Method for depolymerizing polyamide

Abstract

The invention is directed to a method for depolymerizing polyamide of a polymeric material comprising the step of contacting in a solvent the polymeric material with a Brønsted–Lowry acid in the presence of a Lewis acid catalyst, thereby producing a medium having a liquid phase comprising monomers derived from said polyamide. Figure Abstract : None

Description

METHOD FOR DEPOLYMERIZING POLYAMIDE

[0001] The present invention is relative to method for depolymerizing polyamide. More particularly, the method of the invention is directed to the depolymerization of polyamide within a polymeric material. The invention is also relative to a compound or compounds generated by the method of the invention.

[0002] Polymers are used in a very large number of fields. This is not only because of their diversity regarding mechanical, physical and chemical properties, but also because of their relatively low production costs. Polymers are used for example in the fields of chemical or pharmaceutical industry, in construction, electronics, aeronautics, automotive and packaging. The textile industry also uses polymers abundantly.

[0003] More generally, polymers are the basic constituents of many everyday materials, particularly plastics and textiles. A plastic material is essentially made of polymer which, after molding and / or shaping operations, results in an object. Plastics generally have high molecular weights and are usually derived from petrochemicals. Some other plastics may be derived from a natural source. On a global level, plastic materials are increasing all over the world [cf. Jambeck, J. R. et al. Plastic waste inputs from land into the ocean. Science 347, 768-771 (2015)].

[0004] One of the most important synthetic polymers in various industries is polyamide. Polyamides are polymers with regularly repeating amide bonds along a polymer backbone. Such amide bonds can be formed by condensation of a carboxylic acid and an amine, whereby a nitrogen-carbonyl carbon bond is formed. Depending on the number of monomers linked together, a polymer may have a plurality of structural units with such nitrogen-carbonyl carbon bonds. The monomers used to produce polyamides include diamines, lactams, amino-carboxylic acids and / or dicarboxylic acids.

[0005] The two most commonly used polyamides are the so-called polyamide 6.6 and the polyamide 6 (also respectively known as nylon 6.6 or nylon 6). Polyamide 6.6 is produced from hexamethylenediamine and adipic acid by polycondensation with water splitting. Polyamide 6, in turn, is produced by ring-opening polymerization of ε-caprolactam with water as a starter. Because of their strength and toughness, polyamides are often used as construction materials.

[0006] However, polymers and / or plastics have a non-neglectable environmental impact.

[0007] Today, there is a growing interest in recycling technologies that enable polymers to be valued and / or reused. In particular, research focusses on recovering monomers used in the synthesis of the polymer, or at least recovering oligomers and / or other low-molecular chemical compounds. Ideally, new polymers can then be synthesized from these recovered monomers and / or oligomers.

[0008] The state of the art discloses various recycling processes to recover compounds from degraded polymers. Most of the relevant processes are so called tertiary recycling methods which implicate at least one chemical recycling method and heat.

[0009] Chemical recycling methods are generally divided into two categories : those that regenerate starting monomers, and optionally oligomers (mainly hydrolysis) and those that generate other types of molecules with applications in fine chemistry or as fuel (including transesterifications, aminolysis, methanolysis, etc.). Numerous chemical recycling methods exist in the literature [cf. DOI:10.1002 / pol.20230154 or DOI:10.1016 / j.xcrp.2023.101341, DOI:10.1039 / d1ra08217e.

[0010] Regarding specific recycling of polyamide, the state of the art discloses numerous methods including acid hydrolysis [cf. DOI:10.1021 / acssuschemeng.0c05706], aminolysis by acid catalysis [cf. DOI:10.1039 / D3CC05462D and US5395974], solvolysis [cf. DOI:10.1007 / s10924-018-1314-4 & US5668277], alcoholysis [cf. DOI:10.1007 / s10163-015-0425-4 & EP1801101], organometallic catalysis [cf. DOI:10.1002 / ange.202212543], and formaldehyde depolymerization [cf. WO2023280768].

[0011] Yet, all the solutions of the state of the art are either operated at rather extreme reaction conditions or use highly toxic compounds.

[0012] The high costs as well as the drastic operating conditions of existing recycling methods (e.g., very high temperatures and pressures), result both in economic and ecological problems. New solutions are needed. Moreover, new recycling methods must keep pace with changing legislations all over the world mostly facing environmental issues.

[0013] Also, the complexity of polymers on the market is a major hindrance to efficient recycling. The majority of those polymers are in fact polymer blends, containing more than one polymer, additives, pigments or plasticizers. The separation of these different materials is a technological challenge and constitutes a major brake on recycling polymeric materials [cf. DOI: 10.1021 / acsapm.1c00648]. More particularly, recycling of mixed polyamide materials has become an important issue in contemporary society and especially in the textile, automotive, and construction industry [cf. DOI: 10.1098 / rstb.2008.0311 and DOI: 10.1016 / j.cogsc.2023.100763]

[0014] The present invention improves the situation.

[0015] To this end, the invention is directed to a method for depolymerizing polyamide of a polymeric material comprising the step of:

[0016] i.contacting in a solvent the polymeric material with a Brønsted–Lowry acid in the presence of a Lewis acid catalyst, thereby producing a medium having a liquid phase comprising monomers derived from said polyamide.

[0017] According to a particularly preferred embodiment of the present invention, the polymeric material is made of polyamide and at least a second polymer, and wherein contacting said polymeric material in stepi.induces selective depolymerizing of the polyamide within the polymeric material, thereby producing said medium that further comprises a solid phase of said second polymer.

[0018] In this embodiment, the solid phase of the second polymer is preferentially constituted of at least 90%, preferentially 100% of said second polymer.

[0019] According to a preferred embodiment, the polymeric material after stepi.is reduced of at least 90%, preferentially 100% of said polyamide.

[0020] According to a preferred embodiment, the medium further comprises oligomers derived from said polyamide, and wherein the ratio of said monomers relative to said oligomers is ranged from 99:1 to 70:30.

[0021] According to a preferred embodiment, the method further comprises the step of:ii.extracting the medium in order to isolate said monomers, and optionally oligomers, and subsequently evaporating said solvent in order to recover the monomers, and optionally oligomers.

[0022] According to a preferred embodiment when the method comprises a second polymer, the method of the invention further comprises the step of:iii.filtering the solid phase from said medium, and subsequently washing and drying said solid phase in order to recover the second polymer.

[0023] According to another embodiment, the second polymer is selected from the group consisting of a polyurethane copolymer, cotton copolymer, wool copolymer, a polyester copolymer, silicon copolymer, elastane and cellulosic material.

[0024] According to a preferred embodiment, the solvent is selected from the group consisting of ethanol, anisole, tetrahydrofuran, preferentially 2-methyl-tetrahydrofuran, acetone, water, dioxolane, dioxane, dimethoxyethane, o-dichlorobenzene, dimethyl sulfoxide, methanol, isopropanol, ethylene glycol, acetic acid, trioxane, chloroform and a combination thereof.

[0025] According to a preferred embodiment, the Brønsted–Lowry acid is selected from the group consisting of a mineral acid and an organic acid,

[0026] wherein the mineral acid is selected from HX, X being selected from Cl, Br, I, H2SO4, H3PO4,nitric acid, sulfuric acid, phosphomolybdic acid, para-toluenesulfonic acid and methylsulfonic acid., and

[0027] wherein the organic acid is selected from a compound of formula (I):

[0028] RCOOH (I)

[0029] R being selected from hydrogen, C1-C8alkyl, a perfluoroalkyl group, and an aryl group preferentially benzyl or phenyl.

[0030] According to another preferred embodiment, the Brønsted–Lowry acid is selected from the group consisting of mono-carboxylic acid derivatives, di-carboxylic acid derivatives and tri-carboxylic acid derivatives, preferentially oxalic acid and citric acid.

[0031] According to a preferred embodiment, the Lewis acid is a metal catalyst comprising a metal selected from aluminum, preferentially aluminum (III), preferentially Boron (III), bismuth, preferentially bismuth (III), cerium, preferentially cerium (III), iron, preferentially iron (II) or (III), manganese, copper, preferentially copper (II), lanthanum, preferentially lanthanum (III), magnesium, preferentially magnesium (II), tin, preferentially tin (IV), titanium, preferentially titanium (IV), zirconium, preferentially zirconium (IV), calcium, zinc, preferentially zinc (II), and salts thereof, preferentially chloride salts.

[0032] According to another embodiment, the Lewis acid is selected from a metal triflate compound and a metal halogen compound, preferentially wherein said metal is iron, zinc or bismuth.

[0033] According to a preferred embodiment, stepi.is operated at a temperature less than or equal to 110°C, preferentially less than or equal to 100°C, less than or equal to 90°C, or less than or equal to 80°C.

[0034] According to a preferred embodiment, the polymeric material is a synthetic material.

[0035] According to an embodiment, the polymeric material comprises additives. The additives can be selected from dyes, mineral fillers, antioxidants and a mixture thereof.

[0036] According to an embodiment, the polymeric material can comprise common impurities.

[0037] According to a preferred embodiment, the second polymer is elastane. More preferentially, the elastane is recovered as a fiber or in a knitted form.

[0038] According to an embodiment, the monomers can be selected from adipic acid, adipic acid derivatives, diamine, diamine derivatives, ε-aminocaproic acid.

[0039] According to a preferred embodiment, contacting duration in stepi.is of 0.1 hour to 72 hours, preferentially 1 hour to 72 hours, more preferentially 12 hours to 72 hours. .

[0040] According to a preferred embodiment, contacting in stepi.is carried out under stirring at between 100 rpm and 1500 rpm, preferentially at 600 rpm.

[0041] According to a preferred embodiment, the pressure in stepi.is at atmospheric pressure.

[0042] According to another embodiment of the method according to the invention, the polymeric material is constituted of polyamide.

[0043] Another object of the present invention is a compound generated by the method described above.

[0044] According to an embodiment, the compound is selected from the group consisting of a monomer, an oligomer, and a polymer.

[0045] In a particular embodiment, the compound can be elastane or cotton PET. In another embodiment, the compound can be a ε-caprolactam derivative or a HMDA derivative.

[0046] Other features and advantages of the invention will stand out and / or become clear upon reading the following description, which comprises specific examples given in an illustrative and non-limiting manner, as well as from the drawings in which:

[0047] shows a 1stchemical equation according to an embodiment of the invention;

[0048] shows a 2ndchemical equation according to another embodiment of the invention;

[0049] shows a 3rdchemical equation according to another embodiment of the invention;

[0050] shows a 4thchemical equation according to another embodiment of the invention;

[0051] shows a 5thchemical equation according to another embodiment of the invention;

[0052] shows a 6thchemical equation according to another embodiment of the invention;

[0053] shows a 7thchemical equation according to another embodiment of the invention;

[0054] shows an 8thchemical equation according to another embodiment of the invention;

[0055] shows a 9thchemical equation according to another embodiment of the invention;

[0056] shows a 10thchemical equation according to another embodiment of the invention;

[0057] shows an 11thchemical equation according to another embodiment of the invention;

[0058] shows a 12thchemical equation according to another embodiment of the invention;

[0059] shows a 13thchemical equation according to another embodiment of the invention;

[0060] shows a 14thchemical equation according to another embodiment of the invention;

[0061] shows a 15thchemical equation according to another embodiment of the invention;

[0062] shows a 16thchemical equation according to another embodiment of the invention; and

[0063] shows a 17thchemical equation according to a comparative example not according to the invention.

[0064] The drawings and the description herein contain, for the most part, elements of definite nature. Therefore, description and drawings not only are being used to better understand the present invention, but also to contribute to the definition therefor, when appropriate.

[0065] In the present description the term "polymeric material" refers to a material comprising at least a polymer. More particularly, according to the invention, a polymeric material is a material comprising at least polyamide. This means that a polymeric material in the sense of the invention can for example comprise polyamide exclusively or can comprise polyamide in combination with at least another polymer. Further, a polymeric material in the sense of the invention can comprise polyamide and two or more other polymers. Furthermore, a polymeric material in the sense of the invention can comprise polyamide, one or more other polymers and additive(s) and / or dye(s). A polymeric material in the sense of the invention can also comprise polyamide and cotton fiber and / or yarn and / or a cellulosic material. More generally, a polymeric material in the sense of the invention can comprise polyamide, one or more other polymers or not, cotton fiber and / or yarn and / or a cellulosic material or none of the three latter, and optionally additive(s) and / or dye(s). The term polymeric material thus encompasses for example a plastic material or a textile material. It also encompasses a material composed of polyamide and polyurethane (with or without additive(s) and / or dye(s)). It further encompasses a material composed of polyamide and elastane (with or without additive(s) and / or dye(s)). Other examples include polyamide blended with (or coated on) polyesters, polypropylene, rubber and / or polyolefin.

[0066] In the present description the term "catalyst" refers to any compound capable of modifying, in particular by increasing, the rate of the chemical reaction in which it participates, and which is regenerated at the end of the reaction. This definition encompasses both regular catalysts, i.e., compounds which exert their catalytic activity without needing to undergo any modification or conversion, and compounds called pre-catalysts which are introduced into the reaction medium and converted there into a catalyst. Therefore, in the present description, no formal distinction is made between catalyst and pre-catalyst.

[0067] The present invention is directed to a method for depolymerizing polyamide of a polymeric material comprising the step ofi.contacting in a solvent the polymeric material with a Brønsted–Lowry acid in the presence of a catalyst, thereby producing a medium having a liquid phase comprising monomers derived from said polyamide.

[0068] The solvent can be present in the range: 0.01M-1M, preferably 0.2-0.6M. The Brønsted–Lowry acid can be present in the range : 1-30 equivalent, preferably 2-12 equivalent. The number of equivalent is calculated with regard to the molecular weight of one repeating unit of the polymers. The Lewis catalyst is present in the range : 0.01-80 wt%, preferably between 1-10 wt%.

[0069] The present invention is thus generally directed to a method for depolymerizing polyamide. In other words, the invention is arranged to depolymerize polyamide of a polymeric material, whether the polymeric material comprises polyamide or is constituted of polyamide. The invention may be used for recycling plastic and / or textile materials. It can be used in the preparation of aromatic and aliphatic compounds, which in turn may be used as fuels, synthesis intermediates, raw materials in the field of construction. More generally, the invention may be used in petrochemical, electrical, electronic, textile, aeronautical, automotive, pharmaceutical, cosmetic and / or agrochemical industries.

[0070] The bonds targeted and selectively cleaved by the depolymerization method of the invention are nitrogen-carbonyl bonds of amide functions (-CO-N-). Thus, the C-N bonds of functions in which the carbon atom is linked to another carbon atom by a sp or sp2 multiple bond (for example C=C-O) are not cleaved during the depolymerization process of the invention. For example, aryl ethers found in polyphenols are not cleaved. Urethane type bonds (O-CO-N) are not cleaved during the reaction. Consequently, elastane will not depolymerize during the method of the invention, i.e. during the main depolymerization reaction of the invention. The single, double and triple C-C bonds are also not cleaved by the depolymerization method of the invention. For example, polystyrene (PS) is not depolymerized by the method of the invention.

[0071] Consequently, the invention not only enables the transformation of polyamide into its monomers and optionally oligomers, but it also enables the selective depolymerization of polyamide within materials that comprise other polymers (often referred to as mixed materials or blend materials).

[0072] Accordingly, in a preferred embodiment of the invention, the polymeric material is made of polyamide and at least a second polymer. In this particular embodiment, contacting said polymeric material in stepi.induces selective depolymerizing of the polyamide within the polymeric material, thereby producing a medium that not only comprises monomers (and optionally oligomers) derived from the polyamide, but further comprises a solid phase of said second polymer.

[0073] Thus, the invention enables the selective recovery of a copolymer from mixed materials resulting from the depolymerization process, such as cellulosic polymers, polyurethane (PU), polyesters, etc. The recovered second polymer (copolymer) can be used in construction, petrochemical, electrical, electronics, textile, aeronautics, automotive, pharmaceutical, cosmetics and agrochemical industries.

[0074] There have been attempts in the art to depolymerize polymeric materials having polyamide and another polymer. EP0575860 discloses a process for recovering caprolactam from a starting material containing both polycaprolactam and materials that are insoluble in acidic solvents. However, this document uses a radically different chemical approach as the present invention. In particular, EP0575860 uses several chemical reactions in different steps to decompose the starting material. A first preliminary step comprises the use of an acid solvent to dissolve polycaprolactam of the starting material. Polycaprolactam can thus be recovered in liquid form and the insoluble materials of the starting material can be separated therefrom. At this stage no depolymerization takes place. Hence at this stage, there are no monomers derived from polycaprolactam (i.e. polyamide) present in the reaction medium (this is contrary to the invention). In a second step, the polycaprolactam is then introduced in a depolymerization reactor in order to recover caprolactam. Only at this stage a depolymerization takes place. This depolymerization, however, is executed on a single polymer without any other material present. Consequently, the method of EP0575860 is very different from the method of the present invention wherein a selective depolymerization takes place within a polymeric starting material having at least two polymers. More generally, EP0575860 does not disclose anywhere a selective depolymerizing of polyamide within a polymeric material. This, however, is a crucial step of the one-stage method of the invention. Also, experimental conditions in a depolymerization reactor as used in EP0575860 are very excessive regarding temperature (e.g. 480°C). This is also very different from the present invention that manages to use very mild reaction conditions.

[0075] The present invention also concerns the use of aromatic and aliphatic compounds obtained by the depolymerization process of oxygenated polymeric materials according to the invention, in the manufacture of fuels, electronic components, plastic polymers, rubber, medicines, vitamins, cosmetics, perfumes, food products, synthetic yarns and fibers, synthetic leathers, glues, pesticides, fertilizers.

[0076] On a general note, the present invention can also be used as an analytical tool to determine the content of the copolymers blended with polyamide by selectively depolymerizing the polyamide to recover on one hand the monomers and optionally oligomers derived from the polyamide and on the other hand the non-depolymerized materials (which are usually other polymers).

[0077] The invention thus drastically improves the situation with regard to the recyclings methods disclosed in the state of the art.

[0078] In fact, the main known polyamide recycling methods each have drawbacks, especially when it comes to blended polymeric materials.

[0079] The method known as acid hydrolysis / acidolysis enables the recycling of several types of polyamide (PA) polymers such as PA6,6 and PA10,10. Yet, this method involves heating a solution of hydrochloric acid diluted in water to 200°C to allow depolymerization of the PA. Pressure generated in the reactor are about 20 bars. This depolymerization method thus takes place at very high temperatures and pressures. Further, the reaction requires the use of a microwave reactor, which does not allow, or at least limits, the scale-up of this method. In other words, this method is limited in industrial application. Furthermore, fibers such as elastane or cotton cannot withstand the drastic reaction conditions. Fibers and cotton are destroyed or degraded during or after the reaction.

[0080] The method known as aminolysis is a reaction of PA6,6 carried out at 200°C and 1 bar in the presence of ammonia in ethylene glycol as solvent and a Lewis acid catalyst. The presence of a Lewis acid catalyst favors the production of the expected products thanks to the oxophilicity of the catalyst that is somewhat activating the PA. Here again the depolymerization reaction takes place at very high temperatures. This method does not recover the monomers used in the polyamide industry. It recovers a diamine compound and a diamide compound. Fibers such as elastane or cotton cannot withstand the operating conditions and are destroyed / degraded during or after the reaction. The depolymerization of polyamide plastics using this method requires the reaction atmosphere to be changed, which means evacuating the reaction system and then replacing the atmosphere with ammonia. This action has to be repeated, which is operatively invasive and thus limits its application.

[0081] The method known as solvolysis is another approach to polyamide depolymerization. It is also referred to as glycolysis. This method can use ethylene glycol as a solvent while operating at high temperatures. More particularly, this method is set for the depolymerization of PA6,6 based on a mixture of ethylene glycol and triethylenetriamine (TETA) at 190°C in the presence of 2% by weight diammonium hydrogen phosphate as catalyst. The reaction yielded substances with molecular weights ranging from 90 to 250 g.mol-1corresponding to PA6,6 monomers and short oligomers. A method for producing monomers from polyamide 6 is also known from US 5,668,277. In the method, polyamide 6 is split using ammonia, an amine or a mixture thereof as an activating reagent. The reaction takes place at a reaction temperature between 200°C and 400°C and a pressure of around 0.5 atm to 5 atm. The reaction products produced include ε-caprolactam and ε-caprolactam precursor molecules such as ε-aminocaproic acid, which can be used directly for the new synthesis of polyamides. Solvolysis is thus accompanied by rather drastic operating conditions. In particular, the extreme pressure conditions are invasive and copolymers such as elastane are degraded within the process.

[0082] The method known as alcoholysis is a process for producing monomers from a polymer comprising a structural unit with a nitrogen-carbonyl carbon bond. The process involves cleaving the nitrogen-carbonylcarbon bond in a chemical reaction using an alcohol containing one or more carbon atoms as the activating reagent. The reaction does not require a catalyst, but requires to be carried out at a reaction temperature of >350°C. The process can be carried out on polyamide 6, from which up to 97% of the monomer ε-caprolactam can be recovered. Aside the high temperature, the depolymerization reaction also requires high pressures. Fibers such as elastane or cotton cannot withstand the operating conditions, and are destroyed / or degraded during or after the reaction. The depolymerization of polyamide plastics using this method requires the reaction atmosphere to be changed or pressurized vessels, which means evacuating the reaction system and then replacing the atmosphere with ammonia. This action has to be repeated, which is invasive and limits the application of this method.

[0083] The method known as organometallic polyamide depolymerization or as Tobin Marks polyamide depolymerization is related to an organometallic catalysis system for depolymerizing polyamide without reaction solvents. The method is using a lanthanide catalyst and metallocene derivatives (lanthanides and transition metals) under an inert atmosphere to produce the corresponding PA6 monomer, i.e., ε-caprolactam. The reaction takes place at temperatures between 220°C and 240°C under static vacuum. The catalysts need to be handled in an inert atmosphere, i.e., reaction prepared in a glove box under inert atmosphere. In about 4 hours, the reaction recovers the monomer in yields of about 90%. However, similarly to the other methods of the art, the depolymerization reaction take place at high temperatures >200°C and are therefore very energy-intensive. Fibers such as elastane or cotton cannot withstand such conditions and are destroyed / degraded during or after the reaction. The catalysts used in the reaction are highly sensitive to oxygen and humidity, and require specific equipment in order to be properly handled. The reaction only is suited to be carried out on PA6 polyamide and cannot be applied to PA6,6 polymers. The depolymerization of polyamide-type plastics with this system requires vacuum, which calls for specific equipment and therefore limits its use.

[0084] The method known as formaldehyde depolymerization involves the use of formaldehyde or para-formaldehyde in the presence of a Lewis acid as catalyst (Bi(OTf)3) and optionally in presence of dioxane or chloroform as solvent. The reaction is conducted in sealed vessels at 165 °C. The depolymerization reaction takes place at moderate to high temperatures (165 °C), but sealed vessels are needed. Formaldehyde is a toxic and environmentally harmful compound. Formaldehyde is a proven carcinogen and mutagen with acute toxicity. It is also a highly volatile (VOC: Volatile Organic Compound). Its volatility, combined with its toxicity / dangerousness, makes this compound an undesirable by-product on an industrial scale. The monomeric and oligomeric compounds generated during this reaction cannot be reused directly to recreate a polyamide based polymeric material, as they mainly obtain acetamide derivatives. A further step is required to obtain industrially exploitable monomers.

[0085] As a consequence, known chemical recycling or tertiary recycling methods have significant operational drawbacks, and especially the need to operate depolymerization reactions at very high temperatures and pressures, and the need to use of toxic compounds to catalyze the reactions. Further, there are no or very little methods that aim the recycling of several types of polymers at the same time (copolymer or blended polymeric material). None of the methods are satisfactory with regard to the additives present in the materials.

[0086] The recycling industry, and especially companies dealing with the recycling of plastics and textiles involving chemical recycling, thus face a major problem with regard to polyamide materials. More particularly, and to sum-up, two main problems must be faced when it comes to the recycling of polyamide and / or blended materials containing polyamides:

[0087] The first problem is the inability to process mixed materials since they are complex to separate into their respective compounds. The separation generally requires a very high technicity. Further, such a separation generates a lot of waste. Consequently, this type of processing is mostly neglected and the industry mainly only concentrates on raw material having a purity of > 95%.

[0088] The second problem is regarding the high energy costs of recycling processes. Indeed, most of the known processes are run at temperatures over 250°C, at high pressures and with toxic chemical solvents. As a consequence, chemical recycling is generally very costly and limited with regard to the actual environmental benefit of the recycling processes.

[0089] No method has been developed in the art which is able to properly separate a blended polymeric material to recover one polymer on one hand, while depolymerizing the second one on the other hand in order to obtain the corresponding monomers and optionally oligomers. The invention does. In fact, in a blended polymeric material comprising polyamide, the invention is able to depolymerize said polyamide and recover any other polymer comprised in the material. The invention thus provides a method of tertiary recycling for polymeric materials that overcomes problems of the prior art.

[0090] The invention provides a depolymerization process that can be applied to the recycling of polymeric materials, especially mixed polymeric materials, into compounds with high added value or even into monomer. Advantageously, the method of the invention:

[0091] - is environmentally friendly;

[0092] - can be processed under mild operating conditions (<110°C) and is thus of industrial interest;

[0093] - uses only sustainable and / or bio-sourced solvents;

[0094] - has a very high selectivity with respect to the targeted polymer;

[0095] - leaves the co-polymers of polyamide blend materials intact;

[0096] - is avoiding the use of polluting, rare and / or expensive metal-based catalysts;

[0097] - is efficient, i.e., the polyamide material is converted into chemical compounds of high purity (at least 90 moles % of the total number of moles of compounds obtained) or at least into compounds that can be easily purified;

[0098] - provides good selectivity with respect to the chemical compounds obtained;

[0099] - allows selective cleavage of certain bonds in the polyamide polymer material;

[0100] - is general and versatile and can be adapted to the type of polyamide polymeric material to be depolymerized; and / or

[0101] - is able to withstand any additives present in the mixed polymeric materials to be depolymerized.

[0102] More particularly, the method of the invention has the advantage of resisting the presence of additive(s) in polymer materials. No catalyst poisoning problems are observed with additives commonly used in polymer materials. As mentioned above, the challenge of recycling is not limited to the depolymerization of the polymer present alone in the reaction medium (pure polymer) but also extends to its depolymerization in a commercial material that can contain additives such as dyes, fillers minerals, antioxidants, etc. The presence of these additives in the material can deactivate the catalyst used to carry out the depolymerization, and thus render the reaction ineffective. The invention is not affected by this problem. The method of the invention is therefore of great industrial interest because it is capable of resisting the additives and / or impurities present in the starting polymeric material, which, for example, may be plastic waste.

[0103] Furthermore, by controlling the operating conditions, the depolymerization of a polymeric material comprising a mixture of polyamide(s) and / or polyurethane(s) is selective. Without wishing to be bound by theory, the difference in reactivity of the nitrogen-carbonyl bonds of an amide function and an urethane function can favor the selective cleavage of one of these functions relative to the other. Additionally, the electronic effect (e.g., inductive effects related to the polarization of a bond and mesomeric effects due to electron delocalization) and steric hindrance of the substituents near the nitrogen-carbonyl bond may have an impact on the reactivity of the bond to be cleaved. For example, in the case of a material comprising a PA6 + elastane mixture or a material comprising a PA6.6 + cotton mixture, the PA6 and the PA6.6 are selectively cleaved. Moreover, within a standard filtration step, the elastane originally mixed with the PA6 and PA6,6 can be recovered as a fiber and even as a knitted material in pure form from the reaction described in the patent.

[0104] There is a very high synergistic effect between the Bronsted acid and the Lewis acid catalyst which is leading to excellent conversion. The solvent enables a high reaction rate. As an example, without ethanol, the reaction rate drops drastically.

[0105] A preferred embodiment of particular interest is when the polymeric material is made of polyamide and at least a second polymer. Contacting the polymeric material in stepi.with a Brønsted–Lowry acid and a Lewis acid catalyst in a solvent induces selective depolymerizing of the polyamide within the polymeric material. Thereby the reaction is producing a medium that not only comprises a liquid phase comprising monomers and optionally oligomers derived from the polyamide, but also that further comprises a solid phase of said second polymer. The solid phase of the second polymer is constituted of at least 90%, preferentially 100% of said second polymer. The solid phase may comprise or be constituted of polyurethane or elastane for example.

[0106] The method of the invention enables to strip the original polymeric material of the polyamide contained therein. After stepi.of contacting the polymeric material with the Brønsted–Lowry acid and the Lewis acid catalyst in a solvent, the polymeric material is reduced (or deprived) of at least 90%, preferentially 100% of said polyamide.

[0107] The polyamide that is being depolymerized during the method of the invention is degraded into monomers. Such monomers can be adipic acid, adipic acid derivatives, diamine, diamine derivatives, ε-aminocaproic acid, ε-aminocaproic acid or ε-caprolactam. The monomers can be recovered in the liquid phase of the reaction medium. Depending on the reaction time and ingredients used, the liquid phase of the reaction medium may further comprise oligomers derived from the polyamide. Usually, the ratio of said monomers relative to said oligomers is ranged from 99:1 to 70:30.

[0108] According to an embodiment of the invention, the above-mentioned monomers, and optionally the oligomers, may be recovered from the reaction medium in a stepii.subsequent to contacting the polymeric material with the Brønsted–Lowry acid and the Lewis acid catalyst in a solvent. For this, the monomers and / or oligomers may be isolated by medium extraction. The monomers and / or oligomers are then recovered by evaporating the solvent. As an example, the extraction of adipic acid derivatives, can be achieved by basification of water (KOH or NaOH) followed by a second extraction to recover the hexamethylenediamine (HMDA). Recovery of monomers can also be done by precipitation of the HMDA salts adding another organic solvent miscible with water. Then a basification and a second precipitation which allows to recover the adipic acid derivatives. Purification of the monomers can be done by recrystallisation, column chromatography or distillation.

[0109] When the polymeric material comprises a second polymer, the method of the invention may further comprise a step of:iii.filtering the medium in order to recover a solid phase. As explained, polymers other than polyamide are not degraded into the liquid phase of the medium. Consequently, other polymers of the polymeric material remain intact or almost intact in a solid form. The second polymer is thus recovered as a solid, and can be washed and dried before being recovered.Washing can be done for instance with EtOH and water.

[0110] According to an embodiment, the second polymer may be a polyurethane copolymer, cotton copolymer, wool copolymer a polyester copolymer, elastane, cellulosic material, silicon copolymers, polyolefin copolymers or cotton PET.

[0111] According to a preferred embodiment of the invention, the polymeric material used in the method of the invention is a blended material composed of polyamide and polyurethane. Polyurethane is an industrially significant synthetic polymer. Polyurethanes are characterized by regularly repeating urethane groups. As with amide bonds, part of these urethane groups is a nitrogen-carbonyl-carbon bond, whereby urethane groups have an additional oxygen atom in contrast to amide groups. Polyurethanes are formed during the polyaddition reaction of polyols with polyisocyanates. The reaction of dialcohols (also called diols) with diisocyanates leads to linear polyurethanes. The reaction of compounds such as triisocyanate-diisocyanate mixtures with triol-diol mixtures leads to cross-linked polyurethanes. Depending on the degree of cross-linking and the isocyanate and alcohol components used, polymers with different properties are produced. Polyurethanes can thus form thermosets, thermoplastics or elastomers. Polyurethanes are most frequently used in the textile industry in the form of elastane. However, they can also be used as adhesives, resins, foams, molding compounds or else. In the textile industry, elastane is very often used to impart elasticity and flexibility to polyamide fibers. This is why the textile industry vastly uses blended polymeric material comprising polyamide and elastane. Such blended material is for example used in underwear.

[0112] The present invention enables the selective recovery of elastane from blended material composed of polyamide and elastane. The elastane can be recovered as a solid phase in the reaction medium. The liquid phase of the reaction medium contains monomers (and maybe oligomers) derived from the polyamide initially mixed with the elastane in the polymeric material.

[0113] According to a preferred embodiment, stepi.is operated at a temperature less than or equal to 110°C, preferentially less than or equal to 100°C, less than or equal to 90°C, or less than or equal to 80°C. Heating can be carried out by means of a sand bath or oil bath. Such a low temperature is a major operating advantage since the reaction can be carried out in simple vessel. There is consequently no need of the use of one or more specific apparatus enabling high temperature and / or high pressure associated that enables bringing a solvent above its fusion point. In addition, the low temperature used in the invention limits the costs, particularly given the current economic fluctuations with regard to energy prices.

[0114] The contacting duration in stepi.is preferentially of 0.1 hours to 72 hours. For example, the contacting time might be 24 hours, 36 hours, 48 hours or 60 hours. The contacting in stepi.is preferentially carried out under stirring at 600 rpm. Stirring can be made by means of a magnetic stirrer. The pressure in stepi.is preferentially at atmospheric pressure. Hence, no apparatus is needed to control pressure.

[0115] The Brønsted–Lowry acid compound used in the invention is preferably chosen from mineral acids and organic acids.

[0116] The mineral acids can be selected from HX, X being selected from Cl, Br, I, H2SO4, H3PO4,nitric acid, sulfuric acid, phosphomolybdic acid, para-toluenesulfonic acid, methylsulfonic acid.

[0117] The organic acids can be selected from a compound of formula (I):

[0118] RCOOH (I)

[0119] R being selected from hydrogen, C1-C8alkyl, such as methyl, ethyl, propyl, butyl, etc., a perfluoroalkyl group, and an aryl group preferentially benzyl or phenyl.

[0120] The acid can be selected for mono, di- or tri carboxylic acid derivatives. The acid can be selected from oxalic acid, citric acid, etc.

[0121] The Lewis acid can be a metal catalyst. Preferably, the metal catalyst can comprise a metal from the following group : aluminum, bismuth, cerium, iron, manganese, copper, lanthanum, magnesium, tin, titanium, zirconium, calcium, niobium or zinc. The metals can preferably be used in the form of oxides. The metals can preferably be used in the form of their chloride salts. The use of other salts is also possible. Preferred oxidation states of the aforementioned metal catalysts are aluminum (III), boron (III), bismuth (III), cerium (III), iron (III) and iron (II), copper (II), lanthanum (III), magnesium (II), tin (IV), titanium (IV), zirconium (IV) or zinc (II).

[0122] According to an embodiment of the invention, a metal triflate compound or a metal halogen compound, preferably iron, zinc or bismuth, can be used as the metal catalyst. Triflate compounds can be used as Lewis acids in the reaction carried out in the invention. The advantage of these salt compounds is the great stability of the triflate anion. Even when dissolved in water, the triflate anion does not react further, unlike many other classic Lewis acids. Consequently, the reaction can be substantially controlled and / or undesirable side reactions can be avoided.

[0123] Regarding the metal halogen compound, preferred embodiments are directed to iron halogen, zinc halogen, aluminum halogen, cerium (III) halogen, scandium halogen, neodymium halogen, samarium halogen, yttrium halogen, lanthanum halogen or gadolinium halogen.

[0124] Regarding the triflate metal salts, preferred embodiments are directed to bismuth triflate, zinc triflate, aluminum triflate, cerium (III) triflate, scandium triflate, neodymium triflate, samarium triflate, yttrium triflate, lanthanum triflate or gadolinium triflate.

[0125] According to an embodiment, the method of the invention is carried out in the presence of an additive and / or a ligand for the catalyst. Such additives can be a nitrogen containing compound such as triethanolamine, triethylamine, TBD, DBU, Pyridine, DMAP, 2-aminopyridyne.

[0126] According to an embodiment, the method of the invention is carried out in the presence of an additive and / or a ligand for the catalyst. Such additives can be a phosphine derivative of following formula:

[0127] PR1R2R3

[0128] The aromatic groups R1, R2and R3of the phosphine ligand PR1R2R3are preferably selected from the group consisting of phenyl, o-tolyl, m-tolyl, p-tolyl,3,5-dimethylphenyl, 4-n-butylphenyl, 4-methoxyphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl, 3,5-di-tert-butyl-4-methoxyphenyl, 4-chlorophenyl, 3,5-Bis(trifluoromethyl)phenyl, benzyl, naphthyl, dinaphthyl, pyridyl, bisphenyl, furyl and thienyl.

[0129] The hydrocarbyl groups R1, R2and R3of the phosphine ligand PR1R2R3contain 1 to 20 carbon atoms, preferably 2 to 15 carbon atoms, more preferably 3 and 10 Between the carbon atoms. Preferably, the hydrocarbyl groupsR1, R2and R3of the phosphine ligand PR1R2R3complexed with nickel are selected from the group formed by the following groups: methyl, ethyl, propyl, isopropyl , N-butyl, tertiary butyl, pentyl, cyclopentyl, hexyl, cyclohexyl, octyl, 2-ethylhexyl, benzyl and adamantyl.

[0130] The invention preferably uses a so-called “green” solvent that is non-toxic and environmentally neutral. According to an embodiment, the solvent used in the invention is selected from the group consisting of ethanol, anisole, tetrahydrofuran, preferentially 2-methyl-tetrahydrofuran, acetone, ethyl acetate, water, dioxolane, dioxane, dimethoxyethane, o-dichlorobenzene, dimethyl sulfoxide, methanol, isopropanol, ethylene glycol, acetic acid, trioxane, chloroform and a combination thereof. The solvent system may be used in the reaction of the invention as a combination of the aforementioned solvents with a ratio between two solvents ranging from 0 / 100 excluded to 100 / 0 excluded (ratio expressed in volume).

[0131] All in all, one major advantage of the invention are the mild operating conditions of the invention (low temperature, atmospheric pressure, non-toxic materials etc.). Especially, the solvent, which is the main chemical in the reaction in terms of mass and quantity, can be a mixture of green solvent(s) with water. The solvent can be recycled by distillation under vacuum and therefore the consumption is limited. These mild conditions enable in particular to conserve the original state and / or properties of the non-depolymerized material when the invention is carried out on a blended material comprising at least one polymer that is combined to polyamide. The polyamide that is ultimately depolymerized from the blended material, leaves behind the not-target material (i.e., not-target polymer) in its original state or almost original state. For example, elastic properties of elastane or strength of cotton fibers are not degraded by the method of the invention. The invention is pioneer with regard to the recovery of elastane materials.

[0132] GENERAL EXPERIMENTAL PROTOCOL ACCORDING TO THE INVENTION FOR REDUCING POLYAMIDE-BASED POLYMERIC MATERIAL.

[0133] 1. Under air, the polymeric material is placed in a round bottom flask equipped with a magnetic stirrer and a reflux condenser, followed by the addition of solvents and a Brønsted–Lowry acid. Alternatively, the round bottom flask can be replaced by 30 mL reaction tube. Both embodiments are suitable for the reaction.

[0134] 2. The catalyst is added to the reaction medium. The catalyst is generally ranging from 1 to 0.001 molar equivalents calculated in respect with the molar number of the polymeric material added initially.

[0135] 3. Optionally, a ligand of the catalyst and / or additives may be added as the last ingredient to the reaction medium.

[0136] 4. The reaction flask (or tube) is capped with a septa and heated within a sand or oil bath preheated at the desired temperature. The invention enables the reaction to operate at relatively low temperatures ranging from about 20°C to 110°C. The reaction is stirred at the set temperature for a desired time, generally ranging from about 12h to 72h. The reaction is monitored by proton NMR.

[0137] In the case where the polymeric material is made of polyamide, the polymeric material solubilizes during the reaction. The solubilized polyamide is thus contained in a liquid phase. Solubilized polyamide is ideally constituted of monomers only, but may be constituted of a mixture of monomers and oligomers.

[0138] In the case where the polymeric material is made of polyamide and at least another polymer, the polymeric material partially solubilizes during the reaction. The polyamide is depolymerized (into monomers, and optionally oligomers) while the other polymer(s) remain as a solid phase. The other polymer(s) is / are not soluble at the end of the reaction and can be recovered by filtration.

[0139] 4. When the reaction is done (after 0.1 h to 72 h, more particularly after 12 h to 72 h) the reaction mixture is cooled down to room temperature and filtered to recover the solid phase (also referred to as copolymer), i.e. the polymeric material from which the polyamide moiety has been extracted. The solid phase is washed with hot ethanol and water in order to recover the desired copolymer.

[0140] 5. Regarding the solubilized polyamide (i.e. PA6,6, PA10,10, etc.): The organic solvent of the filtrate is evaporated. The solution is then extracted with ethyl acetate several times. The organic phases are joined and the solvent is evaporated in order to recover monomers of the original polyamide, or optionally a mixture of monomers and oligomers of the original polyamide (e.g. a mixture of dicarboxylic acid derivatives).

[0141] 6. The aqueous phase (e.g. diamine) is evaporated to offer a solid (with the presence of the dye). The solid is then recrystallized in a mixture of water / EtOH / acetone. An off-white / grey precipitate was obtained and filter off. (If the precipitate is still colored by the dye, the recrystallization can be repeated to obtain the pure compounds).

[0142] Alternatively above steps 5. and 6. can be:

[0143] 5bis. Regarding the solubilized polyamide (i.e. PA6, PA6.6, etc.): To the crude reaction mixture is added acetone until a grey / white solid precipitate. It is worth noting that the precipitate can be colored with the dye of the starting material. The precipitate is filtered off and dried in an oven (60 °C) until the mass of the solid does not evolve anymore.

[0144] 6bis. In case of PA6.6, PA10.10, etc.: The volatiles of the filtrate are evaporated under reduced pressure (or distilled off). The remaining aqueous phase is extracted with several times. The organic phases are joined and the solvent is evaporated in order to recover monomers of the original polyamide, or optionally a mixture of monomers and oligomers of the original polyamide (e.g. a mixture of dicarboxylic acid derivatives).

[0145] Examples of the present invention are presented below. For instance, examples of depolymerization of synthetic or bio-sourced polymeric materials in the presence of various other polymers are provided. Some of the tested catalysts are for example FeCl3, FeCl2, AlCl3, ZnCl2, CaCl2, Fe(OTf)3, Zn(OTf)2, La(OTf)3, Bi(OTf)3, Y(OTf)3, Sc(OTf)3, etc. The Brønsted–Lowry acid preferentially used are HCl, H2SO4, CH3CO2H, HCO2H, CF3CO2H, CF3SO3H 4-CH3-C6H4-SO3H. Suitable polar organic solvents include dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, dioxane, dimethoxyethane, o-dichlorobenzene, dimethyl sulfoxide, methanol, ethanol, isopropanol, acetone, ethyl acetate, ethylene glycol, acetic acid, trioxane or chloroform, preferably methanol, ethanol or 2-methylTHF. The polymeric materials used are composed of PA6 and / or PA6.6 mixed with PET, elastane, cotton and wool. The polyamides used are textile waste received by lingerie and clothing brands as well as textile manufacturers.

[0146] The depolymerization of the polyamide according to the invention generates monomers. Oligomers may be generated as well. In order to determine the ratio of monomers vs. oligomers, one can define the conversion as the rate of the hydrolysis of the polyamide that is being studied. The conversion therefore, reflects the number of bonds between the monomers which have been broken within the given depolymerization. The conversion is determined by means of NMR analysis of the crude reaction mixture. In fact, it is possible to assess the ratio between the polyamide (PA) remaining in solution and the products which are mainly hexamethylenediamine (HMDA) derivatives and adipic acid (AA) derivatives. This methodology to determine the conversion is known from Pahovnic and Žagar [cf. DOI:10.1021 / acssuschemeng.0c05706].

[0147] By taking into account the known signal in NMR spectra of each component of the reaction mixture, it is possible to determine the conversion with the following formula:

[0148]

[0149] Wherein IPAis the integration of the peak of PA at 3.0 ppm and IHMDAis the integration of the peaks of HMDA at 2.75 ppm.

[0150] In the event there is some remaining solid (i.e. unreacted polyamide) which cannot be taken into the crude NMR analysis, the remaining solid in the reaction is filtered off the reaction, dried until the mass is not evolving anymore and then it is weighed. The mass of the remaining solid is used to established a fixed-conversion. Said fixed-conversion is then multiplied by the conversion of the crude NMR analysis to provide the final conversion of the reaction.

[0151] In the case of a mixed material in which polyamide is blended with another polymer, the conversion calculation needs to take into account the polymer that is not depolymerized during the depolymerization reaction. More particularly, the second polymer (or non-depolymerized polymer) is dried until the mass is stabilized. It is then weighed. The second polymer is preferably characterized by FTIR or NMR (when possible) to assess the purity and the content of polyamide left in the polymers in case the depolymerization reaction is not complete (i.e., not 100% of PA is transformed into monomers and optionally oligomers). In that case, the weight of the second polymer which is not affected by the reaction of polymerization is deducted from the original mass of the starting mixed material of the reaction to assess precisely the conversion.

[0152] Given the fact that the depolymerization method of the invention is focusing on the efficiency, i.e., the conversion rate of the reaction, the yield is not of particular interest. However, the yield can be determined by the molar quantity of the products compared to the molar quantity of one monomer in the polyamide starting material. Yields are generally determined only for isolated products. This means that yields are calculated when the reaction is worked-up and the products are purified and isolated by adapted purification techniques (distillation, recrystallisation, extraction, column chromatography, etc.).

[0153] The examples described herein are not limiting the scope of the claimed invention. In the examples, the most commonly used polymers (for example: PA6 and PA6.6) are given. The quantity of Brønsted–Lowry acid needed to carry out the depolymerization reaction according to the invention is substantially dependent on the type of polymeric material used. It should be noted that, by approximation, and in order to calculate the molar yield of the depolymerization reactions, the starting material may be considered as being exclusively formed of the polymer studied.

[0154] The yield of chemical compounds with an average molar mass of less than 600 g / mol obtained by the method of the invention depends on the starting polymer material. Further, the yield depends on the operating conditions applied as explained above, and in particular depends on the reaction time. The yield is generally good (from 68 to 98 molar % relative to the total number of moles of monomer units present in the polymer(s) of the starting material.

[0155] As mentioned above, by approximation, and in order to effectively calculate the molar yield of the depolymerization process, the starting polymer material is considered to be constituted or exclusively formed of the polymer studied.EXAMPLES

[0156] Example 1: Reaction on black polyamide-based boxer (>98% purity) in EtOH.

[0157] shows the chemical equation.

[0158] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, black PA6,6 from an underwear (elastane <2%) is added followed by 8 mL of a EtOH. Then, 1 mL of HCl in water (37%, 12 M) is added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The tube is capped with a septum and placed in a sand heating bath at 80°C. The reaction medium is stirred for 14 h at 600 rpm. The reaction led to a conversion to the corresponding monomers of 34%.

[0159] It is the first time that such a reaction occurs at 75°C having such a high level of conversion rate within 14 h. Therefore, further reactions with different concentrations and different reaction times were carried out. One of them was found to be very productive since in the presence of ZnCl2 as a catalyst at reflux for 48 h, the NMR conversion was determined as 76%. No more textile was observable in the reaction mixture (nor any solid see below example 2).

[0160] Example 2: Reaction on black polyamide-based boxer (>98% purity) in EtOH with ZnCl2catalyst.

[0161] shows the chemical equation.

[0162] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, black PA6,6 from an underwear (elastane <2%) is added followed by 8 mL of a mixture of EtOH / water. Then, 1 mL of HCl in water (37%, 12 M) is added to the reaction mixture followed by the catalysts (4 wt% of ZnCl2). The tube is capped with a septum and placed in a sand heating bath at 80°C. The reaction medium is stirred for 48 h at 600 rpm. The reaction led to a full conversion of the starting material and led to the corresponding monomers with a conversion of 76% and 24% of oligomers.

[0163] Example 3: Reaction on black polyamide-based textile (76% PA, 24% Elastane) in EtOH / H2O with FeCl3catalyst and recovery of the elastane.

[0164] shows the chemical equation.

[0165] Following the experimental procedure described above, in a 250 mL round bottom flask equipped with a magnetic stirrer, 5 g of black PA6,6 from a textile in one piece (elastane ca. 24%) are added followed by 40 mL of a solvent mixture of EtOH / H2O (1 / 1 : v / v). Then, 10 mL of HCl in water (37%, 12 M) are added to the reaction mixture followed by a catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 80°C. The reaction medium is stirred for 72 h at 600 rpm. After this time, the reaction is filtered. A slightly colored knitted fiber is recovered. The textile is elastic and recovered as 24 wt% of the starting materials, e.g., 1.202 g.

[0166] The reaction led to a full conversion of the polyamide starting material and led to the corresponding monomers with a conversion rate of 81%.

[0167] Example 4: Reaction on purple polyamide-based textile (94% PA, 6% Elastane) in EtOH / H2O with FeCl3catalyst and recovery of the elastane.

[0168] shows the chemical equation.

[0169] Following the experimental procedure described above, in a 250 mL round bottom flask equipped with a magnetic stirrer, 5 g of purple PA6,6 from textile in one piece (elastane content c.a. 6%) are added followed by 40 mL of a solvent mixture of EtOH / H2O (1 / 1 : v / v). Then, 10 mL of HCl in water (37%, 12 M) are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The flask is placed in a sand heating bath at 90°C. The reaction medium is stirred for 72 h at 600 rpm. After this time, the reaction is filtered. A slightly pink-colored knitted fiber is recovered. The textile is elastic and was recovered as 6 wt% of the starting materials, e.g. 0.302 g. The textile is pure elastane according to FTIR spectroscopy.

[0170] The reaction led to a full conversion of the polyamide starting material and led to the corresponding monomers with a conversion of 67%.

[0171] Example 5: Reaction on white PA6-based textile (84% PA, 16% Elastane) in EtOH / H2O with FeCl3catalyst and recovery of the elastane.

[0172] shows the chemical equation.

[0173] Following the experimental procedure described above, in a 25 mL round bottom flask equipped with a magnetic stirrer, 0.5 g of white PA6 tights in one piece (elastane content c.a. 16%) is added followed by 8 mL of a mixture of solvent EtOH / H2O (1 / 1 : v / v). Then, 1 mL of HCl in water (37%, 12 M) is added to the reaction mixture followed by the catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 12 h at 600 rpm. After this time, the reaction is filtered. A fiber is recovered.

[0174] The textile is elastic and was recovered as 16 wt% of the starting materials, e.g. 0.099 g. The textile is pure elastane according to FTIR spectroscopy.

[0175] The reaction led to a full conversion of the polyamide starting material and led to the corresponding monomers with a conversion of 49%.

[0176] Example 6: Comparison of acid used in the reaction.

[0177] shows the chemical equation.

[0178] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 0.5 g of black PA6,6 underwear in one piece (elastane content <2%) is added followed by 8 mL of a solvent mixture of EtOH / H2O (1 / 1 : v / v). Then, 12 equivalents of selected acid are added to the reaction mixture followed by the catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 12 h at 600 rpm. After this time, the reaction is filtered.

[0179] Results regarding the tested acids are reported in table 1 below:

[0180] AcidConversion of the polyamideRatio monomers / oligomersHCl100%99 / 1H2SO4100%99 / 1Acetic Acid>5%NDNo acid>5%NDpTsOH100%96 / 4Ortho Phosphoric acid100%54 / 46Phosphomolybdic acid100%ND

[0181] Table 1 : Tested Acids

[0182] Example 7: Effect of the catalyst on PA6,6.

[0183] shows the chemical equation.

[0184] In a 30 mL tube equipped with a magnetic stirrer, Black PA6,6 based boxer mixed with elastane from an underwear is added followed by 8 mL of a EtOH / Water mixture (1 / 1 : v / v). Then, 1 mL of HCl in water (37%, 12 M) is added to the reaction mixture followed by the selected catalyst (10 wt%). The tube is capped with a septum and placed in a sand heating bath at 90°C. The reaction medium is stirred for 48 h at 600 rpm. After this time, the reaction is filtered.

[0185] Results regarding the tested catalysts are reported in table 2 below:

[0186] CatalystConversion of the PA6,6.Conversion into monomersTextile remainingAlCl3100%74%94 mg (elastane)ZnCl2100%87%86 mg (elastane)Cu(OAc)2[UNCOMPLETE REACTION]ND>49%205 mg (elastane / PA)La(OTf)3100%87%NoneFe(OTf)3100%94%NoneY(OTf)3100%61%None

[0187] Table 2 : Tested Catalysts

[0188] Example 8: Effect of additives within the system on PA6,6.

[0189] shows the chemical equation.

[0190] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 0.5 g of black PA6,6 underwear in one piece (elastane content <2%) is added followed by 8 mL of a mixture of solvent EtOH / H2O (1 / 1 : v / v). Then, 1 mL of HCl (37%) is added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). Then the respective additive (2.0 equiv. compared to the catalyst loading) is added to the reaction mixture. The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 16 h at 600 rpm. After this time, the reaction is filtered.

[0191] Results regarding the tested additives are reported in table 3 below:

[0192] AdditiveConversion of polyamideRatio monomers / oligomersTriethanolamine100%71 / 29TBD100%85 / 15PPh3100%ND2-cyanopyridine100%63 / 37DBU100%65 / 35DMAP100%77 / 23

[0193] Table 3 : Tested Additives

[0194] Example 9: Effect of solvent within the system on PA6,6.

[0195] shows the chemical equation.

[0196] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 0.5 g of black PA6,6 underwear in one piece (elastane content <2%) is added followed by 8 mL of solvent. Then, 1 mL of HCl (37%) is added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). Then the additives are added to the reaction mixture. The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 16 h at 600 rpm. After this time, the reaction is filtered.

[0197] Results regarding the tested solvents are reported in table 4 below:

[0198] SolventConversion of polyamideRatio monomers / oligomersEtOH / H2O : 1 / 0>10%NDEtOH / H2O : 6 / 223%60 / 40EtOH / H2O : 4 / 4100%72 / 28EtOH / H2O : 2 / 6100%58 / 42EtOH / H2O : 0 / 8100%34 / 66Me-THF100%NDDMSO76%NDAcetone100%NDaEtOH / H2O / acetone : 4 / 4 / 1100%84 / 16H2O / Acetone : 4 / 4100%91 / 9AcOET100%NDa

[0199] Table 4 : Tested Solvents.a1h instead of 16h.

[0200] Example 10: Determination of the elastane content in a polyamide based mixed material from an underwear.

[0201] The determination of the content of elastane within a boxer in polyamide was performed in two reactions, a first one for the body part of the boxer and a second one on the rubber part of the boxer.

[0202] 1stReaction: Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 5 g of black PA6,6 boxer body in one piece are added, followed by 40 mL of a mixture of EtOH / H2O (1 / 1 : v / v). Then, 10 mL of HCl (37%) are added to the reaction mixture followed by the catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 72 h at 600 rpm. After this time, the reaction is filtered. 101 mg of elastane was recovered.

[0203] The body of the boxer contains 2% of elastane and 98% of polyamide.

[0204] 2ndReaction: Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 0.5 g of black PA6,6 boxer rubber in one piece is added followed by 8 mL of a mixture of EtOH / H2O (1 / 1 : v / v). Then, 1 mL of HCl (37%) is added to the reaction mixture followed by the catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 72 h at 600 rpm. After this time, the reaction is filtered. 86 mg of elastane was recovered as a knitted textile composed only of elastane.

[0205] The rubber part of the boxer contains 17% of elastane and 83% of polyamide.

[0206] Example 11: Recovery of cotton fiber from a mixed polyamide-based material.

[0207] shows the chemical equation.

[0208] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirrer, 5 g of black PA6,6 containing sewing in cotton thread / yarn in one piece (elastane content <2%) are added followed by 8 mL of a mixture of solvent. Then, 10 mL of HCl (37%) are added to the reaction mixture followed by the catalyst (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 72 h at 600 rpm. The thread of cotton was recovered intact and the conversion of the PA6,6 into monomers was determined as 87%.

[0209] Example 12: Depolymerization of an entire bra.

[0210] shows the chemical equation.

[0211] Following the experimental procedure described above, in a 500 mL round bottom flask equipped with a magnetic stirrer and a reflux condenser, 20 g of a purple bra containing sewing in PET thread / yarn, elastane, rubber, metal pieces, polypropylene in one piece are added followed by 200 mL of a mixture of solvent. Then, 40 mL of HCl (37%) are added to the reaction mixture followed by the catalyst (4 wt% of ZnCl2). The flask is placed in a sand heating bath at 100°C. The reaction medium is stirred for 72 h at 600 rpm. The thread of PET elastane, rubber, metal pieces, polypropylene were recovered intact and the conversion of the PA6,6 into monomers was determined as 100%. The work-up of the reaction and the following precipitation of the monomer led to the recovery of 10.2g of pure e-aminocaproic acid derivatives.

[0212] By executing the method of the invention, the nature of the final product obtained by the depolymerization might change. More particularly, the nature of the final product directly depends on the nature of the starting material used in the method of the invention. Furthermore, the final product may take various forms or aspects depending on the selected solvent, Brønsted–Lowry acid and catalyst, as well as depending on the reaction time (duration of the reaction).

[0213] In the context of the present invention, selectivity relates to the nature of the products formed as well as the nature of the cleaved bonds.

[0214] The invention described above provides a method for depolymerizing polyamide in mixed materials by selectively depolymerizing said polyamide. The selective depolymerization is achieved by selective cleavage of nitrogen-carbonyl bonds of amide functions (-CO-N-) in the presence of different copolymers such as polyurethanes, cotton, wool, polyesters. According to a preferred embodiment of the invention, a step of bringing the polyamide blended polymeric material into contact with a Brønsted–Lowry acid and a catalyst of the type Lewis acid in a solvent (i.e., an environmentally acceptable solvent). The reaction of the invention only requires a temperature inferior or equal to 110°C. The operating conditions of the invention do not require any specific apparatus to handle pressure. Moreover, the polymer conversion rate of the present invention into the corresponding monomers, and optionally oligomers is very high (>90%). The depolymerization of polyamide at such low temperature, i.e. below or equal to 110°C is a pioneer achievement in the field of the invention. The mild operating conditions seem to be linked to the combinational use of an Bronsted acid, a catalyst based on Lewis acid and a well-defined solvent system. The present invention describes for the first-time reactions of depolymerization of polyamide-based materials (textile, plastics, etc.) at a temperature below 110°C, no pressure and in green bio-based and unharmful solvents. The recovery of a (co- or blended) synthetic (elastane) and natural (cotton) polymer in its original form (knitted for example) from a blended material containing polyamide thanks to a reaction of depolymerization of polyamide of textile and plastics has never been reported. The present invention described for the first time the recovery of elastane in its original form from the reaction of depolymerization of polyamide-based materials blended with elastane, polyurethane, cotton, wool, cellulosic material. More generally, the combination of Brønsted–Lowry acid and Lewis acid has never been reported for the reaction of depolymerization of polyamide materials. Said differently, the invention describes the first use of a combination of Brønsted–Lowry acid and Lewis acid catalysts for the selective depolymerization of polyamide based-materials. Further, the use of a combination of green bio-based and unharmful solvents such as ethanol, anisole, MeTHF, acetone, ethyl acetate and water for the depolymerization of polyamide-based materials at low temperature has never been reported to date. The invention described the first the use of a green system solvent which enables the reaction of depolymerization of polyamide to proceed at low temperature.

[0215] Regarding a very preferred embodiment of the invention, the polymeric material is made of at least a first polymer and a second polymer. It is a blended polymeric material. It is in solid form, such as a textile (e.g., underwear). In this embodiment, the invention may be defined as a:

[0216] Method for depolymerizing a polymeric material made of at least a first polymer and a second polymer, said method comprising the steps of:

[0217] a. contacting in a solvent said polymeric material with a Brønsted–Lowry acid in the presence of a Lewis acid catalyst, in order to selectively depolymerizing said first polymer within polymeric material, thereby obtaining monomers and optionally oligomers, of depolymerized first polymer from the polymeric material; and

[0218] b. collecting the polymeric material, wherein said polymeric material is reduced of at least 90%, preferentially 100% of the original content of said first polymer in the polymeric material and wherein said first polymer is polyamide.

[0219] The monomers, and optionally oligomers, obtained by above step a. are derived from the polyamide contained in the blended polymeric material. The monomers, and optionally oligomers, can be recovered in the liquid phase of the reaction medium.

[0220] The final material (i.e., the polymeric material after step a.) is generally constituted at least of 90% of the second polymer. The polymeric material can be recovered as a solid phase from the reaction medium. The polymeric material is stripped or deprived of polyamide after above step a. of the depolymerizing method.

[0221] Of course, the present invention can also be applied to materials that are composed of a non-polymeric material, such as a metal, and a polymeric material such as polyamide. For example, metals that are coated with polyamide can undergo the method of the invention and thus one can recover on one side the degraded polyamide (monomers and optionally oligomers), and on the other side the intact metal that has been stripped of its polyamide coating. Another example would be metals that are coated with polymeric material composed of a blend of polyamide and at least another polymer (such as elastane or else). If applied to the method of the invention, one could recover the stripped metal, the degraded polyamide (monomers and optionally oligomers), and an intact other polymer (such as elastane or else).

[0222] The method of the invention may be defined in the present description as comprising one or more steps. However, in practice the method of the invention is carried out in one single chemical reaction. This is shown in the figures relative to the invention. This is also reflected by the single stepi.as defined by the invention. Particular embodiments of the invention may contain further steps, such as a collecting step or a purification step (e.g. stepsii.and / oriii.). Yet, these further steps are subsequent to the single step (i.) of a chemical reaction which depolymerizes polyamide within a polymeric material which contains at least polyamide and another polymer.

[0223] Further examples have been carried out by the Applicant. Here again, the examples show a one-step (or one-operation, or one-stage) method consisting of a single chemical reaction.

[0224] Example 13: Reaction on blue polyamide-based textile (75 / 25 PA6 / EA) in EtOH with FeCl3 catalyst.

[0225] shows the chemical equation.

[0226] Following the experimental procedure described above, in a 250 mL round bottom flask with a magnetic stirer, 25 g of blue textile from pre-consumer waste (elastane = 25 wt%) are added followed by 50 mL of EtOH. Then, 25 mL of HCl in water (37%, 12 M) and 25 mL of water are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The reaction is heated to reflux and stirred for 6 h. After this time, the solvent is distilled from the reaction medium, and the corresponding monomers are isolated and purified according the description above to yield 80% ACA

[0227] Example 14: Effect of solvent within the system on PA6,6.

[0228] shows the chemical equation.

[0229] Following the experimental procedure described above, in a 30 mL tube equipped with a magnetic stirer, 1 g of blue PA6 textile cut into small pieces (1*1*1 cm) (elastane content = 25%) is added followed by 4 mL of a selected solvent. Then, 2 mL of HCl (37%) and 2 mL of water are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The flask is placed in a heating block at 100 °C. The reaction is allowed to stir for 12 h at 600 rpm. After this time, the reaction is filtered. The results are depicted in table 5 below.Selected SolventConversionRatio monomers / oligomersAcetonitrile100%52 / 48EtOH100%52 / 48Hexane100%82 / 18 (partial degradation of EA)THF100%64 / 36

[0230] Table 5: Effect of solvent.

[0231] Example 15: No use of water during the reaction.

[0232] shows the chemical equation.

[0233] Following the experimental procedure described above, in a 250 mL round bottom flask equipped with a magnetic stirrer, 25 g of blue PA6 tights in one piece (elastane content c.a. 25%) are added followed by EtOH (100 mL). Then, 25 mL of H2SO4or H3PO4are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The flask is placed in a sand heating bath at 100 °C. The reaction is allowed to stir for 12 h at 600 rpm. After this time, the reaction is filtered. The textile was completely recovered, and the elasticity of the elastane was assessed by elongation methodology. NMR analysis of the crude mixture did not unveil the presence of monomers indicating the absence of reaction and conversion.

[0234] A table comparing the use of water vs. the absence of water is shown in table 6 below.AcidConversion of the polymers.Ratio monomers / oligomersH2SO4(with 1V of Water)100%99 / 1pTsOH (with 1V of Water)100%96 / 4Ortho Phosphoric acid (with 1V of Water)100%54 / 46H2SO40% (NMR)(degradation of the elastane)Ortho Phosphoric acid0% (NMR)(degradation of the elastane)pTsOH0% (NMR)(degradation of the elastane)

[0235] Table 6: Presence of water vs. absence of water.

[0236] Example 16: Reaction on blue polyamide-based textile (75 / 25 PA6 / EA) and airbags (75 / 25 PA6.6 / silicone) in EtOH with FeCl3 catalyst and HCl.

[0237] shows the chemical equation.

[0238] Following the experimental procedure described above, in a 500 mL round bottom flask with a magnetic stirrer, 10 g of blue textile from pre-consumer waste (elastane = 25 wt%) and 10 g of airbags (PA6.6 / silicone) are added followed by 40 mL of EtOH. Then, 20 mL of HCl in water (37%, 12 M) and 20 mL of water are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The reaction is heated to reflux and stirred for 16 h. After this time, the solvent is distilled from the reaction medium, and the corresponding monomers can be isolated and purified following the above-described procedure.

[0239] Example 17: Reaction on blue polyamide-based textile (75 / 25 PA6 / EA) and airbags (75 / 25 PA6.6 / silicone) in EtOH with FeCl3 catalyst and H2SO4.

[0240] shows the chemical equation.

[0241] Following the experimental procedure described above, in a 500 mL round bottom flask with a magnetic stirer, 10 g of blue textile from pre-consumer waste (elastane = 25 wt%) and 10 g of airbags (PA6.6 / silicone) are added followed by 40 mL of EtOH. Then, 14 mL of H2SO4in water and 20 mL of water are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The reaction is heated to reflux and stirred for 16 h. After this time, the solvent is distilled from the reaction medium, and the corresponding monomers are isolated and purified.

[0242] Example 18: Reaction on blue polyamide-based textile (75 / 25 PA6 / EA) and airbags (75 / 25 PA6.6 / silicone) without organic solvent with FeCl3catalyst.

[0243] shows the chemical equation

[0244] Following the experimental procedure described above, in a 250 mL round bottom flask with a magnetic stirer, 20 g of blue textile from pre-consumer waste (elastane = 25 wt%) are added, followed by the addition of 20 mL of HCl in water (37%, 12 M) and 20 mL of water are added to the reaction mixture followed by the catalysts (4 wt% of FeCl3). The reaction is heated to reflux and stirred for 16 h. After this time, the solvent is distilled from the reaction medium, and the corresponding monomers are isolated and purified following the described procedure. The Elastane in these conditions is completely decomposed (i.e. degraded).

[0245] As mentioned above, a particularly preferred embodiment is regarding a method for depolymerizing polyamide of a polymeric material comprising the step of:i.contacting in a solvent the polymeric material with a Brønsted–Lowry acid in the presence of a Lewis acid catalyst, thereby producing a medium having a liquid phase comprising monomers derived from said polyamide, and wherein the polymeric material is made of polyamide and at least a second polymer, and wherein contacting said polymeric material in stepi.induces selective depolymerizing of the polyamide within the polymeric material, thereby producing said medium that further comprises a solid phase of said second polymer. This is a one-step method (i.e. single step:i.).

[0246] When considering figures 1 to 11, the invention may be defined as a method for depolymerization of a polyamide with both a Bronsted acid and a Lewis acid in an aliphatic alcoholic solvent with water to a composition with monomers containing a (protonated) amine and / or an esterified carboxylic acid. This provides a method having a major advantage of mild operating conditions.

[0247] When further considering the above section GENERAL EXPERIMENTAL PROTOCOL ACCORDING TO THE INVENTION FOR REDUCING POLYAMIDE-BASED POLYMERIC MATERIAL and the details of the respective examples of figures 1-11 (including table 4) the invention may be defined more broadly, as a method for depolymerization of a polyamide with both a Bronsted acid and a Lewis acid in an organic solvent with water to a composition with monomers containing a (protonated) amine and / or an esterified carboxylic acid.

[0248] The organic solvents tested by the Applicant are suited for the chemical reaction of the method according to the invention with regard to the depolymerization of polyamide on one hand, and the recovery of a second polymer (preferentially elastane) on the other hand. This is enabled by the single chemical reaction of the invention using a Bronsted acid and a Lewis acid.

[0249] Preferred organic solvents include dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, dioxane, dimethoxyethane, o-dichlorobenzene, dimethyl sulfoxide, methanol, ethanol, acetone, ethyl acetate, ethylene glycol, trioxane or chloroform, preferably methanol, ethanol or 2-methylTHF, or a combination thereof.

[0250] According to a particularly preferred embodiment of the invention, the organic solvent used in the invention is combined with water. This embodiment drastically enhances the chemical reaction of the invention. The use of a mixture of organic solvent and water enables that the second polymer, which preferentially is elastane, is not degraded or at least almost not degraded. However, when hexane is used as an organic solvent, the elastane is partially degraded which may not be desirable. Depending on the subsequent use and / or recycling of the second polymer (preferably elastane) the organic solvent may be chosen. Preferably, polar organic solvents may be used in order to assure that the second polymer (e.g. elastane) is not degraded. More preferably, oxygen, nitrogen and / or halogen (preferably chlorine) containing polar solvent may be used. Yet, whatever organic solvent with water is used, the separation of depolymerized polyamide from the remaining second polymer (elastane) by selective depolymerization is assured. Physical separation is easily manageable (filtration for example). The combination of organic solvents with water described herein with reference to the invention enables for the first time to recover physically intact elastane from polymeric materials containing elastane and polyamide (or if hexane is used as organic solvent, it is possible to recover almost intact elastane). More generally the invention enables the recovery of intact specific polymers on one hand, and monomers of polyamide on the other hand, from starting materials comprising a mixture or a combination of polyamide and other specific polymers.

[0251] .

Claims

Method for depolymerizing polyamide of a polymeric material comprising the step of:i.contacting in a solvent the polymeric material with a Brønsted–Lowry acid in the presence of a Lewis acid catalyst, thereby producing a medium having a liquid phase comprising monomers derived from said polyamide, and wherein the polymeric material is made of polyamide and at least a second polymer, and wherein contacting said polymeric material in stepi.induces selective depolymerizing of the polyamide within the polymeric material, thereby producing said medium that further comprises a solid phase of said second polymer.Method according to claim 2, wherein the solid phase of the second polymer is constituted of at least 90%, preferentially 100% of said second polymer.Method according to any of the preceding claims, wherein the polymeric material after stepi.is reduced of at least 90%, preferentially 100% of said polyamide.Method according to any of the preceding claims, wherein said medium further comprises oligomers derived from said polyamide, and wherein the ratio of said monomers relative to said oligomers is ranged from 99:1 to 70:30.Method according to any of the preceding claims, further comprising the step of:ii.extracting the medium in order to isolate said monomers, and optionally oligomers, and subsequently evaporating said solvent in order to recover the monomers, and optionally oligomers.Method according to any of the claims 2 to 6, further comprising the step of:iii.filtering the solid phase from said medium, and subsequently washing and drying said solid phase in order to recover the second polymer.Method according to any of the preceding claims, wherein said second polymer is selected from the group consisting of a polyurethane copolymer, cotton copolymer, wool copolymer a polyester copolymer, silicon copolymer, elastane and cellulosic material.Method according to any of the preceding claims, wherein stepi.is operated at a temperature less than or equal to 110°C, preferentially less than or equal to 100°C, less than or equal to 90°C, or less than or equal to 80°C.Method according to preceding claims 2 to 9, wherein the second polymer is elastane.Method according to claim 10, wherein said elastane is recovered as a fiber or in a knitted form.Method according to any of the preceding claims, wherein the pressure in stepi.is at atmospheric pressure.A compound generated by the method according to one of the preceding claims, wherein said compound is selected from the group consisting of a monomer, monomer derivatives, an oligomer, a polymer, elastane, cotton and PET a ε-caprolactam derivative or a HMDA derivative.

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