Paper and Its Uses/Chapter 1
PAPER AND ITS USES
CHAPTER I
RAW MATERIALS
Papermaking is an industry which is in many ways handmaiden to other industries. In the case of letterpress, lithographic, and plate printing it furnishes the supporting medium, without which the dissemination of knowledge would be more difficult. Long ago the printer appreciated the fact that the invention of the art of typography enlarged the sum of the world's knowledge, but perhaps he has not always been ready to give the papermaker a fair share of the credit. It must be conceded that while many things will serve as printing surfaces, the question of cost decides against their general use, and that paper is the principal material employed for written and printed books. It is with these uses that this work deals, while some others are touched upon.
The history of papermaking takes us back beyond the Christian era—the Chinese being credited with the production of paper from vegetable fibres about 80 to 150 B.C. The ancient Egyptians made paper from the stems of the tall reed which we know as the papyrus. By skilfully flattening out layers of the stems, forming them into sheets, and preparing the surface for writing, the Egyptians provided themselves with excellent paper.
European papermaking dates from the eleventh century, and English papermaking from the fifteenth century. The colophon to Wynkyn de Worde's "De Proprietatibus Rerum" mentions the paper mill of John Tate at Stevenage in Bedfordshire. Early English papers were made from rag fibres, and rag papers still hold the premier place.
Cellulose is the substance of which the permanent cell membranes of plants are composed, and it forms the bulk of the tissues of wood and similar plant structures. In most cases the presence of colouring matter and various waxy and resinous substances taken up by the growing plant render the cellulose very impure, and it is desirable that, as far as possible, all impurities should be removed before the fibres are made into paper. Cotton is the purest form of cellulose found in nature, 91 per cent. of the natural cotton fibre being pure cellulose, while esparto yields only about 50 per cent. of its weight as cellulose. Notwithstanding the many different varieties of plants, the chemical composition of the fibres is practically identical. One of the principal characteristics of cellulose is its extreme permanence, which is principally due to the fact that it forms but few chemical combinations with other substances.
Vegetable fibres of all kinds may be converted into paper, but no new fibre threatens those now employed, unless it can be obtained in large quantities, responds readily to the usual bleaching reagents, and can be delivered to the papermaker at a price which enables it to compete successfully with the fibres at present in use at the paper mill. In some cases the plant fibres are reduced to pulp near the place of growth, in others the raw material is transported in its entirety. Other sources of supply are the wastes of other industries, and wastes which have no other uses.
The classification may take place as follows: (a) waste—rags, sails, sacking, ropes, textile wastes, waste paper; (b) plant stems and wood—straw, esparto, bamboo, papyrus, hedychium; (c) pulps or half-stuffs—straw, esparto, delta cellulose (or reed pulp), bamboo, chemical wood, mechanical wood.
Rags are the cast-off fabrics of the civilised world. Having served their purpose in administering to the comfort of mankind, they are sorted, graded, and offered in the market for papermakers. For the manufacture of paper for bank-notes new linen cuttings are used, but this is an exceptional material for a special purpose. Sail cloth, bagging, sacking and ropes, made from hemp, jute, manilla hemp, having reached the waste market, are regenerated in the mill as paper. Waste paper of all kinds is sorted and re-made into paper or boards.
Esparto is the principal material that finds its way to the papermaker in its original state. It is a wiry grass, growing extensively in Spain and Africa, and is harvested and packed in bales for export. Straw is generally imported as half-stuff. Bamboo, papyrus, and hedychium are being used in quite a small way in this country, but may be extensively used in the future.
Straw, esparto, reed pulp, and bamboo are obtainable as half-stuff or pulp, that is, they are already divested of the portions of the plant which are non-fibrous, and therefore useless to the papermaker. Wood pulp is the chief material converted into paper, and may be prepared as chemical or mechanical. Chemical wood pulp is prepared, after removing the bark from the felled trees, and cutting the logs into chips, by boiling with caustic soda solution (soda pulp), with a mixture of caustic soda and sulphate of soda (sulphate pulp), or with bi-sulphite of lime (sulphite pulp). Mechanical wood pulp is obtained by cutting the logs into short lengths, removing the bark, and grinding to pulp on a large grindstone, the surface of which is freely supplied with water. The water renders the reduction to pulp an easier matter, and also serves to carry the pulp forward for subsequent treatment.
In speaking of paper it is usual to refer to the material from which it is made, e.g., rag, rope, esparto, manilla or wood papers. It does not always follow that the papers are composed entirely of those fibres, but the prefix of "pure" or "all" will generally indicate the genuine articles. Paper which is free from mechanical wood pulp is sometimes referred to as "free."
The strongest and best papers are made from cotton or linen rag fibres. Linen is made from the fibres of the flax. In the raw state the fibres are from 1 inch to 112 inches in length, and less than 11000 of an inch in diameter. Examined microscopically the fibres appear to be smooth, cylindrical, with markings like the joints of a cane, slight cross markings, and a very fine channel running through the fibres. Papers made from linen are close, strong, and durable. Cotton is the seed-hair of the cotton plant, having a length of 115 to 112 inches with the diameter about the same as that of linen fibres. Cotton is tubular, has a large channel, and on drying the tube collapses and twists upon itself, as many as 300 twists in the length of a single fibre having been observed. This twisting assists in keeping the spun cotton together, and also makes the felting of the subsequent paper more efficient. Papers made from cotton are softer than those made from linen, and the tenderest rags, such as worn muslins, are employed for blotting papers. Hemp is obtained from the stem of the hemp plant, and the papermaker receives it in the form of old ropes and string. The dimensions and properties of the fibre are similar to those of the fibre of linen. Jute is the inner bark of an Indian plant, producing fibres 110 of an inch in length by 11000 of an inch in diameter. The fibre is smooth, difficult to bleach, but the resulting paper is strong and tough. The fibre of the manilla hemp is not as long as the ordinary hemp, being about 14 of an inch by 11000 of an inch, cannot be bleached to a good white, so a white manilla paper is considerably lower in colour than other white papers. Manilla paper is, however, very tough and strong, and though a large quantity of "manilla" paper is made entirely of wood pulp, there is a great difference between the real and the imitation.
The fibres from straw are small, only about 116 of an inch by 12000 of an inch, and consequently straw papers are much weaker than those made from longer and broader fibres, but, as an admixture, straw still finds a place in writing papers, giving translucency and rattle. Esparto fibres are also very short and fine, about 140 to 116 of an inch by 12000 of an inch, making a light bulky paper when used by itself, and blended with other materials—with rags for good writings, and with chemical wood for fine printings and litho. papers—to impart special characteristics, such as opacity and softness, which may be lacking in the other fibres. The well-known featherweight papers, used for bulky volumes of fiction, are frequently manufactured from esparto fibre alone.
The fibres of the various wood pulps vary considerably in length, breadth, and thickness, being from 125 of an inch to 18 of an inch long, and generally very thin. Fibres of various shapes are met with in wood pulps, some not unlike linen fibres, but many others so distinct as to be unlike all those that have been already described. Broad, ribbon-like fibres, some pitted, and others perforated, all are very thin, lying closely together, so that a paper made entirely from sulphite wood pulp is rather harsh and fairly transparent. Papers produced from soda pulp are softer and more opaque than those made from sulphite pulp. Mechanical wood pulp is made up of little pieces of wood with all the resins and other impurities of the original wood, and when examined carefully, the fragments of wood can be seen, and the splinters appear to be held together by the plant cells. Mechanical wood pulp possesses very little felting quality, and requires the addition of larger fibres, such as chemical wood, in order to make paper successfully.
From the foregoing list and descriptions it can be seen that papermakers have a variety of fibres at their command, and it is by selecting, sometimes by blending, fibres of different characteristics, that the manufacture of the large variety of papers is possible. Some of the demands made by the world of paper users are for papers which are very strong or very soft, absorbent, resistant to grease or water, very light, very dense, and the selection of the fibres and their treatment call for special knowledge and skill on the part of the papermaker.
In addition to fibre, most papers contain sizing, sometimes loading or filling. Sizing may be animal or vegetable, the animal size being gelatine or glue obtained from various animal substances, and the vegetable size being made of a combination of resin with soda. Alum is used to assist in fixing the size in the paper. Mineral matters are employed for filling or loading; china clay is the principal, others being barium sulphate (barytes, blanc fixe), calcium sulphate (gypsum, terra alba, annaline, pearl hardening, crown filler), satin white, magnesium silicate (asbestine, talc, agalite). Colouring matters are required for the majority of papers. For white papers small quantities of blue and red colours are used, while for coloured papers aniline dyes are employed in a large variety, as well as the various pigments.