Isolation of high-purity residual lignins from eucalypt paper pulps by cellulase and proteinase treatments followed by solvent extraction

In the context of environmentally-friendly bleaching in paper pulp manufacturing, an enzymatic procedure was developed for the isolation of residual lignins from eucalypt pulp. The method was based on the hydrolysis and complete solubilization of pulp cellulose using a combination of Trichoderma cellulase and Aspergillus β-glucosidase, followed by lignin purification using Bacillus protease (for hydrolysis of contaminating cellulase) and extraction of lignin with dimethylacetamide (DMAC) and NaOH. This method was applied to both unbleached and totally chlorine free bleached eucalypt kraft pulps. The different fractions obtained were analyzed by Fourier-transform infrared spectroscopy and pyrolysis-gas chromatography/mass spectrometry to evaluate the effect of the different isolation steps, and optimize the lignin isolation procedure. Depending of the type of pulp and its delignification degree most of the lignin was recovered from the cellulase hydrolyzate or the non-hydrolyzable residue. High-purity lignins were obtained from pulps by a new isolation procedure that included double solvent purification after combining the two fractions from protease treatment. This method is being used to analyze the effect of chlorine-free reagents (including enzymes) in clean bleaching sequences.