U.S. patent application number 11/259991 was filed with the patent office on 2007-07-05 for treatment of cellulose during bleaching with agent capable of reducing carbonyl groups.
This patent application is currently assigned to Borregaard ChemCell. Invention is credited to Ove Bartholsen, Asbjorn E. Braketas, Torgeir Hjerde, Justin T. Scarpello.
Application Number | 20070151680 11/259991 |
Document ID | / |
Family ID | 29779253 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151680 |
Kind Code |
A1 |
Scarpello; Justin T. ; et
al. |
July 5, 2007 |
Treatment of cellulose during bleaching with agent capable of
reducing carbonyl groups
Abstract
The present invention relates to a method for treating a mixture
containing cellulose, comprising at least one step of adding at
least one agent capable of reducing carbonyl groups. The invention
further relates to a specialty cellulose pulp, obtained by a method
comprising treatment. Furthermore, the invention relates to the use
of the specialty cellulose pulp according to the invention or the
specialty cellulose pulp obtained by a method according to the
invention for the production of cellulose derivatives or materials
containing cellulose molecules, including but not limited to,
cellulose ethers or cellulose esters. Cellulose derivatives
obtained from the specialty cellulose pulp according to the
invention display increased viscosity and/or improved brightness
over cellulose derivatives obtained from specialty cellulose pulp
not subjected to the inventive treatment.
Inventors: |
Scarpello; Justin T.; (Oslo,
NO) ; Braketas; Asbjorn E.; (Sarpsborg, NO) ;
Bartholsen; Ove; (Borgenhaugen, NO) ; Hjerde;
Torgeir; (Sarpsborg, NO) |
Correspondence
Address: |
FOLEY & LARDNER LLP
1530 PAGE MILL ROAD
PALO ALTO
CA
94304
US
|
Assignee: |
Borregaard ChemCell
|
Family ID: |
29779253 |
Appl. No.: |
11/259991 |
Filed: |
October 26, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10184009 |
Jun 26, 2002 |
|
|
|
11259991 |
Oct 26, 2005 |
|
|
|
Current U.S.
Class: |
162/9 ; 162/95;
8/116.1 |
Current CPC
Class: |
C08B 11/12 20130101;
D21C 9/1084 20130101; D21C 9/1057 20130101; C08B 1/06 20130101;
C08B 1/02 20130101; C08B 1/00 20130101 |
Class at
Publication: |
162/009 ;
162/095; 008/116.1 |
International
Class: |
D21C 9/00 20060101
D21C009/00 |
Claims
1-12. (canceled)
13. Specialty cellulose pulp, obtainable by a process comprising at
least one step of treating a mixture containing cellulose that has
not been pulped or that has been pulped chemically or chemically
and mechanically, characterized in that the treatment comprises at
least one step of adding at least one agent capable of reducing
carbonyl.
14. Specialty cellulose pulp according to claim 13, characterized
in that the viscosity or the brightness, or both, of cellulose
derivatives obtained from said specialty cellulose pulp are
increased over the viscosity or the ISO brightness, or both,
obtained from a specialty cellulose pulp that has not been treated
with the at least one step of adding at least one agent capable of
reducing carbonyl groups.
15 and 16 (canceled)
17. A specialty cellulose pulp produced by treating a mixture
containing cellulose that has not been pulped or that has been
pulped chemically or chemically and mechanically, wherein the
method comprises: a) providing the mixture as an aqueous slurry; b)
subjecting the slurry to a multi-stage bleaching process; and c)
during at least one step of the multi-stage bleaching process,
adding a sufficient amount of at least one agent capable of
reducing carbonyl groups of the cellulose to produce at least a
partially reduced cellulose wherein at least the terminal step of
the multi-stage bleaching process comprises the addition of at
least one agent capable of reducing carbonyl groups of the
cellulose to produce at least a partially reduced cellulose.
18. The specialty cellulose pulp of claim 17, wherein the mixture
containing cellulose is obtained from (i) chemically or chemically
and mechanically pulping wood or is obtained from (ii) unpulped
cotton linters or from any combination of (i) and (ii).
19. The specialty cellulose pulp of claim 17, wherein the aqueous
slurry has a cellulose content of from 0.1 to 40%. by weight based
on the total weight.
20. The specialty cellulose pulp of claim 17, wherein the agent
capable of reducing carbonyl groups is selected from the group
consisting of borohydrides, dimethylamine borane (DMAB), lithium
aluminum hydride (LiAlH), and mixtures thereof.
21. The specialty cellulose pulp of claim 17, wherein the
sufficient amount of the agent capable of reducing carbonyl groups
added to the slurry is from 0.1 to 200 grammoles per ton of the
mixture containing cellulose.
22. The specialty cellulose pulp of claim 17, wherein the step of
adding at least one agent capable of reducing carbonyl groups is
performed at temperatures from ambient to 80.degree. C.
23. The specialty cellulose pulp of claim 17, wherein the step of
adding at least one agent capable of reducing carbonyl groups is
performed at a pH value from 8 to 14.
24. The specialty cellulose pulp of claim 17, wherein the method
further comprises performing at least one step of post-processing
of the cellulose, wherein said post-processing is selected from the
group consisting of de-hydration, filtering, drying, pressing,
vacuum drying, enzyme treatment and removal of fines.
25. The specialty cellulose pulp of claim 24, wherein the
post-processing step is a step of drying.
26. The specialty cellulose pulp of claim 17, wherein an oxidizing
agent is added concurrently with the reducing agent.
27. The specialty cellulose pulp of claim 17, wherein the
multi-stage bleaching process is performed in batch mode or
continuously.
28. The specialty cellulose pulp of claim 17, wherein the specialty
cellulose pulp when converted to a cellulose ether has an increased
brightness of 5% to 80% of the brightness of a cellulose ether that
has not been treated with at least one agent capable of reducing
carbonyl groups.
29. The specialty cellulose pulp of claim 17, wherein the specialty
cellulose pulp when converted to a cellulose ether has a viscosity
that is increased by at least 8% to 50% over the viscosity of
cellulose that has not been treated with at least one agent capable
of reducing carbonyl groups.
Description
[0001] This application is a divisional of U.S. application Ser.
No. 10/184,009, filed Jun. 26, 2002.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for treating a
mixture containing cellulose, comprising at least one step of
adding at least one agent capable of reducing carbonyl groups. The
invention further relates to a specialty cellulose pulp, obtained
by a method comprising said treatment. Furthermore, the invention
relates to the use of the specialty cellulose pulp according to the
invention or the specialty cellulose pulp obtained by a method
according to the invention for the production of cellulose
derivatives or materials containing cellulose molecules as a raw
material, including but not limited to, cellulose ethers or
cellulose esters. Cellulose derivatives obtained from the specialty
cellulose pulp according to the invention display increased
viscosity and/or improved brightness over cellulose derivatives
obtained from specialty cellulose pulp not subjected to the
inventive treatment.
BACKGROUND OF THE INVENTION
[0003] The method according to the invention can be employed for
any mixture containing cellulose. Such mixtures include, by way of
example, the treatment of mixtures containing cellulose leading to
specialty cellulose pulp which is used to illustrate the particular
embodiments. However, this shall not be construed to mean that the
method as claimed is only applicable to specialty cellulose pulp.
For the purpose of the present invention, wherever applicable, the
term "specialty cellulose pulp" is synonymous to the general term
"pulp".
[0004] Specialty cellulose pulp is used to manufacture a number of
products that require physical and chemical properties not provided
by the pulp used for the manufacture of standard paper, linerboard
or cardboard. Specialty cellulose pulp therefore differs from the
major portion of cellulose pulp produced in the world today.
[0005] Any treatment that a mixture containing cellulose is
subjected to, in particular if it is to be used as specialty
cellulose pulp, has to be performed as to maintain the properties
important to the end use, in particular the integrity of the
cellulose molecules themselves. One of the most important steps of
treatment of a mixture containing cellulose, typically obtained
from pulping wood, is a step of bleaching, or, in most
applications, a multi-stage bleaching process. Bleaching is
commonly achieved by treating a pulp slurry with chemicals that
either remove colored compounds such as lignin, or alter the
structure of colored compounds so that they are no longer colored.
The extent to which a specialty cellulose is bleached depends on
the requirements for the end-product manufactured from the
specialty cellulose pulp.
[0006] The expert in the field typically understands a bleaching
process as one that increases the ISO brightness of a mixture
containing cellulose. Furthermore, the expert in the field
typically understands that bleaching is achieved primarily by
oxidation processes, i.e. bleaching of any mixture containing
cellulose according to the prior art typically involves the
application of an oxidizing agent. For environmental reasons,
common elemental chlorine bleaching using chlorine and/or
hypochlorite is successively replaced by elemental chlorine free
bleaching (ECF) processes, wherein chlorine dioxide replaces
chlorine and/or hypochlorite. Totally chlorine free (TCF) bleaching
uses chlorine-free bleaching agents such as oxygen or peroxides. A
method for the non-chlorine bleaching of cellulose pulp using
oxygen gas in sophisticated treatment stages is described in, for
example, U.S. Pat. No. 6,126,782. Other oxidizing agents are ozone
or enzymes. JP-A 0 6 033 390 for example discloses a method for
using ozone to bleach pulp. A main concern is to limit the
oxidizing agent exposure time in order to limit damage to the
cellulose molecules.
[0007] In summary, bleaching techniques known to the expert in the
field typically involve oxidizing agents. The degree of ISO
brightness achievable by these methods of bleaching is limited to
the extent that strong oxidizing agents (or highly concentrated
oxidizing agents) which would result in a high degree of ISO
brightness also tend to damage the cellulose molecules. In
particular, strong or highly concentrated oxidizing agents tend to
reduce the degree of polymerization (DP) of the cellulose.
[0008] A process known as "reductive bleaching" is used commonly
for brightening virgin mechanical pulps or pulp from recycled
newsprint. In this process, a reducing agent, typically sodium
borohydride, is used to generate sodium hydrosulfite in situ from
primary chemicals, i.e. the reducing agent is not used to reduce
carbonyl-groups in the pulp but to generate a bleaching agent. This
process is disclosed, e.g. on pages 502 through 504 of "Pulp
Bleaching; Principles and Practice", Dence and Reeve (Eds.), TAPPI
Press, 1996.
[0009] The use of reducing agents is also known in the context of
late stages of the treatment of cellulose pulps. For example, U.S.
Pat. No. 5,501,711 discloses the use of borohydrides to treat
cellulose fabric that already had been subjected to a bleaching
treatment. Here, the application of reducing agents improves the
dyeability of said cellulosic fibers. The U.S. Pat. No. 6,217,621
relates to stripping textile fibers, including cellulose acetates
and other products obtained from specialty cellulose pulp, of their
dyes by using reducing agents such as borohydrides.
[0010] Another process involving the use of reducing agents in the
context of the treatment of cellulose pulp is disclosed in U.S.
Pat. No. 5,035,772. Said process involves treating a cellulose pulp
that had already been bleached with one or more reducing agents in
order to reduce carbonyl groups on the lignin contained in the
cellulose pulp. The process includes adding a complexing agent
together with the reducing agent and processing the mixture at a
temperature not greater than 40.degree. C. This treatment is
followed by at least one further step: either a treatment with a
chemical that will block the phenolic hydroxyl groups of the lignin
and/or a treatment to convert short-wave light quanta to long wave
light quanta. The object of the process according to the U.S. Pat.
No. 5,035,772 is to prevent the yellowing with age of lignin
contained in (high yield) cellulose pulps. The process is to be
used with groundwood pulp, refiner pulp, thermo-mechanical and
chemical-mechanical pulp for paper manufacture. Therefore, the U.S.
Pat. No. 5,035,772 does not relate at all to the treatment of
specialty cellulose pulp.
[0011] Finally, the possible use of borohydrides has been discussed
in "Pulp Bleaching; Principles and Practice", Dence and Reeve
(Eds.), TAPPI Press, 1996, page 297, wherein a borohydride is
mentioned as a possible additive to eliminate some of the loss in
strength of paper induced by the alkaline extraction.
[0012] The object of the present invention was to provide a method
of treating a mixture containing cellulose, preferably a mixture
containing cellulose leading to specialty cellulose pulp, so that
the degree of brightness or the viscosity of cellulose derivatives
obtained therefrom, or both, is/are increased over the prior art.
In addition, as a result, a specialty cellulose pulp as such,
leading to cellulose derivatives with increased viscosity and/or
brightness was to be provided.
SUMMARY OF THE INVENTION
[0013] Surprisingly, it was found that this object could be
achieved by treating a mixture containing cellulose with at least
one step of adding at least one agent capable of reducing carbonyl
groups. This treatment can be performed at any stage of processing
a mixture containing cellulose into specialty cellulose pulp once a
mixture containing cellulose has been obtained from (i) chemically
pulping wood (="cooking"), (ii) chemically and mechanically pulping
wood or (iii) unpulped cotton or (iv) any combination of (i) to
(iii). The inventive treatment is either the sole step of the
entire process or is performed prior to bleaching and/or after
bleaching or is performed as at least one step of a multi-stage
bleaching process.
[0014] The solution according to the invention is particularly
surprising since the prior art does not teach that treating a
mixture containing cellulose, i.e. treating a pulp, leads to
cellulose derivatives obtainable from the treated pulp with
improved viscosity and/or brightness in comparison to a similar
cellulose derivative obtained by the same process but excluding the
inventive step of adding at least one agent capable of reducing
carbonyl groups.
[0015] The present invention therefore relates to a method for
treating a mixture containing cellulose, comprising at least one
step of adding at least one agent capable of reducing carbonyl
groups. The invention further relates to a specialty cellulose
pulp, obtained by a method comprising said treatment. Furthermore,
the invention relates to the use of the specialty cellulose pulp
according to the invention or the specialty cellulose pulp obtained
by a method according to the invention for the production of
cellulose derivatives or materials containing cellulose molecules
as a raw material, including but not limited to, cellulose ethers
or cellulose esters. Cellulose derivatives obtained from the
specialty cellulose pulp according to the invention display
increased viscosity and/or improved brightness over cellulose
derivatives obtained from specialty cellulose pulp not subjected to
the inventive treatment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In FIG. 1, the viscosity of the end product obtained from
the inventive specialty cellulose pulp, CMC, (vertical axis; units:
mPas) is shown as a function of the limiting viscosity number of
the specialty cellulose pulp as defined in the standard "SCAN-CM
15:99"(horizontal axis, units: ml/g).
[0017] In FIG. 2, the brightness of CMC powder (vertical axis,
units: % brightness) is shown as a function of the intrinsic
brightness of the specialty cellulose pulp from which the CMC
powder has been obtained by means of etherification (horizontal
axis; units: % brightness)
[0018] FIG. 3 shows a typical particle size distribution of a CMC
powder after grinding in the Fritsch Pulvarisette 19 knife mill as
used in Examples 1, 2 and 3. The horizontal x-axis represents the
particle diameter in .mu.m. while the vertical y-axis represents
the volume of the corresponding particles in %.
DETAILED DESCRIPTION OF THE INVENTION
[0019] A "mixture containing cellulose" according to the invention
is any mixture that contains the glucose polymer of cellulose. No
principal limitations exist as to the state of the cellulose
source, i.e. it may be solid, liquid, a suspension, slurry, paste
or powder. Furthermore, no limits exist as to the origin of the
cellulose. In a preferred embodiment, the mixture containing
cellulose is derived from cotton linters and/or wood. In a
particularly preferred embodiment, the mixture containing cellulose
is derived from wood. Other cellulose sources, in particular annual
plants and/or biomass, (micro)biologically produced and/or derived
cellulose, or cellulose from all types of cell walls are included
as well.
[0020] Furthermore, no limitations exist with respect to the degree
of polymerization of the mixture containing cellulose, as well as
of any product, such as specialty cellulose pulp and/or derivatives
thereof, obtained from said mixture containing cellulose.
[0021] According to the invention, the mixture containing cellulose
may be derived from raw materials that need to be pulped. In
general, the term "pulping" refers to any process that separates
the cellulose from the at least one component that holds the
cellulose together in the raw material. For example, in wood, the
cellulose is held together by lignin and hemicellulose in fibers.
The pulping process is meant to separate, at least partly, the
lignin from the carbohydrate moieties of these fibers.
[0022] As to pulping processes, three different methods are
commonly discerned: (i) chemical pulping (or "cooking"), (ii)
mechanical (or "groundwood") pulping and (iii) semi-chemical or
chemical-mechanical pulping. In (i), the raw material, typically
wood, is cooked in a "digester" at elevated temperatures with
chemicals suited to break the bonds between the cellulose molecules
and the lignin. In (ii), the raw material is typically pressed
against a grinder which physically separates the fibers. The
process (iii) refers to any combination of (i) and (ii). In the
context of the present invention, no principal limitations exist as
to how the pulping is to be performed, so long as the pulping
results in a mixture containing cellulose that can be subjected to
the treatment according to the invention.
[0023] "Pulping" may not be necessary for all raw materials. For
example, if cotton linters are used as the mixture containing
cellulose, no chemical or mechanical pulping is necessary prior to
any subsequent treatment, including the inventive treatment and/or
bleaching.
[0024] A mixture containing cellulose that has been pulped as
described above, is commonly referred to as "pulp". In the context
of the present invention, the term "pulp" is to be seen as more
general than the term "mixture containing cellulose", since the
term "pulp" is meant to refer to the mixture containing cellulose
before the inventive treatment as well as to the treated mixture,
for example the specialty cellulose pulp as obtained after the
inventive treatment. By contrast, the term "mixture containing
cellulose" is only meant to describe the pulp before the treatment
according to the invention.
[0025] Although the inventive method of treating a mixture
containing cellulose with the objective to obtain specialty
cellulose pulp can be, in principle, performed with any mixture
containing cellulose, the method according to the invention is
particularly effective, and therefore preferred, when applied to a
mixture containing cellulose derived from wood. It is further
preferred to pulp the wood chemically prior to the inventive
treatment.
[0026] As far as wood as a source for the mixture containing
cellulose is concerned, both hardwood and softwood tree species may
be used. Examples of softwoods include but are not limited to:
pines, in particular Southern pine, White pine, Caribbean pine;
Western hemlock; spruces, in particular Norway Spruce, Sitka
Spruce; Douglas fir or the like. Examples of hardwoods include, but
are not limited to: gum, maple, oak, eucalyptus, poplar, beech, or
aspen. Mixtures of two or more types of soft and/or hard wood are
included as well.
[0027] Prior to the at least one step of adding at least one agent
capable of reducing carbonyl groups and/or prior and/or during
and/or after any step of pulping, the mixture containing cellulose
may be optionally subjected to any type of pietreatment. Such types
of pretreatment include but are not limited to enzyme treatments,
mechanical refining, addition of additives, addition of complexing
agents, treatment with delignification and other catalysts, the
removal of fines as well as any combination of the aforementioned
steps.
[0028] After the mixture containing cellulose has been prepared
and/or obtained and/or pretreated and/or treated with at least one
agent capable of reducing carbonyl groups (i.e. the inventive
treatment), the mixture may be subjected to a bleaching process.
The term "bleaching" as used in the context of the present
invention refers to any treatment of the mixture containing
cellulose in which the degree of brightness after the bleaching is
increased over the degree of brightness before bleaching. The term
"ISO brightness" as used in the context of the present invention is
defined in "ISO 2470-1999 --paper, boards and pulp--measurements of
the diffuse blue reflectance factor (ISO brightness)" and refers to
the brightness of the pulp. It is important to discriminate this
term from the term "brightness" as used in the context of the
present invention, which refers to the brightness of the end
product, i.e. the derivative of the specialty cellulose pulp. A
standard for measuring said brightness according to the invention
is given in Example 6. In principle, bleaching can be performed
with any agent capable of achieving the above mentioned
objective.
[0029] At least one stage of the processing of the mixture
containing cellulose, obtained after pulping as has been described
above, at least one agent capable of reducing carbonyl groups
(=reducing agent) is added to the mixture containing cellulose. As
a reducing agent in the context of the present invention, every
compound or mixture of compounds can be used that results in at
least the partial reduction of at least a part of the carbonyl
groups in at least one of the components contained within the
pulp.
[0030] Carbonyl groups form a part of the molecular structure of
the main compounds in any mixture containing cellulose. As
compounds are to be named, by way of example, cellulose,
hemicellulose, lignin and resins. The carbonyl groups according to
the invention that are, at least partially, reduced in the
inventive step of adding a reducing agent, may either be naturally
present in the raw-material structures or may be generated during
processing or both. This is particularly true of the mixtures
containing cellulose used for the manufacture of specialty
cellulose pulps derived from wood but is also the case, to a lesser
extent, for pulp derived from other raw materials, such as pulp
derived from cotton linters.
[0031] In principle, any agent that at least partially reduces at
least a part of the carbonyl-groups present in the mixture
containing cellulose can be used. Borohydrides are particularly
preferred, while water-compatible borohydride salts are further
preferred. Such salts include but are not limited to sodium
borohydride, potassium borohydride, lithium borohydride, sodium
cyanoborohydride, sodium triacetoxyborohydride, sodium
trimethoxyborohydride, tetramethylammonium borohydride,
tetramethylammonium triacetoxyborohydride, tetraethylammonium
borohydride, tetrabutylammonium borohydride, tetrabutylammonium
cyanoborohydride, cetyltrimethylammonium borohydride,
benzyltriethylammonium borohydride, Bis(triphenyl-phosphine)
copper(I) borohydride, lithium aluminium hydride,
dimethylamineborane (DMAB) and mixtures of at least two of these.
Preferably, said reducing agents used should be water-soluble.
[0032] The reducing agent can be used by itself, in combination
with other reducing agents and/or in combination with stabilizers
such as calcium hydroxide, magnesium bicarbonate or other mildly
basic salts. Further additional substances with other purposes may
be added as well.
[0033] The reducing agents and/or additional substances may be
added as a solid, a powder, a dispersion, suspension, emulsion or
as a solution. In a preferred embodiment, if borohydrides are used,
they are used in powder form or in the form of a standard solution,
e.g. sodium borohydride, which can be purchased as a 12 wt %
solution in 40 wt % aqueous sodium hydroxide (e.g. Borol.RTM. from
Rohm and Haas, Hydrafin.TM. from Finnish Chemicals (Nokia) Ltd).
All commercially available forms of these chemicals, as well as any
chemical of this kind prepared in a laboratory, may be used to
carry out the treatment of a mixture containing cellulose as
disclosed here.
[0034] As has been mentioned above, the reducing agent may be added
at any stage of the processing of the mixture containing cellulose.
In a preferred embodiment, the reducing agent is added in at least
one step during a multi-stage bleaching process.
[0035] In a particularly preferred embodiment, the at least one
reducing agent is added, i.e. the inventive treatment is performed,
at least as the last stage or after the last stage of a multi-stage
bleaching process.
[0036] The content of reducing agent added in at least one step may
vary from 0.01 to 500 g, preferably from 0.1 gmoles/ton mixture
containing cellulose (dry basis) to 200 gmoles/ton mixture
containing cellulose, depending on the chemical additives and the
specific composition of the mixture containing cellulose. In a
preferred embodiment of the invention, wherein sodium borohydride
is added as the carbonyl-reducing agent and the sole purpose of the
at least one step of the treatment is the chemical reduction of
carbonyl groups, the charge is between 0.3 and 100 gmoles/ton
mixture containing cellulose (on a dry basis).
[0037] In a further preferred embodiment, where sodium borohydride
is added as the carbonyl-reducing agent and an additional purpose
of the at least one step of the treatment is the delignification of
the mixture containing cellulose, the charge is from 0.1 and 500
gmoles/ton mixture containing cellulose (on a dry basis),
preferably from 0.1 to 80 gmoles/ton.
[0038] In a preferred embodiment, the reducing agent is added as
the at least one agent in at least one stage of a multi-stage
bleaching process and/or is added as at least one of at least two
agents in at least one stages of a multi-stage bleaching process.
In particular, the reducing agents can be added simultaneously
during the addition of one or more oxidizing agents, known to the
expert in the field as the traditional bleaching agents, at one or
more stages during a multi-stage bleaching process. It is also
conceivable, that adding reducing and oxidizing agents occur as
alternating or subsequent steps, optionally separated by steps of
washing or otherwise treating the specialty cellulose pulp.
[0039] The reducing agent may be added together with any other
agent or substance, so long as the at least one additional agent
does not prevent the reducing agent to at least partly reduce at
least a part of the carbonyl groups. In a preferred embodiment, the
pH achieved in the pulp upon adding the at least one reducing agent
is below 12.
[0040] As far as the at least one oxidizing agent that may be added
in a multi-stage bleaching process is concerned, any agent(s) known
to the expert in the field may be used. Examples of such oxidizing
agents may be selected from but are not limited the following
group: chlorine, chlorine dioxide, hypochlorite, chlorite, oxygen,
per-compounds such as peroxide, and ozone, as well as mixtures of
two or more of the aforementioned substances.
[0041] Another agent that is commonly used during the bleaching
process of a specialty cellulose pulp, namely sodium hydroxide, may
be added before and/or during and/or after any of the at least one
step of bleaching as mentioned above. The main purpose of adding
sodium hydroxide is the extraction of at least a part of the
hemicellulose portion of the pulp, as well as, to some extent,
regulation of the pH value. The amount and/or conditions under
which the sodium hydroxide is to be added are known to the expert
in the art.
[0042] The aforementioned treatment of the mixture containing
cellulose, can be carried out in any reaction device known to the
expert in the field in the context of pulp bleaching processes, for
example in a bleaching tower, so long as the device is adapted to
comply with health and safety issues related to the use of the
specific reducing agent(s) and/or any other agent used. There are
no limitations as to the design and/or function of the reaction
device. For example, it may be a vessel or a tube, operated in
batch mode or continuously.
[0043] In a preferred embodiment, said reaction device will be a
steel tower of the type known to the expert for commercial-scale
cellulose pulp bleaching processes. In a further preferred
embodiment, the device will be of dimensions such that cellulose
retention time under, reaction conditions ranges up to 6 hours.
Preferably, the device is of sufficient dimensions so that the
reaction time ranges up to 3.5 hours. The actual size of the
reaction device is, inter alia, determined by the pulp production
rate in a continuous process and, correspondingly, by the batch
volume in a batch process. Preferably, the reaction device is
fitted with a fan capable of maintaining a level of hydrogen gas
well below the explosion limit since hydrogen gas may be generated
during treatment with a borohydride. Any other method capable of
keeping the amount of hydrogen in the reaction device below the
explosion limit, such as hydrogen scavengers, controlled reactions
of hydrogen or purging the reaction device with inert gases or
mixtures containing inert gases may be used as well.
[0044] The mixture containing cellulose that is to be subjected to
the at least one step of the treatment according to the invention
is pumped into the aforementioned reaction device. Preferably, it
is pumped in the device in the form of an aqueous slurry, having a
content ranging from 0.1 to 40 wt % of pulp based on dry mass of
the mixture containing cellulose, preferably a content ranging from
1 to 25wt %, further preferred ranging from 5 to 15 wt %. The
mixing of the slurry with the reducing agents may take place either
inside or outside the reaction device, by means of a chemical mixer
or any other means that produces homogeneous mixing. Any other
chemicals added to the reactor device (e.g. for pH adjustment,
bleaching purposes, hemicellulose extraction purposes or as
chemical aids to the main chemical functions in the process stage)
may also be mixed into the slurry inside or outside the reaction
device. Preferably, any mixing takes place outside of the reactor
device, as this facilitates the formation of an homogeneous
reaction slurry.
[0045] As far as the temperature at which the at least one reducing
agent is added to the mixture containing cellulose, is concerned,
any temperature is conceivable at which the at least one reducing
agent at least partly reduces carbonyl groups contained in the
mixture. In case of an integrated method comprising several process
stages, in particular several stages of bleaching, the process
temperature may be chosen to be suitable for all stages. In a
preferred embodiment, the temperature will be set as to optimize
the integrated process, or, if necessary, regulated as to optimize
each stage individually. In a further preferred embodiment, the
multi-stage bleaching process is carried out at a temperature
ranging from ambient temperature to 140.degree. C.
[0046] In a further preferred embodiment and in particular if the
chemical reduction of carbonyl groups in the pulp is the primary
object, the temperature for the bleaching process ranges from
ambient temperature to 80.degree. C., further preferred from
35.degree. C. to 75.degree. C. and yet further preferred from
50.degree. C. to 60.degree. C. Furthermore, if the function of the
inventive treatment also relates to delignification or to any form
of bleaching, in addition to chemical reduction of carbonyl groups,
the temperature of the reaction device is set to a value that
allows the best combination of bleaching action and chemical
reduction of carbonyl groups. In a process stage of the process in
which common bleaching chemicals known to the expert in the field
are used, temperatures should preferably range from ambient
temperature to 80.degree. C., further preferred from 30.degree. C.
to 70.degree. C.
[0047] The heating of the reactor device is effected using heaters
or heat-exchangers of the type known to the expert in the
field.
[0048] The pH-value of the pulp slurry containing the previously
described active chemical agents should be between 7 and 14. As for
the case of temperature, the pH of a preferred embodiment of the
invention depends on the full process function of the process stage
in question.
[0049] Most preferably, especially if sodium borohydride is used as
the carbony-reducing chemical, the pH should be maintained between
8 and 14, in a preferred embodiment between 10 and 13 as to
minimize decomposition of the borohydride moiety and subsequent
hydrogen gas release. A pH between 11 and 12 is particularly
preferred. For the same reason, it is preferable to adjust the pH
of the pulp slurry to a sufficiently high pH prior to the addition
of sodium borohydride. This can be achieved by adding sodium
hydroxide to the slurry at a point between the previous process
stage and the addition of sodium borohydride. The amount of sodium
hydroxide added depends on the pH of the mixture containing
cellulose that is fed from the previous process stage.
[0050] Should the process stage where the invention is applied have
the additional function of delignification or other bleaching
action using common bleaching chemicals, the pH of the slurry in
the reactor device should preferably be set at a value from pH 8 to
14, wherein the specific value chosen should best suit the optimal
combination of bleaching and chemical reduction of carbonyl groups
in the pulp.
[0051] As a result of the treatment of the mixture containing
cellulose described above, in particular after treating said
mixture in a bleaching process comprising at least one stage of
adding a reducing agent, a treated mixture containing cellulose is
obtained. In the context of the present invention, this mixture is
referred to as (treated) "specialty cellulose pulp", i.e. as a pulp
that has been treated and can now be further processed to obtain
specialty cellulose products. By way of example, one class of
products obtainable from specialty cellulose pulp are cellulose
ethers.
[0052] Said cellulose ethers, for example sodium
carboxymethylcellulose, methylcellulose,
methylhydroxyethylcellulose, methylhydroxypropylcellulose,
hydroxyehylcellulose, hydroxypropylcellulose, ethylcellulose, and
mixtures of at least two components thereof, are used as additives
in a large range of household and industrial products. The main
purpose of adding said cellulose ethers to other materials lies in
the possibility of controlling the rheological properties of said
materials. The viscosity of the cellulose ether solution
(henceforth termed cellulose ether viscosity), which is strongly
related to the degree of polymerisation (DP) of the cellulose in
the pulp feedstock, is therefore one of the most important
properties of cellulose ethers.
[0053] The upper limit of cellulose ether viscosity that can be
obtained is per se limited by the upper limit of the cellulose DP
in the specialty cellulose pulp from which the cellulose ether is
derived, as well as by the DP of the cellulose ether molecule
following etherification.
[0054] Furthermore, in a large proportion of products containing
cellulose ethers, the appearance of the product is of high
importance. Value is often attached to a cellulose ether solid that
is as white as possible, and to a cellulose ether solution that is
as transparent as possible. The upper limit of brightness of
cellulose ether that may be achieved is principally limited by the
upper limit of the ISO brightness of the specialty cellulose pulp
from which it is derived.
[0055] The brightness achievable for commercial cellulose ether
products is also indirectly limited by the viscosity of the
specialty cellulose pulp feed-stock. This is because of a tradeoff
in the production of specialty cellulose pulp between high ISO
brightness and high cellulose DP in the specialty cellulose
pulp.
[0056] The specialty cellulose pulp as obtained after the inventive
treatment with at least one agent capable of reducing carbonyl
group and after any other optional treatment, in particular after
bleaching in a multi-stage bleaching process, can now be subjected
to any step of post-treatment.
[0057] Of particular importance in this context is the removal of
water from the specialty cellulose pulp. This can be achieved by
filtering, pressing, drying at temperatures above room temperature,
applying a pressure that is below the partial pressure of water
etc. Examples of other post-bleaching steps, that may be applied
either prior to, during, or after water removal, are, but are not
limited to, removal of fines, enzyme treatments, and the addition
of or treatments with chemical agents to improve pulp
processability characteristics. In a preferred embodiment, the
specialty cellulose is present in the form of a solid sheet or
powder, preferably obtained after at least one step of
post-treatment.
[0058] The specialty cellulose pulp obtained as described above can
be subjected to any step of further processing and/or
derivatization. Of particular interest in the context of the
present invention is any process of forming cellulose derivatives.
Cellulose ethers and/or cellulose esters are of particular
importance in this context. Following bleaching and post-treatment
(including a possible stage of drying), the specialty cellulose
sheets are packed in a roll or sheets of a given configuration
determined by the cellulose derivative producer and transported to
the cellulose derivative producer. There, the sheets are typically
cut up or ground to a powder. In the case of cellulose ethers, the
pulp pieces or powder is typically pre-treated with sodium
hydroxide at below room temperature and reacted with the desired
etherifying agents in an oxygen-free environment at temperatures
between 60 and 100.degree. C. The cellulose ether product is washed
free of salts, dried and often ground to become the final
product.
[0059] The viscosity of a cellulose ether as obtained from the
specialty cellulose pulp as described above can be improved by at
least 8-50% using the treatment as disclosed in this invention
compared to the same product not subjected to the at least one step
of adding of at least one reducing agent during the processing of
the specialty cellulose pulp. Characteristic advantages of the
method according to the invention over the prior art for
etherification products obtained from the specialty cellulose pulp
(in a substantially oxygen-free environment) are illustrated in
FIG. 1 and FIG. 2.
[0060] In FIG. 1, the effect of the method according to the
invention as applied to a mixture containing cellulose from wood
pulp is shown. The viscosity of a sodium carboxymethyl cellulose
(CMC), i.e. a cellulose derivative obtained via etherification from
the specialty cellulose pulp according to the invention, is shown
in FIG. 1. Here the viscosity of the end product, CMC, (vertical
axis; units: mPas) is shown as a function of the limiting viscosity
number of the specialty cellulose pulp as defined in the standard
"SCAN-CM 15:99" (horizontal axis, units: ml/g).
[0061] It can be seen that across a broad range of specialty
cellulose degree of polymerization (as represented by its limiting
viscosity number values), the corresponding viscosity of a 1%
aqueous solution of CMC varies linearly, irrespective of whether
the mixture containing cellulose is treated according to the
invention (open squares; solid line indicates least square fit) or
if the mixture had not been treated with at least one reducing
agent (open triangles). The data clearly show two distinct linear
relationships for treated and untreated pulps. However, the
viscosity of the CMC resulting from the treated specialty cellulose
pulp is constantly about 200 mPas higher than the viscosity of the
untreated, but otherwise same, mixture. These data provide clear
evidence that specialty cellulose pulp that had not been treated
according to the invention does not reach its fullest degree of
polymerization (DP) during etherification, as evidenced by a
significantly lower viscosity of the end product.
[0062] The large effect of the at least partial reduction of
carbonyl groups in a specialty cellulose pulp on the brightness of
its cellulose ether derivative was particularly unexpected. It has
been found that the brightness could be improved from 5% to 80%.
This effect is shown in FIG. 2, where the brightness of CMC powder
(vertical axis, units: % brightness) is shown as a function of the
intrinsic ISO brightness of the specialty cellulose pulp from which
the CMC powder has been obtained by means of etherification
(horizontal axis; units: % brightness). It can be clearly seen that
the brightness of the treated specialty cellulose pulp (open
squares) results in a brightness that is from 5 to 20% higher than
the corresponding brightness of the powder resulting from the
untreated specialty cellulose pulp (open triangles).
[0063] The present invention also relates to the product of the
inventive process, i.e. to a treated specialty cellulose pulp
obtainable by a process, comprising the treatment of a mixture
containing cellulose, wherein the treatment comprises at least one
step of adding at least one agent capable of reducing carbonyl
groups. In particular, an integrated process may be employed. This
process comprises at least the following steps: [0064] (I) Chemical
or chemical and mechanical pulping of a raw material containing
cellulose resulting in a mixture (I) containing cellulose; [0065]
(II) treating an unpulped mixture containing cellulose or treating
a mixture (I) containing cellulose, wherein the treatment comprises
at least one step of adding at least one agent capable of reducing
carbonyl groups, resulting in a treated specialty cellulose pulp
(II); [0066] (III) at least one step of post-processing of the
specialty cellulose pulp (II); [0067] wherein the steps (I) and
(III) are optional.
[0068] In a preferred embodiment, step (II) is performed as part of
a multi-stage bleaching process. In a further preferred embodiment,
the step (III) of post-processing comprises at least one step of
removing water and/or of drying at temperatures above room
temperature.
[0069] The specialty cellulose pulp as claimed in this invention
can be used for any application for which specialty cellulose pulp
is better suited than regular pulp used for the manufacture of
paper or cardboard. In particular, all applications in which
cellulose molecules alone or in combination with other materials
can be used, are included.
[0070] By way of example but without the intent to limit the scope
of the invention, the following areas of use are mentioned:
manufacture of cellulose derivatives, in particular of cellulose
ethers or cellulose esters; textile fibers, in particular viscose
or high tenacity rayon yarn, non-woven fabrics; micro-crystalline
cellulose, formulations for food, in particular as edible diet
food, pharmaceutical or cosmetics applications, technical filters,
absorbing materials, fluff fibers, photographic papers, as an
additive during plastic molding, the use of said fibers in graft
co-polymerisation, as a component in composite materials,
applications in packaging, paints, inks, thickeners, LCD screens,
high value specialty papers, laminates, battery separators,
electrical circuits and the like.
EXAMPLES
[0071] In the following, working examples are used to illustrate
the present invention. These examples, however are not meant to
limit the scope of the invention as described above.
Example 1
Production of Specialty Cellulose Pulp According to the Invention
and Subsequent Carboxymethylation
[0072] Norway spruce was cooked in batch using the acid sulfite
process. Once cooking was complete, the pulp had a mean kappa
number (SCAN method C 1:77) of 46. This pulp was transferred to a
bleach plant typical of the design found in other bleach plants
used in the manufacture of specialty and other cellulose pulps.
[0073] In this first example the pulp bleaching process consists of
four distinct, industrial scale stages, working continuously and in
series, followed in series by a one stage, industrial-scale
embodiment of the inventive treatment. All these stages, with the
exception of the inventive treatments, are variations on bleach
treatments common in the specialty cellulose and other cellulose
pulp industries, and are well known to one skilled in the art.
[0074] The main treatment at each of the five stages comprising
this example is carried out in stainless steel reactors commonly
known as bleach towers, some of which are lined inside with
chemically resistant materials, typical of those commonly used in
the specialty cellulose and other cellulose pulp industries. Some
additional but important procedures, such as washing, dilution,
filtration, and chemical dosing, are carried out either prior to
the pulp entering, or after the pulp leaving the towers. Details of
the conditions inside each of the five towers and the bleaching,
extraction chemical, and reducing agent dosages used in this
example of the invention can be found in Table 1. TABLE-US-00001
TABLE 1 Details of the conditions inside the towers at each stage
of processing in Example 1. Treatment stage Parameter Units Level
E.sub.0 NaOH Kg/ton pulp (dry) 57 Temperature .degree. C. 95
Residence time Minutes 132 Consistency % 11.5 Borol Solution .RTM.
Kg/ton pulp (dry) 5 D.sub.0 pH -- 2 Temperature .degree. C. 15
Residence time Minutes 43 Consistency % 3.5 ClO.sub.2 Kg/ton pulp
(dry) 8.2 P.sub.0 pH -- 11 Temperature .degree. C. 35 Residence
time Minutes 126 Consistency % 10 H.sub.2O.sub.2 Kg/ton pulp (dry)
2 D.sub.1 pH -- 2.5 Temperature .degree. C. 45 Residence time
Minutes 148 Consistency % 10 ClO.sub.2 Kg/ton pulp (dry) 10 B pH --
11.6 Temperature .degree. C. 53 Residence time Minutes 163
Consistency % 10 Borol Solution .RTM. Kg/ton pulp (dry) 5
[0075] The term "consistency" as used in the context of the present
invention refers to the dry mass of pulp in weight percent with
respect to the total mass of pulp.
[0076] The first stage of this example of the invention, the stage
(E.sub.0), is an alkaline extraction. In this stage, in addition to
the main component NaOH, a borohydride is added in the form of
Borol Solution.RTM. (a 12 wt % solution of sodium borohydride in 40
wt % aqueous sodium hydroxide purchased from Rohm and Haas). The
dosage of Borol Solution.RTM. was 5 kg/ton pulp (dry basis) which
amounts to 15.9 gmoles of sodium borohydride per ton dry pulp. This
dosage was carried out immediately prior to the pulp entering the
tower. Prior to the dosage of sodium borohydride, the pulp was
twice washed with deionized water, passed over a filter and press
dewatered. Following pressing and prior to the sodium borohydride
dosage, 58 kg/ton pulp (dry basis) of sodium hydroxide was dosed.
Immediately prior to the pulp entering the E.sub.0 tower, the
consistency of the pulp slurry was 11.5%. In the E.sub.0 bleach
tower, the temperature was maintained at 95.degree. C. The
residence time of the pulp slurry at the base of the E.sub.0 tower
was 132 minutes. The alkaline extraction stage serves the purpose
of hemicellulose removal and the borohydride serves as an additive
to eliminate some of the loss in strength of paper induced by the
alkaline extraction.
[0077] The second stage, namely the stage (D.sub.0), is a chlorine
dioxide treatment. Prior to entering the D.sub.0 tower, the pulp
slurry was pressed and washed with deionized water, then washed a
second time over a filter. Prior to the pulp entering the D.sub.0
tower, the pH was adjusted to 1.9, and 8.2 kg/ton pulp (dry basis)
of chlorine dioxide was dosed. Following this chemical dosage, the
consistency of the pulp slurry was 3.5%. In the D.sub.0 tower, the
temperature was maintained at 15.degree. C. The residence time of
the pulp slurry in the D.sub.0 tower was 43 minutes.
[0078] The third stage, namely the stage (P.sub.0), is an oxidative
bleaching stage using hydrogen peroxide. Prior to entering the
P.sub.0 tower, the pulp-slurry was washed with deionized water over
a filter. The pH of the pulp slurry was then adjusted to 10.9 using
sodium hydroxide, and 2.0 kg/ton pulp (dry basis) hydrogen peroxide
was added. The consistency of the pulp slurry was then 10%. In the
P.sub.0 tower, the temperature was maintained at 35.degree. C. The
residence time of the pulp slurry in the P.sub.0 bleach tower was
125 minutes.
[0079] The fourth stage, namely the stage (D.sub.1), is a chlorine
dioxide treatment. Prior to entering the D.sub.1 tower, the pulp
was washed with deionized water over a filter. The pH of the pulp
slurry was then adjusted to 2.5 using sulphur dioxide, and 10
kg/ton pulp (dry basis) of chlorine dioxide was dosed. In the
D.sub.1 tower, the temperature was maintained at 45.degree. C. The
residence time of the pulp slurry in the D.sub.1 tower was 148
minutes.
[0080] The fifth stage of this example of the invention, namely the
stage (B), has the sole purpose of effecting chemical reduction of
the carbonyl groups in the pulp, and is therefore the inventive
borohydride treatment. Sodium borohydride was dosed in the form of
Borol Solution.RTM.. The dosage of Borol Solution.RTM. was 5 kg/ton
pulp (dry basis), which amounts to 15.9 gmoles of sodium
borohydride per ton dry pulp. This dosage was carried out
immediately prior to the pulp entering the B tower. Prior to the
dosage of sodium borohydride, the pulp was washed with deionized
water over a filter and the pH of the slurry adjusted to 11.5 using
sodium hydroxide. Immediately prior to the slurry entering the B
tower, its consistency was 10%. In the B tower, the temperature was
maintained at 55.degree. C. The residence time of the pulp slurry
in the B tower was 163 minutes.
[0081] After leaving the B tower, the pulp slurry was washed with
deionized water over a filter and the pH adjusted to 4. The pulp
was then transported to the drying section of the specialty
cellulose manufacturing process, where it was screened, washed in
deionized water, and dried to a moisture content of 7%. The dried
pulp was packed in a form (approx. 20 ton rolls) typical of
finished product specialty cellulose that is ready for sale to
other parties wishing to use this as raw material for a cellulose
derivatization.
[0082] The properties of the finished specialty cellulose product
can be found in Table 2. TABLE-US-00002 TABLE 2 Selected properties
of specialty cellulose pulp produced according to Example 1.
Brightness (ISO 2470-1999) (%) 82.00 Limiting viscosity number
(SCAN-CM 15:99) (ml/[[.]]g) 1532 S18 (SCAN-C2:61) (alkali
solubility of pulp; in %) 7.02
[0083] A 50 g sample of the specialty cellulose pulp manufactured
using the inventive treatment described above and with properties
as found in Table 2 was subjected to etherification yielding sodium
carboxymethyl cellulose (CMC).
[0084] The aforementioned specialty cellulose pulp sample was first
ground using a knife mill (Fritsch pulvarisette 19). The resulting
specialty cellulose pulp powder had a mean particle size of 200
.mu.m as measured by a Coulter LS 200 particle analyzer. 35 g of
powder (weighed on a dry basis) and was subsequently etherified to
carboxymethyl cellulose according to the carboxymethylation
procedure described in Example 4. The 1 wt % solution viscosity and
powder brightness of the resultant carboxymethyl cellulose product
was measured. The corresponding values can be found in Table 3.
TABLE-US-00003 TABLE 3 Selected properties of CMC made from
specialty cellulose pulp produced as per Example 1. The degree of
substitution of the CMC was 1.05. Viscosity of 1 wt % aqueous
solution (mPa s [[mPa s]]) 1840 Powder brightness (%) 71.1
[0085] Details of the procedures used for viscosity and brightness
measurements of CMC can be found in Example 4.
[0086] EXAMPLE 2
Production of Specialty Cellulose Pulp and Subsequent
Carboxymethylation without the Inventive Treatment (Comparative
Example)
[0087] In this example, exactly the same processing conditions as
described in Example 1 (within the repeatability limits for an
industrial scale process) were used in the stages E.sub.0, D.sub.0,
P.sub.0 and D.sub.1. However, no inventive treatment stage was
applied in the form of the addition of sodium borohydride or any
other agent capable of reducing carbonyl groups at stage B. In this
comparative Example 2, an oxidative bleaching stage using hydrogen
peroxide (P.sub.1) was directly substituted for the inventive stage
B that had been applied in Example 1. Therefore, in this case, the
pulp bleaching process consisted of five distinct, industrial scale
stages, working continuously and in series. Details of the
conditions inside each of the five towers and the bleaching and
extraction chemical dosages used in this example of the invention
can be found in Table 4. TABLE-US-00004 TABLE 4 Details of the
conditions inside the towers at each stage of processing in Example
2. Treatment stage Parameter Units Level E.sub.0 NaOH Kg/ton pulp
(dry) 58 Temperature .degree. C. 95 Residence time Minutes 134.
Consistency % 11.5 Borol Solution .RTM. Kg/ton pulp (dry) 5.
D.sub.0 pH -- 1.9 Temperature .degree. C. 15 Residence time Minutes
43 Consistency % 3.5 ClO.sub.2 Kg/ton pulp (dry) 8.9 P.sub.0 pH --
11 Temperature .degree. C. 35 Residence time Minutes 126
Consistency % 10 H.sub.2O.sub.2 Kg/ton pulp (dry) 2 D.sub.1 pH --
2.5 Temperature .degree. C. 45 Residence time Minutes 148
Consistency % 10 ClO.sub.2 Kg/ton pulp (dry) 10 P.sub.1 pH -- 11.6
Temperature .degree. C. 29 Residence time Minutes 163 Consistency %
10 H.sub.2O.sub.2 Kg/ton pulp (dry) 2.5
[0088] The stage P.sub.1, being the 5.sup.th treatment stage during
the bleaching of the specialty cellulose pulp in this example, was
a hydrogen peroxide treatment. The chemical reactor (bleach tower)
used for this treatment was the same tower used as stage B in
Example 1. Prior to entering the P.sub.1 tower, the pulp was washed
with deionized water over a filter and 2.5 kg/ton pulp (dry basis)
was then dosed simultaneous to the pH of the slurry being adjusted
to 11.8 using sodium hydroxide. Immediately prior to the slurry
entering the P.sub.1 tower, its consistency was 10%. In the P.sub.1
tower, the temperature was maintained at 29.degree. C. The
residence time of the pulp slurry in the P.sub.1 tower was 163
minutes.
[0089] The properties of the finished specialty cellulose product
can be found in Table 5. TABLE-US-00005 TABLE 5 Selected properties
of specialty cellulose pulp produced according to Example 2.
Brightness (ISO 2470-1999) (%) 85.80 Limiting viscosity number
(SCAN-CM 15:99) (ml/g) 1574 S18 (SCAN-C2:61) (alkali solubility of
pulp; in %) 7.00
[0090] A 50 g sample of the specialty cellulose pulp manufactured
using the treatment described above and with properties as found in
Table 5 was subjected to etherification to sodium carboxymethyl
cellulose (CMC).
[0091] The aforementioned specialty cellulose pulp sample was first
ground using a knife mill (Fritsch pulvarisette 19). The resultant
specialty cellulose pulp powder had a mean particle size of 200
.quadrature.m as measured by a Coulter LS 200 particle analyzer. 35
g of powder (weighed on a dry basis) was subsequently etherified to
carboxymethyl cellulose according to the carboxymethylation
procedure described in Example 4. Relevant properties of the
resultant carboxymethyl cellulose product were measured, and their
values are found in Table 6. TABLE-US-00006 TABLE 6 Selected
properties of CMC made from specialty cellulose pulp produced as
per Example 2. The degree of substitution of the CMC was 1.05.
Viscosity of 1 wt % aqueous solution (mPa s [[mpa s]]) 1530 Powder
brightness (%) 70.6
[0092] A comparison of the 1 wt % solution viscosity of the CMC
obtained from specialty cellulose pulp obtained from Example 1
(Table 3) with that from Example 2 (Table 6), reveals a
substantially superior CMC viscosity of the CMC derived from pulp
from Example 1 (20% higher). This is despite the limiting viscosity
number of the pulp from Example 1 being 42 units lower than the
pulp from Example 2.
[0093] Furthermore, despite the ISO pulp brightness of the
specialty cellulose pulp from Example 1 being 3 units lower than
the pulp from Example 2, the CMC powder brightness is of the same
magnitude. These improvements in CMC viscosity per unit pulp
viscosity, and CMC brightness per unit pulp brightness, are
indicative of the effect of the inventive treatment disclosed
here.
[0094] Details of the procedures used for viscosity and brightness
measurements of CMC can be found in Examples 5 and 6.
EXAMPLE 3
Post-bleaching Processing of Specialty Cellulose Pulp using the
Inventive Treatment and Subsequent Carboxymethylation
[0095] In this example, a 50 g sample of the specialty cellulose
pulp manufactured using the treatment described in Example 2 and
with properties as found in Table 4 was treated as per an
embodiment of the inventive treatment.
[0096] The 50 g pulp sample was partitioned into two equal halves
of 25 g each. These samples were separately wet and torn into
strips in 2.5 L of deionized water. The pulp suspension was then
homogenized using a desintegrator (a steel rotor blade of 6 cm
diameter rotating at 600 RPM for 30 seconds). Both pulp suspensions
were transferred into the same sealable plastic container. Into the
pulp suspension was added 0.233 g of Borol Solution.RTM., amounting
to 5 kg of Borol Solution.RTM./ton pulp (dry basis), or 15.9 gmoles
of sodium borohydride per ton pulp (dry basis). The pH was then
adjusted to 11.2 using sodium hydroxide.
[0097] The container containing the pulp suspension was sealed and
shaken, and set in a water bath at a temperature of 55.degree. C.
for 180 minutes. The pulp suspension was then washed twice with 5 l
of deionized water and dried to a moisture content of 7%. The
limiting viscosity number and the ISO brightness of the pulp
following the inventive treatment were found to be unchanged from
those of the pulp prior to applying the inventive treatment. The
pulp properties are therefore the ones found in Table 5.
[0098] This specialty cellulose pulp sample was then ground using a
knife mill (Fritsch pulvarisette 19). The resultant specialty
cellulose pulp powder had a mean particle size of 200 .mu.m as
measured by a Coulter LS 200 particle analyzer. 35 g of powder
(weighed on a dry basis) was subsequently etherified to
carboxymethyl cellulose according to the carboxymethylation
procedure described in Example 4. Relevant properties of the
resultant carboxymethyl cellulose product were measured, and their
values are found in Table 7. TABLE-US-00007 TABLE 7 Selected
properties of CMC made from specialty cellulose pulp produced as
per Example 7. The degree of substitution of the CMC was 1.05.
Viscosity of 1 wt % aqueous solution (mPa s [[mpa s]]) 1870 Powder
brightness (%) 75.6
[0099] A comparison of the 1 wt % solution viscosity of the CMC
obtained from specialty cellulose pulp obtained from Example 3
(Table 7) with that from Example 2 (Table 6), reveals a
substantially superior CMC viscosity of the CMC derived from pulp
from Example 2 (22% higher). This is despite having the same
limiting viscosity number of the pulp.
[0100] Furthermore, the CMC powder brightness of the CMC obtained
from specialty cellulose pulp obtained from Example 3 is 5 units,
or 7%, higher than the CMC from example 2. This is despite the two
pulps having the same ISO brightness values. These improvements in
CMC viscosity per unit pulp viscosity, and CMC brightness per unit
pulp ISO brightness, are indicative of the effect of the inventive
treatment disclosed here.
EXAMPLE 4
Carboxymethylation Procedure (as used in Examples 1 through 3)
[0101] Chemicals: Specialty Cellulose pulp, treated as per
invention (Borregaard ChemCell, Sarpsborg, Norway); iso-propanol
(87 wt-% in H.sub.2O and 100 wt-%, .rho..sub.iso=0.780 g
ml.sup.-1); N.sub.2 (g); sodium hydroxide (s); sodium
monochloroacetate, 99% pure (s); acetic acid; phenolphthalein;
methanol (70 wt-%, .rho..sub.meth=0.891 g ml.sup.-1); silver
nitrate solution (0.1 M); deionized water. [0102] Equipment:
Refrigerator; analytical balance accurate to 1/100.sup.th of gram;
Parr-reactor complete with stirring (cooled), external
heating-element, internal cooling element, N.sub.2 feed and
temperature control; knife mill (Fritsch Pulverisette 19);
measuring cylinders (100 ml, 500 ml); glass beaker; plastic beakers
(100 ml, 2 liter); graduated pipette (2-10 ml); glass mixing rod;
vacuum flask; ceramic vacuum funnel; black band filter paper; watch
glass (25 cm diameter); vacuum dryer.
[0103] The purpose of this example is to illustrate the process
leading from the specialty cellulose pulp according to the
invention to the derivative end product, in this case an etherified
derivative. However, any other derivatization would be conceivable
in this context, in particular any process of esterification.
[0104] 35 g (dry basis) of specialty cellulose pulp ground in the
knife mill was introduced into the Parr-reactor. Immediately
following this, precooled (5.degree. C.) iso-propanol solution (448
ml 100% iso-propanol+40.7 ml deionized water) was then poured into
the reactor. The heating jacket was fixed in place and the reactor
sealed. The stirrer arm and its cooler were then connected. The
nitrogen gas feed was turned on and the flow-rate regulated to 100
m/min. The cooling water feeding both the stirrer and reactor
cooling coil was turned on.
[0105] Stirring was set to 250 rpm and the temperature controller
program (0.degree. C. for 15 mins; 5.degree. C. per min for 2 mins
to 10.degree. C. for 60 mins; 1.degree. C. per minute for 50 mins
to 60.degree. C. for 60 minutes; 5.degree. C. per minute for 6 mins
to 20.degree. C. for 30 mins) was initiated.
[0106] After 15 minutes at 0.degree. C., 22.0 g NaOH
(NaOH-to-cellulose molar ratio is 2.5) in 20.4 ml deionized water
was introduced to the reactor. This is done rapidly to avoid oxygen
entering the reactor. Immediately afterwards, 78 ml iso-propanol
(100%) was rapidly introduced. The stirring speed was then
increased to 500 rpm for a few seconds to attain a uniform mixture
then decreased again to 250 rpm and the reactor was left for 60
minutes at 10.degree. C.
[0107] 51.3 g sodium monochloroacetate (MCA) (MCA-to-cellulose
molar ratio is 2.0) was mixed with 44 ml of iso-propanol (87%) and
rapidly introduced to the reactor. The remaining, undissolved MCA
residue was washed into the reactor with a further 44 ml of 87%
iso-propanol. The stirring speed was then set at 500 rpm for a few
seconds, then set back to 250 rpm. The temperature program then
ensured the reactor contents were heated to 60.degree. C. over 50
minutes and remained at this temperature for 60 minutes. The total
reaction time (with MCA) was therefore 120 minutes.
[0108] At the completion of 60 minutes at 60.degree. C., the
reactor contents were neutralised (phenolphthalein indicator) using
an acetic acid solution (5 g acetic acid in 10 ml 87%
iso-propanol). The reactor contents were vacuum-filtered and the
product was first washed with 700 ml of iso-propanol (87%), then
four times with 700 ml of methanol (70%). After the 5.sup.th and
final wash, the filtrate methanol was checked for being chloride
free using a few drops of AgNO.sub.3. No precipitation of AgCl was
observed meaning the product was sufficiently chloride free.
[0109] The washed product was dried in a vacuum drying cabinet at
60.degree. C. overnight. The product was weighed to 1/100.sup.th of
a gram and its moisture content determined. The product was then
ground to a powder of mean particle size of 119 .mu.m and a
particle size distribution as shown in FIG. 1, in the knife
mill.
EXAMPLE 5
Procedure for Measurement of the Viscositv of a CMC Solution.
[0110] 2.00 g of CMC powder (dry basis) was dissolved in 200 ml of
deionized water using a mechanical stirrer arm rotating at 200 rpm
over the course of I hour at room temperature. The 1 wt % CMC
solution was then transferred to a constant temperature water bath
set at 20.degree. C.
[0111] An Anton Paar Physica UDS 200 was used to perform the
viscosity measurement. The temperature bath on the instrument was
first set to 20.degree. C., and the spindle (MK 25/8) was mounted.
The measurement program was initiated and 5.5 ml of 1 wt % CMC
solution is placed in the receptor below the spindle. The spindle
was set in the "measuring position" and surplus sample was removed.
Measurement was initiated and the dynamic viscosity in mPas was
read as that reported from the machine measurement at a shear rate
of 11.3 s.sup.-1 as the spindle is on the way up.
EXAMPLE 6
Procedure for Measurement of the Brightness of a CMC Powder
[0112] CMC powder was placed into a stainless steel receptor fitted
with a threaded press and a glass plate that ensured a pressed,
smooth powder surface. After the CMC powder was placed on the glass
plate, the press was screwed into place, and the device was turned
upside down and disassembled. The powder then lay on the circular
glass plate with the smoothed powder surface facing upwards. The
plate and powder sample was then placed in a Minolta CM-3630
apparatus, and the CMC powder brightness read at a wavelength of
457 nm. Each sample was prepared twice and the average of
brightness readings is reported.
[0113] It should be noted that in order to obtain complete
reproducibility of this procedure, any CMC powder analyzed must
have the same or a very similar mean particle size and a particle
size distribution as that described in FIG. 3. FIG. 3 shows a
typical particle size distribution of a CMC powder after grinding
in the Fritsch Pulvarisette 19 knife mill as used in Examples 1, 2
and 3. The horizontal x-axis represents the particle diameter in
.mu.m while the vertical y-axis represents the volume of the
corresponding particles in %.
* * * * *