Note: Descriptions are shown in the official language in which they were submitted.
869(1~7
-
Related Application
The invention hereof is related to the generic
invention disclosed in applicants' copending Canadian
Application No. 208,438, filed September fl, 1974, now
Canadian Patent No. 1,031,925, issued May 30, 1978 but is
specific to defiberized lignocellulosic material for the
manufacture of paper or paper like products in which enhanced
interfiber bonding is effected in contradistinction to
surface to surface interface bonding of sol~d ~ood~
Back'ground'of'the'In'v'en'tion
Bonding of lignocellulosic fiber materials, such
as wood fiber, is widely used commercially as for example in
the manufacture of paper or fiber products. In present
commercial bonding procedures, bonding among the fibers is ' '
based primarily on physical forces created by the large
surface of finely interlocked cellulose fibers. For
increasing the bonding strength of such'product, one-may
add to the pulpr before mat or sheet formation, sizing
substances s'uch as starch or xesins as adhesiYes. Strength
~0 increase by such procedure is only moderate, and moreover
the use thereof increases costs. Strength may also be
~ .
--1--
bm:
., . ~ ,, , . i , . . . . . .
,
., . , ' ~ ' , , ' ; ' ' , , , ~
.. . ..
- ; , ..
;9~7
.,
increased by formation (fibrillation) of lonyer and more
refined fibers. This involves, however, more complicated
and costly chemical pulping procedures, and results in
lower yieldr of about 45% in the Kraft process, compared to
95% in mechanical pulping.
Summary 'and Ob'je'cts' of' the'In~enti'on
In the invention hereof, less expensive sources of
lignocellulosic fibers are rendered available for the
production of paper or paper like products, which'provide
physical properties comparable to more expensive fiber
sources. Thus, high lignin content mechanical pu~p Cground
wood), semi-mechanical or semi-chemical pulp provide sources
for the production of products of incre~sed strength, such
as liner board ~r other flexibIe paper, which could not
normally be obtained otherwise. Such objective is achieved
by increasing the interfiber bonding strength among the
fibers, by~ thoroughly dispersing throughout a mat of the'
fibers, an oxidizing agent which'results in foxmation of
interfiber chemical linkages effected by oxidation upon
application of heat.
Ground wood, whi'ch is no~ widely emp~oyed as a
source for newsprint or ot~er high llgn-in content fibers,
can by the invention hereof be employed for the''manufacture
of much stronger flexible sheets not heretofore obtainable
from ground wood, such as liner board used in the manufacture
, .
bm:
. .
~ : ,
,
~ ~8~907
of corrugated paper and cartons. Ground wood is mechanically
ground in the presence of water, and is known as mechanical
pulp. Substantially no lignin is removed by such mechanical
treatment.
Although the invention hereof is particularly
applicable to ground wood as it enables an inexpensive
source of fiber to be used for paper products requiring
strength properties not heretofore obtainable from ground wood,
it may be employed with other sources of defiberized
lignocellulosic material wherein at least some of the lignin
is present such as semi-chemical and semi-mechanical pulps,
which normally form weaker paper mats than fully delignified
lignocellulosic material. In this connection, to obtain the
oxidative bonding reaction, at least some lignin should remain
in the defiberized material, or lignin like material, such
as phenolics added thereto~
The chemical reactions involved in the process
hereof are not fully understood, Wood is a high-polymeric
substance composed of three classes of materials--carbohydrates
(primarily cellulose), lignin and extractives. While
cellulose is a polysaccharide built up of glucose units,
lignin appears to be a polymeric phenolic material, the
structure of which is still not fully understood. Not much is
known about the bond between the carbohydrates and lignin,
- although, generally speaking, lignin seems to function as a
binder for cellulose microfibrils. The function of extractives
appears to be manifold; their disease protective function is
probably the most important.
bm:
. . . , . . :: .
~ - ' ' ' . , .
~C~8~9~)7
, _,
In oxidation of lignocellulosic materials several
reaction systems may be involved at the same time. Based on
the present day chemical knowledge, it can be assumed that
the oxidation o~ phenolic units contained in lignin structure
is either the main or at least one of the main reactions
leading to self bonding of lignocellulosic materials. In
this case the intermediate formation of free radicals is
likely to take place, coupling under the formation of
- lignin-to-lignin linkages. It cannot be excluded, however,
that to some extent polysaccharide-to-polysaccharide and
lignin-to-polysaccharide bonding also takes place during
this oxidation.
In effecting the oxidation reaction, a mat of the
defiberized material is provided in which an oxidant is
thoroughly dispersed uniformly therethrough. The mat is
formed into a sheet under pressure and heat for a time
sufficient to effect the oxidative reaction. In this connection,
the oxidizing agent may also be employed with a promoter to
promote the oxidative bonding.
The invention hereof may readily be performed on a
paper making machine wherein a paper mat is formed in the
conventional manner. The mat is then sprayed or roller coated
with the oxidant in a liquid carrier which wets the mat, and
with a catalyst to promote the reaction. They may both be
contained in the same carrier or applied separately to the
sheet in the machine as will be discussed more fully
hereinafter.
From the preceding it is seen that the invention has
as its objects, among others, the provision of an improved
--4--
bm:
.
~ ~)86g~7
method of effecting increased interfiber bonding among fibers
of defiberized lignocellulosic material by effecting an
oxidative reaction among the fibers, which method is simple
to perform and renders available less expensive sowrces of
pulp for the manufacture of paper or paperboard sheets
requiring strength, and which is economical and simple to
perform. Other objects will become apparent from the following
more detailed description, and accompanying drawing in which:
The single Fig. 1 is a schematic side elevational
view of a conventional Fourdrinier paper making machine in
which the invention hereof may be performed in various ways;
parts being broken away to shorten the view.
Prior Art
Heritage U.S. Patent No. 2,125,634, dated August 2,
1938, discloses bleaching of paper pulp in a paper making
machine by applying hydrogen peroxide to the wet or partially
wet mat in minute concentrations in the presence of an alkali
such as sodium silicate, at a point ahead OL or in advance of
the dry end of the dryer, solely to bleach the sheet or pulp.
However, it has been found pursuant to this invention that
hydrogen peroxide alone will not effect oxidative bonding
reaction among the fibers to impart increased interfiber bonding
but must be used with a catalyst such as zirconium -tetrachloride
or ferrous sulfate. Moreover, the pH of the hydrogen peroxide
solution should be below pH 7, and the concentration of the
hydrogen peroxide in the carrier above 1% to be effective, and
desirably above 5%, and may be as high an 50%.
--5--
, .. .
bm:
~., : - .
.: , , ~ . : . . : , . . .
,', ' . ~ ' . ' .:
.
. . ~ ,., . : ; .
. .. : ,: .
~8~9617
SUM~IARY OF TH~ INVENTION
In one particular aspect the present invention provides
the method of increasing interfiber bonding among fibers of
defiberized lignocellulosic material containing a substantial
proportion of the natural lignin content which comprises
dispersing substantially throughout a sheet of such material
an-oxidizing agent selected from the class consisting of per
compounds, nitrates and chlorates, maintaining an acid pH
where a per compound is used, and applying heat and pressure
to said sheet for a time and temperature sufficient to
effect said bonding by oxidative bonding reaction.
In another particular aspect the present invention provides
the method of making flexible paper from wood pulp containing
ground wood which comprises continuously forming a sheet
from said pulp in a paper making machine, effecting penetration
substantlally throughout the sheet of an oxidizing agent in
a fluid carrier by wetting the sheet therewith, and roller
pressing said sheet in said paper making machine at such pH
under heat and for a time sufficient to effect interfiber
bonding among fibers of the mat by oxidative bonding reaction,
said oxidizing agent being selected from the class consisting
of per compounds, nitrates and chlorates, said fluid carrier
having an acid pH where the oxidant is a per compound.
In yet further aspects the invention provides flexible
paper, liner board and fiber board of improved interfiber
bonding produced by appli.cant's novel methods.
jl/b~c~ 5a-
~:P
,!
., ,. . .:
~0869~7
. ~
Detailed Description
In performing the method hereoE, a lignocellulosic
mat of for example ground wood fiber is formed in the usual
manner as a continuous sheet. After the sheet is formed, it
is wetted with a liquid carrier containing an oxidizing agent
which penetrates the sheet thoroughly and covers the surfaces
of the individual fibers. The wetting may be effected in any
suitable manner such as by spraying the liquid carrier
containing oxidant over a surface of the sheet or by roller
coating the same on such surface. Usually, as will be
discussed more fully hereinafter, it is desirable to employ
a catalyst which is also uniformly dispersed throughout the
sheet to promote oxidation by the oxldant. Various procedures
of oxidant application to the sheet may be employed, such as:
1. The lignocellulosic fiber sheet may be simply
wetted with a liquid carrier containing an oxidant of the type
effective without a catalyst discussed hereinafter, or with a
mixture of oxidant and catalyst, followed by application of -
heat and pressure. The effectiveness varles depending upon
factors such as type of oxidant, temperature and time.
Hydrogen peroxide, used with a catalyst, sùch as zirconium
tetrachloride, can be effectively employed in this manner
of application.
2. In many instances a higher level of interfiber
bonding may be obtained if the lignocellulosic sheet is first
wetted with an oxidant thoroughly penetrating the sheet,
presumably to increase the number of carboxyl groups in the
lignocellulosic material, followed by treatment with a liquid
carrier containing a transition metal catalyst. Subsequent
, -6-
~ ..~ .
bm:
, ~ . ~ .. .. .
,
.
.
... . .. . ~ . :
. . . . .
~:. , . : . :.
~8~g~7
wettiny with a liquid carrier containing hydrogen peroxide
forms a Fenton reagent with the transition metal catalyst,
which is a very efEective oxidizing agent for the
lignocellulosic fibers. Pressing under an elevated temperature
is then effected.
3. Another mode of application is first to wet the
sheet with a liquid carrier contain:ing a peroxide such as a
peraeid to incorporate peroxy groups into the lignocellulosie
material. After sueh ineorporation, a liquid carrier
eontaining a transition metal eatalyst is added to the
material, followed by application of pressure at an elevated
temperature to form the flexible paper sheet~
4. In some eommercial processes which are known as
dry or semi-dry processes used in the production of fiberboards
or hardboards, the dry or semi-dry pulp is formed as a
relatively thick mat which may be 2 or 3 inches in thickness,
and then compacted into a relatively thin rigid board.
Because o~ the initial thickness of such mat, it may be
difficult to obtain uniform penetration or dispersion
throughout the mat by spraying or roller spreading the carrier
containing the desired oxidizing agent on the mat surface,
To insure such uniform penetration the oxidizing
agent if used along, and the catalyst if employed with the
oxidant have to be thoroughly intermixed with fiber. If the
catalyst does no-t react with the oxidant at ambient temperature,
they may be both included in the same liquid carrier~ However
some catalysts may react with the oxidant at ambient
temperature, such as hydrogen peroxide and ferrous sulfate~
In such event to produce the reaction initially in the fiber,
bm:
: . , ,: .: . .
~ : : ..... : : : : . .
,: : - . : . ., . ~ :
~L~186907
the catalyst and the oxidant are applied separately in two
steps. For example, the carrier and oxidant may be applied
first, and then the carrier and catalyst, or vice versa
Also, an oxidizing agent may be mixed with one half of the
material for formation of the mat, and a transition metal
catalyst thoroughly mixed with the other half, followed by
mixing of the two parts together which results in uniform
incorporation of oxidant and catalyst in the mat. The mat
is then compacted under pressure and heat to form the desired
10 product.
From the preceding it is seen that particular
procedures for performing the method hereof may vary widely.
In the manufacture of flexible paper and related products such
as flexible liner board, the method hereof can be performed
readily on a conventional paper making machine. It is only
necessary to spray or otherwise apply to the fiber sheets in
the machine a liquid carrier containing oxidant~ catalyst, or
oxidant and catalyst as the case may be~ in the manner outlined
above. The liquid carrier penetrates the sheet thoroughly.
20 Also, the agents might be included in the water slurry prior
to dehydration of the sheet on the paper making machine~
There are numerous oxidizing agents and catalysts
that may be employed as will be listed subsequently. It is
only necessary, irrespective of the system of oxidant or
of catalyst used, to effect the oxidative bonding reaction
among the fibers of the lignocellulosic material at an
elevated temperature and for a tirne sufficient to effect such
interfiber bonding. The oxidative reaction is effected
primarily by heat but it is desirably conducted under pressure
--8--
bm:
. ~ . : ., . ., : . : .
.
' -: ' . . ' ': , : ',
,
~L~869(~7
-
as well as heat, such as by plates in a conventional press
or by the pressure effected by calender rolls in a paper
making machine. In this connection, relatively dry paper
already formed may be wetted in the manner related with
oxidant or oxidant and catalyst, and when heated increased
oxidative bonding will occur.
The temperature and time for obtaining the oxidative
bonding reaction among the fibers will vary depending upon the
oxidants and the character of the fibrous material. As
usual, the lower the temperature the longer the reacting time
and vice versa. The reacting temperature should not exceed
the temperature at which charring of the lignocellulosic
material will occur. Also, the pressure applied should not
exceed that at which the lignocellulosic material is crushed.
With higher amounts of some oxidants such as
hydrogen peroxide, and compatible catalysts the pressing or
reacting temperature may be as low as ambient. A suitable
temperature range is between 20C and 200C with a reaction
time of 0.5 to 5.0 minutes at a pressure of between atmospheric
and 950 psi.
As a solvent or liquid carrier for the oxidant, any
liquid may be employed which does not react with the wood such
as water or alcohol. The solvent readily escapes as vapor
during the pressing and drying of the mat.
The amount and concentration of oxidant solution
will also vary widely depending upon the chemical character of
the oxidant, the type of lignocelluloslc material, and
reaction conditions. In general, an amoun-t of carrier solution
(which need not be a true solution but which may be a
suspension) is used which will provide from 1 0 to 6.0~ of
,., _g_
bm:
. , , ~ . . .. ... . . ..
,',: ' :;' '' " ,' ' '", ,' ' ' ~' '., '' .',
.: , . . . . . .
~ ~0~ )7
oxidant based on the dry weight of the lignocellulosic
material but this range is not critical as even small amounts
of reagent are effective. Large amounts serve no useful
purpose. For any given oxidant one can readily determine the
amounts and conditions of treatment which will produce
optimum oxidative bonding.
As noted above, a large number of oxidants may be
used for the purposes of this invention to effect the
interfiber bonding of defiberized lignocellulosic material by
oxidative bonding. The oxidants fall into two classes, namely,
(1) oxides of chlorine and nitrogen and their derivatives and
(2) per compounds.
Some of these oxidants are effective alone without
catalysts while others require a catalyst in conjunction
therewith to promote the oxidative bonding. Those that can
be used alone without catalysts include:
Nitric acid;
Nitrates such as ammonium nitrate, magnesium nitrate,
potassium nitrate and sodium nitrate;
Nitrites such as sodium nitrite;
Chlorates such as sodium chlorate and potassium
chlorate;
Chlorites such as sodium chlorite;
Perchlorates such as potassium perchlorate;
Halogens such as chlorine and bromine; and
Hypochlorites such as calcium hypochlorite and
ammonium hypochlorite.
As will be seen, these are oxidants of the first
class, namely oxides of chlorine or nitrogen and their
deriva-tives.
.~,
--10--
'' ` '' ' ' '.' ~
- ~:
..
: . . ' , , . ' : ,
.. . . . . . ~.
: . " . ,~ ~ . .:, . .
_~ ~08~
The following oxidants, which are of the second class
(per compounds), usually require promoters or catalysts
to be effec-tive comprise:
Per compounds, for example peroxides, such as barium
peroxide, hydrogen peroxide and sodium peroxide;
Per acids, such as peracetic acid, persulfuric acid,
and salts of per acids, such as persulfates (and other organic
and other inorganic "per" compounds) such as ammonium
persulfate, potassium persulfate and po-tassium perborate;
and
Ozone and ozonides.
The use of chlorites and hypochlorites is effective
as a peroxidizing agent in first treating the mat, followed by
treatment with hydrogen peroxide oxidant and a transition
metal catalyst. Also, incorporation of peracids into the
sheet such as persulfuric acid followed by treatment with a
transition metal catalyst is very effective.
In general, the oxidative bonding is especially
effective if the pH of the carrier solution is on the acid
2- side, desirably at about the natural pH of woods used in paper
manufacture, namely about 3 - 6. The pH may be adjusted by
addition of~acid of alkalil as required.
Catalysts which are preferably employed can be
applied in the liquid carrier mixed with the oxidant or
separately. Any suitable catalysts may be employed which will
advantageously speed up and enhance the bonding action of the
oxidant used. They include metal salts such as ferric, ferrous,
manganese, chromium, lead, copper and cobalt, or corresponding
oxides which are well known promoters of many oxidative
-11-
bm:
:,:: . . . ,: : ; , '. .
)7
reactions. Catalysts also include various organic and
inorganic reducing ayents such as hydroquinone, pyrogallol,
tannins, hydrazine and bisulfites. The amount of catalyst
used is relatively small compared to the amount of oxidant
and usually will vary from 0.01% to 1.0~ b~ weight of the
oxidant, but this range is not critical.
The following are typical examples of hand prepared
samples prepared by conventional laboratory procedures
demonstrating the principles of the instant invéntlon:
EXAMPLE 1
A mat of Western hemlock ground wood fibers about
l foot square, was formed on a sieve screen of about 120
mesh from a water slurry of about 4% consistency. It was
pressed between such screen and another similar sieve screen
to a thickness of about 0.1 in., to partially dehydrate the
resultant mat to a consistency of aboùt ~0~, and the mat
while still wet was then sprayed with a water carrier
containing about 15% by weight of hydrogen peroxide and
about 0.75% by weight of zirconium tetrachloride; the total
amount of carrier, oxidant and catalyst being about 6.5~
by weight of the dry weight of fibers. After allowing the
carrier an~d its contents to penetrate the mat which took
about 1 minute, the mat was promptly pressed between two 120
mesh sieve screans at a temperature of about 150C and
pressure of about 700 lbs. per sq. inch ~psi) for about 2
minutes to thus form a flexible paper sheet suitable for use
as liner board. The physical properties of this sheet and
those of following Examples 2 and 3 are noted in subsequent
Table I which also includes properties of control samples
-12-
.~
bm:
: - -. : . . . . .
- :
.' ' .. ~-: : : . ~
,
' :,' ' ' , ' ' ' ' ' '~' : ' ~ ,
. . .. . .
.: ~ . . . .
~ 869~7
which were treated in the same way as in the examples but
without the oxidant.
In this example, it will be noted that the
oxidants and the catalyst were both applied from the same
water carrier.
EXAMPLE 2
.
A mat of one foot squaxe was ~ormed of Western
hemlock ground wood ~iber from a water slurry contai~ing
about 5% by weight of the ground wood and 0.125% of sodium
hypochlorite as a preoxidant thoroughly dispersed in the
wood fiber. It was pressed as in Example 1 to partially
dehydrate the resultant mat to a consistency of about 40~,
and was then sprayed with a 2.5% water solution of ferrous
sulfate catalyst in the amount of about 5~ solution to the
weight of dry fibers. After the solution was allowed to
penetrate the mat as in Example 1, it was sprayed with a 20%
water solution of hydrogen peroxide in the amount of about
5% of solution to the weight of dry fiber, and was then
pressed between two sieve screens as in Example 1 at a
temperature of about 150C and pressure of 700 psi for two
minutes which resulted in a flexible paper sheet.
In this example, the impregnation with hypochlorite
as a preoxidant, is followed by sequential catalyst and
oxidant addition.
EXAMPLE 3
A mat one foot square was formed as in Example 1
from a water slurry of Western ground wood fiber. After
draining and partial dehydrating by pressing between two
sieve screens, the mat was sprayed with 7.5% water solution
-13-
bm:
..... ...... .
.. , . .. ~, ,
: .: . . , .,.... :~
: ':'' ' : ' " , ' ~ ' ' , ~., ! .. . .
, ~ , .
~ ' .'' . '
07
of persulfuric acid in the amount of 10% of the solution
to the weight of dry fiber. After allowing the penetration
to occur (about 2 minutes) the sheet was sprayed with 2O5%
water solution of ferrous sulfate in the amount of 10%
solution to the weight of dry fiber, and was pressed as in
Examples 1 and 2 at a temperature at about 150C and pressure
of 700 psi for about two minutes. This example illustrates
sequential addition of oxidant and catalyst.
The physical properties of the paper sheet
materials produced under conditions of Examples 1 through 3
are noted in the following Table I, which as noted above also
includes the properties of control samples which were treated
in the same way as in Examples 1 through 3 but without the
oxidizing agents.
TABLE I
'Example Thickness I ~ensity Tensile strength Thickness _
i j swelling
in. gr/ft2 dry 24 hrs. %
soaked
_ _ _ ...
1 0.023 55 1987 512 39
'~ 2 0.025 54 2649 663 34
3 0.024 56 2505 495 26
L trol ~ _ 57 2037 282 51 ¦
The data set forth in the Table for each example is
an average of 10 tests. From the Table, it will be noted
that the thickness and density resulting from all tests are
substantially the same. The dry tensile strength data of
Examples 2 and 3 evidence the efficaciousness of the oxidative
interfiber bonding achieved under -the conditions described
in these examples.
~14-
.~ .
bm:
. ,.. . . , . . . : : : :
"'. ' . ' ' ~ ''' ' ' .
.
. ~
~8i~90~7
It is noteworthy that the tensile strengths of
the sheets after they had been soaked in water for 24 hours
establish the marked improvement in wet strength of Examples
1 through 3 compared to the control. Also, it will be
observed that the control had a much higher percent of
thickness swelling than the sheets of Examples 1 through 3,
which evidences the bonding strength obtained by the method
of this invention. The less the swelling, the higher the
bonding strength, or decrease in hygroscopicity.
EXAMPLE 4
A rigid hard board suitable as a building board
panel was produced in the following manner. Western hemlock
ground wood fibers were sprayed with a 1.25% water solution
of sodium hypochlorite followed by spraying with a 1.25% -
water solution of ferrous sulfate both in the amount of about
100~ solution to the weight of dry fibers. After thorough
mixing, a mat was formed from a water slurry containing about
5~i by weight of treated fibers. After draining and partial
dehydration by pressing the sheet between t~o sieve screens
as in the previous examples, the sheet was sprayed with a
20~ water solution of hydrogen peroxide in the amount of 10
to dry weight of ibers. After such treatment, the sheet
was pressed between two sieve screens at a temperature of
150C and pres~ure of about 850 psi for five minutes to
produce hardboard of 0.117 in thickness and 1.055 speciEic
gravity. Table II, below, depicts the physical data obtained
by an average oE ten tests on samples produced by Example ~,
compared to a control which was not treated with oxidizing
agents, also an average oE 10 tests.
-15-
bm:
~ ,
", . . ' :' ' '' ~ ', '
., ' ' ,~ . .
.
,
,; . . , . .' ;'';' '., ' ~ .' '' . :
86907
TABLE II
Example Thickness Specific Tensile strength Thickness
gravity P' ,i swelling
_in. dry ~ éd %
4 0.117 1.055 4322 1424 26,6
Control 0.123 1,034 4103 667 52.2
EXAMPLE 5
This example is one wherein hard board is produced
from a relatively thick ma-t which is compacted to a relatively
thin rigid board. One part of ground wood fiber particles was
sprayed with a 1.25% water solution of sodium hypochlorite as
a preoxidizing agent followed by spraying with a 1.25% water
solution of ferrous sulfate both in the amount of about 10% by
weight of the fiber on a dry basis. The other part was sprayed
with a 20% water solution of hydrogen peroxide also in the
amount of 10% by weight of the dry weight of fibers, The
thoroughly wet sprayed parts were then thoroughly mixed
together; and a sheet of about a thickness of about 2 inches
was formed and then pressed between sieve screens of about
120 mesh to dehydrate the mat to a water consistency of about
40%. The mat was conveyed on the screens into a press in the
usual manner, and the mat was compressed to a thickness of
about 1/8 inch under a temperature of about 150C and pressure
of about 850 psi for about 2 minutes which resulted in a
rigid hard board suitable for building purposes.
Thickness of the board was 0.120 in.; specific
gravity 1.071; dry tensile strength 4,416 psi; tensile strength
after 24 hrs. soa~ing in water 1,519 psi~ and thickness
swelling 24.4%.
-16-
bm:
.- : . ,
.
,
- ~ :
86~7
As was noted above, the method hereof is particularly
adapted for performance in a paper making machine, Referring
to Fig. 1, a conventional type of Fourdrinier machine is
schematically illustrated. It comprises headbox 2 from which
a slurry of defiberized material, such as ground wood, is
discharged onto a Fourdrinier wire or table 3 on which the
mat is initially formed. From wire 3, the wet web of paper is
continuously discharged into press section 4 through which it
is continuously conveyed through press rolls 6, and wherein
the moisture content is reduced by mechanical pressure effected
by the ral:ls. The thus partially dehydrated sheet is
continuously conveyed through dryer section 7 which removes
remaining moisture from the sheet by means of heat and vapor -
transfer; the dryer section comprising a large number of
heated drying rolls 8. From the dxyer section, the now
substantially dehydrated sheet passes through calender stack
9 comprising a series of smooth surfaced, heated calender rolls
11 which control the thickness of the sheet, its smoothness
and other characteristics. The calendered sheet is then
wound into a roll 12.
As previously related, the oxidant or oxidant and
catalyst may be applied to the defibered lignocellulosic
material in various ways rendering the method hereof very
versatile. For example, with reference to paper ma]sing machine
application, if only an oxidant or oxidant and catalyst i5
applied, the liquid carrier containing the oxidant or mixture
of oxidant and catalyst may be suitably added at positions
indicated at A, B or C in the machine, which results in
penetration of the oxidant, or catalyst and oxidant, into the
-17-
bm:
: : . : . .
. , .
1~36~a17
,
sheet.
Where mild preoxidation o~ the sheet is desirable, a
small amount of the preoxidizing agent, such as sodium
hypochlorite, may be added in the slurry in the headbox, or at
position A. The carrier containing the transition metal
catalyst may be added midway in the dryer section indicated
at position B, and the carrier containing hydrogen peroxide
oxidant at position C just ahead of calendar stack or rolls
Where the sheet is to be treated with a peracid or
peroxide, it may be added at position D~ just before the press
section; and the carrier contain.ing a transition metal
catalyst at position B or C Both surfaces or only one
surface of the sheet may be wetted. Also, a catalyst solution
may be applied to one surface and the oxidant solution to the
other surface of the sheet as long as they are thoroughly
intermixed in the mat.
From the preceding, it is seen that the procedure
comprises a two step process, namely (a) treatment of the
defibered lignocellulosic material with oxidant or oxidant
and catalyst before pressing, namely before bringing the fiber
surfaces into sufficient contact, and (b) effecting the bond
formation reaction by temperature increase, and desirably
under pressure.
bm:
. .. . `
' ''' ~ ~
.. .
: :
'
