Production and characterization of thin films based on soy protein isolate with kraft lignin and tannins obtained by casting

In the present study, soy protein isolate (SPI) multifunctional bioplastics were prepared by casting, with the addition of tannins extracted from Stryphnodendron adstringens and kraft lignin. The films were obtained through biopolymer composites and blends method, prepared at three pHs (8.5, 9.5 and 10.5) and characterized by thermochemical studies, Fourier-transform infrared spectroscopy, scanning electron microscopy, water vapor permeability (WVP), antioxidant activity, water contact angle, surface energy, wettability, and mechanical tests. The composites presented better results when compared to the blend and control films, respectively, in the polarity, hydrophobicity, WVP and especially in the antioxidant activity tests. Nevertheless, no significant difference between the samples was noticed in the thermochemical and spectroscopic studies. The results presented the potential of the composites to produce SPI biopolymers with tannins and kraft lignin, leading to the development of multifunctional materials as an alternative for sustainable packaging.