U.S. patent application number 10/583340 was filed with the patent office on 2007-07-19 for method for reducing brightness reversion of mechanical pulps and high-yield chemical pulps.
This patent application is currently assigned to KEMIRA OYJ. Invention is credited to Johanna Buchert, Stina Gronqvist, Arto Paren, Mikael Svedman, Liisa Viikari, Veli-Matti Vuorenpalo.
Application Number | 20070163735 10/583340 |
Document ID | / |
Family ID | 29763592 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163735 |
Kind Code |
A1 |
Buchert; Johanna ; et
al. |
July 19, 2007 |
Method for reducing brightness reversion of mechanical pulps and
high-yield chemical pulps
Abstract
The present invention concerns a process for reducing the
susceptibility of lignocellulosic material to unwanted yellowing,
particularly yellowing caused by light and heat. According to the
invention, the fibres are activated enzymatically or chemically and
then contacted with a modifying agent capable of bonding to the
oxidized fibre material, rendering the lignocellulosic fibre
material improved resistance to brightness reversion. By means of
the invention, brightness reversion caused by light or heat or a
combination thereof can be retarded and even stopped.
Inventors: |
Buchert; Johanna; (Espoo,
FI) ; Viikari; Liisa; (Helsinki, FI) ;
Gronqvist; Stina; (Tolkkinen, FI) ; Svedman;
Mikael; (Vaasa, FI) ; Paren; Arto;
(Kuusankoski, FI) ; Vuorenpalo; Veli-Matti; (Oulu,
FI) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
KEMIRA OYJ
Porkkalankatu 3
Helsinki
FI
FI-00180
|
Family ID: |
29763592 |
Appl. No.: |
10/583340 |
Filed: |
December 23, 2004 |
PCT Filed: |
December 23, 2004 |
PCT NO: |
PCT/FI04/00797 |
371 Date: |
October 2, 2006 |
Current U.S.
Class: |
162/9 ;
162/157.6; 162/72 |
Current CPC
Class: |
D21H 11/20 20130101;
D21C 9/005 20130101; D21H 21/143 20130101; D21C 5/005 20130101 |
Class at
Publication: |
162/009 ;
162/072; 162/157.6 |
International
Class: |
D21C 9/00 20060101
D21C009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2003 |
FI |
20031904 |
Claims
1. A process for producing a fibre material having reduced
susceptibility to yellowing, comprising activating the fibres of
the matrix with an oxidizing agent capable of oxidizing phenolic or
similar structural groups, which may undergo reactions conducive to
the formation of coloured sites on the fibres, and attaching to the
oxidized sites at least one modifying agent to block the reactivity
of the oxidized sites.
2. The process according to claim 1, wherein activation is carried
out enzymatically or chemically.
3. The process according to claim 1, comprising the steps of
reacting the lignocellulosic fibrous matrix with an oxidizing agent
in the presence of a catalyst capable of catalyzing the oxidation
of phenolic or similar structural groups by said oxidizing agent to
provide an oxidized fibre material, and contacting the oxidized
fibre material with a modifying agent containing at least one first
functional portion, which is compatible with the oxidized fibre
material, said modifying agent being capable of providing the
lignocellulosic fibre material with properties reducing
susceptibility to yellowing.
4. The process according to claim 3, wherein the modifying agent is
activated with an oxidizing agent.
5. The process according to claim 1, wherein the modifying agent is
a brightness reversion inhibitor.
6. The process according to claim 1, wherein the modifying agent is
selected from the group comprising C.sub.1-4 alkanols, unsaturated
carboxylic acids, monocarboxylic unsaturated fatty acids, and
monocarboxylic unsaturated fatty acids containing a minimum of two
double bonds, preferably two conjugated double bonds.
7. The process according to claim 6, wherein the modifying agent is
linoleic acid or linolenic acid.
8. The process according to claim 1, wherein the modifying agent is
selected from the group of antioxidants.
9. The process according to claim 1, wherein the catalyst capable
of catalyzing the oxidation of phenolic or similar structural
groups is an enzyme or an chemical agent.
10. The process according to claim 9, wherein the enzyme capable of
catalyzing the oxidation of phenolic or similar structural groups
is selected from the group of peroxidases and oxidases.
11. The process according to claim 10, wherein the enzyme is
selected the group of laccases (EC 1.10.3.2), catechol oxidases (EC
1.10.3.1), tyrosinases (EC 1.14.18.1), bilirubin oxidases (EC
1.3.3.5), horseradish peroxidase (EC 1.11.1.7), manganese
peroxidase (EC 1.11.1.13) and lignin peroxidase (EC 1.11.1.14).
12. The process according to claim 1, wherein the enzyme dosage is
about 1 to 100,000 nkat/g, preferably 10-500 nkat/g, and it is
employed in an amount of 0.0001 to 10 mg protein/g of dry
matter.
13. The process according to claim 9, wherein the chemical agent is
selected from the group of per-compounds, in particular from the
group consisting of alkali metal persulphates and hydrogen
peroxide.
14. The process according to claim 1, wherein the oxidizing agent
is selected from the group of oxygen, hydrogen peroxide and
oxygen-containing gases, such as air.
15. The process according to claim 1, wherein oxygen or
oxygen-containing gas is introduced into the aqueous slurry during
the reaction.
16. The process according to claim 1, wherein the reaction of step
(a) is carried out in an aqueous or dry phase at a consistency of 1
to 95% by weight, preferably about 2 to 40% by weight, of the fibre
material.
17. The process according to claim 1, wherein the reaction is
carried out at temperature in the range of from 5 to 100.degree.
C.
18. Method of reducing light or heat induced brightness reversion
of mechanical or high-yield chemical pulp, comprising the steps of
enzymatically or chemically oxidizing phenolic groups of the pulp
and bonding to the oxidized phenolic groups a substance capable of
forming a colourless lignin derivative unable to participate in
yellowing reactions.
19. The process according to claim 1, wherein the reaction steps
are carried out sequentially or simultaneously.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to fibrous products. In
particular, the present invention concerns a process for reducing
the susceptibility of lignocellulosic material to unwanted
brightness reversion, in particular to brightness reversion caused
by light or heat.
[0003] 2. Description of Related Art
[0004] It is well-known in the art that light (UV light in
particular), heat, moisture and chemicals can give rise to changes
in the brightness of cellulose pulps. Usually, such changes result
in reduced reflectivity, particularly in blue light. This
phenomenon is known as brightness reversion or yellowing and can be
caused by various factors depending on which type of pulp is
concerned. Heat and damp are the main causes of the brightness
reversion of chemical (lignin-free) pulps, whereas mechanical pulps
mostly yellow when they are exposed to light. The brightness
reversion of mechanical pulps also varies depending on the raw
material (type of wood), production method (with or without
chemical pretreatment), and after-treatment (bleaching with
different reagents) used. Thus, for instance, sulphonation and
peroxide bleaching greatly increase the susceptibility of pulp to
light-induced yellowing.
[0005] The brightness reversion of lignocellulosic pulps and
products made from such pulps can be reduced or even prevented in
various ways, for instance by means of impregnation or surface
treatment using UV screens, antioxidants, or polymers, or by
coating the surface with a coating layer or a layer of
non-yellowing chemical pulp. Various additives are described in the
patent literature. Thus, U.S. Pat. No. 4,978,363 discloses a
composition and method for treating fibers based on a mixture of an
organopolysiloxane having at least one amino-substituted
hydrocarbon radical directly bonded to a silicon atom and a higher
fatty carboxylic acid. The carboxylic acid reacts with the amino
radicals to reduce yellowing and oxidation of the fiber treatment.
The composition and method provide non-yellowing fibers and a
treatment agent that does not gel during use, such as when exposed
to carbon dioxide and/or used to treat carbon fibers.
[0006] U.S. Pat. No. 6,599,326 discloses inhibition of pulp and
paper yellowing using hydroxylamines and other coadditives.
Chemical pulps or papers, especially kraft pulps or papers, which
may still contain traces of lignin, have enhanced resistance to
yellowing when they contain an effective stabilizing amount of a
N,N-dialkylhydroxylamine, an ester, amide or thio substituted
N,N-dialkylhydroxylamine or N,N-dibenzylhydroxylamine or an
ammonium salt thereof. This performance is often further enhanced
by the presence of one or more coadditives selected from the group
consisting of UV absorbers, polymeric inhibitors, nitrones,
fluorescent whitening agents and metal chelating agents.
Combinations of hydroxylamines or their salts, benzotriazole or
benzophenone UV absorbers and a metal chelating agent are,
according to the cited patent, considered particularly effective.
As specific examples, the patent mentions N,N-diethylhydroxylamine
and N,N-dibenzyl-hydroxylamine.
[0007] Many of the additives that have been found to prevent
yellowing are expensive or problematic from an environmental point
of view; others are only effective when introduced in so large
amounts that they may have a negative effect on other properties of
the product or be uneconomical. Accordingly, there is still a need
for methods of preventing yellowing
SUMMARY OF THE INVENTION
[0008] It is an aim of the present invention to eliminate the
problems of the prior art and to provide a new method of reducing
or preventing yellowing. The method aims at effectively reducing
both light- and heat-induced brightness reversion of mechanical
pulps and high-yield chemical pulps.
[0009] The invention is based on the finding that the reactions
that take place during oxidation, in particular enzymatic
oxidation, of lignin appear to be similar to the reactions that
cause brightness reversion. Therefore, the initial reaction causing
brightness reversion can be activated by enzymatic or chemical
means and simultaneously immediately blocked by targeted
functionalization, by retarding or stopping the reactions.
[0010] Thus, the present invention provides a method of modifying
fibres by bonding of new compounds to the oxidized fibres via
radical pathways. In particular, the aim of the bonding of the
compounds is to stabilize the structure by forming a colourless
lignin derivative unable to participate in yellowing reactions.
[0011] According to the invention, new fibrous products with
modified properties are produced by activating the fibres of the
matrix with an oxidizing agent capable of oxidizing phenolic or
similar structural groups, which may undergo reactions conducive to
the formation of coloured sites on the fibres, and attaching to the
oxidized sites at least one modifying agent to block the reactivity
of the oxidized sites. The activation is preferably carried out
enzymatically although it is equally possible to use chemical
agents for achieving oxidation/radicalization.
[0012] The modifying agent has at least one functional site or
reactive structure, which provides for binding of the modifying
compound to the lignocellulosic fibre material, in particular at
the oxidized phenolic groups or corresponding chemical structures
of the fibres, which have been oxidized during the activation
step.
[0013] Based on the above, the present invention provides a process
for producing a fibre material having increased resistance to
brightness reversion, comprising a lignocellulosic fibrous matrix
with phenolic or similar structural groups and a modifying agent
reducing the susceptibility of yellowing, including the steps of
[0014] reacting the lignocellulosic fibrous matrix with an
oxidizing agent in the presence of a catalyst capable of catalyzing
the oxidation of phenolic or similar structural groups by said
oxidizing agent to provide an oxidized fibre material, and [0015]
contacting the oxidized fibre material with a modifying agent
containing at least one first functional site, which is capable of
bonding to oxidized fibre material, said modifying agent being
capable of imparting to the lignocellulosic fibre material improved
resistance to brightness reversion caused by light or heat or
combinations thereof.
[0016] It should be noted that the term "catalyst" is to be given a
broad interpretation in the present context, and it covers any
agent capable of possibly--but not exclusively--in combination with
a separate oxidation agent, of achieving oxidation of the phenolic
or similar groups.
[0017] Another embodiment of the invention provides a method of
reducing light or heat induced brightness reversion of mechanical
or high-yield chemical pulp, comprising the steps of enzymatically
or chemically oxidizing phenolic groups of the pulp and bonding to
the oxidized phenolic groups a substance capable of forming a
colourless lignin derivative unable to participate in yellowing
reactions.
[0018] More specifically, the present invention is mainly
characterized by what is stated in the characterizing parts of
claims 1 and 18.
[0019] The present invention provides important advantages.
Importantly, the invention makes it possible to produce novel kinds
of fibrous materials having improved brightness reversion. By means
of the process, the modifying agents can be reliable attached to
the fibres, and the improved resistance to yellowing will not be
significantly impaired by, e.g., extensive washing of the fibres
prior to forming the material into a paper or cardboard web.
[0020] Further details and advantages of the invention will become
apparent from the following detailed description and the appended
working examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 depict in graphical form yellowing of spruce TMP
samples as function of irradiation energy.
DETAILED DESCRIPTION OF THE INVENTION
[0022] As mentioned above, the invention generally relates to a
method of producing fibre compositions with reduced susceptibility
to yellowing.
[0023] The fibre matrix comprises fibres containing phenolic or
similar structural groups, which are capable of being oxidized by
suitable oxidizing agents. Such fibres are typically
"lignocellulosic" fibre materials, which include fibre made of
annual or perennial plants or wooden raw material by, for example,
mechanical, chemimechanical or chemical pulping. During industrial
refining of wood by, e.g., refiner mechanical pulping (RMP),
pressurized refiner mechanical pulping (PRMP), thermomechanical
pulping (TMP), groundwood (GW) or pressurized groundwood (PGW) or
chemithermomechanical pulping (CTMP), a woody raw material, derived
from different wood species as for example hardwood and softwood
species, is refined into fine fibres in processes, which separate
the individual fibres from each other. The fibres are typically
split between the lamellas along the interlamellar lignin layer,
leaving a fibre surface, which is at least partly covered with
lignin or lignin-compounds having a phenolic basic structure
[0024] Within the scope of the present invention, also chemical
pulps are included if they are susceptible to brightness reversion
and have a residual content of lignin sufficient to give at least a
minimum amount of phenolic groups necessary for providing binding
sites for the modifying agent. Generally, the concentration of
lignin in the fibre matrix should be at least 0.1 wt-%, preferably
at least about 1.0 wt-%.
[0025] In addition to paper- and paperboard-making pulps of the
above kind, also other kinds of fibres of plant origin can be
treated, such as bagasse, jute, flax and hemp.
[0026] An essential feature of the invention is to block brightness
reversion by modifications of phenolic hydroxyls, alfa-carbonyls
and/or alfa-hydroxyls on the fibres. In particular, by subjecting
lignin structures to enzymatic oxidation to yield oxidized groups
of the aforesaid kind, the normal reactions causing brightness
reversion can be attained. These reactions are then stopped by
bonding a desired compound to the activated, oxidized groups.
[0027] In the first stage of the present process, the
lignocellulosic fibre material is reacted with a substance capable
of catalyzing the oxidation of phenolic or similar structural
groups to provide an oxidized fibre material. Typically, the
substance is an enzyme and the enzymatic reaction is carried out by
contacting the lignocellulosic fibre material with an oxidizing
agent, which is capable--in the presence of the enzyme--of
oxidizing the phenolic or similar structural groups to provide an
oxidized fibre material. Such oxidizing agents are selected from
the group of oxygen and oxygen-containing gases, such as air, and
hydrogen peroxide. Oxygen can be supplied by various means, such as
efficient mixing, foaming, gases enriched with oxygen or oxygen
supplied by enzymatic or chemical means, such as peroxides to the
solution. Peroxides can be added or produced in situ.
[0028] According to an embodiment of the invention, the oxidative
enzymes capable of catalyzing oxidation of phenolic groups, are
selected from, e.g. the group of phenoloxidases (E.C.1.10.3.2
benzenediol:oxygen oxidoreductase) and catalyzing the oxidation of
o- and p-substituted phenolic hydroxyl and amino/amine groups in
monomeric and polymeric aromatic compounds. The oxidative reaction
leads to the formation of phenoxy radicals. Another groups of
enzymes comprise the peroxidases and other oxidases. "Peroxidases"
are enzymes, which catalyze oxidative reaction using hydrogen
peroxide as their electron acceptor, whereas "oxidases" are
enzymes, which catalyze oxidative reactions using molecular oxygen
as their electron acceptor.
[0029] In the method of the present invention, the enzyme used may
be for example laccase, tyrosinase, peroxidase or oxidase, in
particular, the enzyme is selected from the group of laccases (EC
1.10.3.2), catechol oxidases (EC 1.10.3.1), tyrosinases (EC
1.14.18.1), bilirubin oxidases (EC 1.3.3.5), horseradish peroxidase
(EC 1.11.1.7), manganese peroxidase (EC 1.11.1.13) and lignin
peroxidase (EC 1.11.1.14).
[0030] The amount of the enzyme is selected depending on the
activity of the individual enzyme and the desired effect on the
fibre. Advantageously, the enzyme is employed in an amount of
0.0001 to 10 mg protein/g of dry matter fiber.
[0031] Different dosages can be used, but advantageously a dosage
of about 1 to 100,000 nkat/g, more advantageously 10-500
nkat/g.
[0032] In addition to enzymes, also chemical agents, such as alkali
metal persulphates and hydrogen peroxide and other per-compounds,
can be used for achieving oxidization of the phenolic groups and
for forming phenoxy radicals. The dosage of the chemical agent is,
depending on the chemical agent and on the pulp (i.e. on the amount
of phenolic groups contained therein), typically in the range of
about 0.01 to 100 kg/ton, preferably about 0.1 to about 50 kg/ton,
e.g. about 0.5 to 20 kg/ton. In the case of chemical agents, no
separate oxidation agent needs to be added. The per-compound will
achieve the aimed oxidation of the phonolic groups.
[0033] The activation treatment is carried out in a liquid medium,
preferably in an aqueous medium, such as in water or an aqueous
solution, at a temperature in the range of 5 to 100.degree. C.,
typically about 10 to 85.degree. C. Normally, a temperature of
20-80.degree. C. is preferred. The consistency of the pulp is,
generally, 0.5 to 95% by weight, typically about 1 to 50% by
weight, in particular about 2 to 40% by weight. The pH of the
medium is preferably slightly acidic, in particular the pH is about
2 to 10, in the case of phenoloxidases. The chemical agents are
usually employed at slightly acidic conditions, such as at pH 3 to
6. Peroxidases are typically employed at pH of about 3 to 12. The
reaction mixture is stirred during oxidation. Other enzymes can be
used under similar conditions, preferably at pH 2-10.
[0034] In the second step of the process, a modifying agent capable
of reducing the susceptibility to yellowing of lignocellulosic
fibres is bonded to the oxidized phenolic or similar structural
groups of the matrix. Such a modifying agent typically exhibits at
least one first functional site, which is compatible with the
fibrous matrix, and at least one second functional site or
structure providing for the above technical effect, as will be
explained in more detail below.
[0035] The first functional site comprises in particular functional
groups, which are capable of contacting and binding to the fibre at
the oxidized phenolic or similar structural groups or at its
vicinity. The bond formed between the oxidized phenolic or similar
residue can be covalent or ionic or even based on hydrogen bonding.
Typical functionalities of the first functional site include
reactive groups, such as hydroxyl (including phenolic hydroxy
groups), carboxy, anhydride, aldehyde, ketone, amino, amine, amide,
imine, imidine and derivatives and salts thereof, to mention some
examples. Also electronegative bonds, such as carbon-to-carbon
double bonds, carbon-to-hetero atom (e.g. C.dbd.N, C.dbd.O) as well
as oxo or azo-bridges can provide for bonding to the oxidized
residues.
[0036] It is essential that the modifying agent is chemically or
physically bonded to the fibre matrix to such an extent that at
least an essential part of it cannot be removed. One criterion,
which can be applied to test this feature, is washing in aqueous
medium, because often the fibrous matrix will be processed in an
aqueous environment, and it is important that it retains the new
and valuable properties even after such processing. Thus,
preferably, at least 10 mol-%, in particular at least 20 mol-%, and
preferably at least 30 mol-%, of the modifying agent remains
attached to the matrix after washing or leaching in an aqueous
medium.
[0037] According to an embodiment of the invention, the modifying
agent is activated with an oxidizing agent.
[0038] The interaction of the oxidized lignocellulosic material and
the modifying agent, resulting in bonding of the modifying agent to
the lignocellulosic material, typically takes place in liquid
phase, usually in water or in another aqueous medium. The pulp or
other lignocellulosic fibrous matrix is suspended in the medium and
it is contacted with the modifying agent or a precursor thereof,
which is dissolved or dispersed in the same medium. The conditions
can vary freely, although it is preferred to carry out the
contacting under mixing or stirring. The temperature is generally
between the melting point and the boiling point of the medium;
preferably it is about 5 to 100.degree. C. Depending on the
modifying agent or its precursor, the pH of the medium can be
neutral or weakly alkaline or acidic (pH typically about 2 to 12).
It is preferred to avoid strongly alkaline or acidic conditions
because they can cause hydrolyzation of the fibrous matrix. Normal
pressure (ambient pressure) is also preferred, although it is
possible to carry out the process under reduced or elevated
pressure in pressure resistant equipment. Generally, the
consistency of the fibrous material is about 0.5 to 95% by weight
during the contacting stage.
[0039] According to a particularly preferred embodiment, the first
and the second stages of the process are carried out in the same
reaction medium, without separating the fibrous matrix after the
oxidation step. The conditions (consistency, temperature, pH,
pressure) can, though, even in this embodiment be different during
the various processing stages.
[0040] The first and the second stages of the process are carried
out sequentially or simultaneously. However, it should be noted
that the first step of the process aims at the formation in the
fibrous substrate of phenoxy radicals, which are capable of binding
modifying agents. Some modifying agents will form substrates for
the oxidative enzymes used in the invention, and in that case, it
is preferred to first add the oxidative enzymes and to allow the
enzyme interact with the fibrous substrate containing phenolic or
similar groups, e.g. for 0.1 to 180 minutes, in particular about 1
to 30 minutes to achieve oxidation of the phenolic groups, and to
add the modifying agents after the enzymatic oxidation.
[0041] The same observations are true for the chemical oxidation
agents mentioned above. As Example 3 shows, reasonably good results
are obtained with the simultaneous application of oxidation agent
and modifying agent, although the best results are attained when
steps one and two are carried our sequentially.
[0042] According to one preferred embodiment, the modifying agent
is an aliphatic or aromatic, monocyclic, bicyclic or tricyclic
substance. The aliphatic compound can be an unsaturated carboxylic
acid, advantageously a monocarboxylic unsaturated fatty acid,
having 4 to 30 carbon atoms. In particular, the modifying agent can
be a monocarboxylic, unsaturated fatty acids containing a minimum
of two double bonds, preferably two conjugated double bonds. Such
fatty acids have an even number of carbon atoms, typically in the
range of 16 to 22. It is also possible to use lower alkanols, i.e.
alcoholic compounds comprising 1 to 6, in particular 1 to 4 carbon
atoms. Examples include n- and i-propanol and n- and t-butanol.
[0043] Examples of particularly suitable compounds are constituted
by linoleic and linolenic acid. It would appear that the
unsaturated fatty acid bonds to the oxidized groups or structure
via one of the double bonds.
[0044] Other suitable compounds include antioxidants, such as
tocopherol and beta-carotene.
[0045] The compound can have special properties, such as capability
to trap radicals and form colourless substituents.
[0046] The above two steps can be carried sequentially or
simultaneously. Also other compounds, such as papermaking chemicals
may be present during the reaction steps.
[0047] After the above processing, the modified fibre having new
properties is generally separated from the liquid reaction and
further used in target applications.
[0048] The following non-limiting examples illustrate the
invention:
EXAMPLE 1
[0049] A 5 g portion of bleached spruce TMP was suspended in water.
The pH of the suspension was adjusted to pH 4.5 by addition of
acid. The suspension was stirred at RT. Laccase dosage was 1000
nkat/g of pulp dry matter and the final pulp consistency was 7.5%.
After 30 minutes laccase reaction, 0.15 mmol linoleic acid/g of
pulp dry matter was added to the pulp suspension. After 1 h total
reaction time, the pulp suspension was filtered and the pulp was
washed thoroughly with water. Handsheets were prepared. For
comparison purposes, reference treatments were carried out using
the same procedure as described above but without addition of
laccase or linoleic acid or both. The light-fastness on the pulps
was tested with Xenotest 150S light exposure and weathering test
instrument using "window glass" filter. The brightness of the
handsheets was measured as function of irradiation dosage. The
results are presented graphically in FIG. 1.
[0050] From the results presented in FIG. 1, it is apparent that
the addition of linoleic acid and laccase was found to decrease the
yellowing tendency of the pulp. In other words, addition of a
modifying agent in the presence of an oxidizing agent and a
suitable catalyst, the yellowing tendency of pulp was
decreased.
EXAMPLE 2
Bonding of New Compounds to TMP
[0051] A 5 g portion of spruce TMP was suspended in water. The pH
of the suspension was adjusted to pH 4.5 by addition of acid. The
suspension was stirred at RT. Laccase dosage was 1000 nkat/g of
pulp dry matter and the final pulp consistency was 7.5%. After 30
minutes laccase reaction the new compound was added to the pulp
suspension. After 1 h total reaction time, the pulp suspension was
filtered and the pulp was washed thoroughly with water. Handsheets
were prepared. For comparison purposes, reference treatments were
carried out using the same procedure as described above but without
addition of laccase or the new compound. The light-fastness on the
pulps was tested with Xenotest 150S light exposure and weathering
test instrument using "window glass" filter. The changes in the ISO
brightnesses after irradiation are summarized in Table 1.
TABLE-US-00001 TABLE 1 .DELTA. Brightness Irradation (as ISO-
Treatment (Whm.sup.2) Brightness) TMP Reference 1260 10 TMP +
laccase + ferulic acid (0.15 mmol/g) 1260 3 TMP + laccase + vinyl
laurate (0.3 mmol/g) 1260 2
EXAMPLE 3
[0052] Sample A: Peroxide bleached aspen-CTMP-pulp was treated with
sodium persulphate (dosage 5 kg/ton of pulp) and linoleic acid (5
kg) at 80.degree. C., at pH 5 for 60 minutes. The treatment was
carried out at a consistency of 10%.
[0053] Sample B: The pulp sample was treated in the same way as
Sample A except that ammonium persulphate (5 kg) was used instead
of Na-persulphate.
[0054] Sample C: The pulp sample was treated in the same way as
Samples A and B except that hydrogen peroxide was used instead of
persulphate. The pH of the test was 4.
[0055] Sample D: The pulp sample was treated as Sample A but
t-butanol (5 kg) was used instead of linoleic acid.
[0056] Sample E: The pulp sample was treated in the same way as
Sample A, but no linoleic was added. After the treatment with
persulphate, a separate treatment was made with linoleic acid (5
kg) at 80.degree. C. at a consistency of 10%. The duration of the
treatment was 30 min, and the pH was 5
[0057] Sample F: The sample was prepared as Sample D, but without
using any t-butanol. After the persulphate treatment, a separate
treatment (30 min, pH 5) with t-butanol was carried out at a
consistency of 10% and a temperature of 80.degree. C., the dosage
being 5 kg/ton of pulp.
[0058] Sheets were manufactured from the pulp samples and their
brightness stability was tested with a Xenotest S150 using a
"window pane" filter. The radiation of the Xenotest-apparatus
corresponded to that of sunlight through a window pane, but the
intensity of the radiation was much stronger (accelerated test).
The brightness of the samples was determined after a 2 h radiation
(corresponds to 1260 wh/m.sup.2)
[0059] The results are indicated in Table 2 below: TABLE-US-00002
TABLE 2 Sample Brightness reduction (.DELTA. Brightness, % ISO)
Reference (untreated) 10.4 A 6.9 B 7.2 C 6.8 D 7.2 E 6.1 F 6.1
[0060] As apparent from the above results, the brightness stability
of the samples treated by the present invention has been improved
by even more than 4 units.
* * * * *