Simple Modifications of Epoxy into Vitrimer with Superior Processibility, Balanced Properties, and Versatile Applications

Mingen Fei

doi:10.7273/000006319

Epoxy resin stands as a remarkable engineering polymer, renowned for its exceptional mechanical performance, chemical resistance, and thermal stability. These qualities render it a versatile material that finds extensive employment across diverse industries. Nevertheless, a significant challenge arises once epoxy products undergo curing, forming enduring crosslinked networks, thereby impeding their recyclability and reuse potential. This quandary leads to the inconvenient disposal of waste epoxy items, often resulting in careless abandonment and environmentally harmful incineration practices. This research introduces dynamic chemistry into traditional epoxy resins, revolutionizing their recyclability and reusability. A spectrum of modified epoxy resins variations has been developed and showcased, highlighting their capacity for recycling and reuse in various applications. Additionally, recognizing the nonrenewable origins of current epoxy resins, the incorporation of biobased ingredients has been pursued to create new epoxy resins. This innovation not only broadens the range of epoxy resin options but also contributes to the ongoing quest for a sustainable society.In the realm of traditional acid-cured epoxy systems, the integration of methacrylate groups was served as a pivotal tool for the purpose of modification. A groundbreaking strategy was taken by incorporating glycidyl methacrylate in conjunction with soybean oil-based dimer acid. This combination resulted in the creation of three distinct epoxy resins, which were utilized to extend the main chain and finely adjust the mechanical properties of the resulting materials, ranging from rigid to flexible polymers. Leveraging the sensitivity of methacrylate moieties to UV light, these resins can be rapidly manufactured using photocuring methods. Moreover, these resins hold great potential as biobased UV inks for DLP 3D printing. The presence of hydroxyl-ester bonds within the system enables the cured polymer to undergo dynamic transesterification, allowing for reprocessing and repairing when subjected to heat. This unique characteristic bestows the printed objects with remarkable welding and shape-changing properties, thereby amplifying their adaptability and broadening their horizon of conceivable applications. As for amine-cured epoxies, commercially available aldehydes were introduced into the crosslinked networks to transform commonly used bisphenol A epoxy DER 331 into a Schiff base vitrimer. The as-mixed resin exhibited outstanding flowability that is in favor of material processing. Throughout the curing process, diamine exhibited the capacity to engage in two distinct reactions: it could either react with aldehyde to form dynamic imine bond, or it could react with epoxy to build a crosslinked network. Hence, by manipulating the equivalent of amine/aldehyde/epoxy, the obtained vitrimer exhibited tunable mechanical and thermal properties. Notably, the formation of flexible imine chains by diamine and dialdehyde provided the vitrimer with impressive toughness in contrast to commercial epoxy thermosets. Moreover, the dynamic behaviors of Schiff base vitrimer is controllable by its chemical structure. Different aldehydes were adopted in this system to investigate the exchange efficiency of Schiff base vitrimer via control the chemical structure. Model compounds were synthesized to elucidate the mechanism of the locations of substituents affecting the dynamic behaviors of Schiff base vitrimers. This ternary Schiff base epoxy vitrimer has been successfully demonstrated for applications in carbon fiber composites and coatings. The resulting composites can be decomposed under mild conditions (200°C, 4h, 0.2 M HCl) in a pressure reactor, and the recovered carbon fiber presented performance comparable to the original material. The coating formulated from this epoxy vitrimer showed comparable hardness, adhesion, and solvent resistance, and could undergo repairing after heating while being removed with a mild acidic solution. Building upon the precedent of the ternary epoxy vitrimer system, a more sustainable approach was pursued by employing renewable hempseed oil-based epoxy and limonene amine to fashion an environmentally friendly resin and its corresponding hemp fiber composite. Considering the inherent challenge of the feeble interface in biocomposite, the introduction of amino silane into the formulation was undertaken to act as a coupling agent. Notably, the pliant nature of the silane not only facilitated improved interfacial interactions but also contributed to the heightened toughness of the resulting vitrimer. Intriguingly, both the ester bonds originating from the hempseed oil-based epoxy and the imine bonds within the system exhibited susceptibility to aminolysis. This attribute proved crucial as it allowed for the vitrimer and its associated biocomposite to undergo degradation under mild conditions, specifically in an ethanolamine solution maintained at 100°C for a duration of 3 hours.

Simple Modifications of Epoxy into Vitrimer with Superior Processibility, Balanced Properties, and Versatile Applications

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