Abstract
Magnesium lignosulfonate and kraft lignin were activated by different oxidizing agents for use in phenolic resin composites used for the production of abrasive components. The physicochemical properties of the oxidized materials were analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), dynamic mechanical-thermal analysis (DMTA) and inverse gas chromatography (IGC). The homogeneity of the model abrasive composites containing the studied products was assessed based on observations obtained using a scanning electron microscope (SEM). FTIR and XPS analysis of the oxidized products indicated that the activation process leads mainly to the formation of carbonyl groups. The IGC technique was used to assess changes in the surface energy and the acid–base properties of the studied biopolymers. The changes in the acid–base properties suggest that more groups acting as electron donors appear on the oxidized surface of the materials. DMTA studies showed that the model composites with 5% magnesium lignosulfonate oxidized by H2O2 had the best thermomechanical properties. Based on the results it was possible to propose a hypothetical mechanism of the oxidation of the natural polymers. The use of such oxidized products may improve the thermomechanical properties of abrasive articles.
Highlights
Lignin was one of the first biopolymers to be discovered
Based on X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis, it was possible to propose a hypothetical mechanism for the activation of kraft lignin and magnesium lignosulfonate by NaIO4 and H2O2
Lignosulfonate oxidized to quinone groups, whereas in kraft lignin hydroxyl groups present at the C-α are transformed to carbonyl groups
Summary
Lignin was one of the first biopolymers to be discovered. The first mention of lignin as an “encrusting material” in wood comes from Payen in 1839. Component C 1s C, not present in kraft lignin when unmodified or activated using NaIO4, shifted by 1.1 ± 0.1 eV from component C 1s B in the direction of increasing binding energies, is attributed to carbon atoms from carbonyl groups. For kraft lignin when unmodified or activated using NaIO4, the signal from carbonyl groups is not present; the signal is visible for the sample oxidized using H2O2, which confirms that this oxidation process was successful. Component O 1s A, with binding energy 532.0 ± 0.3 eV, corresponds to oxygen atoms from carbonyl groups in the magnesium lignosulfonate samples. The results of XPS analysis can be considered as confirmation of the formation of new carbonyl groups in the structure of magnesium lignosulfonate and kraft lignin. It can be concluded that the activation process was performed successfully
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