Characterisation of plasma-induced polystyrene grafts onto polypropylene-polyethylene copolymer substrate using Raman microprobe spectroscopy

Full text: Surface modification of polymers by plasma-induced grafting offers many advantages since unique surfaces can be produced. Plasma-induced graft polymerisation is similar to γ-radiation graft polymerisation using the pre-irradiation technique. In both cases, active species (free radicals or peroxides) are generated separately on the surface of the substrate before a monomer can be introduced for the grafting reaction. The nature of the surface produced after plasma treatment is dependent on the nature of the gas, the type of substrate, operating parameters, etc. In this work, optimum conditions are described for plasma treatment of polypropylene-polyethylene copolymer substrates, which were then exposed to an oxygen-containing atmosphere prior to polymerisation. The extent of grafting was investigated by Raman microprobe spectroscopy, an analytical technique used extensively for polymer characterisation. 3-D maps were utilised to explore the extent of modification after plasma treatment, as well as the distribution of the grafts. It was found that the crystallinity of the polymer decreases after plasma treatment. In addition, it was found that the polystyrene grafts were distributed heterogeneously not only on the surface but also in the bulk of the substrate