Highly purified wood fibers as paper-making material

Abstract

A semicommercial scale study has been made at the National Bureau of Standards of the manufacture of bond types of papers from commercial highly purified wood firbers for uses requiring permanency. As a part of the investigation, the experimental papers produced were tested for strength, chemical purity, and aging properties. The strength tests included bursting, tensile, and tearing strength and folding endurance. The chemical-purity tests included alpha cellulose content, copper number, acidity, and quantitative tests for the sizing materials present. The accelerated aging test used consisted of heating the papers in air to a temperature of 100°C. for 72 hours, and then measuring the extent of change in the various strength and chemical properties. By studying the effects of variations in beating conditions on the properties of finished papers a method of beating well adapted for this kind of fiber was evolved. The papers had excellent strength properties, exceeding, in the case of the bond papers, the strength requirements of the highest-grade bond papers purchased by the Government Printing Office (U.S.A.) and, in the case of the currency-type papers, the strength requirements for United States currency. The experimental papers possessed also other characteristics desirable in these types of paper. Some of the possible factors influencing the aging properties which arise in the process of converting pulp into paper were studied, including effects of beating; alum (acidity), rosin, and starch used in beater sizing; and glue, starch, alum, and formaldehyde used for surface sizing. The amount of beating required to produce the desired characteristics in the papers had no apparent effect upon the chemical properties of the fibers or upon their stability. A definite relation between the acidity of the rosin-sized papers and their stability was noted. A marked lowering in stability was caused by the use of excessive amounts of alum. By careful control of the acidity of the stock in the beater -i.e., amount of alum added to the beater -it was possible to prepare well-sized papers of very high stability. Other factors being alike, papers with the lowest rosin content had the best resistance to accelerated aging. In general the addition of starch in the beater caused an increase in the strength of the paper and had no deleterious effect upon the stability of the finished paper. The effects produced were practically the same for the two kinds of starch products used, one prepared by a process of acid hydrolysis and the other by a process of oxidation. Unsized and rosin-sized papers were surface sized with glue and starch solutions. In general the bursting strength, tensile breaking strength, and elongation increased on surface sizing and the tearing strength decreased proportionally with the amount of size taken up by the basic paper. No such relation appeared to hold in the case of the folding endurance, which increased on surface sizing about 10 per cent on the average. In the case of the currency type papers, which had exceptionally high folding endurances before sizing, a slight decrease in folding endurance on surface sizing with glue was noted. For the specific samples of glue and starch used in this work, little difference in the final results obtained with them was noted. In general the stability of the papers toward accelerated aging was improved by surface sizing. This protective effect was somewhat more pronounced in the case of glue sizing than in the case of starch sizing. When alum was used in moderate amounts as a preservative for the glue or starch in the surface-sizing baths, it caused no deleterious effect on the paper as far as could be determined by the tests applied.