Note: Descriptions are shown in the official language in which they were submitted.
11~51(~7
IMPROVED PROCEDURE FOR FORMING REFINER PULPS
The present invention is directed to the formation of
impxoved mechanical wood pulps 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
disruption of a woody substance by mechanical action to
yield a product consisting mainly of liberated and separated
single woody fibres 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 *he woody material and which, in softwoods, are
known botanically as parenchyma cells and tracheids. These
fibres inherently have diameters generally below 0.05 mm and
in the case of wood species commonly used in pulp formation
~nd paper making, such as, spruce, balsam, pine, aspen and
poplar, considerably below ~05 mm.
"Refiner pulps" are a class of mechanical pulps formed
by passing particulated cellulosic fibrous material, usually
- wood chips through a small gap betwean two ribbed parallel
,
plates rotating with respect to each other (known as a disc
refiner). The procedure may be effected at atmosph?sric
pressure, the product being known as "refinèr mechanical pulp"
2S (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 "thermo-
mechanical pUlp~? ~TMP). The refining process usually is effe?~-
ted 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, fibrillation and bonding. Usually about
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11~51~7
half the overall refining energy of about 100 to about 120horsepower-days per ton is applied to the f~IEr~ration stage.
Because mechanical wood pulps can be made in yields
over 95% with minimal pollution problems, there is strong
5 incentive to increase their usage in paper manufacture.
In general, however, it is not possible to transport a sheet,
formed entirely of mechanical pulp, at high speed through
the forming, pressing, drying and reeling sections of the
paper making machine, without an unacceptable number of
10 breaks. Chemical pulp is usually added to the furnish to
improve its machine runnability. Traditionally newsprint is
manufactured from a furnish consisting of about three parts
groundwood or other mechanical pulp and one part chemical
pulp.
"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
r paper making machine and allows the dry sheet to be reeled
and printed with not more than an acceptable number of breaks.
20 In effect, runability is a measure of the efficiency with which
the paper passes through the paper machine and printing press.
The chemical pulp component is usually manufactured
by the kraft or sulphite process in yields ranging from about
45 to 65%. Chemical pulps are expensive, make heavy demands
25 on the mills wood resources, and entail formidable pollution
problems. As already noted, mechanical wood pulps are
obtained in yields in excess of 95% with minimal pollution
problems.
Despite all the disadvantages associated with the use
30 o~ chemical pulps, they are generally employed in making news-
print because runability is the key ~o paper making machine
and press-room efficiency, which in turn i9 the key to profit-
ability.
In accordance with this invention, there is provided
35 a process for the formation of an improved refiner pulp which
is suitable for use as a replacement for chemical pulps in
many applications, including newsprint furnish.
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~1~5107
The process of this invention results in an increase
in the elongation to rupture (hereinater known as "wet
stretchi'~ 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 ~igh wet stress-
strain characteristics, in combination with rapid drainage,
are the fundamental pulp properties which impro~e the
runability of a newsprint ~urnish.
The fibre-to-fibre bonding within a dry paper sheet
formed from the pulp produced by the process of the invention
is impro~ed, thereby resulting in the desirable properties
of increased tensile and burst strengths and increased
shaet density.
One important feature of this invention is that there
is formed a refiner ~ulp which ca~ be used as a
substitute, in whole or in part, for chemical pulp in many
of its applications and which results from a procedure which
does not produce more than insignificant quantities of pollu-
20 ting effluents, in complete contrast to chemical pulping pro- !
cedures,where large quantities of polluting effluents must be
handled. The overall energy requirements of the refining
operation to provide a predetermined level of pulp quality
also are decreased, as compared with the conventional refiner
pulp-formation operation.
The process of the invention comprises three steps,
namely (a) subjecting particulated cellulosic fibrous mater-
ial to mechanical action in a disc refiner to form a pulp
consisting mainly of single fibres and fragments thereof,
30 (b) chemical reaation of the pulp with a soluble salt of
sulfurous acid under certain precise elevated temperature
and pressure conditions as detailed below, and (c) subjecting
the chemically-treated pulp to mechanical action to refine the
same and improve the pulp quality.
The cellulosic fibrous material species and refining
conditions required to manufacture a usable mechanical pulp
are well known to the art. For example, it is well known
that most hardwoods cannot be refined to yield ~echanical
.
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11~5107
pulps with adequate strengths. Application of the invention
is restricted to refiner pulps which are generated from soft-
woods, or other cellulosic fibrous material species which are
recognized in the industry as being suitable for the prepara-
tion of refiner pulps. The invention is described furtherwith particular reference to wood species.
The three individual steps comprising the proces
of the invention are discussed separately below:
STEP (a) Fibre Separation
A wood fibre consists essentially of a cell wall,
whose outer surface is made up of cellulose-rich fibrillar
layers 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.
lS The process of the invention requires that, in the
initial liberation of the ibre from the wood in a disc
refiner, the fracture occurs mainly in the Sl and S2 layers,
thus exposing the cellulose-rich fibrillar material which is
the source of the fibrillation characteristic of a good mech-
20 anical pulp. Since this fibre morphology is established at
- the moment of fibre liberation, it is necessary that the pro-
cess of fibre liberation proceed largely to completion.
Therefore, the product of the initial mechanical fibre separa-
tion step of the proce~s of the invention must consist mainly
25 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 temperatuxe exceeds the thermal softening
30 point of lignin, fibre separation occurs in the middle
lamellae to yield a smooth fibre with a lignin-rich surface.
This fibre i8 difficult or impossible to fibrillate by
further refining and is generally unsuitable for use as a
mechanical pulp. Hence the initial fibre separation step
35 in this invention is effected at a temperature below the
thermal softening point of lignin. The latter temperature is
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il~5107
s
variable with the wood species, duration of heating and re-
fining conditions, but is generally below about 150C.
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,
5 using sulphite as the treating chemical, is disclosed in U.S.
Patent No. 4,116,758. The products of the latter process are
smooth walled fibres showing little tendency to fibrillation,
similar to those described abo~e resulting from refining above
the lignin softening temperature, and are unsuitable for use
10 as a mechanical pulp in this invention.
It is within the scope of this invention, however, to
add the chemicals required in the subsequent treatment step
to the wood chips prior to their entering the disc refiner, pro,
vided that the temperature and time of contact is such that
15 no substantial reaction occurs and no significant chemical
softening of the chips results. The disc refiner acts as an
e~ficient mixer of the pulp and chemicals at the high con-
sistency normally encountered.
It is also withi~ the scope of the invention to
20 subject the wood chips, prior to refining, to steam under
pressure at a temperature below the thermal softening tempera-
-ture of the lignin, typically below about 140C in accordance
with conventional industrial practice in TMæ manufacture.
A product of step (a), suitable for further treatment
25 in accordance with this invention, is obtainable simply by
following the first stage refining procedures well known to
the art, for the production of a good mechanical pulp. This
is usually accomplished by presteaming wood chips, usually at
a temperature of about 120~ to about 135C and 1 to 2
30 atmospheres pressure for 2 to 10 minutes, then passing the
presteamed wood chips, which have not been softened by
chemical action, through a disc refiner at a temperature below
the thermal softening temperature of the lignin, and applying
sufficient refining energy to yield a mechanical wood pulp
35 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
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11~5i~7
consistency of about 10 to about 40% by weight, usually
about 25 to 30% by weight.
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 o~ sulphurous acid, usually sodium sulphite. The reac-
tion is effected at temperatures above about 110C under a
superatmospheric pressure for a time sufficient to yield a
chemically-treated 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 in-
sufficient to cause s~stantial dissolution of lignin with
consequent loss of yield and generation of polluting
ef~luents. The exact nature of the chemical reactions in-
volved in the chemical treatment effected in this invention
are not fully understood, but are thought to involve sulphon-
ation.
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 ~e specified exactly,
but is readily established by experimentationO
The alkali re~uirement may ~e 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 sodium carbonate.
The pH of the mixture, however, is preferably kept below
about 12 because hemicelluloses are dissolved from wood
fibre by higher pH's r with consequent loss in yield.
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1145107
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
5 lower concentrations down to about 1% by weight may be used
with reduced beneficial effect, with the provision that the
residual sulphite content of the mixture, as measured iodi-
metrically, does not fall substantially to zero before
termination of the reaction. Below 1% by weight of sodium
10 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
15 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
T and about 12, and contains sodium sulphite and sufficient
alkali to maintain a pH greater than 3 throughout the
20 reaction.
The reactions of sulphite with wood are known to
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
25 this complex subject has been summarized by G. Gellerstedt
in Svensk Papperstidning nr. 16, 1976, p. 537 to 543.
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 I 8
30 greater than 3 and pre~erably over 7, and at temperatures
over about 110C, and preferably over about 130C. Other
reactions of woody substances with sulphite which proceed
at lower pH's and at temperatures below lQ0C are known,
such as those described by H.~. Kvisgaard in Norsk
35 Skogindustri 1~, no. 4, 1965, p,155-163. Such reactions,
however, are not ef~ective to produce an improvement in wet
and dry properties, in fibre flexihility and consolidàtion
and in power requirements, such as is contemplated in this
invention.
11451~)7
We have found that the maximum improvement, namely,
maximum increase in wet stretch, maximum improvement in
stress-strain, maximum increase in strength characteristics,
and maximum decrease in refiner power requirements for the
5 second stage (step ~c) discussed below~, is obtained from
the process of the invention when the mechanical pulp ~rom
step (a) with adaed chemical is heate~ at about 160C for
30 minutes. As with any other chemical reaction, the temper-
ature can be lowered if the reaction time is increased.
10 Below about 120C, reaction time becomes impractically long,
and below liOC, 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
15 of 1 to 2 minutes. We prefer not to operate 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
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 and energy requirements
are less than may be otherwise obtained by operating under
optimum conditions. If the reaction time is too long,
substantial dissolution o~ the lignin from the pulp, in the
treating chemical occurs, with consequent loss of yield and
formation of polluting effluent. While the process is still
operable to produce property improvements under these condi-
tiong gome of the advantages of wood economy and low~ollution are lost and generally are avoided.
The chemical treatment is operable over a time-
temperature range from about lLoC for about 12 hours to
about 200C for about 1 minute. It is understood that an
increase in temperature must be accompanied by 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,
ll~SlV7
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
5 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,
lO since wood losses and the pollution capability of the 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 required vary with wood species, chemical
lS charge and consistency, but will fall within the limits of
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 quite
20 distinct from the methods used in 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 ti-e., fibre bundles) by circulating hot
cooking liquor through a bed of the woody ~,aterial. With the
2S mechanical pulp produced in step (a~ of the process of the
invention, the resistance to 10w of liquor is so great that
circulation of liquor 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 entexs
30 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-
35 ferred because it is easier to secure uniform mixing ofchemical and pulp below that level. The consistency range of
about 15% to about 50~ by wei~ht, therefore, is preferred for
reasons of convenience, but the operability of the process is
not limited by consistency.
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51S~7
The chemical treatment step in the process of the
invention i5 also distinguished from chemical pulping process-
es in that the process of the invention cannot be oonducted prac~ically in a
ba1:ch process,such as is used in chemical pulping. ~his is
because the thermal insulating properties of the mechanical
pu:Lp are so high that a large pulp mass cannot be heated
`~ to reaction temperature by conduction in a reasonable length
of time. The chemica1 treatment may be carried out batch-
wise using dielectric or microwave heating techniques but
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
lS removed simultaneously from the other end.
Step (c) Refining
In the third, and final, step of the process of the
invention, the product of step (c~ is subjected to further
refining action in a disc refiner, following the usual
practice of the industry for second stage refining of a
mechanical wood pulp. The results of this second refinir.g
action differ from those obtained with an ordinary
mechanical wood pulp because the application of steps La~
and ~b~ in accordance with this invention places the pulp
in the required physical and chemical configuration to
utilize further refining energy efficiently and economically.
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 enërgy demand~ The product
of step ~b) may be refined to equivalent quality with
significantly less energy, while achieving a faster drainage,
as compared to mechanical pulp from step (a) which has not
been subjected to step (b~. These results are illustrated
graphically in Figure 1, in which a measure of pulp quality
is plotted against refining power for two cases. The measure
of pulp quality employed was the tensile strength of the wet
web, measured at 5~ wet stretch to eliminate the effects o
pulp latency. Similar plots are obtained using such other
measures of pulp quality as breaking length or burst factor.
~145107
11
Point A in Figure 1 defines the state of the pulp at
the completion of step (a) of the process of the invention.
Point B represents the same pulp after completion of step
(b~. The line B-C gives the properties of the pulps derived
5 from step (b~ by the application of varying amounts of
refining energy in accordance with step (cJ of the process
of the invention. The line A-D represents the properties
~f pUlpe obt~ined by directly refining the product of step
(a~, without the application of step (b). The dramatic
10 effect of the chemical treatment of step (bl in improving
the drainage of refined pulp, as measured by Canadian
Standard Freeness (C.S.F.), in increasing the pulp strength,
. .
and in decreasing the energy requirements in the appli-
cation of the refining o step ~c) is clearly e~ident from
15 the graphical representation of Figure 1.
The consistencies employed in the application of step
(c) may be varied over the range normally employed in the
second stage refining of a mechanical wood pulp, but the
properties of the product depend to some extent on the refin-
20 ing consistency chosen. Higher consistencies over about 20by weight yield products with higher wet stretch while
lower consistencies tend to produce pulps with higher strength.
By adjustments in refinin~ consistency, the desired balance
between wet stretch and strength for a particular application
25 can be achieved. For most applications, it is preferred to
carry out the refining step (c) at consistencies between
about 1% and about 35% by welght.
The amount o~ energy applied in step Cc~ may be
varied according to the desired properties of the product and
30 the intended end use. The degree o~ refining to which the
pulp is subjected is usually controlled by the freeness of
the finished 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
3~ freeness than magazine grade paper stock. For newsprint
application, it is preferred to refine to a freeness in the
range about 100 to about 400 C.S.F. in step ~c2.
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11451V7
The invention is illustrated by the following
Examples:
Exam_le 1
Spruce chips were pre-steamed for 25 minutes at 35
psig and fed to a 1000 HP Sprout-Waldron 36 ICP refiner under
the following conditions:
Throughput: - 25.0 tons per day
Discharge consistency: 25 - 30%
Specific energy: 45 horsepower-days per ton
The pulp from the pressurized refiner, consisting
mainly of single fibers, and substantially free of particles
greater than 0.05 mm in diameter, was divided in three portions.
One portion was mixed with 10% by weight of sodium sulphite
at pH 9 and heated at 18% consistency at 90C for 1 hour.
15 Another portion was mixed with 10% sodium sulphite at pH 7
and heated at 18% consistency and 160C under a pressure of
75 psig for 1 hour. A third portion was untreated. Each
portion was then refined further in a 12 inch Sprout-Waldron
open ischarge refiner at 18% consistency and a specific
20 energy input at 63 horsepower-days per ton. All three pulps
thus received a total of 113 horsepower-days per ton of
refining energy.
The usual practice in mechanical pulping is to remove
latency prior to screening, cleaning and final use. This pro-
25 cedure was explained by L. R. Beath, M. T. Neill and F. A.Masse in an arti~le entitled "Latency in Mechanical Pulps",
Pulp and Paper Magazine of Cànada 67 (10)T423(1966). To
correspond to this common industrial practice, latency was
removed from our pulps by treatment at 90C for 15 minutes,
30 prior to testing. The properties of these pulps are compared
ln the following Table I:
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11~5107
13
TABLE I
T~eatment None 90C 160C
Yield, % 100 98 93
Freeness 194 197 80
Drainage, sec. 0.83 0.93 2.16
.
Wet tensile, N/m 62 63 75
Wet s`tretch, % 3.3 3.7 5.3
Wet caliper, mm 0.344 0.353 0.302
Bulk 2.68 2.57 2.12
Burst 16 17 23
Breaking Length 3100 3300 5100
Using the same total refining power, the untreated
sample and the sample treated at 90C refined to essentially
the same ~reeness with insignificant differences in wet
and dry properties. By contrast, the sample treated at 160C
' refined to lower freeness with the same power, yielding over
60% increases in wet stretch and breaking length, as well as
significant increases in wet tensile strength and burst. The
drainage rate is much faster than an untreated TMP
of similar quality.
The wet caliper and bulk are measures of the fiber's
ability to consolidate in the paper sheet. The low values
obtained with the pulp treated at 160C arè indicative of a
flexible fiber which consolidates well to form a dense,
coherent sheet.
Example 2
A TMP prepared in a pressurized refiner as described
in Example 1 was mixed with 10% sodium sulphite at pH 9.0 and
heated at 18% consistency at 160C and 75 psig for 1 hour.
Samples of the treated and untreated TMP were then refined
to comparable freeness levels, and the pulp properties
measured after latency removal at 90C for 15 minutes. Power
consumptions and the corresponding pulp properties are out-
lined in the followlng Table II:
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5107
14
TABLE II
Untreated Treated Untreated Treated
Power, HPD/T 126 101 101 82
Freeness 107 118 305 331
Drainage, sec. 1.27 1.63 0.66 0.83
-
Wet tensile, N~m 58 77 59 76
Wet stretch, % 4.0 5.1 3.3 4.3
Wet caliper, mm 0.322 0.290 0.385 0.326
Bulk 2.47 1.92 3.14 2.08
Burst 14 28 14 32
Breaking Length 3200 5600 2800 5800
Yield, % 100 94 100 96
These data show, that by treatment according to the
' process of the invention, power requirements to reach a
desired freeness and drainage target can be reduced over 20%.
In addition these power savings are accompanied by substantial
improvements in wet web properties, in dry strengths, and in
fiber consolidation.
Example 3
Southern pine pulp from the pressurized first stage
refiner of a commercial newsprint mill was treated at 145C
for 1 hour with 10~ by weight of sodium sulphite at pH 9.
The resulting pulp was then refined at power inputs of 19 and
38 horsepower-days per ton in a 12 inch Sprout-Waldron
refiner.
The untreated pulp was refined in a like manner. The
properties of these products after delatency treatment at
90C fcr 15 minutes, are listed in the following Table III:
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5107
TABLE III
Untreated Treated
Refining Power, HPD/T 38 19 38
Freeness, C.S.F. 194 243 146
Drainage, sec. 0.64 0.65 0.82
Wet tensile, N/m 36 42 46
Wet stretch, % 4.4 5.4 5.9
Ca~iper, mm 0.402 0.375 0.348
Bulk 3.65 2.74 2.56
Burst 9 19 20
Breaking length 2100 3400 3800
Tear 67 92 89
These data illustrate the application of the process
of the invention to a difficult species; southern pine has a
' 15 stiffer, thicker fiber than spruce and in general yields a
lower quality TMP. However by application of the process of
the invention, a product of equal or better quality to that
conventionally obtained can be made, with the following
added advantages.
1) Less power is needed to reach equal freeness.
2) At equal power inputs, the treated pulp refined
to lower freeness, with large improvements in both wet and
dry properties. Burst and breaking length are approximately
doubled.
3) At half the second stage power input and higher
freeness, the treated product is still superior to the
product derived from untreated TMP.
4) The process of the invention results in ma~or
improvements in fiber consolidation as shown by the decrease
in wet caliper and bulk.
Example 4
Spruce chips were refined in a Bauer 420 open dis-
charge refiner at a rate of 65 tons per day and a specific
energy of 60 hoxsepower-days per ton. One portion of this
~5 RMP was mixed with 10% sodium sulphite at pH 9 and hèated at
145C and 50 psi pressure for one hour. Both treated and
.,
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11'~51()7
16
untreated pulps were further re~ined in a 12-inch Sprout-
Waldron refiner at 20% consistency. The resulting RMP's
had the properties outlined in the following Table IV,
after latency removal at 90C for 15 minutes.
TABLE IV
Untreated Treated
Secondary Refining Power
HPD/T 0 45 45 32
Freeness, C.S.F. 388 122 81 156
10 Drainage, sec. 0.61 1.16 2.3 1.28
Wet Web Properties
Tensile, N/m 36 56 63 68
Stretch, ~ 3.2 4.3 5.6 4.7
Caliper, mm 0.454 0.336 0.287 0.311
15 Dry_~roperties
Bulk 3.98 2.70 1.98 2.22
Burst 8 16 23 25
Breaking Length 1700 3300 4900 4700
St~etch 1.2 1.8 1.7 1.9
20 Tear 61 66 52 69
This example illustrates several points. The RMP
from the primary refiner (first column) requires additional
application of refining power for the development of adequate
properties. The application of a further `45 horsepower-days
per ton of refining power results in the greatly improved
properties listed in column 2. However application of the
same amount of power to an RMP which has been treated accor-
ding to the present invention results in a product with lower
freeness and superior wet and dry properties ~column 3).
Alternatively by application of only 3~ horsepower days per
ton of additional refining power, a pulp is produced with
comparable freeness and drainage characteristics but signifi-
cantly improved in all Wet and dry properties, shown in
column 4.
This illustrates that the process of the invention
is applicable to refiner mechanical pulps as well as thermo-
mechanical pulp.
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1~451~)7
17
In summary of this disclosure, the present invention
is directed to the formation of an improved mechanical pulp
which can be used as a substitute for chemical pulp.
Modifications are possible within the scope of this invention.
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