Fibres for Paper-making.
Although the vegetable world has been explored from time to time for new supplies of cellulose, and some plants have been found serviceable in certain directions, yet the number of fibres in actual use is very limited.
The following table indicates the principal sources of the material required for paper-making:—
| Fibre. | Source of the Fibre. | Application of the Fibre. |
| Linen | Rags, textile waste. | High class writings and printings. |
| Cotton | Rags, textile waste. | High class writings and printings. |
| Esparto | Natural grass. | Writings and printings. |
| Straw | Straw from various cereals—wheat, barley, oats, etc. | Printings, box and card boards. |
| Wood | Mechanically ground wood. | Cheap papers, boxboards, middles, tickets and cards, writings and printings. |
| „ | Chemically prepared wood. | Writings and printings. |
| Flax | Threads, waste from spinning mills. | Wrappings, boards, cable papers. |
| Hemp | Spinning refuse, old rope, sailcloth, etc. | Wrappings, boards, cable papers, strong writings. |
| Jute | Waste, old gunny bags. | Wrappings, boxboard, cards. |
| Bamboo | Natural stems. | Writings and printings (not in Europe, and only limited quantities elsewhere). |
| Ramie | Bast fibres of the plant; textile refuse. | Rarely used, except in special cases. |
| Bagasse | Sugar-cane refuse. | Common papers (chiefly experimental results). |
| Manila Hemp | Textile and rope refuse. | Wrappings, cable papers. |
Exploiting New Fibres.—The exploitation of any new paper-making fibre requires attention to certain important details, which may be fairly considered in the following order:—
(1) Supply.—The supply of material must be plentiful and obtainable in large quantities. Too often this question is entirely neglected by those who bring new fibres to the notice of paper-makers, probably because they do not realise that enormous quantities of material are necessary to supply even a very small section of the paper trade, the fact being that few plants yield more than half their weight of paper-making fibre.
(2) Suitability.—The fibre should be properly examined as to its chemical and physical properties in a laboratory equipped with appliances for its conversion into bleached paper pulp on a small scale. The examination of the fibre would include tests as to the amount of pulp which can be obtained from one ton of raw material, the approximate cost of treatment, and details as to the value of the fibre for paper-making.
(3) Cost of Raw Material.—If the supply of material seems to be sufficient, and the paper pulp obtained possesses suitable qualities, then it is necessary to get accurate information as to the cost of the fibre delivered to some given spot at or near the place of collection.
The exploitation of any new fibre for paper-making purposes will involve a recognition of the fact that the raw material must be converted into pulp at or near the place where the material is most abundant.
The only interesting exception to this is the case of esparto fibre, which is imported into England in large amount, but this is only possible because esparto possesses most valuable paper-making qualities, and is obtained in countries close to England, where large quantities are consumed. It is doubtful whether other fibres could be utilised in the same way.
(4) The Cost of Manufacture at or near the place of collection requires to be carefully worked out, due consideration being given to the actual cost of chemicals on the spot, cost of labour, and the conditions under which the maintenance of machinery can be efficiently looked after.
(5) Carriage and Freight Charges are the last, but by no means the least, items of importance. It is not too much to say that the whole success of the exploitation of new paper-making fibre hangs entirely upon this item, the majority of many fibres which have been brought to the notice of the trade being suitable, but impracticable, solely on account of these and similar commercial considerations.
In the pages of the trade press for the last few years the following fibres have been noticed:—
(1) Flax Pulp.—This material was to be obtained from flax straw. Attempts were made on a commercial scale to produce quantities of flax fibre, but so far the efforts made have not been very successful.
(2) Ramie Fibre.—This material has been exploited over and over again, chiefly for textile trades, its application as a paper-making material being limited to small quantities used for special purposes such as bank notes. The fibre is too valuable, except for textile industries, and can only come into the paper trade as a waste material from such sources.
(3) Tobacco Fibre has been before the trade for some years, the idea being to utilise tobacco stems and other tobacco waste for the manufacture of paper suitable for use as wrappers for cigars, cigarettes, and similar purposes.
(4) Agave Fibre.—This name is given to a large and important genus of fibre-yielding plants found chiefly in Central America. It is also found in India, and in 1878 an experiment was made for the manufacture of paper at a mill near Bombay, but this did not give any satisfactory results, probably on account of the primitive methods used in treatment.
(5) Bagasse.—The waste material from sugar-cane has been looked upon for many years as a desirable fibre, much time and labour having been given to the utilisation of this material. In spite of these efforts bagasse still remains an almost useless and unworkable material. This is partly due to inferiority of the pulp and partly due to difficulties connected with its treatment. Probably cultivation of the plant for the sake of its fibre instead of the sugar might give better results.
(6) Peat.—The attempts made to utilise peat for paper-making are probably fresh in the minds of those paper-makers interested in the production of wrappers and boxboards. The nature of peat, however, is such as to exclude the hope of making any useful article. The material has been exploited by companies in Austria, Ireland, and Canada on a fairly large scale, with but a limited amount of success.
(7) Cotton-seed Hulls.—Many patents have been taken out for the chemical treatment of cotton-seed waste and having for their object the removal of the particles of seed hulls, so as to obtain a pure cotton pulp. The scheme sounds attractive, but there are so many conditions which have to be taken account of that the commercial success of any undertaking based on the use of cotton-seed hulls is very questionable. The fact is that the hulls have a market value quite apart from the possibility of their application to paper-making, and this initial cost would prevent paper-makers from buying the material owing to the large quantity necessary for the manufacture of one ton of pure pulp.
(8) Apocynum.—This plant is said to be utilised to some extent by the Russian Government in the manufacture of bank notes, the plant being cultivated at Poltava. This is an instance of the particular application of a fibrous material in limited quantities, a proposition which is always feasible in the case of special requirements.
(9) Cornstalk.—This fibre has been chiefly exploited in America, experts having been attracted by the enormous quantities of cornstalk available in the several wheat-producing States. The manufacture of paper pulp from this material on a large scale has yet to be established.
(10) Japanese Paper Fibres.—In Eastern countries a great number of fibrous plants are utilised in small quantities for the manufacture of special papers. It is obvious that in these Eastern countries the employment of fibres which are not cultivated in large bulk is readily possible when the question of price obtained for the paper and the cost of production are considered. Of such fibres may be mentioned the Mitsumata and Kodzu, easy of cultivation and giving a good yield of material per acre of ground. The waxed papers used for stencils in duplicating work on the typewriter are made from these fibres. The paper Mulberry is also a well-known fibre; while a third species particularly valuable for thin papers is the Gampi.
(11) Antaimoto Fibre.—The bark of this shrub is utilised in Madagascar in very small quantities for local purposes and possesses little interest for paper-makers.
(12) Refuse Hempstalk.—The suggestion of the use of this material comes from Italy, the hempstalk having been experimented with at San Cesario Mill. This also is a fibre of a local interest only. The percentage of cellulose is very high, being over 50 per cent.
(13) Papyrus.—The revival of this celebrated material is of comparatively recent date. It should be noted that the manufacture of papyrus as carried out by the Egyptians, by smoothing out layers of bark in order to utilise them as sheets of paper, and the present day proposals which involve the production of paper pulp from papyrus, are two entirely different propositions, and the success of the old Egyptian method cannot be referred to as any assurance of success for the production of paper from papyrus along modern lines. The exploitation of this fibre must follow the lines of modern research and commercial investigation, and its value, if any, could then be established.
(14) Pousolsia.—This is a fibre of the same family as hemp and ramie. The value of this material is at present unknown, but the ultimate fibre appears to possess a most extraordinary length. Very little information is available at present as to its value for paper-making.
(15) Bamboo.—This material has been before the paper trade for many years, having first been exploited seriously by Mr. Thomas Routledge in 1875. Since that date a good deal of work has been done in connection with the fibre, but not until recently has the investigation been made of a sufficiently extensive character to enable paper-makers to form some conclusions as to the best methods of obtaining a reliable paper pulp. The researches of the writer in India go to prove that with any fibre it is necessary to take into account all the factors likely to affect the final cost of the paper pulp delivered to any given paper mill.
The figures given in a report recently published, “The Manufacture of Paper and Paper Pulp in Burma,” show the necessity of thorough investigation into all the points likely to affect the final results, viz., the price at which the paper pulp can be sold in England, assuming that the fibre in question is suitable for the manufacture of paper.
Examination of Fibres.—The exact chemical analysis of a new fibre is necessary in order to establish completely its value for textile and paper-making purposes, but the investigation of the suitability of the fibre for paper-making may be simplified by simple reduction of the raw material with caustic soda. The following process is sufficient for all practical purposes:—
Condition of Sample.—A record should be made of the general appearance of the sample, its condition and the amount available for the investigation. Any information available as to the source of supply and the growth of the plant should also be noted.
Preparation of Sample.—The material is cut up into small pieces. The most convenient appliance for this purpose is a mitre cutter as used by picture-frame makers. If the sample is a piece of wood, sections one inch thick cut across the grain of the wood are most suitable, as they can be readily cut up into thin flakes by this machine.
Moisture in Sample.—A small average sample should be dried at 100° C. for the determination of moisture.
Treatment with Caustic Soda.—About two hundred grams of the raw material is closely packed into a small digester or autoclave and covered with a solution of caustic soda having a specific gravity of 1·050. A perforated lead disc should be placed above the sample in the digester to prevent any of it from floating above the level of the solution. The material should be digested for five or six hours at a pressure of 50 lbs. The conditions of treatment here given will need to be varied according to the nature of the fibre. Some materials can be readily converted into pulp with weaker liquor and at a lower pressure, while others will require prolonged treatment. These conditions must be varied according to judgment or according to the effects produced by the conditions already set out.
Unbleached Pulp.—The contents of the digester are emptied out into an ordinary circular sieve provided with a fine copper wire bottom, having a mesh of about sixteen to the inch. The sieve is immersed in water and the contents partially washed with hot water. The partially washed material is squeezed out by hand and tied up in a strong cloth and then kneaded thoroughly by hand in a basin of water which is repeatedly renewed until the fibre is thoroughly washed. The process of kneading at the same time reduces the fibre to the condition of pulp. The water is carefully squeezed out of the pulp by hand, and the moist pulp is then divided into two equal parts, the first of which is made up into sheets of any convenient size, care being taken that none of the fibre is lost. These sheets are then dried in the air and preserved as samples of unbleached pulp, a record being made of the weight produced.
Bleached Pulp.—The second portion of the moist pulp is mixed with a solution of bleach, the strength of which has been accurately determined by the usual methods. The amount of bleach added should be about 20 per cent. of the weight of air-dry fibre present in the moist sample of pulp. The pulp should be bleached at a temperature not exceeding 38° C., and when the colour has reached a maximum the amount of bleach remaining in solution is ascertained by titration with standard arsenic solution. In this way the amount of bleaching powder required to bleach the pulp is determined. The product is then made up into sheets of pulp which are dried by exposure to air and subsequently weighed.
Yield of Pulp.—The percentage yield of finished pulp obtained from the raw material is determined from the figures arrived at in the experiment described, and the weight of raw material necessary to produce one ton of bleached pulp is readily calculated.
Examination of Bleached Fibre.—The fibre should be carefully examined under the microscope and a record made of general microscopic features, especially with reference to the length and diameter of the fibres, and the proportion of cellular matter present, if any.
Sample of Paper.—It is only in the case of short-fibred material similar to esparto and straw that sheets of paper capable of giving comparative results as to strength can be made. The figures obtained with fibrous materials of this kind are only comparative, because it is possible in practice to make a much stronger sheet of paper when the material is beaten properly under normal conditions.
A similar investigation should be made by submitting the fibre to treatment with bisulphite of lime, that is to say, if the fibre lends itself to such a process. A lead-lined digester is necessary, and the solution employed is bisulphite of lime prepared according to the directions given on page [160].
The preparation of sulphite pulp requires more attention than the manufacture of soda pulp. It is most important that the digester should be absolutely tight in order to prevent the escape of any free sulphurous acid gas, and the contents of the digester must be heated slowly until the maximum pressure has been reached.
[CHAPTER III]
THE MANUFACTURE OF PAPER FROM RAGS
Fig. 6.—A Rag Sorting House.
The word rag is used to designate a very wide range of raw material suitable for conversion into paper. In the case of high-class hand-made writing papers only the best qualities are employed, such as new linen and cotton cuttings from factories, or well-sorted rags of domestic origin. The usual classification adopted by merchants who supply the paper mills is somewhat as follows:—
New white linen cuttings (from textile factories).
New white cotton cuttings (from textile factories).
Fine whites (domestic rags).
Outshots (a quality between fines and seconds).
Seconds (a grade inferior to fines).
Thirds (inferior and dirty well-worn rags).
Coloured prints (of all grades and colours).
Fustians and canvas.
Manila and hemp rope.
Baggy, gunny, and jute.
The total amount of rag used in England for paper-making is not known. The only figures available refer to rags imported; and these cannot be regarded as a measure of consumption, which could only be arrived at by first ascertaining the quantity of home rags used. The imports of rag at stated periods are given in the appended table:—
Rags Imported into England.
| — | 1872. | 1882. | 1892. | 1902. | 1905. |
| Weight (tons) | 22,254 | 21,200 | 23,032 | 18,692 | 23,681 |
| Value | £373,035 | £303,349 | £214,065 | £173,732 | £224,232 |
Sorting and Cutting.—All rags on arrival at the mill are carefully sorted. This process is conducted entirely by women, who sort and cut up the rags at special tables provided with cutting knives curved in shape similar to a scythe. These are fixed at an angle in the centre of the table, with the back towards and in front of each work-woman. The top of the table is made of thick coarse wire so that some of the dirt and foreign impurities may fall through. All buttons, hooks and eyes, pins, leather, pieces of rubber, and other articles are carefully removed, while seams and hems are also opened out. The rags are cut into slips 3-5 inches long and then recut crosswise, and thrown into suitable baskets or receptacles standing round the table, by which means the sorting operation is effectually carried out. The care and attention given to the sorting is an important item in the manufacture of papers of uniform quality, and in the best mills the sorting is carried out to such an extent that twenty or twenty-five grades are obtained.
Fig. 7.—A Rag Duster.
Dusting.—The rags are next passed through a machine which removes dirt. This is a hollow cylindrical or conical drum having an external covering of coarse wire cloth, which rotates inside a wooden box. The shaft is provided with projecting spikes, so that the rags are violently agitated in their passage through the machine. The dirt and other impurities fall through the wire on to the floor of the room, while the clean rags are discharged from the lower end of the drum. The loss in weight varies according to the condition of the rags. With good materials the loss may only be 1-2 per cent., while with dirty common rags the loss during cleaning and dusting may amount to 10 per cent.
Fig. 8.—A Rag Cutter.
Boiling.—The further purification of the rags is effected by a chemical treatment, viz., boiling at a high temperature with alkaline substances, which process removes fatty, glutinous, and starchy matter from the material.
Fig. 9.—Interior of Paper Mill for Hand-made Paper (R. Batchelor & Sons).
For this purpose a spherical digester is used, generally 7-9 feet diameter, and capable of holding 2-2½ tons of rag. The boiler or digester is filled with dusted rags, and the requisite amount of alkaline solution added. The manhole is then closed, and steam admitted through the hollow trunnions until the pressure reaches 20 or 30 lbs., at which pressure the boiling is continued for three to six hours according to requirements, the digester rotating slowly the whole time in order that the rags may be evenly and thoroughly boiled.
Fig. 10.—View of a Rag Boiler, showing connections.
The liquor employed for boiling is a solution of caustic soda, carbonate of soda, or milk of lime. In the case of caustic soda the amount required varies from 5 to 10 per cent. of the weight of rag. Caustic soda is preferable to lime, because it acts upon the grease and other fatty matters, forming a soluble compound which is freely removed in the subsequent process of washing. Many paper-makers, however, use milk of lime, carefully strained through fine cloth, almost exclusively. Considerable experience and skill are necessary in this operation in order to avoid injury to the fibre not only as regards its strength, but also its colour.
Washing.—When the rags have been sufficiently boiled, the steam is turned off and the pressure allowed to fall. This can be effected quickly by blowing off from a valve fixed at the bottom of the boiler opposite to the manhole. The cover is removed from the boiler and the boiler slowly rotated in order that the contents may be discharged into a tank placed below. The “black liquor,” as it is called, is then drained away from the rags, which are immediately subjected to a preliminary washing. The process of washing must be carried out in a thorough manner in order to remove all soluble compounds, which if left would cause an unnecessary waste of bleach in the subsequent stages of purification. There are many schemes employed for washing, most of them being devised with the idea of using a minimum quantity of water.
The most general practice, in the absence of special machinery, is the preliminary treatment in the tank below the digester, followed by a more complete washing process in a machine known as a breaking engine.
This apparatus is a shallow oval-shaped vessel with circular ends, divided lengthwise by a partition called a mid-feather, which, however, does not extend the full length of the apparatus. In one of the two channels into which the vessel is thus divided a heavy roll is fitted, which is provided with a number of steel knives. On the floor of this channel there is fixed a “bed-plate,” also provided with projecting knives which are parallel with the knives in the roll. The distance between the knives in the roll and those in the “bed-plate” may be altered as required by means of an adjusting screw. In the other channel of the breaking engine there is fitted a “drum-washer,” which serves for the removal of the dirty water from the machine. This drum is divided into sections by means of partitions which reach from the centre to the circumference. The surface of the “drum-washer” consists of a fine brass wire cloth supported by a coarser material placed underneath.
Fig. 11.—A Breaking and Washing Engine.
The breaking engine is half filled with clean water, and the rags are thrown into the engine until it is suitably filled. The rotation of the heavy roll causes the mixture of rags and water to circulate round the vessel, the floor of which is so constructed that the pulp is drawn between the roll and “bed-plate” and discharged over the “backfall,” which is that portion of the sloping floor behind the “bed-plate.”
The “drum-washer” rotates with its surface in contact with the mixture in the engine, so that the dirty water passes through the wire cloth and is caught in the curved sections or buckets inside the drum and discharged into a trough adjacent to the centre, and thereby conveyed away from the engine. Clean water is allowed to run into the vessel at one end while the dirty water is discharged by means of the “drum-washer.” At the same time the rags are broken up by means of the knives on the roll, so that when the rags are sufficiently washed, a process which usually occupies four hours, they are also partially disintegrated.
Bleaching.—The clean disintegrated rag is next bleached by means of ordinary bleaching powder solution. Bleaching powder is a substance prepared by the action of chlorine gas on dry slaked lime, resulting in the formation of a compound which has the property of bleaching or “whitening” vegetable matters. The clear solution obtained by treating the powder with water is utilised by the paper-maker for bleaching the rag pulp.
Various methods are used for this purpose. Sometimes the requisite volume of clear bleach liquor is added to the pulp in the breaker, and the material kept in constant circulation until the operation has been completed. In other cases the broken pulp is transferred to a “potcher,” which is a vessel similar in shape to the breaker, but merely provided with paddles for keeping the pulp in circulation, and bleached by the addition of chloride of lime solution.
Another method frequently adopted is to discharge the pulp from the breaker, immediately after the addition of the bleach, into brick or cement tanks, allowing the bleaching action to proceed spontaneously without prolonged agitation.
In some instances the process is hastened by adding dilute sulphuric acid to the pulp after the bleach liquor has been run in, or by heating the mixture with steam. For high-class papers such devices as this are seldom resorted to, as experience shows that the colour of pulp bleached by drastic methods does not maintain a high standard.
The pulp is then thoroughly washed in order to remove every trace of residual bleach, and also the soluble compounds which have been formed during the operation. Very large quantities of water, clear and free from suspended dirt, are necessary. In some mills any excess of bleach is neutralised by the use of an “antichlor” such as sodium hyposulphite, or sodium sulphite, but the best results are undoubtedly obtained when the quantity of chemicals used is kept at a minimum.
If the pulp is bleached in a breaker or potcher, the washing is effected by the aid of the drum-washer. With pulp treated in steeping tanks, fresh water is allowed to percolate or drain slowly through the mass.