Effects of flame and corona treatment on extrusion coated paper properties

Polymer and paper structures have been used in several fields, especially in the packaging industry. This study shows how flame and corona treatment modify the most important properties of fiber-based packaging materials: printability, sealability, and barrier effectiveness against water vapor, oxygen, and grease. A high level of wetting or oxygen content of the surface after flame or corona treatment did not lead to improved print quality (i.e., better toner adhesion and high visual quality for the extrusion coatings). Flame treatment improved visual quality and toner adhesion of low-density polyethylene (LDPE) coating, but increased minimum sealing temperatures and reduced seal strengths of the coating. The reduced sealability likely resulted from cross-linking of the LDPE surface, which reduced chain mobility and limited the amount of chain interdiffusion across the seal interface. Polypropylene (PP) coating sealability was enhanced by flame treatment, whereas corona treatment improved the sealability of both coatings. The reason for the improved sealability was chain-scission, not cross-linking, which is the dominant reaction for flame-treated PP and corona-treated LDPE and PP coatings. Flame treatment also improved the water vapor and oxygen barrier ability by increasing the surface crystallinity of coatings.