Surface functionalized polypropylene: Synthesis, characterization, and adhesion properties

Modification of polypropylene by hyperbranched grafting with a poly(acrylic acid) graft was carried out using techniques previously used with gold, al uminum, silicon, and polyethylene surfaces. An initial etching oxidation pr oduced a modified polypropylene that was presumed to contain carboxylic aci d functional groups (though none were detected by IR spectroscopy). Then, a series of repetitive grafting experiments using an alpha,omega -diamine de rivative of poly(tert-butyl acrylate) were used to produce surfaces contain ing significant amounts of poly(acrylic acid). The resulting surfaces were characterized by ATR-IR spectroscopy, contact angle measurements, and XPS s pectroscopy. Treatment of the surfaces with alkali produced a more hydrophi lic carboxylate surface. Treatment of these surfaces first with ethyl chlor oformate followed by pentadecylfluorooctylamine produced a hydrophobic fluo rinated surface. Mechanical tests show that such surface modification not o nly serves as a route to modify polypropylene's hydrophilicity/hydrophobici ty-such modification substantially affects the adhesive strength between th is modified polypropylene and an epoxy adhesive. Double cantilever beam tes ts show that adhesion increases from 2 J/m(2) for unmodified polypropylene to up to 29 J/m(2) with the modified polypropylene.