Tailoring Electromechanical Properties of Natural Rubber Vitrimers by Cross-Linkers

Abstract

The growing demand for smart polymeric transducers such as dielectric elastomer actuators and energy harvesters has urged the use of sustainable and recyclable elastomeric materials. Vitrimer chemistry has shed light on future reprocessable and recyclable thermosets and elastomers. In this work, epoxidized natural rubber (ENR) vitrimers were prepared using diacid or triacid cross-linkers and formed covalently cross-linking networks via thermally triggered reversible β-hydroxy ester bonds. The crosslinked ENR elastomers exhibited Arrhenius-type viscoelastic behavior with a complete stress relaxation between 140 and 160 °C, that is, vitrimer characteristics, which were highly dependent on the cross-linking temperature. The mechanical and dielectric properties of the ENR vitrimers can be tuned by varying the molecular structure and concentration of the cross-linkers. Among the diacid and triacid cross-linkers, Pripol 1017 fatty polyacid (P1017) and 3,3′-dithiopropionic acid (DTPA) had similar effects on the cross-linking density and mechanical properties of the ENR vitrimers. The highest tensile strength of 8.70 ± 1.9 or 15.6 ± 2.6 MPa was obtained at 6 mol % of P1017 or DTPA, respectively. While for diamide-based diacid cross-linker (DME), 8 mol % was needed to reach the highest tensile strength of 13.1 ± 2.7 MPa for the elastomer. The three ENR vitrimers showed increased relative permittivity ε′ = 5∼7 at 1 kHz while maintaining low dielectric losses compared to traditional dicumyl peroxide-cured ENR, with ε′ = 3.57 at 1 kHz. With the optimized acidic crosslinker concentrations of P1017 at 6 mol %, DTPA at 6 mol %, and DME at 8 mol %, the ENR vitrimers exhibited improved actuation capabilities at lower electrical fields. Utilizing dynamic cross-linkers to tune the electromechanical properties of dielectric elastomers and the reversibly cross-linked polymer networks will open new opportunities for smart and sustainable dielectric elastomer devices.

Effect of electron beam irradiation on thermal stability and crystallization behavior of flexible copolyester/multiwalled carbon nanotubes nanocomposites

“…The EB irradiation aimed to crosslink the PBAT matrix to minimize their viscoelastic segmental mobility during mechanical deformation and increase the elastic deformability. Crosslinking and enhanced elastic deformability of the polymer nanocomposites will enhance their electromechanical response and thermoelectric performance 34,35 . The crosslinking of the polymer matrix was confirmed by gel formation in the irradiated samples, as suggested by their solubility behavior in chloroform (results of crosslinking, electrical and mechanical properties are not presented in this paper).…”

“…Crosslinking and enhanced elastic deformability of the polymer nanocomposites will enhance their electromechanical response and thermoelectric performance. 34,35 The crosslinking of the polymer matrix was confirmed by gel formation in the irradiated samples, as suggested by their solubility behavior in chloroform (results of crosslinking, electrical and mechanical properties are not presented in this paper). However, it must be considered that there is always an interplay between crosslinking and degradation.…”

The role of chemical microstructures and compositions on the actuation performance of dielectric elastomers: A materials research perspective

“…Even though the formation of permanent crosslinks is an issue that might eventually leads to the hindering of full stress relaxation in elastomer. [129] The incorporation of suitable ceramic fillers was found to be highly effective toward developing elastomeric actuator with high dielectric constant and low dielectric loss. Introducing perovskite nanoparticles such as BT could ameliorate the overall dielectric response in NR.…”

“…Even though the formation of permanent crosslinks is an issue that might eventually leads to the hindering of full stress relaxation in elastomer. [ 129 ]…”