Low-Density Board from Carbonized Wood Waste I. Board preparation by wet-forming process

The possibility of making low-density board from carbonized wood-waste was examined with a wet-forming process. Pulverized sugi (Cryptomeria japonica D. Don)-wood-waste charcoal, disintegrated waste news paper and a high-molecular-weight phenol resol were used to form boards. To a slurry of a mixture of charcoal particles and pulp fibers an aqueous alkaline resol solution was added and then neutralized with phosphoric acid under agitation. The resol precipitated to form down-like flocks which were deposited on the surfaces of the particles. These resol flocks were considered to perform as an adhesive, melting and curing in the hot-pressing stage. The flexural strength and modulus of elasticity of the board increased as the mix ratio of pulp fiber increased, whereas the Young's modulus of compression in the direction of the board thickness decreased. An increase in the amount of adhesive brought about a great increase in the flexural strength and modulus of elasticity, but only a slight increase in the Young's modulus of the board. The flexural strength of the board decreased as the particle size of the charcoal increased. It is plausible that the collapse of charcoal particles in the hot-pressing stage increases as the particle size increases. Although the boards absorb considerable amounts of water, the volumetric changes are very small.