液晶增强聚对苯二甲酸乙二醇酯复合材料的进展

Progress of Liquid-Crystalline Polymer Reinforced Poly(Ethylene Terephthalate) Composite

系统介绍了液晶(聚合物)(LCP)的种类与含量对LCP增强聚对苯二甲酸乙二醇酯(PET)复合材料相容性、结晶性、流变及力学性能的影响。当LCP为刚性4-羟基苯甲酸-2-羟基萘-6-甲酸共聚物(HBA-HNA)(Vectra)时,由于热塑性PET与向列型HBA-HNA不发生熔融酯交换反应,复合材料的相容性差、力学性能弱。而当LCP为商业化、半柔性4-羟基苯甲酸-对苯二甲酸-乙二醇共聚物(PHB-PET)时,因PET与PHB-PET中的PET柔性链段之间发生了酯交换反应,两组分间的相容性增加,但PET基体相与PHB-PET分散相均因分子链规整性的降低而分别导致结晶性与液晶性减弱,因此复合材料的力学性能通常在酯交换反应程度时最佳。以癸二酸-4,4'-二羟基联苯-4-羟基苯甲酸共聚物(SBH)为代表的LCP与PET进行熔融共混;无论LCP中是否存在柔性链段(如:SBH),其对PET基体的影响都与PHB-PET或HBA-HNA基本类似。虽然可以向不相容PET/LCP复合物中填充无机填料以实现增强,但更多的是引入少量第三组分增容剂对PET/LCP进行增容,从而有效提高复合材料的力学性能。此外,探讨了拉伸比、剪切速率、加工温度、超声处理、模具温度与保温时间、共挤出等工艺条件对PET/LCP复合材料流变与力学性能的影响。当在PET熔体中引入少量离子基团时,PET的离子与LCP的酯基之间的离子-偶极相互作用改善了相容性,同时,离子静电自组装所形成离子簇的诱导成核增加了PET相的结晶度,两者协同提高了PET/LCP复合材料的力学性能;而且,该熔融离子化改性技术有望成为LCP增强PET复合材料的未来发展方向之一。

Effects of the type and concentration of liquid-crystalline polymers （LCP） have been reviewed on the eompatibility,crystallinity,rheological and mechanical properties of the LCP reinforced poly （ethylene terephthalate） （PET） composite systematically. When the LCP is a rigid poly （4-hydroxybenzoie acid-ran-2-hydroxynaphthalene-6-carboxylic acid） （HBA-HNA） （Vectra）, the composite exhibit weak mechanical properties from their poor compatibility due to the failure of the thermoplastic PET to undergo melt transesterification with the nematie HBA-HNA. However,when the LCP is a commereialized,semiflexible copolymer of 4-hydroxybenzoic acid, terephthalie acid, and ethylene glycol （PHB-PET） , the compatibility of the composite is improved due to an occurrence of transesterification between the PET and the PET flexible chain segments of the PHB-PET,while concurrently the erystallinity of the PET matrix phase and the liquid crystallinity of the PHB-PET dispersed phase both are reduced as a consequence of their decreased chain tacticity from the transesterification, giving rise to maxima in the mechanical properties of the composite usually at an optimum degree of transesterification. Laboratory-synthesized LCP, such as a copolymer of sebacic acid ,4,4＇-dihydroxybiphenyl, and 4-hydroxybenzoie acid （SBH） as a representative, also are melt-compounded with PET; when the LCP contain （as SBH does） and do not contain flexible moieties （ i. e. , chain segments） ,respectively,their effects on the PET matrix essentially are similar to those of PHB-PET and HBA-HNA. Although inorganic fillers are filled into incompatible PET/LCP composite to mechanically strengthen them,a small amount of third-component compatibilizer has more predominantly been introduced to compatibilize the PET/LCP, thereby effectively improve their mechanical properties. In addition, influences have been discussed of the process conditions such as extension ratio, shear rate,processing temperature, ultrasonic treatment, mold temperature and its holding time, coextrusion, on the rheological and mechanical properties of PET/LCP composite. When a small number of ionic groups are covalently introduced into a PET melt,the PET-LCP compatibility is enhanced through the ion-dipole interactions between the PET ionic groups and the LCP ester groups, and meanwhile the PET phase crystallinity is increased owing to its additional nucleation induced by the ionic aggregates formed from electrostatic self-assembly of the ionic groups, both of which synergistically improve the mechanical properties of the PET/LCP composite. The PET modification via melt ionization is expected to become one of the future directions for the development of LCP reinforced PET composite.