From Scrap to Print: Upcycling Aerospace CF/PEKK Prepreg Waste for 3D Printing

Published in Composites Communications (2025).

Closing the Loop on High-Performance Composite Manufacturing

The aerospace industry generates significant quantities of carbon fiber reinforced thermoplastic composite scrap: offcuts from automated fiber placement, rejected parts, and post-cure trimming waste. For materials like CF/PEKK and CF/PEEK — which cost hundreds of dollars per kilogram and represent some of the most energy-intensive materials to produce — discarding this scrap is both economically wasteful and environmentally problematic.

But reclaiming these scraps is not straightforward. Unlike commodity plastics, thermoplastic composites are difficult to reprocess without degrading the fibers, the matrix, or both. The key question this work addresses: can we convert aerospace prepreg waste into a printable feedstock for additive manufacturing, and do the resulting parts have useful mechanical properties?

The Upcycling Process

Our approach takes CF/PEKK prepreg offcuts and processes them through a series of size-reduction and compounding steps to produce a granulated feedstock suitable for Fused Granule Fabrication (FGF) — also known as large-format FDM with pellet or granule feedstocks. FGF is particularly well-suited here because it can handle the irregular particle sizes typical of chopped composite scrap.

Key Results

• Processability: Upcycled CF/PEKK granules can be successfully printed via FGF without significant thermal degradation, confirmed by thermal analysis
• Mechanical performance: Tensile and flexural properties of upcycled parts are competitive with virgin short-fiber PEKK compounds for non-primary structure applications
• Fiber retention: Average fiber length in printed parts is characterized, quantifying the trade-off between processability and reinforcement efficiency
• Economic pathway: A preliminary analysis shows the upcycling route is commercially viable at small scale, with clear paths to improvement at larger volumes

This work contributes to the emerging field of circular economy for advanced composites and demonstrates a practical route to recover value from aerospace manufacturing waste.