Structure Control Of Dry Jet Wet Spinning Polyacrylonitrile Primary Fiber And Its Influence On Its Stretchability

The dry jet wet spinning process can not only improve the spinning speed and reduce the production cost,but also prepare high-quality precursor to improve the performance of carbon fiber.Therefore,dry-jet-wet process has gradually become a main production mode of PAN precursor.The structure and properties of PAN precursor restrict the quality of carbon fiber,but the preparation process of PAN precursor is long and complex,among which the most important processes affecting the structure and properties of PAN precursor are solidification molding,drying densification and steam drafting.Therefore,in this paper,SEM,XRD and bulk density measurement were used to study the effects of coagulation,drying and densification conditions on the structure and mechanical properties of PAN primary fiber.Meanwhile,the steam stretchability of different primary fibers was verified.When the coagulation bath concentration and temperature were higher than 55%and 25? respectively,the fiber cross-section morphology gradually changed from waist shape to ellipse and then to circle shape with the increase of coagulation bath concentration and temperature.With the increase of coagulation bath concentration and temperature,the crystallinity and compactness of the primary fibers increased first and then decreased.The results showed that the preferred process conditions to prepare fibers with a circular cross-section were the forming conditions of 74%concentration and 35?,and the crystallinity and compactness of the fiber cross-section were better.The height of air layer had little effect on the shape of fiber section,and the increase of draft ratio of coagulation bath promoted the change of fiber section from ellipse to circle.The crystallinity and bulk density of the primary fibers were improved by increasing of air layer height and draft ratio,but the higher air layer height caused the fiber to stick together,and the excessive draft ratio also led to the broken wire.The crystallinity and densification of primary fibers were increased by the increase of densification temperature.The cross-section shapes of fibers were affected weakly by the increase of densification temperature.The high densification temperature led to the decrease of fiber properties.The primary fibers with good properties were prepared at 120??140?.The primary fibers with good compactness and high crystallinity had relatively low maximum draw ratio in steam draft,but at the same draw ratio,the primary fibers with good compactness and high crystallinity had high mechanical properties.Through the analysis,the main technologies suitable for dry wet spinning are as follows:air layer height:5mm;coagulation bath temperature:35?;coagulation bath concentration:74%;coagulation bath draft ratio:3.1;densification temperature:120??140?.