Modulating effect of Mg-Al-CO3 layered double hydroxides on the thermal stability of PVC resin

Mg-Al-CO3 layered double hydroxides (hydrotalcite-like materials) with different Mg/Al molar ratios and having small particle size and narrow size distribution have been prepared by a method involving separate nucleation and aging steps and characterized by XRD, FT-IR and TG-DTA, which clearly demonstrated that the charge density of the layers decreased with increasing Mg/Al molar ratio. Therefore, the electrostatic force of attraction between layers and interlayer counter-ions as well as the driving force for anion exchange decreased. Varying amounts of Mg-A1-CO3 layered double hydroxides with different Mg/Al molar ratio were mixed with PVC resin. Thermal aging tests of the resulting PVC composites were carried out in a thermal aging test box at 180 +/- 1 degrees C by observing the colour change of the samples. The results showed that Mg-Al-CO3 layered double hydroxide with Mg/Al=2 has the best stabilizing effect on PVC because of its higher layer charge density and consequent stronger driving force for uptake of Cl- in the interlayer galleries. Uptake of Cl- inhibits the autocatalytic dehydrochlorination of PVC which is responsible for its degradation. The optimum loading of layered double hydroxides was determined. (c) 2004 Elsevier Ltd. All rights reserved.