Lab-scale manufacturing of thermoplastic matrix-continuous carbon fiber filaments for additive manufacturing: melt impregnation, properties of the filaments and its printed composites

Additive manufacturing encounters significant barriers to its broader application in large-scale production. This research seeks to mitigate critical limitations, including a trade-off between impregnation speed and quality in filament preparation and inconsistent fiber distribution in continuous carbon filaments (CCFs), mainly attributed to the rounding process of unidirectional tapes and insufficient interlayer adhesion. A novel lab-scale impregnation line was engineered to address these challenges, facilitating the production of CCFs using three distinct types of carbon fiber in conjunction with recycled glycol-modified poly(ethylene terephthalate) (rPETG) resin. This new lab-scale process produces uniform fiber distribution within PETG matrix and prevents S-shaped distortions typically observed in conventionally rounded tapes. The type of carbon fiber sizing influences the impregnation process and tensile strength of the CCFs. Specifically, CCFs with flexible sizing demonstrated a 15% reduction in tensile strength due to fuzz formation during impregnation. These CCFs were subsequently employed in 3D printing applications, with the fabricated composite components subjected to interlaminar shear strength (ILSS) testing. The study concludes that recycled PETG is a viable additive manufacturing material when combined with appropriately sized carbon fibers. Additionally, it highlights the advantages of omitting the rounding stage, which enhances the quality of CCF and optimizes production efficiency. Highlights: A lab-scale direct melt impregnation system was designed in this study. The impact of different sizing types on carbon fibers was investigated. 3D-printed continuous fiber filaments were prepared. New lab-scale process produces uniform fiber distribution within PETG matrix. S-shaped distortions observed in conventionally rounded tapes were prevented.