Process for the degradation of polyurethane and liquid process medium obtained thereby

Abstract

A process for the degradation of polyurethane, wherein a polyurethane-containing material is heated in the presence of an aqueous solution containing 1 to 10 mass percent urea at excess pressure to a temperature of 190°C to 250°C, wherein the heating is carried out over a period of 20 minutes to 240 minutes, wherein the ratio between urea-containing aqueous solution and polyurethane-containing material is 0.4 ml / g to 5 ml / g.

Description

[0001] The invention relates to a method for the degradation of polyurethane and a process medium obtainable via this method.

[0002] Polyurethanes, due to their many adjustable properties, are widely used in products for both industrial and household applications. Examples of such products include foams, paints, adhesives, potting compounds, hoses, seals, floor coverings, mattresses, automotive parts, sports equipment components, shoe parts, and the like.

[0003] Accordingly, a high proportion of polyurethane waste is generated when the corresponding products are damaged or have reached the end of their service life.

[0004] In the past, several solutions have been proposed for processing polyurethane waste. Several patents describe processes in which polyurethane waste is dissolved in aliphatic diols, for example, US patents 4,044,046 A, 3,632,530 A, and 4,162,995 A, as well as German patent application DE 2 304 444 A. US patent 4,316,992 A proposes dissolution in high-boiling saturated alcohol, and US patent 4,039,568 A proposes dissolution in the presence of various alcoholates. A disadvantage of all these processes is that they require hydrocarbons in the form of diols. German patent DE 30 37 545 C2 discloses the use of at least 50% urea solutions at temperatures of up to 165 °C.

[0005] The object of the invention is to provide alternative solutions, preferably using substances that are less harmful to the environment than diols. The invention is defined by the features of the independent claims.

[0006] Advantageous further training and development opportunities are subject to dependent claims.

[0007] The problem is solved in a first aspect by a process for the degradation of polyurethane, in which a polyurethane-containing material is heated under overpressure to a temperature of 190 °C to 250 °C in the presence of an aqueous solution containing 1 to 10% by mass of urea, the heating taking place over a period of 20 to 240 minutes, wherein the ratio between urea-containing aqueous solution and polyurethane-containing material is 0.4 ml / g to 5 ml / g. At the beginning of the process, the polyurethane-containing material is present in or together with the aqueous, urea-containing solution.After the selected treatment duration, the polyurethane component of the polyurethane-containing material, originally in solid form, is partially or completely converted into substances contained in a liquid process medium. This liquid medium is derived from the urea-containing aqueous solution present at the beginning of the process. The process medium may still contain solids, such as solids that were embedded in or adhering to the solid polyurethane, or other plastics. The liquid process medium contains degradation products and / or further derivatives derived from the original polyurethane.By converting it into the liquid process medium, it is advantageously possible to transform originally solid polyurethane into a more easily handled form, and, if necessary, to isolate valuable materials from the resulting liquid process medium or to use them profitably in further reactions.

[0008] Overpressure is defined as any pressure higher than ambient atmospheric pressure. According to one embodiment, heating takes place at a pressure of 1.05 bar to 100 bar. Examples of pressure ranges are 10 bar to 45 bar, for example, 12 bar to 40 bar, or 25 bar to 35 bar. For the sake of simplified process control, overpressure is defined as the equilibrium pressure established during heating, for example, the equilibrium pressure reached when heating in a pressure vessel.

[0009] The process is carried out over a period of 20 to 240 minutes, particularly 90 to 240 minutes, for example, 120 to 240 minutes. A preferred period is between 40 and 180 minutes. The reaction temperature can remain constant at a single value within the specified temperature range or assume different values ​​within the specified temperature range. The period is preferably a single continuous period, but can also be composed cumulatively of separate periods during which the intended temperature conditions are maintained. Extensive tests have shown that at a temperature of 245 °C and a duration of 240 minutes, the first signs of solid formation appeared.Taking into account a predetermined duration of 240 min for the temperature treatment, a temperature of 250°C is therefore considered a practical upper limit for the temperature.

[0010] This process opens up the possibility of achieving the degradation of polyurethane using urea, a substance that occurs naturally in the environment and is therefore naturally biodegradable.

[0011] Polyurethane-containing material can refer to material that, in addition to polyurethane and separately from it, contains a non-polyurethane component. For example, polyurethane in combination with a component of another plastic, such as styrene-acrylonitrile particles, a metal component, a glass component, or a component of an inorganic material, such as calcium carbonate. Examples without limitations include polyurethane articles containing metal fasteners, or composite materials of polyurethane and another plastic, such as refrigerator parts that contain polyurethane as a thermal insulation layer and other plastics as a coating. However, polyurethane-containing material can also be understood as material consisting solely of polyurethane.The polyurethane itself can be pure polyurethane, or a polyurethane containing other substances, such as plasticizers, microbicidal agents, antioxidants, stabilizers (e.g., against UV light), flame retardants, dyes, or residues of polymerization initiators. The term "polyurethane-containing material" can also encompass a mixture of different polyurethane-containing materials, for example, materials that each contain different types of polyurethane.

[0012] The degradation of polyurethane can occur partially, but depending on the chosen process parameters, it can lead via intermediate stages, in which the polyurethane is present in a fragmented form, to the complete degradation of the polyurethane contained in the material, so that the polyurethane is no longer present as a solid.

[0013] Polyurethane is understood, as is customary in the field, to be a polymer which has as its characteristic group the urethane group according to the following formula (I):

[0014] Polyurethanes are generally obtainable by the polyaddition of dihydric or higher alcohols of formula (II) HO-R'-OH (II), where R' represents a low molecular weight or even already polymeric aliphatic or aromatic residue, which optionally comprises at least one further hydroxyl group, with diisocyanates of the general formula (III) O=C=NRN=C=O (III), where R has the same meaning as R'.

[0015] The chemistry and the technical production and processing of polyurethanes are generally known to those skilled in the art and are described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, 6th Completely Revised Edition, Wiley-VHC Verlag GmbH & Co. KGaA, Weinheim, Germany, 2003, Volume 28, pages 667-722. Most polyurethane foams (hereinafter also referred to as PUR foams) are produced on the basis of aromatic isocyanates. The most important representatives of this group are mixtures of the isomers 2,4-toluene diisocyanate and 2,6-toluene diisocyanate (TDI), as well as mixtures of isomers of diphenylmethane diisocyanate (MDI), for which non-restrictive examples include diphenylmethane 2,2'-diisocyanate (2,2'-MDI), diphenylmethane 2,4'-diisocyanate (2,4'-MDI) and diphenylmethane 4,4'-diisocyanate (4,4'-MDI), and prepolymerized MDI.TDI 80 is the most important diisocyanate used in flexible foam production, with the number 80 referring to the percentage of the highly reactive isomer 2,4-toluene diisocyanate. Polyethers, polyesters, or diamines are preferably used as polyol components. The properties can also be modified by adding stabilizers such as silicone polyether copolymers, epoxides, benzophenone, and other substances. Additives can also vary the foam's properties. For example, phosphoric acid esters are used as flame retardants. Mechanical reinforcing agents such as carbon fibers can also be incorporated into the foams and represent examples of non-polyurethanes that can be included as additional components in the polyurethane-based material. Fillers such as calcium carbonate can also be used.

[0016] The polyurethane can be foamed polyurethane or non-porous polyurethane, with non-restrictive examples of non-porous polyurethane being polyurethane hoses or polyurethane sealants.

[0017] According to a particular embodiment of the process, the material comprises, or consists of, polyurethane (PUR), flexible polyurethane foam (PUR flexible foam), rigid polyurethane foam (PUR rigid foam), shredder light fraction, or a mixture of two or more of these. The term "shredder light fraction" is familiar to those skilled in the waste management industry and generally describes a heterogeneous mixture that can consist of various plastics, organic and inorganic materials, the specific composition depending on the type of shredded waste. An example of a shredder light fraction is generated during the recycling of refrigerators, where the foaming of cavities consists of rigid polyurethane foam, possibly with the addition of other plastics, such as plastics resulting from cable glands.Shredded light fraction from refrigerator recycling may still contain mineral components, for example due to fillers contained in the polyurethane.

[0018] Non-restrictive examples of sources of polyurethane-containing material include production waste from the mattress, automotive, construction, furniture, footwear, electrical, and sports / leisure industries, or defective or no longer used products from these industries, such as mattresses; bodywork or other vehicle parts such as bumpers, dashboards, headrests, armrests, or carpets; wall panels or pipe insulation; furniture or furniture parts; shoes or shoe parts such as soles or toecaps; cable sheathing, plugs, connectors, or parts thereof; or sports equipment such as snowboards or roller skate wheels.

[0019] Within the framework of the process according to the invention, polyurethane-containing material can in particular be polyurethane foams (hereinafter also referred to as PUR foams) selected from the following compositions: flexible PUR foams based on non-reactive polyether polyols (so-called standard polyether polyols) with molecular weights around 3000 g / mol, filled (with SAN copolymers, i.e., styrene-acrylonitrile copolymers) or unfilled; flexible PUR foams based on reactive high-resilience polyether polyols with molecular weights of more than 3000 g / mol, filled (with SAN copolymers or PHD, i.e.,Polyurea dispersion) or unfilled; flexible polyurethane foams based on reactive 6-functional polyether polyols; flexible polyurethane foams based on hypersoft polyether polyols; flexible polyurethane foams based on polyether polyols and mixtures thereof, resulting in viscoelastic foams and which may also contain PEG (polyethylene glycol) as a component; flexible polyurethane foams based on polyester polyols, filled or unfilled; flexible polyurethane foams based on the aforementioned polyol mixtures in combination with TDI or MDI; and rigid or semi-rigid polyurethane foams based on the aforementioned polyol mixtures in combination with TDI or MDI, as well as integral rigid foams consisting of the aforementioned components.

[0020] According to special training courses, the PUR foams include one or more representatives from the product family of flexible foams and / or one or more representatives from the product family of rigid foams.

[0021] Flexible foams include plastics such as standard polyether foams, high-resilience polyether foams, combustion-modified polyether foams (CME), combustion-modified high-resilience polyether foams (CMHR), viscoelastic polyether foams, and polyester foams. Exemplary compositions are known to those skilled in the art and are described, for example, in German patent applications DE 3630225 C2, US 3,905,924 A, and DE 10 2007 051 089 A1.

[0022] Preferably, these flexible foams comprise the following components or consist of combinations of two or more of them: Isocyanates: 2,4- and / or 2,6-toluene diisocyanate (TDI) and any mixtures of these isomers; 4,4'- and / or 2,2'- diphenylmethane diisocyanates (MDI) and any mixtures of these isomers; Polymer MDI (“crude” MDI) and MDI prepolymerized with polyhydric polyols (preferably di- and / or trihydric polyethers); and / or Any mixtures of TDI and MDI from the aforementioned isomers and forms. Polyols: Polyether polyols and / or polyester polyols, such as are known per se for the production of cellular and homogeneous polyurethane foams and which are described, for example, in DE-A 2 832 253 (pages 11-18).

[0023] Examples include: (Standard) polyethers with hydroxyl groups (functionalities) of preferably 2 and 3; (standard) polyethers filled with SAN (styrene-acrylic-nitrile) solids with hydroxyl groups (functionalities) of preferably 2 and 3; Hypersoft polyether with functionalities of preferably 3; Reactive polyethers with primary hydroxyl groups, preferably with functionalities of 3, 5 and 6; Reactive polyethers filled with SAN (styrene-acrylonitrile) solid or PHD (polyurea dispersion) with primary hydroxyl groups, preferably with a functionality of 3; Reactive polyols prepolymerized with TDI, preferably with a functionality of 3; non-reactive polyols prepolymerized with TDI, also known as so-called “quasi-prepolymers” (QPP), preferably with a functionality of 3, in which the polyols are present in excess of the TDI; Polyols based on renewable raw materials and with varying functionalities. Natural oil products with varying numbers of hydroxyl groups, with castor oil serving as a non-restrictive example; Compounds with amino or hydroxyl groups that serve as chain extenders or crosslinkers and typically have 2 to 8, preferably 2 to 4, hydrogen atoms reactive towards isocyanates, for example diethanolamine, triethanolamine, diisopropanolamine, sorbitol, glycerol and urea.

[0024] These flexible foams, like the rigid foams mentioned below, optionally include one or more additional substances selected from: catalysts of the type known per se, such as tertiary amines and reactive (incorporable) amines; tin(II) compounds and zinc compounds; surfactants such as emulsifiers, foam stabilizers, flame retardants, sorbitol, glycerol, diamines, urea, tertiary amines, and siloxane-based or non-siloxane-based stabilizers.

[0025] The rigid foams of this special type can be found, for example, in products such as insulation boards (also as sandwich panels with different facing layers), in-situ foams, sprayed foams, foams produced using the overlay method, foams for solar collector fillings, foams for pipe insulation, filling and assembly foams, and block foams. The compositions are sufficiently well known to those skilled in the art and are comprehensively described, for example, in EP 0 318 784 A2.

[0026] Preferably, these rigid foams comprise the following components or consist of combinations of two or more of them: Isocyanates: 2,4- and / or 2,6-toluene diisocyanate (TDI) and any mixtures of these isomers; 4,4'- and / or 2,2'- diphenylmethane diisocyanates (MDI) and any mixtures of these isomers; Polymer MDI (“raw” MDI) and MDI prepolymerized with multivalent polyols (preferably divalent and / or trivalent polyethers); Any mixtures of TDI and MDI from the aforementioned isomers and forms, but preferably polymer MDI (crude MDI).

[0027] Besides foams, other examples of polyurethane include polyurethane elastomers and polyurethane thermosets.

[0028] The process according to the invention can be carried out discontinuously, continuously or semi-continuously.

[0029] In the discontinuous process, also known as the batch process, the starting materials are placed in a reaction vessel, exposed to the reaction conditions, and then the reaction product is removed after the treatment time has elapsed. The reaction vessel is then loaded with a new batch of starting materials.

[0030] In the continuous process, polyurethane-containing material and urea-containing aqueous solution are not simply fed into the reaction vessel once before the reaction begins, but continuously. Similarly, liquid process medium is also continuously withdrawn. Typically, the feed and withdrawal occur at different points. In particular, the polyurethane-containing material, together with the urea-containing aqueous solution, can be pushed from the feed point to the withdrawal point or transported within the reaction vessel by active conveying devices. Accordingly, a low degree of degradation is present near the feed point, while the polyurethane-containing material, together with the urea-containing aqueous solution, migrates or is transported towards the withdrawal point, exhibiting a higher degree of degradation with respect to the polyurethane as it approaches the withdrawal point.

[0031] Semi-continuous processes represent any possible transitional form between the two processes mentioned above. For example, the removal of the liquid process medium after a batch process may not be substantially complete. As another example, as a modification of a continuous process, the feeding of new polyurethane-containing material and / or urea-containing aqueous solution may not be continuous, so that new polyurethane-containing material and / or urea-containing aqueous solution is not fed in at all times, but rather only at specific times, for example, periodically, or after a certain degree of degradation of the polyurethane in the reaction vessel has been determined.

[0032] Any type of conventionally available device can be used as a reaction vessel, or it can be easily adapted by a person skilled in the art for the purposes of the process according to the invention. Examples include pressure vessels or pressure reactors designed for batch filling and providing reaction volumes ranging from laboratory scale, for example, 0.1 to 10 liters, through intermediate ranges from 10 liters to 1 cubic meter, up to large-scale industrial volumes from 1 cubic meter to dozens or hundreds of cubic meters. Alternatively, the pressure vessels or pressure reactors can be designed for continuous or semi-continuous operation and include pressure locks for feeding in polyurethane-containing material or for removing the liquid process medium.

[0033] The polyurethane-containing material can be used in its whole form. For example, a polyurethane foam can be moistened or saturated with the urea-containing aqueous solution and then heated to a temperature in the range of 190°C to 250°C.

[0034] Preferably, however, the polyurethane-containing material is used in a comminution. Standard comminution methods can be employed; for example, the polyurethane-containing material can be cut, torn, shredded into flakes, granulated, ground, or pulverized, optionally after prior temperature reduction to increase brittleness. Non-limiting examples for the size of the comminution products obtained are approximately 0.5 cm. 3 up to 10 cm 3 (0.5 ml to 10 ml), such as about 1 cm 3 up to 5 cm 3, in particular for porous or polyurethane-containing material with a large surface area, or comminution products with a diameter, measured at their largest point, of at most approximately 10, 5, 2, 1, 0.5, 0.1, 0.05, or 0.01 millimeters. Comminution can take place during the process using appropriate devices in the reaction vessel; however, preferably the reaction vessel is filled with polyurethane-containing material in already comminutioned form. If the polyurethane-containing material is not merely wetted by the urea-containing solution but is completely absorbed by it, then essentially a suspension of the polyurethane-containing material in the urea-containing aqueous solution exists.

[0035] Based on the total mass of the aqueous solution, the proportion of urea in the aqueous solution is 1 to 10% by mass, such as 1 to 7% by mass, for example, 1.5 to 5% by mass, 1.5 to 4% by mass, 2 to 4% by mass, 2.5 to 3.5% by mass, or 3% by mass. Examples of other ranges or concentrations are 5 to 10% by mass, 1% by mass, 5% by mass, 7.5% by mass, and 10% by mass. A range between 1% by mass and 10% by mass is preferred from the perspective of the ratio between the amount of urea used and the degree of polyurethane degradation achieved, for example, 2% by mass to 7.5% by mass, such as 3% by mass to 5% by mass.

[0036] The process is preferably carried out in the absence of air, with optionally allowing small residual amounts of air, for example 20% or 10% of the volume of the reaction vessel in which the degradation process is carried out, or is carried out in the absence of air, or in the presence of an inert gas, for example nitrogen gas. Preferably, the process is carried out in the presence of an inert gas.

[0037] In a particular embodiment, the aqueous solution comprises 2.5 to 10 percent by mass of urea, and the heating takes place over a period of 45 to 250 minutes.

[0038] The ratio between urea-containing aqueous solution and polyurethane-containing material is 0.4 ml / g to 5 ml / g, for example, 0.4 ml / g to 1.0 ml / g. Particularly with a low ratio between the volume of urea-containing aqueous solution used and the amount of polyurethane treated, efficient use of the volume available for the degradation process is achieved. With regard to polyurethane foam, a quantity of 0.4 ml / g represents a lower limit at which the polyurethane foam is still sufficiently moistened with the aqueous urea-containing solution to enable the desired degradation of the polyurethane.

[0039] The process optionally includes a further step to recover at least some of the liquid process medium obtained after heating. Accordingly, the liquid process medium is completely or partially removed from the reaction vessel. This then provides an optional basis for further steps, such as fractionation into individual substances or groups of substances that can be disposed of more efficiently or, ideally, used as raw material sources.

[0040] According to one embodiment, it is provided that any solids contained in the recovered liquid process medium are removed. These solids may be, for example, metal parts, particles of other plastics, or particulate reaction or degradation products of the polyurethanes or polyurethane components. Methods for removing solids are known to those skilled in the art and include, for example, sedimentation, centrifugation, or filtration.

[0041] According to a preferred embodiment, the aqueous solution containing 1 to 10% by mass of urea is free of polyols, for example, diols, and / or free of carboxylic acids and / or free of ammonia. This advantageously avoids environmentally harmful substances. According to a particular embodiment, the aqueous solution consists of water and 1 to 10% by mass of urea.

[0042] During the degradation process, the polyurethane is partially or completely converted into the liquid process medium. Accordingly, polyurethane-containing materials, which are initially in solid form and require a large volume, especially if the polyurethane is in foam form, can be converted into more easily handled liquids, namely the liquid process medium, with a lower volume requirement. Furthermore, it is possible to fractionate and / or isolate the substances contained in the liquid process medium and / or, if necessary, to reuse or recycle them.

[0043] Further advantages, features and details will become apparent from the following description, in which - possibly with reference to the figure - at least one embodiment is described in detail.

[0044] Fig.Figure 1 shows a three-dimensional diagram illustrating the degree of degradation of polyurethane-containing material as a function of temperature and duration of the process. Example 1 - Polyurethane flexible foams

[0045] Two polyurethane soft foams based on TDI and MDI respectively (product names: R 4030 and R 5535, source: Eurofoam Deutschland GmbH Schaumstoffe, Wiesbaden, Germany) were absorbed at 20.0 g and 19.6 g respectively in 32.2 ml and 35.7 ml respectively of 7.5% urea solution and treated for 180 minutes at 190 °C in a closed pressure vessel. Table 1: Weight of polyurethane soft foam [g] Urea content of the aqueous solution [mass %] Volume of aqueous solution used [ml] Decrease [%] 20,0 (R 4030) 7,5 32,2 50 19,6 (R 5535) 7,5 35,7 90 180 min at 190°C

[0046] After cooling, the samples taken were semi-quantitatively classified by visual inspection with regard to the degree of degradation of solid polyurethane and the corresponding disappearance of detectable solid material and its transfer into the liquid process medium, whereby (as in all other subsequent tests) “0%” indicates that no degradation of polyurethane has yet taken place, and accordingly the originally used amount of solid polyurethane was still completely present, whereas “100%” indicates complete degradation and corresponding transfer of the polyurethane into the liquid process medium.

[0047] In both cases, partial degradation occurred, with varying amounts of solids remaining in the form of apparently compacted foam residues in the liquid process medium. Example 2 - Polyurethane integral foam

[0048] Two samples of flexible polyurethane integral foam based on ether and a cast elastomer marketed under the brand name Colo-Fast® (BASF, SE, Ludwigshafen, Germany) were weighed at 25 g and 35 g respectively in 40 ml of 3% urea solution and treated for 240 minutes at 245 °C in a closed pressure vessel that was 80% full. Table 2: Weight of polyurethane integral foam [g] Urea content of the aqueous solution [mass percent] Volume of aqueous solution used [ml] Decrease [%] 25 (Ether base) 3 40 100 35 (Colo-Fast) 3 40 100 240 min at 245°C

[0049] The polyurethane materials used completely degraded, however a small proportion of particles was detected, which may have been due to polymerization. Example 3 - non-foamed polyurethane

[0050] In a series of experiments, solid, non-foamed polyurethanes were used for the degradation process. Blue polyurethane plastic tubing of the type "PUN" (Festo Gesellschaft mbH, Vienna, Austria) was shredded, and 1 g of each was heated in 25 ml of an aqueous urea solution with a urea concentration of 1%, 5%, 7.5%, or 10% by mass in a closed pressure vessel for 150 minutes at 210 °C. The experiments primarily served to determine the influence of the urea concentration and to ascertain the degradability of solid polyurethanes (Table 3). Weight of polyurethane hose [g] Urea content of the aqueous solution [mass percent] Volume of aqueous solution used [ml] Decrease [%] 30 1 25 100 30 5 25 100 5 7,5 20 100 5 7,5 20 100 30 7,5 25 100 30 10 25 100 150 min at 210°C

[0051] The results showed that in all samples, no traces of the originally used solid polyurethane were detectable in the resulting liquid process medium. Therefore, under the specified test conditions, non-foamed polyurethanes are biodegradable. Example 4 - thermosetting polyurethane

[0052] As a further example of non-foamed polyurethanes, a thermoset polyurethane core with a density of 165 g / l, used in skis, was used for the degradation process. The core was crushed and 15 g were heated in 40 ml of an aqueous urea solution with a urea content of 3% by mass for 150 minutes at 210 °C in a closed pressure vessel filled to 80% of the available volume (remaining volume 20%: air). Table 4: Weight of polyurethane ski core material [g] Urea content of the aqueous solution [mass percent] Volume of aqueous solution [ml] Decrease [%] 15 3 40 100 150 min at 210°C

[0053] As a result, it was found that no traces of the originally used non-foamed polyurethane could be detected in the resulting liquid phase. Example 5 - elastomeric polyurethanes

[0054] Examples of elastomeric polyurethanes used were microcellular polyurethane springs marketed under the brand name Cellasto® (BASF SE, Ludwigshafen, Germany) and the cast elastomer Colo-Fast® (BASF SE, Ludwigshafen, Germany). The samples were crushed and heated in separate batches in 40 ml of an aqueous urea solution with a urea content of 3% by mass for 150 minutes at 210 °C in a closed pressure vessel filled to 80% of the available volume (remaining volume 20%: air). Table 5: Weight of elastomeric polyurethane [g] Urea content of the aqueous solution [mass percent] Volume of aqueous solution used [ml] Decrease [%] 35 (Cellasto® (Sample 1) 3 40 100 40 (Cellasto® (Sample 2) 3 40 100 35 (Colo-Fast® 3 40 100 150 min at 210 °C

[0055] As a result, it was found that in all approaches no traces of the originally used elastomeric polyurethane could be detected in the obtained liquid phase. Example 6

[0056] In a series of experiments, the aforementioned polyurethane foams R 4030 and R 5535 were heated in an aqueous urea solution with a urea content of 7.5 mass percent at a temperature of 230 °C in a closed pressure vessel for 60 minutes, 90 minutes or 120 minutes. Table 6: Weight of polyurethane foam [g] Urea content of aqueous solution [mass percent] Volume of aqueous solution used [ml] Duration [min] Decrease [%] 9,98 (R 4030) 7,5 25 60 50 10,47 (R 5535) 7,5 25 60 50 9,93 (R 4030) 7,5 25 60 50 10,36 (R 5535) 7,5 25 60 50 10,08 (R 4030) 7,5 25 90 90 10,04 (R 5535) 7,5 25 90 90 10,15 (R 4030) 7,5 25 120 100 10,23 (R 5535) 7,5 25 120 100 different time durations at 230°C

[0057] At the degradation rate classified as 50%, the foam structures dissolved and became pasty; at the apparatus classified as 90%, the foam structure was almost completely liquefied; and at the 100% degradation, it was 100% liquefied. Example 7 - Time series and temperature series

[0058] After previous experiments had shown that, in principle, any type of polyurethane-containing material could be degraded using the method, a new series of experiments was conducted with the aim of systematically determining the temperature and time dependence of the degradation. This involved using a mixture of different polyurethane-containing materials, namely a mixture of equal weight proportions with a starting weight of 4.15 g each. a) Standard foam (standard foam grade TDI 80-based) with filler (calcium carbonate) and SAN polymer particles (N 4045 WS), b) highly resilient polyurethane foam [HR (high resilience) foam grade TDI 80 / TDI65-based) with filler (calcium carbonate) and SAN polymer particles (R 4040 WS), c) highly resilient polyurethane foam [HR (high resilience) foam grade MDI-based) with filler (calcium carbonate) and SAN polymer particles (R 5535 WS), and d) viscoelastic foam (viscoelastic foam grade MDI-based) without fillers.

[0059] The polyurethane-containing material obtained in this manner was shredded and mixed with a 3% urea solution at a ratio of 0.582 ml of urea solution per gram of polyurethane-containing material. Samples were heated in sealed pressure vessels in a heating oven at an equilibrium pressure of 190 °C, 210 °C, 230 °C, and 245 °C, respectively, and taken after dwell times of 60 minutes, 90 minutes, 120 minutes, 180 minutes, and 240 minutes at the respective temperature. Three samples were prepared and analyzed simultaneously at each time point.

[0060] After cooling, the samples taken were visually inspected and semi-quantitatively classified with regard to the degree of degradation of solid polyurethane, and thus the disappearance of detectable solid material and its transfer into the liquid process medium, by calculating the average of each of the three samples. The result is in Fig. Figure 1 shows the data, with the horizontal x-axis representing the duration of the heat treatment at a given temperature in minutes, the vertical z-axis representing the semi-quantitative degradation rate in percent, and the y-axis (leading into the plane of the image) showing the three selected temperatures of 190 °C, 210 °C, 230 °C, and 245 °C. It is evident that higher degradation rates can be achieved more quickly with increasing temperature up to 245 °C. Example 8 - Control test without overpressure

[0061] In a control experiment, 2 g each of TDI polyurethane foam (product name: R 4030; source: Eurofoam Deutschland GmbH Schaumstoffe, Wiesbaden, Germany) and MDI polyurethane foam (product name: R5535; source: Eurofoam Deutschland GmbH Schaumstoffe, Wiesbaden, Germany) were mixed with 40 ml of 7.5% urea solution in two separate batches and treated in a glass flask at a temperature of 100 °C to 110 °C at ambient pressure in a heating oven, with liquid loss being replenished by adding water. After 4.5 hours, no degradation was observed.

[0062] The described process enables the degradation of polyurethane and is therefore commercially applicable.

Claims

[1] Method for the degradation of polyurethane, wherein a polyurethane-containing material is heated under overpressure to a temperature of 190°C to 250°C in the presence of an aqueous solution containing 1 to 10% by mass of urea, the heating taking place over a period of 20 minutes to 240 minutes, wherein the ratio between urea-containing aqueous solution and polyurethane-containing material is 0.4 ml / g to 5 ml / g. [2] Method according to claim 1, characterized by that the heating takes place at a pressure of 1.05 bar to 100 bar. [3] Method according to any one of the preceding claims, characterized by that the overpressure is an equilibrium pressure that is established upon heating. [4] Method according to any one of the preceding claims, characterized by that after heating, at least some of the liquid process medium obtained is recovered. [5] Method according to claim 4, characterized bythat solids are removed from the obtained liquid process medium. [6] Method according to any one of the preceding claims, characterized by that the aqueous solution is polyol-free and / or carboxylic acid-free and / or ammonia-free. [7] Method according to any one of the preceding claims, characterized by that the aqueous solution consists of water and urea. [8] Liquid process medium obtainable by a process according to any of the preceding claims, wherein the heating is carried out over a period of 20 minutes to 240 minutes, wherein the aqueous solution contains 1 to 10% by mass of urea and the ratio between urea-containing aqueous solution and polyurethane-containing material is 0.4 ml / g to 5 ml / g.

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