Study on the Thermal Stabilizing Process of Layered Double Hydroxides in PVC Resin

Zhi Rao; Kaitao Li; Pingli Liu; Yanjun Lin; Xiang Lyu

doi:10.3390/molecules28237792

Study on the Thermal Stabilizing Process of Layered Double Hydroxides in PVC Resin

Molecules. 2023 Nov 27;28(23):7792. doi: 10.3390/molecules28237792.

Authors

Zhi Rao¹, Kaitao Li², Pingli Liu¹, Yanjun Lin², Xiang Lyu³

Affiliations

¹ Department of Applied Engineering, Gandong College, Fuzhou 344000, China.
² State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
³ Electrification and Energy Infrastructures Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.

Abstract

Poly(vinyl chloride) (PVC) is widely used in various fields and requires the use of thermal stabilizers to enhance its thermal stability during processing because of its poor thermal stability. Layered double hydroxides (LDHs) are widely considered to be one kind of highly efficient and environmentally friendly PVC thermal stabilizer. To investigate the thermal stabilizing process of layered double hydroxides (LDHs) in PVC resin, PVC and MgAl-LDHs powders with different interlayer anions (CO₃^2-, Cl^-, and NO₃^-) were physically mixed and aged at 180 °C. The structure of LDHs at different aging times was studied using XRD, SEM, and FT-IR. The results show that the thermal stabilizing process of LDHs on PVC mainly has three stages. In the first stage, the layers of LDHs undergo a reaction with HCl, which is released during the thermal decomposition of PVC. Subsequently, the ion exchange process occurs between Cl^- and interlayer CO₃^2-, resulting in the formation of MgAl-Cl-LDHs. Finally, the layers of MgAl-Cl-LDHs react with HCl slowly. During the thermal stabilizing process of MgAl-Cl-LDHs, the peak intensity of XRD reduces slightly, and no new XRD peak emerges. It indicates that only the first step happens for MgAl-Cl-LDHs. The TG-DTA analysis of LDHs indicates that the interaction of LDHs with different interlayer anions has the following order: NO₃^- < CO₃^2- < Cl^-, according to the early coloring in the thermal aging test of PVC composites. The results of the thermal aging tests suggest that LDHs with a weak interaction between interlayer anions and layers can enhance the early stability of PVC significantly. Furthermore, the thermal aging test demonstrates that LDHs with high HCl absorption capacities exhibit superior long-term stabilizing effects on PVC resin. This finding provides a valuable hint for designing an LDHs/PVC resin with a novel structure and excellent thermal stability.

Keywords: LDHs; PVC; thermal stabilizer; thermal stabilizing process.

Grants and funding

This work was supported by Development Program (863 Program, 2013AA032501), the Fundamental Research Funds for the Central Universities (YS1406), Science and Technology Research Project of Education Department of Jiangxi Province (GJJ218608), President Foundation of Gandong college (YZJJ202203) and President Foundation of Gandong college (YZJJ202204).