ABSTRACT: This article examines the physical and mechanical
characteristics of mixtures of two different synthetic
rubbers, namely styrene-butadiene rubber (SBR) and
nitril-butadiene rubber (NBR), with novolac type phenolicresin
(PH). According to Taguchi experimental design
method, it is shown that the addition of PH increases the
crosslinking density of rubber phase probably due to its
curative effects. Thermal analysis of the blends indicates
that, contrary to NBR/PH blend, thermal stability of SBR/
PH blend is dependent on sulfur content due to predominant
polysulfidic crosslinks formed in SBR. Slight shift in
glass-transition temperature (Tg) of pure SBR and NBR
vulcanizates by the addition of PH suggests that both
SBR/PH and NBR/PH are incompatible blends with a partially
soluble PH in the rubber phase. Two-phase morphology
of the mixtures is also evidenced by scanning electron
microscopy. Correlation of the rubber/PH modulus versus
PH concentration by Halpin-Tsai model shows a deviation
from the model. Presence of PH in the rubber phase is
thought to vary the mechanical properties of the rubber
phase by changing both the crosslinking density and rigidity
of the molecular network of the rubber, leading to
misuse of modulus of pure rubber in Halpin-Tsai equation.