Polyaniline–palladium composite coatings for metallization of polyethylene substrate

The coating of low-density polyethylene (LDPE) films with a polyaniline–palladium composite layer was investigated. The LDPE surface was first graft copolymerized with acrylic acid (AAc) to enhance the adhesion of the polyaniline–palladium layer. Two methods of forming the polyaniline–palladium layer on the LDPE were investigated. In Method 1, polyaniline was first deposited on the AAc-graft copolymerized LDPE, followed by reaction with Pd(NO3)2. This results in a layer of palladium being deposited on the polyaniline surface. In Method 2, polyaniline powder was first reacted with Pd(NO3)2 and the powder was then treated with N-methylpyrrolidinone and coated on the AAc-graft copolymerized LDPE. In both the methods, the amount of palladium deposited can be varied by controlling the reaction time and the proportion of palladium to polyaniline used. In Method 2, nanosized palladium metal particles are distributed in the polyaniline coating rather than confined to the surface of the polyaniline layer. In both the cases, the palladium metal particles confer surface conductivity to the LDPE substrate even with the polyaniline in the undoped state. The adhesion of the polyaniline–palladium coating to the AAc-graft copolymerized LDPE substrate is excellent at low palladium content but is significantly weakened when a high palladium content interferes with the interactions between the polyaniline and the AAc-graft copolymerized chains. A high grafting density of AAc will promote better adhesion.