Scanning probe microscopy of pine and birch kraft pulp fibres

Fibres of the conventional pine and birch kraft pulps were characterized by scanning probe microscopy (SPM). The surface characteristics of these pulps taken at the early stages of pulping were compared with those from later stages of pulping (with or without subsequent oxygen/alkali delignification). It was observed that during delignification a granular surface structure was replaced by a fibrillar surface containing various disruptions. The granular and fibrillar regions were particularly well resolved by using phase imaging in tapping mode of SPM. It was concluded that the granular structure corresponded to surface lignin since the decrease in the relative amount of the granular phase correlated well to a decreasing kappa value of pulps. The surface concentration of lignin, e.g. at the end of pulping was much higher than the bulk lignin concentration. Eventually individual microfibrils (estimated diameter ranging from 0.01 to 0.03 mu m) were observed for both pulps in the cases where delignification was almost completed. (C) 1999 Elsevier Science Ltd. All rights reserved.