Wheat straw-based particleboards with citric acid as adhesive; influence of mat moisture and adhesive content

ABSTRAC In this study, the properties of particleboard made from wheat straw using citric acid (CA) as a bio-adhesive were investigated. The effects of mat moisture content (MC) and adhesive on mechanical properties (flexural strength, modulus of elasticity, internal strength) and physical properties (thickness shrinkage and water absorption) of straw particleboard were evaluated. To control the MC of the mat, the resinated straw particles were oven dried at different times (2 to 14 hours) and temperatures (80 and 100 °C) to obtain a mat with MC between 20 and 0.5%. The effects of an adhesive content of 15, 20, 25 and 30% (based on the dry mass of the straw) on the properties of the panels were also studied. The best MC of the mat before hot pressing was about 11% (drying of the particles in 2 hours at 100 °C), and the corresponding board had the highest mechanical and the lowest physical properties. Further decreasing the MC of the mat from about 11% to 0.5% had a negative effect on the mechanical and physical properties of the straw particleboard. Increasing the adhesive content from 15% to 30% improved all mechanical and physical properties of the panels; however, the changes in the range of 20% to 30% of adhesive content on the flexural properties and water absorption were not significant. In general, the results showed that due to the acidic nature of CA, it is possible to produce particleboard from wheat straw without pretreating the straw particles before use.