Differential scanning calorimetric studies of the reaction between lignocellulosic materials and hydrogen peroxide using model compounds

Abstract

Reaction of hydrogen peroxide with twenty lignocellulosic polymers and model compounds was studied by differential scanning calorimetry at 6722 kPa (975 psi) in nitrogen and oxygen atmospheres. Two exotherms were identified. Exotherm A peaked between 109 and 186°C in N 2 and O 2 with the heat of reaction Δ H a ranging from 738 to 2638 cal g −1. Exotherm B peaked between 180 and 254° C in either atmosphere with Δ H b = 109–346 cal g −1 in N 2 and with Δ H b= 1356–4325 cal g −1 in O 2. With one exception, exotherm B appeared in N 2 only in the case of the materials which possessed acetal or hemiacetal linkages. It was concluded that exotherm A resulted from decomposition of H 2O 2 under formation of O 2 and oxidation of organic compounds, while exotherm B resulted from oxidation of hydroxyl groups by O 2. A mechanism was proposed for the formation of O 2, which involved hydrolysis of acetal or hemiacetal linkages to aldehydes or ketones, formation of α-hydroxyperoxides by addition of H 2O 2, oxidation of a-hydroxyperoxides by hydroxyl radicals, decomposition of the resulting free radicals under formation of superoxyl radicals and oxidation of superoxyl radicals either by hydrogen peroxide or by hydroxyl radicals to oxygen.