Chemical changes of heat treated pine and eucalypt wood monitored by FTIR

Abstract

A hardwood, Eucalyptus globulus Labill., and a softwood Pinus pinaster Aiton., were heat treated at temperatures between 170 and 210ºC in an oven and in an autoclave. The samples were pre-extracted with dichloromethane, ethanol and water and ground prior to Fourier Transform Infrared (FTIR) spectroscopic analysis.The heat treatment caused significant changes in the chemical composition and structure of wood, in lignin and polysaccharides. Hemicelluloses were the first to degrade as proved by the initial decrease of the 1730 cm -1 peak due to the breaking of acetyl groups in xylan. Hardwood lignin changed more than softwood lignin, with a shift of maximum absorption from 1505 cm -1 to approximately 1512 cm -1 due to decrease of methoxyl groups, loss of syringyl units or breaking of aliphatic side-chains. The macromolecular structure becomes more condensed and there is a clear increase of non-conjugated (1740 cm -1 ) in relation to conjugated groups (1650 cm -1 ). However, the changes induced by the thermal treatment are difficult to monitor by FTIR spectroscopy due to the different chemical reactions occurring simultaneously.

Chemical Analysis of Densification, Drying, and Heat Treatment of Scots pine (Pinus sylvestris L.) through a Hot-Pressing Process

“…With respect to the esterification reaction of the acid and hydroxyl radicals in wood, similar results were obtained by Kotilainen et al (2000), Tjeerdsma and Militz (2005), and Esteves et al (2013). During esterification, the absorption intensity at 1269 cm -1 increases because of vibrating acetyl ester groups, which was observed in the specimens (Table 5).…”

Aging of wood under long-term storage in a salt environment

“…The region from 1709 to 1738 cm -1 (including 1730 cm -1 ) can be assigned to the C=O stretch in unconjugated ketones, carbonyl stretching vibration of the acetyl group of hemicellulose (Terpáková et al 2012) and in ester groups frequently of carbohydrate origin (Faix 1991). It is assumed that hemicelluloses degraded by breaking acetyl groups in xylan (Esteves et al 2013). The region from 1225 to 1235 cm -1 origins from the OH vibration (deformation in plane), also from COOH (Fengel and Ludwig 1991).…”

Effects of Ageing on the Color and Surface Chemistry of Paulownia Wood (P. elongata) from Fast Growing Crops

“…Infrared spectra are sensitive indicators of chemical changes, especially light-induced natural and accelerated ageing (Colom et al 2003;Pandey 2005;Pandey and Vuorinen 2008;Chang et al 2010a,b;Roşu et al 2010;Tolvaj et al 2013). Moreover, chemical changes in thermally treated wood revealed by FTIR (Tdjeersma and Militz 2005;Esteves et al 2013;Chen et al 2014;Tolvaj et al 2014b;Fabiyi and Ogunleye 2015) may be helpful in understanding temperature-induced ageing (Matsuo et al 2011).…”

“…Temperature-induced ageing (in the absence of light) is the combined effect of hydrolytic and thermo-oxidative processes of wood components, mainly of hemicelluloses (the most labile) leading to formation of chromophore containing products. Cleavage of lignin units followed by condensation and depolymerisation of cellulose may also occur, with the whole process being highly influenced by the environmental conditions (presence of air and humidity) (Tdjeersma and Militz 2005;Esteves et al 2013;Froidevaux and Navi 2013;Chen et al 2014;Kránitz et al 2016). For wood used over a long period under ambient temperature conditions, ageing may be due to the combined effect of thermal oxidation by air-oxygen and acid hydrolysis by bound water and acids contained in the wood, whilst in dry heat conditions thermal oxidation is the main factor for color change during ageing (Matsuo et al 2011).…”