Abstract

The weight percentage gain and the acetyl group content of wood due to acetylation with acetic anhydride have been analysed by means of Fourier transform infrared spectroscopy (FT-IR) and Fourier transform near infrared spectroscopy (FT-NIR). Spruce wood of various sample shapes, chemically modified by applying acetic anhydride with and without catalysts and, as close as possible to industrial applications were selected from the sample sets used previously for calibration/quantification. In the previous paper, band assignments were provided to an extent to understand the functional groups upon which the calibrations were based. In the present work the qualitative results are extensively discussed with respect to the literature including old and new band assignments. Therefore, this article features some characteristics of a review. It has been proved that, using either FT-IR or FT-NIR, it is possible to follow chemical changes in wood due to acetylation. Fourier self-deconvolution and second derivatives of the mid-infrared spectra provided identical additional information. The disappearance of functional groups, such as hydroxyl groups, as well as the appearance of carbonyl groups and methyl groups in the acetyl ester groups, allowed us to confirm results from other studies including the accessibility and reactivity of the hydroxyl groups. A new, definitive band assignment of the second overtone of the C=O stretching vibration from acetyl groups at 5242 cm⁻¹ was possible. Furthermore, it is shown that, with increasing weight percentage gain, aromatic esters are formed which can be distinguished from the alkyl esters in FT-IR. However, certain questions concerning the accessibility and reactivity of the hydroxyl groups and band assignment still remain.

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