Note: Descriptions are shown in the official language in which they were submitted.
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LIGHT-STABLE LIGNOCELLULOSIC MATERIALS AND THEIR
PRODUCTION
BACKGROUND OF THE 1NVENTION
TECHNICAL FIELD
The current invention relates to the field of wood, pulp and paper
production. . More specifically, it relates to the production of light-stable
lignocellulosic materials, in particular, the production of mechanical wood
1o pulps and papers with much improved light stability, as well as to the
resulting pulps and papers having improved light stability.
BACKGROUND ART
The primary components of wood are the fibrous, hydrophilic
carbohydrates (cellulose and hemicelluloses) and the three-dimensional,
hydrophobic lignin. For the purpose of making papers, wood, either in the
form of whole Logs, wood chips or sawmill residues, must first be reduced
to pulps (discrete fibres) by a chemical or mechanical pulping process. In
chemical pulping of wood, pulps are produced in a yield of 45-55% through
2o the dissolution of lignin by the pulping chemicals. One example of
chemical pulps is the so-called kraft pulp produced from the kraft pulping
process where sodium hydroxide and sodium sulfide are used as the pulping
chemicals. In mechanical pulping of wood, pulps are formed in a yield of
90-98% through the action of mechanical forces that separate the fibres but
retain lignin. Examples of mechanical wood pulps are the
thermomechanical pulp (TMP) produced from the thermomechanical
pulping process and the chemithermomechanical pulp (CTMP) produced
from the chemithermomechanical pulping process. Depending on their end
uses, papers are produced from chemical wood pulps or mechanical wood
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pulps, or a combination of both, together with various papermaking
additives.
High-yield, lignin-containing mechanical wood pulps have a light,
yellow-brown colour. Bleaching of these pulps to a whiter colour is
necessary if they are to be used alone or in combination with bleached
chemical pulps to make high-quality papers. The whiteness of pulps and
papers is commonly estimated by ISO brightness determination which
measures the directional reflectance of light at 457 nm of the papers
[TAPPI Test Methods, T452 om-92, Tappi Press: Atlanta, 1996].
Unbleached, lignin-containing mechanical wood pulps have ISO brightness
values between 45-65%, depending on the wood species and the pulping
conditions.
The current industrial processes for the bleaching of mechanical
wood pulps are the alkaline hydrogen peroxide process and the sodium
~5 hydrosulfite process with the former being the superior one in terms of
brightness gain [Presley and Hill in: Pulp Bleaching - P~iheiple ayad
Practice, ed. Dence and Reeve, p. 459, Tappi Press: Atlanta, 1996].
Alkaline hydrogen peroxide, in the presence of peroxide stabilizers such as
sodium silicate and magnesium sulfate, is capable of bleaching mechanical
2o wood pulps such as spruce TMP from an initial brightness of 55-60% to 70-
80%. Alkaline hydrogen peroxide bleaching of mechanical wood pulps can
be carried out in a single-stage or multistage in one or more than one
refiner, bleach tower, storage vessel, dryer or mixer. Alternatively, the
bleaching chemicals can also be impregnated into the wood chips in one or
2s more than one impregnator and the bleaching achieved during impregnation
before refining [Bonn, CPPA 1990 ~ Annual Meeting Preprints, B 109 -
B114, Montreal, Quebec,1990].
High-yield, lignin-containing mechanical wood pulps, unbleached or
bleached, have properties such as high opacity (low show-through) that are
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desirable for the production of printing and writing papers. However,
papers produced from mechanical pulps yellow (lose their brightness)
rapidly when exposed to light. Such a light-induced yellowing has limited
the wider use of mechanical wood pulps in high-quality papers such as
s printing and writing papers.
The light-induced yellowing (brightness reversion) of lignin-
containing mechanical wood pulps is known to be due to the, oxidation of
lignin. Over the past fifty .years or so, many methods have been reported
for the improvement of the light/brightness stability of mechanical wood
' pulps or papers. These methods involve either a chemical treatment on
pulps aimed at the modification of the yellowing-causing lignin functional
groups or a surface treatment on papers made from mechanical pulps with
yellowing inhibitors such as an UV absorber [Heitner, in: Photochemist~y
of Lighocellulosic Materials, ed. Heitner and Scaiano, p.192 - 204, ACS
1s Symposium Series 531,'ACS 1993].
European patent, No. 0,280,332, published on August 31, 1988
describes a pulp chemical treatment method that improves the
light/brightness stability of peroxide-bleached mechanical wood pulps.
This pulp treatment method involves the reduction of lignin b'-carbonyl and
(-carbonyl groups with sodium borohydride, the blocking of the phenolic
hydroxyl groups with gaseous ethylene or propylene oxide and, in some
cases, the application of a fluorescent chemical. The treatment is rather
complicated with washing, dewatering and temperature adjustment between
the borohydride and the gaseous ethylene or propylene oxide treatment.
Several paper surface treatment methods that improve the
light/brightness stability of papers made from mechanical pulps have been
described. One example of these methods can be found in United States
patent, No. 5,080,754, issued on January 14, 1992. The method comprises
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the steps of forming mechanical pulps into a paper sheet and treating the
paper sheet with a formyl compound yellowing inhibitor by spraying the
inhibitor in a solution or solid form onto the paper sheet. Although this
method and many other surface treatment methods reported elsewhere are
s effective in improving the brightness stability of the papers, the methods
can not be applied to pulps and thus are of no use to pulp mills that only
produce mechanical pulps. In addition, because high-quality papers need to
contain some chemical wood pulps to give other desired properties such as
sheet smoothness and strength, application of yellowing inhibitors to such
1o papers is deemed less efficient as some of the inhibitors will be wasted to
cover the surface occupied by the light-stable chemical wood pulps.
PCT, WO 99/0510, of Ciba Specialty Chemicals and published
Feb. 4, 1999 and US Patent, No. 6,254,72.4B 1 issued to Ciba Specialty
Chemicals on July 3, 2001 describe the use of hindered. nitroxide radicals,
is particularly derivatives of 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl
(4-hydroxy-TEMPO) as effective yellowing inhibitors alone or when
combined with an UV absorber and other coadditives. All the examples
provided in these publications involve syringe-injecting/spraying of an
inhibitor solution to already-formed paper sheets, similar to other paper
2o surface treatment methods reported elsewhere in the prior art. Although the
descriptions are broad, indicating that the extremely broad class of
inhibitors can be added to pulps, pulp slurries and papers, at all possible
manufacturing stages, there is no teaching of how the inhibitors might be
successfully applied to pulp slurries and retained by the pulps. From these
2s publications, it is not evident at all how the inhibitors, particularly
those
water-soluble ones, can be retained by pulp fibres on pulp slurries in
aqueous media. The actual teachings are of coating the paper sheets with
the inhibitors. It has recently been concluded that the inhibitor system
based on hindered nitroxide radicals has no affinity for pulp fibres and thus
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must be applied to the surface of already-formed papers, in the press or
dryer section of the paper machine, or on an off line coater [Yuan et al.,
P~oceedihgs to 87'h PAPTAC Annual Meeting, Montreal, Quebec, C43-C52,
2001].
s Hindered nitroxide radicals have deep orange colors and are known
to be much less desirable yellowing inhibitors than their more expensive,
colorless hydroxyamine derivatives. Surface coating of 1.0%, by wt. (based
on pulp) of 4-hydroxy-TEMPO to paper sheets has been shown to cause the
brightness of the sheets to drop by about 7 ISO points [Cunkle, et al.,
1o Proceedings to 10'h Inte~hational Symposium ou Wood and Pulpiyag
Chemistry, Tlol. 1, 718-721, 1999]. Colorless hydroxyamine derivatives of
nitroxide radicals are prepared by treatment of the radicals with a reducing
agent such as a metal hydride [Rozantsev, in: Free Nit~oxyl Radicals, p. 94,
ed. Ulrich, Plenum Press, New York, 1970].
Hindered amine light stabilizers (HALS) have been widely used for
the Iight stabilization of synthetic polymers such as polyolefins [Minagawa,
Polymer Deg~adatiou and Stability 25: 121-141, 1989]. Application of
hindered amine light stabilizers to papers made from lignin-containing
mechanical wood pulps, however, was found to have no or even a
2o detrimental effect on the brightness stability of the papers [Fornier De
Violet, et al., Cellulose Chem. Techhol. 24: 225-235, 1990].
The light-induced yellowing (brightness reversion) of mechanical
wood pulps is known to be due to the oxidation of lignin phenoxy radicals
generated from lignin phenols and b'-carbonyl or d-hydroxyl-~-O-4 ethers
2s to the yellow o-quinones [Leary, .I. Pulp Paper Sci. 20 6 : J154-160,
1994].
Chemical modifications of the yellowing-causing lignin functional groups
such as the reduction of lignin ~l-carbonyl groups by borohydride and the
blocking of the lignin phenolic Hydroxyl groups by gaseous ethylene oxide
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can be performed on pulps to give mechanical pulps with improved
brightness stability. However, the modifications of lignin functional groups
require the use of a large amount of chemical reagents and a rather
complicated treatment procedure. The use of yellowing inhibitors such as
s UV absorbers and/or radical scavengers to prevent the formation and/or the
oxidation of the phenoxy radicals is an alternative method for yellowing
inhibition. However, one drawback of such a method is that it is only
,applicable to, already-formed papers.
UV absorbers possessing an epoxide or isocyanate functional group
to have been grafted to the surface of wood in organic media to improve the
light stability of the wood [Williams, J. Appl, Polym. Sci. 28: 2093-2103,
1983; Grelier, et al., Holzfo~schuyag 51: 511-518, 1997].
PCT, WO 00/40618, issued July 13, 2000 reports the introduction of
a primary amino group (NH2) into mechanical wood pulps via the reactions
15 of the pulps sequentially with epichlorohydrin and ammonium hydroxide.
The chemically modified pulps, which are insoluble in aqueous media,
could be blended with the unmodified mechanical wood pulps to provide
pulps with improved strength properties. The improved strength properties
were speculated to be due to the cross-linking (formation of imino C=N
2o bonds) between the amino groups in the modified pulps with the carbonyl
groups in the unmodified pulps. The reaction of a carbonyl (C=O) group
and a primary amino (NH2) group to give an imine (imino bond) (C=N) and
water (H20) is known to be a reversible (equilibrium) reaction [Kemp and
Vellaccio, iu Organic Chemistry, p. 289, Worth Publishers Inc., New York,
2s 1980]. As such, the formation of imine is highly unfavorable in the
presence of additional water.
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DISCLOSURE OF THE INVENTION
This invention seeks to provide a method for the production of a
light-stable lignocellulosic material.
The invention also seeks to provide novel lignocellulosic material
s obtainable by the method of the invention.
The invention further seeks to provide a paper containing the novel
lignocellulosic material of the invention.
In accordance with one aspect of the invention, there is provided a
method for the production of light-stable, lignocellulosic materials such as
1o mechanical wood pulps comprising reacting the materials with a water-
soluble, yellowing inhibitor possessing a primary or secondary amino group
of the formula A, B, C or D wherein Y is oxyl (O') or hydroxyl (OH) in an
aqueous medium, or with a water-soluble hindered amine light stabilizer of
the formula A or B wherein Y is hydrogen (H) in an alkaline peroxide
~s bleaching medium or in an aqueous medium with a subsequent bleaching of
the materials in an alkaline peroxide bleaching medium:
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g
R1_ ~
R2 kR3
Rq. N Rs
Y
Rl-NH
R2~ R3
R4/'N Rs
Y
H
I
Rl-NH 2+
R2 ~R3 ~x~p
R4 /1j Rs
H OH~
m
H
R1-NH 2+
R2~ R3 ~X~ k iD)
/N Rs
H OH m
2o wherein Rl is hydrogen or an alkyl group (CH2)"H that is
unsubstituted or substituted by 1 to 2n+1 number of a hydroxyl,
ether, thio, thioether, benzyl, amino, ester, amide, carboxyl and/or
carboxylate [(COO-)rM~] group, and/or radicals derived from an
organic ultraviolet absorber, RZ, R3, R4 and RS are independently
alkyl group (CH2)nH that are unsubstituted or substituted by 1 to
2n+1 number of a hydroxyl, ether, thio, thioether, amino, ester,
amide, carboxyl and/or carboxylate [(COO-)rM'~] group, and/or
radicals derived from an organic ultraviolet absorber; X is an
inorganic or organic anion, n is 1 to 14, preferably 1 to 6, and more
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preferably 1 to 4, k is 1 to 3, p is 1 or 2, M is an ammonium or metal
ion, and r is l, 2 or 3, and the total charge of 2m is equal to kp.
In another aspect of the invention, there is provided a novel
lignocellulosic material, for example, a pulp obtained by the method of the
s invention.
In still another aspect of the invention, there is provided a paper
containing the novel lignocellulosic material.
DESCRIPTION OF BEST MODES
to In one embodiment, the present invention produces light-stable
lignocellulosic materials such as various wood products and mechanical
wood pulps by developing water-soluble, fibre-reactive yellowing inhibitors
and attaching them to the lignocellulosic materials, for example wood
pulps, in aqueous media. The resulting light-stable mechanical wood pulps
15 can then be used to make papers composed mainly of mechanical wood
pulps, including high quality printing and writing papers as well as
newsprint and telephone directory, with improved brightness stability.
These pulps can also be used to replace a part of the chemical wood pulps
in high-quality papers such as printing and writing papers.
2o It has now been discovered that lignocellulosic materials such as
mechanical wood pulps with much improved light/brightness stability can
be produced by reaction of the material with a water-soluble, fibre-reactive
yellowing inhibitor possessing a primary or secondary amino (-NH2 or -
NHR) functional group in an aqueous medium, or with a water-soluble,
25 hindered amine light stabilizer (HALS) possessing a primary or secondary
amino (-NHa or -NHR) functional group in an alkaline peroxide bleaching
medium, or in an aqueous medium with a subsequent bleaching of the
material in an alkaline peroxide bleaching medium.
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Alkaline peroxide bleaching medium in the present specification
contemplates the medium used for a single-stage or multi-stage alkaline
hydrogen peroxide bleaching of wood pulps in one or more than one
refiner, bleach tower, pulp mixer, and/or any other vessel or the medium
s used for a single-stage or multi-stage alkaline hydrogen peroxide
impregnation of wood chips in one or more than one impregnator. An
aqueous medium in the present specification includes the said alkaline
peroxide bleaching medium.
Thus in one aspect of the invention there is provided a method for
1o the production of a light-stable lignocellulosic material such as
mechanical
wood pulp comprising reacting the material with a water-soluble yellowing
inhibitor possessing a primary or secondary amino group in an aqueous
medium, or with a water-soluble hindered amine light stabilizer possessing
a primary or secondary amino group in an alkaline peroxide bleaching
is medium or in an aqueous medium with a subsequent bleaching of the
material in an alkaline peroxide bleaching medium.
In another aspect of the invention there is provided a light-stable,
lignin-containing mechanical wood pulp comprising a lignin-containing
mechanical wood pulp having a water-soluble yellowing inhibitor
2o possessing a primary or secondary amino group, said inhibitor being linked
to said pulp via said amino group.
In other aspects of the invention there is provided a paper sheet in
which the pulp component comprises a pulp of the invention, as described
hereinbefore, as the sole pulp component or in conjunction with chemical
25 wood pulp.
Paper sheet in the present specification contemplates paper or
paperboard.
Thus, in accordance with the present invention, water-soluble, fibre-
reactive yellowing inhibitors and hindered amine light stabilizers are
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provided that are capable of forming covalent bonds to and thus being
retained by lignocellulosic materials such as mechanical wood pulp fibres
in aqueous media. Prior to the present invention, no yellowing inhibitors
possessing an epoxide, isocyanate, or any other functional groups have been
attached to wood pulp fibres, either in organic or in aqueous media. Also
prior to the present invention, hindered amine light stabilizer has been
found to be detrimental to the brightness stability of papers. made from
mechanical pulps. No hindered amine light stabilizer has previously been
used in any pulping or bleaching process to make pulps or papers.
Unexpectedly and surprisingly, it has been found, during attempts to
attach 4-amino-TEMPO to mechanical wood pulps via sequential reactions
of the pulps with the sodium salt of 4-[2'-(4',6'-dichloro-s-triaznyl)]amino-
benzene sulfonic acid and 4-amino-TEMPO, that brightness stability
improvement is achieved by the reaction between the pulp fibres and the
1s water-soluble 4-amino-TEMPO. It has also been discovered that water-
soluble yellowing inhibitors possessing a primary or a secondary amino (-
NHa or NHR) group are extremely reactive towards lignocellulosic
materials and they can be chemically attached to the materials with great
ease in an aqueous medium. Furthermore, it has been discovered that
20 lignocellulosic materials with improved light/brightness stability can be
produced by reacting the materials with a hindered amine light stabilizer
possessing a primary or secondary amino (-NHS, or NHR) group in an
alkaline peroxide bleaching medium, or in an aqueous medium with a
subsequent bleaching of the materials in an alkaline peroxide bleaching
2s medium.
The present invention is based on such surprising discoveries.
The importance of the amino group in providing the fibre-reactivity
to the yellowing inhibitors is explicitly demonstrated in examples 1 and 2 of
the present invention where 4-amino-TEMPO but not 4-hydroxy-TEMPO is
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shown to be reactive towards mechanical wood pulp fibres. Pulps reacted
with 4-amino-TEMPO in aqueous media and then washed repeatedly with
water retain a significant amount of the radical scavenger (as indicated by
the increased nitrogen content of the pulps) and show much higher
s brightness stability than the control samples. Under identical conditions,
pulps treated with 4-hydroxy-TEMPO do not retain any of the reagent and
do not show any improved brightness stability. The importance of the
amino group in providing the fibre-reactivity to hindered amine light
stabilizers is also explicitly demonstrated in example 25 of the present
invention where addition of 4-amino-2,2,6,6-tetramethylpiperidine, but not
4-oxo-2,2,6,6-tetramethylpiperidine, to an alkaline peroxide bleaching of
the pulp is shown to provide the pulp with improved brightness stability.
The unexpected facile reaction between the water-soluble, yellowing
inhibitors or hindered amine light stabilizers (HALS) possessing a primary
1s or secondary amino (-NH2 and NHR) group and lignocellulosic materials
such as mechanical wood pulps in aqueous media as discovered in the
present invention, appears to be due to a type of reaction that is unaffected
or accelerated by the presence of water.
In particular embodiments of the present invention, lignocellulosic
2o materials such as mechanical wood pulps with much improved
light/brightness stability can be produced by reaction with a water-soluble,
yellowing inhibitor possessing a primary or secondary amino (-NH2 or,
NHR) functional group of the formula A, B, C or D wherein Y is oxyl (O')
or hydroxyl (OH) in an aqueous medium, or with a water-soluble hindered
2s amine light stabilizer (HALS) of formula A or B wherein Y is hydrogen (H)
in an alkaline peroxide bleaching medium or in an aqueous medium with a
subsequent bleaching of the materials in an alkaline peroxide bleaching
medium:
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R1_~
Rz kR3 CA)
~t N Rs
Y
R1_~
R2l"\ R3 ~B)
R't N Rs
Y
H
I
Rl-NH 2+
R2 ~R3 ~~~p ~C)
~a ~N Rs
H OH
m
H
R1-~ 2+
R2 R3 ~Xlp C
R4 H OH Rs
m
wherein R1 is hydrogen or an alkyl group (CH2)nH that is unsubstituted or
substituted by 1 to 2n+1 number of a hydroxyl, ether, thio, thioether,
benzyl, amino, ester, amide, carboxyl and/or carboxylate [(COO-)rM'~]
group, and/or radicals derived from an organic ultraviolet absorber such as
2s 2,4-dihydroxybenzophenone; R2, R3, R4 and RS are independently alkyl
groups (CH2)nH unsubstituted or substituted by 1 to 2n+1 number of a
hydroxyl, ether, thio, thioether, benzyl, amino, ester, amide, carboxyl and/or
carboxylate [(COO-)rM~] group, and/or radicals derived from an organic
ultraviolet absorber, such as 2,4-dihydroxybenzophenone; X is an inorganic
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or organic anion, such as carbonate, bicarbonate, chloride,, bisulfate,
sulfate,
formate, acetate, citrate, phosphate, oxalate, ascorbate, n is 1 to 14,
preferably 1 to 6, and more preferably 1 to 4, k is 1 to 3, p is 1 or 2, M is
an
ammonium or metal ion, especially an alkali metal or alkaline earth metal
ion, r is 1, 2 or 3, and the total charge of 2m is equal to the total charge
of
kp.
In this specification, a "radical derived from an organic ultraviolet
absorber" means a radical of the absorber which has the ultraviolet
absorbing characteristic of the absorber and thus introduces such
characteristic into the inhibitor or stabilizer of formulae A to D.
One example of the water-soluble, fibre-reactive yellowing
inhibitors is the commercially available radical scavenger, 4-amino-2,2,6,6-
tetramethylpiperidine-N-oxyl (4-amino-TEMPO) (available from Aldrich).
The reactions of the inhibitors with the lignocellulosic materials can be
1s suitably carried out at a temperature of 20 - 120 °C and a
consistency of 1.5
to 40% in an alkaline peroxide bleaching medium or an aqueous medium in
a pH range of 3.5-12.5. The inhibitor charge can suitably range from 0.01
to 2.0% by weight based on oven-dried (OD) lignocellulosic material, e.g.
pulp weight, preferably at least 0.05%, more preferably at least 0.1% and
2o most preferably from 0.2 to 1.0%, by weight. The reaction may
conveniently be carried out in a.time of 5 minutes to several days (e.g. 3 to
5 days). Unexpectedly and surprisingly, mechanical wood pulps reacted
with yellowing inhibitors of formula A or B where Y is oxyl such as 4-
amino-TEMPO have initial ISO brightness similar to or only slightly lower
2s than the control pulps. Only reactions of the pulps with ~ 0.5% (OD pulp)
of 4-amino-TEMPO and at pH ~ 6.5 cause a small drop (1.0 - 3.0 ISO
brightness points) in the initial brightness. Such an unexpected, much less
detrimental effect of 4-amino-TEMPO and other nitroxide radicals of
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formula A or B on the initial brightness of the inhibitor-attached pulps is
explicitly demonstrated in example 4. A BTMP pulp reacted with 1% (OD
pulp) of 4-amino-TEMPO has an ISO brightness only 1.9 points lower than
the control pulp compared to a drop of 7.1 ISO brightness points when a
s sheet is coated with 1% (OD pulp) of 4-amino-TEMPO. The brightness
stability of the pulp reacted with 4-amino-TEMPO is similar to that of the
sheet coated with 4-amino-TEMPO.
It has also been found that the small drop in initial brightness when
pulps are reacted with ~ 0.5% (OD pulp) of 4-amino-TEMPO or other
1o nitroxide radicals of formula A or B at ~ pH 6.5 can be avoided by carrying
out the reaction in the presence of, or followed by a separate treatment
using a reducing agent such as ascorbic acid or sodium b0rohydride. The
small drop in initial brightness when pulps are reacted with ~ 0.5% (OD
pulp) of 4-amino-TEMPO can also be avoided by carrying out the reaction
is at pH < 6.5 by addition to the reaction media of, or by treating the
resulting
pulps with a small amount of an organic or inorganic acid such as citric
acid, hydrochloric acid or sulfurous acid in the form of aqueous sulfur
dioxide (S02).
The reaction with the inhibitor may be carned out in the presence or
2o absence of air or oxygen.
One example of the said water-soluble, fibre-reactive, hindered
amine light stabilizers (HALS) (formulas A and B where Y is hydrogen) is
4-amino-2,2,6,6-tetramethylpiperidine (available from Aldrich). The
reactions of HALS with lignocellulosic materials can be carried out
2s similarly to the reactions of the yellowing inhibitors. The alkaline
peroxide
bleaching media used for the reactions of the said fibre-reactive yellowing
inhibitors or HALS with and the bleaching of, mechanical wood pulps can
be carried out at a temperature of 20 - 120 °C, a consistency of 1.5 -
50%
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and a bleaching time of five minutes - several days. The alkaline peroxide
impregnation of the wood chips in the presence of the said yellowing
inhibitors or hindered amine light stabilizers can be carried out at a
temperature of 40 - 90 °C, a solid content of 30 - 60%, by weight, and
an
s impregnation time of five minutes to two hours. The charge of bleaching or
impregnation chemicals, hydrogen peroxide, sodium hydroxide (or
hydroxide or oxide of other metals), sodium silicate and magnesium sulfate
can be varied depending on the target brightness, the economics, the mill
configurations and other process conditions. The charge of a fibre-reactive
~o yellowing inhibitor or hindered amine light stabilizer can suitably range
from 0.05 to 2.0% by weight based on oven-dried (OD) pulp weight,
preferably from 0.1 to 1.0%, by weight.
The reaction with the stabilizer, and the bleaching can be carried out
in the presence or absence of air or oxygen.
is Further according to the present invention, mechanical wood pulps
with nearly complete brightness stability can be produced by reaction with
the said yellowing inhibitors or HALS, and then by coating of the paper
made from the resulting pulps with an organic or inorganic ultraviolet
absorber, if Rl, R2, R3, R4 and RS in the said yellowing inhibitors or HALS
2o do not contain an organic ultraviolet absorber.
In the particular use of 4-amino-TEMPO the modified pulp may be
produced in accordance with Scheme 1 below.
NH2 H O Pulp=NH
Pulp +
N
O' O'
Scheme 1. Attachment of 4-amino-TEMPO to mechanical pulps.
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The invention contemplates this method, the modified pulp and
paper containing the modified pulp.
The modified pulp of the invention may be the sole pulp component
of a paper sheet formed from the pulp, or it may be employed in
s conjunction with chemical wood pulp. Thus the paper may have a pulp
component comprising 1 to 100% by weight of the modified pulp of the
invention and 0 to 99%, by weight of a chemical wood pulp, to a total of
100%.
It has also been found advantageous to react ih-situ or treat the pulp
1o reacted with ~ 0.5% (OD pulp) of the inhibitors of formulas A and B where
Y is oxyl with a reducing agent such as ascorbic acid or sodium
borohydride, or an acid such as hydrochloric acid or citric acid.
BRIEF DESCRIPTION OF THE DRAWINGS
~s
FIG. 1 shows the post colour (PC) numbers versus ambient office
fluorescent light exposure times of a spruce bleached thermomechanical
pulp (BTMP) and the BTMP pulps reacted, respectively, with 1.0% and
0.2% (based on pulp) of a water-soluble yellowing inhibitor, 4-amino-
20 2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) to produce
modified pulps of much improved light/brightness stability in accordance
with the invention;
FIG. 2 shows the ISO brightness values versus light exposure times
2s of the same pulps;
FIG. 3 shows the ISO brightness values versus ambient office light
exposure times of a spruce BTMP and a spruce BTMP pulp bleached in the
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l~
presence of 1.0%, by wt., (based on pulp) of a hindered amine light
stabilizer, 4-amino-2,2,6,6-tetramethylpiperidine to produce a bleached
pulp of improved brightness/light stability in accordance with the invention;
and
s FIG. 4 shows the PC numbers versus light exposure times of the
same pulps.
EXAMPLES
The present invention is illustrated but not limited by the following
~o examples:
General Procedure A Employed in the Examples: Reaction at Low
Consistency
Unless otherwise specified, a known amount of a mechanical wood
pulp is mixed with deionized water to give a pulp consistency of 1.5%.
15 "Consistency" is the weight percentage of pulp in a pulp and water mixture.
The pulp slurry is purged with N2 and kept at room temperature (~ 20
°C) or
heated to a desired temperature. A said Water-soluble, yellowing inhibitor
or HALS (0.01 - 2.0% on pulp) is added. The pH of the pulp slurry is
adjusted to a desired value (3.5 - 12.5) by addition of a small amount of
2o NaOH or 6% SOZ solution. The pulp slurry is stirred for 3 hours unless
otherwise specified. The pH of the pulp slurry is then adjusted to near
neutral (pH 6.5 - 7.0) when necessary. The pulp slurry is diluted, unless
otherwise specified, with deionized water to 0.5 to 1.0% consistency,
filtered and washed with deionized water. Unless otherwise specified, the
2s filtered pulp is diluted with deionized water, stirred and filtered two
more °
times.
General Procedure B Employed in the Examples: Reaction at
Medium to High Consistency
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A said water-soluble yellowing inhibitor or HALS (0.01 - 2.0% on
pulp) is dissolved in a known amount of deionized water that when mixed
with a mechanical pulp will give a desired consistency (5.0 to 40%
consistency). The pH of the inhibitor solution is adjusted to a desired value
s and the inhibitor solution is added to the pulp in a polyethylene bag. The
bag is sealed and immersed in a hot water bath set at 40 °C for 3
hours,
unless otherwise specified, with manual mixing of the pulp every hour. The
bag is then removed and cooled in a cold water bath to room temperature (~
20 °C). The pH of the pulp slurry is adjusted to near neutral (pH 6.5 -
7.0)
1o when necessary. The pulp slurry is then diluted with deionized water to 0.5
to 1.0% consistency, filtered and washed with deionized water. Unless
otherwise specified, the filtered pulp is diluted with deionized water,
stirred
and filtered two more times.
15 General Procedure C Employed in the Examples: Reaction in an
Alkaline Peroxide Bleaching Medium
Prior to bleaching, the mechanical wood pulp is treated/chelated with
a chelating agent such as diethylenetriaminopentaacetic acid, pentasodium
salt (DTPA-Nas) (0.2-0.6%) at 50 °C, pH 5-6 and 2% consistency for 30
2o minutes to remove metal ions [Ali et al. J. Pulp Paper Sci., 12 6 : J166-
172, 1986]. Alternatively, the chelating agent is added directly to the
bleaching of the pulps, thus eliminating the pretreatment stage. Chelated or
unchelated mechanical pulp (normally 12 g OD) is mixed in a Hobart mixer
with a known amount of magnesium sulfate, sodium silicate, sodium
2s hydroxide, hydrogen peroxide, a chelating agent (for unchelated pulp), a
fibre-reactive yellowing inhibitor or HALS (0.01 - 2.0% on pulp) and
deionized water to give a pulp of desired consistency (5.0 - 40%). For
bleaching at a temperature < 100 °C, the pulp is then transferred to a
polyethylene bag, sealed, and immersed in a hot water bath set at a known
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temperature (> 20 °C, < 100 °C) for a known bleaching time with
occasional manual mixing. For bleaching at ~ 100 °C, the pulp is placed
in
a pyrex beaker, covered with a watch glass and heated in an autoclave oven
set at a known temperature (100 -120 °C) for a known bleaching time. At
s the end of bleaching, the pulp, either in the bag or in the beaker is
cooled~in
a cold water bath to room temperature (~ 20 °C). The pulp is diluted
with
deionized water, unless otherwise specified, to a consistency of 0.25 to
1.0%. The pH of the pulp slurry is adjusted to 6.5 by addition of 6%
aqueous sulfur dioxide solution or 1N sulfuric acid. The pulp is filtered
1o with recycling of the filtrate to recover fines, and washed thoroughly with
deionized water, unless otherwise specified.
Nitrogen Content Analysis and Light-Induced Yellowing Experiment
Handsheets of an inhibitor or HALS-reacted bleached mechanical
1s wood pulp and the original (control) pulp are prepared according to CPPA
Test Method, Standard C.S, respectively. Total nitrogen contents of the
sheets are measured on selected samples according to TAPPI Test Methods,
T418 om-90. Accelerated light-induced yellowing experiments of the
sheets are performed in a light box (LuzChem Res. Inc.) equipped with 8
2o FBTSCW fluorescent lamps (Albrite Lighting Ltd.) in a constant 23 °C
and
50% humidity room. Unless otherwise specified, the light intensity inside
the light box is measured to be 1950 b' 20 foot-candle. Ambient office light
exposures of selected handsheets are earned out by placing the handsheet
samples on a laboratory bench under normal cool-white fluorescent office
lights at a normal distance of about six feet with the lights being on 24
hours a day. Unless otherwise specified, the light intensity for such
ambient fluorescent office light is measured to be 145 b' 2 foot-candle.
Measurements of the % ISO brightness of the samples on a Technibrite
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Micro TB-1C instrument according to TAPPI Test Methods, T 452 om-92,
are done at different time intervals and converted to post color number (PC
number).
s PC number is defined as follows:
PC = ~(1~S)after - (~s)before~ x 100
k/s = ( 1 - Rinf)Z/2 Ri,, f
where k and s are the absorption and scattering coefficients, respectively,
and Rig is the value of ISO brightness. The relationship between R;~ and
the chromophore concentration is non-linear while the PC number is
roughly linear to the concentration of the chromophore. The lower the PC
1s number is, the less yellow (brighter) the sample.
EXAMPLE 1
Spruce peroxide-bleached TMP (BTMP) pulps (ISO brightness 75.2
%, total nitrogen content = 0.05% on pulp) were treated with the Ha0-
20. soluble 4-hydroxy-TEMPO (2.0% OD pulp) and 4-amino-TEMPO (2.0%
OD pulp), respectively, at 60 °C and pH 9.5 according to the
general
procedure A disclosed above. Table 1 lists the PC numbers of the original
BTMP, the BTMP pulps treated with 4-hydroxy-TEMPO and 4-amino-
TEMPO, respectively, versus the accelerated light exposure times.
2s Treatment with 4-amino-TEMPO greatly improves the brightness stability
of the BTMP pulp while treatment with 4-hydroxy-TEMPO does not
improve the brightness stability of the pulp. The total nitrogen contents of
the 4-hydroxy-TEMPO treated and 4-amino-TEMPO treated BTMP pulps
are 0.04% and 0.16% (on pulp), respectively, which correspond to an
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attachment of 0.0% (on pulp) of 4-hydroxy-TEMPO and 0.67% (on pulp)
of 4-amino-TEMPO to the BTMP pulps.
TABLE 1
PC Number
of the
Bleached
TMP
Pulps
versus
Accelerated
Light
Exposure
Time (hours)
Time BTMP BTMP treated with BTMP treated with
(h)
4-hydroxy-TEMPO 4-amino-TEMPO
0 0.0 0.0 0.0
6 1.8 2.0 0.6
24 4.4 4.8 1.4
48 7.4 8.1 2.3
72 10.1 11.0 3.3
98 12.7 13.8 4.4
170 19.0 - 21.0 7.2
218 22.8 25.1 1 9.0
266 25.8 28.3 10.5
337 30.3 32.9 12.7
,
EXAMPLE 2
The same BTMP pulps as the ones used in example 1 were treated
with the H20-soluble 4-hydroxy-TEMPO (2.0% OD pulp) and 4-amino-
TEMPO (2.0% OD pulp), respectively, at room temperature (~ 20 °C)
and
pH 6.5 - 7.0 according to the general procedure A disclosed. Table 2 lists
the PC numbers of the original BTMP, the BTMP pulps treated with 4-
hydroxy-TEMPO and 4-amino-TEMPO, respectively, versus the
accelerated light exposure times. Again, treatment with 4-amino-TEMPO
greatly improves the brightness stability of the BTMP pulp while treatment
~s with 4-hydroxy-TEMPO does not improve the brightness stability of the
pulp as seen by inspection of the PC numbers. The total nitrogen contents
of the BTMP pulps treated with 4-hydroxy-TEMPO and 4-amino-TEMPO
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23
are 0.05% and 0.19% (on pulp), respectively, which correspond to an
attachment of 0.0% (on pulp) of 4-hydroxy-TEMPO and 0.85% (on pulp)
of 4-amino-TEMPO to the BTMP pulps.
TABLE 2
PC Number of the Bleached TMP Pulps versus Accelerated Light Exposure
Time (hours)
Time (h) BTMP BTMP treated with BTMP treated with
4-hydroxy-TEMPO 4-amino-TEMPO
0 0.0 0.0 0.0
6 1.8 1.9 0.7
24 4.4 4.4 1.6
48 7.4 7.1 2.6
72 10.1 9.7 3.6
98 12.7 12.5 4.7
170 19.0 19.0 7.6
218 22.8 22.9 9.4
266 25.8 26.1 11.0
337 30.3 30.4 13.1
EXAMPLE 3
The same BTMP pulps as the ones used in example 1 were treated
with the H20-soluble 4-amino-TEMPO at a charge of 2.0% and 1.0% (OD
1o pulp), respectively, at room temperature (~ 20 °C) and pH 6.5 - 7.0
according to the general procedure A disclosed. Table 3 lists the PC
numbers of the original BTMP and the two 4-amino-TEMPO treated BTMP
pulps versus the accelerated light exposure times. Treatment with 4-amino-
TEMPO at a charge of 1.0% (OD pulp) is nearly as effective as treatment
~5 with 4-amino-TEMPO at a charge of 2.0% (OD pulp) in improving the
brightness stability of the pulps. The total nitrogen contents of the BTMP
pulps treated with 2.0% and 1.0% of 4-amino-TEMPO are 0.19% and
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0.15% (on pulp), respectively, which correspond to an attachment of 0.85%
and 0.61% (on pulp) of 4-amino-TEMPO to the BTMP pulps.
TABLE 3
PC Number of the Bleached TMP Pulps versus Accelerated Light Exposure Time
(hours)
Time (h) BTMP BTMP treated with BTMP treated with
4-amino-TEMPO (2%) 4-amino-TEMPO (1%)
0 0.0 0.0 0.0
6 1.8 0.7 0.8
24 4.4 1.6 1.7
48 7.4 2.6 2.8
72 10.1 3.6 3.9
98 12.7 4.7 5.0
170 19.0 7.6 8.0
218 22.8 9.4 ~ 9.9
266 25.8 11.0 11.7
337 30.3 13.1 14.0
EXAMPLE 4
A spruce BTMP pulp (ISO brightness 76.2%) was reacted with 1.0%
(OD pulp) of 4-amino-TEMPO at room temperature and pH 6.5 - 7.0
according to the general procedure A disclosed. It was also used to prepare
a handsheet and then coated with 1 % (OD pulp) of 4-amino-TEMPO.
Table 4 shows the PC numbers as well as the ISO brightness values of the
original BTMP handsheet, the BTMP handsheet coated with 4-amino-
TEMPO and the handsheet of the BTMP reacted with 4-amino-TEMPO
versus the accelerated light exposure times, respectively. Reaction of the
pulp with 4-amino-TEMPO not only gives a handsheet with similar
brightness stabilization to that coated with 4-amino-TEMPO, but also
provides the pulp/handsheet with a much higher initial brightness than the
sheet coated with 4-amino-TEMPO.
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TABLE 4
PC Number
[ISO
brightness]
of the
BTMP
Pulps
versus
Accelerated
Light
Exposure Time
Tune BTMP BTMP coated with BTMP reacted with
(h)
4-amino-TEMPO 4-amino-TEMPO
0 0.0 [76.2%]0.0 [69.1%] 0.0 [74.3%]
6 ~ 1.8 [72.0%]1.0 [67.4%] 0.6 [72.8%]
24 4.7 [66.6%]2.4 [65.2%] 1.5 [71.0%]
48 7.3 [62.8%]3.7 [63.3%] 2.4 [69.2%]
72 10.1 [59.5%]4.9 [61.8%] 3.5 [67.3%]
96 12.5 [57.0%]5.8 [60.7%] 4.4 [65.8%]
168 19.2 [51.5%]8.1 [58.2%] 7.3 [61.9%]
216 22.7 [49.1%]9.3 [57.0%] 9.0 [59.9%]
264 26.0 [47.1%]10.5 [55.9%] 10.7 [58.1%]
EXAMPLE 5
5 The same BTMP pulp as the ones used in example 1 was treated
with the Ha0-soluble 4-amino-TEMPO at a charge of 1.0% (OD pulp) at
room temperature (~ 20 °C) and pH 6.5 - 7.0 according to the general
procedure A disclosed. The treated pulp was divided into two equivalent
portions. One portion of the pulp was further treated with ascorbic acid
10 ( 1 % OD. pulp) at room temperature (~ 20 °C) for one hour at 1.5%
consistency. Table 5 lists the PC numbers and the ISO brightness values of
the original BTMP, the 4-amino-TEMPO treated BTMP pulp, and the 4-
amino-TEMPO and ascorbic acid treated BTMP pulp versus the accelerated
light exposure times. Sequential treatment with 4-amino-TEMPO and
1s ascorbic acid not only gives a pulp with much improved brightness stability
but also provides a pulp with initial brightness similar to the control pulp.
The total nitrogen contents of both the 4-amino-TEMPO treated BTMP and
the 4-amino-TEMPO, ascorbic acid treated BTMP are 0.15% (on pulp),
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which correspond to an attachment of 0.61% (on pulp) of 4-amino-TEMPO
to both the BTMP pulps. .
TABLE 5
PC Ntunber
[ISO
brightness]
of the
Bleached
TMP
Pulps
versus
Accelerated
Light Exposure
Time (hours)
Time BTMP BTMP treated withBTMP treated with
(h)
4-amino-TEMPO 4-amino-TEMPO and
ascorbic acid
0 0.0 [75.2%]0.0 [73.6%] 0.0 [75.0%]
6 1.8 [71.0%]0.8 [71.9%] 0.8 [73.0%]
24 4.4 [66.4%]1.7 [70.0%] 1.8 [70.9%]
48 7.4 [62.2%]2.8 [68.0%] 2.9 [68.8%]
72 10.1 [59.1%]3.9 [66.2%] 3.9 [67.1%]
9.8 12.7 [56.5%]5.0 [64.5%] 5.0 [65.4%]
170 19.0 [51.3%]8.0 [60.7%] 8.0 [61.4%]
218 22.8 [48.8%]9.9 [58.6%] 9.8 [59.3%]
266 25.8 [47.0%]11.7 [56.8%] ~ 11.5 [57.5%]
337 30.3 [44.6%]14.0 [54.7%] 13.8 [55.4%]
EXAMPLE 6
Spruce peroxide-bleached TMP (BTMP) pulps (ISO brightness 76.4
%, total nitrogen content = 0.046% on pulp) were treated with 1.0% (OD
pulp) of 4-amino-TEMPO at room temperature (~ 20 °C) and at pH 6.5 -
7.0 and 5.5 - 6.0, respectively, according to the general procedure A
disclosed. Table 6 shows the PC numbers as well as the ISO brightness of
the original BTMP and the two 4-amino-TEMPO treated BTMP pulps
versus the accelerated light exposure times. Treatment of the bleached
TMP pulps with 4-amino-TEMPO at pH 5.5-6.0 is also effective in greatly
1s improving the brightness stability of the pulps. It is also effective in
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improving the initial brightness of the BTMP pulp treated with 4-amino-
TEMPO.
TABLE 6
PC Number
of the
Bleached
TMP
Pulps
versus
Accelerated
Light
Exposure
Time
(hours)
Time BTMP BTMP treated with BTMP treated with
(h)
4-amino-TEMPO 4-amino-TEMPO
pH6.5-7.0 pH5.5-6.0
0 0.0 [76.4%]0.0 [74.6%] 0.0 [75.1 %]
6 1.9 [71.8%]0.7 [72.9%] 0.8 [73.1 %]
24 4.9 [66.3%]1.5 [71.1%] 1.6 [71.3%]
48 7.9 [62.1%]2.6 [69.1%] 2.7.[69.3%]
72 10.6 [59.0%]3.6 [67.3%] 3.7 [67.5%]
96 13.1 [56.5%]4.6 [65.8%] 4.9 [65.6%]
168 19.2 [51.5%]7.3 [62.0%] 7.9 [61.5%]
216 22.7 [49.1%]9.3 [59.7%] 10.0 [59.1%]
264 26.1 [47.1%], 11.0 [57.9%] 11.9 [57.2%]
336 30.4 [44.8%]13.3 [55.7%] 14.4 [54.9%]
EXAMPLE 7
The same BTMP pulps as the one used in example 5 were treated
with 1.0% (OD pulp) of 4-amino-TEMPO at 60 °C and pH 6.5-7.0, and at
room temperature (~ 20 °C) and pH 6.5 - 7.0 without purging the pulp
to slurry with NZ (i.e. in the presence of air/O~), respectively, according to
the
general procedure A disclosed. Table 7 lists the PC numbers of the original
BTMP and the two 4-amino-TEMPO treated BTMP pulps versus the
accelerated light exposure times. Treatment of the bleached TMP pulp with
4-amino-TEMPO at 60 °C or in the presence of air/oxygen is also
effective
in greatly improving the brightness stability of the pulp.
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TABLE 7
PC Number
of
the
Bleached
TMP
Pulps
versus
Accelerated
Light
Exposure
Time
(hours)
Time BTMP BTMP treated with BTMP treated with
(h)
4-amino-TEMPO 4-amino-TEMPO
at 60 C with NZ at ~ 20 C without NZ
purging purging
0 0.0 0.0 0.0
6 1.9 0.7 0.8
24 4.9 1.7 1.6
48 7.9 2.8 2.8
72 10.6 4.0 ~ ~ 3.8
96 13.1 s.0 4.9
168 19.2 8.4 7.9
216 22.7 10.3 9.7
264 26.1 12.3 11.7
336 30.4 14.9 14.1
EXAMPLE 8
Spruce BTMP pulps (ISO brightness 76.4% or 75.5%, total nitrogen
s content = 0.046%) were reacted with 1.0% and 0.2% (OD pulp) of 4-
amino-TEMPO, respectively, at room temperature and pH 6.5 - 7.0
according to the general procedure A disclosed. Tables 8.1 and 8.2 show
the PC numbers as well as the ISO brightness values of the BTMP and the
4-amino-TEMPO reacted BTMP pulps versus the accelerated and ambient
office light exposure times, respectively. The brightness stability of the
BTMP pulps can be dramatically improved by reaction with 1.0% or 0.2%
(OD pulp) of 4-amino-TEMPO, particularly when the pulps are exposed to
ambient light. The total nitrogen contents of the BTMP pulps reacted with
1.0% and 0.2% of 4-amino-TEMPO are 0.140% and 0.073% (on pulp),
1s respectively, which correspond to an attachment of 0.57% and 0.16% (on
pulp) of 4-amino-TEMPO to the BTMP pulps. Data of the PC numbers and
ISO brightness values versus ambient light exposure times for the control
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BTMP pulp and the BTMP pulps reacted with 4-amino-TEMPO are shown
in Figures 1 and 2, respectively.
TABLE 8.1
PC Number [ISO Brightness] of the BTMP Pulps versus Accelerated Light
Exposure Time (hours)
Time BTMP BTMP reacted with BTMP reacted with
(h)
4-amino-TEMPO (1%) 4-amino-TEMPO (0.2%)
0 0.0 [76.4%]0.0 [74.6%] 0.0 [76.0%]
6 1.9 [71.8%]0.7 [72.9%] 1.2 [73.0%]
24 4.9 [66.3%]1.5 [71.1%] 2.6 [70.0%]
48 7.9 [62.1 2.6 [69.1 %] 4.2 [67.2%]
%]
72 10.6 [59.0%]3.6 [67.3%] 6.1 [64.4%]
96 13.1 [56.5%]4.6 [65.8%] 7.8 [62.1%]
168 19.2 [51.5%]7.3 [62.0%] 12.4 [57.0%]
216 22.7 [49.1%]9.3 [59.7%] 15.3 [54.4%]
264 26.1 [47.1%]11.0 [57.9%] 17.8 [52.4%]
336 30.4 [44.8%]13.3 [55.7%] 21.2 [50.0%]
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TABLE 8.2
PC Number
[ISO
Brightness]
of
the
BTMP
Pulps
versus
Ambient
Light
Exposure
Time (days)
Time BTMP BTMP reacted with BTMP reacted with
(d)
4-amino-TEMPO (1%)4-amino-TEMPO (0.2%)
0 0.0 [75.5%]0.0 [73.9%] 0.0 [75.8%]
1 0.4 [74.5%]-0.1 [74.1%] 0.1 [75.5%]
2 0.8 [73.6%]0.0 [74.0%] 0.2 [75.2%]
3 1.1 [72.9%]0.0 [73.8%] 0.3 [74.9%]
4 1.4 [72.1 0.1 [73.6%] 0.5 [74.6%]
%]
7 2.3 [70.3%]0.3 [73.2%] 0.8 [73.8%]
9 2.9 [69.1%]0.5 [72.8%] 1.0 [72.8%]
11 3.6 [68.0%]0.6 [72.1%] 1.2 [72.1%]
14 4.3 [66.7%]0.8 [71.9%] 1.5 [71.9%]
17 5.3 [65.2%]~ 1.1 [71.5%] 1.9 [71.3%]
20 6.3 [63.8%]1.3 [71.1%] 2.3 [70.5%]
22 6.9 [63.0%]1.4 [70.8%] 2.6 [70.0%]
24 7.4 [62.3%]1.6 [70.5%] 2.8 [69.5%]
27 8.3 [61.2%]1.8 [70.1%] 3.2 [68.9%]
29 9.0 [60.4%]1.9 [69.8%] 3.4 [68.4%]
31 9.5 [59.8%]2.0 [69.6%] 3.8 [67.8%]
34 10.5 [58.8%]2.2 [69.2%] 4.1 [67.2%]
36 11.0 [58.2%]2.4 [68.9%] 4.4 [66.7%]
38 11.6 [57.6%]2.6 [68.6%] 4.8 [66.2%]
43 13.1 [56.2%]2.9 [68.0%] 5.5 [65.1%]
45 13.6 [55.7%]~ 3.1 [67.7%] 5:8 [64.7%]
48 14.4 [55.0%]3.3 [67.4%] 6.3 [64.0%]
50 14.9 [54.6%]3.4 [67.2%] 6.6 [63.6%]
52 15.6 [54.0%]3.6 [66.9%] 6.9 [63.2%]
56 16.7 [53.1%]3.8 [66.5%] 7.5 [62.4%]
57 17.0 [52.9%]3.9 [66.4%] 7.6 [66.4%]
59 17.6 [52.4%]4.1 [66.0%] 7.9 [61.8%]
~
62 18.4 [51.8%]4.3 [65.8%] 8.4 [61.3%]
64 18.9 [51.5%]4.5 [65.5%] 8.8 [60.8%]
66 19.4 [51.1%]4.7 [65.2%] 9.1 [60.4%]
69 20.0 [50.7%]4.8 [65.0%] 9.5 [59.9%]
71 20.5 [50.3%]5.0 [64.7%] 9.8 [59.6%]
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~~T A T~TDT D' D
The same BTMP pulp as the ones used in example 6 was treated
with 1.0% (OD pulp) of 4-amino-TEMPO at room temperature and pH 5.5 -
6.0 according to the general procedure A disclosed. Handsheets of the 4-
amino-TEMPO treated pulp and the original (control) pulp were then
coated with 1% (OD pulp) of an ultraviolet absorber, the sodium salt of 2-
(3'-sulfo-5'-sec-butyl-6'-hydroxyphenyl)benzotriazole (Cibafast W)
dissolved in ethanol. Table 9 shows the PC numbers of the original BTMP,
the original BTMP coated with the UVA, the 4-amino-TEMPO treated
1o BTMP, and the 4-amino-TEMPO treated BTMP coated with the LTVA
versus the accelerated light exposure times, respectively. A nearly
complete brightness stabilization of the BTMP pulp can be achieved by
reaction of the pulp with 4-amino-TEMPO and then by coating the sheet
made from the 4-amino-TEMPO-reacted pulp with the LTVA.
is
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TABLE 9
PC
Number
of
the
Bleached
TMP
Pulps
versus
Accelerated
Light
Exposure
Time
(hours)
Time BTMP BTMP BTMP reacted BTMP reacted with
with
(h) coated 4-amino-TEMPO 4-amino-TEMPO
with WA and coated with
UVA
0 0.0 0.0 0.0 0.0
6 1.9 1.0 0.8 0.3
24 4.3 2.4 1.5 0.5
48 7.0 4.1 2.5 0.9
72 9.5 5.6 3.4 1.2
96 12.1 7.1 4.3 1.5
144 16.4 10.0 6.5 2.2
168 18.4 11.4 7.6 2.5
192 20.2 12.9 8.6 3.1
216 22.0 14.0 9.6 3.4
240 23.5 15.3 10.6 3.8
EXAMPLE 10
The same BTMP pulps as the ones used in example 6 were treated
s with 1.0% (OD pulp) of 4-amino-TEMPO at room temperature and pH 5.5 -
6.0 for 0.5 hour according to the general procedure A disclosed, and treated
with 1.0% (OD pulp) of 4-amino-TEMPO at 40 °C, and at 5% and 10%
consistency (Cs.), respectively, according to the general procedure B
disclosed. Table 10 shows the PC numbers of the original BTMP, the three
4-amino-TEMPO treated BTMP pulps versus the accelerated light exposure
times, respectively. The reaction of 4-amino-TEMPO with pulps can be
carried out at various consistencies for 0.5 or 3 hours to give pulps with
much improved brightness stability.
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TABLE 10
PC Number
of
the
Bleached
TMP
Pulps
versus
Accelerated
Light
Exposure
Time
(hours)
Time BTMP BTMP treated BTMP treated BTMP treated
(h) with with
4-amino-TEMPO 4-amino-TEMPO with
(1.5% Cs., 0.5 (5% Cs., 3 h) 4-amino-
h)
TEMPO
(10% Cs.,
3 h)
0 0.0 0.0 0.0 0.0
6 1.7 0.6 0.7 0.7
24 4.1 1.3 1.6 1.7
48 6.8 2.2 2.7 2.8
96 12.1 4.0 ' 4.7 4.8
168 18.8 6.5 7.6 7.7
216 22.9 8.4 9.5 10.1
264 25.5 9.9 11.1 . 12.1
336 29.8 12.0 13.4 14.8
EXAMPLE 11
A spruce BTMP pulp (total nitrogen content = 0.034% on pulp) was
s treated with 1.0% (OD pulp) of 3-amino-2,2,5,5-tetramethyl-1-
pyrrolidinyloxy (formula B where Rl = H, R2 = R3 = R4 = RS = CH3 and Y
= oxyl), 3-amino-TEMpyrrolidinyl0 (purchased from Arcos Organics) at
room temperature and pH 6.5 - 7.0 according to the general procedure A
disclosed. Table 11 lists the PC numbers and ISO brightness values of the
original BTMP and the BTMP pulp treated with 3-amino-
TEMpyrrolidinyl0 versus the accelerated light (light intensity = 1940 b' 40
foot-candle) exposure times. Treatment of the pulp with 3-amino-
TEMpyrrolidinyl0 provides a .noticeable improvement of brightness
stability to the pulp. The total nitrogen content of the BTMP pulp treated
with 3-amino-TEMpyrrolidinyl0 is 0.078% (on pulp), respectively, which
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corresponds to an attachment of 0.25% (on pulp) of the inhibitor to the
BTMP pulp.
TABLE 11
PC Number [ISO Brightness] of the BTMP Pulps versus Accelerated Light
Exposure Time (hours)
Time (h) BTMP BTMP treated with
3-amino-TEMpyrrolidinyl0
0 0.0 [76.6%] 0.0 [75.9%]
6 1.9 [72.0%] ~ 1.0 [73.4%]
24 4.9 [66.4%] 2.9 [69.5%]
48 7.9 [62.2%] 5.3 [65.5%]
72 10.6 [59.1%] 7.5 [62.4%]
144 17.5 [52.8%] 14.0 [55.5%]
192 21.4 [50.0%] 18.1 [52.2%]
240 25.1 [47.7%] 21.6 [49.7%]
336 30.8 [44.6%] 27.7 [46.1%]
EXAMPLE 12
Spruce BTMP pulps (total nitrogen content = 0.032% on pulp) were
treated with 1.0% and 0.5% (OD pulp) of 1-hydroxyl-4-amino-2,2,6,6-
tetramethylpiperidine dihydrochloride (formula C where Rl = H, R2 = R3 =
R4 = RS = CH3, X = Cl, m = k = 1 and p = 2), 4-amino-TEMPOH-2HC1,
prepared from the reaction of 4-amino-TEMPO and hydrochloric acid in
ethanol according to a literature procedure [Sosnovsky and Cai, J. O~g.
Chem. 60: 3414-3418, 1995], at room temperature and pH 6.5 - 7.0
according to the general procedure A disclosed. The same spruce BTMP
is pulp is also treated with 0.5% (OD pulp) of 4-amino-TEMPOH-2HCl at 40
°C and 20% consistency according to the general procedure B disclosed.
Table 12 lists the PC numbers as well as the ISO brightness values of the
original BTMP and the three treated BTMP pulps versus the accelerated
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light (light intensity = 1950 b' 80 foot-candle) exposure times. The BTMP
pulps treated with 4-amino-TEMPOH-2HC1 have slightly higher initial
brightness and much higher brightness stability than the control pulp. The .
total nitrogen contents of the three treated BTMP pulps are 0.112%, 0.082%
s and 0.078% (on pulp), respectively, which correspond to an attachment of
0.70%, 0.44%, and 0.40% (on pulp) of the inhibitor to the BTMP pulps,
respectively.
TABLE 12
PC
Number
[ISO
Brightness]
of
the
BTMP
Pulps
versus
Accelerated
Light
Exposure Time
(h)
Time BTMP BTMP treated BTMP treated BTMP treated
with
(h) with 4-amino-TEMPOH- with
4-amino- 2HC1 4-amino-
TEMPOH-2HC1 (0.5%, 1.5% Cs.)TEMPOH-
(1.0/0, 1.5% 2HC1
Cs.)
(0.5%, 20%
Cs.)
0 0.0 [76.1%]0.0 [76.3%] 0.0 [76.7%] 0.0 [76.8%]
6 1.8 [71.8%]0.7 [74.4%] 0.8 [74.6%] 1.0 [74.2%]
24 4.5 [66.8%]1.6 [72.3%] 1.9 [72.0%] 2.3 [71.3%]
72 9.6 [60.0%]3.6 [68.4%] 4.7 [66.8%] 5.3 [65.9%]
144 16.7 [53.3%]6.7 [63.7%] 9.0 [60.9%] 10.1 [59.7%]
192 20.4 [50.6%]8.6 [61.2%] 11.5 [58.2%] 12.8 [56.9%]
240 23.9 [48.3%]10.4 [59.2%] 13.7 [56.0%] 15.3 [54.7%]
312 27.9 [46.0%]12.7 [56.8%] 16.7 [53.5%] 18.4 [52.2%]
to
EXAMPLE 13
The same BTMP pulps as the ones used in example 12 were treated
with 1.0% (OD pulp) of 1-hydroxyl-4-amino-2,2,6,6-tetramethylpiperidine
sulfuric acid salt, 4-amino-TEMPOH-SA, and 1-hydroxyl-4-amino-2,2,6,6-
1s tetramethylpiperidine citric acid salt, 4-amino-TEMPOH-CA, both prepared
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from the reaction of 4-amino-TEMPO and the corresponding acids in
ethanol according to a literature procedure [Sosnovsky and Cai, J. O~g.
Chem. 60: 3414-3418, 1995], respectively, at room temperature and pH 6.5
- 7.0 according to the general procedure A disclosed. They were also
s treated with 4-amino-TEMPOH-CA and 4-amino-TEMPOH-2HCl,
respectively, at room temperature and pH 6.5 - 7.0 for 10 minutes according
to the general procedure A disclosed. Table 13 lists the PC numbers of the
original BTMP and the BTMP pulps treated with the said inhibitors versus
the accelerated light (light intensity = 180 b 40 foot-candle) exposure
1o times. Treatment of the pulps with 4-amino-TEMPOH-SA, 4-amino-
TEMPOH-CA or 4-amino-TEMPOH-2HC1 for 3 hours or 10 minutes
provides the pulps with much improved brightness stability.
TABLE 13
PC Number of the Bleached TMP Pulps versus Accelerated Light Exposure Time
(hours)
Time (h) BTMP SA salt CA salt CA salt 4-amino-TEMPOH-
(3 h) (3 h) (10 min) 2HC1
( 10 min)
0 0.0 0.0 0.0 0.0 0.0
6 1.5 1.1 0.6 0.6 0.4
24 4.0 2.6 1.7 1.6 1.1
.
48 6.4 4.0 2.9 3.0 1.9
96 11.2 6.7 5.6 5.9 3.7
216 21.0 12.7 11.9 12.7 8.0
264 24.3 14.9 14.3 15.3 9.7
EXAMPLE 14
A chelated spruce TMP pulps were bleached with ~ 5% H202, 4%
NaOH, 3% Na2Si03 and 0.05% Mg, (as MgS04) at 60 °C and 10 or 20%
consistency in the absence (0.0%) and in the presence of 0.5% (OD pulp) of
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4-amino-TEMPO or 1:0% (OD pulp) of 4-amino-TEMPOH-2HC1,
respectively, according to the general procedure C disclosed. Table 14 lists
the PC numbers of the control BTMP (bleached in the absence of 4-amino-
TEMPO or 4-amino-TEMPOH-2HC1) and the BTMP pulps bleached in the
presence of 4-amino-TEMPO or 4-amino-TEMPOH-2HC1 versus the
accelerated light (light intensity = 1850 b'. 25) exposure times,
respectively.
Addition of 4-amino-TEMPO or 4-amino-TEMPOH-2HC1 to alkaline
peroxide bleaching of the pulps allows both the reaction of the fibre-
reactive yellowing inhibitors with the pulps and the bleaching of the pulps
to to occur at the same time to give bleached pulps with much improved
brightness stability.
TABLE 14
PC Number of the Bleached TMP Pulps versus Accelerated Light Exposure Time
(hours)
Time (h) BTMP BTMP bleached in the BTMP bleached in the
(20% Cs.) presence presence
of 4-amino-TEMPO (0.5%) of 4-amino-TEMPOH-
(10% Cs.) 2HC1 (1.0%)
(20% Cs.)
0 0.0 0.0 0.0
6 1.8 1.0 0.9
24 4.4 2.4 2.4
48 7.0 4.2 3.7
96 11.9 7.9 6.4
216 21.5 16.1 12.4
264 24.7 18.8 14.6
i s EXAMPLE 15
An aspen unbleached CTMP and an aspen peroxide-bleached CTMP
(BCTMP) were reacted, respectively, with 1.0% (OD pulp) of 4-amino- ,
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TEMPOH-2HC1 at room temperature and pH 6.5 - 7.0 according to the
general procedure A disclosed except without purging the pulp slurries with
N2. Table 15 lists the PC numbers as well as the ISO brightness values of
the original CTMP and BCTMP pulps, and the CTMP and BCTMP pulps
treated with 4-amino-TEMPOH-2HC1 versus the accelerated light. (light
intensity = 1936 d 20 foot-candle) exposure times. Treatment of both the .
CTMP and BCTMP pulps with 4-amino-TEMPOH-2HCl provides the
pulps with much improved brightness stability as well as slightly higher
initial brightness values.
TABLE 15
PC Number
[ISO brightness]
of the Unbleached
and Bleached
Aspen CTMP
Pulps versus osure Time
Accelerated (hours)
Light Exp
Time (h) CTMP CTMP treated BCTMP CTMP treated
with
4-amino- with
TEMPOH-2HC1 4-amino-
TEMPOH-
2HC1
0 0.0 [67.9%]0.0 [68.6%] 0.0 [79.3%]0.0 [79.7%]
24 1.9 [64.9%]0.6 [67.6%] 2.8 [72.0%]1.3 [75.7%]
48 3.0 [63.4%]1.1 [66.7%] 4.5 [68.7%]2.0 [73.9%]
96 5.3 [60.6%]2.1 [65.1%] 7.6 [63.8%]3.3 [71.0%]
168 8.4 [57.2%]3.7 [62.9%] 11.7 [58.9%]5.1 [67.7%]
216 10.2 [55.5%]4.7 [61.7%] 14.0 [56.5%]6.2 [66.0%]
264 12.0 [54.0%]5.9 [60.3%] 16.4 [54.4%]7.4 [64.2%]
336 14.4 [52.1%]7.4 [58.7%] 19.6 [51.9%]9.0 [62.1%]
EXAMPLE 16
Spruce BTMP pulps (total nitrogen content = 0.037% on pulp) were
~s treated with 0.5% and 0.1% (OD pulp) of 4-amino-TEMPO, respectively, at
room temperature and pH 6.5-7.0 according to the general procedure A
disclosed. Table 16 lists the PC numbers as well as the ISO brightness
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values of the original BTMP and the two BTMP pulps treated with 4-
amino-TEMPO versus some of the ambient office light (light intensity .--
145 'd 10 foot-candle) exposure times. The brightness stability of the
BTMP pulp can be dramatically improved by treatment with 0.5% (OD
s pulp) of 4-amino-TEMPO, and significantly improved with 0.1 % (OD
pulp) of 4-amino-TEMPO. The total nitrogen contents of the BTMP pulps
treated with 0.5% and 0.1% of 4-amino-TEMPO are 0.103% and 0.052%
(on pulp), respectively, which correspond to an attachment of 0.40% and
0.09% (on pulp) of 4-amino-TEMPO to the BTMP pulps, respectively.
Table 16
PC Number [ISO brightness] of the BTMP pulps versus Ambient Light Exposure
Time (days)
Time BTMP BTMP treated with BTMP treated with
(d)
4-amino-TEMPO (0.5%)4-amino-TEMPO
(0.1 %)
0 0.0 [76.2%] 0.0 [75.1 %] 0.0 [76.2%]
8 2.7 [70.0%] 0.5 [73.9%] 1.2 [73.2%]
14 4.5 [66.8%] 1.0 [72.7%] 2.2 [71.1%]
21 6.5 [63.9%] 1.7 [71.3%] 3.2 [69.0%]
28 8.4 [61.4%] 2.3 [70.0%] 4.4 [67.0%]
39 ~ 11.4 [58.1%]3.4 [68.0%] 6.4 [64.1%]
49 . 14.1 [55.5%]4.6 [66.1%] 8.2 [61.7%]
58 16.8 [53.3%]5.8 [64.2%] 10.3 [59.3%]
70 20.1 [50.8%]7.4 [62.2%] 12.7 [56.8%]
81 22.5 [49.2%]8.7 [60.6%] 14.6 [55.1 %]
92 25.2 [47.6%]10.1 [59.0%] 16.9 [53.2%]
EXAMPLE 17
An aspen BCTMP pulp obtained from a Western Canadian pulp mill
1s and a laboratory bleached, mixed (black spruce/pine/fir) softwood
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groundwood pulp (GWP) obtained from an Eastern Canadian pulp mill
were reacted with 0.5% (OD pulp) of 4-amino-TEMPOH-2HC1 at room
temperature and pH 6.5 - 7.0 according to the general procedure A
disclosed except without purging the pulp slurries with NZ. Table 17 lists
5 the PC numbers as well as the ISO brightness values of the original
BCTMP and the bleached GWP (BGWP) pulps, and the BCTMP and
BGWP pulps treated with 4-amino-TEMPOH-2HCl versus some of the
ambient office light (light intensity = 84 b' S foot-candle) exposure times.
Treatment of both the BCTMP and BGWP pulps with 4-amino-TEMPOH-
10 2HC1 provides the pulps with much improved brightness stability.
TABLE 17
PC
Number
[ISO
Brightness]
of
the
Mill
Aspen
BCTMP
Pulps
and
Mixed
Softwood
BGWP Pulps
versus Ambient
Light Exposure
Time (days)
Time BCTMP treated BGWP BGWP treated
(d)
BCTMP
with with
4-amino- 4-amino-
TEMPOH-2HCl TEMPOH-2HCl
0 0.0 [82.4%] 0.0 [82.5%] 0.0 [80.6%] 0.0 [80.9%]
7 0.6 [80.0%] 0.3 [81.1%] 1.1 [77.1%] 0.3 [79.8%]
14 1.1 [78.3%] 0.6 [80.1%] 2.1 [74.5%] 0.6 [78.8%]
21 1.6 [76.8%] 0.9 [79.2%] 3.1 [72.0%] 0.9 [77.8%]
28 2.1 [75.5%] 1.1 [78.6%] 4.1 [70.0%] 1.2 [77.0%]
49 3.7 [71.8%] 1.7 [76.7%] 7.2 [64.9%] 2.0 [74.8%]
84 6.6 [66.4%] 2.8 [73.7%] 12.6 [58.3%]3.6 [71.1%]
91 7.3 [65.3%] 3.2 [72.9%] 13.6 [57.2%]3.9 [70.6%]
EXAMPLE 18
1s An aspen BCTMP pulp (ISO brightness 80.8%) was treated with
1.0% (OD pulp) of 4-amino-TEMPOH-2HC1 at room temperature and pH
6.5 - 7.0 according to the general procedure A disclosed except without
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purging the pulp slurry with N2. Various amounts of the original BCTMP
and the 4-amino-TEMPOH-2HC1 treated BCTMP pulps were blended,
respectively, with a fully bleached aspen kraft pulp (ISO brightness =
86.5%) to given fully bleached aspen kraft pulps containing various amounts
s of the BCTMP or the 4-amino-TEMPOH-2HCl treated BCTMP. Table 18
lists the PC numbers as well as brightness values of four of the blended
pulps versus some of the ambient light (light intensity = 79 b' 7 foot-candle)
exposure times. Fully bleached kraft pulps containing, for example 20% of
the 4-amino-TEMPOH-2HCl treated BCTMP pulps have much higher
1o brightness stability than those containing same amounts of the untreated
BCTMP pulps. A much higher portion (e.g. 40%) of the treated BCTMP
pulps than untreated BCTMP pulps (e.g. 10%) can be combined with .fully
bleached kraft pulps to give blended pulps with similar brightness stability.
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TABLE 18
PC Number [ISO Brightness] of Fully Bleached Aspen Kraft Pulps Containing
Various Amounts of Aspen BCTMP Pulps versus Ambient Light Exposure Time
(days)
Time (d) 10% BCTMP 20% BCTMP 20% treated 40% treated
BCTMP BCTMP
0 0.0 [86.1%] 0.0 [85.7%] 0.0 [85.6%] 0.0 [84.8%]
0.3 [84.7%] 0.3 [84.0%] 0.2 [84.4%] 0.3 [83.5%]
9 0.4 [84.1%] 0.5 [83.2%] 0.3 [84.0%] 0.4 [83.0%]
20 0.7 [82.7%] 1.0 [81.2%] 0.6 [82.8%] 0.7 [81.7%]
30 0.9 [81.7%] 1.4 [79.8%] 0.8 [82.0%] 0.9 [80.8%]
40 1.1 [80.9%] 1.7 [78.6%] 0.9 [81.4%] 1.1 [80.I%]
49 1.4 [80.0%] 2.1 [77.5%] 1.1 [80.7%] 1.3 [79.4%]
58 1.5 [79.5%] 2.4 [76.6%] 1.3 [80.1%] 1.5 [78.9%]
68 1.8 [78.7%] 2.7 [75.6%] 1.5 [79.4%] 1.7 [78.2%]
79 2.0 [77.9%] 3.2 [74.5%] 1.7 [78.7%] 1.9 [77.5%]
~
91 2.3 [77.1%] 3.6 [73.5%] 1.9 [78.0%] 2.1 [76.8%]
\
EXAMPLE 19
A chelated spruce TMP was bleached with 5% H202, 4% NaOH, 3%
s NaaSi03, 0.05% Mg (as MgS04) and, 0.0% (control) and 1.0% (OD pulp)
of 4-amino-2,2,6,6-tetramethylpiperidine, respectively, at 60 °C and
20%
consistency for 3 hours according to the general procedure C disclosed.
Table 19 lists the ISO brightness values as well as the PC numbers of the
two BTMP pulps versus the ambient light exposure times, respectively.
' Data of the ISO brightness values and the PC numbers versus the ambient
light (light intensity = 85 b' 3 foot-candle) exposure times of the pulps are
given in Figures 3 and 4, respectively. Bleaching of the pulp in the
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presence of 4-amino-2,2,6,6-tetramethylpiperidine gives a bleached pulp
with much improved brightness stability.
TABLE 19
PC Number
[ISO
Brightness]
of the
BTMP
Pulps
versus
Ambient
Light
Exposure
Time (days)
Time BTMP (control)BTMP bleached in the presence of
(d) 4-amino-
2,2,6,6-tetramethylpiperidine
0 0.0 [75.9%] 0.0 [75.4%]
2 0.5 [74.7%] 0.0 [75.5%]
l . l [73.2%] 0.1 [75.1 %]
9 1.8 [71.6%] 0.4 [74.5%]
12 2.4 [70.5%] 0.6 [74.0%]
14 2.8 [69.7%] 0.7 [73.7%]
16 3.1 [69.0%] 0.8 [73.3%]
21 4.1 [67.3%] 1.1 [72.7%]
23 4.6 [66.5%] 1.3 [72.3%]
26 5.2 [65.7%] 1.6 [71.7%]
28 5.2 [65.6%] 1.9 [71.0%]
30 5.9 [64.6%] 2.1 [70.6%]
33 6.5 [63.8%] 2.4 [70.1%]
35 6.8 [63.3%] 2.5 [69.8%]
37 7.3 [62.7%] 2.7 [69.5%]
40 7.9 [61.8%] 3.0 [68.9%]
42 8.3 [61.5%] 3.1 [68.7%]
44 8.6 [61.1%] 3.3 [68.4%]
47 9.4 [60.2%] 3.6 [67.8%]
49 9.7 [59.8%] 3.7 [67.7%]
51 10.1 [59.3%] 4.0 [67.2%]
54 10.6 [58.8%] 4.2 [66.9%]
56 1I.0 [58.4%] 4.3 [66.6%]
58 11.4 [57.9%] 4.5 [66.3%]
62 12.5 [56.9%] 5.1 [65.5%]
69 13.8 [55.7%] 5.7 [64.6%]
72 14.3 [55.2%] 5.9 [64.4%]
75 14.9 [54.7%] 6.2 [63.9%]
79 15.6 [54.1%] 6.5 [63.5%]
82 16.2 [53.7%] 6.7 [63.1%]
84 16.7 [53.2%] 7.0 [62.8%]
86 16.9 [53.1%] 7.1 [62.6%]
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EXAMPLE 20
A chelated spruce TMP was bleached with 5% H202, 4% NaOH, 3%
Na2Si03, 0.05% Mg (as MgS04) and, 0.0% (control), 0.2% and 1.0% (OD
pulp) of 4-amino-2,2,6,6-tetramethylpiperidine (abbreviated as amino-
s HALS hereafter), respectively, at 60 °C and 20% consistency for 3
hours
according to the general procedure C disclosed. A portion of a handsheet
made from the control BTMP was coated with 1.0% (OD pulp) of amino-
HALS dissolved in deionized water. Table 20 shows the PC numbers of the
control BTMP, the control BTMP coated with amino-HALS, the BTMP
to bleached in the presence of 0.2% and 1.0% (OD pulp) of amino-HALS,
respectively, versus the ambient light (light intensity = 85 ~l 3 foot-candle)
exposure times. Coating of the BTMP with amino-HALS produces a
detrimental effect on the brightness stability of the BTMP sheet, consistent
with the results reported in the prior art. However, bleaching of the pulps in
15 the presence of amino-HALS (0.2 or 1.0% on pulp) provides the bleached
pulps with much improved brightness stability.
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TABLE 20
PC Numbers
of the
Bleached
TMP
Pulps
versus
Ambient
Light
Exposure
Times
(days)
Time BTMP BTMP coatedBTMP bleached BTMP bleached
(d) in
with 1.0% the presence of in the presence
0.2%
amino-H_AT,Samino-_H_AT.S of 1.0% amino-
HALS
0 0.0 0.0 0.0 0.0
3 0.7 1.0 0.5 0.1
5 1.1 1.6 0.8 0.3
7 1.5 2.1 1.1 0.4
1 0 2.1 2.8 1.6 0.7
12 2.5 3.2 1.9 0.9
1 4 2.9 3.7 2.2 1.0
1 9 4.0 4.8 3.1 1.6
2 1 4.4 5.2 3.4 1.8
24 5.1 5.9 3.9 2.1
26 5.5 6.3 4.2 2.3
28 5.9 6.6 4.6 2.5
3 1 6.5 7.2 5.0 2.8
3 3 6.9 7.5 5.3 3.0
35 7.2 ~ 7.7 5.6 3.1
3 8 7.9 8.2 6.1 3.4
40 8.2 8.4 6.4 3.6
EXAMPLE 2
A chelated spruce TMP was bleached with 5% HZO~, 4% NaOH, 3%
s Na2Si03, 0.05% Mg (as MgS04) and 0.0% amino-HALS (control BTMP) at
60 °C and 20% consistency for 3 hours according to the general
procedure
C disclosed. The same chelated spruce TMP was bleached with 5% H202,
4% NaOH, 3% Na2Si03, 0.05% Mg (as MgS04) in the presence of 1.0%
(OD pulp) of amino-HALS at 20% consistency and 60 °C, 70 °C and
80 °C,
1o respectively, for 3 hours according to the general procedure C disclosed.
Table 21 shows the PC numbers of the control BTMP, the BTMP pulps
bleached in the presence of 1.0% (OD pulp) of amino-HALS at various
temperatures versus the ambient light (light intensity = 85 t~ 3 foot-candle)
exposure times, respectively. Bleaching of the spruce TMP pulps in the
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presence of amino-HALS at various temperatures provides the bleached
pulps much improved brightness stability.
TABLE 21
PC
Numbers
of
the
BTMP
Pulps
versus
Ambient
Light
Exposure
Times
(days)
Time BTMP BTMP bleached BTMP bleached BTMP bleached
in the
(d) in the presencepresence of amino-in the presence
of
amino-HALS HALS at 70 C of amino-HALS
at
60 C at 80 C
0 0.0 0.0 0.0 0.0
3 0.7 ~ 0.1 0.1 0.1
1.1 0.3 0.2 0.2
7 1.5 0.4 0.4 0.4
1 2.1 0.7 0.6 0.5
0
12 2.5 0.9 0.8 0.7
14 2.9 1.0 0.9 0.8
19 4.0 1.6 1.4 1.2
21 4.4 1.8 1.5 1.4
24 5.1 2.1 1.7 1.6
26 5.5 2.3 1.9 1.7
28 5.9 2.5 2.0 1.8
3 6.5 2.8 2.3 2.1
1
33 6.9 3.0 2.4 2.2
3 7.2 3.1 2.6 2.4
5
38 7.9 3.4 - 2.8 2.7
40 8.2 3.6 3.0 2.8
s
EXAMPLE 22
A chelated spruce TMP was bleached with 5% H202, 4% NaOH, 3%
NaZSi03, 0.05% Mg (as MgS04) and 0.0% amino-HALS (control BTMP) at
60 °C and 20% consistency for 3 hours according to the general
procedure
to C disclosed. The same chelated spruce TMP pulps were also bleached with
5% H202, 4% NaOH, 3% Na2Si03, 0.05% Mg (as MgS04), and with 5%
H202, 5% NaOH, 3% Na2Si03, 0.05% Mg (as MgS04), respectively, in the
presence of 1.0% amino-HALS at 60 °C and 20% consistency for 3 hours
according to the general procedure C disclosed. Table 22 shows the PC
is numbers of the control BTMP, the BTMP bleached in the presence of 1.0%
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amino-HALS at two different NaOH charges versus the ambient light (light
intensity = 85 d 3 foot-candle) exposure times, respectively. Bleaching of
the spruce TMP pulps in the presence of amino-HALS at two different
NaOH charges provides the bleached pulps with much improved brightness
s stability.
TABLE 22
PC Numbers of the Bleached TMP Pulps versus Ambient Light Exposure Times
(days)
Time BTMP BTMP bleached in the BTMP bleached in
presence the
(d) of amino-PLATS (4% NaOH)presence of amino-_H_AT.S
(5% NaOH)
0 0.0 0.0 0.0
3 0.7 0.1 0.3
1.1 0.3 0.4
~
7 1.5 0.4 0.7
2.1 0.7 1.0
12 2.5 0.9 1.3
14 2.9 1.0 1.5
19 4.0 1.6 2.1
'
21 4.4 1.8 2.4
24 5.1 2.1 2.8
26 5.5 2.3 3.0
28 5.9 2.5 3.3
31 6.5 2.8 3.7
33 6.9 3.0 3.9
35 7.2 3.1 4.1
38 7.9 3.4 4.5
40 8.2 3.6 4.7
EXAMPLE 23
1o A chelated spruce TMP was bleached with alkaline hydrogen
peroxide in two stages to give a control BTMP pulp (abbreviated as P1P2).
The first-stage (P1) bleaching was carried out using 2% H202, 1.5% NaOH,
3% NaaSi03, 0.05% Mg (as MgS04) at 60 °C and 10% consistency for 3
hours according to the general procedure C disclosed. The second-stage
1sr (P2) bleaching was carned out using 4% H202, 3% NaOH, 3% Na2Si03,
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0.05% Mg (as MgS04) at 60 °C and 20% consistency for 3 hours according
to the general procedure C disclosed. The same chelated spruce TMP were
also bleached in two stages with the same amount of bleaching chemicals,
temperature, time and consistency except that either the P 1 or P2-stage was
s carried out in the presence of .1.0% (OD pulp) of amino-HALS. Table 23
shows the PC numbers of the control P 1 P2, the P 1 P2 bleached pulps with
P1 or P2 bleached in the presence of 1.0% (OD pulp) of amino-HALS
versus the ambient light (light intensity = 85 b' 3 foot-candle) exposure
times. Addition of amino-HALS to either P1 or P2-stage of a two-stage
1o P1P2 bleaching of the spruce TMP pulps provides the bleached pulps with
much improved brightness stability.
TABLE 23
Numbers of the
Bleached TMP
Pulps versus
Light Exposure
Times (days)
PC
_ P1P2 P1P2 with P1 bleached P1P2 with P2 bleached
Time in the in
(d) (control)presence of amino-HALSthe presence of amino-
HALS
0 0.0 0.0 0.0
3 0.8 0.2 0.4
1.2 0.3 0.5
7 1.7. 0.s 0.7
2.3 0.8 1.0
12 2.7 1.1 1.3
14 3.1 1.3 1.5
19 4.1 1.8 2.1
21 4.6 2.1 2.3
24 5.2 2.4 2.7
26 5.5 2.6 2.9
28 5.9 2.8 3.1
31 6.6 3.2 3.5
33 7.0 3.4 3.8
35 7.4 3.6 4.0
~
38 8.0 3.9 4.5
40 8.4 4.1 4.7
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EXAMPLE 24
A chelated spruce TMP was bleached with alkaline hydrogen
peroxide in two stages to give a control P 1 P2 pulp. The P 1 bleaching was
carried out using 2% H202, 1.5% NaOH, 3% Na2Si03, 0.05% Mg (as
s MgS04) at 60 °C and 10% consistency for 3 hours according to the
general
procedure C1 disclosed. The P2 bleaching was carried out using 4% H20a,
3% NaOH, 3% Na2Si03, 0.05% Mg (as MgS04) at 60 °C and 20%
consistency for 3 hours according to the general procedure C disclosed.
The same chelated spruce TMP was also bleached in two stages in the same
to manner except that after the P1 stage, the pulp was treated with 1.0% (OD
pulp) of amino-HALS at room temperature and pH 6.5 - 7.0 for 3 hours
according to the general procedure A disclosed. Table 24 shows the PC
numbers of the control P 1 P2 pulp, and the P 1 P2 pulp that involved a
treatment of the pulp with 1.0% (OD pulp) of amino-HALS after P1 and
~s before P2 bleaching, versus the ambient light (light intensity = ~5 b' 3
foot-
candle) exposure times. Treatment of the P1 pulp with amino-HALS before
the P2 stage provides the P1P2 pulp with much improved brightness
stability.
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TABLE 24
PC Numbers s versus Light Exposure Times
of the (days)
Bleached
TMP Pulp
Time (d) P1P2 P1/amino-HALS
treatment/P2
0 0.0 0.0
2 0.6 0.2
5 1.3 0.5
7 1.'7 0.7
9 2.1 0.9
14 3.2 1.5
16 3.6 1.7
19 4.4 2.2
21 4.7 2.4
23 5.1 2.6
26 5.8 3.0
28 6.2 3.3
30 6.7 3.6
33 7.2 4.0
35 7.7 4.2
37 8.1 4.5
40 8.7 4.9
EXAMPLE 25
A chelated spruce TMP was bleached with 5% H20a, 4% NaOH, 3%
5 Na2Si03, 0.05% Mg (as MgS04) at 60 °C and 20% consistency for 3 hours
according to the general procedure C disclosed to give a control BTMP.
The same chelated spruce TMP pulps were also bleached with 5% H202,
4% NaOH, 3% Na2Si03, 0.05% Mg (as MgS04) and, in the presence of
1.0% 4-amino-2,2,6,6-tetramethylpiperidine (abbreviated as amino-HALS),
and 1.0% of % 4-oxo-2,2,6,6-tetramethylpiperidine (abbreviated as oxo-
HALS), respectively, at 60 °C and 20% consistency for 3 hours
according
to the general procedure C disclosed. Table 25 shows the PC numbers of
the control BTMP, the BTMP pulps bleached in the presence of 1.0% (OD
pulp) of amino-HALS and 1.0% (OD pulp) of oxo-HALS, respectively,
15 versus the ambient light (light intensity = 85 b' 3 foot-candle) exposure
times. Bleaching of the spruce TMP pulp in the presence of amino-HALS
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but not oxo-HALS provides the bleached pulp with much improved
brightness stability.
TABLE 25
PC Numbers
of the
BTMP
Pulps
versus
Ambient
Light
Exposure
Times
(days)
Time BTMP BTMP bleached in the BTMP bleached in the
(d) presence of amino-KATpresence of oxo-HALS
S
0 0.0 0.0 0.0
2 0.5 0.0 0.4
4 0.8 0.1 0.7
7 1.4 0.3 1.2
11 2.1 0.6 1.9
14 2.6 0.8 2.4
16 3.1 1.0 2.8
18 3.5 1.1 3.2
21 4.0 1.4 3.8
23 4.4 1.5 4.2
25 4.9 1.8 4.6
28 5.4 2.0 5.3
30 5.8 2.1 5.6
35 6.8 2.6 6.7
37 7.2 2.8 7.1
39 7.5 2.9 7.5
42 8.1 3.2 8.1
EXAMPLE 26
A chelated spruce TMP was bleached with 5% H2O2, 4% NaOH, 3%
NaZSi03, 0.05% Mg (as MgS04) and, 0.0% (control) and 1.0% (OD pulp)
of amino-HALS, respectively, at 60 °C and 20% consistency for 3 hours
according to the general procedure C disclosed. A portion of a handsheet
made from the control BTMP and a portion of a handsheet made from the
BTMP bleached in the presence of amino-HALS were coated with 1.0% of
2,4-dihydroxybenzophenone (abbreviated as DHBP) (Aldrich) dissolved in
ethanol. Table 26 shows the PC numbers of the control BTMP, the control
is BTMP coated with DHBP, the BTMP bleached in the presence of amino-
HALS, and the BTMP bleached in the presence of amino-HALS and then
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coated with DHBP versus the ambient light (light intensity = 85 b' 3 foot
candle) exposure times, respectively. A nearly complete brightness
stabilization of the BTMP pulp can be achieved by bleaching of the pulp in
the presence of amino-HALS and then by coating the sheet made from such
s a bleached pulp with an ultraviolet absorber such as DHBP.
TABLE 26
PC Number
of
the
Bleached
TMP
Pulps
versus
Ambient
Light
Exposure
Time
(days)
Time BTMP BTMP coatedBTMP bleached BTMP bleached
(d)
with DHBP with amino-HALS with amino-HALS
and coated with
DHBP
0 0.0 0.0 0.0 0.0
2 0.5 0.1 0.0 -0.1
4 0.9 0.3 0.2 -0.1
7 1.4 0.6 0.4 0.0
9 1.8 0.7 0.5 0.0
1 1 2.2 0.9 0.7 0.1
1 4 2.8 1.2 0.9 0.2
1 8 3.6 1.7 1.3 0.4
2 1 4.1 2.0 1.5 0.5
23 4.5 2.2 1.8 0.6
25 4.9 2.3 1.9 0.6
2 8 5.5 2.7 2.2 0.7
3 0 5.8 ' 2.8 2.3 0.8
,
3 2 6.2 3.0 2.5 0.8
3 5 6.8 3.4 2.8 0.9
3 7 7.1 3.5 3.0 I.0
42 8.1 4.0 3.5 1.2
EXAMPLE 27
1o Spruce BTMP pulps (ISO brightness 75.7%) were reacted with 1.0%
(OD pulp) of 4-amino-TEMPO at room temperature and pH 6.5 - 7.0
according to the general procedure A disclosed, except without purging the
pulp slurry with N2 and that tap water (conductivity 25.2 :S/cm) and a mill
process water such as a mill peroxide bleaching filtrate containing
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S3
dissolving lignin (conductivity 3.47 x 103 :S/cm) were, respectively, used
for the treatment and that tap water was used for the washing of the pulps.
A same BTMP pulp was also reacted with 1.0% (OD pulp) of 4-amino-
TEMPO in deionized water (conductivity 0.68 :S/cm) at room temperature
S and pH 6.S - 7.0 according to the general procedure A disclosed, except
without purging the pulp slurry with N2. Table 27 lists the PC numbers of
the original BTMP, the BTMP pulps reacted with 4-amino-TEMPO in the
deionized (DI), tap and mill waters, respectively, versus ambient office Iight
(light intensity = 8S b 3 foot-candle) exposure times. Reaction of the pulps
1o with 4-amino-TEMPO in tap or mill process water also provides the pulps
with much improved brightness stability.
TABLE 27
PC number
of
the
Bleached
TMP
Pulps
versus
Ambient
Office
Light
Exposure
Time (days)
Time BTMP BTMP reacted BTMP reacted BTMP reacted
(d) with
with inhibitorwith inhibitorinhibitor in
in in mill
DT water tap water water
0 ~ 0.0 0.0 0.0 0.0
2 0.7 -0.1 0.0 0.2
4 1.1 0.0 0.1 0.4
7 1.7 0.1 0.3 0.7
9 2.1 0.1 0.4 0.8
1 1 2.S 0.2 O.S 1.0
1 4 3.2 0.4 0.7 1.3
1 6 3.6 0.4 0.8 1.S
1 8 4.I 0.5 0.9 1.6
2 1 4.7 0.6 1.0 1.9
23 S.2 0.7 1.2 2.1
2S S.7 0.8 1.3 2.3
28 6.3 0.9 I.6 2.5
3 0 6.7 1.0 1.S 2.7
32 7.2 1.0 1.6 2.9
3 S 7.8 1.1 1.8 3.1
3 7 8.4 1.2 1.9 3.3
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It is understood that the invention is not to be limited to the
brightness stabilization of the Various mechanical wood pulps described, as
the invention can be applied to other lignin-containing mechanical wood
pulps of the same or different wood species or to other lignocellulosic
s materials such as wood products by those skilled in the art.
