Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
11~5106
PROCEDURE FOR IMPROVING PROPERTIES OF
MECHANICAL WOOD PULPS
The present invention is directed to the treatment
of mechanical wood pulps to improve their properties so as to
5 render the same useful for substitution for chemical pulps.
The term "mechanical pulp" as used herein has its
normal meaning in the art and refers to the product of dis-
ruption of a woody substance by mechanical action to yield a
product consisting mainly of liberated and separated single
10 woody fi~xes and their fragments and which is suitable for use
in the manufacture of paper.
The term "fibre" as used herein also has its normal
meaning in the art and refers to individual plant cells which
make up the woody material and whicll, in softwoods, are known
15 botanically as parenchyma cells and tracheids. These fibres
inherently have average diameters generally beIow 0.05 mm
and in the case of wood species commonly used in pulp formation
and paper making, such as, spruce, balsam, pine, aspen and
poplar, considerably below 0.05 mm.
Traditionally newsprint has been manufactured from
a furnish consisting of about three parts of groundwood pulp
and one part of chemical pulp. Groundwood pulp is the cheap-
est component of the furnish and contributes several desirable
properties to the sheet, including paper opacity and ink
25 acceptance during printing.
The chemical pulp component of the furnish is
usually manufactured by either the well-known kraft process
or sulphite process in yields ranging from about 45 to about
65%. Chemical pulps are expensive to produce, make heavy
~o demands on wood resources and entail formidable pollution
problems.
Chemical pulps are used in newsprint furnishes since
they impart properties to thq furnish which improve its run-
ability.
"Runability" refers to that combination of properties
which allows the wet web to be transported at high speed
through the forming, pressing and drying sections of the
paper making machine and allows the dry sheet to be reeled
and printed with not more than an acceptable number of breaks.
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In effect, runability is a measure of the efficiency with
which the paper passes through the paper machine and printing
pr~ess.
Despite all the aforementioned disadvantages assoc-
5 iated with the use of chemical pulps, they are generallyemployed in making newsprint because runability is the key to
paper making machine and press-room efficiency, which in
turn is the key to profitability.
In accordance with this invention, there is provided
10 a process for the formation of an improved mechanical pulp
which is suitable as a replacement for chemical pulps in many
applications, including newsprint furnish.
The process of this invention results in an increase
in the elongation to rupture (hereinafter known as "wet
15 stretch") and an improvement in the stress-strain properties
of the wet web formed from the pulp, while simultaneously
maintaining rapid drainage. We have discovered a hitherto
unknown phenomenon that high wet stretch and high stress-
strain characteristics, in combination with rapid drainage,
20 are fundamental pulp properties which improve the runability
of a newsprint furnish.
The fibre-to-fibre bonding within a dry paper sheet
formed from the pulp produced by the process of the invention
is improved, thereby resulting in the desirable properties of
25 increased tensile and burst strengths and increased sheet
densit~.
One important feature of this invention is that
there is formed a modified mechanical pulp which can be used
as a substitute, in whole or in part, for chemical pulp in
30 many of its applications and which result~ ~rom a proaedure
which does not produce more than insignificant quantities of
polluting effluents, in complete contrast to chemical pulp-
ing procedures, where large quantities of polluting effluents
must be handled.
-35 The process of the invention comprises two steps,
~amely (a) subjecting particulated cellulosic fibrou~ material
to mechanical action to form a pulp consisting mainly of
single fibres and fragments thereof, and (b) chemical reac-
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tion of the pulp with a soluble salt of sulfurous acid under
certain precise elevated temperature and pressure conditions
as detailed below.
The present invention is applicable to
5 refiner pulps. "Refiner pulps" are a class of
mechanical pulps formed by passing particulated cellulosic
fibrous material, usually wood chips, through a small gap
between two ribbed parallel plates rotating with respect to
each other (known as a disc refiner). The procedure may be
effected at atmospheric pressure, the product being known as
"refiner mechanical pulp" (RMP), or under pressure, typically
about 1 to 2 atmospheres greater than atmospheric pressure,
and at elevated temperature, such as, about 120C, the product
being known as "thermomechanical pulp" (TMP). The refining
15 process usually is effected in two stages. In the first
stage, the fibres are separated and liberated and in the
second stage, additional refining energy is supplied to
increase the fibre flexibility and conformability, fibrilla-
tion and bonding. Usually about half the overall refining
energy of about 100 to about 120 horsepower-days per ton is
applied to the fibre-li~eration stage.
The two individual steps comprising the process of
the invention are discussed separately below.
Step (a) Preparation of the Mechanical Pulp
As noted above, refiner pulps are usually produced
in two steps, namely, fibre separation by mechanical action
and refining by mechanical action. The character of the re-
finer pulp and its response to subsequent treatment in the
process o the invention depends on the conditions that pre-
vail at the moment of fibre separation in a disc refiner.
A wood fibre consists essentially of a cell wall,
whose outer surface is made up of cellulose-rich fibrillar
layPrs known as the Sl and S2 layers. In wood, the space
between the fibres known as the middle lamellae, is filled
with a lignin-rich material.
The process of the invention requires that, in the
initial liberation of the fibre from the wood in a disc
refiner, the fracture occurs mainly in the Sl and S2 layers,
1145106
thus exposing the cellulose-rich fibrillar material which is
the source of the fibrillation characteristic of a good mech-
a~ical pulp Since this fibre morphology is established at
the moment of fibre liberation, it is necessary that the
process of fibre liberation proceed largely to completion.
Therefore, the product of the initial mechanical fibre separa-
tion step of the process of the invention must consist
mainly of single wood fibres, which inherently have average
diameters less than 0.05 mm. More than the minimum energy to
accomplish this separation may be applied, but is unnecessary.
It is well known that, in thermomechanical pulping,
if the refining temperature exceeds the thermal softening
point of lignin, fibre separation occurs in the middle
lamellae to yield a smooth fibre with a lignin-rich surface.
This fibre is difficult or impossible to fibrillate by
further refining and is generally unsuitable for use as a
mechanical pulp. Hence the initial fibre separation step
in this invention is effected at a temperature below the
thermal softening point of lignin. The latter temperature i5
variable with the wood species, duration of heating and re-
fining conditions, but is generally below about 150C.
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Attempts have been made to decrease the energy required
for fibre separation and improve pulp quality by a chemical
softening of the wood prior to refining. Such a process,
using sulphite as the treating chemical, is disclosed in U.S.
Patent No. 4,116,758. The products of the latter process are
smoo~h walled fibres sh~wing little tendency to ~ibrillatlon,
similar to those described above resulting from refining above
the lignin so~tening temperature, and are unsuitable for use
as a mechanical pulp in this invention.
It is within the scope of this invention, however, to
add the chemicals required in the chemical treatment step
to the wood chips prior to their entering the disc re~iner, pro-
vided that the temperature and time of contact is such that
no substantial reaction occurs and no significant chemical
softening of the chips results. The disc refiner acts as an
efficient mixer o~ the pulp and chemicals at the high con-
sistency normally encountered.
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It is also within the scope of the invention to
subject the wood chips, prior to refining, to steam under
pressure at a temperature below the thermal softening temper~-
ture of the lignin, typically below about 140C in accordance
5 with conventional industrial practice in TMP manufacture
A suitable product of fibre separation is obtainable
simply by following the first stage refining procedures well
known to the art, for the Production of a good thermo-
mechanical pulp (TMP). This
lO is usually accomplished by presteaming wood chips, usually at
a temperature of about 120~ to about 135~C and l to 2
atmospheres pressure for 2 to lO minutes, then passing the
presteamed wood chips, which have not been softened by
chemical action, through a disc refiner at a temperature ~elow
15 the thermal softening temperature of the lignin, and applying
sufficient refining energy to yield a mechanical wood pulp
consisting mostly of single fibres and their fragments, such
fibres and fragments being predominantly below 0.05 mm in
average diameter. This operation is generally effected at a
consistency of about lO to about 40% by weight, usually
about 25 to 30% by weight. The fibre separation may be
effected at atmospheric pressure, if desired, but the results
attainable in subsequent processing are in general inferior
to those attainable from the product of a pressurized refiner.
Once the mechanical pulp is obtained by fibre
separation, the ~ulp may be subjected to fur~her refining action
in a disc refiner, following the usual practice of the in-
dustry for the seCOnd stage refining of a mechanical wood
pulp. It is well known that the quality of a mechanical wood
pulp can be improved by increased refining but at a cost of
slower drainage and increased energy demand.
The consistencies employed in the application of the
refining step may be varied over the range normally employed in the
second stage refining of a mechanical wood pulp, ~ut the
properties of the product depend to some extent on the refin-
ing consistency chosen. Higher consistencies over about 20%
by weight yield products with higher wet stretch while
lower consistencies tend to produce pulps with higher strength.
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By adjustments in refining consistency, the desired balance
between wet stretch and strength for a particular application
can be achieved. For most applications, it is preferred to
carry out the refining step at consistencie~ between
about 1% and about 35~ by weight.
An alternative method of manufacture of refiner
mechanical pulps is to supply all of the energy needed to
separate and to refine the fibres in a single step. In this
method, the material passes between the refiner plates only
once and is known to the art as single stage refiner
mechanical pulp. In the process of this invention, either
single stage or multistage refining may be used.
The amount of energy applied in the refining step may be
varied according to the desired properties of the product and
the intended end use. The degree of refining to which the
pulp is subjected is usually controlled by the freeness of
the refined pulp. For most applications, this freeness
should fall within the range of about 50 to about 700
C.S.F. For example, boxboard stock is typically of higher
freeness than magazine grade paper stock. For newsprint
application, it is preferred to re ine to a freeness in the
range about 100 to about 400 C.S.F.
STEP (b) Chemical Reaction
.
After the required physical form of the wood fibre
is obtained in Step (a), the chemical nature of the fibre is
modified by reaction with an aqueous solution of a soluble
salt of sulphurous acid, usually sodium s~llphite.
Other soluble salts of sulfurou9 acid may be used, such as,
potassium sulfite and ammonium sulphite but these materials
are le~s preferred.
The reaction is effected at temperatures above
about 110C under a superatmospheric pressure for a time
sufficient to yield a chemically-treated refiner mechanical
wood pulp capable of forming a paper web having improved wet
stretch and stress-strain properties and exhibiting rapid
drainage, but for a time insufficient to cause substantial
dissolution of lignin with consequent loss of yield and gener-
ation of polluting effluents. The exact nature of the
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114SlV6
chemical reactions involved in the chemical treatment effected
in this invention are not fully understood, but are thought
to involve sulphonation and deacetylation.
During the reaction, the pH of the solution drops and
alkali is consumed. It is essential to the process of the
present invention that sufficient alkali be present in the
chemical charge to prevent a pH drop below 3 during treatment,
otherwise there is a risk of damaging the fibres through
hydrolytic action with consequent loss of strength. The
exact amount of alkali required varies according to the acetyl
content of the wood supply and cannot be specified exactly,
but is readily established by experimentation.
The alkali requirement may be met entirely with
sodium sulphite. However, since only half of the sodium
of sodium sulphite is available for neutralization, it is
usually more economical to meet part of the alkali require-
ments by additions of sodium hydroxide or sQdium carbonate.
The pH of the mixture, however, is preferably kept below
about 12 because hemicelluloses are dissolved from wood
fibre by higher pH's, with consequent loss in yield.
In a preferred embodiment of the invention, the
amount of sodium sulphite used in the chemical treatment is
in the range of about 4% to about 15% by weight based on the
mechanical wood pulp resulting from step (a), although
lower concentrations down to about 1% by weight may be used
with reduced beneficial effect, with the provision that the
residual sulphite content of 'he mixture, as measured iodi-
metrically, does not fall substantially to zero before
termination of the reaction. Below 1% by weight of sodium
sulphite,improvements are too small to justify the expense
of treatment. Similarly improvements are observed with
chemical charges up to about 25% by weight of the pulp, but
the additional cost is not justified by the small additional
improvement. Generally, therefore, a chemical charge of
between about 1% and about 25~ by weight, preferably between
about 4% and about 15% by weight, of the mechanical pulp, is
used. The chemical charge preferably has a pH between about
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1145106
7 and about 12, and contains sodium sulphite and sufficient
alkali to maintain a pH greater than 3 throughout the
reaction.
The reactions of sulphite with wood are known to
5 consist of a large number of different reactions, whose
rates are dependent on reaction conditions, particularly
pH and temperature. The present state of our knowledge of
this complex subject has been summarized by G. Gellerstedt
in Svensk Papperstidning nr. 16, 1976, p. 537 to 543.
10 It has been established that the reactions necessary for the
application of the process of the invention and the results
attained thereby are those that proceed at pH's
greater than 3 and preferably over 7, and at temperatures
over about 110C, and preferably over about 130C. Other
15 reactions of woody substances wit~ sulphite which proceed
at lower pH's and at temperatures below lQ0C are known,
such as those described by H.J. Kvisgaard in Norsk
Skogindustri lq, no. 4, 1965, p.155-163. Such reactions,
however, are not effective to produce an improvement in wet
~20 and dry properties and in fibre flexibility and consolidation,
such as is contemplated in this invention.
We have found that the maximum improvement, namely,
maximum increase in wet stretch, maximum improvement in stress-
strain and maximum increase in strength characteristics is
25 ob~ained from the process of the invention when the mechanical
pulp from step (a) with added chemical is heated at about 160C
for 30 minutes. As with any other chemical reaction, the tem-
perature aan be lowered if the reaction time i9 increased.
Below about 120C, reaction time becomes impractically long~
and below 110C, the required reactions effectively cease.
Similarly, the reaction temperature can be increased if the
reaction time is shortened. The practical upper limit of
temperature appears to be about 200C with reaction times
of 1 to 2 minutes. We prefer not to opexate under these
extreme conditions because the precise control of conditions
and reaction times needed to achieve an optimum product
are difficult to secure.
It is also possible to operate at shorter or longer
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:114S106
than the optimum reaction times to produce a less than
optimum but still useful result. If the reaction time is
shorter than optimum, the improvements in wet stretch,
stress-strain and strength properties
are less than may be otherwise obtained by operating under
optimum conditions. If the reaction time is too long,
substantial dissolution of the lignin from the pulp, in the
treating chemical occurs, with consequent loss of yield and
formation o~ polluting effluent. While the process i5 still
operable to produce property improvements under these condi-
tions some of the advantages of wood economy and low
pollution are lost and generally are avoided.
The chemical treatment is operable over a time-
temperature range from about 110C for about 12 hours to
about 200C for about 1 minute. It is understood that an
increase in temperature must be accompanied ~y a concomit-
tant decrease in reaction time. For example, the process
is not operable at a temperature of 200C for 12 hours.
To derive maximum benefits from the chemical treatment step,
it is preferred to operate in the more limited range of about
130C for about 2 hours to about 180C for about 15 minutes.
Because of uncertainties in specifying the exact
upper limits of the chemical treatment step in terms of
time and temperature, it is considered more useful and
precise to specify the upper limit in terms of the effect of
the chemical treatment on pulp yield therefrom. Reaction
conditions which decrease the yield, based on mechanical wood
pulp, below about 85% are outside the scope of our process,
since wood losses and the pollution capability of ~he spent
~ aqueous phase become significant and intolerable beyond this
limit. It is preferred to select maximum reaction conditions
such that the yield of treated pulp is greater than about 90%.
The exact conditions requirea vary with wood species, chemical
charge and consistency, but will fall within the limits of
35 time and temperature as defined above, and are easily estab-
lished by experimentation.
The chemical reaction which is effected in step (b)
on the mechanical wood pulp resulting from step (a) is ~uite
11~5
distinct from the methods used iIl the pulping of woody sub-
stances with sulphite or bisulphite to form chemical pulp. In
sulphite pulping, heat and chemical are supplied to the woody
material in chip form (i.e., fibre bundles) by circulating hot
cooking liquor through a bed of the woody material. With the
mechanical pulp produced in step (a) of the process of the
invention, the resistance to flow of liquor is so great that
circulation of li~uor therethrough is impractical. In con-
sequence, all of the chemical required to effect the reaction
of step (b) must be incorporated in the pulp when it enters
the reactor. It is advantageous to incorporate the chemical
in solution in a volume of water which can be totally absorbed
by the pulp. In practice this means that the consistency
after chemical addition normally should be above about 15~
by weight. Consistencies below about 50~ by weight are pre-
ferred because it is easier to secure uniform mixing o~
chemical and pulp below that level. The consistency range of
about 15% to about 50~ by weight, therefore, is preferred for
reasons of convenience, but the operability of the process is
not limited by consistency.
The chemical treatment step in the process of the
invention is also distinguished from chemical pulping process- !
es in that ~he process of the invention cannot be oonducted practically in a
batch process,such as is used in chemical pulping. This is
because the thermal insulating properties of the mechanical
pulp are so high that a large pulp mass cannot be heated
to reaction temperature by conduction in a reasonable length
of time. The chemical treatment may be carried out batch-
wise using dielectric or microwave heating techniques but
30 such methods are expensive. It is preferred to carry out
the chemical reaction step in an apparatus wherein pulp is
continuously raised to reaction temperature and introduced
into one end of a reaction vessel of such size as to
provide the desired reaction duration, while treated pulp is
35 removed simultaneously from the other end.
The invention is illustrated by the following
Examples:
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11
Example 1
This Example illustrates application of the process
of the invention to commercial RMP mechanical pulps.
Screened stock to the mill, manufactured from
5 spruce chips and from jack pine chips in a Bauer 480 refiner,
was mixed with 10~ by weight of sodium sulphite at pH 9
and heated at 15% consistency, at 145C for 1 hour.
The usual practice in mechanical pulping is to re-
move latency prior to screening, cleaning and final use.
10 This procedure was explained by L.R.Beath et al in an article
entitled "Latency in Mechanical Pulps", Pulp and Paper
Magazine of Canada, vol. 67 (10) page T423 (1966). To
correspond to this common practice, latency was removed from
the pulps formed in this and subsequent Examples by treatment
15 at 90C for 15 minutes prior to testing.
The properties of the pulp are compared in the
following Table I:
TABLE I
Jack Pine _ Spruce
Untreated TreatedUntreated Treated
Yield, ~ 1~0 ~3 lOa ~6
Freenes~,C.S.F. 180 210 185 175
Wet Stretch, % 4.3 4.6 4.1 5.1
Wet Tensile, N/m 44 48 61 70
25 Bulk, cm /g 3.39 2.68 3.12 2.38
Burst Factor 11 17 15 24
Brea~;ing Length, km 24~0 3200 3100 4400
Tear Factor 56 72 79 81
Jack pine is considered an inferior species because
of its low strength. It will be seen from the results of the
above Table I that by utilization of the process of the inven-
tion, the properties of this inferior species can be
improved to yield a pulp comparable in properties to spruce
RMP. By the application of the process of the invention,
spruce RMP yields a product comparable to untreated spruce
TMP.
The results set forth in Table I show that, with
both species, wet stretch and wet tensile strength ar~
improved.
These properties are essential to paper machine
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12
rlmability. With both species, bulk is reduced markedly.
This is the result of more flexible fibres which consolidate
better to yield a denser, better bonded sheet. The results
of this can also be seen in the improved strength measure-
ments, namely burst and breaking length.
The process of the invention is effective in in-
creasing the tear factor of jack pine, a property in which
this species normally is deficient.
Example 2
This Example illustrates the greatly superior pro-
perties obtained by applying the process of the invention to
a preferred mechanical pulp, spruce TMP.
Spruce chips were presteamed for 25 minutes at 35
psig and fed to a 1000 HP Sprout-Waldron 36 ICP pressurized
refiner under the following conditions:
Throughput: 25.0 tons per day
Discharge consistency: 25 to 30%
Specific energy: 45 horsepower days per ton
The pulp from the pressurized refiner, consisting
mainly of single fibres, was refined to 200 Canadian Standard
Freeness in a 1500 HP Bauer 412, open discharge refiner,
mixed with 10% by weight sodium sulphite at pH 9 and heated
at 15% consistency at 145C for 1 hour. After latency re-
~al, the properties set forth in the following Table II were
25 measured: -
TABLE II
Untreated Treated
Yield, % 100 94
Freeness, C.S.F. 198 179
30 Wet Stretch, % 4.7 10.1
Wet Tensile, N/m 81 72
Bulk, cm /g 2.7 1.9
Burst Factor 21 30
Breaking Length, m 3400 5400
35 Dry Stretch, ~ 1.8 2~3
The greatly improved product obtained by the appli-
cation of the process of the invention by starting with a
preferred mechanical pulp, namely TMP, rather than RMP, is
e~ident by ~omparison of the results set forth in Table II
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13
above with those set forth in Table I in Example 1. The
exceptional wet stretch of the pulp produced in this Example,
in combination with the augmented strength-properties and
high freeness, are the unique properties which permit use of
the treated TMP as a replacement for low ~ield chemical
pulps in newsprint nanufacture.
Example 3
This Example illustrates the necessity of employing
a proper mechanical pulp as a starting material, i.e. a pulp
consisting substantially of separated single fibres, in order
to produce a useful product.
A sample of spruce chips was refined in a 12 inch
Sprout-Waldron refiner at wide plate gap setting. The
product, designated "A", consisted mainly of fibre bundles
in the range of 0.05 to 0.1 mm in diameter. Product "B" was
prepared from spruce chips in a Sprout-Waldron 36 ICP pressur-
ized refiner and consisted essentially of separated single
fibers, substantially free of particles with diameters greater
than 0.05 mm.
Each pulp was then treated under twd conditions
within the scope of this invention, namely 140C for 30
minutes at 1~ consistency with 4 wt.% sodium sulphite at
ph ~ , and with 10 wt.% sodium sulphite at pH 9
The resulting products had the properties set forth
in Table III below:
TABLE III
Product "A" Product "B"
Untreated 4% 10~ Untreated ~% 10%
Drainage time, sec. 0~57 0.56 0.76 1.32 0.95 1.16
30 Wet Stretch, % 2.6 2.9 2~7 9.7 7.9 7.9
Burst Factor 2 2 4 22 18 24
Breaking Length, m 500 500 700 3600 3050 3820
Tear Factor 17 16 13 105 108 96
Dry Stretch 0.6 0.6 0.6 1.9 2.5 2.9
The results of the above Table III show that a pro-
duct consisting mainly of fibre bundles (i.e. product "A")
is, for the purposes of paper making, virtually with~ut
strength, and application of the chemical treatment step of
this invention is incapable of developing useful paper making
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properties.
Microscopic examination of product "A" after thechemical treatment showed that no dissociation of fiber
bundles had occurred. These results are in agreement with
5 the common industrial experience that a stock containing any
substantial amount of fibre bundles cannot be used in the
manufacture of newsprint.
By contrast to the results obtained with product
"A", product "B" is usable in paper making without the appli-
cation of chemical treatment, but is greatly improved by theapplication of this invention. It will be seen from the
results of Table III that treatment under the milder condi-
tions, i.e. 4% sodium sulphite, greatly improves wet stretch
and drainage, without beneficial effect on dry strength.
Treatment with more chemical (i.e. 10% sodium sulphite)
improves wet stretch and dry strength with less beneficial
effect on drainage. The chemically-treated pulp exhibited
much faster draining than a pulp in which comparable proper-
ties are developed by refining alone. The results set forth
in this Example illustrate the flexibility of the process
of the invention in modifying the properties of a mechanical
pulp (i.e. product "~") according to the requirements for a
particular application.
Example 4
This Example illustrates the effect of temperature
of chemical treatment on pulp properties.
Samples of commercial spruce RMP were heated with
10% sodium sulphite by weight at pH 9.0 and at a consistency
of 15~ for one hour at 100C and 130C, giving the results
reproduced in the following Table IV:
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Table IV
Untreated 100C 130C
Yield, % 100 100 96
Freeness, C.S.F. 134 134 144
5 Dxainage Time, sec. 1.62 1.39 1.52
Wet Stretch, ~ 4.6 4.6 5.5
Wet Tensile, N/m 75 73 79
B~lk, cm /g 2.93 2.92 2.50
Burst Factor 18 19 22
10 Breaking Length, m 3400 3400 4000
The results of the above Table IV show that no
measurable improvement in pulp properties is obtained by reac-
tion at 100C, but useful improvements are produced at 130C.
Exam~le 5
This Example illustrates application of the inven-
tion to southern pine TMP.
A sample of screened stock from a commercial TMP
plant operating on southern pine wa~ treated at 20 % consis-
tency with 10% sodium sulphite at pH 9 at 145C for 1 hour.
20 The properties of the pulp before and after treatment were
as follows:
Table ~
Untreated Treated
Yield, % lQn ~5
25Freeness, C.S.F. 70 74
Drainage, sec. 1.57 2.Q0
Wet Stretch, % 6.7 8.1
Wet Tensile, N/m 55 59
Wet Caliper, mm Q,34 0. 3a
30 Bulk, cm /g 2.96 2.36
Burst Factor 13 20
Breaking Length, m 2600 3800
Dry Stretch 1.6 2.0
Tear Factor 5~ 71
The results set forth in the above Table V con-
~irm the well known fact that mechanical pulps derived from
southern pine are much inferior to spruce pulps, and also
show that application of the process of the invention im- -
proves the quality of southern pine TMP in every measured
40 property. The improvement in tear is particularly valuable.
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Example 6
This Example illustrates the use of a pulp prepared
by the process of the invention to replace chemical pulp
completely in a groundwood based newsprint furnish on a
high speed paper machine.
Approximately 50 tons of pulp at 225 to 250 C.S.F.
were prepared in a Jylha, 5 Mw/1500 rpm tandem TMP system
pressurized to 1 to 1.5 atmospheres. Specific refining
energy was 75 horsepower-days per ton. This pulp, mixed with
sodium sulphite at pH 9 r was heated at 150C in a Pandia
continuous digester for a retention time estimated at 30
minutes. The chemically-treated pulp after centricleaning
was used to replace a mixture of semi~leached kraft and lcw yield sulphite
in the furnish to a commercial paper machine running at 2400
ft./min. The mechanical component of this furnish was about
70% groundwood, 30% TMP. This substitution had no adverse
effect on paper machine operation through the duration of a
7-hour trial.
The recor~ of this trial are reproduced in the
following Table VI:
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17
Table VI
Before Durin~ After
Furnish
Groundwood (%) 57 50 58
TMP (%) 25 22 26
Semibleached kraft (%) 9 0 8
Unbleached sulphite (%j 9 0 8
Treated TMP (%) O 2g 0
Paper Machine Conditions
Wire speed (m/min) 693 694 695
Reel speed (m/min) 724 724 724
Headbox pressure (kPa) 63.2 63.8 63.3
Slice opening (mm) 10 10 10
Supercalender speed (m/min) 700 700 700
Linear pressure (K N/m) 190 190 190
Paper Characteristics 2
Basis weight (g/m ) 48.1 49.8 48.7
Bulk (cc/g) 1.56 1.57 1.56
Tensile Index M.D. (Nm/g) 44.5 41.9 41.2
Stretch M.D. (%) 2 1.05 1.13 1.11
Tear C.D. (mN m ~g) 222 196 203
Burst Index (kPa m /g) 1.43 1.31 1.32
Roughness 1 kg T.S. (m/min) 86 101 87
W.S. 97 104 92
Brightness I.S.O. (%) 60.9 59.2 61.2
Opacity I.S.O. (%) 93.9 93.6 93.6
Porosity (m/min) 224 213 216
Caliper uncalendered ~m 120 127 123
calendered ~m 75 78 76
The results of the above Table VI illustrate that
a treated mechanical pulp formed by the procedure of this
invention may be used satisfactorily to replace chemical
pulp in groundwood-based newsprint, so that the problems of
pollution and excessive consumption of wood and energy
attendant the production of chemical pulps can be eliminated
from newsprint manu~acture. As far as the applicants are
a~are, such an accomplishment has not been heretofore
reported.
In summary of this disclosure, the present invention
40 provides a process of treatment of wood chips to form a
chemically-treated mechanical pulp of superior properties
which is useful as a replacement for chemical pulp in many
applications, including newsprint. Modifications are possible
within the scope of this invention.
.
