Synergism of calcium and zinc soaps on thermal stabilization of poly(vinyl chloride) (PVC) was studied using solvent casted films of PVC having commercial zinc and calcium soaps in different proportions. The metal soaps were characterized by X-ray diffraction and X-ray emission techniques. The films that were heated at 80 degreesC for 4 h for the removal of the last traces of solvent methyl ethyl ketone were tested for thermal stability by heating at 160 degreesC for 30 min. Heated films were characterized by infrared and ultraviolet-visible spectroscopy, differential scanning calorimetry and thermal gravimetric analysis (TGA) methods. The migration of Zn2+, Ca2+ and H+ cations to water at 80 degreesC was also studied. While UV spectroscopic analysis and ion migration indicated synergism on PVC heat stability for 4:1 Ca to Zn soaps ratio, this was not confirmed by TGA. (C) 2001 Elsevier Science Ltd. All rights reserved.