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[Jonathon Tanks](https://orcid.org/0000-0002-0232-8240), [Kenji Tamura](https://orcid.org/0000-0001-6578-0923)

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[Room‐Temperature Material Recycling/Upcycling of Polyamide Waste Enabled by Cosolvent‐Tunable Dissolution Kinetics](https://mdr.nims.go.jp/datasets/910dc912-2433-4644-8521-017f93cc054a)

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Room‐Temperature Material Recycling/Upcycling of Polyamide Waste Enabled by Cosolvent‐Tunable Dissolution KineticsResearch ArticleHow to cite: Angew. Chem. Int. Ed. 2025, 64, e202502474doi.org/10.1002/anie.202502474Sustainable ChemistryRoom-Temperature Material Recycling/Upcycling of Polyamide WasteEnabled by Cosolvent-Tunable Dissolution KineticsJonathon Tanks* and Kenji Tamura*Abstract: Polyamides (PAs, nylons) are a ubiquitous class of high-performance plastics used extensively in a wide range ofapplications. Their high resistance to many common solvents and tendency to hydrolyze in strong acids or bases createsa major hurdle to low-emissions material recycling (i.e., resource separation and recovery). In the present study, thefirst detailed investigation into the molecular mechanisms of polyamide dissolution, we show that introducing a weaklyhydrogen-bonding cosolvent into formic acid can effectively tune the solvent–solvent and solvent–polymer interactions,drastically accelerates the room-temperature dissolution kinetics of common (short-chain) polyamides such as PA6 andPA66, as well as long-chain and semi-aromatic varieties. The recovered polymers show no change in their chemicalstructures or properties, and sufficient selectivity allows for fillers such as short and long fibers, inorganic nanoparticles,metals, and other mixed polymer phases to be recovered at high efficiency (>95%) along with recirculation of all solvents(>98%). This cosolvent-enabled approach has the potential to make polyamide recycling more sustainable and economicalby reducing the energy input and CO2 emissions required to separate and recover the various constituent materials fromautomotive and electrical components, textiles, and beyond.IntroductionPolyamides (PAs, or nylon) exhibit excellent heat resistanceand mechanical properties, making them a key materialin numerous industries ranging from automotive, electri-cal/electronics, textiles, and fishing/leisure and represent amarket size of 8 Mt yr−1 valued at 40 bil $ yr−1 (Figure 1a).[1,2]The synthesis of conventional polyamides such as PA6 andPA66 uses non-renewable feedstocks and carries a largecarbon footprint (6-9 kg CO2-eq kg−1) energy demand (35–60 MJ kg−1).[3,4] Recycling technology for PAs has receivedfar less attention than other plastics, e.g., PET, despite theirhigh cost and widespread use. As a result, polyamides oftenend up in landfills and even the ocean.[1,3,5]PAs are commonly used in blends and composites contain-ing secondary materials (SM) such as fibers/microparticles,[*] Dr. J. TanksResearch Center for Structural Materials, National Institute forMaterials Science, 1-2-1 Sengen, Tsukuba 305-0047, JapanE-mail: tanks.jonathon@nims.go.jpDr. K. TamuraResearch Center for Electronic and Optical Materials, NationalInstitute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, JapanE-mail: tamura.kenji@nims.go.jpAdditional supporting information can be found online in theSupporting Information section© 2025 The Author(s). Angewandte Chemie International Editionpublished by Wiley-VCH GmbH. This is an open access article underthe terms of the Creative Commons Attribution-NonCommercialLicense, which permits use, distribution and reproduction in anymedium, provided the original work is properly cited and is not usedfor commercial purposes.metals, and polyesters, some of which are high-value orcarry a large carbon footprint and should be recovered forboth resource circularity and carbon neutrality (Figure 1a).Chemical recycling (de-/re-polymerization) can regeneratea high-quality product (i.e., large contribution to resourcecircularity), but it is a fundamentally high-temperatureprocess (180–300 °C) with high energy demand for boththe depolymerization and repolymerization steps (i.e., smallcontribution to carbon neutrality).[1,6–10] Some promisingstrategies for chemical recycling under milder conditionsinclude the synthesis of novel lactam monomers with lowerring strain energy or catalyzed conversion of commercialPAs into tertiary amine-based value-added chemicals,[11,12]but these approaches still have the downsides of relatively lowyield (40%–85%) and high energy demand (>180 °C, >15 hr).By contrast, mechanical recycling (grinding/extrusion) istechnologically simple and boasts the lowest carbon emissionsof any plastic recycling method available, but separationof PAs from SMs is too difficult to make it impractical inmany cases and the resulting materials often show degradedperformance.[13–16]Physical recycling (dissolution/precipitation) can selec-tively dissolve certain plastics and recover the target mate-rials without complete deconstruction into monomers.[17–22]Patented processes like Creasolv[23,24] or STRAP[25,26] involvedissolving waste plastic products such as packaging filmsin a polymer-specific solvent system, by which constituentmaterials can then be separated and purified. The solventsare usually selected using Hansen solubility parameter (HSP)theory[27] or COSMO-RS[25,26,28,29] implicit solvation models,the former of which is a thermodynamic model of interactionsexpressed by cohesive energy density, and the latter of whichis a molecular model of interactions expressed by surfaceAngew. Chem. Int. Ed. 2025, 64, e202502474 (1 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbHhttps://orcid.org/0000-0002-0232-8240https://orcid.org/0000-0001-6578-0923mailto:tanks.jonathon@nims.go.jpmailto:tamura.kenji@nims.go.jphttp://creativecommons.org/licenses/by-nc/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fanie.202502474&domain=pdf&date_stamp=2025-06-05Research ArticleFigure 1. a) Polyamide (PA) components and products, ranging from structural/electrical composites to textiles. The high-value components typicallycontain polyamide mixed with valuable secondary materials. b) Conventional dissolution-based approaches involve solvent selection by solubilityparameter (e.g., HSP) theory and require high temperatures and relatively long treatment times, resulting in high energy consumption and a largecarbon footprint. c) This work demonstrates that a cosolvent strategy accelerates PA dissolution in formic acid at room temperature, resulting in anunprecedented reduction in energy consumption and overall carbon footprint.charge distribution in response to a dielectric continuum.However, these techniques often fail to accurately reproduceinteractions in strongly hydrogen-bonded organic moleculesdue to the complex nature of these systems compared tononpolar and aprotic-polar systems.[28,29]The majority of research studies and patented technolo-gies regarding PA dissolution—mostly electrospinning, butsome recycling—employ either formic acid (FA) or polarsolvents (e.g., benzyl alcohol), which vary widely in theiragreement with HSP predictions (Figure S1).[17–24] WhileFA can dissolve PA6 and other short-chain PAs at roomtemperature, the slow kinetics can make complete dissolutiontake up to 24 hr depending on the recyclate geometry.Other polar solvents require high temperatures (140 °C–200 °C) and long dissolution times (4–24 hr),[1,17–24] whichis comparable to chemical recycling conditions in termsof carbon footprint (Figure 1b). Furthermore, long-chainPAs (e.g., PA12 and bio-based PA11) only dissolve in pureFA at elevated temperatures (−80 °C) and require longdissolution times (4–24 hr).[30,31] High-performance semi-aromatic polyphthalamides (PPAs) are even more resistantto these solvents and do not dissolve even under harshconditions. By contrast, fluorinated alcohols and acids such ashexafluoroisopropanol (HFIP) and trifluoroacetic acid (TFA)can easily dissolve a range of PAs (short- and long-chain)at ambient conditions,[32] but they are too expensive to beused in an economically viable scaled-up recycling process.There is an urgent need for a versatile and cost-effectiverecycling method that can recover valuable resources froma range of polyamide-containing waste with minimal carbonemissions.[33–35]In this work, we present the first (to the authors’ knowl-edge) detailed elucidation of the molecular mechanisms ofpolyamide dissolution through a combination of experimentsand density functional theory (DFT) calculations, and morespecifically demonstrate that the addition of a weakly H-bonding cosolvent to formic acid (FA) drastically enhancesthe dissolution kinetics of polyamides without heat or agita-tion, resulting in complete dissolution in under 1 hr at roomtemperature. This novel cosolvent strategy can be used in adissolution-based physical recycling process that is universaland rapid for any aliphatic-containing polyamide and canAngew. Chem. Int. Ed. 2025, 64, e202502474 (2 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleFigure 2. (a) Photographs and (b) mass change measurements of PA6 pellets dissolving at room temperature (no agitation) in formic acid(FA)-based cosolvent system with different cosolvent ratios (w/w). (c) Apparent viscosity of PA6 solutions with different solids concentrations andcosolvent fractions. (d) Schematic of the solid-liquid interface during crystal dissolution, where km is a measure of mass transfer across the boundarylayer (thickness lb) according to the Noyes-Whitney model. (e) Influence of cosolvent fraction on the mass transfer coefficient km and totaldissolution time.be performed at ambient conditions with very low energyconsumption (Figure 1c). Application to a variety of differentpolyamides and fillers with high yield and quality demon-strates the merit of this approach toward separation andrecovery of valuable resources such as carbon and glass fibers,metals, and nanofillers, in addition to all. Carbon footprint andeconomic cost were calculated to be substantially lower thanother physical or chemical recycling methods.Results and DiscussionPolyamide Dissolution in a Cosolvent SystemIt is well known that short-chain PAs dissolve in FA at roomtemperature (RT), but it can take up to 12 h for complete dis-solution. As shown in Figure 2a, PA6 formed a slightly cloudysolution after 4 hr in pure FA (RT, no agitation), whereasPA66 became completely clear (Figure S2). After screeningvarious solvents (see Supporting Information), a measurablepositive effect on the dissolution rate of PA6 was onlyobserved for chlorinated hydrocarbons like dichloromethane(DCM), chloroform (CHCl3), and dichloroethane (DCE);they have characteristic low polarity and the ability to formweak H-bonds and effectively solvate hydrocarbons.[36] Ethylacetate (EtOAc), MEK, and THF are similar to DCM interms of, e.g. viscosity and HSPs, but they had the oppositeeffect of decreasing overall solubility. H-bond titration of PA6solutions revealed that FA is more sensitive than PA to thecosolvent and that solubility shows strong negative correla-tion with the cosolvent’s donor number (DN) (Figure S3).This means it must act as a weak H-bond donor (HBD)and poor H-bond acceptor (HBA) to promote polyamidedissolution. This characteristic has been demonstrated forfluorinated polar solvents such as HFIP,[37] suggesting thatchlorinated hydrocarbons combined with formic acid canserve the same role.DCM was selected as the primary cosolvent for ourstudy due to its compatibility with FA, relatively low cost,and low boiling point. PAs do not dissolve in pure DCMat RT (Figure 2a), contrary to predictions by HSP theoryand implicit solvation models which do not account forexplicit H-bonding (Figure S1). PA6 dissolution in FA/DCMmixtures is accelerated by varying degrees depending on thecosolvent ratio, reaching a maximum at 1:1 w/w (i.e., DCMfraction of fDCM = 0.5) and reversing to a slower rate atfDCM = 0.7 (Figure 2b). When fDCM > 0.7, only swelling withlimited dissolution is observed. Viscosity measurements ofPA6 solutions at different solids concentrations and cosolventratios, shown in Figure 2c normalized to the molar ratio ofFA to amide units, made it clear that higher fDCM correlatesto lower solution viscosity with the lowest value obtainedwhen fDCM = 0.7, which tells us that dissolution rate is notnecessarily affected by viscosity of the bulk solvent or solution(Figure S2).Considering the polyamide as a semi-crystalline solid,the dissolution of the crystalline fraction would be the rate-limiting step. Employing the Brunner–Nernst model[38,39] toanalyze the mass transfer process at the polymer-solventinterface (Figure 2d; details in Supporting Information), wefound that the mass transfer coefficient (km) for PA through aboundary layer (Lb) between bulk crystal and bulk solventincreases linearly with cosolvent fraction up to fDCM = 0.5and then sharply decreases at fDCM = 0.7 (Figure 2e), andAngew. Chem. Int. Ed. 2025, 64, e202502474 (3 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleFigure 3. a) Molecular electrostatic potentials (MEP), binding energies (kJ/mol), and H-bond lengths (Å) for dimers of FA (FF), DCM (CC), andFA/DCM (FC). b) FTIR spectra of FA with different cosolvent fractions (fDCM), and c) magnified carbonyl region with deconvoluted peaks for open(FFo) and closed (FFc) and monomer (F) forms of FA, and the FC dimer. (d) Changes in integrated areas of carbonyl bands representing eachinteraction shown in (c) for different cosolvent fractions. (e) Structure and MEP of H-bonded PA6 oligomer representing the α-phase crystal andschematic of solvent interaction sites. f) Approximate binding energies for FA and DCM at each binding site. g) Total solvation energy �Gsolv andapproximated H-bond and vdW components.its independence of specific surface area suggests a surfaceerosion-type dissolution mechanism (Figure S4).Cosolvent-Regulated Intermolecular InteractionsDFT calculations of binding energies (�Ebind) at the M06-2X/def2-TZVP level[40,41] for dimers of pure FA and DCMand FA/DCM are shown in Figure 3a (see SupportingInformation for details). FA in bulk solvent form is assumedto consist primarily of so-called “open” dimers (FFo)[42–48]with moderately large �Ebind dominated by H-bonding, whilethe mildly polar DCM dimer has a smaller �Ebind dominatedby van der Waals (vdW) interactions.[49–51] Combining theminto the solvent-cosolvent dimer (FC) yields smaller �Ebindand longer H-bond lengths than pure FA (Figures 3a and S5),with FA and DCM acting as the HBA and HBD, respectively.FTIR spectroscopy of the cosolvent system revealed ablue-shift in the C═O region of FA with increasing fDCM(Figures 3b–d) which was reproduced by DFT (Figure S5).We attribute this shift to the transition from FF clusters to FCand (albeit rare) F monomers.[42–51] These results imply thepresence of weak hydrogen bonds between FA and DCM,with the largest shift occurring between 0.5 < fDCM < 0.7.Replacing DCM with EtOAc, which negatively affectedPA6 solubility, gives a FC dimer with larger �Ebind than FF(Figure S5), supporting our assertion that weak H-bondsplay a major role in dissolution kinetics. We next examinedthe solvent-polymer interactions using DFT and FTIR.The PA6 oligomer used in our DFT study is the α-phasecrystal configuration (PA6-α)[52–54] depicted in Figure 3e, withpossible solvent interaction sites identified as the amide group(-CONH) and methylene groups (-CH2) that act throughHBA/HBD or vdW-dominant interactions, respectively. Theindividual binding energies of FA and DCM monomers withPA6 at these sites are compared in Figure 3f. Figure 3g showssteady growth of the so-called solvation energy (�Gsolv)of PA6-α, which we take as the binding energy betweenan explicit solvent cluster and polymer oligomers, withincreasing cosolvent fraction up to fDCM = 0.9 (see SupportingInformation for details). Final solvated structures for 0 ≤fDCM < 0.7 show full breakage of H-bonds and conformationalchange of the alkyl segment, whereas H-bonds are partiallyand fully intact at fDCM = 0.7 and 0.9, respectively (Figure S6).Using the binding energies of individual solvent-polymerinteractions to decompose �Gsolv into approximate H-bondand vdW components, we see that poor affinity of FA towardmethylene units in PA6 results in a large endergonic vdWcomponent, but the strong H-bond component is largeenough to create a net exergonic interaction that exceeds the�Ebind of PA6-α; this explains why short-chain PAs dissolvein pure FA at room temperature. As fDCM increases, thetwo components approach each other while the total �Gsolvcontinues to grow larger until fDCM = 0.9, at which pointthe H-bond component grows smaller than the pure PA6-αbinding energy (Figure S7, Table S3).Cosolvent Effect on Dissolution KineticssH-bonds within the polyamide crystal must be broken fordissolution to occur, which is only probable when the solvent-polymer interaction (i.e., �Gsolv) has a sufficiently largeH-bond component, specifically the HBD contribution. Thisexplains why PAs do not dissolve in pure DCM or evenFA/DCM at fDCM = 0.9, whereas polycaprolactone (PCL)Angew. Chem. Int. Ed. 2025, 64, e202502474 (4 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch Articlereadily dissolves in DCM despite only differing from PA6 bythe amide/ester moiety.[55] In addition to the thermodynamicaspects of solubility, the dissolution kinetics must also beaffected by the balance of H-bond and vdW contributions.Thus, two conditions for enhancing dissolution kinetics are 1)overcoming inter-chain attraction by vdW interactions withmethylene units, and 2) ensuring preferential solvent-polymerinteraction by tuning the solvent–solvent interactions.In particular, polyamides are semi-crystalline polymerstypically exhibiting a highly stable α-phase crystal formedby H-bonding; this must be overcome for decrystallizationoccur, followed by conventional dissolution mechanisms (i.e.,disentanglement and diffusion).[56] DFT calculations of PA6-α (H-bonded oligomers) and solvated PA6 chains in explicitsolvent clusters indicated that the N─H and C═O bonds donot significantly change when going from crystal to solution,as the corresponding HBA/HBD simply changes from PA toFA with similar binding energies (Figures 3 and S8). However,our calculations show that the carbonyl C─N (CONH) bondis sensitive to the HBA/HBD species, and experimental andtheoretical studies have demonstrated that -CONH exhibitsdistinctly different IR absorption bands (850–1100 cm−1)depending on the crystal structure.[52–54] By monitoring thisband for a thin PA6 film exposed to FA/DCM (1:1 w/w)using transmission-mode FTIR, we found an exponential-typedecrease over time that indicates rapid decrystallization in theearly stages of solvent contact (Figure S8).To explain the relationship between solution properties(i.e., viscosity, �Gsolv, and D) and dissolution rate, we considerthe conditions for dissolution listed above and hypothesizethat thermodynamics may affect kinetics for polyamides in away similar to inorganic and molecular crystals.[57–59] If a large(negative) value of total solvation energy �Gsolv promotessolubility, and a minimum H-bond component is required tobreak H-bonds in the crystal, the dissolution process can bethought of as a competition between the mutual solvation ofFA/cosolvent and the solvation of polyamide. The additionof weakly H-bonding cosolvent does two things: i) breaks upthe FA network through weak-HBD/poor-HBA action, andii) increases vdW interactions with the polyamide, both ofwhich promote more favorable solvent–polymer interactions(Figure 4a).The question becomes, at what point does the cosolventnegatively affect dissolution kinetics despite more favorable�Gsolv? Considering the role of cosolvent described above, wecontend that the beneficial effect of cosolvent on dissolutionkinetics reaches a maximum when the solvent–cosolventinteractions (FC) are nearly balanced by the solvent–polymerinteractions (SP). Above a certain cosolvent fraction (e.g.,fDCM = 0.5), the amount of FA available to interact withboth cosolvent and amide groups is reduced, so the rate-limiting step of decrystallization by H-bond breakage isslower despite larger �Gsolv (see H-bond titration results,Figure S3). Figure 4b displays the initial dissolution rates (rD)of PA6-α in terms of polymer chains (moles) per unit surfacearea (cm2) per unit time (sec), as a function of competitivesolvation:rD = f (�Gsolv) ≈ f (�ESP − �EFC ) (1)As the cosolvent ratio increases, FA–FA interactionsdecrease slowly at first while DCM-DCM interactionsincrease slowly and this trade-off results in an initial increasein FA–DCM interactions until fDCM = 0.5, but the FA-FA interactions decrease more rapidly above this point(Table S3), as reflected by the FA carbonyl shift (Figure 3d).Meanwhile, the polyamide solvation energy continues toincrease due to favorable vdW. Thus, the quantity �ESP–�EFC drastically decreases at fDCM > 0.5 and corresponds toreduced rD (and km).Recycling Protocol and Regenerated PAThe unprecedented dissolution kinetics achieved by thepresent cosolvent strategy can be utilized to establish aroom-temperature protocol for dissolution-based recycling ofPA-containing waste with an ultra-small carbon footprint.Figure 5a illustrates the general scheme for polyamide-targeted rapid dissolution with photos of some specificconditions for separating and recovering PAs as well assecondary materials (SMs). After precipitating the polymerin acetone (PA6: 99.2% yield), we completely separated andrecovered all three solvents by sequential rotary evaporationwith high yield (FA: 99.5%, DCM: 98.5%, acetone: 98.2%).The evaporation rate of the cosolvent system is considerablylower than that expected for a linear mixture, suggesting thatDCM is stabilized by interactions with FA and thus solventloss by evaporation is subdued (Figure S9). Residual solventsin recycled PA6 and PA66 after just one washing cycle wereexamined by headspace gas chromatography (HS-GC) andrevealed minor and trace amounts of FA (200–300 ppm)and DCM (1 ppm), respectively (Table S4). There are nouniversal limits for residual solvent in recycled plastics ingeneral, as different plastic types and applications (e.g., foodpackaging versus electrical components) all have differentpurity requirements, but the levels in our study are well belowthe strict limits set for pharmaceuticals, for example (FA:<5000 ppm, DCM: <600 ppm).[60]Unlike past research reports and patentedtechnologies,[17,23,24] this formic acid-based cosolvent systemdoes not cause any change in molecular weight or chemicalstructure such as hydrolysis or oxidation, as shown by GPC,FTIR, and DSC analyses (Figures 5b–d and S10). Conductingthe recycling process at lower temperatures also reduces therisk of hydrolysis, since dissolution and degradation coexistwith competing temperature-dependent kinetics. Mostimportantly, no significant changes in mechanical propertieswere observed, as the unchanged strength, modulus, andelongation can be seen in Figures 5e and S10. The majorityof PA dissolution studies from the literature either indicate adecrease in material quality of the range 5%–15% (in termsof Mw or tensile properties) or simply do not report therecycled material’s structure/properties.[17–24,61]Low-Emissions Resource RecoveryWe extended the survey to include molding compoundscontaining various polyamides (PA6, PA66, PA11, PA12,Angew. Chem. Int. Ed. 2025, 64, e202502474 (5 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleFigure 4. (a) Illustration of proposed mechanism for cosolvent-enhanced dissolution kinetics of polyamide: weak H-bonding solvents break up thestrong FA network, increasing solvent-polymer interaction and accelerating the decrystallization process. In pure FA, the solvent-solvent interaction(FF) and solvent-amide interaction (SP) are strong, while the solvent-methylene interaction (SP) is weak. By contrast, DCM regulates the H-bondedsolvent network to weaken solvent-solvent interaction (FC) while the SP at both amide and methylene sites are strong. (b) The continuousrelationship between the observed dissolution rate (moles of PA chains per unit surface area per unit time) and the difference betweensolvent-polymer interaction (solvation energy) and solvent-cosolvent interaction.Figure 5. a) Schematic of a dissolution-based recycling protocol with photographs for specific example conditions. Waste components containing PAplastic (with or without secondary materials, SMs) are dissolved in the cosolvent system at room temperature without the need for agitation, yieldinga PA solution that can be separated into SMs and PAs prior to precipitation, washing and drying. The difference in boiling points for FA, cosolventand antisolvent allow them to be fully recovered by sequential evaporation. b) Molecular weight (Mw) and polydispersity index (PDI) of PA6, PA66,and PPA (PA6I/6T) before and after one dissolution/regeneration cycle. c) FTIR spectra, d) DSC scans, and e) tensile stress-strain curves of virginand regenerated (neat) PA6.and PA6I/6T) and fillers (CF, GF, fluoromica, and sericite),all of which dissolved within an hour at room temper-ature without any agitation (Figure 6a). Although PA11and PA12 have been reported to dissolve in FA/DCM atRT for electrospinning and film casting applications,[30,31]investigation into the dissolution mechanism and kinetics hasnot been reported and our work is the first demonstrationof rapid RT dissolution of semi-aromatic in addition toshort- and long-chain polyamides. Note that while the semi-aromatic amorphous PA6I/6T rapidly dissolved (−30 min),fully aromatic PPTA (aramid) was completely undissolvedeven after several months of immersion (Figure S11). Thus,we concluded that any aliphatic-containing PAs are soluble inthis cosolvent system. Although we have focused on PA6 inAngew. Chem. Int. Ed. 2025, 64, e202502474 (6 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleFigure 6. (a) RT dissolution of various PA-based molding compounds: PA6, PA66, PA11, PA12, PA6I/6T, carbon fiber (CF), glass fiber (GF), nanoclay(mica, sericite); symbols indicate the category of composite. Insets are photographs of the solutions (obtained within 30–40 min), and percentages(f,p) indicate the recovery yield of the filler material and polyamide, respectively. (b) Carbon footprint described by the global warming potential metric(GWP, kg CO2-eq/kg of material) and primary energy demand (PED, MJ/kg of material) of neat PA6 for different recycling methodologies (Detailscan be found in the SI). (c) GWP and PED of carbon and glass fibers recovered from PA-based composites; the inset is an enlarged view of GF. Errorbars in (b),(c) represent conservative values if solvent recovery efficiency decreases. (d) Application of the cosolvent-based dissolution approach torealistic automotive and electrical components: SMs commonly used together with PA (GF, Cu, PI, flame retardants) were efficiently recovered inpristine condition from model and real components. (e) Comparison of GWPs for each constituent material in their virgin and recovered states.most of our experiments, we verified the molecular weightsof different PAs by GPC and found no significant changes(Figures S10 and S12). The resin and fillers could easily beseparated by centrifugation to yield >98% recovery in allcases. SEM observation and WAXD measurements confirmthat the resin was fully removed from the fillers and neitherthe surface nor bulk were chemically damaged throughoutthe entire process (Figures 6a and S11), since mechanicalagitation is not necessary.We performed a grave-to-gate life cycle analysis (LCA)using the cut-off method[62,63] to investigate the impact ofrecycling method on global warming potential (GWP) andprimary energy demand (PED) associated with reintroducingpolyamides into the market, and technoeconomic analysis(TEA) gave the minimum selling price (MSP) needed tobreak even (see Supporting Information for details). PA6,PA66, and PPAs carry large GWPs (i.e., carbon footprints)and PED of around 6–9 kg CO2-eq kg−1 and 50–60 MJ kg−1for virgin polymer pellets, respectively, which combined withtheir typical market price ranging from −2.5 $ kg−1 (PA6) upto 15 $ kg−1 (PPAs) translates to high-value resources in termsof embodied carbon and cost.[1,2,6–12] Cutting-edge chemicalrecycling technology[10] can produce pristine PAs via hydro-genative depolymerization followed by repolymerization viatypical condensation reactions, with a grave-to-gate GWP andPED for recycled PA6 (rPA6) about 50% lower than theAngew. Chem. Int. Ed. 2025, 64, e202502474 (7 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleFigure 7. a) Rapid, RT dissolution/separation and fabrication of functional composites: Fishing nets exposed to artificial sea water for 3 months wererapidly dissolved at room-temperature in the cosolvent system and separated to recover PA6, PE, and Pb, followed by dispersion of carbonnanotubes (CNTs) via one-pot solution mixing and injection molding to fabricate rPA6/CNT specimens. b) Tensile behavior and c) thermalconductivity of recycled/upcycled PA6. d) Property summary of recycled/upcycled PA6 materials. e) Multi-functional performance of rPA6/CNT (interms of strength and thermal conductivity) compared to similar reported composites (see Supporting Information). f) Rapid, RTdissolution/separation and fabrication of structural composites: Waste textiles containing PA6 and polyurethane (removed along with dyes byDMSO) were rapidly dissolved at room-temperature in the cosolvent system and precipitated to recover PA6, followed by lamination with wovencarbon fibers previously recycled (rCF) using the cosolvent system. Tensile behavior of g) rPA6 resin and h) rPA6/rCF laminates. Carbon footprintand economic analysis of CF laminates and CNT nanocomposites: i) GWP, j) PED, and k) MSP.virgin material (Figure 6b and Tables S7–S8). By comparison,conventional dissolution methods using polar solvents[1,24]produce fewer carbon emissions than depolymerization, butenergy demand for the high temperatures necessary fordissolution is still considerably large. A hypothetical case ofpure FA as solvent reduces the GWP substantially, but theslow dissolution kinetics influences output rate and ultimatelyresults in large energy demand. Our cosolvent strategy foraccelerating PA dissolution kinetics at RT without agitationcan potentially reduce the GWP of any aliphatic-containingPA down to 0.8 kg CO2-eq with a PED of just 16 MJ kg−1;this is over 50% lower than depolymerization or conventionaldissolution, and roughly 80% lower than virgin material.Since a variety of SMs can also be recovered in pristinecondition, we also considered the recovery of valuableresources such as glass fibers (GF), which are used in highvolume, and carbon fibers (CF), which carry a large carbonfootprint and high cost (Figure 6c). If our cosolvent-basedapproach was used to recovery only the fibers (i.e., ignoringthe plastic) in model compounds containing 30 wt% shortfibers, allocating the full GWP and PED to the fiber fractionalone would still yield drastically reduced emissions comparedto virgin fibers.We further demonstrate this by dissolving PA-basedcomposites as found in automotive and electrical/electroniccomponents (Figures 6d and S13). In addition to PA66,which is rapidly dissolved under ambient conditions, GF,polyimide (PI), and copper were efficiently recovered inpristine condition, and even flame retardant (identified asmelamine-cyanurate) were easily separated and recovered inhigh yield; this attests to the practical merit of the cosolventsystem for efficient recycling of realistic composites. Thecorresponding GWP and PED for each high-value constituentis shown in Figure 6e. In addition, the MSP (i.e., grave-to-gatecost) was calculated as 1.4 $ kg−1 for all types of PA plastic,which is 50% lower than virgin PA6 and 90% lower thanvirgin PPAs (Table S9). When high-value SMs are producedthrough the process, the cost is distributed to each constituentand the MSP of PAs and fibers can be reduced to 0.8 and 2.1 $kg−1, respectively.Angew. Chem. Int. Ed. 2025, 64, e202502474 (8 of 10) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 31, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202502474 by National Institute For, Wiley Online Library on [17/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons LicenseResearch ArticleLow-emissions Upcycling of PA WasteFinally, we extend our approach to upcycle real PA waste intovaluable composite materials. Figure 7a shows a facile processin which used fishing nets (containing PA6, PE, and Pb)are rapidly dissolved in the FA/DCM system and separated(see Movie S1), after which carbon nanotubes (CNTs) aremixed into the PA6 to produce functional nanocomposites(Figure S14). The tensile properties and thermal conductivity(Figures 7b–e) are competitive with similar nanocompositesproduced using pristine materials as reported in the literature(see Supporting Information for details). Similarly, PA6was extracted from used textile waste (containing PA6, PUelastomer, and dyes) by first removing the acid dye andelastomer in DMSO before rapidly dissolving the PA inFA/DCM (see Movie S2) and laminating with recycled carbonfiber cloth (rCF) that was previously recovered by dissolution(Figure 7f). The tensile properties of the recovered neatPA (rPA6) were lower than virgin PA6 (Figure 7g), likelyto a difference in grades, but the mechanical performanceof the rPA6/rCF laminates exceeded 85% of the virginequivalent and thus could be used in structural applications.LCA/TEA calculations summarized in Figure 7i of the GWP,PED, and MSP of these two upcycled composite materialsshow reductions of up to 90% compared to similar virginmaterials. This demonstrates that rapid, dissolution-basedroom-temperature recycling processes with minimal carbonemissions can achieve a good balance between materialperformance, carbon footprint, and cost. Our cosolventstrategy for drastically enhancing RT dissolution kinetics isone promising approach to accomplish this.ConclusionClosing the loop for polyamides remains difficult due to thehigh energy demand and carbon emissions associated withcurrent dissolution-based recycling methods, despite showinggreat promise for efficient separation of valuable materials inmixed polyamide waste. In this work, we have demonstratedthat formic acid, a relatively cheap and environmentallybenign solvent known to dissolve short-chain PAs, can beused for rapid, room-temperature recycling of all varietiesof PAs when a weak hydrogen-bonding cosolvent is added.Through a combination of experiments and DFT calculations,we showed that: 1) polyamides dissolve when the interactionswith H-bonding solvents (having both HBA and HBDcharacteristics) are more favorable than polymer-polymerinteractions, and 2) the cosolvent can tune the solvationbehavior of FA toward PA with drastically accelerated disso-lution rates by regulating both solvent–solvent and solvent–polymer interactions. While DCM (or another chlorinatedsolvent) was used as a model cosolvent, the major value of thiswork is the improved understanding of how cosolvent systemsinteract with polyamides at the molecular level, providing afoundation for future work on cosolvent design.Calculations of carbon emissions and energy demandassociated with the cosolvent-based recycling process indicatethat unprecended performance can be achieved, reaching lessthan 0.8 kg CO2-eq kg−1 and 15 MJ kg−1, respectively. Asformic acid can be directly synthesized from CO2,[64,65] futuredevelopments could see RT recycling processes reduce emis-sions even further. Besides a stand-alone dissolution-basedrecycling protocol, this cosolvent strategy can also be appliedin intermediate steps in the chemical recycling process in caseswhere separation using conventional methods is difficult.Further work is needed to find more environmentally-friendlyalternative solvents, but we anticipate the findings in this studywill guide the design of cosolvent systems for applicationto other high-value plastics in order to realize resourcecircularity and carbon neutrality.Supporting InformationDetails regarding experimental and computational methods,as well as supplementary results and LCA/TEA calculationscan be found in the Supporting Information.AcknowledgementsThe authors thank M. Kamon (NIMS) for assistance withsample preparation and characterization, DJK Corp. for GPCanalysis, Sumika Chemical Analysis Service Ltd. for HS-GCanalysis, and K. 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See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Room-Temperature Material Recycling/Upcycling of Polyamide Waste Enabled by Cosolvent-Tunable Dissolution Kinetics  Introduction  Results and Discussion  Polyamide Dissolution in a Cosolvent System  Cosolvent-Regulated Intermolecular Interactions  Cosolvent Effect on Dissolution Kineticss  Recycling Protocol and Regenerated PA  Low-Emissions Resource Recovery  Low-emissions Upcycling of PA Waste  Conclusion  Supporting Information  Acknowledgements  Conflict of Interests  Data Availability Statement  2025-07-12T16:46:07+0530 Preflight Ticket Signature