SYNERGY IN INTUMESCENCE - APPLICATION TO BETA-CYCLODEXTRIN CARBONIZATION AGENT INTUMESCENT ADDITIVES FOR FIRE-RETARDANT POLYETHYLENE FORMULATIONS

The study first compares the FR performances of ammonium pyrophosphate (PY)-xylitol, PY-d-sorbitol and PY-beta-cyclodextrin additives system s with the classical ammonium polyphosphate-pentaerythritol intumescen t system in low density polyethylene(LDPE)-based formulations. It show s that beta-cyclodextrin, a starch derivative, whose thermal degradati on leads to high amounts of carbonaceous residue, is not a carbon sour ce of interest in intumescent FR additives for LDPE-based formulations . A comparative study using X-ray diffraction and Raman spectroscopy s hows that the absence of the FR property may be connected both to the development of a free radical reaction in the additive system in the t emperature range corresponding to processing reactions and to the pres ence of a crystalline phase in the carbonaceous materials formed from the additive. Secondly, it is shown using the Sheffe procedure for exp eriments with mixtures that a synergistic effect exists in the ammoniu m pyrophosphate-d-sorbitol-beta-cyclodextrin system. In particular, th e method gives the corresponding composition of the additive mixture. The improved performance is explained by the formation of a large amou nt of carbonaceous residue when the formulation degrades. Moreover, th e synergistic effect is discussed as a competition between antagonisti c effects related to chemical characteristics of the char: amounts of free radical in carbon, structural organisation of the char and the pr esence of crystalline phases. (C) 1997 Elsevier Science Limited.