystallization activation energy.The results of CRYSTAF test showed,along with the increment of the ethylene content,an increase in the tacticity of propylene homopolymers and decreases in the isotacticity、long crystallizable sequence content.