Preparation of rare earth complexes with curcumin and their stabilization for PVC

Abstract

La, Nd, Pr, Ce, Eu and Sm complexes with curcumin have been prepared by the reaction of rare earth nitrate with curcumin in alcohol solution. Six complexes have been characterized by FT-IR, 1H NMR, ICP-MS and TG. The results reveal that the structure of complexes is binary complexes, and then the complexes are marked as RE⋅L2. The initial decomposition temperature of RE⋅L2 is above 260°C, much higher than the processing temperature of PVC. These RE⋅L2 are characterized as PVC heat stabilizers for the first time. The effect of RE⋅L2 on the static and dynamic thermal stability of PVC is investigated by Congo red test and torque rheometer. The results show that the static thermal stability time of PVC is higher than 25.1 min, especially that of PVC with Ce⋅L2 is up to 36.3 min. The dynamic thermal stability time of PVC is higher than 15.3 min, especially that of PVC with Nd⋅L2 is up to 22.0 min. The probably thermal stability mechanism of RE⋅L2 for PVC was proposed based on the measurement of FT-IR, Congo red test and torque rheometer. RE⋅L2 could coordinate with Cl and insular or conjugated double bonds on PVC chains. Also, the cross-linked chains through RE⋅L2 might be formed. Consequently, the dehydrochlorination of PVC and oxidative degradation of the insular or conjugated double bonds were relieved.