Thermal Stability of Poly (vinyl chloride) Formulations Containing Iron Additives as a Replacement for Antimony Oxide

Poly (vinyl chloride) [PVC] is a widely used commodity polymer with particular application for wire and cable coating, and for pipe and profile extrusion. For processing, PVC must be heavily plasticized. In addition, a number of other additives are usually introduced to promote thermal stability, to enhance processability and to inhibit flammability. Antimony oxide is often used in PVC formulations. However, the growing concern about the negative health and environmental impacts of antimony oxide has stimulated efforts to find suitable replacements. Iron compounds have been examined as suitable replacements for antimony oxide. PVC formulations containing 45 phr of Pevalen plasticizer, 50 phr of magnesium hydroxide and 2 or 10 phr of an iron additive were processed using a two-roll mill at 180°C. The thermal degradation and flammability of these materials have been evaluated utilizing thermogravimetry (TGA) and limiting oxygen index (LOI) measurements. All of the iron additives are effective in increasing LOI for combustion of the blends and in promoting char formation. The impact of the presence of all the iron additives is comparable and independent of the oxidation level of iron. Based on considerations of cost and availability, simple iron oxide may be the additive of choice. Keywords: PVC additives; Antimony oxide replacements; Combustibility of formulated PVC; Impact of additives on the thermal stability of PVC;