Colored microporous polyethylene films: effect of porous structure on dye adsorption

Microporous polyethylene (PE) films with good mechanical properties have been produced by high-speed extrusion from the melt followed by annealing, uniaxial stretching and thermal fixation. The films have pores of 0.15-0.45 mum size and relief on the scale of 1-2 mum. Coloration of the films with fluorescent dyes, 3-aminobenzanthrone and derivatives of 1,8-naphthalimide, was performed at the room temperature. The quantity of adsorbed dye depends upon the spin draw ratio of PE membranes and has an influence upon their color shade. The color effect is not observed in the case of only extruded or annealed PE films treated in the same way. The enhanced adhesion of the dyes on porous films is related to their high surface area. Specifically, the interactions between dye and polymer at pore walls provide color stability of the microporous films. The effect of relevant properties of both PE membranes (pores relief and lamellar thickness) and dye molecules (aspect ratio and cohesion) is discussed.