Tensile Behavior of Carbon Fibers Impregnated with Thermoplastics Using Coextrusion Technique.

To increase printing speed and quality, a route consisting of using two sequential coextruders to form impregnated fiber immediately before feeding it to the printer. Such an approach, aimed at allowing the use of the most common industrial 12K carbon fibers for additive manufacturing, prevents damage to composite fibers during transportation, storage, and loading. An elaborate system was used to prepare carbon fibers impregnated with polypropylene, ethylene vinyl acetate, and their blends. The used scheme allows the production of composite fibers containing from 60 to 80 wt. % of carbon fibers. It was found that the elastic modulus of the composite fibers is close to those for raw carbon fibers and does not depend on the used polymer. It shows that the used carbon fiber path in the polymer melt and two sequential calibrating nozzles result in a high degree of orientation of the elementary filaments in the fiber at impregnation and maintain the elastic properties of the carbon fiber in the resulting composite. The tensile strength of the composite fibers depends on the polymer content in the composite fiber; the highest tensile strength was observed for fibers impregnated with ethylene vinyl acetate when increasing the coextrusion temperature up to 220 °C, which results in a composite fiber with a polymer content of 30 wt. %. A decrease in the polymer content in composite fibers results in a decrease in strength.