Leibniz Institute for Polymer Research Dresden e. V. (IPF) and the Sächsisches Textilforschungsinstitut e. V. Chemnitz (STFI) are working together in a joint research project for resizing of recycled carbon fibers (rCF) for nonwoven manufacturing
In current recycling processes, polymer matrix and sizing are removed from the carbon fibers. In the ReCarboSize project, methods for resizing rCF were investigated. Unsized and sized rCF do not only show differences in processing behavior during the nonwoven production, but also in the mechanical properties of the produced fiber-reinforced polymer composites.
The increasing amount of carbon fibers (CF) for the use in fiber-reinforced polymers requires recycling strategies that enable a second use and preferably a cascade use of CF. In order to implement new recycling routes for CF, an increase in the mechanical performance of the rCF itself, but also of the composite materials made from it, is urgently required.
Better sizing
The development of new sizing concepts contributes significantly to the interaction with the polymer matrix systems leading to an improvement in the mechanical properties of rCF-reinforced composites. From an economic point of view, rCF products can reduce the costs of lightweight construction if they are used either alone or in combination with new carbon fibers or glass fibers. From a textile technology perspective, the sizing of rCF is necessary to improve the processing behavior, e. g. in the nonwoven fabric process. STFI studies have shown that the processing of unsized fibers can lead to significantly increased fiber damage in the process or that nonwoven formation is not possible in some cases.
Reassuring research results
At the IPF, preliminary tests were carried out on a laboratory scale on the distribution of the sizing after spray and dip application; concentrations and application quantities were varied. Fluorescent agents have proven to be a helpful additive in the assessment of sizing distribution.
The aim of the work at the IPF was to develop sizings for the thermoplastic matrices polyamide 6 (PA6) and polyphenylene sulphide (PPS), while the Belgian partner Centexbel investigated sizings for thermoset matrices (epoxy resin, polyurethane).
With good sizing distribution, better processing of the fibers in the nonwoven production process was observed at the STFI. In addition, the fiber-matrix adhesion for the PPS composites could be significantly increased (fig. 1).
Upscaling of the tests was made possible by the involvement of a recycling company, which took over the application of selected sizings on rCF on a kg scale. By this way successful upscaling for a comprehensive mechanical characterization of the fibre composite panels at the STFI was achieved (fig. 2). Subsequent application of the sizing to prefabricated nonwovens led to a lower mechanical performance compared to the application to rCF before processing into a nonwoven.
The project partners are planning follow-up projects to the now completed ReCarboSize research project in order to further advance the use of rCF in fiber-reinforced polymers.
IGF-CORNET project, submitted via Forschungskuratorium Textil (FKT): “ReCarboSize: Improved sizing for recycled carbon fibers to optimize adhesion with polymer matrices and to improve processing behaviour in the production of composite materials”; IGF project no. 297 EBR, duration 10/2021-08/2024.
Partners involved: Sächsisches Textilforschungsinstitut e. V. Chemnitz (STFI), Leibniz-Institut für Polymerforschung Dresden e. V. (IPF), Centexbel Grâce-Hollogne/Belgien (Centexbel)
Contact:
Leibniz-Institut für Polymerforschung Dresden e. V. (IPF)
Prof. Dr.-Ing. Christina Scheffler
+49 351 46 58-373
scheffler@ipfdd.de
www.ipfdd.de
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