Heat sealing of semicrystalline polymer films. III. Effect of corona discharge treatment of LLDPE

Abstract

AbstractThe effects of corona‐discharge treatment (CDT) of commercial polyethylene (PE) Linear low‐density PE (LLDPE) were studied with special emphasis on the heat‐seal behavior of treated films. A range of treat levels, representative of those used in industry, was obtained by varying the applied power to a commercial, on‐line treater. Film surfaces were characterized by XPS and wetting‐tension measurements. The primary effect of CDT on the heat‐sealing behavior of LLDPE films is a transition in the failure mode of heat seals from a normal tearing or inseparable bond to a peelable seal. In addition, CDT increases the seal initiation temperature 5–17°C and decreases the plateau seal strength 5–20% as the treat level, or wetting tension, increases from 31 to 56 dynes/cm. These effects are attributed to cross‐linking during corona treatment, which restricts polymer mobility near the surface and limits the extent of interdiffusion and entaglements across the seal interface. Results of heat‐sealing studies with electron‐beam‐irradiated PE, chemically oxidized PE, and CDT polypropylene (PP) provide indirect evidence for the proposed surface cross‐linking mechanism. The effect of commercial levels of slip additives on the heat‐seal behavior was also investigated. © 1994 John Wiley & Sons, Inc.