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Permanent polymer networks present an important sustainability challenge. Irreversible covalent crosslinks impart these materials excellent mechanical properties, thermal and chemical resistance, yet also render them difficult to repair and to recycle. Self-healing mechanisms can extend the lifetime of thermosets and elastomers, improving their durability and making their lifecycle more sustainable. In addition to the lifetime extension, this paper reviews the sustainability of self-healing polymers from a holistic point of view. The entire lifecycle of self-healing polymers is critically assessed with reference to the green chemistry principles and sustainable development. The relation between the self-healing chemistries and the sustainability aspects of each of the phases of the lifecycle are discussed, starting from the feedstocks, monomer functionalisation and polymer synthesis, to processing and manufacturing as well as end-of-life considerations, i.e. recycling or (bio)degradation. The review provides a toolbox for the development of more sustainable thermosets, elastomers and their composites. It is of utmost importance to consider the entire lifecycle of self-healing materials, derived products and – by extension – any material or product. The self-healing ability and often related recyclability should primarily reduce the amount of new materials that are necessary to fulfill societal needs, by extending the lifetime of products and maximizing reprocessing into new products. Increasing healing efficiency and the number of healing cycles improves the overall environmental impact relative to the extended service lifetime. Renewable resources derived from biomass, recycling processes or waste streams should be the first choice to create new self-healing polymers. Finally, biodegradability can be considered as a complementary end-of-life scenario upon accidental loss of self-healing polymer to the environment, provided that the biodegradation does not start under the prospected use conditions of the self-healing polymers and products, but can be postponed until contact with stimuli present in the environment. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Facile mechanochemical synthesis of g-C 3 N 4 -ZnO and -Fe 2 O 3 composite photocatalyts. • Maximum benzaldehyde selectivity (70%) for the g-C 3 N 4 -Fe 2 O 3 composite sample. • Crystallinity and surface concentration of the oxides control the selectivity of benzyl alcohol oxidation. Abstract Graphitic carbon nitride (CN) enriched with ZnO or Fe 2 O 3 were synthesized using a simple one-pot mechanochemical method. By using this method, composite samples were synthetized without the production of any potentially hazardous waste. Synthesized materials were used as catalysts during selective photo-oxidation of benzyl alcohol. Both composite materials displayed an enhancement of activity and benzaldehyde selectivity with respect to the pure CN. The most active catalyst was Fe 2 O 3 /g-C 3 N 4 (Fe/CN). Conversion and benzaldehyde selectivity of this sample were 20 and 70%, respectively. It showed a considerable increase of benzaldehyde selectivity compared to the pure CN and TiO 2 P25 commercial reference. A complete structural and electronic characterization using Scanning Electron Microscopy-Energy Dispersive (SEM-EDX), BET measurements, X-ray diffraction (XRD), X-ray Photoelectron (XPS), and UV–visible spectroscopies was carried out. The characterization analysis pointed out the leading role of the crystallinity and surface concentration over the activity and benzaldehyde selectivity of the reaction. [ABSTRACT FROM AUTHOR]

[Display omitted] • A glassy thermoset based on thermoreversible Diels-Alder crosslinks has been manufactured using selective laser sintering. • Powder morphology and flow properties are suitable for selective laser sintering applications. • Built parts show great healing performance, correcting partial curing and porosity generated during printing under a thermal posttreatment. • Built parts are reprocessable and recyclable without altering their chemical nature. Selective Laser Sintering (SLS) is a well-known additive manufacturing technique that builds 3D complex structures by sintering powder particles together upon laser irradiation. In the polymer field, thermoset resins are a popular choice for a plethora of applications due to their great mechanical properties and thermochemical stability. However, due to their irreversible crosslinked nature, they are hard to be processed using SLS. Herein, a covalently crosslinked polymer thermoset based on thermally reversible Diels-Alder (DA) bonds has been printed using SLS. The thermoreversible network exhibits a glassy behavior due to its high crosslinked density and glass transition temperature and was successfully milled into a suitable particle size, morphology and flow for SLS applications. At low temperatures, the DA equilibrium shifts towards the formation of the DA crosslinks, while at high temperatures the DA adducts gradually dissociate, allowing flow and reprocessability at temperatures above 131˚C. Furthermore, the printed parts exhibit healing ability when heated above their glass transition temperature, reaching a fracture stress and Young's Modulus of 25.4 MPa and 1416 MPa, respectively. Thus, the dynamic nature of the network extends the build lifetime upon damage and also brings the opportunity of recycling or reprocessing, enhancing circularity compared to classic thermosets. [ABSTRACT FROM AUTHOR]

Self-healing materials have been intensively studied as materials that can mimic healing properties of biological systems. Reversible polymer networks based on Diels-Alder thermoreversible covalent bonds exhibit great healing performance by controlling the temperature of the system. Despite the attractive applications of self-healing materials, most of them are restricted to the repair of narrow cracks due to their restricted mobility in the solid state. In this work, magnetite (Fe 3 O 4) particles are used to create self-healing magnetic composites. The use of a conventional magnet to apply a magnetic driving force is proposed for the closure of wide damage gaps in the solid state without the need of either mechanical intervention or liquid-like flow inside the material, limiting the structural stability. Thermal, mechanical and chemical characterization of different composites are performed in this study and the healing efficiency is evaluated to assess their potential to close and heal large damage sizes. Image 1 • Synthesis and characterization of magnetic Diels-Alder thermoreversible elastomeric composites with self-healing ability. • The effect of Fe 3 O 4 nanoparticles on the reaction kinetics, thermodynamics and viscoelastic behaviour of the formed composites. • Magnetic composites experience damage gap closure under the application of an external magnetic field. • Optimum in filler loading between magnetic response and healing efficiency. [ABSTRACT FROM AUTHOR]