General Characteristics of Fillers and Composites

Fillers are added to polymers to modify their basic properties or to lower production costs of final products. They act on almost all properties, including density, hardness, tensile strength, impact strength, chemical resistance, heat distortion temperature, processibility, and even the appearance of final products. Fillers are widely used with rubbers and thermosetting resins, mainly phenoplasts and aminoplasts. Their use in thermoplastics is still limited, but it is rapidly developing [1,2]. 

It is possible to distinguish between two kinds of plastic composites [3]  

The high-performance composite. The plastic material is used to encapsulate reinforcing elements (continuous fibers) to produce suitable shapes and structures [4,5]. This is also called unidirectional reinforcement. In this case the plastic material is the minor constituent (20-50% by volume) and the composite is normally in the form of a laminate. 

The low-performance composite. In this case the properties of the composite are nearer to those of the plastic material, the major constituent. Short fibrous or particulate reinforcing fillers are added in small quantity (5-25% by volume) to enhance physical properties of the plastic material, making its processibility easier or increasing its overall quality. 

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