Recyclable Catalyst-Free Elastomeric Vitrimers: Dynamic Covalent Bonds in Ethylene-Glycidyl Methacrylate/Zinc Ionomer of Ethylene/Methacrylic Acid Blends
Rafael Braga da Cunha, Louise Brasileiro Quirino Brito, Pankaj Agrawal, Gustavo de Figueiredo Brito, Tomás Jefférson Alves de Mélo
Abstract
High Resolution Image Download MS PowerPoint Slide Elastomer materials featuring covalent cross-links deliver essential elastic performance for various applications. Despite their benefits, challenges like the need for toxic chemical additives, emissions of harmful vapors, and difficulties in recycling these materials continue to pose environmental and health concerns. Vitrimers emerge as an option, allowing the recyclability of vulcanized elastomers through the use of dynamic covalent bonds. However, for these to occur, it is generally necessary to use toxic external catalysts, which generate negative side effects on the material and cause environmental problems. In this study, we propose a novel approach to address these challenges by incorporating dynamic covalent bonds into ethylene-glycidyl methacrylate (E-GMA)/zinc ionomer (EMAZn) blends, yielding catalyst-free vitrimers. Notably, the zinc in the ionomer acts similar to a transesterification catalyst, facilitating the material’s adaptability without additional chemicals. Through a series of reactions including esterification and subsequent transesterification, the E-GMA/EMAZn blends are transformed into vitrimers capable of rearranging their topological structure at elevated temperatures. This endows the vitrimers with recyclability and reshaping abilities, all without the need for an external catalyst, making them environmentally favorable, practical, and scalable. Utilizing two commercially produced polymers on a large scale ensures cost-effectiveness and avoids the need for slow and expensive chemical processes. Methodologically, experiments were carried out to evaluate the properties of the prepared vitrimers. Results revealed significant findings: stress relaxation analysis demonstrated rapid adaptation to applied forces ( G ( t ) < 100 s); cross-linking analysis showed activation energies between 23.5 and 81 kJ/mol; self-healing experiments achieved up to 94% recovery for the least cross-linked blend; shape memory assessments exhibited a maximum recovery of 88% and the ability to maintain multiple temporary shapes. Additionally, recycling experiments confirmed the material’s feasibility for sustainable reprocessing. This work presents a promising and sustainable solution to the challenges associated with traditional rubber/elastomer cross-linking methods, offering the potential for greener and more efficient rubber materials.