These copolymers combine the mechanical resistance of
dispersed styrenic phases with the elastomeric character of
a polybutadiene or poly(ethylene-butadiene) matrix. SBS
and SEBS copolymers are never used in their pure form due
to their poor processing properties and high cost [2]. To
obtain a satisfactory balance of properties and improved
processing, they must be compounded with oils, fillers or
other polymers. Mineral oils are added to lower hardness
and to improve processability [3]. Often, 20–40 wt% SEBS is
blended with PP or PE to make stiffer compounds. SEBS-PPoil
blends have been commercialized since the early 1990s
[4]. The plasticizer molecules lower the cohesive forces
between the polymer chains, increasing chain mobility. If
the oil is paraffinic in nature, it can be located in both
phases (elastomer and PP), hence affecting the rheological
and mechanical properties of both components. Sengupta
and Noordemeer published a relevant study relating
properties and morphology of SEBS-PP blends containing a
high amount of oil (140 phr, as is usual in commercial formulations)
[4]. A particular feature of such TPE compounds
is that co-continuous morphologies can be obtained over a
wide composition range. According to Veenstra [5], the
elastic moduli of blends with co-continuous morphologies
are significantly higher than the moduli of the same blends
with a droplet/matrix morphology if the minor phase is the
component with the highest modulus.
Various fillers and reinforcements have been introduced
into thermoplastic elastomers to enhance processability,
permeability, mechanical and thermal properties, as well as