Chemical influence of ethanol and ethanol-water solutions on the structural components of cork

Abstract Behaviour of cork structural components (suberin, lignin and polysaccharides) during ethanol-water treatments was studied with different temperatures (135–185 °C), times (53–187 min) and ethanol concentrations (0–100 %), using response surface experimental design. The severity factor combining temperature and time was calculated to indicate different severity conditions (SF 3.1 to 4.6). Extractive-free cork was autoclaved, and mass loss and chemical composition of cork were determined. Mass loss was small, increasing with severity: 3.9 % of cork for SF 3.1, 11.4 % for SF 4.6. The ethanol-treated cork contained soluble material in dichloromethane (DCM) resulting from suberin depolymerization that increased with severity: 1.0 % and 5.4 % of the treated cork for SF 3.1 and 4.6 respectively. Little chemical changes occurred, mostly restricted to the most severe conditions with suberin only decreasing 5 % and lignin 18 % in relation to their original amounts. ATR-FTIR spectra showed very similar chemical profiles between samples. Lignin composition by analytical pyrolysis remained unaltered. Modelling cork depolymerization using solid mass yield and DCM solubles showed very good fit. Overall cork demonstrated considerable stability in ethanol-water processes, confirming higher resistance compared to lignocellulosic materials. Suberin proved remarkably strong and moderate delignification occurred but not to an extent that could impart cork performance properties.