Changes in volume and weight of vulcanizates after
immersion in solvents and oils at room temperature
for 7 days are shown in Table VII and Figure 4, respectively.
As expected, epoxidation of NR should
increase resistance in certain solvents and oils. ENR
showed much less swelling than NR in petroleum
ether (L2), engine oil (O2), gear oil (O3), ASTM oil
(O4), and motor oil (O5). The degree of epoxidation
must be high enough to decrease swelling in toluene
(L1). It is established that 50 mol % epoxidation
could lead to oil resistance equal to that of NBR. ENR
was inferior to NR in DMF (L3) and brake fluid (O1).
Our results coincided with data reported by Gelling,4
although more severe testing conditions were used.
The vulcanizates were immersed in oils at 70°C for 7
days. Changes in volume and weight are displayed in
Figure 5. Epoxidation improves oil resistance in all
oils, except in brake fluid. So far, it has been shown
that the in situ epoxidation of NR improves resistance
to hydrocarbon oils, whereas the reverse is true for
more polar liquids such as break fluid (O1).