Eco-Friendly Photoreversible Adhesives Derived from Coumarin-Functionalized Epoxy Soybean Oil

Abstract

The increasing demand for high-performance thermosetting adhesive materials is causing the continuous depletion of fossil reserves and has led to environmental pollution by accumulating recalcitrant plastic waste as thermosetting polymer networks are hard to recycle or reuse. This is particularly true in the case of their use as adhesives, where not only can a crosslinked adhesive not be recovered but multi-material components and devices can be difficult to readily separate, making reuse and recycling complex. Bio-based feedstocks and reusable polymeric materials can start to address these issues and reduce their environmental impact. In this work, we developed sustainable green adhesives which are reversible in architecture (changing from thermoset to non-crosslinked material) by combining bio-renewable epoxidized soybean oil (ESO) and non-toxic coumarins, which can readily undergo reversible [2 + 2] cycloaddition reaction under the appropriate wavelength of UV light. A series of coumarin-modified ESO materials were synthesized and chemically characterized by 1H NMR, 13C NMR, Fourier-transform infrared (FTIR) spectroscopy, and gel permeation chromatography. The extent and kinetics of the polymerization of all systems were monitored and calculated using UV–visible spectroscopy. The photoreversibility of these synthesized polymer networks was also chemically investigated and quantified with UV–visible spectroscopy and FTIR techniques. The physical properties of the materials were tested as well as their ability to heal defects such as scratches on the surface when stimulated by the appropriate UV light. Systems with a more flexible coumarin arm showed a superior adhesion strength with a measurable lap shear strength of 3.1 MPa with a minimum of 0.045 J cm–2 dose of 365 nm UV irradiation and with an excellent reuse efficiency of 94%.

Designed to Degrade: Tailoring Polyesters for Circularity

“…The noncomplete reversibility after photocleavage and photodimerization is a continuous challenge for the development of photoreversible materials. This is often attributed to a combination of side reactions, resulting in irreversible structures as well as equilibrium between dimerized and cleaved structures . To increase the reversibility, several studies investigated the relationship between substituents, substituent positions, and resulting photoreactions.…”

“…There is still limited work on combining polyester-based adhesives with photoreversibility. However, end-functionalization of epoxidized soybean oil (ESO) with coumarin units lead to self-healable and thermally stable adhesives . Incorporation of flexible ester linkers between the ESO backbone and coumarin units led to more efficient dimerization and photocleavage reactions with 75–80% yield compared to 36% yield for the sample without a linker.…”

Low-Shrinkage and Degradable UV Imprint Lithography Based on Biomass-Derived Epoxidized Soybean Oil and Cardanol

“…Renewable vegetable oil such as cardanol − and epoxy soybean oil (ESO) − is more and more adopted in engineering materials attributed to its wide source and low price. − For instance, Wang and Zhou modified cardanol through a click reaction to synthesize two kinds of biobased polyols, compounding them with hexamethylene diisocyanate trimers to obtain thermosetting polyurethane films with high elastic modulus, tensile strength, and hardness . Liu et al prepared a pressure-sensitive adhesive with high bonding strength and peeling performance by cross-linking diaminohexane with ESO in a one-pot method.…”

Research on Toughening Polylactic Acid by an Epoxy Soybean Oil Curing Network Based on Dynamic Cross-Linking

“…Epoxidized soybean oil (ESO) belongs to the category of environmentally friendly plant oils, characterized by its cost-effectiveness and sustainability. Both ESO and citric acid (CA) are biologically sourced and exhibit green and biodegradable properties. − However, a lack of compatibility between ESO and the PLA substrate has hindered the desired toughening effect. To address this, a ring-opening reaction was initiated between epoxidized soybean oil and anhydrous citric acid with the aid of a catalyst and thermal ester exchange, thereby enabling dynamic cross-linking of the network.…”