The aim of this study is to understand better the oxidation mechanism of the oxidation of fatty acids applied on wood surfaces. The drying process of air-drying fatty acid based systems has been extensively studied in coating systems but this has in most cases been performed on other substrates than wood. Currently, what is not understood is how wood components are chemically affected by the radicals involved in auto-oxidation and thus the effect of wood OH-radicals on unsaturated fatty acids has been evaluated in the present work. In the study presented here, the auto-oxidation process of methyl linoleate was measured in combination with wood compounds at 70 °C. The influence of wood model compounds, having phenolic, non-phenolic and polysaccharide structures, on auto-oxidation of methyl linoleate (ML) was observed by infrared spectroscopy (RT-IR). In our previous work it was observed that phenolic groups and radical conjugation are the main contributors to an antioxidant effect of lignin compounds on the oxidation rate of the methyl linoleate (Salehi 2010). The auto-oxidation process of methyl linoleate was measured in combination with 1 wt% reducing and non-reducing hemicellulose model compounds (HMC) at 70 °C. The effect of HMC on the methyl linoleate auto-oxidation process was also compared with the effects of glycerol and glycraldehyde, using same analytical method and reaction conditions. The IR-spectra of methyl linoleate with 1wt% carbohydrates before and after oxidation were analyzed and peak intensity variations in the region of 3010 cm-1 were calculated during the oxidation process. Hemicellulose model compounds were found to accelerate the radical reactions. Moreover, same analytical methods have been used to characterize the effect of different wood species on the mechanism of fatty acids auto-oxidation. The results indicated that hardwood have strong antioxidant activity on ML oxidation time, while ML oxidized faster with softwood (25 wt% relative to ML).
Keywords: Auto-oxidation, Methyl linoleate, Wood model compounds, Softwood, Hardwood
Authors
Salehi M. A.
Wallenberg Wood Science Centre (WWSC) and Department of Fibre and Polymer Technology, Stockholm, Sweden
Henriksson G.
Department of Fibre and Polymer Technology, School of Chemical Science and Engineering. KTH, Royal Institute of Technology Stockholm, Sweden
Johansson M.
Department of Fibre and Polymer Technology, School of Chemical Science and Engineering. KTH, Royal Institute of Technology Stockholm, Sweden
Login to download the PDF