Effects of coagulation bath on the structure and property of porous PU membranes
In order to explore the forming condition and the performance of porous PU membrane with asymmetrical heterostructure along the thickness direction,wet method was applied for pre-paring PU membrane.The microstructure of the as-prepared porous PU membrane was system-atically studied upon the effects of the composition and the ratio of the coagulation bath.Besides,the impact of the micropores structure on the air permeability,water adsorption,porosity and mechanical property was discussed and analyzed.The main results found are as follows:When both DMF and NaCl were added into the deionized water coagulation bath,a skin layer with rela-tively compact structure was observed on the surface,enhancing the mechanical property of the membranes;For samples solidified with the presence of only DMF,the interior of the membrane seemed lack of obvious pores but was mainly characterized by fluctuant pleated structure,which connected together and formed microchannels for air flow,thus resulting in good air permeability;For samples solidified with the assistance of only NaCl,the interior of the membrane was presen-ted as spongy-like honeycomb structure,and the skin and back layer were dotted with large-size pores,which leading to good water absorption.For samples solidified with ethanol,the internal structure was demonstrated as typical closed-cell foam feature,which renders the samples with moderate in air permeability,water absorption and mechanical property.
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