METHOD FOR PRODUCING A REINFORCED FIBER COMPOSITE

PROCEDE DE FABRICATION D'UNE NAPPE DE FIBRES RENFORCEE

English Abstract

The invention relates to a method for producing a reinforced fiber composite
which contains cellulosic fibers, the cellulose being present in the
crystalline structure cellulose II, by bringing said fiber composite into
contact with an aqueous solution of N-methylmorpholin-N-oxide (NMMO) at an
elevated temperature and subsequently washing said fiber composite. Said
method is characterized in that the fiber composite is brought into contact
with the aqueous solution in such a way that the reationship -947 +
0.30xlog(10)t + 0.046xT - 3.53xC + 645xlog(10)C where t is the time in minutes
during which the fiber composite is kept in contact with the aqueous NMMO
solution, T is the temperature of the aqueous NMMO solution in ~C and C is the
concentration of the NMMO in % mass in relation to the aqueous NMMO solution,
gives a figure in the region of 0.30 and 1.70 on the condition that the
temperature T is less than 130 ~C and the concentration C lies in the region
of 70 to 84 % mass.

French Abstract

L'invention concerne un procédé de fabrication d'une nappe de fibres renforcée contenant des fibres cellulosiques. La cellulose est présente sous la forme de la structure cristalline cellulose II. Ce procédé consiste à mettre en contact la nappe de fibres avec une solution aqueuse de N-méthylmorpholin-N-oxyde (NMMO) à une température élevée puis à laver la nappe de fibres. Le procédé selon l'invention est caractérisé en ce que la mise en contact est réalisée de telle manière que l'on obtienne un nombre compris entre 0,30 et 1,70 pour la relation -947 + 0,30xlog¿(10)? t + 0,046xT - 3,53xC + 645xlog¿(10)? C où t représente le temps, exprimé en minutes, pendant lequel la nappe de fibres est mise en contact avec la solution aqueuse de NMMO, T représente la température de la solution aqueuse NMMO en ·C et où C représente la concentration de NMMO en % en masse, par rapport à la solution aqueuse de NMMO, cela à condition que la température T soit inférieure à 130 ·C et la concentration C soit comprise entre 70 et 84 % en masse.

Claims

Claims:
1. A process for producing a strengthened fiber assembly containing cellulosic fibers
with the cellulose being present in the crystalline structure of cellulose II, by contacting the
fiber assembly with an aqueous solution of N-methylmorpholine-N-oxide (NMMO) at
elevated temperature and subsequently washing the fiber assembly, characterized in that
contacting is effected in a manner that from the relation
-947 + 0.30xlog(10)t + 0.046xT - 3.53xC + 645xlog(10)C
wherein t indicates the time in minutes during which the fiber assembly is contacted with the
aqueous NMMO solution, T indicates the temperature of the aqueous NMMO solution in °C
and C is the concentration of NMMO in % by mass, based on the aqueous NMMO solution, a
number in the range of 0.30 to 1.70 results with the proviso that the temperature T is smaller
than 130°C and the concentration C ranges between 70 and 84 % by mass.
2. A process according to claim 1, characterized in that the parameters t, T and C are
chosen such that a number in the range of 0.5 to 1.5 results from the relation.
3. A process according to claim 2, characterized in that the parameters t, T and C are
chosen such that a number in the range of 0.8 to 1.2 results from the relation.
4. A process according to any one of claims 1 to 3, characterized in that the temperature
T is smaller than 100°C.
5. A process according to any one of claims 1 to 4, characterized in that the fiber
assembly is pressed prior to washing.
6. A process according to any one of claims 1 to 5, characterized in that a fiber assembly
whose fibers have at least partially been produced according to the amine oxide process is
used for strengthening.
7. A process according to any one of claims 1 to 5, characterized in that a fiber assembly
whose fibers have at least partially been produced according to the viscose process is used for
strengthening.

Description

CA 022~1728 1998-10-14
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Process for Producin~g a Strer~thened Fiber A~c~rnhly
The present invention relates to a process for producing a strengthened fiber assembly
cont~ining cellulosic fibers with the cellulose being present in the crystalline structure of
cellulose II, by contacting the fiber assembly with an aqueous solution of N-
methylmorpholine-N-oxide (NMMO) at elevated temperature and subsequently washing the
fiber assembly.
For the purposes of this description and the annexed claims, the expression "fiber assembly"
is to denote any kind of wovens, nonwovens or random webs.
During the past years, a number of processes in which cellulose is dissolved in an organic
solvent, a combination of an organic solvent with an inorganic salt, or in aqueous salt
solutions, without forming a derivative have been described as alternatives to the viscose
process. Cellulose fibers made of such solutions were given the generic name lyocell by
BISFA (The Tntern~tional Bureau for the Standardisation of Man-Made Fibres). According to
the BISFA definition, lyocell is a cellulose fiber obtained from an organic solvent by means of
a spinning process. By "organic solvent", a ~ e of an organic chemical and water is
understood by BISFA.
To date but a single process for the production of a cellulose fiber of the lyocell type has,
however, become accepted to the point of large-scale realization, namely the amine oxide
process. In that process, N-methylmorpholine-N-oxide (NMMO) is preferably used as the
solvent. For the purposes of the instant specification, the term "tertiary amine oxides"
substitutionally is referred to by the abbreviation " NMMO", NMMO additionally
representing the presently plef~lled N-methylmorpholine-N-oxide.
Tertiary amine oxides have been known for long as alternative solvents for cellulose. Thus, it
is known, for instance, from U.S. Patent No. 2,179,181 that tertiary amine oxides are capable
of dissolving high-quality chemical pulp without the formation of derivatives and that
cellulose moulded bodies such as fibers may be obtained from such solutions by precipitation.
U.S. Patents Nos. 3,447,939, 3,447,956 and 3,508,941 describe further processes for the
production of cellulose solutions with cyclic amine oxides being used as the preferred
solvents. In all of those processes, cellulose is physically dissolved at elevated temperature.
In EP-A - 0 356 419 to applicant a process is decribed, which preferably is carried out in a
thin-layer treating apparatus in which a suspension of the comminlltecl pulp in an aqueous
tertiary amine oxide is spread in the form of a thin layer, transported over a heating surface,
while the surface of the thin layer is exposed to a vacuum. During transportation of the

CA 022~1728 1998-10-14
suspension over the heating surface water is evaporated and the cellulose can be dissolved
such that a spinnable cellulose solution is discharged from the thin-layer treating apparatus.
A process and an arrangement for spinning cellulose solutions are known, for instance, from
WO 93/19230 to applicant. There, the spinning solution is spun in the hot state and the
filaments obtained are introduced into a plecipilation bath in order to precipitate the cellulose
contained therein, the filaments being cooled prior to their introduction into the precipitation
bath. Cooling is effected immediately after moulding and, preferably, consists in horizontally
blowing air at the cellulose moulded body.
German Patent No. 902 427 describes the strengthening of a fleece of cellulose fibers by
means of a lye bath co~ g S to 15 % NaOH. The celluose fibers are swollen by the lye
bath and thereby strengthened.
From WO 95/07386 to applicant, a process for producing paper is known, in which an
aqueous suspension of commin~-te-l cellulose material is mechanically treated and
subsequently subjected to a sheet forming procedure, the suspension cont~ining tertiary amine
oxide. That process allows for the production of high-strength paper.
A process for strengthening a fibrous material is known from US-A - 3,447,956.
Strengthening is effected in that the fibrous m~t~n~l iS soaked with an amine oxide and heated
to a temperature at which the amine oxide is able to strengthen the fibrous material. Proposed
fibrous materials are wovens and nonwovens cOI~t~ natural cellulosic fibers such as, e.g.,
wood pulp, cotton, linen, but also synthetic fibers such as rayon (viscose fibers). Particularly
plefe..ed is the treatment of paper with amine oxide. In doing so, NMMO apparently is used
as a monohydrate in the molten or liquid state or dissolved in a volatile solvent capable of
being evaporated.
From WO 96/37653 fiber assemblies provided with a cellulosic coat, impregnation or sheath
are known. Those fiber assemblies are produced by coating the fiber assembly on one side
with a solution of cellulose in aqueous NMMO, whereupon the layer is coagulated in a water
bath.
US-A - 4,196,282 describes the three-component system NMMO/H2O/cellulose and the so-
called "dissolution frame", i.e., those conditions under which the cellulose dissolves in
aqueous NMMO.

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Furthermore, it is known that cellulose fibers may be swollen with NMMO (Chancy et al.,
"Swelling and Dissolution of Cellulose in Amine OxidelWater Systems"; J. App. Pol. Sci:
Appl. Pol. Symp. 37, 239-259 (1983)).
The invention has as its object to provide a process of the initially defined kind, in which a
fiber assembly can be strengthened without cumbersome evaporation of a volatile solvent and
without requiring the use, or preparation by evaporation, of an NMMO monohydrate.
The process according to the invention for producing a strengthened fiber assembly
cont~ining cellulosic fibers with the cellulose being present in the crystalline structure of
cellulose II, by contacting the fiber assembly with an aqueous solution of N-
methylmorpholine-N-oxide (N~O) at elevated temperature and subsequently washing the
fiber assembly is characterized in that contacting is effected in a manner that from the relation
-947 + 0.30xlog(,0)t + 0.046xT - 3.53xC + 645xlog(10)C
wherein t indicates the time in min~tes during which the fiber assembly is contacted with the
aqueous NMMO solution, T indicates the temperature of the aqueous NMMO solution in ~C
and C is the concentration of NMMO in % by mass, based on the aqueous NMMO solution, a
number in the range of 0.30 to 1.70 and, preferably, in the range of 0.5 to 1.5 and, in a
particularly pl~f~ d manner, in the range of 0.8 to 1.2 results with the proviso that the
temperature T is smaller than 130~C and the concentration C ranges between 70 and 84 % by
mass.
The invention is based on the finding that, for strengthening an assembly of cellulose fibers
such as, e.g., a nonwoven, the three parameters mentioned, i.e., the concentration of the
NMMO solution, its temperature and the time of impregnation, app~ently are essential and
sufficient and that, in addition, they must be chosen such that the above relation is met. If, in
contrast, these parameters are chosen such that a value smaller than 0.30 results from the
relation, no strengthening of the assembly will be obtained. If, on the other hand, the
parameters are chosen such that a value of more than 1.70 results from the relation, the
dissolution of the fiber assembly in the NMMO solution is observed.
In the process according to the invention, the temperature T preferably is smaller than 100~C.
A particular embodiment of the process according to the invention is characterized in that the
fiber assembly is pressed before washing. Pressing may be effected in a simple manner, e.g.,
by conducting the nonwoven between two rolls exerting a p-es~u-e on the fiber assembly.

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The use of a fiber assembly cont~ining fibers produced at least partially according to the
amine oxide process or the viscose process has proved particularly successful in the process
according to the invention.
The invention will be explained in more detail by way of the following examples.
Ge~eral workin~ in~truction
Slightly needle punched viscose nonwovens each having a size of 12 x 16 cm and a weight
per unit area of about 70 g/cm2 were immersed into an aqueous NMMO solution between two
sieves and allowed to impregnate, whereupon the impregnated nonwovens were pressed by
means of a laboratory press (pressing plessul~: 3 bars; corresponding to a line pressure of 12.6
N/mm at a nonwoven width of 12 cm). After this, the pressed nonwovens were washed with
tap water for 15 minuteS
Fx~les
According to the above working instruction, several tests were carried out, the parameters to
be set according to the invention, i.e., the concentration of the respective NMMO solution (in
% by mass, based on the total mass of the solution), its temperature (in ~C) and the time of
impregnation (in minlltes) having been chosen as indicated in Table 1 below. A11 of the
examples comply with the above-defined relation. The values resulting with the respective
parameters are also apparent from the Table.
Table 1
Ex. NMMO Concentration Temperature Time Value
84.0 80 0.08 0.95
2 82.0 80 0.08 1.30
3 82.0 70 0.17 0.94
4 80.6 70 0.50 1.20
80.6 80 0.08 1.42
6 80.6 80 0.50 1.66
7 78.2 70 1.00 1.29
8 76.2 70 0.50 1.00
9 76.2 80 0.17 1.32
73.9 70 4.00 0.81
11 74.2 80 0.50 1.07
12 74.2 90 0.17 1.39
13 71.9 90 2.00 1.02

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14 71.9 100 0.17 1.16
70.0 100 0.50 0.49
Examples 1 to 15 fall within the scope of invention, since the values resulting from the above-
mentioned relation with the NMMO concentrations, tempeldlu~es and times of impregnation
are within the range defined by the invention. All of the nonwovens were found to be
strengthened after having been treated according to the invention.
Similarly good results could be obtained with a nonwoven comprised of fibers produced
according to the amine oxide process.
Compar~tive Fxan~ples
For reasons of comparison, additional tests were carried out according to the general working
instruction, yet the parameters had been chosen such that the relation was not met. These
examples are summarized in Table 2.
Table 2
Ex. NMMOConcentrationTemperature Time Value
16 82.0 90 0.17 1.86
17 80.6 80 1.00 1.75
18 80.6 90 0.08 1.88
19 78.2 80 2.00 1.84
78.2 90 0.08 1.88
21 76.2 90 0.50 1.92
22 76.2 100 0.08 2.14
23 74.2 100 0.08 1.75
24 72.2 70 4.00 0.29
72.2 120 4.00 2.59
26 70.0 80 12.0 -0.10
27 70.0 90 2.00 0.21
28 70.0 100 0.08 0.25
In case of Examples 16 to 23 and 25, whose parameters yielded values larger than 1.70, the
nonwoven dissolved in the NMMO solution.
In case of Examples 24 and 26 to 28, whose parameters yielded values smaller than 0.30, no
strengthening of the nonwoven was obtained.