Heat treatment to increase self-bonding property of binderless boards manufactured from rice straw

Abstract Rice straw is an abundant agricultural waste globally, but it has not been used effectively. Binderless boards manufactured without synthetic resins are an environment-friendly material, and they are also a possible way to utilize rice straw. However, the presence of wax and silica on the surface of rice straw reduces the bonding ability. The study objective was to manufacture binderless boards from heat-treated rice straws and investigate the effect of heat treatment on the self-bonding properties. Heat treatment was performed on chips or powder from rice straw (≤50 mm, 1 mm) at 200 °C, 1.5 MPa for 0–60 min. Heat-treated rice straw (≤50 mm, 1 mm, 150 µm) was hot-pressed to form binderless boards at 220 °C and 5 MPa for 10 min. The resulting board was 300 × 300 × 5 mm, 0.8 g/cm3. The mechanical and physical properties of the boards were tested according to the JIS A5905-2014 standards. Electron microscopy (SEM), particle-size distribution, and gas chromatography-mass spectrometry (GC-MS) analyses were conducted to examine the effect of heat treatment. The results showed that heat treatment for more than 40 min increased internal bonding because of physical and chemical changes in the rice straw.