Mechanical effects of the plasma surface treatment on carbon fabrics used in composite materials

The benefit obtained from plasma treatment of carbon fiber fabrics in terms of increasing the adhesive properties with a 30% bio-based epoxy resin is investigated in this study. The fabric samples were treated using the Atmospheric Pressure Plasma Jet by adopting two different sources of gas, nitrogen and N2H2 hydrogen-nitrogen mixture, varying the primary and secondary process parameters in order to find the optimal configuration. An initial confirmation regarding the efficiency of the treatment and the correct choice of parameters was obtained primarily by surface chemical-optical characterization with Micro-Raman spectroscopy and Attenuated Total Reflection (ATR) analysis. The effective ablative and/or chemical mixing action of the species on the surface were identified through the use of the latter methods considering the presence of new grafted functional groups - amino, hydroxyl and carboxylic based - on a naturally non-polar surface of carbon fiber fabrics. After chemical characterization, pre-cracked samples were made with untreated and treated fabrics by using vacuum infusion as manufacturing method. Finally, to evaluate the effectiveness of the treatment in terms of mechanical resistance and delamination characteristics, the Double Cantilever Beam test and the End Notched Flexural test were carried out. In particular, both procedures were performed according to the ASTM D5528 and ASTM D7905 standards for the evaluation of the fracture toughness GC on Mode I and Mode II with the adoption of Digital Image Correlation (DIC) instrumentation and equipment to facilitate the analysis of crack propagation.