Effect of wheat straw content on mechanical, moisture, and formability performance of hot-pressed PLA biocomposite boards

Wheat straw-reinforced polylactic acid composite boards were produced using hot pressing to examine how wheat straw content affects mechanical performance, moisture absorption, and formability. Wheat straw was chosen as a reinforcement because it is a plentiful agricultural residue with low cost, low density, and high lignocellulosic content, providing both environmental and structural benefits when combined with PLA. 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 ranging 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 17.52 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 h, 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 approximately 40–50 wt% offers the best balance of strength, moisture resistance, and processability for board manufacturing.