聚酰胺酸溶液成膜过程中的传质行为

为了研究聚酰胺酸溶液成膜过程中的传质行为,采用自制液膜干燥实验装置在线测定聚酰胺酸溶液质量的变化.假设气、液两相传质通量相等的条件下,计算了溶剂气相传质系数和液面蒸气压.在此基础上考察了干燥温度、液膜厚度、溶液相对分子质量对液膜表面蒸气压的影响.结果表明,成膜过程中存在溶剂蒸发与聚酰胺酸溶液亚胺化反应的相互竞争.干燥初期溶剂蒸气压迅速升高,液膜表面溶剂的扩散为控制步骤;而干燥后期溶剂蒸气压较小,溶剂在膜内部扩散成为控制步骤.同时随着液膜厚度的增加、干燥温度的升高及溶液相对分子质量的减少,液面蒸气压的最大值呈现增大趋势.

Mass transfer of PAA solution during the drying process

The change of the mass of PAA solution were determined for the mass transfer in the drying process.In case of the equal mass transfer flux of gas phase and liquid phase,the gas mass-transfer coefficient and the surface vapor pressure in this system were calculated.The effects of the drying process such as molecular weight,drying temperature and polyamide film thickness on the surface vapor pressure were studied.It was shown that in the process and mechanism of film-forming there were solvent evaporation and imidization.In the initial stage of drying process,surface diffusion was the control step,while in the late stage of drying process,internal diffusion was the control step.The maximal value of the surface vapor pressure increased with the increasing of polyamide film thickness,and drying temperature reduced as the molecular weight reduced.