| The structure and properties of carbon fiber precursors directly affects the mechanical properties of carbon fibers, and provide a theoretical basis for carbon fibers performance. We carry out the research on carbon fiber precursors from liquefied wood in phenol. In this paper, structure of precursors in curing process were systemically studied, containing microcrystalline structureor, pore structure; The effects of factors of curing process on chmical groups of precursors and the evolution on molecular structure of precursors were investigated; dynamical parameter and thermostability were analyzed by TG. Theresults are as follows:(1)XRD shows:Fir powder has typical diffraction peaks of cellulose I. After liquefication, typical peaks of cellulose I disappeared, instead of a large diffuse peak appeared, so carbon atoms of liquefied wood is amorphous structure. A new diffraction peaks appeared at 18.8 in as-spun fibers and precursors which means the establishment of new structure, carbon atoms change into crystalline structure. The crystallinity of precursors bigger than as-spun fibers. The factors of Curing affect crystallinity of precursors. The crystallinity of precursors increased obviously with increasing the hydrochloric acid concentration,the maximum crystallinity of 28.79% when the hydrochloric acid concentration got to 15%. The crystallinity of precursors were gradually improved at different curing temperature,the fastest growing rate curing temperature of 85℃, and improved the curing temperature, the crystallinity decreased. Improve the heating rate, the crystallinity of precursors increased, but the heating rate higher than 15℃/t, crystallinity increased sharply and then rapidly declined.(2)Adsorption isotherm curve of as-spun fibers and precursors belong to type II adsorption isotherm. BET surface area were 0.517m2/g of as-spun fiber and 0.142 m2/g of precursor, less than 1 m2/g, average pore radius were less than 2nm, so they are non-porous structure materials.(3)The absorption peak of Hydroxyl of 3440 cm-1 was increased and shifted to lower wave as time, methylene ether bond of 1172 cm-1 was high at 3 h, then broadened and methylene absorption peak of 2930 cm-1 occurred at 4 h. It is concluded that more hydroxymethyl phenols were formed by CH2OH reacted with fibers in longer time, then condensated between hydroxymethyl phenols or hydroxymethyl phenol with phenol, so cross-linking increased of precursors.85℃is a turing point for Hydroxyl of 3426 cm-1 and methylene ether bond of 1172 cm-1, because +CH2OH reacted with fibers and formed a highly cross-linking structure. At a lower concentration of hydrochloric acid, the higher hydrochloric acid concentration the stronger absorption peaks of 3426 cm-1 and 1172 cm-1, when hydrochloric acidconcentration over than 15%, the absorption peaks reduced. When the Heating rate is 15℃/h, the ydroxyl, methylene ether, benzene ring absorption peak were significantly lower, methylene absorption peak.15℃/h was a turning point for the group, quickly heating rate formed a dense layer at the surface of precursors, and affected the degree of integration +CH20H and fibers.(4)The as-spun fibers and precursors main elements were C and O, but the ratio of O/C increased after curing treatment. The two can fit three peaks,graphite carbon, carbon connected phonolic hydroxyl, carbonyl. Curing treatment, carbon connected phonolic hydroxyl rised to 40.26% from 16.3%.(5)the apparent activation energy of as-spun fibers is 31.31 KJ/mol, after curing treatment, the apparent activation energy of precursors was 39.18 KJ/mol, indicating a hughly cross-linked network structure was formed between curing reaction. When the hydrochloric acid concentration got to 15%,the weight loss rate of precursors reached a minimum 38.72%. Curing time increased from 1 h to 4 h, the weight loss rate decreased to 59.96%. The minimum weight loss of 46.39% appeared at 85℃, when curing temperature is higher than 85℃, the weight loss rete of precursors gone up,59.96% of weight loss rate in 95℃. |
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