Dissertation > Industrial Technology > Chemical Industry > The chemical fiber industry > General issues > Basic theory

Characterization and Mechanisms Analysis of Thermal Relaxation and Light-Heat Aging of High Performance Fibers

Author LiuJunJie
Tutor YuWeiDong
School Donghua University
Course Textile Material and Textiles Design
Keywords Dynamic mechanical thermal mechanics High performance fiber Thermal degradation Activation energy Photoaging Tensile Properties Modulus loss
CLC TQ340.1
Type PhD thesis
Year 2011
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High-performance fiber with its unique mechanical physical and chemical properties, is widely used in national defense, aviation, aerospace, shipbuilding, sports equipment, automotive, construction and other industrial sectors. In normal use, in addition to the requirements of the fiber with high strength, high modulus, light outside, also require fiber with good light and heat stability and thermal dynamic mechanical behavior, namely the use of high-performance fiber in harsh environments such as high and low temperature, high irradiance the composite of light and heat, high humidity or corrosive liquids and combinations thereof, under the conditions needed stability to maintain its shape and bearing. Therefore, the behavior of high-performance fibers in such a complex environment, the need for simulation and characterization to solve practical reliability evaluation, to provide a scientific basis for high-performance fiber preparation, processing, fiber products, molding and use. This thesis, the main force for the characterization and analysis of the mechanical behavior and aging characteristics of several high-performance fibers heat, light composite conditions. Using dynamic mechanical thermal mechanical analysis (DMA) on the UHMW-PE fiber, Kevlar (?) Fibers and Nomex (?) Fibers discussed. Analysis of the characteristics of the thermal mechanical relaxation spectra of the three fibers, UHMW-PE fiber in the -130 ° C, respectively, in the vicinity of -60 ° C and 90 ℃ relaxation peak, followed by γ, β and α relaxation. Wherein α relaxation corresponding to the transition of the crystalline portion of relaxation, and therefore the temperature corresponding to crystalline transition temperature. The γ relaxation corresponding to the fiber amorphous part of the secondary transition, belonging to the client group, the side group such movement. β relaxation corresponds to the fiber amorphous region of the glass transition. UHMW-PE fiber after thermal aging of its crystalline structure and the transition temperature by DSC and XRD analysis, monoclinic crystalline phase decreasing trend. Analysis of the heat aging treatment on the fiber of Kevlar ? (?) Fiber and Nomex (?) Dynamic mechanical thermal mechanics. Heat treatment of 200 ° C after the Kevlar ? (?) Fibers and intact, the most obvious difference is based on the loss tangent tanδ of γ transition temperature, up to 28.2%; smallest is based on the storage modulus of only 1.1% of the β transformation temperature; heat treatment 200 the ℃ after Nomexr (?) fibers and intact, the most obvious difference is based on the loss modulus E \, three Overall, the transition temperature of the secondary transition the β temperature differences compared to the other two, but the difference in rate of a transition temperature of less than β, and γ transition temperature differences similar to the heating rate in the DMA test, analysis With the improvement of the heating rate and mechanism of the frequency of the relaxation spectrum. transition temperature toward high temperature, the measured result of a difference of up to 30 ° C, the reason is that the test sample lag due to the relaxation behavior. frequency dependence by Arrhenius law and Vogle-Fulcher law comparison shows Vogle-Fulcher law fitting effect improved significantly higher than conventional Arrhenius law, the frequency of the number and the glass transition temperature of the reciprocal of Q is more inclined to a nonlinear relationship. discussed four high-performance fiber thermal photoaging shape characteristics change after thermal aging, mechanical properties remains rate of PBO gt; Terlon (?) gt; Kevlar (?) gt; Nomex (?) and the light treatment preferably is Kevlar ?, strength holding ratio (?) fibers and Terlon (?) fibers. Compared to thermal aging, photoaging damage to the fiber was significantly higher the PbO and Nomex (?) fibers are relatively greatest damage, wherein PBO light treatment 200h after breaking strength of only 20 to 30 percent, and the thermal aging of 300 ° C, both maintained above 70%, its sort of optical damage completely reversed, the fiber to be the most vulnerable to the optical damage. obviously light related to the difference between the mechanism of thermal aging, thermal aging is fibers Acta softening process, photoaging Photooxidation Photofragmentation process, damage to the fiber is significantly better than the thermal aging. analyzed by X-ray diffraction and IR test heat, light and aging changes in crystal structure of the four kinds of high-performance fibers and chemical structures. with increasing heat treatment temperature, Kevlar (?) the degree of crystallinity of the fiber is increased and Nomex ? (?) the fibers and Terlon (?) fibers decreases, wherein Nomex (?) fiber in high Wen Shijing by the great destruction of PBO fiber crystallinity decreased after increasing relative to the other three fibers, its degree of crystallinity at high temperatures is very high, around 80%. before and after the change index shows that the comparative calculations photoaging the fiber light stability: Terlon (?) gt; Kevlar (?) gt; Nomex (?) gt; of PBO analysis of light, heat aging of Kevlar (?) fibers and Terlon ( ?) fiber heat degradation the kinetic feature point temperature, activation energy, and energy level. Kevlar (?) the peak temperature of the fibers is higher in nitrogen than the air atmosphere of approximately 50 to 70 ° C after the light after the degradation rate is lower than intact, to the light 200h, from 11% to about 2.5%; activation energy of the reaction and the reaction order gradually decreases with increased illumination time, the activation energy difference 47kJ/mol reaction order decreases from 1.18 to 0.14. while Kevlar ( ?) fiber illumination time 60 and 200h, fiber thermal degradation rate decreases, the illumination time of 100h, the degradation rate even than as it is about 5%. thermal gravimetric analysis of the fibers of Kevlar (?), compared three expressions thermal degradation kinetics the Coats-Redfem, Friedman and Freeman-Carroll. results show that the Coats-Redfern method is more close to the measured Kevlar (?) fiber thermal degradation behavior, but the premise is accurate to assume that a reaction n (n = 1, or N ≠ 1), before thus selected the activation energy of the AE calculation equation, thereby accurately solution Kevlar ? (?) ΔE value of the fiber. Friedman, linear correlation γ is relatively low, but the method and concise and direct expression, a style seeking two values ??ΔE and n is also the most commonly used calculation, only the reaction n greater reach 1.80, subject to interpretation. Freeman-Carroll at the start and the end of the reaction area and thermal re- expression in the form of the equation of thermal degradation dynamics parameters based on the slope of the trajectory consistent with Friedman, can be analyzed to determine reaction order and linear correlation is improved, but the resulting reaction n small, up to 0.35, has yet to be verified. the same time, the analysis of the different thermal aging temperature processing of thermal degradation of the fiber to Terlon (?) fiber object as it is greater than the rate of weight loss after heat treatment of the fiber mass loss rate of four high-performance fiber optical thermal compound shape, characteristics of aging alone light, heat aging with the opposite sex. the photothermal composite conditions, Kevlar (?) and Terlon (?) fiber mechanics to maintain performance than Nomex (?) fiber is better, Kevlar (?) short fiber time breaking force mechanics to maintain the rate of about 80%. Nomex (?) fiber breaking strength retention rate after 24 hours of light and hot under 100 ° C, only about 70% lower than the light and heat alone mechanical properties. PBO fiber breaking strength loss rate in the complex role of light and heat presents rapid decline, and loss of mechanical properties of light and heat alone compared to a large to heat, light aging the linear superposition measured differences discussion and analysis of Kevlar (?) the calculated value of the fiber higher than the linear superposition of the measured value of about 20%; Terlon (?) the measured value of the fiber is 61.4% less than the linear superposition of the theoretical value of 79%; Nomex (?) the measured values ??with the theoretical value of the fiber maximum close to 40% difference; the PBO fiber measured their linear superposition of theoretical value lower than 16% Four high-performance fiber the photothermal composite aging mechanics to maintain rate was significantly lower than the linear superposition of separate light aging and thermal aging, into a nonlinear superposition significant interaction. therefore it is necessary to study the role of light and heat composite high-performance fiber low temperatures high performance the decay of the properties of the fibers, and found that after the low temperature treatment after 24h, Kevlar (?) the highest strength retention of the fibers, more than 85% higher than in the 300 ° C heat treatment 77.9%; for while, Terlon (?) after the processing of the low temperature fiber, mechanical retention rate was 80%, compared with the heat treatment at 300 ℃ Nomex ? (?) when the fibers in the low temperature process mechanics maintaining the lowest rate, only about 58%, while during the heat treatment is relatively high, mechanical holding rate of about 3% higher; reach more than 80%, this Nomex fiber is relatively weak low temperature resistance and mechanical retention PBO fiber low temperature treatment in about 70% and heat treatment at 300 ℃ 72% similar. aging of low-temperature processing with heat, light and light thermal compound comparative analysis found that low-temperature processing and thermal aging treatment subsequent stretching performance trends similar to the mechanical properties of the fibers have different degrees of damage. the optical treatment after the aging treatment and photothermal composite PBO fibers and Nomex (?) The fiber tensile properties after the low temperature treatment with decapitation morphology having a significant difference in the low temperature process of impact on the fibers, the different treatment temperature needs further study demonstrated impact on the mechanical properties, structure and composition of high-performance fibers.

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