聚丙烯-g-聚氨酯共聚物的非等温结晶动力学研究

用DSC法研究了聚丙烯 (PP)和聚丙烯接枝聚氨酯的共聚物 (PP g PU)在不同冷却速率下的非等温结晶动力学 .用Avrami方程和莫志深改进法对DSC测定结果进行了处理 ,结果表明 ,PP g PU的动力学参数能很好的符合Avrami方程和莫志深改进方程 .PP接枝了聚氨酯支链后 ,结晶速率增大 ,球晶的生长和成核机制也相应发生改变 ,而其变化规律与接枝物的组成和结构密切相关

NON-ISOTHERMAL CRYSTALLIZATION BEHAVIOR OF POLYPROPYLENE GRAFTED POLYURETHANE

The non isothermal crystallization kinetics of polypropylene grafted polyurethane (PP g PU) copolymers under the different cooling rate has been studied by DSC.A kinetic equation for nonisothermal crystallization was employed to analyze the crystallization characteristics of PP and PP g PU.The results show that in the range of cooling rate of 2.5 to 40 K/min,the kinetics of non isothermal crystallization of PP and PP g PU with different PU content can fit the Avrami equation and a combination of Avrami Ozwa method.The presence of the PU branches in PP g PU results in less crystallization enthalpy and higher crystallization temperature upon cooling.All the PP g PU copolymers have higher nucleation rate and overall rate of crystallization assuming that the spherulitic growth was initiated by heterogeneous nucleation alone,as characterized by the higher values of Z c and low values of t 1/2 than those of pure PP.The crystallization rate is not only dependent upon the cooling rate,but also dependent on the composition ratio of PP g PU copolymers.It was found that,due to stronger hydrogen bonding effect among the PU branch chains,the mode of nucleation and the growth of the crystallites changed after grafting.The hydrogen bonding effect can accelerate the heterogeneous nucleation by strengthening the adsorption effect between PP chains,and result in different crystalline behavior from other PP copolymers,as proved by the fact that the n values of PP g PU copolymers increased with increasing cooling rate.