Optimization of organo-layered double hydroxide dispersion in LDPE-based nanocomposites

Low-density polyethylene/layered double hydroxide (LDPE/LDH) nanocomposites were prepared via melt extrusion using organo-LDH particles and maleic anhydride functionalized polyethylene as compatibilizer. Processing parameters, preparation method, and feed composition were properly modulated until obtaining nanocomposites with intercalated/exfoliated morphologies, and an uniform distribution of nanolayers, as evidenced by X-ray diffraction and transmission electron microscopy analysis. These materials showed a significant improvement of the thermal-oxidative stability, which increased of about 50-C during the first step of the degradation process. Moreover, a remarkable reduction of the oxygen permeability, proportional to the aspect ratio of LDH stacks dispersed in the polyolefin matrix was evidenced, indicating the possible application of nanocomposite films as food packaging materials. As highlighted by dynamic mechanical thermal analysis, interactions at the interface between LDH layers and polymer chains caused a shift of the LDPE b-relaxation toward higher temperatures and a reduction of the peak intensity with respect to the matrix. It was also found that the storage modulus of the nanocomposites was lower in all the temperature range with respect to the reference samples. Finally, on-line capillary rheometer measurements evidenced that the shear thinning behavior of the nanocomposites was dominated by the matrix so that the melt processability was not compromised by the presence of the filler.