Internal geometry of woven composite laminates with “fuzzy” carbon nanotube grafted fibers

Radially aligned carbon nanotubes (A-CNTs) grown on micron-scale fibers promise structural composites with high mechanical performance and multi-functional properties. Changes in the internal structure of woven composite laminates after A-CNT growth are studied here utilizing micro-computed tomography. The laminates are produced by vacuum impregnation in a closed mold with and without clamping pressure. Two A-CNT lengths are investigated: 4-6 μm and 17-19 μm. A-CNTs were found to increase the distance between fibers, scaled by the A-CNT length. This “swelling” resulted in an increased cross-sectional area, crimp and in-plane misalignment of the yarns. The laminate thickness doubled for laminates with long A-CNTs compared to shorter ones. The laminate with long A-CNTs produced under pressure showed a remarkable alteration of the internal structure. Fibers migrated within the fabric plane, filling almost completely the resin rich pockets. Further research is needed to understand the effect of these changes on the composite mechanical performance.