Modified Lignocellulosic Materials as Intumescing Flame Retardants in Bio-Based Polymers
Douglas M. Fox, Department of Chemistry, American University
Date: Tuesday , June 26, 2012
Time: 10:30 AM
Place: NIST, Bldg. 224, Rm. B245
In recent years, intumescing flame retardants (IFRs) have found increased attention, in part because they have relatively low toxicities and low smoke emissions. However, the formulations are somewhat hydrophilic and can leach out of the polymer over time. In addition, they usually lead to undesirable mechanical and viscoelastic properties of the polymer, such as reduced toughness and melt viscosity. In an effort to address these issues, we have begun examining the use of lignocellulosic materials as flame retardant components in bio-based polymers. This has the additional benefit of increasing the sustainability of the flame retardants used.
Initial studies examined the use of cellulose as a replacement for pentaerythritol in ammonium polyphosphate based IFRs for poly(lactic acid). The cellulose was modified with a Phenyl POSS compound to increase char and improve the flammability characteristics of the composite. Combustion and dynamic mechanical analysis studies indicated that this approach was as effective as conventional IFRs, while simultaneously increasing the stiffness and oxidative thermal stability of the composite. Current studies examine modification of the cellulose with phosphoric acid to reduce or eliminate the need for ammonium polyphosphate. We have also examined the use of lignosulfonates as IFRs in a standard diamine cured epoxy resin. Cone calorimetry and gasification studies indicate good char formation and reduced heat release rates, but poor compatibility with the epoxy. We are currently examining the use of epoxy resins derived from natural materials to potentially improve compatibility and sustainability at the same time. To examine the dispersion and interface of the lignocellulosic materials in the polymer matrixes, we have utilized fluorescent tags and a Forster Resonance Energy Transfer (FRET) approach. The latest developments in identifying a thermally stable FRET donor/acceptor couple for use in melt blending will be discussed.