Synthesis of polypropylene/Mg3Al–X (X = CO32−, NO3−, Cl−, SO42−) LDH nanocomposites using a solvent mixing method: thermal and melt rheological properties

Abstract

In this contribution, polypropylene (PP) nanocomposites with four different inorganic anion (CO₃²⁻, NO₃⁻, Cl⁻, and SO₄²⁻) intercalated Mg₃Al layered double hydroxides (LDHs) as nanofillers were prepared using a solvent mixing method for the first time. The influence of interlayer inorganic anions on the thermal stability, melting and recrystallisation behavior and rheological property of PP was then systematically compared. The thermal stability was significantly improved, with Mg₃Al–CO₃ and Mg₃Al–Cl LDHs, and T_0.5 increased by about 44 °C compared to pure PP. The incorporation of LDHs increased the melting temperature (T_m) and the recrystallization temperature (T_c) of PP by about 3–4 °C and 10–13 °C, respectively. The influence on the storage modulus (G′) and loss modulus (G′′) follows the order of Mg₃Al–SO₄ > Mg₃Al–NO₃ > Mg₃Al–CO₃ > Mg₃Al–Cl. Although the incorporation of all LDHs led to an improvement in the thermal stability, T_m, T_c, G′, G′′, and complex viscosity of PP/Mg₃Al–X LDH nanocomposites, the extent of changes varied with the type of inter-layer anions. The study finally demonstrated that even very similar inorganic anions such as CO₃²⁻, NO₃⁻, Cl⁻, and SO₄²⁻ could lead to a significant difference in the property of the synthesized PP/LDH nanocomposites, and it must be taken into account for the future design of polymer/LDH nanocomposites.