Wheat straw content (10-90 wt%) governs mechanical performance, moisture uptake and formability in hot-pressed polylactic acid biocomposite boards

Wheat straw-reinforced polylactic acid composite boards were fabricated by hot pressing to quantify how the wheat straw content governs mechanical performance, moisture uptake, and formability. An L9 (3 ³ ) orthogonal design using 40 wt% wheat straw was first applied to screen processing parameters, and the selected condition was 180°C, 14 MPa and 20 min. Using this fixed condition and a constant batch mass, boards with wheat straw contents from 10 to 90 wt% were prepared. Tensile and bending strength increased with straw content up to 50 wt% and then decreased, reaching 11.26 MPa and 17.54 MPa at 50 wt%. Impact strength decreased with increasing straw content and was approximately 5.12 kJ/m ² at 60 wt%. Density decreased from about 1.23 g/cm ^− 3 for neat polylactic acid to below 0.95 g/cm ^− 3 at 80 to 90 wt%. Water absorption increased with immersion time and approached saturation at approximately 100 hours, with the uptake rising markedly at 70 to 90 wt%. X-ray diffraction indicated a reduction in crystallinity without a change in crystal form, while scanning electron microscopy revealed increased porosity and interfacial debonding above 60 wt%. A wheat straw content of about 40 to 50 wt% provided the best balance among strength, moisture resistance and processability for board manufacture.