Investigation of surface properties of plasma-modified polyamide 6 and polyamide 6/layered silicate nanocomposites

Polyamide 6 and polyamide 6/layered silicate nanocomposites were treated by oxygen plasma and the resulting surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared-attenuated total reflection (FTIR-ATR). The surface properties were also analyzed by water contact angle measurements and Taber abrasion test. It is found that plasma treatment had different effects on the surfaces of the homopolymer and the polymer nanocomposites. Furthermore, both plasma duration and nanoclay content affect the contact angle and degree of abrasion resistance. In pure polyamide 6, plasma treatment caused the surface to be highly hydrophilic due to the formation of cyclic cis-amide species. Polymer nanocomposites treated with plasma also became more hydrophilic due to oxidation and enrichment of clay at the surface. The abrasion resistance of pure polyamide 6 was increased after exposure to plasma. This is attributed to cross-linking of polymer chains when exposed to plasma. For the polymer nanocomposites, an improvement in abrasion resistance was obtained in samples with low clay content when exposed to plasma for a short time. This is also due to cross-linking as well as the higher abrasion resistance of clay. However, longer exposure to plasma resulted in poorer abrasion resistance due to self-aggregation of clay particles which can be easily removed from the surface. A model was proposed to explain the effect of oxygen plasma on polymer nanocomposite surface.