Lignin behavior during the autocatalyzed methanol pulping of Eucalyptus globulus - Changes in molecular weight and functionality

The molecular weight distribution and functional group contents (phenolic and carbonyl) of lignin samples from the autocatalyzed pulping of Eucalyptus globulus wood were determined. A total of 17 pulping runs were carried out at different conditions according to a surface response design experimental matrix (central composite). The influence of pulping temperature (170-200 degrees C), pulping time (40-120 min) and methanol concentration (30-70 %, w/w) on the characteristics of the isolated lignins was studied. Empirical models were developed and used to predict the lignin properties as a function of the cooking conditions. Under high temperature, long cooking time and low alcohol concentration, a rise in functional groups content and a drop in molecular weight of lignin can be observed.