Crosslinking ExxonMobil Vistalon^Ò 2504 EPDM at 177°C using 11.5 phr DC40P-SP2 provides a dramatic 50% increase in ts2 scorch time protection when compared to 10.0 phr DC40KE (the standard 40% assay dicumyl peroxide). (Refer to Table 5 and Figure 4.) Furthermore, using SP2 technology with dicumyl peroxide increased the scorch time without increasing the cure time at 177°C (350°F), i.e. the tc90 cure time of 4.7 minutes remains essentially unchanged. This grade of EPDM is quite popular for injection molding applications, particularly for automotive gaskets, due to its low Mooney viscosity of 25 Mooney Units at 125°F, with an ENB of 4.7% and an ethylene content of 57.5%.

The data in Table 6 and Figure 5 shows that compounding this EPDM formulation with DC40P-SP2 at a relatively high drop-temperature of 138°C (280°F), provides an 204% increase in ts2 scorch time from 7.0 to 21.26 minutes or about ~3 times the original scorch time provided by the standard DC40KE peroxide.

In summary, using DC40P-SP2 to crosslink EPDM by injection molding provides better mold fill and a longer injection time with no change in cure time while alleviating scorch related problems of hot-tear and scrap. The longer scorch time at compounding temperatures can help to shorten mixing time by allowing use of a one-pass mixing operation or faster mixing speeds. All of these changes can improve productivity and lower the cost of production.

Table 6

Mixing EPDM with DC40P-SP2 at 138°C: 204% increase in ts2
Compounding Vistalon 2504 EPDM at 138°C
RPA: 280°F (138°C), 1°arc, 100 cpm
	10phr DC40KE	11.5 phr DC40P-SP2
ML (dN-m)	3.22	3.05
ts1 (min)	4.61	18.70
% increase in ts1	---	306%
ts2 (min)	7.00	21.26
% increase in ts2	---	204%