**2. Preparation of the Cu/LDPE composite films**

The low density polyethylene (LDPE) in pellets used in this work has a melting temperature of 107°C, a crystallinity around 40% (as determined by differential scanning calorimetry (DSC) with a heating rate of 10°C/min) and a density at room temperature of 0.9 g/cm3 . The particles sizes were < 38 μm and were supplied by Sigma-Aldrich. High purity toluene (99%) supplied by Sigma-Aldrish was used as solvent for the preparation of the solution made films. Different solutions of LDPEtoluene at 1% in the absence and in the presence of copper microparticles were prepared at 80° C. and cooled to room temperature. After total evaporation of the solvent in a Teflon mold, thin films (50 to 60 μm thick) were obtained [25].
