Gas Transport in Surface Grafted Polypropylene Films with Polyacrylic Acid Chains

VANINA COSTAMAGNA; MIRIAM STRUMIA; MAR LOPEZ GONZALEZ; EVARISTO RIANDE

Journal Polymer Science: Part B: Polymer Physics

Año: 2007 p. 2421 - 2431

Abstract: This work describes the grafting reaction of poly(acrylic acid) onto the surface of polypropylene films carried out with ultraviolet radiation, using benzophenone as photoinitiator and water as solvent. By increasing the reaction time, graft percentages of 3.5%, 6.5%, 12.9%, 19.8%, 29.4% and 36.0% were obtained. Micrographs of the modified films show that grafting exclusively occurs on the polypropylene films surface. The values of the permeability coefficients  of oxygen, nitrogen, carbon dioxide, carbon monoxide, argon, methane, ethane, ethylene and propane across the grafted films undergo a sharp drop. The interpretation of the permeation results suggest that radicals created in the tertiary carbons of the grafted chains by effect of UV light or by chain transfer reactions may highly crosslink the poly(acrylic acid) grafted layer. A rigid layer involving strong hydrogen bonding and chains crosslinking is already formed at grafting percentages of 3.5% that strongly hinders gas permeation across it. Destruction of hydrogen bonding by partially replacing protons of acrylic acid residues by sodium/silver cations increases the permeability of the surface grafted films. Finally, the films permselectivity is hardly affected by the grafting layer.