Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
;6558
This invention relates to a process for strengthening
mechanically prepared lignocellulosic pulp by chemical
treatment.
Lignocellulosic pulp prepared by mechanical means,
for example, grinding, costs less to produce than ligno-
cellulosic pulp prepared by chemical means such as the
sulphate process. A mechanical process also gives a higher
yield of pulp than a chemical process. Because of these
advantages it is desirable to use mechanical pulps to the
fullest possible extent in paper making, However, the use
of mechanical pulps is limited by their low papermaking
strength.
We have now found that lignocellulosic mechanical
pulp can be strengthened by treating it initially with a
chlorine-containing reagent followed after washing by
treatment with caustic with or without admixture with
peroxide, The treatment provides a marked improvement
in the physical properties of the pulp as shown by burst
factor, tear factor (for deciduous woods), folding endurance
and breaking length measurements,
Thus the principal object of the invention is to
provide a means for improving the strength of fibrous
lignocellulosic material prepared by mechanical methods.
Additional ob~ects will appear hereinafter,
The process of this invention comprises the treatment
of fibrous lignocellulosic material prepared at least partially
by mechanical means by the steps of
1) treating the material with a chlorine-containing
reagent,
~a~56~51~3
2) washing the material with water,
3) treating the washed material with alkali metal
hydroxide with or without admixture with hydrogen peroxide
or alkali peroxide, and
4) washing the material with water
The lignocellulosic material for which the process
of this application is applicable includes pulp prepared
by ~echanical disintegration of wood in the presence of
water, thermo-mechanical pulp, chemi-mechanical pulp and
semi-chemical pulp. The disinte~ration may be carried out
by stone grinders or by refiners such as the Bauer double-
disc refiner.
The preferred chlorine-containing reagents are chlorine
and chlorine dioxide. However, alkali metal chlorates, chlor-
ites or hypochlorites may be employed. The alkali metal
chlorates and chlorites may be employed in acidic medium by
admixture with an acid such as hydrochloric. A mixture of
alkali metal chlorate, hydrochloric acid and a catalytic amount
of vanadium pentoxide may be used. Also a mixture of alkali
metal chlorite and chlorine has been found effective.
During the first step of a preferred embodiment of
the process,aqueous pulp at a consistency of 2,0% to 35,0%
by weight, preferably 3,0% to 6.0% by weight, is treated
with 0.5% to 8,0% by weight, preferably 0,5% to 4,0% by
weight, of chlorine dioxide at 25C to 90C, preferably
40C to 70C, for a period of 1/2 hour to 5 hours, preferably
1 hour to 2 hours, The treated pulp is then washed with
water,
-- 2
~os~ss~
During the third st~p of a pr~ferred embodiment of
the process,aqueous pulp at a consistency of 6,0% to 35,0%
~y weight, preferably 12,0% to 18,0% by weight, is treated
1~ with 2% to 16% by weight, preferably 4% to 8% by weight of
i alkali metal hydroxide and 0,2% to 4,0% by weight, pre~er-
ably 0,5% to 2,0% by weight of hydrogen peroxide and option-
ally up to 5.0% by weight of alkali metal silicate and/or
up to 1.0% by weight of a magnesium salt at 20C. to 80C.,
preferably at 20C. to 40C. for a period o~ 1 to 72 hours,
pre~erably 2 to 4 hours. The pulp is then washed with water.
In the first step the reagent employed may be
chlorine, When employing chlorine the pulp at a consis-
tency~ of 2.0% to 12,0% by weight is treated with 1.0% to
8,0% chlorine at 10C to 60C for a period of 5 to 120
minutes.
In the third step the hydrogen peroxide reagent
may be omitted, the treatment being with alkali metal
hydroxide only.
The preferred alkali metal hydroxide reagent of
the third step is sodium hydroxide,
The process of this invention provides a mechanical
pulp having increased papermaking strength.
The invention is illustrated additionally by the
following Examples but its scope is not limited to the
e~bodiments shown therein, The physical properties shown
were measured by the following procedures,
-- 3
1~)51~55~3
~Iandsheet Formation TAPPI T 205 m-58
(hot disintegration)
Brightness TAPPI T 217 m-47 (Elrepho,
pulp soured with SO2)
Opacity CPPA E-2P
j Freeness TAPPI T 227 m-58
¦ sulk TAPPI T 220 m-60
¦ Tear Factor TAPPI T 220 m-60
Burst Factor TAPPI T 220 m-60
~reaking Length TAPPI T 220 m-60
Elongation TAPPI T 220 m-6~
~olding Endurance TAPPI T 220 m-60
~0.5 Kg tension)
EXAMPLE 1
` 30 grams (oven dry basis) of a hardwood groundwood
pulp composed mainly of cottonwood species were placed in a
covered glass vessel equipped with a stirrer, Water was
added to give a consistency of 3,3% by weight and stirring
! was commenced. An aqueous solution of chlorine dioxide
- was then introduced below the surface of the pulp, the
amount being sufficient to gi~e a charge of chlorine
dioxide equivalent to 1% of the dry weight of the pulp
and a final consistency of 3,0% by weight. After treatment
for 60 minutes at 40C the pulp suspension was filtered to
remove most of the liquor and resuspended in 3 litres of
water and filtered again~ The partially treated pulp was
then transferred to a plastic bag and an aqueous solution
of sodium hydroxide and hydrogen peroxideand magnesium
sulphate was added to give charges of the three chemicals of
8.0%, 1.0% and 0.05% by weight respectively, the final consis-
565S8
tency being 9% by weight. The reac-tion was continued at 40C.
for 3 hours, following which the pulp was filtered and washed
twice with water.
The resulting pulp was evaluated for yield, brightness
and mechanical properties, and its characteristics were
compared with those of the untreated pulp as shown in the
accompanying Table I.
;
EXAMPLE 2
40 grams ~oven dry basis) of a softwood groundwood
pulp composed mainly of spruce and balsam species were
treated in a manner similar to that described in Example 1
except that the chlorine dioxide step was carried out for
1 hour at 40C and the charges of chlorine dioxide, sodium
hydroxide and hydrogen peroxide were respectively 2,0%,
4,0% and 1.0% by weight. This experiment was carried out
six times and the results averaged. These results are
compared in the accompanying Table I with the corresponding
- data for the untreated pulp,
EXAMPLE 3
The procedure of Example 2 was repeated except that
the charges of chlorine dioxide, sodium hydroxide and hydroyen
peroxide were doubled to 4,0%, 8,0% and 2.0% by weight respect- -
ively, The results are shown in the accompanying Table I.
EXAMPLE 4
30 grams (oven dry basis) of a hardwood groundwood
pulp composed mainly of cottonwood species were placed in a
covered glass vessel equipped with a stirrer, Water was added
to give a consistency of 5,0~/O by weight and stirring was
commenced, An aqueous solution of chlorine was ~hen introduced
- 5 - ,
~C~56558
below the surface o~ the pulp, the amount being sufficient to
give a charge of chlorine equivalent to 8.0% of the dry weight
of the pulp and a final consistency of 3.0% by weight. After
treatment for 30 minutes at 25C the pulp suspension was
filtered to remove most of the liquor and resuspended in
3 litres of water and filtered again. The partially treated
pulp was then transferred to a plastic bag and an aqueous
solution of sodium hydroxide and hydrogen peroxide and magnesium
sulphate was added to give charges o~ the three chemicals of
8.0%, 0.5% and 0.05% by weight respectively, the final consis-
tency being 12.0% by weight. The reaction was continued at
40C. for 3 hours, following which the pulp was filtered and
washed twice with water.
The resulting pulp was evaluated for yield, brightness
and mechanical properties and its characteristics were compared
with those of the untreated pulp as shown in the accompanying
Table I.
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¦ EXAMPLE 5
40 grams (oven dry basis)` of the sof-twood groundwood of
Example 2 were placed in a covered glass vessel equipped with
a stirrer. Water was added to give a consistency of approxi-
mately 4% by weight and stirring was commenced. An aqueous
solution of chlorine was then introduced below the surface of
the pulp, the amount being sufficient to give a charge of
chlorine equivalent to 2% o~ the dry weight of the pulp and
a final consistency of 3.0% by weight. After treatment ~or
30 minutes at 2SC. the pulp suspension was filtered to remove
most of the liquor, resuspended in 3 litres o~ water and
filtered again. The partially treated pulp was then transferred
to a plastic bag and an aqueous solution o~ sodium hydroxide,
hydrogen peroxide and 41 Bé sodium silicate and magnesium
sulphate was added to give charges of the four chemicals of
4%, 1%, 5% and 0.05% by weight respectively, the final consis-
tency being 12.0% by weight. The reaction was continued at
40C. for 3 hours following which the pulp was filtered and
washed twice with water.
The resulting pulp was evaluated for yield, brightness
and mechanical properties with the results shown in Table II.
EXAMPLE 6
The procedure of Example 1 was repeated except that the
charges of chlorine dioxide, sodium hydroxide and hydrogen
peroxide were 2.0%, 4.8% and 2.0% respectively. The properties
of the resulting pulp are shown in Table II. The brightness
obtained was 2 points higher than could be obtained by bleaching
the same pulp in the conventional manner with 2.0% hydrogen
peroxide, 1.9% sodium hydroxide, 5% 41 Bé sodium silicate and
0.05% magnesium sulphate.
- -- 8 --
` ~565S8
EX~MPLE 7
40 grams (oven dry basis) of the softwood groundwood
of Example 2 was placed in a glass jar. Water was added to
give a consistency of approximately 10% and the pulp was
broken up by stirring. An aqueous solution of chlorine dioxide
was then introduced below the surface of the pulp, the amount
being sufficien-t to give a charge of chlorine dioxide equivalent
to 4% of the weight of the pulp and a final consistency of
6.0% by weight. The pulp suspension was mixed by vigorous
shaking and the reaction was allowed to continue for 3 hours
at room temperature, following which the pulp was filtered,
resuspended in 3 litres of water and filtered again. The
partially treated pulp was then transferred to a plastic bag
and an aqueous solution of sodium hydroxide was added to give
a charge of sodium hydroxide equivalent to 8% of the wei~ht
of the pulp, the final consistency being 12.0% by weight.
The reaction was continued at 80C. for 3 hours, folLowing
which the pulp was filtered and washed twice with water. Its
properties are shown in Table II.
2 0 EX~MPLE 8
The procedure of Example 1 was repeated except that
hydrogen peroxide and magnesium sulphate were omitted from the
liquor used in the alkaline stage. The properties of the
- resulting pulp are shown in Table II.
EX~MPLE 9
The procedure of Example 5 was repeated except that 8%
chlorine was used in the first stage, and both hydrogen peroxide,
sodium silicate and magnesium sulphate were omitted from the
liquor used in the alkaline stage, which ~as carried out at
60C. for 2 hours. The results are shown in Table II.
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- - --
~5~558
EX~MPLE 10
150 grams of bisulphite chemi-mechanical pulp, prepared
in 88% yield from softwood chips composed mainly of spruce and
balsam species in the laboratory, were treated as described in
Example 2. Subsamples of the resulting pulp were beaten to
varying degrees in a laboratory PFI mill and their properties
determined as a function of the degree of beating. In Table ~II
the resulting data are summarized and compared with corres-
ponding data for the untreated pulp.
EXAMPLE 11
150 grams of busulphite chemi-mechanical pulp, prepared
- in 82% yield from hardwood chips composed chiefly of aspen, were
treated as described in Example 10, wi-th the results shown in
Table III.
EXAMPLE 12
150 grams of a softwood cold soda pulp prepared in the
laboratory from chips composed mainly of spruce and balsam
species were treated as described in Example 10. With increasing
~ degree of beating, the tear factor of the treated pulp increased,
`- 20 whereas that of the untreated pulp decreased. At a tear factor
of 53, the breaking length of the treated pulp was 3.1 km., while
that of the untreated pulp was I.9 km.
EXAMPLE 13
150 grams of an 85% yield neutral sulphite chemi-mechanical
pulp prepared in the laboratory from chips composed chiefly of
aspen wood were treated as described in Example 10. Some proper-
ties of the treated pulp are compared with those of the untreated
pulp in Table III.
-- 11 --
1056558
EXAMPLE 14
150 grams of a 79% yield alkaline sulphi-te semi-chemical
pulp prepared in the laboratory from softwood chips composed
mainly of spruce and balsam species were treated as described in
Example 10. Properties of the treated and untreated pulps are
compared in Table III.
EXAMPLE 15
150 grams of a commercially produced, coarse softwood
thermo-mechanical pulp were treated as described in Example 10.
Properties of the treated and untreated pulps are compared in
Table III.
EXAMPLE 16
50 grams of commercial screened softwood thermo-mechanical
pulp were treated in a manner similar to that described in
Example 1 except that the chlorine dioxide stage was carried out
' ' for 1 hour at 40C. and the charges of chlorine dioxide, sodium
hydroxide and hydrogen peroxide were respectively 2.0%, 8.0%,
and 2.0% by weight. Upon completion of the a~kaline stage the
' pulp was diluted to 2% consistency and the pH adjusted to 5.0
by addition of an aqueous solution of sulphur dioxide. Following,
- this, it was filtered and washed with water. The properties of
the resulting pulp are compared with those of the untreated pulp
in Table IV.
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- 12 -
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EX~MPLE 17
50 grams of a commercial soEtwood refiner groundwood were
treated according to -the procedure described in Example 2. The
experiment was then repeated three times, each time replacing the
sodiunl hydroxide used in the alkaline s-tage with an equivalent
amount of an alternative base. The amounts and bases used were
3.5% NH40H, 6.2% Na4C03.H20 and 3.7% Ca(OH)2. The properties
I of the four resulting pulps are compared with those of -the
j original refiner groundwood in l'able V.
EXAMPLE 18
50 grams of a commercial softwood refiner goundwood were
treated according to the procedure describe~ in Example 2,
e~cept that 4% chlorine dioxide was used in the first stage and
8% ~odiu~ hydroxide was used in the second stage~ The exper-
iment was then repeated four times, each time replacing the
chlorine dioxide used in the first stage with an equivalent
amount of an alternative oxidant. The amounts and oxidants
used were as follows: (a) 6.7% NaC10~ with 3.2% HCl,
¦ (b) 5.4% NaCl02 with 2.1% C12, (c~ 6.4% NaCl03 with 4% HCl and
0.032% V205, and ~d) 10% NaOCl. The properties of the five
resulting pulps are compar~ with those of the original refiner
groundwood in Table VI.
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