LU501979B1

LU501979B1 - Chemical recycling of polyurethane foams with amines

Info

Publication number: LU501979B1
Application number: LU501979A
Authority: LU
Inventors: Blaz Zdovc; David Pahovnik; Ema Zagar; Maja Grdadolnik
Original assignee: Kemijski Inst
Priority date: 2022-04-29
Filing date: 2022-04-29
Publication date: 2023-10-30
Also published as: WO2023209022A1

Abstract

The present invention relates to recycling of polyurethane, in particular polyurethane foams by aminolysis with reagents comprising both primary and tertiary amino groups in the structure to recover polyols of comparable quality to the commercial ones.

Description

Chemical recycling of polyurethane foams with amines LU501979

Abstract

The present invention relates to recycling of polyurethane, in particular polyurethane foams by aminolysis with reagents comprising both primary 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 amine 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 for building insulation. Since PUF s 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.‘

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,>'® hydrolysis, ‘8-17 acidolysis, 18-22 and aminolysis.23-3"

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. 1

Aminolysis is a reaction in which the amine reagent displaces the polyol at the LU501979 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).°? US patent No. 3,117,940° describes a method for improved liquefaction of

PU plastics. À 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,°? US 3,708,440,5* US 3,738,946,°° and US 4,014,809).° 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 amine 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).%7 In US patent No. 6,750,260 B2,% 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. Patent WO 2015/027319 A1°° 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“ 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 B14! 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*? describes the recycling of

PUF waste with aminolysis using aromatic amine or alkanolamine, such as 2 diethanolamine and triethanolamine (tertiary amine) at temperatures from 150 to 250 °C LU501979 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 B14 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-N-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% 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*° 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.®046:47. Alkanolamines such as ethanolamine, diethanolamine, and triethanolamine (tertiary amine) are reported to be used as catalysts in PU recycling, with

PUF/amine ratios ranging from 500/1 to 10/1. Patent application US 2008/0047824 A%S, similar to DE 4217524 A144, 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

B14” 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.?®* 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 3 der Wal?* published a patent US 5,274,0044% and later a paper on a combined chemical LU501979 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® provided insight into the reaction mechanism of PUF 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?’ studied the degradation of biodegradable PUF based on wattle tannin by aminolysis with aniline.

Xue and co-workers?® 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?® 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.°° 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, (alkanol)amines are not used as the primary and/or sole amine reagent for PUF degradation.32-3941-43 4

Neither patents nor published literature describes the aminolysis of PUFs with LU501979 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 tertiary amino groups in the structure of the same reagent. The primary 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 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 amino group and at least one tertiary amino group is not particularly limited, provided that both the primary amino group and 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, Figure 2), and highly branched polyethylenimine (PEI: hyperbranched or dendrimer; Figure 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- LU501979 methyl-piperazin-1-yl)-ethylamine, 1,4-bis(3-aminopropyl)piperazine, 1-(2- aminoethyl)piperazine, 3,3-diamino-N-methyldipropylamine, 3-(dimethylamino)-1- propylamine, N,N-dimethylethylenediamine, N,N-dimethyldipropylenetriamine, polypropylenimine tetramine dendrimers of different generation (reagents shown in Figure 3), and the like, as well as combinations of two or more amine reagents comprising both primary and tertiary amino groups.

The reaction mixtures can be heated in step (ii) by conventional heating method or by microwaves as an energetically favorable, time- and cost-effective method, which shortens the reaction time, improves the degradation degree 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 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.

Aminolysis can be performed as a one-pot reaction or as a 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- pot reaction, the entire amount of amine reagent is added to the reaction mixture at once, whereas in a two-step process amine reagent is added in two steps as described below.

When amine reagent with the structure described above is used in molar amounts equal to or greater than 4 primary amino groups per PU urethane group, complete 6 degradation of the urethane groups is achieved, and after purification, fully hydroxyl- LU501979 functionalized recycled polyol is obtained with comparable molecular weight and structural characteristics to that of virgin polyol (Example 1).

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 amine/urethane group), incomplete degradation of urethane groups of PU is observed, however the amount of aromatic diamine released 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 ragent under basic conditions by one of the possible thermal degradation mechanisms.*°*" 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 wherein the amine reagent is added in two steps, the first portion to the PU to be recycled and the second portion to the product obtained in the first step of reaction, after being separated from the reaction mixture. . Thus, in a particular embodiment, the method of the invention comprises: (i.1) mixing the polyurethane to be recycled with a first amount of the reagent, (i.1) heating the resulting reaction mixture to yield crude recycled polyol (RP), (iit.1) recovering the crude RP, (i.2) mixing the crude RP with a second amount of the reagent, (i.2) heating the resulting reaction mixture to yield RP, and (1.2) recovering the RP, 7 wherein in step (i.1), the reagent is added in an amount of equal to or more than 2 primary LU501979 amino groups per PU urethane group and less than 4 primary amino groups per PU urethane group, and in step (1.2), the reagent is added in at least 1.5 or higher amount (to 3-fold excess) of primary amino 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 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-amine 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, preferably the same amino reagent is added in at least 1.5 or higher amount (3-fold excess) of primary amino groups relative to the remaining urethane groups (Example 2). Alternatively, a different amino reagent can be used for the second aminolysis cycle.

Comparing the one- and two-step aminolysis processes, the one-pot aminolysis requires less time than the two-step aminolysis. However, one-pot 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 flexible PUs based on homopolyether polyol, copolyether polyol, polyester polyol or others. The virgin or recycled polyol can be used as the medium. After the reaction, the polyols are simply poured off the reaction mixtures. 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. 8

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 (HCl/water). Next, thus obtained RP is washed with water (Milli-Q H2O), and finally dried.

Complete degradation of urethane groups and successful purification of RP are confirmed by '"H NMR, SEC/UV-MALS-RI, FTIR, HPLC, and MALDI-TOF MS in the case of homopolymeric polyols (Figures 4 and 5 for unpurified RP and Figures 4-8 for purified

RP). 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 polyol (RP), 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 9

Fig. 1 Reaction scheme of aminolysis of PUF with primary amine reagent, leading to the LU501979

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 tertiary amino groups in the structure.

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

Fig. 4 "H NMR spectra of commercial polyether polyol (1), purified RP (2), and crude RP (3) obtained by PUF aminolysis and recorded in DMSO-ds. Complete degradation of the urethane groups in RP ((2) and (3)) is confirmed in the magnified spectra recorded in DMSO-ds 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-d 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 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 LU501979 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).

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 amine/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 10.2 wt% of TDA is formed.

Example 2 6 g of PUF is mixed with 3 g of virgin/recycled polyol (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 0.14 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 only 7.9 wt% TDA per polyol is formed in both reaction steps.

Example 3

To test whether the efficiency of a combination of two amine degradation reagents, one contains only primary amino groups (reactant) and the other containing only a tertiary amino group (catalyst) 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). 11

The results show that the amine reagent, which structure consists of primary and tertiary functional amino groups, is much more effective and guarantees complete degradation of urethane groups and thus the synthesis of high-quality recycled polyols.

Results of aminolysis of PUFs

The 'H NMR spectra (Fig. 4) of crude recycled polyol (upper phase) obtained by aminolysis with TREN or PEI800, recorded in DMSO-d, show characteristic signals of polyol methyl, methylene, and methyne protons of the repeating PO unit (-CHz; 1.04 ppm and -CHz, -CH<; 3.15-3.70 ppm), polyol methyl signal next to the remaining nondegraded urethane groups (-NHCOO-CH(CHa3)—; 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 (H2N-(CH3(CesHs))-NHCOO-CH<; 1.87, 1.96 and 2.00 ppm), aromatic protons of urethane-bound residues of TDA isomers (Har; 6.45, 6.54, 6.74 and 6.79 ppm), and amine protons of urethane-bound TDA isomers (—

NHz; 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 "H NMR spectra of

RPs recorded in DMSO-d; 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 (H2N-(CHz(CeHe))-NH2), respectively, aromatic proton signals (H2N-(CH3(CeHe))-NHz; 5.75, 5.88, 5.92 and 6.54 ppm), and amine protons (-NHz; 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 (-CHz) of the terminal units at 2.05, 2.07, 2.08 ppm, aromatic signals between 6-7 ppm and amine protons (-NHz) at the chemical shifts from 4.68 to 4.71 ppm. In the "H NMR spectra of the purified RPs, the methyl, aromatic and amine 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 Figure 4) 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 Figure 4) also shows the presence of low molecular weight residues of hard segments, such as isomers of TDA detected at longer elution times (22- 12

37 minutes). Low molecular weight side products are completely removed by purification LU501979 of RP (chromatogram (2) in Figure 4).

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 hydroxyl- functionalized analogue (black), thus confirming complete degradation of urethane groups.

The FTIR spectra (Fig. 7) of commercial polyether polyol and its recycled analogue obtained by PUF aminolysis process are in perfect agreement. The broad band at 3474 cm” inthe FTIR spectra is due to the stretching vibration of the polyol hydroxyl end groups.

The bands between 3060 and 2750 cm”! correspond to the C-H stretching vibrations and the bands at 1454 cm“ and 1373 cm correspond to the C-H bending vibrations of the methyl, methylene and methyne groups of the polyol. The intense band at 1094 cm” is due to the C-O-C stretching vibration of the polyol ether groups.

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Claims

Claims LU501979

1. A method of recycling polyurethane (PU) to polyols, comprising (i) mixing the polyurethane to be recycled with a reagent comprising at least one primary amino group and at least one tertiary amino group in the structure, (il) heating the resulting reaction mixture to yield recycled polyol (RP), and (ii) recovering the RP.

2. The method of claim 1, wherein the reagent is selected from the group consisting of tris(2-aminoethyl)amine (TREN), highly branched polyethylenimine (PEI), tris(3-aminopropyl)amine, 2-(4-methyl-piperazin-1- yl)-ethylamine, 1,4-bis(3-aminopropyl)piperazine, 1-(2- aminoethyl)piperazine, 3,3’-diamino-N-methyldipropylamine, 3- (dimethylamino)-1-propylamine, N,N-dimethylethylenediamine, N,N- dimethyldipropylenetriamine, and polypropylenimine tetramine dendrimer of generation 1 (DAB-Am-4), and combinations thereof, and/or wherein the PU to be recycled comprises PU foam.

3. The method of claim 1 or 2, wherein the reagent is used in an amount equal to or greater than 2 primary amino groups per PU urethane group, preferably in an amount equal to or greater than 3 primary amino groups per PU urethane group and in particular equal to or greater than 4 primary amino groups per PU urethane group.

4. The method according to any one of the preceding claims, wherein the heating in step (ii) comprises subjecting the reaction mixture to irradiation by microwaves (MW) or conventional heating.

6. The method according to any one of the preceding claims, wherein in step (ii), the reaction mixture is heated to temperatures in the range of about 150 — 230°C, preferably 220°C or lower. 18

7. The method according to any one of the preceding claims, wherein in step LU501979 (ii), the reaction mixture is heated for about 20-50 min, in particular for about 30-40 min, preferably for about 30 min.

8. The method according to any one of the preceding claims, further comprising 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 heating in step (ii).

9. The method according to any one of the preceding claims, wherein the method is carried out as a one-pot reaction, with the entire amount of reagent being added at once.

10. The method according to any one of claims 1-8, wherein the method is carried out as a two-step reaction, comprising

(1.1) mixing the polyurethane to be recycled with a first amount of the reagent,

(i.1) heating the resulting reaction mixture to yield crude recycled polyol (RP), (iii.1) recovering the crude RP,

(i.2) mixing the crude RP with a second amount of the reagent,

(i.2) heating the resulting reaction mixture to yield RP, and (iii.2) recovering the RP, wherein in step (i.1), the reagent is added in an amount of more than 2 primary amino groups per PU urethane group and less than 4 primary amino groups per PU urethane group, and in step (i.2), the reagent is added in at least 1.5 or higher amount (3-fold excess) of primary amino groups relative to the remaining urethane groups in the crude RP.

11. The method according to claim 10, wherein in steps (i.1) and (i.2), the same or a different reagent is used. 19

12. The method according to claim 10 or 11, wherein in step (ii.1), the reaction mixture is heated for about 20-30 min, in particular for about 30 min, and in step (ii.2), the reaction mixture is heated for about 15-30 min, in particular for about 20 min.

13. The method according to any one of the preceding claims, further comprising a step (iv) of purifying the recovered RP, in particular by by treatment with an acidic solution, e.g. HCl/water, washing with water, and drying.

14. A recycled polyol, obtained by the method of any one of the preceding claims.

15. Use of a recycled polyol according to claim 14 as a reagent for polyurethane synthesis, in particular for the synthesis of polyurethane foams either flexible or hard polyurethane foams.