Phosphorus Flame Retardants from Crop Plant Phenolic Acids

While polymeric materials have had an enormously positive impact on the development of modern society, for most applications they must be flame retarded. This may be accomplished in a variety of ways, most notably by introduction of a suitable additive during processing. Traditionally, organohalogen compounds, particularly brominated aromatics, have been effective, affordable, popular gas-phase flame retardants. However, these compounds readily migrate from a polymer matrix into which they have been incorporated, persist in the environment, tend to bioaccumulate and may pose risks to human health. For this reason, the use of these compounds is coming under increasing regulatory pressure worldwide. Phosphorus compounds derived from renewable biosources provide attractive alternatives to these traditional organophophorus flame retardants and are generally nontoxic and readily available at modest cost. Phenolics are ubiquitous in nature and may be isolated from numerous plants. Gallic acid (3,4,5-trihydroxybenzoic acid) is a constituent of many edible plants, nuts and legumes. 3,5-Dihydroxybenzoic acid may be found in several plants, principally buckwheat. Both of these compounds may serve as the base for the generation of a series of phosphorus esters, both phosphonate and phosphate, that display good flame retardancy in DGEBA (diglycidyl ether of bisphenol A) epoxy.