TG/MS, Py-GC/MS and THM-GC/MS study of the composition and thermal behavior of extractive components of Robinia pseudoacacia

Abstract

The thermal behavior and composition of extractives of 1-year-old shoots of Robinia pseudoacacia (black locust) have been studied. The extractives have been eliminated from the wood samples with Soxhlet extraction using different solvents. The study of the thermal decomposition of the extracted materials has been performed with thermogravimetry/mass spectrometry (TG/MS). For the qualitative analysis of the extracted compounds pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and thermally assisted hydrolysis and methylation-gas chromatography/mass spectrometry (THM-GC/MS) methods have been used. The thermal behavior of the original and extracted wood samples has also been investigated with the same thermal methods. The obtained results imply that the extractives decompose in the same temperature range as the natural polymers that make up the cell walls of plants. Although the decomposition pathways of polysaccharides and lignin are not altered by the extractive compounds, the extractives evolve additional products influencing the product distribution of the whole wood samples. The comparison of extraction procedures has shown that the quality of the solvent and the extraction time significantly influence the amount of extracts eliminated from the plant sample. All the applied solvents (ethanol, acetone and dichloromethane) were capable of removing the phytosterols from the wood. However, fatty acid esters remained in the extracted wood samples in significant amounts even after successive extraction by dichloromethane, ethanol and water.