Effect of surface structure, wax and silica on the properties of binderless board made from rice straw

Abstract

When boards were manufactured from rice straw with UF resin, morphological differences, wax and silica adversely affected the boards' properties. The effects of the surface structures such as trichomes and protuberances were examined owing to improve the properties of binderless boards made from rice straw. The effects of silica and wax on the properties of binderless boards were also investigated. Trichomes and protuberances were broken by fine grinding. Wax was removed by extraction with hexane. Silica content was conditioned by fractionation of rice straw. Binderless boards were manufactured by hot-pressing, and their mechanical properties and water resistance were evaluated. Fine grinding increased both the mechanical properties and water resistance of binderless boards. One of the reasons was that size reduction of particles increased the bonding area. Another important reason was that the trichomes and protuberances that inhibit self-bonding were removed by fine grinding. The removal of wax increased self-bonding, and did not decrease the water resistance of boards. De-dusting decreased silica by a small amount, but this did not affect self-bonding. Hence, extraction of hexane and fine grinding were effective in increasing self-bonding of binderless boards made from rice straw. Owing to these pretreatments, the internal bonding and thickness swelling of the binderless boards made from rice straw met the requirements for particleboard and MDF of Japanese Industrial standards (JIS).