Solid state polymerization of poly (ethylene terephthalate).

摘要

Pre-crystallization is a necessary step in solid state polymerization (SSP) process in order to prevent pellets from sticking and to dry Poly (ethylene terephthalate) (PET) pellets. This work studied the effect of pre-crystallization temperature and time on the moisture content, crystallinity, SSP rate, and the quality of solid stated products (melting behavior and carboxyl end group), where moisture content affects SSP rate and carboxyl end group of solid stated product; crystallinity determines the sticking tendency; melting behavior and carboxyl end groups provide us the information of the melt process properties for injection molding.; The factors that affect the sticking of pellets include temperature, time, pressure, initial crystallinity, chemical structure of PET, dimension of pellets, and moisture content. In this study, a simple and accurate method has been developed to measure the sticking degree. Based on the measurement of sticking degree, the sticking mechanisms including physical sticking and chemical sticking are suggested. The measurement of sticking degree can be used to decide the optimal operation conditions in crystallizer and preheater, and SSP reactor.; Pure nitrogen must be used to keep the SSP system inert and purge the small molecular byproducts (ethylene glycol, water, AA, etc.) out. The small amount of oxygen in the nitrogen purge gas may affect the properties of the solid-stated product through the thermo-oxidative degradation. This study focuses on systematically investigating the effect of small amount oxygen (less than 1%) in nitrogen on SSP rate (IV), appearance property (yellowness index), and property of melt process (AA generation rate and concentration of carboxyl end group). A possible oxidation mechanism is suggested.; The catalyst system affects the reaction rate, color of product, and side reactions. PET manufacturers are researching different titanium complex to replace the existing antimony because of its potential hazard to health. This study was not intended to design a new chemical structure of titanium catalyst to solve the existing problems of titanium catalyst (high yellowness and high AA generation). This study only focuses on comparing the general properties of solid stated PET based on antimony and titanium catalysts. The standard process used for production of PET from EG and TPA or DMT can be modified by addition of a small amount of comonomer to create PET copolymer with some improved processing and physical properties. In bottle industry, isophthalic acid (IPA) is extensively used. In our study, the SSP rate and melting behavior of PET with 2--10mol% IPA are studied. IPA in PET increases the SSP reaction rate and decreases melting temperature. (Abstract shortened by UMI.)