Note: Descriptions are shown in the official language in which they were submitted.
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HIGH STRETCH PAPER AND METHOD OF PRODUCING THE SAME
CROSS-REFERENCE TO RELATED APPLICATIONS
[001] The present application claims benefit of U.S. Provisional
Application No. 62/624,879
filed February 1, 2018, the content of which is hereby incorporated by
reference in their entirety.
FIELD
[002] The present relates to papers with high extensibility, their
composition and method for
producing the same. More particularly, the present relates to high stretch
paper including some pulp
fibers that have been treated mechanically in order to induce fiber curl and
kinks.
BACKGROUND
[003] The extensibility of paper, also referred to as stretch or elongation
at break, is a key
property of paper. Paper products are generally brittle and most of them have
low extensibility. As
a result, paper is rarely used in applications involving large deformations of
the material. Many
different approaches have been tested over the years to increase the stretch
of paper and
overcome this limitation.
Papermaking treatment to increase stretch potential
[004] One of the most important factors controlling the extensibility of
paper is the amount of
sheet shrinkage taking place during drying. The underlying mechanism is the
shrinkage of fibers in
the transverse dimensions as water evaporates from the cell wall. That process
takes place after
fiber-fiber bonds have formed in the network so that fibers cannot move
relative to each other. As a
result, transverse shrinkage of one fiber compresses its crossing fiber in the
axial direction, and the
paper shrinks in all directions. The amount of shrinkage incurred by the paper
depends very
strongly on the restraint applied during drying: sheets dried without
restraint shrink a lot more than
those dried fully restrained. The amount of drying shrinkage that can take
place under unrestrained
conditions is limited to between 3 and 10%. Furthermore, while free-drying of
paper is a simple
method to increase stretch, its applicability to commercial products
manufactured on a paper
machine is limited.
[005] Stretch of paper can also be increased by inducing deformations of
the fibrous network.
This is achieved by applying in-plane compressive forces on the wet paper
during papermaking.
An example of that approach is the Clupak process which is described in U.S.
2,624,245. In that
process, the wet sheet is pressed between two rolls rotating at different
speeds. One is a steel roll
while the other is covered with a rubber that is stretched in front of the
nip. The sheet adheres to
the rubber surface as it enters the nip and gets compacted in the machine
direction (MD) as the
rubber is allowed to contract. The amount of compaction can be substantial and
is controlled by
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adjusting the speed difference between the two rolls. The Clupak and other
related processes (e.g.,
Expanda, see also U.S. 7,918,966) are commonly used in the manufacturing of
sack grade paper.
They can provide gains in MD stretch as high as 30%. However, they have little
impact on the
elongation at break in the cross direction (CD). Furthermore, only a small
fraction of existing paper
machines are fitted with the equipment needed to produce such papers.
[006] The creping process is another very effective approach to increase
stretch in the
machine direction. It is commonly used in the production of tissue paper and
is done by a doctor
blade that scrapes the paper off a drying cylinder (Yankee). The high-speed
collision between the
paper and blade results in large out-of-plane deformations of the paper in the
machine direction.
The length scales associated with these deformations depend on a number of
factors including
pulp characteristics, blade geometry, strength of adhesion between paper and
Yankee and speed
difference between the Yankee and the final section of the paper machine.
After creping, the
stretch of paper in the machine direction is typically above 10%. However,
creping, like the Clupak
process, has little impact on the elongation at break in the CD direction.
This severely limits the
range of applications for which creped papers can be used.
Fiber selection
[007] It is also possible to increase sheet extensibility by selecting pulp
fibers with desirable
characteristics or by modifying these fibers through mechanical, chemical or
combined
mechanical/chemical means. The mechanical properties of wood pulp fibers are
determined to a
large extent by the thickest layer (S2) of the fiber cell wall. That layer
consists of helically wound
cellulose fibrils oriented at some angle relative to the fiber axis. The
fibrils are held together by
some hemicellulose and lignin. In general, the larger the fibril angle, the
more extensible the fiber
is. For instance, juvenile fibers, which have high fibril angle, tend to be
more extensible than
latewood fibers. The impact of fibril angle on stretch has been observed in
both softwood and
hardwood unbleached kraft pulps. Gains in paper stretch of at most 2 to 3% can
be achieved by
utilizing pulp fractions with high fibril angle.
Chemical addition
[008] The addition of extensible polymers to paper is another approach for
increasing its
elongation at break. The objective is to produce a composite material with
properties intermediate
between those of the polymer and those of the paper produced without it.
Polymers available as
aqueous dispersions (latexes) are commonly used for that purpose. They are
generally added to
the pulp prior to papermaking or to the pre-formed fiber network during
papermaking. For example,
Alince (1977, Svensk Papperstidning, 13: 417) has shown that addition of
styrene-butadiene latex
to a kraft pulp could increase paper stretch by up to 4%. Ankerfors and
LindstrOm (WO
2011/087438) similarly added various amounts of thermoplastic latex to a never-
dried bleached
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softwood kraft pulp to produce a mouldable material. Handsheets prepared with
17% by weight of
polylactide latex and warm-pressed under varying conditions of temperature and
pressure had
elongations at break around 9%. Waterhouse (1976, Tappi J., 59: 106) used the
second approach:
he impregnated wet (never-dried) handsheets with latex and found that, after
wet pressing and
drying, the elongation at maximum load of the papers could be as high as 18%.
However, these
values of elongation at maximum load were observed at levels of latex addition
above 30% and
with minimal restraint applied to the sheet during drying, a situation not
representative of typical
conditions on a paper machine. Stokes (U.S. 4,849,278) similarly prepared a
flexible and
stretchable paper by saturating a web that was previously creped while in a
semi-dry state with a
soft polymer characterized by a glass transition temperature between -45 C and
0 C. The resulting
saturated substrate, which has an elongation at break in machine direction in
the range from about
18% to 30%, can be used as label stock for squeezable containers. The
elongations at break
obtained in the CD direction were significantly lower as the approach relies
on the use of a creping
process.
Foam-forming
[009]
Torniainan et al. (U.S. 20170260694) used a foam-forming process to produce
extensible
fiber sheets comprising natural and reinforcing fibers as well as a binder and
a foaming agent.
Sheets produced with their approach have elongations at break between 3 and
50%. Depending
on furnish and choice of binder, they can also be biodegradable and/or
recyclable. However, the
fiber sheets are produced with a foam-laid method which is significantly
different from conventional
papermaking. As a result, extensive and costly modifications would be required
in order to produce
such extensible fiber sheets on a conventional paper machine.
Fiber chemical treatment to increase stretch potential
[0010] A number of different chemical processes have been used to modify pulp
fibers in order
to increase paper stretch. For example, hydroxyethylation and
hydroxypropylation have been
found to have a positive impact on both paper strength and stretch. The
selective oxidation of
some hydroxyl groups of cellulose has also been shown to improve both single
fiber and network
extensibility. Chemical grafting of acrylate polymers onto the pulp fibers is
another modification that
can improve elongation at break. In general, chemical modification of the
fiber involves a decrease
in crystallinity of the cellulose. In turn, this leads to an increase in fiber
swelling, drying shrinkage
and/or the amount, strength or compliance of fiber-fiber bonds in the sheet;
all of these effects
generally have a positive impact on sheet elongation. That impact depends
strongly on the specific
process used as well as the conditions under which the paper is dried.
Regarding such chemical
processes, the highest elongation at break measured was slightly below 16% on
hydroxypropylated sheets dried unrestrained. The same sheets dried under more
realistic
restrained conditions had an elongation at break of only 5%. It should also be
noted that the
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approaches discussed above involve chemical reactions that can be costly and
difficult to
scale-up.
Fiber treatment to induce fiber curl and kink
[0011] In the
pulping process, wood chips are subjected to various treatments including
mechanical, chemical or both to produce individualized fibers with suitable
properties for
papermaking applications. The mechanical treatment causes some fiber
structural distortions such
as curl and kinks. Those distortions can cause loss in fiber properties such
as bonding potential,
and ultimately lead to loss in paper strength properties. With appropriate
papermaking processes,
most of those distortions can be removed; however, for some specialty grades
such as tissue and
towel, the presence of those structural features results in some desirable
properties for those
grades such as high extensibility, higher bulk, softness and absorbency.
Therefore for those
applications, pulp manufacturers prefer to preserve fiber curl and kinks and
in some cases, even
further increase and enhance those structural features.
[0012] Curl and kinks are produced when wood fibers are subjected to
continuous application of
normal/compression and shear forces, possibly followed by chemical cross-
linking. Several
technologies have been either used, or in some cases developed, to
preferentially induce high
level of curl and kinks in mechanical and/or chemical wood fibers. Depending
on the equipment
and processes, those technologies can be grouped into the following main
categories: (i)
mechanical treatment, (ii) chemical cross-linking, (iii) heat treatment or,
(iv) a combination thereof.
Mechanical treatment to induce fiber curl and kink
[0013] The stretch potential of papermaking fibers depends strongly on the
amount of axial
compression they undergo during production. Specifically, fibers in the wood
or pulp experience
mechanical stresses in operations such as chipping, defiberizing, plug-screw
feeding and refining.
For pulps, the amount of fiber deformation typically increases with the
consistency of the
suspension. As a result, various medium or high consistency mechanical
treatments can be used
to induce dislocations and microcompressions in pulp fibers. While these
treatments increase the
stretch potential of the fibers, papers made from these fibers are usually
weak and they do not
exhibit improved stretch properties.
[0014] The
decrease in tensile strength is attributed to large-scale fiber deformations
such as
kinks and curl produced during the mechanical treatment. These deformations
lead to poor
bonding between the fibers and to non-uniform stress distribution in the
network when the paper is
strained. As a result, the sheet breaks before the full stretch potential of
the fibers can be realized.
One mechanical treatment that can improve stretch is high-consistency refining
(HCR) of the pulp
under atmospheric or pressurized conditions. During HCR, fibers undergo
continuous normal and
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shear fatigue loading causing structural distortions and their outer cell wall
is also fibrillated, thus
improving fiber-fiber bonding. As a result, papers made from refined fibers
are both stronger and
more extensible than those produced from the unrefined pulp. Paper stretch can
also be improved
by combining high and low-consistency refining of the pulp. The low-
consistency refining is
performed in order to further straighten the pulp fibers after the high-
consistency treatment. It
promotes fiber-fiber bonding and improves the ability of the fiber network to
transfer stress when
placed under load. The gain in paper stretch obtained by HCR or by a
combination of
high-consistency and low-consistency treatments is usually limited to a few
percent.
[0015] Several types of equipment have been used to apply forces inducing curl
and kinks. Eber
et al. (U.S. 4,488,932) used hammermilling and refining to subject pulp webs
to shear forces to
produce curly fibers. They showed that paper bulk increased when treated
fibers were blended
with untreated ones to produce the sheet. Kasser used a Kollergang mill to
induce fiber curl (U.S.
4,409,065). In Kasser's process, refined kraft fibers were subjected to
mechanical treatment to
increase stretch for application in sack paper. CareIs et al. (U.S. 7,390,378)
used a rotating drum
to subject wood fibers to forces as fibers followed a spiral downstream path
inside the drum, and
stated that fiber curl increased by almost 150% with this technique. Hill et
al. (U.S. 2,516,384)
proposed a conceptual design to subject wood fiber nodules to continuous
compression-decompression forces to create kinks and curl. Their design
consists of two
off-centred concentric cylinders where the outer cylinder is stationary and
the inner cylinder is
rotating. The pulp nodules are in the gap between the cylinders and the
rotation of the inner
cylinder generates compression forces.
[0016] Steam explosion process was also used to produce curly fibers for
applications such as
absorbent grades. In this technique, wood fibers are cooked under high
temperature and pressure.
Once the required cooking time is elapsed, the cooking vessel is decompressed
rapidly (to
atmospheric pressure) and fibers are recovered. The sudden decompression
creates structural
distortions into fiber structure and produces highly curled fibers. Hu (U.S.
6,413,362) used a similar
technique to produce curly fibers. Hu proposed mechanical treatment of fibers
(in hammermill or in
a refiner) prior to cooking and steam explosion. Hermans et al. (U.S.
5,501,768) used the
commercial BIVIS equipment to induce curl into fiber structure. BIVIS is
composed of a screw
press where wood chips/fibers are subjected to compression-decompression zones
as they move
along the press flights. At various intervals, fibers are pressed and forced
to pass through small
holes. The continuous application of compression-decompression forces creates
distortions such
as curl and kinks into fiber structure.
[0017] Plug screw is another piece of commercial equipment which was used to
induce fiber curl
and kinks. The equipment is usually part of the pressurized refining system to
create pulp plug in
order to maintain pressure at the feeding port of the steaming tube. For
example, Minton (U.S.
4,976,819) used a plug screw process and subjected fibers to compression
forces varying from 2:1
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to 8:1 in compression ratio. Minton produced curly fibers for tissue and multi-
ply board
applications.
[0018] A widely
used equipment to induce fiber curl and kinks are mechanical refiners
(atmospheric or pressurized), with or without plug screw. Generally the
applied refining specific
energy was kept low and only adequate for dispersing or defiberizing the pulp
nodules. The impact
of various operating conditions such as consistency, plate pattern, pressure,
etc. on fiber curls and
kinks was evaluated. The produced fibers were used in a wide range of
applications from tissue to
absorbent grades and boards.
[0019] Above results have shown that in order to achieve high fiber curl and
to preserve it
throughout the process, two conditions should be met; first, mechanical
treatment of fibers under
high pressure/temperature and second, no extra refining afterward. With high
consistency refining
or mechanical treatment of fibers under atmospheric condition (such as in
chips impregnator), the
maximum achievable curl index would generally be below 0.2 while with
mechanical treatment
under high pressures (such as in plug screw), curl indices of 0.2 to 0.45
could be obtained.
Mechanical and heat treatment to induce fiber curl and kink
[0020] It has been shown that when mechanical methods are used to induce curl
and kinks, the
structural distortions are not permanent and part of the curl is removed when
fibers are agitated
with water at low consistencies. It has also been shown that if after
mechanical treatment, fibers
are heat treated, the induced curl will stay permanent even if fibers are
agitated at low consistency
for an extended amount of time. A common method of heat treatment is drying
fibers in flash dryers.
Ko et al. (U.S. 6,837,970) and Hu et al. (U.S. 7,364,639) used mechanical
treatment (in BIVIS or
refiners) followed by heat treatment in flash dryers to produce permanently
curly fibers. Barbe et al.
(U.S. 4,431,479) used a similar approach, i.e. inducing fiber curl using high-
consistency refining
and then heat treating the curled fibers in a digester at 100 C - 170 C and
heating time of 2-60
minutes. To reduce the impact of heat treatment on mechanical pulp brightness,
Barbe et al. also
suggested that brightening chemicals could be added to the pulp during the
heat treatment
process.
Chemical treatment to induce fiber curl and kink
[0021] Chemical treatment has also been used to produce curly fibers. The
chemical treatment
consists of crosslinking individualized cellulose fibers (crosslinking between
cellulose molecules of
a single fiber rather than separate fibers) and has been thoroughly described.
[0022] Among the above-mentioned approaches to increase stretch, many can only
increase
stretch by a few percent, which is insufficient for some applications. Others
like creping or wet
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compaction have a large impact on elongation, but only in the machine
direction. Furthermore,
those approaches require specialized equipment on the paper machine which most
mills do not
have access to. Chemical modification of the fibers (as described above) can
be an effective way
to increase stretch but it is costly and usually works better when the paper
is dried without restraint.
[0023]
Therefore, there is a need for a different method for producing highly
stretchable paper
that is cost-effective, that does not compromise the sustainable character of
paper and that can be
easily implemented in a mill.
SUM MARY
[0024] In
accordance with the present disclosure there is provided a method for
manufacturing
an extensible paper, the method comprising the steps of: providing pulp fibers
in form of a pulp
having a first length-weighted average curl index (Cmi) between 0 and 0.3;
mechanically treating
the pulp fibers using a pulp compression process under a pressure of from 2 to
20 bars and
expending an energy of 60 to 100 kWh/tonne, to induce fiber deformations such
that the resulting
pulp fibers have a second length-weighted average curl index (Cm2) higher than
the first
length-weighted average curl index and between 0.1 and 0.45; forming a wet web
using the
mechanically treated pulp fibers; drying the wet web under restraint to form a
dried web; and adding
a polymer to the dried web.
[0025] In a
particular embodiment, the pulp has a consistency above 20% by dry weight
before
the pulp compression process.
[0026] In a
particular embodiment, chemical additives are added to the pulp before it
undergoes
the compression process.
[0027] In a
particular embodiment, the pressure of the pulp compression process is from 3
to 8
bars.
[0028] In a
particular embodiment, the pulp fibers are refined prior to undergoing
mechanical
treatment.
[0029] In a
particular embodiment, the pulp compression process is a plug screw feeding
process.
[0030] In a
further embodiment, the pulp compression process is a hammer mill, a
Kollergang
mill, a BIVIS device, an explosion pulping device or a revolving drum.
[0031] In a
particular embodiment, the pulp is subjected to a separate heat treatment
after the
pulp compression process.
[0032] In a
particular embodiment, the second length-weighted average curl index (Cm2) is
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between 0.25 and 0.45.
[0033] In a particular embodiment, the polymer is a bio-based polymer, a
biodegradable polymer
and/or a petroleum-based polymer. The petroleum-based polymer can be a
thermoplastic polymer
or copolymer selected from the group consisting of polyethylene,
polypropylene, polyethylene
terephthalate, styrene-butadiene copolymers, acrylonitrile-butadiene
copolymers, acrylic polymer,
acrylic copolymer, vinyl acetate polymers, vinyl acetate copolymers, and vinyl
chloride-vinylidene
chloride copolymers. The polymer can be in the form of an aqueous dispersion
or latex.
[0034] In a particular embodiment, the polymer can be added by
impregnation, and can be added
in an amount of from 2 to 40 wt%. Impregnation of the dried web can comprise
flooding the web with
a water-based or molten polymer, removing the excess polymer from the surface
of the web and
drying the web under restrain to evaporate the water.
[0035] In a particular embodiment, a cross-linking agent is added to the
pulp after mechanically
treating the pulp fibers.
[0036] In a particular embodiment, the pulp is a mechanical, chemi-
mechanical or chemical pulp.
[0037] In an embodiment, the polymer is in the form of an aqueous
dispersion or latex.
[0038] In another embodiment, a chemical additive is added to the pulp
prior or after
mechanically treating the pulp.
[0039] In an embodiment, the chemical additive is a plasticizer.
[0040] In another embodiment, the chemical additive is a strength additive,
a sizing agent, or a
cross linking agent.
[0041] In a further embodiment, the chemical additive is a starch, a
carboxymethyl cellulose, a
polyacrylamide derivative, a dispersant, a debonding agent, cellulose fibrils,
polyamide-epichlorohydrin, melamine, urea formaldehyde, or a polyimine.
[0042] In accordance to another embodiment, the method described herein
further comprises
chemically and/or heat treating the pulp after mechanically treating the pulp.
[0043] In another embodiment, the pulp is a combination of different pulps.
[0044] In accordance with the present disclosure there is provided an
extensible paper
comprising: pulp fibers having a length-weighted average curl index Cm of
between 0.1 and 0.45;
and a polymer in an amount of from 2 to 40 wt% based on the weight of the
extensible paper;
wherein the extensible paper has a Gurley air resistance below 20 s/100 mL and
an elongation at
break of at least 7%.
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[0045] In a particular embodiment, the elongation at break is from 10% to
90%.
[0046] In a particular embodiment, the extensible paper is a polymer-
impregnated extensible
paper.
[0047] In a particular embodiment, the curl index of the fibers contained
in the extensible paper is
of from 0.25 to 0.45.
[0048] In a particular embodiment, the impregnated polymer is present in an
amount of 10 wt%.
[0049] In another embodiment, it is provided an extensible paper produced
by the method as
described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0050] Figure 1 is a flowchart showing a method for producing an extensible
paper according to
an embodiment, wherein optional steps are identified with dashed lines.
[0051] Figure 2A to 2D are micrographs showing the fiber morphology
modifications induced by
mechanical treatments of a never-dried-unbleached kraft pulp; wherein in (A)
untreated fibers, (B)
mechanically treated fibers with higher fiber curl, (C) Refined fibers with
surface fibrillation and (D)
fibers subjected to refining followed by mechanical curl inducement with both
surface fibrillation
and high curl.
[0052] Figure 3 is a graph showing the curl index (Cm) of mechanical (T MP),
chemi-mechanical
(BCTMP), at low and high freeness, and kraft pulps, made with various wood
species (mainly black
spruce, aspen or Douglas fir), as a function of the pressure applied (bars)
during treatment in plug
screw.
[0053] Figure 4 is a graph showing the number of kinks (per mm) of mechanical
(TMP),
chemi-mechanical (BCTMP), at low and high freeness, and kraft pulps, made with
various wood
species (mainly black spruce, aspen or Douglas fir), as a function of the
pressure applied (bars)
during treatment in plug screw.
[0054] Figures 5A and 5B are graphs showing the Water Retention Value (WRV in
g/g), wherein
in (A) mechanically treated chemical pulp fibers and (B) mechanically treated
mechanical pulp
fibers, as a function of the pressure applied (bars) during treatment in plug
screw, with and without
heat treatment;
[0055] Figures 6A to 6D are bar charts showing the elastic modulus (A),
tensile index (B),
elongation at break (C) and specific volume (D) of standard handsheets made
from an unrefined
NBSK pulp and handsheets made from the same NBSK pulp after mechanical
treatment in a plug
screw.
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[0056] Figures 7A to 70 are bar charts showing the elastic modulus (A),
tensile index (B),
elongation at break (C) and specific volume (D) of handsheets made from an
unrefined NBSK pulp
and impregnated with 10 wt% of an acrylic copolymer and handsheets made from
the same NBSK
pulp after mechanical treatment in a plug screw and impregnated with 10 wt% of
an acrylic
copolymer.
[0057] Figure 8 is a graph showing the tensile index (N=m/g) as a function
of the elongation at
break (%) of extensible papers in accordance with an embodiment.
[0058] Figure 9 is a schematic illustration showing a system for producing
fibers suitable for
making extensible papers in accordance with an embodiment.
[0059] Figure 10 is a graph showing the forming depth (mm) as a function of
the elongation at
break (%) of an extensible paper in accordance with an embodiment.
DETAILED DESCRIPTION
[0060] It is provided the manufacture of highly extensible, lignocellulosic
fiber-based papers
(hereafter referred to as "extensible paper"). The flowchart in Fig. 1
illustrates possible
embodiments for the method for manufacturing the extensible papers that is
presented below and
encompassed herein.
[0061] The extensible paper comprises pulp fibers having an initial, or
first, length-weighted
average curl index Cum. The fibers are provided in pulp form, which can have a
consistency
(percentage of oven dry mass in the pulp) of above 20% relative to the mass of
the pulp. In some
embodiment, the pulp has a consistency of between 20% and 50%.
[0062] Curl index and kinks were measured using the Fiber Quality Analyzer
(FQA) from OpTest
Equipment Inc. Curl index (C): is defined as the ratio of the true contour
length L of the fiber divided
by the projected length I of the fiber minus 1 (C = ¨ 1). The curl index is
calculated for each
individual fiber. A curl index of zero indicates that no curl is present. The
term "length-weighted curl
index" or "average length-weighted curl index" as used herein (hereafter
referred to as "curl index")
represents the mean curl index length-weighted (Cm) reported by FQA as the sum
of individual C
E cc
of each fiber multiplied by its contour length divided by the summation of the
contour (Cm= Li ¨).
EL,
The first length-weighted average curl index (Cum) can be between 0 and 0.3.
Therefore, the fibers
can be free of curl and/or kink or can be slightly curly. Preferably, the
initial length-weighted
average curl index is of 0 to 0.15.
[0063] The pulp fibers can be mechanical, chemi-mechanical and chemical
pulps. In a particular
embodiment, the pulp fibers are chemical pulp fibers produced by the kraft
process. The kraft
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fibers can contain significant amounts of residual lignin as indicated by a
high Kappa number.
[0064] In a
particular embodiment, and as shown in Fig. 1, at least a portion of the
lignocellulosic
pulp fibers 10 composing the extensible paper have been mechanically treated
13 to induce curl
and/or kinks. Curly pulp fibers can be obtained by mechanical treatment 13,
with no chemical
addition 14, using high consistency pressurized refining installations (or
high consistency pulp
compression process) found in pulp and paper mills. In some embodiments,
chemical additives 22
such as plasticizers can also be added to the pulp. In an embodiment, curl
inducement is produced
by subjecting the pulp fibers 10 to compressive and shear forces in a plug
screw device. The plug
screw device can be part of a pressurized refining system. Mechanical curl
inducement can also
be produced by using other devices such as hammer mill, Kollergang mill, BIVIS
device, explosion
pulping device or specialized custom-designed equipment such as revolving
drum.
[0065] The mechanical treatment 13 induces fiber deformations such that the
resulting pulp
fibers have a second length-weighted average curl index (CBA/2) higher than
the first average curl
index. The second curl index can be between 0.1 and 0.45, preferably between
0.25 and 0.45.
Figs. 2A to 20 illustrate the changes in fiber morphology induced by
mechanical treatment in the
case of a never-dried unbleached kraft pulp. The changes in morphology result
from compressive
and shear forces exerted on the fibers during treatment.
[0066] The
level of curl obtained, defined by the second curl index, will depend at least
in part on
the type of pulp, the extent of mechanical treatment and the wood species.
According to Figs. 3
and 4, which show the change in curl index and number of kinks per mm,
respectively, with
increasing treatment pressure for different mechanical, chemi-mechanical and
chemical pulps, a
higher curl index is achieved with kraft pulp as compared to mechanical pulps.
The term "kink
index" (KI) as used herein refers to the sum of the number, Nx, of kinks (an
abrupt change in fiber
curvature) within a range of "x" kink angles [deg], divided by the total fiber
length of all the fibers, LT.
The calculation of kink index by FQA gives more weight on higher angles
(Kl= 2N(21-45)+3N(46-90)+4N(91-180)
). The term "kinks per mm" is calculated by dividing the total number of
LT
kinks, Nx, by total fiber length, LT.
[0067] Fig. 3
also shows that for kraft pulp fibers, the curl index reaches a plateau above
a
pressure of about 6 bars in the plug screw. It has been found that, while curl
is typically a good
indicator of stretch potential, the elongation at break can increase with
increasing treatment
pressure, even in the region where curl has reached a plateau. Without being
bound to theory, it is
suggested that, for certain pulp fibers, other mechanisms than curl also play
a role in affecting the
paper stretch. For example, in case of kraft fibers, structural wall micro-
compressions can affect
paper stretch, and such micro-compressions may increase as the kraft fibers
are compressed and
sheared in the plug screw.
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[0068] The
degree of fiber deformation (i.e. the curl index or kink index) resulting from
the
mechanical treatment can be controlled through the amount of heat and pressure
supplied during
the process. In a particular embodiment, the system pressure of the mechanical
treatment is
between 2 to 20 bars, preferably 3 to 8 bars and most preferably 3 to 6 bars.
The specific energy
consumed in the high consistency process, such as plug screw process, is about
60-100
kWh/tonne.
[0069] Still
referring to Fig. 1, the pulp fibers 10 can be heat treated 14 after the
mechanical
treatment. Heat treatment 14 can lead to additional cross-linking (chemical
bonds) within the cell
wall of mechanically treated fibers. Structural features of fibers (such as
curls and kinks) can be
made more permanent and the water resistance of the fibers can be improved
with an additional
cross-linking of the individual fibers. Therefore, additional cross-linking
can be desirable in
applications requiring higher water resistance. In a particular embodiment,
the heat treatment
process comprises maintaining the mechanically treated pulp fibers (previously
dried to less than 5%
moisture content) in a chamber with recirculating air at elevated temperature
for a certain amount
of time. The time of the heat treatment can be of from 3 to 10 min. As shown
in Figs. 5A and 5B,
wherein the evolution of water retention values (WRV) of chemical pulp fibers
(Fig. 5A) and of
mechanical pulp fibers (Fig. 5B) that were mechanically treated, with (.) and
without (o) heat
treatment are compared, it has been found that WRV decreases after heat
treatment for both
mechanical and chemical pulp fibers.
[0070] A
chemical treatment 14 can also be used, in place of or additionally to the
heat
treatment (see Fig. 1), and to induce additional cross-linking within
individual fibers. This typically
leads to the closing of micro-structural pores within the cell wall of the
fibers and to the lowering of
the water retention value. Table 1 shows the WRV for mechanical and chemical
fibers after
combined mechanical and chemical treatments to induce curl. A chemical
additive22 can also be
added in the pulp 10 prior to the mechanical treatment 13.
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Table 1
Water retention value (WRV) of mechanical and chemical pulp fibers after
combined mechanical
and chemical treatments to induce curl
Pulp condition WRV (g water/g dry pulp)
Mechanical pulp (100% BCTMP, no treatment) 0.973
SBSK (southern pine kraft pulp, no treatment) 0.837
NBSK pulp (no treatment) 0.791
Mechanically curled NBSK pulp (14 bars) 0.620
Chemically curled & cross-linked NBSK (harvested from a
0.190
commercial diaper)
[0071] In an embodiment, after mechanical treatment 13 (for example by plug
screw), the pulp
fibers are transferred through a steaming tube. The residence time in the
steaming tube is 2 to 4
minutes and preferably 2 minutes. After the steaming tube, pulp fibers are
blown out of the refiner,
while the refiner disks are kept fully open.
[0072] The pulp fibers 10 can be refined prior to the mechanical treatment
13. For example,
referring to Fig. 1, the pulp fibers 10 can be fed to a refiner 12 at
consistencies above 20% and,
after refining, the pulp is fed to the plug screw 13. During the refining
process, varying refining
specific energies can be used to produce pulps with a range of strength
properties.
[0073] Once the fibers are treated, by mechanical treatment 13 and
optionally by pre-refining 12,
chemical and/or heat treatment 14, a wet web is formed with the treated pulp
fibers after blending
15 and using a papermaking process 16. The term "wet web" as used herein can
be understood as
a sheet of pulp formed by even distribution of a pulp on a surface.
[0074] The wet web is then dried 17 under restraint to form a dried web. As
mentioned above,
the amount of shrinkage incurred by the paper depends on the restraint applied
during drying, so
that wet web dried without restraint will shrink more than wet web dried fully
restrained. The drying
restraint can be applied to the wet web by applying in-plane tension,
mechanically fixing its edges
to avoid dimensional changes in the plane of the web during drying or by any
other restraining or
compressing means.
[0075] The method for manufacturing the extensible paper then comprises the
addition to the
dried web of a polymer 19. Synergistic interactions between the treated fibers
and thermoplastic
polymer in the paper can then occur and provide high stretch. The polymer is
preferentially soft
and stretchy. The polymer can be bio-based, biodegradable and/or petroleum-
based. Examples of
biodegradable polymers include polylactic acid, polydroxyalkanoates and
natural latex (Hevea
13
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Brasiliensis). Examples of petroleum-based polymers include thermoplastics
such as polyethylene,
polypropylene and polyethylene terephthalate. The petroleum-based polymer can
also be selected
from synthetic latexes such as styrene-butadiene copolymers, acrylonitrile-
butadiene copolymers,
acrylic, vinyl acetate polymers and copolymers, and vinyl chloride-vinylidene
chloride copolymers.
[0076] After the papermaking and drying processes of the web prepared with the
mechanically
treated fibers, the polymer can be added as a water-based dispersion to the
base paper by
impregnation, coating, sizing or spraying. In a preferred embodiment, the
polymer is a latex with
low glass transition temperature added to the paper by impregnation. The term
"impregnation" as
used herein comprises flooding the web with a water-based polymer, removing
the excess polymer
from the surface of the web and drying the web in order to evaporate the
water. An optional
calendering step 18 may occur before the addition of the polymer 19 or after,
in order to notably
compact the paper surface to improve for example its smoothness and gloss.
[0077] The combination of mechanically treated fibers and addition of polymer
provides a
composite material having properties that are intermediate between those of a
paper and those of
a plastic. High stretch potential is imparted to the fibers during mechanical
treatment and the low
elastic modulus of the paper allows the load applied during tensile testing to
be shared between
the pulp fibers and polymer in the sheet.
[0078] In an embodiment, the polymer is added in an amount of from 2 to 40 wt%
of the
extensible paper. Preferably, 5 - 20 wt% of polymer is added.
[0079] Figs. 6A to 60 compare the elastic modulus (Fig. 6A), tensile
strength (Fig. 6B),
elongation at break (Fig. 60) and specific volume (Fig. 60) of standard
handsheets made from a
Northern Bleached Softwood Kraft (NBSK) and from the same NBSK pulp after
mechanical
treatment in a plug screw under an applied pressure of 8 bars. While
mechanical treatment of the
pulp fibers increases their stretch potential, Figs. 6A to 60 show that
handsheets made of such
mechanically treated fibers undergo large decreases in elastic modulus
(stiffness) and tensile
strength and a small decrease in elongation at break. The large decrease in
tensile strength might
be due to a reduction in the total fiber to fiber bonded area and to the
presence of kinks in the
fibers that cannot transmit forces across the network during tensile loading.
It will be understood
that such decrease in tensile strength prevents any gain in stretch potential
to be realized in a
paper made from the mechanically treated pulp fibers without the addition of
the polymer.
[0080] According to Fig. 60, mechanical treatment of the pulp fibers leads
to a significant
increase in specific volume or porosity. The extensible paper can therefore be
used in applications
requiring both high extensibility and high permeability.
[0081] As illustrated by Figs. 7A to 70, an increase in elongation at break
can be observed, even
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at low dosages of the polymer, and depends on the type polymer added and the
method used. In
the examples of Figs. 7A to 70, 10% by weight of an acrylic copolymer (Acronal
LA 471 S from
BASF) was added by impregnation to basesheets made from the original NBSK pulp
or from the
NBSK pulp after mechanical treatment. The total grammage, including pulp
fibers and polymer,
was 60 g/m2 in both cases. While the addition of the polymer can increase the
stretch of
basesheets made from the original NBSK pulp from 2.3% to 5.1%, the addition of
the polymer to
basesheets made from the mechanically treated NBSK pulp can increase the
stretch from 2.0% to
14.8%.
[0082] As shown in Fig. 1, a polymer 21 can also be added to the pulp prior to
papermaking. In
that case, the polymer can be in the form of fiber or as a water-based
dispersion (latex). If the
polymer is added to the pulp as a latex, then a retention aid can also be
added to the pulp to help
retain the polymer during the papermaking process.
[0083] In a
particular embodiment, the method includes the addition of strength additives
within
the pulp. The strength additives improve the strength properties of the
extensible paper. The
strength additive can include dry-strength agents, such as starch,
polyacrylamide derivatives and
cellulose fibrils. Examples of strength additive also include wet-strength
agents such as
polyamide-epichlorohydrin, melamine, urea formaldehyde and polyimines. Other
additives, such
as sizing agents, debonders, dispersants, cross linking agent, or cellulose
fibrils, can also be added
to the pulp prior to papermaking process.
[0084] Strength
additives can be added to the pulp alone or together with retention aids that
help retain the strength additive in the wet web during papermaking. As
mentioned in the examples
below, basesheets made from the mechanically treated NBSK pulp prepared in
presence of 1% by
weight of polyamide-epichlorohydrin resin, and impregnated with 10% by weight
of an acrylic
copolymer (Acronal LA 471 S), presented a dry and wet tensile strengths of
11.6 and 4.87 N=m/g,
respectively. By comparison, the dry and wet tensile strengths of basesheets
prepared without the
strength additive but impregnated with latex were 9.7 and 1.05 N=m/g,
respectively. Therefore, the
presence of a strength additive in the extensible paper increases its dry and
wet tensile strengths.
The elastic modulus and the burst strength of the extensible paper are also
increased by the
addition of a strength additive.
[0085] As shown in Fig. 1, more than one pulp can be included in the
composition of the
extensible paper. The optional additional pulp 24 can include regular
chemical, mechanical and
high-yield pulps and other natural fibers as well as man-made fibers
dispersible in water. The fibers
in the additional pulp can also be mechanically treated 13.
[0086] In a
particular embodiment, the extensible paper is manufactured in a continuous
papermaking process. However, the polymer addition can also be performed
offline during
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converting operations.
[0087] The extendible paper as described herein comprises at least
mechanically treated pulp
fibers obtained by the above-defined treatment, and a polymer defined herein
in an amount of from
2 to 40 wt% based on the weight of the extendible paper. The polymer is
preferably added by
impregnation, as described herein, so that the extensible polymer is
preferably a
polymer-impregnated extensible paper, having a polymer content of between 2 to
40 wt%,
preferably 10 wt%. The length-weighted average curl index Cm of the
mechanically treated pulp
fiber is of at least 0.1. The curl index can be of 0.1-0.45, preferably 0.2-
0.45, and more preferably
0.25-045. The extensible paper can also comprise other components such as
strength additives, a
cross-linking agent, retention aids, or other type of pulps added during the
manufacturing process.
[0088] In a
particular embodiment, the extensible paper is dried under restraint and a
polymer
has been added after drying. The combination of mechanical treatment,
restrained drying and
addition of polymer after drying leads to a Gurley air resistance below 20
s/100 mL while providing
high extensibility. The porosity and elongation at break of the resulting
extensible paper are
increased and shrinkage is decreased. The elongation at break can be of at
least 10%, more
particularly of 10 to 90%. The specific properties of the extensible paper,
obtained by the
combination of the method steps identified above, allows extending the use of
paper to
non-traditional applications, and provides a green alternative to plastic
products, while using
existing pulp and paper manufacturing processes.
[0089] The properties of the paper can be tailored to meet a wide range of end-
use
requirements. For example, the paper can have a relatively high elongation at
break and relatively
low strength, and therefore have properties similar to that of plastic
materials. The paper can also
have high tensile strength and an elongation at break of at least 10%.
[0090] The
extensible paper can be used in applications that include: mulch film for
horticultural
applications, sack paper and bag for packaging applications, and barrier or
wrapping material for
protecting items such as wood lumber, paper rolls, home furniture, building
materials and
thermoformed packaging products. The extensible paper can also be a high
grammage
paperboard. For example the extensible paper can have a grammage of from 25 to
300 g/m2. In
this case, the high grammage paperboard can be moulded into 3D shapes suitable
for various
packaging applications.
[0091] The
properties of the extensible paper (wet and dry tensile strengths, tear
strength, burst
strength, tensile energy absorption and Gurley air resistance) can be
controlled by changing the
manufacturing process and/or the composition of the extensible paper. For
example, it is possible
to (i) vary the proportion of mechanically treated fibers, (ii) vary the
amount and type of polymer in
the extensible paper, (iii) vary the type of pulp that is mechanically
treated, (iv) vary the level of
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induced curl (the second curl index), (v) vary the refining energy and
occurrence through
mechanical treatment, (vi) add other pulps and (vii) use additives such as wet
and dry strength
agents, retention aids and sizing agents. More particularly, possible
approaches to increase
elongation at break include: increasing the amount of polymer in the
composition of the paper,
using a polymer with higher stretch potential, increasing the pressure applied
to the pulp during
mechanical treatment. Possible approaches to increase their tensile and burst
strengths include
refining the pulp before or after mechanical treatment, adding one or several
stronger pulps,
adding strength additives to the paper, using a polymer with higher strength
properties.
[0092] Fig. 8
illustrates the wide range of tensile strength and elongation at break
achieved with
various embodiments of the extensible paper.
[0093] The
present disclosure will be more readily understood by referring to the
following
examples, which are given to illustrate the disclosure rather than to limit
its scope.
Description of Methods
Preparation of mechanically curled fibers
[0094] Different types of pulps including chemical (kraft), mechanical (TMP)
and
chemi-thermo-mechanical (CTMP) or bleached chemi-thermo-mechanical (BCTMP)
were used to
produce curly fibers for different applications.
[0095] A pilot
plant pressurized refining system was used, as illustrated in Fig. 9, to
produce
fibers with structural curl and kinks. The system comprised a chip/fiber bin
30, plug screw 32,
steaming tube feeding system 34, a 22" single disk refiner 36 and cyclone 40.
The pressure of the
system was varied from 3 to 16 bars in order to produce fibers with different
curl and kink index
values. Steaming time of 2 to 4 minutes was covered and the pulp consistency
was varied from 28%
to 50%. The wood species included Canadian eastern black spruce, balsam fir,
Canadian western
spruce-lodgepole pine and balsam fir (SPF), aspen, and Douglas fir. The fiber
curl and kink
indexes were measured using a Fiber Quality Analyzer (FQA).
Determination of Water Retention Value (WRV)
[0096] The following procedure was used to measure the water retention value
(WRV) of pulps.
The pulp was dispersed in water at about 1% consistency. Then the dispersed
pulp was drained
over a 150 mesh inside a deckle. The resulting pulp pad was separated in three
subdivided-pads
and a portion of each subdivided-pad was added in one of three specially-
fitted centrifuge tubes.
The loaded centrifuge tubes were taken in pairs and adjusted to the same
weight by adding a little
water to the lighter one. Each pair was mounted in opposite holes in the
centrifuge rotor and the
uncapped tubes were centrifuged at 900g (g=Earth's gravitational force) for 30
minutes. The pulp
pad portions were then transferred from the tubes to pre-weighted bottles.
During the transfer, the
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pulp pad portions were broken into half a dozen small pieces. Stoppers were
installed on the
bottles and each bottle with the stopper was reweighed. The bottles and their
content were then
put to dry at 105 C. After drying for at least 4 hours in the oven, the weight
of the bottles was
measured and the WRV calculated based on the three subdivided-pads.
Impregnation of basesheet with latex:
[0097] Synthetic latex was added to the basesheet using the following
procedure. (1) The
basesheet is first placed between two mesh holders with square holes 4 mm a
side. (2) The two
mesh holders and basesheet were completely immersed in a bath of latex for 1
minute. (3) The
mesh holders and basesheet were retrieved from the bath and placed over a
blotter lying flat on a
counter. (4) The top mesh was removed and the basesheet was covered with a
piece of satin. A
second blotter was placed on top of the satin. (5) The whole assembly was
flipped over so that the
blotter originally in contact with the counter was on top. The blotter and
mesh were removed and
the side of the basesheet that was then exposed was covered with another piece
of satin and then
another blotter. (6) A couching roll weighing 28 lbs. was passed twice (back
and forth motion) over
the assembly. (7) The top blotter and piece of satin were removed and the
basesheet was peeled
from the bottom piece of satin. (8) The basesheet was placed against a drying
plate covered with
Teflon and the drying plate and handsheets were placed into the recessed rim
of a drying ring,
such that the handsheet was in contact with the surface of the recessed rim.
Several drying rings
were stacked in such a way that each handsheet was facing up. (9) The stack of
drying rims was
loaded with a 10 lbs weight to insure uniform drying restraint over the area
of the handsheet(s) and
to prevent shrinkage. (10) The amount of latex thus added to the basesheet can
be controlled by
adjusting the solids content of the latex bath. In general, the amount of
polymer transferred to the
basesheet increases nonlinearly with the solids content of the bath. For each
type of latex tested,
that relationship was obtained experimentally by first repeating the procedure
detailed above three
or four times, varying the solids content of the bath each time. A quadratic
fit to the data was then
used to determine the solids content to use in subsequent experiments in order
to achieve a given
addition level.
Analysis of handsheets
[0098] Analysis of handsheets prepared according to the present method, with
or without
polymer addition, was performed according to the PAPTAC standard methods of
Table 2 below.
Table 2
PAPTAC standard methods for analysing handsheets
Method Reference
Grammage of paper and paperboard PAPTAC Standard 0.3
Thickness and apparent density of paper and paperboard PAPTAC Standard 0.4
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Tensile breaking properties of paper and paperboard (Constant rate
PAPTAC Standard 0.34
of elongation method)
Moisture determination for chemical and physical analysis PAPTAC Standard
G.3
Bursting strength of paper PAPTAC Standard 0.8
Air resistance of paper PAPTAC Standard 0.14
Internal tearing resistance of paper, paperboard and pulp
PAPTAC Standard 0.9
handsheets
[0099] To measure the tensile properties of rewetted handsheets, the
handsheets were first
immersed in water for 1 minute and then placed between two blotters to remove
the excess water.
Tensile breaking properties of the rewetted handsheets were then measured
according to
Standard 0.34.
Measure of formability
[00100] An in-house method was developed to form paper into three-dimensional
shapes. The
device involves a spherical die attached to an lnstron testing system. The
spherical die was
lowered at a specified speed into a paper sample clamped between two plates so
that no sliding of
the paper into the forming cavity could take place. The total displacement of
the sphere at failure
provided a measure of formability. Forming ratios were defined as the forming
depth over the base
diameter.
EXAMPLE I
[00101] This example illustrates how the properties of a paper a described
herein, made from a
Northern Bleached Softwood Kraft (NBSK) pulp consisting of black spruce
fibers, can be controlled
by mechanical treatment, by impregnation of latex and by addition of polyamide-
epichlorohydrin
(PAE). In total, five different sets of handsheets were prepared and their
composition is given in
Table 3. In addition, the mechanical properties measured on the first and
second sets of
handsheets are shown on the first two lines of Table 4.
Table 3
Composition of five sets of handsheets
Set # Pulp Additives
1 Northern Bleached Softwood Kraft (NBSK)
2 NBSK 10% Acronal LA 471S
3 NBSK after mechanical treatment (8 bars)
4 NBSK after mechanical treatment (8 bars) 10% Acronal LA 471S
10% Acronal LA 471S
NBSK after mechanical treatment (8 bars)
1% polyamide-epichlorohydrin
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Table 4
Mechanical properties of the five sets of handsheets
Wet
Tensile TEA Elastic Tear
Set Caliper Stretch Burst
Index Tensile
Index Index Modulus Index
(pm) (%) (kPa m2/g) Index
(N=m/g) (mJ/g) (km) (mN m2/g )
(N=m/g)
1 118 2.3 31.2 520 485 25.8 1.90 1.47
2 119 5.1 31.7 1230 320 21.0 4.17 2.72
3 145 2.0 10.6 150 185 10.5 0.60 0.51
4 155 14.8 9.7 1200 85 24.0 2.19 1.05
145 23.4 11.6 2300 105 23.4 2.78 4.87
the target grammage was 60 g/m2 in all cases and TEA stands for Tensile Energy
Absorption
[00102] The first set (#1) corresponds to standard handsheets (of grammage 60
g/m2) made from
the original pulp.
[00103] The second set (#2) of handsheets of grammage 54 g/m2 was prepared
from the same
pulp. The handsheets of the second set were dried under restraint and then
impregnated with an
ester acrylate copolymer (Acronal LA 471S, from BASF) using the procedure
described herein.
The target grammage of the paper, including pulp fibers and latex, was 60
g/m2. This corresponds
to a latex content of 10% by weight. As shown by the results of Table 4 (lines
1 and 2), the addition
of latex led to an increase in the elongation at break of from 2.3 to 5.1%. It
also had a positive
impact on burst and Tensile Energy Absorption (TEA) indices as well as on wet
tensile strength.
The elastic modulus decreased from 485 to 320 km.
[00104] The third set (#3) of standard handsheets was prepared from the same
commercial
NBSK pulp that was treated mechanically in a plug-screw feeder to induce
deformations and curl in
the fibers. The pressure applied to the pulp during the mechanical treatment
was 8 bars. The
sheets prepared from the treated fibers were bulky and weak. As shown by the
results of Table 4
(line 3), mechanical treatment of the pulp led to a large decrease in all
strength properties of the
paper. In particular, the tensile strength decreased from 31.2 to 10.6 N.m/g
and the elongation at
break from 2.3% to 2.0%. The elastic modulus also decreased from 485 km to 185
km while caliper
increased from 118 to 145 pm.
[00105] The fourth set (#4) of handsheets was prepared from the mechanically
treated pulp, this
time at a grammage of 54 g/m2. These handsheets were then impregnated with 10
wt% of the latex
Acronal LA 471S. As shown by the results of Table 4 (line 4), the impregnated
handsheets had an
elongation at break of 14.8%, which represents more than seven time the
elongation at break of
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the same handsheets without latex. The TEA index, which is a measure of how
much energy must
be expended to break the paper, also increased from 150 to 1200 mJ/g.
[00106] The fifth set (#5) of handsheets was produced from the mechanically
treated fibers of the
third set, but here 1 wt% of polyamide-epichlorohydrin (PAE), a commonly used
wet-strength agent,
was added to the pulp prior to making handsheets of grammage 54 g/m2. The
handsheets of the
fifth set were then impregnated with 10 wt% of the latex Acronal LA 471S. As
shown in line 5 of
Table 4, addition of PAE to the pulp had a large positive impact on the dry
and wet tensile strengths
as well as on the tensile energy absorption of the sheets impregnated with
latex.
EXAMPLE II
[00107] This example illustrates how the properties of a paper as described
herein, made from a
never-dried unbleached softwood kraft (UBSK), can be controlled by mechanical
treatment, by
impregnation of latex and by addition of polyamide-epichlorohydrin (PAE). In
total, four different
sets of handsheets were prepared for this example.
[00108] The first set (#1) corresponds to standard handsheets prepared from
the original UBSK
pulp (#1). The second set (#2) corresponds to handsheets made from the UBSK
pulps but with 1%
PAE added to the pulp prior to sheetmaking and 10% latex added to the dry
sheets by
impregnation. The third set (#3) corresponds to standard handsheets prepared
from the UBSK
pulp after treatment in a plug-screw feeder at a pressure of 3.5 bars (#3).
The fourth set (#4)
corresponds to handsheets made from the UBSK pulps after treatment in a plug-
screw feeder at a
pressure of 3.5 bars and with 1% PAE added to the pulp prior to sheet making
and 10% latex
added to the dry sheets by impregnation.
[00109] The composition and mechanical properties of the different sets of
handsheets are
summarized respectively in Tables 5 and 6 below. A comparison of data from the
first and fourth
sets (#1 and #4) shows that mechanical treatment of the pulp combined with the
addition of PAE
and latex leads to large increases in stretch, tensile energy absorption and
wet tensile strength.
The handsheets of the fourth set (#4) also have a much lower modulus and they
are weaker in the
dry state than sheets made from the original pulp (tensile index of 30.2 N.m/g
compared to 48.3
N. m/g).
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Table 5
Composition of the four sets of handsheets
Set # Pulp Additives
1 Unbleached Northern Softwood Kraft
(UBSK)
10% Acronal LA 471S
2 UBSK
1% polyamide-epichlorohydrin
3 UBSK after mechanical treatment
(3.5 bars)
10% Acronal LA 471S
4 UBSK after mechanical treatment
(3.5 bars)
1% polyamide-epichlorohydrin
Table 6
Mechanical properties of the four sets of handsheets
Wet
Tensile TEA Elastic Tear
Set Caliper Stretch Burst Index Tensile
Index Index Modulus Index
# (pm) (%) (kPa m2/g) Index
(N=m/g) (mJ/g) (km) (mN m
2/g)
(N=m/g)
1 117 2.3 48.3 760 620 27.3 3.11 1.90
2 115 4.2 67.8 1800 410 10.8 7.07 18.0
3 141 1.8 14.8 200 230 16.7 0.90 0.53
4 130 9.7 30.2 2300 230 26.7 4.00 8.86
The target grammage was 60 g/m2 in all cases
EXAMPLE Ill
[00110] This example illustrates how the properties of the paper encompassed
herein can be
controlled by varying the amount of polymer in the sheet. The starting pulp in
this case was a
Northern Bleached Softwood Kraft pulp (NBSK) different from the one used in
Example II. In total,
five different sets of handsheets were prepared for this example.
[00111] The first set (#1) corresponds to standard handsheets made from the
original NBSK pulp,
the second set (#2) corresponds to standard handsheets made from the pulp
after mechanical
treatment in a plug-screw feeder at 12 bars, the third, fourth and fifth set
corresponds to
handsheets made from the mechanically treated pulp and impregnated with 10%
(#3), 20% (#4) or
30% (#5) of latex (Acronal LA 471S). The grammage of the handsheets (including
pulp fibers and
latex) was 60 g/m2 in all cases. The composition and mechanical properties of
the different sets of
handsheets are summarized in Tables 7 and 8, respectively.
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[00112] As reported in Examples ll and III, plug-screw treatment alone had a
negative impact on
all mechanical properties, including elongation at break, which decreases from
2.5 to 1.7%.
However, highly extensible papers were produced when the handsheets made from
the
mechanically treated fibers were subsequently impregnated with latex. The
elongations at break of
measured on handsheets containing 10%, 20% and 30% latex, were of 27.2%, 46.2%
and 61.8%
respectively.
Table 7
Composition of the five sets of handsheets
Set # Pulp Additives
1 Northern Bleached Softwood Kraft (NBSK)
2 NBSK after mechanical treatment (12 bars)
3 NBSK after mechanical treatment (12 bars) 10% Acronal LA 471S
4 NBSK after mechanical treatment (12 bars) 20% Acronal LA 471S
NBSK after mechanical treatment (12 bars) 30% Acronal LA 471S
Table 8
Mechanical properties of the five sets of handsheets
Tensile Elastic Burst
Caliper Stretch TEA Index Tear Index
Set # Index Modulus Index (kPa
(pm) (%) (mJ/g) (mN m
2/g)
(N=m/g) (km) m2/g )
1 123 2.5 23.1 400 390 19.2 1.51
2 155 1.7 7.5 95 130 7.6 0.35
3 191 27.2 7.4 1700 41 17.5 1.32
4 165 46.2 8.9 3450 30 18.8 2.41
5 158 61.8 9.3 4600 22 15.6 2.59
The target grammage was 60 girrizin all cases
EXAMPLE IV
[00113] This example illustrates the impact of changing the pressure applied
to the pulp during
the mechanical treatment on the final properties of the stretchable paper. The
starting pulp was the
same NBSK pulp used in Example IV. In total, three different sets of
handsheets were prepared, all
of them impregnated with 10% of a styrene-butadiene latex (CF 638NA,
manufactured by Dow
Chemical).
[00114] The handsheets of the first set (#1) were prepared from the original
NBSK pulp while
those of the second (#2) and third (#3) sets were made from the original NBSK
pulp after treatment
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in a plug-screw feeder at pressures of 6 bars (#2) and 16 bars (#3). The
composition and
mechanical properties of the different handsheets are given in Tables 9 and 10
below.
[00115] The results from Table 10 show that the elongation at break of the
handsheets
impregnated with latex increases with the amount of pressure applied to the
pulp during the
mechanical treatment. By contrast, the mechanical properties such as tensile
strength and burst
resistance decrease when the applied pressure increases.
Table 9
Composition of the three sets of handsheets
Set # Pulp Additives
1 Northern Bleached Softwood Kraft (NBSK) 10% CF 638NA
2 NBSK after mechanical treatment (6 bars) 10% CF 638NA
3 NBSK after mechanical treatment (16 bars) 10% CF 638NA
Table 10
Mechanical properties of the three sets of handsheets
Tensile Elastic Burst
Caliper Stretch TEA Index Tear Index
Set # Index Modulus Index
(pm) (%) (mJ/g) (mN m2/g)
(N=m/g) (km) (kPa m2,1g)
1 132 5.6 31.0 1200 260 18.1 3.37
2 159 7.1 18.3 990 150 17.8 2.21
3 187 9.7 14.4 1080 90 12.9 1.78
The target grammage was 60 girrizin all cases
EXAMPLE V
[00116] This example illustrates the impact of pulp refining prior to the
mechanical treatment. The
starting pulp in this case was a never-dried Unbleached Softwood Kraft pulp
(UBSK) similar to that
used in Example III. In the present example, the pulp was refined at high-
consistency in a
double-disk refiner prior to mechanical treatment in a plug-screw feeder. The
amount of energy
expended during refining was 1000 kWh/tonne while the subsequent mechanical
treatment was
performed at a pressure of 3.5 bars.
[00117] Tables 11 and 12 detail the composition and mechanical properties of
the four sets of
handsheets. The first set (#1) corresponds to standard handsheets prepared
from the original
UBSK pulp (#1). The second set (#2) corresponds to handsheets made from the
UBSK pulps after
refining treatment. The third set (#3) corresponds to handsheets prepared from
the UBSK pulp
after refining treatment and treatment in a plug-screw feeder at a pressure of
3.5 bars (#3). The
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fourth set (#4) corresponds to handsheets prepared from the UBSK pulp after
refining treatment
and treatment in a plug-screw feeder at a pressure of 3.5 bars with 10% latex
added to the dry
sheets by impregnation.
[00118] As shown in Table 12, refining of the pulp has a large impact on its
strength so that even
after plug-screw treatment, paper made from the treated pulp has a tensile
index above 30 N.m/g.
Handsheets made from the treated pulp and impregnated with 10% latex has an
elongation at
break of 11.9%, a TEA index 2,600 mJ/g and a Gurley air resistance of only 2.6
s/100mL. The
skilled person will appreciate that the combination of high elongation at
break, high toughness and
high permeability makes the extensible paper suitable for sack grade
applications.
Table 11
Composition of the four sets of handsheets
Set # Pulp Additives
1 Unbleached Northern Softwood Kraft (UBSK)
2 UBSK after refining
3 UBSK after refining and mechanical treatment
4 UBSK after refining and mechanical treatment 10% Acronal LA
471S
Table 12
Mechanical properties of the four sets of handsheets
Gurley Air
Tensile TEA Elastic Burst
Set Caliper Stretch Tear Index
Resistanc
Index Index Modulus Index
# (pm) (%) (mN m
2/g)
(N=m/g) (mJ/g) (km) (kPa m2/g )
(s/100mL)
1 125 1.9 40.9 560 580 26.4 3.26 2.1
2 110 5.1 83.9 2900 680 17.3 7.24 430
3 135 4.2 33.6 1100 420 21.6 2.54 5.9
4 11.9 27.5 2600 240 22.3 2.6
The target grammage was 60 g/m2 in all cases
EXAMPLE VI
[00119] It is illustrated how the properties of the stretchable paper as
described herein change
with the type of polymer added to the basesheet.
[00120] In total, ten different sets of handsheets were prepared in Example
VII. The starting pulp
for the first five set was the same NBSK pulp used in Examples IV and V. The
first set (#1) was
prepared from the NBSK pulp mechanically treated in a plug-screw feeder at a
pressure of 16 bars.
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Basesheets made from the mechanically treated pulp but of lower grammage were
also prepared
for the second to fifth sets (#2 to #5). The basesheets were impregnated with
four different latexes
added in an amount of 10% by weight: CF 638NA (#2) , Styronal NX 4222X , BASF
(#3), Acronal
LA 471S (#4) and Acronal S504NA, BASF (#5). The composition and mechanical
properties of the
handsheets from the five sets are given in Tables 13 and 14, respectively.
[00121] The results from Table 14 show that the mechanical properties of the
stretchable paper
depend on the nature of the latex that is used. In this particular example,
the latex used for the
fourth set (#4) is the one that provides the highest elongation at break the
latex used for the
second set (#2) provides the highest increase in strength (relative to the
base paper made from the
mechanically treated fibers).
[00122] The starting pulp for sets #6 to #10 was also the same NBSK pulp than
in Example II. In
this case, the pulp was refined in a double disk refiner and then treated
mechanically in a
plug-screw feeder. The energy expended during refining was 1000 kWh/tonne
while the pressure
inside the plug-screw feeder during treatment was 3.5 bars. The basesheets of
the seventh and
eighth sets were impregnated with 10% (#7) and 20 % (#8) of the synthetic
latex Acronal LA 471S
while those of the fourth and fifth sets were impregnated with 10% (#9) and
20% (#10) of a natural
latex provided by the company Chemionics. Tables 13 and 14 show the
composition and
mechanical properties for the five sets of handsheets prepared herein.
[00123] The results of Table 14 show that while the elongation at break
obtained with the natural
latex is not as high as the elongation at break obtained with the synthetic
one, it is still possible to
produce an extensible paper that is essentially 100% bio-based and
biodegradable and has an
elongation at break (or stretch) of 10% or more at relatively low dosages of
the natural polymer.
Table 13
Composition of the different sets of handsheets
Set # Pulp Additives
1 NBSK after mechanical treatment (16 bars)
2 same 10% CP 638NA
3 same 10% Styronal NX 4222X (BASF)
4 same 10% Acronal LA 471S
same 10% Acronal S504NA (BASF)
Set # Pulp Additives
6 NBSK after refining and mechanical treatment (3.5 bars)
7 same 10% Acronal LA 471S
8 same 20% Acronal LA 471S
9 same 10% natural latex
same 20% natural latex
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Table 14
Mechanical properties of the different sets of handsheets produced.
Elastic
Caliper Stretch Tensile Index TEA Index Tear Index
Burst Index
Set # Modulus
(1m1) (0/0) (N=m/g) (mJ/g) (mN m2/g) (kPa
m2/g)
(km)
1 143 1.4 6.7 65 135 6.6 0.42
2 187 9.7 14.4 1100 680 12.9 1.78
3 170 11.5 6.9 650 60 15.5 0.71
4 181 17.5 9.3 1300 45 14.9 1.17
167 10.6 11.9 940 70 14.2 1.79
Elastic
Caliper Stretch Tensile Index TEA Index Tear
Index Burst Index
Set # Modulus
(1-wrI) (0/0) (N=m/g) (mJ/g) (mN m2/g) (kPa m2/g)
(km)
1 149 4.2 21.1 700 280 16.6 1.56
2 148 16.1 19.6 2600 175 18.8 2.47
3 151 34.0 16.7 4500 120 13.6 2.92
4 154 9.3 16.1 1200 130 18.1 1.78
5 145 12.0 17.2 1600 95 23.6 2.15
The target grammage was 60 g/m2 in all cases
EXAMPLE VII
[00124] This example illustrates how extensible papers can be prepared from
mixtures of two
different pulps. It also illustrates the impact of latex content and type on
the mechanical properties
of the extensible papers. It finally shows how papers prepared in accordance
with an embodiment
can be moulded into three-dimensional shapes.
[00125] Two different pulps produced from the same commercial NBSK pulp were
used in the
example. The first pulp (P1) was produced by treating mechanically the NBSK
pulp in a plug-screw
feeder at a pressure of 3.5 bars. The second pulp (P2) was produced by
refining the NBSK pulp in
a double-disk refiner. The amount of energy expended during refining was 1000
kWh/tonne.
Twelve different sets of handsheets were prepared from various mixtures of the
two pulps. Nine of
these sets included in their composition up to 20% by weight of latex added by
impregnation to the
basesheets. The composition and mechanical properties of the different sets of
handsheets are
shown in Tables 15 and 16, respectively.
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Table 15
Composition of the different sets of handsheets
Set # Pulp Additives
1 100%P2 -
2 50% P1, 50% P2 -
3 100%P1 -
4 100%P2 20% Acronal S 728
50% P1, 50% P2 10% Acronal S 728
6 50% P1, 50% P2 20% Acronal S 728
7 100%P1 20% Acronal S 728
8 100%P1 20% Acronal LA 471
9 50% P1, 50% P2 10%Acronal
LA 471
50% P1, 50% P2 20% Acronal LA 471
11 100%P2 20% Acronal LA 471
20% SNP S-1420-L
12 100%P1
Polyurethane dispersion
Table 16
Mechanical properties and formability of the sets of handsheets produced
Maximum
Set Tensile Index TEA Index Maximum
load
Stretch (%) Forming Depth
# (N=m/g) (mJ/g) (N)
(mm)
1 5.53 54.3 2223 11.3 185.86
2 4.7 27.7 1032 9.7 87.44
3 2.2 13.2 220 7.3 28.4
4 7.6 66.1 3254 13.8 295.8
5 7.6 40.0 2288 13.6 204.6
6 10.0 45.8 3081 14.8 252.0
7 11.8 31.6 2633 17.1 216.8
8 41.1 10.2 3335 25.5 98.2
9 13.9 22.3 2560 15.4 120.3
10 26.8 22.3 4796 19.6 170.2
11 15.3 38.6 4585 16.1 230.4
12 21.5 30.0 4802 20.8 319.9
Total grammage (including latex) was 80 g/m2 in all cases
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[00126] The results from Table 16 illustrate the wide range of mechanical
properties that can be
obtained by varying the composition of the paper. The elongations at break
that were measured
varied between 2.2% and 41.1%, with the highest elongations at break obtained
with the
mechanically treated pulp (P1) impregnated with 20% by weight of latex Acronal
LA 471S (#8). By
contrast, the highest tensile index was measured on the sample produced with
pulp P2 and
containing 20% by weight of Acronal S 728 (#4). According to Table 15, at the
same latex addition
level, the properties of the handsheets containing equal proportions of the
two pulps were usually
intermediate between those of the handsheets produced only with each of the
pulps.
[00127] All the handsheets produced in Example VIII were also tested for
formability by using a
device developed in-house for that particular purpose. As described above, the
forming depth data
shown in Table 16 were obtained by first placing a spherical die (of diameter
9 cm) in contact with a
paper sample clamped between two plates so that no sliding of the paper into
the forming cavity
could take place. The spherical die was then lowered at constant speed into
the paper sample until
the latter failed. The total displacement of the sphere during the experiment
thus provided a
measure of maximum forming depth for each sample. The maximum load applied to
the sample
during testing was also recorded in each case.
[00128] According to Table 16, the sample made form pulp P1 and containing 20%
Acronal LA
471 (#8) had the highest formability, with a maximum forming depth of 25.5 mm.
This corresponds
to a forming ratio (defined as the ratio of forming depth to base diameter) of
about 0.3. This is
remarkably high for a paper formed in a process where no sliding is allowed
(see Fig. 10). It
illustrates the strong correlation between the maximum forming depth measured
herein and the
elongation at break measured in standard tensile testing.
EXAMPLE VIII
[00129] This example illustrates the impact of mechanical treatment and latex
impregnation on
handsheets prepared with thermo-mechanical pulp (TMP).
[00130] The thermomechanical pulp (TMP) was produced in the pilot plant in 3-
stage refining
using eastern black spruce wood chips. In the first stage, wood chips were
refined in the
pressurized 22" single disk refiner (see Fig. 9). The consecutive stages were
done in a 36" double
disc atmospheric refiner. The total refining specific energy was about 2482
kWh/t. In total, four sets
of handsheets were produced from the TMP pulp. The composition for each set is
given in Table
17.
[00131] The first and second sets correspond to standard handsheets (of
grammage 60 g/m2)
made from the original TMP pulps (#1) and from the TMP pulp after mechanical
treatment (#2). For
the third and fourth sets, handsheets of grammage 54 g/m2 were first prepared
from the original
TMP pulps (#3) and from the TMP pulp after mechanical treatment (#4), dried
under restraint and
then impregnated with an ester acrylate copolymer (Acronal LA 471S). The
target grammage of
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the paper, including pulp fibers and latex, was 60 g/m2. This corresponds to a
latex content of 10%
by weight.
[00132] The mechanical properties of the handsheets were measured under
traction in both dry
and wet states and are presented in Table 18 below. Caliper, out-of-plane tear
strength and burst
resistance were also measured. According to the results of Table 18, the
mechanical treatment of
the TMP pulp decreased tensile strength while increasing stretch slightly.
Table 18 also shows that
latex addition to the basesheet increased the elongation at break from 2.14%
to 3.73% in the case
of the untreated TMP pulp, and from 2.37% to 4.83% in the case of the TMP pulp
mechanically
treated in the plug screw at a pressure of 6 bars.
Table 17
Composition of the four sets of handsheets
Set # Pulp Additives
1 Thermo-mechanical pulp (TMP)
2 TMP after mechanical treatment (6
bars)
3 TMP 10% Acronal LA 471S
4 TMP after mechanical treatment (6
bars) 10% Acronal LA 471S
Table 18
Properties measured on the four sets of handsheets
Wet
Tensile TEA Elastic Tear
Set Caliper Stretch Burst
Index Tensile
Index Index Modulus Index
(pm) (%) (kPa m2/g) Index
(N=m/g) (mJ/g) (km) (mN m2/g )
(N=m/g)
1 168 2.14 41.4 520 385 7.85 2.63 4.32
2 185 2.37 26.4 430 260 7.64 1.69 2.60
3 162 3.73 44.3 1090 306 6.21 3.75 4.46
4 173 4.83 29.4 1020 210 6.50 2.51 2.95
The target grammage was 60 g/m2 in all cases. TEA stands for Tensile Energy
Absorption
EXAMPLE IX
[00133] This example illustrates the impact of the amount of latex on
handsheets prepared with
thermo-mechanical pulp (TMP) and latex impregnation.
[00134] The thermomechanical pulp (TMP) was produced in the pilot plant in 3-
stage refining
using eastern black spruce wood chips. In the first stage, wood chips were
refined in the
pressurized 22" single disk refiner to about 255 kWhit (see Fig. 9). In the
second and third stages,
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a 36" double disc atmospheric refiner was used to refine the pulp to 1597
kWhit and 1883 kWh/t,
respectively. To induce further curl and kinks, the produced pulp was then
treated in the
pressurized refining system plug screw to a pressure of 16 bars. In total,
three different sets of
handsheets were prepared from that pulp and their composition is shown in
Table 19.
[00135] The first set (#1) corresponds to standard handsheets of grammage 60
g/m2 prepared
form the TMP mechanically treated pulp. The second and third sets correspond
to handsheets of
grammage 54 g/m2 and 42 g/m2 prepared from the TTMP mechanically treated pulp
impregnated
with 10% (#2) and 30% (#3) of latex Acronal LA 471S using the procedure
described herein. The
target grammage of the paper, including pulp fibers and latex, was 60 g/m2.
The physical and
mechanical properties measured on these three sets of handsheets are shown in
Table 20.
[00136] According to Table 20 the elongation at break, TEA index and wet
tensile index increased
with increasing amount of latex, while the elastic modulus decreased.
Table 19
Composition of the three sets of handsheets
Set # Pulp Additives
1 TMP after mechanical treatment (16
bars)
2 TMP after mechanical treatment (16
bars) 10% Acronal LA 471S
3 TMP after mechanical treatment (16
bars) 30% Acronal LA 471S
Table 20
Properties measured on the three sets of handsheets
Wet
Tensile TEA Elastic Tear
Set Caliper Stretch Burst
Index Tensile
Index Index Modulus Index
(pm) (%) (kPa m2/g) Index
(N=m/g) (mJ/g) (km) (mN m2/g )
(N=m/g)
1 199 2.05 4.61 68 59.8 2.13 N/A 0.72
2 206 7.06 9.27 480 52.6 2.94 0.76 1.69
3 166 18.5 7.24 1120 34.6 2.33 0.89 1.95
The target grammage (including fibers and polymer) was 60 g/m2 in all cases
EXAMPLE X
[00137] This example illustrates how the point of addition of the latex
impacts the mechanical
properties of extensible papers as described herein.
[00138] A commercial NBSK pulp with a high content of Douglas fir fibers was
used in the
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example. The pulp was first treated in a plug-screw feeder at 3.5 bars. Two
different sets of
handsheets were then prepared from the treated pulp. The first set (#1) of
handsheets of
grammage 54 g/m2 was prepared from the treated pulp and dried under restraint.
The dried
handsheets were then impregnated with an ester acrylate copolymer (Acronal LA
471S, from
BASF) using the procedure described herein. The target grammage of the paper,
including pulp
fibers and latex, was 60 g/m2. This corresponds to a latex content of 10% by
weight. The second
set (#2) of handsheets of grammage 54 g/m2 was also prepared from the treated
pulp but
handsheets from the second set were not allowed to dry prior to impregnation
with polymer.
Instead, handsheets from the second set were impregnated with the ester
acrylate copolymer
(Acronal LA 471S) after the pressing steps described in PAPTAC standard 0.4.
The target
grammage of the paper, including pulp fibers and latex was also 60 g/m2. The
mechanical
properties of papers from set #1 and set #2 are summarized in Table 21.
Results from Table 21
show that both the elongation at break and tensile strength of papers from set
#1 are higher than
those of papers from set #2, indicating that, in order to achieve optimal
performance, it is
preferable to dry the handsheets prior to impregnation with latex.
Table 21
Properties measured on the two sets of handsheets
Tensile TEA Elastic Tear
Set Caliper Stretch Burst Index
Index Index Modulus Index
(pm) (%) (kPa m2/g)
(N=m/g) (mJ/g) (km) (mN m2 /g)
1 156 13.4 11.4 1300 96 21.6 1.75
2 195 11.9 9.8 975 96 22.4 1.76
The target grammage (including fibers and polymer) was 60 g/m2 in all cases
EXAMPLE XI
[00139] This example illustrates the impact on the final properties of the
stretchable paper
encompassed herein of changing: a) the pressure applied to the pulp during the
mechanical
treatment and b) the amount of polymer added to the sheet. The starting pulp
for this example was
a Northern Bleached Hardwood Kraft (NBHK) pulp comprising a majority of aspen
fibers. In total,
fourteen different sets of handsheets were prepared for this example. The
grammage of
handsheets prior to impregnation with latex was 60 g/m2 in all cases.
[00140] The handsheets of sets #1 to #4 were prepared from the original NBHK
pulp. Sets #5 to
#8 were prepared from the NBHK pulp after treatment in a plug-screw at a
pressure of 3.5 bars.
Sets #9 to #11 were prepared from the NBHK pulp after treatment in a plug-
screw at a pressure of
9 bars. Sets #12 to #14 were prepared from the NBHK pulp after treatment in a
plug-screw at a
pressure of 15 bars. The different sets also differ in the amount of latex
added to the handsheets.
The composition and mechanical properties of the different handsheets are
given in Tables 22 and
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23 below.
[00141] Results from Table 23 illustrate the large increase in elongation at
break achieved by
making handsheets from a mechanically treated pulp and subsequently
impregnating the
handsheet with an extensible polymer. Measured values of elongation at break
increased with the
amount of polymer added to the handsheet. For this pulp, applied pressure
above 3.5 bars had no
significant impact on stretch potential.
Table 22
Composition of the fourteen sets of handsheets
Set # Pulp Additives
1 -
2 5.4% Acronal LA 471S
Northern Bleached Hardwood Kraft (NBHK)
3 10.1% Acronal LA 471S
4 20.3% Acronal LA 471S
6 5.4% Acronal LA 471S
NBHK after mechanical treatment (3.5 bars)
7 10.1% Acronal LA 471S
8 20.9% Acronal LA 471S
9
NBHK after mechanical treatment (9 bars) 10.4% Acronal LA 471S
11 19.4% Acronal LA 471S
12
13 NBHK after mechanical treatment (15 bars) 9.8% Acronal LA
471S
14 18.7% Acronal LA 471S
Table 23
Physical and mechanical properties of the different sets of handsheets
Tensile Elastic
Grammage Stretch TEA Index
Set # Caliper (pm) Index Modulus
(g/m2)
(/0) (mJ/g)
(N=m/g) (km)
1 60.7 131 1.20 14.3 120 258
2 61.9 144 3.15 8.9 219 116
3 64.3 142 6.98 10.6 626 123
4 72.6 142 13.48 11.3 1291 84
5 61.1 149 1.27 10.5 96 182
6 59.9 151 5.66 6.8 326 77
7 63.6 154 11.00 7.8 737 71
8 73.9 154 28.18 8.4 1966 53
9 59.8 145 1.12 7.7 59 127
10 69.2 174 10.26 6.2 530 43
11 73.7 162 27.09 6.9 1584 40
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Tensile Elastic
Grammage Stretch TEA Index
Set # Caliper (pm) Index Modulus
(g/m2)
(/0) (mJ/g)
(N=m/g) (km)
12 59.2 157 0.96 5.5 35 97
13 68.7 184 12.76 5.6 595 36
14 73.1 170 26.88 5.7 1304 28
EXAMPLE XII
[00142] This example illustrates the impact of grammage on the final
properties of the stretchable
paper as described herein. The pulp used for this example was a Northern
Bleached Softwood
Kraft (NBSK) pulp treated mechanically in a plug-screw feeder at 3.5 bars. In
total, eleven different
sets of handsheets were prepared for this example.
[00143] The handsheets of sets #1 to #5 were prepared at a target grammage of
60 g/m2 prior to
impregnation with varying amounts of latex. Sets #6 to #8 were prepared at a
target grammage of
40 g/m2 prior to impregnation and sets #11 to #13 at a target grammage of 20
g/m2, also prior to
impregnation. The composition and mechanical properties of the different
handsheets are given in
Tables 24 and 25 below.
[00144] Results from Table 25 indicate that the increase in elongation at
break with polymer
content is similar for handsheets prepared at a target grammage of 40 or 60
g/m2 (prior to
impregnation). At the same polymer addition level, the elongation at break
measured on the
handsheets prepared at 20 g/m2 was lower than that measured on handsheets
prepared at the two
higher grammages. Furthermore, at the same latex addition level, tensile index
increased with
handsheet grammage. However, the differences were less pronounced as polymer
content was
increased.
Table 24
Composition of the eleven sets of handsheets
Set # Pulp Additives
1
2 5.40% Acronal
LA 471S
NBSK treated mechanically at 3.5 bars
3 10.0% Acronal LA 471S
(target grammage of 60 g/m2 prior to impregnation)
4 21.3% Acronal
LA 471S
35.5% Acronal LA 471S
6
NBSK treated mechanically at 3.5 bars
7 10.6% Acronal LA 471S
(target grammage of 40 g/m2 prior to impregnation)
8 16.7% Acronal
LA 471S
9
NBSK treated mechanically at 3.5 bars
2 11.5% Acronal LA 471S
(target grammage of 20 g/mprior to impregnation)
11 18.6% Acronal
LA 471S
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Table 25
Physical and mechanical properties of the different sets of handsheets of
Example 13
Elastic
Tensile
Grammage Stretch TEA Index Modulus
Set # Caliper (pm) Index
(g/n12) (/0) (mJ/g)
(N=m/g)
(km)
1 57.6 130 1.88 13.1 185 218
2 60.2 167 8.56 8.8 654 99
3 67.2 162 16.44 10.8 1522 90
4 77.9 165 37.35 12.4 3807 62
88.6 164 65.53 13.2 6850 46
6 39.1 104 1.28 9.1 82 159
7 41.7 118 18.38 9.9 1521 61
8 44.7 111 32.63 11.9 3180 59
9 20.8 69 1.43 4.6 42 57
24.8 85 13.57 8.4 951 41
11 24.7 78 26.78 9.7 2233 40
EXAMPLE XIII
[00145] This example illustrates that man-made fibers can be added to the
furnish from which the
stretchable paper as encompassed herein is made. The pulp used for this
example was a Northern
Bleached Softwood Kraft (NBSK) pulp treated mechanically in a plug-screw
feeder at 3.5 bars. The
man-made fibers were bicomponent fibers (bico) of length 6 mm and linear
density 1.3 dTex
comprising a PET core and PE sheath (T455, manufactured by Trevira). Four
different sets of
handsheets were prepared for this example.
[00146] The handsheets of set #1 were made from a mixture consisting of 80 wt%
treated NBSK
pulp and 20 wt% bicomponent fibers. The handsheets of set #2 were made from
the same mixture
as set #1 but they were subsequently subjected to a heat treatment to melt the
outer layer of the
bicomponent fibers. The handsheets of set #3 were made from the same mixture
as set #1 but
they were subsequently impregnated with latex. The handsheets of set #4 were
also made from
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the same mixture as set #1 but they were subsequently subjected to the same
heat treatment as
set #2 and then impregnated with latex. All handsheets were prepared at a
target grammage of 60
g/m2 prior to impregnation, and no wet-pressing pressure was applied during
the sheet making
process. The composition and mechanical properties of the different handsheets
are given in
Tables 26 and 27 below.
[00147] Results from Table 27 indicate that heat treatment is required to
develop the potential of
bicomponent fibers. Results also illustrate how, in certain embodiments, a
combination of
bicomponent fibers and impregnation with latex can improve both the elongation
at break and
tensile strength of the stretchable paper.
Table 26
Composition and heat treatment of the four sets of handsheets
Set # Composition Heat treatment
1 80% treated NBSK and 20% PET/PE bico
2 80% treated NBSK and 20% PET/PE bico 5 minutes at 160 C
69.4% treated NBSK, 17.4% PET/PE bico and
3
13.2% Acronal LA 471S
69.5% treated NBSK, 17.5% PET/PE bico and
4 5 minutes at 160 C
13.0% Acronal LA 471S
Table 27
Physical and mechanical properties of the different sets of handsheets of
Example 14
Tensile Elastic
G ram mage Caliper Stretch TEA Index
Set # Index Modulus
(g/m2)
(pm) (%) (mJ/g)
(1\1=m/g) (km)
1 58.2 330 3.11 2.9 67 28
2 65.8 352 10.7 12.4 1010 76
3 75.0 299 16.7 6.2 873 32
4 74.1 328 24.0 15.7 2756 41
EXAMPLE XIV
[00148] This example illustrates that the stretchable paper as encompassed
herein can be made
from blends of different types of pulp. The pulps used for this example were a
Northern Bleached
Softwood Kraft (NBSK) pulp treated mechanically in a plug-screw feeder at 3.5
bars and a
Northern Bleached Harwood Kraft (NBHK) pulp treated under the same conditions.
For this
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example, fourteen different sets of handsheets were prepared from different
mixtures of the two
pulps and with different amounts of latex added by impregnation. Target
grammage prior to
impregnation with latex was 60 g/m2 in all cases. The composition and
mechanical properties of
the different sets of handsheets are given in Tables 28 and 29 below.
[00149] Results from Table 29 indicate that elongation at break increases with
the content of
treated NBSK in the pulp mixture and with the latex content in the handsheet
after impregnation.
Substitution of some NBSK with NBHK is expected to improve sheet formation on
commercial
paper machines.
Table 28
Composition of the fourteen sets of handsheets
Set # Furnish Additives
1 -
2 5.0% Acronal LA
471S
100% treated NBSK
3 10.0% Acronal
LA 4715
4 21.3% Acronal
LA 4715
_
66.6% treated NBSK
6 11.0% Acronal LA 471S
33.3% treated NBHK
7 21.0% Acronal
LA 4715
8 -
33.3% treated NBSK
9 11.3% Acronal LA 471S
66.6% treated NBHK
21.1% Acronal LA 4715
11 -
12 5.4% Acronal LA
471S
100% treated NBHK
13 10.1% Acronal
LA 4715
14 20.9% Acronal
LA 4715
Table 29
Physical and mechanical properties of the different sets of handsheets
Tensile Elastic
Grammage Stretch TEA Index
Set # Caliper (pm) Index Modulus
(g/m2)
(/0) (mJ/g)
(N=m/g) (km)
1 57.64 130 1.88 13.1 185 218
2 60.16 167 8.56 8.8 654 99
3 67.21 162 16.44 10.8 1522 90
4 77.90 165 37.35 12.4 3807 62
5 60.6 144 1.72 11.8 149 185
6 70.0 170 11.52 9.9 936 67
7 72.1 163 37.94 11.6 3564 67
8 59.4 144 1.49 11.0 117 176
9 69.3 167 13.85 9.2 1075 67
10 73.0 163 32.52 10.1 2704 55
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Tensile Elastic
Grammage Stretch TEA Index
Set # Caliper (pm) Index Modulus
(g/m2)
(/0) (mJ/g)
(N=m/g) (km)
11 61.1 149 1.27 10.5 96 182
12 59.9 151 5.66 6.8 326 77
13 63.6 154 11.00 7.8 737 71
14 73.9 154 28.18 8.4 1966 53
EXAMPLE XV
[00150] This example illustrates how additives can be added to the pulp prior
to mechanical
treatment to improve the final properties of the stretchable paper as
encompassed herein. The
starting pulp used for this example was a Northern Bleached Softwood Kraft
(NBSK) pulp at an
initial consistency of 47%. The additive was glycerol, added to the pulp at a
dosage of 5 wt%.
Samples of NBSK with or without glycerol addition were treated mechanically in
the plug-screw of
a commercial meat grinder (Weston ProSeries tm #8) to induce fiber deformation
and curl. FQA
measurements confirmed that the curl index obtained with the meat grinder was
close to what is
obtained with a pilot scale plug screw at a pressure of 3.5 bars. Handsheets
were then prepared
from the mechanically treated pulps at a target grammage of 60 g/m2. Some of
the handsheets
were finally impregnated with latex. In total, four different sets of
handsheets were prepared for this
example. Their composition and mechanical properties are given in Tables 30
and 31 below.
[00151] Results from Table 31 indicate that handsheets prepared with the pulp
containing
glycerol prior to mechanical treatment have higher strength, elongation at
break, tensile energy
absorption and elastic modulus than the corresponding handsheets made from the
pulp without
glycerol. The same conclusion holds after these handsheets have been
impregnated with latex.
Table 30
Composition of the four sets of handsheets
Set # Pulp Latex addition
1 NBSK, mechanically treated
2 NBSK, mechanically treated 19.2% Acronal LA 471S
3 NBSK added with glycerol,
mechanically treated
4 NBSK added with glycerol,
mechanically treated 19.3% Acronal LA 471S
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Table 31
Physical and mechanical properties of the different sets of handsheets of
Example 16
Tensile Elastic
Grammage Caliper Stretch TEA Index
Set # Index Modulus
(g/m2)
(pm) (%) (mJ/g)
(1\1=m/g) (km)
1 57.6 172 1.55 12.1 138 209
2 60.2 191 32.59 9.9 2652 69
3 67.2 164 1.65 16.7 200 271
4 77.9 171 37.38 11.6 3396 81
EXAMPLE XVI
[00152] These examples illustrate how the properties of the stretchable paper
as described
herein change with the type of polymer added to the basesheet. The pulp used
for this example
was a Northern Bleached Softwood Kraft (NBSK) pulp treated mechanically in a
plug-screw feeder
at 3.5 bars. For this example, five different sets of basesheets were prepared
from that pulp at a
target grammage of 60 g/m2 prior to impregnation. These basesheets were then
impregnated with
the following polymers: the acrylic copolymer latex Acronal LA 471S used in
previous examples,
two different grades of PLA latexes manufactured by the company Konishiyasu
(grades 1005 and
3000), a medium-chain-length polyhydroxyalkanoate (mcl-PHA) synthesized by
Prof. Bruce
Ramsay at Queen's University and a mixture of polyvinyl alcohol (PVOH) and
sodium borate. The
mcl-PHA polymer was first melted at 150 C prior to its addition to the
basesheet. The handsheets
impregnated with the PLA latex grade 1005 were subsequently subjected to a
heat treatment in an
oven at 170 C for 5 minutes to fully develop the properties of the polymer.
The composition and
mechanical properties of the different sets of handsheets produced for this
example are given in
Tables 32 and 33 below.
[00153] Results from Table 33 indicate that a wide range of mechanical
properties can be
obtained by varying the type of polymer added to the basesheet. For example,
handsheets
impregnated with the synthetic polymer Acronal LA 471S had very high
elongation at break. By
contrast, handsheets impregnated with the two PLA latexes had high tensile
strength and
elongations at break sufficient for many applications.
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Table 32
Composition of the five sets of handsheets
Set # Pulp Polymer
1 21.3% Acronal
LA 471S
2 24.2% PLA
(grade 1005)
3 NBSK mechanically treated at 3.5 bars 24.0% PLA
(grade 3000)
4 58.7% mcl-PHA
23.5% PVOH and sodium borate
Table 33
Physical and mechanical properties of the different sets of handsheets
Tensile Elastic
Grammage Caliper Stretch TEA Index
Set # Index Modulus
(g/m2)
(pm) (%) (mJ/g)
(1\1=m/g) (km)
1 77.9 164 37.35 12.4 3810 62
2 82.4 220 7.21 39.6 2050 257
3 79.6 173 9.85 24.3 1750 153
4 161.5 - 13.87 12.0 1335 49
5 83.4 - 3.46 40.6 1020 315
[00154] While this disclosure has been described in connection with specific
embodiments
thereof, it will be understood that it is capable of further modifications and
this application is
intended to cover any variations, uses, or adaptations, including such
departures from the present
disclosure as come within known or customary practice within the art, and as
may be applied to the
essential features hereinbefore set forth, and as follows in the scope of the
appended claims.
