Modified Preparation And Property Researches Of Zein Composite Membranes

With the introduction of the plastic restriction policy,the environment-friendly biodegradable plastics are favored by more and more packaging professionals,and gradually widely used in the packaging industry.At present,the commonly used degradable plastics are mainly PLA/PBAT mixed-based materials,that is,the mixture of bio-based polylactic acid(PLA)and petroleum-based biodegradable polyester(PBAT),which has the advantages of strength,toughness,stability,low cost and mature technology.However,petroleum-based materials depend on petroleum,which is not a long-term sustainable development strategy.In the future,the key of solving the pollution problem of plastic products is to develop pure bio-based degradable plastics is.Zein is a multi protein mixture extracted from corn starch,which has excellent film-forming properties and unique hydrophobicity.It is an ideal biodegradable plastic film material with broad application prospects.However,pure zein film is difficult to be directly used in the production of degradable plastic film due to its brittleness,low strength and poor stability.Therefore,different modification methods and modifiers can be used to modify zein film to meet the application requirements in packaging industry.In this paper,three kinds of zein based composite films,including zein composite films modified by Tween 20,TiO2 composite films and SiO2 cross-linked composite films,were prepared by casting method.Through the analysis of the surface and cross-section morphology,group characteristics,tensile properties,hydrophobicity,water absorption,barrier property,thermal stability and other properties of the composite membrane,the effects of the type and amount of modifier on the properties of zein based composite membrane were studied,and the comprehensive evaluation of the modification effects of emulsifier addition,nano rigid filler filling and coupling agent modification were carried out.The addition of Tween 20 improved the uniformity,tensile properties and oxygen barrier properties of zein/eugenol composite membrane,but decreased the surface hydrophobicity and increased the water vapor transmission.Due to the strong spatial repulsion effect of Tween 20 hydrophilic subunits,the surface of the composite film was smooth and the tensile properties were improved.The tensile strength of membrance was the highest when the content of Tween 20 was 0.4 wt.%.However,when a number of Tween 20 was added,it was easy to form Tween 20 micelles in the membrane,which destroyed the uniformity of the membrane structure,resulting in poor barrier property and low tensile strength.However,the hydrophilicity of the composite membrane surface and water vapor transmission were enhanced by exposing hydrophilic groups of Tween 20.As increase of TiO2 contents in zein/TiO2 composite membrane,the porosity of membrane surface and tensile strength were improved,but the water absorption,water vapor transmission and surface hydrophobicity were increased.The results showed that the compatibility between TiO2 and zein matrix was good when the content of TiO2 was 1.0 wt.%.Although the composite film was still porous,the tensile strength of the composite film reached the maximum of 15.11±1.57 MPa.When a number of TiO2 was added,it will lead to the agglomeration of TiO2,and the continuity of membrane structure will be destroyed,and the interaction between polymer chains will be weaken.Therefore,when the amount of TiO2 was more than 1.0 wt.%,the tensile strength decreased,oxygen barrier and water vapor barrier properties decreased,while the hydrophilicity and water absorption increased with the increase of hydrophilic TiO2.The surface morphology,tensile properties,hydrophobicity and barrier properties of SiO2 composite films modified by KH-560 were improved well.Compared with the unmodified film,the surface of SiO2 composite film modified by KH-560 was more even,the internal pore density,oxygen barrier properties and water vapor transmission were improved.The improvement of tensile properties was due to the formation of Si-O-Si covalent bond in the composite film modified by KH-560.The tensile properties of the composite film were improved well when the addition of KH-560 was 1.0%v/v and 2.0%v/v.After modification,the polar hydroxyl group of the composite membrane decreased,while the hydrophobic end group of KH-560 was exposed,so the water absorption of the composite membrane was very small.When the KH-560 content was 1.0%v/v,the composite film had good barrier performance,low water absorption and high tensile strength.The disadvantage was that the elongation at break was low,so it can be used as a harder plastic material.When the KH-560 content was 2.0%v/v,the elongation at break of the composite film was more than 1.0%v/v,and the KH-560 film was 67.65%,which can be used as a softer plastic material.Through the comparative analysis of emulsifier modification,nano-rigid filler filling and coupling agent crosslinking methods and modification effects,it was found that the coupling agent was the best.In the process of coupling agent modification,KH-560 and SiO2 formed a more stable covalent bond,which was conducive to the improvement of the microstructure and performance of the composite membrane.