The Study On Preparation And Properties Of PET/PEN Blend Fibers

Poly(ethylene2,6-naphthalate)(PEN) is a new kind of high-performance polyesters which has a similar chemical structure with ploy(ethylene terephthalate)(PET) in recent years. Compared with PET fibers, PEN fibers have more obvious advantages in many aspects, such as mechanical property, thermal stability, chemical stability and gas barrier property and so on, which is mainly due to the structure of naphthalene that helps to increase stiffness in main chain. So these PEN fibers can be applied in industrial fields of tyre cord, conveyor belt and brake pipe etc. However, as a result of the stiffness of PEN, the crystallization temperature increases and the crystallization rate decreases and then the melt spinning properties are affected. Coupled with relatively high costs, large-scale application of PEN fibers has also been hindered. Therefore, in this article, after adding a certain proportion of PEN into PET matrix, the studies on preparation, structure and performance of PET/PEN blend fibers are carried out. The purpose of the research is to develop a kind of moderately priced and well-performed blend fibers in combination with price advantages of PET and performance advantages of PEN so as to explore applications of PEN in civil fields. The main researches in this topic are as follows:PET/PEN blend resins with PEN contents of 10%, 30% and 50% respectively are prepared by direct melting blend via double-screw extruder. It can be discovered that the thermal stability of blends was improved to some extent with the increase of PEN contents. In addition, PET/PEN blends is a partially compatible system and this should be attribute to the eater exchange reaction during melting process. The transesterification of PET and PEN increased the compatibility between them. On the other hand, it causes a relatively negative influence on crystallization of polymer blends, leading to a whole crystallization difficulty. Then, PET/PEN fibers are prepared via melt spinning, which presents an increase in modulus, heat-resistance and anti-ultraviolet capabilities and a decrease in breaking strength compared to pure PET. The main explanation is that eater exchange reaction has influenced the blends system, making crystallization difficulty and leading to a decrease in strength. Thus, controlling eater exchange reaction is the key to improve properties of PET/PEN blend fibers.Based on the research results of PET/PEN blend fiber, the triphenyl phosphite(TPPi) was selected as the ester exchange inhibitor and added into the PET/PEN blends in which the PEN contents was 30%. It was found that the crystalline property of the blend resin was greatly improved when the 0.5wt%TPPi was added into the blends more than other contents of TPPi.After a five-times drawing, the properties of PET/PEN fiber had been promoted, the final fracture strength and modulus of blend fiber was increased to 5.81 c N/dtex and 153.5c N/dtex,which was better than the pure PET fiber whose was 5.25 c N/dtex and 101.5c N/detx. The crystalline property and orientation of the fiber was 34.04% and 87.1%, which was similar to the pure PET fiber at the same drawing conditions. The strength retention rate after the heat treatment rose to 57.49% as the pure PET was 49.90% and the UV absorption band from 320cm-1 extended to 350cm-1.