Polyolefins and Fillers Used in Composites

Before examining the properties of polyolefin-filler composites, it is appropriate to consider the characteristics of the polyolefin and filler components. This is, of course, because the properties of a composite depend on the characteristics of its component parts. 

Among polyolefins, polypropylene has recently become an attractive candidate for many engineering applications. New polymerization processes introduced in the last decade make polypropylene one of the most favorable matrices for high-volume composites and blends. Relatively low priced, excellent chemical resistance, good processibility and the possibility to modify, it is spreading into automotive, land transport, home appliances and other industries. The mass application of PP in automobiles, mass transport vehicles, household appliances and the construction industry requires stiffness and fracture toughness similar to those of engineering plastics (ABS, 

The action of particulate fillers on a thermoplastic is dependent on factors that can be classified as extensity, intensity and geometrical factors. The extensity factor is the amount of filler surface area per m of the composite in contact with the plastic. The intensity factor is the specific activity of this solid surface per m of interface, determined by the chemical and physical nature of the filler surface in relation to the plastic. Geometrical factors are the structure including shape of filler (anisotropic such as such as lamellar, plate, needle and isotropic such as spherical), their particle size and size distribution as well as porosity. Among those the chemical nature of the filler surface plays most vital role in determining the degree of plastic-filler interaction. 

While unique properties, such as dimensional stability or increased modulus, are the usual motivation for exploiting particulate filled eomposites, special attention must be paid to other mechanical properties, such as yield and ultimate strength and fracture toughness, since they are often degraded by the presence of fillers [20], 

In this experimental investigation multiple composite systems containing polypropylene and four different particulate fillers were selected for evaluation. Composites were prepared with and without additives to compare the effect of different chemical modifiers. 

---