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.