Preparation and thermal stability of bio-based Na/Zn composite liquid stabilizers for poly(vinyl chloride)

In this work, the adduct of maleic anhydride and methyl eleostearate (MAME) and dimer fatty acid (DFA) were converted to the sodium and zinc salts (L-Zn-MAME, L-Na-MAME, L-Zn-DFA, and L-Na-DFA), respectively, which were subsequently turned into Na/Zn composite liquid stabilizers(LTS-Na/Zn-MAME and LTS-Na/Zn-DFA) by formula combination. Na salts, Zn salts and mixed Na/Zn salts from these fatty acid salts were used as thermal stabilizers for poly(vinyl chloride) (PVC). The chemical structures of MAME, DFA, and their liquid zinc and sodium salts were verified using Fourier transform infrared (FTIR) spectra. Thermal stability and mechanical properties of the sodium and zinc salts, and their Na/Zn composite liquid stabilizers derived from MAME and DFA for PVC were investigated using discoloration and dynamic mechanical analyses, TGA-FTIR-MS, thermal decomposition kinetics, and Congo red and tensile tests. Thermal stability of pure PVC is poor, but membrane thermal stability can be improved by integrating thermal stabilizers. Results show that L-Na-MAME has an outstanding synergistic effect with the commercial general calcium/zinc stearate composite heat stabilizer(CaSt2/ZnSt2). CaSt2/ZnSt2/LTS-Na-MAME, LTS-Na/Zn-MAME and CaSt2/LTS-Zn-DFA/LTS-Na-DFA also have a better heat-stabilizing impact on PVC than CaSt2/ZnSt2, especially LTS-Na/Zn-MAME can more effectively enhance the primary coloring of PVC. In comparison to blank PVC and PVC/CaSt2/ZnSt2, both PVC/LTS-Na/Zn-MAME and PVC/LTS-Na/Zn-DFA display a larger elongation at break and acceptable tensile strength. The new stabilizers can largely enhance the heat stability of PVC resins, endowing PVC products with good plasticization performance, and can fully or partially replace the general calcium zinc stearate composite heat stabilizer and other heat stabilization products.