Non Halogenated Flame Retardants from Readily Available, Non Toxic Biosources
Summary
Organohalogen flame retardants have long been preferred by the polymer industry. In particular, brominated diphenyl ethers have been prominent flame retardants. They can be readily prepared from byproducts of phenol production. As a consequence, they are widely available at modest cost. More importantly, they are effective gas-phase-active flame retardants and may be used at levels below that which would lead to significant changes in the properties of a polymer matrix into which they have been incorporated. However, despite the attractiveness of these materials, it has been increasingly recognized that their use may impose severe negative consequences. At high temperature, as in a fire, these compounds are converted to volatile, very toxic dioxans and furans. They may also migrate from a polymer matrix and enter the environment in which the polymer or fabricated item is used. More importantly, they migrate from items discarded in a landfill and enter the natural environment where they are stable, persist, bioaccumulate and may ultimately enter the human food chain. Human exposure to these materials may lead to a number of disease states, most arising from endocrine disruption. Consequently, the use of these compounds is under increasing societal and regulatory pressure worldwide. Some have been banned from use and others removed from the market voluntarily. Suitable alternatives are being rapidly developed. In the main, these have been organophosphorus compounds. Those derived from readily-available, inexpensive and nontoxic biomaterial precursors are particularly attractive. Effective organophosphorus flame retardants have been prepared using a variety of biobased precursors. Perhaps most notable are those generated from isosorbide, gallic acid or hyperbranched glycerol/adipic acid poly(ester)s, readily available, in a single step, from two nontoxic biomonomers. Using the Martin-Smith statistical approach for the selection of appropriate monomer ratios, hyperbranched poly(ester)s of precise molecular weight, structure, and endgroup functionality may be produced. Because of the hyperbranched structure these materials function as effective plasticizers and may be endcapped with a variety of phosphorus moieties to generate either solid-phase active or gas-phase-active flame retardants compatible with a range of polymer matricies.
About the Speaker
Bob A. Howell is professor emeritus of organic chemistry/polymer science at Central Michigan University. He has over thirty years of experience in the area of polymers and polymer additives. Research interests include the use of hyperbranched poly(ester)s for the release of active agents, structural stability of styrene polymers, PVC formulation/stabilization, nitroxylmediated radical polymerization, and thermal methods of analysis/kinetics. A current major focus is the development of nontoxic, biodegradable, environmentally-friendly flame retardants based on renewable biomaterials.
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