Six Taiwanese biomass materials, namely: rice (Oryza sativa L.) hull; rice bran; sugarcane (Saccharum officinarum L.) bagasse; Taiwan acacia (Acacia confusa Merr.) bark; Taiwan acacia foliage; and Taiwan acacia leaf, were extracted with a 22% solution of sodium hydroxide at 95 degreesC for 16 h and at an elevated temperature of 135 degreesC for 4 h. These extracts were reacted with 44% formalin for 2 h at 60 and 80 degreesC, respectively, to investigate their reactivity toward formaldehyde. The free formaldehyde in the reaction mixtures was quantitatively determined by hydroxylamine hydrochloride titration to an end point of pH 4. Extraction temperature, reaction temperature, and type of biomass material were found to significantly influence the reactivity of the extracts with formaldehyde. The 135 degreesC extracts of sugarcane bagasse absorbed the highest amount of formaldehyde while the 95 degreesC extracts of Taiwan acacia foliage absorbed the least amount of formaldehyde. (C) 2001 Elsevier Science Ltd. All rights reserved.