Thermal analysis of polymer layered silicate nanocomposites. Identification of nanostructure development by DSC

Abstract

It has been shown, for three different polymer layered silicate (PLS) nanocomposite systems, how differential scanning calorimetry (DSC) can identify the different reactions of homopolymerisation and of crosslinking that occur in the intra- and extra-gallery regions of these nanocomposites, respectively, and hence how DSC can be used to assess the cure conditions for optimising their nanostructure. The PLS nanocomposites are based upon: (i) diglycidyl ether of bisphenol-A (DGEBA) cured with a polyoxypropylene diamine; (ii) DGEBA cured with an -NH2 terminated hyperbranched polymer (HBP); and (iii) tri-glycidyl p-amino phenol (TGAP) cured with a diamine. In each case, the existence of both intra- and extra-gallery reactions in the DSC cure curves, and whether they occur simultaneously or sequentially, and in what order, are identified and correlated with the nanostructure as observed by small angle X-ray scattering and transmission electron microscopy. In particular, it is shown that the intra-gallery reaction must precede the extra-gallery for significant exfoliation to occur. In accordance with this scenario, the TGAP/diamine system displays the greatest degree of exfoliation, the DGEBA/diamine system the least, with the DGEBA/HBP system intermediate. For those systems in which significant exfoliation occurs, the DSC cure curves also allow the optimum cure conditions, such as the isothermal cure temperature, to be determined.