Oxidation of methyl linoleate in the presence of lignin

The overall aim of this study is to develop new wood modifications using vegetable oils to obtain improved durability of wood materials in an environmentally friendly way. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies were used to study oxidation and possible chemical coupling reactions between polyunsaturated fatty acids and model lignin compounds in order to better understand the interactions between oxidatively drying systems such as vegetable oils or alkyds with the lignin part in wood. This was done by studying mixtures of different model lignin compounds and methyl linoleate. The oxidation process was analyzed at 70 °C both in methyl linoleate alone and in combination with 20 wt% of lignin model compounds. The effects of those compounds on the oil polymerization processes were monitored by NMR (both 13C and 1H experiments) and the domain specific reactivity and patterning were then combined with FT-IR data. No covalent bonds having formed between the oil and the model compounds were detected by combination of several 13C/1H 2D NMR methods. From the spectra, the oxidation degrees of model compounds were calculated, and for some lignin model compounds alcohols were oxidized to carbonyls during the process. Those results were in excellent agreement with FT-IR data and oxidation mechanisms were proposed. The combination of both analytical techniques was necessary to have a better understanding of these systems: NMR demonstrated the absence of chemical bond and quantified oxidation degree of model lignin molecules while FT-IR focused on oil oxidation.

► Oxidation of methyl linoleate in the presence of lignin model compounds.
► Effect of different lignin structures.
► Co-oxidation of lignins can occur depending on lignin structure.
► FTIR and NMR versatile analytical techniques for the study.