Description:BACKGROUND

FIELD OF THE DISCLOSURE
[0001] Various embodiments of the disclosure relate generally to methods of processing polyamides. More specifically, various embodiments of the disclosure relate to upcycling of polyamides to form polyamide-vitrimers.

DESCRIPTION OF THE RELATED ART

[0002] Polyamides, commonly referred to as nylons, are characterized by their strong intermolecular hydrogen bonding, which contributes to their notable resistance to solvents and chemicals. Due to their exceptional mechanical properties, such as high strength, durability, thermal stability, and chemical resistance, polyamides (PAs) are widely utilized in various applications. However, the same resilience that makes polyamides durable also poses significant challenges in terms of degradation, rendering them difficult to recycle.
[0003] In recent years, the increasing consumption of plastics has raised serious environmental concerns, mainly due to their resistance to degradation. As part of the global movement towards a circular plastics economy, recycling plastic waste has become crucial in reducing reliance on fossil fuels used in the production of virgin plastics. Current recycling methods predominantly employ open-loop recycling, in which the end product is different from the original and generally of lower quality, a process known as downcycling. In open-loop recycling, the inclusion of virgin polymers is often necessary to achieve the desired performance of the final product. In contrast, closed-loop recycling aims to maintain the properties of the original plastic, producing final products of comparable or higher quality, known as upcycling, thereby minimizing or eliminating the need for virgin polymers.
[0004] The absence of efficient chemical recycling methods for polyamides has resulted in the widespread practice of waste-to-energy (WtE) incineration. While this may be suitable for plastics like polyethylene (PE) or polypropylene (PP), the incineration of nitrogen-containing plastics such as polyamides results in the emission of not only carbon dioxide (CO₂) but also harmful nitrogen oxide (NOx) gases, contributing to greenhouse gas pollution. Depolymerization of polyamides back into their monomers, a potential recycling approach, typically requires extreme reaction conditions and extended reaction times, which can lead to low yields and undesired by-products, making the process economically unfeasible. There is a pressing need to develop new and efficient recycling methods that reduce greenhouse gas emissions and promote a circular economy for polyamide materials.
[0005] Vitrimerization is an emerging technology for converting polymer waste into high-value products. Vitrimer chemistry is based on dynamic covalent bonds, which transform permanent covalent linkages into covalent adaptable networks (CANs). These adaptable networks enable polymer reprocessing and recycling while preserving the original material properties, even after multiple recycling cycles.
[0006] Despite their adaptability in vitrimerization processes, the amide bonds in polyamides are particularly thermally stable and chemically resistant. As a result, vitrimerization of polyamides often requires harsh reaction conditions, such as high temperatures, extended reaction times, and the use of appropriate catalysts, to achieve the desired recyclability.
[0007] Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY

[0008] According to embodiments of the present disclosure, a method of processing a polyamide to form a polyamide-vitrimer in solution is provided. The method comprises heating a reaction mixture comprising a polyamide, a multifunctional amine, and a catalyst at a temperature in a range of 140°C to 200°C for a duration of time in a range of 20 hours to 48 hours under a nitrogen atmosphere to produce the polyamide-vitrimer. A tensile strength of the polyamide-vitrimer is greater than a tensile strength of the polyamide.

[0009] In another embodiment of the present disclosure, a method of processing a polyamide to form a polyamide-vitrimer is provided. The method comprises performing a melt extrusion of a polyamide with a multifunctional amine and a catalyst at a temperature in a range of 175°C to 300°C in an extruder for a residence time in a range of 1 minute to 10 minutes to form the polyamide-vitrimer. A tensile strength of the polyamide-vitrimer is greater than a tensile strength of the polyamide.
[0010] According to embodiments of the present disclosure, a polyamide-vitrimer formed using one or both of the inventive methods is provided. The polyamide-vitrimer comprises a polyamide crosslinked with a multifunctional amine, wherein a concentration of the multifunctional amine in the polyamide-vitrimer ranges from 1 weight percent to 10 weight percent.
[0011] In yet another embodiment, a method of enhancing a tensile strength of a polyamide is provided. The method comprises crosslinking the polyamide with a multifunctional amine in presence of a catalyst to form a polyamide-vitrimer. A concentration of the multifunctional amine in the polyamide-vitrimer is in a range of 1 weight percent to 10 weight percent. The polyamide comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof. The catalyst comprises boric acid, aluminum chloride (AlCl3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), and hafnium (IV) triflate. The multifunctional amine comprises meta-phenylenediamine, para-phenylenediamine, benzene triamine, cycloaliphatic secondary diamine, cycloaliphatic triamine, xylene diamine, tris(3-aminopropyl)amine, 4H-1,2,4-triazole-3,4,5-triamine, 2,4,6-triaminopyrimidine, diethylenetriamine (DETA), triethylenetetramine (TETA), Triaminocyclohexane (TACH), melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof.
[0012] In some embodiments, the polyamide of the polyamide-vitrimer comprises poly(tetramethylene adipamide) (nylon 4,6), poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene azelamide) (nylon 6,9), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(4-aminobutyric acid) (nylon 4); poly(6-aminohexanoic acid) (nylon 6), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminoocatanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-amino- undecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), caprolactam/hexamethylene adipamide copolymer (nylon 6/6,6), hexamethylene adipamide/caprolactam copolymer (nylon 6,6/6), hexamethylene adipamide/hexamethylene-azelamide copolymer (nylon 6,6/6,9), copolymers of polyamide with styrene, copolymer of polyamide and acrylonitrile butadiene styrene (ABS), copolymer of polyamide and styrene-butadiene styrene (SBS), copolymer of polyamide and polyphenylene oxide (PPO), polyamide elastomers, polyamide blends, filled polyamides or combinations thereof.
[0013] In some embodiments, the polyamide of the polyamide-vitrimer comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
[0015] The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
[0016] All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
[0017] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure.
[0018] As used herein, the term “polymer” is referred to as comprising a monomer, the monomer is present in the polymer in the polymerized form of the monomer.
[0019] As used herein, "elastomer" or "elastomeric composition" refers to any polymer or composition of polymers (such as blends of polymers) consistent with the ASTM D1566 definition. Elastomers include mixed blends of polymers such as melt mixing and/or reactor blends of polymers. The terms may be used interchangeably with the term "rubber."
[0020] Plastic recycling refers to a process whereby useful products may be produced from waste plastics/polymers after reprocessing or melting the waste plastics. However, polymers after recycling usually possess inferior properties when compared to their virgin counterparts. The extent of degradation may depend on degradation during use of the polymer, cycle life, and the severity of conditions applied during reprocessing.
[0021] Vitrimers are a class of polymers containing reversible dynamic covalent bonds that can reorganize upon application of external stimuli allowing the material to be reshaped, repaired, or recycled while mostly retaining its original properties. Polymers containing dynamic covalent bonds are known to form covalent adaptable networks (CANs). The polyamide-vitrimers of the present disclosure, form associative CANs, which means that existing covalent bonds are only broken when new ones are formed. The formation of CANs through dynamic crosslinkers renders the polyamide-vitrimers recyclable or reprocessable.
[0022] KR102702027B1 disclosed crosslinking a polyamide using a polyammonium salt as the crosslinker in a multi-step, solid-state process. The solid-state polymerization of KR102702027B1 was conducted preferably in an open vessel between the polyamide, and the ammonium salt in the presence of a transamidation catalyst in powder form, below the melting point of the components, for 20 to 30 hours.
[0023] In one embodiment, the present disclosure provides a solution-phase method 100 of processing a polyamide to form a polyamide-vitrimer. The method comprises step 102 of heating a reaction mixture comprising a polyamide, a multifunctional amine, and a catalyst at a temperature in a range of 140°C to 200°C for a duration of time in a range of 20 hours to 48 hours under a nitrogen atmosphere to produce the polyamide-vitrimer.
[0024] The processing of the polyamide, in one instance, relates to recycling of the polyamide. In some embodiments, the processing of the polyamide relates to forming the polyamide-vitrimer. The formation of the polyamide-vitrimer results in an upcycling of the polyamide whereby a mechanical property of the polyamide-vitrimer is on par or superior to a mechanical property of the polyamide it is formed from.
[0025] The mechanical properties of the polyamide may be characterized in terms of tensile strength and/or elongation at yield. When a tensile strength of the polyamide is enhanced upon processing it implies that the processed polyamide is of greater mechanical strength than that of the polyamide. As used herein, the term “tensile strength” is defined as the maximum tensile load a material can withstand before it breaks. The tensile strength is determined using a tensile test and the tensile strength corresponds to the highest point of the stress-strain curve plotted from the test. “Elongation at yield” is the deformation of plastic material at yield point. The yield point corresponds to a point when an increase in strain is not marked by a significant increase in stress of the material. Elongation at yield is the ability of a plastic material to resist change of shape before it deforms irreversibly. Elongation at yield is the ratio between increased length and initial length at the yield point. As used herein, the term “yield strength” or “yield stress’ is defined as the minimum stress at which a solid will undergo permanent deformation or plastic flow without a significant increase in the load or external force.
[0026] Suitable polyamides comprise crystalline or resinous, high molecular weight solid polymers, including copolymers, having recurring amide units within the polymer chain. Polyamides may be prepared by ring-opening polymerization of one or more lactams such as caprolactam, pyrrolidione, lauryl lactam, aminoundecanoic lactam, or amino acid; or by condensation of dibasic acids and diamines.
[0027] The polyamide comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof. Post-consumer recycled (PCR) plastics refer to plastic waste generated by consumers after the use of plastic products. The composition of PCR plastics can vary significantly due to the diverse mix of polymers and additives used by different manufacturers. This variation in composition makes the recycling of PCR plastics more complex and challenging. In contrast, post-industrial recycled (PIR) plastics are derived from plastic waste produced during industrial and manufacturing processes and are of known composition. PIR plastics are generally easier to recycle as they typically originate from a single source and are of known composition. PCR polyamide and PIR polyamide must be sufficiently cleaned, and of controlled moisture content to produce new products of acceptable quality. In one embodiment, the polyamide comprises post-consumer recycled (PCR) polyamide. In another embodiment, the polyamide comprises virgin polyamide. It is preferred that the polyamide be PCR polyamide or PIR polyamide as it enhances a mechanical property of the polyamide. In one embodiment, the method of processing polyamide to form the polyamide-vitrimer may enhance a cycle life of the polyamide.
[0028] As used herein, the term “cycle life” refers to a number of times a polyamide polymer may be recycled. In one embodiment, the number of times the polyamide may be recycled is in a range of 1 to 3 times, preferably more than 3 to 5 times, and most preferably more than 5 times.
[0029] Examples of polyamides comprise poly(tetramethylene adipamide) (nylon 4,6), poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene azelamide) (nylon 6,9), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(4-aminobutyric acid) (nylon 4); poly(6-aminohexanoic acid) (nylon 6), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminoocatanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-amino- undecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), caprolactam/hexamethylene adipamide copolymer (nylon 6/6,6), hexamethylene adipamide/caprolactam copolymer (nylon 6,6/6), hexamethylene adipamide/hexamethylene-azelamide copolymer (nylon 6,6/6,9), blends of polyamide with styrene, blends of polyamide and acrylonitrile butadiene styrene (ABS), blends of polyamide and styrene-butadiene styrene (SBS), blends of polyamide and polyphenylene oxide (PPO), blends of polyamide and ethylene propylene diene monomer (EPDM) polymer, polyamide blends, polyamide copolymers, filled polyamides or combinations thereof.
[0030] As used herein, the term “copolymer” refers to a polymer derived from more than one species of monomer, where the copolymer includes repeating units of each of the monomers.
[0031] As used herein, the term “blend” refers to a mixture of two or more polymers or copolymers that have been blended together to create a new material with different physical properties.
[0032] As used herein, the term “filled polyamides” refers to a polyamide that has been reinforced with various filler materials to enhance its mechanical, thermal, or electrical properties. Examples of filler material include glass fibers, minerals such as talc, and calcium carbonate, carbon fibers, nanoclays, aramid fibers, or the like.
[0033] The polyamide may be in the form of film, nettings, granules, flakes, powders, pellets, or combinations thereof. When the polyamide is PCR polyamide or PIR polyamide, the polyamide may be a single layered structure, or a multilayered structure such as an EPDM coated polyamide fibre. The single layered structure or the multilayered structure may be made of same and/or different type of polyamide material of differing compositions.
[0034] In embodiments where the polyamide is PCR polyamide and/or PIR polyamide, the polyamide is washed to remove any contaminants or residues and dried to remove moisture before processing. In particular, polyamide being hygroscopic may be dried in a vacuum oven at a temperature in a range of 50°C to 90°C for a time in a range of 5 to 18 hours before use to remove moisture.
[0035] The multifunctional amine functions as the dynamic crosslinker for the formation of CANs to form the polyamide-vitrimers. Examples of multifunctional amines include phenylenediamine, benzene triamine, cycloaliphatic secondary diamine, cycloaliphatic triamine, xylene diamine, tris(3-aminopropyl)amine, 4H-1,2,4-triazole-3,4,5-triamine, 2,4,6-triaminopyrimidine, diethylenetriamine (DETA), triethylenetetramine (TETA), Triaminocyclohexane (TACH), melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof. In one embodiment, the multifunctional amine includes melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof. As used herein, the term “multifunctional amines” refers to compounds having more than one amine group. In some embodiments, the multifunctional amines comprise melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof.
[0036] The catalysts in the present disclosure include Lewis acid catalysts. Examples of catalysts include boric acid, aluminum chloride (AlCl3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), and hafnium (IV) triflate.
[0037] The polyamide and the catalyst are dissolved in a solvent to form a solution. In one embodiment, the polyamide is dissolved in the solvent followed by the addition of the catalyst. The solvent dissolves the polyamide without any chemical reaction with the polyamide. Examples of solvents include meta cresol (m-cresol), ortho-cresol (o-cresol), phenol, formic acid, hexafluoroisopropanol, and the like. Dissolving the polymer in the solvent may require heating to a temperature in a range of 120°C to 180°C with constant stirring. The multifunctional amine is provided in the solution comprising the polyamide and the catalyst to form a reaction mixture.
[0038] A concentration of the multifunctional amine in the reaction mixture is in a range of 1 to 10% by weight. In some embodiments, the multifunctional amine is present in the reaction mixture in a range of 1 to 5% by weight. A concentration of the catalyst in the reaction mixture is in a range of 0.1% to 5% by weight. In some embodiments, the catalyst is present in the reaction mixture in a range of 0.1 to 2% by weight.
[0039] The reaction mixture is heated to a temperature in a range of 140°C to 200°C for a duration of time in a range of 20 hours to 30 hours under a nitrogen atmosphere to produce the polyamide-vitrimer. The polyamide in the reaction mixture reacts with the multifunctional amine in the presence of the catalyst to form covalent adaptive network (CAN) through transamidation whereby amine groups of the amide and amine of the multifunctional amines are exchanged. The CAN formation is a reversible process as the bonds formed can break and exchange again under favorable conditions, such as high temperature. A representative reaction scheme between amide group of the polyamide and melamine, a multifunctional amine to form the crosslinked polyamide (polyamide-vitrimer) is shown below:

[0040] During polyamide-vitrimer formation, the multifunctional amine attacks (nucleophilic attack) the carbonyl group of an amide bond of the polyamide, and the CAN formation leads to the release of the amine group from the polyamide and the formation of a new amide bond with the amine group from the multifunctional amine. The catalyst of the present disclosure promotes protonation of the multifunctional amine for nucleophilic attack and also helps in chain scission of the polyamide, thus accelerating the process.
[0041] In certain embodiments, deionized water is added after a certain time in a range of 5 to 10 hours to promote forward reaction to produce the polyamide-vitrimer. The addition of water generates excess hydrogen ions (H+) which promotes polyamide-vitrimer formation.
[0042] A choice of the multifunctional amine affects the degree of crosslinking and the properties of the polyamide-vitrimer. For example, a triamine having three amine groups generates more crosslinking in the vitrimer when compared to a diamine having two amine groups. As will be appreciated, increase in crosslinking may enhance a tensile strength of the vitrimer but may reduce an elongation at yield of the vitrimer. Hence for applications requiring higher tensile strength at the cost of elongation at yield, a triamine or tetraamine may be utilized for the amidation reaction. In certain embodiments, a mixture of multifunctional amines may be utilized to obtain the desired property of the vitrimer.
[0043] The method further comprises adding an additive, a stabilizer, or combinations thereof to form the polyamide-vitrimer comprising these. The stabilizers include UV stabilizers, heat stabilizers, and the like. Example such stabilizers include phenolic antioxidant, phosphite, pentaerythritol tetrakis [3- [3,5-di-tert-butyl-4-hydroxyphenyl]propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 3,3',3',5,5',5'-hexa-tert-butyl-a,a',a'-(mesitylene-2,4,6-triyl) tri-p-cresol or combinations thereof. Examples of additives include antistatic agents, antimicrobial agents, dyes, fillers, plasticizers, flame retardants, or combinations thereof. It is also envisioned that the additive, the stabilizer, or combinations thereof may be added to the polyamide-vitrimer post formation of the polyamide-vitrimer. Upon completion of the reaction, the polyamide-vitrimer is separated from the reaction mixture, washed, and dried.
[0044] In yet another embodiment, a method 200 of producing a polyamide-vitrimer is provided. At step 202, melt extrusion of a polyamide with a multifunctional amine and a catalyst is performed. The melt extrusion is performed at a temperature in a range of 175°C to 300°C in an extruder for a residence time in a range of 1 minute to 5 minutes to form the polyamide-vitrimer.
[0045] The polyamide, the multifunctional amine, and the catalyst are similar to the polyamide, the multifunctional amine, and the catalyst, as described previously with respect to the method 100.
[0046] The melt extrusion 202 is performed in an extruder such as a single-screw extruder, or a twin-screw extruder. The processing parameters of the extruder may be varied to facilitate one or more of the melt extrusion of the polyamide and the multifunctional amine by optimizing the melting of the polyamide, homogeneous mixing between the polyamide, the multifunctional amine and the catalyst, and efficient reaction between the polyamide and the multifunctional amine. Examples of such process parameters include, but are not limited to, type of extruder, geometrical design of the extruder, screw speed, residence time of material in the extruder, feed rate of the material into the extruder, temperature, and die geometry through which a product is extruded. In one embodiment, the extruder is a twin-screw extruder that facilitates enhanced mixing between the polyamide and the multifunctional amine when compared to a single-screw extruder. The extrusion may be performed at a temperature corresponding to the melting temperature of the polyamide. In some embodiments, the melting temperature is in a range of 175°C to 300°C. In some embodiments, the residence time is in a range of 1 to 10 minutes. In some embodiments, screw speed is in a range of 100 to 150 rotations per minute (rpm) in a twin-screw extruder. The extrusion, in one embodiment, is performed in a twin-screw extruder at a temperature of 240°C to 275°C, at screw speeds of 100-150 rotations per minute (rpm) and at a residence time in a range of 1 to 5 minutes.
[0047] A concentration of the multifunctional amine extruded with the polyamide is in a range of 1 to 10% by weight. In some embodiments, the multifunctional amine is present in the reaction mixture in a range of 1 to 5% by weight. A concentration of the catalyst in the reaction mixture is in a range of 0.1% to 5% by weight. In some embodiments, the catalyst is present in the reaction mixture in a range of 0.1 to 2% by weight.
[0048] The method further comprises adding an additive, a stabilizer, or combinations thereof during melt extrusion to form the polyamide-vitrimer comprising these. The additive, and the stabilizer are as discussed previously with respect to the method 100. The additive, the stabilizer, or combinations thereof may be added to the polyamide-vitrimer post formation of the polyamide-vitrimer.
[0049] The extruded polyamide-vitrimer after the melt extrusion at step 202 may be immediately quenched in a water bath and pelletized. Such pellets can be used for subsequent molding, or shaping.
[0050] The polyamide-vitrimers of the present disclosure prepared according to methods 100 and/or 200 may be shaped in the form of films, sheets, foams, particles, granules, beads, rods, plates, strips, stems, tubes, etc. via any process known to those skilled in the art. Examples of such processes include extrusion, casting, compression molding and the like.
[0051] The inventive methods 100 and 200 provide a single-step method for processing polyamides to form polyamide-vitrimers. The inventive method 100 provides a method for processing polyamides in solution at milder temperature conditions. In solution, the distribution of reactants (namely, polyamide, multifunctional amine and catalyst) is more homogeneous, when compared to solid-state reactions conducted at similar temperatures, leading to a more evenly crosslinked polyamide (polyamide-vitrimer). The enhanced mixing in the solution ensures homogeneity, prevents defects due to localized heating (such as for example, in solid-state), making it ideal for achieving consistent polyamide-vitrimer product.
[0052] The inventive method 200 provides a melt-phase extrusion of the polyamide at a higher temperature than that of the method 100 but at shorter timescales. Melt extrusion ensures uniform distribution of polyamide, catalyst and the multifunctional amine throughout and along the process, as it is continuous. When compared to solid state reaction for vitrimer formation, melt extrusion provides precise temperature control, faster processing, and improved mechanical properties of the polyamide-vitrimer. The time scale of the reaction described in method 200 is under 10 minutes making it more economical and beneficial. Both methods 100 and 200 thus provide a viable alternative to prior art methods for processing polyamides (irrespective of the source, for example, PCR and/or PIR polyamides) or combinations of polyamides to provide a polyamide having higher mechanical strength. Further, the mechanical property of the polyamide-vitrimer may be fine-tuned by choice of suitable dynamic crosslinkers and concentration of the dynamic crosslinkers.
[0053] The methods 100 and/or 200 may be performed as a batch process, or as a continuous process.
[0054] The inventive method (100, 200) for polyamide processing has a recovery rate of greater than 90% when the polyamide is post-consumer recycled polyamide or PIR polyamide. In another embodiment, the inventive method for polyamide processing has a recovery rate of greater than 94% when the polyamide is PCR polyamide or PIR polyamide. As used herein, the term “recovery rate” corresponds to a percentage of an amount of product recovered to an amount of reactants. With such a high recovery rate it is possible to reprocess PCR polyamides or PIR polyamides without adding virgin polyamide to establish a closed-loop recycling process.
[0055] The polyamide-vitrimers of the present disclosure exhibit mechanical strength (tensile strength) greater than a mechanical strength of polyamide, PCR polyamide or PIR polyamide from which they are derived. The inventive process and the polyamide-vitrimers produced thereof result in an upcycling of polyamides. The reprocessability of the polyamide-vitrimers overcomes the challenges of recycling polyamide waste, and enables transformation of polyamide waste into mechanically stronger polyamides while retaining other properties of polyamides that make them versatile. The polyamide-vitrimers may be reprocessed multiple times without degradation of their mechanical properties when compared to polyamides not containing the inventive polyamide-vitrimers. It is a particular advantage of the present disclosure, irrespective of the additives present in PCR polyamides and/or PIR polyamides, the polyamides may be reprocessed using the disclosed method and the inventive dynamic crosslinkers to result in an upcycled polyamide.
[0056] As the polyamide-vitrimers of the present disclosure exhibit mechanical strength superior to PCR polyamide, they may be used without blending with virgin polyamide, which otherwise might be required to compensate for mechanical property loss. This contributes further to a closed-loop plastics economy minimizing dependence on virgin polyamides and minimizing plastic waste generation. The present disclosure thus provides a sustainable solution to address plastic waste and reduce the environmental impact of plastic waste and dependence on fossil fuels.
[0057] In some embodiments, an article is provided comprising the polyamide-vitrimers of the present disclosure formed according to methods 100 and/or 200. The article may further comprise other polyamides, polyamide copolymers, polyamide blends, filled polyamides or combinations thereof. The article may further comprise an additive, a stabilizer, or combinations thereof, such as the additive, the stabilizer as described previously. The articles may be formed by molding, blow molding, injection molding, filament winding, continuous molding or film-insert molding, infusion, pultrusion, RTM (resin transfer molding), RIM (reaction-injection molding), 3D printing, or any other method known to those skilled in the art.

EXAMPLES
EXAMPLE 1
Processing of polyamide in solution to form polyamide-vitrimer
[0058] 1 equivalent of melamine crosslinker (LOBA Chemical) was taken with 1 equivalent of Nylon 66 (black filled grade sourced from fishing nets) in m-cresol along with 10 mol% of boric acid (99% ACS, ISO grade from SD Fine Chemical Limited) to form a reaction mixture. The reaction was carried out at 150 ͦC in nitrogen atmosphere with stirring at 200 rpm for 24 hours. After 7 hours of reaction, 0.066 mole (equivalent mole of boric acid) of deionized (DI) water was gradually added to the reaction mixture to make sure the availability of H+ ion to take the reaction forward. A mild colour change from pale yellow to orangish yellow was observed after adding the DI water to the reaction mixture.
[0059] After 24 hours of reaction, the mixture was decanted to remove the precipitate from the solution and the solution was heated with acetone to remove any dissolved polymer. Both the precipitate and the re-precipitated material were washed in acetone and dried separately in a hot air oven for about 24 hours at 90 ͦC. The dried materials were mixed and ground to powder using a pestle and mortar. The powder was dispersed in a mixture of dimethyl sulphoxide (DMSO) and DI water in a ratio of 80:20 and stirred for 24 hours to remove any unreacted melamine. The mixture was poured into a Buchner funnel and washed under a vacuum with DMSO followed by acetone and DI water. Each wash was repeated for at least 5 times. A final wash with DI water was done to ensure the purity of the sample. The powder was dried again in a hot air oven for 24 hours at 90 ͦC. The dried and conditioned sample was then analyzed. Fourier-transform infrared (FTIR) spectra confirmed the formation of the polyamide-vitrimer.

EXAMPLE 2
Processing of polyamide in an extruder to form a polyamide-vitrimer
[0060] PCR Nylon 66 (unfilled and filled grades was sourced from automotive part regrinds and PCR Nylon 6, black filled grade was sourced from fishing nets. Their virgin counterparts (Zytel 66, UBE 6) for this study were provided by Chime Performance Plastics Private Limited.
[0061] DSM Explore Twin screw extruder 15cc with co-rotating conical screw configuration with a recirculating chamber for residence time control was run in tandem with DSM Explore Manual Injection molding machine fitted with Tensile dumbbell mould conforming with ASTM D638 Type V dimensions. All nylons, irrespective of grade and type, are hygroscopic in nature. Hence the material was heat conditioned for 24 hours at 90°C in a hot air oven.
[0062] The heat conditioned PCR Nylon 66 (PCRNY 66) was taken along with melamine crosslinker (LOBA Chemical), boric acid catalyst (99% ACS, ISO grade from SD Fine Chemical Limited), and Irganox 1010 (BASF) heat stabilizer and fed into the hopper of the extruder at the following processing conditions, temperature of 275°C throughout the zones, screw speed of 150 rotations per minute (RPM) and a residence time of 120 Seconds. Further, batches of samples were made with varying amounts of PCR Nylon from 90 wt% to 99 wt%, melamine from 10 wt% to 1 wt % while the boric acid was taken as 2-5 mol% with respect to melamine. Irganox was fixed at 0.5 wt% for all batches. Zytel, was used as control. The composition of batches of samples are given in Table 1. In Table 1, PCRNY 66 1W% refers to a sample containing 1 wt% of melamine.

No Compound Name Polymer (g) Melamine (g) Boric Acid (mg) Irganox (g)
1 PCRNY 66 1W% 9.845 0.1 5 0.05
2 PCRNY 66 2W% 9.75 0.2 10 0.05
3 PCRNY 66 5W% 9.425 0.5 25 0.05
4 PCRNY 66 10W% 8.745 1 55 0.05
5 Zytel 66 5W% 9.425 0.5 25 0.05
6 PCRNY 6 2W% 9.75 0.2 10 0.05
7 UBE 6 2W% 9.75 0.2 10 0.05

Table 1
Mechanical testing
[0063] According to ASTM D638 (type V) stress-strain properties of the samples given in Table 1 were measured using Universal Testing Machine at room temperature. The testing parameters were load cell: 5 kN, preload force: 0.1 N, cross head speed: 50mm/minute, gauge length: 15mm, number of Samples: 3 per batch for consistency, sample dimension: 50 mm length x 3.6 mm width x 3.3 mm thickness
[0064] The samples were placed between clamps of the Universal Testing Machine - Tensile Testing Module such that the edges of the samples were parallel to the direction of the load. The grips were then tightened to hold the sample securely within the jig. The test sample was then pulled apart at a tensile speed of 50 mm/min until it broke. Table 2 provides the test results of samples 1 to 7 of Table 1. Additionally, testing was performed on virgin nylon 66 without the crosslinker and catalyst (Zytel 66), and PCR polyamide without the crosslinker and the catalyst (PCR NY 66) as shown in Table 2. As shown in Table 2, virgin polyamide (Zytel 66) had a tensile strength of 69 MegaPascal (MPa), which increased to 88±0.70 MPa on vitrimerization confirming the increase in mechanical strength of the polyamide-vitrimer. PCR polyamide (PCR NY 66) had a tensile strength of 76±1.7 MPa which increased from 78±6 MPa with 1 wt% of melamine crosslinker to 88±4 MPa with 5 wt% of melamine crosslinker.

SNo Compound Name Tensile Strength (MPa) Elongation %
1 PCR NY 66 76±1.7 108±36
2 PCRNY 66 1W% 78±6 41±13
3 PCRNY 66 2W% 81±0.5 37±0.6
4 PCRNY 66 5W% 88±4 23±2
5 PCRNY 66 10W% 84±3 15±5
6 Zytel 66 69 172±11
7 Zytel 66 5W% 88±0.70 24±1
8 PCR NY6 61±2.17 260
9 PCRNY 6 2W% 70±0.6 52

Table 2
EXAMPLE 3
Processing of polyamide in an extruder to form a polyamide-vitrimer using different catalysts and dynamic crosslinkers
[0065] A series of samples (Samples 1 to 3) of polyamide-vitrimers were prepared using PCR polyamide (PCRNY 66) and 5 wt% of melamine crosslinker with different catalysts namely, ferric chloride (FeCl3) (PCRNY 66 FeCl3), aluminum chloride (AlCl3) (PCRNY 66 AlCl3), and boric acid (PCRNY 66 boric), as shown in Table 3. Table 3 also shows compositions of polyamide-vitrimer samples 4 and 5 prepared using different crosslinkers 4,4’-oxydianiline (ODA) (PCRNY 6 ODA) and 4,4’-dithiodianiline (DTA) (PCRNY 6 DTA) using boric acid catalyst.

No Compound Name Polymer (g) Crosslinker (g) Catalyst (mg) Irganox (g)
1 PCRNY 66 FeCl3 9.425 0.5 25 0.05
2 PCRNY 66 AlCl3 9.425 0.5 25 0.05
3 PCRNY 66 boric 9.425 0.5 25 0.05
4 PCRNY 6 ODA 9.4475 0.5 20 0.05
5 PCRNY 6 DTA 9.445 0.5 50 0.05

Table 3

Mechanical testing
[0066] The samples, as shown in Table 3, were tested as described previously. Table 4 provides the mechanical testing data of samples of Table 3.

SNo Compound Name Tensile Strength (MPa)
1 PCRNY 66 FeCl3 80±7.75
2 PCRNY 66 AlCl3 61±3.1125
3 PCRNY 66 boric 89±3.4
4 PCRNY 6 ODA 50±0.25
5 PCRNY 6 DTA 62±0.15

Table 4

[0067] As seen from Table 4, tensile strengths of the polyamide-vitrimers change with the catalyst and also with the crosslinkers. Thus by appropriate choice of the catalyst and the crosslinking agents mechanical properties of the polyamide-vitrimers may be fine-tuned.

[0068] It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
 
, Claims:CLAIMS

We Claim:
1. A method (100) of processing a polyamide to form a polyamide-vitrimer in solution comprising:
heating a reaction mixture (102) comprising a polyamide, a multifunctional amine, and a catalyst at a temperature in a range of 140°C to 200°C for a duration of time in a range of 20 hours to 48 hours under a nitrogen atmosphere to form the polyamide-vitrimer, wherein a tensile strength of the polyamide-vitrimer is greater than a tensile strength of the polyamide.
2. The method (100) as claimed in claim 1, wherein the method comprises adding deionized water to promote formation of the polyamide-vitrimer.
3. The method (100) as claimed in claim 1, wherein the polyamide comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof.
4. The method (100) as claimed in claim 1, wherein the polyamide comprises poly(tetramethylene adipamide) (nylon 4,6), poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene azelamide) (nylon 6,9), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(4-aminobutyric acid) (nylon 4); poly(6-aminohexanoic acid) (nylon 6), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminoocatanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-amino- undecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), caprolactam/hexamethylene adipamide copolymer (nylon 6/6,6), hexamethylene adipamide/caprolactam copolymer (nylon 6,6/6), hexamethylene adipamide/hexamethylene-azelamide copolymer (nylon 6,6/6,9), blends of polyamide with styrene, blends of polyamide and acrylonitrile butadiene styrene (ABS), blends of polyamide and styrene-butadiene styrene (SBS), blends of polyamide and polyphenylene oxide (PPO), blends of polyamide and ethylene propylene diene monomer (EPDM) polymer, polyamide blends, polyamide copolymers, filled polyamides or combinations thereof.
5. The method (100) as claimed in claim 1, wherein the multifunctional amine comprises meta-phenylenediamine, para-phenylenediamine, benzene triamine, cycloaliphatic secondary diamine, cycloaliphatic triamine, xylene diamine, tris(3-aminopropyl)amine, 4H-1,2,4-triazole-3,4,5-triamine, 2,4,6-triaminopyrimidine, diethylenetriamine (DETA), triethylenetetramine (TETA), Triaminocyclohexane (TACH), melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof.
6. The method (100) as claimed in claim 1, wherein a concentration of the multifunctional amine in the polyamide-vitrimer is in a range of 1 weight percent to 10 weight percent.
7. The method (100) as claimed in claim 1, wherein the catalyst comprises boric acid, aluminum chloride (AlCl3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), or hafnium (IV) triflate.
8. A method (200) of processing a polyamide to form a polyamide-vitrimer comprising:
performing a melt extrusion (202) of the polyamide with a multifunctional amine and a catalyst at a temperature in a range of 175°C to 300°C in an extruder for a residence time in a range of 1 minute to 5 minutes to form the polyamide-vitrimer, and wherein a tensile strength of the polyamide-vitrimer is greater than a tensile strength of the polyamide.
9. The method (200) as claimed in claim 8, wherein the polyamide comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof.
10. The method (200) as claimed in claim 8, wherein the polyamide comprises poly(tetramethylene adipamide) (nylon 4,6), poly(hexamethylene adipamide) (nylon 6,6), poly(hexamethylene azelamide) (nylon 6,9), poly(hexamethylene sebacamide) (nylon 6,10), poly(heptamethylene pimelamide) (nylon 7,7), poly(octamethylene suberamide) (nylon 8,8), poly(nonamethylene azelamide) (nylon 9,9), poly(decamethylene azelamide) (nylon 10,9), poly(4-aminobutyric acid) (nylon 4); poly(6-aminohexanoic acid) (nylon 6), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminoocatanoic acid)(nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), poly(11-amino- undecanoic acid) (nylon 11), poly(12-aminododecanoic acid) (nylon 12), caprolactam/hexamethylene adipamide copolymer (nylon 6/6,6), hexamethylene adipamide/caprolactam copolymer (nylon 6,6/6), hexamethylene adipamide/hexamethylene-azelamide copolymer (nylon 6,6/6,9), blends of polyamide with styrene, blends of polyamide and acrylonitrile butadiene styrene (ABS), blends of polyamide and styrene-butadiene styrene (SBS), blends of polyamide and polyphenylene oxide (PPO), blends of polyamide and ethylene propylene diene monomer (EPDM) polymer, polyamide blends, polyamide copolymers, filled polyamides or combinations thereof.
11. The method (200) as claimed in claim 8, wherein the multifunctional amine comprises meta-phenylenediamine, para-phenylenediamine, benzene triamine, cycloaliphatic secondary diamine, cycloaliphatic triamine, xylene diamine, tris(3-aminopropyl)amine, 4H-1,2,4-triazole-3,4,5-triamine, 2,4,6-triaminopyrimidine, diethylenetriamine (DETA), triethylenetetramine (TETA), Triaminocyclohexane (TACH), melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof.
12. The method (200) as claimed in claim 8, wherein a concentration of the multifunctional amine in the polyamide-vitrimer is in a range of 1 weight percent to 10 weight percent.
13. The method (200) as claimed in claim 8, wherein the catalyst comprises boric acid, aluminum chloride (AlCl3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), and hafnium (IV) triflate.
14. A method of enhancing a tensile strength of a polyamide comprising:
crosslinking the polyamide with a multifunctional amine in presence of a catalyst to form a polyamide-vitrimer, wherein a concentration of the multifunctional amine in the polyamide-vitrimer is in a range of 1 weight percent to 10 weight percent, wherein the polyamide comprises virgin polyamide, post-consumer recycled (PCR) polyamide, post-industrial recycled (PIR) polyamide, or combinations thereof, wherein the catalyst comprises boric acid, aluminum chloride (AlCl3), ferric chloride (FeCl3), ferric nitrate (Fe(NO3)3), and hafnium (IV) triflate, and wherein the multifunctional amine comprises meta-phenylenediamine, para-phenylenediamine, benzene triamine, cycloaliphatic secondary diamine, cycloaliphatic triamine, xylene diamine, tris(3-aminopropyl)amine, 4H-1,2,4-triazole-3,4,5-triamine, 2,4,6-triaminopyrimidine, diethylenetriamine (DETA), triethylenetetramine (TETA), Triaminocyclohexane (TACH), melamine, tris (2-aminoethyl) amine, 4,4’-oxydianiline, 4,4’-dithiodianiline, or combinations thereof.
15. The method as claimed in claim 14, wherein the method comprises heating a reaction mixture (102) comprising the polyamide, the multifunctional amine, and the catalyst at a temperature in a range of 140°C to 200°C for a duration of time in a range of 20 hours to 48 hours under a nitrogen atmosphere to form the polyamide-vitrimer.
16. The method as claimed in claim 14, wherein the method comprises performing a melt extrusion (202) of the polyamide with the multifunctional amine and the catalyst at a temperature in a range of 175°C to 300°C in an extruder for a residence time in a range of 1 minute to 5 minutes to form the polyamide-vitrimer.
17. A polyamide-vitrimer formed using the method (100, 200) as claimed in any of the claims 1-14.
18. An article formed using the polyamide-vitrimer as claimed in any of the claims 1-17.