Synergistic effect of complexes of ethylenediamine double maleamic acid radical and lanthanum (III) with pentaerythritol on the thermal stability of poly(vinyl chloride)

The basic complex ([LaL·OH·OH2], abbreviated as LaL) was firstly synthesized by maleic anhydride, ethylenediamine, sodium hydroxide and lanthanum chloride. Its structure was characterized by Fourier infrared spectrum (FTIR), elemental analysis, nuclear magnetism resonances (NMR) and thermogravimetric analysis (TGA). The obtained LaL was used as a thermal stabilizer on polyvinyl chloride (PVC) and the stabilization effect was evaluated by TGA, Congo red test and discoloration test. Moreover, LaL as a co-stabilizer mixed with Calcium stearate (CaSt2), Zinc stearate (ZnSt2), and pentaerythritol (PE) in different ratios for polyvinyl chloride (PVC) at 180 °C in air was also investigated. The results indicated that LaL/PE co-stabilizer presented excellent synergistic effect and obvious improvement of stabilization to PVC compared with the others. When the ratio of LaL and PE was 1, the stability time ranged from 6 to 83 min, and had a remarkable improvement in the initial color for PVC. Compared with the pure PVC sample, the reaction energy Ea of LaL/PE/PVC sample in N2 atmosphere increased from 123.50 kJ mol−1 to 161.01 kJ mol−1, and that of in air atmosphere increased from 115.90 kJ mol−1 to 154.48 kJ mol−1. What's more, It could be found that when using LaL/PE/PVC as stabilizer, the temperature of initial degradation (Tonset) of each stage in N2 and air atmosphere occurred at higher values of temperature than other PVC samples, which was further ascertained that LaL/PE is an excellent thermal stabilizer for PVC. Simultaneously, the possible degradation mechanism and synergistic stabilization of LaL/PE co-stabilizer were also investigated by TG-FTIR analysis.