Based On PAN/DMSO Study On Gel Formation Mechanism In Long Period Operation Of Continuous Polymerization

Due to the excellent properties of carbon fiber,now it has become an indispensable material in the military and civilian fields.In industrial production,polyacrylonitrile(PAN)-based carbon fiber dominates.Dry-jet wet spinning process is one of the main processes for the preparation of PAN based carbon fiber raw silk.It is highly valued by the industry because of its fast and efficient characteristics.At the same time,due to the particularity of the process of dry stretch and high stretch rate of dry-jet wet spinning,it makes more demanding requirements on the quality of PAN solution.However,during the production of acrylonitrile(AN)continuous solution polymerization,the formation of gel in solution has become an important factor affecting the quality and properties of the filament and its carbon fiber.Therefore,it is of great significance to study the formation mechanism of gel in the polymerization of acrylonitrile in continuous solution,which will be the scientific basis for the development of corresponding gel inhibition technology.Based on the analysis of gel phenomenon in actual production and modification trial production,the behavior of gel on the surface of metal,ceramic and low surface energy plastics is analyzed,and the formation law of different gels is studied,and the internal mechanism of gel production is revealed.Results show as follows:1?The inner wall of the polymerizer has the tendency of decreasing surface energy.When the flow velocity of the liquid on its surface is relatively slow,because of the adsorption of inner wall,the PAN molecular chains in the solution interlace and fold together,and then desolvent to form the adsorption gel growth points.A large number of exposed PAN molecular chain segments on the surface of many gel growth sites further adsorb the PAN molecular chain segments in the solution through intermolecular forces and intertwine with them to form the adsorption gels.As time goes on,the adsorbed gel system continuously adsorbs the surrounding PAN molecular segments.These PAN molecular chains are continuously compressed in the process of continuous stacking and tangling,and the dispersion medium dimethyl sulfoxide(DMSO)is gradually precipitated,which makes the PAN molecular chains interlaced and entangled more tightly in the gel system,and finally the adsorbed gels can not be completely dissolved by the DMSO.2?In the rough stainless steel surface,there are a lot of poorly polished solder joints,tool scratches and other defects.At the end of these defects,there are many sharp tips with high surface charge density.And the groups of PAN molecular chains in the solution are accompanied by charged groups such as carbon-oxygen double bond and cyanogroup.As a result,PAN molecular chains are constantly drawn to the stainless steel tip and entangled with each other.At the same time,these defects will be filled in and entangled with these clusters of molecular chains,forming a closer physical adsorption.Then,these clusters of molecular chains desolvent to form a rough point gel growth points.Because of the continuity of the tip discharge,the PAN molecular chains on the gel surface also carry the corresponding charge.The PAN molecular chain segments in the solution are gradually adsorbed under the dual action of electrostatic adsorption and intermolecular force.These PAN molecular chains are constantly superimposed and staggered.Finally,the rough point gels are formed.3?When the mixing effect in some parts of the polymerizer is poor,the heat transfer effect will become worse or the contact between the solution and the mixed monomers will be in a relatively static state.Both of these conditions are likely to cause a sharp contraction of some PAN chains in the solution,followed by clumping and desolvation to form microgels.In addition,the adsorption gels will re-enter the solution due to dissolution or rubbing and other reasons,these mixtures re-entered the solution also included microgels.