QUANTITATIVE-ANALYSIS OF CORK (QUERCUS-SUBER L) AND MILLED CORK LIGNIN BY FTIR SPECTROSCOPY, ANALYTICAL PYROLYSIS, AND TOTAL HYDROLYSIS

A ''milled cork lignin'' (MCL) and a lignin-carbohydrate complex (LCC) have been isolated from Quercus suber with respective yields of 1.5% and 0.32%. Cork and the isolates were characterized by FTIR spectroscopy, elemental analysis, OMe determination, analytical pyrolysis (Py/GC/FID) and acid hydrolysis followed by determination of the monomeric sugars released. Cork contains a lignin-like material in 40% yield. MCL was enriched in this material up to 54%. The non-aromatic part contained suberinic acids and polysaccharides. Both FTIR spectroscopy and pyrolysis revealed the preponderance of guaiacyl-type aromatic rings. Pyrolysis released phenols of which 91% were guaiacyl-type. The yield of phenol, o-cresol, dimethylphenol, p-hydroxy benzaldehyde was around 10% and that of syringyl-type phenols only 1%. Acetic acid, as one of the thermal degradation products of suberinic acids, was detected in high yields both in cork and in MCL. The ratio of hexosans/pentosans in cork was 1/0.76, in MCL 1/2.6, and in LCC 1/3.4. The problem related to the differentiation between lignin and the aromatic part of suberin is discussed.