UV-Assisted 3D Printing of Polymer Composites from Thermally and Mechanically Recycled Carbon Fibers

Abstract

Despite the growing global interest in 3D printed carbon fiber reinforced polymers, most of the applications are still limited to high-performance sectors due to the low effectiveness-cost ratio of virgin carbon fibers. However, the use of recycled carbon fibers in 3D printing is almost unexplored, especially for thermoset-based composites. This paper aims to demonstrate the feasibility of recycled carbon fibers 3D printing via UV-assisted direct ink writing. Pyrolyzed recycled carbon fibers with a sizing treatment were firstly shredded to be used as a reinforcement of a thermally and photo-curable acrylic resin. UV-differential scanning calorimetry analyses were then performed to define the material crosslinking of the 3D printable ink. Because of the poor UV reactivity of the resin loaded with carbon fibers, a rheology modifier was added to guarantee shape retention after 3D printing. Thanks to a customized 3D printer based on a commercial apparatus, a batch of specimens was successfully 3D printed. According to the tensile tests and Scanning Electron Microscopy analysis, the material shows good mechanical properties and the absence of layer marks related to the 3D printing. These results will, therefore, pave the way for the use of 3D printed recycled carbon fiber reinforced polymers in new fields of application.

Keywords: additive manufacturing; carbon fibers; crosslinking; mechanical testing; polymer-matrix composites (PMCs); recycling; resins; rheology.

Figure 1

rCFs images after the shredding process and manual sieving: (a) rCFs sizing and shredding with the cutting mill; (b) rCFs fraction after the quad blade chopper shredding and sieving with a dimension higher than 300 µm; (c) rCF fraction with a dimension higher than 100 µm; (d) rCFs fraction with a nominal dimension of 100 µm.

Figure 2

(a) SEM micrographs of rCFs showing the different length; (b) inset of the micrograph; (c) rCF aspect ratio distribution graph.

Figure 3

Characterization of the UV-induced crosslinking of rCF 3D printable inks: UV conversion of 3D printable inks and 3D printed specimens evaluated by UV-DSC.

Figure 4

Rheological step tests for 3D printable inks composed of the ethoxylate bisphenol A diacrylate resin: (a) with 20 wt% of rCFs (0B20AER); (b) with 6 wt% of the urea-modified agent and 15 wt% of rCFs (6B15AER); (c) with 6 wt% of the urea-modified agent and 20 wt% of rCFs (6B20AER) and (d) with 6 wt% of the urea-modified agent and 25 wt% of rCFs (6B25AER).

Figure 5

The previous version of the UV-DIW 3Drag 3D printer (on the left) and the new 3D printing layout for CF reprocessing (on the right).

Figure 6

(a) 3D printing phase with the modified sided-LED apparatus; (b) UV conversion phase; (c) 3D printed tensile specimen with 20 wt% of rCFs.

Figure 7

Mechanical behavior of 20 wt% CF formulation (6B20AER) and neat resin: Stress versus Strain graph (average curves).

Figure 8

SEM micrographs of 3D printed tensile specimen cross-sections with 20 wt% CF formulation (6B20AER): (a) details on voids and overall fibers distribution in the matrix; (b) fibers detachment from the matrix; (c) fiber interactions with the matrix.