Abstract:
This work is a comparative study between Shea butter (SB) and treated distillate aromatic extract
oil (TDAE) as plasticizers in the vulcanization of natural rubber (NR)- carbon black (CB) vulcanizates (—CB—S—NR—). The plasticized CB—S—NR composites extended scorch (Ts2) and
optimum (T90) curing times. The delays in crosslinking reaction were suspected to be due to the
increased viscosity (ML) and insulation of the reacting species (NR, CB, Sulfur and other curing
aids) by the films of plasticizers. This effect increased the activation energy (Ea (KJ/mol)) for
vulcanization. The CB—S—NR— without plasticizer SB (SBO) showed higher ML, crosslinking
density index (ΔM), rheological strength (MH) and low cure reversion properties than others. In
comparison, the SB-loaded CB-S—NR— composites showed improvement in ML, ΔM, T90,
with lower Ea (KJ/mol) than TDAE samples. Also, the SB compounds exhibited higher Young’s
modulus Eo (MPa) than SBO and TDAE compounds. For instance, the Eo (MPa) of SB5 was over 7
and 1200 % higher than SBO and STD5, respectively. However, —CB—S—NR— filled with TDAE
generally showed higher strength (MPa), attributed to stronger CB-NR interactions. Therefore,
environmentally friendly SB could replace petroleum-based oils for compounding rubbers.
