| The soy protein/PVA packaging film obtained by the casting method had excellent biodegradability, but whose mechanical properties may decrease significantly in a humid environment. To improve the phenomenon, in this work blend films from natural soy protein and synthetical poly (vinyl alcohol) reinforced by nano-SiO2 were successfully fabricated. Then the effect of sizes, content and dispersibility of nano-SiO2, pH and others on the properties of soy protein/PVA film was investigated, besides the optimized technology and condition of the film was confirmed and the mathematical model was established, moreover the structure of the soy protein/polyvinyl alcohol film modified by nano-SiO2 was characterized, the degradation properties and fresh keeping performance of the modified film were also studied in this paper. Results show that:1. The single-factor experiments results showed that:When the aqueous suspension of the 30 nm nano-SiO2 dispersed with PVP by ultrasonic dispersion instrument was added directly to the mixed solutions of soy protein and polyvinyl alcohol, the content of nano-SiO2 and PVP were 1.5% and 1.0%, and the pH value was 5.0, as a result, the film showed higher mechanical properties and stronger water resistance.2. Through investigating the effect of different disperse conditions of nano-SiO2 on the properties of soy protein/PVA film, we found that the aqueous suspension of the nano-SiO2 should be treated for 50 min at 45℃ and 140 W by ultrasonic dispersion method. Then different ultrasonic temperature, ultrasonic power and ultrasonic time were considered as trial factors to design the L9(34) orthogonal experiment in to get the optimal distributed processing of nano-SiO2 was:ultrasonic temperature was 45℃, ultrasonic time was 40 min, and ultrasonic power was 160 W.3. The result of the response surface analysis indicated that:The optimum conditions to prepare soy protein/PVA film modified by nano-SiO2 were:the optimal content of nano-SiO2, PVP and pH were 1.75%,1.20% and 5.5 respectively. The regression equation of integrated grade of the film with the three influence factors was:Yx=0.56+0.1 X1+0.1 X2+0.11 X3-0.011 X1 X2 Z2+0.043 X1 X3-0.012 X2 X3-0.12 X,2-0.11 X22-0.15 X32. And the R2 of the regression1 equation was 0.9625. Compared with the original soybean protein/PVA composite film, the tensile strength, breaking elongation and transparency of the modified original soybean protein/PVA composite film, the tensile strength, breaking elongation and transparency of the modified film were increased from 4.61 MPa to 9.76 MPa, from 64.98% to 92.76% and from 15.54% 24.12% respectively, however, did not show significant decrease in the water absorption, slightly to 45.28% from 46.37%.4. DSC, XRD and SEM tests confirmed that the film modified and unmodified were all partially crystalline materials and the addition of nano-SiO2 would do more damage the crystal structure of soy protein/polyvinyl alcohol film. Nano-SiO2 had good compatibility with soy protein and PVA, and a more complex crosslinking network was formed among them. What’s more, FT-IR analysis told us that some new hydrogen bonds and other bonds had formed among nano-SiO2, soy protein and PVA, resulting in the enhancement of molecular interactions. Besides TGA tests showed that soy protein/PVA blend polymer modified by nano-SiO2 had more thermal stability and lower brittleness than pure soy protein/PVA film.5. Soil burial tests and preservation test showed:After 131 days, under the indoor environment of constant temperature and humidity and natural conditions, the weight loss of soy protein/polyvinyl alcohol film and the modified film were 63.93% and 69.34%. The new crosslinking structure forming among nano-SiO2, soy protein and PVA molecules prompted compactness of connection between the molecules and restrained the growth of microorganisms and travels of small-molecule gases through the material, resulting in the speed of microorganism decomposition would be limited. What’s more, in preservation of cherry tomatoes, the higher barrier property of modified film and commercially available polyethylene cling film could effectively limit the gases exchanging from fruit to atmosphere, suppress the physiological activities of fruits, slow the hardness, the soluble solids contents and VC consumption. |
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