Impact of a 2-year environmental exposure on colour, structure and chemistry of cork

Abstract

A field test with two-year-long exposure of natural cork to aboveground and underground conditions was carried out with analysis of CIELAB colour parameters, cellular features by scanning electron microscopy, and surface chemistry by ATR-FTIR. The impact of weathering and soil burial was different regarding changes in colour and surface chemistry. Under atmospheric exposure to weather, cork was bleached (ΔE* 17.1) mainly due to the photooxidation of lignin by UV-radiation and hemicellulose degradation, with suberin remaining mostly unaffected. With soil burial, cork darkened (ΔE* 19.7) while significant depolymerization and degradation of suberin and hemicelluloses occurred in addition to lignin alteration. Only the external one-cell layer at the surface was affected with some cellular expansion and minute cell wall fractures, while the material maintained its characteristics without damage or deterioration signs. The cork weathering features are indicative that it can be used in outdoor applications such as building façades or external equipment, with only surface colour dynamics to be taken into account.