Evaluation of the structural and molecular weight changes of lignin during the treatment of hardwood alkaline peroxide mechanical pulp with laccase and a laccase-mediator-system

Abstract

Alkaline Peroxide Mechanical Pulp (APMP) of triploid of Populus tomentosa was modified by laccase and a Laccase-Mediator-System (LMS). The influence of the following main variables on the pulp physical properties were studied: enzyme dosage, reaction time, treatment temperature, and pH. Under the optimum conditions of laccase treatment – pH 5, temperature 50°C, pulp consistency 4%, and a reaction time of 60 min – the optimum charge of laccase was 2u/g. It was also found that the tensile strength and tear indices of the pulps treated with laccase increased significantly. The two-stage method of enzyme-mild acidic hydrolysis was adopted to isolate lignin from the APMP pulps both before and after enzymatic treatments. The functional groups in all lignin samples were qualitatively and quantitatively analyzed with 31P-NMR spectra. The molecular weight distributions of all the lignin samples were obtained through Gel Permeation Chromatography (GPC) after the lignin samples were benzoylated.