VULCANIZATION OF NITRILE RUBBER .1. EFFECT OF SOME ACCELERATORS ON THE PHYSICOMECHANICAL PROPERTIES OF VULCANIZED NITRILE RUBBER FOR RESISTANCE TO FUEL AND GENERAL USE

Compounding mixtures were prepared based on acrylonitrile-butadiene rubber (Krynac 803) to which increasing parts per hundred rubber (pphr) of the following accelerates were added: tetramethyl thiuram disulfur (TMTD in series A1), tetramethyl thiuram monosulfur (TMTM in series A2), 2-mercaptobenzothiazole (MBT in series A3), and 2,2'-dithiobisbenzothiazole (MBTS in series A4). Effects of the quantity and type of accelerator on the vulcanization characteristics were studied. Physicomechanical investigations and swelling resistance were determined for samples immersed in benzene:benzol mixture at normal temperature. It was found that according to the type and quantity of accelerator, the optimum cure time decreased with increasing the quantity of accelerator. Relatively higher values of scorch time (8 min, at 1.0-3.0 pphr), which seems to ensure safe processing during production was obtained for TMTM (series A2). TMTD (in quantity of 2.0 pphr) led to the highest value of rate of cure (14.0 min-1). The best values of tensile strength (210 kg/cm2, and 208 kg/cm2) were reached in TMTD (series A1) and TMTM (series A2), whereas MBT (series A3) and MBTS (series A4) resulted in tensile strength values of 140 and 155 kg/cm2, respectively. The highest value of modulus (86 kg/cm2) was obtained in TMTD (series Al at 2.0 pphr). Whereas TMTD (series A1) and TMTM (series A2) led to relatively lower values of elongation at break (180% and 190%), it was found that MBT (series A3) and MBTS (series A4) led to higher values (280% and 260%). Small effects on the elasticity were observed when changing the type and quantity of accelerator. Relatively higher values of hardness were reached for series Al and A2 as compared with series A3 and A4. The lowest values of percent volume increase after immersion in benzene:benzol mixture (8.3%) was obtained for A1 (at 1.5 pphr of TMTD), as compared with the other three accelerators.