Synthesis and use of hydrotalcites as heat stabilisers in thermally produced polyvinylchloride polymeric products

Lead-based stabilisers, such as lead sulphate and lead stearate, currently used in the processing of polyvinylchloride (PVC) products are being substituted with more environmentally safe, economically viable and higher quality materials. This study aimed to use hydrotalcites (HTs), which are environmentally non-hazardous and simple to synthesise, to effectively quench the HCl gas evolved during the degradation of PVC. From the results obtained in this study, the effects of varying the metal ion ratios in Mg/Zn/Al-HTs showed many similarities with some variations. The synthesised Mg/Al-HTs, viz. Mg4Al2(OH)12CO3.3H2O and Mg6Al2(OH)16CO3.4H2O, displayed the most superior stability properties, with the latter being the best PVC stabiliser, over the other HTs synthesised. The most important test conducted in this study, demonstrated the synthesised HTs ability to quench the HCl gas evolved as a result of dehydrochlorination, which occurs during the processing of PVC to useful polymeric products. Results from this study also confirmed that approximately 0.2 g of synthesised Mg/Al-HTs adsorbed 0.2 mol of the HCl gas evolved, thus most effectively delayed the onset of degradation of powdered PVC (~10 g) than other HTs synthesised, including the non-stabilised PVC. It is thus evident that Mg/Al-HTs can function as effective heat stabilisers during the processing of PVC, with the potential of inhibiting the degradation of PVC, especially during the evolution of HCl gas.