The importance of polymer surfaces

We are surrounded by polymeric materials. ‘Plastics’ have been replacing ‘traditional’ materials such as metals, wood, glass, paper, leather, etc. ever since the introduction of the first thermosetting resins – and the trend continues. Polymers are therefore pervasive: in the form of mouldings, sheets, fibres and films; in protective coatings (particularly paints), adhesives, sealants and printing inks; in composites with inorganic components as structural materials (e.g. glass fibre/polyester resin for boat hulls or carbon fibre/epoxy resin for aircraft sections). These aspects of polymer application are evident to all. Rather less evident generally is the rapidly increasing importance of polymers in biomedical applications. However, as early as 1981 the annual usage of, for instance, contact lenses, blood bags and catheters was approximately 2, 30 and 200 million items, respectively (Ratner, Yoon & Mates, 1987). Finally, there is the diverse variety of polymers with entirely novel properties which make possible recent or emerging devices (e.g. conducting polymers, optical fibre coatings, drug-release vehicles, liquid crystal displays).

Having established the importance of polymeric materials, per se, it is necessary to emphasise the role of the surface. In many cases surface properties are critical to the end-use or performance of the polymeric article. These include properties related to adhesion (e.g. wetability, printability, adhesive bonding, heat sealability, ‘blocking’, releasability), electrical properties (e.g. static chargeability, triboelectric behaviour, charge storage capacity), wear properties (e.g. friction, lubricity, wearability), optical properties (haze, gloss, stains etc.), biological compatibility (a catch-all for a variety of responses to blood, tissue etc.), permeability, chemical reactivity and crazing. These properties are dependent upon the detailed physical and chemical structure of the polymer surface (the dimensions of this critical region are considered in Section 1.5).