| Dry-wet spinning,also called dry-jet wet spinning,is a spinning method which can not only achieve high performance PAN precursor and carbon fiber,but also reduce production costs by high speed spinning.It has great potential for development.In the solidification stage of spinning,the diffusion of solvent has an important effect on the formation of fiber structure,at the same time,the fiber structure formed at this stage will hinder the redistribution of the solvent.Since high spinning speed of the dry-jet wet spinning shortens the fiber solidification molding time greatly,it is a worthy subject to study how to make the solvent diffusion well and to make the fiber structure suitable for follow-up solvent diffusion in the limited time.The previous research of solvent diffusion is generally limited to the simulation and theoretical calculation of diffusion coefficient.The relationship between solvent diffusion and fiber structure is also limited to macroscopic theoretical analysis,and there is no more detailed analysis of the interaction between the two effects.In order to realize high speed spinning,the research scope of this study is limited in low concentration area.The PAN nascent fibers and water treatment fibers were prepared by dry-wet spinning under different solidification conditions.The solvent content,fiber compactness,distribution of the solvent and density change in the fiber radial direction were qualitatively and quantitatively characterized,and the relationship between the solvent diffusion and the dense structure of the fiber was studied on the whole and micro-area.The main conclusions were as follows:1.The solvent content in PAN nascent fibers decrease with the increase of coagulation bath temperature.Meanwhile,with the concentration of coagulation bath increased to a certain extent,the effect of fiber structure on the diffusion of solvent is highlighted,so that the solvent content of the nascent fiber increase first and then decrease.2.The effect of coagulation bath temperature on the formation of dense structure of PAN nascent fiber and the diffusion of solvent is single,while the effect of coagulation bath concentration is relatively complex.The effect of coagulation bath temperature on the formation of the dense structure and the diffusion of the solvent is generally greater than that of the coagulation bath.3.In the PAN nascent fiber forming process,the initial structure formed by early diffusion has laid the basic structure of the fiber.The solvent diffusion in the late stage of solidification benefits the increase of the core compactness,but it has little effect on the fiber structure which has been formed in the early stage,and the effect of the pre-formed fiber structure on the late solvent diffusion is obvious.4.Due to increased PAN nascent fiber density hinders solvent diffusion,the solvent content of the nascent fiber increases with the density on the whole;in micro-area,both the primary fibers and the water treatment fibers show that lower solvent content leads to higher density,while structure is loose relatively if the solvent content is high.5.The shape of the PAN nascent fiber cross-section has an important effect on solvent distribution and compactness change of the fiber radial.The content of solvent of the outer edge is higher than that of the core in round section fiber,and the compact degree decreases gradually from the cortex to the core.Because of the different stress,the content of the solvent in the core of the non-circular section fiber is reduced,and the density of the core is improved so much that the density of the core is higher than that of the cortex.6?In the research scope of the thesis,under the condition of high concentration(36.2%)and low temperature(5?),the moderate solidification benefits not only the increases of fiber density,but also the reduction of the residual amount of solvent in the fiber.The condition is suitable for the solidification of the PAN precursor by dry-wet spinning. |
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