乙烯-乙酸乙烯酯共聚物热熔胶黏剂在长期热退火过程中的结晶行为

Crystallization Behavior of Ethylene-vinyl Acetate Copolymer Adhesive during Long-term Annealing Process

乙烯-乙酸乙烯酯共聚物(EVA)热熔胶黏剂(简称EVA热熔胶)是一种环保、综合性能优良的高分子材料,其储存和使用条件,尤其是温度和湿度等因素,影响着热熔胶黏剂中的晶体结构,最终影响其力学性能.为了探究结晶与力学性质之间的关系,本文中选用热熔胶黏剂分别在干热、湿热等条件下进行长期热退火实验.研究发现,短时间热退火会导致热熔胶黏剂力学性能的缓慢提升.结合示差量热扫描分析实验结果表明,热熔胶黏剂的力学性能变化主要源于热退火对热熔胶黏剂结晶行为的促进作用.小角X射线散射实验表明,热退火对于晶区厚度并没有显著影响,但通过广角X射线散射实验,发现热退火主要促进晶体在(110)晶面的生长,对于(200)晶面的影响可以忽略.进一步地,通过偏振小角激光散射实验发现,热熔胶黏剂的球晶结构主要由热稳定形较好的片晶构成,在80℃以上的较高温度才能完全熔融.相比较而言,不完善的细小晶体在60℃以下就可以完全熔融,长期热退火可以有效消除热熔胶黏剂中的细小晶体.本文工作研究了热熔胶黏剂在高温或湿热环境中的结晶和力学性能关系,为优化热熔胶黏剂的储存和服役条件提供了实验依据.

Ethylene-vinyl acetate copolymer(EVA)adhesive is an environment-friendly polymer with excellent thermomechanical performance.It is widely used in furniture,cables,pipelines and so on.The storage and service environment of EVA adhesives,such as temperature and humidity,affect the crystal structures and their mechanical properties.To explore the relationship between crystallization and mechanical properties,we treat EVA adhesives with long-term annealing experiments under thermal or thermal/humid conditions,respectively.The results reveal that short time annealing leads to slight improvement in the mechanical properties,which is ascribed to the promoted crystallization determined by the differential scanning calorimetry.The small angle X-ray scattering experiment shows that annealing does not apply significant influence on the crystal thickness,while the wide angle X-ray scattering experiment indicates preferential crystal growth of the(110)plane rather than the(200)plane.Using polarized small angle laser scattering,we further find that spherulites in EVA adhesive is mainly made of thermally stable lamellar crystals which completely melt above 80℃.In comparison,small crystallites can be eliminated below 60℃ during long-term annealing.This work sheds insight into the relationship between crystallization and mechanical properties of EVA adhesive in thermal or humid environments,and provides a key experimental basis for optimizing the storage and service conditions.