Influence of polyethylene glycol-based deep eutectic solvent on vulcanization and mechanical properties of natural rubber gum vulcanizates

Rubber vulcanization generates volatile organic compounds emissions associated with the intermolecular crosslinking reactions at rather higher temperatures mediated by many kinds of indispensable additive. To achieve the carbon peaking and neutrality targets in China, rubber processing industries call for ecofriendly, green additives to satisfy demands of high-efficiency vulcanization at low temperatures. Herein an oligomer deep eutectic solvent (DES) based on polyethylene glycol is used for the first time for regulating vulcanization kinetics of natural rubber (NR) gums. It is found that DES at 0.2-1.0 phr (parts per hundred parts of rubber) dosages could accelerate the vulcanization at 120-140 degrees C without marked influences on crosslinking density and storage modulus at vulcanization equilibrium. The vulcanization of DES-containing gums at 120 degrees C is faster than that of the DES-free one at 140 degrees C while the DES-containing vulcanizates cured at 120 degrees C exhibit nonlinear rheological responses being similar to the DES-free one cured at 140 degrees C. The low-temperature vulcanization in general generates vulcanizates exhibiting higher tensile strength in comparison with those cured at 140 degrees C. Furthermore, DES could not influence the Mullins effect of the vulcanizates undergoing cyclic tension deformation. The results show that the non-volatile DES could be used to adjust the vulcanization kinetics without impact on the crosslinking density and Mullins effect, paving the way for developing energy-saving green vulcanization technologies.