Abstract
Rice straw is a troublesome biomass for an industrial application because of its high silica content and the wax-like substances covering the surface. At manufacturing binderless boards, which are considered environmentally friendly as they do not contain synthetic resins, rice straw silica contributed to water resistance, while the wax-like substances adversely affected self-bonding. This study investigated the effects of steam treatment on the self-bonding of binderless boards manufactured from rice straw. The chemical changes during steam treatment were examined by gas chromatography–mass spectrometry (GC–MS), and their influence on the bonding properties is discussed. Internal bonding strength and water resistance significantly increased by steam treatment. They also increased with increasing pressing temperature, and decreasing particle size. GC/MS analysis showed that not only hemicellulose and lignin, but also amorphous cellulose was decomposed during the steam treatment. Among the degradation products, 5-hydroxymethylfurfural was suggested to contribute to self-bonding during hot-pressing, while furfural was vaporized from the rice straw. Fine-grinding to below 150 μm after steam treatment resulted in high water resistance and an internal bonding strength of 0.6 MPa, which met the Japan Industrial Standards (JIS) requirement for Type-30 medium-density fiberboard (MDF). This mild pretreatment offers an alternative to steam explosion.
Highlights
Rice straw, an agricultural residue of rice production, is a potentially useful lignocellulosic material
The purpose of this study was to investigate the effects of steam treatment on the properties of binderless boards made from rice straw
The drainage was dark in color, including fine particles provided from the defibrated rice straw chips
Summary
An agricultural residue of rice production, is a potentially useful lignocellulosic material. Most rice straw is used for landfill or is burned, but this leads to methane gas production or air pollution. Manufacturing particleboard and fiberboard would be a valuable alternative, with a potentially large market. The characteristics of rice straw tend to lead to low-quality boards. Rice straw is not wetted or penetrated well by hydrophilic urea formaldehyde (UF) resin or phenol formaldehyde (PF) resin, due to its inorganic silica content and wax-like substances covering the surface [1,2,3]. Several pretreatments have been examined to improve these compatibility issues between rice straw and resins.
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