PET的扩链及热致相分离法制膜的研究

发布时间：2018-04-03 17:23

本文选题：聚对苯二甲酸乙二醇酯(PET)　切入点：双酚A氰酸酯(BADCy)　出处：《北京化工大学》2011年博士论文

【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。
[Abstract]:Poly (ethylene terephthalate) (PET) has excellent transparency, chemical resistance and barrier properties. However, PET is easy to undergo thermal degradation, thermal oxidation and water degradation during melt processing.The molecular weight of the product is decreased, the processability is affected, and the mechanical and chemical properties of the product are decreased, which limits its application.In view of the above problems, the chemical chain extension method is used to increase the viscosity of PET and reduce the content of carboxyl terminal, so as to meet the processing requirements of PET.The chain extender of PET in molten state was studied by using cyanate ester Bad Cyclone as chain extender, compared with common chain extender epoxy and diphenyl methane diisocyanate.The melt torque, intrinsic viscosity and viscosity average molecular weight of PET after chain extension were compared. The results showed that the chain extension effect of BADCy on PET was better than that of MDI and epoxy E-51.The chain extension reaction between PET and BADCy was verified by infrared spectroscopy, and the mechanism of BADCy chain extension was explained in detail.By testing the torque, intrinsic viscosity and carboxyl content of PET after chain extension, the effects of reaction time and different rotational speeds on the chain extension effect of PET were studied.The results showed that the molecular weight of PET would be increased with the increase of reaction time, but the thermal degradation would be induced if the reaction time was too long.With the increase of cyanate content, the chain extension effect of PET increased with the increase of chain extension rate.The acceleration of rotational speed is beneficial to the strengthening of shear effect and the mixing effect is strengthened, but the strong shear will lead to the degradation of PET.The rheological properties and crystallization properties of PET after chain extension were characterized by melt flow rate tester, extended rheometer and DSC.It is found that the chain extension of PET limits the movement of PET molecular chain, reduces the fluidity of melt, makes the crystallization imperfect, the crystallization is difficult, and the melting point temperature is low.Cyclization reaction of cyanate ester can take place in heat or under the action of catalyst to form trimer of homopolymer-cyanate ester with triazine ring structure.In this paper, the multifunctional and high network structure of trimer is used to improve the chain extension effect as PET chain extender.The conversion of cyanate monomers was calculated by infrared spectroscopy to characterize the content of trimer.The molecular weight and molecular weight distribution of trimer were further measured by GPC.The effects of trimer content on PET chain extension were compared by measuring torque, intrinsic viscosity, carboxyl content and gel content.The results show that the existence of trimer can increase the chain extension effect of PET, but when the content of trimer is too high, the total functional group activity decreases and the chain extension effect weakens.The rheological properties and crystallization properties of PET after chain extension were characterized by melt flow rate tester, extended rheometer and DSC.It is further proved that chain extension can improve the rheological properties of PET and hinder the crystallization of PET.The effects of initial concentration and molecular weight of PET and cooling temperature on the structure of PET films were studied by scanning electron microscopy (SEM).The results show that the structure of microporous membranes is different due to the different interaction between diluent and polymer.The enriched phase of PET/ benzophenone system with good compatibility shows spherical structure and decreases with the increase of polymer concentration.The PET/NMP and PET/DMSO systems with poor compatibility have honeycomb and double continuous structures, respectively.With the increase of concentration and molecular weight, the pore size becomes smaller and the system changes from liquid-liquid separation to solid-liquid separation.With the increase of cooling temperature, the pore size of PET increases from spherical to flake.
【学位授予单位】：北京化工大学
【学位级别】：博士
【学位授予年份】：2011
【分类号】：O631.3

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