Studies On The Influence Of SIO₂ On The Physical Properties Of Wheat Gluten Film And The Mechanism

In this paper, a physical model of interaction of nano-silica and the wheat gluten was made based on the theory of some theoretical analysis. The best preparation conditions for nano-SiO2-wheat gluten composite films were determined. Then the influence mechanism of the nano-silica on physical properties of wheat gluten film was explored, and the correctness of the previously expected physical model was verified through the connection between the macroscopic physical properties and micro-structure of composite films.Glycerol was selected as the suitable category of plasticizers through experiments. On the index of mechanical properties, the optimum conditions for the preparation of nano-silicon dioxide—wheat gluten films by single factor experiment were as follows: glycerol adding amount of 25 g/100g wheat gluten, ethanol concentration of 50%, pH 11.0, heating temperature 80℃, nano-silica adding amount of 1.2 g/100g wheat gluten. On the index of water absorption, the optimum conditions for the preparation of nano-silicon dioxide—wheat gluten films by single factor experiment were as follows: glycerol adding amount of 30 g/100g wheat gluten, ethanol concentration of 40%, pH 11.5, heating temperature 90℃, nano-silica adding amount of 3.0 g/100g wheat gluten. Therefore, on the basis of these two results the best conditions for the preparation of composite films were: glycerol adding amount of 28 g/100g wheat gluten, ethanol concentration of 45%, pH 11.2, heating temperature 85℃, nano-silica adding amount of 1.8 g/100g wheat gluten. At this point, the tensile strength of silica - wheat gluten composite film was 9.62 MPa, elongation at break was 124.09%, and water absorption was 114%.After the preparation of nano-silica—wheat gluten composite films, the correlation between macro-properties, microstructure of the composite film and the expected physical model was established. In the aspect of macroscopic properties, the thermal decomposition of the film was studied by thermogravimetic analysis, and the glassy transition temperature was studied by differential scanning calorimetry. Thermal gravimetric analysis results showed that the weight loss of the composite film was less than the pure gluten film at the same temperature. The result of differential scanning calorimetry curves showed that the glass transition temperature of the composite film was higher than the pure gluten film, and this upward trend increased with the addition of nanoparticles. Both of these two thermal performance analysis results showed that the heat resistence of the composite films could be improved by the nano-silica. The particle size distribution of the film-forming liquid was studied by laser granularity distributing apparatus, and it was founded that the particle size of the system was increased with the addition of nano-silica. In the aspect of micro-structure, the surface and cross section morphology of the composite membranes were studied by scanning electron microscopy, the constitute of the unit chain of wheat gluten film was studied by Fourier infrared spectroscopy and x-ray photoelectron spectroscopy, and the chain structure of the gluten film-forming liquid was observed by circular dichroism spectroscopy. The microstructure results showed that: a good dispersion mixed system was formed between the nano-particles and gluten matrix, functional groups'places were changed, and binding energies of a variety of atoms were also changed with the addition of nano-silica, and nano-particles also had an influence on the secondary structure of the gluten film-forming liquid. All of these results indicated that the expected physical model on the interaction of the nano-silica and wheat gluten film was reasonable and correct. Since nano-silica and gluten could forme hydrogen bonds and coordination bonds, and play a role of cross-linking, the physical properties of the composite films could be improved, and this could provide a theoretical basis for the preparation of composite materials in adding nano-particles to the protein matrix.