Characterization of alkali-extracted wood by FTIR-ATR spectroscopy

Attenuated total reflectance (ATR) infrared (IR) spectroscopy analyses were performed with silver/white birch (Betula pendula/B. pubescens) and Scots pine (Pinus sylvestris) chips pretreated under alkaline (from 1 to 8% NaOH charge on wood dry solids) conditions to determine the suitability of this method in quickly determining chemical changes caused by varying treatment conditions on wood chemical structure. In addition to the alkali charge, pretreatment conditions varied with respect to temperature (130 and 150 °C) and treatment time (from 30 to 120 min). The spectral data of pretreated wood samples were compared to those of untreated reference samples, and the effects of the pretreatments conducted were determined based on these data. Results indicated that the most essential phenomena taking place during alkaline pretreatments could be detected by applying this simple and rapid spectral method requiring only a small sample amount. Such information included, for example, the cleavage of common lignin and carbohydrate bonds together with the significant removal of organics, especially hemicelluloses during pretreatments.