THE THERMOCHEMICAL DEGRADATION OF CORK

The thermochemical degradation of cork from Quercus suber L. was studied in the temperature range 150-degrees-C-450-degrees-C in relation to mass loss, chemical composition and the influence on the cellular structure. The degradation of cork is strongly dependent on temperature and mass losses become significant at 200-degrees-C (15% of initial dry weight) and increase rapidly for higher temperatures (27% at 250-degrees-C, 49% at 300-degrees-C, 62% at 350-degrees-C) until ashing at 450-degrees-C. The polysaccharides are the most heat sensitive components: at 200-degrees-C, hemicelluloses disappear and cellulose is degraded to a considerable extent. Suberin is more resistant and degradation starts at approx. 250-degrees-C; 300-degrees-C-treated samples only contain 7% suberin. The cellular structure of cork is also significantly influenced by temperature. Upon heating, cells expand and the cell walls stretch, attaining at 250-degrees-C a maximum cell volume increase corresponding to a factor of approximately 2. Above 300-degrees-C, the structure of cell walls is considerably changed and show profound physical damage; in the later stages of pyrolysis, a cellular structure is no longer observed.