Structure and properties of biodegradable wheat gluten bionanocomposites containing lignin nanoparticles

Lignin nanoparticles (LNPs), prepared through precipitation from an ethylene glycol solution by using dilute acidic aqueous solutions, were obtained. Fourier transform infrared spectroscopy confirmed the removal of hemicelluloses from pristine lignin by acidolysis, while the TGA analysis revealed a retained thermal stability of the nanoparticles with respect of pristine lignin. The lignin nanoparticles presented a uniform size distribution and good stability at various aqueous pH mediums. Wheat gluten (WG) bionanocomposites filled with 0, 1 and 3% wt. of LNPs were produced and thermally and mechanically characterized by means of TGA, modulated DSC and DMTA analysis. UV-Vis spectroscopy and water sensitivity measurements were also performed, in order to fully characterize the produced materials. The results indicated that LNPs could also effectively absorb ultraviolet spectrum and improve the water sensitivity of WG bionanocomposites. Moreover, even if the addition of LNPs reduced the transparency at the two different weight contents, it enhanced the mechanical behavior and thermal stability of resulted bionanocomposites. A strong interaction between LNPs and WG matrix, as well as homogeneous distribution of LNPs within the WG matrix, was confirmed by FESEM investigation and mechanical characterization. The reduction of absorbed water as well as the increase in glass transition suggested that LNPs can be beneficial to enlarge the potential applications for WG based materials and confirmed the great potential of using these novel nanofiller in bio-based matrices. (C) 2015 Elsevier B.V. All rights reserved.