(59e) Comparing the Toughening Effects of Modified Graphene Oxide and Core-Shell Rubber on Polyester Resins and Glass Fiber-Reinforced Polyester Composites

This paper investigates the translation of fracture
toughness of polyester resins to the mode I interlaminar fracture toughness of
polyester/glass fiber composites. An unsaturated polyester resin (UPR) and a vinyl
ester resin (VER) were toughened by two very distinctive methods: (1)
incorporating a very low loading (0.04 wt%) of alkyl or vinyl modified graphene oxide (mGO); or (2) adding 5
wt% of core-shell rubber (CSR). Glass fiber
reinforced composites (GFRPs) were fabricated using the toughened resins as the
matrix and various types of fiber mat as reinforcements. Results from compact
tension tests revealed that 0.04 wt% loading of mGO increased the fracture toughness (G_{IC_Resin})
of UPR and VER by as much as 49% and 31%, respectively, without lowering the
modulus and glass transition temperature (T_g).
On the other hand, CSR is a more effective toughener, though at much higher
loading. CSR enhanced the G_{IC_Resin} of UPR and VER by 375% and 600%,
respectively, with a slight decrease in flexural properties and T_g. Flexural properties and mode I interlaminar
fracture toughness (G_{IC_Comp}) of the GFRPs were evaluated. The
incorporation of mGO and CSR did not alter the
flexural properties of the GFRPs, regardless of resin type and fiber
architecture. CSR was not able to increase the G_{IC_Comp}of UPR
laminates; however, CSR increased the G_{IC_Comp} of
VER laminates by 33%. The observed toughening effects do not translate directly
from resin to GFRPs  (i.e. a 600% increase in G_{IC_Resin}of VER by
5 wt% of CSR led to only a 33% enhancement in G_{IC_Comp}). Scanning
electron microscopy of the fractured specimens revealed a weak fiber-matrix
bonding for all GFRP specimens. During the interlaminar fracture toughness
test, the cracks preferentially propagated through the relatively weak
fiber-matrix interface; therefore, the matrix toughening effect provided by mGO or CSR was significantly diminished in the
polyester/glass fiber composites.