Chemical investigation of barks from broad-leaved tree species using EGA-MS and GC/MS

The chemical characterization of the bark from eight broad-leaved trees (Betula pendula, Quercus suber, Quercus ilex, Castanea sativa, Quercus robur, Carpinus betulus, Fagus sylvatica and Populus nigra) was carried out using evolved gas analysis-mass spectrometry (EGA-MS) and gas chromatography/mass spectrometry (GC/MS) following alkaline hydrolysis, solvent extraction and derivatisation with a sylilating agent. Not only does bark account for a high percentage of residues from forestry and the wood industry, but it is also rich in suberin, a biopolyester, whose sub-monomeric units can be converted into value added chemicals, as well as being used as starting blocks for the production of new materials. EGA-MS along with principal component analysis (PCA) of the mass spectral data were used to obtain information on the thermal complexity of the barks and on the thermal degradation areas of all their main chemical constituents: suberin, polysaccharides, lignin, tannins and extractives. GC/MS analysis was used for the depolymerisation of suberin, and to examine its monomeric composition. This enabled us to determine aliphatic and mid-chain substituted long-chain α,ω-diacids and ω-hydroxyacids (all with mainly 16, 18, and 22 carbon atoms) along with aliphatic long-chain alkanoic acids and alkanols. Our results may be useful for the exploiting the investigated barks – but not just for energy recovery. In fact, as their suberin shows a high abundance of mid-chain substituted monomers, alternative uses are possible such as the synthesis of polymeric materials by condensation and cross-linking reactions.