| With the rising awareness about food safety and environment protection approaches,the demand for biodegradable packaging material has increased for the food and packaging industry.Zein has good film-forming properties and can be used as a raw material for biodegradable packaging materials.However,pure zein membranes are fragile and require modification.Nano-silica is a kind of safe and non-toxic nanomaterial,which can improve the mechanical and barrier properties of the film through interaction with the interface of the film matrix.The mechanical action of ultrasound can promote the homogeneous dispersion of nano-particles to form a composite film with better performance.In this paper,ultrasonic technology was introduced to prepare composite films,and nano-silica as the functional additive material.Zein/nano-silica composite films were prepared by casting method,and related performance indexes of composites were measured.The main research findings are as follows:?1?Firstly,the process conditions were obtained through a single factor optimization.The results showed that the optimum conditions for film-forming were:zein concentration,0.18?g/mL?;ethanol concentration,80%,and nano-silica addition,5%?g/g zein?.Furthermore,the amount of composite plasticizer at 40%?g/g zein?increased the tensile strength of the composite film to 9.48MPa,and the elongation at break to 50.71%.Whereas,the ultrasonic conditions?150w,60kHz,&10min?reduced the tensile strength by 15.2%,but the elongation at break was increased by73.7%.The mechanical properties of the ultrasound treatment combinations?A1B1C1D1?and?A1B3C3D3?were found to improve the the tensile strength and elongation at break.?2?In the next phase,the performance and structure of the composite films were measured.The results showed that after modification with plasticizer,the film water vapor transmission coefficient?WVP?was 13.07(×10-11g/m·s·Pa)at room temperature?RH:43%?,while the oxygen transmission rate?POV?value was 144.97?mmoL/kg?.The modificaion with nano-silica decreased the water vapor transmission coefficient?WVP?to 7.21(×10-11g/m·s·Pa),and the oxygen transmission rate?POV?to 99.44?mmoL/kg?.In case of ultrasonic treatment,the resulted values of water vapor transmission coefficient?WVP?and the oxygen transmission rate?POV?were reduced by 8.60%and 11.72%,respectively.Changes in the structure of the composite membrane were also discovered.The addition of composite plasticizer made surface of the film loose and porous;also the crystallinity and the thermal stability were reduced.The incorporation of nano-silica was responsible for the formation of silica aggregates.Furthermore,the nano-silica provided the film with filled pores,better crystallinity and thermal stability.In case of ultrasonic treatment,the nano-particles agglomerated and dispersed uniformly on the surface of the composite film,the cross-sectional voids became smaller;also the reduced crystallinity and better thermal stability was observed.?3?Finally,the measurement results of the storage performance of the ultrasonic nano-composite films indicated that their storage at room temperature?RH:43%?for30 days under different storage temperatures was better.The results after 30 days of storage were:moisture content,13.37%;the water vapor transmission coefficient?WVP?,11.35(×10-11g/m·s·Pa);the oxygen transmission rate?POV?,138.19mmoL/kg;the tensile strength,12.24MPaand the elongation at break,58.53%.In summary,this article studied the optimal ratio of zein/nano-silica composite film preparation,explored the effect of ultrasonic treatment on the performance of the composite membrane,and improved mechanical and barrier properties of the film were observed after ultrasonication.At the same time,the storage performance of the composite films is studied,which provides a theoretical basis for the practical application of these zein/nano-silica films. |
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