Strong high-density composites from wheat straw

• Published in: Composites. Part A, Applied science and manufacturing Applied science and manufacturing, 2025-01, Vol.188, p.108533, Article 108533
• Main Authors: Neudecker, Felix, Veigel, Stefan, Bodner, Sabine C., Keckes, Jozef, Duchoslav, Jiri, Stifter, David, Gindl-Altmutter, Wolfgang
• Format: Article
• Language: English
• Subjects: Biocomposite; Mechanical properties; Strand; Surface analysis
• ISSN: 1359-835X
• DOI: 10.1016/j.compositesa.2024.108533

•Production of a novel strong material based on densified wheat straw strands.•Wax removal and softening of the straw tissue through mild pre-treatments.•Achieving unprecedented tensile strength by splitting and densifying straw stems.•Simultaneously enhanced surface for adhesive bonding.•High flexural strength through bonding of unidirectional aligned straw strands. Wheat straw represents a promising resource for structural materials due to its inherent strength and availability as an underutilized agricultural by-product. However, structural features such as small diameters and a hollow, low-density design, as well as a hydrophobic, waxy surface layer, hinder conventional processing. We present an approach to overcome these hindrances by engineering delignified and densified straw strands into a mechanically strong unidirectional composite material. Wheat straw split into strands along the fiber direction was subjected to water-based and mild alkaline pre-treatments and subsequently densified. As a result, the average tensile strength and modulus of elasticity of straw strands improved to impressive 466 MPa and 26 GPa, respectively. Simultaneously, chemical changes to the surface enabled better adhesive bonding. The resulting unidirectional straw composites exhibited a flexural strength of 190 MPa and an elastic modulus of 20 GPa, well within the range of established wood and bamboo-based materials.