聚氯乙烯接近玻璃化转变温度时的蠕变行为研究

Investigation on Creep Performance of PVC Aged at Relatively Near to Glass Transition Temperature

利用动态力学分析仪,详细研究了小应力作用下聚氯乙烯(PVC)接近玻璃化转变温度(63℃)时的短期蠕变性能.根据Struik-Kohlrausch(SK)方程及Struik移位方法,分析了物理老化对PVC瞬时蠕变柔量的影响,并提出了基于多松弛机制的新模型定量描述初始蠕变柔量、松弛时间和形状因子.结果表明:SK方程虽可表征不同老化时间下PVC的蠕变性能,但通过Struik移位方法却无法获得理想的主曲线,且初始蠕变柔量、松弛时间、形状因子和蠕变率均受物理老化显著影响,并在双对数坐标下随老化时间呈明显的非线性变化;新模型不仅揭示了物理老化控制参量的演化规律,而且极好地预测了PVC在物理老化进程中的高温蠕变行为.

In order to predict mechanical performance of PVC at high operating temperature,a series of short-term tensile creep tests（one-tenth the physical aging time） of PVC were carried out at 63°C imposing a small constant stress using a dynamic mechanical analyzer（DMA）.The Struik-Kohlrausch（SK） formula and Struik shift factor method were attempted to describe these creep data for various physical aging times.A new phenomenological model based on multiple relaxation mechanisms of amorphous polymer was developed to quantitatively describe the SK parameters（initial creep compliance,characteristic retardation time and shape factor） determined by aging times.It was shown that momentary creep compliance curve of PVC at 63℃ coudle be very well fitted by SK formula for each aging time,respectively.However,the SK parameters for the creep curves are not constant during aging process at elevated temperatures,and the evolution of these parameters and creep rate versus aging time curves at double logarithmic coordinates have showed obvious nonlinear phenomenon.Moreover,the creep master curves obtained by the superposition with Struik shifting methods are unsatisfactory in such case.Finally,prediction results calculated from the present model incorporating SK formula are in excellent agreement with the creep experimental data for PVC isothermally aged at relatively near to glass transition temperature.