Healable, recyclable and mechanically robust elastomers with multiple dynamic cross-linking bonds

Effects of borax loading on the self-healing properties of epoxidized natural rubber

A promising approach for developing self-healing polymer materials involves the formation of reversible dynamic crosslinked networks. However, most self-healing systems require external stimuli such as temperature or pressure, to achieve effective healing. In this study, we successfully developed self-healing epoxidized natural rubber (ENR) materials that do not depend on external stimuli by incorporating borax as a crosslinking agent. The results demonstrated that borax facilitates self-healing efficiency through the reversibility of borate-ester and hydrogen bonds. ENR with 10 phr borax exhibits remarkable self-healing performance, achieving 94% efficiency in tensile strength and 95% efficiency in elongation at break after healing at ambient temperature for 24 h. Moreover, the effect of borax loadings on the chemical structure, thermal stability, and mechanical properties of the crosslinked ENR materials were investigated. These findings highlight the crucial role of borax in imparting self-healing properties to ENR without requiring external stimuli, offering an effective approach for developing self-healing elastomers.

Fully Recycled Polyolefin Elastomer-Based Vitrimers with Ultra-High, Universal, Stable, and Switchable Adhesion

Achieving both robust adhesion to arbitrary surfaces and thermal-switchable/recyclable properties has proven challenging, particularly for commodity polyolefins. Herein, a simple and effective route is reported to transform polyolefins elastomer (POE) into a fully recycled epoxy-functionalized POE vitrimers (E-POE vit) with ultra-high, universal, stable, and switchable adhesion via facile free radical grafting and dynamic cross-linking. The resultant E-POE vit exhibits increase in adhesion strength on glass exceeding three to ten times compared to those commonly used polymers, due to the synergy of dense hydrogen (H)-bonds and strong interfacial affinity. In addition, E-POE vit also displays strong adhesion on diverse surfaces ranging from inorganic to organic while maintaining good stability in various harsh environments. More importantly, temperature-sensitive H-bonds allow E-POE vit to switch between attachment-detachment at alternating temperatures, resulting in reversible adhesion without adhesion loss, even after 10 cycles. Moreover, E-POE vit is able to be fully recycled and reused more than ten times via thermo-activated transesterification reactions with negligible change in structure and performance. This work may unlock strategies to fabricate high-performance commercial polymer-based adhesives with adhesion and recyclable features for intelligent and sustainable applications.