Study On The Inductive Effect Of Graphene Oxide Oxygen-containing Structure On PAN Pre-oxidation Process

Since graphene was discovered in 2004,it has gained significant attention due to its excellent physicochemical properties.Graphene is expected to be assembled into macroscopic materials with its original prominent attributes or modify existing materials to improve performance.Graphene oxide(GO)is widely applied in the macroscopic assembly of graphene or the modification of traditional materials due to its good dispersibility.Many scholars have mixed GO or graphene and polyacrylonitrile(PAN)in various proportions to prepare composite fibers in order to improve the property of carbon fibers.But the results show that the property of composite fibers fails to meet the expectations of modification.Compared with the traditional carbon fiber,the performance of composite fibers is poor.The reason is that the effect of graphene(or GO)on the PAN thermal reaction during the pre-oxidation causes the structure and performance of the final carbon fiber to fail to meet the expected modification goal.During the preparation of carbon fiber,it has to go through a series of complicated crafts such as pre-oxidation and carbonization.The change of heat treatment conditions will have a great impact on the structure and performance of carbon fiber.The thermal reaction mechanism of PAN in this process has been discussed in depth in many works.But the lack of research on the interaction between graphene or GO and PAN has become a key factor restricting the high performance of composite fibers.In this paper,graphene-PAN and GO-PAN composite fibers were prepared by wet-spinning.Through the research of enthalpy in pre-oxidation of composite fibers,the effect of ?-? conjugated structure of graphene on dehydrogenation and cyclization reactions of PAN during the pre-oxidation is revealed;By studying the influence of oxygen-containing functional groups in GO on the reaction enthalpy of PAN during pre-oxidation process,the influencing mechanism of oxygen-containing structure on pre-oxidation behavior of PAN is discovered;The study of pre-oxidation and carbonization behavior in composite fiber reveals the synergistic effect of the conjugate induction of graphene,the oxygen-containing structure inside the fiber,and the atmosphereal oxygen in the thermal reaction process on the PAN pre-oxidation structure and its thermal stability.Research indicates:(1)When graphene is added to PAN,the initial temperature and exothermic process of the thermal reaction of PAN are not affected.And this phenomenon is unrelated to ambient atmosphere,but has a certain effect on the reaction enthalpy.After adding GO to PAN,the exothermic process of the thermal reaction changes.With the increase of the amount of GO,the exothermic peak of PAN moves to the higher temperature,and full width at half maximum of peak gradually decreases,the reaction enthalpy almost unchanged.(2)The ?-? conjugated structure of graphene can induce the cyclization and dehydrogenation of PAN.The induced dehydrogenation is mainly pyrolytic dehydrogenation.The ?-? structure in GO still has the inducing effect on PAN cyclization and dehydrogenation.And its induced dehydrogenation is the coexistence of pyrolytic dehydrogenation and oxidative dehydrogenation.The conjugated structure induced by graphene or GO during the pre-oxidation process is not prone to be oxidized.(3)In heat treatment process under anaerobic atmosphere,the structure of PAN induced by graphene does not show better thermal stability,while the structure induced by GO has relatively better thermal stability,which may be resulted of the oxygen-containing structure in graphene oxide.(4)The G-PAN and GO-PAN are pre-oxidized with the size requirements that there is no skin-core structure in composite fiber samples.The PAN sample with lwt%graphene has a carbonization yield of 53.17%at 1000?;while the carbonization yield of PAN sample with 1wt%GO under the same conditions was 47.72%,which may be due to the steric hindrance effect of oxygencontaining functional groups in GO.It resulted in the weaker cyclization inducing effect on PAN.(5)The PAN composite fiber with different content of graphene(or GO)is processed in a pre-oxidation process that simulates the preparation of PAN carbon fiber.As the content of graphene oxide increases from 0.1%to 10%,the carbonization yield of PAN samples at 1000? increases from 55.09%to 66.48%and the rate of weight loss decreases from 44.91%to 33.52%;while for graphene without oxygen-containing functional group,under the same addition content and heat treatment conditions,the carbonization yield of PAN samples at 1000? increases from 54.4%to 63.18%and the rate of weight loss decreases from 45.6%to 36.82%,which are more than the corresponding addition of GO,but all are less than the weight loss percent of pure PAN of 57.42%.(6)Under the same pre-oxidation and carbonization conditions,the content of graphene or GO doesn't affect the graphitization degree of PAN composite fiber,but the graphitization degree of PAN composite fiber with graphene is slightly higher than that of PAN composite fiber with GO.