| Flat acrylic fiber as one of the acrylic products with higher added value has a very wide range of applications in the fields of artificial fur,animal toys,and high-end clothing.For the sodi?m thiocyanate(NaSCN)solvent system,due to the low solid content of polyacrylonitrile(PAN)in the spinning dope,the long spinning process,and the harsh coagulation conditions,the preparation of flat acrylic fiber is more difficult,and the spinning process will occur.Phenomenon such as sticky filaments and skin-core structure cause the product to have many defects,uneven dyeing,low flatness and other problems.The uniformity and stability of the solvent diffusion of the nascent fiber during the coagulation process are one of the main reasons for the above problems,but the research on the solvent diffusion kinetics of wet spinning of flat acrylic fiber in PAN/NaSCN system is very lacking,resulting in a serious lag in the development of flat acrylic fiber in China.To solve the above problems,this paper uses Fick's first and second laws to establish a solvent diffusion kinetic model for circular and flat acrylic fibers.Through experiments,the average concentration of solvents in the filaments under different coagulation conditions is measured,and the results are obtained by reverse fitting Diffusion coefficient under the above solidification conditions.Combining the principle of metal heat treatment and carburization,a solvent diffusion kinetic model of flat acrylic fiber was established,and the effect of solidification process on the distribution of solvent concentration in the thread was studied.Finally,using the above research results,a spinneret for 19D and 27D flat acrylic fiber spinning was designed,and 19D and 27D flat acrylic fiber were prepared by using the above-mentioned spinneret.The specific research content and conclusions are as follows:(1)PAN/NaSCN acrylic wet spinning diffusion kinetics and diffusion coefficient under different solidification conditions.Using Fick's second law,a circular acrylic wet spinning diffusion kinetics model was established.Using the relationship between the average concentration and the natural logarithmic function of the solidification time,the diffusion coefficient under different solidification conditions was solved by reverse fitting.The results show that the diffusion coefficient has a large correlation with the temperature.The increase in the temperature of the spinning dope makes the small solvent molecules move faster in the filament,and the increase in the temperature of the coagulation bath makes the small solvent molecules in the outermost layer of the filament more intense,and the diffusion coefficient When other coagulation conditions remain unchanged,when the temperature of the spinning dope is increased from 50?to 60?,the diffusion coefficient increases from 3.19×10-8 cm2/s to 5.54×10-8 cm2/s,and the same is true for solidification The bath temperature increased from 5?to 15?,and the diffusion coefficient increased from 3.03×10-8cm2/s to 5.06×10-8 cm2/s.The difference in solvent concentration is the driving force for diffusion.The increase in the difference in solvent concentration increases the diffusion coefficient,but the increase in the difference in solvent concentration will cause the skin-core structure to be produced too fast.Under the experimental conditions of this paper,the concentration of the coagulation bath is increased from 10 When the wt%increases to 20 wt%,the diffusion coefficient decreases from4.11×10-8 cm2/s to 2.38×10-8 cm2/s.When other solidification conditions remain unchanged,negative draft has little effect on the diffusion coefficient.(2)Solvent diffusion kinetics of flat acrylic fiber in PAN/NaSCN system.On the basis of Fick's second law,combined with the principle of metal heat treatment and carburization,the solvent diffusion kinetics of flat acrylic wet spinning is established.The diffusion coefficient obtained by the flat acrylic wet spinning diffusion kinetic model is analyzed under different solidification times.The distribution of solvent content inside the filament in the direction of solvent diffusion.The results show that when the temperature of the coagulation bath,the concentration of the coagulation bath,and the negative draft ratio are 5?,14 wt%,and-45%respectively,the temperature of the spinning dope is increased from 50?to 60?,and the solvent of the filament is within 5 seconds.The thickness of the diffusion layer is increased from 20?m to 35?m.When the temperature of the spinning dope is 60?,the coagulation time is extended to 60 s,and the thickness of the solvent diffusion layer is increased to 95?m;when the spinning temperature,coagulation bath concentration,and negative draft When the multiples are 50?,14 wt%,-45%,the temperature of the coagulation bath increases from 5?to 15?,and the thickness of the solvent diffusion layer of the nascent fiber decreases from 20?m to 9?m within 5 s.When the temperature of the coagulation bath is At15?,with the extension of coagulation time,the thickness of the solvent diffusion layer increases slightly;when the temperature of the spinning dope,the temperature of the coagulation bath,and the negative drawing ratio are respectively 50?,5?,and-45%,the concentration of the coagulation bath is 10 wt%,when the solidification time is 5 s,the thickness of the solvent diffusion layer of the thread is 55?m,as the solidification time is extended to 60 s,the thickness of the solvent diffusion layer increases to 91?m;when the coagulation bath concentration increases to 20 wt%,Under the experimental conditions of this subject,the nascent fiber cannot form a solvent diffusion layer under any coagulation time;when other coagulation conditions remain unchanged,the negative draft multiple has little effect on the thickness of the solvent diffusion layer of the thread,but it will cause the filament to fall under the same coagulation time.The solvent content inside the strip increases.(3)Flat spinneret design based on solvent diffusion kinetics model.Combined with the spinning process and spinning equipment of the flat acrylic fiber of Sinopec Anqing Petrochemical Branch,the thickness of the solvent diffusion layer formed by the thread is up to 27?m(0.027mm)under the 7 s'solidification time,and the flat acrylic fiber can be solidified.The width is 54?m(0.054mm),and the width of the spinneret hole is less than 54?m(0.054mm),so the spinneret parameter of 19D flat acrylic fiber is 2b=0.04 mm/2a=1.6 mm,and the same is true for the 27D flat acrylic spinneret The parameter is 2b=0.048 mm/2a=2.4 mm.(4)Preparation of 19D and 27D flat acrylic fibers.According to the designed and processed19D and 27D flat acrylic spinnerets,the effects of coagulation conditions on fiber structure,flatness,breaking strength and elongation at break were studied.The results show that When other coagulation conditions remain unchanged,when the temperature of the spinning dope is increased,the viscosity of the spinning dope is reduced to help maintain the flatness of the flat fiber,but the occurrence of microcracks in the coagulation process will cause a decrease in mechanical properties;the temperature and concentration of the coagulation bath will not increase.Conducive to the solidification and forming of flat acrylic fibers,so that the flatness and mechanical properties are reduced;the increase of the negative draft ratio will reduce the flatness and mechanical properties of the flat fibers.A more reasonable coagulation process for 19D flat acrylic fiber is:spinning dope temperature 55?60?,coagulation bath concentration 0?,coagulation bath concentration 14 wt%,negative draft ratio-40?-45%;27D flat acrylic fiber coagulation process It is:spinning dope temperature 55?60?,coagulation bath concentration 0?,coagulation bath concentration 14 wt%,negative draft ratio-45?-50%.The flatness of the 19D flat acrylic fiber thus obtained is?7,the breaking strength?1.2 c N/dtex,the elongation at break?11.5%,the flatness of the 27D flat acrylic fiber is?10,the breaking strength?1.6 c N/dtex,and the elongation at break.The growth rate is?16%. |
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