【作者】 张艳君；

【导师】 励杭泉；

【作者基本信息】 北京化工大学 ， 材料科学与工程， 2011， 博士

【摘要】 聚对苯二甲酸乙二醇酯(PET)具有优异的透明性,耐化学性和阻隔性被广泛的应用于包装领域,但是在熔融的加工过程中,PET易发生热降解、热氧化和水降解等反应,使其分子量下降,影响了加工性,也使制品的机械性能和化学性能降低,限制了其应用。针对上述问题,本课题使用化学扩链法增加PET的粘度和降低端羧基含量,满足PET的加工需求。使用氰酸酯(BADCy)作为扩链剂,与常用的扩链剂环氧和二苯基甲烷二异氰酸酯(MDI)进行对比,对熔融状态的PET进行扩链。比较了扩链后的PET的熔体扭矩,特性粘度和粘均分子量,结果表明BADCy对PET的扩链效果较MDI和环氧E-51好。采用红外谱图来验证PET和BADCy的扩链反应,并对BADCy的扩链机理进行了详细说明。通过对扩链后PET扭矩,特性粘度以及羧基含量的测试,研究了反应时间,BADCy的含量以及不同转速对PET扩链效果的影响。结果表明,随着反应时间的延长会增加PET的分子量,但是时间过长会引起热降解。随着氰酸酯含量的增加,扩链反应速度增加,PET的扩链效果增加。转速的加快有利于剪切作用的加强,使得混合效果加强,但强烈的剪切会引发PET的降解。通过熔体流动速率(MFR)仪,扩展流变仪以及DSC测试,对扩链后的PET的流变性能以及结晶性能进行了表征。研究发现,PET的扩链限制了PET分子链的运动,使熔体的流动性能降低,结晶不完善,结晶困难,熔点温度低。氰酸酯可在热或在催化剂作用下可发生环化反应,形成带有三嗪环结构的均聚物-氰酸酯的三聚体。本课题利用其三聚体的多官能度,高网络结构来提高其作为PET扩链剂的扩链效果。利用红外谱图计算出氰酸酯单体的转化率用来表征三聚体的含量。通过GPC来进一步测试三聚体的分子量及分子量分布。通过扭矩,特性粘度,羧基含量以及凝胶含量的测试对比了三聚体的含量对PET扩链的影响。结果表明,三聚体的存在可以使PET的扩链效果增加,但是当三聚体含量过高时,总的官能团活性降低,扩链效果减弱。通过熔体流动速率(MFR)仪,扩展流变仪以及DSC的测试,对扩链后的PET的流变性能以及结晶性能进行了表征。进一步的证明了扩链的发生,改善了PET的流变性能,阻碍了PET的结晶。本课题尝试使用热致相分离(TIPS)法制备PET膜,选择二甲基亚砜(DMSO),二苯甲酮,N-甲基吡咯烷酮(NMP)作为PET的稀释剂。通过扫描电镜(SEM)对稀释剂种类,PET初始浓度和分子量以及冷却温度对膜结构的影响进行了研究。结果表明,稀释剂与聚合物的相互作用不同,所制得的微孔膜结构不同。相容性好的PET/二苯甲酮体系,PET富集相呈现球状结构,随着聚合物浓度的增加,PET球尺寸减小。相容性差的PET/NMP和PET/DMSO体系分别呈现蜂窝状和双连续的结构。随着浓度和分子量的增加,孔径变小,体系由液-液相分离转变为固-液相分离。随着冷却温度的增加,其孔径增加,PET的富集相由球状成长为片状。更多还原

【Abstract】 Poly(ethylene terephthalate) (PET) has been widely used in packaging fields due to its transparency, chemical resistance, and barrier properties. However, during melt processing the molecular weight of PET may be easily reduced when subjected to thermal oxidation and hydrolytic degradation. Both degradations lead to reduction in molecular weight and an overall decrease in melt viscosity and melt strength, which limited its processing and application.In the research work of this group, bisphenol-A dicyanate (BADCy) was tried as an extender of PET and compared with conventional ones like diglycidyl ether of bisphenol-A (DGEBA) and methylenediphenyl diisocyanate (MDI). It was found that BADCy being more effective and worthy further studying. FTIR was employed to confirm the reaction between the PET and BADCy during the chain extension. The extending effect was characterized with torque, intrinsic viscosity, and the carboxyl content. As a result, a longer time of chain extension did not result in higher molecular weight, because of the negative effect of reaction heat. The more the amount of BADCy introduced the higher and the earlier the torque maximum exhibited. The enhanced stirring rate enhanced a higher rate of the chain extension reactions, which led to higher temperatures. However, the high temperature accelerated the chain cleavage. Measurement of MFR, storage modulus and dynamic viscosity showed that BADCy indeed extended the molecular weight of PET and reduced mobility of the extended PET. DSC analysis represented that less perfect crystallization of the extended PET for the difficulty in crystallization, lower melting temperatures.It was noticed that BADCy could undergo a cyclotrimerization forming a tri-mer. Such a tri-mer possesses three reactive sites and 3-fold larger molecular weight than the BADCy monomer. It was natural to consider that the tri-mer might be a potential chain extender for PET and the idea was tried in this work.The content of tri-mers was determined using FTIR. The average molecular weights (Mn and Mw) and polydispersity of BADCy tri-mers were determined by GPC for investigating the details of cyclotrimerization. The melt torque, intrinsic viscosity, carboxyl content, and gel content of modified PET were characterized. With increasing the cyclotrimerization reaction temperature of BADCy monomer, the conversion to tri-mers was increased. With a fraction of BADCy tri-mer in the chain extender, the modified PET exhibited higher melt torque, intrinsic viscosity, melt modulus, and melt viscosity than those modified BADCy monomer alone. BADCy tri-mer had a positive effect on the chain extension of PET. However, the fraction of tri-mers in the monomer/tri-mer mixture should be limited to a certain value, otherwise the chain extension would be weakened.In this Paper, the PET membrane was obtained by thermally induced Phase separation (TIPS). The solvent of dimethyl sulfoxide (DMSO), diphenylmethanone and N-methyl pyrrolidone (NMP) were selected as the diluents of PET in TIPS process. SEM was employed to study the structure and morphology of membranes. It was found that the membrane morphology can be controlled with different diluents for the interactions between polymer and diluents. The membrane of cellular structure and lacy structure were formed by liquid-liquid phase separation in PET/NMP and PET/DMSO system with weak interactions, respectively, while the particulate structure was formed by solid-liquid phase separation in PET/di-phenylmethanone system with strong interaction. The pore or particulate size decreased with the increasing of PET concentration and molecular weight. As the cooling temperature increased, the pore or particulate size increased.更多还原