Self-healing silicon-containing eugenol-based epoxy resin based on disulfide bond exchange: Synthesis and structure-property relationships

Recent Development of Functional Bio-Based Epoxy Resins

The development of epoxy resins is mainly dependent on non-renewable petroleum resources, commonly diglycidyl ether bisphenol A (DGEBA)-type epoxy monomers. Most raw materials of these thermoset resins are toxic to the health of human beings. To alleviate concerns about the environment and health, the design and synthesis of bio-based epoxy resins using biomass as raw materials have been widely studied in recent decades to replace petroleum-based epoxy resins. With the improvement in the requirements for the performance of bio-based epoxy resins, the design of bio-based epoxy resins with unique functions has attracted a lot of attention, and bio-based epoxy resins with flame-retardant, recyclable/degradable/reprocessable, antibacterial, and other functional bio-based epoxy resins have been developed to expand the applications of epoxy resins and improve their competitiveness. This review summarizes the research progress of functional bio-based epoxy resins in recent years. First, bio-based epoxy resins were classified according to their unique function, and synthesis strategies of functional bio-based epoxy resins were discussed, then the relationship between structure and performance was revealed to guide the synthesis of functional bio-based epoxy resins and stimulate the development of more types of functional bio-based epoxy resins. Finally, the challenges and opportunities in the development of functional bio-based epoxy resins are presented.

Machine Learning for Deconvolution and Segmentation of Hyperspectral Imaging Data from Biopharmaceutical Resins

Biopharmaceutical resins are pivotal inert matrices used across industry and academia, playing crucial roles in a myriad of applications. For biopharmaceutical process research and development applications, a deep understanding of the physical and chemical properties of the resin itself is frequently required, including for drug purification, drug delivery, and immobilized biocatalysis. Nevertheless, the prevailing methodologies currently employed for elucidating these important aspects of biopharmaceutical resins are often lacking, frequently require significant sample alteration, are destructive or ionizing in nature, and may not adequately provide representative information. In this work, we propose the use of unsupervised machine learning technologies, in the form of both non-negative matrix factorization (NMF) and k-means segmentation, in conjugation with Raman hyperspectral imaging to rapidly elucidate the molecular and spatial properties of biopharmaceutical resins. Leveraging our proposed technology, we offer a new approach to comprehensively understanding important resin-based systems for application across biopharmaceuticals and beyond. Specifically, focusing herein on a representative resin widely utilized across the industry (i.e., Immobead 150P), our findings showcase the ability of our machine learning-based technology to molecularly identify and spatially resolve all chemical species present. Further, we offer a comprehensive evaluation of optimal excitation for hyperspectral imaging data collection, demonstrating results across 532, 638, and 785 nm excitation. In all cases, our proposed technology deconvoluted, both spatially and spectrally, resin and glass substrates via NMF. After NMF deconvolution, image segmentation was also successfully accomplished in all data sets via k-means clustering. To the best of our knowledge, this is the first report utilizing the combination of two unsupervised machine learning methodologies, combining NMF and k-means, for the rapid deconvolution and segmentation of biopharmaceutical resins. As such, we offer a powerful new data-rich experimentation tool for application across multidisciplinary fields for a deeper understanding of resins.

Preparation of Epoxy Resin with Disulfide-Containing Curing Agent and Its Application in Self-Healing Coating

Intrinsic self-healing polymers via dynamic covalent bonds have been attracting extensive attention because of their repeatable self-healing property. Herein, a novel self-healing epoxy resin was synthesized with disulfide-containing curing agent via the condensation of dimethyl 3,3'-dithiodipropionate (DTPA) and polyether amine (PEA). Therefore, in the structure of cured resin, flexible molecular chains and disulfide bonds were imported into the cross-linked polymer networks for triggering self-healing performance. The self-healing reaction of cracked samples was realized under a mild condition (60 °C for 6 h). The distribution of flexible polymer segments, disulfide bonds and hydrogen bonds in cross-linked networks plays a great role in the self-healing process of prepared resins. The molar ratio of PEA and DTPA strongly affects the mechanical performance and self-healing property. Especially when that molar ratio of PEA to DTPA is 2, the cured self-healing resin sample showed great ultimate elongation (795%) and excellent healing efficiency (98%). The products can be used as an organic coating, in which the crack could self-repair during a limited time. The corrosion resistance of a typical cure coating sample has been testified by an immersion experiment and electrochemistry impedance spectrum (EIS). This work provided a simple and low-cost route to prepare a self-healing coating for prolonging the service life of conventional epoxy coatings.

Synthesis of novel vanillin-amine hardeners fully derived from renewable bio feedstocks and their curing with epoxy resins to produce recyclable reprocessable vitrimers

Biobased epoxy vitrimers have reached intense interest in recent decades. The triggerable reverse bonds can be introduced into these crosslinked epoxy vitrimers through epoxy resins or hardeners. This study synthesized two imine hardeners, such as vanillin-butanediamine (V-BDA) and vanillin-hexanediamine (V-HDA), using biobased vanillin, butanediamine, and hexanediamine and their chemical structures were ensured by FTIR, ¹HNMR, ¹³CNMR, and TOF-MS. The two novel hardeners were used to cure epoxy resins, rendering vitrimers with good reprocessability, self-healing, recyclability, and solvent resistance due to the reversible imine bonds. The flexural strengths and modulus of these cured resins were consistent with those of epoxy resins that were hardened with traditional amine-based hardeners. The cured resins maintained 100% of their T_g and flexural properties after being reprocessed up to three times. It was revealed that the cured epoxy vitrimers could be degraded entirely in a particular acidic solution capable of bond-exchanging reactions within 12 h at 50 ᵒC, allowing the thermoset matrix to be chemically recycled and the monomers regenerated. This versatile recyclability, combined with the use of fully biobased feedstocks to prepare the hardeners, provides an attractive approach to help achieve a sustainable circular composite economy.

Self-healing of electrical damage in insulating robust epoxy containing dynamic fluorine-substituted carbamate bonds for green dielectrics

Power systems and electrical grids are critical for the development of renewable energy. Electrical treeing is one of the major factors that lead to electrical damage in insulating dielectrics and decline in the reliability of power equipment and ultimately results in catastrophic failure. Here, we demonstrate that bulk epoxy damaged by electrical treeing is able to efficiently heal repeatedly to recover its original robust performance. The classical dilemma between the insulating properties and electrical-damage healability is overcome by dynamic fluorinated carbamate bonds. Moreover, the dynamic bond enables the epoxy to have admirable degradability, which is demonstrated to be used as an attractive green degradable insulation coating. When used as a matrix for fiber-reinforced composites, the reclaimed glass fibers after decomposing the epoxy maintained their original morphology and functionality. This design provides a novel approach for developing smart and green dielectrics to enhance the reliability, sustainability and lifespan of power equipment and electronics.

Characteristics and Application of Eugenol in the Production of Epoxy and Thermosetting Resin Composites: A Review

The review article presents an analysis of the properties of epoxy and thermosetting resin composites containing eugenol derivatives. Moreover, eugenol properties were characterized using thermogravimeters (TGA) and Fourier-transform infrared spectroscopy (FTIR). The aim of this work was to determine the possibility of using eugenol derivatives in polymer composites based on thermoset resins, which can be used as eco-friendly high-performance materials. Eugenol has been successfully used in the production of epoxy composites as a component of coupling agents, epoxy monomers, flame retardants, curing agents, and modifiers. In addition, it reduced the negative impact of thermoset composites on the environment and, in some cases, enabled their biodegradation. Eugenol-based silane coupling agent improved the properties of natural filler epoxy composites. Moreover, eugenol flame retardant had a positive effect on the fire resistance of the epoxy resin. In turn, eugenol glycidyl ether (GE) was used as a diluent of epoxy ester resins during the vacuum infusion process of epoxy composites with the glass fiber. Eugenol-based epoxy resin was used to make composites with carbon fiber with enhanced thermomechanical properties. Likewise, resins such as bismaleimide resin, phthalonitrile resin, and palm oil-based resin have been used for the production of composites with eugenol derivatives.

Synthesis of a Curing Agent Derived from Limonene and the Study of Its Performance to Polymerize a Biobased Epoxy Resin Using the Epoxy/Thiol-Ene Photopolymerization Technique

This study describes the synthesis of a curing agent derived from limonene as well as its application to prepare biobased thermoset polymers via the epoxy/thiol-ene photopolymerization (ETE) method. A biobased commercial epoxy resin was used to synthesize a crosslinked polymeric matrix of polyether-polythioether type. The preparation of the curing agent required two steps. First, a diamine intermediate was prepared by means of a thiol-ene coupling reaction between limonene and cysteamine hydrochloride. Second, the primary amino groups of the intermediate compound were alkylated using allyl bromide. The obtained ditertiary amine-functionalized limonene compound was purified and characterized by FTIR and NMR spectroscopies along with GC-MS. The curing agent was formulated with a tetrafunctional thiol in stoichiometric ratio, and a photoinitiator at 1 mol % concentration, as the components of a thiol-ene system (TES). Two formulations were prepared in which molar concentrations of 30 and 40 mol % of the TES were added to the epoxy resin. The kinetics of the ETE photopolymerizations were determined by means of Real-Time FTIR spectroscopy, which demonstrated high reactivity by observing photopolymerization rates in the range of 1.50-2.25 s-1 for the epoxy, double bonds and thiol groups. The obtained polymers were analyzed by thermal and thermo-mechanical techniques finding glass transition temperatures (Tg) of 60 °C and 52 °C for the polymers derived from the formulations with 30 mol % and 40 mol % of TES, respectively. Potential applications for these materials can be foreseen in the area of coatings.

Recent advances in dynamic covalent bond-based shape memory polymers

Dynamic covalent bond-based shape memory polymers (DCB-SMPs) are one of most important SMPs which have a wide potential application prospect. Different from common strong covalent bonds, DCBs own relatively weak bonding energy, similarly to the supramolecular interactions of noncovalent bonds, and can dynamically combine and dissociate these bonds. DCB-SMP solids, which can be designed to respond for different stimuli, can provide excellent self-healing, good reprocessability, and high mechanical performance, because DCBs can obtain dynamic cross-linking without sacrificing ultrahigh fixing rates. Furthermore, besides DCB-SMP solids, DCB-SMP hydrogels with responsiveness to various stimuli also have been developed recently, which have special biocompatible soft/wet states. Particularly, DCB-SMPs can be combined with emerging 3D-printing techniques to design various original shapes and subsequently complex shape recovery. This review has summarized recent research studies about SMPs based on various DCBs including DCB-SMP solids, DCB-SMP hydrogels, and the introduction of new 3D-printing techniques using them. Last but not least, the advantages/disadvantages of different DCB-SMPs have been analyzed via polymeric structures and the future development trends in this field have been predicted.

Fabrication of a bi-hydroxyl-bi-DOPO compound with excellent quenching and charring capacities for lignin-based epoxy resin

In this study, lignin-based epoxy resins (EP) were fabricated using lignin, phenol and glyoxal as crosslinking reagents. For improving the flame retardancy, a bi-DOPO compound with bi-hydroxyl structure was successfully synthesized, containing excellent quenching and charring capacities. Good pyrolysis behaviors of as-synthesized flame retardant resulted in significant quenching effect via structure decomposition to release PO and PO₂ free radicals for capturing reactive H and OH radicals produced from epoxy combustion. With addition of 0.18 wt% phosphorus, epoxy composite (10% LPG-ER-4) passed V-0 rating with high limited oxygen index (LOI) value of 35.2%. Cone calorimeter tests showed that heat release (including heat release rate (HRR) and total heat release (THR)) from combustion was reduced with assistance of flame retardant. Char residue analyses illustrated that bi-hydroxyl structure in DOPO-based flame retardant benefited the formation of char layer with higher compactness and integrity to serve as a protective shell of interior epoxy matrix. Furthermore, exterior pore size of char residue was narrowed or blocked to avoid the release of heat and volatiles generated from combustion. This study provided a feasible method to improve flame retardancy of lignin-based EP and proposed flame-retardant mechanism both in gaseous and solid phases.

Research advances in UV-curable self-healing coatings

Self-healing is the ability of a material to recover from physical damage.