Distribution characteristics of rosin size and their effect on the internal sizing of paper

It was attempted to systematically elucidate three aspects of acidic and neutral rosin sizing. These were (a) the relationship between sizing efficiency and the retention behavior of rosin sizes at the wet end, (b) the effect of pulp beating and fiber fines on the size distribution and sizing properties of paper, and (c) the distribution characteristics of rosin size on pulp fiber surfaces in internal paper sizing. Pyrolysis-GC and the oxine extraction method were used to determine the retained amounts of rosin size and aluminum in the paper. Scanning electron microscopy (SEM) and SEM-EDXA (energy dispersing X-ray analyzer) were employed to evaluate the distribution of rosin size on the pulp fiber surfaces. Under neutral to alkaline conditions neutral rosin and acid rosin sizes yielded distinctly differing sizing effects. The results depended to a great degree on the chemical stability of rosin particles and the retention efficiency of each type of sizing agent under the wet-end conditions of papermaking. Pulp beating and fiber fines influenced the size distribution and sizing properties of paper. Both pulp beating and the existence of fiber fines were considered as important contributing factors leading to the observed uneven rosin size distribution. Furthermore, the rosin size was unevenly distributed on the fiber surfaces not only for freeze-dried paper, but also for cured paper, and its distribution was similar for both types of papers and correlated to that of aluminum. A continuous rosin size film could not be formed even after drying by heating. It is proposed that an uneven aluminum distribution on fiber surfaces can be a root cause of non-uniform sizing with rosin.