Influence of the fiber preheating in in-situ pultrusion of continuous fiber-reinforced thermoplastic profiles

Fiber-reinforced plastic composites (FRP) with a thermoplastic matrix are becoming increasingly important as they allow for a bunch of subsequent processing like overmolding, welding and forming into another shape. Thereby, high loads can be well transferred by continuous fibers in the appropriate load direction. That makes continuous fibers embedded in a thermoplastic matrix extremely attractive for lightweight applications. The in-situ pultrusion probably provides the greatest potential of high-quality pultrudates with a maximum fiber volume content due to the excellent impregnation of the fibers by the low viscous reactive monomer melt based on ε-caprolactam. However, the quality of the pultrudates is significantly influenced by the polymerization to polyamide 6 (PA6) in the pultrusion die. Hence, the process parameters like the fiber preheating temperature and haul-off speed are investigated in terms of polymerization and mechanical properties of the profiles. In order to adjust the fiber temperature, a fiber preheating system using hot air is developed. Mechanical and chemical analyzes of produced tubular profiles comprising glass fibers show better mechanical properties with an increased fiber preheating temperature. A reduction in haul-off speed clearly decreases the residual oligomer content of the profiles which is determined by extraction. Due to the advantageous results using the developed fiber preheating, the existing state of the art of in-situ pultrusion should be extended in reference to the equipment technique by a fiber preheating as a standard component.