Application of Strong Acids for Enhanced Woody Film Production from Ball-Milled Wood

Abstract

Our previous study on Japanese beech-derived films revealed that the raw wood material required long dissolution times (3–5 d) in formic acid upon stirring at room temperature. To accelerate this process, we studied the dissolution process of wood and revealed that the addition of a small amount of a strong acid, such as hydrochloric acid, trifluoroacetic acid, or cation-exchange resin, to formic acid shortened the dissolution time from a few minutes to 24 h at room temperature. Visual observations, viscosity measurements, and size exclusion chromatography measurements were conducted by varying the amount of hydrochloric acid and the stirring time, revealing that the higher the acid concentration and the longer the stirring time, the lower the degree of polymerization and molecular weight of the polymer. Tensile tests and scanning electron microscopy revealed that the films prepared from solutions with higher acid concentrations and longer stirring times were slightly more brittle than those made without the addition of strong acid. However, the films were sufficiently strong compared with common plastics. The developed method significantly reduced film-making time, representing a promising step toward the practical application of environmentally friendly wood-derived films.