Prearation And Properties Of Multifunctional Oxygen Barrier Membranes

Gas barrier membranes have attracted more and more attention in the food encapsulation,pharmaceuticals packaging,chip encapsulation and electronic devices.The addition of inorganic materials to macromolecule enhances the barrier properties compared to pure macromolecule.However,there are still some problems that plague the preparation and application of such materials:(1)How to decrease the incompatibility between inorganic materials and polymer to avoid excessive gas permeability.(2)The membrane needs not only barrier,but also multi-function.In order to solve the problems mentioned above,in this dissertation,layered double hydroxides(LDHs)were selected as the membrane building elements.The specific research content is as follows:1.MgAl(CO3)-LDH was prepared by urea decomposition method.MgAl(NO3)-LDH with larger interlayer spacing was obtained by anion exchange from carbonate to nitrate.MgAl-LDH nanosheets were obtained by delaminating MgAl(NO3)-LDH.The modified LDH(named TA@LDH)was obtained by modifying LDH with tannic acid(TA).(TA@LDH/PEO)n composite membranes with high orientation and compact structure were prepared by layer by layer assembly of modified hydrotalcite and polyethylene oxide(PEO).In this work,the(TA@LDH/PEO)50 composite membrane with 50 layers has the best performance,and the oxygen transmittance rate(OTR)is reduced by 96.5%compared with the substrate.(TA@LDH/PEO)50 composite membrane is still 95.5%lower than the initial substrate at 120%strains.For composite membrane stretched 20 times at 100%strain,the OTR was 94.9%lower than that of the initial substrate.The excellent barrier performance is due to the ordered stacking of LDH nanosheets,which extends the entry path of oxygen molecules,and the hydrogen bonding network can increase the residence time of oxygen molecules.In addition,LDH was modified to improve the organic-inorganic interface compatibility and barrier performance.Therefore,the barrier properties of the membranes prepared in this work are better than those reported by most researchers.2.LDH nanoparticles were prepared by coprecipitation method,and then LDH nanosheets were modified by APTES.APTES@LDH was dispersed in dichloromethane solution of polylactic acid(PLA)to prepare coating solution.Finally,we put the coating solution on the coating machine to prepare the APTES@LDH/PLA composite membrane.The OTR of the membranes with APTES@LDH content of 5%and 10%is less than the detection limit of the instrument,which is more than 99%lower than that of the substrate.When the content of LDH is 10%,the WVTR of the composite membrane is reduced by 94.1%.Excellent barrier properties both to oxygen and water molecule are attributed to the good 2D ordering of LDH nanosheets,which increases the diffusion path of gas molecules,commonly known as tortuous pathway.Meanwhile,hydrogen bonds and covalent bonds extend the residence time of oxygen and water vapor molecules.The mechanical properties of composite materials have also been improved to some extent.The green environmental protection,simple process flow and low preparation cost make the composite membrane have a good industrial prospect,and have potential application value in the fields of chip encapsulation,battery packaging,drug and food encapsulation.