Bio-Based Vitrimers from 2,5-Furandicarboxylic Acid as Repairable, Reusable, and Recyclable Epoxy Systems

Closed-loop recyclability of a biomass-derived epoxy-amine thermoset by methanolysis

Epoxy resin thermosets (ERTs) are an important class of polymeric materials. However, owing to their highly cross-linked nature, they suffer from poor recyclability, which contributes to an unacceptable level of environmental pollution. There is a clear need for the design of inherently recyclable ERTs that are based on renewable resources. We present the synthesis and closed-loop recycling of a fully lignocellulose-derivable epoxy resin (DGF/MBCA), prepared from dimethyl ester of 2,5-furandicarboxylic acid (DMFD), 4,4'-methylenebis(cyclohexylamine) (MBCA), and glycidol, which displays excellent thermomechanical properties (a glass transition temperature of 170°C, and a storage modulus at 25°C of 1.2 gigapascals). Notably, the material undergoes methanolysis in the absence of any catalyst, regenerating 90% of the original DMFD. The diamine MBCA and glycidol can subsequently be reformed by acetolysis. Application and recycling of DGF/MBCA in glass and plant fiber composites are demonstrated.

Strategies towards Fully Recyclable Commercial Epoxy Resins: Diels-Alder Structures in Sustainable Composites

The Diels-Alder equilibrium is a widely known process in chemistry that can be used to provide a thermoset structure with recyclability and reprocessability mechanisms. In this study, a commercial epoxy resin is modified through the integration of functional groups into the network structure to provide superior performance. The present study has demonstrated that it is possible to adapt the curing process to efficiently incorporate these moieties in the final structure of commercial epoxy-based resins. It also evaluates the impact that they have on the final properties of the cured composites. In addition, different approaches have been studied for the incorporation of the functional group, adjusting and adapting the stoichiometry of the system components due to the differences in reactivity caused by the presence of the incorporated reactive groups, with the objective of maintaining comparable ratios of epoxy/amine groups in the formulation. Finally, it has been demonstrated that although the Diels-Alder equilibrium responds under external conditions, such as temperature, different sets of parameters and behaviors are to be expected as the structures are integrated into the thermoset, generating new equilibrium temperatures. In this way, the present research has explored sustainable strategies to enable the recyclability of commercial thermoset systems through crosslinking control and its modification.

Preparation, characterization, and application of waterborne lignin-based epoxy resin as eco-friendly wood adhesive

A series of novel waterborne lignin-based epoxy resin emulsions (WLEPs) were successfully synthesized, and then the WLEPs were cured with polyamide (PA) to give formaldehyde-free wood adhesives with high-performance. The chemical structures and properties of WLEP emulsions were determined. The effects of the emulsifiers on thermal and mechanical properties of the adhesives were investigated, and the potential application of WLEPs in the formulation of plywood were also evaluated. The results demonstrated that the WLEP dispersions presented excellent storage stability (>180 days) with their viscosities range from 110 mPa·s to 470 mPa·s and particle sizes in the range of 321-696 nm, which were beneficial for the fluidity and permeability of the wood adhesives. Furthermore, the thermal and mechanical properties of adhesives could be tuned effectively by controlling the length of PEG chains. The adhesive bearing PEG 6000 exhibited the highest tensile strength of 24.0 MPa and Young's modulus of 1439 MPa. Notably, the plywood prepared with the resulting adhesives displayed good bonding performance, especially water resistance, which were much higher than the national standard requirement for exterior-grade plywood type I. These results indicated that the WLEPs could be used as sustainable alternatives for traditional formaldehyde-based wood adhesives in practical applications.