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.