Some comments on the modes of action of nanocomposites in the flame retardancy of polymers

• Published in: Fire and materials Vol. 27; no. 1; pp. 1 - 7
• Main Author: Lewin, Menachem
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.01.2003; Wiley
• Subjects: Applied sciences; Building technical equipments; Buildings; Buildings. Public works; clay; Exact sciences and technology; Fire behavior of materials and structures; Fire protection; flame retardancy; Materials; montmorillonite; nanocomposite; Plastics; quaternary ammonium compound; surface free energy; Clay; Pyrolysis; Montmorillonite; Mechanism analysis; Flame retardant; Polymer; Combustion; Free surface; Experimental study; Fire protection; Quaternary ammonium compound; Nanocomposite; Surface energy
• ISSN: 0308-0501; 1099-1018
• DOI: 10.1002/fam.813

Nanocomposites of polymers with montmorillonite (MMT) yield upon pyrolysis and combustion an MMT‐rich surface of the char. The prevalent approach considers this accumulation as due to the gasification of the polymer and subsequent gradual precipitation of the MMT on the surface. According to the present paper, the enrichment in MMT is postulated to be due to a migration or convection of the MMT to the surface driven mainly by the lower surface free energy of the MMT. The role of the surface free energy in the surface structure of polymer blends, especially those involving a silicon‐containing component, is discussed. The enrichment occurs above the glass transition temperature and is temperature dependent. XPS evidence for the accumulation of MMT on the surface of a polystyrene/MMT nanocomposite is reviewed. Its dependence on the stability of the nanocomposite structure, and particularly on the stability of the quaternary ammonium compounds that bind the polymer to the MMT, is pointed out. The importance of the surface free energy in the flame retardancy of polymer blends as well as polymer‐additive mixtures is discussed. Copyright © 2003 John Wiley & Sons, Ltd.