Study of Adhesion Properties of Polypropylene Surfaces by Atomic Force Microscopy Using Chemically Modified Tips : Imaging of Functional Group Distribution

Polypropylene surfaces were investigated by atomic force microscopy (AFM) using chemically modified probes. We show in this contribution that it is possible to locally detect additives on the surface of polypropylene, using tips modified with methyl and hydroxyl terminated self-assembled alkanethiol monolayers. The response of pure additives towards the chemical probes, and the medium wherein the force measurements are realized (water or nitrogen atmosphere), were determined in order to be able to further recognize and localize these compounds on polymer surfaces. The pull-off force measurements have shown that it is possible to discriminate between antioxidants, which show a hydrophobic behaviour, and UV-light stabilizers, which show a more hydrophilic behaviour. Similarly we have measured pull-off forces on a melt-pressed polypropylene sample stabilized with two antioxidants and one UV-light stabilizer. These adhesion forces measurements show that the extreme surface of the polymer presents a hydrophilic behaviour and is mainly composed of an UV-light stabilizer layer. We were able to obtain adhesion maps showing the distribution of these additives on the surface.

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