_TREATMENT OF VARIOUS FIBRES._
Treatment of Straw.--Bentley and Jackson's Boiler.--Boiling
the Straw.--Bertrams' Edge-runner.--M. A. C. Mellier's
Process.--Manilla, Jute, etc.--Waste Paper.--Boiling Waste
Paper.--Ryan's Process for Treating Waste Paper.
=Treatment of Straw.=--As a paper-making material, the employment
of straw is of very early date, a patent for producing paper from
straw having been taken out by Matthias Koops as far back as
1801. The material, however, was used in its unbleached state,
and formed a very ugly paper. White paper was not obtained from
straw until 1841, but no really practical method of treating this
material was devised until about ten years later, in France, when
MM. Coupier and Mellier introduced a process which, with subsequent
modifications, has been extensively adopted. A great advance in
the manufacture of paper from straw has since been effected by the
introduction of various boilers, specially constructed for boiling
the material at high pressures, and for keeping the alkaline
liquors freely circulated amongst the fibre during the progress of
the boiling. These boilers are of different forms--being either
cylindrical or spherical--and are preferably of the revolving type,
which causes the caustic ley employed in the boiling to become
uniformly mixed with the fibre. Sometimes the vomiting boilers
described elsewhere are used by paper-makers in preference to those
referred to.
=Bentley and Jackson's Boiler.=--This boiler, a representation of
which is shown in Fig. 18, is 7 feet in diameter, 18 feet long on
the cylindrical surface, with hemispherical ends of Martin-Siemens
steel plate 7/16 inch thick in the shell, and ½ inch thick in
the ends. It is double riveted in the longitudinal seams, has
two manholes 3 × 2, forged out of solid steel plate. Inside are
two perforated lifting plates or shelves, each 1 foot wide, ¼
inch thick, the full length of the shell, and secured to the ends
by strong angle-irons; it is supported on two turned cast-iron
trunnions. These boilers are tested by hydraulic pressure to 120
lbs. per square inch.
[Illustration: Fig. 18.]
The varieties of straw generally used for paper-making in this
country are wheat and oats, though rye and barley straws are also
used, but in a lesser degree. The treatment of straw differs
greatly at different mills, some makers using strong liquors
and boiling at a lower pressure, while others prefer to use
less caustic soda and boil at a higher pressure. There can be
little doubt, however, that the high temperatures resulting from
boiling at very high steam pressure must deteriorate the fibre
considerably, causing subsequent loss of fibre in the processes of
washing and bleaching.
=Boiling the Straw.=--The straw is first cut into short lengths
of one or two inches by means of a chaff-cutter, or by a machine
similar to a rag-cutter, and the cut material is then driven by
an air-blast through a wooden tube into a chamber having coarse
wire-gauze sides: a second chamber surrounds this, in which the
dust from the straw collects as it passes through the wire gauze.
The winnowed straw, freed from dust and dirt, is then conveyed in
sacks to the boilers. In charging the boilers, a certain quantity
of ley is first introduced, and steam also, and the cut straw then
added, which soon becomes softened, and sinks to the bottom of the
boiler, when further quantities of the material are added, until
the full charge has been given. The requisite proportion of ley
and water is then run in and the head of the boiler secured in its
place. Steam is now turned on, until a pressure of 20 to 40 lbs.,
or even more, has been reached, when the boiling is kept up for
3½ to 8 hours, according to the pressure used and the strength of
the alkaline liquor, which varies from 9° to 16° Tw. From 10 to 20
lbs. of caustic soda per cwt. of straw are generally required to
boil the material thoroughly. The boiling being complete, steam is
turned off, and when the boiler has somewhat cooled, the material,
which is in the form of a pulp, is discharged by the pipes beneath
into a large tank or strainer, the bottom of which is fitted with
a series of plates having long narrow openings or slits, through
which the liquor drains. The pulp is then washed with water, and
again allowed to drain thoroughly, after which it is dug out and
transferred to the potcher to be again washed and bleached. At
some mills the straw is boiled whole and not subjected to any
preliminary cutting In such cases the boiled straw, not being so
fully pulped as when cut into short lengths, is emptied from the
boiler through the manholes used for charging the material into the
boiler.
[Illustration: Fig. 19.]
=Bertrams' Edge-runner.=--For the purpose of crushing the knots
of the straw, and other hard particles derived from weeds, etc.,
a machine termed the "koller-gang" or "edge-runner" is sometimes
employed. This machine, which is manufactured by Bertrams, Limited,
and of which an illustration is given in Fig. 19, consists of two
large millstones, made from hard red granite, the surfaces of
which are sometimes grooved with V-shaped equidistant grooves.
These stones are worked by a horizontal spindle, and are caused to
revolve very rapidly in an iron basin, in which the washed pulp
is placed, and by this means the knots and harder portions of the
fibre not fully acted upon by the caustic alkali, become so reduced
as to be more readily accessible to the action of the bleach,
and thus a very superior straw pulp is produced. In using this
machine in the way indicated, the washed pulp is mixed in a chest
provided with agitators, with water, is then pumped into a second
chest above it, from whence it flows into the basin shown in the
engraving, while the stones are revolving.
=M. A. C. Mellier's Process.=--By this method the straw is first
cut into small lengths as usual; it is then steeped for a few hours
in hot water, and afterwards placed by preference in a jacketed
boiler, the object being to heat the materials without weakening
the ley by the direct introduction of steam into the body of the
material. The boiler is to be heated to a pressure of 70 lbs. to
the square inch, or to a temperature of about 310° F., by which
means, it is said, a considerable saving of alkali is effected,
as also time and fuel, as compared with the ordinary practice of
boiling. The alkaline ley which M. Mellier prefers to use is from
2° to 3° B., or of the specific gravity of from 1·013 to 1·020,
and in the proportion of about 70 gallons of such solution to each
cwt. of straw. The boiler should revolve very slowly, making about
1 or 2 revolutions per minute. The boiling occupies about 3 hours,
at the pressure named, when the steam is turned off and cold water
passed through the jacket of the boiler, which assists in cooling
the pulp, the water thus used being afterwards employed in washing
the pulp. The pulp is then thoroughly washed until the last water
runs off quite clear, when it is next steeped for about an hour
in hot water acidulated with sulphuric acid, in the proportion of
about 2 per cent. of the weight of the fibre. The pulp is then
washed with cold water, when it is ready for bleaching in the usual
way.
=Manilla, Jute, etc.=--Previous to boiling these fibres it is
usual to cut them into short pieces by a machine such as is used
for cutting straw, after which they are cleaned in a willowing and
dusting machine. The boiling is then conducted in the same way as
for esparto. Manilla fibre is not so much used in this country
as in the United States, where its employment forms an important
feature in the manufacture of certain kinds of paper. Some idea of
the extent to which it is used by the paper-makers of America may
be gleaned from the following statement of Mr. Wyatt:--"Another
large and important branch of the American paper trade are the
mills running on news and Manilla paper. Many of these mills turn
out a vast quantity of paper, running up to two hundred tons per
week, besides making their own ground wood pulp. The American news
is composed mainly of ground wood pulp, with an admixture of about
15 to 25 per cent. of sulphite wood or jute fibre, and not much
loading, and the machines are run at high speed. What is termed
Manilla paper is very largely used in the States, and much more so
than with us for common writings, envelopes, and wrapping papers.
The paper is composed of Manilla, jute fibre, old papers, etc., and
is highly finished at the machine. I was told of one mill belonging
to a large company running altogether six mills on news and
Manilla, turning out, with one 96-inch machine and beater capacity
of 1,800 lbs., and one Jordan, 10 to 12 tons of 2,000 lbs., of
Manilla paper per day at an average speed of 200 feet per minute."
Jute is seldom reduced to the condition of a fine white pulp since
the treatment necessary to obtain that condition would result in
a weak fibre; it is usual, therefore, to only partially reduce
the material, when a strong fibre is obtained, which, lacking
in whiteness, is used for coarse papers. This also applies to
Adamsonia, or Baobab, another description of bast obtained from
the West Coast of Africa. These fibres are chiefly used for papers
which require strength rather than whiteness of colour, such as
wrapping papers, &c.
"Broke" paper is a term applied to paper which has been imperfectly
formed on the paper machine or damaged while passing over the
drying cylinders. Imperfect sheets when they are not sold as
_retree_, and clean waste paper, also come under this designation
and are re-converted into pulp after undergoing the treatment
described below.
=Waste Paper.=--In treating waste paper for conversion into pulp
for paper-making, it is doubtless advisable to separate, as far as
can be done economically, papers which have been written upon with
common ink, as old letters, documents, &c., from printed papers,
since the latter require a more severe treatment than the former.
While simple boiling in water containing a little soda-ash will
discharge ordinary writing ink, printer's ink can only be extracted
by using rather strong solutions of soda-ash or caustic soda; and
even with this treatment it can only be rendered serviceable for an
inferior paper, owing to the grey colour of the resulting pulp, due
to the carbon of the printer's ink, upon which the alkali has no
solvent effect.
=Boiling Waste Paper.=--This is sometimes effected in iron vats,
about 8 feet deep and 8 feet in diameter at the bottom, and about
6 inches wider at the top. At the bottom of each vat is a false
bottom, closely perforated with small holes. Steam is introduced
by a pipe below the false bottom, which passes through the
perforations and thus becomes uniformly distributed to all parts
of the vat. To facilitate the emptying of the vats, the false
bottoms have connected to them three or four iron rods, to the
tops of which iron chains are hooked, and by this means the false
bottom, carrying the mass of boiled paper can be raised by a steam
hoisting engine or crane and deposited where desired. When the
boiling is commenced, the vat should first be about one-fourth
filled with a solution of soda-ash, and the steam then turned on.
When the liquor boils, the papers having been previously dusted,
are introduced gradually, and well distributed through the liquor;
if they are thrown into the vat in large quantities at a time, and
especially if they are in a compact state, the portions in contact
may not be reached by the liquor, and an imperfect boiling will be
the result. To ensure a uniform distribution of the boiling liquor
over the surface of the material, an iron pipe extends from the
centre of the false bottom to nearly the top of the vat, and this
pipe is covered with a hood, which causes the soda liquor to be
evenly spread over the whole mass. The vats are either cased with
wood or coated with asbestos to prevent the escape of heat, and
the vessel is covered with a flat iron cover, which is generally
in two halves. The steam enters the tubs at the side, below the
false bottom, and the exhausted liquor is drawn off through a valve
connected to the bottom of the vat. In some mills the liquor is
not drawn off after each boiling, but the boiled paper is hoisted
from the vat as before described, and the liquor strengthened by
the addition of from 10 to 20 lbs. of soda-ash for each 100 lbs.
of the paper to be next boiled. Paper that is thickly coated with
printing ink requires an extra dose of soda-ash. The boiling is
continued for twelve to twenty-four hours according to the nature
and condition of the waste paper under treatment.
Waste papers are frequently boiled, after dusting, in revolving
boilers, in a solution of soda-ash or caustic soda, but it not
unfrequently happens that some portions of the material become so
agglomerated or half pulped during the boiling that the alkali
fails to reach all the ink, and as this cannot be removed by the
after processes of washing and breaking, it remains in the body
of the pulp and necessarily forms a constituent part of the paper
to be produced from it. The mass, when discharged from the boiler
and drained is then conveyed to the washing-engine, in which it
becomes broken and freed from alkali and so much of the ink as may
have been dissolved or loosened, and it is afterwards treated in
the beater and mixed with varying portions of other paper stock,
according to the quality of paper to be produced. In some mills the
boiled waste paper is disintegrated after boiling, by means of the
edge-runner (Fig. 19).
=Ryan's Process for Treating Waste Paper.=--The following process
for treating waste paper so as to produce a "first-class clean
paper" therefrom, was patented by Mr. J. T. Ryan, of Ohio. The
waste paper is first passed through a duster in the usual way, all
thick old books being previously torn apart to separate the leaves.
The papers are then boiled in a hot alkaline liquor without pulping
them, whereby the alkali acts on the surfaces of the papers, and
dissolves off, carrying away all the ink into the liquor. The
papers, which are still in sheet form, are then drained as free as
convenient from the alkaline liquor, and are next washed in the
washing-engine, which leaves the material perfectly clean. It is
then pulped in the beating-engine; and it is claimed that it can be
formed into first-class paper without the addition of any new or
expensive paper stock. The details of the process are thus given by
the patentee: "Into a bucking-keir put a soda-ash solution having
a density of 5° B., at 160° F., put in the stock, and shower for
eight hours at a temperature of 160° F., without pulping the paper,
then lift and drain, and cleanse well in the washing-engine; then
pulp and form into paper. As the draining will always be imperfect,
each charge removed will carry away some of the soda-ash solution,
and leave the remainder of impaired strength. After each drainage
add water to make up for loss in quantity of the solution, and add
enough soda-ash solution at a density of 13° B., to bring all the
liquor up to 5° B. at 160° F. In about eighteen working days the
liquor will have accumulated considerable ink and other matter.
Then blow one half of the liquor, and restore the quantity for
proper working. None of the soda-ash solution is wasted, except
such as falls to drain and what is blown out as last mentioned." In
carrying out this process every care must be taken to guard against
pulping before the alkali is washed out.