Characterization And Properties Of Poly(Lactic Acid) Membrane Modified By Inorganic Nanoparticles

Membrane separation technology has the advantages of high separation efficiency,energy saving,good selectivity and no impurities.At present,the separation membrane which is widely used in industrial production is very difficult to decompose.It will lead to white pollution after being abandoned.Moreover,these membranes are made of petroleum which is non renewable resource and large-scale application of these membranes will lead to energy crisis.Poly（lactic acid）（PLA）is a kind of high performance and green environmental protection polymer material.This resource is extensive and renewable.Compared with petroleum-based polymers,it has the advantages of high biocompatibility and degradation ability,and has a good application prospect.But the hydrophilicity of PLA is poor,so it needs to be modified.In this paper,PLA composite membranes were fabricated via phase inversion method.PLA were used as membrane materials,and titanium dioxide（TiO₂）nanoparticle,aluminium oxide（Al₂O₃）nanoparticle,zirconium oxide（ZrO₂）nanoparticle and montmorillonite nanoparticle were used as additive.The structure and properties of the PLA membranes were characterized by porosity measurement,contact angle measurement,scanning electron microscopy analysis,atomic force microscopy analysis,ultrafiltration test and antifouling experiment.The main research contents of this paper are as follows:（1）The effects of TiO₂ nanoparticle on the structure and properties of PLA membranes were investigated.The experimental results show that when the mass fraction of Ti O₂ nanoparticle in the membrane is lower,the modification effect of TiO₂ nanoparticle on the membrane is better.When the mass fraction of Ti O₂ nanoparticle in the membrane increases from 0%to0.1%,the rejection of the membrane reaches a maximum value of 81.6%,which increases by 21.2%.When the mass fraction of TiO₂ nanoparticle reaches 0.2%,the porosity of the membrane reaches the maximum,the fingerlike hole is more obvious,the membrane surface is the smoothest,and the hydrophilicity of the membrane surface is the strongest.In ultrafiltration experiments,the water flux,flux recovery ratio and humic acid flux all reach the maximum value,and the humic acid flux is the most stable after the filtration of 250min.However,the increase of the mass fraction of Ti O₂nanoparticle will increase the viscosity of the membrane casting solution,decrease the phase separation rate and porosity of the membrane.Excess Ti O₂is easily to aggregate on the surface of the membrane to increase the roughness and weaken the hydrophilicity of the membrane surface,and affects the filtration performance of the membrane.（2）The effects of Al₂O₃ nanoparticle on the structure and properties of PLA membranes were investigated.The experimental results show that when the mass fraction of Al₂O₃ nanoparticle reaches 0.2%,the membrane has the highest porosity,the smoothest surface and the strongest hydrophilicity.When the mass fraction of Al₂O₃ in the membrane increases to 1%,the internal structure of the membrane is changed.The finger hole size increases,which is beneficial to improve the filtration performance of the membrane.The water flux,flux recovery ratio and humic acid flux all reach the maximum value.From the result of antifouling experiment,the decay rate of humic acid flux decreases for the modified PLA membrane.After the filtration of humic acid solution for a long time,humic acid flux decreases not obviously.（3）The effects of ZrO₂ nanoparticle on the structure and properties of PLA membranes were investigated.When the mass fraction of ZrO₂nanoparticle reaches 0.5%,the surface of the membrane is the smoothest.The contact angle result shows that the hydrophilicity of the membrane surface is obviously enhanced.Ultrafiltration experiments show that the water flux of the PLA-ZrO₂ composite membrane is the largest,reaches 816L·m^-2·h^-11 which is 8.5 times higher than that of pure PLA membrane.The flux recovery ratio is close to 100%and humic acid flux is the largest and stablest.When the mass fraction of ZrO₂ nanoparticle increases further,the excessive ZrO₂nanoparticle accumulates on the surface of the membrane and increases the roughness of the membrane surface,the hydrophilicity of the membrane surface is weakened,and the filtration performance of membrane is influenced.（4）The effects of montmorillonite nanoparticle on the structure and properties of PLA membranes were investigated.When the mass fraction of montmorillonite nanoparticle in the membrane is increased from 0%to 0.2%,the modification effect of PLA membrane is better.The porosity of the membrane is the biggest,the fingerlike hole is the most obvious,and the membrane surface is the smoothest.Ultrafiltration test showes tha the water flux was the largest,flux recovery rate was the largest and humic acid flux was the largest and stablest.When the mass fraction of montmorillonite nanoparticle increases further,the hydrophilicity of the membrane surface is enhanced.While the viscosity of the membrane casting solution will be increased,so the porosity of the membrane decreases during the phase separation,resulting in the reduction of filtration performance.