Kinetic color analysis for assessing the effects of borate and glycerol on thermal modification of wood

The effects of borate and glycerol impregnation of Douglas-fir heartwood prior to open-air oven thermal modification at 160–200 °C for 2–4 h on wood color were measured. These materials were used to analyze the effects of modifying agents on thermal decomposition of wood by color nondestructive assessments. Kinetic analysis using time–temperature superposition and the horizontal shift factor were employed to quantify color changes. Lightness values were significantly affected by heating time and temperature, while red/green and yellow/blue values were significantly affected by pretreatments and thermal modification temperatures. Total color differences tended to increase with heating temperature and time. The calculated values of the apparent activation energy on non-impregnated, borate-impregnated and glycerol-impregnated wood ranged from 94.9 to 126.4 kJ/mol, 46.5 to 74.3 kJ/mol and 54.3 to 79.7 kJ/mol, respectively. The results suggest that borate and glycerol decreased the apparent activation energy of thermal degradation reactions and could function as a catalyst to accelerate thermal modification. Time–temperature superposition color kinetic analysis could be used to assess the effects of modifying agents on thermal decomposition.