Effect of imidazolium ionic liquid type on the properties of nitrile rubber composites

We investigated the influence of hydrophilic and hydrophobic imidazolium ionic liquids on the curing kinetic, mechanical, morphological and ionic conductivity properties of nitrile rubber composites. Two room temperature ionic liquids with a common cation—1‐ethyl‐3‐methylimidazolium thiocyanate (EMIM SCN; hydrophilic) and 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI; hydrophobic)—were used. Magnesium–aluminium layered double hydroxide (MgAl‐LDH; also known as hydrotalcite) was added to carboxylated acrylonitrile–butadiene rubber (XNBR) whereas fumed silica Aerosil 380 was used in acrylonitrile–butadiene rubber (NBR) as reinforcing fillers. NBR compounds were vulcanized with a conventional sulfur‐based crosslinking system whereas XNBR compounds were cured with MgAl‐LDH. The optimum cure time reduction and tensile properties improvement were obtained when both ionic liquids were added at 5 parts per hundred rubber (phr). The results revealed that EMIM SCN and EMIM TFSI induced an increase in the AC conductivity of nitrile rubber composites from 10^?10 to 10^?8 and to 10^?7 S cm^?1, respectively (at 15 phr ionic liquid concentration). The presence of ionic liquids in NBR slightly affected the glass transition temperature (T_g) whereas the presence of EMIM TFSI in XNBR contributed to a shift in T_g towards lower temperatures from ?23 to ?31 °C, at 15 phr loading, which can be attributed to the plasticizing behaviour of EMIM TFSI in the XNBR/MgAl‐LDH system. Dynamic mechanical analysis was also carried out and the related parameters, such as the mechanical loss factor and storage modulus, were determined. © 2013 Society of Chemical Industry