Alkaline solvent cooking treatment of cork and component analysis of filtrates
This study aimed to determine the effects of alkaline solvent treatment on the physical properties of cork, and to analysis the filtrate components of cork after cooking treatment. Potassium hydroxide (KOH), alkaline hydrogen peroxide (AHP), and ammonium hydroxide (AOH) were used as solvents. The properties of treated cork including color, volume, hardness, compression resilience ratio, and filtrate components of different solvent treatments were investigated. The results showed an increase in the cork’s volume, changes in color, and decrease in lightness after three solvent treatments. Hardness and compression resilience decreased after three solvents cooking, and the difference in the compression resilience ratio between 15 min and 24 h was at a minimum when cork was cooked in KOH solvent. The analyses of filtrate components after KOH and AHP cooking treatments indicated that the hemicelluloses content was generally higher than lignin content. Moreover, water-soluble lignin, obtained from the three solvent filtrates, consisted of a small amount of monosaccharides, such as arabinan, galactan, glucan, and xylan. Nuclear magnetism (NMR) spectra analysis demonstrated that the lignin in KOH and AOH filtrates consisted of G units and H units, while S units only appeared in KOHimmersed lignin. This study shows that solvent treatment changes cork’s physical and chemical properties based on the solvent type and concentration.