A
similar trend was also observed with flexural strength and modulus
(Fig. 3b). This may be due to the increase in the relative
amount of dissolved rubber as rubber content increases. The
percent elongation-at-break of the blend samples increased continuously
with CTBN content in the blend (Fig. 3a). The flexural
strength and flexural modulus of modified resins decrease with
increasing rubber concentration (refer Fig. 3b), compared with
that of the neat epoxy. This might be due to the increase in the
relative amount of dissolved rubber as rubber content increased.
The formulation with 20 phr of CTBN showed greater impact
strength, which meant that it likely absorbed greater impact energies.
Fig. 3c depicts the variation of impact strength as a function
of the elastomer concentration. The area under the stress–strain
curves, which is a measure of toughness, was moderately higher
for the modified epoxy sample EPC15 having 15 phr of rubber.
The results of the mechanical properties indicated that the
cured resin containing CTBN ranging in between 15 and 20 phr
showed the best balance of properties.