The determination of the alpha-cellulose content and copper number of paper

Abstract

In determining the permanence of a paper it is important to know the purity of the cellulose composing it. The tests most commonly used for the determina-tion of the purity of cellulosic materials are the alpha cellulose and copper number tests. The alpha-cellulose test is based upon the assumption that unmodified cellulose is insoluble in a mercerizing caustic solution. This insoluble portion is termed "alpha cellulose." The copper-number test is based upon the quantita-tive reduction of an alkaline copper solution by the degraded celluloses of the sample. The copper number is the weight of copper so reduced by a definite weight of the sample. Both of these tests have been highly developed for the analysis of cellulosic materials in a loose, fibrous form, such as paper pulp. But the fibers of paper are packed into a dense, compact sheet and, hence, methods which can be applied to other forms of cellulose can not be applied to paper. Also, papers contain several noncellulosic constituents which must be taken into account. Methods which have been proved reliable for the analysis of other forms of cellulosic materials have been modified by the bureau to make them applicable to paper testing. The modification considered of prime importance is the reduction of the sample to a cotton-like form by means of mechanical disintegration. It is also important to correct the results for the amounts of sizing and loading materials in the paper. Several minor details of the methods have been altered for purposes of simplicity and increased accuracy. By the use of the alpha-cellulose method duplicate determinations of the percentage of alpha cellulose agree within 0.3. Duplicate results obtained with the copper-number method seldom vary more than 1 per cent from their mean.