Preparation Of Hydrophilic Polylactic Acid Separation Membrane And Research On Its Performance

A large number of scrapped membranes applied in the industrial activity caused serious pollutions,which affects the development of the ecology and environment.At present,the traditional disposal methods of scrapped membranes usually lead to the occurrence of secondary pollution.The biodegradable membranes can be completely degraded into carbon dioxide and water through a certain biocatalysis process,with no damage to the ecological environment.There are only a few studies on the appilcation of biodegradable membranes in separation.Although PLA has been applied in packaging and medical industry as a biodegradable material,the research in the separation field is still insufficient and the application types are relatively single.In addition,PLA has obvious hydrophobicity,which limits the application in the field of separation.Therefore,it is very important to develop degradable hydrophilic PLA membranes.In the field of oil-water emulsion separation,an asymmetric PLA nanofiber membrane was manufactured by electrospinning with PEO cross-linked network blending at the molecular level,thus realizing the reversal of PLA membrane from hydrophobic to superhydrophilic.The results show that the PEO cross-linked network could be tightly combined with PLA through the winding of molecular chains.The initial water contact angle of the prepared super-hydrophilic PLA nanofiber membrane reaches 44.1°,and can decrease to 0°in 0.9 s,and its underwater oil contact angle reaches 154.7°.The permeation of surfactant-stabilized oil-in-water emulsion was up to 20987 L·m^-2·h^-1·bar^-1,with the separation efficiency as 99.6%,and the separation performance remained stable in 20 cycles.It could not be degraded in the solution of p H=1-12,but could be degraded quickly at the condition of p H=14.In the process of separating surfactant-stabilized oil-in-water emulsion,the separation performance of PLA nanofiber membrane is controlled by the selective wettability,pore size and charge of the membrane.In the field of colloidal separation,the PLA flat and hollow fiber membranes were modified by the synergistic effect of Tween80 and PVP（K30）.The pure water flux of PLA flat membranes prepared by phase inversion reached 112 L·m^-2·h^-1·bar^-1,and the BSA rejection reached 96%.The PLA hollow fiber membrane was prepared by dry jet-wet spinning method.The effects of the flow rate of inner core liquid,air gap,flow rate of casting solution and spinning traction speed on the membrane were analyzed.The prepared PLA hollow fiber membrane has a cross section of a double-fingered pore structure,a loose porous inner surface and a porous outer surface with dense cortical structure.The water contact angle is 50.1°,which is about 20°lower than pure membrane.The pure water flux is 151.2 L·m^-2·h^-1·bar^-1,and the rejection of Fe（OH）₃ reaches 98.5%.Meanwhile,the anti-pollution performance of PLA hollow fiber membrane is improved,and the flux recovery rate reaches 86.8%.This study proves that the blending modification can increase the hydrophilicity of PLA membranes,and regulate the structure of PLA membranes.This study provides a forward-looking and basic research for the preparation and application of biodegradable membranes,and provides some ideas for the hydrophilic modification of hydrophobic membranes.