Esterification of solid wood for plastic forming

Abstract

Plastic formation from wood has recently attracted immense attention as a new method of producing three-dimensional materials by only one press. In this study, hydroxyl groups in (block-shaped) wood were replaced with ester groups to realize plastic formation. FT-IR measurements indicated that most of the hydroxyl groups in the block-shaped wood were replaced by ester groups after 4 h of treatment. The thermal properties of the esterified wood were investigated; the modulus of elasticity decreased remarkably when heated. Particularly, propionylated wood demonstrated a distinct softening point at relatively low temperatures, demonstrating its thermoplasticity. Additionally, the propionylated wood was stretched extensively by pressing with heat, showing its fluidity. Observation of the end grain of the esterified wood samples after pressing revealed that slippage occurred between the cells, resulting in the bulk flow of the wood. Finally, plastic formation using propionylated wood as the raw material was attempted, and a cup-shaped three-dimensional product was successfully formed. Contact angle measurements demonstrated that the cup-shaped molded product exhibited high water resistance. Thereafter, re-forming was attempted, using crushed fragments of the cup-shaped molded product, and a plate-shaped product was successfully re-formed. Thus, esterification is a promising method for increasing fluidity in solid wood, helping to enable its utilization in plastic forming.