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Vitrimers are an innovative class of polymers that boast a remarkable fusion of mechanical and dynamic features, complemented by the added benefit of end-of-life recyclability. This extraordinary blend of properties makes them highly attractive for a variety of applications, such as the automotive sector, soft robotics, and the aerospace industry. At their core, vitrimer materials consist of crosslinked covalent networks that have the ability to dynamically reorganize in response to external factors, including temperature changes, pressure variations, or shifts in pH levels. In this review, the aim is to delve into the latest advancements in the theoretical understanding and computational design of vitrimers. The review begins by offering an overview of the fundamental principles that underlie the behavior of these materials, encompassing their structures, dynamic behavior, and reaction mechanisms. Subsequently, recent progress in the computational design of vitrimers is explored, with a focus on the employment of molecular dynamics (MD)/Monte Carlo (MC) simulations and density functional theory (DFT) calculations. Last, the existing challenges and prospective directions for this field are critically analyzed, emphasizing the necessity for additional theoretical and computational advancements, coupled with experimental validation.

Dynamic polymer networks combine the noteworthy (thermo)mechanical features of thermosets with the processability of thermoplastics. They rely on externally triggered bond exchange reactions, which induce topological rearrangements and, at a sufficiently high rate, a macroscopic reflow of the polymer network. Due to this controlled change in viscosity, dynamic polymers are repairable, malleable, and reprocessable. Herein, several dynamic polyurethane networks were synthetized as model compounds, which were able to undergo thermo-activated transcarbamoylation for the use in rebondable adhesives. Ethylenediamine-N,N,N′,N′-tetra-2-propanol (EDTP) was applied as a transcarbamoylation catalyst, which participates in the curing reaction across its four -OH groups and thus, is covalently attached within the polyurethane network. Both bond exchange rate and (thermo)mechanical properties of the dynamic networks were readily adjusted by the crosslink density and availability of -OH groups. In a last step, the most promising model compound was optimized to prepare an adhesive formulation more suitable for a real case application. Single-lap shear tests were carried out to evaluate the bond strength of this final formulation in adhesively bonded carbon fiber reinforced polymers (CFRP). Exploiting the dynamic nature of the adhesive layer, the debonded CFRP test specimens were rebonded at elevated temperature. The results clearly show that thermally triggered rebonding was feasible by recovering up to 79% of the original bond strength. [ABSTRACT FROM AUTHOR]

Reversible adhesives are crucial for a circular economy of composites as they play a key role for rework, repair, and recycling of adhesively bonded components. Herein, electrically debondable adhesives are prepared by introducing ionic liquids in dynamic thiol–epoxy networks. The function of the ionic liquid in the networks is threefold as it accelerates the curing reaction between thiol and epoxy monomers, facilitates electrical debonding, and catalyzes thermoactivated transesterification reactions, required for rebonding at elevated temperature. A library of 1,3‐dibutylimidazolium‐based ionic liquids with varying anions is synthetized and it is found that 1,3‐dibutyl‐1H‐imidazol‐3‐ium dicyanamide (DiButIm─N(CN)2) is superior in accelerating bond‐exchange reactions between hydroxy and ester moieties at elevated temperature. Thus, a thiol–epoxy resin containing 20 wt% of DiButIm─N(CN)2 is used to impregnate glass fiber mats yielding adhesive connections for aluminum substrates with 10.2 MPa pull‐off strength. The adhesive connections are successfully debonded at the metal–adhesive interface by applying 120 V. The samples are then rebonded via the thermoactivated change in the networks' viscoelastic properties and ≈80% (8.1 MPa) of their original bond strength can be regained. By providing a simple strategy to synthetize reversible adhesives, this approach paves a way toward improved recyclability and repairability of adhesively bonded structures. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced polymer composites (FRPCs) are versatile materials with applications in diverse fields such as transportation, construction, and electronics. With the composites market expected to reach 15.5 Mt by 2026, increasing the sustainability of FRPCs is imperative. The main factors driving the sustainability of FRPCs, namely end‐of‐life management and recyclability, the use of natural, bio‐based, and sustainable materials, as well as biodegradability and product simplification are presented and discussed. [ABSTRACT FROM AUTHOR]

The scientific strategies reported in the literature for developing biobased epoxy vitrimers are summarized. Biomass resources such as lignin, cellulose, or different vegetable oils can be exploited as biobased building blocks for epoxy thermosets as an alternative to the bisphenol‐A‐based ones. Biorenewable resources have been synthesized introducing dynamic covalent bonds in the cross‐linked networks. This combination allows to achieve cross‐linked biobased epoxy networks with thermoset‐like properties at a temperature of use, but showing (re)processability, recyclability, and self‐healing properties above a well‐defined temperature named topology freezing transition temperature (Tv). [ABSTRACT FROM AUTHOR]

Composite laminates were produced by RTM using similar glass and flax fabrics and both vitrimer epoxy and aerospace-grade epoxy, both formulated for liquid molding. Tensile and flexural properties were measured and compared, revealing that the vitrimer composites exhibited equivalent performance in flexural strength and tensile modulus, but slightly lower performance in tensile strength relative to reference epoxy composites. In general, glass–fiber composites outperformed flax–fiber composites in tension. However, both glass and flax–fiber composites yielded roughly equivalent flexural strength and tensile modulus-to-weight ratios. Flax fabrics were recovered from composites by matrix dissolution, and a second-life laminate showed full retention of the mechanical properties relative to those produced from fresh flax. Finally, a demonstration of re-forming was undertaken, showing that simple press-forming can be used to modify the composite shape. However, re-forming to a flat configuration resulted in local fiber damage and a decrease in mechanical properties. An alternative forming method was demonstrated that resulted in less fiber damage, indicating that further refinements might lead to a viable forming and re-forming process. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) composites are renowned for their exceptional mechanical properties, with applications in industries such as automotive, aerospace, medical, civil, and beyond. Despite these merits, a significant challenge in CFRPs lies in their repairability and maintenance. This study, for the first time, delves into the processing and self-healing capability of aromatic thermosetting co-polyester vitrimer-based carbon fiber composites through mechanical testing. Vitrimers are an emerging class of thermosetting polymers, which, owing to their exchangeable covalent bonds, enable the re-formation of bonds across cracks. The specific vitrimer chosen for this study is an aromatic thermosetting co-polyester (ATSP). The mechanical properties of samples were analyzed initially through three-point bending (3PB) testing at room temperature before and after healing (by curing samples for 2 h at 280 °C). Samples were also 3PB tested at 100 °C to analyze their mechanical properties at an elevated temperature for comparison to the samples tested at room temperature. To investigate the fracture properties, optical microscopy images of samples were taken after 3PB tests, which were analyzed to observe crack initiation and crack growth behavior. Through load–displacement curves from double cantilever beam (DCB) mechanical testing, the Mode I crack initiation fracture toughness values of self-healed composites and control composites were calculated to evaluate healing efficiency in ATSP CFRP composites cured at 280 °C for 2 h. Scanning electron microscopy (SEM) showed a similar surface morphology of cracks before and after self-healing. Micro-computed tomography (CT) X-ray imaging confirmed that the healed samples closely resembled the as-fabricated ones, with the exception of some manufacturing voids, caused by outgassing in the initial healing cycle. This research demonstrated the ability for the in situ repair of ATSP CFRPs by restoring the fracture toughness to values comparable to the pristine composite (~289 J/m2). [ABSTRACT FROM AUTHOR]

To facilitate the ongoing transition toward a circular economy, renewable 3D print materials that are both sustainable and competitive must be accessible. However, the growing demand for bio‐based thermosetting resins, which are used as ink for vat photopolymerization, gives rise to environmental concerns in terms of plastic waste management. Therefore, photocurable materials that are renewable and recyclable at the same time are needed. In this work, a mechanically robust and reprocessable 3D printed photopolymer is developed from renewable feedstock. Reaction of malic acid with glycidyl methacrylate introduces both methacrylate moieties that can undergo photopolymerization in the 3D printer, and β‐hydroxyester linkages that can act as dynamic crosslinks via bond exchange reactions. By combining modified malic acid with reactive diluents, a photoinitiator, and phosphate catalyst, three distinct resins are formulated, resulting in bio‐based contents ranging from 43% to 49%. The formulations demonstrate good layer fusion and accurate print quality, while the 3D printed specimens are robust and thermally stable. Notably, the printed object with shortest relaxation time displayed Arrhenius flow behavior with an activation energy of 36.0 kJ mol−1, and its mechanical performance is maintained after being recycled three times. This contributes to the end‐of‐life perspective of photocurable resins in additive manufacturing. [ABSTRACT FROM AUTHOR]

Covalent adaptable networks and vitrimers are novel polymers with dynamic reversible bond exchange reactions for crosslinks, enabling them to modulate their properties between those of thermoplastics and thermosets. They have been gathering interest as materials for their recycling and self-healing properties. In this review, we discuss different molecular simulation efforts that have been used over the last decade to investigate and understand the nanoscale and molecular behaviors of covalent adaptable networks and vitrimers. In particular, molecular dynamics, Monte Carlo, and a hybrid of molecular dynamics and Monte Carlo approaches have been used to model the dynamic bond exchange reaction, which is the main mechanism of interest since it controls both the mechanical and rheological behaviors. The molecular simulation techniques presented yield sufficient results to investigate the structure and dynamics as well as the mechanical and rheological responses of such dynamic networks. The benefits of each method have been highlighted. The use of other tools such as theoretical models and machine learning has been included. We noticed, amongst the most prominent results, that stress relaxes as the bond exchange reaction happens, and that at temperatures higher than the glass transition temperature, the self-healing properties are better since more bond BERs are observed. The lifetime of dynamic covalent crosslinks follows, at moderate to high temperatures, an Arrhenius-like temperature dependence. We note the modeling of certain properties like the melt viscosity with glass transition temperature and the topology freezing transition temperature according to a behavior ruled by either the Williams–Landel–Ferry equation or the Arrhenius equation. Discrepancies between the behavior in dissociative and associative covalent adaptable networks are discussed. We conclude by stating which material parameters and atomistic factors, at the nanoscale, have not yet been taken into account and are lacking in the current literature. [ABSTRACT FROM AUTHOR]

Vitrimers are a novel class of polymers known for their dynamic and recyclable properties. They are gaining significant attention as potential alternatives to traditional thermosets in composite manufacturing due to their repairability and reprocessability. This study explores the environmental sustainability of vitrimers in composite materials through a comprehensive Life Cycle Assessment (LCA) approach. The research focuses on vitrimer composite parts production and their recycling process, with a "from cradle to grave approach". Given the scientific and industrial interest, vitrimer containing disulfide bonds obtained reacting bisphenol A and 4-aminophenyl disulfide (4-AFD or APD) was considered as matrix for the investigated composite part; a traditional epoxy resin matrix composite reinforced with carbon fibers was selected as reference scenario. The recycling process of vitrimer based composites was evaluated, comparing it with conventional thermoset composite recycling method (mechanical recycling). The effects on the environment of these alternatives were evaluated considering different impact categories to provide a comprehensive view of the scenarios. The findings of this study demonstrate that vitrimers can represent a sustainable alternative to traditional thermoset, especially thanks to the possibility of extending the life cycle of a component and recovering continuous filaments from the parts. By shedding light on the potential benefits of vitrimers in reducing the ecological footprint of composite materials, this study contributes valuable insights to sustainable materials development. [ABSTRACT FROM AUTHOR]

Abstract Reversible adhesives are crucial for a circular economy of composites as they play a key role for rework, repair, and recycling of adhesively bonded components. Herein, electrically debondable adhesives are prepared by introducing ionic liquids in dynamic thiol–epoxy networks. The function of the ionic liquid in the networks is threefold as it accelerates the curing reaction between thiol and epoxy monomers, facilitates electrical debonding, and catalyzes thermoactivated transesterification reactions, required for rebonding at elevated temperature. A library of 1,3‐dibutylimidazolium‐based ionic liquids with varying anions is synthetized and it is found that 1,3‐dibutyl‐1H‐imidazol‐3‐ium dicyanamide (DiButIm─N(CN)2) is superior in accelerating bond‐exchange reactions between hydroxy and ester moieties at elevated temperature. Thus, a thiol–epoxy resin containing 20 wt% of DiButIm─N(CN)2 is used to impregnate glass fiber mats yielding adhesive connections for aluminum substrates with 10.2 MPa pull‐off strength. The adhesive connections are successfully debonded at the metal–adhesive interface by applying 120 V. The samples are then rebonded via the thermoactivated change in the networks’ viscoelastic properties and ≈80% (8.1 MPa) of their original bond strength can be regained. By providing a simple strategy to synthetize reversible adhesives, this approach paves a way toward improved recyclability and repairability of adhesively bonded structures.

Abstract Fiber‐reinforced polymer composites (FRPCs) are versatile materials with applications in diverse fields such as transportation, construction, and electronics. With the composites market expected to reach 15.5 Mt by 2026, increasing the sustainability of FRPCs is imperative. The main factors driving the sustainability of FRPCs, namely end‐of‐life management and recyclability, the use of natural, bio‐based, and sustainable materials, as well as biodegradability and product simplification are presented and discussed.

Abstract The scientific strategies reported in the literature for developing biobased epoxy vitrimers are summarized. Biomass resources such as lignin, cellulose, or different vegetable oils can be exploited as biobased building blocks for epoxy thermosets as an alternative to the bisphenol‐A‐based ones. Biorenewable resources have been synthesized introducing dynamic covalent bonds in the cross‐linked networks. This combination allows to achieve cross‐linked biobased epoxy networks with thermoset‐like properties at a temperature of use, but showing (re)processability, recyclability, and self‐healing properties above a well‐defined temperature named topology freezing transition temperature (Tv).

The increased use of plastics and the associated environmental impact has catalyzed research on the development of bio-derived polymers. Bio-based polyesters have gained increased attention due to the abundance of their starting materials and ease of processing. Lignin is naturally occurring in biomass with rich carbon content, whose functionality and rigidity make it an ideal bio-derived candidate for bio-based polyesters. Herein, a lignin-based polyester with good thermal stability and self-repairability was synthesized from carboxylated lignin and epoxidized soybean oil. The synthesized lignin/epoxidized soybean oil (ESO) vitrimer was brittle such that its mechanical performance could not be recorded. However, when polyethylene glycol (PEG) was incorporated as a plasticizer, polymer samples exhibited acceptable ductility. From thermomechanical analysis of the synthesized polyesters, the plasticizer did not impair thermal stability of polymers, but greatly enhanced mechanical properties. Notably, all samples exhibited stability at high temperatures, and good glass transition temperatures (51.0 ± 0.9–78.0 ± 1.2 °C). The highest tensile strength (3.983 ± 0.1 MPa) and storage modulus (1463.67 ± 12.6 MPa) were recorded for the polyester containing 6 % w/w PEG. Moreover, the polymer samples exhibited self-healing capability at 180 °C. This work expands on valorization of lignin through the synthesis of bio-derived materials.

Two different self-healing approaches are studied in this work to analyze the possible contribution of each of the self-healing mechanisms at different temperatures and the possible synergetic effects between them. Thermal and mechanical properties were differently affected by the addition of each of the thermoplastic polymers. This was caused by different phase separations induced during the curing reaction in terms of size and number of the thermoplastic phase domains dispersed within the epoxy matrix and due to the different amounts of thermoplastic polymer that remain solved in the matrix. When using the vitrimeric matrix, phase separation only occurred at the nanometer scale when utilizing poly(bisphenol-A-co-epichlorohydrin) (PBAE) as a thermoplastic agent or higher contents of polycaprolactone (PCL).Self-healing capabilities showed a strong dependence on the temperature used and the type of crack. Low temperatures allowed the thermoplastic phase to flow and fill partially the cracks with moderate levels of self-healing which were only available when phases were separated. Higher temperatures allowed dynamic bonds to induce material healing reaching very high efficiencies but, more importantly, a synergic effect was observed when material was removed from the cracks. In these cases, the flow of the thermoplastic phase filled better the crack and there was an enhanced cooperation between the two healing mechanisms. At higher self-healing temperatures, materials with nanometric size phase separation enabled greater self-healing efficiencies (above 90 %) due to the vitrimeric self-healing capability while the thermoplastic phase helped fill the gaps due to material removal.

Bio‐based polymer building blocks derived from abundant biomass represent a promising class of monomers for the synthesis of sustainable high‐performance polymers. Lignin‐derived vanillin is used as a bio‐based, aromatic molecular platform for chemical modifications. The use of vanillin aldehyde derivatives as monomers with different alkyl chain length, cured with bio‐based and less‐toxic di‐ and triamines, leads to covalent adaptable Schiff base networks and thus enables sustainable and thermally reprocessable high‐performance materials without using highly toxic amines. A process is presented to prepare homogeneous films of crosslinked materials that are thermally reprocessable while maintaining their mechanical performance. The network structures, mechanical properties, and thermal stability of the obtained polymeric sheets are characterized in detail. By systematically adjusting the composition of the network building blocks, the mechanical properties could be varied from tough materials with a high elastic modulus of 1.6 GPa to materials with high flexibility and elastomeric behavior with an elongation at break of 400%. Furthermore, the stress–relaxation behavior of stoichiometric and nonstoichiometric Schiff base vitrimers is investigated. The combination of bio‐based building blocks and the degradability of Schiff base networks under acidic conditions resulted in sustainable, environmentally friendly, chemically and thermomechanically recyclable vitrimers with self‐healing and shape‐memory properties. [ABSTRACT FROM AUTHOR]

An analysis of the influence of common modifiers on the kinetics of the curing process of epoxy-anhydride vitrimers was carried out. As common modifiers to enhance the "vitrimeric" nature of the material, zinc acetylacetonate as a transesterification catalyst and glycerol as a modifier of hydroxyl group content were chosen. The curing process of all obtained compositions was studied by differential scanning calorimetry (DSC) followed by the application of the isoconversional approach. It was shown that additives significantly affect the curing process. The resulting cured polymers were shown to be chemically recyclable by dissolution in the mixture of ethylene glycol and N-methylpirrolidone in a volume ratio of nine to one. The introduction of both zinc acethylacetonate and glycerol to the neat formulation led to a decrease in the dissolution time by 85.7% (from 35 h for the neat epoxy-anhydride formulation to 5 h for the modified formulation). In order to show the opportunity of the secondary use of recyclates, the mixtures based on the basic composition containing 10 wt. % of secondary polymers were also studied. The introduction of a recycled material to neat composition led to the same curing behavior as glycerol-containing systems. [ABSTRACT FROM AUTHOR]

Degradation and reprocessing of thermoset polymers have long been intractable challenges to meet a sustainable future. Star strategies via dynamic cross‐linking hydrogen bonds and/or covalent bonds can afford reprocessable thermosets, but often at the cost of properties or even their functions. Herein, a simple strategy coined as hyperbranched dynamic crosslinking networks (HDCNs) toward in‐practice engineering a petroleum‐based epoxy thermoset into degradable, reconfigurable, and multifunctional vitrimer is provided. The special characteristics of HDCNs involve spatially topological crosslinks for solvent adaption and multi‐dynamic linkages for reversible behaviors. The resulting vitrimer displays mild room‐temperature degradation to dimethylacetamide and can realize the cycling of carbon fiber and epoxy powder from composite. Besides, they have supra toughness and high flexural modulus, high transparency as well as fire‐retardancy surpassing their original thermoset. Notably, it is noted in a chance‐following that ethanol molecule can induce the reconstruction of vitrimer network by ester‐exchange, converting a stiff vitrimer into elastomeric feature, and such material records an ultrahigh modulus (5.45 GPa) at −150 °C for their ultralow‐temperature condition uses. This is shaping up to be a potentially sustainable advanced material to address the post‐consumer thermoset waste, and also provide a newly crosslinked mode for the designs of high‐performance polymer. [ABSTRACT FROM AUTHOR]

The influence of a defined impurity on the network characteristics of vitrimers made from an epoxidized eugenol derivative and various dicarboxylic acids is reported. One major characteristic of the monomer is the fact that it is not "clean" but rather is a mixture of the mono and diepoxidized eugenol derivatives. Mixtures like this could be thought to be representative of many technical grade compounds and the current system therefore serves as a model system to evaluate the effect of epoxide mixtures on the synthesis and the properties of the final vitrimers. The vitrimer preparation is found to be not affected by the different epoxy fractions, but in terms of the properties, there is an effect on the glass transition temperature both with the type of dicarboxylic acid but also with the level of epoxy functionalities present in the system. In spite of this, the ability of the vitrimer to perform the exchange reaction is not affected and all vitrimers can be reshaped or reprocessed showing that the processing is not affected by the changes in epoxy purity. [ABSTRACT FROM AUTHOR]

Abstract To facilitate the ongoing transition toward a circular economy, renewable 3D print materials that are both sustainable and competitive must be accessible. However, the growing demand for bio‐based thermosetting resins, which are used as ink for vat photopolymerization, gives rise to environmental concerns in terms of plastic waste management. Therefore, photocurable materials that are renewable and recyclable at the same time are needed. In this work, a mechanically robust and reprocessable 3D printed photopolymer is developed from renewable feedstock. Reaction of malic acid with glycidyl methacrylate introduces both methacrylate moieties that can undergo photopolymerization in the 3D printer, and β‐hydroxyester linkages that can act as dynamic crosslinks via bond exchange reactions. By combining modified malic acid with reactive diluents, a photoinitiator, and phosphate catalyst, three distinct resins are formulated, resulting in bio‐based contents ranging from 43% to 49%. The formulations demonstrate good layer fusion and accurate print quality, while the 3D printed specimens are robust and thermally stable. Notably, the printed object with shortest relaxation time displayed Arrhenius flow behavior with an activation energy of 36.0 kJ mol−1, and its mechanical performance is maintained after being recycled three times. This contributes to the end‐of‐life perspective of photocurable resins in additive manufacturing.

The concept of holistic sustainability offers novel approaches to minimize the impact of laboratory experiments in the field of engineering polymer materials by utilizing digital smart tools. One of the main tools is the advanced simulation which is a sustainable approach to predict characteristics of systems and materials with minimal environmental impact. Molecular dynamics (MD) has recently become a powerful tool to predict properties of standard materials such as commercial plastics and thermosets. The aim of this study is to determine the minimum model size required to accurately estimate thermal properties of new complex vitrimer materials. In this work, two novel vitrimer variants are introduced. The vitrimers are based on triketone monomers which cross-link following the reversible dynamic covalent bonding exchange mechanism and created both experimentally and numerically. The average glass transition temperature was numerically estimated using MD simulations and verified with experimental data. In the MD model, the cut-off distance was tuned to control the reaction kinetics and consequently reduce the computational time. The results show that a minimum model size of 5000 atoms should be maintained to ensure accuracy. This highlights that thermal properties of new complex vitrimer systems can be numerically estimated at high accuracy using reduced size models and hence save both experimental and computational hours and contribute to the materials green development and testing plans.

Abstract Bio‐based polymer building blocks derived from abundant biomass represent a promising class of monomers for the synthesis of sustainable high‐performance polymers. Lignin‐derived vanillin is used as a bio‐based, aromatic molecular platform for chemical modifications. The use of vanillin aldehyde derivatives as monomers with different alkyl chain length, cured with bio‐based and less‐toxic di‐ and triamines, leads to covalent adaptable Schiff base networks and thus enables sustainable and thermally reprocessable high‐performance materials without using highly toxic amines. A process is presented to prepare homogeneous films of crosslinked materials that are thermally reprocessable while maintaining their mechanical performance. The network structures, mechanical properties, and thermal stability of the obtained polymeric sheets are characterized in detail. By systematically adjusting the composition of the network building blocks, the mechanical properties could be varied from tough materials with a high elastic modulus of 1.6 GPa to materials with high flexibility and elastomeric behavior with an elongation at break of 400%. Furthermore, the stress–relaxation behavior of stoichiometric and nonstoichiometric Schiff base vitrimers is investigated. The combination of bio‐based building blocks and the degradability of Schiff base networks under acidic conditions resulted in sustainable, environmentally friendly, chemically and thermomechanically recyclable vitrimers with self‐healing and shape‐memory properties.

Abstract Vitrimers are an innovative class of polymers that boast a remarkable fusion of mechanical and dynamic features, complemented by the added benefit of end‐of‐life recyclability. This extraordinary blend of properties makes them highly attractive for a variety of applications, such as the automotive sector, soft robotics, and the aerospace industry. At their core, vitrimer materials consist of crosslinked covalent networks that have the ability to dynamically reorganize in response to external factors, including temperature changes, pressure variations, or shifts in pH levels. In this review, the aim is to delve into the latest advancements in the theoretical understanding and computational design of vitrimers. The review begins by offering an overview of the fundamental principles that underlie the behavior of these materials, encompassing their structures, dynamic behavior, and reaction mechanisms. Subsequently, recent progress in the computational design of vitrimers is explored, with a focus on the employment of molecular dynamics (MD)/Monte Carlo (MC) simulations and density functional theory (DFT) calculations. Last, the existing challenges and prospective directions for this field are critically analyzed, emphasizing the necessity for additional theoretical and computational advancements, coupled with experimental validation.

Abstract Degradation and reprocessing of thermoset polymers have long been intractable challenges to meet a sustainable future. Star strategies via dynamic cross‐linking hydrogen bonds and/or covalent bonds can afford reprocessable thermosets, but often at the cost of properties or even their functions. Herein, a simple strategy coined as hyperbranched dynamic crosslinking networks (HDCNs) toward in‐practice engineering a petroleum‐based epoxy thermoset into degradable, reconfigurable, and multifunctional vitrimer is provided. The special characteristics of HDCNs involve spatially topological crosslinks for solvent adaption and multi‐dynamic linkages for reversible behaviors. The resulting vitrimer displays mild room‐temperature degradation to dimethylacetamide and can realize the cycling of carbon fiber and epoxy powder from composite. Besides, they have supra toughness and high flexural modulus, high transparency as well as fire‐retardancy surpassing their original thermoset. Notably, it is noted in a chance‐following that ethanol molecule can induce the reconstruction of vitrimer network by ester‐exchange, converting a stiff vitrimer into elastomeric feature, and such material records an ultrahigh modulus (5.45 GPa) at −150 °C for their ultralow‐temperature condition uses. This is shaping up to be a potentially sustainable advanced material to address the post‐consumer thermoset waste, and also provide a newly crosslinked mode for the designs of high‐performance polymer.

A set of five vitrimers with glass transition temperatures in the range of 80–90 °C were designed to assess the effect of the network structure and disulfide concentration on their dynamic and mechanical properties, and to find the best performing system overall compared to the commercial Araldite LY1564/Aradur 3486 commercial thermoset system. Vitrimer networks were prepared by incorporating mono- and bifunctional epoxy reactive diluents and an amine chain extender into the Araldite LY1564/4-aminophenyldisulfide system. [ABSTRACT FROM AUTHOR]

This work presents a family of functional adhesives based on covalent adaptable networks (CANs). Low-cost and commercially available monomers, including diglycidyl ether of bisphenol A, pentaerythritol tetrakis (3-mercapto propionate) and dipentaerythritol hexakis (3-mercapto propionate), were cured using a base catalyst to produce highly cross-linked materials. The catalyst selection and the study of the curing reaction were performed using differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). The catalyst was chosen for better feasibility of industrial production, characterized by short curing times and relatively low temperatures. Thermal stability and thermomechanical properties of the final materials were evaluated through thermogravimetry (TGA) and dynamic mechanical thermal analysis (DMTA), respectively, revealing glass transition temperatures (Tg) higher than 50 °C. Stress relaxation tests were conducted to investigate the vitrimeric behaviour of the polymers, which exhibited an Arrhenius-type dependence of relaxation times on temperature. Importantly, both materials demonstrated impressive creep resistance up to 70 °C, indicating their suitability for use at elevated service temperatures. Tensile and lap-shear tests were also performed, revealing high lap-shear strength values (up to 16 MPa) comparable to those of commercial adhesives. Furthermore, these vitrimers displayed remarkable properties such as shape memory, shape reconfiguration, and self-welding capabilities, underscoring their excellent potential for a wide range of highly demanding applications in industrial production.

Control of equilibrium and non-equilibrium thermomechanical behavior of poly(diketoenamine) vitrimers is shown by incorporating linear polymer segments varying in molecular weight (MW) and conformational degrees of freedom into the dynamic covalent network. While increasing MW of linear segments yields a lower storage modulus at the rubbery plateau after softening above the glass transition (Tg ), both Tg and the characteristic time of stress relaxation are independently governed by the conformational entropy of the embodied linear segments. Activation energies for bond exchange in the solid state are lower for networks incorporating flexible chains; the network topology freezing temperature decreases with increasing MW of flexible linear segments but increases with increasing MW of stiff segments. Vitrimer reconfigurability is therefore influenced not only by the energetics of bond exchange for a given network density, but also the entropy of polymer chains within the network.

Vitrimers have gained attention as materials with recyclability, self-healing, and shape memory properties. The use of bio-based monomers for the synthesis of vitrimers is relevant because of the use of an environmentally friendly strategy. In this work, resins based on 2-hydroxy-2-phenoxypropyl acrylate and acrylated epoxidized soybean oil were designed and tested by real-time photorheometry, Fourier transform infrared spectroscopy (FT-IR), and mechanical testing to determine suitability for digital light processing 3D printing. The synthesis of vitrimer that could have good thermal properties and vitrimeric abilities, such as shape memory, self-healing, and recyclability properties, was investigated. Because of this, the vitrimer could repair cracks and defects and could have a complex design of several parts, which also contributes to recyclability and decreases costs. The rigidity and viscosity of the resins were reduced with an increasing amount of 2-hydroxy-2-phenoxypropyl acrylate-based monomer. The resin that has the highest amounts of hydroxyl and ester groups that are beneficial for transesterification reactions was chosen for vitrimer synthesis in order to show vitrimeric abilities such as self-healing, shape memory properties, reprocessability, and recyclability. The synthesized vitrimer was applied to digital light processing 3D printing and showed shape memory with a recovery ratio of 100%, self-healing and reprocessability with an efficiency of 47 and 31% and recyclability properties.

A self-healing epoxy material is considered, based on bisphenol A diglycidyl ether and atricarboxylic fatty acid hardener, belonging to a new class of polymers called vitrimers. The res toration of the integrity of such systems in the case of a damage occurs due to the exchange reaction of covalent bonds between the comonomers forming a polymer network. In our previous work, we have developed a model of this material based on the method of reactive dissipative particle dynamics. In this work, we apply our model to study the welding process of vitrimer samples cut into two parts. The control of the integrity of the structure of the systems was carried out using a topological analysis by calculating the distributions over the lengths of simple cycles and the density of the number of load-bearing circuits. It has been shown that the rate of restoration of the integrity of the systems is determined by the concentration of the catalyst and the degree of crosslinking of the polymer. The results obtained also indicate that in the case of a high degree of crosslinking of the polymer, as well as a low catalyst concentration, the structure of the system is highly inhomogeneous.

Polybenzoxazines are high‐performance materials capable of replacing conventional thermosets such as phenolics, epoxies, and bismaleimides in composites manufacturing due to their excellent thermomechanical and chemical behavior. Their versatility and compatibility with biobased precursors make them an attractive option as composite matrices. Like other thermosets, polybenzoxazines are not recyclable and cannot be reprocessed. Incorporating dynamic bonds in benzoxazine monomers can produce vitrimeric polybenzoxazines, which can potentially overcome this limitation and can be tuned to exhibit smart functionalities such as self‐healing and shape memory. Dynamic bond exchange mechanisms for vitrimer development such as transesterification, imine bond, disulfide exchange, transamination, transcarbamoylation, transalkylation, olefin metathesis, transcarbonation, siloxane‐silanol exchange, boronic ester, silyl ether exchange, and dioxaborolane metathesis are potentially applicable to benzoxazine chemistry, with disulfide bond and transesterification having successfully vitrimerized benzoxazines with topological transitions at −8.5 and 88 °C, respectively. Benzoxazine vitrimers featuring glass transitions of 193, 224, and 222–236 °C are now known. These place polybenzoxazines at the forefront of the development of reprocessable and recyclable thermosetting polymers and composite matrices. [ABSTRACT FROM AUTHOR]

ABSTRACTVitrimer is a new type of material that combine the advantages of thermoplastic and thermoset materials. The rapid dynamic exchange reactions at high temperature allow the topology of cross-linked networks to change and rearrange while keeping material structures and properties intact. The concept of vitrimer has emerged to provide a viable strategy for the recycling of high-performance polymer materials, and lots of research works have been carried out for the development of various types of vitrimers. In addition, the recycling strategies for vitrimers are particularly important to determine the performance and potential applications of the recovered materials. Therefore, it is an innovative and valuable perspective to discuss vitrimer materials according to their different recycling strategies. In this review, we start with a brief overview of vitrimers, and then, focus on recycling strategies for vitrimers. Specifically, we highlight the advantages and disadvantages of the two different recycling strategies: physical and chemical recycling methods, and then explore the feasibility of upcycling vitrimers using 3D printing technology. Finally, the impact of recycling strategies on vitrimer materials and the prospects for maximizing the use of vitrimer materials are discussed.

The recent trends of vitrimer studies enhance the thermoset material with superior properties, therefore, it is particularly important to address the critical scientific inquiries in this area using their research metrics. The reported vitrimer systems have been highly required for future real-time applications; however, the inquisitiveness of material exchange mechanisms extends the research studies further. Significantly, more scientific information's are required to achieve the evident prospective outcomes via these materials. This article highlights the trends and developments of the most relevant publications, authors, articles, countries, and keywords in the vitrimer research field over the past 10 years. The represented bibliometric survey would elevate the basic understanding of the current vitrimer research stats and also help follow the particular research community to learn and develop insight. To generate bibliometric networks, bibliometric data has obtained from Scopus and visualised in VOS-viewer; as an overview of that, the highest number of publications were from China, United States, France, United Kingdom, and Spain.

Abstract Polybenzoxazines are high‐performance materials capable of replacing conventional thermosets such as phenolics, epoxies, and bismaleimides in composites manufacturing due to their excellent thermomechanical and chemical behavior. Their versatility and compatibility with biobased precursors make them an attractive option as composite matrices. Like other thermosets, polybenzoxazines are not recyclable and cannot be reprocessed. Incorporating dynamic bonds in benzoxazine monomers can produce vitrimeric polybenzoxazines, which can potentially overcome this limitation and can be tuned to exhibit smart functionalities such as self‐healing and shape memory. Dynamic bond exchange mechanisms for vitrimer development such as transesterification, imine bond, disulfide exchange, transamination, transcarbamoylation, transalkylation, olefin metathesis, transcarbonation, siloxane‐silanol exchange, boronic ester, silyl ether exchange, and dioxaborolane metathesis are potentially applicable to benzoxazine chemistry, with disulfide bond and transesterification having successfully vitrimerized benzoxazines with topological transitions at −8.5 and 88 °C, respectively. Benzoxazine vitrimers featuring glass transitions of 193, 224, and 222–236 °C are now known. These place polybenzoxazines at the forefront of the development of reprocessable and recyclable thermosetting polymers and composite matrices.

A series of poly(thiourethanes) (PTUs) from biobased monomers have been synthesized. Limonene and squalene were transformed into polyfunctional thiols by thiol-ene reaction with thioacetic acid and further saponification. They were then reacted in different proportions with hexamethylene diisocyanate (HDI) in the presence of a catalyst to prepare bio-based poly(thiourethane) vitrimer-like materials. The different functionalities of squalene and limonene thiols (six and two, respectively) allow for changing the characteristics of the final material by only varying their relative proportions in the reactive mixture. The proportions of thiol and isocyanate groups were stoichiometric in all the formulations tested. An acidic and a basic catalyst were tested in the preparation of the networked polymers. As the acidic catalyst, we selected dibutyltin dilaurate (DBTDL), and as the basic catalyst, a tetraphenylborate salt of 1,8-diazabicyclo(5.4.0)undec-7-ene (BGDBU), which has the advantage of only releasing the base at high temperatures. The materials obtained were characterized by thermogravimetry and thermomechanical analysis. The vitrimeric-like behavior was evaluated, and we could see that higher proportions of the limonene derivative in the formulations led to faster stress relaxation of the material. The use of the base catalyst led to a much shorter relaxation time. The materials obtained demonstrated good self-healing efficiency. [ABSTRACT FROM AUTHOR]

Polyethylene (PE) is one of the most widely used polymers in conventional polymer manufacturing processes. However, it remains a challenge to use PE in extrusion-based additive manufacturing (AM). Some of the challenges that this material presents include low self-adhesion and shrinkage during the printing process. These two issues lead to higher mechanical anisotropy when compared to other materials, along with poor dimensional accuracy and warpage. Vitrimers are a new class of polymers that have a dynamic crosslinked network, allowing the material to be healed and reprocessed. Prior studies on polyolefin vitrimers suggest that the crosslinks reduce the degree of crystallinity and increase the dimensional stability at elevated temperatures. In this study, high-density polyethylene (HDPE) and HDPE vitrimers (HDPE-V) were successfully processed using a screw-assisted 3D printer. It was demonstrated that HDPE-V were able to reduce shrinkage during the printing process. This shows that 3D printing with HDPE-V will provide better dimensional stability when compared to regular HDPE. Furthermore, after an annealing process, 3D-printed HDPE-V samples showed a decrease in mechanical anisotropy. This annealing process was only possible in HDPE-V due to their superior dimensional stability at elevated temperatures, with minimal deformation above melting temperature. [ABSTRACT FROM AUTHOR]

Vitrimers have gained attention as materials with recyclability, self-healing, and shape memory properties. The use of bio-based monomers for the synthesis of vitrimers is relevant because of the use of an environmentally friendly strategy. In this work, resins based on 2-hydroxy-2-phenoxypropyl acrylate and acrylated epoxidized soybean oil were designed and tested by real-time photorheometry, Fourier transform infrared spectroscopy (FT-IR), and mechanical testing to determine suitability for digital light processing 3D printing. The synthesis of vitrimer that could have good thermal properties and vitrimeric abilities, such as shape memory, self-healing, and recyclability properties, was investigated. Because of this, the vitrimer could repair cracks and defects and could have a complex design of several parts, which also contributes to recyclability and decreases costs. The rigidity and viscosity of the resins were reduced with an increasing amount of 2-hydroxy-2-phenoxypropyl acrylate-based monomer. The resin that has the highest amounts of hydroxyl and ester groups that are beneficial for transesterification reactions was chosen for vitrimer synthesis in order to show vitrimeric abilities such as self-healing, shape memory properties, reprocessability, and recyclability. The synthesized vitrimer was applied to digital light processing 3D printing and showed shape memory with a recovery ratio of 100%, self-healing and reprocessability with an efficiency of 47 and 31% and recyclability properties. [ABSTRACT FROM AUTHOR]

Disulfide containing vitrimers are being widely studied to get renewable, reprocessable and self-healable resins. The most of them are based on thermally cured epoxy resin. Herein, new thermoset systems based on typical acrylate monomers with photo-curing were synthesized with self-healing capabilities by introducing monomers with disulfide bonds. These disulfide groups are able to exchange upon heating, leading to a renewal of the crosslinks across the damaged surfaces. Different ratios of associative reversible exchange covalent bonds have been studied. The samples were evaluated in terms of thermal and mechanical properties. It was found that the glass transition temperature (Tg) is lower than that corresponding to typical acrylate thermosets, but mechanical properties are better. Increases in hardness of 2.4 times and in elastic modulus of 1.7 times with respect to the reference networks were achieved.Finally, the self-healing properties of the disulfide acrylates were demonstrated by monitoring the repair of a scratch upon heating. A new experimental test for quantifying the self-healing efficiency has been optimized, following the recovery of the surface crack by perfilometry. The composition optimization allows us to achieve repair percentages of 95% in shorter times.

This review is devoted to the description of methods for the self-healing of polymers, polymer composites, and coatings. The self-healing of damages that occur during the operation of the corresponding structures makes it possible to extend the service life of the latter, and in this case, the problem of saving non-renewable resources is simultaneously solved. Two strategies are considered: (a) creating reversible crosslinks in the thermoplastic and (b) introducing a healing agent into cracks. Bond exchange reactions in network polymers (a) proceed as a dissociative process, in which crosslinks are split into their constituent reactive fragments with subsequent regeneration, or as an associative process, the limiting stage of which is the interaction of the reactive end group and the crosslink. The latter process is implemented in vitrimers. Strategy (b) is associated with the use of containers (hollow glass fibers, capsules, microvessels) that burst under the action of a crack. Particular attention is paid to self-healing processes in metallopolymer systems. [ABSTRACT FROM AUTHOR]

As an energy-efficient additive manufacturing process, vat photopolymerization 3D-printing has become a convenient technology to fabricate functional devices with high resolution and freedom in design. However, due to their permanently crosslinked network structure, photopolymers are not easily reprocessed or repaired. To improve the environmental footprint of 3D-printed objects, herein, we combine the dynamic nature of hydroxyl ester links, undergoing a catalyzed transesterification at elevated temperature, with an acrylate monomer derived from renewable resources. As a sustainable building block, we synthesized an acrylated linseed oil and mixed it with selected thiol crosslinkers. By careful selection of the transesterification catalyst, we obtained dynamic thiol-acrylate resins with a high cure rate and decent storage stability, which enabled the digital light processing (DLP) 3D-printing of objects with a structure size of 550 µm. Owing to their dynamic covalent bonds, the thiol-acrylate networks were able to relax 63% of their initial stress within 22 min at 180 °C and showed enhanced toughness after thermal annealing. We exploited the thermo-activated reflow of the dynamic networks to heal and re-shape the 3D-printed objects. The dynamic thiol-acrylate photopolymers also demonstrated promising healing, shape memory, and re-shaping properties, thus offering great potential for various industrial fields such as soft robotics and electronics. [ABSTRACT FROM AUTHOR]

Maleic anhydride‐grafted‐polyethylene was dynamically cross‐linked via reactive melt blending with 4,4′‐dithiodianiline. Thermal and mechanical properties of polyethylene vitrimers with different cross‐linking density were investigated. The results indicate that the degree of crystallinity decreased with increasing cross‐linking density. This behavior was directly related to short‐term and long‐term mechanical properties: vitrimers showed a decrease in yield strength and creep performance. The yield strength of PE vitrimers decreased linearly in relation to the degree of crystallinity. Polarized optical microscopy revealed that the cross‐links inhibit the growth of spherulites structure in polyethylene vitrimers. Thermogravimetric analysis indicated an increase in the onset degradation temperature and decomposition rate for vitrimers with increased cross‐linking density. The stiffness of the vitrimers decreased with increasing cross‐linking density which led to higher damping properties. Finally, it was demonstrated that reprocessing of polyethylene vitrimer was possible without significant impact in mechanical properties. [ABSTRACT FROM AUTHOR]

Plastic waste pollution, including non-biodegradable landfills, leaching of toxic chemicals into soil and waterways, and emission of toxic gases into the atmosphere, is significantly affecting our environment. Conventional plastic waste recycling approaches generally produce lower value materials compared to the original plastic or recover inefficient heat energy. Lately, upcycling or the valorization approach has emerged as a sustainable solution to transform plastic waste into value-added products. In this review, we present an overview of recent advancements in plastic waste upcycling, such as vitrimerization, nanocomposite fabrication, additive manufacturing, catalytic transformation, and industrial biotechnology, envisaged with technical challenges, future developments, and new circular economy opportunities. [ABSTRACT FROM AUTHOR]

In this work, the development of nanocomposite systems based on reduced graphite oxide (rGO) was combined with the development of crosslinked materials characterized by dynamic covalent bonds, i.e., a covalent associative network, starting from ad-hoc synthesized hydroxyl terminated polycaprolactone (PCL-OH). The crosslinking reaction was carried out using methylenediphenyl diisocyanate (MDI) to create systems capable of bond exchanges via transesterification and transcarbamoylation reactions, in the presence of stannous octoate as a catalyst. The above materials were prepared at two different temperatures (120 and 200 °C) and two PCL-OH:MDI ratios. FT-IR measurements proved the formation of urethane bonds in all the prepared samples. Crosslinking was demonstrated by contacting the samples with a solvent capable of dissolving the star-shaped PCL. These tests showed a significant increase in the crosslinked fraction with increasing the temperature and the PCL-OH:MDI ratio. In order to evidence the effect of crosslinking on rGO dispersion and the final properties of the material, a nanocomposite sample was also prepared using a linear commercial PCL, with the nanofiller mixed under the same conditions used to develop the crosslinked systems. The dispersion of rGO, which was investigated using FE-SEM measurements, was similar in the different systems prepared, indicating that the crosslinking process had a minor effect on the dispersibility of the nanofiller. As far as the thermal properties are concerned, the DSC measurements of the prepared samples showed that the crosslinking leads to a decrease in the crystallinity of the polymer, a phenomenon which was particularly evident in the sample prepared at 200 °C with a PCL-OH: MDI ratio of 1:1.33 and was related to the decrease in the polymer chain mobility. Moreover, rGO was found to act as a nucleating agent and increase the crystallization temperature of the nanocomposite sample based on linear commercial PCL, while the contribution of rGO in the crosslinked nanocomposite samples was minor. Rheological measurements confirmed the crosslinking of the PCL-OH system which generates a solid-like behavior depending on the PCL-OH:MDI ratio used. The presence of rGO during crosslinking generated a further huge increase in the viscosity of the melt with a remarkable solid-like behavior, confirming a strong interaction between rGO and crosslinked PCL. Finally, the prepared nanocomposites exhibited self-healing and recyclability properties, thus meeting the requirements for sustainable materials. [ABSTRACT FROM AUTHOR]

While the Michael addition has been employed for more than 130 years for the synthesis of a vast diversity of compounds, the reversibility of this reaction when heteronucleophiles are involved has been generally less considered. First applied to medicinal chemistry, the reversible character of the hetero-Michael reactions has recently been explored for the synthesis of Covalent Adaptable Networks (CANs), in particular the thia-Michael reaction and more recently the aza-Michael reaction. In these cross-linked networks, exchange reactions take place between two Michael adducts by successive dissociation and association steps. In order to understand and precisely control the exchange in these CANs, it is necessary to get an insight into the critical parameters influencing the Michael addition and the dissociation rates of Michael adducts by reconsidering previous studies on these matters. This review presents the progress in the understanding of the thia-Michael reaction over the years as well as the latest developments and plausible future directions to prepare CANs based on this reaction. The potential of aza-Michael reaction for CANs application is highlighted in a specific section with comparison with thia-Michael-based CANs. [ABSTRACT FROM AUTHOR]

Vitrimer is a new, exciting class of sustainable polymers with healing abilities due to their dynamic covalent adaptive networks. However, a limited choice of constituent molecules restricts their property space and potential applications. To overcome this challenge, an innovative approach coupling molecular dynamics (MD) simulations and a novel graph variational autoencoder (VAE) model for inverse design of vitrimer chemistries with desired glass transition temperature (T g ) is presented. The first diverse vitrimer dataset of one million chemistries is curated and T g for 8,424 of them is calculated by high-throughput MD simulations calibrated by a Gaussian process model. The proposed VAE employs dual graph encoders and a latent dimension overlapping scheme which allows for individual representation of multi-component vitrimers. High accuracy and efficiency of the framework are demonstrated by discovering novel vitrimers with desirable T g beyond the training regime. To validate the effectiveness of the framework in experiments, vitrimer chemistries are generated with a target T g = 323 K. By incorporating chemical intuition, a novel vitrimer with T g of 311-317 K is synthesized, experimentally demonstrating healability and flowability. The proposed framework offers an exciting tool for polymer chemists to design and synthesize novel, sustainable polymers for various applications., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)

Vitrimer is a new type of material that combine the advantages of thermoplastic and thermoset materials. The rapid dynamic exchange reactions at high temperature allow the topology of cross-linked networks to change and rearrange while keeping material structures and properties intact. The concept of vitrimer has emerged to provide a viable strategy for the recycling of high-performance polymer materials, and lots of research works have been carried out for the development of various types of vitrimers. In addition, the recycling strategies for vitrimers are particularly important to determine the performance and potential applications of the recovered materials. Therefore, it is an innovative and valuable perspective to discuss vitrimer materials according to their different recycling strategies. In this review, we start with a brief overview of vitrimers, and then, focus on recycling strategies for vitrimers. Specifically, we highlight the advantages and disadvantages of the two different recycling strategies: physical and chemical recycling methods, and then explore the feasibility of upcycling vitrimers using 3D printing technology. Finally, the impact of recycling strategies on vitrimer materials and the prospects for maximizing the use of vitrimer materials are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vitrimers are made from two renewable resources, lignin and epoxidized linseed oil. • Bio-based vitrimer composites are described as new green adhesives. • Vitrimers have shear lap strengths of about 10–17 MPa. • Bio-based adhesives are reprocessable, reweldable and biodegradable. The market of epoxy resin-based adhesives is constantly growing in the automotive, electronics, and healthcare industries thanks to their unique features such as high bonding strength, durability, and corrosion resistance. In this work, alternative sustainable vitrimer adhesives, containing from 20 to 50 wt% of lignin microparticles, were prepared from epoxidized linseed oil (ELO) and a boronic ester dithiol crosslinker (DBEDT), in the absence of solvents and catalysts. The addition of unmodified commercial Kraft lignin to the composites directly influences their thermal and mechanical properties and determines their bonding capacity between several adherent substrates, also affecting the rewelding potential. The lignin-vitrimer composites and the corresponding neat vitrimer matrix exhibited values of lap shear strengths in the range of 9 to 17 MPa, when tested as adhesives with aluminum, stainless steel, and wood specimens, and good to excellent rewelding capability. The amount of lignin microparticles influences the balance between cohesive and adhesive forces during the separation of the adhered aluminum surfaces and the eventual joint failure. In the case of the composites with 20 wt% of lignin, lap shear strength remains constant even after four cycles of rebonding via compression molding, indicating that the best rewelding performance is associated with previous cohesive failure when the adhesive remains on both aluminum sheets' surfaces. In addition, the adhesion was preserved for 83 % of the initial value after 24 h immersed in water. Importantly, biodegradability in both soil and seawater was enhanced by the presence of the lignin filler. In summary, the simple preparation strategy of bio-based vitrimer composites coming from two natural sources could pave the way to green alternatives for industrial applications, such as epoxy-based adhesives. [ABSTRACT FROM AUTHOR]

The increased use of plastics and the associated environmental impact has catalyzed research on the development of bio-derived polymers. Bio-based polyesters have gained increased attention due to the abundance of their starting materials and ease of processing. Lignin is naturally occurring in biomass with rich carbon content, whose functionality and rigidity make it an ideal bio-derived candidate for bio-based polyesters. Herein, a lignin-based polyester with good thermal stability and self-repairability was synthesized from carboxylated lignin and epoxidized soybean oil. The synthesized lignin/epoxidized soybean oil (ESO) vitrimer was brittle such that its mechanical performance could not be recorded. However, when polyethylene glycol (PEG) was incorporated as a plasticizer, polymer samples exhibited acceptable ductility. From thermomechanical analysis of the synthesized polyesters, the plasticizer did not impair thermal stability of polymers, but greatly enhanced mechanical properties. Notably, all samples exhibited stability at high temperatures, and good glass transition temperatures (51.0 ± 0.9–78.0 ± 1.2 °C). The highest tensile strength (3.983 ± 0.1 MPa) and storage modulus (1463.67 ± 12.6 MPa) were recorded for the polyester containing 6 % w/w PEG. Moreover, the polymer samples exhibited self-healing capability at 180 °C. This work expands on valorization of lignin through the synthesis of bio-derived materials. [Display omitted] • Cosolvent enhanced lignocellulosic fractionation (CELF) Lignin was modified by carboxylation and characterized. • Lignin-based polyesters with varying polyethylene glycol (PEG) content were synthesized and characterized. • The synthesized polyesters exhibited good thermal stability and self-healing ability at elevated temperature. • Integration of PEG does not lower the thermal stability of lignin-based polyesters. This paper offers insight that can encourage transition to biobased materials as substitutes for fossil fuel based thermosets. [ABSTRACT FROM AUTHOR]

Upcycling of Waste Polycarbonate to Recyclable Poly(carbonate-imines) with Exceptional Thermal Properties and Unprecedented Flame Retardancy. [Display omitted] • Waste polycarbonate (WPC) was converted into a WPC-derived amine (WPC-NH 2) • Poly(carbonate-imines) (PCIs) were prepared based on WPC-NH 2 and dialdehydes. • The PCIs demonstrate exceptional thermal and unprecedented flame-retardant properties. • The PCIs exhibited stress relaxation and reprocessability. • The structure-hydrolytic stability relationship of PCIs was discussed. This study introduces an innovative method for upcycling waste polycarbonate (WPC) into poly(carbonate-imines) (PCIs), which exhibit exceptional thermal properties and unprecedented flame retardancy. Utilizing a novel insertion reaction of 2-((4-nitrophenoxy)methyl)oxirane with WPC, followed by hydrogenation, we have synthesized WPC-derived amine (WPC-NH 2). This amine is further reacted with bifunctional aldehydes to form PCIs that not only meet vitrimer criteria (characterized by stress relaxation and thermal reprocessability through imine metathesis) but also demonstrate superior thermal stability (T g up to 228 °C) and low thermal expansion (42 ppm/°C). Importantly, these PCIs achieve a UL-94 V-0 rating and exhibit significantly reduced total heat release (11.8 KJ/g), positioning them as prime candidates for sustainable, high-performance materials. The synthesis process supports recycling, showcasing a practical approach to the degradation of PCI-based CFRPs and recovery of intact carbon fibers, underscoring the environmental benefits of this method. [ABSTRACT FROM AUTHOR]