Research on Ageing and Surface Modification of Aramide Fibers
|Keywords||aramide fiber UV ageing surface modification mechanical properties|
Poly (p-phenylene terephthalaramide)(PPTA) fibers, also named as aramide fibers, are a class of linear polymers containing aromatic and amide groups, and have been considered as one of the most important organic fibers today owing to their attractive integrated performances such as super high specific strength and modulus, outstanding thermal stability at the temperature not higher than560℃, and very good acid and alkali-resistance, therefore they have been used in many industries, especially those ask for harsh requirements in integrated performances of materials. However, PPTA fibers have smooth surface and high crystallinity, showing very low intrinsic surface activity and less mechanical interlock to various substrates, and thus leading to very poor adhesion with almost all organic materials. To date, many approaches have been developed to effectively improve the surface activity of PPTA fibers, however they tend to sacrifice the original outstanding properties of PPTA fibers, and thus can not meet the harsh requirements on PPTA fibers proposed by the rapid development of modern industries. Therefore, how to develop a new method for introducing functional groups on the surfaces and improve the surface activity of PPTA fibers without deteriorating the excellent properties of original fibers is still an interesting and challenging topic on PPTA fibers and related composites. Additionally, PPTA fibers have poor UV-resistance in the mild environment and the mechanism of the photo-induced mechanical loss by the short-term UV radiation has never been well elucidated. These are the subjects of this thesis.First, in order to overcome the poor surface activity of PPTA fibers, a new method is set up to facilely and greenly prepared a coating with functional groups on the surface of PPTA fibers through a polymerization using horseradish peroxidase as the catalyst. The effects of this new method on integrated properties of PPTA fibers (PGMA@KF) were intensively evaluated. The results demonstrate that the morphology and element compositions of PGMA@KF fibers can be controlled by the concentration of glycidyl methacrylate (GMA) used. Compared with original fibers, PGMA@KF fibers not only have dramatically increased content of polar groups, higher surface free energy, and rougher surface, but also show obviously increased mechanical properties while maintaining excellent thermal resistance.Second, a comprehensive study on the effects of different length of short-term UV radiation was carried out on the PPTA fibers, and then the mechanism of the photo-induced mechanical loss by the short-term UV radiation was systematically discussed. The results demonstrate that surface etching, photo-induced oxidization and decomposition of amide group in air and segregation of margin group were the main causes of the adverse changes in mechanical behavior induced by the short-term UV radiation, and the short-term UV ageing mainly affect the skin region of PPTA fibers.