DIMENSIONAL STABILITY, MECHANICAL-PROPERTIES, AND COLOR CHANGES OF A LOW-MOLECULAR-WEIGHT MELAMINE-FORMALDEHYDE RESIN IMPREGNATED WOOD

Specimens of sugi (Cryptomeria japonica D. Don) wood were treated with water soluble melamine-formaldehyde resin with low molecular weights. The dimensional stability with moisture, the mechanical properties, a nd the color changes caused by the treatment were investigated. The re sults obtained were as follows: With increases in resin concentrations , the weight percent gain (WPG) increased. Both the bulking efficiency (BE) and the antiswelling efficiency (ASE) were increased up to about 15% concentrations (WPG: 22-34%), followed by a leveling off. The tre ated specimens at a 25% concentration (WPG: 58%) had BE and ASE of abo ut 5 and 42%, respectively. Both BE and ASE of the treated specimens m aintained stability during wetting and drying cycles, but with boiling they decreased drastically. The increases in the modulus of elasticit y (MOE) and the modulus of rupture (MOR) at a 25% concentration were a bout 10% and 18%, respectively. However, slight decreases in MOE and M OR were detected at the low levels of concentrations below 5%. Remarka ble decreases in abrasion resistance and linear increases of the surfa ce hardness with increasing concentrations were observed. The color ch anges by the treatment were not significant. Those with irradiation of a sunshine-carbon-arc light became smaller with increasing concentrat ions.