Investigation of the crosslink structure by using 2,3-dimethylbutene-2 (DMB
) as a model showed that 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexan (Vul
curen(R) VP KA 9188 of Bayer AG) forms novel carba-sulphane crosslinks.
The thiol-amine swelling technique for determination of crosslink density a
nd sulphur crosslink structure was used to show that Vulcuren results in sh
ort sulphur bridges in comparison with a semi-ev vulcanisation system. The
alteration of the crosslink structure and the crosslink density after overc
uring is less for the compound with Vulcuren.
The performance of the bifunctional crosslinker has been investigated in te
rms of static and dynamic properties in a carbon black-filled NR compound i
n comparison with a conventional and semi-ev vulcanisation system and also
in a silica-filled S-SBR/BR compound.
The outstanding performance of the Vulcuren-containing system can be seen b
y comparing the rheometer curves. The reversion tendency is almost nit whil
e the rheometer torque of the other reference compounds decreased considera
bly. By adjusting the sulphur level, the physical properties (tensile stren
gth, hardness, modulus, etc.) of all vulcanisates are very similar after op
timum cure. However, if the same compounds are overcured, a significant imp
rovement in the retention of physical and dynamic properties can be seen fo
r the compound containing Vulcuren. The improved compression set values ind
icate that the network alterations (S-x rupture and formation of shorter cr
osslinks or cyclisation) at high temperature are considerably less when Vul
curen is used.