OPACITY, SMOOTHNESS, AND TOUGHNESS OF MECHANICAL PRINTING PAPERS - THE EFFECT OF SOFTWOOD KRAFT PULP PROPERTIES

The toughness of paper appears to be a linear function of fiber length . Long fibers from old-growth trees provide a considerable toughness, despite their greater coarseness. This allows about 20% less reinforce ment pulp in the printing paper furnish, which in turn has positive ef fects on the opacity of the paper and the cost of the furnish. The tou ghness of paper appears to be a linear function of the proportion of r einforcement pulp, thus no effect of percolation transition is found. Differences between the reinforcement pulps appear to vanish with heav y calendering, and thus the ''best'' pulps should be used in products where the process stages that are critical for runnability take place before calendering.