Preparation Of Sodium Carboxymethyl Cellulose Composite Membrane And Its Application In Food Preservation

With the shortage of petroleum resources and the deterioration of the environmental problems,the development of new bio-based composites to replace petroleum-based packaging materials will attract great attention.Carboxymethyl cellulose sodium(CMC)has the advantages of biodegradability,biocompatibility,safety,non-toxicity,easy film formation,etc.CMC-based films have effective barrier of oxygen,carbon dioxide and lipid.However,the CMC-based films exhibited poor water vapor barrier due to its hydrophilcity.It also does not have antimicrobial activities,which limits its application in food preservation.The study had improved the properties of CMC-based films by incorporation of fillers.According to solution casting method,a ternary blending antimicrobial composite film of CMC,montmorillonite(MMT)and ?-poly-(l-lysine)(?-PL)was prepared.Scanning electron microscopy(SEM),fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),optical properties,mechanical properties,water sensitivities,thermal stability,and antimicrobial activities of the composite films were analyzed.The contents of ?-PL influenced the surface topograghy of the composite films.Hydrogen bond interactions occurred between the film-forming components,and CMC and ?-PL also had electrostatic interactions.The addition of MMT and ?-PL did not affect the amorphous morphology of CMC,but improved the UV barrier property,tensile strength(TS),water contact angle and water vapor permeability(WVP)of the composite films.Compared to pure CMC film,adding 7.5 wt% ?-PL to the CMC matrix,the TS increased more than threefold and the WVP decreased by about 35%,while the thermal stability has not changed obviously.The CMCbased composite films containing ?-PL also displayed good good antimicrobial activities against both bacteria(E.coli and S.aureus)and fungi(B.cinerea and R.oligosporus).When the incorporation of ?-PL got up to 7.5 wt%,the microbial growth inhibition rate of compositie films was above 90%.Furthermore,the CMC/MMT/?-PL 7.5 wt% composite film was selected for strawberry coating preservation,which could prolong strawberry shelf life by 2 days.Cellulose nanocrystals(CNC)are generally considered to be a good filler to enhance the properties of biopolymer-based films due to its biocompatibility,biodegradability,high aspect ratio,and edibility.In this study,CNC was isolated from pea hull by sulfuric acid hydrolysis method.The CNC was needle-like shape with diameter of 10-35 nm,length of 150-415 nm,aspect ratio of 11 and crystallinity index of 0.77.The CNC was added to the CMC matrix,and the SEM,FTIR,XRD,optical properties,mechanical properties,barrier property and thermal stability of composite films were analyzed.SEM result showed that CNC distributed homogeneously in the CMC matrix,FTIR detected strong hydrogen bond interaction between them,and XRD result showed the combination of CMC and CNC diffraction patterns in the composite film.The addition of CNC reduced the transmittance of the composite films,but the school badge covered by the composite films could be seen clearly.In addition,the mechanical properties,water vapor barrier property and thermal stability of composite films were improved.Compared to pure CMC film,adding 5wt% CNC to the CMC matrix,the TS increased by 50.8% and WVP decreased by 24.3%.Moreover,the film-forming solution of CMC/5%CNC was used for red chilies coating preservation,which could prolong the time for red chilies to become wrinkled.The addition of CNC to the CMC matrix can effectively enhance the mechanical and water vapor barrier properties of CMC-based film,but the CMC/CNC composite film does not have antimicrobial activity,which limits the use of the composite film.Therefore,using the CNC as a template and stabilizer,silver nanoparticles(Ag NPs)were synthesized by a hydrothermal redox method.After the reaction,a yellow-brown suspension was obtained which had an obvious characteristic absorption peak at 415 nm,indicating that Ag NPs were synthesized.Transmission electron microscopy(TEM)result confirmed that the spherical Ag NPs with an average diameter of 25 nm dispersed on the surface of CNC without agglomeration.The prepared CNC immobilized Ag NPs(CNC-Ag NPs)were then mixed with CMC to form film solution,then the filter papers were immersed in the mixed film solution,pulled out,and dried to obtain coated paper.The surface morphology,tensile strength index,barrier properties and antimicrobial activities of coated papers were investigated.SEM showed that the coated paper became smooth and some voids were filled.The tensile strength index and barrier properties of coated paper were improved obviously.Compared with uncoated paper,the tensile strength index of CMC/7% CNC-Ag NPs coated paper increased by 110.5%,air permeability decreased by 92.9%,and WVP decreased by 40.3%,45.3%,48.6% and 54.9% corresponding relative humidity(RH)at 97% 76 % 55% and 34%,respectively.CMC/7% CNC-Ag NPs coated paper also showed good antimicrobial activity against both E.coli and S.aureus.In addition,the CMC/7%CNC-Ag NPs coated paper was selected to strawberry packaging testing,which could effectively prevent strawberries from growing mold and prolong the shelf life of strawberries.