Properties of poly(ethylene terephthalate)-poly(ethylene naphthalene 2,6-dicarboxylate) blends with montmorillonite clay

The production and properties of blends of poly(ethylene terephthalate) (PET) and poly(ethylene naphthalene 2,6-dicarboxylate) (PEN) with three modified clays are reported. Octadecylammonium chloride and maleic anhydride (MAH) are used to modify the surface of the montmorillonite-Na+ clay particles (clay-Na+) to produce clay-C18 and clay-MAH, respectively, before they are mixed with the PEUPEN system. The transesterification degree, hydrophobicity and the effect of the clays on the mechanical, rheological and thermal properties are analysed. The PET-PEN/clay-C18 system does not show any improvements in the mechanical properties, which is attributed to poor exfoliation. On the other hand, in the PET-PEN/clay-MAH blends, the modified clay restricts crystallization of the matrix, as evidenced in the low value of the crystallization enthalpy. The process-induced PET-PEN transesterification reaction is affected by the clay particles. Clay-ClS induces the largest proportion of naphthalate-ethylene-terephthalate (NET) blocks, as opposed to clay-Na+ which renders the lowest proportion. The clay readily incorporates in the bulk polymer, but receding contact-angle measurements reveal a small influence of the particles on the surface properties of the sample. The clay-Na+ blend shows a predominant solid-like behaviour, as evidenced by the magnitude of the storage modulus in the low-frequency range, which reflects a high entanglement density and a substantial degree of polymer-particle interactions. (c) 2005 Society of Chemical Industry.