超拉伸聚乙烯的弹性模量和导热性能

ELASTIC MODULUS AND THERMAL CONDUCTIVITY OF ULTRA ORIENTED POLYETHYLENE

为了揭示聚合物分子链伸展、取向的本征特性，发展了两个新的测量方法和实验装置，用于研究拉伸比高达２００的超拉伸聚乙烯凝胶的弹性性能、传热性能和聚合物结构的关系．应用激光脉冲热致超声法给出材料拉伸方向和横向杨氏模量，应用激光脉冲光热辐射法给出拉伸方向，横向和厚度方向的导热系数．随拉伸比λ的增加，轴向杨氏模量急剧的增加，而横向的仅有少许减小．导热系数具有相似的特性．本文发现当λ＝２００时，这种拉伸取向聚乙烯的轴向模量可达钢的８０％，而导热系数甚至可达２倍，直至成为热的良导体，这是由于在高拉伸比时形成了相当数量的伸展分子链构成的针状晶体———晶桥．本文提出晶桥作为短纤维分散相的取向聚合物的结构模型，对于超拉伸聚乙烯的上述特性可以进行统一描述和定量化分析，和实验结果很好符合．

Two new methods have been developed for investigating the Young′s modulus and thermal conductivity of ultra oriented gel polyethylene films with draw ratios between 1 and 200.The laser generated ultrasonic pulse method gives the Young′s modulus in the draw and transverse direction,while the pulsed photothermal radiometry method gives the thermal conductivity in the draw,transverse and thickness direction of the film.The axial Young′s modulus is found to increase sharply with increasing draw ratio while the transverse modulus shows only a slight decrease.The thermal conductivity exhibits a similar behavior.At λ =200,the axial Young′s modulus is about 80% of that of steel while the axial thermal conductivity is about twice that of steel.The great increases in the axial modulus and thermal conductivity arise form the presence of needlelike extended chain crystals (crystalline bridges).We propose a structural model which treats the crystalline bridges as the fiber phase of a short fiber composite.This model provides a good description of the behavior of the axial Young′s modulus and thermal conductivity.