Flame Treatment and Surface Characterisation of Rubber-Modified Polypropylene

The flame treatment of a rubber-modified polypropylene has been studied using XPS, contact angle measurement, SEM, vapour-phase derivatisation, and a composite butt adhesion test. Optimum air-to-gas ratio and the distance from the inner cone tip to the polymer surface were found to be ∼ 11:1 and ∼ 0.5 cm, respectively. The lack of correspondence between contact angle and surface oxygen concentration was proposed to be due to the reorientation/migration of surface functional groups that had been incorporated during flame treatment. SEM shows changes in surface topography induced by intense flame treatment. Trifluoroacetic anhydride (TFAA) was found to derivatise-OH groups selectively by using model polymers. About 30% of the incorporated oxygen on flame-treated polypropylene surfaces was found to be present as-OH. Under most flame conditions studied, the interfacial adhesion with an epoxy adhesive or a polyurethane paint was found in excess of the polymer's cohesive strength. The results obtained are compared with those from a propylene homopolymer and an ethylene/propylene copolymer.