Preparation And Functional Regulation Of Poly(L-lactide) Porous Fiber Membrane

Water pollution is one of the top ten environmental problems.With the development of society,industrial wastewater and domestic sewage are increasing.Wastewater contains large amount of oil,dyes,heavy metals,etc.,which seriously pollutes water sources,causing water shortages and affecting normal human normol life.Among the commonly materials in the field of sewage treatment,the adsorption separation material has the advantages of low-cost,high-efficiency treatment of sewage.But it also has the disadvantages of single adsorption separation capacity,poor recycling ability and difficulty in post-treatment.Among the adsorption separation membrane materials,PLLA（poly（L-lactide））has good mechanical properties with high strength,high modulus,biodegradability,environmental friendliness and easy processing.The electrospinning PLLA membrane has large specific surface area and high porosity.It can be biodegraded when applied to sewage treatment and has great application prospects in the field of sewage treatment.However,PLLA membrane has two main disadvantages when it is used as adsorption separation material.First,PLLA doesn’t contain functional group that can interact with contaminants.second,it is easy to degrade in water.Therefore,it has great significance to develop and prepare PLLA porous fiber membrane which has excellent adsorption performance and oil-water separation ability and good cycle performance.In view of the poor adsorption capacity and weak functionality of PLLA electrospun fiber membranes,this paper proposes the method of electrospinning to improve the adsorption and separation ability of PLLA fiber membrane by introducing functional functional groups and nanoparticles.First,the small molecule compound diethylenetriamine（DETA）containing the primary and secondary amine group andγ-aminopropyltriethoxysilane（KH-550）witch is one of the amino group-containing coupling agent are introduced into the PLLA fiber membrane to improve the hydrophilicity and adsorption capacity.Then,theγ-ferric oxide（γ-Fe₂O₃）mixed with PLLA was electrospun to obtain superhydrophobic,high-efficiency oil absorption capacity and oil-water separation ability PLLA/γ-Fe₂O₃ composite fiber membrane.Finally,PDLA andγ-Fe₂O₃ were introduced into PLLA solution and mixed by electrospinning.The composite fiber membrane was prepared by silk process,and the crystal structure evolution of the fiber membrane was controlled by heat treatment.The PLLA/PDLA/γ-Fe₂O₃ composite membrane containing stereocomposite crystal was prepared.The adsorption capacity,cyclic regenerability and recyclability of the composite fiber membrane were studied.Practical application capabilities.The main research results are as follows:（1）The electrospun functionalized PLLA porous fiber membrane was successfully prepared by simultaneously introducing DETA and KH-550 into the PLLA solution.It was found that the microscopic morphology of the electrospun PLLA porous fiber membrane was affected by the contents of PLLA,DETA and KH-550 in the solution.The morphological characterization showed that the functionalized PLLA fiber showed uniform fiber diameter distribution and porous structure when the PLLA content was 20 wt%（w/v）,the DETA content was 2.0 wt%,and the KH-550 content was 3.0 wt%.Characterization by FTIR and XPS revealed that the N-containing group was introduced into the electrospun membrane,and the concentration of N atoms was about 0.73%,which was beneficial to the improvement of the hydrophilicity of the functionalized PLLA porous fiber membrane.The adsorption performance test found that the functionalized PLLA porous fiber membrane had good adsorption capacity for Congo Red（CR）.The maximum theoretical adsorption was135.7 mg/g using the Langmuir isotherm adsorption model.In addition,the adsorption kinetic model and adsorption thermodynamic parameters were further studied.The results show that the functionalized PLLA fiber membrane obeys the pseudo second-order kinetic model for the CR adsorption behavior and is a spontaneous endothermic process.At the same time,the oil/water separation results showed that the water flux of the functionalized PLLA fiber membrane to the non-emulsified oil/water system and the emulsified oil/water system were 2018 L/（m²h）and 1861 L/（m²h）,respectively.（2）The PLLA/γ-Fe₂O₃ composite fiber membrane was prepared by mixingγ-Fe₂O₃nanoparticles modified with glycine and PLLA.The micromorphology showed that theγ-Fe₂O₃ nanoparticles were uniformly dispersed on the fibers.And the PLLA/γ-Fe₂O₃composite fibers maintained uniform diameter distribution and porous structure.The contact angle test found that theγ-Fe₂O₃ nanoparticles increased the roughness of the fiber surface,and the composite membrane had superhydrophobic and superlipophilic properties.The water adhesion ability and anti-icing test found that the prepared composite fiber membrane also had good water adhesion and ice resistance.The oil absorption test results showed that the composite membrane exhibit excellent oil absorption capacity.And the maximum adsorption capacity reached 268.6 g/g when adsorbing motor oil.The continuous adsorption desorption cycle test results showed that the adsorption capacity was maintained after 10cycles of testing.In addition,the oil-water separation test found that the PLLA/γ-Fe₂O₃composite membrane also exhibited high oil permeation flux.The oil permeation flux reached 1769 L/（m²h）when separating the emulsified oil/water system.The permeate flux could reach 2925 L/（m²h）).（3）The PLLA/PDLA/γ-Fe₂O₃ composite fiber membrane was prepared by mixing electrospinning with PLLA and PDLA and loadingγ-Fe₂O₃,followed by annealing.The crystal structure of the composite film was studied by wide angle X-ray diffraction.The results showed that the composite fiber membrane after annealing produced large number of stereocomplex crystals.The effects of different annealing time on the morphology,surface hydrophobicity,porosity and mechanical properties of the composite fiber membrane were further investigated by means of scanning electron microscopy,contact angle test,porosity test and tensile test.The optimum annealing time of the PLLA/PDLA/γ-Fe₂O₃ composite fiber membrane was 20 min.The oil absorption test found that the composite membrane has adsorption capacity for different types of oil.And the adsorption capacity of silicone oil could reach up to 148.9 g/g.The continuous adsorption desorption cycle test showed that the PLLA/PDLA/γ-Fe₂O₃ composite fiber membrane still maintained good adsorption capacity after 10 cycles of testing.The oil-water separation test results showed that the maximum oil flux of PLLA/PDLA/γ-Fe₂O₃ composite fiber membrane could reach 1146 L/（m²h）.And it maintained high flux after repeated use.