Synergistic effects of zinc-mannitol alkoxide with calcium/zinc stearates and with β-diketone on thermal stability of rigid poly(vinyl chloride)

Zinc-ethanol metal alkoxide was primarily synthesized as an intermediate material toward zinc-mannitol alkoxide (Zn-Man), which was further prepared through the alcohol exchange reaction with the zinc-ethanol alkoxide by mannitol. The synergistic effects of Zn-Man with several commonly used thermal additives such as calcium stearate (CaSt₂), zinc stearate (ZnSt₂), CaSt₂/ZnSt₂ and stearoyl benzoyl methane (β-diketone) on poly(vinyl chloride) (PVC) thermal stability were investigated from conductivity measurement, thermal aging testing and Ultraviolet–visible (UV–vis) spectroscopy. The thermal stability tests showed that Zn-Man distinctly prolonged the long-term thermal stability of rigid PVC. If used with CaSt₂/ZnSt₂ or β-diketone, the thermal stability time (T_s) increased to 165.2 and 164.7 min, respectively, from the initial 101.5 min of PVC stabilized with pure Zn-Man, but excess dosage of CaSt₂/ZnSt₂ or β-diketone deteriorated the long-term thermal stability. The initial coloring was excellently improved when Zn-Man combined with ZnSt₂, CaSt₂/ZnSt₂ or β-diketone; while the synergistic effect between Zn-Man and CaSt₂ was not significant. Moreover, testing results demonstrated that the optimal mass ratio of 3/1 showed better synergistic effects. The thermal stabilizing mechanism was also investigated through the combination of theoretical analysis and experimental testing.