Carbon-Fiber-Recycling Strategies: A Secondary Waste Stream Used for PA6,6 Thermoplastic Composite Applications

Abstract

With a view to achieving sustainable development and a circular economy, this work focused on the possibility to valorize a secondary waste stream of recycled carbon fiber (rCF) to produce a 3D printing usable material with a PA6,6 polymer matrix. The reinforcing fibers implemented in the research are the result of a double-recovery action: starting with pyrolysis, long fibers are obtained, which are used to produce non-woven fabrics, and subsequently, fiber agglomerate wastes obtained from this last process are ground in a ball mill. The effect of different amounts of reinforcement at 5% and 10% by weight on the mechanical properties of 3D-printed thermoplastic composites was investigated. Although the recycled fraction was successfully integrated in the production of filaments for 3D printing and therefore in the production of specimens via the fused deposition modeling technique, the results showed that fibers did not improve the mechanical properties as expected, due to an unsuitable average size distribution and the presence of a predominant dusty fraction ascribed to the non-optimized ball milling process. PA6,6 + 10 wt.% rCF composites exhibited a tensile strength of 59.53 MPa and a tensile modulus of 2.24 GPa, which correspond to an improvement in mechanical behavior of 5% and 21% compared to the neat PA6,6 specimens, respectively. The printed composite specimens loaded with the lowest content of rCF provided the greatest improvement in strength (+9% over the neat sample). Next, a prediction of the “optimum” critical length of carbon fibers was proposed that could be used for future optimization of recycled fiber processing.

The Influence of Thermoplastic Composite Recycling on the Additive Manufacturing Process and In-Use Phase as Candidate Materials for Wearable Devices Applications

“…The application of recycled composite materials in 3D printing has gained significant attention in recent years due to its potential to reduce material waste and environmental impact while generating unique, custom parts and endeavoring to retain their performance requirements. The influence of composite materials on the mechanical properties of additively manufactured parts has been studied by the research community with respect to the correlation between materials and printing settings—such as fiber concentrations, printing direction and infill ratios—with the acquired mechanical characteristics [ 1 , 2 ], as well as with respect to the comparison between fiber-reinforced and pure thermoplastic materials [ 3 , 4 ]. Moreover, methodologies integrating recycling and FFF manufacturing from scraps of wind-turbine blade components have been suggested, including investigations into the mechanical characteristics, the internal microstructure and interface of specimens utilizing recycled glass fibers (rGFs), and PLA [ 5 , 6 ].…”