Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 95/04106 PCT/EP94/02321
REINFORCED BIOLOGICALLY DEGRADABLE POLYMER
The present invention relates to a reinforced
substantially biologically degradable polymer as well as a
process for its production.
Biologically degradable polymers such as starch,
gelatin, cellulose derivatives, etc., or mixtures thereof are
in the course of establishing themselves as polymer materials
in addition to the known plastics, although, to be sure, at
present only for very specific uses such as the encapsulating
of active principles such as drugs, as packaging materials or
packaging aids without special mechanical demands, as dish
ware, cups, and the like. Their use for technical purposes
as so-called "engineering plastics" is greatly limited due to
their relatively poor mechanical properties such as
compressive and tensile strength, as compared with the known
plastics.
One possibility for improving these properties consists
in reinforcing biologically degradable polymers, a technique
which is already known from the use of plastics. As
reinforcing materials, glass fibers or beads stand, in
particular, in the foreground, and recently also carbon
fibers and aramid fibers. These reinforcing agents, however,
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are not biologically degradable; on the contrary, they are
extremely resistant to natural degradation processes.
It is therefore an object of the present invention to
propose a solution for improving the mechanical properties of
biologically degradable polymers.
Another object of the present invention is to propose a
biologically degradable polymer which is suitable for use as
so-called engineering plastic.
In accordance with the invention there is provided a
reinforced, substantially biologically degradable polymer,
characterized by thermoplastic starch or a polymer mixture
containing thermoplastic starch and at least one hydrophobic
biologically degradable polymer, reinforced by natural
fibers, which are incorporated into the polymer, whereby the
thermoplastic starch contains, as swelling or plasticizing
means, glycerol, sorbitol, pentaerythritol or trimethylol
propane or mixtures thereof.
In accordance with the invention, it is proposed to
reinforce a substantially biologically degradable polymer by
natural fibers which are incorporated in a suitable
biologically degradable polymer in accordance with the
methods generally customary in plastics engineering. The
natural fibers can be one of the following: ramie, cotton,
jute, hemp, sisal, flax, linen, silk, abaca and/or mixtures
thereof.
Sisal and ramie fibers are particularly suitable. In
the case of sisal, there are concerned flexible leaf fibers
from leaves of a length of up to 2 meters of the sisal agave
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native to Central America. These hard fibers, at times
referred to also as "sisal hemp" are used, for example, for
the production of ships' hawsers, ropes, brushes, etc. Ramie
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fibers, also known by the name of China grass fibers, are
obtained from the ramie plant, which comes originally from
China, Japan, and Southeast Asia. About 85% of the raw ramie
production of a total of about 100,000 tons of raw fibers
still comes today from China. The high polymer chemical
structure and the special microstructure impart the ramie
fiber dynamic loadability and an extremely high tear strength
in dry as well as in wet state. Under tensile load, the
ramie fiber shows very little elongation as compared, for
instance, with glass, metal, carbon or aramid fibers.
Due to the properties described, sisal fibers and ramie
fibers are particularly suitable as reinforcement, so that it
has already been proposed in the past to combine, for
instance, ramie fibers with metal, aramid and carbon fibers
in plaster, cement and epoxy resins. However, because of
their high price -- ramie fibers cost about twice as much as
cotton fibers -- ramie fibers have not been able to establish
themselves as reinforcement.
In connection, however, with biologically degradable
polymers, natural fibers, such as, in particular, sisal and
ramie fibers, afford an excellent possibility for decisively
improving the mechanical properties of such polymers,
without, however, negatively affecting the biologically
degradability of said polymers. Even more, sisal and ramie
fibers represent a natural replenishing resource so that they
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supply, in combination with starch, cellulose, or other
polymers developed of naturally self-replenishing sources,
reinforced polymers, which are thus completely based on
natural resources. Of course, however, sisal and ramie fibers
also are suitable for the reinforcing of synthetic
biologically degradable polymers such as, for instance,
cellulose derivatives such as cellulose ether, and cellulose
ester or cellulose co-esters as well as aliphatic polyesters
such as polycaprolactone, polyhydroxybut:yric acid, etc., as
well as hydrophobic proteins such as zero and polyvinyl
alrohols, which can be produced by non-one-hundred-percent
hydrolyzation of polyvinyl acetate.
In accordance with the invention, it is proposed to
incorporate 5 to 300 of natural fibers in a biologically
degradable polymer. Of course, it is possible to incorporate
also larger proportions of natural fibers in polymers, but
this results, on the one hand, in problems in connection with
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the incorporating of the fibers into the polymer as a result
of very high shearing forces, while, on the other hand, as
from a certain point, an increase in tensile strength and
elongation upon rupture are obtained only at the expense of,
for instance, increased brittleness.
There has proven particularly advantageous a reinforced
biologically degradable polymer containing thermoplastic
starch or a polymer blend containing thermoplastic starch and
at least one other hydrophobic biologically degradable
polymer. Of course, it is also possible to reinforce, for
instance, disaggregated starch by means of ramie fibers, but
since so-called high-grade engineering plastics are produced
by reinforcement with, for instance, sisal or ramie fibers,
it is of course advantageous to optimize also the basic
starch polymer. In this connection, reference may be had to
international patent application W 90/05161, as well as to
other publications such as "Sorption Behavior of Native and
Thermoplastic Starch" by R.M. Sala and I.A. Tomka, in Die
angewandte makromolekulare Chemie 199:45-63, 1992; as well as
ETH Dissertation No. 9917 of R.M. Sala, Zurich 1992, ETH
Zurich.
In this connection, one can start for instance from a
thermoplastic starch which contains at least one of the
following plasticizing agents or swelling agents:
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Sorbitol, glycerol, pentaerythritol, trimethylol
propane, a polyvinyl alcohol, an ethoxylated polyalcohol or
mixtures of these components. Of course, the thermoplastic
starch can also be digested by another swelling or
plasticizing agent which is suitable for the production
thereof. In contradistinction to disaggregated starch, it is
important that the thermoplastic starch has nat been digested
with water.
In case of the use of a polymer blend comprising
thermoplastic starch, for reinforcement by, for instance,
ramie fibers, the above-indicated hydrophobic biologically
degradable polymers are particularly suited, which polymers,
in their turn, can, as sole polymer components, be reinforced
by ramie fibers. There are concerned here cellulose
derivatives having a degree of substitution less than or
equal to 2, such as cellulose ether, cellulose ester, or
cellulose co-ester;
aliphatic polyesters such as polycaprolactone,
polyhydroxybutyric acid, polyhydroxy-butyric acid/hydroxy-
valeric acid copolymers and poly lactic acid; as well as
hydrophobic proteins, such as, for instance, zein;
and/or
polyvinyl alcohol prepared by a non-one-hundred-per-cent
hydrolyzation of polyvinyl acetate, preferably with a degree
of hydrolyzation of about 88%.
~1~$2~~
As example of a cellulose ether, mention may be made of
cellulose diethyl ether (CDE), which can be processed
thermoplastically at 190°C, for instance with diethyl
tartrate as plasticizes and which are biologically
degradable. The maximum water absorption at 20°C in water is
only just 0.04 parts by weight.
As example of cellulose esters, mention may be made of
cellulose diacetate (CDA) or, as co-ester, cellulose acetate
butyrate, which can be processed thermoplastically with
plasticizers at 180°C and which are biologically degradable.
The maximum water absorption at 20°C in water is only just
0.05 parts by weight.
Polycaprolactone can be processed without plasticizes at
120°C; it is partially crystalline, with a melting point of
between 60°C and 80°C and a vitreous solidification at -
50°C.
Its mechanical properties are comparable to those of low-
density polyethylene. The maximum water absorption at 20°C
is less than 0.01 parts by weight and furthermore
polycaprolactone is biologically degradable. One great
advantage of the use of polycaprolactone is that it is
readily miscible with thermoplastic starch without the
necessity of using a so-called phase mediator.
Polyhydroxybutyric acid/polyhydroxy-valeric acid -
copolymers can be processed thermoplastically, and have good
mechanical properties and a low water absorption of less than
_8_
0.01 parts by weight, and they are furthermore biologically
degradable. The same is true of polylactic acid which,
although it can be readily processed thermoplastically, has
good mechanical properties and is biologically degradable.
Zein, for instance, is proposed as hydrophobic protein,
it being capable of being thermoplastically processed with
0.2 parts by weight of lauric acid or diethyl tartrate at
130°C.
Finally, mention should also be made of polyvinyl
alcohol, known for instance under the brand name Moviol, in
which connection the polyvinyl acetate used for its
production is preferably 88~ hydrolyzed.
A phase mediator which is compatible both with the
thermoplastically processable starch and at the same time
with the hydrophobic polymer is preferably used in such a
polymer mixture. Due to the different cohesion energy
densities of starch and the hydrophobic polymers, block
copolymers generally enter into question, namely ones which
consist of a block soluble in starch and of a block soluble
in the hydrophobic polymer phase. It is, of course,
essential in this connection for the phase mediator also to
be biologically degradable and can be properly processed
thermoplastically. As an example thereof, a polycapro-
lactone/polyvinyl alcohol copolymer may be mentioned.
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As phase mediator, however, there also enter into
consideration reaction products between a hydrophobic
biologically degradable polymer and the thermoplastic starch
which are compatible with the hydrophobic polymer phase. In
this connection, for instance, the biologically degradable
polymer can, for instance, have reactive groups such as, for
instance, epoxy groups or else acid anhydride groups which
react with at least a part of the thermoplastic starch.
The phase mediator to be used and the quantity thereof
to be employed are, finally, a question of optimalization; it
is essential that the polymer mixture to be used for the
production of the foam be as uniform and homogeneous as
possible in order to be able to produce a foam which is also
as uniform as possible.
Before the incorporating of the natural fibers, such as,
for instance, ramie fibers, into the biologically degradable
polymer, the fibers are preferably degummed by removal of
pectins and hemicellulose by known combinations of
biochemical and chemical methods with which manufacturers of
ramie fibers are well acquainted. Previously, natural fibers
were, as a rule, boiled in alkali solutions.
For the incorporation, natural fibers, for instance
ramie fibers, having a fiber length of 0.08 to 5 mm are used.
The incorporation is effected in polymer mixing units
customary in plastics engineering, such as single-shaft or
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twin-shaft extruders or kneaders, in which connection, of
course, the working can also take place batchwise in
suitable mixers. It is essential, upon the incorporating of
ramie fibers into the biologically degradable polymer, that
the mechanical energy introduced as well as the temperature
is so selected that no degradation of the biologically
degradable polymer takes place. In particular, when using
thermoplastic starch, it is important that a temperature
which is clearly less than 200°C be maintained in an
extruder since, otherwise, the starch is strongly degraded.
The further processing of the reinforced plastics is less
critical and can be carried out in, for instance, the case
of thermoplastic starch within a temperature range of 180°C
to 210°C.
Upon the production of the reinforced polymers, other
additives and addition substances can be used, such as
generally customary in the plastics processing industry,
namely lubricants, plasticizers, plasticizing agents,
fillers, mold removal aids, flame-retarding additives,
coloring substances, and/or defoaming agents.
In order to control the mechanical properties of
moldings produced with reinforced biologically degradable
polymers produced in accordance with the invention, it is
also possible to use further biologically degradable or
natural fibers such as cotton, in addition to the sisal or
ramie fibers proposed by way of example in accordance with
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the invention. By the mixing, for instance, of the ramie
fibers with cotton, it is possible to impart flexibility to
moldings produced with the polymers proposed in accordance
with the invention. Finally, what natural fibers such as,
for instance cotton, hemp, jute, sisal, etc. are mixed with
the sisal or ramie fibers, is a question of what is most
optimal.
Another advantage of the incorporating of the ramie
fibers for instance into biologically degradable polymers is
that the water resistance of the polymer is increased. In
particular, when using natural polymers such as starch and
cellulose which as a rule are hydrophilic, this may be an
important advantage.
Another possibility of incorporating natural fibers such
as sisal or ramie fibers consists therein that, due to the
ability of, for instance, the ramie fibers to bind moisture
in capillary-active manner, a certain amount of moisture can
be incorporated latently in a polymer which in itself has
been dried. At a later time, this polymer can then be
processed at elevated temperature and elevated pressure, at
which time the moisture bound in the ramie fiber is liberated
so as to effect the foaming of the polymer. Particularly
when employed in thermoplastic starch, this is an extremely
interesting use since, as already described above, water as
expansion agent can be introduced by the incorporating of
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ramie fibers into the thermoplastic starch which it is
advantageous to process dry, the water being later liberated
so as to produce the foam. In this connection, it has also
been found that by means of this technique for the production
of the foam, one can operate with an extremely small
proportion of expansion agent or water and that a very
uniform light foam having good mechanical properties can be
produced. As compared with this, the starch foam produced in
the prior art by means of water has an extremely irregular
cell structure.
The invention will now be explained in further detail
with reference to examples and series of tests.
Example 1: One starts from thermoplastic starch which
has been prepared by digesting 65% starch with 35% sorbitol.
The operation is carried out in a Theysohn TSK 045TMCOmpounder
(twin-shaft extruder with shafts rotating in the same
direction) with different liquid/solid ratios. The following
temperature profile is selected in the extruder:
Zone 1, 25°C; Zone 2, 130°C; Zone 3, 150°C; Zone 4,
170°C; Zone 5, 150°C; Zone 6, 140°C; Zone 7,
140°C; Zone 8,
170°C.
kg/hr of thermoplastic starch granulates are
introduced into Zone 1 and melted. In Zone 5, 1500 g/hr of
thermoplastic starch, 840 g/hr of ramie fibers having a fiber
length of 0.5 mm, and 200 g/hr of stearic acid are
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furthermore added. The ramie fiber had been pretreated by
moistening or substantially saturating with water before its
admixture. This was followed by mixing and the removal of
the melt and cooling. It should be seen to it in this
connection that the material does not foam already upon the
compounding, which can be obtained by temperatures which are
definitely below 200°C. The following extruder values were
selected:
Speed of rotation of extruder: 200 rpm
Torque: 65% of the maximum torque
Mass pressure (die): 4-8 bar
As an alternative to the procedure used in Example 1,
one can also start from native starch, in which case the
thermoplastic starch is first of all digested by the addition
of sorbitol. It should be seen to it in this connection that
any moisture present in the native starch is removed by the
application of a vacuum. It is essential that the
thermoplastic starch have only a low moisture content upon
the processing or the incorporating and compounding with the
ramie fiber, i.e. that the moisture content is preferably
less than 1% by weight.
Example 2: The same compounding unit is used as in
Example 1. Again, 10 kg/hr of thermoplastic starch
(containing 35 wt.% sorbitol) is added in Zone 1 and melted.
In Zone 5, there then are added an additional 1500 g/hr of
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thermoplastic starch as well as 1200 g/hr of ramie fibers
having a fiber length of 0.5 mm, as well as 200 g/hr of
stearic acid.
Extruder values:
Speed of rotation of the extruder: 200 rpm
Torque: 80% of the maximum torque
Mass pressure (die): 4 bar
Temperature profile compounder:
Zone 1, 25°C; Zone 2, 130°C; Zone 3, 150°C; Zone 4,
170°C; Zone 5, 130°C; Zone 6, 120°C; Zone 7,
120°C; Zone 8,
160°C.
Example 3: As basis in Example 3 there is used native
starch which is added in Zone 1 of a similar compounding unit
as that used in Examples 1 and 2. In Zone 1, 13.5 kg/hr of
starch are added, and in Zone 2 10/kg/hr of sorbitol. This
is followed by the digestion of the starch to form thermo-
plastic starch. The steam produced is drawn off by a vacuum
in Zone 4. In Zone 5, 200 g/hr of finished thermoplastic
starch as well as 1200 g/hr of ramie fibers having a fiber
length of 1 mm as well as 200 g/hr of stearic acid are added.
The melt thus produced is removed and granulated.
Extruder values:
Speed of rotation of the extruder: 200 rpm
Torque: 65% of the maximum torque
Mass pressure (die): 40 bar
~1 ~szs5
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Temperature profile compounder:
Zone 1, 80°C; Zone 2, 160°C; Zone 3, 190°C; Zone 4,
180°C; Zone 5, 160°C; Zone 6, 140°C; Zone 7,
140°C; Zone 8,
170°C.
As the temperature profile clearly shows, temperatures
of between 160°C and 190°C are established in Zones 2 to 4,
which temperatures are necessary or preferred in order to
digest thermoplastic starch. The temperatures are then
reduced to 160°C or less in order to prevent the emergence of
the moisture from the capillaries of the ramie fibers.
Instead of sorbitol, one can, of course, also use
pentaerythritol or glycerol or some other suitable
plasticizes for the digesting of the thermoplastic starch.
Depending on the viscosity of the starch/plasticizer mixture
or the thermoplastic starch thus digested which is
established, lower temperatures can be selected in Zone 4 and
following zones for the incorporating of the ramie fibers.
Example 4: All adjustments as in Example 3, only that
in Zone 5, 400 g/hr of stearic acid are newly added rather
than 200 g/hr.
Extruder values: 200 rpm
Speed of rotation of extruder: 60-65% of the
maximum torque
Mass pressure (die): 30-40 bar
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Example 5: 13.5 kg/hr of starch are added in Zone 1 and
l0 kg/hr of sorbitol in Zone 2. This is followed by
digestion of the starch. Undesired water is removed in Zone
4. 200 g/hr of completely digested thermoplastic starch, 240
g/hr of ramie fibers of a fiber length of 2 mm, and 360 g/hr
of a neutral fatty-acid ester as processing aid are added in
Zone 5. The melt is withdrawn and granulated.
Extruder values:
Speed of rotation of extruder: 250 rpm
Torque: 55~ of the maximum torque
Mass pressure (die): --
Temperature profile of extruder:
Zone 1, 80°C; Zone 2, 160°C; Zone 3, 190°C; Zone 4,
180°C; Zone 5, 170°C; Zone 6, 160°C; Zone 7,
160°C; Zone 8,
170°C.
Example 6: The same procedure as in Example 5, only
that 470 g/hr of processing aid is added in Zone 5 instead of
360 g/hr.
Extruder values:
Speed of rotation of extruder: 250 rpm
Torque: Lower value than Example 5
Mass pressure (die): --
Temperature profile of extruder:
Zone l, 80°C; Zone 2, 160°C; Zone 3, 190°C;
Zone 4, 180°C; Zone 5, 150°C; Zone 6, 135°C; Zone 7,
135°C;
~~6~~~~
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Zone 8, 135°C.
Example 7: 10 kg/hr of completely digested thermo
plastic starch are added in Zone 1, and 160 g/hr of water are
added as processing aid in Zone 2. The water is then removed
in Zone 4. 2000 g/hr of completely digested thermoplastic
starch as well as 2400 g/hr of ramie fibers of a fiber length
of 2 mm, and 360 kg/hr of a neutral fatty-acid ester as
processing aid are added in Zone 5. The melt is then
withdrawn and granulated.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 65% of the maximum value
Mass pressure (die): --
Temperature profile of extruder:
Zorie 1, 40°C; ZOrie 2, 130°C; ZOrie 3, 155°C;
Zone 4, 170°C; Zone 5, 150°C; Zone 6, 140°C; Zone 7,
140°C;
Zone 8, 170°C.
Example 8: 10 kg/hr of completely digested thermo
plastic starch are added in Zone 1, and 160 g/hr of water as
processing aid in Zone 2. The water is removed in Zone 4.
2000 g/hr of completely digested thermoplastic starch as well
as 1200 g/hr of ramie fibers having a fiber length of 1 mm
and 360 g/hr of a neutral fatty-acid ester as processing aid
are added in Zone 5. Thereupon, the melt is withdrawn and
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granulated.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 50-55% of the maximum value
Mass pressure (die): --
Temperature profile of extruder:
Zone 1, 25°C; Zone 2, 130°C; Zone 3, 155°C;
Zone 4, 170°C; Zone 5, 150°C; Zone 6, 140°C; Zone 7,
140°C;
Zone 8, 170°C.
Example 9: Basis: Completely digested thermoplastic
starch with 33% glycerol; fiber length 0.5 mm, water content
of the fiber: 7%.
Temperature profile of compounder:
Zone 1, 100°C; Zone 2, 180°C; Zone 3, 180°C; Zone
4, 150°C; Zone 5, 120°C; Zone 6, 120°C; Zone 7,
120°C; Zone
8, 170°C.
In Zone 1, 15 kg/hr of thermoplastic starch granulate
are added and melted. In addition, 340 g/hr of ramie fibers
are added in Zone 4, and 1500 g/hr of thermoplastic starch
and 200 g/hr of stearic acid in Zone 5. This is followed by
removal of the melt and cooling. It must be seen to it that
the material does not foam already upon the compounding
(temperature 200°C).
Extruder values:
Speed of rotation of extruder: 150 rpm
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Torque: 45% of the maximum torque
Mass pressure (die): 4 bar
Example 10: Completely digested thermoplastic starch
with 33% glycerol; fiber length 0.5 mm, water content of the
fibers: 7%.
Temperature profile of compounder:
Zone 1, 100°C; ZOrie 2, 180°C; ZOrie 3, 180°C;
Zone 4, 150°C; Zone 5, 120°C; Zone 6, 120°C; Zone 7,
120°C;
Zone 8, 170°C.
20 kg/hr of thermoplastic starch granulate are added in
Zone 1 and melted. In addition, 670 g/hr of ramie fibers are
added in Zone 4, and 2500 g/hr of thermoplastic starch and
200 g/hr of stearic acid in Zone 5. This is followed by
removal of the melt and cooling. Temperatures not more than
200°C.
Extruder values:
Speed of rotation of extruder: 100 rpm
Torque: 55% of the maximum torque
Mass pressure (die): 10 bar
Example 11: Completely digested thermoplastic starch
with 33% glycerol; fiber length 0.5 mm, water content of the
fibers: 7%.
Temperature profile of compounder:
ZOrie 1, 60°C; Zone 2, 180°C; ZOrie 3, 180°C;
~'16~~~~
- 20 -
Zone 4, 150°C; Zone 5, 120°C; Zone 6, 120°C; Zone 7,
120°C;
Zone 8, 170°C.
20 kg/hr of thermoplastic starch are added in Zone 1.
1260 g/hr of ramie fibers are added in Zone 4, and 3000 g/hr
of thermoplastic starch and 200 g/hr of stearic acid in Zone
5. Granulation.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 50% of the maximum torque
Mass pressure (die): 12 bar
Example 12: Polymer blend, consisting of 50%
thermoplastic starch (digested with 35% sorbitol and glycerol
in a ratio of 1:1) and 50% polycaprolactone; fiber length 0.5
mm, water content of the fibers: 7%.
Temperature profile of compounder:
ZOrie 1, 60°C; Zone 2, 180°C; ZOrie 3, 180°C;
Zone 4, 120°C; Zone 5, 120°C; Zone 6, 120°C; Zone 7,
120°C;
Zone 8, 150°C.
20 kg/hr of the polymer mixture are added in Zone 1.
1260 g/hr of ramie fibers are added in zone 4.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 50% of the maximum torque
Mass pressure (die): 4.0 bar
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Example 13: Polymer mixture according to Example 12.
Temperature profile of extruder:
Zone 1, 60°C; Zone 2, 180°C; Zone 3, 180°C;
Zone 4, 120°C; Zone 5, 120°C; Zone 6, 120°C; Zone 7,
120°C;
Zone 8, 150°C.
20 kg/hr of a polymer mixture granulate are added in
Zone 1. 2100 g/hr of ramie fibers are added in Zone 4.
Granulation.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 50% of the maximum torque
Mass pressure (die): 4.0 bar
Example 14: In contradistinction to the previously
prepared polymer mixtures in which potato starch served as
starch basis, completely digested corn thermoplastic starch
with 35% sorbitol is used in the present example 14. Fiber
length 0.5 mm; water content of the fibers: 7%.
Temperature profile of extruder:
ZOrie 1, 60°C; ZOrie 2, 160°C; ZOrie 3, 180°C;
Zone 4, 160°C; Zone 5, 160°C; Zone 6, 160°C; Zone 7,
160°C;
Zone 8, 170°C.
Addition of 15 kg/hr of thermoplastic starch in Zone 1.
In addition, 900 g/hr of ramie fibers are added in Zone 4,
and 1500 g/hr of completely digested thermoplastic starch and
400 g/hr of stearic acid in Zone 5.
~~6~~15
- 22 -
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 45% of the maximum torque
Mass pressure (die): 6.0 bar
Examgle 15: Thermoplastic starch similar to Example 14;
length of fiber 0.1 mm; water content of the fibers: 7%.
Temperature profile of extruder:
ZOrie 1, 60°C; ZOrie 2, 160°C; ZOrie 3, 180°C;
Zone 4, 160°C; Zone 5, 160°C; Zone 6, 160°C; Zone 7,
160°C;
Zone 8, 170°C.
Addition of 15 kg/hr of thermoplastic starch in Zone 1.
In Zone 4, in addition, 1800 g/ hr of ramie fibers, and in
Zone 5 1500 g/hr of thermoplastic starch and 400 g/hr of
stearic acid.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 45% of the maximum torque
Mass pressure (die): 10 bar
Example 16: Thermoplastic starch similar to Examples 14
and 15; length of fiber 1.0 mm; water content Of the fibers:
18%.
Temperature profile of extruder:
ZOrie 1, 60°C; ZOrie 2, 160°C; ZOrie 3, 180°C;
Zone 4, 160°C; Zone 5, 160°C; Zone 6, 160°C; Zone 7,
160°C;
2~.6~2~5
- 23 -
Zone 8, 170°C.
In Zone 1, addition of 15 kg/hr of thermoplastic starch.
In Zone 4, addition of 1800 g/hr of ramie fibers. In Zone 5,
addition of 3000 g/hr of thermoplastic starch and 400 g/hr of
stearic acid. Granulation.
Extruder values:
Speed of rotation of extruder: 200 rpm
Torque: 50% of the maximum torque
Mass pressure (die): 6.0 bar
Example 17: Pure polycaprolactone; length of fiber 1.0
mm; water content of the fibers: 18%.
Temperature profile of compounder:
ZOrie 1, 30°C; ZOrie 2, 150°C; ZOrie 3, 150°C;
Zone 4, 80°C; Zone 5, 80°C; Zone 6, 80°C; Zone 7,
80°C; Zone
8, 80°C.
In Zone 1, addition of 15 kg/hr of polycaprolactone. In
Zone 2, addition of 1800 g/hr of ramie fibers, in Zone 5
addition of 5 kg/hr of polycaprolactone.
Extruder values:
Speed of rotation of extruder: 125 rpm
Torque: 45% of the maximum tarque
Mass pressure (die): 5.0 bar
Example 18: Digested corn thermoplastic starch with 32%
sorbitol; length of fiber: 0.5 mm; water content of the
CA 02168215 2003-09-04
24
fibers: 18%.
Temperature profile of compounder:
Zone 1, 60°C; Zone 2, 180°C; Zone 3, 180°C;
Zone 4, 180°C; Zone 5, 180°C; Zone 6, 180°C; Zone 7,
200°C;
Zone 8, 200°C.
In Zone 1, addition of 25 kg/hr of thermoplastic starch.
In Zone 4, addition of 1830 g/hr of ramie fibers; in Zone 5
addition of 4 kg/hr of thermoplastic starch. In this
experiment, foaming was effected directly after the addition
of the fibers within the same process.
Extruder values:
Speed of rotation of extruder: 100 rpm
Torque: 70-80% of the maximum torque
Mass pressure (die): 50 bar
Example 19: The production was effected now, in
contradistinction to the examples indicated above, on a Buss
Ko-Kneader (46 mm screw diameter). As base there was used
starch and plasticizer (35o sorbitol); Length of fiber: 0.5
mm; water content of the fibers: 7%.
Temperature profile in the Buss kneader:
Zone 0, 90°C; Zone 1, 90°C; Zone 2, 130°C; Zone 3,
150°C; Zone 4, 150°C.
The BussMkneader has 4 heating zones (Zones 1-4); Zone 0
corresponds here to the heatable screw.
2~ ~'~21~
- 25 -
The starch was premixed here with 2.5% ramie fibers
(referred to the final product TPS = starch + sorbitol).
13.5 kg/hr starch/fiber mixture and 7 kg/hr sorbitol were
added together in Zone 1. This was followed by the
plasticizing and then cold granulation.
Kneader values:
Kneader speed of rotation: 200 rpm
The specific power consumption is 300 Watt hours/kg
Example 20:
The production was effected with a twin-shaft screw
kneader ZSK 40 of the firm of Werner & Pfleiderer of
Stuttgart.
As basis, there was used a thermoplastic starch
containing portions of polycaprolactone. As fiber material
sisal fibers of an average length of 0.08 mm were used. The
two components were added in Zone 1, namely 8 kg/hr of
thermoplastic starch and 800 g/hr of sisal fibers. This was
followed by extrusion-granulation.
Temperature profile in the kneader:
Zone 1, 30°C; ZOrie 2, 160°C; ZOrie 3, 160°C;
Zone 4, 140°C; Zone 5, 130°C; Zone 6, 130°C; Zone 7,
130°C.
Speed of rotation: 100 rpm
Torque: 35% of the maximum torque
Mass pressure: 10 bar
2I ~82~ 5
- 26 -
Test Series 1:
In this test series, ramie fibers of a length of 4 mm
were admixed in different percentages in a thermoplastic
starch in a Brabender laboratory kneader, the starch
containing 35% sorbitol.
Table 1:
Percentage
of Fiber Starting
(in wt.%) Material 9 17 23 29
Relative tensile
strength (referred to 1 1.8 2.8 3.2 3.7
starting material)
Relative elongation
upon rupture (referred 1 1.3 1..5 1.7 2
to starting material)
Test Series 2:
Ramie fibers were again admixed into the thermoplastic
starch containing 35% sorbitol on a twin-shaft extruder.
Fibers having a length of 0.5 mm were added in percentages of
7.5% and 13%.
2I 682
- 27 -
Table 2:
Starting Material 7.5 wt.% 13 wt.%
(pure TPS) Fibers Fibers
Tensile strength 20 29 42
(N/mm2)
Elongation upon
Rupture (%) 1.6 2.3 3.5
Modules of elasticity 1000 1000 800
(N/mm2)
The decrease in the modules of elasticity in the case of
13% fibers and the unchanged value of the modules of
elasticity in the case of 7.5% fibers is again due to a
slight degradation of the thermoplastic starch. To be sure,
it was found that the degradation could be greatly reduced as
compared with Test Series 1 already by the use of a twin-
shaft extruder and improved manner of procedure. By suitable
design of the machine and optimizing of the procedure, this
can be substantially prevented.
A comparison of the values in Table 1 and Table 2,
insofar as this is possible, shows that the increase in the
relative tensile strength in Table 1 with an increase in the
proportion of ramie fibers is greater than in Table 2. This
effect is due, in particular, to the use of a longer fiber in
Test Series 1.
2~6~~~5
- 28 -
The formulas and test conditions used in Examples 1 to
20 and Test Series 1 and 2, are merely examples which serve
solely further to explain the invention or, for instance, the
production conditions. Of course, it is possible to
reinforce also other polymers or polymer mixtures as natural
fibers, such as, for instance, sisal or ramie fibers. Of
course, it is also possible to use other natural fibers such
as, for instance cotton, jute, hemp, flax, linen, silk, abaca
and/or mixtures thereof instead of sisal or ramie fibers.
The basic concept of the invention is that a polymer or
polymer mixture which in itself is biologically degradable is
prevented from at least partially losing its biologically
degradability by the admixing of a reinforcing agent. By
admixing a natural fiber such as, for instance sisal or ramie
fibers, a respectable reinforcing of the polymer or the
mixture is obtained without impairing the biological
degradability.
