Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD FOR PRODUCING MILK PROTEIN FIBERS AND MILK PROTEIN FIBER
PRODUCTS OBTAINED THEREFROM
DESCRIPTION
The invention relates to a method for producing milk protein fibers, inter
alia for the
textile industry and hygiene and medical products, and to the associated milk
protein
fiber products such as cotton wools, fleeces, loose short fibers, yarns, woven
and
knitted fabrics as well as other products manufactured by means of the fiber
according
to the invention.
STATE OF THE ART
Milk protein fibers belong to the protein fibers which in the widest sense
also include the
natural products wool and silk. Protein fibers have been known for a long time
on the
technical scale. Casein fibers were already produced in the thirties. Casein
is a protein
fraction from the milk of mammals. Casein is produced from skimmed milk which
is
brought to coagulation at 45 `C by means of acids at around pH 4.6 (the
isoelectric
point of casein). Alternatively, lab is used for the coagulation. The solid
matters are
separated or pressed off and washed several times. Finally, a drying at 50 to
80`C is
carried out to obtain a residual water content of less than 10% (ROmpp
Chemielexikon,
Georg-Thieme-Verlag, 19899 under "casein"). Casein is a mixture of several
proteins of
which the most important ones are generally designated as aS1, aS2, 6 and K
(cow's
milk). Since the white to yellowish, slightly hygroscopic casein powder is
insoluble in
water, but soluble in alkalis, it is required for the classical way of
manufacturing by the
solution spinning process to work in the alkaline environment and to subject
the fiber to
other treatment steps and baths afterwards. The proteins are dissolved in
alkalis,
filtered, cleaned, pressed through jets into an acid bath, drawn and hardened
with
formaldehyde or aluminum sulfate (Rompp reference as above).
In the classical wet spinning processes, an aqueous casein solution is set at
a pH value
of 7 to 10 by means of sodium carbonate, agitated at room temperature over 24
hours
and degassed in vacuum before a further processing. The solution is then
extruded into
a coagulation bath which contains aluminum sulfate-octadecahydrate, sodium
chloride
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and sulfurous acid. Afterwards, the milk fiber will be hardened over 24 hours
in a
hardening bath by means of sodium acetate-trihydrate and formalin solution at
a pH
value of 5.5. The fiber will then be cleared of residues of the hardening bath
under
running water over 24 hours and dried at room temperature. The pollution level
provoked by the coagulation bath and the consumption of water are very high.
Furthermore, this method requires a lot of time, the process time is about 60
hours.
From DE PS 905 418 hardening baths are for example known which correspond to
the above statements.
EP 0 051 423 A2 describes a method for the preparation of a material that
contains
casein. Accordingly, a plastic mass made of water and a protein is extruded
into a
gas atmosphere by means of an extruder. In this method it is important that
the
extrusion takes place at a temperature of 100cC, whereas the material has to
be
heated up within the scope of a post-treatment.
This leads to longer production times and an additional energy demand.
Concerning the above known method, the end product shall be used in the field
of
food. For this reason, exclusively proteins are disclosed as classification
substances,
i.e. in particular gluten as well as sources such as fish and meat are
mentioned. The
thus obtained products are water soluble and have no significant tensile
strength.
OBJECT OF THE INVENTION
It is the object of the invention to avoid the above mentioned disadvantages
and to
shorten the processing time. At the same time, the water and energy
consumption
shall be decreased
SOLUTION ACCORDING TO THE INVENTION
Herein, at least one protein obtained from milk is plasticized together with a
plasticizer at temperatures comprised between room temperature and 140C under
mechanical stress and is spun to fibers
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through a jet, wherein the plasticizer is selected from the group: aqueous
polysaccharide solution, alcohol, polyalcohol or mixtures of these substances.
According to the invention, it is proposed to use alcohol or polysaccharide as
plasticizer.
Thanks to the use of these newly proposed plasticizers, it is possible to
produce a milk
protein fiber which does not comprise the disadvantages of the state of the
art.
The invention is based upon the knowledge that the milk proteins and in
particular
casein can be plasticized in the heat by kneading and thus be processed in the
melt
spinning process. In the melt spinning process, the dried meltable raw
material is
thermally plasticized and preferably pressed as melt through jets by means of
gear
pumps or extruders. The melt solidifies after extrusion. The drawn-out thread
is wound
up or further processed as desired. The drawn-out threads can be drawn or also
surface-treated before being wound up.
For achieving an even more gentle treatment, the protein is intensely mixed or
kneaded
with a plasticizer and simultaneously subjected to mechanical stress.
The milk protein is preferably casein or lactalbumin.
The protein obtained from milk can be produced in situ by precipitation from
milk.
According to a first procedure, the milk in form of a mixture with lab, other
suitable
enzymes or acid can be immediately introduced into the process as flocculated
mixture
or the pressed-off flocculated protein can be used in humid form. According to
another
optional procedure, a previously separately obtained, if necessary prepared,
pure or
mixed protein, i.e. a protein fraction from milk, can be used, for example in
the form of a
dried powder.
The milk protein used according to the invention can be mixed with other
proteins in a
proportion of up to 30 % by mass with respect to the milk protein. For this,
other
albumins, such as ovalbumin and vegetable proteins, in particular lupine
protein, soy
protein or wheat proteins, in particular gluten can be used.
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As plasticizers, water alcohols, poly alcohols, gum Arabic, carbohydrates in
aqueous
solution and in particular aqueous polysaccharide solutions can be used. The
moisture
content of the protein fraction has to be considered, if necessary.
In detail, the following plasticizers and associated proportions are
especially preferred:
Alcohols and poly alcohols are used in proportions of up to approximately 10 %
by mass
with regard to the protein, especially preferred is glycerol (glycerine).
Other polyoles, for
example ethylene glycol can be alternatively used. Carbohydrates and
polysaccharides
are respectively used in a proportion preferably comprised between 0.4 and 2 %
by
mass, respectively in 70% aqueous solution. Starches of different origin are
preferred,
such as carrageenan, cellulose, in particular carboxycellulose and chitosan.
The addition of other agents is not excluded. Additives and auxiliary agents,
such as
lipophile additions, glossing agents and crosslinking agents can be especially
provided.
The additives and auxiliary agents shall altogether not exceed a proportion of
maximum
approximately 30 % by mass with regard to the protein. Vegetable oils can be
chosen
as lipophile additions which slightly hydrophobize the fiber already during
the
plasticizing operation. Furthermore, waxes can be used which additionally give
the fiber
stability. Preferred waxes are carnauba wax, beeswax, candelilla wax and other
naturally obtained waxes.
Calcium salts, for example calcium chloride, dialdehyde starch and glucose-O-
lactone
are preferred as crosslinking agents.
In a highly preferred embodiment the plasticizing is realized by means of an
extruder,
wherein all the selected substances are previously mixed and then fed into the
extruder,
or only some substances or only the protein are charged at the beginning and
other
substances are added in the course of the extrusion, i.e. at feeding spots
along the
screw.
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In a highly preferred embodiment it is provided that the protein is fed into
the extruder
as dry powder via a hopper at the entry of the extruder, whereas the
plasticizer and in
particular water is added in a following extrusion step, into the plasticizing
zone.
Furthermore, it is preferred that all dry starting substances are previously
mixed and fed
into the extruder at the beginning, whereas all liquid components are admixed
downstream. At the exit of the extruder, the extruded material is pressed
through a jet
and thus formed to a fiber.
If the protein is used as flocculated raw mixture, the procedure preferably
provides that
a dewatering can take place along the extruder or the other processing device.
Due to the plastification, the operation corresponds to a melt extrusion. In
this
thermoplastic extrusion, the materials are transferred into a plastic state
through heating
and are deformed in this way. Herein, the temperature exceeds the gas
transition
temperature of the protein, such that this one changes from the amorphous to
the
rubber-like plastic state. If the fulling and kneading is very strong, heat
will already be
generated by the mechanical stress such that it can happen that no heat has to
be
supplied from outside. Then, the extrusion already takes place at room
temperature.
However, usually very specific temperatures that allow an optimum
plastification have to
be set in the different extruder zones. Preferably it is extruded within the
extruder
between 30 and 95t, more preferably between 50 and 90t and most preferably
between about 60 and 80`C.
Furthermore it is preferred that the formed fiber will be wound up after
getting out of the
jet and will be dried before and/or after this step.
After the formed fiber has left the jet, it can be cut immediately ¨ for
example be
chopped into short fibers ¨ or be further processed to staple fibers.
Immediately after the formed fiber has left the jet or in at least one
subsequent
processing step, the fiber can alternatively be further processed to a plied
yarn, can be
in particular twisted, be loosely coiled up to a cotton wool or be further
processed to a
fleece.
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In an improvement of the invention, the fiber can furthermore pass through a
bath
before being wound up, although this procedure is not much preferred and
usually not
required. Alternatively the fiber can be subjected to a spraying treatment
after having
left the jet. Herein, smoothing agents, waxes, lipophiles or crosslinking
agents can be
for example applied to the surface of the fiber. In the case of crosslinking
agents, the
above mentioned ones are preferred, i.e. generally different salt solutions,
preferably
calcium chloride solution, dialdehyde starch solution, glucose-6-lactone
solution or
aqueous lactic acid.
The obtained fibers can be used for all imaginable purposes. They are usable
like
common textile fibers and can thus be processed to all kinds of textiles, such
as fabrics,
woven fabrics, knitted fabrics, crocheted textile fabrics, yarns, ropes,
fleeces, felts etc.
Also cotton wools, loose fiber insulating materials, filters and membranes can
be
obtained from the fibers according to the invention. The application fields of
the milk
fibers therefore comprise, inter alia, the textile technique, building
insulation and
building materials, hygiene products and, due to inherent antibacterial
properties,
medical products, such as swabs, filters and membranes.
Part of this invention is therefore also a milk protein fiber product that
contains fibers
which contain a thermally-mechanically plasticized milk protein and have in
particular be
obtained by means of a method according to the invention as described above.
If the fibers are loosely coiled up, it is for example possible to produce
cotton wools or
fleeces which can for example be used as filling and padding material.
It is especially preferred that the fibers are twisted to yarns. Herein, it is
both possible to
twist several milk protein fibers which have been produced by means of the
method
according to this invention with each other and to twist the milk protein
fibers with other
natural or synthetic fibers in a combination. Elastane (spandex), viscose,
silk or wool
can be for example used as other fibers which can also be spun and/or twisted
in
mixtures to plied yarns.
Single fibers are obtained by a discontinuous procedure. The fibers can also
be cut to
short fibers or staple fibers.
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Fabrics can on the other hand be produced from the obtained fibers, filaments
or yarns.
Woven and knitted fabrics of all kinds therefore also represent milk protein
fiber
products according to this invention.
ADVANTAGES OF THE INVENTION
The advantages obtained by the invention are in particular based upon the fact
that
during the production of milk protein fibers the extrusion process allows
excluding
substances which present a risk to health and are harmful to the environment
from the
process and from the fiber itself. Furthermore, considerable resources of
energy, water,
time and manpower can be saved, which also improves the environmental
protection
and increases the economical efficiency. The especially advantageous
properties of the
fibers which are highly suitable as textile fibers are based upon the
solidifying structural
changes (textile structure) which occur during the plasticizing. More detailed
knowledge
about the mechanistic aspects has not been gained so far.
EXAMPLES
In the following, the invention will be described in detail by means of an
exemplary
embodiment. The exemplary embodiment only serves to illustrating purposes and
shall
not limit the invention. On the base of this exemplary embodiment and his know-
how,
the man skilled in the art can find other possible embodiments by varying the
parameters.
Example 1: Production of a milk protein fiber having a strength of 20 dtex.
The extrusion
is realized by a single-screw extruder type 30 E of the company Dr. Collin
having a
diameter of 30 mm. The heating is realized by four cylinder heating zones with
the
following temperature development: 65r, 74r, 75r , 60r:
temperature 65 74 75 60
function material water plasticizing outlet zone head
jet
supply supply zone
heating zone I II Ill IV
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The casein powder is supplied via a vibrating conveyor. The water is added in
a
proportion of 1:2 (water : casein) by means of a peristaltic pump. The fiber
strength is
defined by the jet strength. The fiber can for example have a strength of 20
dtex. The
fibers are wound up by means of a winding machine and dried at room
temperature.
The course of the extrusion becomes additionally apparent in figure 1.
The extruder 1 is filled with the casein powder via a hopper 2. The casein
powder is
heated up in the extruder. The addition of water as plasticizer is realized by
means of a
peristaltic pump. The final product is pressed through a jet 4. The fiber
strand is wound
up by means of a suitable winding technology and dried on the winder 5 at room
temperature.
