Abstract

The present invention relates to recycling of polyurethanes, in particular polyurethane foams by aminolysis with reagents comprising both primary and/or secondary and tertiary amino groups in the structure to recover, depending on reaction conditions, either fully hydroxyl-functionalized polyols of comparable quality to the virgin ones, or partially aromatic amino functionalized polyols.

Background

Polyurethanes (PU) are a diverse group of materials, among which PU foams (PUFs) are an important class of materials. Flexible PUFs are used for upholstered furniture, mattresses, and automotive seats, while rigid PUFs are used mainly for building insulation. Since PUFs account for a large portion of the total production and consumption of PUs, they generate an increasing amount of waste, which requires efficient waste management. Due to stringent environmental regulations and the need for a circular economy, sustainable approaches to the production of PUFs, such as recycling and the use of bio-derived feedstock, are emerging as the most suitable solutions. ¹

PUFs have a thermostable, cross-linked structure. Therefore, decomposition of the PUF network by chemical degradation is the best option for their sustainable recycling. In this way, recycled polyols (RPs) are obtained, which can be reused for variety of applications. Currently, RPs can also be used to synthesize flexible PUFs of the same quality, but only part of the virgin polyol in the PUF formulation is replaced by the recycled one. Over the years, many chemical methods have been developed and applied for PUF recycling, such as glycolysis, ² ' ¹⁵ hydrolysis, ^16,17 acidolysis, ^18-22 and aminolysis. ^23-31

The methods of chemical recycling of PUFs are based on the degradation of urethane groups in the polymer structure, resulting in the release of RP and residues of PUF hard segments (oligoureas), which are terminated with the degradation reagent used. PUF hard segments consisting of oligourea sequences can also be degraded to some extent thermally or by other side reactions, leading to the excessive formation of unwanted toxic aromatic amines. The degree of degradation of urethane bonds and urea bonds of hard segments in PUF structure depends on the experimental conditions used. Aminolysis is a reaction in which the amine reagent displaces the polyol at the urethane bond, forming free RP and a urea bond between the reagent and the end group of the oligourea segments (Fig. 1). Amine reagents already used for PUF degradation include various alkanolamines and amines containing primary and secondary groups in the structure, as well as ammonia in the so-called ammonolysis reaction (US patent No. 4, 162, 995). ³² US patent No. 3, 117,940 ³³ describes a method for improved liquefaction of PU-based plastics. A variety of PU plastics (including PU cellular plastics known as PUFs) are dissolved in primary amines in the presence of tertiary amine as a catalyst at temperatures above 70 °C. A few patents describe the use of alkanolamines for the chemical degradation of PUF waste, mostly for rigid PUFs (US 4, 162, 995, ³² US 3, 708, 440, ³⁴ US 3, 738, 946, ³⁵ and US 4,014, 809). ³⁶ All describe chemical degradation of PUFs at elevated temperatures (up to 250 °C) in the presence of alkanolamines via alcoholysis/glycolysis pathway rather than aminolysis mechanism. Reported alkanolamine reagents, which are used in amounts up to 20 wt.% per PUF, include diethanolamine, triethanolamine, dipropanolamine, diisopropanolamine, N-(2- hydroxypropyl)ethanolamine, 3,3'-iminobis(2-hydroxybutane), where some of the aforementioned amines include the tertiary amino group in the structure, such as triethanolamine. Tertiary amines, such as triethylenediamine, dimethylpiperazine, triethanolamine or dimethylaniline, used in catalytic amounts, are proposed as suitable catalysts that allow lowering the reaction temperature in the glycolysis of PU resins (US patent No. 3, 632, 530). ³⁷ In another patent, a method for recycling PU materials (including PUFs) using different glycols in combination with aliphatic amines or polyamines, where preferred amines contain at least two primary and at least one tertiary amino group (e. g. A/,A/-bis-(3-aminopropyl)-A/-methylamine, A/,A/-bis(2-aminopropyl)-A/-methylamine, N,N- bis(2-aminoethyl)-/V-methylamine), is reported (DE 10 2007 020 541 A1). ³⁸ Similarly, patent EP 2 270 083 ³⁹ describes a method for producing polyol components from PUF waste using glycols and aliphatic amines, such as A/,A/-bis-(3-aminopropyl)-A/- methylamine, and finally specific mixture of fatty acids is added. In US patent No. 6,750,260 B2, ⁴⁰ various chemolysis processes are proposed. Here, aminolysis with preferably low molecular weight diamines is described to be carried out at atmospheric pressure and lower temperatures compared to PUF glycolysis, but the type of amine reagents is not precisely defined. In patent FR 1 429 011 ⁴¹ aminolysis of PU materials (including PUFs) using aliphatic, cycloaliphatic and aromatic amines, which act both as solvent and reagent, is described. Reagents containing primary and/or secondary and tertiary amino groups in the molecule are not mentioned. European patent application No. EP 1 142 945 A2 ⁴² describes a method of aminolysis using polyamine compounds as a solubilizer for polyurethane resins (including PUFs), typically toluenediamine, but also diaminodiphenylmethane, polymethyl polyphenyl polyamine, and mixtures thereof. Patent WO 2015/027319 A1 ⁴³ aims to improve the efficiency of various chemolysis methods, highlighting glycolysis as the most promising by using low molecular weight glycols, while bases (including amines and alkanolamines) are used as catalysts. Aminolysis of PUFs is also mentioned as a possible chemical degradation pathway, but no further details are given. Patent EP 1 149 862 A1 ⁴⁴ deals with recycling of rigid PUFs either by glycolysis or aminolysis. Amine reagents such as ethanolamine and tolylenediamine in a PUF/amine reagent ratio of 1/0.4 to 1/5 (wt%) are proposed. Patent EP 3 098 257 B1 ⁴⁵ describes glycerolysis using eco-reagent (crude glycerol) at temperatures between 150-290 °C, preferably from 220 to 240 °C, using catalysts that include alkanolamines such as ethanolamine, diethanolamine and triethanolamine (tertiary amine). Patent CN 10,3012, 838A ⁴⁶ describes the recycling of PUF waste with aminolysis using aromatic amine or alkanolamine, such as diethanolamine and triethanolamine (tertiary amine) at temperatures from 150 to 250 °C in the presence of a catalyst, such as acetate, titanic acid ester of a metal base or alkaline earth metal. The heating of reaction mixtures is carried out in conventional manner, so that the reaction time is up to 20 hours. US patent No. 6,683,119 B1 ⁴⁷ presents an improved process for chemical recycling of PU waste, combining glycolysis and aminolysis using conventional heating. PU waste is added to a mixture of diol and secondary alkylamine, such as di-/V-butylamine. The reaction is performed at temperatures between 120-220 °C. Secondary alkylamine acts as a reagent and catalyst, so it should not be added in excess, preferably in a ratio of PU/diol/amine of 100/50/25 to 100/25/6. DE 4 217 524 A1 ⁴⁸ describes an improved method for recovering isocyanate-reacted components using a combination of different reagents selected from water, amino compounds having a molecular weight of 177 to 399 Da, and optionally mono-, di-, or polyfunctional alcohols having a molecular weight of 32 to 250 Da. Amine reagents include ammonia, primary or secondary amines (alkylamines such as butylamine or (cyclo)hexylamine) and alkanolamines such as aminoethanol or N- methylaminoethanol, also hexamethylenediamine, diaminodiphenylmethane or, optionally alkyl-substituted, toluenediamine. The patents mentioned so far use conventional heating of reaction mixtures. The patent EP 2 480 584B1 ⁴⁹ describes the recycling of rigid PUFs using bioreagents from renewable sources with active hydroxyl functional groups at elevated temperatures (from 150 to 300 °C). In contrast to the energy consuming conventional heating of reaction mixtures, microwave heating has also been proposed as a way to reduce energy costs. ^30,50,51 Alkanolamines such as ethanolamine, diethanolamine, and triethanolamine (tertiary amine) are reported to be used only as catalysts in PU recycling, with PUF/amine ratios ranging from 500/1 to 10/1. Patent application US 2008/0047824 A, ⁵⁰ similar to DE 4 217 524 A1 ⁴⁸ , describes the chemical degradation of PU using one or more reactive reagents such as water, amino compounds with molecular weight of 177 to 399 Da, and mono-, di-, or polyfunctional alcohols with a molecular weight of 32 to 2500 Da, but using microwaves as the heat source instead of conventional heating. Tertiary amine, such as 1 ,1 ,1-diazabycyclooctane (DABCO), was used as catalyst. Patent EP 2 183 311 B1 ⁵¹ describes glycolysis of PUF waste using microwave heating of reaction mixtures up to 300 °C in the presence of alkanolamines such as ethanolamine, diethanolamine and triethanolamine tertiary amine as catalysts.

In the published literature, Korshak et al. ²³ performed aminolysis of linear polyurethane with aniline for six hours using conventional heating. They confirmed successful degradation of PU, as evidenced by the decrease in PU molecular weight. Van der Wai ²⁴ published a patent US 5,274,004 ⁵² and later a paper on a combined chemical recycling process for PU waste. The degradation of urethane bonds in a variety of PUs was carried out with alkanolamines in the presence of metal hydroxides (MOH) at elevated temperature (120 °C) to obtain RPs. To eliminate the presence of aromatic diamines in the RP, the authors proposed alkoxylation as the second step of PU recycling. The final product is a mixture of alkoxylated RP, alkoxylated aromatic amines, and alkoxylated short-chain carbamates or/and ureas, and these recycled products were used as partial replacement (20 and 40 wt. %) of virgin polyol in formulation for flexible PUF synthesis. Kanaya and Takahashi ²⁵ provided insight into the reaction mechanism of PUFs with alkanolamines by investigating the type of the functional group of (mono)ethanolamine (MEA) and diethanolamine amine (DEA) involved in the degradation of urethane bonds in flexible PUFs prepared from methylene diphenyl isocyanate (MDI). It was shown that alcoholysis by the hydroxyl group of MEA predominates over aminolysis, so that the degradation of PUF by alkanolamine (e.g., MEA) cannot be specified as aminolysis but rather as a combination of alcoholysis and aminolysis reactions. Ge and Sakai ²⁷ studied the degradation of biodegradable PUF based on wattle tannin by aminolysis with aniline. Xue and co-workers ²⁸ used various types of aliphatic amines (diethylene triamine (DETA), triethylene tetramine (TETA), and tetraethylene pentamine (TEPA)) to degrade the rigid PUF waste. They found that extent of PUF degradation depends on the basicity of the amine reagent used. The obtained products were used as curing agents for epoxy resin. Aminolysis of rigid PUFs was also performed by Chuayjuljit and co-workers ²⁹ using diethylenetriamine (DETA) with or without the presence of a catalyst (NaOH). They confirmed that metal hydroxides play a role in the degradation of urethane and urea groups. Modification of PUF recycling by aminolysis with ethylene diamine (EDA) was published by Rane et al. ³⁰ To minimize the extent of side reactions in aminolysis, which were not specified, they performed aminolysis with microwaves under varying reaction time and temperature. The main advantage of microwave heating was a reduction in reaction time from 3.0 to 0.5 hours and also the extent of side reactions involved was lower. The successful PUF degradation was confirmed by the determination of hydroxyl and amine values of the obtained products. The recycled product was further used in polyurethane urea-based coatings.

Most of the literature describes the use of primary (alkanol)amines in combination with glycol reagents as well as the use of tertiary (alkanol)amine reagents acting as catalysts in the alcoholysis/glycolysis of PUFs. However, in most cases, amines are not used as the primary and/or sole amine reagent for PUF degradation. ³² ' ^43,45 ' ⁴⁷

Neither patents nor published literature describes the aminolysis of PUFs with amine reagents acting simultaneously as reagent and catalyst. However, this would be favorable for an effective and sustainable method of chemical recycling of PUF waste.

Description of the invention

It has been found in the present invention that certain amine reagents are capable of acting simultaneously as reagent and catalyst. These reagents are amines containing both primary and/or secondary and tertiary amino groups in the structure of the same reagent. The primary and/or secondary amino group actively participates as a reagent in the degradation of urethane groups, while the tertiary amino group catalyzes the aminolysis reaction, allowing efficient degradation of PU urethane groups.

Thus, the present invention provides a method of recycling polyurethane to polyols, comprising:

(i) mixing the polyurethane to be recycled with a reagent comprising at least one primary and/or secondary amino group and at least one tertiary amino group,

(ii) heating the resulting mixture to yield recycled polyol (RP), and

(iii) recovering the RP. The polyurethanes (PU) used as a starting material can be any waste PUs, in particular PUFs with either flexible or rigid structure, which are used for example as mattresses, in upholstered furniture, automotive seats, and for building insulation, respectively.

The reagent comprising at least one primary and/or secondary amino group and at least one tertiary amino group is not particularly limited, provided that both the primary and/or secondary amino group as well as the tertiary amino group are part of a single compound, for example bound to the same framework structure. Particularly preferred amine degradation reagents according to the invention for use in step (i) include tris(2- aminoethyl)amine (TREN, Fig. 2), and highly branched polyethylenimine (PEI: hyperbranched or dendrimer; Fig. 2) with various molecular weights. TREN contains three primary amino groups and one tertiary amino group in its structure. PEI dendrimers consist of multiple primary and tertiary amino groups due to their fully branched structure, while hyperbranched PEIs contain secondary amino groups in addition to primary and tertiary amino groups.

Equally effective are the following amine reagents: tris(3-aminopropyl)amine, 2-(4- methyl-piperazin-1 -yl)-ethylamine, 1 ,4-bis(3-aminopropyl)piperazine, 1 -(2- aminoethyl)piperazine, 3,3’-diamino-/V-methyldipropylamine, 3-(dimethylamino)-1 - propylamine, A/,/V-dimethylethylenediamine, A/./V-dimethyldipropylenetriamine, polypropylenimine tetramine dendrimers of different generation (reagents shown in Fig. 3), and the like, as well as combinations of two or more amine reagents comprising, among which one of the reagent used contains both primary and/or secondary as well as tertiary amino groups in the structure.

The above-defined reagent comprising at least one primary and/or secondary amino group as well as at least one tertiary amino group in its structure is used either as the sole reagent for PU degradation or it is used in the second step of one pot-degradation of PU or it is used to completely degrade urethane groups of partially aromatic amino functionalized recycled polyols recovered from PU in the first degradation step. That means that the proposed aminolysis reaction is carried out in the absence of any additional reagents such as diols, glycols, diacids, water, etc. If, any additional amine reagents are used with the aim to reduce the cost of the PU degradation process, then they are used in the first step of the two-step process, while the second step is always performed with the amine reagents containing both primary and/or secondary as well as tertiary amino group in the structure, which is a prerequisite to completely degrade the urethane groups. The reaction mixtures can be heated by conventional heating method or by microwaves as an energetically favorable, time- and cost-effective method, which shortens the reaction time, improves the degree of degradation and reaction yield, and reduces the extent of side reactions.

Aminolysis reactions of PU, e.g. flexible PUF can be carried out at 150 - 230 °C, preferably 220 °C or lower, for about 20 to 50 min, in particular for up to 30-40 min, preferably 30 min, with various amounts of the amine reagent containing primary and/or secondary as well as tertiary amino groups in the structure. The amine reagent is preferably used in an amount equal to or greater than 2 primary amino groups per PU urethane group, more preferably in an amount equal to or greater than 3 primary amino groups per PU urethane group and in particular in an amount equal to or greater than 4 primary amino groups per PU urethane group.

Optionally, the method of the invention further comprises a step of preheating the reaction mixture of (i) to a temperature in a range of about 120-180 °C, preferably about 175 °C, in a span of about 2-5 min, preferably about 3 min, before subjecting the mixture to a main heating in step (ii). Preheating is favorable to ensure partial liquefaction of the PU and better stirring of the reaction mixture.

Aminolysis can be performed as one-step or two-step reaction using conventional or microwave heating of the reaction mixtures. The degree of degradation of urethane groups increases with increasing amount of degradation reagent used. In a one-step reaction, the entire amount of amine reagent is added to the reaction mixture at once, whereas in a two-step as well as two-step, one-pot process amine reagent(s) is added in two steps as described below.

When amine reagent containing primary and/or secondary as well as tertiary amino groups in the structure is used in molar amounts equal to or greater than 4 primary amino groups per PU urethane group, complete degradation of the urethane groups is achieved, and after purification, fully hydroxyl-functionalized recycled polyol is obtained with comparable molecular weight and structural characteristics to that of virgin polyol (Examples 1 and 2).

Fully hydroxyl-functionalized RP is a consequence of the complete degradation of the PU urethane groups. When amine reagent is used in molar amounts less than 4/1 (primary amino/urethane group), incomplete degradation of urethane groups of PU is observed, however the amount of aromatic diamine formed during reaction is lower. The incomplete degradation of urethane groups leads to RPs partially functionalized with aromatic amino end groups (in addition to hydroxyl end groups). The content of aromatic amino functionalized end groups is in direct correlation with the degree of degradation of urethane groups and depends on the amount of reagent used and the reaction temperature and time applied. A sufficiently large amount of the amine reagent is also necessary to prevent the formation of double bonds at the polyol chain ends that can be formed at insufficient amounts of amine degradation reagent under basic conditions by one of the possible thermal degradation mechanisms. ⁵³ ' ⁵⁵ Double bonds at the polyol chain ends are inactive for polymerization with the diisocyanate and reduce the degree of PU cross-linking. This problem becomes apparent only when the amine reagent is used in molar amounts of less than 2/1 (primary amino groups of the amine reagents per urethane group in the PU structure).

Complete degradation of the urethane groups can also be achieved by a two-step aminolysis process at a reduced amount of the necessary amine degradation reagent containing primary and/or secondary as well as tertiary amino groups in the structure, wherein amine reagent is added in two steps, the first portion to the PU to be recycled and the second portion to the product of the crude RP obtained in the first step of reaction, after being separated from the reaction mixture. Amine reagent in the first aminolysis step could be any amine reagent containing primary and/or secondary amino group (HMDA, TREN, DETA, etc.). However, in the second step, the amine reagent with primary and/or secondary as well as tertiary amino groups in the same structure, such as TREN or any of the above mentioned amine reagents, must be used to run the reaction to completion.

Thus, in a particular embodiment, the method of the invention comprises:

(i.1 ) mixing the polyurethane to be recycled with a first amount of a first amine reagent, which can be any amine reagent containing primary and/or secondary amino group(s) in the structure,

(11.1) heating the resulting reaction mixture to yield crude recycled polyol (RP),

(111.1) recovering the crude RP,

(1.2) mixing the crude RP with a second amount of a reagent, which is the reagent comprising at least one primary and/or secondary amino group as well as at least one tertiary amino group in the structure,

(11.2) heating the resulting reaction mixture to yield RP, and

(111.2) recovering the RP, wherein in step (i.1 ), the first amine reagent is added in an amount of equal to or more than 2 primary and/or secondary amino groups per PU urethane group and less than 4 primary and/or secondaryamino groups per PU urethane group, and in step (i.2), the reagent is added in at least 1 .5 or higher amount (to 4-fold excess) of primary amino and/or secondary groups relative to the remaining urethane groups in the crude RP.

Optionally, a preheating step is carried out before the main heating in step (ii.1). The reaction mixture of (i.1 ) is preferably preheated to a temperature in a range of about 120-180 °C, more preferably about 175°C, in a span of about 2-5 min, preferably about 3 min, before subjecting the mixture to heating in step (ii.1).

In the first step, the molar amount of amine reagent should be greater than 2/1 and less than 4/1 (primary and/or secondary amino groups of amine reagents per urethane group in the PU structure) to achieve a degree of degradation of urethane groups (other groups are amino functionalized) of around 85-90% or more without formation of double bonds at the polyol chain-ends.

The resulting crude RP comprises partially aromatic amino functionalized recycled polyol. It is recovered in step (iii.1 ), for example by decanting, and subjected to a second degradation step.

In the second aminolysis cycle, amine reagent, which must contain primary and/or secondary as well as tertiary amino groups in the same structure, is added in at least 1 .5 or higher amount, at least 4-fold excess or preferably 6-fold excess of primary amino groups relative to the remaining urethane groups (Example 3). The first amine reagent added in step (i.1 ) can be the same as or different from the reagent used in step (i.2). In particular embodiments, a different amine reagent can be used for the first aminolysis cycle (Example 4).

Preferably, in both the first and second aminolysis steps, the first amine reagent and the reagent comprising at least one primary and/or secondary amino group and at least one tertiary amino group in its structure, respectively, are the only reagents used. That is, the reaction is preferably carried out in the absence of any additional reagents such as diols, glycols, diacids, water, etc., so that the reaction mechanism of PU degradation is only aminolysis in the absence of any glycolysis, hydrolysis, alcoholysis or acidolysis. This reduces the occurrence of by-products.

Complete degradation of urethane groups can also be achieved by two-step, one- pot aminolysis, where amine reagents in first and second step are added consecutively into the same reaction mixture. Performing aminolysis in two-steps in one-pot was introduced to reduce the amount of reagent containing both primary and/or secondary and tertiary amino groups in the same structure. Amine reagent in the first aminolysis step could be any amine reagent containing primary and/or secondary amino group (HMDA, TREN, DETA, etc.). In the second step, the amine reagent with primary and/or secondary as well as tertiary amino groups in the same structure, such as TREN or any of the above mentioned amine reagents, must be used to run the reaction to completion.

Thus, in a particular embodiment, the method of the invention comprises:

(i.1 ) mixing the polyurethane to be recycled with a first amount of a first amine reagent, which contains primary and/or secondary amino group(s) in the structure,

(ii.1) heating the resulting reaction mixture,

(1.2) mixing the reaction mixture with a second amount of a reagent, which is the reagent comprising at least one primary and/or secondary amino group as well as at least one tertiary amino group in the structure,

(11.2) heating the resulting reaction mixture to yield RP, and

(111.2) recovering the RP, wherein in step (i.1 ), the first amine reagent is added in an amount of equal to or more than 2 primary and/or secondary amino groups per PU urethane group and less than 4 primary and/or secondary amino groups per PU urethane group, and in step (i.2), the reagent is added in at least 1 .5 or higher amount and preferably in 6-fold excess of primary amino and/or secondary groups relative to the remaining urethane groups in the crude RP.

Optionally, a preheating step is carried out before the main heating in step (ii.1). The reaction mixture of (i.1) is preferably preheated to a temperature in a range of about 120-180 °C, more preferably about 175 °C, in a span of about 2-5 min, preferably about 3 min, before subjecting the mixture to heating in step (ii.1).

In the first step, the molar amount of the first amine reagent should be greater than 2/1 and less than 4/1 (primary and/or secondary amino groups of amine reagents per urethane group in the PU structure) to achieve a degree of degradation of urethane groups (other groups are amino functionalized) of around 85-90% or more without formation of double bonds at the polyol chain-ends. The first amine reagent added in step (i.1) of two- step, one-pot aminolysis is different from the reagent used in step (i.2). The resulting reaction mixture contains partially aromatic amino functionalized crude recycled polyol (RP).

In the second aminolysis cycle, the reagent, which must contain both primary and/or secondary and tertiary amino groups in the same structure, is added to the reaction mixture in at least 1.5 or higher amount (preferably in 6-fold excess per remaining urethane groups) (Examples 5).

Preferably, in the first aminolysis step, the first amine reagent contains either primary and/or secondary amino groups, whereas in the second aminolysis step a reagent comprising at least one primary and/or secondary amino group as well as at least one tertiary amino group in its structure has to be used The reaction is preferably carried out with a combination of amine reagents in the absence of any additional reagents such as diols, alcohols, glycols, water, diacids, etc., so aminolysis of PU is the only degradation mechanism. This reduces the occurrence of by-products.

Comparing the one- and two-step aminolysis processes, the one-step aminolysis requires less time than the two-step aminolysis. However, one-step aminolysis requires a larger amount of reagent to run the reaction to completion, and the amount of aromatic diamine released is higher. Aminolysis is suitable for chemical recycling of PUFs synthesized from homo- or copolyether polyols. The virgin or recycled polyol can be used as the medium, or no medium is required if effective stirring of the reaction mixtures is ensured (e.g. by mechanical stirring). After the reaction, the polyols are simply poured off the reaction mixtures or extracted from reaction mixture by using a good solvent for the polyol (ethyl acetate, chloroform, dichloromethane, etc). The obtained recycled polyols contain only a very small amount of side products; the main one is aromatic diamine, which is soluble to some extent in the polyol, and a trace amount of urea.

Crude recycled polyols contain soluble aromatic diamines to some extent and trace amounts of urea as remnants of oligourea hard segments. These side products can be easily removed from the RPs by purification with acidic solution (HCI/water). Next, thus obtained RP is washed with water (Milli-Q H ₂ O), and finally dried.

Complete degradation of urethane groups and successful purification of RPs are confirmed by ¹ H NMR, SEC/UV-MALS-RI, FTIR, HPLC, and MALDI-TOF MS (Figs. 4 and 5 for unpurified RP and Figs. 4-12 for purified RPs). Purified recycled polyols are additionally characterized by determination of hydroxyl number and acid value by conventional titration and water content by Karl Fischer titration.

The present invention further provides a recycled polyols (RPs), obtained by the method described herein. The quality of the obtained RPs (structure, end group functionality, molecular weight characteristics, purity) is comparable to that of their commercial analogues.

A further aspect of the present invention concerns the use of a recycled polyol obtained by the method described herein as a reagent, in particular for the synthesis of polyurethane foams. Purified RPs can be used as substitutes for commercial polyols in the formulations for the synthesis of PU, in particular new flexible PUFs without affecting the properties of PUFs even if they are exclusively prepared from RPs thus obtained. Purified RPs can successfully be used in various amounts, including 100%, in the formulation for the synthesis of PU, in particular new flexible PUFs without adjustment of the formulation. The PUFs made even from 100% RP are of the same quality as the foams made from 100% virgin polyols.

Crude or purified RPs can also be used in a variety of other applications, as its structural and molecular weight properties match those of the commercial polyols.

The invention will be further described by reference to the following figures and examples.

Figures

Fig. 1 Reaction scheme of aminolysis of PUF with primary amine reagent, leading to the RP and the residues of PUF hard segments terminated via urea bonds with the amine reagent.

Fig. 2 Structure of tris(2-aminoethyl)amine (TREN) and branched polyethylenimine (PEI) reagents containing primary and/or secondary and tertiary amino groups in the structure.

Fig. 3 Proposed amine reagents containing primary and/or secondary and tertiary amino groups in the structure.

Fig. 4 ¹ H NMR spectra of commercial polyether polyol (1), purified RP (2), and crude RP (3) obtained by PUF aminolysis and recorded in DMSO-c/e. Complete degradation of the urethane groups in RP ((2) and (3)) is confirmed in the magnified spectra recorded in DMSO-c/e with added TFA (to shift the signal of the amino groups toward a lower magnetic field) by the absence of the peak at 4.88 ppm belonging to the methyne group of the polyol adjacent to the urethane group. The presence of TDA in DMSO- /e is indicated by asterisks (*).

Fig. 5 SEC/MALS-RI chromatograms of commercial polyether polyol (1), purified RP (2), and crude RP obtained by PUF aminolysis (3).

Fig. 6 MALDI-TOF mass spectra of commercial PPO-based polyether polyol (1) and purified recycled analogue obtained by PUF aminolysis (2), where complete degradation of urethane groups was achieved. The measured monoisotopic signals are denoted in the magnified regions of the mass spectra and are in good agreement with the calculated exact masses (M) ionized with the sodium ion for the proposed structures. Fig. 7 FTIR spectra of commercial polyether polyol (1) and purified recycled analogue obtained by PUF aminolysis (2), where complete degradation of urethane groups was achieved.

Fig. 8 (A) MALDI-TOF mass spectra, (B) magnified ¹ H NMR spectra, (C) SEC/UV-RI chromatograms, and (D) FTIR spectra of VP5611 (1) and the corresponding RPs obtained with 13.2 wt% TREN (4.00 Eqs of TREN amino per PUF urethane group) with RP as medium (2) and without the use of medium (bulk) (3) at 220 °C for 30 min. The ¹ H NMR spectra were normalized to the methyl group of the PO repeating units. Peak assignment refers to polyol methyl (a), methylene, and methyne protons (b,c) of the repeating PO unit (-CH ₃ ; 1.04 ppm and -CH ₂ , -CH<; 3.15-3.70 ppm). The residual DMSO solvent peak in the ¹ H NMR spectra is indicated with an asterisk. The solid and dashed curves in the SEC/UV-RI chromatograms represent the Rl and UV detector responses, respectively.

Fig. 9 HPLC-ELS chromatograms obtained on a mixed-mode column (A) with magnified area (B) for commercial polyether polyol (1) and purified RPs with a degree of degradation of urethane groups of > 99% (2) and 68% (3). The low intensity peaks at elution volumes of 4.65 mL and 8.32 mL represent the polyol chains functionalized with the aromatic amino group at one chain end and a dimer in which two polyol chains are linked with a hard segment, respectively (both types of polyols are the result of incomplete urethane group degradation).

Fig. 10 Comparison of (A) MALDI-TOF MS, (B) ¹ H NMR, (C) SEC/RI-UV and (D) HPLC characterization results for purified RP (2) recovered from PPO-based PUF by a two-step aminolysis procedure with TREN and the corresponding VP5611 (1). The measured monoisotopic signals of the fully hydroxyl-functionalized polyol in MALDI-TOF mass spectra are shown in the magnified regions of (A). The ¹ H NMR spectra were normalized to the methyl group of the PO repeating units. Peak assignment refers to polyol methyl (a), methylene, and methyne protons (b,c) of the repeating PO unit (-CH ₃ ; 1.04 ppm and -CH ₂ , -CH<; 3.15-3.70 ppm). The residual DMSO solvent peak in the ¹ H NMR spectra is indicated with an asterisk. The solid and dashed curves in (C) represent the Rl and UV detector responses, respectively.

Fig. 11 (A) MALDI-TOF mass spectra, (B) magnified ¹ H NMR spectra, (C) SEC/UV-RI chromatograms, (D) FTIR spectra and (E) HPLC chromatograms of VP5611 (1) and the corresponding fully hydroxyl-functionalized RP (2) obtained by two-step aminolysis, where the first aminolysis step was performed with HMDA (4.00 Eqs of HMDA amino per PUF urethane group) at 220 °C for 30 min and the second aminolysis step with TREN (6.00 Eqs of TREN amino per PUF urethane group) at 220 °C for 20 min. The ¹ H NMR spectra were normalized to the methyl group of the PO repeating units. Peak assignment refers to polyol methyl (a), methylene, and methyne protons (b,c) of the repeating PO unit (-CH ₃ ; 1.04 ppm and -CH ₂ , - CH<; 3.15-3.70 ppm). The residual DMSO solvent peak in the ¹ H NMR spectra is indicated with an asterisk. The solid and dashed curves in the SEC/UV-RI chromatograms represent the Rl and UV detector responses, respectively.

Fig. 12 (A) MALDI-TOF mass spectra, (B) magnified ¹ H NMR spectra, (C) SEC/UV-RI chromatograms and (D) FTIR spectra of VP5611 (1) and the corresponding fully hydroxyl-functionalized RP (2) obtained by two-step aminolysis carried out at 220 °C in one-pot manner by successively adding HMDA (4.00 Eqs of HMDA amino per PUF urethane group, for 30 min) and TREN (6.00 Eqs of TREN amino per PUF urethane group, for 20 min) to the same reaction mixture. The ¹ H NMR spectra were normalized to the methyl group of the PO repeating units. Peak assignment refers to polyol methyl (a), methylene, and methyne protons (b,c) of the repeating PO unit (-CH ₃ ; 1.04 ppm and -CH ₂ , -CH<; 3.15-3.70 ppm). The residual DMSO solvent peak in the ¹ H NMR spectra is indicated with an asterisk. The solid and dashed curves in the SEC/UV-RI chromatograms represent the Rl and UV detector responses, respectively.

Examples

Example 1

6 g of homopolyether polyol-based PUF is mixed with 3 g of virgin or recycled polyether polyol (medium) and 0.79 g of TREN (primary amino/urethane group = 4/1). The reaction is preheated to 175 °C in a span of 3 minutes to ensure partial liquefaction of the PUF. Then the main reaction cycle is carried out at 220 °C for 30 minutes. In this case, complete degradation of the urethane groups is achieved and recycled polyol contains about 10 wt.% aromatic amine (TDA).

Example 2 6 g of homopolyether polyol-based PUF is mixed with 0.79 g of TREN (primary amino/urethane group = 4/1) without the use of any medium (reaction performed in bulk). The reaction is preheated to 175 °C in a span of 3 minutes. The preheating step is repeated two-times to ensure partial liquefaction of the PUF and sufficient mixing of reaction mixture with a magnetic stir bar. Then the main reaction cycle is carried out at 220 °C for 30 minutes. Full degradation of the urethane groups in PUF structure is achieved and recycled polyol contains about 16 wt.% aromatic amine (TDA).

Example 3

6 g of PUF is mixed with 3 g of virgin or recycled polyol (medium) or no medium and 0.435 g of TREN. The reaction is preheated to 175 °C in a span of 3 minutes to ensure partial liquefaction of the PUF. Then the main reaction cycle is carried out at 220 °C for 30 minutes. After completion of the reaction, the crude RP is poured off. Then, 6 g of thus obtained RP is mixed with 0.075 g of TREN. The second reaction cycle is carried out at 220 °C for 20 minutes. In the second step, complete degradation of urethane groups is achieved and RP contains only 7.9 wt.% TDA per polyol.

Example 4

6 g of PUF is mixed with 3 g of virgin or recycled polyol (medium) or no medium and 0.92 g of HMDA. The reaction is preheated to 175 °C in a span of 3 minutes to ensure partial liquefaction of the PUF. Then the main reaction cycle is carried out at 220 °C for 30 minutes. After completion of the reaction, the crude RP is poured off. Then, 6 g of thus obtained RP is mixed with 0.105 g of TREN. The second reaction cycle is carried out at 220 °C for 20 minutes. In the second step, complete degradation of urethane groups is achieved and RP contains only 9.6 wt.% TDA.

Example 5

6 g of PUF is mixed with 3 g of virgin or recycled polyol (medium) or no medium and 0.92 g of HMDA. The reaction is preheated to 175 °C in a span of 3 minutes to ensure partial liquefaction of the PUF. Then the main reaction cycle is carried out at 220 °C for 30 minutes. Afterwards, 0.125 g of TREN is added to the same reaction mixture. The second reaction cycle is carried out at 220 °C for 20 minutes. In the second step, complete degradation of urethane groups is achieved and RP contains only 8.8 wt% TDA.

Example 6 To test whether the efficiency of a combination of an amine degradation reagent containing only primary amino groups (reactant) and a catalyst containing only a tertiary amino group in the structure, is as effective as our amine reagents, which contain both types of amino groups in the same molecule, the degradation of PUFs was carried out using the reagent hexamethylenediamine (HMDA) and the commercial catalyst B11 catalyst (mixture of dimethylaminoethoxyethanol and bis(2-dimethylaminoethyl)ether).

The results show that the amine reagent, which structure consists of primary and/or secondary as well as tertiary functional amino groups, is much more effective and guarantees complete degradation of the urethane groups in the PUF structure and thus the synthesis of high-quality recycled polyols, while the PUF degradation with the reagent containing only primary amino groups in the presence of a catalyst containing only tertially amino group in the structure is less effective and leads to partially aromatic aminofunctionalized recycled polyol.

Results of aminolysis of PUFs

The ¹ H NMR spectra (Fig. 4) of crude recycled polyol (upper phase) obtained by aminolysis with TREN or PEI800, recorded in DMSO- /e, show characteristic signals of polyol methyl, methylene, and methyne protons of the repeating PO unit (-CH ₃ ; 1.04 ppm and -CH ₂ , -CH<; 3.15-3.70 ppm), polyol methyl signal next to the remaining nondegraded urethane groups (-NHCOO-CH(CH ₃ )-; 1.18 ppm), the signals of the methyl protons of the residues of both TDA isomers attached to the polyol via urethane groups due to incomplete degradation of the urethane groups (H ₂ N-(CH ₃ (CeH ₆ ))-NHCOO-CH<; 1.87, 1.96 and 2.00 ppm), aromatic protons of urethane-bound residues of TDA isomers (H _Ar ; 6.45, 6.54, 6.74 and 6.79 ppm), and amino protons of urethane-bound TDA isomers (- NH ₂ ; from 4.73 to 4.80 ppm). The polyol methyne signal (-NHCOO-CH<) adjacent to the remaining urethane groups is at the chemical shift of 4.88 ppm in the ¹ H NMR spectra of RPs recorded in DMSO-c/e with the addition of TFA. The 2,6-TDA and 2,4-TDA isomers soluble in polyol show methyl proton signals at 1 .79 and 1 .88 ppm (H ₂ N-(CH ₃ (CeH ₆ ))-NH ₂ ), respectively, aromatic proton signals (H ₂ N-(CH ₃ (CeH ₆ ))-NH ₂ ; 5.75, 5.88, 5.92 and 6.54 ppm), and amino protons (-NH ₂ ; from 4.43 to 4.46 ppm). The hydroxyl groups of RPs (-OH) are at 4.40 ppm. The urea can be found in trace amounts, with methyl proton signals (-CH ₃ ) of the terminal units at 2.05, 2.07, 2.08 ppm, aromatic signals between 6-7 ppm and amino protons (-NH ₂ ) at the chemical shifts from 4.68 to 4.71 ppm. In the ¹ H NMR spectra of the purified RPs, the methyl, aromatic and amino protons of the two TDA isomers and urea are not observed.

The SEC/UV-MALS-RI chromatogram (Fig. 5) of the obtained purified recycled polyol (chromatogram (2) in Fig. 5) shows the presence of polyol at 9.4 minutes. The high degree of degradation of the PUF network is confirmed by the absence of any high molecular weight species. In addition to the polyol peak, the chromatogram of the crude RP (chromatogram (3) in Fig. 5) also shows the presence of low molecular weight residues of hard segments, such as isomers of TDA detected at longer elution times (22-37 minutes). Low molecular weight side products are completely removed by purification of RP (chromatogram (2) in Fig. 5).

The MALDI-TOF mass spectrum (Fig. 6) of purified PPO-based RP (spectrum (2)) shows a single peak population corresponding to that of the commercial hydroxylfunctionalized analogue (spectrum (1)), thus confirming complete degradation of urethane groups.

The FTIR spectra (Fig. 7) of commercial polyether polyol ((1), black) and its recycled analogue ((2), blue) obtained by PUF aminolysis process are in perfect agreement. The broad band at 3474 cm' ¹ in the FTIR spectra is due to the stretching vibration of the polyol hydroxyl end groups. The bands between 3060 and 2750 cm' ¹ correspond to the C-H stretching vibrations and the bands at 1454 cm' ¹ and 1373 cm' ¹ correspond to the C-H bending vibrations of the methyl, methylene and methyne groups of the polyol. The intense band at 1094 cm' ¹ is due to the C-O-C stretching vibration of the polyol ether groups.

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