Study On The Gradient Morphology Of PS/PP And PA6/LDPE Blending Fibers By Melt Spinning

The gradient morphology of natural biomaterials endows them excellent performance. This kind of phenomena greatly inspires us so much, that we come up with good idea to improve comprehensive properties of fibers by preparing blending fibers with gradient morphology by melt spinning. The study on the mechanism of gradient morphology formed in blending fibers by melt spinning provides theoretical foundation for preparing new functional fibers.The blending fibers of polypropylene/polystyrene (PS/PP) and polyamide 6/low density polyethylene (PA6/LDPE) with biomimetic gradient structure were obtained through melt spinning. The rheological behaviors of PS, PP, PA6 and LDPE, the effect of viscosity ratios, spinning speed, blending ratios on gradient morphology, and evolution mechanism of dispersed phase during fiber formation processing were systematically studied. Some exciting results were showed as follows.Firstly, the study of rheological properties of each component showed that the shear viscosity of PS was higher than PP's in shear flow field. The extensional viscosity of PS was higher than that of PP when temperature was above 190℃in elongation flow field. The viscosity of PA6 was lower than that of LDPE at lower shear rate and extensional rate. But the result was opposite at higher shear rate and extensional rate.Secondly, by comparing the fibrils distribution of the take-up fiber with different take-up velocity with that of the extruded fiber, it was found that the gradient morphology was formed mainly in the non-isothermal uniaxial elongation flow field, but the shear stress had no effects on it. At the same time, it was found that the radial migration and gradient tensile phenomenon existed in fiber formation process. Combined with the changes of parameters on the spinning line and the analysis of the polymer melts fiowability, it was concluded that the dispersed phase migration of blending fiber was formed mainly in the small range after extruding the spinneret hole. The differently rheological properties of four polymers and the radial difference of temperature, stress and velocity on the spinning line caused oppositely gradient distribution in the two blending systems. That is the fibril diameter was smaller and fibril number was larger in the central region of PS/PP blending fiber than that in surface region. Oppositely, the diameter of fibril was bigger and fibril number was less in the central region of PA6/LDPE blending fiber than that in surface region. At the same time, the gradient distribution of fibrils proved the parameters disparity along the radial direction of strand silk on the spinning line.Lastly, increasing of the viscosity ratio and take-up velocity was beneficial to form gradient distribution. The increasing of dispersed phase content only enlarged fibrils diameter, and had no effect on its gradient distribution. The dispersed phase was only dispersed in the surface region of PS/PP blending fiber by reducing dispersed phase content or increasing of take-up velocity at the base of increasing of the viscosity ratio.In this paper, we successfully prepared the blending fibers with biomimetic gradient structure, and controlled the gradient distribution of fibrils by studying on the formation of disperse phase in fibers. The production costs could be reduced by preparing the blending fibers in which the dispersed phase was only dispersed in the surface region. At the same time, the research supplied fundamental data of melt-spinning dynamics.