Clay Nanocomposites formed with Polar Ethylene Copolymers for Fire Retardant Applications
Christopher Preston, Gandara Amarasinghe, Thanh Vu, Robert Shanks
CRC For Polymers
Australia

Keywords: nanocomposite, extrusion, fire-retardant

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Polyolefins generally do not form intercalated nanocomposites in the presence of a layered silicate clay as readily as polar polymers such as polyamides. This is usually attributed to the absence of a chemical driving force in the polyolefin to displace the intercalating agent, and the subsequent formation of a stable interaction with the silicate layers.

To overcome these limitations, polar side-chains grafted to the polyolefin backbone have been utilized to aid in the intercalation and exfoliation of layered clays. For example, maleated polypropylene has been used to aid in the preparation of exfoliated polypropylene nanocomposites. The use of polyolefins, containing polar comonomers, to provide the interaction, appears to have received less attention. The investigation of polyolefin nanocomposites is important as such polymer/clay hybrid materials have been found to demonstrate enhanced flame retardancy compared to the virgin polymer.

Ethylene-vinyl acetate copolymers (EVA) appear to be the most widely studied and used of this class of materials. Several other polar ethylene copolymers and terpolymers have been investigated for their performance as nanocomposite matrices. Composites of the polymers and clay have been formed by both melt- and solution-blending. Melt-blended samples were prepared on a 25 mm twin-screw extruder operating at 380 rpm with an screw configured for intensive mixing, while the solution-blended materials were prepared by mixing the polymers and clay in boiling xylene and subsequent precipitation into acetone. Analyses of the structure, mechanical properties, thermal stability, fire retardancy and crystalline melting of the prepared composites have been performed.