. The general trend is increase of storage modulus
with increase in peroxide content with exception of sample
0.7 and temperatures above 180 C.
storage modulus
Fig. 11. Storage modulus from DMA as a function of peroxide content
measured at various temperatures.
Fig. 9 illustrates the dependence of gel content on peroxide
content of the cross-linked samples. It can be seen
and samples with 0.2 and 0.3 wt.% of peroxide. While the
pure EOC survived the DMA test only till 80 C the sample
with 0.3 wt.% of peroxide ran till 160 C. Even though the
network was not fully created there is a big change in
the storage modulus curve. The 0.4–0.6 wt.% of peroxide
curves have very similar trend and they are close to each
other; just there is a small increase with increase in peroxide
level. 0.7 curve has highest value of storage modulus
till 180 C, then it is rapidly decreasing and has lower value
than the 0.6 curve. In the 180–200 C temperature range
the degradation of 0.7 samples is decreasing the mechanical
properties. The effect of peroxide content on storage
modulus at various temperatures is very nicely visible on
Fi
9 illustrates the dependence of gel content on peroxide
content of the cross-linked samples. It can be seen
that as the peroxide content increases, gel content also increases
with an exception in the case of 0.2 and 0.3 wt.% of
peroxide. In the case of 0.2 and 0.3, there was no insoluble
fraction left out after extracting with xylene, which implies
that the cross-linking reaction lead only to longer molecules
but the network was not created. There is a sharp increase
(0–54%) in gel content from 0.3 to 0.4 wt.% of
peroxide. Then, in the case of 0.5, 0.6 and 0.7, gel content
gradually increases with increasing peroxide content. Increase
in gel content is due to increase in cross-link network
and thus cross-link density
Fig. 10 shows storage modulus as a function of temperature.
While for samples with 0.2 and 0.3 wt.% of peroxide
the gel content was zero (no difference from pure EOC), the
DMA analysis revealed big difference between pure EOC
and samples with 0.2 and 0.3 wt.% of peroxide. While the
pure EOC survived the DMA test only till 80 C the sample
with 0.3 wt.% of peroxide ran till 160 C. Even though the
network was not fully created there is a big change in
the storage modulus curve. The 0.4–0.6 wt.% of peroxide
curves have very similar trend and they are close to each
other; just there is a small increase with increase in peroxide
level. 0.7 curve has highest value of storage modulus
till 180 C, then it is rapidly decreasing and has lower value
than the 0.6 curve. In the 180–200 C temperature range
the degradation of 0.7 samples is decreasing the mechanical
properties. The effect of peroxide content on storage
modulus at various temperatures is very nicely visible on
Fi
Fig. 11. The general trend is increase of storage modulus
with increase in peroxide content with exception of sample
0.7 and temperatures above 180 C.
Fig. 14 depicts the creep compliance behavior of crosslinked
EOC samples at 150 C and 0.05 MPa stress level. As
we can see from the figure, elongation and thus creep reduces
as the peroxide content increases. Or, in other words
cross-linking and thus strength of the samples increases
when the peroxide level increases. This data are in good
agreement with earlier shown RPA results.
5. Conclusions
EOC can be effectively cross-linked by dicumyl peroxide.
The maximum modulus values were found for
0.7 wt.% of peroxide content cross-linked at 150 C for
150 min. Higher temperatures speed up the process at the
cost of lower modulus. The lowest tand values were found
also for this 0.7 wt.% of peroxide content cross-linked in
150–170 C temperature range. Cross-linking study followed
by Arrhenius equation treatment and activation energy
evaluation suggested an optimum peroxide level
being in 0.5–0.6 wt.% range. The highest cross-linking rate
was found for 0.6% of peroxide at 200 C. At higher peroxide
levels (starting at 0.7 wt.%) the degradation affects seriously
the crosslinking especially at higher temperatures
(180–200 C). This fact is again proven by the storage modulus
and tand results obtained by the DMA. Gel content
which has shown an increasing trend with increase in peroxide
content is due to the increased cross-link network.
Creep test results at 150 C also support the claim that increase
in modulus and gel content is caused by increase in
peroxide level.
Ac