Study On Phase Transition Of PAN/DMSO Solution During Gelation And Fiberization

The gel transition of polyacrylonitrile(PAN)solution during the spinning process was investigated by rheology,dynamic light scattering,X-ray diffraction and polarized infrared spectroscopy methods in this thesis.The influencing factors and mechanism of gelation transition were explored by characterizing the thermal driving force of gelation transition,gel stability,and the morphology of PAN chains within the gel.The effect of gelation transition on the aggregation structure of PAN nascent fibers was also discussed from the viewpoints of crystalline and orientation structure.The results indicated that,(1)The increasing of the molecular weight of PAN would reduce the thermal driving force headed for the gel transition of PAN solution.When the viscosity average molecular weight of PAN reaches 13.3 × 104,the gel transition temperature rises to 33.1?.The higher the molecular weight of PAN,the more physical crosslink points can be formed between the PAN chains,as well as the more stable the gel network structure.(2)Additives with higher polarity than dimethyl sulfoxide(DMSO)solvent could reduce the thermal driving force needed for the gel transition of PAN solution,and increase the physical cross-linking between PAN chains,thereby forming highly elastic and stable gel.A model of the gel transition of the PAN solution in the fiberization process was proposed from the perspective of polymer chains morphology to describe the formation and evolution of the gel structure.The mechanism of gel transition is the formation of large-scale PAN molecular clusters.The additive could weaken the intermolecular force between PAN segments and solvents,therefore promoting the fusion of polymer clusters,and accelerating the formation of macromolecular clusters.The mechanism of increasing the molecular weight is similar to above.(3)The higher the degree of gelation of the spinning solution in the solidification stage or the more developed gel structure of the spinning dope,could inhibit the crystallization of PAN nascent fibers.The former inhibits nucleation,while the latter inhibits the growth of nuclei.The former can enhance the degree of orientation of the nascent fibers,while the latter can reduce the degree of orientation.