Characterization and interphase mechanical properties of epoxy/PVP blends

Applying sizing material (poly n-vinylpyrrolidone or PVP) around graphite fibers enhances the mechanical properties of carbon fiber reinforced epoxy composites. Understanding the influence of the interphase region between the carbon fiber and epoxy matrix is crucial in enhancing the performance of carbon fiber reinforced epoxy composite materials. In this work, simulated interphase regions, in the form of pure and modified epoxies were synthesized in the laboratory. Several characterization techniques were used to identify the properties of these modified epoxies. They were: 1) Tensile Tests: 2) Fracture Toughness Tests; 3) Thermogravimetric Analysis (TGA): 4) Differential Scanning Calorimetry (nSC); 5) Fourier Transform Infrared (FTIR) Spectrometry: and ()) Water Absorption. Young's modulus, yield stress, yield strain. ultimate tensile stress. ultimate tensile strain, tensile toughness, fracture toughness, and strain energy release rate were obtained from tensile and fracture tests. DSC and FTIR experiments were employed in this study to show the miscibility of PVP and epoxy resin. The pure and modified epoxy samples were immersed in water for about a month to determine their water absorptivity. Almost all epoxies remained unchanged in stiffness, with the exception of the sample 40 wt. % PVP. Only the pure epoxy and light PVP loading epoxies exhibited yield points. The ultimate properties worsened significantly with the increase of PVP loading. A decreasing trend was found in fracture toughness as PVP loading increased. All pure and modified epoxies exhibited sharp glass transition temperatures and the T_g's followed the Fox prediction. Downward frequencies shifting of carhonyl and hydroxyl groups were obtained from the PVP/epoxy blends by infrared study. This was believed to show evidence of hydrogen bond formation. All epoxy and modified epoxies were swollen in water absorption experiments. The samples reached equilibrium after about one month and water absorptivity was found to be a function of PVP content. These experiments sought to demonstrate the characteristics of the interphase region of the composites.