Flammability of Polymer Clay Nanocomposites Consortium:Final Report

Published

April 4, 2005

Author(s)

Jeffrey W. Gilman, Takashi Kashiwagi, A B. Morgan, Rick D. Davis, Richard H. Harris Jr., L D. Brassell

Abstract

In 1997 NIST reported that polymer layered-silicate (clay) nanocomposites exhibit reduced flammability, in the form of reduced heat release rate (HRR). The unique character of this new approach to flame retard polymeric materials was the dual benefit of reduced flammability and improved physical properties. However, the details of the fire retardant (FR) mechanism were not well understood. The potential this new flame retardant approach offered motivated the formation, in October of 1998, of a NIST led consortium to study the flammability mechanism of these materials. This report covers the research results of the second year of the program. The goals for the second year were: 1) to develop an understanding of the formation of the clay-reinforced carbonaceous char, and 2) to explore synergistic, co-additive, flame retardants: with the objective of further reducing the flammability of the nanocomposites. The results of experiments aimed at determining the nature of the char which forms during burning of PS/ MMT nanocomposites revealed that the char is comprised of clay and two types of carbon. Transmission electron microscopy (TEM) and x-ray diffraction (XRD) revealed that the clay and carbon form large multi-layer stacks with clay inter gallery spacings of 1.3 nm. The ratio of clay to carbon is 1:1. The two types of carbon differ in their thermal stability. The more prevalent type has a peak Tdec in air of 372.0 oC 3.8 oC and the more stable carbon has a peak Tdec of 546.0 oC 10.7 oC. The ratio of carbon types is 3:1. The results of experiments aimed at evaluating synergistic, co-additive flame retardants indicated that several additives enhance the flame retardant effect of nanocomposites. A melamine-MMT was found to be the best in terms of lowering the heat release rate and increasing the ignition time in PA-6 nanocomposites. In polypropylene (PP) nanocomposites synthetic mica formulations were found more effective at reducing the mass loss rate than MMT and synthetic fluoro-hectorite. The addition of Mg(OH)2 was found to further lower the peak MLR and to delay the initial MLR when combined with synthetic mica in PP nanocomposites. Similar effects were found when combining MMT, Al(OH)3 in poly(ethylene-co-vinyl acetate) (EVA) nanocomposites.

Citation

Special Publication (NIST SP) -

NIST Pub Series

Special Publication (NIST SP)

Pub Type

NIST Pubs

Keywords

char, clay, gasification, heat release rate, nanocomposites

Citation

Gilman, J. , Kashiwagi, T. , Morgan, A. , Davis, R. , Harris, R. and Brassell, L. (2005), Flammability of Polymer Clay Nanocomposites Consortium:Final Report, Special Publication (NIST SP), National Institute of Standards and Technology, Gaithersburg, MD (Accessed April 16, 2024)