Characterization of spruce thermomechanical pulps at the fiber cell wall level: a method for quantitatively assessing pulp fiber development using Simons’ stain

Fiber development of mechanical pulps is normally assessed by a combination of conventional numerical analyses of fiber features using FiberMaster, PulpEye, and Kajaani instruments. When observed, changes in fiber morphology are normally subjective with use of light- and electron microscopy observations of representative fibers. Thus, visualization and quantification of changes in the fiber cell wall, like delaminaton/internal fibrillation (D/IF) induced during processing, would offer a great advantage. Here, we developed a method using Simons’ stain (SS) that allows quantification of pulp fiber development in terms of fiber wall D/IF during different process conditions, as well as statistical analysis of whole pulp fiber populations of different thermomechanical pulp (TMP) types for the degree of D/IF developed in pulp fibers. The attributes of SS for producing different colored reactions (blue, green, orange, etc.) in pulp fibers through cell wall modification during processing were used in correlation with light microscopy. The method readily measured the degree of cell wall D/IF of pulp fibers from different double-disc refined TMPs produced using varying levels of specific energy and refining pressures. The SS method revealed the presence of five sub-fiber populations in a whole pulp of a given TMP type representing different categories of fibers that possessed varying degrees of cell wall D/IF as a result of process conditions/treatments. Results of statistical analysis indicated that, while D/IF was significantly induced by both the applied refining pressure and specific energy, the effect of energy had the greatest influence. Based on statistical analysis for Bauer McNett fractions of 10, 30, and 50 mesh, we suggest that fraction 30 is the most suitable fiber fraction for the analysis of TMPs using fiber characterization procedures, as this fraction possesses the most treated fibers. The method provided useful information regarding pulp fiber development at the cell wall level that has the potential to explain pulp and paper properties developed in furnishes. The present SS method represents a valuable tool for assessing fiber development at the cell wall level in mechanical pulping.