Controllable transition from finger-like pores to inter-connected pores of PLLA membranes

•Novel dialysis membrane material PLLA.•Inter-connected bicontinuous structure of PLLA membrane was firstly prepared.•The unique effects of PEO on PLLA phase separation process.•Better solute clearance rate of PLLA membranes with bicontinuous structure.

Poly (l-lactic acid) (PLLA) flat sheet membranes with inter-connected pores were prepared via non-solvent induced phase separation process. Polyethylene oxide (PEO) with molecule weight of 100 kD was used as additives. The morphology evolution from the partial to total inter-connected pores in cross section was accomplished by adjusting the PEO concentration. Besides, the effect of different molecule weight of polyethylene glycol (PEG), high coagulation intensity, different mass fraction ratios of PEO to PLLA and the casting solution exposure time in air on morphologies of PLLA membranes were also investigated respectively. Finally, as a hemodialysis membrane, the water permeability, solute clearance rate and mechanical properties were determined. It was shown that PLLA membrane with highly inter-connected pores exhibited a higher water flux of 225 L/hm2 and tensile strain of 83%. The clearance of the as-prepared membranes to urea and lysozyme is 77% and 33% respectively, while keeping BSA rejection with 90%.