Comparison of the effects of antimony trioxide and zinc, calcium and copper stannates on the thermal degradation of polyamide-6,6

Thermal and thermo-oxidative decompositions of polyamide 6.6 (PA66) in the presence and absence of zinc (ZnSt), calcium (CaSt) and copper stannates (CuSt), and in the presence of antimony trioxide (ATO), have been studied by TGA-FTIR and pyrolysis GC/MS. It is shown that whilst ATO has a negligible effect on the rate of decomposition and products of pyrolysis under both slow heating on a TGA and rapid heating on a pyrolysis/GC/ MS apparatus, the stannates have a catalytic effect in the order ZnSt approximate to CaSt > CuSt, evident through release of volatiles at a lower temperature and in a different product distribution following rapid high temperature py-rolysis. In particular, rapid pyrolysis at high temperature in the presence of the stannates promotes formation amongst the pyrolysis products of, for example, 6-aminohexanenitrile. 1,6-hexanediamine, 1-methyl-3-formylin-dole and 1,2,3,7-tetramethylindole, whilst yields of others are reduced, e.g., hexanedinitrile, caprolactam, diaminomethylidene(2-hydroxypropyl)azanium, prop-2-enenitrile (acrylonitrile) and azacyclodecan-5-ol. We suggest that these effects arise from complexation of the electropositive metal in the stannate (Zn, Ca or Cu) with the C=O groups of PA66, thus weakening the C(O)-C and C-N bonds adjacent to the C=O groups. The fact that ZnSt has the most pronounced effect on the pyrolysis product distribution and CuSt the least, we explain in terms of the order of electropositivity of the metal (Zn>Ca>Cu).

Automated summary

The thermal and thermo-oxidative decompositions of polyamide 6.6 (PA66) were studied with the presence of zinc (ZnSt), calcium (CaSt), and copper stannates (CuSt). The results showed that these stannates had a catalytic effect, with ZnSt having the most pronounced effect and CuSt having the least. This effect is believed to be related to the electropositivity of the metal.