【作者】 蔡光明；

【导师】 于伟东；

【作者基本信息】 东华大学 ， 纺织材料与纺织品设计， 2010， 博士

【摘要】 高性能纤维材料优异的光、热稳定性及力学性能,是其在特殊场合应用的基础。而使用场合的苛刻条件和本身的耐久与稳定性是必须明确的。因此,本文对高性能纤维材料在热、光辐射、力及其复合作用下老化、降解、弯曲疲劳及其对应的老化机理进行表征研究,以此为这类材料的制备和高性能化,及其光、热稳定性的表征提供方法与指导。利用TGA-DTA/FTIR表征了Kevlar 49、Kevlar 129、Nomex、PBO四种高性能纤维在空气和氮气中的热降解性能,获得了各纤维在两种气氛中的特征温度,发现PBO纤维的起始和终止分解温度最高即耐热性能最好；Nomex纤维尽管起始分解温度不到450℃,但其终止分解温度接近800℃；四种纤维在空气中的各特征温度均低于在氮气中。利用热动力学理论,分析了各纤维在两个不同阶段的活化能和反应级数,发现除第一阶段Nomex纤维在空气中活化能更高,其它各阶段活化能均是空气中低于氮气中,反应级数接近。在空气中各种纤维的热裂解释放的气体主要为CO2、CO、H2O、NO2、HCN、还含有少量的NH3,其中CO2的吸收峰最为强烈；在氮气环境中高温裂解后的主要气体为CO2、CO、H2O、NO2、NO、HCN、还含有少量的苯环化合物,与空气中相比裂解产物中多了NO,且裂解产物中CO始终存在；依据裂解气体的构成,这类纤维的裂解均具有毒性。利用Py-GC/MS联用仪分析了Kevlar49、Kevlar 129、Nomex、PBO四种纤维的裂解过程,CO2占相当大比例,裂解产物有较多的含苯环的小分子物质出现,在600℃和700℃时Kevlar49、Kevlar 129裂解碎片较多,750℃是碎片量减少,而Nomex纤维在750℃时仍有较多的裂解碎片。对于PBO纤维由于其裂解温度较高,在750℃时的裂解产物中PBO的重复单元体、CO2占相当大比例,与其它三种纤维相比,分解产物中苯含量较少,其裂解性相对较安全。实现了柔性材料光力和光热复合下的原位测量,对芳纶纤维在力、光和光、热复合作用下的老化性能研究,表明在10%应力作用下进行光老化,芳纶纤维的断裂强力和伸长保持率仅为75%和69%,较光单独作用下明显下降,纤维的形态和微细结构降解得更为剧烈；光热复合作用下芳纶纤维的力学性能较光和热单独作用下降解更快,同时纤维的表面形态和结构较光和热单独作用降解更显著,故在实际使用过程中应考虑冗余设计。在本课题组自制准定点弯曲疲劳测试仪(FiBFAN)上,实现了微纳米尺度弯曲疲劳握持器的设计与成型,能有效的对纤维弯曲疲劳性能进行评价。该仪器可以原位测量不同温度下材料的弯曲疲劳性能,还能够原位观测和拍摄材料的弯曲疲劳破坏过程和纤维的断裂破坏形态,能够实时记录弯曲疲劳过程中的循环应力。利用定点弯曲疲劳仪研究了几种高性能纤维的弯曲疲劳性能,发现预加应力和弯曲角度是影响弯曲疲劳寿命最主要的因素,弯曲频率对弯曲疲劳寿命也有一定的影响。通过弯曲疲劳破坏的形态分析,发现Kevlar纤维和PBO纤维是原纤化劈裂破坏,高强聚乙烯为塑性积累断裂,而Nomex纤维表现为舌状的撕裂断裂。对比Kevlar、PBO、高强聚乙烯和Nomex纤维的弯曲疲劳特征值发现高强聚乙烯最耐弯曲疲劳。同时研究了热、湿、光老化对高性能纤维弯曲疲劳性能的影响,随着温度的增加,高强聚乙烯纤维的疲劳寿命减小,当温度增加到100℃,其弯曲疲劳寿命仅为20℃的30%。湿对纤维弯曲疲劳性能影响不大,Kevlar 49和PBO纤维在湿环境下弯曲疲劳寿命略有降低。光老化对Kevlar 49的弯曲疲劳影响较大,光老化一定时间后,纤维的弯曲疲劳寿命明显减小利用Kevlar长丝和芳纶1313长丝为原料通过机织的方法得到了Kevlar纯纺和Kevlar/芳纶1313混纤和交织三种结构的织物。实测表明,2.5 cm宽Kevlar纯纺经向强力为2500N以上,纬向为3248N；相近密度下混纤织物经向仅有1632N,纬向为1854N；交织织物经向强力为1300N,高于纬向；但交织织物的耐磨性能最好。织物加工过程的损伤分析,发现在加工过程中,经向损伤接近30%,大于纬向。反光和透光性测量表明,不同组织结构的芳纶织物透射和反射性能有一定的差别,但差别不大；纯纺、混纤、交织织物反光和透光性无甚差别。更多还原

【Abstract】 The excellent light, thermal stabilities and mechanical properties of the high-performance fiber are the basis for the application of special occasions. The used harsh conditions of high-performance fiber, and the durability and stability must be clear. Therefore, the aging, degradation and bending fatigue of high-performance fiber under thermal, light radiation, and the combined effect occasions were investigated. The corresponding aging mechanisms also were discussed. These studies provided some guidance for the preparation of such materials, their modification for high performance, and the characterization of theirs’light and thermal stabilities.The thermal degradations of the high-performance fibers, including Kevlar 49, Kevlar 129, Nomex, and PBO in the air and nitrogen were characterized by TGA-DTA/FTIR. The characteristic temperatures of the kinds of fibers in the two atmospheres were obtained. The heat resistance of PBO fiber was best and decomposition temperatures of the beginning and termination were the highest; despite the beginning decomposition temperatures of the Nomex fibers were the lowest and less than 450℃, the termination decomposition temperature was close to 800℃. The characteristic temperatures of the four kinds of fibers in the air were lower than the in nitrogen. The activation energy and reaction order in two different stages of the fibers were analyzed with the thermal dynamics theory. And it was found that, the activation energy of Nomex in the air was higher than in nitrogen in the first stage; the activation energy of the fibers in the air were lower than in the nitrogen in the other stages; and the reaction order were close in the two atmospheres. The gases released by the pyrolysis in air were mainly CO2, CO, H2O, NO, HCN, also containing a small amount of NH3, and the absorption peak of CO2 were the strongest. The gases released by the pyrolysis in nitrogen were mainly CO2, CO, H2O, NO2, NO, HCN, also containing a small amount of benzene compounds. The NO was exited in nitrogen, and the CO as pyrolysis product exited persistently. So the pyrolysis of these fibers was toxic based on the compositions of pyrolysis gas. The pyrolysis processes of Kevlar 49, Kevlar 129, Nomex, PBO were analyzed using Py-GC/MS spectrometer, respectively. It was found that the proportion of CO2 is large in pyrolysis products; and more small molecules containing benzene ring appeared in the pyrolysis products. There were more cleavage fragments of Kevlar 49, Kevlar 129 at 600℃and 700℃, and the cleavage fragments were reduced at 750℃. But there were still more cleavage fragments of Nomex fibers at 750℃.The pyrolysis temperature of PBO fiber was higher. So the proportion of the PBO repeat unit body and CO2 were large in the pyrolysis products at 750℃. The benzene contents of PBO were less than the other three fibers, and the pyrolysis of PBO was considerable safer.The in-situ measurements of flexible materials under the light—stress combined condition, light—thermal combined condition were achieved. The aging properties of aramid fiber under the two combined conditions were investigated, respectively. It was found that the maintain rate of the breaking strength and elongation were 75% and 69% under 10% stress and light combined condition. Which were significantly decreased compared with under the action of light alone. Meanwhile, the damage of the fiber morphology and fine structure were more seriously. The mechanical properties of aramid fibers under light and heat combined effect decreased faster than light or heat alone; and the fiber surface morphology and structure were more significant degradation too. So the redundancy design should be considered in the practical using process.The micro-nano-scale bending fatigue grip design and molding were realized using fixed bending fatigue analyser (FiBFAN) which was made in TMT team(Textile Materials and Technology Lab), and the bending fatigue of the fibers can be effectively evaluated. The bending fatigue performance of flexible materials under different temperature conditions can be measured in situ by the instrument. It also allows for observation of the bending fatigue fracture process and fiber fracture morphology in situ. The cycle stress in the bending fatigue process can be recorded in real time.The bending fatigue properties of several high-performance fibers were investigated using the fixed-point bending fatigue analysis apparatus. It was found that the pre-tension and bending angle were the most important factors which affected the bending fatigue life; the bending frequency also had certain effect on the bending fatigue life. Through the analysis of the bending fatigue morphology, it can be found that the bending fatigue fracture of Kevlar and PBO fibers was resulted in fibrillation split; the high strength polyethylene was because of the plastic accumulation; while the fracture-ends of Nomex fiber were the tongue shape of the tear fraqcture. The resistance to bending fatigue of high-strength polyethylene was the best compared with Kevlar, PBO, and Nomex fibers. The influences of heat, moisture, light on the bending fatigue of high-performance fibers were also studied. The fatigue life of high strength polyethylene fiber decreased when the temperature increased. The bending fatigue life at 100℃was only 30% of the bending fatigue life at 20℃. The moisture had little effect on the bending fatigue properties of the fiber. And the bending fatigue life of Kevlar 49 and PBO fiber in the wet environment is slightly lower. The light aging of the Kevlar 49 was greater, and after a certain time of light aging, the bending fatigue life of the fibers significantly reduced.Pure Kevlar fabric, Kevlar/aramid 1313 blended and Kevlar/aramid 1313 interwoven fabrics with three structures were obtained using the Kevlar and Nomex filament yarn as the raw materials. It was found that the warp strength of pure Kevlar fabric whose width was 2.5 cm was more than 2500N; and the weft strength was 3248N by experiments. With the similar density, the warp strength of Kevlar/aramid 1313blended fabric was only 1632N; and the weft strength was 1854N. The warp strength of Kevlar/aramid 1313interwoven fabric was 1300 N, which was higher than the weft direction; but the wear resistance of Kevlar/aramid 1313interwoven fabric was the best.. The warp damage of the fabrics was nearly 30% during processing, which was bigger than the weft direction. The reflection and transmittance of different structure Kevlar fabric was different, but the differences were not big according the measurements. There was not much difference of reflection and transmittance among these three kinds of fabrics.更多还原