Research On Modification Of Wheat Gluten Materials

Wheat gluten (WG) is a natural agro-polymer with the advantage of degradability, rich resource and low cost. However, wheat gluten plastic is brittle and water sensitive in comparison with traditional plastics. In this thesis, water-borne cationic polyurethane (WCPU) and montmorillonite (MMT) were used to blend with wheat gluten to control the brittleness and lower water sensitive.Water-borne cationic polyurethane (WCPU) was made up of polyester diol (P2356), diisocyanate diphenyl methane (MDI) and N-methyl diethanol amine and was used to blend with wheat gluten in solution. The blend power of WG/WCPU was obtained by freeze-dryer. And then the blend powder was thermally compression-molded to form a blend sheet. Using Raman and Fourier transform infrared spectroscopy (FTIR), the intensity of cross-link and hydrogen-bondings have been analyzed. The FTIR results reveal that the content of hydrogen-bonded carbonyl in WG decreases with the increase of WCPU content. The effect of the WCPU content on the mechanical and thermal properties have also been investigated. With increasing WCPU content, Young's modulus and tensile strength decrease, whereas the elongation at break is improved. It has been observed from dynamic mechanical analysis (DMA) that the glass transition temperature (Tg) of the plastized WG is lower than that of pristine WG obviously.FTIR also used to analyze the secondary structure of the WG/WCPU blends. The absorption in the amide I of wheat protein was separated by least squares curve fitting. The results show that the hydrogen-bonds ofβsheets in WG decrease firstly and then increase with increasing the content of WCPU in blends. It demonstrates that the hydrogen-bonds in WG can be weakened and the WG/WCPU blend sheets are plastic. The water uptake of the blend sheets display that the water swelling of the sheets are of Fick's process, and the water diffusion in the sheets are predominant in the early time. Scanning electron microscope (SEM) images of the WG/WCPU reflect that the blends of WG and WCPU are effective and homogenous.The effect of temperature on the secondary structure of WG conditioned at the following WCPU contents,20%,40% and 60%, was studied by FTIR spectroscopy in situ tracking over the temperature range of 23～120℃. When WCPU content is 20wt%, there are distinctive changes occurred in the low-frequency region of amide I band (1640-1616 cm-1). This is attributed to the changes in theβ-sheet structure. Hydrogen-bonds ofβsheets in WG decrease obviously at 45～50℃and 80～90℃. And the characteristic peaks of Hydrogen-bondings ofβsheets shift toward lower frequency.Protein-based nanocomposites consisting of wheat gluten matrix reduced by Na2SO3, WCPU and MMT were processed by casting. The objective was to investigate the effect of introduction of MMT on properties of modified WG sheets. FTIR was used to analyze the secondary structure of the WG/WCPU/MMT blends. The results show that the hydrogen-bonds of (3 sheets decrease with the increasing of MMT content. Contact angles, water uptake and water vapor permeation of the modified WG films show that the presence of MMT brings on a significant reduction of water sensitivity of WG-based materials, when MMT content is at 3% in the composite, the effect on the property of WG is most obvious. TGA results show that the presence of MMT do not have obvious effect on the thermal stability of WG and DMA results show that the presence of MMT can reduce the damping behaviors of WG.