FIELD OF THE INVENTION
[0001] The present invention relates to a wet-laid nonwoven comprising long fibers, and
nanofibrillar cellulose, and a method of manufacturing such by using a wet-laying
technology. The fibers of the nonwoven may be synthetic fibers including both mineral,
ceramic and polymer fibers, optionally together with natural fibers. By wet-laying
is here understood both liquid-laying and foam-laying, i.e. laying fibers suspended
in liquid or foam on a foraminous surface.
[0002] The fields of use for the present invention relate in particular to healthcare, medical,
surgical, personal care (wipes, napkins, hair-removal/depilatory strips, etc.), textiles
(clothing), geotextiles, construction materials (plaster boards, acoustic panels,
flooring materials), composite products (glass mat, natural fibers + PP/PLA fibers)
decoration (wallpaper, indoor banners), automotive, filtration, agriculture, furniture,
leisure, protective packaging, domestic use (for instance table tops, coffee pods
and like beverage products).
PRIOR ART
[0003] A nonwoven substrate is characterized by entangling individual fibers to form a coherent
web or batt. In other words, a nonwoven is a fabric-like material made of long synthetic
fibers, bonded together by chemical, mechanical, heat or solvent treatment. The term
is used predominantly in the textile manufacturing industry to denote fabrics, such
as felt, which are neither woven nor knitted. Nonwoven materials typically lack strength.
Generally, it comprises synthetic and optionally natural fibers. These fibers may
be oriented randomly or more regularly depending on the technique used to make the
nonwoven.
[0004] In the manufacture of nonwoven, including also glass fiber substrates, the following
processes, among others, are commonly used:
- carding;
- air laying;
- meltblown (spun laid); and
- wet-laying (or paper route) including both liquid-laying and foam-laying technologies.
[0005] The cohesion of the nonwoven may be produced during its manufacture or also in a
subsequent step. This consolidation may be conducted mechanically (needle punching),
thermally, or chemically (incorporating a chemical binder) for example.
[0006] Nonwovens are distinguished from paper-type fibrous substrates in that they comprise
long fibers whereas fibers constituting paper are shorter. By definition, paper is
a web-like product formed of short natural fibers having a length of less than 4 mm.
Naturally, paper comprises various fillers, sizing agents, retention agents etc, but
the only fibrous constituent is short natural fiber.
[0007] Nevertheless, the prior art also comprises nonwovens containing, in addition to synthetic
fibers, short cellulose fibers. These are generally made by the wet-laid process.
[0008] Regardless, generally, bearing in mind the presence of long synthetic fibers having
preferably fiber diameters exceeding 0.8 µm, a nonwoven does not comprise as many
hydrogen bonds, which give paper a certain strength.
[0009] Consequently, the mechanical properties of nonwovens depend not only on the nature
and quantity of fibers used, but also how they are made. In this context, a hydroentangling
or needle punching step or a binding agent being present may improve the cohesion
of the nonwoven at equal basis weight.
[0010] The Applicant has developed a new nonwoven whose strength properties are improved
compared to nonwovens of the prior art, and without increasing its weight or the ratio
between its weight per unit of surface area and its thickness.
DESCRIPTION OF THE INVENTION
[0011] The Applicant has discovered that incorporating a low quantity of nanofibrillar cellulose
(NFC) in the nonwoven according to the invention improves the mechanical properties
compared with nonwovens of the prior art with the same weight and thickness.
[0012] More specifically, the present invention relates to a wet-laid nonwoven comprising
natural and/or synthetic fibers. It further comprises nanofibrillar cellulose in an
amount of between 0.1 and 20% by dry weight compared with the dry weight of said nonwoven.
[0013] Generally, the nonwoven according to the invention has a tensile strength (ISO standard
1924-2) in the machine direction that is, when divided by basis weight, greater than
5 Nm/g. It is advantageously between 5 and 12 Nm/g. Further, its tear resistance (ISO
standard 1974 - 1990 E) in the machine direction is, when divided by basis weight,
generally greater than 5 mNm
2/g. It is advantageously between 5 and 15 mNm
2/g.
[0014] According to a further specific embodiment, the wet-laid nonwoven may comprise up
to 99% natural fibers, preferably between 0 and 89% natural fibers, or advantageously
between 39.9 and 89%, and more advantageously between 59.9 and 80%, by dry weight
compared with the dry weight of said nonwoven.
[0015] Further, the wet-laid nonwoven comprises between 0 and 90% synthetic fibers, preferably
between 10 and 60%, more advantageously between 19.9 and 60%, even more advantageously
between 19.9 and 40%, by dry weight compared with the dry weight of said nonwoven.
[0016] In an advantageous manner, the nonwoven comprises between 0.1 and 20% nanofibrillar
cellulose, more advantageously between 1 and 5%, by dry weight compared with the dry
weight of said nonwoven.
[0017] It advantageously comprises between 0.1 and 20% nanofibrillar cellulose when the
nonwoven comprises up to 90% synthetic fibers, which does not mean that the nonwoven
is necessarily devoid of natural fibers.
[0018] The nonwoven identified in the invention is advantageously constituted of x% natural
fibers, y% synthetic fibers, and z% NFC. All the intermediate percentages resulting
from at least two upper and/or lower values of the ranges indicated above are also
within the scope of the invention, such that x + y + z = 100.
[0019] In other words, these percentages explicitly disclose a wet-laid nonwoven comprising
80% natural fibers, 5% NFC and 15% synthetic fibers, by dry weight compared with the
dry weight of said nonwoven. In the same manner, the nonwoven comprising 30% natural
fibers, 60% synthetic fibers and 10% NFC is explicitly disclosed.
[0020] A further feature of the nonwoven of the present invention is that it comprises long
fibers in an amount of at least 15% by dry weight of the nonwoven, i.e. fibers having
a length of at least 5 mm, preferably more than 7 mm, more preferably more than 10
mm. Advantageously the nonwoven of the invention comprises long fibers in an amount
of at least 18%, more advantageously at least 25% by dry weight of the nonwoven. The
long fibers may be synthetic fibers, natural fibers or a combination of both.
[0021] "Wet-laid nonwoven" is understood to mean a nonwoven obtained from an aqueous suspension
of synthetic fibers, optionally together with natural fibers, and nanofibrillar cellulose.
This suspension may also comprise at least one surfactant. It may then be in the form
of a foam, whereby the nonwoven is obtained from a foam-laid suspension of synthetic
fibers.
[0022] As already stated, a nonwoven comprises entangled fibers arranged randomly or more
regularly. The fibers may be held together by using a binder, an adhesive, heat or
pressure, or by needle punching for example.
[0023] In the scope of the present invention, the synthetic fibers have a relatively high
length/diameter ratio, for example of the order of 600/1. It may be comprised between
100 and 1000. The length of the synthetic fibers is advantageously comprised between
0.1 cm and 4 cm, advantageously between 0.3 and 3 cm. Their diameter or thickness
may be comprised between 2 and 40 micrometers, advantageously between 10 and 20 [micrometers].
Further, synthetic fibers having different lengths and diameters may be used in the
same nonwoven.
[0024] Synthetic fibers, a term also encompassing mineral fibers, may in particular be chosen
here from the group comprising:
- semi-synthetic fibers derived from cellulose, for example viscose, rayon, or lyocell,
cellulose acetate;
- glass carbon, basalt, silicon, ceramic and metallic fibers;
- synthetic polymer fibers; and
- their mixtures.
[0025] According to a preferred embodiment, the synthetic polymer fibers are chosen from
the group comprising polyamide, polyaramide, polyethylene, polypropylene, polyester,
polyvinyl chloride fibers, and their mixtures.
[0026] In addition to the above listed options for synthetic fibers, also so called synthetic
pulp may be used in combination with the above mentioned synthetic fibers or in place
thereof. The synthetic pulp is discussed in detail in
US-B2-8,513,147. In brief it is made of unicomponent fibers that rapidly disperse or dissolve in
water and may be produced by melt-blowing or melt-spinning. The fibers may be prepared
from a single sulfopolyester or a blend of the sulfopolyester with a water-dispersible
or water non-dispersible polymer. Thus, the fiber of the present invention, optionally,
may include a water-dispersible polymer blended with the sulfopolyester. In addition,
the fiber may optionally include a water non-dispersible polymer blended with the
sulfopolyester, provided that the blend is an immiscible blend. The synthetic pulp
may also be manufactured of multicomponent fibers comprising a water-dispersible sulfopolyester
and one or more water non-dispersible polymers.
[0027] Natural fibers are advantageously chosen from the group comprising cellulose-based
natural fibers, for example fibers from wood pulp, cotton, sisal, abaca, kenaf, jute
fibers, bagasse fibers, hemp fibers, flax fibers and their mixtures. Depending on
their origin, these natural fibers may be short (cellulose) or long (bagasse, hemp,
flax).
[0028] According to a specific embodiment, the natural fibers, and more specifically the
cellulose-based fibers, may be bleached fibers. Bleaching of fibers is understood
to mean that the suspension of fibers, or pulp, has undergone a bleaching treatment
according to techniques known to the person skilled in the art.
[0029] Further, according to another specific embodiment, the natural fibers, and more specifically
the cellulose-based fibers, are advantageously refined to less than 21 °SR, even more
advantageously between 10 and 20 °SR.
[0030] The refining corresponds to a dewatering index, expressed in Schopper-Riegler degrees
(°SR). The more the pulp (suspension of natural fibers) is refined, the more water
is retained. A paper whose pulp has been less refined has low resistance properties,
such as for instance paper towel. Refining allows the fibers to branch.
[0031] Refining hydrates and fibrillates the cellulose fibers, thus increasing the specific
surface area of the fibers, whereby the number of hydrogen bonds between fibers is
increased. This increase improves the mechanical properties of the fibrous material.
[0032] Generally, in the paper industry, the fibers are refined to between 25 and 90 °SR,
on average between 50 and 60 °SR.
[0033] Regarding nanofibrillar cellulose (NFC), this is a nanofiber whose diameter, or thickness,
is advantageously comprised between 5 and 100 nanometers, more advantageously of the
order of 20 nanometers. Further, the length of the nanofibrils is less than 1 micrometer.
It is advantageously comprised between 0.1 and 1 micrometer, more advantageously between
400 and 500 nanometers.
[0034] Nanofibrillar cellulose may in particular be prepared by dissolving pulp from resinous
wood, from long fibers (softwood cellulose pulp), or from a mixture of pine and spruce.
[0035] This dissolving of pulp may undergo the following treatment to produce nanofibrillar
cellulose:
- first refining to 25 °SR;
- enzymatic treatment at 50°C in the presence of endoglucanase;
- second refining to 80 °SR; and
- several passes in a homogenizer.
[0036] The synthetic fibers come from synthetic materials, i.e. man-made materials. However,
these synthetic materials may be biodegradable and/or compostable.
[0037] Biodegradable/compostable synthetic fibers may in particular be chosen from the group
comprising PLA-type polyesters (polylactic acid), PHA/PHB (polyhydroxyalkanoate/polyhydroxybutyrate),
and PCL (polycaprolactone) or similar; polyvinyl alcohol; cellulose acetate; and their
mixtures.
[0038] Accordingly, depending on the nature of these constituents, the nonwoven identified
in the invention may be biodegradable and/or compostable.
[0039] The synthetic fibers and/or the natural fibers and/or the nanofibrillar cellulose
may come from respective recycling processes.
[0040] According to a specific embodiment, the nonwoven identified in the invention may
also comprise additives such as pigments, inorganic fillers (titanium, calcium carbonate,
kaolin, etc.) binders, strengthening agents, dispersants, and retention agents. These
additives are preferably added by impregnating the nonwoven with a solution comprising
at least one additive. They may also be added to the aqueous suspension of fibers.
[0041] The retention agent is advantageously a cationic polymer. The person skilled in the
art will know how to choose the right compound. It is added into the aqueous suspension
of fibers. It advantageously represents between 0.01% and 2% by dry weight of the
suspension (100 g to 20 kg per ton of fibers/NFC).
[0042] The binding agent may in particular be chosen from the group comprising binders based
upon polyacrylics, polystyrene acrylics, polyvinyl acetate, polyvinyl acrylate, polystyrene
butadienes, polyethylene vinyl acetate, polyvinyl chloride, polyvinyl alcohol and
its derivatives (polyvinyl ethylalcohol), polyethylene vinyl chloride, polyurethane,
polyamides, polyolefins (polyethylene and polypropylene), polyesters, elastomers of
natural origin, urea formaldehyde, melamine formaldehyde, phenol formaldehyde, polymers
from starch, and their mixtures.
[0043] These additives represent advantageously between 5 and 95 parts by dry weight, per
100 parts by weight of the dry nonwoven, even more advantageously between 20 and 60
parts by dry weight.
[0044] Generally, the nonwoven that is identified in the invention may have a basis weight
advantageously between 5 and 1000 g/m
2, more advantageously between 40 and 160 g/m
2.
[0045] The ratio between the thickness and the weight per unit of surface area (basis weight)
of the nonwoven is commonly denoted as "bulk", which is advantageously between 2 and
6 cm
3/g, more advantageously of the order of 4.5 cm
3/g.
[0046] Generally, the thickness of the nonwoven increases with basis weight whereas the
bulk advantageously remains constant.
[0047] According to a specific embodiment, the wet-laid nonwoven according to the invention
may comprise one or more layers of compositions that are identical or different.
[0048] Advantageously, the wet-laid nonwoven according to the invention has air permeability
(related to porosity) greater than 50 L/m
2/s, advantageously between 500 and 2000 L/m
2/s.
[0049] The present invention further relates to a manufacturing process for the wet-laid
nonwoven described hereinbefore, according to which, on a fiber web machine, a wet-laid
suspension of at least synthetic fibers is deposited onto a foraminous surface, wherein
nanofibrillar cellulose is added before, during or after depositing the synthetic
fibers on the foraminous surface such that the nonwoven is impregnated with NFC for
its entire thickness.
[0050] The present invention further relates to a manufacturing process for the wet-laid
nonwoven, wherein the resulting nonwoven is dried.
[0051] The present invention further relates to a manufacturing process for the wet-laid
nonwoven, wherein the nonwoven is soaked with a solution comprising at least one additive
and the resulting nonwoven is dried.
[0052] According to a specific embodiment, the suspension of synthetic fibers may also comprise
at least one surfactant. Therefore this is a suspension that may be in the form of
a foam. More specifically, this is a foam comprising fibers in suspension.
[0053] The NFC may be added in the form of a suspension in water or in foam:
- in the headbox to be mixed with the fiber suspension,
- before the headbox into at least one fiber suspension,
- during depositing the synthetic fibers on the foraminous surface, for instance by
means of spraying on the fibrous suspension,
- after depositing the synthetic fibers on the foraminous surface, for instance by means
of spraying on the nonwoven to be formed,
- optionally to be mixed with natural fibers prior to their deposition, or
- after the nonwoven is formed, for instance by spraying on the nonwoven such that the
NFC penetrates into the thickness of the nonwoven, whereby the nonwoven is impregnated
with NFC throughout its entire thickness.
- after the nonwoven is formed, for instance by means of an impregnation step, where
both faces of the nonwoven are in contact with the NFC prior to treatment in a nip
between two rolls (or one roll and a counter-surface), which make the NFC penetrate
into the thickness of the nonwoven, whereby the nonwoven is impregnated with NFC throughout
its entire thickness. This step is conducted before, during or after the optional
impregnation of the nonwoven with a suspension comprising at least one binding agent.
However, according to a specific embodiment, NFC may also be added during a step where
the nonwoven is impregnated with a suspension comprising at least one binding agent.
[0054] The NFC suspension may also comprise at least one surfactant. It can therefore be
in the form of a foam. Therefore suspension in water is also understood to mean a
suspension in the form of a foam. More specifically, this is a foam comprising NFC
in suspension.
[0055] NFC and synthetic fibers, optionally together with natural fibers, represent advantageously
from 0.01 to 1% by dry weight compared with the dry weight of the suspension of synthetic
fibers, optionally together with natural fibers, advantageously between 0.01 and 0.1
%.
[0056] The wet-laid nonwoven identified in the invention may in particular find application
in the fields of healthcare, medical, surgical, personal care (wipes, hair-removal
strips, etc.), textiles (clothing), geotextiles, construction materials, decoration
(wallpaper), automotive, filtration, agriculture, furniture, leisure, and domestic
use.
[0057] The invention and the benefits it brings will be clearer upon reading the following
figures and examples, given to illustrate the invention and not to limit it in any
way.
FIGURES
[0058]
Figure 1 represents the tensile strength of nonwovens according to the invention as
a function of basis weight, compared to a nonwoven of the prior art example 1.
Figure 2 represents the tear resistance of nonwovens according to the invention as
a function of basis weight, compared to a nonwoven of the prior art example 1.
Figure 3 represents the permeability of nonwovens according to the invention as a
function of basis weight, compared to a nonwoven of the prior art example 1.
EXAMPLES OF EMBODIMENTS OF THE INVENTION
Example 1:
[0059] Thirteen wet-laid nonwovens were prepared from the compositions in table 1, according
to the classic preparation techniques for a wet-laid nonwoven, in this case liquid-laying
on a foraminous surface.
Table 1: Compositions of the 13 wet-laid nonwovens prepared.
Example |
basis weight (g/m2) |
natural fibers(% by weight) |
synthetic fibers (% by weight) |
NFC (% by weight) |
MD tensile strength index (Nm/g) |
MD tear resistance index (mNm2/g) |
1 (PA) |
43 |
cellulose(a) 81% |
Polyester(b) 19% |
0 |
6.15 |
7.98 |
37 |
5.21 |
6.91 |
32 |
5.17 |
6.41 |
2 (INV) |
43 |
cellulose 81% |
polyester 18% |
1 |
6.97 |
8.82 |
37 |
7.4 |
7.89 |
32 |
6.45 |
7.36 |
3 (INV) |
43 |
cellulose 79,5% |
polyester 18% |
2.5 |
8.76 |
9.68 |
37 |
7.16 |
9.31 |
32 |
6.27 |
7.73 |
4 (INV) |
43 |
cellulose 78% |
polyester 17% |
5 |
10.37 |
14.72 |
37 |
8.34 |
10.81 |
32 |
8.47 |
10.59 |
21 |
7.75 |
9.43 |
(a) the natural fiber furnish is formed of 33.3% Celbi PP high dry FSC cellulose pulp,
34.6% Joutseno Pine 90 PEF cellulose pulp, and 32.1% Alabama River softwood cellulose
pulp
(b) the synthetic fiber furnish is formed of Dacron fibers (10 mm 1.7 dtex) from polyester
recycling
MD: in the machine direction
PA: Wet-laid nonwoven according to the prior art
INV: Wet-laid nonwoven according to the invention |
[0060] The 13 nonwovens in examples 1 - 4 were made on a conventional machine for preparing
wet-laid nonwovens. Its operation rate is 20 m/min.
[0061] For each of the 13 experiments (examples 1 - 4), 400 linear meters 50 cm wide of
each were produced.
[0062] The nonwovens were made from a suspension comprising 0.7% by weight nanofibrillar
cellulose, natural fibers and synthetic fibers, compared with the total weight of
the suspension.
[0063] The cellulose fibers (in the form of a paper pulp sheet: 40 kg) are first added to
the pulper for 10 min. The synthetic fibers (9 kg) and the 2% solids content NFC are
then added; that is, for 1%, 2.5% and 5% respectively: 22.7 liters (i.e. 0.45 kg if
it were dry), 56.8 liters (i.e. 1.13 kg if it were dry) and 113.5 liters (i.e. 2.27
kg if it were dry).
[0064] 243 mL of Kymene are then added (agent for wet strength), and 19 mL Hydroperm (dispersing
agent).
[0065] The total volume of the suspension is made up to 6436 liters (i.e. about 0.7% by
weight of fibers and nanofibrillar cellulose, i.e.: 7 g/L).
[0066] These nonwovens have been prepared according to the following steps:
- depositing a wet-laid suspension of synthetic and natural fibers and NFC on a forming
wire so as to form a nonwoven;
- drying the resulting nonwoven.
[0067] The tensile strength, tear resistance, and air permeability properties were then
measured.
Tensile strength (figure 1)
[0068] Generally, at equal basis weight, incorporating NFC improves the tensile strength.
So the nonwoven of the prior art at 43 g/m
2 has similar properties to wet-laid nonwovens of the invention at 32 g/m
2 (example 1 vs. examples 2 - 4 at 32 g/m
2).
[0069] When 5% NFC is added, the tensile strength improvement is 70% on average for nonwovens
from 32 to 43 g/m
2.
[0070] The nonwoven of the invention at 21 g/m
2 comprising 5% NFC (example 4) has similar tensile strength to that of the nonwoven
at 32 g/m
2 of the prior art (example 1).
Tear resistance (figure 2)
[0071] The presence of NFC improves the tear resistance. For example, it is increased by
100% for a nonwoven at 43 g/m
2 comprising 5% NFC (example 1 vs. example 4).
[0072] Further, the nonwoven of the invention at 32 g/m
2 comprising 2.5% NFC has similar properties to that of a nonwoven of the prior art
at 43 g/m
2 (example 1 vs. example 3).
[0073] The nonwoven of the invention at 21 g/m
2 comprising 5% NFC (example 4) has similar tear resistance to that of the nonwoven
of the prior art at 32 g/m
2 (example 1).
Air permeability (figure 3)
[0074] The air permeability of nonwovens according to the invention comprising NFC is lower
than that of nonwovens of the prior art. However, this decrease is less than 10% when
the nonwoven comprises from 1 to 5% NFC and has basis weight between 32 and 43 g/m
2.
[0075] Regarding the wet-laid nonwoven comprising 5% NFC and having basis weight of 21 g/m
2, the porosity is clearly greater than that of the nonwoven of the prior art at 32
g/m
2.
[0076] Consequently, adding NFC is not contrary to maintaining an open nonwoven structure.
Conclusions
[0077] These examples show that adding NFC maintains the mechanical properties of a wet-laid
nonwoven while reducing its basis weight, thereby reducing the necessary quantity
of natural and synthetic fibers (of the order of 25% in this case).
Example 2:
[0078] Three wet-laid nonwovens were prepared from compositions in table 2, according to
the classic preparation techniques for a wet-laid nonwoven i.e. in this case liquid-laying
on a foraminous surface.
Table 2: compositions of three prepared wet-laid nonwovens
Example |
basis weight (g/m2) |
natural fibers (% by weight) |
synthetic fibers (% by weight) |
NFC (% by weight) |
tensile strength index (Nm/g) |
tear resistance index (mNm2/g) |
1b (PA) |
60.2 |
cellulose 0% |
Polylactic acid(c) 100% |
0 |
0 (not measurable) |
0.21 |
2b (INV) |
65.6 |
cellulose 0% |
Polylactic acid(c) 91% |
9 |
9.6 |
5.83 |
3b (INV) |
71.7 |
cellulose 0% |
Polylactic acid(c) 84% |
16 |
13.24 |
10.72 |
(c) Polylactic acid fibers (PLA) (6 mm, 1.7 dtex)
MD: in the machine direction
PA: wet-laid nonwoven according to the prior art
INV: wet-laid nonwoven according to the invention |
[0079] The three nonwovens in examples 1b to 3b were manufactured on a Frank sheet-former
or similar device well known to the person skilled in the art. A retention agent (Percol
1830 by BASF) was used at 0.2% dry weight compared with fiber dry weight.
[0080] The following were used: for example 1 b, 2 g of PLA fibers; for example 2b, 2 g
of PLA and 0.2 g NFC; and for example 3b, 2 g of PLA fibers and 0.4 g NFC. In all
examples NFC and PLA fibers were mixed in water to form a suspension prior to feeding
such on the Frank sheet-former.
[0081] The quantity of retention agent has been adjusted as a function of the quantity of
fibers (PLA and NFC) used to obtain a quantity equal to 0.2% of the nonwoven. The
resulting sheet is dried on a glazing machine between two canvases for 5 minutes.
[0082] The tensile strength, tear resistance, and air permeability properties were then
measured (See tables 2 and 3).
Table 3: air permeability of nonwovens 1 b, 2b and 3b
sample |
1b (PA) |
2b (INV) |
3b (INV |
Textest Porosity at 200 Pa (L/m2/s) |
Not measurable |
1058 |
299 |
Tensile strength
[0083] Adding NFC to the mixture of synthetic fibers considerably increases the mechanical
properties of the nonwoven and in particular the tensile strength. A nonwoven made
only of synthetic fibers (here PLA) has no mechanical cohesion, since the synthetic
fibers cannot generate bonds between themselves in the wet-laid nonwoven manufacturing
process (the paper route). Therefore the tensile strength cannot be measured.
[0084] By adding 10% NFC compared to the quantity of synthetic fibers (example 1 b), it
is possible to generate bonds between the synthetic fibers due to the NFC and to reach
remarkable tensile strength index: 9.6 Nm/g for example 2b and 13.24 Nm/g for example
3b, respectively.
Tear resistance
[0085] Similarly to tensile strength, tear resistance was increased substantially. Nonwoven
1 b not containing NFC has a relatively low tear index value: 0.21 mNm
2/g. Incorporating 10% and 20% NFC in nonwovens 2b and 3b respectively increased the
tear resistance index to values of 5.83 mNm
2/g and 10.72 mNm
2/g respectively, i.e. 2700% and 5100% increase respectively compared with the initial
nonwoven.
Air permeability
[0086] The Textest air permeability measurement device could not measure air permeability
on the nonwoven product with only PLA fibers (example 1a), as the nonwoven was destroyed
when air passed through the sample. By contrast the nonwovens containing NFC were
measureable and have values greater than 50 L/m
2/s and therefore in the range of a classic nonwoven, in particular for example 2b
with a value of 1058 L/m
2/s.
Conclusions:
[0087] These examples show that adding NFC to a mixture of fibers constituted only of synthetic
fibers generates cohesion between the synthetic fibers to allow a nonwoven web to
be produced. Increasing the quantity of NFC also increases the mechanical properties
of a wet-laid nonwoven. Therefore this means the quantity of synthetic fibers required
can be reduced.
Example 3:
[0088] Three wet-laid nonwovens were prepared from compositions in table 4, according to
the classic preparation techniques for a wet-laid nonwoven, i.e. in this case liquid-laying
on a foraminous surface.
Table 4: compositions of three prepared wet-laid nonwovens
Example |
basis weight (g/m2) |
natural fibers (% by weight) |
Mineral Fibers (% by weight) |
NFC (% by weight) |
tensile strength index (Nm/g) |
tear resistance index (mNm2/g) |
1c (PA) |
73.9 |
cellulose 0% |
Glass Fibers(d) 100% |
0 |
0 (not measurable) |
0.22 |
2c (INV) |
78 |
cellulose 0% |
Glass Fibers(d) 91% |
9 |
5.13 |
7.49 |
3c (INV) |
83.3 |
cellulose 0% |
Glass Fibers(d) 84% |
16 |
13.33 |
16 |
(d) Glass Fibers (6 mm, 0.85 dtex)
MD: in the machine direction
PA: wet-laid nonwoven according to the prior art
INV: wet-laid nonwoven according to the invention |
[0089] The three nonwovens in examples 1c to 3c were manufactured on a Frank sheet-former
or similar device well known to the person skilled in the art. A retention agent (Percol
1830 by BASF) was used at 0.2% dry weight compared with fiber dry weight.
[0090] The following were used: for example 1c, 2 g of Glass Fibers; for example 2c, 2 g
of Glass Fibers and 0.2 g NFC; and for example 3c, 2 g of Glass Fibers and 0.4 g NFC.
In all examples NFC and Glass Fibers were mixed in water to form a suspension prior
to feeding such on the Frank sheet-former.
[0091] The quantity of retention agent has been adjusted as a function of the quantity of
fibers (Glass Fibers and NFC) used to obtain a quantity equal to 0.2% of the nonwoven.
The resulting sheet is dried on a glazing machine between two canvases for 12 minutes
at 100 °C.
[0092] The tensile strength, tear resistance, and air permeability properties were then
measured (See tables 4 and 5).
Table 5: air permeability of nonwovens 1c, 2c and 3c
sample |
1c (PA) |
2c (INV) |
3c (INV) |
Textest Porosity at 200 Pa (L/m2/s) |
Not measurable |
1203 |
137 |
Tensile strength
[0093] Adding NFC to the mixture of mineral fibers considerably increases the mechanical
properties of the nonwoven and in particular the tensile strength. A nonwoven made
only of mineral fibers (here Glass Fibers) has no mechanical cohesion, since the mineral
fibers cannot generate bonds between themselves in the wet-laid nonwoven manufacturing
process (the paper route). Therefore the tensile strength cannot be measured.
[0094] By adding 10% NFC compared to the quantity of mineral fibers (example 1c), it is
possible to generate bonds between the mineral fibers due to the NFC and to reach
remarkable tensile strength index: 5.13 Nm/g for example 2c and 13.33 Nm/g for example
3c, respectively.
Tear resistance
[0095] Similarly to tensile strength, tear resistance was increased substantially. Nonwoven
1c not containing NFC has a relatively low tear index value: 0.22 mNm
2/g. Incorporating 10% and 20% NFC in nonwovens 2c and 3c respectively increased the
tear resistance index to values of 7.49 mNm
2/g and 16 mNm
2/g respectively, i.e. 3400% and 7200% increase respectively compared with the initial
nonwoven.
Air permeability
[0096] The Textest air permeability measurement device could not measure air permeability
on the nonwoven product with only Glass Fibers (example 1c), as the nonwoven was destroyed
when air passed through the sample. By contrast the nonwovens containing NFC were
measureable and have values greater than 50 L/m
2/s and therefore in the range of a classic nonwoven, in particular for example 2c
with a value of 1203 L/m
2/s.
Conclusions
[0097] These examples show that adding NFC to a mixture of fibers constituted only of mineral
fibers generates cohesion between the synthetic fibers to allow a nonwoven web to
be produced. Increasing the quantity of NFC also increases the mechanical properties
of a wet-laid nonwoven. Therefore this means the quantity of minerals fibers required
can be reduced.
[0098] The research leading to these results received financial support under the Seventh
Framework Program of the European Community in accordance with grant agreement No.
228802.
1. A wet-laid nonwoven comprising long fibers in an amount of at least 15% by dry weight
compared with the dry weight of said nonwoven, and nanofibrillar cellulose (NFC) in
an amount of between 0.1 and 20% by dry weight compared with the dry weight of said
nonwoven with the balance to 100 percent comprising synthetic and/or natural fibers,
the long fibers having a length of at least 5 mm and being selected from synthetic
and/or natural fibers, and the nonwoven being impregnated with the NFC for its entire
thickness.
2. The wet-laid nonwoven according to claim 1, characterized in that it comprises synthetic fibers in an amount of between 0 and 90% by dry weight compared
with the dry weight of said nonwoven.
3. The wet-laid nonwoven according to claim 1 or 2, characterized in that it comprises natural fibers in an amount of up to 99% by dry weight compared with
the dry weight of said nonwoven.
4. The wet-laid nonwoven according to any one of claims 1 to 3, characterized in that it has a tensile strength in the machine direction greater than 5 Nm/g, and tear
resistance in the machine direction greater than 5 mNm2/g.
5. The wet-laid nonwoven according to any one of claims 1 to 3, characterized in that the synthetic fibers are chosen from the group comprising glass, carbon, silicon,
ceramic, metallic, polymeric fibers, synthetic fibers derived from cellulose, and
their mixtures.
6. The wet-laid nonwoven according to any one of claims 3 or 5, characterized in that the natural fibers are cellulose fibers chosen from the group comprising fibers from
wood pulp, cotton fibers, sisal fibers, abaca fibers, kenaf fibers, jute fibers, bagasse
fibers, hemp fibers, flax fibers and their mixtures.
7. The wet-laid nonwoven according to any one of claim 6, characterized in that the natural fibers are cellulose fibers refined to less than 21 °SR.
8. The wet-laid nonwoven according to any one of claims 1 to 7, characterized in that it has a bulk between 2 and 6 cm3/g.
9. A method of manufacturing the wet-laid nonwoven according to any one of claims 1 to
8, in which method a suspension of synthetic and/or natural fibers is deposited on
a foraminous surface of a fiber web machine, characterized by adding nanofibrillar cellulose (NFC) to the suspension before, during or after depositing
the suspension on the foraminous surface such that the nonwoven is impregnated with
NFC for its entire thickness.
10. The method of manufacturing the wet-laid nonwoven according to claim 9characterized by adding the NFC to one of the synthetic fiber suspension, to the natural fiber suspension
and to a suspension of their mixture prior to depositing the suspension on the foraminous
surface.
11. The method of manufacturing the wet-laid nonwoven according to claim 9 or 10, characterized by applying the NFC onto the suspension deposited on the foraminous surface.
12. The method of manufacturing the wet-laid nonwoven according to any one of claims 9
to 11, characterized by impregnating the wet-laid nonwoven with the nanofibrillar cellulose after the formation
of the nonwoven.
13. The method of manufacturing the wet-laid nonwoven according to claims 9 or 12, characterized by drying the nonwoven before the impregnation thereof with the nanofibrillar cellulose.
14. The method of manufacturing the wet-laid nonwoven according to any one of claims 9
- 13, characterized by soaking the wet-laid nonwoven with a solution comprising at least one additive before
drying of the nonwoven the additive being at least one of nanofibrillar cellulose,
pigments, inorganic fillers (titanium, calcium carbonate, kaolin, etc.) binders, wet
and/or dry strengthening agents, dispersants, and retention agents
15. The method of manufacturing the wet-laid nonwoven according to claim 9, characterized in that the nanofibrillar cellulose is added, in the form of a suspension in water, in the
headbox.