RESIDUAL REACTIVITY FOR SURFACE GRAFTING OF ACRYLIC-ACID ON ARGON GLOW-DISCHARGED POLY(ETHYLENE-TEREPHTHALATE) (PET) FILMS

The wettability of poly(ethylene terephthalate) (PET) films in water was significantly improved upon exposure to argon glow discharge. Depending upon the lengths of glow-discharge exposure, the water contact angle (CA) of the untreated film (73.1-degrees +/- 0.1-degrees) was reduced to between 33.7-degrees and 41.0-degrees on the argon glow-discharged films. Wettability decay was observed during the initial few days. Depending upon the treatment time, the water CA stabilized 4-7 days after the treatment and the extent of the wettability decay ranged from 4.3-degrees to 7.6-degrees. The residual reactivity of the glow-discharged surfaces was captured by exposing the glow-discharged PET to acrylic acid in the liquid and vapor phases. Optimal water CAs of 54.0-degrees and 41.9-degrees were achieved in the liquid-phase and the vapor-phase exposures, respectively. Wettability decay of these acrylic acid-grafted PET surfaces was very small (0-degrees - 1.9-degrees) for the liquid-phase reactions and negligible (0.3-degrees - 0.6-degrees) for the vapor-phase reactions. The near absence of wettability decay or the greater stability of the grafted surfaces suggested the almost complete dissipation of the residual reactivity through reactions with acrylic acid. Surface morphology of the untreated as well as the acrylic acid-grafted PET surfaces were examined and detailed by scanning electron microscopy.