Eucalyptus globulusBark as Source of Tannin Extracts for Application in Leather industry

This paper reports the extraction of Eucalyptus globulus bark and a concentration strategy to obtain a phenolic-rich extract for application in the leather tanning industry. The profiles of total phenolic compounds (TPC) and tannins contents in water and dilute alkali as a function of extraction temperature and time led to the selection of the best conditions concerning extraction yield and selectivity. The selectivity profile for TPC and tannins was established, and a maximum of 20 g per kg of bark was found, representing 2.5 g per L of extract produced. On the basis of these results, the conditions selected to produce the extract for the application envisaged in this work were: water, 140 °C and 120 min. To increase the extract concentration, recirculation of the extracts over fresh bark (similar to a continuous bark extraction process) was performed and evaluated. The increment in phenolic compounds was about 4, attaining the final concentration of 8.6 g/L for TPC and 6.5 g/L for tannins. The final extracts showed leather retanning aptitude equivalent to a commercial extract of chestnut and revealed good performance in the production of leather articles like box-calf and nubuck.