Study On The Weather Fastness Of Polyimide Fibers And The Response Of Flxible Strucures To Their Properties

High-performance polyimide fiber combines high strength and high modulus with good weather resistance and can be used at 200?300? for a long time.The four high-performance organic fibers,polyphthaloyl p-phenylenediamine(PPTA),aramid fiber ?,poly-p-phenylene benzobisoxazole(PBO)and polyimide(PI)fibers were heat treated at 250??450? to study dimensional stability and mechanical properties,tracking the evolution of their chemical structure,condensed structure and morphology after heat treatment,and combing with electron cloud density and bond order to study the heat resistance mechanism.The results showed that under high temperature conditions,the chemical structure damage of PPTA and aramid fiber ? was the main factor leading to the decline of mechanical properties.At the same time,the defect structure and crystallinity of the fiber also had a significant effect on the heat resistance;Before 400?,the PI fiber had the highest strength retention;the PBO fiber had the best thermal dimensional stability.By studying the UV resistance of PPTA,aramid fiber ?,PBO and polyimide fiber,the results showed that the aramid fiber ? and PI fiber had almost no loss of mechanical strength with the illumination of UV lamps,and their UV resistance was the most excellent,followed by PPTA fiber,the strength of PBO fiber decreased fastest with the irradiation of UV lamp,it had the worst UV resistance.By studying the chemical stability of PPTA,aramid fiber ?,PBO and polyimide fiber,the results showed that PPTA and aramid fiber ? had certain loss of mechanical strength after acid solution treatment,their acid resistance was poor,however,their alkali resistance is excellent.And polyimide fiber had poor hydrochloric acid resistance and alkali resistance alkali resistance.After the four fibers were treated with salt solutions and organic solvents at room temperature,there was almost no loss of mechanical strength,indicating that the four fibers were superior in salt tolerance and organic solvent resistance.In order to further study the thermal properties of PI fiber,this paper used the two-step process with BPDA,P-PDA and APB134 as raw materials to prepare a series of BPA-type polyimide fibers from rigid to flexible,and studied the effects of flexible structures on the thermal properties and other properties of PI fibers.The results showed that with the increase of flexible structures,the thermal decomposition temperature of the fiber decreased gradually.The introduction of flexible structures destroyed the regularity of the fiber,the fiber changed from crystalline to amorphous,and the fiber flexibility increased,the elongation at break was greatly improved.In order to further study the effect of ether bond on the performance of polyimide fiber,the polyimide fiber of BPDA/p-PDA/ODA system was prepared by the same spinning conditions.The results showed that the increase of the ether bond didn't have much influence on the strength and the thermal decomposition temperature of the fiber,but the initial modulus of the fiber was lowered and the elongation at break was increased.