Preparation of deep eutectic solvents based on metal ions and their influences on reinforcement and strain softening behaviors of silica filled natural rubber nanocomposites

Abstract

Deep eutectic solvents (DESs) are used as green additives to reduce zinc oxide (ZnO) activator usages and prepare volatile organic compounds-free nanocomposites. Herein highly active DESs containing different metal ions (Zn2+, Sn2+, Mg2+ and Fe3+) are introduced into silica filled natural rubber (NR) nanocomposites for regulating the network structure of rubber matrix and tailoring elasticity, strength and softening behaviors of the nanocomposites. The results show that DESs react with proteins in NR, which introduces hydrogen bonding between DESs and non-rubber components in the crosslinked network. DES can improve dispersion of silica and enhance the interfacial interaction between silica and NR. In comparison with NR nanocomposites containing 2 phr (part per hundred parts of rubber) ZnO, the partial replacement of ZnO with DESs can not only improve vulcanization rate, tensile strength and crosslinking density but also weaken the Mullins effect by reducing dissipation and softening energy densities. Normalization of tensile deformation energy density reveals that stress and softening behaviors are related to crosslinking density of NR and strain amplification effect induced by silica. The investigation is enlightening for mediating the reinforcement and strain softening behaviors and paving the way for manufacture high-performance NR nanocomposites in an energy-saving efficient and ecofriendly approach.