Selective cross-linking of carboxylated acrylonitrile butadiene rubber and study of their technological compatibility with poly(ethylene-co-methyl acrlylate) by means of mechanical, thermal, and chemical analysis

Curing kinetics and ionic interactions in layered double hydroxides–nitrile rubber Mg–Al-LDHs–XNBR composites

The carboxylated butadiene–acrylonitrile XNBR composites containing layered double hydroxides (Mg–Al-LDHs) were prepared with the aim to investigate the effect of various Mg:Al ratio in the filler composition on the rheological behavior, kinetic of curing and viscoelastic properties of final material. Due to the presence of metal cations, LDHs can form ionic cross-links with carboxylic functional groups of XNBR nitrile rubber. The DSC analysis indicated lower ranges of curing temperatures as the Mg:Al ratio raised (90–184 °C for Pural MG63, 88–187 °C for Pural MG70). The apparent energy of activation Ea decreased with increasing Mg:Al ratio reaching the value of 111.46 kJˑmole−1 for XNBR composite containing Pural MG70. The rheological analysis revealed the presence of specific polymer–nanofillers and fillers–fillers interactions. The XNBR–LDHs rubbers exhibited two transitions corresponding to the glass temperature of elastomer Tg (in range of −13.08 to −13.60 °C) and the ionic transition temperature Tα′ (in range of 32.95–37.90 °C). The ionic transition temperature Tα′ was not observed for the nitrile rubber composite containing Pural MG5 with the lowest Mg:Al ratio. The formed ordered ionic phase significantly affected the viscoelastic behavior of XNBR composites at room and sub-zero temperatures leading to the increase in the storage modulus G′. Therefore, among the various possible applications of LDHs, their use in rubber technology offers the potential for production of environmentally friendly rubber products cured without any additional curatives.