Delignification and Densification as a Route to Enable the Use of Wheat Straw for Structural Materials

Cereal straw is an abundant byproduct of crop production. Despite little current use in materials, the biologically optimized structure, which carries the weight of a structure up to 1.5 m high and protects it against environmental impacts, shows considerable potential. In order to be able to use this renewable material for structural purposes, barriers such as small dimensions and a low density have to be overcome. In the present study, lignin was partially removed from wheat straw using an alkaline solution with the aim of increasing the relative cellulose content and improving malleability. Thereafter, a homogeneous, dense, and multi-layered material was produced by densification at elevated temperatures. Outstanding improvements in mechanical performance were obtained compared to the untreated raw material. For the optimum variant, tensile strength increased by a factor of three (average strength 218 MPa) and elastic modulus increased by a factor of four (average 13 GPa), which is within the range of established wood-based structural materials. We propose that mild alkaline treatment as carried out in the present study may significantly facilitate the development of high-value structural materials based on little utilized cereal straw.