Effects of nanosecond laser ablation parameters on surface modification of carbon fiber reinforced polymer composites

Abstract

Removal of contaminants and top polymer layer from the surface of carbon-fiber-reinforced polymer (CFRP) composites is critical for high-quality adhesive-joining with direct bonding to the reinforcing fiber constituents. Surface treatment with a laser beam provides selective removal of the polymer matrix without damaging the fibers and increasing the wettability. However, inhomogeneous thermal properties of CFRP make control of laser ablation difficult as the laser energy absorbed by the carbon fibers is converted into heat and transmitted through the fiber structures during the laser operation. In this study, the effect of scanning speed and laser power on nanosecond laser surface treatment was characterized by scanning electron microscope images and wetting angle measurements. Low scanning speeds allowed laser energy to be conducted as thermal energy through the fibers, which resulted in less epoxy matrix removal and substantial thermal damage. Low laser power partially degraded the epoxy the surface while the high power damaged the carbon fibers. For the studied CFRP specimens consisting of unidirectional [45/0/−45/90]2s stacking of carbon/epoxy prepregs (HexPly®-M91), 100 mJ/mm2 generated by 10 m/s scanning speed and 30 W power appeared as optimum processing parameters for the complete removal of epoxy matrix from the top surface with mostly undamaged carbon fibers and super hydrophilic surface condition.

Controllable Fabrication of Hydrophilic Surface Micro/Nanostructures of CFRP by Femtosecond Laser

“…It revealed the excellent hydrophilicity of the femtosecond laser-processed CFRP. In addition, the wettability of CFRP controlled by femtosecond laser processing can not only achieve hydrophilicity but also achieve hydrophobicity. − This may be attributed to the different laser processing parameters, as well as the different resin composition, resin-fiber composition ratio, carbon fiber arrangement structure, fiber layer spacing, etc., which will affect the results of femtosecond laser processing. The excellent hydrophilicity of the laser-processed CFRP can be speculatively attributed to the intrinsic hydrophilicity of exposed carbon fibers, , the transformation of sp 2 orbitals to sp 3 orbitals of carbons, which can lead to more elevated free energy, , and the carbon fiber-epoxy resin fused micro/nanostructures, which may be beneficial to the capillary effect of water droplets. − The excellent hydrophilicity of laser-processed CFRP should be conducive to enhancing the bonding strength of CFRP used in combination with other materials or reducing the friction resistance of CFRP in close contact with human tissue, hence better meeting the usage requirements of CFRP.…”