T_g以下温度退火对无规聚苯乙烯性能的影响

THE EFFECT OF PHYSICAL AGING ON THE PROPERTIES OF ATACTIC POLYSTYRENE

用调幅式ＤＳＣ等新技术研究了物理老化对无规聚苯乙烯多种性能的影响．随着老化时间的延长，试样的玻璃化转变温度、热焓松弛、峰温、峰高和热焓提高；老化使材料的初始模量，屈服应力和断裂强度都有不同程度的提高；使样品的溶剂扩散速率降低，但对样品的密度和声传播速度几乎没有影响．以上这些结果可从物理老化引起试样中凝聚缠结增加的观点来进行解释．

Effects of physical aging on the structure,mechanical and other properties of atactic polystyrene (a PS) films and fibers are studied by modulated differential scanning calorimetry(MDSC),density,solvent diffusing rate,stress strain behavior and sonic velocity measurements,and the corresponding observations are tentatively explained from the viewpoint of cohesional entanglements.It is shown that the glass transition temperature ( T g),relaxation enthalpy ( ΔH ) and its peak value ( T max ) in the MDSC curves,as well as the initial modulus ( E ),yield strength ( σ y ) and strength at break ( σ b ) all rise with the increase of physical aging time.On the other hand,the solvent diffusing rate slows down after being annealed below its T g,while the sonic velocity and density nearly keep unchanged.The weak interaction(i.e. cohesional entanglements) introduced by the physical aging is similar to van der Waals' force from its physical characteristic.All experimental results are interpreted by the assumption that the number of cohesional entanglements increase during physical aging.