Jian He , Qiufei Chen , Baolin Fan , Min Li , Hongqiang Zhu , Hamza Malik , Hui Zhang , Yong Liu , Jianyong Yu
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引用次数: 0
Abstract
The evolution of the microstructures of polyacrylonitrile (PAN) fibers during successive industrial heat treatments was systematically traced. It was found that the cyclization reaction began in the amorphous zone around the PAN crystals and continued until the pre-low-temperature carbonization phase. From 400 to 1900 °C, the carbonization process was separated into four stages, where the two-dimensional aromatic layers formed by the cyclization cross-links progressively evolve into three-dimensionally ordered carbon microcrystals. The microcrystals tended to in-plane growth during the high-temperature carbonization stage. The aspect ratio of the microcrystals of carbon fiber exhibited the same variation trend as its tensile strength, both reaching their maximum value at 1700 °C. Small-angle X-ray scattering (SAXS) revealed the hereditary evolution from the microfiber structure in the precursor fiber to the banded graphite-like layered structure within the carbon fibers after heat treatment. As the stabilization and carbonization processes progressed, the microvoids within the fibers showed a decrease in cross-sectional dimensions and transitioned to a slit-like configuration accompanied by a decrease in the curvature of the graphitic-like carbon layer. The fluctuating changes in microvoid length and orientation are influenced by the structural relaxation in the middle stage of carbonization, as well as the regular rearrangement of graphite-like structures in the late stage of carbonization. The results of relevant analysis can provide further insights for the development of ultra-high-strength medium-modulus carbon fibers.
期刊介绍：
Polymer Degradation and Stability deals with the degradation reactions and their control which are a major preoccupation of practitioners of the many and diverse aspects of modern polymer technology.
Deteriorative reactions occur during processing, when polymers are subjected to heat, oxygen and mechanical stress, and during the useful life of the materials when oxygen and sunlight are the most important degradative agencies. In more specialised applications, degradation may be induced by high energy radiation, ozone, atmospheric pollutants, mechanical stress, biological action, hydrolysis and many other influences. The mechanisms of these reactions and stabilisation processes must be understood if the technology and application of polymers are to continue to advance. The reporting of investigations of this kind is therefore a major function of this journal.
However there are also new developments in polymer technology in which degradation processes find positive applications. For example, photodegradable plastics are now available, the recycling of polymeric products will become increasingly important, degradation and combustion studies are involved in the definition of the fire hazards which are associated with polymeric materials and the microelectronics industry is vitally dependent upon polymer degradation in the manufacture of its circuitry. Polymer properties may also be improved by processes like curing and grafting, the chemistry of which can be closely related to that which causes physical deterioration in other circumstances.
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