CA2086780A1

CA2086780A1 - Process for size-reducing solid organic polymers

Info

Publication number: CA2086780A1
Application number: CA 2086780
Authority: CA
Inventors: Joachim Wagner; Werner Rasshofer; Karl Peltzer
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1992-01-10
Filing date: 1993-01-06
Publication date: 1993-07-11
Also published as: EP0551655A1; KR930016212A; FI930050A; FI930050A0; DE4207972A1; MX9207581A; JPH05269742A; BR9300041A

Abstract

A PROCESS FOR SIZE-REDUCING SOLID ORGANIC POLYMERS

ABSTRACT OF THE DISCLOSURE
For recycling, solid organic polymers can be size-reduced between rollers which rotate in the same direction or in opposite directions with a predetermined speed ratio or predetermined shear rate ratio in the roller gap. A shear rate of from 0.0001 sec-1 to 100,000 sec-1 is maintained in the gap.
The polymers used have a minimum density of 0.5 kg/m3.

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Description

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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 Mo3829 Le A 28 848-US/CA

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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 Mo3829 Le A 28 848-US/CA

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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 Mo3829 L _ 28 848-US/CA

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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 Mo3829 Le A 28 848-US/CA

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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 Mo3829 Le A 28 848-UStCA
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- 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 Mo3829 Le A 28 848-US/CA

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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 Mo3829 Le A 28 848-US/CA

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g 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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Claims

1. A process for the size reduction of solid organic polymers comprising: passing said polymers 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 gap, wherein a) a shear rate of 0.0001 sec-1 to 100,000 sec-1 is maintained in the gap and b) the 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.

2. The process of Claim 1, wherein that the polymer used has a particle size of from 1 mm to 1 m.

3. The process of Claim 2, wherein that the polymer used has a particle size of from 1 mm to 10 cm.

4. The process of Claim 1, wherein the rollers are driven at different speeds.

5. The process of Claim 1, wherein the rollers are operated in such a way that a shear rate of 100 sec-1 to 20,000 sec-1 is maintained in the roller gap.

6. The process of Claim 5, wherein the rollers are operated in such a way that a shear rate of 1,000 sec-1 to 10,000 sec-1 is maintained in the roller gap.

7. The process of Claim 1, wherein the rollers have an operating temperature of from 0°C to 200°C.

8. The process of Claim 1, wherein the rollers used have a smooth surface.

9. The process of Claim 1, wherein the rollers form a gap smaller than 1 mm during grinding.

10. The process of Claim 1, wherein the material to be ground is cooled.

11. The process of Claim 1, wherein said polymer is a chemically and/or physically crosslinked polyurethane, a polyurea, a polyurethane urea or a composite containing a polyurethane(urea).

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