Properties of pyrolytically recycled carbon fibers and their re-use in composites

Recycling of composite products is a developing field with possibilities to enhance circular economy and sustainable use of resources. Aim of this study is to investigate the properties of recycled carbon fibers and how changes in the fiber surface structure affects the fiber-matrix interphase in a composite structure. In composite applications, virgin carbon fibers typically have a surface sizing deposited onto the fiber surface during manufacturing process to enhance adhesion and ease processing. However, in the literature there is evidence that resizing of thermally recycled carbon fibers may be unnecessary. In this study, the need for resizing of the recycled carbon fibers is also evaluated. The carbon fibres are reclaimed pyrolytically from industrial pre-consumer waste. Single filament tensile tests are used to verify the mechanical properties of the recycled fibers. Changes in the surface structure and properties of the fiber-matrix interphase due to the recycling process are evaluated with electron microscopy, microbond testing as well as thermogravimetric and spectroscopic analysis. The results show that pyrolytic recycling process provides clean and reusable carbon fibers that can be reused with or without resizing in composite applications. However, a decrease in tensile strength is observed.