【作者】 张玉梅；

【导师】 张清华；

【作者基本信息】 东华大学 ， 材料物理与化学， 2014， 硕士

【摘要】 聚酰亚胺纤维作为高技术纤维的一个品种,不仅具有较高的强度和模量,而且耐化学腐蚀性、热氧化稳定性和耐辐射性能非常好。其中,短纤由于其特殊的形态,比表面积较大,在绝缘纸、高性能印刷线路板、无石棉摩擦材料、增强材料方面具有广阔的应用前景。由于聚酰亚胺纤维纺丝成形及环化等工艺的特殊性,短纤的制备较为困难,使该纤维的研究及应用相对缓慢。本文采用了一种溶液沉析的方法制备部分环化的聚酰亚胺(PAA-PI)(也称部分环化的聚酰胺酸)短纤,该方法制备的短纤称为沉析纤维,即将PAA-PI浆液注入高速剪切流动的凝固浴中,液滴在凝固浴受到剪切力而被拉长,发生变形、凝固、原纤化得到部分环化的PAA-PI沉析纤维。该方法省去了复杂的纺丝成形工艺,有利于规模化制备聚酰亚胺短纤维。在低温下将4,4’-二胺基二苯醚(ODA)和均苯四甲酸二酐(PMDA)在溶剂N,N’-二甲基乙酰胺(DMAc)中聚合得聚酰胺酸(PAA)浆液,稀释制备固含量为5%的PAA溶液,通过加入三乙胺和乙酸酐等化学环化剂使PAA大分子链发生化学反应,得到了不同环化程度的聚酰亚胺(PAA-PI)(也称部分环化的聚酰胺酸)。采用乌氏粘度计测试了环化程度对聚合物特性粘度的影响,发现随着环化程度的提高,聚合物的特性粘度增大。通过红外光谱、热失重对其结构和性能进行了表征。热稳定性研究表明,相对于纯PAA,通过部分成环制备的PAA-PI起始分解温度有所降低,这是由于聚合物中少量残存的小分子环化剂的缘故。采用微控电子万能试验机对部分环化的聚酰胺酸薄膜进行力学性能的测试,发现随着环化程度的提高,聚合物分子链中酰亚胺环增多,力学性能增强。采用溶液沉析法制备部分环化的PAA-PI短纤,是将不同环化程度的PAA-PI浆液注入高速剪切流动的凝固浴中,凝固浴由水和DMAc组成,PAA-PI液滴在凝固浴中受到剪切力而被拉长发生变形、凝固、原纤化得到部分环化PAA-PI沉析纤维。采用正交实验的方法,通过测试沉析纤维的平均长度、平均直径以及计算沉析纤维的长径比讨论了剪切速率、浆液浓度及凝固浴浓度三个参数对溶液沉析法制备工艺中短纤成形的影响。研究发现,剪切速率600r/m,浆液浓度3%左右,凝固浴浓度为20%-30%之间时,制备的PAA-PI沉析纤维长径比最大,成形性最好。在该最佳制备工艺参数下,通过电镜测试和分析不同环化程度的沉析纤维的形貌。研究发现,随着环化程度的提高,PAA-PI沉析纤维成纤性变好。鉴于环化程度的提高有利于沉析纤维成形的发现,通过浊点滴定法和凝固动力学实验对溶液沉析法制备短纤的成形机理进行了初步研究。浊点滴定研究了(PAA-PI)-DMAc-H20三元体系相分离过程中各组分的变化,得到了体系的LCP浊点曲线和三元相图,讨论了环化程度对滴定剂(DMAc和H2O的混合溶液)凝固值、体系浊点组成和三元相图的影响。研究发现,随着环化程度的提高,双节线远离PAA-PI轴,均相区减小,(PAA-PI)-DMAc-H20的相容性减弱。表明,PAA部分环化变成PAA-PI后,与DMAc的相容性减弱,促进凝固过程中聚合物溶液中DMAc向凝固浴的扩散,有利于沉析纤维的成形。通过凝固动力学实验观察和测试了聚合物凝固过程和固化速率,发现PAA-PI固化过程及速率与凝固动力学中纤维固化理论一致,即凝固边界层位移的平方与扩散时间成正比。更多还原

【Abstract】 Aromatic polyimide(PI)fibers,as a type of heterocyclic polymer fibers,have exhibited some attractiveness of their properties,such as the outstanding thermal stability and chemical resistance,and the excellent mechanical properties as well as good irradiation resistance.The short PI fiber may be widely utilized in the fields of preparation of insulated paper,high-performance printed circuit boards,non-asbestos friction material and composites because of its special feature of the large specific surface area.The spinning process and cyclization reaction of the PI fiber are so complex that the preparation of PI short fibers is difficult and thus the corresponding research and application of the short fiber are limited.A new method to prepare the short PI fiber by the partially cyclized PAA solutions was introduced in this paper and the short fibers made by this method are called fibrids.The partially cyclized PAA solution was injected into coagulation bath and was stirred with a high-speed In the coagulation bath,partial cyclized PI drops were elongated by the shear force to deform,coagulate and fibrillate.This method is convenient for preparing short PI fibers on a large scale for leaving out the complicated spinning process.The related research includes the following three parts.At first,the equimolar amounts of pyromellitic dianhydride(PMDA)and 4,4’-diaminodiphenylether(ODA)were dissolved in polar solvent dimethylacetamide(DMAc)to produce poly(amic acid)(PAA).The PAA solution was diluted by DMAc into 5 wt%.Then the mixture of acetic anhydride and triethylamine with various amounts was added into diluted PAA solution to prepare the partially imidized PAA with various imidization degree.The effect of imidization degree on polymer intrinsic viscosity was characterized by the ubbelohde viscometer.The result showed that the intrinsic viscosity of polymers increased with the increase of the cyclization degree.The structure and properties of PAA-PI polymer were characterized by FTIR and TGA.TGA results showed that,compared with PAA,the initial decomposition temperatures of partially imidized PAA-PI showed a lower value.This was because that a little of dehydrating reagents were left in polymers.Mechanical properties of partially imidized PAA-PI film were characterized by a tensile testing machine and the result showed that the mechanical properties of the PAA-PI films were enhanced by the imidization process.Short PAA-PI fibers were prepared by the method of solution precipitation.In this method,PAA-PI solutions with various pre-imidization degrees were injected into the high-speed stirred coagulation bath with the mixture of H20 and DMAc.Then short PAA-PI fibers precipited from the system.Three main factors,including the shear rate,the concentration of PAA-PI in the solution and DMAc concentration in the coagulation bath were investigated,which affect the preparation of the fibrids by characterizing the average lengths and diameters of fibrids and calculating the aspect ratio of fibrids.The result showed that the concentration of PAA-PI was about 3%and the concentration of DMAc was between 20%and 30%,the aspect ratio of PAA-PI fibrids was the largest and the properties of the fibrids were the best.The morphology of fibrids was characterized by the PLM.The result showed the formation of partially imidized PAA-PI fiber became better with the increase of the pre-imidization degree.In view of the result of pre-imidization contributing to the formation of the short fibers,the formation mechanism of short PAA-PI fibers was investigated by the cloud point method and the solidification kinetics experiment.The cloud point curve and ternary phase diagrams of(PAA-PI)-DMAc-H20 were obtained by use of the cloud point method to show the changes in the content of each component of the system.The influence of the pre-imidization degree on coagulation values in the coagulation bath was discussed by analyzing the cloud point curve and ternary phase diagram.The result showed that binodal curve was more far away from(PAA-PI)-H20 axis and homogeneous area decreased,leading to the compatibility(PAA-PI)-DMAc-H20 weakened.This demonstrated that,compared with PAA,the compatibility between DMAc and PAA weaken.Then it contributed to the diffusion of DMAc of PAA-PI solution to the coagulation bath and made the fibrids formation better.The solidification rate of PAA-PI was characterized by the solidification kinetics experiments.As a result,the square of the displacement of the solidification layer is proportional to the diffusion time.更多还原