Comparison of Kraft lignin and lignosulfonates addition to wheat gluten-based materials: Mechanical and thermal properties

Two types of industrial lignin, namely Kraft lignin and ammonium lignosulfonates, have been introduced into wheat gluten-based bioplastics. Mechanical, thermomechanical and water vapor sorption properties of the materials have been investigated in detail. The behaviors are clearly distinct depending on the lignin type. The addition of Kraft lignin produces stiffer materials, with increased Young's modulus but almost constant elongation at break. Glass transition temperature is higher and water vapor sensitivity reduced when Kraft lignin is added. Conversely, the incorporation of lignosulfonates leads to materials with higher elongation at break, but almost unchanged water sensitivity and glass transition temperature. Both lignins thus appear as of great interest to tailor the properties of wheat gluten-based materials. Structural differences between Kraft lignin and lignosulfonates are believed to be responsible for the distinct behaviors observed in this study.