Development of Microfiltration Membranes of Biodegradable Plastics

Abstract

Biodegradable plastics, such as poly (L-lactic acid) (PLLA), poly( e-caprolactone) (PCL) and poly (1,4-butylene succinate) (PBS), degrade in natural environments and composting facilities. We have been developing porous membranes of biodegradable plastics to reduce the wastes formed in filtration processes in food and biochemical industries. Microporous membranes of PLLA PCL and PCLPLLA-blends were prepared via thermally induced phase separation. The hydraulic resistance and pore size of the membranes were evaluated by filtration of water and a suspension of yeast cells (6 mu m), respectively. The PLLA membrane had high permeation resistance (low permeability) although it retained yeast cells on the membrane. The PCL membrane passed the yeast cells although it had high permeability. Thus we prepared microporous membranes of polymer blend of the two biodegradable plastics to yield high permeability and high cell retention. The resistance of PCL-PLLA-blend (4:1) membrane was as low as that of the PCL membrane. The polymer blend membrane retained yeast cells in a manner of depth filtration,, which allowed for fast filtration. Microporous membranes of PBS were prepared from PBS-chloroform solutions via immersion precipitation method with a coagulation bath of methanol. Membranes prepared from 10% PBS solutions pre-incubated at 47.5 degrees C show a permeation resistance of 10(11) m(-1) and a retention of the bacterial cells (0.7 phi x 2.5 mu m) of 99%. The microporous membranes of biodegradable plastics will be helpful as prefilters to eliminate the waste of filter and filter aids in food and biochemical industries.