Note: Descriptions are shown in the official language in which they were submitted.
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Pulp-containing biodegradable non-woven fabric and method for
producing the same
FIELD OF THE INVENTION
The present invention relates to a biodegradable non-woven fabric, a method
for
producing a biodegradable non-woven fabric and wipes or tissues comprising the
biodegradable non-woven fabric. In particular, the biodegradable non-woven
fabric may be a plastic-free, entirely compostable non-woven fabric or
substrate
suitable for disposable applications, such as wipes or tissues.
BACKGROUND
Disposable wipes, such as wet toilet wipes or personal care wipes like baby
wipes, facial wipes etc. are very popular for cleaning the skin of human
bodies or
facilities in the household because of their comfort for consumers and
efficacy in
cleaning. However, increasing concerns about plastic contamination of the
environment create an increasing demand for plastic-free and fully
compostable/biodegradable substrates for disposable wipes and similar
products.
Spunlacing (which may also be referred to as hydroentanglement) and needle
punching are technologies conventionally used for producing non-woven fabric
or
substrates suitable as wipes. Spunlacing is a bonding process for wet or dry
fibrous webs where fine, high pressure jets of water penetrate the fibrous web
and cause an entanglement of fibers, thereby providing fabric integrity.
Needle
punching is a bonding process where fibers are mechanically intertwined by
needles.
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Spunlace technology only using compostable fibers made of regenerated
cellulose like Viscose/Rayon, Tencel or Cellulose Acetate or natural fibers
like
cotton provide a technical solution for plastic-free and
compostable/biodegradable disposable wipes but is challenged by the
significant
increase of material cost by replacing PET fibers commonly used in disposable
wipe substrates (e.g. baby wipes) by compostable fibers at an up to 50%
increase of material cost. Due to the too high material cost, such products so
far
have only been used in a niche premium segment but could not replace standard
volume products like baby wipes.
An established approach to reduce material cost of such spunlaced substrates
is
to replace part of the viscose fibers by pulp providing the required
hydrophilic
properties of the wipe substrate. This approach for providing non-woven
fabrics
.. resides in the combined entanglement of a certain amount of relatively
short and
fine fibers and a certain amount of longer fibers.
In general wetlaid/airlaid technology blending fibers and pulp combined with
spunlace technology for bonding without the application of binders as it is
commonly used for the production of dispersible wipes (moist toilet tissue) as
disclosed in EP 2 985 375 Al, the disclosure of which is incorporated herein
by
reference or non-dispersible wipe substrates (airlaced) is facing two
limitations in
the mechanical integrity of the non-woven structure especially after exposure
to
liquid being critical for using such substrates in applications like baby
wipes and
personal care wipes requiring higher mechanical strength and resiliency:
(i) The material strength is low compared to standard spunlace materials even
if
the fiber content is increased compared to the recipe used for dispersible
wipes.
As the pulp fibers are too short and too stiff to be entangled by the
.. hydroentangling process, they are only entrapped in the structure of the
hydroentangled viscose/tencel fibers but do not meaningfully contribute to the
mechanical strength of the web. Therefore such materials require a
significantly
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increased basis weight compared to standard spunlace to achieve similar
mechanical strength.
(ii) As the pulp fibers are only entrapped within the structure of
hydroentangled
viscose/Tencel fibers and do not have bonding points themselves, they can move
and clump together after exposure to liquid/water and mechanical stress and
crumpling of the web destroying the textile structure. Compared to spunlace
and
airlaid materials where the majority of fibers are connected by bonding points
creating a 3-dimensional structure preserving a textile like structure even
after
exposure to liquid/water and mechanical stress/crumpling. This behavior is
considered as "paper like" or "similar to standard toilette tissue" and
perceived
by consumers as poor performance of the wipe. In addition to this perceived
lack
of comfort, the functionality of the wipe negatively impacted by the
clumping/shifting of the pulp fiber as the movement of the pulp fibers within
the
structure changes the local composition of the web in an uncontrolled manner.
The creation of pulp poor areas results in thin spots limiting the barrier and
containment capacity the wipe should provide while areas with an increased
pulp
content create increased thickness or even clumps destroying the desired even
surface and textile touch of the wipe.
(iii) Linting of pulp fibers results from the lack of integration of pulp
fibers by
bonding points to the matrix of the non-woven material resulting in fibers
falling
off the wipe during converting and use when the web is exposed to mechanical
stress (bending, stretching, crunshing...). The loss of pulp fibers when using
a
wipe for cleaning purposes is limiting the field of potential applications and
is
considered by users as a product deficiency.
Thus, the hitherto known technologies face challenges on cost and technical
performance.
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OBJECTS OF THE INVENTION
The present invention aims at overcoming the above described problems and
drawbacks. Thus, it may be an object of the present invention to provide a
biodegradable, compostable non-woven fabric suitable for disposable
applications, such as wipes, with tailored or adjustable properties, in
particular in
terms of (wet) strength and resiliency, and at low cost.
SUMMARY OF THE INVENTION
The present inventor has made diligent studies and has found that the
mechanical properties (such as strength and/or resiliency) of a non-woven
fabric
made by mechanically entangling a blend of pulp fibers and biodegradable
fibers
may be improved by (i) adding a biodegradable binder potentially including
softening agents like glycerol after formation of an entangled textile
structure
from biodegradable fibers and pulp fibers, by (ii) adding a preferably
compostable wet-strength agent prior to the head box before formation of a
textile structure from biodegradable fibers and pulp fibers, and/or by (iii)
blending biodegradable binder fibers (in particular biodegradable
thermobonding
fibers) to a fiber blend comprising biodegradable fibers and pulp fibers,
these
objects can be solved. Without wishing to be bound by any theory, the present
inventor assumes that by any of the above measures (i) to (iii), bonding
points
(in particular covalent bondings) at the pulp fibers may be created bonding
them
together and fixing them to an integrated structure within the structure of
the
spunlaced fibers. As a result, a pulp-web-structure may be formed which is
integrated into (or embedded in) the structure of entangled biodegradable
fibers
such that a structure is created where the pulp fibers may not substantially
move
within the entangled fiber structure even after exposure to a liquid, such as
water, and crumpling the web or applying mechanical strength to the web. As a
result, an extraction and clumping of pulp fibers may be avoided maintaining
the
functionality of the non-woven material. In addition, by tailoring the ratio
of
biodegradable fibers and pulp fibers as well as the content of wet-strength
agent,
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binder and/or binder fiber, it may be possible to properly adjust the material
properties in a wide range and to avoid pulp fibers moving and clumping after
exposing the substrate to liquid/water and tailoring the desired web-strength
and
resiliency. This may allow the design of wipe substrates with similar
properties
5 like spunlace materials also in the wet state and replacing a high
content of
compostable fibers by much lower cost pulp fibers.
Accordingly, the present invention relates to a biodegradable non-woven fabric
comprising biodegradable fibers and pulp fibers, wherein at least a part of
the
.. biodegradable fibers is entangled with each other (at least partly
entrapping pulp
fibers), and wherein at least a part of the pulp fibers is covalently bonded
(fixed,
adhered) to each other (together) by at least one of the group consisting of a
biodegradable binder, a biodegradable wet-strength agent and a biodegradable
binder fiber (thereby forming a pulp-web-structure integrated into the
structure
of entangled biodegradable fibers such that a structure is created where the
pulp
fibers form an integrated structure themselves and/or may not substantially
individually move within the entangled fiber structure even after exposure to
a
liquid, such as water).
.. The present invention further relates to a method for producing a
biodegradable
non-woven fabric, comprising the steps of (a) forming a fibrous web from a
fiber
blend comprising biodegradable fibers and pulp fibers or forming a layer of
biodegradable fibers on a tissue carrier, (b) entangling at least a part of
the
biodegradable fibers with each other (thereby enclosing at least a part of the
pulp fiber) by subjecting the fibrous web (or layer of tissue/fibers) to a
water-jet
treatment, and (c) drying the entangled fibrous web (at a temperature
sufficient
to cure applied binders), wherein the method further comprises at least one
(such as one, any two or all three) of the following steps: (i) applying a
biodegradable binder to the entangled fibrous web prior to the drying step
(c),
(ii) adding a biodegradable wet-strength agent to the fiber blend, and (iii)
blending a biodegradable binder fiber to the fiber blend.
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In addition, the present invention relates to a biodegradable non-woven fabric
obtainable by a method for producing a biodegradable non-woven fabric as
described herein.
Moreover, the present invention relates to a wipe or tissue comprising or
consisting of the biodegradable non-woven fabric as described herein.
Furthermore, the present invention relates to the use of a biodegradable
binder,
a biodegradable wet-strength agent and/or a biodegradable binder fiber for
imparting resiliency to a wipe or tissue comprising a biodegradable non-woven
fabric.
Other objects and many of the attendant advantages of embodiments of the
present invention will be readily appreciated and become better understood by
reference to the following detailed description of embodiments and the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows photographs of a reference sample subjected to a crumpling test
wherein the photograph on the left-hand side illustrates a flat moistened
sample
prior to crumpling, the photograph in the middle illustrates the sample
crumpled
in a fist and the photograph on the right-hand side illustrates the sample
after
crumpling.
Figure 2 shows photographs of a sample of a biodegradable non-woven fabric
according to an embodiment of the invention subjected to a crumpling test
wherein the photograph on the left-hand side illustrates a flat moistened
sample
prior to crumpling, the photograph in the middle illustrates the sample
crumpled
in a fist and the photograph on the right-hand side illustrates the sample
after
crumpling.
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Figure 3 illustrates an exemplary set-up for the 2-point bending stiffness
measurements.
Figure 4 illustrates an exemplary set-up for the Circular Bend Force
.. measurements. The set-up is not drawn to scale.
DETAILLED DESCRIPTION OF THE INVENTION
Hereinafter, details of the present invention and other features and
advantages
.. thereof will be described. However, the present invention is not limited to
the
following specific descriptions, but they are rather for illustrative purposes
only.
It should be noted that features described in connection with one exemplary
embodiment or exemplary aspect may be combined with any other exemplary
embodiment or exemplary aspect, in particular features described with any
exemplary embodiment of a biodegradable non-woven fabric may be combined
with any other exemplary embodiment of a biodegradable non-woven fabric, with
any exemplary embodiment of a method for producing a biodegradable non-
woven fabric , with any exemplary embodiment a wipe or tissue and with any
exemplary embodiment of a use and vice versa, unless specifically stated
otherwise.
Where an indefinite or definite article is used when referring to a singular
term,
such as "a", "an" or "the", a plural of that term is also included and vice
versa,
unless specifically stated otherwise, whereas the word "one" or the number
"1",
as used herein, typically means "just one" or "exactly one".
The expression "comprising", as used herein, includes not only the meaning of
"comprising", "including" or "containing", but may also encompass "consisting
essentially of" and "consisting of".
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Unless specifically stated otherwise, the expression "at least a part of", as
used
herein, may mean at least 5 % thereof, in particular at least 10 % thereof, in
particular at least 15 % thereof, in particular at least 20 % thereof, in
particular
at least 25 % thereof, in particular at least 30 % thereof, in particular at
least 35
% thereof, in particular at least 40 % thereof, in particular at least 45 %
thereof,
in particular at least 50 % thereof, in particular at least 55 % thereof, in
particular at least 60 % thereof, in particular at least 65 % thereof, in
particular
at least 70 % thereof, in particular at least 75 % thereof, in particular at
least 80
% thereof, in particular at least 85 % thereof, in particular at least 90 %
thereof,
in particular at least 95 % thereof, in particular at least 98 % thereof, and
may
also mean 100 % thereof.
In a first aspect, the present invention relates to a biodegradable non-woven
fabric.
The term "non-woven fabric", as used herein, may in particular mean a web of
individual fibers which are at least partially intertwined, but not in a
regular
manner as in a knitted or woven fabric.
.. The term "biodegradable" (which may also be referred to as "compostable"),
as
used herein, may in particular mean that the material concerned, such as the
biodegradable non-woven fabric, the biodegradable fibers, the biodegradable
binder fiber, the biodegradable wet-strength agent, the biodegradable binder
and
the like, complies at least with the requirements for industrial
compostability, for
instance in accordance with EN 13432, and preferably also with the
requirements
for home compostability and is most preferred also marine biodegradable. The
term "marine biodegradable", as used herein, may in particular mean that the
material biodegrades by more than 90% by weight within 12 month storage in
sea water at min. 15 C and exposure to daylight.
The biodegradable non-woven fabric comprises biodegradable fibers and pulp
fibers.
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In an embodiment, the biodegradable fibers comprise cellulosic fibers. The
term
"cellulosic fibers", as used herein, may in particular denote fibers based on
cellulose, in particular modified or regenerated cellulose fibers, such as
fibers
prepared from cellulose, or cellulose derivates, such as ethyl cellulose,
cellulose
acetate and the like. The term "regenerated cellulose fibers", as used herein,
may in particular denote manmade cellulose fibers obtained by a solvent
spinning process.
In an embodiment, the regenerated cellulose fibers may be selected from the
group consisting of viscose (rayon) or lyocell (tencel).
Viscose is a type of solvent spun fiber produced according to the viscose
process
typically involving an intermediate dissolution of cellulose as cellulose
xanthate
and subsequent spinning to fibers.
Lyocell is a type of solvent spun fiber produced according to the aminoxide
process typically involving the dissolution of cellulose in N-methylmorpholine
N-
oxide and subsequent spinning to fibers.
In an embodiment, the biodegradable fibers may have an average fiber length of
from 1 mm to 100 mm, for instance an average fiber length of from 3 mm to 80
mm, for instance an average fiber length of from 5 to 70 mm, for instance an
average fiber length of from 10 to 65 mm, for instance an average fiber length
of
.. from 15 to 60 mm, for instance an average fiber length of from 18 to 50 mm,
such as an average fiber length of from 20 to 40 mm.
In an embodiment, the biodegradable fibers may have an average fiber length of
from 1 mm to 12 mm, in particular of from 3 mm to 10 mm. This may be
advantageous, in particular when the non-woven fabric is prepared by an
airlaid
process.
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In an embodiment, the biodegradable fibers may have an average fiber length of
from 1 mm to 12 mm, in particular of from 3 mm to 8 mm. This may be
advantageous, in particular when the non-woven fabric is prepared by a wetlaid
process.
5
In an embodiment, the biodegradable fibers may have an average fiber length of
from 10 mm to 100 mm, in particular of from 10 mm to 80 mm. This may be
advantageous, in particular when the non-woven fabric is prepared by an airlay
process.
In an embodiment, the biodegradable fibers may have an average fiber length of
from 15 mm to 60 mm. This may be advantageous, in particular when the non-
woven fabric is prepared by a carding process.
In an embodiment, the biodegradable fibers may have a fiber coarseness of from
0.5 to 10 dtex, in particular from 0.5 to 4.0 dtex or from 1.0 to 10 dtex,
such as
from 1.0 to 2.5 dtex.
In an embodiment, the biodegradable fibers may be comprised in an amount of
from 10 to 80 wt.-%, such as in an amount of from 15 to 70 wt.-%, such as in
an amount of from 20 to 60 wt.-%, such as in an amount of from 25 to 50 wt.-
%, such as in an amount of from 30 to 40 wt.-%, based on the total weight of
the non-woven fabric.
In an embodiment, the pulp fibers may be natural pulp fibers, in particular
pulp
fibers of natural origin, such as softwood pulp fibers or hardwood pulp
fibers.
Pulp may in particular denote a (lignocellulosic) fibrous material prepared by
chemically or mechanically separating cellulose fibers from wood or the like,
such
as by a kraft process (sulfate process).
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In an embodiment, the pulp fibers may have an average fiber length of from 1.0
mm to 4.0 mm, for instance from 1.5 mm to 3.5 mm, such as from 2.0 mm to
3.2 mm.
In an embodiment, the pulp fibers may have a fiber coarseness of from 0.3 to
3.5 dtex, such as from 0.6 to 2.5 dtex.
In an embodiment, the pulp fibers may be comprised in an amount of from 20 to
90 wt.-%, such as in an amount of from 30 to 85 wt.-%, such as in an amount of
from 40 to 80 wt.-%, such as in an amount of from 50 to 75 wt.-%, such as in
an amount of from 60 to 70 wt.-%, based on the total weight of the non-woven
fabric.
In the biodegradable non-woven fabric, at least a part of the biodegradable
fibers
is entangled with each other. In particular, at least a part of the
biodegradable
fibers may be entangled with each other such that at least a part of the pulp
fibers is entrapped (with)in the entangled biodegradable fibers.
The term "entangled", as used herein, may in particular mean that the
biodegradable fibers are at least partly intertwined with each other, thereby
imparting strength, such as tear strength or tensile strength, to the non-
woven
fabric. Entangling of the biodegradable fibers might in particular be achieved
by a
treatment of a fibrous web with water jets, as will be explained in further
detail
below, which may also be referred to as "hydroentanglement" or "spunlacing"
.. and the entangled fibers may thus also be referred to as "hydroentangled
fibers"
or "spunlaced fibers". Alternatively, entangling of the biodegradable fibers
might
be achieved by needle punching where the biodegradable fibers are mechanically
intertwined by means of needles. Alternatively to blending the biodegradable
fibers and the pulp forming a layer by means of airlaid or carding or airlay
plus
airlaid to be fed into the spunlacing unit, the layer of biodegradable fibers
may
also be formed on top of a layer of tissue using carding or airlay or airlaid
technology and then be fed into the spunlacing unit which is disintegrating
the
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tissue forming a web of at least partially entangled biodegradable fibers
enclosing at least part of the pulp fibers.
In the biodegradable non-woven fabric, at least a part of the pulp fibers is
covalently bonded (fixed, adhered) to each other (thereby forming an
integrated
pulp layer within the biodegradable spunlaced fiber structure) by at least one
of
the group consisting of a biodegradable binder, a biodegradable wet-strength
agent and a biodegradable binder fiber. As a result of this at least partial
covalent bonding of pulp fibers together, a pulp-web-structure may be formed
which is integrated into (or embedded in) the structure of entangled
biodegradable fibers such that a structure is created where the pulp fibers
may
not substantially move within the entangled fiber structure even after
exposure
to a liquid, such as water. Moreover, a clumping of pulp fibers may be
substantially avoided. Therefore, the bonding of the pulp fibers is preferably
initiated by application of heat after entangling the biodegradable fibers by
means of hydroentangling or needle punching.
In addition to the bonding of the pulp fibers together, at least one of the
group
consisting of a biodegradable binder, a biodegradable wet-strength agent and a
biodegradable binder fiber may optionally, but not necessarily, also bond the
biodegradable fibers, in particular the entangled biodegradable fibers,
together
and may optionally, but not necessarily, also bond pulp fibers to the
biodegradable fibers, in particular to the entangled biodegradable fibers.
However, without wishing to be bound by any theory, it is believed that the
(large) majority of the at least one of the group consisting of a
biodegradable
binder, a biodegradable wet-strength agent and a biodegradable binder fiber
bonds the pulp fibers together (rather than bonding to the biodegradable
fibers)
thereby forming a pulp-web-structure which may also (but does need to) bond to
the structure of entangled biodegradable fibers. In addition, the increase in
bulkiness due to the formation of a pulp-web-structure and the resulting
integration or embedding thereof within the structure of entangled
biodegradable
fibers is believed sufficient (even without bonding to the biodegradable
fibers) for
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substantially limiting a free movement of the pulp within the entangled fiber
structure even after exposure to a liquid, such as water, and for
substantially
avoiding extraction and/or clumping. Furthermore, the formation of a layer of
inter-bonded pulp fibers within the structure of entangled biodegradable
fibers
may increase the resiliency of the material.
In an embodiment, at least a part of the pulp fibers is bonded to each other
by a
biodegradable binder fiber. The term "binder fiber", as used herein, may in
particular denote a fiber that is able to bind (e.g. by thermobonding, by
forming
covalent bonds, by ionic interactions or the like) to each other or to other
fibers.
Preferably, the biodegradable binder fiber is a biodegradable thermobonding
(or
thermally activatable) fiber. The biodegradable binder fiber may in particular
be
a biodegradable thermoplastic fiber. The term "thermoplastic fibers", as used
herein, may in particular denote fibers that soften and/or partly melt when
exposed to heat and are capable to bind with each other or to other non-
thermoplastic fibers, such as cellulose fibers, upon cooling and
resolidifying.
In an embodiment, the biodegradable binder fiber comprises a multicomponent
fiber, in particular a bicomponent fiber, such as bicomponent fibers of the
sheath-core type. Bicomponent fibers are composed of two sorts of polymers
having different physical and/or chemical characteristics, in particular
different
melting characteristics. A bicomponent fiber of the sheath-core type typically
has
a core of a higher melting point component and a sheath of a lower melting
point
component.
For example, the biodegradable binder fiber may comprise polylactic acid
(PLA),
polybutylene succinate (PBS), polybutyratadipate terephthalate (polybutylene
adipate terephthalate, PBAT), and other biodegradable thermoplastic polymers.
Combinations of two or more thereof may also be applied.
In an embodiment, the biodegradable binder fiber may be comprised in an
amount of from 0.1 to 30 wt.-%, such as in an amount of 0.2 to 20 wt.-%, such
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as in an amount of from 0.2 to 10 wt.-%, such as in an amount of from 0.2 to
7.5 wt.-%, such as in an amount of from 0.35 to 5 wt.-%, such as in an amount
of from 0.5 to 4 wt.-%, based on the total weight of the non-woven fabric.
In an embodiment, at least a part of the pulp fibers is bonded to each other
by a
biodegradable wet-strength agent. The term "wet-strength agent", as used
herein, may in particular denote an agent that improves the tensile strength
of
the non-woven web in the wet state, for instance by forming covalent bonds. In
particular, it may be preferred that the wet-strength agent is biodegradable.
However, it may also be possible to use a non-biodegradable wet-strength agent
(for instance in small amounts not negatively impacting the
biodegradability/compostability) which may significantly increase the wet
tensile
strength of the non-woven fabric.
For example, the biodegradable wet-strength agent may be selected from the
group consisting of chitosan, modified starch, cellulose derivatives and
others.
Combinations of two or more thereof may also be applied. The term "cellulosic
derivatives", as used herein, may in particular denote chemically modified
(for
instance methylated, ethylated, hydroxypropylated, acetylated and/or
carboxylated) cellulose compounds, and may in particular include cellulose
ethers
and cellulose esters, such as methylcellulose, ethylcellulose, hydroxyethyl
cellulose, hydroxypropyl cellulose, carboxymethyl cellulose or cellulose
acetate.
In an embodiment, the biodegradable wet-strength agent may be comprised in
an amount of from 0.1 to 3 wt.-%, such as in an amount of from 0.2 to 2 wt.-%,
such as in an amount of from 0.35 to 1.5 wt.-%, such as in an amount of from
0.5 to 1 wt.-%, based on the total weight of the non-woven fabric.
In an embodiment, the biodegradable non-woven fabric may comprise a further
wet-strength agent, in particular a non-biodegradable wet-strength agent. An
example of the further wet-strength agent may include an epichlorhydrine
resin,
such as a polyamine-polyamide-epichlorohydrine resin.
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In an embodiment, at least a part of the pulp fibers is bonded to each other
by a
biodegradable binder. The term "binder", as used herein, may in particular
denote a chemical compound that is able to bind (e.g. by forming covalent
5 bonds, by ionic interactions or the like) to two or more fibers, thereby
interconnecting the fibers, resulting in an increased tensile strength of the
web or
fabric.
For example, the biodegradable binder may be selected from the group
10 consisting of chitosan, modified starch, cellulose derivatives, in
particular blends
of carboxymethylcellulose and citric acid, protein based binders, such as
casein,
and others. Combinations of two or more thereof may also be applied. Further
suitable biodegradable binders are disclosed in WO 2014/117964 Al, the
disclosure of which is incorporated herein by reference.
In an embodiment, the biodegradable binder may be comprised in an in amount
of from 0.05 to 5 wt.-%, such as in an amount of from 0.1 to 4 wt.-%, such as
in
an amount of from 0.25 to 3 wt.-%, such as in an amount of from 0.5 to 2 wt.-
%, based on the total weight of the non-woven fabric.
In an embodiment, the biodegradable binder further comprises an additive, such
as glycerol, (configured for) acting as softening agent improving the
flexibility
and drapability of the (dried treated) non-woven fabric. In other words,
glycerol
or similar softening additives may be added to the biodegradable binder or wet-
strength agent in order to improve the flexibility and drapability of the
dried
treated non-woven fabric.
A wet-strength agent within the meaning of the present application and a
binder
within the meaning of the present application may in particular be
distinguished
by the time of its application. A wet-strength agent is typically added to a
fiber
blend prior to formation of a fibrous web or textile structure. For instance,
a wet-
strength agent may be applied into or prior to a head box of a paper-making
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machine. A binder is typically applied after formation of a fibrous web or
textile
structure, and may even be applied after entanglement of the fibrous web. For
instance, a binder may be applied or added to an entangled fibrous web, but
preferable prior to drying the entangled web. It is also feasible to apply the
binder after drying the hydroentangled web but this would be less efficient
due to
the necessity of drying the web twice. A binder fiber may be added to the
blend
of the other fibers prior to formation of a fibrous web or textile structure.
In an embodiment, at least a part of the pulp fibers may be bonded to each
other
by a biodegradable wet-strength agent and/or by a biodegradable binder, and
optionally further by a biodegradable binder fiber. In particular, at least a
part of
the pulp fibers may be bonded to each other only by a biodegradable wet-
strength agent; at least a part of the pulp fibers may be bonded to each other
only by a biodegradable binder; at least a part of the pulp fibers may be
bonded
.. to each other by a biodegradable wet-strength agent and by a biodegradable
binder; at least a part of the pulp fibers may be bonded to each other by a
biodegradable wet-strength agent and by a biodegradable binder fiber; at least
a
part of the pulp fibers may be bonded to each other by a biodegradable binder
and by a biodegradable binder fiber; and/or at least a part of the pulp fibers
may
be bonded to each other by a biodegradable binder, by a biodegradable wet-
strength agent and by a biodegradable binder fiber.
In an embodiment, substantially all fibers comprised in the biodegradable non-
woven fabric may be biodegradable fibers, in particular substantially all
fibers
comprised in the biodegradable non-woven fabric may be the biodegradable
fibers, the pulp fibers and optionally the biodegradable binder fiber
described
herein. In other words, it may be possible that the biodegradable non-woven
fabric does substantially not comprise any other fibers than biodegradable
fibers,
in particular no other fibers than the biodegradable fibers, the pulp fibers
and
optionally the biodegradable binder fiber described herein. With regard to
embodiments comprising "substantially no other fibers than biodegradable
fibers", other fibers than biodegradable fibers, if any, may still be present
in
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relatively minor amounts of up to 10, up to 5, up to 3, up to 2, or up to 1
wt.-%
based on the total weight of the non-woven fabric.
In an embodiment, the biodegradable non-woven fabric may have a grammage
or basis weight of from 20 to 150 g/m2, such as from 30 to 125 g/m2, such as
from 40 to 100 g/m2, such as from 50 to 80 g/m2.
In an embodiment, the non-woven fabric is non-dispersible in water, rather
than
dispersible. The term "dispersible" may in particular denote the property of a
.. non-woven fabric to be capable of disintegrating or decomposing in water by
applying a relatively low mechanical energy, such as a situation that
typically
occurs in a toilet upon flushing. In particular, when being flushed, a
dispersible
non-woven fabric may be no longer intact, for instance a certain amount of
individual fibers or of fiber aggregates may be released from the fabric
and/or
the fabric may break to several pieces. The term "non-dispersible", as used
herein, may accordingly denote the property of the non-woven fabric to be
capable of resisting to disintegration in water upon applying a relatively low
mechanical energy, such as a situation that typically occurs in a toilet upon
flushing.
In an embodiment, the non-woven fabric may be treated (impregnated) with a
liquid or a lotion. In other words, the non-woven fabric may further comprise
a
liquid or a lotion. In such situation, the non-woven fabric may in particular
represent a wet wipe or wet tissue. The liquid or the lotion is not
particularly
limited, and any liquid or lotion customary in the field of wet wipes or wet
tissues
may be applied. Typically, the liquid or the lotion may comprise a solvent,
such
as water, an alcohol, or mixtures thereof, surfactants or detergents, skin
care
agents, emollients, humectants, perfumes, preservatives etc. depending on the
intended use.
In an embodiment, the biodegradable non-woven fabric shows an increase of
material resiliency characterized by a Circular Bend Stiffness Force
determined in
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accordance with modified ASTM D 4032-94 as described further below of more
than 25%, preferably more than 50% and most preferably more than 75%,
compared to a non-woven fabric without any one of a biodegradable binder
fiber,
a biodegradable wet-strength agent and a biodegradable binder.
In an embodiment, the biodegradable non-woven fabric shows an increase of
material resiliency characterized by a bending stiffness in machine direction
(MD)
and/or in cross direction (CD) determined in accordance with modified ISO 5628
(DIN 53 121) as described further below of more than 25%, preferably more
than 50% and most preferably more than 75%, compared to a non-woven fabric
without any one of a biodegradable binder fiber, a biodegradable wet-strength
agent and a biodegradable binder.
In a second aspect, the present invention relates to a method for producing a
biodegradable non-woven fabric, in particular of a biodegradable non-woven
fabric as described herein.
The method comprises the steps of:
(a) forming a fibrous web from a fiber blend comprising biodegradable
fibers and pulp fibers or alternatively forming a layer of biodegradable
fibers
combined with a tissue/paper layer;
(b) entangling at least a part of the biodegradable fibers with each other
by subjecting the fibrous web or the fibrous web combined with a tissue layer
to
a water-jet treatment; and
(c) drying the entangled fibrous web.
The method further comprises at least one (such as one, any two or all three)
of
the following steps:
(i) applying a biodegradable binder to the entangled fibrous web prior to
drying the entangled fibrous web,
(ii) adding a biodegradable wet-strength agent to the fiber blend, and
(iii) blending a biodegradable binder fiber to the fiber blend.
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In step (a), the fibrous web may be prepared for instance by a conventional
wet-
laid process using a wet-laid machine, such as an inclined wire or flat wire
machine, or a dry-forming air-laid non-woven manufacturing process. A
conventional wet-lay process is described for instance in US 2004/0129632 Al,
the disclosure of which is incorporated herein by reference. A suitable dry-
forming air-laid non-woven manufacturing process is described for instance in
US
3,905,864, the disclosure of which is incorporated herein by reference. Thus,
the
fibrous web may be formed for instance by a wet-laid process or an air-laid
process.
In an embodiment, the fibrous web is formed by a wet-laid process. In another
embodiment, the fibrous web is formed by an air-laid process. Also a
combination of a carding process or an airlay process combined with an airlaid
process is suitable for forming a layer of biodegradable fibers combined with
a
layer of pulp fibers. Instead of the airlaid process the pulp fibers can also
be fed
into the process as a tissue/paper layer getting combined with the fiber layer
prior to entering the hydroentangling section where the tissue/pulp get
disintegrated and blended with the biodegradable fibers.
The fiber blend used for forming the fibrous web comprises biodegradable
fibers
and pulp fibers and may optionally further comprise a biodegradable binder
fiber
and/or a biodegradable wet-strength agent.
In step (b), at least a part of the biodegradable fibers are entangled with
each
other by subjecting the fibrous web to a water-jet treatment. In particular,
at
least a part of the biodegradable fibers may be entangled with each other such
that at least a part of the pulp fibers may be enclosed (with)in the entangled
biodegradable fibers (the entangled fibrous web of biodegradable fibers).
The term "water-jet treatment", as used herein, may in particular mean a
process of mechanically entangling fibers by giving the fibrous web an impact
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with jets of water. Water-jet treatment may also be referred to as
hydroentanglement or spunlacing. Water-jet treatment typically involves the
ejection of fine, high pressure jets of water from a plurality of nozzles on a
fibrous web provided on a conveyor belt or forming-wire. The water jets
5 .. penetrate the web, hit the belt where they may be reflected and pass
again the
web causing the fibers to entangle. Thus, by subjecting the fibrous web to the
water-jet treatment, the fibers are entangled, in particular hydroentangled.
In an embodiment, a biodegradable binder may be applied to the entangled
10 fibrous web. The biodegradable binder may be applied in the form of a
solution
or dispersion to the entangled fibrous web. For instance, the biodegradable
binder may be applied by spraying or other means of liquid application like a
size-press, foulard or other. It may be favorable to remove excessive water
prior
to application of the binder especially in case of spray application by
application
15 .. of vacuum, pressure or other removing excessive water to avoid dilution
of the
binder.
In an embodiment, a softening agent like glycerol is added to the
biodegradable
binder providing an enhanced flexibility/drapeability (reduced stiffness) of
the
20 finished non-woven especially in the dry state.
In step (c), the drying of the entangled fibrous web may preferably be carried
out such that the biodegradable binder fiber softens and/or partly melts, in
particular is thermally activated, and/or that the biodegradable wet-strength
agent and/or the biodegradable binder is cured, in particular undergoes a
chemical reaction. In particular, the drying is preferably carried out at a
(sufficiently high) temperature to thermally activate the biodegradable binder
fiber and/or to cause a chemical reaction of the biodegradable wet-strength
agent and/or the biodegradable binder, for instance at a temperature of more
than 80 C, such as more than 100 C, such as more than 120 C, such as more
than 140 C, such as more than 180 C, depending on the specific biodegradable
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binder fiber, biodegradable wet-strength agent and/or biodegradable binder
used.
In a third aspect, the present invention relates to a biodegradable non-woven
fabric obtainable by a method for producing a biodegradable non-woven fabric
as
described herein. In particular, a biodegradable non-woven fabric obtainable
by a
method for producing a biodegradable non-woven fabric as described herein may
have any of the properties or features of a biodegradable non-woven fabric
according to the first aspect, as described in the foregoing.
In a fourth aspect, the present invention relates to a wipe or tissue
comprising or
consisting of the biodegradable non-woven fabric as described herein. In
particular, the non-woven fabric according to the present invention may be
usable as a wipe or a tissue.
In an embodiment, the wipe or tissue may be a dry wipe or dry tissue. Dry
wipes
may be particularly suitable for use as kitchen tissue/towel, shop floor towel
and
paper towel, enabling the soakage of liquids.
In an embodiment, the wipe or tissue may be a wet wipe or wet tissue. For
instance, the wet wipe may be treated with a liquid or a lotion, as described
in
further detail above. Wet wipes may be particularly suitable for personal care
applications cleaning the skin of a human body, including the private parts
thereof. Thus, wet wipes may be particularly suitable for personal care use
such
as facial wipes or baby wipes.
In an embodiment, the wipe is selected from the group consisting facial wipes,
cosmetic wipes, baby wipes, sanitary wipes, kitchen towel, paper towel,
handkerchiefs (facial tissue), cleaning tissue, cleansing tissue, floor mop
and
hard surface cleaning wipe.
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In a fifth aspect, the present invention relates to the use of a biodegradable
binder, a biodegradable wet-strength agent and/or a biodegradable binder fiber
for imparting resiliency to a wipe or tissue comprising a biodegradable non-
woven fabric (or for increasing resiliency of a wipe or tissue comprising a
.. biodegradable non-woven fabric). The biodegradable binder, the
biodegradable
wet-strength agent and/or the biodegradable binder fiber may be in particular
those exemplified above. The present inventors have found that by using a
biodegradable binder, a biodegradable wet-strength agent and/or a
biodegradable binder fiber in a biodegradable non-woven fabric, the resulting
non-woven fabric as well as a wipe or tissue comprising the same may be
imparted with resiliency. The term "resiliency", as used herein, may in
particular
denote a property of a textile like structure, such as an elasticity or
capability of
at least partly reverting to an original shape after crumpling. The resiliency
may
be characterized for instance by a Circular Bend Stiffness Force determined in
accordance with modified ASTM D 4032-94 and/or a bending stiffness in machine
direction (MD) and/or in cross direction (CD) determined in accordance with
modified ISO 5628 (DIN 53 121) as described in further detail below.
The present invention is further described by the following examples, which
are
solely for the purpose of illustrating specific embodiments, and are not
construed
as limiting the scope of the invention in any way.
Examples
A blend of 20 wt.-% of viscose fibers and 80 wt.-% of natural pulp fibers have
been processed on an inclined wire machine with a basis weight of 60 g/m2 and
hydroentangled by application of water jets and dried as described in the
patent
EP 2 985 375 B1.
As this wetlaid material does not contain any binder, the substrate is used as
"base substrate" to demonstrate the effect of different binder applications.
Due
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to the lack of binder the substrate can get "reactivated" by application of
the
aqueous binder system simulating an in-line process.
This layer of entangled fibers has been treated in 3 different ways:
a) An aqueous solution of carboxymethyl cellulose (0.4 wt.%), citric acid (0.1
wt.%) and sodium dihydrogenphosphate (0.06 wt.%) is sprayed at room
temperature (25 C) on the surface of the base substrate described above so
that the solution is evenly distributed on the surface of base substrate and
gets sucked into the material by capillary force. The sample is dried in a lab
oven at 120 C without direct contact to a hot surface (air drying). The
amount of aqueous solution of carboxymethyl cellulose and citric acid is
chosen to achieve the following material composition after drying of the
material to constant weight at 120 C
= 19.6 wt.% viscose fibers
= 78.2 wt.% pulp fibers
= 1.5 wt.% carboxymethyl cellulose
= 0.5 wt.% citric acid
= 0.25 wt.% sodium dihydrogenphosphate
b) An aqueous solution of carboxymethyl cellulose (0.4 wt.%), citric acid (0.1
wt.%), sodium dihydrogenphosphate (0.06 wt.%) and glycerol (1 wt.%) is
sprayed at room temperature (25 C) on the surface of the base substrate
described above so that the solution is evenly distributed on the surface of
the base substrate and gets sucked into the base substrate by capillary force.
The sample is dried in a lab oven at 120 C without direct contact to a hot
surface (air drying). The amount of aqueous solution of carboxymethyl
cellulose and citric acid and glycerol is chosen to achieve the following
material composition after drying of the material to constant weight at 120 C
= 18.8 wt.% viscose fibers
= 75 wt.% pulp fibers
= 1.5 wt.% carboxymethyl cellulose
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= 0.5 wt.% citric acid
= 0.25 wt.% sodium dihydrogenphosphate
= 4 wt.% glycerol
c) An aqueous solution of carboxymethyl cellulose (0.4 wt.%) citric acid (0.1
wt.%), sodium dihydrogenphosphate (0.06 wt.%) and epichlorohydrin based
wet-strength agent (Kymmene GHP 20, 0.05 wt.%) is sprayed at room
temperature (25 C) on the surface of the base substrate described above so
that the solution is evenly distributed on the surface of the base substrate
and gets sucked into the base substrate by capillary force. The sample is
dried in a lab oven at 120 C without direct contact to a hot surface (air
drying). The amount of aqueous solution of carboxymethyl cellulose and citric
acid and wet-strength agent is chosen to achieve the following material
composition after drying of the material to constant weight at 120 C
= 19.5 wt.% viscose fibers
= 78 wt.% pulp fibers
= 1.5 wt.% carboxymethyl cellulose
= 0.5 wt.% citric acid
= 0.25 wt.% sodium dihydrogenphosphate
= 0.25 wt.% epichlorohydrin based wet-strength agent
In order to determine the impact of the treatment of the hydroentangled blend
of
viscose and pulp fibers on the mechanical properties, especially the
flexibility and
resilience of the base substrate and the treated samples a) , b) and c), the
following material properties got measured which are summarized in table 1
below:
1) Tensile strength ASTM D5035 measured at 200% moisture content
2) Elongation at break (ASTM D5035) measured at 200% moisture content
3) Circular Bend Stiffness Force modified ASTM D 4032-94 at 200% moisture
content (see below)
4) Bursting pressure (ASTM D774) measured at 200% moisture content
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5) 2-point bending stiffness modified ISO 5628 (DIN 53 121) at 200% moisture
content
The measurement of the 2-point bending stiffness is used to characterize the
5 resiliency of the material describing the capability of a material to
resist to get
crumpled up.
Measurement of the 2-point bending stiffness according to modified ISO 5628
(DIN 53 121):
The 2-point bending stiffness has been measured according to a modified ISO
5628 (DIN 53 121) test. Fig. 3 illustrates an exemplary set-up for the sample
measurements. This can be done either by measuring the force needed to bend a
test piece to a predetermined angle, or by measuring and determining the
bending stiffness, which is an elastic property of the material.
A test piece (38 mm x 50 mm) with a defined moisture content is placed in the
clamp. Upon starting the measurement, the clamp turns slowly to move the free
end of the test piece in contact with the load cell. The test piece is bent to
the
selected angle of 30 . The instrument records the force throughout the
measurement process. The clamp then returns to the start position and the test
piece can be released.
A Lorentzen-Wettre bending tester 016-94281 has been used to perform the
determination of the bending force and the bending stiffness, using the
following
parameter set-up: Bending angle a=30 ; Bending length L=1mm; Bending
velocity: 5 /s;
Test piece width 38 mm.
The bending stiffness Sb 30-1 has been computed using the corresponding
formula:
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Bending force x Bending length L2 x 60
Bending stiffness =
it x Bending angle a x Test piece width
The measurement is repeated 6 times and the mean value of these
measurements is used.
The measurement of the Circular Bend Force is used to characterize the
resiliency of the material describing the capability of a material to recover
after
getting crumpled up.
Measurement of the Circular Bend Stiffness Force according to modified ASTM D
4032-94:
The Circular Bend Stiffness Force has been measured according to a modified
ASTM D 4032-94 test. Fig. 4 illustrates an exemplary set-up for the Circular
Bend
Force measurements (not to scale).
The Circular Bend Stiffness Force is measured as the force required to push a
sample (38 mm x 38 mm) with a moisture content of 200 wt.% positioned on
top of an orifice into the orifice with a piston at a defined penetration
distance
(see Fig. 3).
The piston is made of smoothly polished stainless steel with a length of 72 mm
and a diameter of 6.3 mm having tip shaped as a round-nose with a radius of 3
mm and is used to push the sample into an orifice in a smoothly polished
stainless-steel plate of the dimensions 102 mm x 102 mm x 6.4 mm with a
diameter of 18.75 mm. The lap edge of the orifice is at a 45 angel to a depth
of
4.8 mm.
The force required to push the sample lying flat of the surface of the orifice
with
the piston positioned central on top of the orifice into the orifice is
measured
using a load cell positioned between the piston and a drive moving the piston
into the orifice. A Zwick Z.2.5/TN1S has been used to move the piston and to
measure the force.
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The Circular Bend Stiffness Force is defined as the max. force measured when
pushing the sample with the piston at a speed of 500 mm/min into the orifice
to
a depth of 6.4 mm. The measurement is repeated 5 times and the mean value of
these measurements is used.
Table 1
Sample Tensile Tensile Elongation Elongation Bending Bending
Circular Bursting
strength strength at break at break stiffness
stiffness bend pressure
MD wet* CD wet* MD wet* CD wet* MD wet* CD
wet* stiffness wet*
(N/50mm) (N/50mm) (0/0) (k) (pNm) (pNm) force
wet* (kPa)
(N)
Reference 7.5 5.4 30.0 48.7 0.48 0.31 0.020
32.8
a) 8.3 4.9 34.6 57.0 1.44
0.62 0.033 36.7
b) 13.1 7.3 27.8 53.0 1.31
0.75 0.025 34.2
c) 16.3 10.8 23.8 46.5 1.59
0.67 0.045 41.2
*Samples contain a water content of 200 wt.%
sample Tensile Tensile Elongation Elongation Bending Bending
Circular
strength strength at break at break stiffness
stiffness bend
MD dry** CD dry** MD dry** CD dry** MD dry** CD dry**
stiffness
(N/50mm) (N/50mm) (0/0) (k) (pNm) (pNm) force dry
(N)
Reference 16.57 8.42 11.96 31.70 8.71 2.95 0.195
a) 29.28 15.48 8.60 32.49 23.12
7.46 0.452
b) 30.28 16.30 8.22 26.61 19.75
8.51 0.398
c) 29.52 15.13 7.53 28.18 19.07
8.29 0.400
** samples have a moisture content of 8%
MD=machine direction of the sample
CD=cross direction of the sample
The data in table 1 show an increasing value of resilience of the web against
mechanical deformation measured both by the bending stiffness and the circular
bend stiffness force. The positive effect of adding a wet-strength agent
(sample
c)) is also evident as reflected by the increased values at similar binder
content.
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Comparing both the bending stiffness and the Circular Bend Stiffness Force
(dry)
of the reference material and sample a) reveal the significant increase of
material stiffness of the dry material after application of the binder and the
softening effect of addition of glycerol reducing the material stiffness which
is of
importance for the application as dry wipe. For applications as wet-wipe the
added solution/lotion is functioning as a wetting agent, so that the addition
of
glycerol may not be required.
There are no standardized measurements available describing quantifying the
capability of a web to resist crumpling. However, the effect can be easily
demonstrated by soaking the samples to a water content of 400 wt.-% and
crumpling a sample of 20 cm x 20 cm in the fist.
Figure 1 shows photographs of a reference sample subjected to a crumpling test
wherein the photograph on the left-hand side illustrates a flat moistened
sample
prior to crumpling, the photograph in the middle illustrates the sample
crumpled
in a fist and the photograph on the right-hand side illustrates the sample
after
crumpling.
Figure 2 shows photographs of a sample of a biodegradable non-woven fabric
according to an embodiment of the invention subjected to a crumpling test
wherein the photograph on the left-hand side illustrates a flat moistened
sample
prior to crumpling, the photograph in the middle illustrates the sample
crumpled
in a fist and the photograph on the right-hand side illustrates the sample
after
crumpling.
While the reference sample remains as a clump of material similar to a tissue
without wet-strength agent as shown in Fig. 1, the other samples have the
capability to unfold as shown in Fig. 2 which is more distinct the stronger
the
bonding of the pulp fibers is which correlates with an increasing burst
pressure
and circular bending force.
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The simple crumpling test demonstrates the substantially increased resiliency
of
the hydroentangled blend of biodegradable fibers and pulp fibers by adding a
binder after hydroentanglement which bonds the pulp fibers together forming a
layer with integrity within the structure of the entangled biodegradable
fibers.
This is clearly seen by an increase of the Circular Bend Stiffness Force
measuring
the resistance of the material against getting crumpled trying to move the
sheet
back into the original flat shape prior to crumpling. Comparing the tensile
strength and elongation at break data of sample a) and the reference reveal
that
these properties alone are not suitable to characterize/predict the effect of
increased resiliency.
While the present invention has been described in detail by way of specific
embodiments and examples, the invention is not limited thereto and various
alterations and modifications are possible, without departing from the scope
of
the invention.
