often added as a softener and processing aid, obtaining good
microscopic images becomes very difficult.
Soft rubber–plastic blends, especially those based on PP as
the plastic, are quite common thermoplastic elastomer
materials [2]. Compounds of these blends are very popular
materials for soft-touch applications such as grips on tools,
sports goods, automotive and medical, because the properties
of the rubber and the PP phase can be easily tailored into a
single product. Understanding the structure–property relationship
in these materials is vital for making blends with tailored
properties. Studies into these relationships are, however, rather
limited, because visualising the blend morphology in these
systems has turned out to be rather difficult.
The present paper gives a relative comparison of different
microscopic methods that can be used to identify the
morphology of highly oil-extended thermoplastic elastomer
(TPE) blends based on a soft rubber phase and isotactic
polypropylene (PP). TPE blends of two different rubbers with
PP were selected for this study. One of them was a dynamically
vulcanized blend of ethylene–propylene–diene rubber (EPDM)
and PP, and the other one was a blend of styrene–ethylene–
butylene–styrene rubber (SEBS) and PP. Dynamic vulcanization
implies cross-linking the EPDM phase during the process
of melt mixing with PP and the resulting dynamically
vulcanized EPDM/PP blends are also referred as thermoplastic
vulcanizates (TPVs) [2]. To address the problem of identifying
the morphology in case of high loading of rubber along with
high loading of oil, all the compositions selected for this study
had rubber contents larger than 80 wt% and oil contents higher
than 100 wt% with respect to PP. In an attempt to visualise the
3D morphology, electron tomography was carried out on these
blends and models of the 3D morphology were constructed.
Details of electron tomography principles are given in Refs.
[3,4] and its application to polymers including thermoplastic
elastomer blends are reported in Refs. [5–7].