Study On The Aging Mechanism And Safety Of Polyether Polyurethane Fibers

Polyether polyurethane fibers were affected by the high temperature and UV radiation when they were used as the adaptive material in Z-pinch accelerator while the fibers were also affected by the alkaline environment during the dyeing and finishing process.After aged under these environment,several properties like elongation of the fibers degraded,which would affect the safety of fibers in use.Hence,from the perspective of fiber's intrinsic safety and the safety of fibers in use,accelerated aging method was used to simulate high temperature environment,alkali solution immersion environment and UV radiation&high temperature&high humidity environment.Furthermore,the aging mechanism and safety of fibers under these environments were studied in this paper.The main research results were concluded as follows.?1?FTIR,¹H NMR,AFM,DSC,DMA,TG,MCC and universal material testing machine were used to investigate the microwave aging mechanism and properties'changes of PU fibers.It was found that,during the aging process,the CH₂ between benzene rings were oxidized to C=O while the NH,C-O-C and hydrogen bonds were broken up.With the increase of aging time,the surface roughness of fibers increased while pits and clusters appeared on the smooth surface successively.Besides,the mobility of segments decreased and the compatibility of segments increased resulting in the decrease of Tg,s,?35?Tg,s,storage modulus and the degree of microphase separation.Also,tensile elongation at break,resilient elastic recovery at 300%and internal friction of fibers all decreased.Meanwhile,the thermal stability of fibers decreased while heat release capacity?HRC?,peak heat release rate?pHRR?and total heat release?THR?all increased.This indicated combustion potential and potential fire risk of fibers would increase when they were used under high temperature for a long term.?2?FTIR,GPC,DMA,moisture absorption measurements and mechanical property tests were used to investigate the alkaline solution immersion mechanism and properties'changes of fibers.It was found that,during the aging process,the hydrolysis occurred in carbamate and urea groups of fibers.Furthermore,the type of hydrogen bonds gradually transformed from intramolecular hydrogen bonds of NH_C=O=O to intramolecular hydrogen bonds between NH and water molecules,which decreased the degree of microphase separation and increased the degree of microphase mixing.Besides,weight-average molar mass and number-average molar mass of fibers decreased and molecular weight distribution broadened.The behaviour of sorption curves in unaged and aged 60h fibers conformed to Fickian diffusion,while the behaviour of sorption curves in aged 120h,180h,240h and 300h fibers didn't conform to Fickian diffusion.Moreover,the internal friction of fibers decreased and the volume relaxation process of segments became faster,causing the increase of the creep strain,along with the decrease of the soft chains relaxation apparent activation energy,tensile elongation at break and resilient elastic recovery at 300%.?3?FTIR,SAXS,AFM,DMA,mechanical property tests and fault tree analysis were used to investigate synergetic aging mechanism of fibers under UV irradiation in high temperature and high humidity environment.It was found that,six reactions were included during the aging process,the first reaction was to form hydrogen peroxide in the presence of UV irradiation,water and oxygen environment;the second reaction was assigned to the formation of carboxylic acids and alcohols under high temperature and high humidity;the third reaction was the post-curing reaction occurred by the isocyanate generated under depolymerization and aging products?alcohols?generated from the second reaction;the forth reaction showed the re-polymerization occurred by aging products?alcohols?and hard segments;the fifth reaction was to form quinone products under UV irradiation;the break up of chemical bonds and chain scissions caused by UV exposure was considered as the sixth reaction.From 0.6-0.9W/m²,thermal motion of the molecules was accelerated under high temperature while the loose molecular structure of fibers was formed under high humidity.Thus,high temperature and high humidity had a positive effect on the first,second,third and forth reaction which were associated with the high humidity and had a negative effect on the fifth and sixth reaction.However,from 1.2-1.5W/m²,UV irradiation was more destructive while the first,second,third and forth reaction were suppressed and the fifth and sixth reaction were promoted.Moreover,from 0.6-0.9W/m²,UV irradiation could promote the degree of microphase separation,leading to the increase of internal friction,T_g,s and radius of gyration;from 1.2-1.5W/m²,UV irradiation could destroy the microphase separated structure,leading to the decrease of internal friction,T_g,s and radius of gyration.During the synergetic aging process,tensile elongation at break and resilient elastic recovery at 300%of fibers both decreased.For polyurethane fibers used as adaptive fibers in Z-pinch accelerators,to solve the fiber's mechanical failure problem,it was necessary to strictly control the quality of the fiber in produce stage to ensure the consummate structure and excellent performance of the fiber.What's more,the strict inspection system and effective punishment measures was also needed in use.