【作者】 宋媛媛；

【导师】 李光；

【作者基本信息】 东华大学 ， 材料学， 2011， 硕士

【摘要】 双向拉伸聚酯薄膜(BOPET)由于具有优良的综合性能,使其应用范围十分广泛,已由主要用于包装发展到电子、光学、影像、磁性等现代工业领域。但是BOPET仍然存在一些固有的缺陷,如结晶速度慢,作为电绝缘材料耐热级别低等,这些都使其应用和发展受到限制。针对这些问题,本文主要对PET进行第三单体共聚改性,以提高其结晶和热稳定性能。本文采用丙三醇(GL)、4,4’-联苯二甲酸(BPDA)分别作为第三单体参与由对苯二甲酸与乙二醇直接酯化聚合制得了丙三醇和联苯二甲酸改性聚酯：GL-PET(其中GL含量300-1800ppm)和BPDA-PET(其中BPDA5-25mol%)。用核磁共振(NMR)和红外(FR-IR)分析了共聚酯的分子结构与组成,由GPC和粘度法测定了产物的分子量。结果表明,GL和BPDA都参与了共聚合反应,成功连接到PET大分子链上,且产物具有与纯PET一样高的分子量。利用差示扫描量热仪(DSC)测试不同升温速度下的GL-PET共聚酯的非等温结晶过程,并用Avrami, Ozawa,莫志深法等分别计算分析了共聚酯的结晶动力学,结果表明：GL-PET的结晶速率大于纯PET,结晶活化能也低于纯PET的相应值,但GL-PET的结晶速率和动力学结晶能力并非与GL含量线性相关,而是在GL含量为900ppm时结晶速率常数最高,动力学结晶能力最强。通过比较不同方法,发现Avrami和莫志深法等能对GL-PET非等温结晶过程进行比较合理的分析。对BPDA-PET共聚酯的DSC分析表明：BPDA-PET的玻璃化转变温度随BPDA含量的增加而提高,其熔点则呈下降趋势；结合XRD和DMA的分析,发现BPDA-PET中的结晶主要是PET的结晶结构,但在BPDA含量25mol%时,稍有联苯二甲酸二甲酯(PEBB)的结晶特性。所以,大多数未结晶的PEBB链段滞留在无定形区,它们也与PET链段不相容,所以BPDA-PET呈现出两个玻璃化转变。利用热失重分析(TGA)对BPDA-PET共聚酯在氮气和空气下的热稳定性进行考察,结果发现在氮气气氛中PET及BPDA-PET共聚酯只存在一个降解台阶,BPDA-PET的热稳定性高于PET,且随着BPDA链段含量的增加,共聚酯的热稳定性提高；当气氛为空气时所有样品都存在两个降解阶段(第二台阶非常弱),第一阶段的降解行为与氮气气氛中的相似,但各试样在空气气氛中起始分解温度都下降了近30℃,PETBB的起始热分解温度高于PET。推测这是由手空气中的氧在第一阶段起了催化剂的作用,第二阶段为第一阶段产物的进一步氧化。采用Friedman和Chang法求算了BPDA-PET体系在一定升温速率下在氮气和空气中的降解活化能和反应级数。表明BPDA-PET降解活化能增大,反应级数n也变大。更多还原

【Abstract】 Biaxially oriented polyester film (BOPET) with excellent performance shows a wide range of applications from packaging to electron, optics, image, magnetic, etc. But BOPET film still has some intrinsic defects, such as slow crystallization rate, low heat resistance level, especially as electrical insulating materials. To solve these problems, PET was modified by adding the third monomers during its polymerization process to produce copolyesters which could improve the crystallization and thermal stability of BOPET films.Modified copolyesters were prepared from TPA and EG, with Blycerol (GL) and 4,4’-bibenzoic acid (BPDA) as the third monomor respectively. Molecular structure and composition of the copolyesters were confirmed by NMR and FT-IR, and molecular weight of the copolyesters were measured by GPC and intrinsic viscosity. The results demonstrated that not only GL and BPDA successfully linked to PET macromolecular chain by copolymerization respectively, but also high molecular weight polymers were obtained.Non-isothermal crystallization processes of GL-PET copolyesters were investigated by differential scanning calorimetry (DSC) under different heating rates, and the crystallization kinetics of copolymers were analyzed through Avrami Ozawa and combined Avrami with Ozawa equations respectively. The results indicated that the crystallization rates of GL-PET were higher and the crystallizabilities of them were lower than that of pure PET. But the crystallization rates and kinetic crystallizabilities of GL-PET were not linear correlation with contents of GL. When content of GL was 900ppm, the copolyester diplayed the highest crystallization rate constant and kinetic crystallizability. By comparing different methods, the modified Avrami and combined Avrami with Ozawa equations were found to analyze the non-isothermal crystallization processes reasonably.The DSC analysis of BPDA-PET copolyester showed that with the increasing content of BPDA, the glass transition temperature (Tg) of BPDA-PET was enhanced and the melting point (Tm) decreased. Combining XRD and DMA results, it was showed that crystallization in BPDA-PET was mainly composed of crystal structure of PET, but when content of BPDA was 25%, the copolyester exhibited a few crystalline characteristic of PEBB. Thus most of uncrystallized PEBB sequences which were also incompatible with PET retained in amorphous regions, so BPDA-PET appeared two glass transitions.The thermal stabilities of BPDA-PET copolyester in nitrogen and air atmosphere were tested via thermogravimetry analysis (TGA), and the results showed that PET and BPDA-PET copolyester had only one weight-loss stage. The thermal stability of BPDA-PET was enhanced with the increasing content of BPDA unit. In air, all the samples would show two weight-loss stages (the second was weak), and the degradation behavior during the first stage was similar with that in nitrogen although the onset degradation temperature decreased nearly 30℃, still BPDA-PET possessed higher onset degradation temperature than PET. It was deduced that the oxygen in air acted as a catalyzer in the first weight-loss stage and the second stage should be explained to the further oxidative of the first stage. The Friedman and Chang methods were used to calculate the decomposition activation energy and reaction order of different heating rates under nitrogen and air atmosphere, which indicated that the decomposition activation energy of BPDA-PET enhanced and the reaction order n increased too.更多还原