非晶态聚合物主转变弛豫峰与玻璃化转变过程的相关性研究

RELATION BETWEEN T_g AND α-PEAK IN AMORPHOUS POLYMER PVC

从弛豫理论出发,在不同的时效时间和不同降温速率下,测量了非晶聚合物PVC玻璃化转变过程中与时间参量密切相关的α峰峰温(T_α)的响应关系,得出以下结论:1)玻璃化转变温度(T_g)一般是指非晶态聚合物热平衡态与非平衡态的温度转变点(T_t),是温度变化造成的热弛豫过程的直接结果,而α内耗峰是在动态力学测量过程中得到的聚合物玻璃态与高弹态(橡胶态)的分界点处的力学弛豫过程,表现为动态模量锐变过程,是非晶态聚合物热平衡态下的特征内耗峰.两者都与非晶态结构的存在紧密相关,它们的表观行为取决于非晶聚合物热平衡态下的同一个本征的弛豫时间,但它们的表征是完全不同的两种物理过程.弛豫时间对温度的强烈依赖性造成玻璃化转变过程的存在,而热平衡态的弛豫性质是α内耗峰存在的前提.2)α峰是稳定的力学弛豫峰,其弛豫机制是在热平衡态下独立存在的,但在不同的测量条件下,它的峰参数受到时效敏感区热处理条件的影响,存在着一个过程内耗峰叠加在α峰上.

A systematic study of the effect of physical ageing and cooling rate on a-relaxation peak are carried out in PVC. It was said that a-peak and Tg are not the same concept. Both are closely connected with amorphous state, but show different behaviours in the same pre-treatment conditions: varying physical ageing time in sub- Tg or changing cooling rate from Tg + 20 'C to room temperature . Some interesting results were obtained as follows:When Tg lowers with increacing ageing time or decreacing cooling rate, a-peak temperature (Ta) keeps constant. On the other hand, the intensity of the a-peak decreases. This behaviour shows that a- relaxation peak is not a typical linear anelastic internal friction peak, as there is a quenching peak added on it.A detail discussion will be given in this paper.