Bond Formation by Wood Surface Reactions Part II. Chemical Mechanisms of Nitric Acid Activation

Abstract Previous research on chemical bonding has shown that a wood bond can be achieved by surface reactions when the wood is chemically activated prior to pressing. Activation by nitric acid appears to produce the most consistent results. The objective of this study was to elucidate the chemical mechanisms of nitric acid activation through the use of analytical instrumental techniques and identification of wood degradation products. Infrared and ultra-violet spectroscopic analysis of nitric acid treated sugar maple and isolated wood polymers indicated extensive oxidation, nitration and hydrolysis of the wood polysaccharides and lignin. The major effects were noted at ambient temperature although additional treatment at 100°C caused further modification. The lignin and xylan (hemicellulose) were the most extensively modified components as monitored by Klason lignin, Kjeldahl nitrogen and sugar analyses. Lignin is heavily nitrated and over 30% of the xylan (xylose) is lost during nitric acid treatment. The major degradation product isolated from nitric acid treated maple was 2, 4-dinitroguaiacol. These findings suggest that oxidation, nitration and hydrolysis of wood polymers are important aspects of nitric acid activation of wood surfaces.