Preparation And Applications Of Polyoxy-Methylene (POM)/poly(L-lactide) (PLLA) Functional Composite Membranes

To obtain the functional Polyoxymethylene?POM?and poly?L-lactide??PLLA?blends,the POM/PLLA nanofibrous membranes?NFMs?with surface pores and internal channels,the aminolized POM/PLLA NFMs,the silver nanoparticles?Ag NPs?immobilized POM/PLLA NFMs and the gold nanoparticles?Au NPs?immobilized POM/PLLA nanocomposite films have been designed and prepared.Furthermore,their applications in enzyme immobilization,the catalytic reducing reactions and Surface-enhanced Raman Scattering?SERS?have been investigated.?1?Preparation of POM/PLLA NFMs by electrospinning procedureThe POM/PLLA NFMs with surficial and internal porous structure have been fabricated through electrospinning technology and chloroform extraction.Parameters such as polymer concentration,electrospinning voltage and POM/PLLA ratio were optimized and their effects on the morphologies and diameter of nanofibers were explored The mechanism of the porous structure formation of nanofibers were studied based on the results of differential scanning calorimeter?DSC?and X-ray diffraction?XRD?analysis.Furthermore,the mechanical and hydrophilic/hydrophobic properties were also studied.?2?Aminolyzed POM/PLLA NFMs as surpports for lipase immobilizationThe aminolyzed POM/PLLA NFMs were prepared by electrospinning processure and aminolysis reaction.The morphologies of NFMs were characterized by scanning electron micrographs?SEM?and transmission electron micrographs?TEM?,the surface properties were characterized by X-ray photoelectron spectroscopy?XPS?,fourier transform infrared?FT-IR?spectroscopy and droplet shape analysis.The aminolyzed POM/PLLA NFMs were used as supports for lipase immobilization.The structures of immobilize lipase were characterized by SEM,FTIR and confocal laser scanning microscope?CLSM?.The optimal conditions for the immobilization of the enzyme on the fiber membrane were determined as follows:the concentration of the enzyme solution was 1.0mg/m L and the immobilization time was 12h.The optimal temperature of the immobilized enzyme was determined to be 40°C and the optimum pH was 5.0.The maximum reaction rate of the olive oil emulsion was 232.56U/mg and the Michaelis-Menten constant was 11.70mg/m L under the optimum conditions.Compared to free enzyme,immobilized enzyme catalytic activity,thermal stability and reusability increased significantly.?3?Ag NPs immobilized POM/PLLA NFMs as efficient catalysts for 4-NA reductionAg NPs immobilized POM/PLLA NFMs?POM/PLLA/Ag?were obtained by chemical plating.First,SnCl₂/PdCl₂ was used to activate the fiber surface,and the fibers with Pd nanoparticles as active sites were prepared.The in-situ loading of Ag nanoparticles on fibers was achieved by using the in-situ reduction method of glucose.The size and dispersion of Ag nanoparticles were controlled by adjusting the loading time.The morphologies of Ag nanoparticles were characterized by XPS,thermogravimetric analysis?TGA?and XRD.The chemical valence,loading and crystal structure of Ag nanoparticles were characterized by XPS,TGA and XRD.The catalytic performance of POM/PLLA/Ag NFMs were evaluated by catalytic reduction of p-nitroaniline?4-NA?as model reaction.The conversion of 4-NA was 99.7%and the reaction rate constant was 21.25×10^-3s^-1.At the same time,the conversion rate was more than99%.The POM/PLLA/Ag NFMs,were continuously catalyzed for 240min and the 4-NA conversion was higher than 90%in the continuous catalytic test.?4?Ag NPs immobilized POM/PLLA porous membranes as SERS flexible substratesFirstly,POM/PLLA membranes were prepared by melt hot pressing,secondly,NaOH and hexamethylene diamine were used to prepare the membranes with amino groups and three-dimensional contiuous porous structures.Finally,POM/PLLA/Au were obtained by in-situ deposition method using the chelation between amino groups and Au³⁺ions.XRD,XPS and Ultra Violet-Visable spectropy?UV-Vis?were used to characterize the crystal structure,chemical valence and aggregation morphologies of Au nanoparticles.The effect of reduction time on the deposition of Au nanoparticles were investigated.The POM/PLLA/Au membranes exhibited both high SERS sensitivity and good Raman signal reproductivity for rhodamine 6G?R6G?,The minimum detection concentration was 10^-14M and the enhancement factor was calculated to be1.54×10⁹.