[0001] The present invention relates to a lyocell fiber with a novel cross sectional structure,
a method for producing same as well as to products comprising the lyocell fiber.
State of the art:
[0002] Cellulose based fibers are employed in a wide variety of applications. Due to ever
increasing demands even for such fibers based on renewable resources such as wood
attempts have been made to increase the variety of raw materials which may be employed
for the production of such fibers. At the same time a demand exists towards a further
functionalization of such fibers, targeting specific fiber properties. Another aim
is to mimic properties and structure of natural fibers. Fibers based on cellulose
regeneration differ in their structure from natural fibers in that they typically
do not show any internal /lumen. For example viscose fibers show an oval cross section
comprising a dense sheath and a sponge like core of the fiber. Lyocell fibers on the
other hand show a circular cross section with a three layered structure, comprising
an outer compact skin with a thickness of 100 to 150 nm and a small pore size of from
2 to 5 nm, followed by a middle layer with increasing porosity and a dense, non-porous
core.
[0003] It is known from the literature that fiber properties correlate with the structure
of the fiber cross section. Nevertheless, the process for preparing lyocell fibers
offers only limited options to influence fiber properties and structure. However,
it would be advantageous if means existed to influence fiber properties to a greater
extend even in the lyocell process. One option would be to either add additives to
employ by-products of the cellulose production in order to further vary the structure
and/or properties of lyocell fibers.
[0004] It is for example known that chemical pre-treatment may influence fiber properties.
US 6042769 shows an example of chemical treatments to enhance fibrillation tendency. It discloses
chemical treatments to reduce the DP (degree of polymerization) by 200 units, thereby
increasing fibrillation tendency. Chemical treatments mentioned in this patent refer
to the use of bleaching reagents, such as sodium hypochlorite or mineral acids, such
as hydrochloric acid, sulfuric acid or nitric acid. A commercialization of this procedure
did not succeed up to now.
[0005] US 6706237 discloses that meltblown fibers obtained from hemicelluloses rich pulps show a decreased
or reduced tendency to fibrillate.
US 8420004 discloses another example of meltblown fibers for producing non-woven fabrics.
[0006] For viscose fibers it has been shown that the addition of hemicelluloses dissolved
in NaOH to the spinning viscose enables the modification of fiber properties (
WO2014086883). However, these modifications were always accompanied by a decrease of other important
fiber properties, such as tenacity. Such modifications are restricted to the viscose
process and cannot at all be applied to lyocell fibers. The use of the direct solvent
NMMO excludes the addition of any extra water and NaOH on an industrial scale.
[0007] An attempt has been made to alter the fiber properties by using pulps rich in hemicelluloses.
Most publications deal with other ionic liquids than NMMO in a lab scale. Only a few
publications are relevant for the lyocell process with NMMO.
Zhang et al. (Polymer Engineering and Science 2007, 47, 702-706 and
Journal of Applied Polymer Science, 2008, 107, 636-641) describe lyocell fibers with higher hemicellulose contents. The authors postulate
that the fibers tend to show an enhanced fiber fibrillation resistance, lower crystallinity
and better dyeability. They also postulate that the tensile strength only decreases
insignificantly and that the fiber properties could be even increased further by higher
hemicelluloses concentrations in the spinning dope.
The fibers described in the papers by Zhang et al. are produced with lab equipment
not allowing the production of lyocell fibers in commercial quality These fibers,
not being produced with sufficient drawing and an sufficient after-treatment therefore
can be expected to show different structure and properties compared to the fibers
produced at production scale at titers reflecting market applications. In addition,
no information is provided in the paper concerning the distribution of the hemicelluloses
over the cross section of the lyocell fibers, nor on the structure of the three layered
cross section
[0008] In this regard it is known for viscose fibers that an increase in hemicellulose content
leads to an enrichment of the hemicellulose content at the surface of the fiber, with
a rapid decrease towards the core of the fiber (
Schild and Liftinger Cellulose 2014 21:3031-3039).
No research has been done on standard lyocell fibers up to now, but it is assumed
that cellulosic fibers act similar.
Object of the present invention
[0009] In view of the increasing demands for fibers based on cellulose raw materials it
is the object of the present invention to provide cellulose based fibers with improved
properties. In particular it would be advantageous to provide fibers with increased
WRV and/or reduced crystallinity, preferably while maintaining a substantial degree
of the beneficial mechanical properties of lyocell fibers.
Brief description of the invention
[0010] The present inventors accordingly provide the fiber as defined in claim 1, the method
for producing same as described in claim 12 as well as products containing same as
defined in claim 17 and the use as defined in claim 9. Preferred embodiments are described
in the respective subclaims as well as in the specification.
[0011] In particular the present invention provides the following embodiments, which are
further explained and illustrated below.
- 1.) Lyocell fiber with an enhanced porous structure over the fiber cross section and
a crystallinity of 40 % or less.
- 2.) Lyocell fiber according to embodiment 1, with a WRV of 70 % or greater.
- 3.) Lyocell fiber according to embodiment 1 or 2, with an entire staining over the
whole fiber cross section using a fluorescent staining dye.
- 4.) Lyocell fiber according to any one of the preceding embodiments, wherein the pulp
employed for the fiber formation comprises cellulose and hemicelluloses, with a hemicelluloses
content of at least 7 wt.-%
- 5.) Lyocell fiber according to any one of embodiments 1 to 4, having a titer of 6.7
dtex or less, such as 2.2 dtex or less, preferably 1.3 dtex or less.
- 6.) Lyocell fiber according to any one of embodiments 1 to 5, produced from a pulp
having a hemicelluloses content of 7 wt.-% or more and 25 wt.-% or less.
- 7.) Lyocell fiber according to any one of embodiments 1 to 6, wherein the hemicellulose
comprises a ratio of C5/Xylan to C6/Mannan of from 125:1 to 1:3, preferably of from
25:1 to 1:2.
- 8.) Lyocell fiber according to any one of embodiments 6 or 7, wherein the pulp comprises
6 wt.-% or more xylan, preferably 8 wt.-% or more, more preferably 12 wt.-% or more
and/or 3 wt.-% or more mannan, preferably 5 wt.-% or more mannan, and/or 1 wt.-% or
less mannan.
- 9.) Use of a pulp for producing a fiber according to any one of embodiments 1 to 8,
wherein the pulp has a hemicelluloses content of 7 wt.-% or more and 25 wt.-% or less.
- 10.) Use according to embodiment 9, wherein the hemicellulose comprises a ratio of
C5/Xylan to C6/Mannan of from 125:1 to 1:3, preferably of from 25:1 to 1:2.
- 11.) Use according to any one of embodiments 9 or 10, wherein the pulp comprises 5
wt.-% or more xylan, preferably 8 wt.-% or more, more preferably 10 wt.-% or more
and/or 3 wt.-% or more mannan, preferably 5 wt.-% or more mannan, and/or 1 wt.-% or
less mannan.
- 12.) Method for producing the lyocell fiber according to any one of embodiments 1
to 8 using a direct dissolution process.
- 13.) Method for producing the lyocell fiber according to embodiment 12 using a amine
oxide process, where an aqueous solution of the amine oxide and the pulp form a cellulose
suspension and a shapeable solution which gets shaped and coagulated in a spin bath
obtaining the lyocell fiber after washing and pre-treatment steps.
- 14.) Method for producing the lyocell fiber according to embodiment 13 using an aqueous
tertiary amine oxide, preferably aqueous NMMO.
- 15.) Method according to any one of embodiments 12 to 14, wherein the spinning solution
contains a pulp with a hemicelluloses content of greater than 10 wt.-% based on the
total weight of cellulose and hemicelluloses contained.
- 16.) Lyocell fiber, use or method according to any one of the preceding embodiments,
wherein the pulp has a scan viscosity of from 300 to 440 ml/g.
- 17.) Product, comprising the lyocell fiber according to any one of embodiments 1 to
8 or 16, or the fiber produced according to any one of embodiments 12 to 16.
- 18.) Product according to embodiment 16, wherein the product is a non-woven fabric.
- 19.) Product according to embodiment 16 and/or 17, selected among tissues and wipes.
Brief description of the Figures
[0012]
Figure 1 shows a comparison of the fiber in accordance with the present invention
as compared to a standard lyocell fiber and a standard viscose fiber after fluorescent
staining. The fiber in accordance with the present invention shows an even distribution
of the stained areas throughout the entire cross section of the fiber, whereas the
standard viscose fiber displays only a superficial staining of the outer sheath part
of the fiber. The standard lyocell fiber depicts in contrast an unstained core
Figure 2 shows the velocity of enzymatic peeling and Figure 3 the xylan distribution
over the fiber cross section in comparison to a standard lyocell fiber and a xylan
enriched viscose fiber. The hemicellulose concentration of the fiber according to
the present invention is almost constant over the fiber cross section while the concentration
of the standard lyocell fiber decreases rapidly from the shell to the core. The same
was observed for a viscose fiber enriched with xylan.
Detailed description of the invention
[0013] As defined in claim 1 the fiber in accordance with the present invention is a lyocell
fiber with a novel structure of the cross section, as compared to standard lyocell
fibers. While the three layered structure known from standard lyocell fibers is maintained,
at least the inner core layer shows an increased porosity, as compared with standard
lyocell fibers. The term increased porosity as employed herein refers to the fact
that the novel fibers as described herein do show a staining behavior differing from
standard Lyocell fibers. While the latter ones only allow for a staining of the outer
two layers, the novel fibers in accordance with the present invention can be stained
over the entire cross section with fluorescent dyes
A quantitative measure of this novel property can be seen in the possibility to stain
the entire cross section of a fiber using the methodology as described in example
5. Fibers in accordance with the present invention show a staining (using the method
as described in example 5) over the entire cross section after 24 h or less, preferably
12 h or less, even more preferably 6 h or less, such as 3 h or less.
In embodiments also the surface layer may be less thick and/or the pore size, which
is typically for standard lyocell fibers in the range of from 2 to 5 nm, may be larger.
[0014] As defined in claim 1 the fiber in accordance with the present invention is a lyocell
fiber.
The lyocell process is well known in the art and relates to a direct dissolution process
of cellulose wood pulp or other cellulose-based feedstock in a polar solvent (for
example N-methylmorpholine N-oxide [NMMO, NMO] or ionic liquids). Commercially, the
technology is used to produce a family of cellulose staple fibers (commercially available
from Lenzing AG, Lenzing, Austria under the trademark TENCEL® or TENCEL™) which are
widely used in the textile and nonwoven industry. Other cellulose bodies from lyocell
technology have also been produced.
According to this method the solution of cellulose is extruded in a so called dry-wet-spinning
process by means of a forming tool and the moulded solution is guided for example
over an air gap into a precipitation bath, where the moulded body is obtained by precipitation
of the cellulose. The molding is washed and optionally dried after further treatment
steps.
Such lyocell fibers are well known in the art and the general methodology to produce
same is for example disclosed in
US 4,246,221 and its analytics in the BISFA (
The International Bureau for the Standardization of Man-Made Fibers) publication "Terminology
of Man-Made Fibres", 2009 edition. Both references are included herewith in their entirety by reference.
[0015] The term lyocell fiber as employed herein defines a fiber obtained by this process,
as it has been found that fibers in accordance with the present invention differ greatly
from fibers for example obtained from a meltblown process, even if using a direct
dissolution process of cellulose wood pulp or other cellulose-based feedstock in a
polar solvent (for example N-methylmorpholine N-oxide [NMMO, NMO] or ionic liquids)
in order to produce the starting material.
[0016] The term hemicelluloses as employed herein refers to materials known to the skilled
person which are present in wood and other cellulosic raw material such as annual
plants, i.e. the raw material from which cellulose typically is obtained. Hemicelluloses
are present in wood and other plants in form of branched short chain polysaccharides
built up by pentoses and/or hexoses (C5 and / or C6-sugar units). The main building
blocks are mannose, xylose, glucose, rhamnose and galactose. The back bone of the
polysaccharides can consist of only one unit (f.e. xylan) or of two or more units
(e.g. mannan). Side chains consist of arabinose groups, acetyl groups, galactose groups
and O-acetyl groups as well as 4-O-methylglucuronic acid groups. The exact hemicellulose
structure varies significantly within wood species. Due to the presence of sidechains
hemicelluloses show much lower crystallinity compared to cellulose. It is well known
that mannan predominantly associates with cellulose and xylan with lignin. In sum,
hemicelluloses influence the hydrophilicity, the accessibility and degradation behavior
of the cellulose-lignin aggregate. During processing of wood and pulp, side chains
are cleaved off and the degree of polymerization is decreased. The term hemicelluloses
as known by the skilled person and as employed herein comprises hemicelluloses in
its native state, hemicelluloses degraded by ordinary processing and hemicelluloses
chemically modified by special process steps (e. g. derivatization) as well as short
chain celluloses and other short chain polysaccharides with a degree of polymerization
(DP) of up to 500.
[0017] The pulps preferably employed in the present invention do show as outlined herein
a high content of hemicelluloses. Compared with the standard low hemicellulose content
pulp employed for the preparation of standard lyocell fibers the preferred pulps employed
in accordance with the present invention do show also other differences, which are
outlined below.
[0018] Compared with standard pulps the pulps as employed herein display a more fluffy appearance,
which results after milling (during preparation of starting materials for the formation
of spinning solutions for the lyocell process), in the presence of a high proportion
of larger particles. As a result the bulk density is much lower, compared with standard
pulps having a low hemicellulose content. This low bulk density requires adaptions
in the dosage parameters (f.e. dosage from at least 2 storage devices). In addition
the pulps employed in accordance with the present invention are more difficult to
impregnate with NMMO. This can be seen by evaluating the impregnating behavior according
to the Cobb evaluation. While standard pulps do show a Cobb value of typically more
than 2.8 g/g (determined according to DIN EN ISO 535 with the adaptation of employing
an aqueous solution of 78% NMMO at 75° C with an impregnation time of 2 minutes),
the pulps employed in the present invention do show Cobb values of about 2.3 g/g.
This requires an adaptation during spinning solution preparation, such as increased
dissolution time (f.e. explained in
WO 9428214 and
WO 9633934) and/or temperature and/or increased searing during dissolution (f.e.
WO9633221,
WO9805702 and
WO 9428217). This ensures the preparation of a spinning solution enabling the use of the pulps
described herein in standard lyocell spinning processes.
[0019] In one preferred embodiment of the present invention the pulp employed for the preparation
of the lyocell products, preferably fibers, as described herein, has a scan viscosity
in the range of from 300-440 ml/g, especially 320-420 ml/g, more preferably 320 to
400 ml/g. The scan viscosity is determined in accordance with SCAN-CM 15:99 in a cupriethylenediamine
solution, a methodology which is known to the skilled person and which can be carried
out on commercially available devices, such as the device Auto PulplVA PSLRheotek
available from psl-rheotek. The scan viscosity is an important parameter influencing
in particular processing of the pulp to prepare spinning solutions. Even if two pulps
seem to be of great similarity as raw material for the lyocell-process, different
scan viscosities will lead to completely different behaviour different during processing.
In a direct solvent spun process like the lyocell-process the pulp is dissolved in
NMMO as such. No ripening step exists comparable to the viscose process where the
degree of polymerization of the cellulose is adjusted to the needs of the process.
Therefore, the specifications for the viscosity of the raw material pulp typically
are within a small range. Otherwise, problems during production may arise. In accordance
with the present invention it has been found to be advantageous if the pulp viscosity
is as defined above. Lower viscosities compromise mechanical properties of the lyocell
products. Higher viscosities in particular may lead to the viscosity of the spinning
dope being higher and therefore, spinning will be slower. With a slower spinning velocity
lower draw ratios will be attained, which significantly alters the fiber structure
and its properties (
Carbohydrate Polymers 2018, 181, 893-901; Structural analysis of loncell-F fibres from birch wood, Shirin Asaadia; Michael
Hummel; Patrik Ahvenainen; Marta Gubitosic; Ulf Olsson, Herbert Sixta). This will
require process adaptations and will lead to a decrease in mill capacity. Employing
pulps with the viscosities as defined here enables smooth processing and production
of high quality products.
[0020] As employed herein the terms lyocell process and lyocell technology relate to a direct
dissolution process of cellulose wood pulp or other cellulose-based feedstock in a
polar solvent (for example N-methylmorpholine N-oxide [NMMO, NMO] or ionic liquids).
Commercially, the technology is used to produce a family of cellulose staple fibers
(commercially available from Lenzing AG, Lenzing, Austria under the trademark TENCEL®
or TENCEL™) which are widely used in the textile and nonwoven industry. Other cellulose
bodies from lyocell technology have also been produced. According to this method the
solution of cellulose is usually extruded in a so called dry-wet-spinning process
by means of a forming tool and the moulded solution gets for example over an air gap
into a precipitation bath, where the moulded body is obtained by precipitation of
the cellulose. The moulding is washed and optionally dried after further treatment
steps. A process for production of lyocell fibers is described, for instance, in
US 4,246,221,
WO 93/19230,
WO95/02082 or
WO97/38153. As far as the present application discusses the drawbacks associated with the prior
art and the unique properties for novel products as disclosed and claimed herein in
the context of using laboratory equipment (in particular in the prior art) or (semi-commercial)
pilot plants and commercial fiber spinning units, the present invention is to be understood
to referring to larger scale plants/units, which may be considered as follows concerning
their respective production capacity:
semi-commercial pilot plant: about1 kt/a
commercial unit >30 kt/a
[0021] The task and object mentioned above was solved by lyocell fibers with enhanced porosity
of the core layer of a lyocell fiber. The fibers in accordance with the present invention
show, due to the specific structure, improved properties, such as improved dyeability,
increased enzymatic degradability, etc.
Standard lyocell fibers are currently commercially produced from high quality wood
pulps with high α-cellulose content and low non-cellulose contents such as hemicelluloses.
Commercially available lyocell fibers such as TENCEL™fibers produced from Lenzing
AG, show excellent fiber properties for non-wovens and textile applications.
[0022] The present invention overcomes the shortcomings of the state of the art by providing
lyocell fibers as described herein.
[0023] Preferably these are produced from hemicellulose-rich pulps with a hemicellulose
content of at least 7 wt.-%. Contrary to the disclosure in the prior art discussed
above, such high hemicellulose content surprisingly, for lyocell fibers of the present
invention, gives rise to an increased porosity of the core layer of the lyocell fiber
structure, while having only minor effect on the mechanical properties of the fibers.
Accordingly the present invention surprisingly achieves the tasks as outlined above
while using cellulose based raw material with a higher hemicelluloses content, as
compared for standard lyocell fibers.
[0024] As already outlined above,
Zhang et al (Polym. Engin. Sci. 2007, 47, 702-706) describe fibers with high hemicellulose contents. The hemicelluloses are described
as acting as plasticizers within the fiber. The authors argue that hemicelluloses
allow the cellulose chains to align more easily, which would assumably lead to a higher
density of the fiber. Contrary thereto however, the present invention provides fibers
with completely different properties as with the higher hemicelluloses content the
porosity, in particular of the inner core layer of the lyocell fiber increases drastically.
One possible explanation for these contrasting findings may be the fact that the fibers
in accordance with the present invention are fibers produced using large scale production
equipment, while the fibers described in the paper by Zhang et al. are produced with
lab equipment not allowing the production of lyocell fibers in commercial quality
(as for example drawing ratios, production velocities and after-treatment do not reflect
scale-up qualities). The fibers, not being produced with sufficient drawing and a
sufficient after-treatment therefore show different structure and properties compared
to the fibers produced at production (semi)-commercial scale.
[0025] The content of hemicelluloses in the pulps may be from 7 wt.-% up to 25 wt.-%, such
as from 8 to 20, and in embodiments from 10 to 15 wt.-%. The hemicellulose content
may be adjusted according to procedures known in the art. The hemicellulose may be
the hemicelluloses originating from the woof from which the pulp is obtained, it is
however also possible to add individual hemicelluloses depending on the desired fiber
properties from other sources to high purity cellulose with a low original hemicellulose
content. The addition of individual hemicelluloses may also be employed to adjust
the composition of the hemicelluloses content, for example to adjust the ratio of
hexoses to pentoses.
[0026] The pulp enabling the preparation of the fibers in accordance with the present invention
preferably shows a ratio of C5/xylan to C6/mannan of from 125:1 to 1:3, preferably
in the range of 25:1 to 1:2, such as from 10:1 to 1:1. The hemicellulose content may
be 7 wt.-% or more, preferable 10 wt.-% or more and in embodiments up to 25 wt.-%
or even 30 wt.-%. In embodiments the xylan content is 5 wt.-% or more, such as 8 wt.-%
or more, and in embodiments 10 wt.-% or more. In embodiments, either in isolation
or in combination with the above mentioned hemicelluloses and/or xylan contents, the
mannan content is 3 wt.-% or more, such as 5 wt.-% or more. In other embodiments the
mannan content, preferably in combination with a high xylan content as defined above,
may be 1 wt.-% or less, such as 0.2 wt.-% or 0.1 wt.-% or less.
[0027] The fibers in accordance with the present invention typically have a titer of 6.7
dtex or less, such as 2.2 dtex or less, such as 1.7 dtex, or even lower, such as 1.3
dtex or even lower, depending on the desired application. If the fiber is intended
to be used in non-woven applications a titer of from 1.5 to 1.8 dtex typically is
suitable while for textile applications lower tites such as from 1.2 to 1.5 dtex are
suitable. However, the present invention also covers fibers with much lower titers,
with suitable lower limits for titers being 0.5 dtex or higher, such as 0.8 dtex or
higher, and in embodiments 1.3 dtex or higher. These upper and lower values as disclosed
here define ranges of from 0.5 to 9 dtex, and including all further ranges formed
by combining any one of the upper values with any one of the lower values. Surprisingly
the present invention enables the formation of fibers with the desired titers over
the whole application range, from non-woven applications to textile applications.
[0028] The fiber in accordance with the present invention preferably shows a reduced crystallinity,
preferably of 40% or less. The fiber in accordance with the present invention preferably
shows a WRV of 70% or more, more preferably 75% or more. Illustrative ranges of WRV
of the fibers of the present invention, in particular in combination with the crystallinity
values described herein, are form 72% to 90%, such as from 75% to 85%. The fiber in
accordance with the present invention does not show any sulfuric smell so that olfactoric
drawbacks of viscose fibers are overcome, while properties such as WRV and working
capacity enable the use of the fibers of the present invention as viscose replacement
fibers.
[0029] The fiber in accordance with the present invention, in isolation or in any combination
with features outlined above as preferred for the claimed fiber, has a crystallinity
of 40 % or less, preferably 39 % or less. In particular fibers to be employed for
non woven applications do show preferably a low crystallinity of for example from
39 to 30%, such as from 38 to 33 %. The present invention however is not limited to
these exemplary crystallinity values. As explained above, in comparison to standard
lyocell fibers the fibers in accordance with the present invention do show a reduced
crystallinity of 40 % or less.
[0030] The fiber in accordance with the present invention may be prepared using lyocell
technology employing a solution of cellulose and a spinning process employing a precipitation
bath according to standard lyocell processes, known to the skilled person. It is important
that the process employs a solution in equilibrium state in accordance with large
scale processing methods, as this enhances the properties and structures associated
with the present invention, without sacrificing the mechanical properties to an extend
detrimental for the intended end use.
[0031] The fiber in accordance with the present invention shows a novel type of distribution
of the hemicelluloses over the cross section of the fiber. While for standard lyocell
fibers the hemicelluloses is concentrated within the surface region of the fiber the
fibers in accordance with the present invention show an even distribution of the hemicelluloses
over the entire cross section of the fiber. Such a distribution enhances the functionality
of the fiber, as hemicelluloses increase for example binding properties towards other
additives with a matching chemical reactivity. In addition the even distribution of
the hemicelluloses may also contribute towards stabilizing the novel structure of
the fibers in accordance with the present invention, comprising larger pores volumes
in the surface layer and a porous core layer. This novel structure enhances uptake
as well as retention of other molecules, such as dyes or moisture and also contributes
towards a faster degradation, in particular biological (enzymatic) degradation.
[0032] The fibers in accordance with the present invention may be employed for a variety
of applications, such as the production of non-woven fabrics, but also textiles. The
fibers in accordance with the present invention may be employed as the only fiber
of a desired product or they maybe mixed with other types of fibers. The mixing ratio
can depend from the desired end use. If for example a non-woven or textile product
with enhanced coloring and color retention is desired the fibers in accordance with
the present invention may be present in a higher amount, relative to other fibers
according to the prior art, in order to secure the desired properties, while in other
applications a lower relative amount of fibers of the present invention may be sufficient.
[0033] As far as the present application refers to parameters, such as crystallinity, scan
viscosity etc., it is to be understood that same are determined as outlined herein,
in the general part of the description and/or as outlined in the following examples.
In this regard it is to be understood that the parameter values and ranges as defined
herein in relation to fibers refer to properties determined with fibers derived from
pulp and containing only additives, such as processing aids typically added to the
dope as well as other additives, such as matting agents (TiO
2, which often is added in amounts of 0.75 wt.-%), in a total amount of up to 1 wt.-%
(based on fiber weight). The unique and particular properties as reported herein are
properties of the fibers as such, and not properties obtained by addition of particular
additives and/or post spinning treatments (such as fibrillation improving treatments
etc.).
[0034] However, it is clear to the average skilled person that the fibers as disclosed and
claimed herein may comprise additives, such as inorganic fillers etc. in usual amounts
as long as the presence of these additives has no detrimental effect on dope preparation
and spinning operation. The type of such additives as well as the respective addition
amounts are known to the skilled person.
Examples:
Example 1: Lyocell fiber production and analysis
[0035] 3 different fibers were produced using 3 different types of pulp with different hemicellulose
contents (table 1). The lyocell fibers were produced according to
WO93/19230 dissolving the pulps in NMMO and spinning them over an air-gap into a precipitation
bath to receive fibers with titers from 1.3 dtex to 2.2 dtex, without and with matting
agent (0.75% TiO
2).
Table 1: Sugar contents of the different pulps for the lyocell fiber production
sugar [%ATS] |
reference pulp |
hemi-rich pulp 1 |
hemi-rich pulp 2 |
Glucan |
95.5 |
82.2 |
82.3 |
Xylan |
2.3 |
8.3 |
14 |
Mannan |
0.2 |
5.7 |
<0.2 |
Arabinan |
<0.1 |
0.3 |
<0.1 |
Rhaman |
<0.1 |
<0.1 |
<0.1 |
Galactan |
<0.1 |
0.2 |
<0.1 |
[0036] The fiber properties of the lyocell fibers produced were analyzed. The results are
summarized in table 2. Fiber 1 is produced from hemi-rich pulp 1 and fiber 2 from
hemi-rich pulp 2. The standard lyocell (CLY) fibers are produced from the standard
lyocell reference pulp. Bright indicates a textile fiber without matting agent, whereas
the dull fibers contain the matting agent identified above.
Table 2: Fiber properties (working capacity determined in accordance with BISFA definitions)
fiber type |
Titer [dtex] |
working capacity [cN/tex*%] |
FFk [cN/tex] |
FDk [%] |
1.3 dtex / 38 mm fiber 1 bright |
1.33 |
410 |
31 |
13.2 |
1.3 dtex / 38 mm CLY standard bright |
1.28 |
491 |
35.7 |
13.8 |
1.7 dtex / 38 mm fiber 1 bright |
1.69 |
380 |
30.4 |
12.5 |
1.7 dtex / 38 mm CLY standard bright |
1.65 |
571 |
38.6 |
14.8 |
2.2 dtex / 38 mm fiber 1 bright |
2.12 |
339 |
28.2 |
12.1 |
2.2 dtex / 38 mm CLY standard bright |
2.14 |
559 |
41.7 |
13.4 |
1.7 dtex / 38 mm fiber 1 dull |
1.67 |
333 |
28.7 |
11.6 |
1.7 dtex / 38 mm CLY standard dull |
1.71 |
384 |
32.1 |
11.9 |
1.7 dtex /38 mm fiber 2 dull |
1.72 |
315 |
27.6 |
11.4 |
1.7 dtex / 38 mm CLY standard dull (pulp 2) |
1.75 |
386 |
30.6 |
12.6 |
[0037] The displayed results show that the fibers in accordance with the present invention
may be prepared over the commercially relevant range of fiber titers, while maintaining
sufficient mechanical properties, in particular working capacity, to render these
fibers suitable as viscose replacement fibers.
Example 2: Crystallinity measurements
[0038] Crystallinities of the fibers of Example 1 are measured using a FT/IR with a Bruker
MultiRAM FT-Raman spectrometer with a Nd-Yag-laser at 1064 nm and 500mW. The fibers
are pressed into pellets for a smooth surface. Fourfold determination with a spectral
resolution of 4 cm
-1 with 100 scans respectively. Evaluation of the measurements was done using a chemometric
method (calibration with WAXS-data).
[0039] It can be seen that the crystallinities of the fibers of the present invention (fiber
1 and 2) decrease by 16 and 15% respectively compared to the standard CLY fibers.
Table 3: Crystallinities of the different lyocell fibers
fiber type |
crystallinity [%] |
1.3 dtex / 38 mm CLY standard bright |
44 |
1.3 dtex / 40 mm viscose standard bright |
29 |
1.3 dtex / 38 mm fiber 1 bright |
37 |
1.7 dtex / 38 mm CLY standard dull |
47 |
1.7 dtex / 40 mm viscose standard dull |
34 |
1.7 dtex / 38 mm fiber 1 dull |
40 |
1.7 dtex / 38 mm fiber 2 dull |
39 |
Example 3: WRV determination
[0040] For determining the water retention value, a defined quantity of dry fibers is introduced
into special centrifuge tubes (with an outlet for the water). The fibers are allowed
to swell in deionized water for 5 minutes. Then they are centrifuged at 3000 rpm for
15 minutes, whereupon the moist cellulose is weighed right away. The moist cellulose
is dried for 4 hours at 105 °C, whereupon the dry weight is determined. The WRV is
calculated using the following formula:

[0041] The water retention value (WRV) is a measured value that indicates how much water
of a moisture penetrated sample is retained after centrifuging. The water retention
value is expressed as a percentage relative to the dry weight of the sample.
[0042] In table 4 the water retention values of the fibers of the present invention (fiber
1 and 2) compared to the reference fibers are listed and an increase of the WRV by
19% and 26% respectively compared to standard CLY fibers can be observed.
Table 4: WRV of the different lyocell fibers
fiber type |
WRV [%] |
1.3 dtex / 38 mm CLY standard bright |
69.6 |
1.3 dtex / 40 mm viscose standard bright |
89.9 |
1.3 dtex / 38 mm fiber 1 bright |
82.8 |
1.7 dtex / 38 mm CLY standard dull |
65.3 |
1.7 dtex / 38 mm fiber 1 dull |
82.5 |
1.7 dtex / 38 mm fiber 2 dull |
78.0 |
[0043] These results prove that the fibers in accordance with the present invention display
a WRV rendering these fibers suitable as viscose replacement fibers.
Example 4: Orientation and porosity
[0044] The new fibers produced from hemi-rich pulp 1 showed a higher water retention value
which indicates an increased pore size and number over the whole fiber cross section.
For standard lyocell fibers a low WRV is known combined with a very high orientation
of the polymer chains described by high crystallinity. For the new fibers, also the
crystallinity decreased significantly underlining a lower orientation of the polymer
chains and giving rise to an enhanced pore volume. The results were verified for different
fiber types with different titers of 1.3 and 1.7 dtex and the effect is therefore
independent of the titer or diameter of the final lyocell fiber.
Table 5: Orientation and porosity of different fiber types.
property |
lyocell standard dull |
fiber 1 dull |
lyocell standard bright |
fiber 1 bright |
crystallinity [%] |
47 |
40 |
44 |
37 |
polymer orientation |
high |
decreased |
high |
decreased |
WRV [%] |
65.3 |
82.5 |
69.6 |
82.8 |
core porosity |
standard |
increased pore volume |
standard |
increased pore volume |
Example 5: Comparison of fluorescent staining
[0045] The fibers of Example 1 fiber 1 bright (1.3 dtex/ 38 mm), CLY standard bright (1.3
dtex / 38 mm) as well as standard viscose standard bright fibers (1.3 dtex / 38 mm)
were subjected to staining with Uvitex BHT according to the method of
Abu-Rous (J.Appl. Polym.Sci., 2007, 106:2083-2091). The fibers obtained were evaluated after different intervals of immersion in the
dye solution, at periods of from 5 min to 24 h. Due to the big size of the dye molecules
the penetration is restricted to areas with bigger pore volumes. Conclusions can be
drawn from the extent of dye penetration about the porous structure of the fiber cross
section. The intensity of the color gives indications about the number of pores and
voids, their size and chemical binding of the dye molecules to the inner surface of
the fiber pores. Chemical binding is mainly attributed to hemicelluloses and non-crystalline
regions. Surprisingly, the fibers in accordance with the present invention showed
a fast and complete staining of the entire cross section of the fiber as shown in
Figure 1. The fiber is more easily penetrated indicating an increased accessibility
due to a bigger pore size and number in the new fibers, a lower crystallinity as shown
in Example 2 and a higher hemicellulose content over the whole fiber cross section
as shown in Example 6. The viscose fibers showed an uptake of the dye up to 3 h, thereafter
no further uptake of dye was observed. At the same time, the dye uptake was restricted
to the outer regions of the viscose fiber. The standard lyocell fibers showed a similar
behavior, although the staining was somewhat faster and more intense, compared to
the viscose fibers. However, the staining was restricted to the shell and middle layer
of the fiber with no staining of the dense and compact core layer of the standard
lyocell fibers.
Table 6: Comparison of time and extend of staining
property |
standard viscose fiber |
standard lyocell fiber |
fiber 1 bright |
Velocity of staining |
Slow |
Middle |
Fast |
Staining extend |
Only outer regions |
Shell and middle layer |
Entire cross section |
Intensity of coloring |
Slight |
Intense |
Intense |
Example 6: Enzymatic peeling
[0046] The lyocell fibers evaluated in Example 1 were subjected to an enzymatic peeling
test according to
Sjöberg et al (Biomacromolecules 6:3146-3151, 2005). A viscose fiber with an enhanced xylan content of 7.5% was chosen for comparison
from the paper by Schild and Liftinger (2014). This xylan content is close to the
xylan content of the new fiber with 6.9%. The test enables the generation of data
concerning the hemicellulose distribution over the cross section of fibers, in particular
xylan (by HPLC determination) including information relating to different densities
and structures of layers (as denser layers show a slower response as well as layers
with smaller pore sizes).
[0047] The standard lyocell fibers (1.3 dtex / 38 mm bright) as well as the xylan enriched
viscose fibers (1.3 dtex / 38mm bright) showed a slow peeling rate (fig. 2). This
effect is even more pronounced for prolonged peeling times due to the denser cores.
At the same time, the xylan liberation determined corresponds to fibers with high
hemicellulose content at the surface of the fiber and a sharp concentration decrease
towards the core (fig. 3). Contrary thereto, the fibers in accordance with the present
invention show a peeling behavior corresponding to a fiber structure with an even
distribution of the hemicellulose content over the entire cross section. Additionally,
the peeling is much faster. This is even more astonishing and completely new as this
phenomenon could not be achieved with xylan enriched viscose fibers. Due to the faster
peeling rate it can be concluded that the new fibers have more porous core and surface
layers with increased pore sizes and numbers and a homogenous distribution of the
xylan over the whole fiber cross section.
1. Lyocell fiber with an enhanced porous structure over the fiber cross section and a
crystallinity of 40% or less.
2. Lyocell fiber according to claim 1, with a WRV of 70 % or greater.
3. Lyocell fiber according to claim 1 or 2 with an entire staining over the whole fiber
cross section using a fluorescent staining dye.
4. Lyocell fiber according to any one of the preceding claims, wherein the pulp employed
for the fiber formation comprises cellulose and hemicelluloses, with a hemicelluloses
content of at least 7 wt.-%.
5. Lyocell fiber according to any one of claims 1 to 4, having a titer of 6.7 dtex or
less, prefereably 2.2 dtex or less, even more preferably 1.3 dtex or less.
6. Lyocell fiber according to any one of claims 1 to 5, produced from a pulp having a
hemicelluloses content of 7 wt.-% or more and 25 wt.-% or less.
7. Lyocell fiber according to any one of claims 1 to 6, wherein the hemicellulose comprises
a ratio of C5/xylan to C6/mannan of from 125:1 to 1:3, preferably of from 25:1 to
1:2.
8. Lyocell fiber according to any one of claims 6 or 7, wherein the pulp comprises 6
wt.-% or more xylan, preferably 8 wt.-% or more, more preferably 12 wt.-% or more
and/or 3 wt.-% or more mannan, preferably 5 wt.-% or more mannan, and/or 1 wt.-% or
less mannan.
9. Use of a pulp for producing a fiber according to any one of claims 1 to 8, wherein
the pulp has a hemicelluloses content of 7 wt.-% or more and 25 wt.-% or less.
10. Use according to claim 8, wherein the hemicellulose comprises a ratio of C5/xylan
to C6/mannan of from 125:1 to 1:3, preferably of from 25:1 to 1:2.
11. Use according to any one of claims 9 or 10, wherein the pulp comprises 5 wt.-% or
more xylan, preferably 8 wt.-% or more, more preferably 10 wt.-% or more and/or 3
wt.-% or more mannan, preferably 5 wt.-% or more mannan, and/or 1 wt.-% or less mannan.
12. Method for producing the lyocell fiber according to any one of claims 1 to 8 using
a direct dissolution process.
13. Method for producing the lyocell fiber according to claim 12 using a amine oxide process,
where an aqueous solution of the amine oxide and the pulp form a cellulose suspension
and a shapeable solution which gets shaped and coagulated in a spin bath obtaining
the lyocell fiber after washing and pre-treatment steps.
14. Method for producing the lyocell fiber according to claim 13 using an aqueous tertiary
amine oxide, preferably aqueous NMMO.
15. Method according to any one of claims 12 to 14, wherein the spinning solution contains
a pulp with a hemicelluloses content of greater than 10 wt.-% based on the total weight
of cellulose and hemicelluloses contained.
16. Lyocell fiber, use or method according to any of the preceding claims, wherein the
pulp has a scan viscosity of from 300 to 440ml/g.
17. Product, comprising the lyocell fiber according to any one of claims 1 to 8 or 16,
or the fiber produced according to any one of claims 12 to 16.
18. Product according to claim 17, wherein the product is a non-woven fabric.
19. Product according to claim 17 and/or 18, selected among tissues and wipes.