Moisture adsorption behaviour of esterified rubber wood (Hevea brasiliensis)

Rubber wood (Hevea brasiliensis) esterified with acetic anhydride, maleic anhydride and phthalic anhydride was studied for moisture adsorption behaviour. FTIR spectroscopic technique was used to analyse the chemical changes in the wood through the correspondent reactions. Spectra indicated increasing intensity of the C=O and C-O stretching bands, and reduction in O-H stretching vibrations that reflects formation of less hygroscopic ester bonds with hydroxyl groups of cell wall polymers. Moisture adsorption isotherms show low equilibrium moisture content in esterified wood at all relative humidity values as compared to a control. The adsorption data was analysed by applying Hailwood-Horrobin theory which separated the adsorbed water into hydrated water and dissolved water corresponding to mono-layer and multi-layer adsorption. Curve for M-h and M-s were similar in pattern for esterified wood and control with different magnitude. Low M-h and M-s in esterified wood indicate reduction in moisture adsorption sites. Inaccessible fraction of wood for water vapour was increased by 43%, 32% and 26% in acetic, maleic and phthalic anhydride treated wood, respectively, compared to the control. Acetic anhydride treatment was found most effective in reducing hygroscopicity of wood.