Note: Descriptions are shown in the official language in which they were submitted.
208~7~
A PROCESS FOR SIZE-REDUCING SOLID ORGANIC POLYMERS
BACKGROUND OF THE INVENTION
All processes for the recycling of solid organic polymers
(e.g., plastics) comprise a size-reducing stage. The cost of
the size-reducing stage generally determines the economy o~ the
process. Moreover, the cost factor decides whether the
ecologically desirable recycling of waste plastics is actually
practicable. Inexpensive size reduction is also desirable for
organic natural polymers, such as cellulose (wood, straw).
lo Accordingly, the problem addressed by the present
invention was to provide a process which would enable powders
to be efficiently produced from solid organic polymers
including plast;cs, rubber-plastic composites or
plastic-containing mixtures and blends and organic natural
polymers, such as cellulose (wood, straw).
The s;ze reduct;on of such materials in mills or extruders
is already known. Where mills are used, the starting materials
must already be s;ze-reduced to a s;gn;f;cant extent -
generally shredded and then granulated. However, with very
small particle sizes, as required for many recycling processes,
mills of any design are too expensive because machines of this
type allow only low throughputs. In many cases, powders can
only be produced by cryogenic grindiny which is very expensive
in energy costs due to the refrigerants required.
Another known method for the size reduction of waste
rubber is the use of extruders (e.g., German
Offenlegungsschrift 3,332,629 and J. Janik and L. Bouskova,
Int. Polym. Sci. Technol. (1990) 17(3), T/33/T37). However,
even with this method the materials again have to be
size-reduced (generally granulated) beforehand. Difficulties
are also presented by bridge formation in the feed zone of the
extruder where the materials involved are of only low density
and have a highly fissured surface which makes continuous
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powder production difficult. Known extruder grinding processes
yield powders having a particle size in the range from 300 ~m
to 500 ~m
It is also kno~n that pieces of used rubber can be
granulated on grooved rollers. In this case, special grooved
rollers are used for preliminary s;ze-reduction of pieces of
old tires for extruder grinding. Minimum particle sizes oF
approximately 3 mm are obtained.
DESCRIPTION OF THE INVENTION
It has now surprisingly been found that the above
difficulties can be overcome by using rollers and applying the
process described in detail hereinafter.
Accordingly, the present invention relates to a process
for the size reduction, preferably to powder, of solid organic
polymers (including plastics or plastic-containing composites
or mixtures or blends and organic natural polymers, such as
cellulose (wood~ straw)~ between rollers which rotate in the
same direction or in opposite directions with a predetermined
speed ratio or a predetermined shear rate ratio in the roller
20 gap.
The process according to the inventiDn is characterized in
that
a) a shear rate of 0.0001 sec~1 to 100,000 sec~1 is
maintained in the gap and
b) the solid oryanic polymers used either on their own
or in the form of composites or mixtures or blends
have a minimum density of 0.5 kg/m3.
It is known that there are various geometries for the
design of rollers. For example, cylindrical or conical rollers
may be used.
The solid organic polymers used preferably have a size of
1 mm to 1 m ~nd, more preferably, 1 mm to 10 cm with
thicknesses of up to about 10 cm.
~he rollers are operated in such a way that a shear rate
of from O.OOOI to 100~000 sec~1, preferably from 100 to 20,000
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sec 1 and most preferably from 1,000 to lO,000 sec l is
maintained in the roller gap.
Preliminary size reduction depends on the material ~-
involved, but in general is only necessary to a particle
diameter of about 10 cm. The materials to be size reduced may
be cooled. However, they are preferably used without cooling.
The rollers may be heated during the grinding process, but are
preferably not heated; i~stead they are cooled to dissipate the
heat generated during the grinding process.
In one particular embodiment of the process, the rollers
have an operating temperature of 0C to 200~, preferably in
the range from 0C to 30C and more preferably in the range
from 10C to 25~C.
The rol1ers used can have a mat or, preferably, a smooth
surface.
In another particular embodiment, the rollers form a gap
below 1 mm, preferably below 0.5 mm and more preferably below
0.1 mm during grinding.
The material being size-reduced is preferably cooled
during grinding. This may be done directly by addition of wacer
or indirectly by cooling of the rollers. Cooling is
particularly advantageous ~Jhere the material to be ground is
relatively hard and elastic.
The grind;ng process may be carried out in various ways.
For example, it is possible when using only one pair of rollers
to decrease the roller gap based upon the particle size of the
material being ground as grinding progresses by displacing one
of the rollers in the direction of the other roller. In this
case, the material to be ground is passed repeatedly through
the roller gap. It is also possible to arrange several rollers
in a cascade and optionally to make the roller gaps gradually
smaller.
Several different or identical roller assemblies in a
cascade have the additional advantage that a relatively fine
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particle size can be obtained in a continuous grinding process
with higher throughputs.
The present ;nvent;on affords many advantages wh;ch could
not be achieved by hitherto known processes, namely:
- large fragments can be fed into the size reduction
step without significant preliminary size reduction
- solid organic polymers differing considerably in
density may be processed together
- very soft organic polymers of low dens;ty can also be
~o size-reduced
- mixtures of thermoplastics and thermosets can be
processed
- mixtures of brittle and elastic or soft and elastic
materials can be processed
~ it is now possible to injection-mold mixtures o~
thermoplastics and thermosets which, hitherto, could
not be injection-molded because of an excessive
thermoset component or ~hich now have better
properties because the thermoset particles are now
embedded very firmly in the thermoplastic matrix by
virtue of their very small size and good distribution
- particularly fine-particle powders can be produced
- where the grinding machine is encapsulated, halogen
containing blow;ng gases are effectively released
from the cells of foamed polymers and extracted.
The process is economical so that many recycling measures
based on powder/granules can also assume economic s;gnificance.
In addition, the following features are associated with the
process according to the invention:
- all plastics and organic natural polymers can be
size-reduced.
- all plastics and organic natural polymers in any
combination may be size-reduced together.
- all plastics and organic natural polymers in any form
of an - optionally only partial - force-locking bond
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may be size-reduced together. The temperature profi1es and
shear ratios of the roller grinding process may also be
selected so that, in the event of a force-locking ~ond
between lamination, surface coating, decorations and other
surface coatings and foam-like support, the support is size-
reduced while the lamination remains largely intact. ~
- all plastics and organic natural polymers in any form of a `
mixture or blend may be size-reduced together.
- all plastics and natural organic polymers in any form of a
mixture, blend or composite with any non-plastics may be
size-reduced together, for example, wood, glass, ceramic,
cloth or metal.
Preferred plastics are thermoplastic or thermoset polyurethanes,
polyurethane ureas or polyureas, blends/composites thereof with other
plastics; polycarbonàte and polycarbonate b1ends with other plastics;
acrylonitrile-butadiene-styrene ("ABS") polymers and ABS blends with
other plastics; polyvinyl chloride ("PVC") and PVC blends with other
plastics; polypheny1ene su1fide ("PPS") and PPS blends with other
p1astics; polybutylene terephthalate ("PBT") and PBT blends with
other plastics; liquid crystal polymers ("LCP") and LCP blends with
other plastics; polyethYlene terephthalate ("PET") and PET blends
with other plastics; polyether ketones ("PEK") and PEK blends with
other plastics; styrene maleic acid anhydride ("SMA") and SMA blends
with other plastics; polystyrene ("PS") and PS blends with other
plastics; polytetrafluoroethylene ("PTFE") and PTFE b1ends with
other plastics; po1ymethylmethacrylate ("PMMA") and PMMA blends with
other plastics; polyoxymethy1ene ("POM") and POM b1ends with other
p1astics; polyamide or polyamide blends with other thermoplastics;
polyolefins or polyolefin blends with other thermoplastics.
The plastics mentioned may be further modified. lhus,
they may contain typical inorganic (preferably mineral) or
organic fillers or reinforcing materials in fibrous form, sheet
form or any other form with continuous or discrete structures.
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They may also contain typical processing aids or additiYes for
improYing mechanical properties, surface or ageing properties.
The plastics may also be lacquered or otherwise
surface-modified by currentless or electrolytic metallization
or plating, surface etchiny, or plasma treatment.
Particularly preferred plastics are thermoplastic or
thermoset polyurethanes, polyurethane ureas or polyureas as
described, for example, in Kunststoff-Handbuch, Vol. 7,
"Polyurethane", Carl Hanser Verlag, Munchen/Wien, 1st Edition,
1966 and 2nd Ed;t;on, 1983. These polyurethanes, polyurethane
ureas or polyureas have a density above 0.5 kg/m3 and are used,
for example, for the production of bumpers, roofs, glove
compartments, boot linings, interior door linings, head
restra;nts, seats, dashboards, consoles, in energy-absorbing
foams, and the like.
Other part;cularly preferred mater;als are compos;tes or
m;xtures of these thermoplastic or thermoset polyurethanes,
polyurethane ureas or polyureas with materials of the type used
for the production of composites, for example glass mats,
textiles, plast;c films, ~oam films, wood or even
thermoset~bonded cellulose materials.
The powders thus produced are su;table as a start;ng
mater;al for various recycling techniques:
- thermoplastics may be subjected in powder form to
convent;onal thermoplastic process;ng and can be
processed and blended relatively easily.
- polyurethanes may advantageously be used in thls
powder form ;n chemolytic processes, for example
glycolysis, alcoholysis, aminolysis and hydrolys;s.
- the powder form is also advantageous for flow molding
and ;nject;on mold;ng; -th;s appl;es ;n part;cular to
lac~uered starting material.
- for use as a filling material similar to or identical
with the matrix ;n polyurethane res;n formulations,
the powder form ;n f;ne distr;bution ;s an essent;al
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requirement for good properties and a good surface
finish.
- the polymer powders thus produced can be used with
advantage for thermal treatment processes.
The invention is further illustrated but is not intended
to be limited by the following examples in which all parts and
percentages are by weight unless otherwise specified.
EXAMPLES
Berstorff type SK 6612 laboratory rollers (Berstorff,
Hannover) were used in the Examples. This machine comprises
two f;xedly mounted rollers 62 cm in circumference and 45 cm in
length rotatable independently at speeds of 7 to 31.5 minl.
The roller gap can be reduced to less than 0.025 mm. The
rollers are not heated dur;ng grinding.
The particle size distribution was measured with a Malvern
Particle Sizer, Model 2600 (Malvern, Ct. Malvern, UK). This
measuring instrument operates on the basis of light diffraction
spectroscopy in the particle size range from l ~m to about 1
mm.
For measurement, the powder-form samples were stirred into
water and dispersed for about 60 secs. with ultrasonication
(using a Branson XL machine manufactured by Branson,
Hilden/FRG). The average particle sizes indicated are those
particle si~es (= diameter of the spheres of equal mass) at
which 50% of all the particles are smaller and 50% of all the
part;cles larger than the value indicated.
Examp3e 1
A glass-fiber~reinforced RIM polyurethane urea with a
density of about 1,200 kg/m3 was used ~or powder product;on.
This starting material had been produced as described below
using a polyol component consisting of:
67.40 parts of a polyether, OH value 35, obtained by
successive addition of first 87% by weight
propylene oxide and then 13% by weight ethylene
oxide to trimethylol propane
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24 parts of a mixture of 65 parts 1-methyl-3,5-
diethyl-2,4-diaminobenzene and 35 parts
1-methyl-3,5-diethyl-2,6-diaminobenzene (DETDA)
2 parts of a polyricinoleic acid ester with an
acid value > 5
4.7 parts of a 2:1:1 mixture of DE~DA, zinc stearate
and bis-(3-dimethylaminopropyl)-amine
0.7 part Dabco 33 LV, an aminic catalyst made by Air
Products
0.1 part UL 28, a tin catalyst made by Witco
0.1 part B S404, a siloxane stabilizer made by
Goldschmidt AG
lO0 parts of this polyol formulation were mixed with 45.6
parts ground Glasfaser MF 7901 (a prDduct of Bayer AG,
Leverkusen/FRG), corresponding to a glass content of 22.5% by
weight.
100 parts of this polyol/glass mixture were processed with
40 parts of a polyisocyanate on the principle of reaction
injection molding using a closed plate mold to form a plate-like
molding of 295 x 180 x 4 mm. The polyisocyanate used was a
reaction product of 4,4'-diisocyanatodiphenyl methane with
tripropylene glycol having an NC0 content of 24.5~ by weight.
The molding thus produced was subjected to mechanical
preliminary size reduction into fragments measuring 10 cm x
10 cm x 4 mm.
These fragments were ground on the rollers under the following
conditions (~ithout further size reduction):
Speed roller 1: 24 min~1
Speed roller 2: 6 min 1
Roller gap: 180 um
Average shear rate: 1,047 sec
Number of passages through the roller gap: 3
Average particle size obtained: 200 ~m
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Example 2
This Example describes the size reduction of polyurethane
foam with a density of 450 kg/m3. The foam was produced as
follows:
90 g polyether (molecular weight 4,800~ obtained by
addition of propylene oxide (87%) and ethylene
oxide (13%) onto trimethylol propane,
2.5 g water,
2 9 ta11 oil and
0.4 g d;methylaminopropyl formamide were mixed with 47
g of a polyphenyl polymethylene polyisocyanate,
which had been obtained by phosgenation of an
aniline/formaldehyde condensa~e and had an NCO
content of 31~o by weight, and the resulting
mixture was introduced into the mold.
A temperature-controlled metal plate mold with cavity
dimensions of 20 x 20 x 4 cm was filled ~ith the mixture o~
sta~ting materials mentioned above. The molding was demolded
after a reaction and cure time of 5 minutes.
The moldings obtaine~ were separately heated in a
recirculating air drying cabinet at 120C; the density of the
foam was about 450 kg/m3.
The plate was then roller-ground under the following
conditions without preliminary size reduction:
Speed roller 1: 20 r.p.m.
Speed rol1er 2: 10 r.p.m.
Roller gap: 60 um
Average shear rate: 1,745 sec
Number of passages through the roller gap: 3
3o Average partic1e size obtained:65 ~m
Example 3
This Example describes the production of powder from
flexible polyurethane foam with a density of about 50 kg/m .
The following formulation was used for production of the
flexible foam:
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A component:
100 parts polyether polyol, OH value 28~ obtained by
propoxylation of trimethylol propane and
subsequent ethoxylation of the
propoxylation product (PO:EO ratio by
weight = 87:13)
3 parts water
0.12 part bis-dimethylaminoethyl ether
0.5 part a 33% by weight solution of
lo triethylenediamine in dipropylene glycol
0.6 part a mixture of aliphatic amines ("Vernetzer
56", a product of Bayer AG)
0.4 part a commercially available polysiloxane
stabilizer (Stabilisator KS 43, a product
of Bayer AG)
B component:
50.7 parts a polyisocyanate mixture of the diphenyl
methane series with a content of 85% by
weight d;isocyanatod;phenyl methane isomers
which in turn consist essentially o~ 25% by
weight 2,4'-diisocyanatodiphenyl methane
and, for the rest, of 4,4'-diisocyanato-
diphenyl methane.
~he A component was mixed with the B component in a
high-pressure mach;ne and the reaction mixture was introduced
into a 40 liter box mold heated to about 50C. The mold was
closed and the molding was removed from the mold after about 6
minutes. The filled weight was 2.38 kg.
Mechanical data:
Density, DIN 53 420: 55 kg/m
Compression hardness, DIN 53 577: 6.4 kPa
Tensile strength, DIN 53 571: 158 kPa
Elongation at break, DIN 53 571: 132%
Compression set, DIN 53 572 50% Ct value: 6.7%
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The foam thus produced was direct1y roller-ground under the
following conditions without further preliminary size reduction:
Speed rol1er 1: 20 r.p.m.
Speed roller 2: 10 r.p.m.
Roller gap: 100 ,um
Average shear rate: 13047 sec 1
Number o~ passages through the roller gap: 3 `-
Average particle size obtained: 127 ~m
Example_4
This Example describes the size reduction of a composite element
of the type used, for example, for dashboards in auto manufacture. :
This composite element has the fol10wing material composition:
PVC/ABS cover film, foam (for ~ormulation, see Example 2 above),
Fibrit support (phenolic-bonded cellulose material).
Speed roller 1: 28 r.p.m.
Speed roller 2: 10 r.p.m.
Roller gap: 75 um
Average shear rate: 2,515 sec 1
Number of passages through the roller gap: 4
Average particle size obtained:80 ,um
Example 5
Straw o~ the type left as waste after the threshing of
harvested wheat was cut to a length of 10 cm to 40 cm and reduced
to powder on the rolls.
Speed roller 1: 31 r.p.m.
Speed roller 2: 8 r.p.m.
Roller gap: 55 ,um
Average shear rate: 4,380 sec 1
Number of passages through the roller gap: 4
Average particle size obtained: 0.1 mm
Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely ~or that purpose and that variations
can be made therein by those skilled in the art without departing
from the spirit and scope of the invention except as it may be
limited by the claims.
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