A reinforced thermoplastic is a neat resin that has been reinforced or modified by one or more additives.
These additives can be particulate fillers or fibers reinforcements.
The choice is determined by the properties required in the end product.
Fillers are minerals, metallic powders, glass spheres, and organic materials, and are used to increase stiffness, reduce mould shrinkage, afford flame resistance, improve processing, decrease wear resistance and can lower costs to the compounder.
Reinforcements are chosen to improve physical, mechanical, and thermal properties.
Short fibre reinforced materials are extrusion compounded: the polymer and the chopped reinforcing fibre are blended together, run through an extruder, stranded and pelletized.