Water As a Medium for Microwave-Assisted Grafting of Maleic Anhydride Onto a Polypropylene Film to Improve Its Adhesion with a Polyamide 6 Film

Maleic anhydride (MAH)-modified polypropylene (PP), denoted as PP-g-MAH, is often prepared by melt grafting of MAH onto PP through reactive extrusion. A major problem of this process is the presence of a large amount of residual (unreacted) MAH in the polymer, which is harmful for applications like food packaging. This work aims to study microwave-assisted grafting of MAH onto PP film surfaces using water instead of organic solvents as a medium to reduce MAH residues in PP. Microwave irradiation shortens the grafting time by accelerating the decomposition of initiator. Addition of a very small amount (2%) of xylene to water swells the PP film surfaces of about 12 mu m thick to which the MAH grafting is confined. The adhesive strength of a double layer film based on PP-g-MAH (moisture barrier layer) and polyamide 6 (PA6, oxygen barrier layer) reaches 13.3 N/15 mm instead of 2.4 N/15 mm for that based on PP and PA6. A much less amount of the oil-soluble benzoyl peroxide is more efficient as an initiator for MAH grafting than water-soluble ammonium persulfate.