EP4642834A1

EP4642834A1 - Recycling process

Info

Publication number: EP4642834A1
Application number: EP23843983.0A
Authority: EP
Inventors: Lukas Friedrich Berto WILM; Markus Schuette; Stefan Bokern; Elmar Poeselt; Goekhan BAKIS; Heinz-Dieter Lutter; Alina WILDEIS; Laura Meyer; Philipp Maximilian JUNG
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2022-12-30
Filing date: 2023-12-29
Publication date: 2025-11-05
Also published as: KR20250133909A; JP2026502381A; CN120435508A; WO2024141650A1

Abstract

The present invention relates to a process for recycling a polyurethane from a composition comprising an elastic polyurethane (PU1) and at least one further material comprising the steps of providing a composition (CW) comprising a polyurethane (PU1) and at least one further material; bringing the composition (CW) into contact with a solvent mixture (SM) comprising at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). The present invention also relates to the polyurethane obtained or obtainable according to said process as well as the use of the polyurethane accord- ing to the present invention for the preparation of a shaped article.

Description

Recycling process The present invention relates to a process for recycling a polyurethane from a composition com- prising an elastic polyurethane (PU1) and at least one further material comprising the steps of providing a composition (CW) comprising a polyurethane (PU1) and at least one further mate- rial; bringing the composition (CW) into contact with a solvent mixture (SM) comprising at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is en- riched in dissolved polyurethane (PU1). The present invention also relates to the polyurethane obtained or obtainable according to said process as well as the use of the polyurethane accord- ing to the present invention for the preparation of a shaped article. Hand-in-hand with the vigorous growth of the polyurethane production industry, there has been a concomitant increase in the problem of removing and re-using polyurethane waste or reject goods. There is therefore considerable interest both on ecological and on economic grounds for industrially utilizing the ever-increasing quantities of polyurethane waste. Different strategies have been suggested in the literature. US4115298A discloses process for splitting up polyurethane waste into activated polyhydroxy compounds which may be reused for the production of polyurethane plastics. The process broadly comprises reacting the polyure- thane waste with lactams or equilibrium associates of lactams and active hydrogen containing compounds at elevated temperatures. Also US4160749A is directed to a process for dissociating cellular and non-cellular polyure- thane resins into re-usable starting products for the isocyanate polyaddition process, wherein the polyurethane is reacted with associates of lactams and adduct-formers having at least two Zerewitinoff-active hydrogen atoms at elevated temperature. The depolymerization is one way to recover waste products. However, it would be preferable to reuse the polyurethane without depolymerization thus reducing the costs of the process. For ex- ample US 2005/0096400 A1 discloses a method of recycling polyurethane-containing material. The method comprises combining a polyurethane-containing material with a solvent and form- ing a solution of the polyurethane-containing material and the solvent. Multi-material systems are difficult to recycle because not all of the waste components can be recycled through the same process. Examples of multi-material systems are shoe scraps, mixed material fibers or composites. Classic polar organic solvents cannot be used on an industrial scale due to their price, toxicity, explosion hazard and high boiling point. An energy-efficient, non-toxic separation process that selectively extracts polyurethanes PU from multi-material sys- tems does not exist. In particular mixed fibers containing polyurethanes (Spandex, PU) and polyamides are a prob- lem for the textile industry since already slight contamination with Spandex (PU) is enough to prevent the polyamide fibers from being recycled. Therefore, it was an object of the present invention to provide a process for separating elastic polyurethanes from other materials and additives which may be present in a waste composition. This object is solved by a process for recycling a polyurethane from a composition comprising an elastic polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising a polyurethane (PU1) and at least one fur- ther material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising at least one alcohol and at least one compound (A1) selected from the group con- sisting of cyclic amides at a temperature below the boiling point of the alcohol to ob- tain a solution (S1) which is enriched in dissolved polyurethane (PU1). It has surprisingly been found that it is possible to selectively dissolve the polyurethane in the solvent mixture (SM) comprising an alcohol and a cyclic amide, for example a lactam using the process according to the present invention. It has been found that the elastic polyurethane can be dissolved without degradation of the polymeric structure. This allows to recover the polyure- thane from a composition without depolymerizing the polyurethane. Thus, the polyurethane can easily be separated from other materials such as for example polyamide or polyester based fi- bers. The polyurethane (PU1) is an elastic polyurethane, preferably a thermally processable polyure- thane, in particular a thermoplastic polyurethane. It has been found that in particular thermo- plastic polyurethanes which are based on an aromatic isocyanate can be easily dissolved in the solvent mixture (SM) and thus be separated from other materials. Depending on the process conditions used, it is possible to separate for example a thermoplastic polyurethane based on an aromatic isocyanate from other polyurethane materials such as thermoplastic polyurethanes based on aliphatic isocyanates. Generally, polyurethanes are produced by a reaction between a polyisocyanate component and a polyol component. Particularly suitable foams are for example foams which can be thermoplastically processed such as for example foams as disclosed in WO 2019/122122 A1. Further materials, such as flame retardands, polymerization catalysts, fillers, pigments and surfactants may be added in the production process of the polymers. Organic polyisocyanates that can be used in the preparation of polyurethanes are any of the known organic di- and polyisocyanates, preferably aromatic isocyanates. Preferably, an isocya- nate component having a functionality in the range of 1.9 to 2.2 is used according to the present invention, in particular in the range of from 1.95 to 2.1, more preferable in the range of from 1.95 to 2.05, most preferable in the range of from 1.96 to 2.03. Individual examples which may be mentioned are tolylene 2,4 and 2,6-diisocyanate (TDI) and the corresponding isomer mixtures, diphenylmethane 4,4’ , 2,4’ and 2,2’ diisocyanate (MDI) and the corresponding isomer mixtures, mixtures composed of diphenylmethane 4,4’- and 2,4’- diisocyanates, polyphenyl polymethylene polyisocyanates, mixtures composed of diphenylme- thane 4,4’-, 2,4’- and 2,2’- diisocyanates The organic di- and polyisocyanates may be used indi- vidually or in the form of mixtures. If isocyanates having a higher functionality are used in these mixtures, the functionality of the mixture preferably is not more than 2.2. In addition, the propor- tion of isocyanates having a higher functionality must not be more than 10% by weight, prefera- bly not more than 5% by weight, based on the overall mixture of isocyanates. Compounds which may be used for the preparation of polyurethanes which have at least two hydrogen atoms reactive toward isocyanate groups are those which bear at least two reactive groups selected from OH groups, SH groups, NH groups, NH2 groups, and acidic CH groups. Preferably polyols are used and in particular polyether alcohols and/or polyester alcohols whose OH numbers are in the range from 25 to 800 mg KOH/g. According to the present invention, preferably a polyol component having a functionality in the range of 1.7 to 2.2 is used, in partic- ular in the range of from 1.7 to 2.1, more preferable in the range of from 1.7 to 2.05, most pref- erable in the range of from 1.7 to 2.03. It is also possible here to use mixtures of polyols. If poly- ols having a higher functionality are used in these polyol mixtures, the functionality of the mix- ture preferably is not more than 2.2. In addition, the proportion of polyols having a higher func- tionality must not be more than 10% by weight, preferably not more than 5% by weight, based on the overall mixture of polyols. The polyester alcohols used are mostly prepared via condensation of polyhydric alcohols, pref- erably diols, having from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms, with poly- basic carboxylic acids having from 2 to 12 carbon atoms, e.g. succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, or preferably phthalic acid, isophthalic acid, terephthalic acid, or the isomeric naphtha- lenedicarboxylic acids. Polyether polyols particularly used are those prepared by known processes, e.g. via anionic polymerization of alkylene oxides onto H-functional starter substances in the presence of cata- lysts, preferably alkali metal hydroxides or double-metal-cyanide catalysts (DMC catalysts). Al- kylene oxides used are mostly ethylene oxide or propylene oxide, or else tetrahydrofuran, vari- ous butylene oxides, or styrene oxide, and preferably pure propylene 1,2-oxide. The alkylene oxides can be used alone, in alternating succession, or in the form of a mixture. Starter sub- stances particularly used are compounds having at least 2, preferably from 2 to 8, hydroxy groups or having at least two primary amino groups in the molecule. Starter substances used and having at least 2, preferably from 2 to 8, hydroxy groups in the molecule are preferably tri- methylolpropane, glycerol, pentaerythritol, sugar compounds, such as glucose, sorbitol, manni- tol, and sucrose, polyhydric phenols, resols, e.g. oligomeric condensates composed of phenol and formaldehyde, and Mannich condensates composed of phenols, of formaldehyde, and of dialkanolamines, and also melamine. Starter substances used and having at least two primary amino groups in the molecule are preferably aromatic di and/or polyamines, such as phe- nylenediamines, 2,3-, 2,4-, 3,4 , and 2,6 tolylenediamine, and 4,4’-, 2,4’-, and 2,2’ diaminodiphe- nyl¬methane, and also aliphatic di and polyamines, such as ethylenediamine. The preferred functionality of the polyether polyols is from 2 to 8 and their preferred hydroxy numbers are from 25 to 800 mg KOH/g, in particular from 150 to 570 mg KOH/g. Other compounds having at least two hydrogen atoms reactive toward isocyanate are chain ex- tenders which may be used concomitantly, if appropriate. Chain extenders preferably used are alkanolamines and in particular diols with molecular weights below 400, preferably from 60 to 300. The amount advantageously used of chain extenders, or mixtures of these is from 1 to 20% by weight, preferably from 2 to 5% by weight, based on the polyol component. Common polyols used in huge quantities are, e.g., polyester polyols, low molecular weight polyols such as ethylene glycol or propylene glycol, or high molecular weight polyether polyols based on glycerol, ethylene glycol, polypropylene glycol, polytetramethylene glycol, and polyesterpolyols. In addition, one or more blowing agents may also be present in the production of the elastic pol- yurethane used. Blowing agents used may be chemically active blowing agents and/or physi- cally active compounds. Chemical blowing agents are understood to mean compounds that form gaseous products by reaction with isocyanate, for example water and carboxylic acids or carboxylic acid derivatives, for example hydrogencitrates, hydrogencarbonates or azodicarbon- amides, such as Celegoene^ , Tracel^ , Hydrocerol^ or mixtures thereof, water being a preferred blowing agent. Physical blowing agents are understood to mean compounds that are dissolved or emulsified in the feedstocks for polyurethane production and evaporate under the conditions of polyurethane formation. These are, for example, hydrocarbons, halogenated hydrocarbons, and other com- pounds, for example perfluorinated alkanes, such as perfluorohexane, hydrochlorofluorocar- bons, and ethers, esters, ketones and/or acetals, for example (cyclo)aliphatic hydrocarbons having 4 to 8 carbon atoms, hydrofluoroolefins (HFOs), or gases, such as carbon dioxide, or mixtures thereof. In a preferred embodiment, the blowing agent used is a mixture of these blow- ing agents comprising water, more preferably exclusively water. In a preferred embodiment, the water content is from 0.1% to 6% by weight, preferably 1% to 5% by weight, more preferably 2.5% to 4% by weight, based on the total weight of the elastic polyurethane foam. Preferably, the polyurethane (PU1) is based on an isocyanate component having a functionality in the range of 1.9 to 2.2 and a polyol component having a functionality in the range of 1.7 to 2.2. The term “aromatic diisocyanate”, refers to molecules having two isocyanate groups attached directly and/or indirectly to the aromatic ring. Aromatic diisocyanates typically have 8 to 18 carbon atoms. Examples of aromatic diisocyanates include, but are not limited to, 1,2-, 1,3-, and 1,4- phenylene diisocyanates, naphthylene-1, 5-diisocyanate, 2,4- and 2,6-toluene diisocyanate, 2,4'- , 4,4'- and 2,2’-biphenyl diisocyanates, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate, 1,2-, 1,3- and 1,4-xylylene diisocyanates and m-tetramethylxylyene diisocyanate (TMXDI), and mix- tures thereof. Preferred aromatic diisocyanates are 2,4- and 2,6-toluene diisocyanate, 2,4'-, 4,4'- and 2,2’-biphenyl diisocyanates, 2,2'-, 2,4'- and 4,4'-diphenylmethane diisocyanate, 1,2-, 1,3- and 1,4-xylylene diisocyanates and m-tetramethylxylyene diisocyanate (TMXDI) and mixtures thereof. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an ar- omatic isocyanate. It has been surprisingly found that the process according to the present invention allows to se- lectively dissolve the elastic polyurethane using mild conditions, in particular the thermally pro- cessable polyurethane, and separate remaining residues such as polyamides, rubber, EVA, paint, soot, pigments, flame retardants, talc, glass fibers, textiles or even polyurethanes based on aliphatic isocyanates or thermoset polyurethanes by simple filtration. In particular thermoplastic polyurethanes with a low content of chain extender are highly soluble in the solvent mixture (SM). Preferably the content of chain extender in the polyurethane (PU1) is below 40%, more preferable below 30%, in particular below 20%. In particular, the content of aliphatic chain extender in the polyurethane (PU1) is below 20%, more preferable below 15%, in particular below 12.5%. The process according to the present invention comprises steps (a), and (b). The process may also comprise further steps. According to step (a), a composition (CW) comprising a polyure- thane (PU1) and at least one further material is provided. According to step (b), the composition (CW) is brought into contact with a solvent mixture (SM) comprising at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides to obtain a solu- tion (S1) which is enriched in dissolved polyurethane (PU1). The composition (CW) usually comprises further materials such as further polymers or further waste materials. The composition may also comprise additives which are frequently used in pol- yurethanes such as fillers, such as chalk, flame retardants, such as melamine or pigments. The properties of suitable compositions (CW) which may be used in the process of the present invention may vary in broad ranges. Preferably, the elastic polyurethane is thermally processable, in particular thermoplastic and thermally processable. According to the present invention, any waste composition comprising an elastic polyurehtane, in particular comprising a thermally processable polyurethane may be used. For example, waste foams or mixed fibers comprising polyurethanes may be used as a starting material in step (a) of the process of the present invention. The waste composition used in the present invention may be obtained from items produced from polyurethanes at a time after use for the purpose for which they were manufactured. Before subjecting to step (a) of the process of the present invention, the items may be subjected to mechanical comminution that is, further sorting and bringing the items into appropriate sizes, e.g., by shredding, sieving or separation by rates of density, i.e. by air, a liquid or magnetically. Suitable sepatation methods may be supported by spectroscopic analysis such as for example IR spectroscopy. Optionally, these fragments may then undergo processes to eliminate impurities, e.g. paper labels. Depending on the composition of the waste material it may be subjected to extraction to remove soluble additives prior to step (a). The composition (CW) may for example comprise further polymeric materials but also inorganic materials. Depending on the process conditions applied, it is also possible to separate different polyurethanes, in particluar thermoplastic polyurethanes based on aliphatic isocyanates can be separated from thermoplastic polyurethanes based on aromatic isocyanates using mild conditions. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein composition (CW) comprises a polyamide, a polyester and/or a cellulose based polymer. According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein composition (CW) comprises a material selected from pol- yurethanes based on aliphatic isocyanates, a thermoset polyurethanes, rubber, ethylene-vinyl acetate copolymers, soot, talc, pigments or cellulose based polymers. The properties of the waste composition used as starting material in the process according to the present invention may vary in broad ranges. The waste composition can be comminuted by conventional methods, such as for example dis- closed in “Recycling von Polyurethan-Kunststoffen”, W. Raßhofer, Hüthig (Heidelberg), 1994, for example by shredding, e.g. in a rotation mill or rotary mill at room temperature, to a particle size of ordinarily less than 100 mm, or even less than 20 mm, or ground, e.g. by known cold grinding processes. It is also possible that a particle size of less than 5 mm is selected, for ex- ample a particle size in the range of 0.01 mm to 5 mm, and preferably in the range of 0.01 mm to 1 mm. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the composition (CW) is subjected to a mechanical treatment prior to step (a), selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments. According to the present invention, it is also possible to subject composition (CW) to a heat treatment prior to step (a) or between steps (a) and (b) of the process according to the present invention. The composition may be heated to a temperature in the range of from 150 to 220°C, preferably in a range of from 150°C to 200°C, more preferable in a range of from 150 to 170°C. Heating may for example be conducted for a duration from 1 to 120 minutes, preferably from 10 to 90 minutes or particularly preferable from 30 to 60 minutes. Suitable techniques are in princi- ple known to the person skilled in the art and include for example heating the composition in an oven. The treatment may be conducted continuously or also batchwise according to the present invention. According to step (b), a solvent mixture (SM) is used which comprises at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides. It has been found that it is possible to dissolve the elastic polyurethane in the solvent mixture under mild conditions. Step (b) is carried out at a temperature below the boiling point of the alcohol used, for example at a temperature in the range of from 20 to 50°C, preferably in the range of from 15 to 40°C, more preferable at a temperature in the range of from 20 to 30°C. Typically, the treat- ment according to step (b) is carried out for a duration of 1 minute to 48 hours, preferably for a duration of 1 hour to 24 hours, in particular of 1 to 10 hours. According to the present invention, typically at least 50 % by weight of the polyurethane (PU1) present in the composition are dis- solved, for example at least 60% by weight, preferably at least 70% by weight and particularly preferable up to 100% by weight of the polyurethane (PU1) are dissolved in the solvent mixture (SM). Compound (A1) is selected from cyclic amides. In principle, any cyclic amide can be used ac- cording to the present invention, as long as a solvent mixture (SM) with an alcohol can be formed. The cyclic amide is preferably selected from the group consisting of lactams, for example capro- lactam and/or valerolactam, at least one cyclic urea or mixtures thereof, particularly preferably caprolactam. Suitable cyclic amides are for example also compounds containing at least one cyclic urea of the general formula (I): wherein -X- is a 1 to 6-membered, preferably 2 to 4-membered and particularly preferably 3- membered radical which may be substituted. This gives rise to a cyclic urea structure according to formula (I), the ring of which, including the urea structure -NH-C(O)-NR-, has 4 to 9 members, in particular 6 members. Preferably, the members of the X radical are selected from the group consisting of -NR¹-, -O-, -CR²R³-, -N= and -CR⁴=. In the case of the -CR⁴= or -N= radical, the neighboring member also consists of a -CR⁴= or -N= member, so that the double bond can form between the two members. The radicals R¹ to R⁴ are each independently hydrogen, an alkyl radical, preferably ethyl or methyl, or halogen, for example a fluoride radical or a chloride radi- cal. In a very particularly preferred embodiment, X is -(CH2)3-. The radical R according to for- mula (I) represents a substituted or unsubstituted alkyl or heteroalkyl group, a substituted or un- substituted aryl group or a substituted or unsubstituted alkyl-aryl or heteroalkyl-aryl group. Ex- amples of possible substituents are halogen groups, alkyl groups, hydroxyl groups or amine groups. In a preferred embodiment of the invention, R contains at least one isocyanate-reactive hydrogen atom, for example an —OH or —NH₂ group. Preferably R is methyl, ethyl, propyl, pentyl, hexyl, one or more alkylene oxide moieties, for example oxyethylene, oxypropylene or mixtures of oxyethylene and oxypropylene, and phenyl, or phenyl ether. R is particularly prefer- ably -methyl, ethyl, oxyethylene, oxypropylene or phenyl methoxy ester, very particularly prefer- ably methyl. Bridged cyclic urea structures can likewise be used as cyclic urea compounds, with two cyclic urea structures being bridged via the radical R. R is very particularly preferably a linear, unsubstituted hydrocarbon radical selected from me- thyl, ethyl, propyl, pentyl and hexyl, in particular R is a methyl radical. Preferably, compound (A1) is a lactam. According to a further embodiment, the present inven- tion also is directed to the process as disclosed above, wherein compound (A1) is a lactam. Particularly suitable examples include lactams of omega-amino carboxylic acids, such as 3- amino propionic acid, 4-amino butyric acid, 5-amino valeric acid, 6-amino caproic acid or 10- amino capric acid; N-substituted azalactams, such as 1-N-methyl-hexahydro-1,4-diazepinone- (3); 1-N-butyl-hexahydro-1,4-diazepinone-(3); 1-N-alpha-pyridyl-hexahydro-1,4-diazepinone-(3), and the like. Particularly suitable are for example 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and lauro- lactam. According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the lactam is selected from the group consisting of 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and laurolactam. Suitable alcohols for solvent mixture (SM) are in particular monools and diols with 1 to 12 car- bon atoms, in particular 1 to 6 carbon atoms, for example methanol, ethanol, propanol, butanol, ethandiol, propandiol, or butandiol. According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the alcohol is selected from the group consisting of methanol, ethanol and propanol. According to the present invention, solvent mixture (SM) might also contain two or more lactams or two or more alcohols. The mixing ratio of the lactams and alcohols might vary in broad ranges as long as a homogeneous solution is obtained. Preferably, the molar ratio of the at least one lactam and the at least one alcohol in the solvent mixture (SM) is in the range of from 2:1 to 1:2, in particular in the range of from 1.5:1 to 1:1.5, more preferable in the range of from 1.2:1 to 1:1.2. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the molar ratio of the at least one lactam and the at least one alcohol in the solvent mixture (SM) is in the range of from 2:1 to 1:2. The solvent mixture (SM) is used in an amount suitable to dissolve the polyurethane (PU1) in step (b) of the process according to the present invention. Suitable amounts depend on the sol- vent mixture used and the polyurethane. Typically, the weight ratio of the composition (CW) and the solvent mixture (SM) is in the range of 1:2 to 1:20, preferably in the range of from 1:2 to 1:10. According to a further embodiment, the present invention also is directed to the process as dis- closed above, wherein the weight ratio of the composition (CW) and the solvent mixture (SM) is in the range of 1:2 to 1:20. According to step (b), a solution (S1), which is enriched in dissolved polyurethane (PU1) is ob- tained. Typically, the composition (CW) is not dissolved completely and residues remain which do not dissolve in the solvent mixture (SM) used under the process conditions applied. The so- lution (S1) preferably is separated from the insoluble residues by suitable separation steps. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the process further comprises step (c) (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b). The separation may be carried out in customary devices in a fashion known to the person skilled in the art. Suitable methods are in particular physical separation methods such as filtra- tion, decanting or centrifuging, in particular filtration. According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the separation ac- cording to step (c) is conducted by a physical separation method. The separation, in particular the filtration may be carried out discontinuously in batch mode or continuously, semi-continuously. After the separation, suitable washing steps may be applied according to the process of the pre- sent invention. According to the present invention, it is also possible to combine step (b) and step (c) and op- tionally a washing step. It is for example possible to conduct step (b) in combination with step (c) as a washing step or an extraction step. Suitable apparatuses are in principle known to the person skilled in the art. In this case it is also possible to remove the polyurethane from further components of composi- tion (CW) such as for example fibers present in composition (CW), like glass fibers or polyamide fibers, and allow for recycling of said further components. According to step (c), the solution (S1) is obtained. The polyurethane (PU1) may be recovered from solution (S1) using suitable methods. It is for example possible to remove the solvent to obtain the polyurethane as such. According to the present invention it is also possible to add suitable compounds to solution (S1) which result in the precipitation of the polyurethane. It is for example possible to add water to the solution in a suitable amount to result in the precipitation of the polyurethane which may then be isolated using a filtration step. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the process further comprises step (d) (d) addition of water to the solution (S1) to obtain the polyurethane. According to the present invention, step (d) can be carried out by addition of water to the solu- tion (S1) as such or after a suitable treatment, for example after at least partially removing the solvent. According to a further embodiment of the present invention, one or more components of the solvent mixture are removed prior to step (d) or the solvent mixture is partially removed prior to step (d). According to an alternative further embodiment, the present invention is also directed to the pro- cess as disclosed above, wherein the process further comprises step (d*) (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1). According to the present invention, it is also possible that one or more components of the sol- vent mixture are removed or that the solvent mixture is only partially removed. In particular, the alcohol present in the solvent mixture can for example be easily removed at ambient tempera- ture under reduced pressure. The process of the present invention also may comprise further steps such as washing steps to remove traces of the remaining solvents or drying steps. According to the present invention, it is also possible to use the solution (S1) obtained in step (d) as such for the preparation of a shaped article. Processes for preparing a shaped article from a solution containing a dissolved polyurethane are in principle known to the person skilled in the art and include for example processes for preparing membranes or processes for syn- thetic leather production, or processes for preparing fibers from solution such as for example spinning processes. Suitable processes are for example disclosed in “New materials permeable to water vapor”, H. Träubel, Springer-Verlag, 1999, chapter 8. The process according to the present invention comprises steps (a), and (b) and optionally (c) and/or (d)/(d*) but may also comprise further steps. The process may for example comprise fur- ther purification steps or heat treatments. According to a further embodiment, the present inven- tion is also directed to the process as disclosed above, wherein the process comprises further purification steps. Suitable treatment steps are in principle known to the person skilled in the art. Suitable treatment and/or purification steps may be carried out between steps (a) and (b), or between steps (b) and (c) or between steps (c) and (d). According to a further aspect, the present invention is also directed to the polyurethane ob- tained or obtainable according to a process as disclosed above. Preferably, the polyurethane obtained is thermoplastic and preferably can be processed thermally, for example by extrusion or injection molding. The polyurethane obtained according to the process of the present invention may be used with- out further modifications for any suitable application. It is also possible to use the polyurethane in a mixture with further compounds, in particular further polyurethanes or additives for the prep- aration of shaped articles. It is also possible to prepare blends comprising the polyurethane ob- tained according to the present invention. In principle, processes for preparing shaped article from polyurethanes are known to the person skilled in the art. According to a further aspect, the present invention is also directed to the use of the polyure- thane according to the present invention or a polyurethane obtained or obtainable according to the process of the present invention for the preparation of a shaped article. In principle, polyurethane (PU1) obtained in the process can be reused as such. However, for some applications, it might also be advantageous to subject the polyurethane (PU1) to a treatment suitable to obtain the individual building blocks which in turn might be separated and reused, for example for the preparation of polyurethanes. It is for example possible to depolymerize polyure- thane (PU1) and reuse the components obtained. Processes for depolymerizing polyurethanes are in principle known to the person skilled in the art and include for example hydrolysis, glycolysis or aminolysis. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the process further comprises step (e) (e) depolymerization of the polyurethane (PU1). Suitable conditions for the depolymerization are in principle known to the person skilled in the art. Preferably, depolymerization according to step (e) is carried out by a method selected from hydrolysis, glycolysis, hydrogenation or by aminolysis. According to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the depolymeriza- tion according to step (e) is carried out by a method selected from hydrolysis, glycolysis, hydro- genation or by aminolysis. Preferably, hydrolysis is carried out in the presence of a catalytic active component, ionic liquids or phase transfer catalysts or a base. The resulting products of the depolymerization may be separated using suitable separation techniques. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the hydrolysis is carried out in the presence of a catalytic active compo- nent, ionic liquids or phase transfer catalysts or a base. Also methods for depolymerization by glycolysis are in principle known. Preferably, glycolysis is carried out in the presence of a base. Therefore, according to a further embodiment, the present invention is also directed to the process as disclosed above, wherein the glycolysis is carried out in the presence of a metal catalyst. Suitable methods for depolymerization by hydrogenation include the hydrogenation in the pres- ence of a hydrogenation catalyst. Therefore, according to a further embodiment, the present in- vention is also directed to the process as disclosed above, wherein the hydrogenation is carried out in the presence of a hydrogenation catalyst. Usually, the depolymerization results in a mixture of components which might be separated us- ing suitable separation techniques. The process according to the present invention might also comprise the separation of the isocyanate component or the amine derivative thereof and the polyol components. According to a further embodiment, the present invention is also directed to the process as dis- closed above, wherein the process further comprises a step (f) (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. The work-up of the depolymerization product, in particular the isolation of the polyamine and the polyol can be realized case dependent, for example by extractive work-up, precipitation of the amine component as a hydrochloride, as a urea (in case of an aminolysis), chromatography or distillation under reduced pressure. Preferably, the work up comprises several steps. In work-up by distillation, compounds are separated according to their volatility, with more vola- tile compounds being separated first. Additives, water or solvents used in the depolymerization can also be removed via distillation prior further work-up of the polyol-polyamine mixtures. Gen- erally, the “volatility” of a liquid may be described using its vapor pressure, wherein a high vapor pressure indicates a high volatility, and vice versa. In the event that the polyamine is more volatile than the polyol as it is for example the case for TDA, MDA and NDA, the polyamine is recovered from the depolymerization product via distilla- tion, preferably via distillation at reduced pressure. After distilling-off the polyamine, a distillation bottoms remains which contains the polyol. Suitable conditions for the distillation are in principle known to the person skilled in the art. Alternatively, the polyol may be recovered by extraction from the depolymerization mixture us- ing a suitable extractant or a pair of extractants. It is also possible to precipitate the polyamine component in the form of it´s hydrochloride by adding HCl and extracting the polyol component with a suitable solvent for example as described in DE2854940A1, which is preferably dissolv- ing the polyol component but not the hydrochlorides of the polyamine component. The hydro- chloride of the polyamine component can after separation then either be transferred to the free polyamine by adding a base but also directly used in the phosgenation to generate new polyiso- cyanates for the polyurethane synthesize. In case of MDA*HCl the hydrochloride can be used in MDA synthesis step by condensation of aniline and formaldehyde. It is understood that the separation process described above can be combined with any of the various embodiments of the inventive process described herein. The polyol composition obtained in the depolymerization process and also the isocyanate can be reused, for example in the preparation of polyurethanes. According to a further aspect, the pre- sent invention is also directed to polyol composition obtained or obtainable according to the pro- cess of any one of claims as disclosed above. According to a further aspect, the present invention is also directed to the use of said polyol composition or a polyol composition obtained or obtainable according to the process of the pre- sent invention for the preparation of polyurethanes or polyisocyanurates. Further embodiments of the present invention can be found in the claims and the examples. It will be appreciated that the features of the subject matter/processes/uses according to the invention that are mentioned above and elucidated below are usable not only in the combination specified in each case but also in other combinations without departing from the scope of the invention. For example, the combination of a preferred feature with a particularly preferred feature or of a feature not characterized further with a particularly preferred feature etc. is thus also encompassed implicitly even if this combination is not mentioned explicitly. Illustrative embodiments of the present invention are listed below, but these do not restrict the present invention. In particular, the present invention also encompasses those embodiments which result from the dependency references and hence combinations specified hereinafter. 1. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 2. The process according to embodiment 1, wherein the polyurethane (PU1) is a thermo- plastic polyurethane based on an aromatic isocyanate. 3. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. 4. The process according to any one of embodiments 1 to 3, wherein composition (CW) comprises a polyamide, a polyester and/or a cellulose based polymer. 5. The process according to any one of embodiments 1 to 4, wherein composition (CW) comprises a material selected from polyurethanes based on aliphatic isocyanates, a ther- moset polyurethanes, rubber, ethylene-vinyl acetate copolymers, soot, talc, pigments or cellulose based polymers. 6. The process according to any one of embodiments 1 to 5, wherein compound (A1) is a lactam. 7. The process according to any one of embodiments 1 to 6, wherein compound (A1) is se- lected from the group consisting of 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and laurolactam. 8. The process according to any one of embodiments 1 to 7, wherein the alcohol is selected from the group consisting of methanol, ethanol and propanol. 9. The process according to any one of embodiments 1 to 8, wherein the lactam is selected from the group consisting of 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and lauro- lactam and the alcohol is selected from the group consisting of methanol, ethanol and pro- panol. 10. The process according to any one of embodiments 1 to 9, wherein the lactam is epsilon- caprolactam and the alcohol is selected from the group consisting of methanol, ethanol and propanol, preferably methanol. 11. The process according to any one of embodiments 1 to 10, wherein the molar ratio of the at least one lactam and the at least one alcohol in the solvent mixture (SM) is in the range of from 2:1 to 1:2. 12. The process according to any one of embodiments 1 or 11, wherein the process further comprises step (c) (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b). 13. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b). 14. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. 15. The process according to any one of embodiments 12 to 14, wherein the separation ac- cording to step (c) is conducted by a physical separation method. 16. The process according to any one of embodiments 1 to 15, wherein the composition (CW) is subjected to a mechanical treatment prior to step (a), selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments. 17. The process according to any one of embodiments 1 to 16, wherein the process further comprises step (d) (d) addition of water to the solution (S1) to obtain the polyurethane. 18. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane. 19. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane, wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. The process according to any one of embodiments 1 to 16, wherein the process further comprises step (d*) (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1). A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1). A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1), wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. The process according to any one of embodiments 17 to 22, wherein the process further comprises step (e) (e) depolymerization of the polyurethane (PU1). A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane, (e) depolymerization of the polyurethane (PU1). A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane, (e) depolymerization of the polyurethane (PU1), wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1), (e) depolymerization of the polyurethane (PU1). A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1), (e) depolymerization of the polyurethane (PU1), wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. The process according to any one of embodiments 23 to 27, wherein the depolymerization according to step (e) is carried out by a method selected from hydrolysis, glycolysis, hydro- genation or by aminolysis. The process according to any one of embodiments 23 to 28, wherein the process further comprises a step (f) (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane, (e) depolymerization of the polyurethane (PU1), (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d) addition of water to the solution (S1) to obtain the polyurethane, (e) depolymerization of the polyurethane (PU1), (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization, wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1), (e) depolymerization of the polyurethane (PU1), (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1), (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b), (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1), (e) depolymerization of the polyurethane (PU1), (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization, wherein the polyurethane (PU1) is a thermoplastic polyurethane based on an aromatic isocyanate. Polyurethane obtained or obtainable according to a process according to any one of em- bodiments 1 to 22. Use of the polyurethane according to embodiment 34 or a polyurethane obtained or ob- tainable according to the process of any one of embodiments 1 to 22 for the preparation of a shaped article. Polyol composition obtained or obtainable according to the process of any one of embodi- ments 23 to 33. Use of the polyol composition according to embodiment 36 or a polyol composition ob- tained or obtainable according to the process of any one of embodiments 23 to 33 for the preparation of polyurethanes or polyisocyanurates. 38. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 39. The process according to embodiment 38, wherein the polyurethane (PU1) is a thermo- plastic polyurethane based on an aromatic isocyanate. 40. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material, wherein the polyurethane (PU1) is a thermoplastic polyure- thane based on an aromatic isocyanate; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 41. The process according to any one of embodiments 38 to 40, wherein the content of chain extender in the polyurethane (PU1) is below 40%. 42. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material, wherein the polyurethane (PU1) is a thermoplastic polyure- thane based on an aromatic isocyanate and wherein the content of chain extender in the polyurethane (PU1) is below 40%; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 43. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material, wherein the content of chain extender in the polyurethane (PU1) is below 40%; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 44. The process according to any one of embodiments 38 to 43, wherein composition (CW) comprises a polyamide, a polyester and/or a cellulose based polymer. 45. The process according to any one of embodiments 38 to 44, wherein composition (CW) comprises a material selected from polyurethanes based on aliphatic isocyanates, a ther- moset polyurethanes, rubber, ethylene-vinyl acetate copolymers, soot, talc, pigments or cellulose based polymers. 46. The process according to any one of embodiments 38 to 45, wherein compound (A1) is a lactam. 47. The process according to any one of embodiments 38 to 46, wherein compound (A1) is selected from the group consisting of 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and laurolactam. 48. The process according to any one of embodiments 38 to 47, wherein the alcohol is se- lected from the group consisting of methanol, ethanol and propanol. 49. The process according to any one of embodiments 38 to 48, wherein the molar ratio of the at least one lactam and the at least one alcohol in the solvent mixture (SM) is in the range of from 2:1 to 1:2. 50. The process according to any one of embodiments 38 to 49, wherein the process further comprises step (c) (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b). 51. The process according to embodiment 50, wherein the separation according to step (c) is conducted by a physical separation method. 52. The process according to any one of embodiments 38 to 51, wherein the composition (CW) is subjected to a mechanical treatment prior to step (a), selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments. 53. The process according to any one of embodiments 38 to 52, wherein the process further comprises step (d) (d) addition of water to the solution (S1) to obtain the polyurethane. 54. The process according to any one of embodiments 38 to 52, wherein the process further comprises step (d*) (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1). 55. The process according to embodiment 53 or 54, wherein the process further comprises step (e) (e) depolymerization of the polyurethane (PU1). 56. The process according to embodiment 55, wherein the depolymerization according to step (e) is carried out by a method selected from hydrolysis, glycolysis, hydrogenation or by aminolysis. 57. The process according to any one of embodiments 55 or 56, wherein the process further comprises a step (f) (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. 58. Polyurethane obtained or obtainable according to a process according to any one of em- bodiments 38 to 54. 59. Use of the polyurethane according to embodiment 58 or a polyurethane obtained or ob- tainable according to the process of any one of embodiments 38 to 54 for the preparation of a shaped article. 60. Polyol composition obtained or obtainable according to the process of any one of embodi- ments 55 to 57. 61. Use of the polyol composition according to embodiment 60 or a polyol composition ob- tained or obtainable according to the process of any one of embodiments 55 to 57 for the preparation of polyurethanes or polyisocyanurates. The invention is further described by examples. The examples relate to practical and in some cases preferred embodiments of the invention that do not limit the scope of the invention. Examples 1. Example 1 Various samples of post-consumer sports shoe waste consisting of different materials (PU, textile fibres, EVA, rubber, styrene block copolymers,) were tested. The different samples contained different amounts of elastic PU. 300 g each of the samples were added to 1.5 L caprolactam/MeOH solution and the mix- ture was stirred overnight at room temperature. The resulting suspension was then filtered and all insoluble components were removed. The non-soluble components of the samples were washed with water and emerged from the process unchanged, allowing to recycle the materials separately. 1.5 L of water were added to the solution so that a precipitate formed. The precipitate was filtered off and washed with water. Depending on the sample, up to 65% by weight of ma- terial based on the weight of the waste composition were isolated. The material was char- acterized by IR spectroscopy and processed on an extruder. For comparison, a thermo- plastic polyurethane with similar composition according to the IR spectroscopy was pro- cessed on the extruder in the same way. The properties of the samples are summarized in table 1. Table 1 fresh TPU recycled sample molecular weight [g/mol] 82000 84000 Shore hardness 73 74 Tensile strength [MPa] 22 16 Elongation at break [%] 720 810 2. Solubility of thermoplastic polyurethanes The solubility of different TPU samples was tested.1 g of a TPU sample were cut into small pieces and 15 g of a mixture of caprolactam and methanol were added. The mixture was stirred at room temperature. The results are summarized in table 2. Table 2 Time until sample TPU composition was completely dissolved 20h polyetherpolyol, aromatic isocyanate, 1,4-bu- tanediol tender Sample F 20h components identical to sample E + 15% polysty- rene Sample G x differs from sample A in that an excess isocya- nate is used (index 1050) Sample H 48h polar polyesterpolyol, aromatic isocyanate, 1,4-butanediol Sample I x components identical to sample H but higher con- tent of 1,4-butanediol Sample P 10h polar polyesterpolyol, aromatic isocyanate, 1,4- butanediol, glass fibre (*) Sample Q 36h same components used as for sample P but higher content of chain extender (*) Comparison of chain extender content: Sample S > Sample R > Sample Q > Sample P Sample C > Sample B> Sample A Surprisingly, only the TPUs based on aromatic isocyanates were soluble in the mixture of caprolactam and methanol. None of the aliphatic TPUs in the test series were dissolved under the conditions applied. Furthermore, it was observed that a higher content of aliphatic chain extender reduced the solubility. If the respective content was too high, the TPU was no longer soluble at RT (see sample H vs. sample I or sample P vs. sample R (samples P, R and S consist of the same raw materials and differ only in the proportion by weight of the raw materials)). Literature cited: US4115298A US4160749A “Recycling von Polyurethan-Kunststoffen”, W. Raßhofer, Hüthig (Heidelberg), 1994 “New materials permeable to water vapor”, H. Träubel, Springer-Verlag, 1999, chapter 8

Claims

Claims 1. A process for recycling a polyurethane from a composition comprising a polyurethane (PU1) and at least one further material comprising the steps of (a) providing a composition (CW) comprising an elastic polyurethane (PU1) and at least one further material; (b) bringing the composition (CW) into contact with a solvent mixture (SM) comprising and at least one alcohol and at least one compound (A1) selected from the group consisting of cyclic amides at a temperature below the boiling point of the alcohol to obtain a solution (S1) which is enriched in dissolved polyurethane (PU1). 2. The process according to claim 1, wherein the polyurethane (PU1) is a thermoplastic poly- urethane based on an aromatic isocyanate. 3. The process according to any one of claims 1 or 2, wherein the content of chain extender in the polyurethane (PU1) is below 40%. 4. The process according to any one of claims 1 to 3, wherein composition (CW) comprises a polyamide, a polyester and/or a cellulose based polymer. 5. The process according to any one of claims 1 to 4, wherein composition (CW) comprises a material selected from polyurethanes based on aliphatic isocyanates, a thermoset poly- urethanes, rubber, ethylene-vinyl acetate copolymers, soot, talc, pigments or cellulose based polymers. 6. The process according to any one of claims 1 to 5, wherein compound (A1) is a lactam. 7. The process according to any one of claims 1 to 6, wherein compound (A1) is selected from the group consisting of 2-pyrrolidone, 2-piperidone, epsilon-caprolactam and lauro- lactam. 8. The process according to any one of claims 1 to 7, wherein the alcohol is selected from the group consisting of methanol, ethanol and propanol. 9. The process according to any one of claims 1 to 8, wherein the molar ratio of the at least one lactam and the at least one alcohol in the solvent mixture (SM) is in the range of from 2:1 to 1:2. 10. The process according to any one of claims 1 to 9, wherein the process further comprises step (c) (c) separating the solution (S1), which is enriched in dissolved polyurethane (PU1) and the residue of the composition (CW) obtained in (b). 11. The process according to claim 10, wherein the separation according to step (c) is con- ducted by a physical separation method. 12. The process according to any one of claims 1 to 11, wherein the composition (CW) is sub- jected to a mechanical treatment prior to step (a), selected from the group consisting of milling, beating, shredding, tearing and mixtures of two or more of these treatments. 13. The process according to any one of claims 1 to 12, wherein the process further com- prises step (d) (d) addition of water to the solution (S1) to obtain the polyurethane. 14. The process according to any one of claims 1 to 12, wherein the process further com- prises step (d*) (d*) removal of the solvent mixture form the solution (S1) to obtain the polyurethane (PU1). 15. The process according to claim 13 or 14, wherein the process further comprises step (e) (e) depolymerization of the polyurethane (PU1). 16. The process according to claim 15, wherein the depolymerization according to step (e) is carried out by a method selected from hydrolysis, glycolysis, hydrogenation or by aminoly- sis. 17. The process according to any one of claims 15 or 16, wherein the process further comprises a step (f) (f) separation of the isocyanate component or the amine derivative thereof and the polyol components obtained in the depolymerization. 18. Polyurethane obtained or obtainable according to a process according to any one of claims 1 to 14. 19. Use of the polyurethane according to claim 18 or a polyurethane obtained or obtainable according to the process of any one of claims 1 to 14 for the preparation of a shaped arti- cle. 20. Polyol composition obtained or obtainable according to the process of any one of claims 15 to 17. 21. Use of the polyol composition according to claim 20 or a polyol composition obtained or obtainable according to the process of any one of claims 15 to 17 for the preparation of polyurethanes or polyisocyanurates.