U.S. patent application number 14/428377 was filed with the patent office on 2015-08-13 for method of producing dissolving pulp, dissolving pulp and use of method.
The applicant listed for this patent is Teknologian Tutkimuskeskus VTT Oy. Invention is credited to Sari Asikainen, Ali Harlin, Marjo Maattanen, Eino Sivonen, Kyosti Valta.
Application Number | 20150225901 14/428377 |
Document ID | / |
Family ID | 50277690 |
Filed Date | 2015-08-13 |
United States Patent
Application |
20150225901 |
Kind Code |
A1 |
Asikainen; Sari ; et
al. |
August 13, 2015 |
Method of producing dissolving pulp, dissolving pulp and use of
method
Abstract
A method of producing dissolving pulp from a recycled fibrous
feedstock. The method comprises providing a fibrous material
comprising cellulose, lignin and hemicellulose, said fibre source
further having a lignin content of 0.1 to 7% lignin and an ash
content of up to 3%; subjecting the fibrous material to an alkaline
extraction at a temperature of about 0 to 25.degree. C., to produce
fibres having a reduced content of hemicellulose; subjecting the
fibres thus obtained to a bleaching treatment carried out with
oxidative chemical reagents in order to reduce the lignin content
of the fibres; and recovering the fibres thus obtained. By means of
the method, dissolving pulp can be produced from recycled paper and
cardboard products.
Inventors: |
Asikainen; Sari; (Espoo,
FI) ; Maattanen; Marjo; (Espoo, FI) ; Harlin;
Ali; (Espoo, FI) ; Valta; Kyosti; (Espoo,
FI) ; Sivonen; Eino; (Espoo, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Teknologian Tutkimuskeskus VTT Oy |
Espoo |
|
FI |
|
|
Family ID: |
50277690 |
Appl. No.: |
14/428377 |
Filed: |
September 16, 2013 |
PCT Filed: |
September 16, 2013 |
PCT NO: |
PCT/FI2013/050892 |
371 Date: |
March 16, 2015 |
Current U.S.
Class: |
162/9 ;
162/14 |
Current CPC
Class: |
D21C 9/153 20130101;
D21C 11/0007 20130101; D21C 5/005 20130101; D21C 9/002 20130101;
Y02W 30/64 20150501; D21C 9/163 20130101; D21C 5/025 20130101; Y02W
30/648 20150501; D21C 3/02 20130101; D21H 11/14 20130101; D21H
21/32 20130101; D21C 9/12 20130101; D21C 9/14 20130101; D21C 9/166
20130101; D21C 9/16 20130101; D21C 5/02 20130101; D21H 11/20
20130101 |
International
Class: |
D21H 21/32 20060101
D21H021/32; D21C 11/00 20060101 D21C011/00; D21C 9/00 20060101
D21C009/00; D21H 11/14 20060101 D21H011/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2012 |
FI |
20125953 |
Claims
1. A method of producing dissolving pulp from a recycled fibrous
feedstock, comprising the steps of providing a fibrous material
comprising cellulose, lignin and hemicellulose, said fibre source
further having a lignin content of 0.1 to 7% lignin and an ash
content of up to 3%; subjecting the fibrous material to an alkaline
extraction at a temperature of about 0 to 25.degree. C., to produce
fibres having a reduced content of hemicellulose; subjecting the
fibres thus obtained to a bleaching treatment carried out with
oxidative chemical reagents in order to reduce the lignin content
of the fibres; and recovering the fibres thus obtained.
2. The method according to claim 1, wherein the recycled fibrous
feedstock is selected from recycled paper and recycled cardboard
products and combinations thereof which comprise at least 1% by
weight of lignocellulosic fibre materials.
3. The method according to claim 1, wherein the fibrous material
comprises the recycled fibrous feedstock or is produced
therefrom.
4. The method according to claim 1, wherein the fibrous material
comprises at least 50% by weight of cellulosic fibres.
5. The method according to claim 1, wherein the fibrous material
comprises 50 to 95% by weight of fibres of chemical pulping and 5
to 50% by weight of fibres of mechanical pulping.
6. The method according to claim 1, wherein the cellulosic fibres
are derived from deciduous tree, coniferous tree or combinations
thereof.
7. The method according to claim 1, wherein the fibres recovered
after bleaching are subjected to a chemical treatment for
increasing accessibility of the cellulosic fibres.
8. The method according to claim 1, wherein the recovered fibres
are subjected in an aqueous slurry to acid treatment, whereby the
pH of the slurry is less than 3.5.
9. The method according to claim 1, wherein the fibrous feedstock
comprises recycled paper or recycled cardboard products or
combinations thereof having an original ash content of up to 10% or
more, which have been subjected to a mechanical or chemical
operation for reducing the ash content to less than about 3, in
order to provide said fibrous material.
10. The method according to claim 1, wherein the fibrous feedstock
comprises recycled paper or recycled cardboard products or
combinations thereof having an original lignin content of up to 20%
by weight, which have been subjected to chemical delignification
with an alkaline cooking chemical for reducing the lignin content
to less than 10% by weight in order to provide said fibrous
material.
11. The method according to claim 10, wherein the delignification
is carried out by kraft pulping, soda pulping or oxygen
delignification.
12. The method according to claim 1, wherein said bleaching is
carried out with oxidative chemicals selected from the group of
peroxides and peracids, chlorine dioxide, hypochlorite and ozone
and combinations thereof.
13. The method according to claim 1, wherein the recycled papers
are selected from office papers, and the recycled cardboard
products are selected from liner clippings.
14. The method according to claim 1, wherein the fibres recovered
exhibit at least one of the following properties: a lignin content
of less than 0.7% by weight; a viscosity of 250 ml/g or more; a
Fock value of 55% or better; cellulose 90% or more; and a R18%
value of 88% or better
15. The method according to claim 1, wherein the fibres recovered
exhibit a hemicellulose content of 0.1 up to 10% by weight.
16. A dissolving pulp produced by a method according to the steps
of: providing a fibrous material comprising cellulose lignin and
hemicellulose, fibre source further having a lignin content of 0.1
to 7% lignin and an ash content of up to 3%; subjecting the fibrous
material to an alkaline extraction at a temperature of about 0 to
25.degree. C., to produce fibres having a reduced content of
hemicellulose; subjecting the fibres thus obtained to a bleaching
treatment carried out with oxidative chemical reagents in order to
reduce the content of the fibres; and recovering the fibres thus
obtained.
17. (canceled)
18. (canceled)
19. (canceled)
Description
[0001] The present invention relates to dissolving pulps. In
particular the invention concerns a method of producing dissolving
pulps according to the preamble of claim 1.
[0002] In a method of the present kind, a cellulosic feedstock is
subjected, optionally after a pretreatment step which comprises
reducing the content of lignin or hemicelluloses or both, to cold
alkaline extraction.
[0003] The present invention also relates to uses of the
method.
[0004] The demand for dissolving pulps has increased during the
recent years. In particular, dissolving pulps are much sought for
as raw-material for special fibres, and since the demand has
surpassed the supply, the price of suitable dissolving pulp stocks
has soared. At the same time, the supply of competing
raw-materials, such as cotton, has been limited.
[0005] Typically dissolving pulps are produced directly from wood
raw-materials by suitable cooking methods which are particularly
tailored for making dissolving pulps. There are also disclosed in
literature various approaches for converting industrial paper pulps
into dissolving pulp, e.g. extraction with alkaline agents and
optionally enzymatic treatments with hemicellulases to remove
hemicelluloses, such as xylan, from the pulps. In this respect
reference is made to Hyatt, J., Fengel, R., Edgar, J. &
Alvarez, M., Process for the co-production of dissolving-grade pulp
and xylan and International Patent Application No. WO 9816682.
[0006] U.S. Pat. No. 6,254,722 discloses a method of producing
dissolving pulps from cellulosic fibers, more particularly from
recycled waste paper formed by envelope clippings and ledger
papers, wherein the fibre source is subjected to an extraction with
aqueous sodium hydroxide in order to remove or degrade
hemicelluloses at a temperature of about 23.degree. C.
[0007] Thus, the method is based on a specific kind of cellulosic,
in practice lignin-free raw-material which is not particularly
abundant.
[0008] WO 2010/104458 is directed to a process for combining the
production of cellulosic fiber products from virgin lignocellulosic
fibres such as wood and straw in a kraft, sulfite or soda AQ pulp
mill with a process for dissolving cellulose using a new solvent
system wherein at least a part of the spent cellulose solvent
chemicals are recovered in one or more unit operations in the pulp
mill chemical recovery cycle.
[0009] EP 0 637 351 discloses the preparation of a variety of
wood-free and white paper products from recyclable paper and card
products having low lignin content.
[0010] It is an aim of the present invention, to provide dissolving
pulps from recycled cellulosic fibres which are available in large
volumes and which form an inexpensive feedstock.
[0011] In particular it is an aim of the present invention to
provide dissolving pulps from recycled cellulosic fibres that are
already degraded in terms of mechanical properties and that
typically contain difficult to remove compounds and dirt.
[0012] The present invention is based on the concept of using as a
cellulosic feedstock for the production of dissolving pulps or
similar fibrous products, which are capable of being subjected to
dissolution with dissolving reagents, recycled or circulated papers
or cardboards which contain cellulose, lignin and hemicelluloses.
The recycled or circulated papers or cardboards may also contain
fillers, metals, fines and other impurities. Such a feedstock is
modified, if necessary, to provide a fibrous raw-material having a
low to modest lignin content and a low ash content. The fibrous
raw-material is then subjected to cold alkaline extraction to
reduce hemicelluloses concentration, and to a bleaching treatment
with an oxidative chemical reagent to reduce lignin content, and
the fibrous material thus obtained is recovered as pulp.
[0013] The method can be used for preparing pulp for the production
of regenerated cellulosic fibres, films and foams, impregnated
fiber products, and for the production of cellulosic derivatives,
and for the production of nanocellulosic products. Particularly
interesting applications are in the field of production of
regenerated cellulosic products by the viscose process, NMMO
process, enzymatic processes and the carbamate process.
[0014] More specifically, the method of the present invention in
mainly characterized by what is stated in the characterizing
portion of claim 1.
[0015] The uses according to the present invention are
characterized by what is stated in claims 17 to 19.
[0016] Considerable advantages are obtained by the present
invention. Thus, is has been found that recycled fibres for paper
and cardboard products serve well as raw-material for dissolving
pulps. Based on results obtained, dissolving pulps produced by the
present technology have properties comparable with or even superior
to the commercial reference pulps used for reference. For example
recycled fluting pulp gave dissolving pulps having excellent
properties in terms of the Fock value and could be used for
producing regenerated fibres, as evidenced by excessive spinning
testing, and films.
[0017] Also uncoated fines papers (office papers) were useful and
gave good results when the pulp was dissolved using dissolution
chemicals such as carbamic acid.
[0018] The present invention which utilizes recycled fibers for
preparing dissolving pulps represents an important step toward a
more sustainable and non-polluting textile industry.
[0019] The present invention provides for the manufacture for other
products than e.g. paper, cardboard and similar traditional
products which are prepared from the instant raw-materials. The
cellulose material of the used fibres can be recovered and
subjected to chemical modification to provide cellulose chemicals
or regenerated fibre. These targets place high demands on the
quality of the cellulose.
[0020] In the present invention, recycled fibres which exhibit
mechanical properties which are weakened and which typically
contain substances and impurities and dirt which are difficult to
remove. Conventionally, dispersion of recycled fibres aims at
decomposing printing ink and sticky compounds and other impurities
to smaller compounds and to remove them from the fibres to allow
for removal from the fibrous pulp at a later stage. These kinds of
conventional processing steps are not sufficient to provide fibres
suitable for the above mentioned aims, such as dissolving pulp.
[0021] Next the invention will be examined in more detail with
reference to a number of working examples.
[0022] In the attached drawings,
[0023] FIG. 1 shows the process scheme for an embodiment of a
method of preparing dissolving pulp from deinked fine paper
according to the present technology;
[0024] FIG. 2 shows the corresponding process scheme for an
embodiment of a method, according to the present technology, of
preparing dissolving pulp from cardboard; and
[0025] FIG. 3 shows schematically a spinning line consisting of
three godet rolls, one stretching bath with hot demineralised
water, two washing baths with cold demineralised water and a fibre
collector.
[0026] As discussed above, the present method of producing
dissolving pulp from a recycled fibrous feedstock, comprises in
combination the following steps: [0027] providing a fibrous
material comprising cellulose, lignin and hemicellulose, said fibre
source further having a lignin content of 0.1 to 7% lignin and an
ash content of up to 3%; [0028] subjecting the fibrous material to
an alkaline extraction at a temperature of about 0 to 25.degree.
C., to produce fibres having a reduced content of hemicellulose;
[0029] subjecting the fibres thus obtained to a bleaching treatment
carried out with oxidative chemical reagents in order to reduce the
lignin content of the fibres; and [0030] recovering the fibres thus
obtained.
[0031] In a preferred embodiment, the recycled fibrous feedstock is
selected from recycled paper and recycled cardboard products and
combinations thereof which comprise at least 1%, typically at least
5%, and in particular about 7 to 50%, by weight of lignocellulosic
fibre materials. Examples of suitable feedstock materials are the
following: office papers and other fine papers which typically are
uncoated, envelopes papers, single layered or multilayered
cardboards, fluting and liner sheets of corrugated boards, and
folding box boards. In a particular embodiment, the recycled papers
are selected from office papers, and the recycled cardboard
products are selected from liner clippings. As will be discussed
below, the recycled paper or cardboard product can be deinked in
conventional manner before further processing.
[0032] The fibrous material typically comprises at least 50% by
weight of cellulosic fibres. The fibres can consist of up to 100%
by weight of cellulose (woodfree) fibres. Typically, the fibres of
the fibrous material are formed by mixtures of fibres obtained from
chemical and mechanical pulping. In one embodiment, the fibrous
material comprises 50 to 95% by weight of fibres of chemical
pulping and 5 to 50% by weight of fibres of mechanical pulping. The
fibres of the mechanical pulping are generally rich in lignin, the
concentration of which may be up to 20% by weight of the dry
fibres.
[0033] The cellulosic fibres of the fibrous material can be derived
from deciduous tree, coniferous tree or combinations thereof.
Examples of deciduous tree species include birch, aspen and other
species of the Populus genus, alder, eucalyptus, mixed tropical
wood and mixtures of the above mentioned species. Examples of
coniferous tree species include spruce and pine and mixtures
thereof.
[0034] Preferably at the most 70%, in particular at the most 60%,
by weight of the fibre source consists of fibres derived from
deciduous tree.
[0035] In an embodiment, the fibrous material comprises the
recycled fibrous feedstock as such.
[0036] In a another embodiment, the fibrous feedstock comprises
recycled paper or recycled cardboard products or combinations
thereof having an original ash content of up to 10% or more, for
example up to 20%, which have been subjected to pretreatment for
reducing the ash content to less than about 3, in order to provide
said fibrous material. In such an embodiment, the feedstock can be
subjected to a mechanical or chemical operation, for example by
fine classification or sieving, to lower the content from about 10
to 20% to 3% or less.
[0037] In still another embodiment, which can be combined with the
previous one, the fibrous feedstock comprises recycled paper or
recycled cardboard products or combinations thereof having an
original lignin content of up to 20% by weight, which is subjected
to chemical delignification for reducing the lignin content to less
than 10% by weight, in particular less than 5% by weight, in order
to provide said fibrous material.
[0038] The pre-processing can be effected for example by an
alkaline treatment using hydroxide or carbonate compounds, such as
alkali metal or earth alkaline metal hydroxides or carbonates or
combinations thereof. In particular, the delignification can be
carried out by kraft pulping, soda pulping typically or oxygen
delignification, preferably at an increased temperature (of
50-200.degree. C.). The kraft pulping or soda pulping are typically
carried out about 140-180.degree. C. and the oxygen delignification
at 80-120.degree. C.
[0039] During the alkaline conditions of the pre-treatment, also
the hemicelluloses content will be reduced.
[0040] In a third embodiment which can be combined with both of the
two earlier embodiments, the fibrous feedstock is first subjected
to a preliminary step involving removal of impurities, washing or,
in particular, deinking or pulping, for example for removing
polymer films or coatings. This embodiment is applicable to printed
matter made of paper and cardboard, alike.
[0041] Next, the fibrous material obtained, comprising the recycled
feedstock or comprising the recycled feedstock which has been
treated as explained above for reducing the ash and lignin content,
is subjected to alkaline extraction (cold alkali extraction).
[0042] Typically, the cold alkali treatment is carried out by
mixing the fibrous material with an alkali solution, for example
with a concentrated alkali solution, so as to obtain a mixture
containing from about 50 and up to 200 g/l, in particular 50 to 150
g/l of the alkali. The solution is allowed to be absorbed into the
fibrous material at a temperature of 0 to 40.degree. C., preferably
10-25.degree. C. The alkali dissolve hemicelluloses from the
fibrous material and the hemicellulose containing solution is
separated from the fibrous material and separately recovered.
[0043] The obtained fibrous mass can be used as such as a
dissolving pulp.
[0044] However it can also be subjected to a bleaching treatment
carried out with oxidative chemical reagents and subsequent
alkaline extraction in order to reduce the lignin content of the
fibres. Various bleaching treatment employing oxygen, peroxide and
peroxo acids, chlorine dioxide, hypochlorite and ozone can be
employed.
[0045] The fibres recovered after bleaching are subjected to a
chemical treatment for increasing accessibility of the cellulosic
fibres, which treatment is preferably carried out with an enzyme
selected from the group of endoglucanases, or with
hypochlorite.
[0046] In another embodiment, the recovered fibres, optionally
after a chemical treatment for increasing accessibility of the
cellulosic fibres, are subjected in an aqueous slurry to acid
treatment, whereby the pH of the slurry is less than 3.5.
[0047] Turning now to the drawings, FIG. 1 depicts a specific
embodiment of a method for preparing dissolving pulp from deinked
fine paper.
[0048] The first stage shown in the drawing is designated "Super
DDJ filtration". The aim of this stage is to remove inorganic
impurities (decreasing ash content) from the pulp. The second stage
is the cold caustic extraction stage (CCE). By this treatment,
hemicelluloses, especially xylan, are removed. The treatment of the
deinked fine paper is continued by three-stage bleaching sequence,
(DEpD) for removing residual lignin and to increase the pulp
brightness and purity. After bleaching, preparation is continued by
enzymatic treatment with endoglucanase (EG). The targets of this
stage are to increase the pulp reactivity and to adjust the
viscosity (or degree of polymerisation). The final, fifth step is
acid washing (A). The objective of this stage is the removal of
metals from the pulp.
[0049] FIG. 2 shows the treatment stages of cardboard.
[0050] The first stage of the preparation of dissolving pulp from
the cardboard is Super DDJ filtration. Just as in the embodiment of
FIG. 1, the aim of this stage is to remove inorganic impurities
(decreasing ash content). The second stage in the process is an
alkaline soda cooking. This stage removes lignin and
hemicelluloses. Processing is then continued with cold caustic
extraction stage (CCE). The objective of this stage is to remove
hemicelluloses, especially xylan. The treatment of cardboard is
continued by three-stage bleaching sequence, (DEpD) for removing
the residual lignin and to increase the pulp brightness and purity.
After bleaching, preparation is continued by enzymatic treatment
with endoglucanase (EG). The targets of this stage are to increase
the pulp reactivity and to adjust the viscosity (or polymerisation
degree). Finally, just as in the procedure of FIG. 1, the obtained
pulp is acid washed (A) in order to remove metals. Typically acid
wash is carried out at a pH of below 3.
[0051] As a result of a process according to the present invention,
fibres are recovered which exhibit at least one of the following
properties: [0052] a lignin content of less than 0.7% by weight, in
particular a lignin content of 0.3 to 0.6% by weight; [0053] a
viscosity of 250 ml/g or more, preferably 550 ml/g or more; [0054]
a Fock value of 55% or better; [0055] cellulose 90% or more; and
[0056] a R18% value of 88% or better
[0057] Typically, the fibres exhibit a hemicellulose content of 0.1
up to 10% by weight. A method as discussed above produces a
dissolving pulp which can be used in the production of regenerated
cellulosic fibres, films and foams, impregnated fiber products, and
for the production of cellulosic derivatives, and for the
production of nanocellulosic products.
[0058] Specifically, the pulp can be used for the production of
regenerated cellulosic products for example by regeneration
processes selected from the group of viscose process, NMMO process,
enzymatic processes and the carbamate process.
[0059] In a particular embodiment, the method and the pulp can be
used for the production of regenerated cellulosic products by
carbamate process of a mechanochemical solvent free dry technique.
In this respect reference is made in particular to the methods
disclosed in U.S. Pat. No. 7,662,953 and U.S. Pat. No. 8,066,903,
the contents of which is herewith incorporated by reference.
[0060] The following non-limiting examples illustrate the present
technology.
Materials and Analysis Methods
[0061] The fibre raw material used in Example 1 was deinked fine
paper and that in Example 2 was recycled cardboard. The detailed
fibre compositions of the raw materials are presented in Table 1.
The deinked fine paper had the following fibre composition: about
90% of wood free pulp fibres and 10% of wood containing pulp
fibres. In the recycled cardboard the composition ratio wood free
pulp fibres to wood containing pulp fibres was about 70:30.
TABLE-US-00001 TABLE 1 Fibre composition of recycled raw materials
wood free pulps wood containing pulps Bleached Softwood
Semichemical/ Mechanical/ hardwood (unbl.) CTMP CTMP
Softwood:Hardwood kraft, % kraft, % hardwood, % softwood, % ratio
Fine paper 62 30 2 6 36:64 Cardboard 26 41 (27) 33 -- 41:59
[0062] The chemical composition and other properties of the raw
materials used in the experiments are presented in Tables 2 and 3.
Due to the higher portion of wood containing pulp fibres in the
cardboard, it had higher lignin, extractives and cellulose content,
and lower brightness than the fine paper. The fine paper was
deinked and therefore it had lower ash content, and the pulp
brightness was higher.
TABLE-US-00002 TABLE 2 Chemical composition of recycled raw
materials Extrac- Gluco- Cellulose % Lignin % tives % Xylan %
mannan % Fine paper 76.6 2.4 0.2 15.9 4.9 Cardboard 57.6 16.6 5
14.5 6.3
TABLE-US-00003 TABLE 3 Properties of recycled raw materials Bright-
Kappa Viscosity Ash at Ash at ness % number % ml/g 525.degree. C. %
900.degree. C. % Fine paper 79.9 8.7 800 2.0 1.4 Cardboard 32.8
82.7 740 7.9 6.0
[0063] The properties of the raw materials and the produced pulps
in Example 1 and 2 were analysed using the methods described in
Table 4.
[0064] The polysaccharide composition, i.e. content of cellulose,
xylan and glucomannan, was calculated based on Janson's method
/1/.
[0065] In these calculations, the fine paper was supposed to
consist of 64% of chemical hardwood fibres (birch) and 36% of
chemical softwood fibres (pine).
[0066] The composition of the cardboard was supposed to be 59% of
chemical hardwood fibres and 41% of chemical softwood fibres.
[0067] R18 analysis was used to measure alkali resistance of the
pulp. It tells the amount of fibre material which does not dissolve
to 18% NaOH solution at room temperature during one hour.
[0068] The Fock method was used to describe the reactivity of
dissolving pulp /2/. In this method pulp is dissolved in an excess
of NaOH and CS.sub.2. Cellulose xanthate is formed and a certain
amount of the xanthate is thereafter regenerated. Finally the
cellulose yield was determined.
TABLE-US-00004 TABLE 4 Analysis methods used for raw materials and
produced pulps Fibre composition internal based on microscopy
Chemical composition: acetone extract SCAN-CM 49: 03 lignin TAPPI-T
222 om-02 modif carbohydrates SCAN-CM 71: 09 content of cellulose,
Based on Janson J., Analytik der xylan and glucomannan
Polysaccharide in Holz und Zellstoff, Faserforschung und
Textiltechnik 25, 1974, p. 375-382. Ash content: 525.degree. C. ISO
1762: 2001 900.degree. C. ISO 2144: 199 Brightness ISO 2470-1: 2009
from splitted sheet Kappa number ISO 302: 2004 Viscosity ISO 5351:
2010 Metal content wet combustion (the samples are dissolved in
nitric acid in a microwave oven before the analysis) + ICP-AES R18
ISO 699: 1982 Fock Based on Fock, W., Das Papier 13(3), p. 92-95,
(1959).
[0069] The produced dissolving pulps were dissolved using carbamate
treatment. After the carbamate treatment the wet spinning was
performed. Table 5 shows the methods used in analysing the
carbamated pulps and carbamate solutions. Table 6 shows the methods
used for analysing the wet spun fibres.
TABLE-US-00005 TABLE 5 Analysis method used for carbamated pulps
and carbamate solutions DP degree of polymerization the viscosity
is determined according to ISO 5351: 2010 to evaluate the DP on the
empirical basis (Gullichsen, J., Paulapuro, H, Papermaking Science
and technology, Fapet 2000/3/) Nitrogen content Kjeltek device
Degree of purity of by washing and by measuring the the carbamate
pulp content of residues Viscosity of the carbamate conventional
ball method (Sihtola, H. solution Paperi ja puu 44(1962): 5, pp.
295- 300/4/) and/or by a Brookfield viscometer Fibre residue of the
microscopically by using a subjective solution scale from 1 to 5 in
such a way that 1: clear solution with no fibres and %: turbid
solution containing a lot of whole fibres, fibre bundles and/or
gel-like structures
[0070] The wet spun fibres were tested as follows: The fibres were
conditioned at a relative humidity of 65 and temperature of
20.degree. C. for at least 24 h. The mechanical properties were
determined as an average of 20 measurements according to the ISO
1973 and ISO 5079 standards using a Vibroskop and Vibrodyn testing
machines (Lenzing AG). The tests included titre, tenacity,
elongation, Young's modulus at 1% elongation and work of rupture.
The rate of elongation was 20 mm min-1 and the gauge length 20
mm.
EXAMPLE 1
Preparation of Dissolving Pulp from Deinked Fine Paper
[0071] The treatment stages of the deinked fine paper are presented
in FIG. 1.
[0072] The first stage of the preparation of dissolving pulp from
deinked fine paper was Super DDJ filtration. The aim of this stage
was to remove inorganic impurities (decreasing ash content) from
the pulp. Raw material was diluted (about 0.5-1% consistency) and
filtrated using a tank with a 200-mesh wire and a mixer. This
procedure was repeated eight times. Ash content decreased from 2.0%
to 0.6%.
[0073] The second stage was cold caustic extraction stage (CCE).
The objective of this stage was the removal of hemicelluloses,
especially Xylan. Extraction stage was carried out at room
temperature using 70 g NaOH/l alkali concentration and 10%
consistency for one hour. After CCE stage pulp was washed five
times by diluting it to 5% consistency with cold deionised water
and dewatering it to about 15% consistency. After that the pulp was
diluted to 4% consistency and pH was adjusted to 7. The next day
the pulp was dewatered to 25-30% consistency.
[0074] The treatment of the deinked fine paper was continued by
three-stage bleaching sequence, (DEpD). The target of the bleaching
was to remove the residual lignin and to increase the pulp
brightness and purity. Bleaching conditions are shown in Table
6.
TABLE-US-00006 TABLE 6 Bleaching conditions for DEpD sequence D0 Ep
D1 ClO.sub.2 charge as act. Cl, % 1.5 1.0 NaOH charge, % 0.9 0.1
H.sub.2O.sub.2 charge, % 0.5 Reaction time, min 60 60 120
Temperature, .degree. C. 60 75 70 Consistency, % 9 10 9
[0075] In D-stages preheated pulp was added to the reactor first
and after that water and acid or alkali (for pH adjustment). After
mixing pH was measured, and chlorine dioxide was charged into the
reactor, and the cover of the reactor was closed immediately.
During the reaction time the pulp was mixed. After the reaction
time, final pH was measured from the pulp in the reaction
temperature. The residual chlorine content of the bleaching
filtrate was determined. The pulp was diluted and washed in a
standard way.
[0076] In hydrogen peroxide assisted alkaline extraction stage (Ep)
the pulp and most of water was heated to the reaction temperature
in a microwave oven and placed into the reactor. Alkali and
hydrogen peroxide with additional water was charged and the pulp
slurry was mixed and pH was measured. During the reaction time the
pulp slurry was mixed. After the reaction time, final pH was
measured from the pulp in the reaction temperature. The residual
hydrogen peroxide content of the bleaching filtrate was determined.
The pulp was diluted and washed in a standard way.
[0077] Washing between bleaching stages was always a standard
laboratory washing: Pulp was diluted to 5% consistency with
deionized water, which temperature was the same as that of the
preceding bleaching stage. After dewatering, the pulp was washed
two times with cold deionized water with amount equivalent to ten
times the absolutely dry pulp amount.
[0078] After the bleaching, preparation was continued by enzymatic
treatment with endoglucanase (EG). The targets of this stage were
to increase the pulp reactivity and to adjust the viscosity (or
degree of polymerisation). Enzyme charge was about 6 ml/kg. At
first the pulp and part of water were heated to the reaction
temperature in a microwave oven and placed into the reactor. Then
pH of the pulp was adjusted with sulphur acid to pH value of 5.
Enzyme was mixed with the rest of the preheated water and added
into reactor. Reaction conditions were as follows: 50.degree. C.,
9% consistency and 120 minutes. After the reaction time pulp was
washed with hot water (>85.degree. C.) by diluting pulp to 4%
consistency (retention time 10 minutes). After dewatering, the pulp
was washed two times with cold deionized water with amount
equivalent to ten times the absolutely dry pulp amount.
[0079] The next step was acid washing (A). The objective of this
stage was the removal of metals from the pulp. Acid wash was
carried out at pH 2.5, room temperature and in 2.5% consistency.
Sulphur acid was used for pH adjustment. The pulp was diluted and
washed in a standard way. The last preparation stage was drying of
the pulp. Drying was carried out over night in an oven having
temperature of about 40.degree. C.
[0080] Preparation procedure described above gave dissolving pulp,
which had alkali resistance of 93.9%, reactivity of (according to
Fock method) 62.9%, viscosity of 510 ml/g, xylan content of 4.8%,
lignin content of 0.2%, extractives content of 0.08% and ash
content of 0.04%. These properties are rather typical or even
better than those with commercial dissolving pulps. Only the pulp
reactivity was slightly lower and the xylan content higher. The
properties of the produced dissolving pulp are presented in Tables
7 and 8.
TABLE-US-00007 TABLE 7 Chemical composition of dissolving pulp
produced from deinked fine paper. Extrac- Gluco- Cellulose % Lignin
% tives % Xylan % mannan % Fine paper 90.4 0.2 0.08 4.8 4.3
TABLE-US-00008 TABLE 8 Properties of dissolving pulp produced from
deinked fine paper. Viscos- Ash at Ash at Bright- Kappa ity
525.degree. C. 900.degree. C. R18 Fock ness % number ml/g % % % %
Fine 87.1 0.9 510 0.05 0.04 93.8 62.9 paper
EXAMPLE 2
Preparation of Dissolving Pulp from Cardboard
[0081] The treatment stages of cardboard are presented in FIG.
2.
[0082] The first stage of the preparation of dissolving pulp from
the cardboard was Super DDJ filtration. The aim of this stage was
to remove inorganic impurities (decreasing ash content). Raw
material was diluted (about 0.5-1% consistency) and filtrated using
a tank with a 200-mesh wire and a mixer. This was repeated eight
times. Ash content decreased from 7.9% to 1.4%.
[0083] The second stage was alkaline soda cooking. The target of
this stage was the removal of lignin and hemicelluloses. Cooking
conditions were as follows: NaOH charge 20%, cooking temperature
165.degree. C., H factor 1000 and liquor to wood ratio 6. After
cooking stage pulp was washed and then the delignification was
continued with oxygen delignification stage. Process conditions
were as follows: 12% consistency, 100.degree. C. temperature, 4%
NaOH charge, 13.5 bar oxygen pressure and 95 minutes reaction time.
After the oxygen delignification the pulp was washed.
[0084] Processing was continued with cold caustic extraction stage
(CCE). The objective of this stage was to remove hemicelluloses,
especially Xylan. Extraction stage was carried out at room
temperature using 70 g NaOH/1 alkali concentration and 10%
consistency for one hour. After CCE stage the pulp was washed five
times by diluting it to 5% consistency with cold deionised water
and dewatering it to about 15% consistency. After that the pulp was
diluted to 4% consistency and pH was adjusted to 7. The next day
the pulp was dewatered to 25-30% consistency.
[0085] The treatment of card board was continued by three-stage
bleaching sequence, (DEpD). The target of the bleaching was to
remove the residual lignin and to increase the pulp brightness and
purity. Bleaching conditions are shown in Table 9.
TABLE-US-00009 TABLE 9 Bleaching conditions for DEpD sequence D0 Ep
D1 ClO.sub.2 charge as act. Cl, % 1.0 0.4 NaOH charge, % 0.9 0.05
H.sub.2O.sub.2 charge, % 0.5 Reaction time, min 60 60 120
Temperature, .degree. C. 60 75 70 Consistency, % 9 10 9
[0086] In D-stages preheated pulp was added to the reactor first
and after that water and acid or alkali (for pH adjustment). After
mixing pH was measured, and chlorine dioxide was charged into the
reactor, and the cover of the reactor was closed immediately.
During the reaction time the pulp was mixed. After the reaction
time, final pH was measured from the pulp in the reaction
temperature. The residual chlorine content of the bleaching
filtrate was determined. The pulp was diluted and washed in a
standard way.
[0087] In hydrogen peroxide assisted alkaline extraction stage (Ep)
the pulp and most of water was heated to the reaction temperature
in a microwave oven and placed into the reactor. Alkali and
hydrogen peroxide with additional water was charged and the pulp
slurry was mixed and pH was measured. During the reaction time the
pulp slurry was mixed. After the reaction time, final pH was
measured from the pulp in the reaction temperature. The residual
hydrogen peroxide content of the bleaching filtrate was determined.
The pulp was diluted and washed in a standard way.
[0088] Washing between bleaching stages was always a standard
laboratory washing: Pulp was diluted to 5% consistency with
deionized water, which temperature was the same as that of the
preceding bleaching stage. After dewatering, the pulp was washed
two times with cold deionized water with amount equivalent to ten
times the absolutely dry pulp amount.
[0089] After the bleaching, preparation was continued by enzymatic
treatment with endoglucanase (EG). The targets of this stage were
to increase the pulp reactivity and to adjust the viscosity (or
degree of polymerisation). Enzyme charge was about 6 ml/kg. At
first the pulp and part of water were heated to the reaction
temperature in a microwave oven and placed into the reactor. Then
pulp pH was adjusted with sulphur acid to 5. Enzyme was mixed with
the rest of the preheated water and added into reactor. Reaction
conditions were 50.degree. C., 9% consistency and 120 minutes.
After reaction time pulp was washed with hot water (>85.degree.
C.) by diluting pulp to 4% consistency (retention time 10 minutes).
After dewatering, the pulp was washed two times with cold deionized
water with amount equivalent to ten times the absolutely dry pulp
amount.
[0090] Next pulp was acid washed (A) in order to remove metals.
Acid wash was carried out at pH 2.5, room temperature and in 2.5%
consistency. Sulphur acid was used for pH adjustment. The pulp was
diluted and washed in a standard way. The last preparation stage
was drying of the pulp. Drying was carried out over night in an
oven having temperature about 40.degree. C.
[0091] Preparation procedure described above gave dissolving pulp,
which had alkali resistance of 90.7%, reactivity of (according to
Fock method) 81.1%, viscosity of 250 ml/g, xylan content of 4.2%,
lignin content of 0.6%, extractives content of <0.05% and ash
content of 0.11%. These properties are rather typical or even
better than those of commercial dissolving pulps. The xylan content
of the pulp was higher, and also the lignin content was slightly
higher than that of the commercial dissolving pulp (<0.5%). The
properties of the produced dissolving pulp are presented in Tables
10 and 11.
TABLE-US-00010 TABLE 10 Chemical composition of dissolving pulp
produced from cardboard Extrac- Gluco- Cellulose % Lignin % tives %
Xylan % mannan % Cardboard 91.2 0.6 <0.05 4.2 3.8
TABLE-US-00011 TABLE 11 Properties of dissolving pulp produced from
cardboard Viscos- Ash at Ash at Bright- Kappa ity 525.degree. C.
900.degree. C. R18 Fock ness % number ml/g % % % % Cardboard 85.9
0.6 250 0.11 0.08 90.7 81.1
EXAMPLE 3
Treatment of the Dissolving Pulps (Example 1 and 2) Using Carbamate
Method and Wet Spinning
Carbamate Treatment
[0092] The obtained dissolving pulps (Example 1 and 2) were treated
using carbamate method /5, 7/. In this method is first prepared
carbamate cellulose which is then dissolved in NaOH-solution which
is finally spinned and regenerated into fibres. The carbamation
synthesis is done in dry state with urea. The urea feed is 20%
calculated from dry pulp. Dissolving is performed in two steps,
first by moistening cellulose carbamate pulp with a dilute alkaline
solution, as cold as possible, to the pulp under intensive
stirring. The technique utilizes the low freezing point of the
aqueous NaOH solution at the concentration of 18%, wherein the
freezing point is below -20.degree. C., and the intensive stirring
function of the dissolve mixer device during the dosage. It is
possible to prepare solutions of high quality and having high dry
matter content in a mixing time of a few minutes only.
[0093] Table 12 indicates the characteristics of pulps after of the
carbamate reaction. DP (Degree of polymerization) gives an estimate
of the mechanical and physical properties of the final product
(e.g. fibres and films) and it is the main adjustable parameter in
the process. The higher the DP level, the more diluted solutions
must be used, if the level of viscosity is limited because of
application technique (here fiber spinning) The optimal DP level
and cellulose content must be found separately in each case.
Normally, on the manufacture of regenerated fibres, the desired DP
level is in the range from 200 to 400. N % the nitrogen content of
the solution indicates the degree of substitution. The degree of
substitution refers to the average number of substituent attached
to one glucose unit.
TABLE-US-00012 TABLE 12 Characteristics of pulps after carbamate
reaction Carbamated pulp grade DP N % Fine paper 289 1.5 Cardboard
290 2.2 ref commercial dissolving pulp 330 1.2
Wet Spinning
[0094] The fibres were spun using a laboratory wet spinning machine
/6/. The spin dope was pushed from a sealed reservoir to a gear
pump by nitrogen gas. The spinning head with one spinneret was
immersed in a vertical spin bath tank. The spinneret used had
100-250 orifices of 45-51 lm and was made of a gold/platinum
material. The spinning line consisted of three godet rolls, one
stretching bath with hot demineralised water, two washing baths
with cold demineralised water and a fibre collector (FIG. 3). A
solution of sodium lauryl sulphate (0.1%) was used to lubricate the
godet rolls I, II, III during spinning.
[0095] Table 13 shows the common processing and material parameters
for the laboratory wet spinning trials.
TABLE-US-00013 TABLE 13 Common processing and material parameters
of example spinning trials Cellulose concentration % 6.3 Solution
NaOH % 8.5 Solution ZnO % 1 Solution temperature C. 2 Spin bath
temperature C. 20 Spin bath content 8% H.sub.2SO.sub.4, 10%
Na.sub.2SO.sub.4 Solution ball viscosity s (T 20.degree. C.) 20
Solution turbidity NTU <50 Filtering sieve figure .mu.m 10
Spinneret n .times. d - .mu.m 100 .times. 51 Line speed VIII m/min
20
[0096] Table 14 shows the processing stretch ratio, fibre titre and
mechanical properties of the fibres obtained in wet spinning
TABLE-US-00014 TABLE 14 Processing stretch ratio, fibre titre, and
mechanical properties of example fibres Stretch Titre Tenacity Pulp
grade ratio % (dtex) (cN/dtex) Stretch % Fine paper 60 2.42 1.93 21
80 2.31 2.02 20 100 1.97 2.00 17 120 1.86 2.07 16 Cardboard 60 2.55
1.72 22 80 2.40 1.83 20 100 2.06 1.91 18 140 1.99 1.97 16 Ref
commercial dissolving pulp 60 2.58 1.98 21 80 2.10 2.01 18 100 1.97
2.14 15 Ref viscose/6/ 1.9 2.1
[0097] Summarizing the above, it can be noted that the process of
the present technology comprises in a preferred embodiment a stage
for removing inorganic impurities, a cold caustic extraction stage
for the xylan extraction, bleaching with oxidative chemicals for
delignification and to increase the pulp brightness and purity, a
stage to increase the reactivity of pulps and to adjust pulp
viscosity (or degree of polymerisation), and finally acid washing
for metals removal. For the raw material having high initial lignin
content additional delignification stages can be carried out using
alkaline delignification agents.
[0098] With the technology disclosed, including the above
purification procedure, dissolving pulps having alkali resistance
(R18) and cellulose content of over 90% and reactivity of 60 to
85%, in particular 63 to 81%, measured using Fock method, can be
prepared.
[0099] The dissolving pulps thus obtained have very good mechanical
properties. During testing it has been found that the tenacity of
fibers is approximately the same as for native dissolved reference
cellulose made from commercial dissolving pulp and approximately
the same as for existing commercial viscose nonwoven fibers.
"Approximately" stands for a variation of max..+-.10%.
[0100] A particular use for the dissolving pulps prepared from
recycled fibers is as a raw-material for the carbamate process.
[0101] As is apparent from the above, the present invention
achieves considerable advantages. It has surprisingly been found
that by means of the present invention recycled fibres, even
mechanically degraded and weakened fibres, selected from but not
limited to recycled or circulated papers or cardboards containing
cellulose, lignin and hemicelluloses, further containing fillers,
metals, fines and other impurities that are typically difficult to
remove, serve well as raw material for dissolving pulps. Based on
the examples given, dissolving pulps produced by the present
technology have properties comparable with or even superior to the
commercial reference pulps used for reference.
REFERENCES
[0102] 1. Janson J., Analytik der Polysaccharide in Holz und
Zellstoff, Faserforschung und Textiltechnik 25, 1974, p. 375-382.
[0103] 2. Fock, W. Eine modifizierte method zur Bestimmung der
Reaktivitat von Zellstoffen fur viskosherstellung. Das Papier
13(3), p. 92-95, (1959) [0104] 3. Gullichsen, J., Paulapuro, H,
Papermaking Science and Technology, Fapet 2000. [0105] 4. Sihtola,
H. Paperi ja puu 44(1962):5, pp. 295-300. [0106] 5. U.S. Pat. No.
8,066,903. [0107] 6. Vehvilainen, M., Kamppuri, T., Rom, M.,
Janicki, J., Ciecha ska, D., Gronqvist, S., Siika-aho, M., Elg
Christoffersson, K., Nousiainen, P. Effect of wet spinning
parameters on the properties of novel cellulosic fibres, Cellulose
(2008) 15:671-680. [0108] 7. U.S. Pat. No. 7,662,953 [0109] 8. U.S.
Pat. No. 6,254,722 [0110] 9. WO2010/104458 [0111] 10. European
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