Recyclable Epoxy Resin via Simultaneous Dual Permanent/Reversible Crosslinking Based on Diels–Alder Chemistry

Thin-film conformal fluorescent SU8-phenylenediamine

The SU8 polymer is a negative photoresist widely used to produce high-quality coatings, with controllable thicknesses ranging from nanometers to millimeters, depending on fabrication protocols. Apart from conventional use cases in microelectronics and fluidics, SU8 is quite an attractive platform in nanophotonics. This material, being straightforwardly processed by ultraviolet lithography, is transparent to wavelengths longer than 500 nm. However, introducing fluorescent agents within the SU8 matrix remains a challenge owing to its high hydrophobicity. Here, we develop a process, where colorful quantum dots co-participate in the polymerization process by epoxide amination and become a part of a new fluorescent material - SU8-phenylenediamine. Through comprehensive characterization methods, including XPS and 1H-NMR analyses, we demonstrate that m-PD covalently binds to SU8 epoxy sites with its molecular amine, virtually forming a new material and not just a mixture of two compounds. After characterizing the new strongly fluorescent platform, thin 300 nm films were created on several surfaces, including a conformal coverage of a nanofluidic capillary. This new process provides opportunities to incorporate various functional molecules into optoelectronic devices without the need for multistep deposition and surface functionalization.

3R Composites: Knockdown Effect Assessment and Repair Efficiency via Mechanical and NDE Testing

In this study, the mechanical properties of purposefully synthesized vitrimer repairable epoxy composites were investigated and compared to conventional, commercial systems. The purpose was to assess the knockdown effect, or the relative property deterioration, from the use of the vitrimer in several testing configurations. Mechanical tests were performed using ILSS, low-velocity impact, and compression after impact configurations. At modeled structure level, the lap strap geometry that can simulate the stiffening of a composite panel was tested. Several non-destructive evaluation techniques were utilized simultaneously with the mechanical testing in order to evaluate (i) the production quality, (ii) the damage during or after mechanical testing, and (iii) the repair efficiency. Results indicated that the new repairable composites had the same mechanical properties as the conventional aerospace-grade RTM6 composites. The electrical resistance change method proved to be a valuable technique for monitoring deformations before the initiation of the debonding and the progress of the damage with consistency and high sensitivity in real time. In terms of repair efficiency, the values ranged from 70% to 100%.

Designing End-of-life Recyclable Polymers via Diels-Alder Chemistry: A Review on the Kinetics of Reversible Reactions

The purpose of this review is to critically assess the kinetic behaviour of the furan/maleimide Diels-Alder click reaction. The popularity of this reaction is evident and still continues to grow, which is likely attributed to its reversibility at temperatures above 100°C, and due to its bio-based "roots" in terms of raw materials. This chemistry has been used to form thermo-reversible crosslinks in polymer networks, and thus allows the polymer field to design strong, but also end-of-life recyclable thermosets and rubbers. In this context, the rate at which the forward reaction (Diels-Alder for crosslinking) and its reverse (retro Diels-Alder for de-crosslinking) proceed as function of temperature is of crucial importance in assessing the feasibility of the design in real-life products. Differences in kinetics based from various studies are not well understood, but are potentially caused by chemical side groups, mass transfer limitations, and on the analysis methods being employed. In this work we attempt to place all the relevant studies in perspective with respect to each other, and thereby offer a general guide on how to assess their recycling kinetics. This review sheds light on the kinetics on the furan/maleimide Diels-Alder reaction. This popular reaction opens up a path to develop end-of-life recyclable polymer networks with self-healing properties. The factors affecting reaction kinetics are discussed, and the importance of accurate reaction kinetics in the context of polymer reprocessing is highlighted. This article is protected by copyright. All rights reserved.