The availability of a considerable amount of waste carbon fiber (CF) and the increased pressure to recycle/reuse materials at the end of their life cycle have put the utilization of recycled CF (rCF) under the spotlight. This article reports the successful manufacturing of hybrid yarns consisting of staple CF cut from virgin CF filament yarn and polyamide 6 fibers of defined lengths (40 and 60 mm). Carding and drawing are performed to prepare slivers with improved fiber orientation and mixing for the manufacturing of hybrid yarns. The slivers are then spun into hybrid yarns on a flyer machine. The investigations reveal the influence of fiber length and mixing ratio on the quality of the card web, slivers and on the strength of the hybrid yarns. The findings based on the results of this research work will help realize value-added products from rCF on an industrial scale in the near future.

This article reports the successful manufacturing of hybrid yarns from virgin staple CF (40 or 60 mm) or recycled staple CF (rCF) by mixing with polyamide 6 (PA 6) fibers of defined length. The hybrid yarns are produced using an optimized process route of carding, drawing, and flyer machine. Furthermore, the influence of CF length, CF type (i.e. virgin or rCF), CF volume content, and twist of the yarn are also investigated regarding the tensile properties of unidirectionally laid (UD) thermoplastic composites. The results show that CF length, yarn twist, and CF content of composites play a big role on the tensile properties of thermoplastic composites. From the comparison of tensile strength of UD composites produced from 40 and 60 mm virgin staple CF, it can be seen that the increase of yarn twist decreases the tensile strength. However, the effect of twist on the tensile properties of UD composites manufactured from 40 mm virgin staple CF is insignificant. The tensile strength of UD thermoplastic composites manufactured from the hybrid yarn with 40 and 60 mm virgin staple CF and rCF is found to be 771 ± 100, 838 ± 81, and 801 ± 53.4 MPa, respectively, in the case of 87 T/m containing 50 volume% CF.

The aim of this paper is to highlight recent developments in the processing of waste carbon fibre for thermoplastic composites. Initially, injection moulding and nonwoven technologies have been used to integrate waste carbon fibres into fibre-reinforced thermoplastic composites. Recently, tape and hybrid yarn spinning technologies have been developed to produce tape and hybrid yarn structures from waste carbon fibre, which are then used to manufacture recycled carbon fibre-reinforced thermoplastics with much higher efficiency. The hybrid yarn spinning technologies enable the development of various fibrous structures with higher fibre orientation, compactness and fibre volume fraction. Therefore, thermoplastic composites manufactured from hybrid yarns possess a good potential for use in load-bearing structural applications. In this paper, a comprehensive review on novel and existing technologies employed for the processing of waste carbon fibre in addition to different quality aspects of waste carbon fibre is presented.

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The processing of recycled carbon fibres (rCFs) into hybrid yarn constructions is a promising recycling option, converting rCF into products with added value. Along with fibre length and strength, the sizing of rCF crucially affects their processing behaviour and subsequent composite properties. This article reports on the influence of sizing on the processing properties of rCF by mixing with polyamide (PA) 6 fibres to form a hybrid yarn construction. Moreover, resulting composite properties were studied as well. Thus, commercially available CF with thermoplastic and thermoset matrix compatible sizing in addition to pyrolyzed rCF without sizing was used for the investigations presented in this article. Results revealed that different sizing strongly influence the processing of rCF and PA 6 into hybrid yarn constructions. The opening and bending behaviour of rCF bundles with different sizing varied during the carding process so that various degrees of fibre shortening occurred. As expected, the sizing developed for thermoplastic matrix enabled the highest tensile and flexural strengths in thermoplastic composites. These findings greatly contribute to the understanding of rCF processing from different or unknown sources on industrial scale.