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Description  |
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BACKGROUND OF THE INVENTION
The growing of plants in greenhouses made of plastic or glass is known. A
clear cover can be penetrated by both short wave and long wave radiation
in the range of visual light. It is also known that greenhouse covers
transmit more short wave radiation than long wave radiation, the heating
effect of the light in the green houses taking effect in that the short
wave radiation is converted to long wave radiation within the greenhouse.
The greenhouse principal has also been used in growing fields in such way
that covers have been formed to a bow over the surface of the field or the
cover has been applied to the surface of the earth. The cover materials
used for such purposes in the fields have been of plastic or paper through
which the plants grow. This known technique produces several advantages,
namely, temperature increase by using transmitting covers so that short
wave radiation is converted to heat, the prevention of evaporation of the
water by paper covers, and the hindering of the growing of weeds under
covers using a film that transmits light.
The need for weed killers is the same when using clear covers or in the
case of growing without any cover, and in some cases, even more so in the
case of the use of covers because by using a clear cover the humidity is
condensed on the inside of the film and good conditions are formed for the
growth of weeds around the growing plants. Furthermore, the fact that the
earth is exposed between the films as a result of earth terracing used to
fasten the films, results in an improvement of the growing conditions for
weeds.
Previously known films have been decomposed to small pieces as a result of
ultraviolet radiation. Attempts have been made to achieve films that are
degraded by ultraviolet radiation to such extent that microorganisms may
be able to continue the degradation and to completely degrade the films.
However, degradation in these previously known films has not been
complete. In practice, the edge of the cover film covered by the earth
remains in the field because the UV-radiation cannot transmit through the
earth to degrade the film. Even a little piece of earth or a dust layer on
the film hinders the energy of the UV-light to enter the film, which is
needed for the degradation of the polymer bonds.
In theory, the films are degraded by means of UV-light even after the
plants begin to cover the same, and further in theory, the degradation
being to such small pieces that they do not cause problems in the field.
In practice, however, the degradation is not complete as a result of
UV-light, which results in more and more plastic material in the field
because the synthetic polymer itself in the so called composite films is
not biologically degraded. The synthetic polymers do not absorb water and
since the biological degradation takes place by means of enzymes produced
by microbes, no biological degradation can occur because these enzymes act
only in the presence of water.
Synthetic polymers, the molecules of which consist of, for example, about
12,000 successive carbon atoms, should be degraded to about 500 pieces
with the lengths of about 10 carbon atoms before the rate of biological
degradation has any importance whatsoever. However, the structure of the
plastic films is already essentially changed in the stage when the polymer
has been degraded to pieces containing thousands of carbon atoms. A
plastic film, degraded in this way, could cause serious environmental
problems. As a result, the use of films of this type has recently
decreased. Problems have also arisen from the toxic residues that are
caused by such degradation.
Methods are also previously known in which the film is removed from the
field after the growing season has ended. Use of such films is, however,
very expensive. Furthermore, in previously known methods, it is mainly
thin films that have been used, because their preparation is much cheaper.
However, it is difficult to remove such films from the field because the
films are easily decomposed. In previously known solutions, the film has
covered only about 50-70% of the growing surface because it has become
necessary to leave exposed earth between the films for the fastening
terracing.
In the our earlier Finnish Application FI-891905, the problem of
degradation of the film has been improved by fastening the film to the
growing surface by quiltings, as a result of which the entire growing
surface is covered by the film. In the solution of this Finnish
application, the degradation of the film by means of UV-light is improved
because the entire film is on the ground. However, the problem remains
that even by use of a UV-degradable film, more and more plastic is
retained in the field, because these films are not biologically degraded.
Biologically degradable materials can be degraded biologically as a result
of their chemical structure, by the act of microorganisms, such as mould,
fungi and bacteria, when they are put in contact with the earth, or by
being brought into contact with microorganisms in another manner, under
conditions in which the microbes can grow. The term "biologically
degradable" is used herein to refer to degradation of the type in which
the degradation takes place by the act of living organisms such as
microorganisms. The term "degradable" per se, is used with reference to
the degradation, of for example, ethylene polymers which, by the act of
different additives or other substances degrade into smaller pieces,
without microorganisms effecting such degradation.
Attempts have been made to study the biological degradation of plastic
films, and even to provide this in different ways, for example, by means
of mould cultures. (Compare with ASTM-Standard, STM G 21-70 1980, that has
been used in the investigations of so called biological degradation of
plastic materials). The growth of mould on plastic films has, however, not
shown anything about the biological degradation despite the growing of the
mould. The growth of mould on plastic films has been considered to be in
correlation to the amounts of additives in the films, with no influence on
the synthetic polymer itself.
Generally it can be stated that the film material is degraded into pieces
if it does not contain antioxidants, but contains, for example
UV-catalysts which break the C--C bond of the synthetic polymer molecule.
If the plastic molecules contain double bonds, these are degraded with
less energy, even without any catalyst.
The biological degradation of the synthetic material requires hydrophilic
water soluble groups. The polymer must be broken so that such hydrophilic
chemical group is formed that can be enzymatically degraded, for example a
carbonyl or carboxyl group. The degradation product of the biological
degradation of the film must be water, carbon dioxide and biomass.
Several attempts have been made to prepare such biologically degradable
films that consist of a combination of a synthetic polymer and a
biopolymer in which a catalyst sensitive to UV-light has generally been
added. A substance that degrades synthetic polymers by using light as
catalyst is known, for example, from the patent publication EP-230143.
It has been thought that synthetic plastic material is able to absorb water
if hydrophilic groups are included therein by means of a biologically
degradable polymer. Starch is the cheapest biologically degradable polymer
for this purpose, the use of which, in addition, should decrease
production costs of the film because its price is lower than that of the
polyethylene. Since the gelatinized starch alone forms a very brittle
film, that is sensitive to water, it is commonly known that the starch
must be combined with other substances that can be used in the film in
order to arrive at a satisfactory product.
Polyethylene (PE) is the most commonly used synthetic polymer for preparing
films with desired physical properties. Early attempts to produce PE-films
by blowing technique from compositions with a high proportions of starch,
>30% (w/w) have, however, not been successful. The reason is that starch
is a very coarse material (particle size 20-150 .mu.m) that interferes
with the making of thin films. Furthermore, in the blowing technique, the
starch particle and the molten plastic mass move with different speeds in
a blowing technique carried out at normal blowing temperatures
(170.degree. C.) which results in brittle and breakable material with
holes being formed. In other words, it has not been possible to make such
film by blowing because the film necessarily becomes too thick.
Attempts have also been made to bring chemical bonds about the starch
particles in order to facilitate the mixing of the synthetic polymer
therewith. Such films have been described, for example in the following
patent publications, U.S. Pat. No. 4,337,181, GB-1,487,050 and
GB-1,485,833. In these known films, the enzymes can in theory degrade the
material because the material is, at least in theory, to some extent wet.
However, the technique is very expensive and furthermore, the material has
several disadvantages, namely, poor tensile strength, thick films cannot
be produced and the films do not stretch.
Attempts have also been made to add other reactive groups into the film
material, for example double bonds. When the material contains double
bonds and it reacts with oxygen and a metal catalyst, (for example, Fe3+),
reactive peroxides (--C--O--O --C--) are formed. Thus, free oxygen atoms
and radicals are formed resulting in the bonds between the carbon atoms
being degraded, and for example carboxyl groups and smaller
carbon-hydrogen chains are formed. The phenomenon has been used in films
that contain a metal catalyst (note for example, Patent Publication EP-86
310 154.9). When the resulting film material contains carboxyl groups
(RCOOH), the same can be degraded by the action of enzymes from the
microorganisms if surrounded by water. In other words, reactive groups and
catalysts have been added to the film material by means of which
biologically degradable RCOOH-- groups are obtained under given
conditions. However, these materials are very expensive to produce.
In U.S. Pat. No. 4,337,181, starch, ethylene-acrylic acid copolymers, and
optionally polyethylene have been mixed and blowed to a film by using
additives that neutralize a portion of the functional acid groups of the
copolymer. This method makes the use of wet starch possible, but requires
expensive additives. According to the EP Patent Application 0 230 143, the
photodegradation must be facilitated by using photodegradable substances
that comprise a photosensitive substance and an ethylene/carbon monoxide
copolymer. Preferably, the photosensitive substance is a heavy metal
dithiocarbamate or a heavy metal dithiophosphonate. As previously stated,
ethylene copolymers that contain carbonyl groups are degradable by means
of ultraviolet light, but the life span of these copolymers, is not
sufficiently long.
Additionally, U.S. Pat. No. 3,901,838, mentions films that consist of a
biologically degradable thermoplastic polymer and a degradable ethylene
polymer, the mixing being carried out in a conventional mixture and the
powdering in a mill. British Patent No. 1,483,838, teaches a biologically
degradable film comprising a biologically degradable substance that is
homogenously dispersed in a material forming a non-biologically degradable
film that is not dissolved in water, the biologically degradable substance
being present in an amount of 40-60% of the weight of the film material.
In this solution, the biologically degradable substance is a finely
divided substance that absorbs water, the film being made of an aqueous
dispersion of these substances. The film is, in other words, made from a
dispersion in organic solvents or in aqueous systems and because of the
physical properties, the same cannot be used as a growing film.
In summary, it can be stated that the degradation of cover films is a
two-pronged problem. On the one hand, it is desired that the film not be
degraded as long as it is used. On the other hand, when the use of the
film is complete, it is desired that the same be returned to the ecosystem
in a form that does not cause harm to the environment. Under these
conditions, the macromolecules should be split into smaller compounds that
in turn can be used as food for the organisms through which they should be
returned to the food cycle.
For the most part of commercial vinyl plastics, polyethylenes,
polypropylenes, polystyrenes, polyvinyl chlorides and aromatic polyesters
withstand microbial degradation. The only polymers that are biologically
degraded are highly oxidated products such as cellulose, aliphatic
polyesters and polyurethanes based on polyester. Since these can be
degraded to water soluble short chains, they can be used as food by
microbes. Treatments that lower the molecular weight and perhaps also
change the chemical structure, expose the polymers to the degradation
action of the microbes. When, for examples polyethylene is acidified with
nitrous acid, waxy compounds on which thermophilic mushrooms can grow, are
obtained. An intensive ultraviolet radiation can also cause chemical
changes in the plastics as, for example, forming of carbonyl groups in
which ketones are a part of the metabolism of the microorganism.
UV-radiation, photo degradable additives, morphological surface, additives,
antioxidants and molecular weight all have an influence on the biological
degradation of polyethylene. The biological degradation of paraffin can be
compared with the degradation of polyethylene. In the beginning of the
degradation, the main influencing factor is the UV-light and/or oxidation
agents. However, once the carbonyl groups have been produced, the
microorganisms attack the same and degrade the polyethylene chain to
shorter fractions, carbon dioxide and water being the end products. The
biological degradation and the ambient factors have a strong synergism,
which is why the result can never be explained by only one factor. This is
because the degradation is a combined result of factors including
temperature, UV-light, water, the microbes and their foods. The presence
of water is always a condition for biological degradation.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a film which
begins to degrade by the action of UV-light and which then is biologically
degraded, and wherein the film despite being subject to these forms of
degradation is sufficiently strong and stable to withstand an entire
growing season and then to be biologically degraded during the next
growing season.
It is a further object of the present invention to provide a film that is
degraded by UV-light and which bonds water and is thus biologically
degradable.
It is still a further object of the present invention to provide a material
that is degraded in two stages, in the first stage being crumbled and then
finally biologically degraded in the earth. The film is mechanically
sufficiently strong to withstand application conditions and be degraded
not later than during the following season so that the final biological
degradation does not occur during the first growing season.
It is still another object of the present invention to provide a
biologically degradable film based on a synthetic polymer, for example, a
polyolefin, such as polyethylene or polypropylene, and a biologically
degradable polymer such as starch or cellulose.
It is yet another object of the present invention to avoid the
disadvantages of earlier materials that consist of biopolymers and
synthetic polymers which formed a thick and brittle film which was too
expensive for actual preparation and which either did not result in
complete biological degradation or in which the biological degradation was
too slow.
With the above and other objects in view, the present invention mainly
comprises:
(a) finely dividing a biologically degradable polymer (biopolymer) into
small particles in an aqueous suspension by means of enzymes that split
said biologically degradable polymer to smaller macromolecules and release
small molecule compounds from the surface of the biologically degradable
polymer particles,
(b) emulsifying the thus obtained suspension of particles, after the
desired particle size has been achieved, in a vegetable oil so that the
particles that are coated with enzyme protein become coated with vegetable
based oil whereby at the same time the degradation action of the enzyme is
interrupted,
(c) separating the oil-coated particles from the suspension to remove the
small molecules after which the particles are dried and pulverized, and
(d) forming a final film in a film extruder after mixing the biopolymer
with a synthetic polymer. The synthetic polymer may contain additives
generally used in such films.
The plastic film of the present invention is mainly characterized in that
the biologically degradable polymer is homogeneously distributed in the
synthetic polymer in particle form, there is a protein layer around the
biologically degradable particles and an oil film that covers the protein
layer.
The synthetic polymer that is used according to the present invention can
be any olefin and there is no problem with the melting index of the
olefin. Both linear components such as LLDPE, LDPE or HDPE or branched
forms can be used. There are, however, certain properties that the
polymers should have.
For example, the synthetic and biological material must fit. In other
words, the biopolymer that is mixed with the synthetic polymer must be
able to withstand the melting temperature of the synthetic polymer used in
the preparation of the premixed batch or master batch which used in
connection with blowing and drawing of the film. By proceeding in
accordance with the present invention, the biopolymer can be homogenouesly
distributed in the synthetic polymer, due to the small particle size of
the biopolymer and the manner of coating. Furthermore, the synthetic
polymer should not contain any antioxidants that prevent the degrading
effect of UV-light and peroxides.
The biopolymer to be used can be made of various different starting
materials such as starch, cellulose, rye flour, wheat flour and other
biological materials that are milled. In earlier attempts to mix
biopolymers with synthetic polymers, the particle size, which was too big,
has caused problems and it was not possible to make a film, in addition to
which the large particles are difficult to mix in the melt mass.
By proceeding in accordance with the present invention, particles are used
of such small size (smaller than 10 .mu.m), preferably 0.5-5 .mu.m, that
is is possible to produce a film having a thickness of 20-40 .mu.m, and in
some cases even 10 .mu.m. By the use of particles sizes which are so small
according to the present invention, it is possible to include in the
synthetic polymer 40% of such biopolymer materials that have not been
chemically modified. Particles of such small size cannot be made in
previously known manner using mills. In accordance with the present
invention, enzymes are used to make the sufficiently small particle size
of the biopolymer. Thus, for example, the .alpha.-amylase enzymes
(.alpha.-1,4-glucan-4-glucan-hydrolase) split dextrines from starch, which
are gradually released from the larger particles. If, for example,
cellulose is used, the usable enzymes are the cellulases, for example
1,4-.alpha.-D-glucanase, that split cellulose dextrines or
cellobiohydrolases from cellulose into cellobiose products. In this
manner, the biopolymer can finally be completely degraded and dissolved in
water.
When it is desired to degrade the biopolymer particles in the invention to
only a given limited size, the process can simply be interrupted when the
desired particle size has been achieved, this being accomplished by the
addition of the vegetable oil, and generally an emulsifier, to the
suspension which is vigorously stirred. This results in a vegetable based
oil layer being formed on the enzyme protein on the surface of the
particle, for example, soya, rape, sunflower, or another corresponding
oil. Simple mixing of the biopolymer and the oil does not lead to the
desired results. However, the biopolymer particles are dissolved in water,
and for example, calcium chloride (CaCl.sub.2) is added to the suspension
so that the ionic strength is suitable for the enzyme and in the case of
.alpha.-amylase), the concentration of Ca.sup.2+ of the co-factor of the
enzyme is suitable for the action of the .alpha.-amylase. In addition, the
pH value of the suspension is regulated so as to be suitable for the
action of the enzymes. According to the invention, it is advantageous to
use an .alpha.-amylase whose activity depends on the temperature (for
example, high temperature .alpha.-amylase KLAA). The mixing of the
biopolymer first takes place in cold water if starch is used, to prevent
gelatinization, and then the system is warmed to be suitable for the
action of the enzyme, which in the case of KLAA is to a temperature of
about 55.degree. C.
The entire process is carried out in a large reactor vessel in which there
is a mixture surrounded by a mantle. The temperature is regulated in known
manner, for example, by means of a thermostat. Enzyme is added to the
system and as its activity and other properties are given, the
temperature, pH and ionic strength of the mixture can be regulated exactly
forward and the time required for the degradation can be defined to
achieve the desired particle size.
The amount of enzyme is such as to be able to quantitatively cover the
biopolymer particle and thus form a protein mantle on the particle. When
the desired particle size is achieved, the oil is added by means of an
emulsifier to form the oil into small droplet as a result of which the oil
mantle is formed around the protein layer which surrounds the biopolymer
particle, and the degradation process is immediately stopped since the oil
prevents the action of the enzyme by isolating it from the water and by
bonding to the enzyme protein. A mantle of oil is collected around the
protein mantle in this manner. The amount of oil is about 0.5-15% of the
amount of the biopolymer, depending on the quality and mixing conditions
of the biopolymer.
In the stage in which the oil is added to the biopolymer mass, the mixture
is further stirred vigorously, in which the temperature is rapidly
decreased, preferably to below 10.degree. C.
It is at this time desirable to separate the particles, coated with protein
and oil, from the suspension and from the small molecules dissolved in the
suspension, from the dextrine in the case of starch and low sugars. The
mixing is stopped and the particles are separated from the suspension
either by permitting the same to precipitate or by centrifuging. From the
standpoint of the invention, it is very important that the obtained
biopolymer particles are free from split products, since otherwise large
particles are reformed in the preparation of a optimal master batch and
during the preparation of the film, and for example, the dextrines burn in
the temperature used in the preparation. The enzyme has, for example,
split dextrines from starch to obtain small particles. The split dextrines
must be removed from the mixture, which is the reason that the particles
are centrifuged or decanted. Since it is important that all the dextrines
be removed, the particles are washed with water before drying. They are
then pulverized and mixed with the other film material.
The particles should be separated by decanting or centrifuging, wherein the
water phase is removed, not directly by drying, because in that case,
aggregates of particles are formed that contain small molecules such as
dextrines. After the separation, the particles are dried from the
suspension, by spray drying. After the drying, the particles are
pulverized. This is most preferably effected by the so called FP method (a
fine pulverization technology developed by Oy Finnpulva Ab, as disclosed
in their brochure). This method is carried out so that the particles
collide under high pressure and small volume, rapidly against each other,
to in effect pulverize the particles mechanically. Air and the mixed
material to be pulverized in this method are led through two notches to a
collision line at a suitable angle. The temperature can be maintained in a
desired range so that the material will be absolutely dry.
According to the invention, it is also possible, and at time preferable, to
carry out the pulverization using previously known methods, for example by
means of mills. After the pulverization, it is preferable to granulate the
particles into granulates together with the synthetic polymer in a screw
extruder. The granulates contain about 60-80% biopolymer. These granulates
form a so-called masterbatch, or a premixed preparate, that contains
biopolymer and synthetic polymer. A melt mass coming from the screw
extruder, is split into pellets and cooled in an air stream. The pellets
can also be cooled with water and thereafter dried. A suitable synthetic
polymer is, for example, polyethylene. The granulation must be carried out
with a polymer which has the right melting index depending on the
biopolymer. These granulates form the premixed preparate of biopolymer and
synthetic polymer.
If it is desired to include a catalyst in the film, a second premixed
preparate is made in granulate form that consists of a metal catalyst and
a synthetic polymer and this can also be carried out in an extruder. The
metal catalyst may be for example, anhydrous FeCl.sub.3 and in this
premix, its concentration is 0.1-1%. Other usable metal catalysts include,
for example Cu.sup.2+, Se.sup.2+, Zn.sup.2+, which, in other words, are
known oxidation agents for vegetable based oils, that are necessary, for
example to form carbonyl groups, when the C--C bonds are split. The carbon
chains can then be degraded biologically from these groups.
The melting index of the used polymers is preferably about 4, which means
that the preparation temperature of the plastic film can be about
150.degree. C. Since in accordance with the preferred embodiment of the
invention, the process proceeds using premixed preparates from both the
catalyst and the biopolymer ("the masterbatches), any real mixing in this
case is not carried out inside the film extruder, but instead, the
premixing occurs in a prior extruder. It is possible to carry out the real
mixing as late as the film extruder. If a catalyst is used, it is
preferred to keep it separate from the biopolymer as long as possible.
In the actual film extruder, the final film is then prepared by feeding
into the extruder, in accordance with an advantageous embodiment of the
present invention:
(a) a premix of catalyst (masterbatch I), that contains 0.1-1% metal
catalyst and synthetic polymer,
(b) a premix of polymer (masterbatch II), that contains 60-80%, preferably
about 60%, biopolymer and synthetic polymer, and
(c) in addition, and if desired, and depending on the desired final
product, 1-50% synthetic polymers and additives can be added to the film
extruder, for example, pigments and other optical agents.
All the compounds that are desired to be present in the final film are
mixed in the film extruder.
The transmission and absorption of the radiation of the film depends on the
added particle amounts and so called pigment component. Dye can be added,
either by pressing it against the surface of the film, or by mixing with
the film material. The degradation age of the final film is longer the
less particles is less larger particles are used, and on the other hand,
the more oil or catalysts used, the shorter the degradation age.
The catalyst is kept separate until it is added to the film in as late a
stage as possible. Generally, it is added to the film because it is not
certain that there is enough catalyst in the earth or that the degradation
effect of the UV-light will be sufficient. The material of the invention
is essentially dry until it reaches the earth.
The amount and the size of the particles of the biopolymer are selected so
that there are contacts between the same and so that they are able to
absorb water, become wet and thus be degraded by means of microogranisms.
The film will not break too soon when the proportional amounts of the
biopolymer and the synthetic polymer are properly selected. If there are
too many particles in the film material, the strength properties become
lessened. In accordance with the invention, a required amount of the
biopolymer is homogenously included in the film, also in thin films, so
that it can be degraded biologically. The earth receives new nutritives
when the film is degraded because all of the additives are of such quality
as to act as earth improving agents when they are degraded. The cover film
of the invention is thus an extremely advantageous film to be used in
plant growing and it is degraded in the environment and the rate of
degradation can be regulated after the use (one month to two years). The
strength of the film can be regulated to withstand the application
conditions by taking the thickness of the film, the fastening technique
and weather conditions into consideration. In addition, the particle size
of the biological material is regulated after the use.
The film material of the present invention can also be used as packing
material.
The present invention affords a new advantageous way to include reactive
groups in film materials since the biological material is coated with
chemically reactive material, with vegetable oil, the effect of which is
directed to the carbon-carbon bonds of the polymer and the coatings of the
particles of the invention have a positive influence on their mixing
properties with the synthetic polymers. In use, the layer of film that
absorbs light best, is placed against the surface of the earth, and the
entire film is fastened on the surface of the substrate. The rate and
manner of degradation of the film is regulated so that weeds do not have
time to produce seeds during the growing season. The film is regulated to
remain until the end of the growing season and the degradation proceeds by
way of a "fragment form" that is harmless from the standpoint of the
harvesting of the crops. The final degradation by moulding takings place
at the beginning of the following growing season.
The variation possibilities of the film material of the invention are
extensive and have several advantages.
The film can advantageously be used in connection with the method in which
the entire area of the growth surface is covered with a cover film, in
which method the growth of the weed is prevent (Finnish Patent Application
No. 891906).
The film transmits light and the plant penetrates the film only at sowing
and setting time. The use thereof raises the average temperature of the
growth and retains moisture, at the same time that the forming of a
temperature or humidity gradiant in the earth is prevented. Under the
film, the earth becomes overgrown with grass, in other words, the
biological activity increases and the compression of the earth is
prevented. The up take of food by the plants is improved, the need for
fertilization is decreased, ventilation occurs earlier and the yield is
increased. The ability of the plants to withstand diseases and their
preserving properties are improved.
The cover film of the invention and the cover growing technique form a new
growing culture and the advantages thereof as best used in the application
system of the Finnish Patent No. 891905.
DESCRIPTION OF PREFERRED EMBODIMENT
The following example is given to further illustrate the present invention.
The scope of the invention is not, however, meant to be limited to the
specific details thereof.
EXAMPLE
500 kg barley starch (dry) was suspended in 100 liter of cold aqueous
suspension of CaCl.sub.2 containing 500 mg calcium per liter. The pH of
the suspension was regulated to between 6.0-6.5. The suspension was
vigorously agitated.
The temperature of the suspension was raised in a thermostatic reaction
vessel to 55.degree. C. during vigorous agitation.
100 mili. novo units of .alpha.-amylase enzyme was added to the suspension
in a 5 liter vessel and maintained therein until the average particle size
of the barley starch was decreased to a value below 500 .mu.m. This
required fifteen minutes.
The suspension of starch-enzyme wa added to 50 liter vegetable oil (rape
oil) containing a small amount of an emulsifier. The suspension was
vigorously agitated while cooling to a temperature of 10.degree. C.
The cold suspension was left standing for twelve hours whereby the
particles coated with enzyme and oil precipitated to the bottom of the
reaction vessel and the oil that had not been bound to the particles was
separated on the surface of the water.
The aqueous phase was removed from the reaction vessel between the
precipitate of the particles and the thin oil layer on the surface.
500 liters CaCl.sub.2 solution (the same as at the start of the process)
was added to the concentrated suspension and vigorously agitated so that
the remaining water soluble small molecules were washed away with the
aqueous suspension. The suspension was then permitted to stand for twelve
hours under cool conditions. The aqueous layer was again removed.
The concentrated suspension was vigorously agitated so that all of the
added oil was mixed with the particles. The suspension was dried with a
spray dryer provided with a nozzle of the Rotary Atomizer type so that the
dry content of the final product was 95%.
The dried powder was finely divided by a spray divider to decompose the
larger particles formed in the spray dryer back to the particle structure
formed in the reaction vessel and at the same time the particles were
dried to a dry content of 99%. The spray powdering device used was the
Finnpulva Oy FP2 device. A pressure of 7 bar and a temperature of
150.degree. C. was used in the FP2 device.
From the powder produced in the FP2 device, the distribution of the
particle size was defined by means of a Malvern 2600 device to define a
suitable enzyme concentration and reaction time in the reaction vessel so
that the desired particle size was obtained.
The resulting powder was mixed with polyolefin in a film extruder and the
resulting film was extruded therefrom for use as covering for growing
plants, and the like.
While the invention has been described with respect to specific details, it
is apparent that variations and modifications of the invention can be made
without departing from the spirit or scope thereof.
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