Bulk and Process Related Properties

The common fillers used in plastics are minerals (densities from 2.4-2.S g/cm ), which give a composite of higher density than that of the unfilled polymer (densities of 0.8-1.9 g/cm ). The density of a composite of known composition can be calculated according to the linear rule of mixtures (Equation 8.1), where p,., pf and pp are the densities of the composite, filler and matrix, respectively, and mf is the mass fraction of filler. 

Increased density is usually undesirable because products must inevitably be transported to be sold, or installed. This may result in increased transportation costs. Weight increases are undesirable when the material is to be used to make cars, trucks, trains, aeroplanes or spacecraft. Recent European legislation on packaging will also penalise by weight. 

Decreased density is possible through use of fillers such as wood flour (or fibre), hollow glass microspheres, hollow polymer microspheres [22] (e.g., Expancel ) or hollow spheres from fly ash. Eow-density thermoplastic composites are useful for products that must float. 

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