MXPA97006379A - Recycling of polyurethanes microcelula - Google Patents

Abstract

The polyurethanes are recycled by grinding to particle sizes of 0.01 to 2 millimeters and further to the polyaddition mixture to prepare polyurethanes of (a) polyisocyanates, (b) substances reactive to isocyanates and having active hydrogens, and, if desired, (c) chain and / or crosslinking elongation agents, catalysts, swelling agents and customary additives in an amount of 0.1 percent to 40 percent by weight, based on the mixture of polyadici

Description

"RECYCLING OF MICROCELLULAR POLYURETHANES" The present invention relates to a process for the recycling of icrocellular polyurethanes. Chemical processes such as hydrolysis, hydrogenation, pyrolysis and glycolysis are suitable for the recycling of polyurethanes. In addition, the polyurethanes can be dissolved in isocyanates and the resulting mixture, after purification, can be reused (DE-A-43 16 389). Common to these processes is the fact that polyurethanes can be reintroduced into their production process only at considerable cost and usually not without a loss of quality (eg, reduced isocyanate content in the component after dissolution). ). Additional processes for recycling include the preparation of compacted polyurethanes of crushed elastomers ("flaking bonds") or use as fillers or fillers in the preparation of new components ("Recycling of Polyurethanes - Current State Report", KW Kroesen and DA Hicks, 1993, Cellular Polymers, document 16, 1-6). The introduction of crushed polyurethanes into the polyol component for preparing polyisocyanate polyaddition products is described in US Patent Number 4 692 470, wherein the air introduced with the polyurethanes caused considerable problems which became evident in an undesirable increase in viscosity . This problem was solved by moistening the polyurethane crushed with volatile hydrocarbons. The addition of these substances can be disadvantageous for systems in which these materials are not used as swelling agents and should be avoided. A loss in the quality of the polyurethane that is prepared using recycled polyurethanes compared to the recycled elastomers can only be avoided with difficulty in the known processes, particularly in the case of microcellular polyurethane elastomers. An object of the present invention is to develop a process for the recycling of polyurethanes, where these can be reintroduced into the production process to prepare polyurethanes without losses in quality that have to be accepted. We have discovered that this object is achieved by grinding the polyurethanes and using them in a first reaction step together with a mixture comprising the ground polyurethanes in an amount of 0.1 percent to 40 percent by weight, based on the polyaddition mixture. (a) polyisocyanates, (b) substances which are reactive to isocyanates and contain active hydrogens, and, if desired (c) chain and / or crosslinking agents, catalysts, swelling agents and customary additives, for preparing a prepolymer and in a second step, react this prepolymer with water and, if desired, (c) to provide the polyurethane. Polyurethanes crushed by known milling methods and having a preferred particle size of 0.01 to 2 millimeters, in particular 0.1 to 2 millimeters, are preferably based on the components (a), (b) and if used, (c) used in the polyaddition. According to the present invention, the proportion of comminuted polyurethanes can be from 0.1 percent to 40 percent by weight, preferably from 1 percent to 20 percent by weight, based on the weight of the polyaddition reaction mixture. The polyurethanes used usually have a cellular structure. Preference is given to the use of cellular polyurethane elastomers, preferably with particularity to microcellular polyurethane elastomers, in particular those having the same structure as those which are capable of being obtained from the starting materials (a), (b) and , if desired (c), by means of a polyaddition reaction. This has the advantage that microcellular polyurethane elastomers can, due to their remarkable buffering properties together with excellent volume compressibility, be recirculated to produce shock and vibration damping systems (for a total view of microcellular polyurethane elastomers)., see for example: "Naphthalene 1,5-Diisocyanate as a Building Block for High Performance Polyurethane Elastomers", E.C. Prolingheuer, J.J. Lindsay and H. Klei ann, 1989, Journal of Elastomers and Plastics, 21, 100-121). Specific preference is given to the use of microcellular polyurethane elastomers obtained as waste from the production process where they will be recycled. Before use according to the present invention the ground polyurethanes are sufficiently dried by known methods. Drying is usually carried out at a temperature of 80 ° C to 150 ° C and is usually completed after 1 to 24 hours. To prepare the polyurethane elastomers, the substances (a) and (b) and the comminuted polyurethanes, if desired together with (c), are reacted with an equivalence ratio of NCO groups to the sum of the reactive hydrogens of 0.8 to 1.2: 1, preferably 0.95 to 1.1: 1, by the process of a single operation that is described in the literature, at generally customary temperatures of 80 ° C to 160 ° C, preferably 90 ° C to 150 ° C ° C. The comminuted elastomers can be introduced into the component (b) and / or into a prepolymer, preferably in the prepolymer, without prior wetting of the ground material with the volatile substances, as is necessary in accordance with US Pat. No. 4,692,470 During the usual processing time of the prepolymer or the 5 hour reaction mixture, an increase in viscosity or a decrease in reactivity does not have a detrimental effect on the production process. Preference is given to employing the prepolymer process where, in particular, prepolymers containing isocyanate are used. These may be prepared by reacting a mixture comprising the comminuted polyurethane elastomers and at least one organic polyisocyanate (a), at least one compound (b) which is reactive to the isocyanates and, if desired, (c). The prepolymers preferably have isocyanite contents of 1 percent to 30 percent by weight, particularly preferably 3 percent to 15 percent by weight, based on total weight. The synthesis of the prepolymer is usually carried out at a temperature of 80 ° C to 160 ° C, preferably 90 ° C to 150 ° C. The reaction is usually completed after 15 to 200 minutes. This prepolymer is subsequently reacted to a mixture consisting of component (b) and, if desired, (c), and having an equivalence ratio of NCO groups to the sum of the reactive hydrogens from 0.8 to 1.2: 1 , preferably from 0.95 to 1.1: 1, to provide the desired polyurethane elastomer. The appropriate substrates (a) and (b) for preparing the microcellular polyurethane elastomers are the known compounds of polyurethane chemistry, about which the following can be said:; a) The polyisocyanates (a) used are aromatic, aliphatic and / or cycloaliphatic diisocyanates. Examples of the aromatic diisocyanates are: 1,5-naphthylene diisocyanate (1,5-NDI), 2,4- and 2,6-toluene diisocyanate (TDI) and also their mixtures, 2,4'-, 2 , 2'-diphenylmethane and preferably 4,4'-diisocyanate (MDl) and also mixtures of at least two of these isomers, 3,3'-dimethylbiphenyl diisocyanate, e.g., 3, 3'-dimethyl- 4,4 '-diisocyanatobiphenyl, 1,2-diphenylethane diisocyanate and phenylene diisocyanate, preferably 1,4-phenylene diisocyanate (PPDI). The aromatic isocyanates are used individually or as a mixture of at least two different isocyanates. The aliphatic, branched or preferably linear diisocyanates having from 4 to 2 carbon atoms, preferably from 4 to 6 carbon atoms, which may be mentioned are. 1,12-diisocyanate of dodecane, 1,4-diisocyanate of 2-ethylbutane, 1,5-methylpentane diisocyanate and / or 1,5-butane diisocyanate, preferably 1,6-hexamethylene diisocyanate (HDI). Cycloaliphatic diisocyanates having from 6 to 18 carbon atoms, preferably from 6 to 12 carbon atoms in the alkylsubstituted or non-alkylsubstituted cycloalkyl radical which can be used are, for example: 1,3- and / or 1, 4- cyclohexane diisocyanate, 2,4- and / or 2,6-hexahydrotolylene diisocyanate, 4, '-, 2,4'- and / or 2,2'-dicyclohexanomethane diisocyanate, preferably 1-isocyanato- 3 , 3, 5-trimethyl-5-isocyanatomethylcyclohexane (IPDI): b) Compounds (b) that are reactive to isocyanates usually comprise polyhydroxyl compounds having a functionality of 2 to 3, preferably 2, of a molecular weight of 500 to 6000 grams per mole, preferably 800 to 3500 grams per mole, particularly preferably 1000 to 3300 grams per mole. Examples of the compounds that can be used as (b) are: polyester polyols derived from organic dicarboxylic acids and / or dicarboxylic acid derivatives and dihydric or trihydric alcohols, and / or dialkylene glycols, polycarbonates containing hydroxyl, hydroxycarboxylic acids or lactones, polyacetals such as water-insoluble polyoxymethylenes or methylals such as polybutanediol methylal or polyhexanediol methylal, polyoxyalkylene polyols, such as polyoxybutylene glycols, polyoxypropylene glycols, polyoxybutylene polyoxypropylene glycols, polyoxybutylene polyoxyethylene glycols and polyoxybutylene polyoxypropylene polyoxyethylene glycols or mixtures of at least two of the aforementioned polyhydroxyl compounds. Preference is given to the use of difunctional polyhydroxyl compounds which are selected from the groups consisting of polyester polyols, hydroxyl-containing polycarbonates and polyoxybutylene glycols and also mixtures of at least two of these groups. The polyhydroxyl compounds can be prepared by known methods. Otherwise, the reaction can be carried out under conditions known per se and using customary additives as described, for example, in Patent Number EP-A-482 476. In this way, the known chain-lengthening agents customary (v.gr, diamines and alkanolamines, preferably alkanediols having from 2 to 12 carbon atoms, particularly preferably having 2, 4 or 6 carbon atoms, and dialkylene glycols as well as polyoxylaylene glycols) and / or at least the trifunctional crosslinking agents can be used in a weight ratio of 5 percent to 50 percent by weight to prepare the rigid polyurethane elastomers, preferably from 30 percent to 50 percent by weight based on the component (b). In addition, known swelling agents such as materials having a boiling temperature at atmospheric pressure within the range of -40 ° C to 120 ° C, gases and also solid swelling agents and water, customary catalysts such as inorganic and organic tin compounds and intensely basic amines, e.g., in a proportion of 0.001 percent to 3 percent by weight, in particular from 0.01 percent to 1 percent by weight, based on the weight of the components ( a) and (b), the chain-lengthening agents and cross-linking agents and also the ground polyurethane elastomers and the customary additives can be used. The additives may comprise, for example: substances of a surfactant, foam stabilizers, cell regulators, fillers or fillers, flame retardants, nucleating agents, oxidation inhibitors, stabilizers, lubricants and mold release agents, coloring substances and pigments. Additional details regarding the usual basic auxiliary starting materials and additives can be prepared in the specialized literature (see, inter alia, "Kunststoff-Handbuch", volume 7, Polyurethane, Second Edition, 1983, edited by G. Oertel, Carl Hanser Verlag, Munich). The microcellular polyurethane elastomers prepared by the process of the present invention have densities of 0.35 to 0.80 gram per cubic centimeter and are used to produce molded parts which, because of their very good damping properties, are used, inter alia, for spring elements and dampers, e.g., in vehicles and in machine construction. The microcellular polyurethane elastomers prepared according to the present invention with comminuted microcellular polyurethane elastomers which are incorporated into the reaction mixture and reacted therein have unexpected excellent static and dynamic properties corresponding to those of the comparison products which they have been prepared without the recycled elastomers. This is demonstrated by means of the following examples: Examples Comparison Example 1 a) Preparation of a prepolymer containing isocyanate groups and based on 1, 5-NDI. 1000 grams (0.5 mole) of a polyethanediol adipate having an average molecular weight of 2000 (calculated from the experimentally determined hydroxyl number) was heated to a temperature of 140 ° C and at this temperature they were mixed and reacted with 240 grams. (1.14 moles) of 1.5-NDI solid, while stirring vigorously. This provided a prepolymer having an NCO content of 4.20 weight percent and a viscosity at 90 ° C of 2300 mPas (which is measured using a Haake rotation viscometer, by means of which the viscosities of the following are also measured) examples). b) Production of cellular molding stones The crosslinking component comprised: 20.7 parts by weight of 2,2 ', 6,6'-tetraisopropyldiphenylcarbodiimide 2.9 parts by weight of a mixture of ethoxylated oleic and ricinoleic acids having an average of 9 oxyethylene units 3.8 parts by weight of the monoethanolamine salt of N-alkylbenzenesulfonic acid having alkyl radicals of 9 to 15 carbon atoms 36.3 parts by weight of the sodium salt of sulfated castor oil 36.3 parts by weight of water , and 0.03 part by weight of a mixture of 30 weight percent pentamethyldiethylenetriamine, and 70 weight percent of N-methyl-N 1 - (dimethylaminomethyl) -piperazine 200 grams of the isocyanate prepolymer prepared as described in the Comparison Example and heated to 90 ° C were stirred vigorously for about 8 seconds with 4.64 grams of the crosslinking agent component. The reaction mixture was then placed in a lockable metal mold heated to 80 ° C and the mold closed and the reaction mixture allowed to cure.

After 25 minutes, the microcellular cast was removed from the mold and heated for 16 hours at 110 ° C for additional thermal counting.

Example 1 a) Preparation of a prepolymer containing isocyanate groups and based on 1,5-NDI together with 4 percent of the milled material, 1000 grams (0.5 mole) of a polyethanediol adipate having an average molecular weight of 2000 ( which is calculated from the experimentally determined hydroxyl number) were heated to a temperature of 140 ° C and at this temperature they were mixed and reacted with 240 grams (1.14 moles) of solid 1.5-NDI, while stirring vigorously. After cooling to 90 ° C, the prepolymer was mixed while stirring with 49.6 grams of a crushed microcellular polyurethane elastomer based on 1,5-NDI and which is prepared as described in Comparison Example 1 (particle size) average of 500 micrometers, drying for 6 hours at 120 ° C). This provided a prepolymer having an NCO content of 3.95 weight percent and a viscosity of 3600 mPas. b) Production of the cellular molded parts Shaped parts were produced by a method similar to that described in Comparative Example I from 100 parts by weight of the prepolymer described in Example 1, and 4.36 parts by weight of the component of the crosslinking that is described in Comparison Example Ib. The castings were removed from the mold after 30 minutes and heated for 16 hours at 110 ° C for additional thermal cure.

Example 2 a) Preparation of a prepolymer containing isocyanate groups and based on 1,5-NDI, together with 6 percent of the milled material 1000 grams (0.5 mole) of a polyethanediol adipate having a molecular weight was heated average of 2000 (which is calculated from the experimentally determined hydroxyl number) at a temperature of 140 ° C and at this temperature were mixed and reacted with 240 grams (1.14 moles) of 1.5-NDI solid, while stirring vigorously. After cooling to 90 ° C, the prepolymer was mixed while stirring with 74.4 grams of a crushed microcellular polyurethane elastomer based on 1,5-NDI and prepared as described in Comparison Example I (average particle size of 500 micrometers, drying for 6 hours at 120 ° C). This provided a prepolymer having an NCO content of 3.89 weight percent and a viscosity at 90 ° C of 3700 mPas. b) Production of cellular molded parts Shaped parts were produced by a method similar to that described in Comparative Example I from 200 parts by weight of the prepolymer described in Example 2a and 4.28 parts by weight of the crosslinking agent component described in Comparative Example Ib. The castings were removed from the mold after 30 minutes and heated for 16 hours at 110 ° C for additional thermal cure.

Example 3 a) Preparation of a prepolymer containing isocyanate groups and based on 1,5-NDI together with 8 percent of the ground material 1000 grams (0.5 mole) of a polyethanediol adipate having an average molecular weight of 2000 (calculated from the experimentally determined hydroxyl number) at a temperature of 140 ° C and at this temperature were mixed and reacted with 240 grams (1.14 moles) of 1.5-NDI solid, while vigorously stirring. After cooling to 90 ° C, the prepolymer was mixed while stirring with 99.2 grams of a microcellular polyurethane elastomer crushed based on 1,5-NDI and which was prepared as described in Comparative Example I (average particle size 500 micrometers, dried for 6 hours at 120 ° C). This provided a prepolymer having an NCO content of 3.83 weight percent and a viscosity at 90 ° C of 3800 mPas. b) Production of cellular molded parts Shaped parts were produced by a method similar to that described in Comparative Example I from 200 parts by weight of the prepolymer described in Example 3a and 4.2 parts by weight of the crosslinking agent component. it is described in Comparison Example Ib. The castings were removed from the mold after 30 minutes and heated for 16 hours at 110 ° C for additional thermal cure.

Example 4 a) Preparation of a prepolymer containing isocyanate groups and based on 1,5-NDI together with 4 percent of the milled material 1000 grams (0.5 mole) of a polyethanediol adipate having an average molecular weight of 2000 was heated (calculated from the experimentally determined hydroxyl number) at a temperature of 130 ° C and at this temperature were mixed while vigorously shaken with 49.6 grams of a crushed microcellular polyurethane elastomer based on 1,5-NDI and which was prepared as described in Comparison Example 1 (Average particle size of 500 microns dried for 6 hours at 120 ° C). The mixture was heated to 140 ° C and at this temperature it was mixed and reacted with 240 grams (1.14 moles) of 1.5-NDI while stirring vigorously. This provides a prepolymer having an NCO content of 3.97 weight percent and a viscosity at 90 ° C of 3200 mPas. b) Production of cellular molded parts Shaped parts were produced by a method similar to that described in Comparative Example I from 200 parts by weight of the prepolymer described in Example 4a and 4.32 parts by weight of the crosslinking agent component described in Example lb of Comparison. The castings were removed from the mold after 30 minutes and heated for 16 hours at 110 ° C for additional thermal cure.

Example 5 a) Preparation of a prepolymer containing isocyanate groups and based on 1,5-NDI together with 4 percent of the ground material. 1000 grams (0.5 mol) of a polyethanediol adipate having an average molecular weight of 2000 (calculated from the experimentally determined hydroxyl number) at a temperature of 140 ° C and at this temperature were mixed and reacted with 240 grams (1.14 moles) of solid 1.5-NDI, while stirring vigorously. At a temperature of 130 ° C, the prepolymer was mixed while stirring with 49.6 grams of a crushed microcellular polyurethane elastomer based on 1,5-NDI and which was prepared as described in Comparison Example I (particle size) average of 500 microns) drying for 6 hours at 120 ° C). This provided a prepolymer having an NCO content of 3.97 weight percent and a viscosity at 90 ° C of 3300 mPas. b) Production of cellular molded parts Shaped parts were produced by a method similar to that described in Comparative Example I from 200 parts by weight of prepolymer described in Example 5a and 4.38 parts by weight of the crosslinking agent component. it is described in Comparison Example Ib. The molded parts were removed from the mold after 30 minutes and heated for 16 hours at 110 ° C, for additional thermal curing. The cell castings produced as described in the Comparison Example and in Examples 1 to 5 were used to measure the static and dynamic mechanical properties of the microcellular PU elastomers.

The static mechanical properties measured were tensile strength in accordance with DIN 53 571, elongation at break in accordance with DIN 53 571, resistance to break propagation in accordance with DIN 53 515 and compression solidification at 80 ° C by means of a modification of DIB 53 572 using separators of 18 millimeters of height and test specimens that have a base area of 40 x 40 millimeters and a height of 30 + 1 millimeter. Compression solidification (CS) was calculated according to the equation: H0"H2 CS = • 100 [%] H0 - H! Where HQ is the original height of the test specimen in millimeters, Hi is the height of the specimen of test in the deformed state in millimeters, and? .2 is the height of the test specimen after decompression in millimeters.The dynamic mechanical properties were determined using an increase in displacement (DI) at maximum strength and consolidation (CN). The molded part to measure the consolidation was a cylindrical test spring that has three segment constrictions and a height of 100 millimeters, an external diameter of 50 millimeters and an internal diameter of 10 millimeters. After charging the spring through 100,000 charging cycles at a force of 6 kN and a frequency of 1.2 Hz, the CN was measured as the difference between the initial and final heights of the test spring and was reported as a percentage. Consolidation is a measure of the permanent deformation of cellular PU elastomers during the cyclic fatigue test. The smaller this consolidation is, the better the dynamic performance of the material will be. The height HR to determine the consolidation after the dynamic test is determined after recording the characteristic line of the spring: HQ is the initial height; The molded part is pre-compressed three times using maximum force (maximum force for characteristic lines) and the characteristic line is then recorded in the fourth cycle at a compression rate of 50 millimeters per minute. After 10 minutes, H] _ is determined; this is the height of the component after registering the characteristic line. Only then, the dynamic test begins. HR = residual height after the dynamic test measured after being stored for 24 hours at 23 ° C / 50 percent relative atmospheric humidity after the end of the dynamic test. The reference point (= initial height) used to determine the permanent consolidation after the dynamic test is HQ, the height of the spring in a completely "as new" condition without any compression: "O" HR CN = x xoo [%] H0 The dynamic test was carried out without additional cooling in a room conditioned with air at 23 ° C and relative atmospheric humidity of 50 percent. The mechanical properties measured in the test specimens are summarized in the following table. The static and dynamic mechanical properties of the cellular polyurethane (PU) elastomers of the present invention show no differences compared to the elastomers prepared in the comparison experiment. In this way, as shown in Table 1, the properties such as compression solidification, tensile strength, elongation, resistance to propagation to break, consolidation and displacement increase for Examples 1 to 5 correspond to those for Example I Comparison.

Table Static and dynamic mechanical properties of cellular PUR elastomers as described in Comparative Example I and Examples 1 and 5 Example Comparison Example Proportion of the ground material [%] - 4 6 8 4 4 Content of NCO [%] 4.2 3.95 3.89 3.83 3.97 3.97 Viscosity at 90 ° C [mPas] 2300 3600 3700 3800 3200 3300 Static mechanical properties Solidification by compression 13.9 12 15.3 14.3 14.9 15.8 (80 ° C) [%] Resistance to tension [N / mpr] 4.4 4.9 4.6 3.8 4.6 5.2 Elongation [%] 370 370 340 280 360 380 Resistance to break preparation [N / mm] 16.6 17.1 18.1 16.9 16.4 18.2 Dynamic mechanical properties Consolidation [%] 6-8 6.0- 6.8- 6.0- 5.8- 7.2- 7.0 7.2 7.9 7.2 7.5 Increase in displacement [mm] 1.4- 2.0- 2.-0 1.9- 2.1- 2.4- 2.1 2.1 2.6 2.3 2.2 2.5

Claims (6)

R E I V I N D I C A C I O N E S:

1. A process for the recycling of microcellular polyurethanes which comprises grinding the polyurethanes and using them in a first reaction step, together with a mixture comprising the ground polyurethanes in an amount of 0.1 percent or 40 percent by weight, based on the polyaddition mixture, (a) polyisocyanates, (b) substances which are reactive to isocyanates and contain active hydrogens, and, if desired (c) chain and / or crosslinking agents, catalysts, blowing agents and customary additives, for prepare a prepolymer and in a second step, react this prepolymer with water and, if desired, (c) to provide the polyurethane.

2. A process according to claim 1, wherein the comminuted polyurethanes have a particle size of 0.1 to 2 millimeters.

3. A process according to claim 1, wherein the crushed polyurethanes used are microcellular polyurethane elastomers having the same structure as the polyurethanes obtainable from the starting materials (a), (b) and, if desired, ( c), by means of a polyaddition reaction.

4. A process according to claim 1, wherein the prepolymer has an NCO content of 1 percent to 30 percent by weight.

5. A process according to claim 1, wherein the polyisocyanates (a) used are toluene diisocyanate, diphenylmethane diisocyanate, 3,3 '-dimethyl-4,4'-diisocyanatobiphenyl, an aliphatic diisocyanate having from 4 to 12 carbon atoms or a cycloaliphatic diisocyanate having from 6 to 18 carbon atoms or 1, 5-naphthylene diisocyanate.

6. A process according to claim 1, wherein the component (b) used comprises polyhydroxyl compounds having a functionality of 2 to 3 and a molecular weight of 500 to 600 grams per mole.