A "one-pot" method for synthesizing zinc tryptophan and its derivatives as highly efficient PVC thermal stabilizer with excellent mechanical properties

Zinc Tryptophan (Trp-Zn) and zinc N-(salicylic) tryptophan (SalTrp-Zn) were synthesized from tryptophan, zinc acetate, and salicylic aldehyde by one-pot method, respectively. The structure was analyzed by FT-IR, 1H NMR, and elemental analysis. PVC samples were prepared by stirring method and solvent film process, and then the thermal properties of PVC samples were studied by thermal aging chamber test, Congo red test, electrical conductivity test, and thermogravimetric analysis (TGA). The thermal stability of Trp-Zn and SalTrp-Zn stabilized PVC samples was better than calcium and zinc soaps used in industry. The thermal stability time was up to 80 min, and it was a long-acting thermal stabilizer. After the addition of CaSt2 and Trp-Zn stabilizer in different proportions, the thermal stability of PVC was obviously improved, and the initial whiteness of the film was improved after the combination of Trp-Zn/SalTrp-Zn. In addition, the tensile test verified that the PVC samples stabilized by Trp-Zn and SalTrp-Zn had the highest elongation at break. The addition of Trp-Zn can reduce the elastic modulus of PVC, effectively improve the mechanical properties of PVC, and make the PVC film have better toughness and elasticity. Through DMA and EDS tests, it can be seen that Trp, SalTrp-Zn had good compatibility with PVC and DOP. The quantum chemical calculation of Trp-Zn, SalTrp-Zn and vinyl chloride models was carried out, and the thermal stability mechanism of thermal stabilizer on PVC was analyzed accurately, mainly the absorption mechanism of HCl and the substitution mechanism of unstable chlorine atoms.