Highly Efficient Pre-oxidation Of Polyacrylonitrile Fiber And Responsivity Of Pre-oxidative Characteristic Structure

The thermal stabilization of polyacrylonitrile(PAN)carbon fiber is a very important and indispensable step in the production process.Under the catalysis of air oxygen,the cyano group of the PAN undergoes cleavage and cyclization,and the cyclization structure easily reacts with oxygen to generate oxygen structures,the presence of oxygen structures can lead to a decrease of performance in the carbon fibers.So,scientific optimization of the pre-oxidation process has become a focus of attention.Based on the review and analysis of a large number of documents,the paper carried out the research on the highly efficient pre-oxidation of PAN fibers and responsivity of pre-oxidative characteristic structure.By means of nuclear magnetic resonance(13C-NMR),element analysis(EA O mode),bulk density,mechanical properties,and so on,according to pre-oxidative equivalent time that correlates temperature effects with time effects,the pre-oxidative characteristic structures and the effect of temperature and time of PAN fibers were studied to establish the highly efficient formation mechanism of pre-oxidative structure.The results showed that:1.Based on the structural characteristics and evolution of the pre-oxidation process of PAN fibers,the oxygen structure and the cyclization structure of the fibers were quantitatively analyzed.The ratio of the two,the oxygen-to-cyclization ratio(OC),was defined as the characteristic structural parameter of the pre-oxidative fibers.When the OC of the fibers is 0.29,the carbon fibers has the best mechanical properties and the tensile strength is 5.51 GPa.2.The OC of PAN pre-oxidative fibers shows a decreasing and increasing rule with the pre-oxidation process.Under the pre-oxidative temperature lower than 230?,the cyclization structure of fibers increases rapidly,and the oxidation reaction does not occur easily,the OC value decreased with the progress of pre-oxidation.The pre-oxidative temperature ranged from 230-250?,and the OC decreased slowly.After the pre-oxidative temperature was greater than 250?,the oxidation reaction rate increased significantly,and the OC value gradually increased.3.Using OC as a control parameter to study the coupling effect of temperature and time in pre-oxidation of PAN fiber,a new pre-oxidation process was developed.Under the premise that the mechanical properties of prepared carbon fibers isn't reduced,the thermal treatment temperature zone is reduced from the traditional four zone to three zone,the total thermal treatment time was reduced from 60 minutes to 30 minutes.In this paper,the effects of PAN pre-oxidative fibers' cyclization structure,oxygen structure and oxygen cyclization ratio on the mechanical properties of carbon fibers was clarified,on this basis,the pre-oxidative equivalent time was used to explore the effect of time and temperature on the pre-oxidation process at different times,and the highly efficient control method of the pre-oxidative structure of PAN fibers was discussed which has great guiding significance to stabilization process in the future.