Chemistry Reference
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intercalated structure of undisrupted tactoids. High-speed shear mixing
combined with ultrasonication reduced the platelet tactoids toward much
smaller scales and exfoliation, which in turn provided better properties
compared to a shear mixing method alone. Compared to neat polymer, only
1 wt% of clay dispersed by ultrasonication improved the nanocomposite
tensile strength and modulus by 22 and 13%, respectively. In other words,
tensile modulus could be increased up to 34% by 6 wt% clay without any
sacrifice of strength. The T
g
was also increased by 4-6 1C depending on the
OMMT concentration.
Tan et al.
205
studied anhydride-cured ESO nanocomposites. OMMT of 1 to
5 wt% concentration was dispersed into ESO by ultrasonication. The surface
modifier, OMMT, and imidazole, co-catalyze the epoxy-anhydride curing
reaction and, with an exfoliated structure, the tensile strength of the nano-
composite was increased with OMMT loading of up to 4 wt%. The tensile
modulus, T
g
and thermal stability of the nanocomposite were also increased
but the fracture toughness and elongation-at-break were reduced due to
higher stiffness and cross-link density. In a similar anhydride-cured ESO-
clay nanocomposite system, Tanrattanakul and Saithai
112
indicated that
exfoliation was prone to occur only at low OMMT content and higher clay
concentrations led to intercalated structures with aggregations.
Miyagawa et al.
206,207
reported nanocomposites of anhydride-cured blends
of DGEBF and ELO. Clay nanoplatelets were almost completely exfoliated
and homogeneously dispersed in the epoxy network after ultrasonication
dispersion. The resulting nanocomposites showed higher storage moduli
than the neat polymer to offset a reduced storage modulus caused by re-
placement of DGEBF by ELO. However, the Izod impact strength did not
change after adding the clay, while the heat distortional temperature, and T
g
were lower due to the plasticizing effect of the modifier (OMMT). The nano-
composite was used as a matrix for carbon-fiber-reinforced polymer compos-
ites,
208
and the results indicated that the interlaminar shear strength of the
composite was improved after adding 5 wt% intercalated clay, but the exfoli-
ated clay nanoplatelets were less effective in preventing crack propagation.
More significant improvements in strength have been observed for EVO-
based nanocomposites of low T
g
. Nanocomposite tensile strength and
modulus were increased more than 300% for 8 wt% OMMT, as reported by Liu
et al.
209
TETA was used as a curing agent for ESO, and the OMMT was dis-
persed in ESO by ultrasonication to form an intercalated structure. The T
g
was
increased from 11.8 1C for the neat polymer to 20.7 1C with 5 wt% clay. Higher
OMMT concentrations led to a reduction in properties, due to clay aggregation.
Shabeer et al.
210
synthesized nanocomposites using EAS and anhydride.
Two types of dispersion technique, pneumatic and ultrasonication, were
carried out to disperse the OMMT into EAS. The nanoclay was readily
exfoliated into the resin due to a clay interaction and reaction with the
anhydride. Tensile testing showed that the OMMT improved the tensile
modulus and strength by 625% and 340%, respectively. These significant
improvements in strength were explained by a strong interaction of epoxy
