Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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D~SCRIP~ION
This invention relates to compositions includ-
ing plastics, i.e. synthetic polymers and organic
biodegradable fillers particularly natural starch
granules. examples of such compositions are pub-
lished in U.K. Patent Specifications Nos. 1,485,833and 1,487,050.
he present invention is concerned with the
incorporation of the filler part of the formulation.
As the primary application of the invention is to
compositions based on plastics and natural starch
granule formulations we shall hereinafter, in the
descriptive part of the specification, refer to the
Miller as starch. the use of other granular organic
fillers such as lactose is not excluded.
We have proposed incorporating starch composi-
tions by fluxing the plastic material and then
adding the starch in a special purpose machine such
as a mill having two rollers or an internal mixer.
Because this fluxing and adding constitutes an
extra operation before the plastics composition can
be processed in a final conversion operation such as
film extrusion, pipe extrusion, or injection mould-
ing, it adds an extra processing cost to the overall
operation and it is customary to minimise this extra
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cost by making the initial mixing at a high starch
concentration referred to as a l'masterbatch" which
is subsequently diluted with unfilled polymer at
the final conversion, thus reducing the tonnage
passing through the masterbatching stage.
It has occasionally proved possible to add
limited amounts, of the order of 1 - ~/o, of starch
directly to the polymer entering the final conver-
sion operation 7 where the heat softening and mixing
part of the machinetakes the form of an extruder
screw in a heated barrel, but this soon gives rise
to mixing and dispersing problems as the concentra-
tion is raised and, in the case of natural starch,
when the added concentration reaches 15 - 30% an
15 extra complication is revealed in the form of dry
friction between the relatively large starch
granule.
It has now been discovered that this latter
problem can be readily overcome by pre-mixing a small
amolmt of a fluid lubricating substance ultimately
compatible with the polymer., with the starch
whereupon at least 3~/o ox starch can be directly
blended immediately prior to final conversion,
with most thermoplastics. the lubricating substance
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which is plastic in state may be a liquid oil or
a wax meltable into a liquid. The substance will
hereinafter be referred to as a lubricant. It has
further been observed that, when the dry friction
is eliminated by the addition of a lubricant as
described the extreme ease of dispersion of dry
natural starch in molten polymers is developed
to its full, this ease of dispersion being attribu-
table to the virtual absence of very wine particles.
Further in accordance with the invention the
starch is preformed with the lubricant into discrete
particles or pellets which particles or pellets are
mixed with the plastics prior to final conversion.
this is particularly advantageous when the starch
granules are rendered hydrophobic in accordance
with the teachings of U.E. Patent No. 1t~l87~050O
Such granules are difficult to handle and store in
the raw state and the present invention makes it
possible for the hydrophobic starch to be supplied
to converters, extruders etc. as particles or
pellets comprising a blend of starch and lubricant.
urther and in accordance with another aspect
of the invention it has been found possible to use
the starch as a vehicle for introducing into
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plastics compositions a variet;y ox modifying S'lb
stances such as fire retardants, smoke suppres-
sa2ts, fertilisers, crop nutrients such as nitrates
and phosphates and insecticides and the likeO
5 It is necessary thaw these added substances should
be soluble in a solvent which ls no a solvent for
starch grains, thus enabling thy starch grains
to be coated with a su~stantiall~ uniform layer ox
the additive by blending together the additive
l solution at a appropriate concentration and the
starch material followed by a drying stage to re-
move the solvent. This dry stage can conveniently
be achieved by the well known process ox spray
dr~i~g or the operations of mixing and drying can
be combined by introducing the additive solution
into the starch which is being maintained in the
form of a fluid bed by a stream of gas which is at
a temperature appropriate to accomplish the dr~i~g
action.
In accordance with one broad aspect, the
invention relates to a plastics based composition
including starch granules and a modifying substance
of the kind set out in the specification, such
substance being soluble in a solvent which is not
a solvent for starch rains
The following Examples illustrate the two
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aspects of the present invention:
EXAMPLE 1 - Comparative test Yæ ring the
extrusion characteristics of lastics
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blend with and without lubricant.
.
dry blend of natural maize starch grains and
polyethylene granules where the polyethylene had
a melt flow index of 2 and a de~sit~ of o918 was
introduced into the hopper ox an extrusion machine
ox screw diameter 45 mm and : D ratio 20 : 10
the screw was a aormal 3 section diminishing depth
configuration designed for the extrusion ox polo-
ethylene 7 and the machine settings of temperature
and speed were alæo appropriate to the extrusion of
15 polyeth~leneO With a starch concentration of 2~o
by weight the starch friction produced much noise
and the product was obviously i~perfectl~ mixed and
oontai~ed many partioles of burst and discoloured
starch. When this operation was repeated using the
20 techniques of the present inve~ion but using a
tarch which had been cold pretended with a lo
of ethyl oleate, a oil material, calculated on
the weight of the starch together with Lo% of
calcium ~tearate~ another oil material, calculated
25 on the weight of the starch then the extrusion opera-
tion worked normall;sr, producing a smooth and uniform
product with no discolouration. the eth;yl oleate
is an autoxidisable material as described it our
Patent Speci~icatio~ Nos. 1,485~833 and
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1,487,050. The starch granules ma be untreated
but preferably have the surfaces thereof modified
(rendered hydrophobic) by reaction with a compound
which readily reacts with hydroxyl groups to form
an ester or an ether. This is in accordance with the
teachings of Patent No. 1,487~050.
EXAMPLE 2
00 grams of a lubricant, ref`ined paraffin
wax of melting range 50 - 55C was fused in a water
jacketted pan and maintained at a temperature about
10C above its melting point. 600 grams of corn
starch dried to below 1% moixtuxe content and pre-
heated to 70C was added smoothly whilst agitating
the mass with a slow speed stirrer. When all the
starch was dispersed and no lumps or agglomerates
remained the resulting fluid paste was poured into
shallow metal trays and allowed to cool and solidify
in the form of layers some 3 mm thick which were sub-
sequently broken into fragments and sieved through
a screen with 4 mm square apertures yieldirlg uniform
particles or pellets. these granules when mixed
with low density polyethylene of density 00912 arld
melt flow index 2 in the ratio of 8.33 parts by
weight of starch concentrate to 91.67 parts by weight
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of polyethylene could be fed to the hopper of a
conventional film blowing extrusion machine (a 45 mm
screw diameter with : D ratio of 20 : 1 and made
by Samafor limited, France) could be converted to
plastic film of 50 micrometre thickness in which
the starch could be seen to be uniformly dispersed
- and was present at a concentration of ~/o by weight
.
400 grams of refined paraffin wax of melting
range 50 - 55C was fused in a water jacketted
kettleland maintained at a temperature of about
10C above its melting point. 600 grams of warm
dry hydrophobic corn starch (prepared as described
in British Patent Specification NoO 1,4877050 was
then mixed into the fluid wax by low speed stirring
followed by 50 grams of iso-octyl oleate, 50 grams
of calcium oxide of particle size 5 micrometres and
below, and 200 grams of rutile titanium dioxide.
the resulting fluid paste was refired by passing
it through a Pascall & CoO 9" x 3" triple roll mill
with its rolls heated to 60C~ the output being
received in shallow trays where it was allowed to
cool and solidify in sheets about 3 thick
before being broken into fragments and screened through
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a 4 mm aperture sieve. The sieved particles or
pellets were blended with low density pclyethylene
of density 0.912 and MF1 2 in the ratio 11 parts
by weight of granules to 89 parts by weight of
polyethylene before extruding as described in
Example 2 to give a white smooth film 50 micrometres
thick and containing 6% starch, ~/o pigment 0.6%
oleic ester autoxidant and 0.5% calcium oxide dessicant.
600 grams of dry hydrophobic starch prepared
as described in British Patent Jo. 1,487~050 was
placed in a high speed fluidizing mixer made by
~enschel AG and having a mIxing chamber capacity of
about 20 litres. In the mixer were also placed 50
grams of iso-octyl oleate, 50 grams of calcium
oxide powder of particle size,5 micrometres and
less, and 150 grams of roughly powdered paraffin
wax of melting range 50 - 55 C. The mixer was run
at high speed until. the wax fused, and then at
lower speed allowing the temperature to fall to about
40C when the blend could be discharged as a warm
dry powder which could be fed to a single punch
tabletting machine bar Manest~ & Co. The product
from the tabletting machine was in the form of small
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firm uniform tablets (pellet or granule) of dimen-
sions similar to customary plastics granul0s. A
blend of the starch concentrate granules with
polyethene in such proportions as to give a starch
concentration of 6% by weight in the final product
was converted into plastic film as in the previous
examples.
warm blend of starch, iso-octyloleate1
calcium oxide and wax dispersed in a high speed
mixer and discharged warm as described in hxample
4 was transferred to a Manesty Co. 'Rotogran'
oscillating bar granulating machine in which it was
forced by moving steel bars through a coarse
screen. The product was a coarse granular powder
which could be blended with low density polyethylene
and extruded into uniform film as described in
Example 3O
In the above examples 2 to 5 paraffin wax
could be replaced for example by a low molecular
weight polyethylene wax. There is no limitation
to low density olyethylene, successful films
could be blown from High Density polyethylene.
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where is no limitation to film blowiug, thick
sections were extruded in other polyolefines
and also starch filled pol9prop~lene film was
prepared by extrusion casting onto a chilled
casting rollerO
E~MPIE 6 -
I.
slurry was prepared of corn starch in water
by suspending 220 grams of undried maize starch in
1 litre of water. Sufficient ammonium molybdate was
the dissolved in the suspension water to cor-
respond to a final concentration of lo of the
weight of the starch. This slurry was then intro-
duced into the spray system of a laboratory spray
drying unit by compressed air at 'I kg/cm2 and
with the chamber air inlet temperature of 165 and
outlet temperature of 65C. The product recovered
from the output cyclone was a free flow dry white
powder which was used as a filler for plasticised
PVC compositions containing 50 p.h.r. of D.O.P.
plasticiser and 0.5 p~h.r~ of lead stearate stabil-
iser, the modified starch concentration being
adjusted to 3~/0 by weight ox the whole formulationO
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The mixing was accomplished on a steam heated 2-roll
mill at 150C. The product in the form of a sheet
approximately 2.5 mm thick when compared with a
similar formulation except for the ommission of
the ammonium mol~bdate gave rise to a much lower
generation of smoke in a combustion test. Again
the starch granules are preferably rendered h~dro-
phobic in accordance with the teachings of Patent
No. 1~487,050.
