PARTICLE-SIZE AND SHAPE EFFECTS IN MATERIALS SCIENCE - EXAMPLES FROM POLYMER AND PAPER SYSTEMS

Large quantities of clay minerals (and other micron-sized mineral powders) are used widely in materials science. Mineral fillers are major components, for example, of paints, rubber, plastics and paper and board. While the original object of such incorporation was to reduce costs, performance is now being ''engineered'' by design or choice of the relevant mineral particles. This paper concentrates on the use of mineral powders in polymer and paper science. In both application areas, the size and shape of the mineral particles can affect mechanical properties such as stiffness and tensile and impact strength. However, other characteristics are also modified. For example, the drainage rate in paper formation and the rheology of a polymer melt, properties which are critically important to the rate of processing of the relevant materials, can be greatly affected. Finally, the size and shape of the mineral particles also affect appearance, i.e. the smoothness, uniformity, optical properties etc. Mechanical and rheological data are presented for mineral-filled polypropylene, as are mechanical and optical data for filled and coated paper.