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Summary Four softwood and three hardwood species were liquefied using polyethylene glycol (PEG) or glycerol-containing PEG solvent systems as liquefaction reagents under defined reaction conditions: wood / liquefaction reagent / sulfuric acid = 3.00/9.00/0.27 gram, at 150 °C. The percentage residues and hydroxyl numbers were determined as an estimate of polyol value of the solution. The PEG system yielded 10–30% residual materials even under the best reaction conditions since low -OH group content resulted to re-condensation of liquefied wood (LW). The hydroxyl numbers linearly decreased from 210 to 100 mg KOH/g on extended (150 min) reaction time. On the other hand, addition of 10% glycerol to the PEG system resulted in small amount of unliquefied residues (~ 3%) and a stable hydroxyl number, regardless of the wood species tested. In case of 60 min reaction time, the mean residue value was 5.8% and a corresponding mean hydroxyl number of 216.1 mg KOH/g was obtained. This system is deemed suitable for liquefaction of a wide variety of wood species.

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