Mixed acylation of Scots pine sawdust and impact on hydrophobicity

Abstract

Acetic–fatty esters of Scots pine sawdust (SPS) were obtained by reaction of SPS with mixtures containing acetic–fatty anhydrides and no solvent or catalyst. Such mixtures were synthesized by reaction between a carboxylic acid and acetic anhydride. The global reaction of acetic anhydride and a fatty acid yields at equilibrium a mixture of five compounds: acetic–fatty anhydride, acetic anhydride, fatty acid, acetic acid and fatty anhydride. The influence of temperature, molar ratio, reaction time and length of the fatty chain on the esterification and on the ratio of grafted acetyl/fatty acyl was investigated. Static contact angles (CAs) with water were measured over 5 min. CA values were dependent on the fatty acyl content and independent of the acetyl content. The minimum ester content of the oleoyl group required to obtain permanent water repellency was 25 mmol kg⁻¹. Water vapour adsorption measurements indicated that in contrast to water repellency, hydrophobicity to water vapour was correlated with the total mass acyl content.

Keywords:

• Acetylation
• fatty acylation
• hydrophobicity
• mixed anhydrides
• wettability
• wood esters

Acknowledgements

We thank LAPEYRE (France) for a research grant and Mr Michael Charton for his valuable technical help.