Paper Materials

The Outlook.

A consideration of the problem of raw mate rial supplies is, therefore, on the whole reassuring. Difficult and complex as many of the issues undoubtedly are, and likely as they are to cause anxiety from time to time, all the indications appear to confirm the belief that the world is, on the whole, alert to them, and that future requirements will be met.

In the industrially more advanced countries of Europe and North America it appears likely that the raw materials at present in use will continue to be available and will have to be relied upon to meet future requirements. New materials are, however, continually being suggested and tried in these markets, but they do not displace or compete with those already in use. The fact is that the materials thus in use to-day are in use because of certain optimum combinations of ultimate fibre length, cellulose percent age, adequate market supplies of standard quality, suitability for economic manipulation in the factory, and so on, realizable by using them and not as obviously realizable by using other materials suggested from time to time. And the paper industry is one of severe competition at hard cut prices, and it is therefore not easy for a new material to establish itself in use. The conditions are undoubtedly very exacting, and to stand any chance of success at all the material must satisfy a number of simultaneous condi tions, and do it fairly obviously, otherwise the manufacturer will not feel free to take the risk of adjusting his mill procedure to the adoption of it as a raw material. And thus, in spite of con tinuously rising prices, no new material of any real importance has appeared since esparto and wood first came into use about 186o and 188o respectively.

Classification of Material.

In the modern sense, paper may be regarded as a tissue of fibrous cellulosic material, the individual fibres of the original raw material from which it was made hav ing been first separated from one another by mechanical or chemical action, and thereafter felted together to form the tissue. The fibrous cellulosic materials available to the practical paper manufacturer may be broadly catalogued as follows : For whites, writings and printings—rags, esparto, woodpulp.

For browns, wrappings and boards—wood, hemp, jute, straw, waste paper.

For the better grades the cellulosic materials should be pure cellulose, that is, freed from the incrustants with which cellulose is so frequently associated in the plant : for other grades it is frequently preferable to remove the incrustants only partially or not at all. Ordinarily the elongated cells known as fibres are the portions of the plant which are of value for paper, but the ordinary short plant cells are also sometimes of value.

Pure cellulose fibres, free from incrustants, are easily obtained from cotton, since the plant forms the cotton fibres without in crustants (other than slight traces of resinous substance easily removed by treatment with a dilute solution of soda ash), and without any short cells adhering to them. In flax, hemp and jute, the plant forms typically massive bundles of fibres in which the fibres adhere to one another more firmly than they do to the cellular matter surrounding them, and from which they are freed, industrially, by a variety of processes such as retting, scutching and so on. In wood, esparto and straw the fibres are most inti

mately associated with incrustants (lignone or pectin, with which they form the so-called "compound celluloses"), from which the pure cellulose fibres can be separated only by a drastic chemical treatment that, in effect, resolves the material, dissolves away the incrustant and leaves the cellulose proper undissolved. Cot ton, flax and hemp, thus processed, give high yields of cellulose having considerable resistance to chemical treatment, and amounting to 75% and upwards of the original fibre weight. Wood, esparto, jute, straw, bamboo, etc., give a lower yield of cellulose (4o to 6o%) which is less resistant to chemical action.

(I) Rags.—Rags, as they come to the rag boiler, vary greatly in regard to material, cleanliness, colour and strength, and they are graded and valued accordingly. They may contain new linen and cotton cuttings, fine white linens and cottons and inferior similar materials, coloured rags, gunny, rope, sailcloth, canvas, hemp, flax waste, manila, bagging and so on. Cotton, linen, sailcloth and canvas are made into high class hand made and machine made writing papers : rope, gunny, bagging and textile wastes of all sorts are made into wrappers and boards. Rags reach the mill in bales; they are first dusted to remove as much dirt as possible, and are then sorted into grades and such foreign matters as buttons, hooks, leather, rubber, etc., likely to diminish the value of the final paper are removed. The rags are then cut up into small pieces a few inches square, either by hand for the highest grades of papers or by machines for the lower grades. The cutting machines consist of pairs of revolving cylinders carrying one set of knives to cut the rags into strips and another set to cut the strips transversely into short pieces. The pieces are then dusted and shredded in a machine known as a "willow," consisting of an iron drum, bristling externally with iron spikes, revolving inside a box armed internally with similar spikes: a wire grating in the base of the box allows dirt to fall through. The rags are then boiled with solutions of chemicals to remove fatty and greasy matter and sizing materials which may be present: caustic soda ash or lime, sometimes T00% of either and sometimes mixtures of both varying in proportion with the grade made or mill practice, is used for this purpose, in quantity about 5 to 8 per cent of the weight of rags treated, dissolved in an appropriate quantity of water. For the highest grades of material this treatment is made the gentlest : water alone or lime water being sometimes used, if feasible: by gentle treatment only can the best qualities of cellulose be fully conserved. The time of boiling is about three to seven hours, at steam pressures about 15 to 3o lb. to the square inch, and a charge of two to three tons, in a cylindrical or spherical boiler mounted on suitable trunnions to allow slow solution, is common practice.