CELLULOSE AND PAPER-MAKING FIBRES
When plants such as flax, cotton, straw, hemp, and other varieties of
the vegetable kingdom are digested with a solution of caustic soda,
washed, and then bleached by means of chloride of lime, a fibrous mass
is obtained more or less white in colour.
This is the substance known to paper-makers as paper pulp, and the
several modifications of it derived from different plants are generally
known to chemists as cellulose.
Although plants differ greatly in physical structure and general
appearance, yet they all contain tissue which under suitable treatment
yields a definite proportion of this fibrous substance. The preparation
of a small quantity of cellulose from materials like straw, rope,
hemp, the stringy bark of garden shrubs, wood, and bamboo can easily
be accomplished without special appliances. Soft materials, such as
straw and hemp, are cut up into short pieces, hard substances like
wood and bamboo are thoroughly hammered out, in order to secure a fine
subdivision of the mass. The fibre so prepared is then placed in a
small iron saucepan, and covered with a solution made up of ten parts
of caustic soda and 100 parts of water. The material is boiled gently
for eight or ten hours, the water which is lost through evaporation
of steam being replaced by fresh quantities of hot water at regular
intervals. When the fibrous mass breaks up readily between the fingers,
it is poured into a sieve, or on a piece of muslin stretched over
a basin, and washed completely with hot water until clean and free
from alkali. Hard pieces and portions which seem incompletely boiled
are removed, and the residual fibres separated out. These fibres are
placed in a weak, clear solution of ordinary bleaching powder, left for
several hours, and subsequently thoroughly washed. This simple process
will give a more or less white fibrous material.
The purest form of cellulose is cotton. A very slight alkaline
treatment, followed by bleaching, is sufficient to remove the
non-fibrous constituents of the plant, and a large yield of cellulose
is obtained. For this reason the cotton fibre ranks high as an almost
ideal material for paper-making, possessing the quality of durability.
Cellulose is an organic compound, containing carbon, hydrogen, and
oxygen in the following proportions:--
Carbon 44·2
Hydrogen 6·3
Oxygen 49·5
-----
100·0
Its composition is represented by the formula C_{6}H_{10}O_{5}.
The celluloses obtained from various plants are not identical either in
physical structure and chemical constitution, or as to their behaviour
when employed for paper-making. In fact, the well-known differences
between the raw materials used for paper-making, and also between the
numerous varieties of finished paper, are to be largely accounted for
and explained by a careful study of the cellulose group, particularly
with reference to the microscopic characteristics and the chemical
composition of the individual species.
The only vegetable substance which may be regarded as a simple
cellulose is cotton, all others being compound celluloses of varying
constitution, the nature of which cannot be appreciated without a
considerable knowledge of chemistry. The classification of such plants,
therefore, in a book of this description must be limited to certain
distinctions having some immediate practical bearing on the question of
paper manufacture.
_Cotton._--Regarded as the typical simple cellulose, containing 91 per
cent. of cellulose, and remarkable for its resistance to the action of
caustic soda.
_Linen._--The cellulose isolated from flax by treatment with alkali or
caustic soda cannot readily be distinguished from cotton cellulose by
chemical analysis or reactions. The difference is almost entirely a
physical one.
Flax is a typical compound cellulose, to which has been given the name
pecto-cellulose on account of certain properties. Other well-known
plants of this class are ramie, aloe, "sunn hemp," manila.
_Esparto._--The cellulose isolated from esparto differs in composition
from cotton cellulose:--
Carbon 41·0
Hydrogen 5·8
Oxygen 53·2
-----
100·0
-----
It is regarded as an oxycellulose, being readily oxidised by exposure
to air at 100° C. Other oxycelluloses familiar to the paper-maker are
straw, sugarcane, bamboo.
_Wood._--The difference between wood and the plants already mentioned
is expressed by the term lignified fibre or ligno-cellulose. This term
is used to indicate that the wood is a compound cellulose containing
non-fibrous constituents, to which has been given the name lignone.
Jute is another example of this class.
* * * * *
These distinctions may be exemplified by reference to a simple
experiment. If three papers, such as a pure rag tissue or a linen
writing, an ordinary esparto printing, and a cheap newspaper containing
about 80 per cent. of mechanical wood, are heated for twenty-four
hours in an oven at a temperature of 105° C., the first will undergo
little, if any, change in colour, while the others will be appreciably
discoloured, the mechanical wood pulp paper most of all.
This change is due to the gradual oxidation of the constituents of
the paper, the ligno-cellulose of the mechanical wood pulp being most
readily affected by the high temperature, and the pure cellulose of the
rag paper being least altered.
The process of oxidation, brought about rapidly under the conditions of
the experiment described, takes place in papers of low quality exposed
to air in the ordinary circumstances of daily use, but of course at an
extremely slow rate. The deterioration of such paper is not, however,
due to the simple oxidation of the cellulose compounds, because other
factors have to be taken into account. The presence of impurities in
the paper on the one hand, and of chemical vapours in the air on the
other, hastens the decay of papers very considerably.
_Percentage of Cellulose in Fibrous Plants._--The value of a vegetable
plant for paper-making is first determined by a close examination
of the physical structure of the cellulose isolated by the ordinary
methods of treatment. If the fibres are weak and short, the raw
material is of little value, and it is at once condemned without
further investigation, but should the fibre prove suitable, then the
question of the percentage of cellulose becomes important.
There are several methods employed for estimating the amount of
cellulose in plants. The process giving a maximum yield is known as the
chlorination method, the details of which are as follows:--About ten
grammes of the air-dried fibre is dried at 100° C. in a water oven for
the determination of moisture. A second ten grammes of the air-dried
fibre is boiled for thirty minutes with a weak solution of pure caustic
soda (ten grammes of caustic soda in 1,000 cubic centimetres of water),
small quantities of distilled water being added at frequent intervals
to replace water lost by evaporation. The residue is then poured on to
a piece of small wire gauze, washed thoroughly, and squeezed out. The
moist mass of fibre is loosened and teased out, placed in a beaker,
and submitted to the action of chlorine gas for an hour. The bright
yellow mass is then washed with water and immersed in a solution of
sodium sulphite (twenty grammes of sodium sulphite in 1,000 cc. of
water). The mixture is slowly heated, and finally boiled for eight to
ten minutes, with the addition of 10 cc. of caustic soda solution. The
residue is washed, immersed in dilute sodium hypochlorite solution
for ten minutes, again washed, first with water containing a little
sulphurous acid and then with pure distilled water. It is finally dried
and weighed.
The second process for estimating cellulose is based upon the use
of bromine and ammonia. About ten grammes of the air-dried fibre is
placed in a well-stoppered wide-mouthed bottle with sufficient bromine
water to cover it. As the reaction proceeds the red solution gradually
decolourises, and further small additions of bromine are necessary. The
mass is then washed, and boiled in a flask connected to a condenser
with a strong solution of ammonia for about three to four hours. The
fibrous residue is washed, again treated with bromine water in the
cold, and subsequently boiled with ammonia. The alternative treatment
with bromine and ammonia is repeated until a white fibrous mass is
obtained.
In practice the paper-maker is confined to two or three methods for the
isolation of the fibres, viz., alkaline processes, which require the
digestion of the material with caustic soda, lime, lime and carbonate
of soda, chiefly applied to the boiling of rags, esparto, and similar
pecto-celluloses; acid processes, in which the material is digested
with sulphurous acid and sulphites. The latter methods are at present
almost exclusively used for the preparation of chemical wood pulp.
_Yields of Cellulose in the Paper Mill._--The object of the paper-maker
is to obtain a maximum yield of cellulose residue at a minimum of cost.
Usually the amount of actual bleached paper pulp obtained in the mill
is less than the percentage obtained by careful quantitative analysis,
for reasons easily understood.
In the first place, the raw material is digested for a stated period
with a carefully measured quantity of caustic soda, for example, at
a certain temperature. Now the conditions of boiling may be varied
by altering one or more of these factors, the period of boiling, the
strength of solution, or the steam pressure, and the paper-maker must
exercise his judgment in fixing the exact relation between the varying
factors so as to produce the best results.
In the second place, the mechanical devices for washing the boiled
pulp and for bleaching cause slight losses of fibre, which cannot be
altogether avoided when operations are conducted on a large scale.
Frequently, also, a greater yield of boiled material may involve
a larger quantity of bleaching powder, so that it is evident the
adjustment of practical conditions requires considerable technical
skill and experience.
The percentage of cellulose in the vegetable plants employed more or
less in the manufacture of paper is given in the following table:--
TABLE SHOWING PERCENTAGE OF CELLULOSE IN FIBROUS PLANTS.
------------------+-------------------------
Fibre. | Cellulose, per cent.
------------------+-------------------------
Cotton | 91·0
Flax | 82·0
Hemp | 77·0
Ramie | 76·0
Manila | 64·0
Jute | 64·0
Wood (pine) | 57·0
Bagasse | 50·0
Bamboo | 48·0
Esparto | 48 to 42
Straw | 48 to 40
------------------+-------------------------
_The Properties of Cellulose._--Cellulose is remarkably inert towards
all ordinary solvents such as water, alcohol, turpentine, benzene,
and similar reagents, a property which renders it extremely useful in
many industries, with the result that the industrial applications of
cellulose are numerous and exceedingly varied.
_Solubility._--Cellulose is dissolved when brought into contact with
certain metallic salts, but it behaves quite differently to ordinary
organic compounds. Sugar, for example, is a crystalline body soluble
in water, and can be recovered in a crystalline state by gradual
evaporation of the water. Cellulose under suitable conditions can be
dissolved, but it cannot be reproduced in structural form identical
with the original substance.
If cellulose is gently heated in a strong aqueous solution of zinc
chloride, it gradually dissolves, a thick syrupy mass being obtained,
which consists of a gelatinous solution of cellulose. If the mixture
is diluted with cold water, a precipitate is produced consisting of
cellulose hydrate intimately associated with oxide of zinc, which
latter can be dissolved out by means of hydrochloric acid. The
resulting product is not, however, the original substance, but a
hydrated cellulose, devoid of any crystalline structure.
Cellulose is also soluble in ammoniacal solutions of cupric oxide, from
which it can be precipitated by acids or by substances which act as
dehydrating agents, _e.g._, alcohol.
_Hydrolysis._--An explanation of the behaviour of cellulose towards the
solvents already mentioned, and towards acid and alkali, requires a
reference to its chemical composition.
The substance is a compound of carbon, hydrogen, and oxygen represented
by the formula
C_{6}H_{10}O_{5}
being one of a class of organic compounds known as carbohydrates,
so designated because the hydrogen and oxygen are present in the
proportions which exist in water.
Water = Hydrogen + Oxygen
H_{2} + O.
The H_{10}O_{5} in the cellulose formula corresponds to 5 (H_{2}O).
When cellulose is acted upon by acid, alkali, and certain metallic
salts, it enters into combination with one or more proportions of
water, forming cellulose hydrates of varying complexity. This change is
usually termed hydrolysis.
With mineral acids like sulphuric and hydrochloric acids, cellulose,
if boiled in weak solutions, is converted into a non-fibrous brittle
substance having the composition
C_{12}H_{20}O_{10} 2 H_{2}O
to which the name _hydra-cellulose_ has been given. Similar changes
occur, but at a much slower rate, when cellulose is in contact with
free acids at ordinary temperatures. For this reason it is important
that paper, when finished, should not be contaminated with free acid.
The nature and extent of the chemical change can be varied by altering
the strength of the acid and the conditions of treatment. The
manufacture of _parchment_ paper is an example of the practical utility
of the chemical reaction between cellulose and acid. A sheet of paper
is dipped into a mixture of three parts of strong sulphuric acid and
one part of water, when it becomes transparent. Left in the solution it
dissolves, but if taken out and dipped into water in order to wash off
the acid the reaction is stopped, and a tough semi-transparent piece of
_parchment_ is obtained. The cellulose is more or less hydrated, having
the composition
C_{12}H_{20}O_{10} H_{2}O,
a substance having the name _amyloid_.
_Oxidation._--Cellulose is only oxidised to any appreciable extent by
acid and alkali if treated under severe conditions. It is remarkable
that the processes necessary for isolating paper pulp from plants when
digested with these chemical reagents do not act upon or destroy the
fibre, and this capacity for resisting oxidation has rendered cellulose
extremely valuable to many of the most important industries.
The resistant power of the cellulose is, however, broken down by the
use of acid and alkali in concentrated form.
Oxalic and acetic acids are obtained when cellulose is heated strongly
at 250° C. with solid caustic soda.
Oxy-cellulose, a white friable powder, is produced by means of strong
mineral acids. Nitric acid at 100° C. attacks the fibre very readily
and produces about 30-40 per cent. of the oxidised cellulose.
CELLULOSE DERIVATIVES.
The great number of compounds and derivatives, _i.e._, substances
obtained by chemical treatment, may be judged from the following list.
The substances of commercial importance are suitably distinguished from
those of merely scientific interest by the printing of the names in
small capitals.
ACETIC ACID.--An important commercial product obtained by the
destructive distillation of wood. The crude pyroligneous acid is
first neutralised with chalk or lime, and the calcium acetate
formed then distilled with sulphuric acid. Wood yields 5 to 10
per cent. of its weight of acetic acid according to the nature of
the wood.
ACETONE.--A solvent for resins, gums, camphor, gun cotton, and other
cellulose products. Prepared by distilling barium or calcium
acetate in iron stills, the acetate being obtained from the crude
acetic acid produced by the dry distillation of wood.
_Acid Cellulose._--(See Hydral-Cellulose.)
_Adipo-Cellulose._--A distinct compound cellulose present in the
complex cuticular tissue of plants, and separated easily by
suitable solvents from the wax and oily constituents also present.
ALKALI CELLULOSE.--When cotton pulp is intimately mixed with strong
caustic soda solution, this compound is formed. It is utilised in
the manufacture of _Viscose_.
_Amyloid._--Strong sulphuric acid acts upon cellulose and converts it
into a gelatinous semi-transparent substance to which the name
amyloid has been given. (See Parchment Paper.)
BALLISTITE.--A smokeless powder composed of nearly equal parts of
nitro-glycerine and nitrated cellulose, with a small quantity of
diphenylamine.
_Carbohydrate._--A large number of important commercial products,
such as cellulose, sugars, starches, and gums, consist of the
elements carbon, hydrogen, and oxygen, associated in varying
proportions. The ratio of hydrogen to oxygen in these compounds
is always 2:1 (H_{2} and O).
Cellulose C_{6}H_{10}O_{5}.
Sugar C_{6}H_{12}O_{6}.
Dextrin _n_ (C_{6}H_{10}O_{5}).
To all these substances the term carbohydrate is applied.
_Celloxin_ (Tollens).--A substance having the stated composition
C_{8}H_{6}O_{6} considered to be present in oxidised derivatives
of cellulose.
CELLULOID.--This well-known material is made by incorporating camphor
with nitro-cellulose, a plastic ivory-like substance being
produced. In practice the process is as follows:--Wood pulp or
wood pulp paper is saturated with a mixture of sulphuric acid
(five parts) and nitric acid (two parts), which produces nitrated
cellulose. The product is washed, ground, and mixed with camphor,
the mastication being effected by heavy iron rollers. The mass
thickens and can be removed in the form of thick sheets. These
sheets are submitted to great pressure between steam-heated
plates. The cake obtained is cut into sheets of any desired
thickness, seasoned by prolonged storage, and afterwards worked
up into boxes, combs, brush-backs, and many other domestic
articles of a useful and ornamental character.
CELLULOSE ACETATE (Cross).--If cellulose is heated with acetic
anhydride at 180° C., viscous solutions of the acetates are
obtained. The process yielding a definite acetate of commercial
value is based upon the following reaction:--100 parts of
cellulose prepared from the sulpho-carbonate are mixed with
120 parts of zinc acetate, heated and dried at 105° C. Acetic
anhydride is added in small quantity, and 100 parts of acetyl
chloride. At a temperature of 50° C. the mixture becomes liquid,
and cellulose acetate is subsequently obtained as a white powder.
The compound can be used in the place of cellulose nitrate, and,
being non-explosive, may gradually replace the latter in many
industrial applications.
_Cellulose-Benzoate._--When alkali cellulose is heated with benzoyl
chloride and excess of caustic soda, this substance is obtained.
_Cellulose Hydrate._--The substances produced by the action of acid
and alkali on cellulose under certain strictly defined conditions
are bodies containing cellulose united with water to form
hydrates. The industrial applications of cellulose based upon
this reaction are described under the special headings.
CELLULOSE NITRATE.--A considerable number of derivatives are obtained
by bringing cellulose into contact with nitric acid. Variations
in the strength of the acid, the temperature of reaction, and the
time of contact determine the nature of the product. The best
known nitrates are:--
Cellulose di-nitrate.
Cellulose tri-nitrate and tetra-nitrate, present chiefly in
pyroxyline.
Cellulose penta-nitrate.
Cellulose hexa-nitrate, the chief constituent of gun-cotton.
CHARCOAL.--Not a cellulose derivative in the strict sense of the
term, charcoal being a residue obtained in the dry distillation
of wood.
COLLODION.--A soluble nitrate of cellulose used in photography. (See
Pyroxyline.)
CORDITE.--A smokeless powder consisting mainly of nitro-glycerine
and gun-cotton mixed with acetone. The materials are thoroughly
incorporated and the resultant paste formed into threads which
are dyed and then cut up into suitable lengths for cartridges.
_Cuto-Cellulose._--Synonymous with adipo-cellulose.
_Dextron._--A compound prepared from the waste liquors of the
bisulphite process used for the manufacture of wood pulp.
Resembles dextrin in its physical properties.
DEXTROSE.--A carbohydrate which can be obtained by the action of
mineral acids on cellulose. Commercial dextrose, or glucose, is
prepared by the conversion of starch with sulphuric acid. The
starch is mixed with dilute acid at a fixed temperature, and the
starch milk obtained poured gradually into a vessel containing
dilute acid, which is maintained at boiling point. The conversion
is complete and rapid.
EXPLOSIVES.--The production of the several cellulose nitrates has
given rise to a great number of highly explosive substances.
_Blasting Gelatine._--A mixture of nitro-glycerine with
cellulose nitrates.
_Amberite_, _Ballistite_, _Cordite_, and other smokeless
powders, consisting of nitro-glycerine and cellulose nitrates in
about equal proportions.
_Sporting powders_ made by mixing nitro-cellulose with
barium nitrate, camphor nitro-benzene, such as _indurite_,
_plastomenite_, etc.
GLUCOSE.--(See Dextrose.)
GUN-COTTON.--An explosive prepared by the action of nitric acid on
cotton. Selected cotton waste suitably opened up is immersed
in a mixture of three parts of nitric acid by weight (1·50 sp.
gr.) and one part of sulphuric acid by weight (1·85 sp. gr.) and
submitted to a number of processes by which the nitration is
properly effected so as to produce a nitro-cellulose of uniform
composition. The material is washed, reduced to pulp, and moulded
into various forms.
_Hemi-Cellulose._--The constituents of plant tissues are extremely
varied in character. Many plants contain substances which
resemble true cellulose, but differing from it in being easily
converted by hydrolysis, and by the action of dilute acids,
into carbohydrates. Plants which contain a large proportion of
such constituents are termed hemi-celluloses. In some cases
certain crystallisable sugars can be obtained by hydrolysis under
suitable conditions.
_Hydral-Cellulose_ (Bumcke).--A compound of merely scientific
interest, resulting from the treatment of cellulose with hydrogen
peroxide. When acted upon by alkali it is decomposed into
cellulose and acid cellulose, the latter a derivative of unstable
composition.
_Hydro-Cellulose._--This product, a white, non-structureless, friable
powder, is obtained by treating cellulose with hydrochloric or
sulphuric acid of moderate strength. The substance itself has
no commercial value, but the reaction is useful in separating
cotton from animal fabrics. If a woollen cloth containing cotton
is soaked in dilute sulphuric acid, washed, and dried at a gentle
heat, the cotton is acted upon, and can be beaten out of the
fabric, the wool resisting the acid treatment.
_Lignin._--The complex mixture of substances which is associated
with cellulose in wood, jute, and other _ligno-celluloses_. The
conversion of wood into chemical pulp effects the removal of this
material more or less completely. The well-known "phloroglucine"
test for mechanical wood in papers is based upon the presence of
_lignin_ in the wood.
_Ligno-Cellulose._--Wood and jute are typical bodies consisting of
cellulose and complex non-cellulose, generally described as
lignin, associated together in the plant tissue. The chemistry
of the non-cellulose portion of wood is a matter still under
investigation, its importance from a commercial point of view
being obvious from the fact that the removal of the _lignin_
during the conversion of the wood into wood-cellulose results in
a loss of 50 per cent. of the weight of wood.
_Lustra-Cellulose._--Synonymous with and suggested as a more
appropriate name for the material usually described as
_artificial silk_.
MERCERISED COTTON.--When cotton is immersed in strong solutions of
caustic soda a remarkable change sets in. The physical structure
of the fibre is entirely altered from the long flattened tube
having a large central canal to a shorter cylindrical tube in
which the canal almost disappears. Hydration of the cellulose
takes place, and these changes are taken advantage of in the
production of mercerised cloth (so named from the discoverer of
the reaction, Mercer). Cotton goods, particularly those made of
long stapled cotton, when mercerised, exhibit a beautiful lustre,
and some magnificent crêpon effects are obtained by the process.
_Methoxyl._--A constituent of the complex compound known as
ligno-cellulose, which is present in wood and similar fibres.
The amount of methoxyl in lignified tissue can be accurately
determined, and it has been suggested that the proportion of
methoxyl found in a cheap printing paper could be used as a
measure of mechanical wood pulp present.
_Muco-Cellulose._--This term is applied to certain compound
celluloses present chiefly in mucilages, gums, and in
seaweeds (Algæ). The natural substances are all of commercial
importance--Iceland moss, Carragheen, Algin, etc.
NAPHTHA.--One of the products of the dry distillation of wood,
usually described as wood-naphtha, or wood spirit.
NITRO-CELLULOSE.--The treatment of cellulose with nitric acid gives
a number of nitro-celluloses according to the conditions of the
process. (See Cellulose Nitrates.)
OXALIC ACID.--A substance of great commercial importance prepared
by heating the sawdust of soft wood, such as pine, fir, and
poplar, with strong solutions of mixed caustic soda and potash
to dryness. The wood yields after six hours a greyish mass
containing about 20 per cent. of the acid, which is separated out
by water and then crystallised.
It is used for bleaching, and as a _discharge_ in calico printing
and dyeing.
_Oxy-Cellulose._--A white friable powder produced by treating
cellulose with nitric acid at 100° C. The oxidation of cellulose
is brought about by several reagents such as chromic acid,
hypochlorites of lime and soda, chlorine, and permanganates. The
extent to which cloth has been damaged by overbleaching may be
determined by a simple test with methylene blue solution, which
is readily absorbed by oxy-cellulose present in such fabrics.
PARCHMENT.--A tough paper prepared by the action of sulphuric acid on
unsized paper. (See page 137.)
_Pectins._--(See Pecto-Cellulose.)
_Pecto-Cellulose._--A generic term applied to many important fibrous
materials, such as flax, straw, esparto, bamboo, phormium,
ramie, &c., which on alkaline treatment yield cellulose for
paper-making, and a non-fibrous soluble residue of complex
composition. These soluble derivatives are known as pectin
(C_{32}H_{48}O_{32}), pectic acid (C_{32}H_{44}O_{30}), and
metapectic acid (C_{32}H_{28}O_{36}). Although the soluble
constituents of the pecto-celluloses amount to 50 per cent. by
weight in most cases, no process for the recovery of the product
in a commercial form has yet been devised. (See description of
Soda recovery, page 78.)
PYROXYLINE.--A substance prepared by nitrating cotton. The cotton is
immersed in a mixture of nitric and sulphuric acids of carefully
regulated strength, and subsequently washed free of the acid.
Three volumes of nitric acid (sp. gr. 1·429) are diluted with
two volumes of water and nine volumes of strong sulphuric acid
(sp. gr. 1·839) added. To the solution when cool the cotton is
added in small quantities at a time. The resultant pyroxyline
is soluble in a mixture of equal quantities of alcohol and
ether, and in the soluble form is utilised as _collodion_ for
photography.
SILK, ARTIFICIAL.--A remarkable substance made from wood or cotton
cellulose, closely resembling silk in appearance and physical
properties.
Nitrated cellulose is dissolved in a mixture of equal parts of
alcohol and ether.
The solution is forced through five capillary tubes under
high pressure, and the filament so obtained solidifying at once
is wound together with other similar filaments upon suitable
bobbins. Various modifications of this general process are in
use, such as the solidification of the solution into threads
by passing it into water; the application of solvents less
inflammable than ether and alcohol; the use of other forms of
dissolved cellulose such as those prepared by means of zinc
chloride, ammoniacal copper oxide, or acetic anhydride. In
all cases the yarn or thread is submitted to further chemical
treatment for the removal of nitric acid and to render the
material non-explosive and less inflammable. The finished product
is soft and supple, can be easily bleached and dyed, and is
capable of acquiring a high lustre.
SMOKELESS POWDERS.--(See Explosives.)
_Sulpho-Carbonate._--(See Viscose.)
SULPHATE CELLULOSE.--Chemical wood pulp prepared by the sulphate
process. (See page 107.)
SULPHITE CELLULOSE.--Chemical wood pulp prepared by the sulphite
process. (See page 107.)
VISCOSE.--A soluble sulpho-carbonate of cellulose, prepared by
treating cellulose with a 15 per cent. solution of caustic soda,
and shaking the product with carbon bisulphide in a closed
vessel. The mixture forms a yellowish mass soluble in water,
giving a viscous solution which has some remarkable and valuable
properties.
This _viscose_, on standing, coagulates to a hard mass which
can be turned and polished.
If spread on glass and coagulated by heat, films are obtained
from which the alkaline by-products can be washed out. These
films are transparent, colourless, very tough and hard.
VULCANISED FIBRE.--Fibre or pulp treated with zinc chloride in acid
solution, or otherwise, for the manufacture of hard boards. (See
page 139.)
WILLESDEN GOODS.--Paper, fibre, and textiles when treated with
cuprammonium oxide are partially gelatinised on the surface and
rendered waterproof. (See page 139.)
_Wood Spirit._--(See Naphtha.)
_Xylonite._--(See Celluloid.)
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 | Printings, box and card boards.
| cereals--wheat, barley, |
| oats, etc. |
Wood | Mechanically ground wood. | Cheap papers, boxboards,
| | middles, tickets and cards,
| | writings and printings.
" | Chemically prepared wood. | Writings and printings.
Flax | Threads, waste from | Wrappings, boards, cable
| spinning mills. | papers.
Hemp | Spinning refuse, old rope, | Wrappings, boards, cable
| sailcloth, etc. | 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; | Rarely used, except in special
| textile refuse. | cases.
Bagasse | Sugar-cane refuse. | Common papers (chiefly
| | experimental results).
Manila | Textile and rope refuse. | Wrappings, cable papers.
Hemp | |
--------+----------------------------+--------------------------------
_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.