Mass insulation enhancement of cork stoppers through heat treatment: experimental measurements, modeling, and optimization

Natural cork stoppers, used as bottle sealers for high-end products such as ingredients and flavorings, belong to the highest class in terms of cork quality. Various studies have been carried out to examine the solute diffusion in cork using conventional methods. However, the investigations were limited to natural cork stoppers that had been boiled and cut in a single direction. In this study, the anisotropic cylindrical shape of cork samples was modeled, considering various cutting directions. Additionally, we subjected the stoppers to boiling then to an optimal THT cycle to improve the cork's mechanical qualities. The optimal thermal cycle is determined using TGA analysis. IR and SEM tests are employed to verify the enhancements in the cork. The apparent mass diffusion coefficient (Dapp) is determined by the calibration of the model with the experimental data acquired via the conductometric method. The coefficient values are optimized using the Bat algorithm with a relative error of 10–5. The Dapp was found to be better for the treated cork grown in the Jijel region than for the cork Medea, which is better than of Skikda cork. Regarding the impact of the cutting direction on the Jijel's cork, the results indicate that the mass insulation is higher when the treated stoppers are cut in the tangential-longitudinal direction (DJTLt=4,12.10-13m2s-1) compared to the tangential-radial direction (DJTRt=7,75.10-13m2s-1) and the longitudinal-radial direction (DJLRt=8,53.10-13m2s-1). The treatment, which serves as a solution for the cork industry, showed an improvement in mass insulation 13-fold greater than the natural cork.