The Evolution Of Gradient Structure During Blend Melt Spinning And Its Mechanish

Study of functionally graded fibers had been a important part of fiber modification. Atpresent, it mainly focused on the morphology of dispersed phases of fibers. The evolution ofgradient structure during blend melt spinning was researched seldom. However, melt blendingexperienced the shear flow and the non-isothermal uniaxial tension flow during melt spinning.Thus, it was meaningful to research the evolution of gradient structure during blend melt spinning.On the other hand, study of the mechanism of the evolution of gradient structure during blend meltspinning would enrich and expand the theory system of polymer blending and dynamics of meltspinning. Based on these, this work focused on the mechanism of two-phase morphologyformation and evolution during melt spinning of polypropylene/polystyrene blend fibers.The main research contents and conclusions are summarized as below:Firstly, the elongational rheological properties of the polymers as raw materials werecharacterized, meanwhile, the relationship between the rheological constants and flow fieldstrength were also identified. The results showed that the apparent elongational viscosities of bothPP and PS exhibit a decrease as the enlongation rate increases, which was classified as so-called“enlongation thinning” behavior. Under the same enlongation rate, the elongation viscous flowactivation energy of PS was obviously bigger than that of PS, that’s to say, the dependence ofelongational viscosity of PS on temperature was more significant. The elongation viscous flowactivation energy and the pre-exponential factor for Arrhenius equation of both PP and PS showeda good log-linear relationship with the applied elongation rate. As the elongation rate increased,the dependence of ratio of elongational viscosity on temperature became significant.Secondly, blend fibers in different position of spinning line at various take-up velocities werecaptured, and were observed by scanning electron microscopy to characterize the fibermorphologies. The formation and evolution of the fiber morphologies along the spinning lineswere studied systematically, and the mechanisms of the formation and evolution of the fibermorphologies is proposed. The results showed that the gradient structure of dispersed phase wasinfluence by both the shear flow and the non-isothermal uniaxial tension flow. However, thegradient structure of deformation of dispersed phase was mainly controlled by the non-isothermaluniaxial tension flow during blend melt spinning. The droplet number was larger in the center than near the surface of fibers, and this kind of difference was going to be more obvious along thespinning line. When the spinning speed was small, the diameter of dispersed phases decreasedbetween0to60cm away from the spinneret. When the spinning speed was large enough, such as1000m/min, the diameter of dispersed phases actually increased between20to60cm away fromthe spinneret, which showed that coalescence of dispersed phases decreased had occurred. Inaddition, the coalescence existed more or less in all the surface of fibers studied. Furthermore, thedegree of the deformation of dispersed phases was bigger in the center than near the surface offibers, this difference would be small when the spinning speed was1000m/min.Thirdly, based on the dynamics of melt spinning, this work calculated the axial distributionsof velocity, spinning tension, temperature and elongational viscosity along the spinning lines. Inorder to study the mechanism of the evolution of gradient structure during blend melt spinning, thetheory of droplet deformation and the elongational rheological properties were researched. Theresults showed that the gradient structure of the deformation of dispersed phases were actually dueto the gradient structure of temperature. The model of drop deformation in uniaxial tension flowwhich was put forward by Delaby could predict the deformation of dispersed phase during blendmelt spinning accurately.Finally, looking upon dispersed phase as “the indicator of temperature”, the distribution oftemperature along the radial direction of fibers was calculated. The results showed that thetemperature was higher in the center than near the surface of fibers, and this kind of differencewas going to be decreased along the spinning line. When spinning speed increased, the differenceof temperature between the center and the surface of fibers decreased. However the discipline ofthe gradient of temperature alone the radial direction of fibers was contrary.