Composites manufactured from a novel non-woven veil of recycled carbon fibre were tested in longitudinal tension, 3-point bend and short beam shear to assess their
mechanical properties with respect to other commonly available materials. It was found that their mechanical properties were intermediate between ‘high-end’ unidirectional pre-preg and ‘low-end’ chopped strand mat, and similar to that of other short-fibre reinforced plastics.
A range of oxygen plasma treatments were carried out on the fibres to improve interfacial performance of the composites. It was found that treatment at an intermediate
plasma power of 20 W resulted in the greatest improvement in tensile strength of a 10⁰ off-axis composite. Samples were manufactured from either 2 individual veils (IV) or from 2, 10-layer ‘pre-forms’ (PF). Both exhibited similar improvements in 10⁰ off-axis strength. Thus shadowing of the fibre within the plasma did not appear to be significant.
Overtreatment at higher plasma powers (35 and 50 W for IV and 50 W for PF) resulted in a significant reduction in tensile strength and failure strain.
X-ray Photoelectron Spectroscopy (XPS) showed that plasma treatment at 20 W resulted in the highest level of oxygen functionality on the fibre surface, correlating
with the best interfacial performance. Plasma treatment at 10 and 35 W resulted in slightly elevated surface oxygen content, however the off-axis tensile properties of 10 W treated samples were not significantly improved compared to the untreated control. The poor mechanical performance of the over-treated samples can be attributed to either an overly strong interface resulting from increased adhesion or damage to the fibres as a result of the treatment process. There were large variations in fibre wettability across treatments, such that no discernible pattern was present between wettability and interfacial performance.
XPS and ToF-SIMS analysis showed that there was almost complete coverage of the veil by the binder in the veil-making process, and that silicon contamination on the fibre
itself is likely silica based, and that silicon present in the binder is PDMS.
