Surface Modification And Irradiation Effects On The Structure And Performance Of Domestic PIPD Fiber

PIPD is poly { 2,6-diimidaazo-[4,5-b: 4’, 5’-e]pyridinylene-1,4-(2,5-dihydroxy) phenylene}, it was first developed by Akzo Nobel company, and its excellent mechanical properties and good adhesion properties with the resin making it one of the current concerned high performance organic fiber. However, the preparation process is confidential and the research of PIPD is late in China, which resulted the slow pace of development.Therefore, it is very important to strengthen the research of domestic PIPD fibers. In this paper, the influence of surface modification and gamma ray irradiation on the structure and mechanical pr operties of domestic PIPD fibers were studied. Meanwhile, UV aging resistance of domestic PIPD fiber s, PBO fibers and Kevlar fibers were studied.In this paper, structure and mechanical properties of PIPD fibers were studied by grafting dendritic PAMAM and coating dopamine and silane coupling agent KH-550 on the surface of PIPD fibers. The experimental results showed that, after grafting dendritic PAMAM and coating dopamine, there were particles on the surface of PIPD fibers, they were the aggregates of graft molecular on the fiber surface.The surface wettability of PIPD fiber significantly improved, the number of surface polar groups significantly increased, but the mechanical properties of fibers and the interfacial shear strength of epoxy composites were decreased. This may be due to the damage of the protonation of basic solvent for molecular hydrogen bonding between the PIPD fibers. Resulted in the force between the fiber surface layer microfibers reduced. Because of the fiber surface damage occured before the composites under an external force. After coating silane coupling agent KH-550, uniform KH-550 molecular layer repaired the defects of PIPD fiber surface, so PIPD fiber mechanical strength was improved. A large number of amino in the structure of KH-550 improved the fiber surface wettability, and participated in the curing reaction of the epoxy matrix, formed a chemical bond at the interface, improved the interfacial bond strength of the composite. When the concentration of KH-550 was 20%, the modification effect was the best. The tensile strength and composite materials interfacial shear strength of PIPD fibers increased by 4.6% and 21%.Used γ- ray irradiation for modifying PIPD fibers, by changing the γ- ray irradiation dose, studied the high-energy rays irradiation on the properties and microstructure of PIPD fibers. After γ- ray irradiation, the mechanical strength of the fibers showed a trend of decreasing first and then increasing and decreasing again. When the radiation dose is 600 KGy, the mechanical strength of fiber is the maximized. Nanoindentation test results showed that, After γ- ray irradiation, The nano-hardness and modulus trend of PIPD fibers was the same with the mechanical strength. X-ray diffraction(XRD) analysis showed that the fiber structure and molecular weight have been changed after irradiation, Molecular weight, degree of crystallinity and the grain size decreased first and then increased. When the radiation dose is 600 KGy, molecular weight, degree of crystallinity and grain size were the maximized. In γ- ray irradiation process, molecular degradation and cross-linking reactions occured simultaneously in PIPD fibers. When the radiation dose was small, the imperfect and flawed portion of PIPD fibers degraded. The degradation process to be the main structural changes.Molecular weight, degree of crystallinity, the crystallite size decreased. Meanwhile, the macroscopic properties of hardness, modulus and tensile strength of the f ibers decreased. When the radiation dose was increased, cross-linking reaction to took the advantage of PIPD fibers. At this time a gradual increase in the mechanical properties of the fibers happened. When the radiation dose was more than 600 K Gy, PIPD molecular chain gradually degrade under high-intensity radiation, resulted in the mechanical properties decreased.The tensile strength of ultraviolet aging domestic PIPD fibers, PBO fibers and Kevlar fibers were studied. The experimental results showed that, After 72 h UV aging, Domestic PIPD fiber tensile strength retention rate could be 78%, UV-visible spectroscopy results showed that, in the three fibers, PIPD fiber absorption strength in the ultraviolet region was the lowest. Scanning electron microscopy showed, after UV aging, the surface of PIPD fiber did not change significantly. XRD tests showed that after UV aging, PIPD fibers structure did not change significantly. The degree of crystallinity was the same with the fiber did’t treated. The resistance of UV aging of domestic PIPD fibers are better than the PBO and Kevlar fibers.