Intercalation of epoxy resin in organically modified montmorillonite

Abstract

Various methods of preparation of epoxy resin/clay mixtures, before the addition of the crosslinking agent and curing to form epoxy-based polymer layered silicate (PLS) nanocomposites, have been investigated to determine their effect on the nanostructure. Organically modified montmorillonite clay was used, and the mixtures were prepared by both simple mixing and solvent-based methods. X-ray diffraction shows that intercalation of the resin into the clay galleries occurs for all clay loadings up to 25 wt % and for both preparation methods, but the dispersion of the clay in the resin, observed by optical microscopy, is significantly better for the solvent preparation method. Differential scanning calorimetry (DSC) shows that the intercalated resin has the same molecular mobility as the extra-gallery resin, but suggests that the intercalated resin does not penetrate completely into the galleries. Prolonged storage of the resin/clay mixtures at room temperature leads to changes in the DSC response, as well as in the response to thermogravimetry, which are interpreted as resulting from homopolymerization of the epoxy resin, catalyzed by the onium ion in the modified clay. This confirms and explains the earlier observation of Benson Tolle and Anderson (J Appl Polym Sci 2004, 91, 89) that ''conditioning'' of the resin/clay mixtures at ambient temperature has a significant effect when the crosslinking agent is subsequently added, and indicates that the preparation method has important consequences for the nanostructure development in the PLS nanocomposites.

Identification of nanostructural development in epoxy polymer layered silicate nanocomposites from the interpretation of differential scanning calorimetry and dielectric spectroscopy

“…Small angle X-ray scattering (SAXS) gives clear evidence that the resin penetrates into the clay galleries, the d-spacing increasing from about 2.1 nm for the organically modified clay to about 3.7 nm when the epoxy resin is intercalated, essentially independent of the clay content [18]. On the other hand, the dispersion does depend on the clay content.…”

“…In the case of the epoxy resin alone, the homopolymerisation reaction appears at temperatures over 400 • C and is produced thermally [19]. In the sample with epoxy resin and MMT (EM2), the homopolymerisation reaction occurs around 250 • C, and is attributed to the catalytic effect of the organically modified clay [18]. And finally, in the sample EDM2 the homopolymerisation reaction can be seen to take place at even lower temperatures as a consequence of the effect of the anionic initiator, DMAP.…”

The application of thermal analysis to the study of epoxy–clay nanocomposites

“…4(a) allow an estimate to be made of the proportion of resin that is within the clay galleries. This analysis has been made previously [18], and from a comparison with what would be expected from the d-spacing determined by SAXS it was concluded that the epoxy resin does not penetrate fully into the clay galleries. Indeed, it was estimated that it penetrates only to about one third of the distance towards the centre of the clay particles, which would have important consequences for the subsequent curing and exfoliation process.…”

“…This effect is conventionally measured by SAXS, and the d-spacing is found to increase from 2.1 nm for the organically modified MMT alone to about 3.5-3.9 nm when the epoxy has intercalated into the clay galleries. This intercalated spacing is essentially independent of the clay loading and of the mixing method, be it hand mixing, mechanical mixing, high shear mixing or solvent mixing [18].…”

Property enhancement of epoxy resins by using a combination of polyamide and montmorillonite

“…18 They showed that the intercalated epoxy resin does not penetrate completely into the clay galleries. Their results are in agreement with those of Tolle and Anderson, who showed that preconditioning processes have a significant effect on the exfoliation of the silicate filler, which in turn produced a small improvement in toughness.…”