Spray process to styrene grafting onto polyethylene film surface for paintability enhancement

A direct and fast post-processing method to modify polyethylene (PE) film surface is proposed in order to improve its paintability performance without changing its bulk properties. This goal is achieved by grafting styrene onto the PE film surface using a macrocarbocationic copolymerization reaction where both catalysts and reagents are sprayed directly on softened film respectively. Pure styrene as grafting molecule and aluminium chloride suspended in n-heptane as catalyst are used. Grafting reaction occurrence was assessed by analyzing the reacted film surface before and after extraction of non-grafted reaction products. The results confirmed by three independent analytical techniques evidence reaction occurrence. A graft-copolymer layer remains onto the PE film surface even when physically adhered reaction products were extracted. This layer enhances PE film water affinity and paintability either with water or acrylics paints because of the grafted aromatic group and roughness increase. Besides, this modification increments PE thermal degradation temperature giving another beneficial effect for future film applications. The proposed modification film methodology has potential application in continuous film production as reagents spraying onto softened films could be applicable in a cast film extrusion line.