2. Experimental
2.1. Materials
The polymers used in the present work were ethylene–
propylene–diene terpolymer rubber (Keltanw P597; DSM
Elastomers B.V.; 63 wt% ethylene, 4.5 wt% 5-ethylidene-2-
norbornene (ENB) termonomer), extended with 50 wt% (100
parts per hundred rubber) of paraffinic oil; and a styrene–
ethylene–butylene based tri-block copolymer (KratonwG 1651;
KratonePolymers), with a styrene to rubber ratio of 32:68 wt%.
The PP (Stamylanw P11E10; Sabic Polypropylenes B.V.) was
an extrusion grade with a melt flow index at 230 8C, 2.16 kg of
0.3 g/10 min. The oil used was a paraffinic mineral oil
Sunparw150 containing paraffinic and naphthenic hydrocarbons.
For the EPDM formulation a phenolic resin, Schenectady
SPw 1045 was used as curing agent along with stannous chloride
dihydrate (SnCl2$2H2O; Merck) as catalyst and zinc oxide
(rubber grade; Merck) as acid scavenger. Additionally,
stabilizers Irganoxw 1076 (primary phenolic type antioxidant;
Ciba Geigy) and Irgafosw 168 (secondary phosphite type
antioxidant, Ciba Geigy) were used.
2.2. Melt blending
Ternary blends with a composition of EPDM-or SEBSrubber/
PP/oil were prepared using a Brabender Plasticorder
type 350S with a mixer chamber volume of 390 ml and fitted
with Banbury type rotors. Mixing was carried out at 180 8C at a
rotor speed of 80 rpm. The mixing time was 12 min for TPVs
and 20 min for the SEBS/PP/oil blends.
2.3. Compression moulding
After mixing the materials were compression moulded at
200 8C for 3 min under a pressure of 10 MPa and then cooled
under pressure to about 30 8C. The moulded sheet thickness
was about 2 mm. The sheets were punched into dumbells (ISO-
37, type 2) for tensile measurements.
2.4. Sample preparation and electron microscopy
After compression moulding small samples were taken for
electron microscopic examination. Sample preparations for the
different microscopic techniques used in this work are
described below.
2.4.1. SEM preparations
Samples for SEM were microtomed at K130 8C using a
diamond knife mounted on a Leica Ultramicrotome. The
samples were then fixed, using a double-sided sticky tape, on a
specimen stub. In order to increase the electron density contrast
between the rubber and the PP phase, the samples were vapour
stained for 30 min using a 1% solution of ruthenium tetraoxide.
Conductive paints such as carbon suspensions were dabbed
onto the tape and base of the specimen to provide contact with
the specimen stub. The samples were then coated with a thin
layer of gold. The coating was applied in order to provide an
electrically conductive layer, to suppress surface charges, to
minimize radiation damage and to increase electron emission
during SEM. The SEM experiments were performed on a
Hitachi S800 scanning electron microscope at an operating
voltage of 6 keV.
2.4.2. LVSEM preparations
The LVSEM experiments were done using a Leo 1500
scanning electron microscope at an operating voltage of 1 keV.