Study on structure and properties of polyacrylonitrile-polyamidoxime fibers prepared via grafting method
Polyacrylonitrilated-polyamidoxime(PAN-PAO)fibers were prepared through a three-step method involving poly-merization,modification and grafting.Firstly,low-relative molecular mass PAN was prepared by free radical polymerization;then soluble PAO was prepared by amidoxime modification of PAN with hydroxylamine hydrochloride;finally,PAO was grafted onto carboxylated polyacrylonitrile(PAN-COOH)fibers to prepare PAN-PAO fibers.The effects of polymerization reaction time and temperature on the relative molecular mass of PAN were studied,as were the effects of PAN relative molecular mass,grafting re-action time and temperature on the content of amidoxime(AO)groups in PAN-PAO fibers.The structure and mechanical proper-ties of PAN-PAO fibers were characterized.The results showed that the optimal polymerization reaction conditions were a reaction time of 30 min and reaction temperature of 80 ℃,resulting in a PAN number average relative molecular mass of 29 300;the op-timal grafting reaction conditions were a PAN number average relative molecular mass lower than 30 000,reaction time of 6 h and reaction temperature of 70 ℃,contributing an AO group content of 1.09 mmol/g to the prepared PAN-PAO fibers;the pres-ence of C=N and N—O characteristic peaks in infrared spectra confirmed the successful preparation of PAN-PAO fibers by graft-ing method;and the breaking strength of PAN-PAO fibers was 3.06 cN/dtex when the AO content was 1.1 mmol/g,which was higher than that of polyacrylonitrile-amidoxine(PAN-AO)fibers(2.73 cN/dtex)prepared by direct method.
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