Air dielectric barrier discharges plasma surface treatment of three-dimensional braided carbon fiber reinforced epoxy composites

The deposition of coatings on the surface of three-dimensional braided carbon fiber reinforced epoxy (C3D/EP) composites will be helpful to their applications. However, they are unsuitable to be deposited due to their low surface free energies, poor wettabilities and poor adhesions. Since treatment of polymers or composites by non-thermal plasmas is a fast, versatile and environmentally friendly surface modification technique, the plasma treatment of C3D/EP composites is investigated in this paper. Dielectric barrier discharges (DBD) in ambient air are used. C3D/EP (Vf = 36%) samples with thickness of 2 mm are placed into the plasma configuration. Time for plasma treatment is 30 s, 60 s and 120 s. The chemical and physical changes induced by the treatments on C3D/EP surface are examined using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The water advancing contact angles of the plasma-treated C3D/EP samples change from 98.6° for the untreated sample to the lower value 45.7° after plasma treatment of 30 s and 42.7° of 120 s. XPS results reveal that the composites modified with the DBD at an atmospheric pressure show a significant increase in oxygen-containing and nitrogen-containing groups, such as C–O, O–C=O and NO2. The AFM images of the untreated and plasma-treated C3D/EP samples show that the composites surfaces roughen. The roughness of the untreated C3D/EP is 1.6 nm, while after plasma treatment of 30 s, 60 s and 120 s the values are 2.4 nm, 3.0 nm and 3.9 nm respectively. These results demonstrate that the surfaces of the C3D/EP samples are more active, hydrophilic and rough after plasma treatments using a DBD operating in ambient air.