Effects Of Microwave Heating On The Structure And Properties Of PAN Preoxidized Fibers

PAN-based carbon fibers have excellent properties,including high specific strength,heat resistance and corrosion resistance.It is widely used in aerospace,energy equipment,transportation,sports and leisure.With the rapid development of economy and society,the demand for high-performance PAN-based carbon fiber and its composite products from various industries is increasing.Given the current production capacity,there is a huge gap in the production and demand for PAN-based carbon fibers.Oxidative stabilization is the critical step for preparing PAN-based carbon fibers.Microwave heating has the advantages of uniform heating,fast speed and instantaneous control,which is conducive to solving the problem of temperature gradient.For this reason,this paper proposes an innovative microwave oxidative stabilization.In addition,in order to solve the problem of oxygen concentration gradient,this paper proposes to use a strong oxidant to modify the PAN precursor.These two methods are combined in order to solve the problems of heat and mass transfer in the conventional oxidative stabilization process of PAN precursors,in order to obtain high-performance PAN stabilized fibers.In this paper,the effect of microwave heating on the structure and properties of PAN stabilized fibers was studied.The modification of PAN precursors by oxidants H2O2,KMnO4,and KClO3 was carried out.Microwave heating oxidative stabilization was performed on the modified fibers under the optimal modification conditions.Characterization analysis of dielectric properties,bulk density,chemical structure,chemical composition,crystal structure,microscopic structure,degree of graphitization,and mechanical properties.The main results are as follows:(1)The contact angles of H2O2 and PAN fibers(PFs)were 65.7�and 67.6�,and the wettability was good.H2O2 modification can shorten the oxidative stabilization time and increase the bulk density.Compared with microwave-heated stabilized fibers(MSFs5),H2O2 modified microwave stabilized fibers(H-MSFs5)had a higher bulk density(1.403 g/cm3).H-MSFs5 had a greater extent of reaction(EOR)(0.697),better surface finish,and fewer defects.The fineness of H-MSFs5 was 1.05 dtex,the tensile strength was 1.60 cN/dtex,the initial modulus was 74.13 cN/dtex,and the elongation at break was 3.49%.H-MSFs5 had higher stability and better performance than MSFs5.(2)The contact angles of KMnO4 and PFs were 76.7� and 76.4�,and the wettability was good.The optimal processing conditions were a KMnO4 concentration of 2 wt.%,temperature of 80? and duration of 30 min.PFs were polar materials,and the dielectric constant of the precursors was reduced after modification.Compared with MSFs5,the bulk density of KMnO4 modified microwave stabilized fibers(Mn-MSFs5)was increased by 0.04 g/cm3.EOR increased by 10%.The O content of Mn-MSFs5 and the composition of O-containing functional groups were higher.After oxidative stabilization,the Mn element did not exist on the fiber surface and did not affect the structure of the stabilized fibers.The fineness of Mn-MSFs5 was 1.07 dtex,the tensile strength was 1.52 cN/dtex,the initial modulus was 59.3 cN/dtex,and the elongation at break was 13.5%.Mn-MSFs5 had a higher degree of stabilization and mechanical properties.The chemical reactions of KMnO4 modified PFs in microwave oxidative stabilization were cyclization,dehydrogenation and oxidation.(3)The contact angles of KClO3 and PFs were 66.9� and 66.4�,and the wettability was the best.The optimal processing conditions were a KClO3 concentration of 15 wt.%and duration of 60 min.The dielectric constant of PFs increased after modification.Compared with MSFs5,the bulk density of KClO3 modified microwave stabilized fibers(Cl-MSFs5)was increased by 0.07 g/cm3.The EOR value increased by 8.2%.There was no C1 element on the surface of Cl-MSFs5,which did not affect the structure of the stabilized fibers.The fineness of Cl-MSFs5 was 1.43 dtex,the tensile strength was 1.13 cN/dtex,the initial modulus was 58.24 cN/dtex,and the elongation at break was 4.97%.Cl-MSFs5 had a higher degree of stabilization and mechanical properties.KClO3 modified PFs microwave oxidative stabilization first undergoes cyclization reaction,then dehydrogenation and oxidation reactions.(4)The optimal concentration of modification is 15 wt.%,and the time is 60 min.The stabilized fibers obtained by microwave oxidative stabilization of KClO3 modified PFs has the best mechanical properties and the highest degree of oxidative stabilization.