BPU/PLLA/DO体系的热力学性质对成膜过程及共混膜结构的影响

利用浸沉凝胶相转化法制备医用聚氨酯(BPU)/聚乳酸(PLLA)微孔膜,讨论了BPU/PLLA不同配比时聚合物/1,4-二氧六环/水三元体系的凝胶特性及其对共混膜结构和性能的影响,并初步探讨成膜机理.研究结果表明,随着BPU/PLLA质量比例由90/10变为75/25、50/50、25/75、10/90,聚合物/溶剂/非溶剂三元体系的热力学稳定性增强,凝胶值增大,但是共混溶液的黏度增大;并且,共混膜的孔隙率、膜厚、平均孔径、水蒸汽透过速率及吸水率先增加后降低.这主要是由于随着BPU/PLLA质量比例的变化,动力学扩散过程控制成膜速度转变为成膜体系热力学性质控制成膜速度;成膜过程由延时分相转变为瞬时分相,后又转变为延时分相.

INFLUENCES OF THERMODYNAMIC PROPERFIES OF BPU/PLLA/DO BLENDS ON FORMATION AND STRUCTURE OF THEIR MEMBRANES

The blend porous membranes of biomedical polyurethane(BPU) and poly(L-lactic acid)(PLLA) were prepared by the immersion precipitation phase inversion method.The influences of different BPU/PLLA mass proportions on the coagulation of polymer/dioxane(DO)/water ternary systems was investigated,and the structure and performance of blend porous membranes were characterized and discussed.It was found that the thermodynamics stability of polymer/solvent/nonsolvent ternary systems was enhanced with varying BPU/PLLA mass proportions from 75/25,50/50,25/75 to 10/90,while the viscosity of blend solutions increased.And the porosities,thickness,average pore diameter,water vapor transmittance rate(WVTR) and water uptake of blend membranes increased first and then reduced.But the time reaching the equilibrium water uptake prolonged gradually.The reason was that WVTR and water uptake were controlled by the membrane porosity,while the time reaching the equilibrium water uptake was governed by the hydrophilicity of membrane materials.The changes of membrane structures and performances resulted from the transformation of the membrane-formation mechanism.With BPU/PLLA mass proportion changing from 75/25,50/50,25/75 to 10/90,the main factor controlling the membrane formation was transformed from diffusion kinetics to thermodynamics of membrane-formation systems.The phase separation type was changed from the delayed demixing to the instantaneous demixing first,and then changed to the delayed demixing.