PET化学结构与热力学行为的关系

Relationship between chemical structure and thermodynamic behavior of PET

采用差热分析和红外光谱分析、粘均相对分子质量测定的方法,研究了PET的相对分子质量、端羟基和端羧基含量等化学结构与其玻璃化转变、冷结晶、热结晶行为、熔融行为的关系。结果表明:由于玻璃态中分子链段的局部有序性,PET呈现出双玻璃化转变和双冷结晶峰;随着相对分子质量减小,端羟基和端羧基含量相对增加,PET的玻璃化转变温度升高,冷结晶能力和热结晶能力增强,熔点升高,有利于形成结构完善的增强微纤。相对分子质量和端羧基、端羟基含量对热结晶行为影响的程度比对冷结晶行为的大得多,热结晶过程也由均相成核到既有异相成核,又有均相成核,到以异相成核为主。

The dependence of the glass transition, cool crystallization, thermal crystallization and melting behaviors on the chemical structure of PET, such as the relative molecular weight mass, the contents of carboxy and hydroxyl terminal groups, was studied by differential thermal analysis, infrared spectroscopy and viscosity average molecular weight measurement. The results showed that the double glass transition and double cool crystallization peaks appeared due to the partial order structure of PET mo- lecular chain in glass state. The glass transition temperature of PET raised, the cool crystallization and thermal crystallization ca- pacities enhanced and the melting point increased while the relative molecular weight mass decreasing and the relative contents of carboxy and hydroxyl terminal groups increasing, which benefited to the formation of reinforced micro-fiber with perfect structure. The relative molecular weight mass and the relative contents of carboxy and hydroxyl terminal groups had much greater effects on the thermal crystallization behavior than on the cool crystallization behavior. The mechanism of thermal crystallization process changed from homogeneous nucleation to the combination of homogeneous nucleation and heterogeneous nucleation and finally to heterogeneous nucleation dominantly.