PSI - Issue 68

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R. Lach et al. / Structural Integrity Procedia 00 (2025) 000–000

1338 © 2025 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ECF24 organizers Keywords: thermoplastic UD tapes; unidirectional fibre orientation; melt wetting of endless fibres; processing conditions; morphology; fracture mechanics; structure–property correlations 1. Introduction and processing In recent years fibre-reinforced composites were increasingly applied in facilities for sustainable usage of energy especially wind turbines. In architecture, many examples using fibre-reinforced thermosets to implement novel design concepts are also known. Unfortunately, from the today's point of view, these innovative approaches and concepts are confronted with unsolved problems of recycling or end-of-life utilization, respectively. A possible solution of these problems is maybe the application of thermoplastic matrices for manufacturing fibre-reinforced composites. Thereby, it can be contributed to develop closed-loop cycles of materials. Compared to already well established reinforced thermosets, the additional advantage of endless-fibre reinforced thermoplastic composites is the optimum use of the performance of the reinforcing fibres used within the composites or the subsequent parts. Here, the technology of endless-fibre unidirectionally reinforced thermoplastic tapes (UD tapes, Fig. 1a) comes into play. Using a UD-tape production line (see Fig. 1b) the endless fibres working as unidirectionally oriented reinforcement are covered with the thermoplastic matrix by melt wetting. The modularly drafted impregnation nozzle enables a material-specific adaptation of the process resulting in a wide range of possible polymer matrices. Besides widely used standard thermoplastics such as polyethylene (PE), polypropylene (PP) or polyamide 6 (PA6), high-performance polymers such as PPS or PPA, but also bio-based matrices such as PLA, for example, can be easily applied. Also the reinforcing fibres to be available span from conventional glass fibres via carbon fibres up to basalt fibres. Preliminary tests provide proof of the applicability of cellulose-based fibres for manufacturing UD tapes too. R. Lach et al. / Procedia Structural Integrity 68 (2025) 1337–1342

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Fig. 1. (a) Examples of different UD-tape material systems; (b) UD-tape production line by melt wetting of endless fibers.

Within the scope of recent investigations, besides increasing fibre volume fraction in the UD tapes to be crucial for the mechanical performance, the process efficiency regarding the material consumption was distinctly improved. Thus, after the melt wetting impregnation process, an about 0.25‒0.4 mm thick thermoplastic semi-finished product comprising up to 75 weight-% of fibres is available for a broad spectrum of subsequent processing and application. The thin polymer tapes reinforced with unidirectionally oriented (UD) continuous fibres provide a basis for innovative components used in light weight construction. Besides application of the single UD-tape layers for local reinforcement of injection-moulded parts the tapes can be also processed to two-dimensional multi-layer laminates having a build-up sequence according to the corresponding loading conditions. The application of the flexible tapes is also possible to manufacture fibre-reinforced pressured pipes, for example, by winding. In our case, PP and PA6 were selected as matrix materials and glass fibres (GF) and carbon fibres (CF) as reinforcements (PP/GF and PA6/CF). A UD-tape production line was developed within the laboratory scale. The UD tapes manufactured with this facility were procedurally as well as material-specifically analysed. The PP/GF