G. Kranz et al., THE EFFECT OF FLUORINATION ON THE SURFACE CHARACTERISTICS AND ADHESIVE PROPERTIES OF POLYETHYLENE AND POLYPROPYLENE, International journal of adhesion and adhesives, 14(4), 1994, pp. 243-253
Polyethylene and polypropylene have been treated with fluorine/nitroge
n or fluorine/oxygen/nitrogen mixtures at atmospheric pressure. Change
s in surface chemistry and topography as well as depth of fluorination
have been examined using Fourier transform infra-red analysis, X-ray
photoelectron spectroscopy (X.p.s.), atomic force microscopy (AFM) and
ellipsometry. Even very short exposure times caused a large substitut
ion of the hydrogen atoms by fluorine. No change in surface topography
was noticed at magnifications of up to 5000 times with the scanning e
lectron microscope (SEM), but AFM showed that fluorination led to an i
ncrease of microroughness. The influence of fluorine or fluorine/oxyge
n concentration, as well as time of treatment and time of storage befo
re adhesive bonding, on adhesion of polypropylene to steel was investi
gated with a bending peel test. Significant improvement in peel streng
th was already achieved with minor fluorination intensity. Increase of
fluorination intensity did not lead to further improvement in peel st
rength. Analysis of the fracture surfaces was carried out with the SEM
and by energy dispersive X-ray spectroscopy and X.p.s. The findings s
howed that the samples failed cohesively in the polymer or directly be
neath the fluorinated layer. A model to describe the formation of spec
ific interactions between substrate and adhesive is suggested.