Process for preparing polyol admixtures from recycled polyurethane material

Abstract

A process for obtaining polyols from polyurethane material comprises the steps of - provide a polyol dispersion in a quantity comprised between 30% and 70% of the total weight, a polyurethane in a quantity comprised between 20% and 65% of the total weight, and at least one dicarboxylic acid and / or a corresponding anhydride in a quantity comprised between 5% and 15% of the total weight, - forming a first admixture by adding to the dispersion polyol heated to 180°C 220°C a first part of dicarboxylic acid and / or anhydride representing between 5% and 50% of the total amount of dicarboxylic acid and / or anhydride, - forming a second admixture by adding polyurethane to the first admixture, - leaving the second admixture to react at a temperature comprised between 180 and 220°C for a time of at least 30 minutes, - forming a third admixture by adding the remaining dicarboxylic acid and / or anhydride to the second admixture, and - leaving the third admixture to react at a temperature comprised between 180 and 220°C for a time of at least 30 minutes.

Description

[0001] Process for preparing polyol admixtures from recycled polyurethane material

[0002] The present invention relates to a process for preparing polyol admixtures by recycling polyurethane material, as well as a polyol admixture obtained from this process.

[0003] Polyurethane is one of the most widespread and widely used polymers in the world. In recent decades, polyurethane production has grown significantly, leading to a significant increase in the amount of waste and, at the same time, concerns about its disposal.

[0004] Therefore, the need has arisen to develop processes that can recycle polyurethane material while avoiding other types of environmentally unfriendly disposal, such as landfilling or incineration.

[0005] In particular, great attention has been paid to the recycling of polyurethane through chemical processes (also known as solvolysis processes) rather than through mechanical processes, as the latter have proven to be rather expensive and its products are limited to use in composites and agglomerates. Recycling through chemical processes instead aims to degrade the polyurethane material, e.g. by depolymerisation, breaking it down into polyols and / or other oligomers and smaller molecules.

[0006] In particular, polyols obtained from polyurethane chemical recycling processes can be used, alone or in admixtures with virgin polyols, as starting compounds in the production of new polyurethane, reducing the environmental impact and also the production costs of the new polymer, in accordance with the principles of the circular economy.

[0007] In recent years, several thermo-chemical methods for recycling polyurethane have been developed, including hydrolysis, alcoholysis, aminolysis and glycolysis. The latter is the one that has spread most widely due to its easier applicability. However, the glycolysis process requires high energy and long reaction times that significantly restrict the scale of use; moreover, polyols obtained by polyurethane glycolysis are characterised by a high hydroxyl number and, therefore, their use is limited to the production of rigid polyurethanes.

[0008] More recently, another process for the degradation of polyurethane by solvolysis, called acidolysis, has been developed that has certain advantages over the previous techniques.

[0009] In general terms, acidolysis uses dicarboxylic acids or the corresponding anhydrides to depolymerise polyurethane and convert it into polyols for recycling.

[0010] This reaction is conducted at high temperature in the presence of polyols and, contrary to other methods, can be conducted in one step with good yields, thus also minimising the amount of non-depolymerised residues and energy used. Among the advantages of this technique over other solvolysis techniques is the fact that recycled polyols obtained by acidolysis are potentially suitable for the production of flexible polyurethanes alone or in admixtures with virgin polyols, resulting in polyurethane products with density and morphology comparable to those obtained with all virgin polyols. In addition, it has been shown that recycled polyols obtained by acidolysis contain fewer unreacted aromatic amines and glycols and have lower hydroxyl numbers, expanding their applications for use.

[0011] Examples of processes for producing polyols from recycled polyurethane waste by acidolysis according to known technique are described in DE 102013106364 and in DE 19512778.

[0012] However, despite these advantages and promising results, the Applicant has noted that the recycling process by acidolysis still has some drawbacks.

[0013] In particular, the Applicant has noted that the polyol admixtures obtained from such a recycling process are unstable over time, tending to separate into phases (depending on the density of the components in the admixture) when not shaken vigorously and consistently, and significantly increasing the viscosity.

[0014] These drawbacks make polyol admixtures obtained from recycling processes by acidolysis unsuitable for transport or storage, so that they have to be reused in the production of new polymers in a very short time, often at the same plant, greatly complicating their management and limiting their sales potential.

[0015] The Applicant, in an effort to solve these drawbacks, noted that the polyols obtained from the acidolysis process exhibit a wide distribution of polymer chain lengths, which may justify the high inhomogeneity of the chemicalphysical and rheological properties of the polyol admixture and their high tendency to phase separation.

[0016] Therefore, the Applicant perceived that in order to improve the stability of the polyol admixture obtained from the polyurethane acidolysis reaction, it was necessary to adjust the reaction parameters so as to obtain polyols with a more uniform chain length.

[0017] On the other hand, the Applicant considered that the variation of these reaction parameters should also not lead to a deterioration of other characteristics of the polyol admixture, in particular in terms of viscosity, hydroxyl number, acid number and concentration of free amines in the final admixture.

[0018] The Applicant thus found that by allowing the polyurethane to react for a suitable length of time with only a fraction of the quantity of dicarboxylic acid (or the anhydride corresponding thereto) prepared for the acidolysis process and then administering the remaining part of dicarboxylic acid (or the anhydride corresponding thereto) necessary to complete the acidolysis process, a homogeneous and stable polyol admixture is obtained with excellent values of the above-mentioned characteristics.

[0019] Therefore, in a first aspect thereof, the present invention concerns a process for obtaining polyols from polyurethane.

[0020] Preferably, the process comprises the step of preparing respective quantities of a dispersion polyol, a polyurethane and at least one dicarboxylic acid and / or an anhydride corresponding to said dicarboxylic acid.

[0021] Preferably, the amount of dispersion polyol is comprised between 30% and 70% of the total weight of dispersion polyol, polyurethane and at least one dicarboxylic acid and / or corresponding anhydride.

[0022] Preferably, the amount of polyurethane is comprised between 20% and 65% of the total weight of dispersion polyol, polyurethane and at least one dicarboxylic acid and / or corresponding anhydride.

[0023] Preferably, the amount of at the least one dicarboxylic acid and / or corresponding anhydride is comprised between 5% and 15% of the total weight of dispersion polyol, polyurethane and at least one dicarboxylic acid and / or corresponding anhydride. Preferably, the amount of the at least one dicarboxylic acid and / or corresponding anhydride is divided into a first part and a second part, the latter being formed by the remaining portion of the total amount of dicarboxylic acid and / or corresponding anhydride.

[0024] Preferably, said first part is comprised between 5% and 50% of the total amount of at the least one dicarboxylic acid and / or corresponding anhydride.

[0025] Preferably, the process comprises the step of heating the dispersion polyol to a temperature comprised between 180-220°C.

[0026] Preferably, the process comprises the step of adding to said dispersion polyol said first part of at least one dicarboxylic acid and / or corresponding anhydride, forming a first admixture.

[0027] Preferably, the process comprises the step of adding polyurethane to the first admixture, forming a second admixture.

[0028] Preferably, the process comprises the step of leaving said second admixture to react at a temperature comprised between 180-220°C.

[0029] Preferably, the second admixture is left to react for a time of at least 30 minutes.

[0030] Preferably, the process comprises the step of adding to said second admixture at least one dicarboxylic acid and / or corresponding anhydride, forming a third admixture.

[0031] Preferably, the process comprises the step of leaving said third admixture to react at a temperature comprised between 180-220°C.

[0032] Preferably, the third admixture is left to react for a period of at least 30 minutes.

[0033] This process makes it possible to obtain recycled polyol admixtures with chemical-physical and rheological properties that remain stable for a period of at least several months, allowing them to be transported and stored at times more suitable for industrial production. This makes it possible to market the resulting polyol admixtures and / or use them in plants far away from the recycling site.

[0034] With reference to the process of the present invention, it is clarified that "dispersion polyol" means the polyol in which the process of acidolysis of polyurethane by means of dicarboxylic acid or the corresponding anhydride is conducted.

[0035] The dispersion polyol thus essentially acts as a reaction medium. In fact, the Applicant considers that polyol does not participate, at least appreciably, in the polyurethane degradation reaction by acidolysis, although possible secondary reactions cannot be completely excluded.

[0036] The Applicant has noted that an amount of dispersion polyol less than 30% of the total weight of dispersion polyol, polyurethane and dicarboxylic acid can lead to an excessive viscosity of the reaction admixture, while an amount greater than 70% can lead to an excessive dilution of the polyurethane, making the process economically unviable.

[0037] Furthermore, while it is desirable to be able to recycle as much polyurethane as possible in a single reaction, the Applicant has verified that an amount of polyurethane greater than 65% by weight of the total of dispersion polyol, polyurethane and dicarboxylic acid could make its dispersion in the reaction admixture very difficult, thus hindering the successful outcome of the reaction itself. Conversely, using less than 20% polyurethane with respect to the total weight of the three main components identified above may not be cost- effective.

[0038] The Applicant has further verified that a quantity of the at least one dicarboxylic acid and / or the corresponding anhydride less than 5% with respect to the total weight of dispersion polyol, polyurethane and dicarboxylic acid would be insufficient to conduct the depolymerisation of polyurethane. On the other hand, a quantity of at least one dicarboxylic acid and / or corresponding anhydride in excess of 15% of the total weight of the three main components identified above could result in an excessively high amount of free acids in the final polyol admixture, which would hinder its subsequent reuse.

[0039] Without wishing to be in any way bound by the following assumptions, the Applicant considers that the addition of only a first part of the total amount of dicarboxylic acid envisaged for the acidolysis reaction is sufficient to initiate the polyurethane depolymerisation reaction, while avoiding the reaction of the dicarboxylic acid with the dispersion polyol. This seems to be able to avoid subsequent reactions that may result in very complex and different molecules, affecting the properties of the polyol admixture obtained at the end of the process.

[0040] In this way, the dispersion polyol serves only as a reaction medium.

[0041] The aforementioned depolymerisation reaction mainly takes place in the period of time following the addition of the polyurethane to the admixture formed by the dispersion polyol and the first part of dicarboxylic acid (in other words, when the second admixture is formed). This reaction also leads to the formation of free primary amines.

[0042] However, contrary to what may be assumed, the formation of amines during this step does not give rise to any particular disadvantages. In fact, once the second admixture is allowed to react, the remaining dicarboxylic acid is added, which, in the presence of the previously formed amines, results in the formation of amides, which is the kinetically most favoured reaction.

[0043] Surprisingly, this yields as a product a polyol admixture containing a very low concentration of free primary amines, well below 1000 ppm.

[0044] The resulting polyol admixture will thus consist of a part of dispersion polyol and other polyols obtained precisely from the depolymerisation of polyurethane and polyols containing amide groups.

[0045] Another advantage of the process according to the invention is the possibility of treating both polyurethane materials from polyurethane production processes (post-production waste) and polyurethane materials from consumer products that have reached the end of their life cycle (post-consumer waste). Examples of such products are the stuffing of cushions, seats, mattresses, or shoe soles.

[0046] In a second aspect thereof, the present invention concerns an admixture of polyols from recycled polyurethane material obtained according to a process in accordance with the first aspect of the invention.

[0047] In at least one of the aforesaid aspects, the present invention may have at least one of the following preferred characteristics.

[0048] Preferably, the dispersion polyol has a hydroxyl number comprised between 20-60 mgKOH / g. Preferably, this analytical data is obtained using the ASTM D4274-23 procedure.

[0049] Preferably, the dispersion polyol has an acid number less than 1 mgKOH / g. Preferably, this analytical datum is obtained using the ASTM D7253-22 procedure.

[0050] Preferably, the dispersion polyol has a viscosity comprised between 1000 and 10000 cP, more preferably between 4000 and 8000 cP. Preferably, this analytical datum is obtained using the ASTM D445-94 procedure.

[0051] In this way, a polyol admixture with more similar and homogeneous species is obtained, since the polyols used as monomers in the production of polyurethane also generally exhibit these characteristics.

[0052] In some preferred embodiments, the polyurethane is a flexible, viscoelastic and / or semi-rigid polyurethane.

[0053] More preferably, polyurethane material from the same source is used. This maximises the efficiency of the process.

[0054] To this end, it should be noted that "flexible" polyurethane refers to a polyurethane material with low density and low modulus of elasticity, resulting in a relatively soft consistency, yielding to the touch, and also presenting appreciable springback. Typically, flexible polyurethane consists of an expanded open-cell (foam) structure, has a relatively low degree of crosslinking between the polymer molecules and is used, for example, in the production of mattresses, sponges, cushions and upholstery for sofas, armchairs or seats.

[0055] "Viscoelastic" polyurethane refers to a flexible polyurethane material that also has viscoelastic characteristics, i.e. having delayed springback over time. These polyurethane materials are also known as shape memory polyurethanes.

[0056] By "rigid" polyurethane, on the other hand, we mean a polyurethane material with a relatively high density and elastic modulus, resulting in a relatively rigid consistency that is not very or not at all yielding to the touch. Rigid polyurethane can have an expanded or compact structure, has a high degree of cross-linking between the polymer molecules and is used, for example, in the production of panels or other structures with high thermal insulating properties.

[0057] "Semi-rigid" polyurethane refers to a polyurethane material with an intermediate consistency that is more rigid than flexible polyurethane but without the dimensional stability of rigid foams.

[0058] In some embodiments, the polyurethane used in the recycling process was obtained by reaction of an isocyanate with at least a first polyol, and the dispersion polyol used in the process corresponds to said at least one first polyol used in the production of polyurethane.

[0059] In other words, the dispersion polyol preferably corresponds to the polyol used in the production of the polyurethane to be recycled or, in the event that the polyurethane results from the polymerisation of several polyols, the dispersion polyol corresponds to at least one of these polyols.

[0060] In particular, where the polyurethane has been obtained by reaction of an isocyanate with at least a first short-chain polyol and at least a second long- chain polyol, such as in the production of a viscoelastic polyurethane, the dispersion polyol used in the process preferably corresponds to the first shortchain polyol.

[0061] Advantageously, using the same polyol that was used as the reactant compound in the production of the polyurethane to be recycled maximises yields, as it further increases the chemical affinity of the polyols in the recycling admixture produced, limiting the possibility of phase separation phenomena and the presence of solid residues of unreacted oligomers.

[0062] In some embodiments, the predetermined amount of dispersion polyol is comprised between 35% and 60%, preferably between 40% and 50%, and even more preferably about 45% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride.

[0063] In some embodiments, the predetermined amount of polyurethane is comprised between 30% and 60%, preferably between 40% and 50%, and even more preferably about 45% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride.

[0064] Preferably, all the polyurethane is added to the first admixture after dissolution of the first part of at least one dicarboxylic acid and / or anhydride in the dispersion polyol, forming the second admixture.

[0065] In some embodiments, the weight ratio between the amount of dispersion polyol and the amount of polyurethane is comprised between 0.5: 1 and 1.5: 1, preferably between 0.8: 1 and 1.2: 1, more preferably about 1 : 1.

[0066] In some embodiments, the predetermined quantity of the at least one dicarboxylic acid and / or corresponding anhydride is comprised between 7% and 12%, preferably about 10% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride.

[0067] In some embodiments, the ratio by weight of the total quantity of at least one dicarboxylic acid and / or corresponding anhydride to the amount of polyurethane is comprised between 0.15: 1 and 0.3: 1, preferably between 0.2: 1 and 0.25: 1.

[0068] In some embodiments, said first part of the at least one dicarboxylic acid and / or corresponding anhydride is comprised between 10% and 30%, more preferably between 15% and 25% of the total amount of the at least one dicarboxylic acid and / or corresponding anhydride prepared.

[0069] In some embodiments, the at least one dicarboxylic acid and / or corresponding anhydride is selected from a group consisting of succinic acid, sebacic acid, oxalic acid, adipic acid, phthalic acid and their anhydrides, alone or in combination.

[0070] Preferably, the at least one dicarboxylic acid is saturated.

[0071] The particularly preferred dicarboxylic acid is succinic acid.

[0072] In the preferred embodiment, the total succinic acid, i.e. the total of the first part and the second part, is arranged in an amount equal to about 10% of the total weight of dispersion polyol, polyurethane and dicarboxylic acid.

[0073] Preferably, once the reaction temperature has been reached and before adding the remaining carboxylic acid, the second admixture is left to react for a time comprised between 1 and 3 hours; even more preferably, the second admixture is left to react for about 2 hours.

[0074] These parameters allow the efficiency and yields of the process to be maximised.

[0075] Preferably, the temperature at which said second admixture is left to react is between 190-210°C.

[0076] In some embodiments, the second part of the at least one dicarboxylic acid and / or corresponding anhydride is added to the second admixture by successive additions spaced at least 5 minutes apart. In particular, it is preferable for said at least one dicarboxylic acid and / or corresponding anhydride to be added to said second admixture at successive times consisting essentially of additions made 10-20 minutes apart.

[0077] In any case, it is preferable for the addition of the remaining dicarboxylic acid and / or corresponding anhydride to take place within one hour of the end of the set waiting time for the second admixture to react.

[0078] According to a preferred embodiment, the second part of dicarboxylic acid and / or corresponding anhydride is added in 6 successive additions spaced approximately 10 minutes apart.

[0079] In a preferred embodiment, once all of the second part of at least one dicarboxylic acid and / or corresponding anhydride has been added, the third admixture is left to react for a time period comprised between 1 and 4 hours, more preferably about 2 hours.

[0080] In the preferred embodiment, the third admixture is reacted at a temperature less than the temperature at which the second admixture is left to react, preferably between 180°C and 200°C, e.g. at 190°C.

[0081] At these temperatures, the reaction between the at least one dicarboxylic acid and / or corresponding anhydride with the amines formed in the previous reaction between the first part of the dicarboxylic acid and the polyurethane is further promoted.

[0082] The polyol admixture obtained from the process described above can have a viscosity comprised between 1000 and 10000 cP (measured according to ASTM D445-94), preferably around 4000 - 8000 cP.

[0083] The polyol admixture obtained from the process described above can have a hydroxyl number comprised between 25 and 60 mgKOH / g (measured according to ASTM D4274-94d).

[0084] The polyol admixture obtained from the process described above can have an acid number comprised between 0.2 and 2 mgKOH / g, more preferably between 0.2% and 1%.

[0085] The polyol admixture obtained according to the process described above can be used in the production of new polyurethane on its own or in combination with a virgin polyol, e.g. in weight percentages comprised between 10% and 50%.

[0086] Such a polyol admixture obtained according to the process of the present invention can advantageously be used for the production of flexible polyurethane as well as in the production of viscoelastic polyurethane.

[0087] Example 1 (comparative

[0088] In a 100-litre reactor, 27 kg of a dispersion polyol with the following characteristics were introduced:

[0089] - molar mass: 4500 - 4700 Dalton,

[0090] - viscosity: 1200 - 1500 cP,

[0091] - hydroxyl number: 30-40 mgKOH / g,

[0092] - acid number: less than 0.1 mgKOH / g,

[0093] The dispersion polyol was heated to approximately 210° C and 6 kg of succinic acid was added while stirring continuously.

[0094] After the addition of the succinic acid, 27 kg of coarsely broken up viscoelastic flexible polyurethane from mattress upholstery waste was added, maintaining temperature and stirring.

[0095] The dispersion polyol is substantially the same polyol used in the production of polyurethane for recycling.

[0096] After the addition of polyurethane, the admixture was then stirred at the same temperature for 3 hours so that the acidolysis reaction of the polyurethane could take place.

[0097] The resulting polyol admixture has the following characteristics at the end of the reaction:

[0098] - viscosity: approximately 9000 cP,

[0099] - amine content: approximately 400 ppm,

[0100] - hydroxyl number: 37 mgKOH / g,

[0101] - acid number: 4 mgKOH / g.

[0102] After about a week of storage without stirring, at room temperature, the viscosity of the admixture increased to about 15000 cP and after about 1 month it further increased to about 30000 cP.

[0103] Moreover, already after one week the admixture showed a clear phase separation.

[0104] Example 2 finvention

[0105] In a 100-litre reactor, the same amount of the same dispersion polyol used in Example 1 was introduced into the reactor and heated to a temperature of 210°C while stirring.

[0106] Approximately 1.2 kg of succinic acid was added to the heated dispersion polyol while continuously stirring. This quantity represents about 20% of the succinic acid prepared for the entire process, i.e. a total of 6 kg, as in Example 1.

[0107] Immediately after the addition of the first part of succinic acid, the same amount of the same viscoelastic, coarsely broken flexible polyurethane as in Example 1 was added, maintaining temperature and stirring.

[0108] After the addition of the polyurethane, the admixture was then stirred at a temperature of approximately 200 °C for 2 hours, after which the remaining part of succinic acid (equal to 80% of the total amount of succinic acid prepared for the process) was added. This step was conducted by 6 successive additions of succinic acid spaced approximately 10 minutes apart.

[0109] After the addition of the second part of succinic acid, the admixture was stirred at a temperature of about 190° for about 2 hours.

[0110] The resulting polyol admixture has the following characteristics: viscosity: approximately 5800 cP, amine content: approximately 350 ppm, hydroxyl number: 38 mgKOH / g, acid number: 1.8 mgKOH / g.

[0111] The polyol admixture showed essentially the same viscosity after 10 days, after 20 days and after one month of storage without stirring, at room temperature. During this period, the admixture did not exhibit any phase separation.

[0112] Comparison of the polyol admixtures obtained from Example 1 and, respectively, Example 2 described above, shows that the process of the invention results in a much more stable polyol admixture over time, capable of retaining its rheological properties over a long period of time without incurring undesirable phase separation phenomena.

[0113] In addition, it will be appreciated that the amine content remains very low, as does the hydroxyl number, allowing safe reuse of the polyol admixture also for the production of new flexible or viscoelastic polyurethane.

Claims

Claims1. Process for obtaining polyols from polyurethane material comprising: a) providing respective quantities of a dispersion polyol, a polyurethane and at least one dicarboxylic acid and / or a corresponding anhydride, in which: o the quantity of dispersion polyol is between 30% and 70% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride; o the quantity of polyurethane is between 20% and 65% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride; o the quantity of at least one dicarboxylic acid and / or corresponding anhydride is between 5% and 15% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride; o the quantity of the at least one dicarboxylic acid and / or corresponding anhydride is subdivided into a first portion between 5% and 50% of said quantity and a second portion formed by the remaining portion of said quantity, b) heating the dispersion polyol to a temperature between 180°C and 220°C; c) adding to the dispersion polyol the first portion of the at least one dicarboxylic acid and / or corresponding anhydride, forming a first admixture;d) adding to the first admixture the quantity of the polyurethane, forming a second admixture; e) leaving the second admixture to react at a temperature between 180 and 220°C for a time of at least 30 minutes; f) adding to the second admixture the second portion of the at least one dicarboxylic acid and / or corresponding anhydride, forming a third admixture; g) leaving the third admixture to react at a temperature between 180 and 220°C for a time of at least 30 minutes.

2. Process according to claim 1, wherein the dispersion polyol has a hydroxyl number between 20 and 60 mgKOH / g, an acid number less than 1 mgKOH / g and a viscosity between 1000 and 10,000 cP.

3. Process according to claim 1 or 2, wherein the polyurethane is a flexible polyurethane and / or viscoelastic polyurethane which is obtained by reaction of an isocyanate with at least a first polyol, and wherein the dispersion polyol corresponds to the first polyol.

4. Process according to any one of the preceding claims, wherein the quantity of dispersion polyol is comprised between 40% and 50% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride.

5. Process according to any one of the preceding claims, wherein the ratio by weight between the dispersion polyol and the polyurethane is between 0.5: 1 and 1.5: 1.

6. Process according to any one of the preceding claims, wherein the ratio by weight between the at least one dicarboxylic acid and / orcorresponding anhydride and the polyurethane is between 0.15: 1 and 0.3: 1.

7. Process according to any one of the preceding claims, wherein the at least one dicarboxylic acid and / or corresponding anhydride is selected from a group which is formed by succinic acid, sebacic acid, oxalic acid, adipic acid, phthalic acid and the anhydrides thereof, alone or in combination with each other.

8. Process according to any one of the preceding claims, wherein the at least one dicarboxylic acid is saturated.

9. Process according to the preceding claim, wherein the at least one dicarboxylic acid is succinic acid at a total quantity between 7% and 12% of the total weight of the dispersion polyol, the polyurethane and the at least one dicarboxylic acid and / or corresponding anhydride.

10. Process according to any one of the preceding claims, wherein the second admixture is left to react at a temperature between 190°C and 210°C for a time between 1 and 3 hours.

11. Process according to any one of the preceding claims, wherein the second portion of the at least one dicarboxylic acid and / or corresponding anhydride is added to the second admixture by successive additions which are spaced apart from each other by a time of at least 5 minutes.

12. An admixture of polyols from polyurethane material which is obtained according to any one of the preceding claims.