Study On The Structure And Properties Of Nano-TiO₂/Soybean Oil/Beer Lees/Thermoplastic Starch Composite Films

The biodegradable starch films have attracted more and more attention due to the serious pollution of traditional petroleum-based plastics to the environment.Starch as renewable resources,has the advantages of low cost,wide source and easy biodegradation.However,the native starch-based film has the disadvantages of strong hydrophilicity,weak mechanical properties and barrier properties,and its application range is limited.Therefore,it is of great significance to study the film-forming mechanism and improve the functional characteristics of starch-based film.In this study,starch was physically modified by thermoplastic extrusion to produce thermoplastic starch,and the influence of molecular structure of thermoplastic starches from different botanical sources on the structure and properties of films was investigated.Subsequently,in view of the disadvantages of poor mechanical properties and poor water resistance of thermoplastic starch film,corn starch was used as raw material,and nano-TiO₂was added to enhance the functional characteristics of thermoplastic starch films.The optimum amount of nano-TiO₂was studied.Secondly,in order to improve the flexibility and hydrophobicity of nano-TiO₂/thermoplastic starch composite films,different soybean oil（SO）contents were added to enhance the hydrophobicity,water resistance and mechanical properties of the composite films on the basis of the optimal formula in the previous chapter,and the optimal amount of soybean oil was determined.Finally,in order to improve water resistance and thermal stability of the nano-TiO₂/soybean oil/thermoplastic composite films and improve the utilization rate of byproducts in beer brewing industry by-products and increase economic and environmental benefits,different contents of beer lees were added to enhance the functional characteristics of the composite films on the basis of the optimal formula in the previous chapter,and the optimum amount of beer lees was studied.The results were as follows:（1）In order to illustrate the influence of molecular structure of thermoplastic starches from different botanical sources on the structure and properties of films,the corresponding thermoplastic starch films were prepared to obtain thermoplastic corn starch（TCS）,thermoplastic rice starch（TRS）,thermoplastic sweet potato starch（TSPS）,thermoplastic cassava starch（TCAS）and thermoplastic pea starch film（TPES）.Due to the high content of amylose and B1 chain（DP 13-24）,TPES film had high tensile strength（6.28 MPa）and low water solubility（15.70%）,water absorption（42.35%）and water vapor transmission coefficient(0.285 g·mm·h^-1·m^-2k Pa^-1).Due to the high content of amylopectin,TCAS film had a smoother and more amorphous structure,showing higher elongation at break and opacity.TCS film had the highest transparency and was suitable for packaging fresh vegetables and aquatic products,while TCAS film had the lowest transparency and was suitable for packaging perishable meat products.The research results provided a new theoretical basis for accurately regulating the functional characteristics of thermoplastic starch films to meet different food needs.（2）In order to improve the mechanical properties and barrier properties of thermoplastic starch films,nano-TiO₂/thermoplastic starch composite films with different nano-TiO₂additions（0%～2%）were prepared using twin-screw extruder.The effects of nano-TiO₂on the structure and properties of nano-TiO₂/thermoplastic starch composite films were analyzed and compared.The results showed that the water absorption of the nano-TiO₂/thermoplastic starch composite films decreased from51.23%to 42.35%,and the microstructure of the composite films became more compact and smoother when the addition of nano-TiO₂increased from 0%to 1.5%.When the nano-TiO₂additions reached 2%,the aggregation of nano-TiO₂appeared on the surface of the blending film.Compared with the thermoplastic starch film without nano-TiO₂,the tensile strength of nano-TiO₂/thermoplastic starch composite films with 2%nano-TiO₂addition increased by 42.51%,the elongation at break decreased by 47.03%,the water vapor permeability coefficient decreased by 18.53%,and the water absorption decreased by 16.30%.Thermal stability and resistance to UV-visible light significantly improved.（3）In order to further improve the flexibility and hydrophobicity of nano-TiO₂/thermoplastic starch composite films,nano-TiO₂/soybean oil/thermoplastic starch composite films with different soybean oil additions（0%～8%）were prepared.The results showed that compared with thermoplastic starch composite films without soybean oil,composite films with 4%soybean oil addition had the highest tensile strength（12.82 MPa）and elongation at break（27.00%）,and the lowest water vapor permeability coefficient.The above results showed that soybean oil can be effectively used as both reinforcing agent and hydrophobic agent,had broad application prospects in food packaging.（4）In order to reduce the production cost and enhance the mechanical properties and thermal stability of thermoplastic starch composite films,and to improve the utilization rate of beer lees,a by-product in beer brewing process.Beer lees was used as an organic filler to enhance the performance of nano-TiO₂/soybean oil/beer lees/thermoplastic starch composite films.The structure showed that beer lees inhibited the swelling of composite films in water,thus reducing the water absorption of composite film.With the increase additions of beer lees,the thermal stability of nano-TiO₂/soybean oil/beer lees/thermoplastic starch composite films gradually improved.The composite film containing 2%beer lees had the highest tensile strength（13.43 MPa）,the lowest water vapor permeability coefficient(0.297±0.041 g·mm·h^-1k Pa^-1)and the highest water contact angle（107.2°）.This study would provide a theoretical support for the application of beer lees in nano-TiO₂/soybean oil/beer lees/thermoplastic starch composite films.