Analysis Of The Reaction Process Of PAN Precursor Preoxidation Process By Chromatic Aberration Method

The development of carbon fiber is the competition of technology and cost.Enterprises are constantly pursuing technology maturity,but also constantly considering how to reduce production costs.Quality cost reduction is one of the effective ways to reduce production cost.In this paper,the traditional characterization method of preoxidation degree is broken.Through the study of the correlation between the changes in fiber color and the changes of fiber structure to explore the feasibility of color difference method to characterize the preoxidation process,the standard test method of color difference method to characterize the preoxidation degree is established.The method is used to reflect the preoxidation process on-line quickly and effectively,so as to reduce the cost of detection,solve the process problem which can’t be adjusted in time,reduce the loss of carbon fiber quality cost.In this paper,preoxidation fibers with different structures are prepared by adjusting the key preoxidation process parameters such as temperature,time,drafting etc.Apply multiple characterization methods(e.g.Fourier Transform Infrared Spectroscopy(FT-IR),Color Difference Meter,Differential Scanning Calorimetry(DSC),13C Solid Nuclear Magnetic Spectroscopy(13C-NMR),Density etc),to explore correlation between preoxidation degree and preoxidized fibers color difference at the early stage of preoxidation process for characterizing preoxidation degree on industrial production line.1.The determined test and calculation method can stably characterize preoxidized fibers by L*、a*、b*values after adjusting test factors such as test angle、environment、sample position etc.2.Different chromogenic groups are produced gradually in preoxidized fibers,which can absorb light of a certain wavelength in visible light region,resulting in changes of preoxidized fibers color.The total color difference Δ Eab*and L*can well reflect the rule of the pre-oxidation color change.3.In the early stage of preoxidation,changes in low conjugated groups lead to changes in fiber yellowness,that can be reflected well by lnb value.4.During the preoxidation process,the applied draft does not cause chemical reaction of preoxidized fiber,so there is no correlation between fiber shrinkage and color difference.5.The characteristics of the preoxidized fiber circular structure C=C and C=N have a positive effect on the color difference of the fiber in the early stage of preoxidation,reflected as the obvious change trend of△Eab*and L*.As the temperature rises,the fiber continuously undergoes cyclization,oxidation,dehydrogenation and other reactions,generating more C=N,C=C,C=CH,C=O and other chromophores,forming a network conjugated systems.And the color difference method can accurately relect this process.During the preoxidation process,the conjugation system form gradually in the preoxidized fibers,so as to the change of fiber color.The color change of the preoxidation fibers is the most intuitive performance of the change of fiber internal structure.And chromatic aberration method can indeedly reflect the early stage of preoxidation process and be used to guide production.