Investigation of basic zinc cyanurate as a novel thermal stabilizer for poly(vinyl chloride) and its synergistic effect with calcium stearate

Basic zinc cyanurate (Zn3(C3N3O3)2·ZnO, represented as Zn3Cy2) was synthesized via a precipitation method, and investigated as a thermal stabilizer for poly(vinyl chloride) (PVC) by thermogravimetric analysis (TGA), Congo red test and discoloration test. The thermal stability of PVC was significantly enhanced with the addition of Zn3Cy2. Compared with zinc stearate (ZnSt2), it is observed a significant improvement that Zn3Cy2 could delay the “zinc burning” of PVC. This is attributed to the strong ability of the cyanurate anions in Zn3Cy2 to absorb the hydrogen chloride released by the degradation of PVC. Moreover, mixing Zn3Cy2 with calcium stearate (CaSt2) in different mass ratios greatly promoted the thermal stability of PVC. Excellent synergistic effects could be observed when CaSt2/Zn3Cy2 combined with some commercial auxiliary stabilizers. Addition of dibenzoylmethane (DBM) brought a remarkable increase in initial color for PVC containing CaSt2/Zn3Cy2 while epoxidized soybean oil (ESBO) could improve both initial color and long-term stability.