No abstract

No 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.

Binderless boards are composite boards that rely on self-bonding mechanisms for inter-fibre bonding. Quercus acutissima and Quercus serrata logs degraded by Lentinula edodes (shiitake fungi) were used in this study to investigate whether physical and chemical changes induced by shiitake fungi can enhance board mechanical properties. Binderless boards were manufactured with 0.8 g/cm 3 target density, 220 °C pressing temperature, 5 MPa pressure, and pressing duration of 10 min. Boards made from logs degraded for ≥ 26 months were stronger than control boards and met modulus of rupture (MOR) and internal bonding (IB) requirements for fibreboards. Chemical composition and particle size distribution of the wood powder used to make the boards were determined to elucidate the drivers of board mechanical properties. The proportion of small particles (< 150 µm) showed a strong positive correlation with MOR for both species and hot water extractives showed a strong positive correlation with IB for Q. acutissima boards. Introduction of shiitake fungi pre-treatment to the production process may enhance the mechanical strength of binderless boards.

To produce practicable binderless laminated veneer lumber (LVL) and plywood, their water resistance needs to be improved. The objective of this study was to manufacture highly water-resistant binderless plywood from sugi (Japanese cedar, Cryptomeria japonica), basing on a self-bonding mechanism, without any resins or powders. To achieve this, a pretreatment of wetting and scratching veneers was applied. Two types of wetting conditions, soaking for 12 h, and wetting for 1 min, were examined. Sandpaper or a wire brush was used for scratching. Three veneers were laminated in perpendicular directions and hot pressed at 200-220 °C for 20-45 min using two types of pressing schedule: simple 1-step pressing, or 4-step pressing while gradually increasing the pressure. As a result, whichever wetting time was employed, and regardless of the scratching tool used, plywood could be manufactured with both pretreatments. As the wet shear strength showed a comparable value to dry shear strength, the plywood had high water resistance. The highest wet shear strength was 0.6 MPa, for the plywood made by pretreatment wetting of the surface for 1 min and scratching with a wire brush followed by 1-step pressing at 220 °C for 20 min. This was fairly close to the Japanese Agricultural Standard (JAS) requirement. This study indicated that easy pretreatment and mild pressing conditions achieved a binderless plywood with high water resistance.