The Synthesis of Zinc Complex of Salicylaldehyde Serine Schiff Base and Assessment of Its Efficiency as a Heat Stabilizer for Poly (Vinyl Chloride)

The zinc complex of salicylaldehyde serine Schiff base (ZnL) was synthesized from serine, salicylaldehyde, and zinc diacetate and subsequently applied as a heat stabilizer in poly (vinyl chloride) (PVC). The structure of ZnL was determined using elemental analysis, crucible thermogravimetric method, infrared spectroscopy, thermogravimetric analysis and ¹H NMR spectra. The heat stability effect of ZnL for PVC was investigated using the Congo red and oven aging methods. The results indicated that PVC stabilized by ZnL exhibited a certain degree of original whiteness and long-term heat resistance. In contrast with PVC stabilized by ZnSt₂ and Ca/Zn, ZnL was found to be slightly inferior in terms of whiteness but superior in long-term heat resistance. It was observed that complexation of ZnL with CaSt₂ could enhance both the original whiteness and long-term heat resistance of PVC, while also alleviating the "zinc burning" phenomenon. In contrast, complexation with ZnSt₂ was found to promote "zinc burning" for PVC. Furthermore, the heat stability mechanism of ZnL for PVC was explored through experiments focusing on HCl absorption and active chlorine substitution. The results demonstrated that ZnL could replace active chlorine on the PVC molecule and absorb HCl gas. Finally, auxiliary heat stabilizers such as pentaerythritol (Pe), dibenzoyl methane (DBM), and epoxidized soybean oil (ESBO) were added to ZnL/CaSt₂ to evaluate their synergistic effects. It was found that ESBO in PVC exhibited the best synergistic effect with ZnL/CaSt₂ and was superior to those observed with DBM and Pe. When the ratio of ZnL/CaSt₂/ESBO was set at 0.6/2.4/0.9, PVC demonstrated the optimal thermal stability performance.