Development Of High Stretching Rotor And Its Application In Preparation Of Halogen-Free Retarded EVA

Eco-friendly efficiency halogen-free flame retardant material is the inevitable choice for the development of future polymers.Due to the preparation of halogen-free retardant material needs higher percentage of filling content,special demands for the mixing ability of mixing devices is called for.Development of a rotor element with high stretching performance is of great significance for the preparation of high performance flame retardant composite.In this thesis,a high stretching rotor was developed;Polyflow software was used to analyze the mixing characteristics of the flow field in the two-rotor continuous mixing extruder.The effect of rotor structure and process parameters on the mixing performance was discussed.Formulation of halogen-free flame retardant Ethylene-vinyl acetate copolymer(EVA)was designed.The halogen-free flame retardant EVA was prepared by two-rotor continuous mixing extruder.The mechanical properties,flame retardancy and microstructure of the composites were investigated.The processing technology of flame retardant composite was studied.The influence of rotor structure and rotation speed on mixing characteristic was discussed by combing the results of numerical simulation and the experiment.The main achievements of this thesis are as follows.(1)The developed high stretching rotor had a better stretching and weaker shearing action in comparison with the classic rotors in the mixing process.In the mixing flow field the high stretching zone was at the mixing window,the high shear zone was in the narrow clearance between the tip of a rotor and the inner wall of a chamber.In the tip of rotor wing,material would be affected by strong shearing action and the mixing window would generate elongational flow and folding flow which effectively improved the rotor distributive and dispersive mixing capacity.(2)The distributive and dispersive capability of two rotors continuous mixing extruder enhanced with the increase of rotation speed.The high stretching rotor was superior to the classical rotor at the same rotational speed.Nevertheless,the difference between the two types of rotors was gradually decreased with the increase of the rotational speed.(3)The performance of flame retardant composite prepared by high stretching rotor was superior to that of classical rotor.Increasing the rotational speed in a certain range could improve the mechanical properties of flame retardant composite.When the rotational speed of the high stretching rotor is 600rpm,the composite reached the best performance,with tensile strength 11.59MPa,elongation at break 173.66%and limiting oxygen index 31.5%.All the performance target surpassed the national standard of the halogen-free flame retardant composite.