Kinetic studies of the acetylation reaction of small Pinus radiata blocks

The reaction kinetics between acetic anhydride and small Pinus radiata blocks was found to be diffusion controlled over the temperature range examined (80–120 °C), with an activation energy of 34 kJ/mol obtained from initial rate constants. The rate-limiting diffusion appeared to be through the wood cell wall layers, rather than through to the cell lumen. It was possible to mathematically model the wood block reaction based on reaction time and temperature, and this model could be used to predict acetylation level for similar sized softwood samples. In addition, a technique for estimating extent of reaction of acetylated wood blocks was proposed using solid state carbon NMR spectroscopy. Overall, this study demonstrated the critical importance of the wood ultra-structure, sample size and reaction conditions in determining the rate of acetylation (diffusion- or activation-controlled) in wood and wood-based substrates.