Active Polymer Nanocomposites: Application in Thermoplastic Polymers and in Polymer Foams

Layered double hydroxides (LDH) are very used as fillers in polymer nanocomposites research. They cannot be used in their pristine form (magnesium and aluminum hydroxycarbonates) because they exhibit strong interlayer electrostatic interactions and tight basal spacings so that they require the intercalation of organic anions into clay galleries. The organic modification of LDH increases the filler-polymer compatibility, enlarges the basal spacing of the lamellae (making easier the insertion of the polymeric chains into the gallery), and promotes the exfoliation of the filler into the polymeric matrix. Organically modified LDH/polymer nanocomposites exhibit improved mechanical, thermal, and chemical properties when they are compared with pristine polymers or conventional composites. Moreover, the incorporation of LDH allows us to obtain materials with specific functionalities. For example, the intercalation of antimicrobial molecules into LDH (such as benzoate or stearate) and the use of the modified nanoparticles as fillers results in nanocomposites with antimicrobial activity. In this paper, several benzoate and/or stearate LDH/polypropylene (PP) nanocomposites have been produced for food packaging applications. The O2 permeability coefficient of the nanocomposite named 1.5% o-benzoate/1.5% o-stearate LDH/PP/3% PP-g-MAH reduces by 20% compared to unfilled PP and 30% compared to unfilled PP/3%PP-g-MAH. It is accepted that in such a nanocomposite, the lamellar structure of LDH creates a more tortuous path for the progress of oxygen molecules reducing the gas diffusion. For the novel nanocomposite material, the physical, morphological, mechanical, and gas barrier properties have been measured and the antimicrobial effect has been evaluated. In this paper, some benzoate LDH/polyurethane foam (PU) nanocomposites have been also produced. The filler dispersion into the PU has been investigated by scanning electronic microscopy. It was observed that organic LDH particles were uniformly dispersed into the walls of cells, forming small aggregates. The morphological properties of the foam have been analyzed by nanotomography. LDH/PU nanocomposite showed antibacterial and improved mechanical properties.