Research On Wall Slip Of Polymer Melt In Spinning Process

Wall slip is one of the complex rheological behaviors of viscoelasticity of polymer melt in the process of basic processing. When the shear stress of the polymer melt in the flow channel wall exceeds a certain critical shear stress, the melt will slide along the wall surface, and this phenomenon is called wall slip. This phenomenon is often neglected in the traditional analysis of the flow state of the melt in the flow channel. However, with the development of micro-injection molding(MIM) industry, more and more attentions have been paid to the slip phenomenon with the micro scale effect, and some of experimental studies have been carried out as well. Nevertheless, there is no report in the theory of fiber spinning formation, especially when the melt spinning technologies reached current high-speed spinning, even super high speed spinning, and the wall slip phenomenon become more and more serious when the melt in spinneret micro-hole, leading the special rheology of the polymer melts. Therefore, this paper focuses on the study of slip phenomenon of polymer melt in the spinneret micro-hole, and here hope it can be a reference for theoretical research and productive practice in future.On the base of reading a great number of relative references at home and abroad, this paper outlined the progress of polymer wall slip research, determined the content of mainly research with combined the actual situation of spinning.1.Studied the wall slip in the case of micro scale, and established the corresponding mathematical model; Analyzed rheological state on condition of wall slip in low shear and high shear respectively; Discussed the influences of different pore sizes, surface roughness, temperature and other factors on the slip flow.2.Made numerical simulation of wall slip phenomena in polymer melt. Analyzed the rheological state of melt in the presence of slip based on Navier slip model, and made the numerical simulation of melt flow in different micro channel size and volume flow amount. The result shows that injection pressure and the shear rate of the wall surface on the slip of melt are both decreasing. Besides, the velocity gradient along the cross section of the channel is also decreasing. With the decrease of the characteristic dimension of the micro channel, the wall slip phenomenon of the melt was also increased;The simulation of the flow behavior under different volume flow shows that the melt slip velocity increases with the increase of the shear stress. Finally, made the numerical simulation of different slip coefficient of melt in speed 、pressure、viscosity、distribution of shear rate and extrusion swell in micro-hole.3.Experimental studied melt PET and PA6 on wall slip phenomenon at low shear rate and high shear rate respectively, and discussed the influence of shear stress, surface roughness on the speed of wall slip. Calculated melt PET and PA6‘s slip speed within the two shear rate ranges respectively based on Mooney equation. At the same time, according to the minimum standard error of melt pressure drop and experimental pressure drop under different slip coefficient, determined the slip coefficient of Navier model under different conditions. And finally concluded the critical shear rate when these two melt fracture and have slip condition. Result shows that the slip phenomenon between these two melt states high shear rate is significantly higher than that low shear rate. And the wall slip velocity increases with the increase of shear stress, and the relationship between the two is a power function by calculated; With the decreasing of the micro channel size, the wall slip coefficient of the melt decreases with the decrease of the wall slip coefficient, and this slip phenomenon is stronger. So the result agrees well with theoretical curve. Different micro channel size have different critical of spinning melt fracture shear rate, with the change of diameter with the power function decreasing. Such as 0.2mm jet plate,the critical shear rate of PET and PA6 melt can reach up to 22683.4s-1 and 23167s-1.4.Based on this slip theory is true, did the spinning formation research of polymer melt in different apertures spinneret when its near the shear rate value, tested the mechanical properties of the fiber and discussed the effect of shear rate on spinning process as well. Finally result shows that the polyester melt also has the spinnability of when the shear rate is 2×104s-1, and the fiber has good mechanical properties and also states its unevenness; Concluded that with the increase of shear rate, the unevenness rate of the fiber was decreased obviously, while the strength of fiber was improved.