Divanillin-Based Aromatic Amines: Synthesis and Use as Curing Agents for Fully Vanillin-Based Epoxy Thermosets

Covalent Adaptable Networks with Tailorable Material Properties Based on Divanillin Polyimines

Covalent adaptable networks (CANs) are being developed as future replacements for thermosets as they can retain the high mechanical and chemical robustness inherent to thermosets but also integrate the possibility of reprocessing after material use. Here, covalent adaptable polyimine-based networks were designed with methoxy and allyloxy-substituted divanillin as a core component together with long flexible aliphatic fatty acid-based amines and a short rigid chain triamine, yielding CANs with a high renewable content. The designed series of CANs with reversible imine functionality allowed for fast stress relaxation and tailorability of the thermomechanical properties, as a result of the ratio between long flexible and short rigid amines, with tensile strength (σb) ranging 1.07-18.7 MPa and glass transition temperatures ranging 16-61 °C. The CANs were subsequently successfully reprocessed up to three times without determinantal structure alterations and retained mechanical performance. The CANs were also successfully chemically recycled under acidic conditions, where the starting divanillin monomer was recovered and utilized for the synthesis of a recycled CAN with similar thermal and mechanical properties. This promising class of thermosets bearing sustainable dynamic functionalities opens a window of opportunity for the progressive replacement of fossil-based thermosets.

pH-Responsive, Thermoset Polymer Coatings for Active Protection against Aluminum Corrosion

This paper describes the synthesis and use of multifunctional methacrylic monomers, which contain basic (amine) functional groups, including an example in which an acid-labile tert-butylcarbamate-protected glycine is used to form a novel methacrylic monomer. The "protected" amino acid-derived functional monomer (BOC-Gly-MA) is copolymerized with an epoxide functional methacrylic monomer (GMA), to deliver novel multifunctional polymers, which are processed into powder coatings and used to study filiform corrosion at the surface of an aluminum substrate. The BOC-Gly-MA-containing copolymers were shown to improve a coating's anticorrosion performance, presenting the lowest average filiform corrosion (FFC) track length, total FFC number, and total corroded surface area (CSA) of the coatings investigated. Further to this, a mode of action for the role of BOC-Gly functional polymers in corrosion protection is proposed, supported by both solution and polymer-aluminum interface studies, delivering new insights into the mode of action of pH-responsive polymer coatings.

Bio-based hyperbranched epoxy resins: synthesis and recycling

Epoxy resins (EPs), accounting for about 70% of the thermosetting resin market, have been recognized as the most widely used thermosetting resins in the world. Nowadays, 90% of the world's EPs are obtained from the bisphenol A (BPA)-based epoxide prepolymer. However, certain limitations severely impede further applications of this advanced material, such as limited fossil-based resources, skyrocketing oil prices, nondegradability, and a "seesaw" between toughness and strength. In recent years, more and more research has been devoted to the preparation of novel epoxy materials to overcome the compromise between toughness and strength and solve plastic waste problems. Among them, the development of bio-based hyperbranched epoxy resins (HERs) is unique and attractive. Bio-based HERs synthesized from bio-derived monomers can be used as a matrix resin or a toughener resulting in partially or fully bio-based epoxy thermosets. The introduction of a hyperbranched structure can balance the strength and toughness of epoxy thermosets. Here, we especially focused on the recent progress in the development of bio-based HERs, including the monomer design, synthesis approaches, mechanical properties, degradation, and recycling strategies. In addition, we advance the challenges and perspectives to engineering application of bio-based HERs in the future. Overall, this review presents an up-to-date overview of bio-based HERs and guidance for emerging research on the sustainable development of EPs in versatile high-tech fields.

Polymers without Petrochemicals: Sustainable Routes to Conventional Monomers

Access to a wide range of plastic materials has been rationalized by the increased demand from growing populations and the development of high-throughput production systems. Plastic materials at low costs with reliable properties have been utilized in many everyday products. Multibillion-dollar companies are established around these plastic materials, and each polymer takes years to optimize, secure intellectual property, comply with the regulatory bodies such as the Registration, Evaluation, Authorisation and Restriction of Chemicals and the Environmental Protection Agency and develop consumer confidence. Therefore, developing a fully sustainable new plastic material with even a slightly different chemical structure is a costly and long process. Hence, the production of the common plastic materials with exactly the same chemical structures that does not require any new registration processes better reflects the reality of how to address the critical future of sustainable plastics. In this review, we have highlighted the very recent examples on the synthesis of common monomers using chemicals from sustainable feedstocks that can be used as a like-for-like substitute to prepare conventional petrochemical-free thermoplastics.

Synthesis, Curing and Thermal Behavior of Amine Hardeners from Potentially Renewable Sources

Research into bio-based epoxy resins has intensified in recent decades. Here, it is of great importance to use raw materials whose use does not compete with food production. In addition, the performance of the newly developed materials should be comparable to that of conventional products. Possible starting materials are lignin degradation products, such as vanillin and syringaldehyde, for which new synthesis routes to the desired products must be found and their properties determined. In this article, the first synthesis of two amine hardeners, starting with vanillin and syringaldehyde, using the Smiles rearrangement reaction is reported. The amine hardeners were mixed with bisphenol A diglycidyl ether, and the curing was compared to isophorone diamine, 4-4'-diaminodiphenyl sulfone, and 4-Aminonbenzylamine by means of differential scanning calorimetry. It was found that the two amines prepared are cold-curing. As TG-MS studies showed, the thermal stability of at least one of the polymers prepared with the potentially bio-based amines is comparable to that of the polymer prepared with isophorone diamine, and similar degradation products are formed during pyrolysis.

Recent Research Progress on Lignin-Derived Resins for Natural Fiber Composite Applications

By increasing the environmental concerns and depletion of petroleum resources, bio-based resins have gained interest. Recently, lignin, vanillin (4-hydroxy-3-methoxybenzaldehyde), and divanillin (6,6'-dihydroxy-5,5'-dimethoxybiphenyl-3,3'-dicarbaldehyde)-based resins have attracted attention due to the low cost, environmental benefits, good thermal stability, excellent mechanical properties, and suitability for high-performance natural fiber composite applications. This review highlights the recent use of lignin, vanillin, and divanillin-based resins with natural fiber composites and their synthesized processes. Finally, discussions are made on the curing kinetics, mechanical properties, flame retardancy, and bio-based resins' adhesion property.

Recent developments towards performance-enhancing lignin-based polymers

This review examines recent strategies, challenges, and future opportunities in preparing high-performance polymeric materials from lignin and its derivable compounds.