Heat stabilising flexible PVC with layered double hydroxide derivatives

The layered double hydroxide ([Mg0.667Al0.333(OH)2](CO3)0.167·mH2O) (LDH) has found application as a heat stabiliser for PVC. Derivatives of this compound were synthesised using a hydrothermal method. Emulsion grade PVC was plasticised with 100 phr diisononyl phthalate and stabilised with 30 phr of the LDH filler additives. Heat stabilities were determined at 200 °C. The dynamic heat stability tests were performed on the plastisols using the torque rheometer method. Static heat stability was evaluated on the fused compounds. It was evaluated from discoloration profiles of strips exposed for various lengths of time to heat in a Metrastat oven. The time dependence of hydrogen chloride evolution was followed with a Metrohm Thermomat instrument. The conventional LDH provided the best dynamic heat stability. However, partial replacement of the magnesium with copper significantly delayed the release of volatile HCl. If instead the replacement was done using zinc, better colour retention was achieved.