Study On The Preparation Of Polylactic Acid/TiO₂/GO Antibacterial Double-layer Membrane And The Preservation Effect On Green Peppers

In recent years,with the deepening of the concept of green sustainable development,the research of bio-based polymer food packaging materials has attracted much attention.Polylactic acid（PLA）is an ideal green packaging material,and its biodegradation produces only carbon dioxide and water.However,the high brittleness and limited bacteriostatic effect of pure PLA products make it difficult to apply them directly to reagent food packaging.Therefore,in order to improve the performance of PLA,this study uses nano fillers to enhance the comprehensive performance of PLA.Nano-TiO₂（TiO₂NPs）can improve the performance defects of PLA as a packaging material.The use of TiO₂ NPs can absorb a large amount of ultraviolet radiation,prevent PLA aging and degradation,and has antibacterial properties and the ability to decompose ethylene.However,the photocatalytic activity of TiO₂ NPs is unstable,and it can only be excited under ultraviolet irradiation.Graphene oxide（GO）can make TiO₂ NPs still have photocatalytic activity under sunlight and enhance their stability.Therefore,this experiment explored the preparation of chitosan-PLA/TiO₂ NPs/GO double films,chitosan as the inner membrane and PLA-based fiber membrane as the outer membrane,combined with casting method,electrospinning technology and ultrasonic dispersion technology.Analyze and determine the performance of the membrane.Then conducted a fresh test of green pepper.The results are as follows:Using chitosan as the film-forming material and glycerin as the plasticizer,the effects of different ultrasonic time treatments on the mechanical,barrier and light transmission properties of the chitosan film were studied.The results showed that when the ultrasonic time was 45 min,the tensile strength and elongation at break reached 12.60±0.7 MPa and39.87±1.9%,respectively.Using electrospinning technology,PLA/TiO₂ NPs/GO fiber membranes were prepared.The addition ratio of TiO₂ NPs and GO was studied（TiO₂ NPs:GO=10:0,9:1,8:2,7:3,6:4.5:5）influence on the performance of PLA fiber membrane.At the same time,the effect of different ultrasonic time treatment on the performance of the composite membrane was studied in combination with ultrasound technology.The experimental results show that when TiO₂NPs:GO=7:3 and the ultrasonic time is 30 min,the comprehensive performance of the fiber membrane is the best.XRD and DSC results showed that the addition of TiO₂ NPs and GO increased the crystallinity of PLA.SEM results show that the addition of high concentration of TiO₂ NPs will destroy the morphology of PLA fibers and severe agglomeration in the fibers,while the addition of GO can improve the morphology of the fiber membrane to a certain extent.Mechanical properties indicate that the addition of TiO₂ NPs and GO can significantly improve the tensile strength and elongation at break of PLA fiber membranes.Water vapor permeability experiments show that the addition of TiO₂ NPs and GO increases the passage path of water in the PLA matrix and improves the water barrier of the fiber membrane.Antibacterial experiments showed that the inhibition rate of the composite fiber membrane against E.coli and S.aureus under sunlight for 24 h reached 76.7±1.4%and 73.9±1.8%,respectively.After UV treatment,the inhibition rate reached 94.4±1.8 and 92.6±1.7%,respectively.GO and TiO₂ NPs are mutually reinforcing.A double-layer membrane was prepared by combining chitosan and PLA/TiO₂NPs/GO fiber membrane.The results show that the double-layer film shows better water vapor barrier and light-blocking properties than these single-layer films.At last,The experimental results of fresh pepper packaging at room temperature show that the chitosan-PLA/TiO₂ NPs/GO double layer film can effectively maintain the hardness of the green pepper during storage,reduce the loss of moisture and soluble solids,delay the softening and reddening of the green pepper,and slow down The loss of chlorophyll can better maintain the sensory quality of green peppers,delay the rotten rate of green peppers,and extend the fresh-keeping period of green peppers.