Thermal properties of charring plasticizers from the biobased alcohols, pentaerythritol and 3,5-dihydroxybenzoic acid

To be converted into a useful commercial material, poly(vinyl chloride) (PVC) must generally be heavily plasticized. Owing to its high level of chlorine, PVC is not flammable (limiting oxygen index of 45). However, addition of a plasticizer usually imparts appreciable flammability. The plasticizer is often volatilized from the polymer when it is exposed to heat. In general, plasticizers burn readily and may be the source of the flammability of formulated polymers. This flammability might be controlled by using effective plasticizers that promote char formation at the surface of the burning polymer. Two series of charring compounds, pentaerythritol esters containing aromatic moieties and phosphorus esters of 3,5-dihydroxybenzoates, have been demonstrated to be effective plasticizers for PVC. The thermal degradation of both series of compounds has been examined using thermogravimetry and infrared spectroscopy. For both sets of esters, elimination of an acid is a major degradation process. For the degradation of pentaerythritol esters, a carboxylic acid is a primary degradation product. For the alkyl 3,5-(diphenylphosphato)benzoates, degradation may lead to the formation of either a carbon or a phosphorus acid depending on structure.