Viscoelastic Properties of Polystyrene Nanocomposites Based on Layered Silicates

Abstract

AbstractNanocomposites based on polystyrene (PS) and organophilic layered silicates (organoclays) were prepared and characterised with respect to their morphological and rheological properties. The organoclays were obtained by means of ion exchange of clay with protonated, amine‐terminated PS. Two different exchange agents – a high (Mw = 5 800 g/mol) molecular mass amine functionalised PS, and 2‐phenylethylamine – were used to study the influence of their molecular weight on morphological and rheological properties of corresponding composites. Wide‐angle X‐ray scattering measurements show a significant increase in the interlayer spacing upon the ion exchange. Composites of organoclay prepared from the high molecular mass amine‐terminated PS and PS‐matrix polymer reveal a fine and stable dispersion of exfoliated silicate layers in the PS matrix if the compounding time in a conical twin screw extruder exceeds 180 s at a temperature of 200 °C. This composite, i.e. nanocomposite, shows unique elastic properties which can be understood quantitatively if one assumes that above a characteristic concentration of about 1 vol.‐% percolating strands of platelets are present in the material. Composites of PS and organoclay prepared from 2‐phenylethylamine did not exfoliate and consequently exhibited the rheological behaviour of a conventional composite. Qualitatively all morphological and rheological features of the PS nanocomposite can be entirely understood if one considers this material as a mixture of hairy platelets dispersed in an entangled PS matrix. “Hairy platelets” model for exfoliation of layered silicates.magnified image“Hairy platelets” model for exfoliation of layered silicates.