Effect of some thermally unstable magnesium compounds on the yield of char formed from poly(ethylene terephthalate)

Mixtures of poly(ethylene terephthalate) (PET) with magnesium compounds including carbonate, hydroxide, and oxide, with different weight ratios of the components, were subjected to thermogravimetric measurements up to 850 °C in argon atmosphere. For reference, pure components of the examined mixtures were analyzed at the same conditions. During the heating, PET underwent carbonization and magnesium carbonate and hydroxide decomposed to MgO with evolution of gaseous products (CO2 and/or H2O). As found, carbon yields calculated from the residual masses depended on the qualitative and quantitative composition of the starting mixture. Yields of carbon obtained from PET mixed with MgO did not depend on MgO/PET ratio. However, yields of carbon formed through pyrolysis of PET contained in the mixture with either magnesium carbonate or magnesium hydroxide were in general higher and depended on the weight ratio of components in the starting material. Reasons of these inconsistent results are discussed and explained. An influence of gasification of char on the carbon yield is explained.