Study On The Durability And Stability Of Flexible High Performance Fibers In Thermal And Light Radiation

High performance fibers (HPFs) are widely used in aerospace, military, sports and protective clothes, and so on, because of their high tenacity, high modulus and high temperature-resistant property. However, these features are only compared to those common polymer fibers. There exist some uncertain problems, such as the limits of the high performance fibers, the differences among of them, and their mechanical behaviors under the light, thermal irradiation and hydrolyzation environment even when they are fatigued in bending and twisting condition. Now it is urgent to solve these problems and to improve their shortcomings so that the high performance fiber can make full use of their safe performances. Therefore, in this paper, the thermal, photo and fatigue property of the high performance fibers are systemically studied.Eight kinds of HPFs (Kevlar^?29, Kevlar^?49, Kevlar^?129, Twaron^?2000, Terlon^?, Kermel^?, PBO and UHMW-PE) were compared by using the Thermogravimetry Analyser, and the results showed that i) the sequence of characteristic temperature, including the initial decomposing temperature (T_i), the temperature at the maximum rate of weight loss (T_p) and the temperature of half decomposition (T_1/2) under air atmosphere is similar as that under nitrogen atmosphere;ii) the sequence of the comprehensive temperature (T) is consistent with that of the characteristic temperatures, and the PBO fiber has the highest thermal degradation temperature whether in air or nitrogen atmosphere, Terlon^? fiber is the next, and the other p-aramid and Kermel^? fibers follow, while UHMW-PE fiber is the worst thermal resistant among these samples;iii) the thermal dynamic analysis of these fibers indicates that activation energy of these fibers in air is less than that activation under nitrogen atmosphere, and the reaction order is similar, i.e. the samples degrade more easily under air atmosphere than under nitrogen atmosphere.The PBO, Kevlar" 129 and Kermel fibers were compared on the tensile property under high temperature, and the experimental results still showed that the PBO fiber has the highest tensile retention property. While for UHMW-PE fiber, there is an exponential relationship among the tensile property retention, the temperature and the aging time, which accords with the actual usage. It can be used safely when the temperature is less than 70°C. From the theoretical model on the temperature and the modulus, it can be found that the modulus firstly increased with heat temperature then decreased.The light-stability testing of these high performance fibers was also carried out. The two light sources of xenon arc and carbon arc light were respectively used to simulate the sunlight for the ageing test of HPFs. It can be observed that the light-proof decreases more acutely under carbon arc light than under xenon arc light, the absolute difference between the corresponding parameters is about 5%¹0%, and the aging results verify that the xenon arc light confirms to the actual sunlight. Meanwhile, the PBO fiber showed worse photo-stable property than Kevlar?129 despite PBO has the highest original tenacity and modulus, while the UHMW-PE fiber showed the best light-resistant property among the eight samples. Compared with the PBO, Kevlar?129 and Kermel? fibers, the durability of the Kermel? fiber indicated the rapidest decrease under simulated sunlight irradiation, while Kevlar?129 has the stablest resistance to sunlight. When these fibers have been firstly light irradiated then thermal annealed, the results showed that their mechanical properties decreased rapidly. Therefore, it is very important to pay attention to the HPFs, or to make a safe design, or to take a protection measure in order to avoid fiber damage or even invalidation under the light and thermal combination environment.The static mechanical fatigue measurements of these high performance fibers have been investigated in this dissertation, which involves the bending and torsion fatigue. It can be found there exists a linear relationship among the pre-tension, bending (torsional) angle and the logarithm of the bending (torsional) fatigue cycles. Under the two conditions, the pre-tension effect is higher than the angle effect. Therefore, the high performance fibers should be carefully applied under bending andtwisting conditions with high pre-tension. From the torsional fatigue morphology, it can be found that the twist unevenness occurred during the torsion procedure. Meanwhile, the weakness and twist transfer in these fibers can be figured out. Compared with the aramids, the UHMW-PE fiber has the longest fatigue lifetime whether under bending or torsional condition. Moreover, the UHMW-PE fiber reveals toughness characters, while the aramids show the fibrillation.The high performance fabrics were also treated on light ageing. Both of Kevlar?129 and glass fabric after titanium sol-gel coating are compared. It can be summarized that the light stability of these fabrics have been improved. Through the SEM observation of the gel treated fabrics, the three dimensional net work structure appeared on the fabric surface, which played the active role on light penetration, and the titanium gel could absorb and reflect sunlight, so as to resist sunlight irradiation efficiently. It can also be found that the mechanical properties of Kevlar?129, PBO and Kermel? fibers increased after sol-gel treatment than the original samples under simulated sunlight. Thus, it can be concluded that the sol-gel treated fabrics and fibers all have higher photo stability than the original samples.