Impregnation techniques for fiber bundles or tows

A composite part which is made of a polymer matrix and fibrous reinforcement shows better mechanical properties than the unreinforced version. Prerequisite for the superior mechanical behavior is that the fibers are wetted by the matrix and a good adhesion between fibers and matrix is established. This means that a void-free impregnation of the very slender fiber filaments is the key issue when the production of highquality composite materials or parts are targeted. In case of thermoset resins, the fiber impregnation can easily be carried out due to the low viscosity of the uncured resin. In contrast, well-impregnated composite parts using highly viscous and glutinous thermoplastic melts are much more difficult to realize. The viscosity of the thermoplastic melt (100–1000 Pa) is generally more than two or three orders of magnitude higher than that of the uncured thermoset resins (1–10 Pa). Additionally, the ‘handling’ of the hot impregnation unit, which is necessary for processing the thermoplastic polymers, is less comfortable. Therefore, the impregnation of fiber tows with thermoplastics has been an important research and development topic. Many different routes are followed with the ultimative goal to overcome the problems associated with impregnation of fibers by thermoplastic polymer melts.