Multi-orientated One-dimensional SAXS Study Of Microvoids In PAN-based Carbon Fibers And Fibril

Nowadays, Polyacrylonitrile carbon fiber (PAN-based CF) arewidely used in many fields, such as advanced arms including nuke,strategical missile, secondary planet, aircraft, fighter plane andhidden fighter plane, because of which is the most crucial andimperative part of the reinforce of the composition.The flaws in the microstructure of CF are the mainrestriction of improving CF's performance. So quantitativecharacterization of CF's performance exactly is the foundation toinvestigat and improve the performance of carbon fiber. Theprocess of producing PAN-based CF is very complex whichinduces many flaws. These flaws decrease the strength of fiberobviously. These flaws include the structure flaws between thechain of polymer, holes and pores, crackles in the superficial,dislocations in crystal, impurities and so on. The pores includemacropores, micropores and the pores between the two kinds.But the micropores is the main reason which cause theconcentration of stress and the rupture of fibres. Based on theresults investigated before, PAN-based CF can be considered asystem made up of pores and graphite microlite. The imperfectivestack of the carbon atomic bands result in the formation ofmicrovoids, which seriously influence the performance of carbonfiber. So the study of microvoids attached much attention.Theroutine ways be taken usually to characterize the configuration ofmicropores in carbon fibers include TEM, SEM, BET,SAXS(small-angle x-ray scattering) etc. But the magnitude and thedistribution of microvoids in CF can not be characterized by theseways quantitative. So it is still a urgent question to be resolved. Themicrovoids in fibril will still exist in carbon fibres after seriesproduce process which impact the performance of CF seriously.The badly performance of fibril is the main reason that theperformance of carbon fibre made in china is behindhandrelatively. So charactering the connection between the performanceof fibril and the parameter of production.In this paper, multi-orientated one-dimensional SAXS is takenin a creative way to character the pores in PAN-based CF andfibils. By this way we can learn much information about CF'sstructure, such as mean cross-section radius (R), mean lengthprojected onto the fiber axis (L), relative content, oriented angle ofmicropores and so on. Usually these parameter can be obtainedonly by two-dimensional SAXS. We take the datas of scatteringintensity of differen orinted angle of fibrous axial, and simulate theways of two-dimensional SAXS to calculate the statisticalparameter of fibre by some theorem such as Porod theorem,Guinier method and invariant theorem. These parameter such as theR,L and oriented angle of fibri. This way can also been used tocharater the conformation of other kinds of fibres.Through analyzing the relation between conformation ofmicropore and technical parameter and mechanical performance offibres, we found some influencethe of different mechanicalparameter to fibrous conformation. The performance of carbonfibers have been notable improved after the generative departmentchange the mechanical parameter based on our analyse. This wayresolve the difficult problem of character the microporeconformation in fibers because the equipmen is too expensive to beadopted. So this work have important significance in fact. We candraw some conclusions about the evolvement of microvoids infibers produced by different mechanical parameter:1.During the production stage, the temperature of heattreatment have a deeply effect on the evolvement of microvoids infibers. The mean radius and oriented angle will be diminished inrational temperature of heat treatment, which is benefit for elevatethe performance of carbon fiber. But, the radius and oriented anglewill be enlarged in excessive temperature for thermal expansioneffects, which induce the pores run away out. Many flaws will beproduced during this course at the same time.2.Tensile figure of fibers is also a important parameter whichhave serious influences on the performance of carbon fiber. Tensedin a rational figure, the radius will shrink and t oriented angle willbe diminished. It also will be benefit to elevate performance ofcarbon fiber. On the contrary, excessive tensile figure will also dogreat harm to carbon fiber's performance.3.we also can learn that both coagulator concentration andapplication of steam impacts the evolvement of microvoidsdistinctly during carbon fiber production stage.Accordingly, it is very important to harmonize the technicalparameters in order to make the microvoids' shape changing, whichbenefit to elevate the mechanical capability of carbon fiber.