Among all the toughening fillers, rubber-like materials [1],
especially rubber particles, have shown the highest ability in
toughening epoxy due to their capability of cavitation leading to
large matrix shear yielding [2]. However, even if the resin shows
excellent properties in bulk form, it may behave differently in
laminated composites. Hence, even though the toughening effect of
either liquid rubber or coreeshell rubber to neat epoxy is significant,
their enhanced toughness cannot be fully transferred to the
interlaminar fracture toughness of the carbon fiber reinforced
laminates when used as toughened matrices [3]. It is suggested that
the stiff carbon fibers can restrict the deformation capacities of
rubber modified epoxy matrices, thus reducing their high toughening
effect.
Generally, epoxies with smaller size fillers have higher toughness
than those with larger size fillers [4e6]. In recent years, we
have conducted a systematic study on toughening of bulk epoxy
using nano-sized rubber particles [7]. The fracture energy, GIC, of
these nano-rubber modified epoxies increases with increasing
particle loading. Further, sub-micron coreeshell rubber (CSR) particles
are more efficient than micron-sized liquid rubber (LR) particles
[3] in transferring the toughness from the modified epoxy
matrix to the composite laminate. In our recent work [8], the
toughening effect of nano-rubber on epoxy/carbon fiber laminates
was also studied. Two main points arose from the results obtained