Preparation of Zinc–Lanthanum and Zinc–Aluminum–Lanthanum Layered Double Hydroxides and Analysis of Their Thermal Stabilization Mechanism on PVC

Zinc–lanthanum layered double hydroxides (Zn–La LDHs) and zinc–aluminum–lanthanum layered double hydroxides (Zn–Al–La LDHs) were prepared via a hydrothermal method. The effects of cation ratio, hydrothermal time, and hydrothermal temperature on the structure of these two types of layered double hydroxides (LDHs) and their thermal stability in polyvinyl chloride (PVC) were investigated. The optimal preparation conditions were determined to be n(M²⁺) : n(M³⁺) = 3 : 1, hydrothermal temperature of 170°C, and hydrothermal time of 8 h. The LDHs obtained under optimal conditions were characterized by X-ray powder diffraction, Fourier-transform infrared spectroscopy (FTIR), and thermal analysis. The effects of different preparation conditions of the LDHs on the thermal stability of PVC were studied through Congo red tests and high-temperature aging experiments. The results indicate that both types of LDHs significantly improve the thermal stability of PVC, with Zn–La LDHs exhibiting superior thermal stability compared to Zn–Al–La LDHs. The rare earth LDH thermal stabilizers inhibit the cleavage of C–Cl and C–H bonds in PVC, suppress the generation of HCl and C=C bonds, and reduce the catalytic effect of HCl on the degradation of PVC.