Study On Melting And Mixing Mechanism Of Asymmetric Self - Cleaning Twin Screw Extruder

Blend modification of polymer opens up a broad path for the development and utilization of polymer materials. Compatibilizer has significant influence on blend modification of polymer, and processing equipment also plays an important role in melting and mixing properties of blends. The Co-rotating Non-twin Screws Extruder(CNSE) is a novel type of extrusion equipment, which is originated from the ideas of symmetry break chaotic dynamics and can enhance the chaotic mixing and elongational flow because of the introduction of asymmetric flow channel. The melting and mixing mechanisms are fundamentally different from the traditional twin-screw extruder. It is well known that the melting process plays an important role in energy consumption and morphology of final products. Therefore, it is important to examine the melting and mixing process in the Co-rotating Non-twin Screws Extruder.In this paper, we developed the novel CNSE with the clam-shell split barrel, whose screws rotate at the speed ratio of 2. And then, the melting and mixing process of HDPE/PS and PP/PA6 blends were investigated. And the effects of different configurations of screw elements and kneading discs and operation conditions on the melting process and morphology development were investigated. The equivalent average circle diameter and volume-average particle diameter were used to analyze the particle size of samples at different positions along the screw axes.It is shown that the melting process was mainly divided into four sections, i.e., solid conveying section, partially filled section, transition section, and fully filled section. In the partially filled and transition sections, the degree of fill in the screw with one tip and the screw with two tips was inconsistent and the asymmetry effect appeared. And in the fully filled section of melting, the effect of melting in the one-tip channel and two-tip channel was also asymmetry. The melting performances in CNSE were divided into free conveying in the screw section, pressurized conveying in the screw section, free conveying in the kneading disc section, and pressurized conveying in the kneading disc section. Friction energy dissipation(FED) and plastics energy dissipation(PED) were the mainly melting mechanisms in the free conveying in the screw section; PED and VED were the mainly melting mechanisms in the pressurized conveying in the kneading disc section, and the solid bed was quickly transited into the mode of melt rich melt-solid mixture under the strongly and weakly alternation of VED. The results of statistical analysis of particle size showed that different shape and size of dispersed phase were found in the screw with one tip and the screw with two tips. Because of the faster shear rate, the dispersive mixing ability in the screw with one tip was greater than that in the screw with two tips. By comparing the mechanical properties of CNSE-extruded blends with different handedness screws, we found that the mechanical properties of blends extruded with right-handedness screws were better. It showed that the mixing effect of right-handedness screws was greater.The melting characterization and morphological evolution provide the direct and reliable basis for the design and improvement of Co-rotating Non-twin Screws Extruder.