Epoxy resins have been used as composite matrix materials for over half a century, enabling lightweight materials for a variety of applications. Their properties including high strength, chemical resistance, and ease of processing feature them as prime candidates for composite applications. Currently, high performance epoxy monomers are derived from non-renewable feedstocks, which presents a problem for future generations and technologies regarding sustainability. Many bio-based alternatives have been investigated, but properties fall short of high-performance industry standards due to a lack of appropriate chemical groups. Herein 3 bio-based epoxy monomers, with potential to replace high-performance standards, are compared against 3 petroleum derived industry standards. Industrial high performance aromatic diamine crystalline hardener is used to synthesise resin systems. Tensile, flexural and fracture toughness properties are investigated following ASTM standards. Beyond a practical investigation of the physical properties of these resins a comparison of chemical structure to mechanical properties is made. Free volume investigations using positron annihilation lifetime spectroscopy (PALS) were performed, and can be used to explain to some degree the observed properties of the resin systems. @en

Utilization of sustainable feedstocks to fabricate renewable thermosetting epoxy resins has been of great interest recently; however, their translation into composite structures and benchmark comparisons are poorly understood. Phloroglucinol is a phenolic molecule obtained from brown algae, and its epoxidized form is a high viscosity, high reactivity monomer. In this study, the potential of epoxidized phloroglucinol as a laminating resin was examined in comparison with a bisphenol A diglycidyl ether (BADGE) epoxy monomer employing the Epikure 04908 linear amine hardener system. Utilization of a reactive diluent for PHTE resin was necessary for room temperature laminating applications to reduce viscosity, and the thermomechanical properties of PHTE-based resins and composites are superior to those of BADGE systems.@en

The present study describes the development of cure kinetics and chemo-rheological models for an epoxy vitrimer based on polyimine exchange to elucidate the potential in terms of processing and accurate process selection. Reaction kinetics is investigated using differential scanning calorimetry. A good agreement between the model and data can be demonstrated for different stoichiometries by selecting a parallel reaction approach consisting of an nth-order and an autocatalytic approach. The suggested chemo-rheological model captures the intrinsically high viscosity of the resin over a broad temperature and curing range, even after the gelation point. The Di-Benedetto equation represents the glass transition temperature advancement with cure while combining the rheological Winter-Chambon criterion and the kinetic model determines the degree of cure at the gelation. These results give important advice for improved process modeling of vitrimeric resins, facilitate accurate process selection, and pave the way towards the development of composites based on the matrix system investigated in this work.

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The development of epoxy resin formulations from renewable feedstocks has been thoroughly explored in the chemical literature. A simple one-pot chemical reaction involving sustainable phenolic molecules and epichlorohydrin results in the production of renewable epoxy monomers. These monomers can be cured with amines or anhydrides to yield cross-linked thermosetting resins. Although a wide variety of recipes exist, there is a notable gap in the application of these sustainable resin formulations to engineering contexts. This gap is primarily due to the lack of comprehensive, standardized analyses of these resin recipes, which impede their potential use in advanced composite applications. In this study, we reveal a high-performance resin formulation utilizing epoxidized phloroglucinol derived from brown algae in combination with an aerospace-grade amine hardener. The resin processing and thermomechanical properties are investigated using ASTM standard tests including tensile strength, flexural strength, fracture toughness, and interlaminar shear strength. Given the detailed comparative analysis, the partially renewable resin recipe outperforms petroleum derived analogues.

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The aerospace industry has been benefiting from the utilization of polymer materials since fiber-reinforced polymer composites (FRPC) offer high performances at low densities compared to metals. FRPC facilitated the design of lightweight materials, which is extensively used in aviation today. Since their first integration into structural parts, FRPC has experienced exponential growth over the years and has received a special interest from manufacturing engineering. While FRPC today is a major focus in engineering, the design of polymer matrix relies on polymer chemistry. However, aircraft materials are facing a pressing issue related to sustainability, since their environmental footprint is at an alarming level. In this review, commercial thermosetting polymer composites employed in aircraft structures are exhibited from a chemistry perspective by depicting starting products and curing reactions. The potential of chemistry to help design next-generation sustainable FRPC for structural parts by means of utilization of sustainable feedstock, energy-efficient processing, and recycling, is disseminated.

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A versatile synthetic methodology is presented for the preparation of graft copolymers with mixed graft distributions using reversible addition–fragmentation chain transfer (RAFT). The approach harnesses the ability of Z group-tethered grafts to fragment off the backbone to facilitate intermolecular graft exchange reactions between distinct starting materials.@en