LLDPE/ZnAl LDH-exfoliated nanocomposites: effects of nanolayers on thermal and mechanical properties

Abstract

The exfoliated nanocomposites (LLDPE/ZnAl LDH) were synthesized by refluxing dodecyl sulfate-intercalated ZnAl-layered double hydroxide [Zn₃Al(DS)] in a non-polar xylene solution of linear low density polyethylene (LLDPE). Their thermal and mechanical properties were studied via X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and tensile tests. The molecular dispersion of Zn₃Al(DS) nanolayers within the LLDPE matrix has been verified by the disappearance of the d₀₀₃ XRD diffraction peak of Zn₃Al(DS) and observation of the TEM image. TGA profiles of the LLDPE/ZnAl LDH nanocomposites show a faster charring process in the temperature range from 200 to 400 °C and better thermal stability above 370 °C than that of pure LLDPE. When 30% weight loss was selected as a point of comparison, the thermal decomposition temperature of LLDPE/ZnAl LDH nanocomposites with 5 wt% content of Zn₃Al(DS) is 56 °C higher than that of pure LLDPE. The apparent activation energy values of LLDPE, and the LLDPE/ZnAl LDH nanocomposites with 5 and 10 wt% content of Zn₃Al(DS) are determined as 94, 215, and 150 kJ mol⁻¹, respectively, by the Flynn–Wall method in the kinetic analysis of the thermo-oxidation degradation process. The Young's modulus of the LLDPE/ZnAl LDH nanocomposite with 20 wt% Zn₃Al(DS) has a 59% increase over that of pure LLDPE although its strength and elongation at break show some decrease due to the decrease of the crystallinity of the LLDPE matrix and/or some aggregations of exfoliated nanolayers of Zn₃Al(DS) in the LLDPE matrix.