Preparation And Investigation Of Pre-oxidized Polyacrylonitrile Based Carbon Fibers Modified With Hydroxylammonium Chloride

Systematic investigation of the modification, thermostabilization and mechanism ofpolyacrylonitrile (PAN) based carbon fibers modified via hydroxylamine hydrochloride arereported in this study. The precursor fibers of PAN were prepared through Gel-Spinning fromcommercialized PAN, which MWis90,000, and then modified via hydroxylaminehydrochloride, and pre-oxidized through Thermal stability processing after drawn. Thepreoxidation PAN fibers were prepared. The results showed that the spin-able concentrationwas15-35g/100mL and the as-spun fibers with the highest drawing ratio was prepared withthe concentration of28g/100mL, spun at80℃and solidified at the coagulating bath of10℃.The greatest tensile strengths reached398MPa of modified PAN fiber was achieved throughthe process of modifying in the hydroxylamine hydrochloride solution with the concentrationof1.0mol/mL, pH2.6at the temperature of75℃for5minutes and then drawn at140℃through the drawing rate of25mm/min upto a draw ratio of8. The greatest tensile strengthsreached732MPa of pre-oxidized MPAN1.0-75-5-2.6fiber was achieved through the process ofpre-oxidizing at the temperature of220℃for4hour and firstly drawn at140℃through thedrawing rate of25mm/min upto a draw ratio of12. As showed in the FI-TR spectra of MPANfibers, the C≡N stretching vibrations was shrinking therewith the C=NH vibration wasenlarging as the concentrations, pH, modifying temperatures and time added. The trend wassimilarly happened to pre-oxidized MPAN1.0-75-5-2.6fibers. Whatmore, the C≡N stretchingvibrations was almost disappeared when pre-oxidized above200℃over4hours. Thermalanalysis found that the melting point and percentage crystallinity of MPAN fibers which weremodified in hydroxylamine hydrochloride solution of different concentrations and pH atvarying temperatures for varying time were both decreased significantly with theconcentrations, pH, modifying temperatures and time added. Orientation factor values ofPAN28-80-10and MPAN1.0-75-5-2.6fiber specimens increased as they were drawn at140℃,25mm/min up to a higher draw ratio. But the orientation factor values of pre-oxidizedMPAN1.0-75-5-2.6fibers were decreased as the pre-oxidizing temperatures and time added.Compared with the SEM micrographs of PAN28-80-10drawn at140℃,25mm/min upto a drawratio of12and then preoxidized at varying temperatures for varying time, the preoxidizedpreoxidized MPAN1.0-75-5-2.6prepared the same way had a more tight cross-section with lesswholes. So we can conclude that modification contributed to decrease the preoxiditiontemperature significantly.