Note: Descriptions are shown in the official language in which they were submitted.
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396-17/UMA December 6, 1990
Special Amyloses and Their Use for Producing Biode~radable Plastics
The present invention relates to special amyloses and their use for
producing biodegradable, clear, transparent and flexible plastics.
Using native raw materials and processing them into technical
products has hitherto been of only minor importance, although such
raw materials are available in sufficient quantities and at
acceptable prices. In particular if aspects of environmental policy
are taken into account, however, it is to be expected that these
renewable raw materials will gain increasing importance in the
future.
A raw material which is particularly interesting in this respect
is starch, which is available in sufficient quantity and can be
obtained from a wide variety of sources. Starch consists of the
two components amylose and amylopectin. These components are
polymers composed of glucose units, with chain lengths and
molecular weights extending over a wide range. Whereas amylopectin
has a branched-chain molecular structure, amylose is a long
unbranched-chain molecule. Therefore starch, not least because of
its structure, presents ideal properties as a raw material for
technical products.
The film-forming properties of amylose have long been known. An
essential disadvantage of these films produced from amylose
consists in their brittleness and low elasticity. Accordingly, the
conventional amylose films are not very stable, which has the
negative effect of low crease resistance and tensile strength.
Further disadvantages are their insufficient transparency, their
rough surfaces and the sophisticated processes and equipment that
are required for producing such films.
Attempts made to avoid these disadvantages by adding plasticizers,
e.g. glycerol, sorbitol or, as described in DE-PS 17 45 680,
polyvinyl alcohol, however, did not improve the product properties
so far that these methods could have achieved greater technical
importance. The method of DE-PS 17 45 680 also requires that the
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hot amylose solution is placed on a heated substrate or pressed
through a nozzle into a coagulating bath which contains an acid or
salts for precipitating the amylose film.
Other methods of producing plastics describe the use of chemically
modified amyloses. Thus, GB-PS 965 349 and US-PS 3 117 014 describe
compositions which contain hydroxyalkyl amyloses or other
derivatized amyloses and which are suited for thermoplastic
processing. Let alone that these compositions are intended
exclusively for producing thermoplastic films, the film properties
with respect to transparency and ease of handling achieved with
these mixtures cannot in the least be regarded as ideal. This is
why these plastics so far have not been used for technical
applications.
The object of the present invention therefore was to provide
amyloses which enable, in a simple manner, production of clear,
transparent and flexible plastics and molded parts with improved
properties, in particular sheets and films; these are to be
characterized mainly by easy biodegradability, so that their
disposal by composting will no longer involve major difficulties
and problems.
According to the invention, it was found that the use of specific
amyloses, both in the production of films and sheets by a
simplified casting process and in the production of thermoplastic
molded parts, leads to products with extraordinary properties
compared with prior art, i.e. properties which cannot be achieved
in the same manner if conventional amyloses are used.
The object of the present invention therefore are special amyloses
as described in Claim 1. Another object is a simplified casting
process for producing films and sheets on the basis of these
special amyloses.
The special amyloses according to the invention are complex
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mixtures of different chemical substances, preferably polymeric
glycoses such as amylose and amylopectin, which show a behavior
extraordinary for starches and amyloses. These special amyloses,
which are natural polymers with statistical chain length
distribution and a wide range of molecular weights, naturally are
not accessible to accurate determination of the analytical
structure; in the following, special amyloses are therefore
understood as those fractions of amylose and amylose derivatives
which are characterized by the following behavior:
a) They are swellable in cold water, but not soluble;
b) If heated with stirring above 80 C at atmospheric pressure,
they yield homogenous flowable quasi-solutions typical of
starch, i.e. they do not form gels which are inhomogenous with
respect to flowability. If the solution is cooled to a
temperature of 50 C, this state is maintained for a period of
at least five minutes, without retrogradation. In a
concentration of 5 to 25 weight %, such a solution is
applicable to knife coating onto a plane surface with a gap
width between 100 and 700 ~m.
The special amyloses according to the invention can be obtained
in different manners and from different sources. According to the
invention, the special amyloses are obtained from high-amylose corn
starches, i.e. starches with an amylose content above 65 ~, as are
commercially available under the names Hylon VII (National Starch)
or Eurylon 7 (Roquette), or from high-amylose pea starches.
The special amyloses are preferably obtained from the above
starches according to a newly developed method by treatment with
formamide solution which contains a small proportion of
dichloroacetic acid. The enormous advantage of this method
according to the invention is that it enables the starch to be
decomposed and chemically modified in one step by treatment with
formamide/dichloroacetic acid; this means that, after destruction
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of the granular structure of starch, in particular the molecular-
weight and chain-length distribution of amylose is changed by
decomposition.
According to the invention, the starch is dissolved in the 4- to
6-fold amount of formamide solution which contains 2 weight %
dichloroacetic acid. The dissolution temperature depends
essentially on the type of the starting starch used and ranges
between 130 and 180~C. The solution is kept at this temperature for
a period between 20 and 40 minutes, preferably 30 minutes. During
this period the corn starch is decomposed, and starch degradation
starts.
Subsequently, the solution is slowly cooled down to a temperature
between 110 and 130 C, preferably 120 C, within a period of lO to
20 minutes, and after that kept at this temperature for a period
of 20 to 40 minutes, preferably 30 minutes. This leads to the
molecular-weight and chain-length distributions which bring about
the properties that are characteristic of the special amyloses
acccording to the invention. The end point of the reaction is
indicated by a slight discoloration of the reaction solution.
Further starch degradation is stopped by pouring the hot reaction
solution into iced water. To precipitate the reaction product, a
sufficient amount of precipitant, e.g. methanol or ethanol, is
added to the mixture. The product is separated in a conventional
manner, for example by sucking-off. Fur further purification, the
product is suspended in water, mixed with acetone, and sucked off
again. This procedure is repeated several times. After drying, the
product has a moisture content between 5 and 15 %.
The amylose thus produced has properties that cannot be achieved
by the conventional decomposition and degradation methods.
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According to the invention, special amyloses may also be specific
hydroxyalkyl derivatives of amyloses. Such hydroxyalkyl derivatives
are produced according to conventional methods, for example by
derivatization in alkaline solution, derivatization in aqueous-
alkaline suspension, or according to the method of Gs-ps 869 192.
The experimental conditions are selected in a manner known to a
person skilled in the art such that hydroxyalkyl amyloses with a
degree of substitution between 0.02 and 0.15 are obtained. A degree
of substitution between 0.05 and 0.1 is preferred. According to the
invention, the above high-amylose starches are again used as
starting material for producing the desired derivatized amyloses.
The special amyloses according to the invention can also be
obtained, however, from potatoe starch according to the method of
GB-PS 869 192, taking into account the above reaction parameters;
this method, however, involves much higher effort. The production
of the special amyloses according to the invention is illustrated
by the following examples.
In the production of plastics, the special amyloses are used in a
mixture with appropriate plasticizers. Mixtures for achieving the
object of the invention are composed of:
60 to 97 weight % special amylose and
3 to 40 weight % of a plasticizer.
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Preferably, the following composition is used:
70 to 95 weight % special amylose and
5 to 30 weight % of a plasticizer.
Particularly preferred is a composition containing:
80 to 85 weight % special amylose and
15 to 20 weight % of a plasticizer.
Appropriate plasticizers are plasticizers known from the prior art,
in particular polyhydric alcohols. Preferably used are glycerol,
diethylene glycol, triethylene glycol, sorbitol, polyvinyl alcohol,
citric acid oxide adduct or mixtures of these plasticizers.
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The compositions according to the invention can be used both for
thermoplastic molding of shaped parts or for producing sheets or
films by casting.
Thermoplastic shaping of molded parts using compositions according
to the invention is effected in a conventional manner as used for
other thermoplastics according to current plastics-processing
methods, for example by injection molding, extrusion, blow molding
or by thermoplastic molding methods for producing sheets. The
molded parts thus obtained are stable and flexible and show an
excellent transparency.
According to the invention, the above-described compositions can
also be used in a new method of producing cast sheets; these
compositions have first to be dissolved in a sufficient amount of
an appropriate solvent and subsequently filtered. It is suitable
to effect dissolution and filtration at elevated temperature.
Appropriate solvents are, for example, alcohols, aqueous
formaldehyde or dimethyl sulfoxide. A preferred solvent, however,
is water. The amount of solvent is suitably selected such that the
solution on the one hand is still easy to handle and, on the other,
the removal of the solvent for forming the sheets does not yet
involve too much effort. The amount of solvent therefore, as a
rule, will range between 70 and 100 weight parts, related to the
total weight of the composition of special amylose and plasticizer.
It is of great importance for the production of the amylose films
and sheets to filter the special amylose that is dissolved in the
mixture of solvent and plasticizer prior to forming the sheet,
because this obviously eliminates any defects, crystallites and
impurities from the special amylose, which otherwise would cause
recrystallization of the special amylose and thus deterioration of
the quality of the resultant sheet or film.
After filtration, the film is formed by pouring the adequately warm
solution onto a substrate, and by subsequent removal of the
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solvent. The sheets are suitably cast onto flat-ground materials,
e.g. glass panes. Polyester sheets are preferably used, because
the special amylose film is particularly easy to peel off.
The film cast in this way is suitably dried at a temperature of 20
to 70 C. Drying can be carried out both at atmospheric pressure and
at reduced pressure.
This method yields sheets which, after drying, are easy to peel off
from the substrate, and which are characterized by excellent
clearness and light transmittance. At normal atmospheric humidity,
the sheets are stable, transparent, flexible and crease resistant,
without becoming subsequently turbid (retrogradation), and they
withstand a bending angle of 180 C without fracture of the fold.
These properties are retained for months.
The special amylose according to the invention in the above
compositions thus cannot only be processed into films and sheets
by the above conventional plastics production processes, but
particularly easily also by the casting method according to the
invention. All the products according to the invention are
characterized by satisfactory tensile strength and elongation;
these properties are retained even by films or sheets aged over an
extended period of time. As becomes obvious from the following
embodiments, an increasing proportion of plasticizer reduces the
tensile strength of the special amylose film, while the elongation
is markedly increased.
The degradation behavior, the swelling capacity and the resistance
to aging can be varied by the moisture content of the films and
sheets. Thus, the embrittlement increases with decreasing moisture
content. In the same way, the solubility of the sheets and films
in water can be adjusted in a conventional manner by the type of
plasticizer added, from soluble in cold water via soluble in hot
water to slowly swellable and finally waterproof in cold water.
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The sheets and films produced by the casting method according to
the invention can be made in arbitrary thicknesses, the common
film thickness ranging between 20 and 100 ~m. It is possible to
write on these films with plastic-sheet pens or ball-point pens;
they are resistant to oils and fats as well as to organic solvents
such as acetone, ethanol, esters, and chlorinated solvents.
The molded parts produced using the compositions according to the
invention show a much better transparency and clearness than
conventional molding compositions on the basis of normal amyloses
or amylose derivatives. In addition, these materials, together with
the plasticizers, are much better biodegradable. The films and
sheets thus produced are in addition characterized by
ecotoxicological acceptability, and by food, soil and skin
compatibility, so that they can be used without any problem for
packaging food. In addition, the sheets are fast to light, dyeable,
can be bonded and sealed and are not hygroscopic. The sheets
according to the invention can be used as alternatives to other
conventional plastics, such as polyvinyl chloride and
polypropylene.
The invention is illustrated by the following examples. All the
percentages indicated relate to the total amount of special amylose
and plasticizer.
EXAMPLE 1
Special amylose: 90.9 weight %
Ethylene glycol: 9.1 weight %
83.5 g water in a round-bottomed flask was mixed with 1.5 g
ethylene glycol and heated to 90 C. 15 g special amylose was slowly
added to this solution, with vigorous stirring. Then the solution
was heated for 60 minutes to 100 C. The hot solution was filtered
through a fritted glass filter, and a film from the filtrate, which
still had a temperature of about 50 C, was cast onto a plane
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surface; this film was dried in a drying cabinet at a temperature
between 40 and 70~C. After drying, a clear, transparent, elastic
sheet of 100 ~m thickness was peeled off from the surface.
EXAMPLE 2
Special amylose: 95.24 weight %
Ethylene glycol: 4.76 weight %
In accordance with the method described in Example 1 above, a cast
sheet was produced from a solution of 84.25 g water, 0.75 g
ethylene glycol and 15 g special amylose.
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EXAMPLE 3
Special amylose: 80 weight %
Ethylene glycol: 20 weight %
In accordance with the method described in Example 1 above, a cast
sheet was produced from a solution of 81,25 g water, 3.75 g
ethylene glycol, and 15 g special amylose.
EXAMPLE 4
Special amylose: 95.24 weight %
Triethylene glycol: 4.76 weight %
In accordance with the method described in Example 1 above, a cast
sheet was produced from a solution of 84.25 g water, 0.75 g
triethylene glycol, and 15 g special amylose (hydroxyethyl
amylose).
EXAMPLE 5
Special amylose: 90.9 weight %
Polyvinyl alcohol: 9.1 weight %
In accordance with the method described in Example 1, a cast sheet
was produced from a solution of 83.5 g water, 1.5 g polyvinyl
alcohol, and 15 g special amylose (hydroxyethyl amylose).
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EXAMPLE 6
Special amylose: 66.7 weight %
Ethylene glycol: 33.3 weight %
In accordance with the method described in Example 1, a cast sheet
was produced from a solution of 77.5 g water, 7.5 g ethylene
glycol, and 15 g special amylose ~hydroxyethyl amylose).
EXAMPLE 7
Special amylose: 90.9 weight %
Triethylene glycol: 9.1 weight %
In accordance with the method described in Example 1, a cast sheet
was produced from a solution of 83.5 g water, 1.5 g triethylene
glycol, and 15 g special amylose (hydroxyethyl amylose).
EXAMPLE 8
Special amylose: 90.9 weight %
Glycerol: 9.1 weight %
A cast sheet was produced according to Example 1, using
9.1 weight % glycerol as plasticizer.
EXAMPLE 9
Special amylose: 83.4 %
Glycerol: 16.6 weight %
A cast sheet was produced according to Example 1, using
16.6 weight % glycerol as plasticizer. The solution was filtered
under vacuum.
EXAMPLE 10
Special amylose: 80 weight %
Glycerol: 20 weight %
A cast sheet was produced according to Example 1, using
20 weight % glycerol as plasticizer. The solution was filtered
under vacuum.
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The properties of the cast sheets described in the above examples
as well as in the reference examples are compiled in the following
table.
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EXAMPLE 11
Production of special amylose by treatment with
formamide/dichloroacetic acid
120 g high-amylose corn starch Hylon VII (National Starch) is
dissolved, with stirring, at 145 to 150 C (internal temperature),
in 588 g formamide solution that contains 12 g dichloroacetic acid,
and kept at this temperature for 30 minutes. The solution is then
cooled down to 120C (internal temperature) (duration: about
15 minutes) and kept at this temperature for another 30 minutes.
Subse~uently, the hot reaction solution is poured into about
300 ml iced water. About 200 ml ethanol is added to this mixture
to precipitate the product, which is then sucked off. For
purification, the solid residue is supended in 1 liter water and
precipitated with the same amount of acetone. This procedure is
repeated twice. After drying at room temperature or in the drying
cabinet, a white voluminous powder is obtained.
Yield: 180 g special amylose
EXAMPLE 12
Production of special amylose by derivatization in alkaline
solution
48.6 g high-amylose corn starch Hylon VII or Eurylon 7 is mixed
with 150 ml water and introduced into 1200 ml lN NaOH. 13.2 g
ethylene oxide (liquefied) is slowly added dropwise to this
solution with vigorous stirring, so that the internal temperature
does not rise above 20C, and thereafter stirred for 8 hours. This
results in conversion of the starch into low-ethoxylated starch.
The reaction solution is neutralized with concentrated HCl, reduced
to a volume of 600 ml, and dialyzed against distilled water
(diaphragm: Visking Dyalyse Tubing) for 24 hours. Subsequently, the
product is precipitated with methanol and sucked off. In this
process, disturbing accompanying substances, e.g. in particular
salts and water-soluble starch fragments, are removed. For
purification, the product is suspended in acetone, sucked off and
dried.
Yield: 40 g special amylose (hydroxyethyl amylose).
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EXAMPLE 13
Production of special amylose by ethoxylation according to the
method of GB-PS 869 192
324 g Hylon VII is added batchwise to 1650 ml lN NaOH and stirred
for 2.5 hours. Subsequently, 30 g ethylene oxide (liquefied) is
slowly added dropwise and thereafter stirred for 2 1/4 hours. This
is followed by neutralization with concentrated sulfuric acid. The
neutralized starch solution is added to a solution of 700 g MgSO4
x 7 H2O in 2000 ml water and stirred for 20 hours. The resultant
turbidities are separated (centrifuge). The solution is mixed with
an additional amount of 2 liter MgSO, solution (700 g MgSO4 in two
liters). After 24 hours, a white, flaky precipitate has formed.
The precipitate is filtered off, washed with cold water to remove
MgSO4, and dried.
Yield: 200 g special amylose (hydroxyethyl amylose).
EXAMPLE 14
Production of special amylose by derivatization in aqueous-alkaline
suspension
1000 g high-amylose corn starch Hylon VII or Eurylon 7 or high-
amylose pea starch is added batchwise to a solution of 1200 ml
water, 13 g NaOH and 150 g Na2SO~, and then 360 g propylene oxide
is slowly added dropwise. Then, the solution is kept at 40 C
internal temperature for 8 hours, with vigorous stirring. This is
followed by neutralization with lN H2SO4, and sucking off. The
product is suspended in about 2 liter methanol and again sucked
off. This procedure is repeated twice. The isolated product iæ
dried in air or in the drying cabinet (40 C).
Yield: 1215 g special amylose (hydroxypropyl amylose).
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EXAMPLE 15
Production of thermoplastic sheet
20 g of the special amylose obtained according to Examples 11 to
14 is intimately mixed with 4.45 g ethylene glycol as plasticizer
in a kneading machine and pressed into a thin, transparent and
elastic sheet at a temperature of 100 C, at a molding pressure of
10 t, and for a pressing time of 30 minutes, using a heated press.
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