Study On Preparation Of Ddegradable Polylactic Acid-Chitosan Ultrafiltration Membrane

Benefiting from the rapid development of China’s industry nowadays,ultrafiltration membrane technology has also matured,which forming new white pollution.Based on polylactic acid（PLA）and chitosan（CS）as membrane materials,the experiment in this paper prepared a degradable polylactic acid chitosan ultrafiltration membrane through the non-solvent phase inversion method（NIPS）,and then studied the influence of membrane preparation and performance on membrane application and degradation performance.First of all,according to the Hansen solubility parameter theory,this paper used four solvents dissolve polylactic acid,including:acetic acid（HOAc）,N,N-dimethylacetamide（DMAC）,acetone（Ac）and ethyl acetate（EAc）.Next,PLA ultrafiltration membranes with different structures and properties were prepared by the NIPS method and water was used as a gel bath.The results showed that the acetic acid（HOAc）solvent has a strong ability to dissolve polylactic acid,and its casting liquid viscosity is low,which is beneficial to instantaneous phase separation;Compared with other solvents,for the cross-section,finger-shaped pores occupies a large area ratio,while the sponge-shaped pores occupies a small area ratio;the mechanical properties of the membrane are weak;the pure water flux is relatively high,reaching 90.31L·m^-2·h^-1,but the retention performance is poor,the retention rate of yeast is only 75%.Then,in order to optimize the flux of pure water better,this experiment tried to change the pore size of the membrane,using acetic acid（HOAc）as the solvent,and acetic acid solutions with different chitosan concentrations as the gel bath,and the PLA_CSultrafiltration membrane was prepared by the phase inversion method（NIPS）.The test results show that chitosan exists in the form of particles on the inner surface of the PLA membrane pores.Compared with the PLA membrane,the pore size is increased,and the pure water flux increases from 90.31L·m^-2·h^-1of the PLA membrane to 120.14 L·m^-2·h^-1of the PLA_CSmembrane.The yeast rejection rate is changed by the PLA membrane.75%of PLA is increased to 99%of PLA_CSmembrane.Furthermore,in this experiment,chitosan acetic acid solution was used as the immersion liquid to coat the surface of the PLA membrane to prepare a PLA/CS membrane,and the effect of different concentrations of chitosan on the structure and performance of the PLA film was studied.The results show that compared with PLA membrane,the surface hydrophilicity of PLA/CS membrane is significantly improved,from 104.1°to84.72°,and the pore size is reduced;The flux of pure water is inversely proportional to the concentration of chitosan in the dipping solution.It turns out that excessive high concentration is not conducive to the improvement of membrane performance.When the CS concentration is 0.25wt%,the separation performance of the membrane is the best.Finally,in this experiment,water and Na OH solution were used as degradation solutions,and the degradation performance of PLA,PLAC and PLA/CS membranes was analyzed by combining the two factors of CS content and temperature.Studies have shown that CS has an accelerating effect on the degradation of membranes.The pore size of PLACS and PLA/CS membranes is proportional to its degradation rate.The larger the pore size,the higher the degradation rate;The degradation rate of the three kinds of membranes will increase with the increase of temperature,and the increasing ratios from small to large are PLA,PLA/CS,PLA_CSmembrane;The degradation rate of weight loss in lye is higher than that in water.The greater the alkali concentration and the temperature,the higher the degradation rate.When the membrane is in a 0.1mol/L sodium hydroxide solution at a degradation temperature of 70°C,100%degradation can be completed within2 hours at the fastest.From low to high,the degradation rate of weight loss is PLA membrane,PLA/CS membrane,PLA_CSmembrane in order.