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Claims  |
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We claim:
1. A process for obtaining a melt of destructurized starch containing a
finite amount of electrolytes comprising:
A. providing a unwashed natural starch containing free electrolytes and/or
bound phosphate salts,
B. removing partially or wholly the free electrolytes and/or the metallic
cations from the phosphate groups of the starch,
C. optionally replacing a part or all of the free H.sup.+ -ions of the
phosphate groups with metallic monovalent and/or polyvalent cations,
D. conditioning the obtained starch material to a water content of 10 -25%
by weight calculated on the basis of starch and water, and
E. heating said starch/water composition at an elevated pressure to a
temperature sufficient to essentially destructure the starch while
maintaining said water content until a melt of destructurized starch is
formed.
2. A process according to claim 1, wherein only the free electrolytes are
being washed out.
3. A process according to claim 1, wherein the free electrolytes and the
metallic cations of the bound phosphate groups are washed out.
4. A process according to claim 3, wherein in step B. the cations from the
phosphate groups of the starch are removed to such an extent that the
remaining number of equivalents of M.sup.2+ per 100 anhydro-glucose units
is less than 0.3.
5. The process according to claim 4, wherein when removing the cations from
the phosphate groups of the starch according to step B., a value of the
remaining number of M.sup.2+ per AGU of less than 0.2 and especially a
value less than 0.1 and preferably a value close to zero is obtained.
6. A process according to anyone of the claims 1 to 5, wherein in step C. a
part or all of the free H.sup.+ -ions of the unsubstituted phosphoric acid
groups linked to the starch are being replaced partly or wholly by at
least one metallic monovalent or divalent ion, preferably selected from Na
.sup.+, K.sup.+, NH.sub.4.sup.+, Ca.sup.2+ and Mg.sup.2+.
7. A process according to claim 1, wherein the starch is selected from
potato starch or corn starch, and preferably is potato starch.
8. A process according to claim 7, wherein the destructurized starch
material is conditioned to a water content in the range of about 10 to 25%
and better 10 to 20% calculated to the weight of starch and water,
preferably to a final water content of 12 to 19% and especially 14 to 18%
calculated to the weight of starch and water.
9. A process according to claim 8, wherein said starch contains or is mixed
with extenders, lubricants, plasticizers, and/or coloring agents, wherein
these additives have been added before heating the starch to form the melt
(step E.) or after this step.
10. A process according to claim 9, wherein the solid destructurized
starch/water material is heated to a temperature within the range of about
80 to 200.degree. C., preferably within the range of about 90 to
190.degree. C.
11. A process according to claim 9, wherein the destructurized starch/water
material contains or is mixed with at least one member selected from the
class consisting of extenders, preferably with gelatin; vegetable proteins
preferably sunflower protein, soybean proteins, cotton seed proteins,
peanut proteins, rape seed proteins, blood proteins, egg proteins,
acrylated proteins; water-soluble polysaccharides, preferably alginates,
carrageenans, guar gum, agar-agar, gum arabic, gum ghatti, gum karaya, gum
tragacanth, pectin; water-soluble derivatives of cellulose, preferably
alkylcelluloses, hydroxyalkylcelluloses, hydroxyalkylalkylcelluloses,
cellulose esters and hydroxyalkylcellulose esters, carboxyalkylcelluloses,
carboxyalkylcellulose esters, polyacrylic acids and polyacrylic acid
esters, polymethacrylic acids and polyacrylic acid esters,
polyvinylacetates, polyvinylalcohols, polyvinylacetatephtalates (PVAP),
polyvinylpyrrolidone, polycrotonic acids; phtalated gelatin, gelatin
succinate, crosslinked gelatin, shellac, water soluble chemical
derivatives of starch, cationically modified acrylates and/or
methacrylates possessing in an amount up to and including 50 %, preferably
within the range of 3 % to 10 % based on the weight of all components.
12. A process according to claim 1 or 9, wherein the destructurized
starch/water material contains or is mixed with at least one member
selected from the group consisting of plasticizers, including polyalkylene
oxides, preferably polyethylene glycols, polypropylene glycols,
polyethylene-propylene glycols; glycerol, glycerol monoacetate, diacetate
or triacetate; propylene glycol , sorbitol, sodium diethylsulfosuccinate,
triethyl citrate, tributyl citrate (added in concentrations ranging from
0.5 to 15 %, preferably ranging from 0.5 to 5 % based on the weight of all
the components).
13. A process according to claim 1 or 9, wherein the destructurized starch
contains or is mixed with at least one coloring agent selected from a
member of the group of azo dyes, organic or inorganic pigments, or
coloring agents of natural origin, preferably from oxides of iron or
titanium, said coloring agent being added in concentrations ranging from
0.001 to 10%, preferably 0.5 to 3%, based on the weight of all components.
14. A process according to claim 1 or 11 to 13, wherein the destructurized
starch/water material contains or is mixed with inorganic fillers,
preferably the oxides of magnesium, aluminum, silicon or titanium,
preferably in a concentration in the range of about 0.02 to 3% by weight,
preferably 0.02 to 1% based on the weight of all components.
15. A process according to claim 12, wherein a plasticizer is present and
the sum of the plasticizer and water content does not exceed 25%, and
preferably not exceeds 20%, based on the weight of all the components.
16. A process according to claim 1, wherein the destructurized starch/water
material comprises or is mixed with a material comprising animal or
vegetable fats, preferably in their hydrogenated form, especially those
which are solid at room temperature.
17. A process according to claim 16, wherein the destructurized
starch/water material comprises or is mixed with a material comprising fat
together with at least one member selected from the group of monoand/or
diglycerides or phosphatides, especially lecithin, whereby the total
amounts used of the fats mono-diglycerides and/or lecithins not greater
than 5% and preferably within the range of about 0.5 to 2% by weight of
the total composition.
18. The melt of destructurized starch as obtained by the process according
to claims 1, 5, 10 or 11.
19. The process according to claim 1 further comprising the step of:
F. cooling the melt obtained under step E subsequent to forming the melt
into a shaped article, to a temperature below the glass transition
temperature of said composition to form a solid shaped article.
20. The process according to claim 1 further comprising the step of:
subjecting the resultant melt of step E to a pressure molding process
selected from the group consisting of injection molding, extrusion,
coextrusion, compression molding and combinations thereof to form a shaped
article.
21. A solid article according to claim 20, in the form of bottles, sheets,
films, packaging materials, pipes, rods, laminates, sacks, bags,
granulates or pharmaceutical capsules.
22. A starch containing a finite amount of electrolytes as obtained by a
process comprising:
A. providing a unwashed natural starch containing free electrolytes and/or
bound phosphate salts,
B. removing partially or wholly the free electrolytes and/or the metallic
cations from the phosphate groups of the starch,
C. optionally replacing a part or all of the free H.sup.+ -ions of the free
phosphate groups with metallic monovalent and/or polyvalent cations, and
D. conditioning the obtained starch material to a water content of 10 -25%
by weight calculated on the basis of starch and water. |
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Claims |
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Description |
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The present invention refers to destructurized starch containing a finite
amount of electrolytes and to a process for making same.
It has recently become known that natural starch which is found in
vegetable products and which contains a defined amount of water, can be
treated at elevated temperature and in a closed vessel, thereby at
elevated pressure, to form a melt. The process is conveniently carried out
in an injection molding machine or extruder. The starch is fed through the
hopper onto a rotating, reciprocating screw. The feed material moves along
the screw towards the tip. During this process, its temperature is
increased by means of external heaters around the outside of the barrel
and by the shearing action of the screw. Starting in the feed zone and
continuing in the compression zone, the particulate feed becomes gradually
molten. It is then conveyed through the metering zone, where
homogenization of the melt occurs, to the end of the screw. The molten
material at the tip can then be further treated by injection molding or
extrusion or any other known technique to treat thermoplastic melts.
This treatment, which is described in the European Pat. application No. 84
300 940.8 (Publication No. 118 240) yields a destructurized starch. The
reason for this being that the starch is heated above the melting and
glass transition temperatures of its components so that they undergo
endothermic transitions. As a consequence a melting and disordering of the
molecular structure of the starch granule takes place, so that a
destructurized starch is obtained.
Although such destructurized starch is useful in molding techniques and
extrusion, it has been found, that the molded parts show a relatively high
incidence of surface defects and the processed materials generally have
relatively low extensibilities. Further it was found, that the optimum
processing temperature is in the range from about 140.degree. C. to about
180.degree. C.
It has now been found, that a starch which is treated according to this
invention, yields a material which produces considerably less defects, has
relatively higher extensibilities and can be treated at lower temperatures
and lower pressures to obtain destructurization. The starch material
according to the present invention also exhibits improved flow
characteristics especially for the production of thin walled articles so
that due to the improved processability, defective parts are minimized as
well as necessary subsequent controls reduced. It is further possible to
reproducibly control the temperature of melt-formation.
It is assumed, that many of the phosphate groups which are contained in
certain native starches are bridged by divalent ions such as the calcium
or magnesium ion. The concentration of such phosphate groups, i.e. the
number of phosphate groups present per number of anhydro-glucose units
(AGU), varies considerably for different starches. For potato starch this
concentration is given as about one phosphate group per 200 to 400 AGU.
When such a starch is washed with a sufficient amount of water at a low pH,
i.e. with dilute acid, the phosphate bridges are broken down and the free
phosphate groups are produced. Many phosphate group containing starches
have an "open" structure and can be easily penetrated by an aqueous
medium, so that a considerable part of the divalent bridging cation can be
washed out within a relatively short period of time, i.e. some minutes.
When the bridging calcium ions are washed out e.g. with dilute HCl the
following reaction occurs:
##STR1##
As can be seen, on treatment with acid, unsubstituted phosphoric acid
groups are linked to the starch formed.
Herein one mole of phosphate groups corresponds to two equivalents. One
mole of M.sup.2+ corresponds to two equivalents; one mole of M.sup.+ and
H.sup.+ to one equivalent each. One equivalent is defined as that number
of moles of an ionic species which carries one mole of ionic charge.
As can be seen, from formula (I) above, a phosphate bridge contains 2
phosphate groups and a minimum of one M.sup.2+ -cation and two M.sup.+
cations.
It has also been found, that starch often contains small amounts of free
electrolytes, i.e. electrolytes which are not bound to phosphate groups,
and which generally are water-soluble so that they can be washed out with
water, preferably with demineralized water. These electrolytes may be
present either originally in the potato tubers or may be introduced later
during manufacturing, i.e. during processing with water and drying.
It has now been found that these free electrolytes and the types and
concentrations of the cations associated with the phosphate groups
influence strongly the processability of the starch in the process of
destructurization and melt-formation. Especially it has been found that
when the free electrolytes are being partially or wholly removed and/or
when the M.sup.2+ -ions, which may bridge the phosphate groups or the
metallic M.sup.+ -ions associated with these phosphate groups are
partially or wholly removed, the processability of the starch in the
process of destructurization and melt-formation is remarkably improved and
the disadvantages mentioned above are overcome to a considerable extent.
The present invention refers to a process for obtaining a melt of
destructurized starch containing a finite amount of electrolytes
comprising:
A. providing a starch material containing free electrolytes and/or bound
phosphate salts,
B. removing partially or wholly the free electrolytes and/or the metallic
cations from the phosphate groups of the starch,
C. optionally replacing a part or all of the free H.sup.+ -ions of the
phosphate groups with metallic monovalent and/or polyvalent cations,
D. conditioning the obtained starch material to a water content of 10 - 25
% by weight calculated on the the basis of starch and water, and
E. heating said starch/water composition at an elevated pressure to a
temperature sufficient to essentially destructure the starch while
maintaining said water content until a melt of destructurized starch is
formed.
The present invention also refers to the melt of destructurizcd starch
obtained by said process.
The present invention further refers to the process of
F. cooling said melt (as obtained under E.) optionally after forming the
melt into a shaped article, to a temperature below the glass transition
temperature of said composition to form a solid shaped article.
The present invention further refers to the solid article obtained by said
cooling step F.
The present invention further refers to the use of such melted or
destructurized starch in pressure molding techniques such as pressure
molding, injection molding, blow molding or extrusion.
Optionally such destructurized starch is extruded first and cut into
granules before using it in injection molding or pressure molding
techniques.
Preferred is the process wherein the free electrolytes are washed out
completely. It is further preferred that the metallic cations associated
with the phosphate groups are removed to such an extent that the remaining
number of equivalents of Me.sup.2+ per per 100 anhydro-glucose units is
less than 0.3.
The term destructurized native starch has been explained above. Starch is
to be understood as chemically non-modified starch. As such it includes
for example also gelatinized or cooked starch and includes generally
carbohydrates of natural, vegetable origin, composed mainly of amylose
and/or amylopectin. It may be extracted from various plants, examples
being potatoes, rice, tapioca, corn, and cereals such as rye, oats and
wheat. Starches containing phosphate groups are preferably made from
potato starch as well as corn starch, preferably from potato starch.
Simply washing with demineralized water will completely remove the content
of free electrolytes, but washing with water of low salt content may
suffice. The resulting washed starch can then be processed at a lower
temperature and/or at a lower pressure compared to the non-washed starch.
Neutral water, however, will remove only the free electrolytes. The
processing properties of such a water-washed starch may be further
improved by removing or partially removing also the metallic cations. They
are eliminated by washing the starch with water of a low acid value (pH)
preferably a value lower than 3 which can be obtained by adding
hydrochloric acid, sulfuric acid or any other suitable inorganic or
organic acid to the washing water. Preferably the so treated material is
rinsed afterwards with neutral water.
Washing with acid will regularly also remove the free electrolytes, whilst
washing with neutral water will leave the bound phosphate salts unchanged.
When removing cations from the phosphate groups according to step B., a
value of the remaining number of M.sup.2+ per 100 AGU of less than 0.2 is
preferred and especially a value less than 0.1. Very good results were
obtained with potato starch with values (after treatment) close to zero.
Once the cations are removed from the phosphate groups, the thus obtained
starch will contain free --O--P(O)(OH).sub.2 -groups and will become
acidic. The pH can drop from about 7 to about 3.5 as measured under
standard conditions in a water suspension. In some cases such a low pH may
not be desirable as heating such a starch to higher temperatures may cause
an undesirable degradation of the chain, resp. reduced mechanical
properties of the end product.
A particular aspect of this invention is therefore concerned with the
neutralization of the free acid groups, partially or wholly, resp. with
the replacement of a part or of all the protons (H.sup.+) of the
unsubstituted phosphoric acid groups linked to the starch with other
cations, which may be monovalent or polyvalent. Preferred are monovalent
ions such as Na.sup.+, K.sup.+, NH.sub.4 .sup.+ or divalent ions such as
Ca.sup.2+ or Mg.sup.2+. These ions may be added e.g. in the form of their
hydroxides.
It was found that it is possible to add divalent ions and that such ions,
like calcium or magnesium, previously removed by acid washing, will not
reestablish the original state of the starch, and will have a measured,
positive effect on processing properties.
Whilst the elimination of free electrolytes and of the phosphate-associated
metallic cations will reduce the processing temperatures and pressures,
the neutralization of the free protons will increase these values at a
measured rate. According to this invention it is possible to vary and to
control the temperature of melt formation to optimize process conditions
by adjusting the electrolyte content of the starch.
The influence of the cation content of potato starch (washed with acid and
reintroduction of cations by titrating with the corresponding hydroxides)
can be seen from the following Table 1.
The values for the temperature of melt- formation given in Table 1 are
measured by differential scanning calorimetric analysis (DSC). This
temperature of melt-formation is indicated on the DSC-diagram by a
specific relatively narrow peak just prior to the endothermic change
characteristic of oxidative and thermal degradation. This peak disappears
as soon as the mentioned specific endothermic transition has been
undergone. This last endothermic transition prior to thermal and oxidative
degradation plays an important role in melt-formation, indicated by the
fact that the opaque starch/water melt becomes transparent.
As is known to those skilled in the art, the melt formation behaviour, i.e.
the rate of melt formation, viscosities etc. in a screw and barrel depend
on many factors, such as the size of the barrel, its length and diameter,
screw design, speed of rotation, heating profile, etc. It is also
well-known that the nominal temperatures registered by DSC equipment are,
because of the finite heat capacities of the sample and holders and the
finite rates of heating used, not the temperatures of the samples.
Further, the temperatures of material in the screw of an extruder or
injection molding machine are, because of heats of melt-formation,
structural changes and the shearing action of the screw, not the same as
the set temperatures of the barrel and both of these temperatures are
different from the nominal temperatures registered by the DSC equipment.
For example, the DSC analysis may show the upper transition, i.e. the point
where the opaque starch/water melt become transparent, at a nominal
temperature of 182.degree. C., the temperature having been increased from
30.degree. C. to 180.degree. C. in 900 seconds. In spite of the lower set
temperature and shorter time of the processing, e.g. in the injection
molding equipment, compared with that of the DSC measurements, the upper
transition will be undergone due to the real temperature in the DSC sample
being lower than the nominal temperatures indicated on the DSC and
additionally the set temperatures of the injection molding machine being
lower than the temperatures of the material in the screw.
In Table 1 the nominal DSC-temperatures are given.
TABLE 1
__________________________________________________________________________
Influence of the cation composition of the phosphate
groups of potato starch on the melt-formation temperature
of potato starch at 17% H.sub.2 O.
Cation Composition
(expressed in equi-
Temperature of
valent per 2 equi-
Melt Formation
valents phosphate)
(.degree.C.)
No.
Material Ca.sup.++
Na.sup.+
NH.sub.4 .sup.+
H.sup.+
(DSC)
__________________________________________________________________________
1. Native Starch
1 0.40
-- 0.60
184.5
(RX 1279)
2. Acid-Washed 0 0 -- 2 163.1
Starch (RX 1279)
3. Ca.sup.2+ --Starch
2 0 -- 0 200.5
4. Na.sup.+ --Starch
0 2 -- 0 211.8
5. NH.sub.4.sup.+ --Starch
0 0 2 0 199.1
6. Ca.sup.2+ --Na.sup.+ --H.sup.+ --Starch
1 0.50
-- 0.50
172.6
7. " 1 0.33
-- 0.66
179.1
8. " 1 0 -- 1 182.3
9. " 0 1 -- 1 199.3
10 " 0.33
1 -- 0.66
209.6
" 1 1 -- 0 212.3
__________________________________________________________________________
From Table 1 it can be seen that the melt formation temperature of a native
potato starch which is 184.5.degree. C., can be varied over a broad range
from down to 163.1.degree. C. for a fully acid washed starch up to
212.3.degree. C. for a starch having 1 equivalent Na.sup.+ and 1
equivalent Ca.sup.2+ per two equivalents of phosphate.
It can be seen further that re-introducing calcium in an acid-washed starch
up to the level it was in the corresponding native starch, while
maintaining about the same distribution of the other cations, does not
bring back the melt temperature to the same level. Comparing native starch
of Table 1 with a Ca.sup.2+ -Na.sup.+ -H.sup.+ composition in equivalents
respectively 1-0.40-0.60 and melt formation temperature of 184.5.degree.
C. with Ca.sup.2+ -Na.sup.+ -H.sup.+ starch of composition 1-0.50-0.50,
melt formation temperature of 172.degree. C. and Ca.sup.2+ -Na.sup.+
-H.sup.+ starch of composition 1-0.33-0.66 of melt formation temperature
of 179.1.degree. C., shows this clearly.
The obtained water or acid washed starch material is then conditioned to a
water content in the range of about 10 to 25 % and better 10 to 20 %
calculated to the weight of starch and water. Preferred is a final water
content of 12 to 19 % and especially 14 to 18 % calculated to the weight
of starch and water.
The conditioned starch material with the appropriate water content is then
optionally mixed with further additive as described herein further below
and heated at elevated pressure above its glass transition temperature and
above its melting point. This temperature is preferable within the range
of about 80 -200.degree. C., preferably within the range of about 90 to
190.degree. C., and especially at about 120.degree. C. The minimum
pressure corresponds to the water vapour pressure produced at these
temperatures.
The starch material is heated preferably in a closed volume. A closed
volume can be a closed vessel or the volume created by the sealing action
of the unmolten feed material as happens in the screw of injection molding
or extrusion equipment. In this sense the screw and the barrel of an
injection molding machine or an extruder is to be understood as being a
closed vessel. Pressures created in a closed vessel correspond to the
vapour pressure of water at the used temperature but of course pressure
may be applied as this is normally done in a screw barrel. The preferred
applied pressures to be used are in the range of the pressures which are
applied in extrusion process and known per se, i.e. from zero to 150
.times.10.sup.5 N/m.sup.2 preferably from zero to 100 .times.10.sup.5
N/m.sup.2 and most particularly from zero to 75 .times.10.sup.5 N/m.sup.2.
The melt of destructurized starch according to this invention is e.g.
injected under the normal range of injection pressures used in injection
molding namely for thinner walled articles in the range from 300
.times.10.sup.5 N/m.sup.2 to 3.000 .times.10.sup.5 N/m.sup.2 preferably
700 .times.10.sup.5 -2200 10.sup.5 N/m.sup.2.
The starch material of the present invention may contain or may be mixed
with additives such as extenders, lubricants, plasticizers and/or coloring
agents.
These additives may be added before heating the starch to form the melt
(step E) or after this step. It mainly depends on the intended use of the
destructurized starch.
Such additives are extenders of different kinds, e.g. gelatin, vegetable
proteins such as sunflower protein, soybean proteins, cotton seed
proteins, peanut proteins, rape seed proteins, blood proteins, egg
proteins, acrylated proteins; water-soluble polysaccharides such as:
alginates, carrageenans, guar gum, agar-agar, gum arabic and related gums
(gum ghatti, gum karaya, gum tragacanth) pectin; water-soluble derivatives
of cellulose: alkylcelluloses hydroxyalkylcelluloses and
hydroxyalkylalkylcelluloses, such as: methylcellulose,
hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,
hydroxyethylmethylcellulose, hydroxpropylmethylcellulose,
hydroxybutylmethylcellulose, cellulose esters and hydroxyalkylcellulose
esters such as: celluloseacetylphtalate (CAP),
Hydroxypropylmethylcellulose (HPMCP); carboxyalkylcelluloses,
carboxyalkylalkylcelluloses, carboxyalkylcellulose esters such as:
carboxymethylcellulose and their alkalimetal salts; water-soluble
synthetic polymers such as: polyacrylic acids and polyacrylic acid esters,
polymethacrylic acids and polymethacrylic acid esters, polyvinylacetates,
polyvinylalcohols, polyvinylacetatephthalates (PVAP),
polyvinylpyrrolidone, polycrotonic acids; suitable are also phtalated
gelatin, gelatin succinate, crosslinked gelatin, shellac, water soluble
chemical derivatives of starch, cationically modified acrylates and
methacrylates possessing, for exampe, a tertiary or quaternary amino
group, such as the diethylaminoethyl group, which may be quaternized if
desired; and other similar polymers.
Such extenders may optionally be added in any desired amount preferably
within the range of up to 50 %, preferably within the range of 3 % to 10 %
based on the weight of all components.
Further additives are inorganic fillers, such as the oxides of magnesium,
aluminum, silicon, titanium, etc. preferably in a concentration in the
range of about 0.02 to 3 % by weight preferably 0.02 to 1 % based on the
weight of all components.
Further examples of additives are plasticizers which include polyalkylene
oxides, such as polyethylene glycols, polypropylene glycols,
polyethylene-propylene glycols; organic plasticizers with low molecular
weights, such as glycerol, glycerol monoacetate, diacetate or triacetate;
propylene glycol, sorbitol, sodium diethylsulfosuccinate, triethyl
citrate, tributyl citrate, etc., added in concentrations ranging from 0.5
to 15 %, preferably ranging from 0.5 to 5 % based on the weight of all the
components.
Examples of coloring agents include known azo dyes, organic or inorganic
pigments, or coloring agents of natural origin. Inorganic pigments are
preferred, such as the oxides of iron or titanium, these oxides, known per
se, being added in concentrations ranging from 0.001 to 10 %, preferably
0.5 to 3 %, based on the weight of all the components.
The sum of the plasticizer and water contents should preferably not exceed
25 %, and should most preferably not exceed 20 %, based on the weight of
all the components.
There may further be added compounds to improve the flow properties of the
starch material such as animal or vegetable fats, preferably in their
hydrogenated form, especially those which are solid at room temperature.
These fats have preferably a melting point of 50.degree. C. or higher.
Preferred are Triglycerides with C.sub.12 -, C.sub.14 -, C.sub.16 -, and
C.sub.18 - fatty acids.
These fats can be added alone without adding extenders or plasticizers.
These fats can advantageously be added alone or together with mono- and/or
diglycerides or phosphatides, especially lecithin. The mono- and
diglycerides are preferably derived from the types of fats described
above, i.e. with C.sub.12 -, C.sub.14 -, C.sub.16 -, and C.sub.18 - fatty
acids.
The total amounts used of the fats mono-, diglycerides and/or lecithins are
up to 5 % and preferably within the range of about 0.5 to 2 % by weight of
the total composition.
It is further recommended to add silicondioxide or titaniumdioxide in a
concentration of about 0.02 to 1 % by weight of the total composition.
These compounds act as texturizing agent.
The materials described herein above form on heating and in a closed vessel
a melt with thermoplastic properties, i.e. under controlled water-content
and pressure conditions. Such a melt can be used in various techniques
like thermoplastic materials. These techniques include injection molding,
blow molding, extrusion and coextrusion (rod, pipe and film extrusion),
compression molding, to produce known articles as produced with these
techniques. These articles include bottles, sheets, films, packaging
materials, pipes, rods, laminates, sacks, bags, pharmaceutical capsules.
The following examples further explain the invention.
EXAMPLE 1
Removal of soluble electrolytes by washing native potato starch with
demineralized water.
10 kg of a native potato starch (sample RX 1075, Roquette) were washed in a
Buechner funnel with a total of 50 liters of demineralized water. The
washed starch was then pressed on the filter paper and dried in a
conditioning room until it equilibrated at about 17% H.sub.2 O.
Analysis was carried out before and after washing and the results obtained
are presented in Table 2.
TABLE 2
______________________________________
INITIAL FINAL
(before washing)
(after washing)
______________________________________
No. of AGU 223 262
per phosphate group
No. of AGU 625 645
per M.sup.2+
No. of AGU 312 523
per M.sup.+
______________________________________
From the above results it can be seen that some free phosphate salt has
been washed away from the starch. The washing water was concentrated and
the dissolved salt precipitate by the addition of alcohol to the
concentrate. This precipitate was filtered and purified by dissolving it
again in a small volume of water and precipitating it again.
Conventional analysis of the recovered salt showed that the anion was a
phosphate (strong positive test with molybdate, tests negative for
carbonate, chloride, sulfate). The cations as determined by atomic
absorption spectroscopy were essentially: K.sup.+, Na.sup.+, with minor
amounts of Ca.sup.2+ and Mg.sup.2+.
EXAMPLE 2
Destructurization and melt-formation of washed potato starch (washing with
demineralized water)
Water-washed native potato starch as obtained in example 1, a lubricant
release agent (hydrogenated triglyceride), a melt flow accelerator
(lecithin), and a texturizing agent (TiO.sub.2) were mixed together in the
relative proportions in a high speed powder mixer for 10 minutes so that a
composition of 83 parts of H.sub.2 O-washed potato starch, 0.8 parts of
the hydrogenated triglyceride containing the fatty acids C.sub.18 :
C.sub.16: C.sub.14 in a ratio of 65:31:4 weight percent, 0.4 parts of
lecithin, 0.4 parts of titanium dioxide and 17 parts of water in the form
of a freely flowing powder was obtained. This powder was fed into the
hopper and fed to the screw barrel having the temperature profile and the
screw speed indicated in Table 3 for this trial. It was then injected into
an injection molding tool for pharmaceutical containers. The important
injection molding parameters were recorded and the visual quality of the
molded parts (% defect level) was checked and are given also in Table 3.
TABLE 3
______________________________________
UNWASHED WATER-WASHED
STARCH STARCH
Melt-formation and
(RX 1075, (RX 1075,
Injection molding
Roquette) Roquette)
parameters T.sub.b T.sub.m T.sub.e T.sub.n
T.sub.b T.sub.m T.sub.e T.sub.n
______________________________________
Temp. profile
90/165/165/165
90/165/165/165
[.degree.C.]
Residence Time
690 690
[sec]
Injection Pressure
1830 1500
[bar]
Injection Time
0,2 0,2
Screw Speed 200 200
[rpm]
Back Pressure
110 110
[bar]
Cycle Time 9,5 9,5
[sec]
Quality
Defect Level 0,1 0,01
[%]
T.sub.b = Temperature, beginning of the screw
T.sub.m = Temperature, middle of the screw
T.sub.e = Temperature, end of the screw
T.sub.n = Temperature, nozzle
______________________________________
It can be seen that the washed starch can be processed at a lower injection
pressure and yields an improved quality level of the molded parts.
EXAMPLE 3
(Washing with dilute acid)
600 g of native potato starch were suspended in 700 ml of 0.2N HCl and
stirred for 10 minutes. The suspension was filtered and the starch washed
on the filter three times with 200 ml portions of 0.2N HCl. The starch was
again suspended in 500 ml 0.2N HCl, stirred again for 10 minutes,
filtered, washed three times with 200 ml portions of 0.2N HCl.
After this treatment with HCl the excess of acid was removed by washing
with demineralized (deionized) water in following way: the starch was
washed twice with 200 ml portions of deionized water and then suspended in
500 ml of deionized water. This washing procedure with deionized water (to
remove excess acid) was repeated twice to get the starch free of HCl. This
was controlled by adding silver nitrate to the washing water. When there
was no more silver chloride precipitating in the washing water, the
washing was completed. The washed starch was pressed on the filter paper
and dried in a conditioning room (25.degree. C., 40% RH) until it
equilibrated at about 17.0% H.sub.2 O. In another experiment the wet
starch was treated in a fluidized bed with blowing air at 50.degree. C.
until the moisture content of starch reached 17% by weight (as checked by
periodical sampling of the starch).
Analyses have been carried out before and after the acid washing of starch
and results obtained are given in the following Table 4:
TABLE 4
______________________________________
INITIAL FINAL
(BEFORE WASHING)
(AFTER WASHING)
______________________________________
No. of AGU
266 269
per phosphate
group
No. of AGU
626 18'000
per Me.sup.2+
No. of AGU
617 20'000
per M.sup.+
pH 6.8 3.55
(20 g in
100 ml de-
ionized
water)
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