An Epoxy Nanocomposite System With Greatly Improved Modulus, Strength, And Toughness.

Abstract

The size and shape of α-ZrP can be controlled by altering the reaction conditions .the ion exchange capacity of α-ZrP is as much as six times higher than clay.

the surface of α-ZrP can be easily modified by various charge-carrying ionic polymers to achieve compatibilization and exfoliation of α-ZrP in various polymer matrices.

Therefore, α-ZrP particles are ideal for fundamental study of nanofiller effects, in-cluding the effects of aspect ratio, size, and size distribution of the nanofillers, on polymer nanocomposite properties.

Here, a reduced amount of monoamine- terminated polyether amine was utilized as the surface modifier to achieve exfoliation and dispersion of α-ZrP in epoxy.

Attention will be placed on studying the fracture and toughening mechanisms in both neat and core-shell rubber (CSR) modified α-ZrP based epoxy nanocomposites.

Special attention will be focused on learning how the nanofiller and their surface modifier affect the crack propagation of epoxy matrix. Approaches for achieving a balanced stiffening and toughening effect in epoxy are discussed.

Results and discussion

Tensile behavior

The tensile curves of the epoxy and epoxy nanocom-posites are shown in (Fig.)

The use of monoaminesurface modifier in DGEBA/DDS appears to improve the ductility of the epoxy matrix significantly.

As expected, α-ZrP nanofiller is effective in enhancing both the tensile strength and modulus of the M-epoxy matrix from 90 to 103 MPa and 3.1 to 4.0 GPa, re-

spectively.

The addition of CSR causes the modulus to drop from 4.0 GPa for epoxy/M-α-ZrP to 3.6 GPa for epoxy/M-α-ZrP/CSR, and from 3.1 GPa for M-epoxy to 2.6 GPa for M-epoxy/CSR.

The tensile strength is also decreased from 103 MPa for epoxy/M-α-ZrP to 93 MPa for epoxy/M-α-ZrP/CSR.

Fracture toughness measurements

Their key mechanical properties are listed in Table.

When CSR is utilized to toughen epoxy/M-α-ZrP, a significant increase in K_IC , i.e., from 0.69 to 1.64 MPa m^0.5, is observed. This dramatic increase in fracture toughness by addition of only a small amount of CSR was also observed in epoxy/clay nanocomposites

Toughening mechanisms observation

we can partially attribute the unusual toughening phenomenon to the weak interlayer strength of the intercalated a-ZrP, as evidenced by Figs.

Fig.1.TEM of the crack tip damage zone of epoxy/M-a-ZrP nanocomposite. Delaminated cavities are observed at the crack tip region.

Fig. 2. TEM of crack wake of epoxy/M-a-ZrP nanocomposite. Remnants of delaminated a-ZrP layers (see arrows) are found along the crack wake.

In this case ,this allows the deformation of the matrix prefer-entially along the intercalated M-α-ZrP.

Another interpretation is that the epoxy network is more loosely formed near the α-ZrP particles because of the local high concentration of monoamine surface modifier near α-ZrP, which leads to localized lower crosslink density around α-ZrP in the epoxy matrix.

This, then,helps compensate for the constraint of molecular mobility exerted by the α-ZrP layer structure.

Consequently, the ductility and toughenability of the epoxy/M-a-ZrP is maintained.

Conclusion

The mechanical properties and fracture behavior of synthetic α-ZrP based epoxy nanocomposites, with and without CSR toughening, were investigated. Reasonably good exfoliation and dispersion of α-ZrP was achieved in DGEBA/DDS epoxy matrix.

Exfoliated α-ZrP nanofiller can greatly improve modulus and strength, without compromising the ductility, of the epoxy matrix.

The delamination strength of the intercalated α-ZrP appears to be weak, which leads to preferential delamination, and thus, crack propagation along the

intercalated α-ZrP.

The toughening by incorporation of CSR is found to be effective in improving the K_IC of epoxy nanocomposite.

The main toughening mechanisms in epoxy/M-α-ZrP/CSR are rubber particle cavitation, followed by matrix shear banding.

The main cause for such usual improvement in toughness in epoxy/M-α-ZrP is still unclear. It may be either due to the non-uniform crosslinking of the epoxy matrix because of the presence of the monoamine surface modifier around the α-ZrP particles or due to weak delamination strength of the intercalated α-ZrP particles, or both.

Additional research is still needed to fully understand the fundamental reasons behind such an unusual mechanical behavior observed in epoxy/M-α-ZrP and epoxy/M-α-ZrP/CSR systems.

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