Flow, Mixing And Reaction Of Polymer In Co-rotating Twin Screw Extruder

The overall residence time distribution (RTD) in a co-rotating twin screw extruder (TSE) and the local RTD in kneading block and conveying sections were investigated respectively. As a representative reactive extrusion process, the mixing process and melting reaction of PA6/PA6IcoT blends were studied.The residence time distribution (RTD) evolution along a co-rotating twin-screw extruder with split barrel was experimentally investigated using the pre-mixed particle of anthracene and polystyrene (PS) as tracer. Through the variation of traced concentration of marked pellets, the flow behavior of fluids on screw was described and the average residence time in different functional sections in TSE was derived. The influences of extrusion conditions, shear level, average residence time were discussed.Based on the average residence time of different screw conveying zones and volume flow rate of melting polymer, the fill degree in different conveying screw zones was estimated. The fill degree results indicate that the feed rates, the position of conveying sections are the most important factors. The void volume on screw, screw speed, the distance of neighboring kneading block, temperature of material all would influence the degree of drag flow, therefore influence the residence time curves of fluid. The fill degree results prove that the similar structure of screw elements may have different degree of fill due to neighboring elements affect, and the close alignment of kneading zone may leads materials to be 'besieged' in the zone between them.The phenomena of backflow between kneading elements of TSE was theoretically analysis and experimentally confirmed. At some section of kneading block, the apparent fill degree based on RTD curves are larger than 1 if backflow was neglected. One conceptual flow model was developed to describe the complex flow in kneading block, and the model was successfully used to get the volume of backflow quantitatively. Much better fitting result was achieved when the direction of pressure degradient was considered. The influence of extrusion condition on pressure distribution and backflow volume ratio was discussed also.The transmidation reaction between PA6 and PA6IcoT was successfully characterized through NMR, MWD and its crystallization behavior. When the reaction time was short, the transmidation degree was small, but the variation of MWD was obvious. While the reaction time was prolonged, ¹³C NMR could be used to characterized the exchange reaction quantitatively. The introduction of transmidation catalyst, triphenyl phosphate (abbreviated as TPP), could accelerate the melt reaction but the reaction mechanism is much more complex, the results of ¹³C NMR and MWD analysis indicate that at least parts of TPP plays role of catalyst on the transmidation reaction between the end groups of PA6/PA6IcoT blends.Monte Carlo (MC) method was used to simulate the variation of MWD when the exchange reaction and reorganization reactions in polyamide blends system proceed. The MWD data obtained from GPC experiments were used to test against the simulation. The factors of blends composition, initial MWD distribution, average polydsipersity index of PA6 and PA6IcoT were investigated. The concentration of reactant and the MWD of blends were traced during the simulation process. The simulation results also indicates that the MWD could achieve balance more quickly when the average MW of polymers were close or their compositions were equal,. The results of simulation also could be used to provide beneficial results for characterization of transmidation reaction and prediction of the rheology of the blends.Finally, the crystallization behavior of the blend of aliphatic polyamide (PA6) and amorphous polyamide (PA6IcoT) was studied. It had been shown that the increase of PA6IcoT composition would lead to decrease in overall crystallinity but increase in PA6 crystallinity at non-isothermal crystallization process, and small amount of PA6IcoT would lead to smaller size of nucleus compared to pure PA6. According to the isothermal crystallization kinetics, an increase in PA6IcoT fraction resulted in the decrease of crystallization rate, the Avrami exponent was increased from 4.5 to 6 when the crystallization temperature was increased. The fact that the isothermal crystallization kinetics was influenced greatly by the composition change of PA6 to PA6IcoT demonstrates that the PA6 and PA6IcoT is a miscible blend system.