| The biodegradable food packaging materials have gradually become a research focus with the improvement of people's environmental protection requirements.Wheat gluten?WG?is an important by-product of wheat processing,which has broad prospects on food packaging development.It has great advantage of low price,wide source,excellent film-forming and good barrier of air and oil.In this study,wheat gluten was used as the main film-forming substrate to prepare the composite films,supplemented by wheat-bran cellulose?WC?and one of paraffin wax?PW?,beeswax?BW?,paraffin oil?PAO?and oleic acid?OLA?type.Properties of composite films were studied respectively and stability during storage were researched.The main results are further summarized as follows.1.WG and WC were mixed into alkaline-ethanol system.The blend dispersion was used to prepare composite films using a film casting method.The effect of solid-liquid ratio,wheat-bran cellulose content,the additive amount of glycerol,ethanol concentration,pH values and xanthan gum content in film forming system on physical properties of composite films was investigated.The physical properties contain tensile strength?TS?,elongation at break?EAB?,water vapor permeability?WVP?,water solubility and light transmittance etc.Combining principal component analysis and membership comprehensive evaluation method and taking comprehensive score S as the evaluation index,composite films was optimized by Box-Behnken response surface test method.The results showed that the optimal formula were wheat-bran cellulose content of 36.14%,ethanol concentration of 34.28%with the pH at 11.42.The S score of optimal formula were evaluated at 0.90.Meanwhile,overall score reached 0.88 in the experimental validation,where the composite films have the TS value of 23.42 MPa,EAB value of 10.48%,WVP of 1.62×10-1212 g/?cm·s·Pa?,hydro-solubilty of 22.59%.The results of FT-IR and SEM showed that the material compound in the films generated no new functional groups,but with excellent compatibility.Granulate particles distributed on the surface of films.The structure of fracture surface was difference.2.PW,BW,PAO and OLA was added into composite films with WG and WC,respectively.The effect of lipids on the moisture absorption and water permeability performances of WC/WG films by fitting the isothermal moisture absorption curve models were studied.The change of mechanical properties and surface hydrophobic about composite films were explored.The results showed that PW,BW and PAO can reduce the equilibrium moisture absorption rate and m0,and BW worked best.The Peleg model of composite films have different dynamical process with different RH.PW and BW can reduce the water-molecule bonding strength on the surface of composite films.Except OLA,lipids improved the moisture barrier and surface hydrophobic properties of the composite films.The amount of additives of 15%BW have the minimum WVP.Lipid decreased TS and EAB,while OLA could increase ductility.BW has little influence on TS and EAB of the films.Different lipids generate different micro-structure on the films.Overall,the results showed that composite films with 15%BW has the best hydrophobic with considerable mechanical properties,which have the TS value of 11.91 MPa,EAB value of 8.16%,WVP of 0.76×10-1212 g/?cm·s·Pa?.3.The stability of WC/BW/WG composite films was studied.In 25?and RH 75%,the composite film has the highest water content,week mechanical property and low water-proof capability.When stored at 4?,the composite films have the same properties with those in 25?and RH 75%.High temperature will significantly influence the flexibility and colour.However,the light has no effect on all of the properties of composite films.Above all,the composite films maintain all the properties as long as six weeks in25?with RH 51%.TS,EAB and moisture contents of the composite films were about11.85 MPa,8.24%and 9.42%,which were not significantly different from control;WVP was about 0.813×10-1212 g/?cm·s·Pa?,increased by nearly 6.97%. |
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