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colloids and economic
The increasing importance of polymer colloids stems from several basic origins: first, the desire to reduce the amount of volatile organic compounds (VOC; introduced via solvents or plasticisers) in polymer products due to both environmental protection and economic reasons. Thus polymerisation processes in organic solvents tend to be replaced more and more by emulsion polymerisation using water as dispersing medium. Second, the change from polymer solutions to polymer dispersions allows to achieve higher solid contents at given viscosity, thus allowing easier processing of polymer materials. Finally, polymer dispersions have an important rheological property: they are shear thinning, i.e. dispersions that are highly viscous at rest, flow easily as soon as a shear force is applied. This is a decisive advantage if one thinks of dispersion paints which should be easy to stir and to apply to a wall (shear thinning), but which should no longer flow once at the wall (high zero shear viscosity).