聚氨酯反应挤出过程的数值模拟

采用三维有限元数值模拟结合标量混合分析方法,研究了反应物进料状态、转速及进料单体物质的量之比对聚氨酯在双螺杆挤出机中反应挤出过程的影响。反应进程不仅受停留时间控制,还与组分的均化程度有关。受组分浓度分布的影响,相比于预混进料,采用非预混进料方式导致反应程度较低;提高螺杆转速虽可加速均化过程,但却导致物料在挤出机中的停留时间缩短,因此需结合反应混合特性选取最优转速。通过数值模拟发现,采用90 r/min转速能达到较高反应程度。另外,模拟计算了不同预聚程度进料对反应挤出过程的影响。结果表明,采用二次投料法可阶段性控制聚合反应程度,提高反应挤出过程的稳定性,同时也便于为不同反应阶段的黏度范围匹配对应的反应器。

Numerical Simulation of Reactive Extrusion of Polyurethane

Three dimensional finite element numerical simulation coupled with scalar mixing analysis was employed to investigate the effects of feeding condition,rotating speed and feed monomer ratio on reactive extrusion of polyurethane.The reaction course is controlled by the residence time and the degree of homogenization.The polymerization degree with non-premixed feeding is lower than that of permixed feeding.Higher rotating speed is beneficial to homogenization,while it also leads to the reduction of residence time.Therefore,the rotating speed should be optimized according to the mixing-reaction characteristics.Results show that higher polymerization degree in current study is obtained under 90 r/min.Moreover,the effect of prepolymer feeding on reactive extrusion is also simulated.Results indicate that the polymerization degree can be controlled via two-step feeding in order to improve the stability of reactive extrusion and to match the appropriate reactors for various reaction periods.