Note: Descriptions are shown in the official language in which they were submitted.
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PRO~ FOR PREPliRING A LIGNO~T~T~T~O~-BASED PROD~CT, ~ID PROD~CT
OBT~T~RT.F BY ~l~LS PRO~,~
FIELD OF '1~ lN V I ~ lON
The present invention provides a process for producing a lignocel-
lulose-based product, e.g. paper, paperboard (such as cardboard
and linerboard), corrugated board and the like, from an ap-
propriate lignocellulosic starting material, such as vegetable
~ibres (e.g. vegetable fibres originating from wood, ~lax, cotton,
hemp, jute, bagasse, and the like). The use of the process of the
invention confers ~c~11ent strength on lignocellulose-based
products prepared thereby.
R~rRr~o~n AND BRIEF n~TPTION OF TR~ lNV~ lON
Lignocellulose-based products prepared from lignocellulosic
starting materials, including products manufactured starting from
vegetable ~ibre (e.g. wood fibre) prepared by mechanical (e.g.
thermomechanical) pulping procedures, mechanical/-chemical pulping
procedures (the latter often being denoted ''semi-chemicalll
procedures) or chemical pulping procedures (such as kraft, sulfite
or soda pulping), are indispensable everyday materials. Some of
the most familiar types of such products include paper for writing
or printing, cardboard and corrugated cardboard.
Virtually all grades of paper, cardboard and the like are produced
from aqueous pulp slurry. Typically, the pulp is suspended in
water, mixed with various additives and then passed to equipment
in which the paper, cardboard etc. is formed, pressed and dried.
Irrespective of whether mechanically produced pulp (hereafter
denoted "mechanical pulp"), semi-chemically produced pulp
(hereafter denoted "semi-chemical pulp"), unbleached chemical pulp
or pulp made from recycled fibres (i.e. pulp prepared from
recycled paper, rags and the like) is employed, it is often
necessary to add various strength~n;ng agents to the pulp in order
to obtain an end product having adequate strength properties. In
the case of paper and board for use in packaging and the like, the
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tensile strength and tear strength under dry and wet conditions
are of primary importance; moreover, notably in the case of
certain grades of cardboard (e.g. so-called unbleached board for
the manufacture of corrugated cardboard boxes for packaging,
S transport and the like), the compression strength of the material
is often also an important factor.
In the field of lignocellulose-based products, considerable effort
has been devoted in recent years to the development and
application of strengthPn;ng/binding agents or systems which are
more acceptable from an environm~nt~l and toxicity point of view
than those "traditionally" used. Relevant patent literature in
this respect includes the following:
EP 0 433 258 A1 discloses a procedure for the production of
mechanical pulp from a fibrous product using a chemical and/or
enzymatic treatment in which a "binding agent" is linked with the
lignin in the fibrous product via the formation of radicals on the
lignin part of the fibrous product. This document mentions
"hydrocarbonates", such as cationic starch, and/or proteins as
examples of suitable binding agents. As examples of suitable
enzymes are mentioned laccase, lignin peroxidase and manganese
peroxidase, and as examples of suitable chemical agents are
mentioned hydrogen peroxide with ferro ions, chlorine dioxide,
2~ ozone, and mixtures thereof.
EP 0 565 109 A1 discloses a method for achieving binding of
mechanically produced wood fragments via activation of the lignin
in the middle lamella of the wood cells by incubation with
phenol-oxidizing enzymes. The use of a separate binder is thus
avoided by this method.
US 4,432,921 describes a process for producing a binder for wood
products from a phenolic compound having phenolic groups, and the
process in ~uestion involves treating the phenolic compound with
enzymes to activate and oxidatively polymerize the phenolic
compound, thereby converting it into the binder. The only phenolic
compounds which are specifically mentioned in this document, or
CA 0223l8~8 l998-03-l2
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employed in the working examples given therein, are lignin
sulfonates, and a main purpose of the invention described in US
4,432,921 is the economic exploitation of so-called "sulfite spent
liquor~, which is a liquid waste product produced in large
S quantities through the operation of the sulfite process for the
production o~ chemical pulp, and which contains lignin sulfonates.
With respect to the use of lignin sulfonates - in particular in
the form of sul~ite spent liquor - as phenolic polymers in systems
or processes for strength~n;ng/binding wood products, the
following comments are appropriate:
(i) lignin sulfonates available on a co~m~rcial scale are
generally very impure and of very variable quality [see J.L.
Philippou, Journal of Wood ~h~m;stry and Technoloqy 1(2) (1981)
199-227];
(ii) the very dark colour of spent sulfite liquor renders it
unsuited as a source of lignin sulfonates for the production of,
e.g.j paper products (such as packaging paper, linerboard or
unbleached board for cardboard boxes and the like) having
acceptable colour properties.
The present inventors have surprisingly found that strength~n~
lignocellulose-based products (e.g. paper and paperboard) can be
manufactured by a procedure involving the use of a combination of
a polysaccharide which is substituted with at least substituents
containing a phenolic hydroxy group (in the following often simply
denoted a "phenolic polysaccharide"), an n~; ~i ~ing agent and an
enzyme capable of catalyzing the oxidation of phenolic groups by
the oxidizing agent, and that products produced in this m~nn~r
exhibit strength properties at least comparable to, and often sig-
nificantly better than, those achievable using previously known
processes.
It is appropriate to mention here that PCT application No.
PCT/DK95/00318 (unpublished at the priority date of the present
application; subse~uently published as W0 96/03546) discloses a
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process for the manufacture of a lignocellulose-based product from
a lignocellulosic material, the process comprising treating the
lignocellulosic material and a phenolic polysaccharide with an
enzyme capable of catalyzing the oxidation of phenolic groups, in
S the presence of an oxidizing agent.
It is stated in PCT/DK95/00318 that phenolic substituents in
phenolic polysaccharides suited for use in the context of the
invention described therein m.ay suitably be linked to the
polysaccharide species by ester linkages or ether linkages.
Types of phenolic polysaccharides mentioned in PCT/DK95/00318
include those in which the ph~nol ic substituent of the phenolic
polysaccharide is a substituent derived from a phenolic compound
which occurs in one of the following plant-biosynthetic pathways:
from p-coumaric acid to p-coumaryl alcohol, from p-coumaric acid
to coniferyl alcohol and from p-coumaric acid to sinapyl alcohol;
p-coumaric acid itself and the three mentioned "end products" of
the latter three biosynthetic pathways are also mentioned in this
respect. Disclosed examples of relevant ''intermediatell compounds
formed in these biosynthetic pathways are caffeic acid, ferulic
acid (i.e. 4-hydroxy-3-methoxyc;nn~m;c acid), 5-hydroxy-ferulic
acid and sinapic acid.
More specifically, PCT/DK95/00318 discloses the following types of
phenolic polysaccharides as being suitable in the context of the
invention described therein:
(a) phenolic arabinoxylans, phenolic heteroxylans and phenolic
pectins [such as arabinoxylans and pectins cont~;n;ng "ferulyl"
(i.e. 4-hydroxy-3-methoxycinnamyl) substituents attached via ester
linkages]; and
(b) certain phenolic starches (more specifically starches which
have been chemically modified by the introduction of acyl-type
substituents derived from hydroxy-substituted benzoic acids, such
as 2-, 3- or 4-hydroxybenzoic acid).
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s
DET~TT-Fn n~-C~TPTION OF I~IE lNV~~
r
The present invention thus provides a process ~or the manufacture
S o~ a~lignocellulose-based product ~rom a lignocellulosic material,
the process comprising treating (i) said lignocellulosic material
and (ii) a phenolic polysaccharide other than those speci~ically
disclosed in PCT/DK95/00318 (vide supra)
with (iii) an enzyme capable of catalyzing the oxidation o~
phenolic groups, in the presence of (iv) an o~;~;~ing agent (more
specifically an oxidizing agent appropriate for use with the
enzyme in question, in general an oxidizing agent which in
conjunction with the enzyme is capable o~ bringing about oxidation
of phenolic groups).
Enzymes of the type(s) employed in the process of the present
invention, i.e. enzymes capable of catalyzing the oxidation of
phenolic groups, are believed to lead to the ~ormation, in the
presence o~ an appropriate oxidizing agent, of radicals in the
aromatic moieties of phenolic substituents, such as the phpnolic
~unctionalities in phenolic polysaccharides and in the lignin part
o~ a lignocellulosic substrate.
In this connection, but without being limited to any speci~ic
theory, it is believed that a reaction of central importance in
the process o~ the invention is a reaction between phenolic
substituents (especially those on the lignocellulosic material and
the phenolic polysaccharide, respectively) which have been
"activated" by radical ~ormation as described above.
With reference to the above, the order of mixing/contacting the
~our components, i.e. the lignocellulosic material, the phenolic
polysaccharide, the enzyme and the oxidizing agent, is not
critical as long as the process set-up ensures that the
llactivated'l lignocellulosic material and the "activated" phenolic
polysaccharide are brought together in a way that enables them to
react in the desired m~nnP~ Thus, ~or example, the enzyme and the
oxidizing agent may be mixed with, or otherwise brought into
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contact with, the lignocellulosic material before or after being
mixed with the phenolic polysaccharide.
,~
In the manufacture of - in particular - paper, a technically very
satisfactory embodiment of the process of the invention involves
the continuous spraying of a solution of the phenolic
polysaccharide and a laccase [or another enzyme of the ~ e
type which catalyzes oxidation of phenolic groups by oxygen ( vide
infra) ] at ambient temperature (e.g. about 20-25~C) or a higher
temperature (e.g. a temperature in the vicinity of 40~C) onto a
thin layer of the moving lignocellulosic material (pulp) on the
papermaking machine, in the presence of atmospheric air as oxygen
source.
In some other embodiments of the process of the invention it may
be appropriate to incubate a reaction medium cont~i n; ng the
lignocellulosic material, ph~n~l iC polysaccharide and enzyme in
the presence of oxidizing agent for a period of at least a few
minutes. An incubation time in the range of from 1 minute to 10
hours will generally be suitable, although a period of from 1
minute to 2 hours is preferable.
As already indicated, the process of the invention is well suited
to the production of a variety of types of lignocellulose-based
products, e.g. various paper and paperboard products (such as
cardboard, linerboard and the like).
The lignocellulosic starting material employed in the method of
the invention can be in any appropriate form, e.g. in the form of
vegetable fibre (such as fibres from wood, flax, cotton, hemp,
bagasse, jute and the like), depending on the type of product to
be manufactured.
It will normally be appropriate to employ the lignocellulosic
material in question in an amount corresponding to a weight
percentage of dry lignocellulosic material [dry substance (DS)] in
the medium in the range of 0.1-90~.
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The temperature of the reaction mixture in the process of the
invention may suitably be in the range o~ 10-120~C, as ap-
propriate; however, a temperature in the range of 15-90~C is
generally to be preferred. As illustrated by the working examples
provided herein ( vide in~ra), the reactions involved in a process
of the invention may take place very satisfactorily at ambient
temperatures around 25~C.
Phenolic polysaccharides
As mentioned above, the phenolic polysaccharide employed in the
process of the present invention is a phenolic polysaccharide
other than those speci~ically disclosed in PCT/DK95/00318.
The ph~n~l iC su~stituent(s) in phenolic polysaccharides suited for
use in the context o~ the present invention may suitably be linked
to the polysaccharide species by, e.g., ester linkages or ether
linkages.
Particularly suitable phenolic polysaccharides are those which
exhibit good solubility in water, and thereby in aqueous media in
the context o~ the invention.
It should be noted that the term "polysaccharide" in the context
o~ the present invention refers not only polysaccharides per se,
but also to derivatives - often synthetic derivatives - thereof,
especially derivatives which exhibit greater water solubility than
the ~'parent" polysaccharide.
More speci~ically, some preferred types of phenolic polysac-
charides ~or use in the process o~ the present invention include
the following:
(A) Phenolic starches other than those specifically mentioned in
PCT/DK95/00381 (vide supra), i.e. other than those in which the
phenolic substituents are acyl-type substituents derived from 2-,
3- or 4-hydroxybenzoic acid; and phenolic starch derivatives (i.e.
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starch derivatives into which phenolic substituents have been
introduced by chemical or enzymatic means).
The "parent" starch from which a phenolic starch or phenolic
starch derivative employed in the context of the present invention
is derived may, for example, suitably be any of the commercially
available types of starch. These include starch from potato, corn
(maize), waxy corn (waxy maize), wheat, rice, sorghum, waxy
sorghum, sago, arrowroot and tapioca (cassava, manioc). Relevant
types of starch thus include both high-amylose starches (such as
starch from so-called "high-amylose corn") and high-amylopectin
starches (such as starch from waxy maize, waxy sorghum or
glutinous rice). Potato starch is a very suitable "parent" starch
in the context of the invention.
The starch derivative from which a phenolic starch derivative
employed in the context of the present invention is derived may,
for example, be a starch ester (e.g. a starch acetate) or an
hydroxyalkylstarch (e.g. an hydroxyethyl- or hydroxypropylstarch).
Particularly interesting starch derivatives are so-called
"cationic starches", such as those wherein the cationic
functionality is of the ~uaternary Ammo~;um type. Cationic
starches of the quaternary Ammnn; um type are themselves widely
used in the paper industry as so-called "wet-end additives~l for
illl~Lo~ingl inter alia, strength and drainage, and as binders in
coatings; one example of a comm~rcially available cationic starch
product of the quaternary Ammnn;um type is CerestarTM CC Bond,
available through Cerestar ScAn~inAvia A/S, Holte, Denmark.
Prelim;nAry experiments by the present inventors indicate that a
significant further improvement in the strength of paper products
(paper, cardboard, linerboard and the like) is obt~;nAhle when a
phenolic cationic starch is used in the preparation thereof in the
mAnnPr according to the present invention.
(B) Phenolic celluloses and phenolic cellulose derivatives (i.e.
celluloses and cellulose derivatives into which phenolic
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substituents have been introduced by chemical or enzymatic means).
Some examples of relevant phenolic celluloses are celluloses into
which have been introduced phenolic substituents of one or more of
the types disclosed in PCT/DK95/00381 and listed above (vide
5 supra), e.g. ferulyl substituents, or 2-, 3- or 4-hydroxybenzoyl
substituents.
Owing to the generally poor water-solubility of celluloses per se
and, in many cases, o~ ph~nol ic celluloses, it will normally be
preferable to employ phenolic cellulose derivatives which are
derived ~rom water-soluble cellulose derivatives. Thus, a
cellulose derivative ~rom which a phenolic cellulose derivative
employed in the context of the present invention is derived may,
~or example, suitably be an hydroxyalkylcellulose (e.g. an
hydroxyethyl- or hydroxypropylcellulose), or a carboxymethyl-
cellulose (CMC) or salt thereof (e.g. sodium salt, sometimes known
as carmellose sodium).
(C) Phenolic polysaccharides derived from polysaccharides of the
following types: pectins o~ non- chenopodiaceae origin (notably
pectins which do not naturally contain phenolic substituents, such
as citrus pectin); galacto~nn~n~ [such as guar gum or locust bean
gum (ceratonia)]; arabinogalactan (e.g. ~rom western larch
timber); dextrans; acacia gum (gum arabic); xanthan gum;
tragacanth gum; and carrageenan.
Preferred types of phenolic substituents in phenolic polysac-
charides employed in the context o~ the present invention include
benzyloxy (i.e. phenylmethoxy) groups having an hydroxy
substituent in the aromatic ring. Examples hereof are 2-, 3- and
4-hydroxybenzyloxy. The aromatic ring may optionally ~urther be
substituted with one or more other substituents, e.g. one or more
lower alkyl groups (such as methyl, ethyl, 1-propyl or 2-propyl),
one or more lower alkoxy groups (such as methoxy, ethoxy, 1-
propoxy or 2-propoxy) and/or one or more further hydroxy groups.
An example of a suitable alkoxy-substituted 4-hydroxybenzyloxy
substituent is 3,5-dimethoxy-4-hydroxybenzyloxy (also known as
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"syringyl").
4-Hydroxybenzyloxy and related substituents may be readily
introduced into, for example, starches by a simple and straigh-
tforward chemical procedure (vide infra) employing relatively mildreaction conditions.
The amount of ph~nQlic polysaccharide employed in the process of
the invention will generally be in the range of 0.01-20 weight per
cent (~w/w), typically 0.01-10 ~ w/w, based on the weight of
lignocellulosic material (calculated as dry lignocellulosic
material), and amounts in the range of about 0.02-6 ~ w/w (calcu-
lated in this m~nn~r) will often be very suitable.
~nzymes
In principle, any type of enzyme capable of catalyzing oxidation
of phenolic groups may be employed in the process of the
invention. Preferred enzymes are, however, oxidases [e.y. laccases
(EC 1.10.3.2'), catechol oxidases (EC 1.10.3.1) and bilirubin
oxidases (EC 1.3.3.5)] and peroxidases (EC 1.11.1.7). In some
cases it may be appropriate to employ two or more different
enzymes in the process of the invention.
Among types o~ oxidases (in combination with which oxygen - e.g.
atmospheric oxygen - is an excellent oxidizing agent), laccases
have proved to be well suited for use in the method of the
inventlon .
Laccases are obt~;n~hle from a variety of microbial sources,
notably bacteria and fungi (including filamentous fungi and
yeasts), and suitable examples of laccases include those
obt~;n~hle from strains of Aspergillus, Neurospora (e.g N.
crassa), Podospora, Botrytis, Collybia, Fomes, Lentinus, Pleurot-
us, Trametes [some species/strains of which are known by various
names and/or have previously been classified within other genera;
e.g. Trametes villosa = T. pinsitus = Polyporus pinsitis (also
known as P. pinsitus or P. villosus) = Coriolus pinsitus],
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11
Polyporus, Rhizoctonia (e.g. R. solani), Coprinus (e.g. C.
plicatilis), Psatyrella, Myceliophthora (e.g. M. th~rmophila),
, Schytalidium, Phlebia (e.g. P. radita; see WO 92/01046), Coriolus
(e.g. C hirsutus; see JP 2-238885), Pyricularia or Rigidoporus.
,. 5
Preferred laccases in the context of the invention include laccase
obt~n~hle ~rom Trametes villosa and laccase obtA;n~hle ~rom
Myceliophthora th~rmophila
Peroxidase enzymes (EC 1.11.1) employed in the method of the
invention are preferably per~;~es obt~;n~hle from plants (e.g.
horseradish pero~;~e or soy bean peroxidase) or ~rom
microorganisms, such as fungi or bacteria. In this respect, some
preferred fungi include strains belonging to the subdivision
Deuteromycotina, class Hyphomycetes, e.g. Fusarium, Humicola,
Tricoderma, Myrothecium, Verticillum, Arthromyces, Caldariomyces,
Ulocladium, Embellisia, Cladosporium or Dreschlera, in particular
Fusarium oxysporum (DSM 2672), Humicola insolens, Trichoderma
resii, Myrothecium verrucana (IFO 6113), Verticillum alboatrum,
Verticillum dahlie, Arthromyces ramosus (FERM P-7754), Cal-
dariomyces fumago, Ulocladium chartarum, Embellisia alli or
Dreschlera halodes.
Other preferred fungi include strains belonging to the subdivision
Basidiomycotina, class Basidiomycetes, e.g. Coprinus,
Phanerochaete, Coriolus or Trametes, in particular Coprinus
cinereus f. microsporus (IFO 8371), Coprinus macrorhizus,
Phanerochaete chrysosporium (e.g. NA-12) or Trametes versicolor
(e.g. PR4 28-A).
Further preferred ~ungi include strains belonging to the sub-
division Zygomycotina, class Mycoraceae, e.g. Rhizopus or Mucor,
in particular Mucor hiemalis.
Some preferred bacteria include strains of the order Actino-
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12
mycetales, e.g. Streptomyces spheroides (ATTC 23965), Streptomyces
thP,",o~iolace~s (IFO 12382) or Streptoverticillum verticillium
ssp. verticillium. .,
Other preferred bacteria include Bacillus pumilus (ATCC 12905),
Bacillus stearothermophilus, Rhodobacter sphaeroides, Rho~nmonA.
palustri, Streptococcus lactis, Pse~omon~.~ purrocinia (ATCC
15958) or Pse~nm~n~.~ fluorescens (NRRL B-11).
Further preferred bacteria include strains belonging to
Myxococcus, e.g. M. virescens.
Other potential sources of useful particular peroxidases are
listed in B.C. SAIln~P~s et al., Peroxidase, T.on~on 1964, pp. 41-
43.
When employing oxidases, e.g. laccases, in the process of theinvention, an amount (calculated as pure enzyme protein) in the
range o~ 0.0001-30 mg of n~;~A~e, e.g. laccase, per gram of dry
lignocellulosic material will generally be suitable. More typical
amounts will be amounts in the range of 0.001-10 mg of oxidase
(e.g. laccase) per gram of dry lignocellulosic material.
As mentioned above, preferred laccases in the context of the
invention include Trametes villosa laccase, and when using this
laccase in the process of the invention it will generally be
a~Lo~riate to employ an amount in the range of 0.02-2000 laccase
units (LACU), such as 0.01-1000 LACU, per gram of dry
lignocellulosic material.
When employing peroxidases in the process of the invention, an
amount thereof in the range of 0.00001-30 mg of peroxidase
(calculated as pure enzyme protein) per gram of dry
lignocellulosic material will generally be suitable. More typical
amounts will be amounts in the range o~ 0.0001-10 mg, such as
0.001-1 mg, of peroxidase (calculated as pure enzyme protein) per
gram of dry lignocellulosic material.
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13
As mentioned above, preferred peroxidases in the context of the
invention include Coprinus peroxidases, such as the previously
mentioned C. cinereus peroxidase. When using, ~or example, the
latter peroxidase in the process o~ the invention it will
generally be appropriate to employ an amount in the range o~ 0.02-
5000 peroxidase units (PODU), such as 0.1-2000 PODU, e.g. 0.1-1000
PODU, per gram o~ dry lignocellulosic material.
Determ;n~tion of T. villosa laccase activity and Coprinus
peroxidase activity: The determination of T. villosa laccase
activity is based on the oxidation of syringaldazin to
tetramethoxy azo bis-methylene ~l~nnne under aerobic conditions,
and 1 LACU is the amount of enzyme which converts 1 ~M of
lS syringaldazin per minute under the ~ollowing conditions: 19 ~M
syringaldazin, 23.2 mM acetate buf~er, 30~C, pH 5.5, reaction time
1 minute, shaking; the reaction is monitored spectrophotometric-
ally at 530 nm.
With respect to, in particular, Coprinus ( e.g. C. cinereus)
peroxidase activity, 1 PODU is the amount o~ enzyme which
catalyses the conversion of 1 ~mol of hydrogen peroxide per minute
under the following conditions: 0.88 mM hydrogen peroxide, 1.67 mM
2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate), 0.1 M phosphate
buffer, pH 7.0, incubation at 30~C; the reaction is monitored
photometrically at 418 nm.
Oxidizing aqents
The enzyme(s) and oxidizing agent(s) used in the process o~ the
invention should clearly be matched to one another, and it is
clearly preferable that the oxidizing agent(s) in question
participate(s) only in the oxidative reaction involved in the
binding process, and does/do not otherwise exert any deleterious
effect on the substances/materials involved in the process.
3~
Oxidases, e.g. laccases, are, among other reasons, well suited in
the context o~ the invention since they catalyze oxidation by
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14
molecular oxygen. Thus, reactions taking place in vessels open to
the atmosphere and involving an oxidase as enzyme will be able to
utilize atmospheric oxygen as oxidant; it may, however, be
desirable to forcibly aerate the reaction medium with air or
another oxygen-cont~;ning gas (e.g. oxygen-enriched air or, if ap-
propriate, substantially pure oxygen) during the reaction to
ensure an adequate supply of oxygen.
In the case of peroxidases, hydrogen peroxide is a preferred
peroxide in the context of the invention and is suitably employed
in a concentration (in the reaction medium) in the range of O.Ol-
100 Tr~.
pH in the reaction medium
Depending, inter alia, on the characteristics of the enzyme(s)
employed, the pH in the a~ueous medium (reaction medium) in which
the process of the invention takes place will be in the range of
3-lO, preferably in the range 4-9.
The present invention also relates to a lignocellulose-based
product obt~;n~ by, or obt~;n~hle by, a process according to the
invention as disclosed herein.
EXAMPLES
The potato starch (potato flour) employed as described in the
following was a st~n~rd Danish food-grade retail product
manufactured from Danish potatoes and having a declared content of
ca. 80~ of potato starch, the balance being water. The cationic
starch (often abbreviated hereafter as CS) employed (Cerestar~ CC
Bond) was obtained through Cerestar Sc~n~;n~via A/S, Holte,
Denmark. 4-Acetoxybenzyl acetate was prepared from 4-hydroxybenzyl
alcohol (Fluka, "purum") as described below. The laccase employed
was Trametes villosa laccase, produced by Novo Nordisk A/S,
Bagsvaerd, Denmark. Pre-beaten, unbleached thermomechanical pulp
(TMP) prepared from mixed Sc~n~;n~vian softwood (spruce) was
obt~; n~ from SCA AB, Sundsvall, Sweden.
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Preparation of 4-acetoxybenzyl acetate (4-ABA): 4-Hydroxybenzyl
alcohol (50 grams) was dissolved in pyridine (100 ml). Acetic
anhydride (100 ml) was added, and the solution was kept at room
temperature overnight. The reaction mixture was then evaporated to
L~IIW~ the bulk of volatile components (e.g. acetic anhydride,
acetic acid and pyridine), and r~m~;ning traces of pyridine were
r~lll~ved by co-distillation with toluene. The resulting crude 4-ABA
was used without further purification.
Example 1. Preparation of phenolic starch (PS)
A solution cont~ining phenolic starch was prepared as follows:
A 2~ w/w solution of potato starch was prepared by boiling potato
starch in the appropriate amount of water for 2 hours. The pH of
the solution was adjusted to 10-11 by addition of concentrated
(ca. 33~ w/w ~ ca. 11.5M) aqueous NaOH. A quantity of 4-
acetoxybenzyl acetate corresponding to 5~ w/w of the dry weight of
the amount of starch employed was added in the form of a 10~ w/w
solution in ethyl acetate. The resulting mixture was then stirred
at 60~C for 16 hours. The reaction mixture was allowed to cool to
ambient temperature, and the pH thereof was then adjusted to 5.5
by addition of glacial acetic acid.
Example 2. Comparison of PS/laccase and CS in paper manufacture
St~n~d h~n~fih~ts (ca. 60 g/m2) were prepared fom TMP in accor-
dance with the SCAN st~n~rd C26:76. Four dried sheets were then
immersed and soaked in a freshly prepared aqueous solution (1.2
w/w; temperature 25~C) of PS (prepared as described in Example 1,
above) to which laccase (157 LACU/liter) had been added
imm~ tely prior to the immersion. A second set of four dried
sheets was treated in the same way except that laccase was not
added to the PS solution. The sheets were removed from the
respective solutions and left at ambient temperature for 5
minutes. They were then pressed (0 -~ 4 bar) in a sheet press and
dried at ca. 105~C using a hot-plate drier.
For comparison purposes, a third set of four sheets was treated in
a m~nner completely analogous to that described above for the
CA 022318~8 1998-03-12
W O 97/17492 PCT~DK~ J~6
16
second set o~ sheets (i.e. in the absence of laccase), but using
cationic starch (CS) instead of phenolic starch (PS).
.,
A fourth set of four dried, but otherwise completely untreated,
h~n~heets was employed as control.
The tear-strength and tensile strength of the 4 sheets in each of
the four sets was measured according to SCAN P11:73 and
SCAN P38:80, respectively. The weight increase due to uptake of
the "modified starch" in question (PS + laccase, PS alone, or CS
alone) for the first three sets of sheets was also determined. All
strength and weight measurements were made after
equilibrating/conditioning the sheets at 50~ relative hUmidity and
25~C for a min;~lm of 12 hours.
The average values for each set of sheets are given in Table 1,
below.
T~hle 1.
Treat- Uptake Tear Tensile Grammage Density
ment (~ w/w) Index Index (g/m2) (kg/m)
(10-3 .Nm2/kg) (Nm/g)
~5 Untreated 0 5.35 12.4 62.3 238.0
PS 12.5 6.83 12.2 79.6 284.2
PS/laccase 9.7 7.06 15.1 74.9 272.1
CS 5.9 6.89 15.6 65.0 248.7
The results summarized in Table 1 show that the use of phenolic
starch in combination with a laccase results in enhancement of
paper strength (as measured by Tear Index and Tensile Index) to an
extent similar to that achieved using (non-phenolic) cationic
starch.
Moreover, prel;min~ry results indicate that the use of a
com~ination of a phenolic cationic starch (PCS; prepared from
CA 022318~8 1998-03-12
W O 97/17492 PCTADK95/~_'f~
17
cationic starch of the ~uaternary ~mmnn;um type with chloride as
counterion, using the same method as ~or PS) and a laccase leads
to greater strength enhancement than that obt~;n~hle with CS or
with PS/laccase, particularly when the laccase employed is one
which exhibits a low degree o~ sensitivity to chloride ion (such
as laccase obt~in~hle from Myceliophthora th~rmnphila) .
Since PS and PCS can be prepared straight~orwardly and relatively
cheaply from starch (vide supra) and cationic starch,
respectively, and since the use o~ laccases at the levels re~uired
in the process of the invention is relatively inexpensive,
strength enhanc~m~nt. using embo~im~nts of the process according to
the present invention, exempli~ied here, can thus provide an
attractive alternative to the more ''traditionalll approach
employing cationic starch.
