Chemical recognition of antioxidants and UV-light stabilizers at the surface of polypropylene: Atomic force microscopy with chemically modified tips

We show in this paper that it is possible to locally detect additives on th e surface of polypropylene with chemically modified atomic force microscopy (AFM) tips. Gold-coated AFM tips modified with methyl and hydroxyl termina ted self-assembled alkanethiol monolayers were used to measure adhesion for ces on a process-stabilizing agent (Irgafos 168)., an antioxidant (Irganox 1010), and UV-light stabilizers (Tinuvin 770, Dastib 845, Chimassorb 944, a nd Hostavin N30). Pull-off force measurements carried out on these pure add itive films have shown that it is possible to discriminate between antioxid ants and UV-light stabilizers. We have evidenced a characteristic fingerpri nt for each additive, according to the functionality of the tip used and th e medium wherein the force measurements are realized (water or nitrogen atm osphere). Similarly we have measured pull-off forces on a melt-pressed poly propylene sample stabilized with Irgafos 168, Irganox 1010, and Tinuvin 770 . These adhesion force measurements show that the extreme surface of the po lymer is mainly made of a layer of Tinuvin 770. These results have been com pared to those obtained from time-of-flight secondary ion mass spectrometry measurements.