Morphology and Mechanical Behavior of Exfoliated Epoxy/α-Zirconium Phosphate Nanocomposites

Abstract

The morphology and mechanical properties of synthetic α-zirconium phosphate (α-ZrP) based epoxy nanocomposites with 1 and 2 vol% of α-ZrP loadings were investigated. The state of exfoliation and dispersion were confirmed by X-ray diffraction and direct transmission electron microscopy imaging at various locations in the samples.

Significant improvements in tensile modulus and tensile strength were observed. It is found that the fracture toughness values of the exfoliated epoxy nanocomposite systems are comparable to that of the neat epoxy.

Detailed fracture mechanisms investigation indicates that no sign of crack deflection or nanoplatelet debonding is observed. Only a straight crack path is present. The nanoplatelets are broken into two halves as the crack propagates through them, indicating an existence of strong bonding between the nanoplatelet and epoxy matrix.

Preparation of α-ZrP based epoxy nanocomposites

The interlayer spacing of ZrP crystal prior to surface treatment is 7.6Å. The addition of amine –based sureface modiflier at 0.75:1 molar ratio through dropwise mixing at room temperature expands the interlayer spacing of ZrP to 34Å(i.e.,S-ZrP). The intercalated ZrP was mixed with epoxy monomer(epoxy/S-ZrP) to achieve a finally inorganic ZrP loading of 1 and 2 vol% in epoxy,respectively.

After removal of solvent with a Rotarvapor in a water bath at about 70℃,DDS was added at stoichiometric ratio. The resin mixture was cats in a preheated glass mold and cured in an oven at 180℃ for 2h, followed by 2h of post –cure at 220℃. For comparsion purposes,a neat epoxy plaque(neat epoxy), an epoxy plaque with only surface modifier addition (S-epoxy), and an epoxy panel with 1 and 2 vol% of ZrP without surface treatment (epoxy /ZrP) were also prepared(Table 1)

Results and discussion

1. Morphology characterization

2. A simple geometric model

3. Mechanical property characterization

4. Fracture behavior

Conclusion

A high degree of exfoliation of ZrP nanolayers in an epoxy matrix was achieved and the morphology of epoxy/S-ZrP nanocomposites investigated.
The exfoliated epoxy/S-ZrP nanocmposite with 2 vol% of ZrP exhibits an ordered orientation due to geometric confinement of the surrounding ZrP nanoplatelets. This phenomenon is not observed in the nanocomposite with only 1 vol% of ZrP loading .

The interlayer d-spacing of 2 vol% of ZrP layers in epoxy matrix observed in TEM is in good agreement with that calculated from a simple geometric model. An addition of a small amount of rigid nanoplatelets into epoxy matrices can significantly improve tensile modulus of epoxy.

Upon fracture, the crack propagates in a straight manner in the exfoliated epoxy nanocomposite because the exfoliated nanoplatelets. Do not lead to significant crack tip blunting and /or crack deflection. Consequently, the fracture toughness of the exfoliated epoxy nanocomposite remains the same as that of neat epoxy system.

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