The Study On Mechanics And Mumerical Simulation Of Multi-Layer Polymer Co-Extrusion

The plastic packing industry in our country has been developing at a high-speed since the reform and opening, and more and more people are focusing on the multi-layer thin plastic sheet because of their outstanding performance. While the core technology of fabricating co-extrusion die is monopolized by the developed country, as the result, it is urgent to make the study on the mechanism of multi-layer polymer co-extrusion.Based on the former research achievements, I united the3D non-isothermal computation and multi-layer polymer co-extrusion study to simulate the interface position distribution of multi-layer co-extrusion polymer in hanger die. The3D non-isothermal model has been provided here and the factors effecting the temperature distribution were examined profoundly. Meanwhile, a new model on the interface distribution of3D co-extrusion polymer is developed, and then the relevant influence factors on the interface distribution were investigated. The experiment was carried out to validate the mathematic models developed here.The main achievements and conclusions are as follows:1. Developed the3D non-isothermal mathematic model used for polymer, the relevant equations were discretized on a staggered grid with the finite volume method (FVM) and the programme was developed with VisionFortran language.2. The temperature distribution of polymer melt in coat-hanger die was simulated, and the coat-hanger die was analyzed profoundly. The influence of viscous dissipation resulted by velocity gradient and the conduction convection of energy on the temperature distribution were examined.3. The temperature distribution was predicted and the relevant factors (i.e., die wall temperature, non-Newtonian index, elongation rate) effecting the temperature distribution were examined. The simulation indicates the following results:1) The variation of die wall temperature may bring on the significant effect on the temperature value and the influence may be slight for temperature distribution of polymer melt in coat-hanger die.2) The results of simulation may be not credible based on the assumption of non-Newtonian index to be constant.3) The elastic energy induced by elongation rates is treated as a contribution to viscous dissipation term will result in the simulation value of temperature in polymer melt is a little higher than the corresponding one measured.The conclusions drawn above were verified experimentally.4. Based on the3-D non-isothermal mathematic model, I derived the interface position distribution mathematic model of co-extrusion polymer. The relevant equations were discretized on a staggered grid with the finite volume method (FVM) and the programme was developed with VisionFortran language.5. The interface shape was simulated and the interface position of polymer melt at die exit was examined profoundly.6. Simulation results with the3D non-isothermal non-Newtonian co-extrusion model are consistent with those literatures. Meanwhile, the influence of flow-rate ratio, the viscosity ratio and the die wall temperature on the interface position distribution were discussed and the following conclusions were drawn:1) The viscosity ratio and die wall temperature have the same influence on the position distribution of melt interface, i.e., the variation of viscosity ratio and die wall temperature may have significant influence on the shape of melt interface but be slight for interface position. The higher die temperature will bring the lower viscosity ratio of melts. And then the interface distortion will be improved. 2) The viscosity difference is the key factor to result in the encapsulation phenomenon. When the polymer melts with different viscosity flow in a same channel, the profiles of velocity are distinct. According to the principle of lowest energy consumption, the polymer melt with lower viscosity will flow to the higher shear rate domain, as a result, there always has the trend of polymer melt with lower viscosity packing the melt with higher viscosity.3) The variation of flow-rate ratio may have significant influence on the interface position but be slight for interface distribution.4) In industry production, when the die geometry is fixed, adjusting melt viscosity ratio, melt flow-rate ratio and the die wall temperature may be important measures to ensure the co-extrusion performance to be successful.