P-100 Fibers Research Articles

The effect of surface treatment on graphite nanoplatelets used in fiber reinforced composites

ABSTRACTAtmospheric plasma treatment (APT) was used to surface‐activate graphite nanoplatelets (GnP) as well as highly graphitic P100 fibers used to manufacture composites. X‐ray photoelectron spectroscopy showed an increase in the O/C ratio of the treated surfaces when using either CO or O2 as the active gas, whereas CO exhibited less damage to the treated reinforcement carbon material. APT of P100 fibers resulted in a 75% increase in composite tensile strength when compared to composites using untreated fibers. Surface treatment of GnPs also resulted in GnP/epoxy composites with significantly higher glass transition temperatures (Tg's) and 50% higher flexural strengths than those with no surface treatment because of stronger particle‐to‐resin coupling, which was also evidenced by the fracture surfaces. The effect of GnP loading concentration and plasma treatment duration was also evaluated on the tensile strength of fiber‐reinforced composites. The addition of untreated GnP filler resulted in a decrease in strength up to the 1% loading. However, higher loading conditions resulted in a 20% improvement because of GnP orientation effects. Fracture surfaces suggest that the fibers provided a mechanism for the GnPs to orient themselves parallel to the fiber axis, developing an oriented matrix microstructure that contributes to added crack deflection. Incorporating surface‐treated GnPs in these composites resulted in tensile strengths that were as high as 50% stronger than the untreated systems for all loading conditions. Increased GnP‐to‐matrix bonding as well as enhanced orientation of the GnPs resulted in multifunctional composites with improved mechanical performance. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39994.

Aqueous electrochemical intercalation of bromine into graphite fibers

For the first time, graphite fibers have been electrochemically intercalated with Br − that have the same structure and properties as those intercalated from vapor phase Br 2. This was accomplished by intercalating pitch-based Thornel ® K-1100 graphite fibers at low temperature (near 0 °C) and high currents (2 A) for long times (6 h). The mechanism appears to be that Br − is oxidized to aqueous Br 2 which, when sufficient local concentration builds up, intercalates the fiber. This was confirmed by intercalating K-1100 fiber in a saturated aqueous Br 2 solution without passing an electrical current. The applied voltage does apparently lower the activation energy of the reaction as evidenced by the observation that P-120 and P-100 fibers will not intercalate in aqueous Br 2 unless a voltage is applied.

Fiber contribution to modal damping of polymer matrix composite panels

An analytical method to determine the modal frequencies and damping of flexural vibration of continuous fiber-reinforced composite panels has been developed. Fiber damping effects are included in this method. Damped panel vibration modes are found using a higher-order laminate theory and the Rayleigh-Ritz method with complex eigenvalue analysis. Fiber contribution to modal damping was found to be significant in vibration modes involving longitudinal deformation of fibers. For a [0]g P100/3501-6-square cantilevered laminate, in vacuum and at room temperature (20° C), the predicted first mode damping showed an increase of 77% by including fiber damping. The use of bromine-intercalated P100 fibers resulted in a further predicted increase of 438% in the first mode damping at room temperature. Effects of changes in ply orientation, temperature, and thickness of the laminate on the fiber contribution to damping were examined. Fiber contribution to the damping of an angle-ply laminate can be estimated from the mode shapes and ply orientation of the laminate. Damping of modes exhibiting nearly pure bending or a combination of bending and twisting can be significantly unproved by use of treated (intercalated) fibers. Nomenclature A = area of laminate, m2 C^ = stiffness coefficients of the kth lamina, N/m2 c = volume fraction EL longitudinal Young's modulus, N/m2 h = laminate thickness, m hk = thickness of the &th lamina KT = plane strain bulk modulus, N/m2 M, N = number of modes in the X and Y directions, respectively n = number of laminae or layers q =

Bromination of graphitic pitch-based carbon fibers

Bromination of the du Pont E-130 pitch-based carbon fibers was found to degrade the tensile strength, tensile modulus and oxidation resistance. This degradation was greater when bromination was carried out by exposure to bromine vapor than by the electrochemical method, and is attributed to the physical damage of bromination. This degradation is in contrast to the beneficial effect of bromination of less graphitic fibers, such as Amoco's Thornel P-100. However, bromination decreased the electrical resistivity by up to a factor of 5. This effect is due to the intercalation of bromine, as indicated by the in-plane intercalate superlattice order at room temperature and up to 100°C, at which temperature inplane melting occurred for fibers brominated by either method. A sharp intercalate Raman peak was observed at 240 cm −1, in contrast to the large breadth of this peak in Thornel P-100 fibers.

The effect of length and diameter on the resistivity of bromine intercalated graphite fibers

The resistivity of bromine intercalated graphite fibers has been shown to vary with both the diameter and the length of the fibers. This is due to bromine depletion from the fiber surface. Model calculations assuming a 1.0 μm bromine depletion zone for P-100, and 3.0 μm for vapor-grown graphite fibers fit the respective diameter depletion of their resistivities quite well. Length dependence data imply a bromine depletion zone along the length of P-100 fibers which is also a few microns, but that of vapor grown fibers appears to be as large as 300 μm. Despite these values, micro-filaments, which are much smaller than the expected depletion zones, do form residual bromine intercalation compounds with resistivities about one-half of their pristine value.

Synthesis and stability of Br 2, ICI and IBr intercalated pitch-based graphite fibers

This work presents a further study of the intercalation of halogens in pitch-based fiber and the stability of the resultant intercalation compounds. P-100 fibers were intercalated with purified IBr at 50 °C to produce high electrical conductivity graphite intercalation compounds (GICs). After intercalation and subsequent equilibration in ambient atmosphere, the fibers average a five-fold conductivity,enhancement over the pristine fiber, and after nine weeks in air, the conductivity, σ, degrades by only 1%. The intercalation of ICl in P-100 was performed in vacuum-sealed vessels at 50 °C, 20° and 0 °C. Both the lowest equilibrium resistivity and its smallest ambient gain were observed for fibers reacted at 20 °C. P-100 brominated at 68 °C in vacuum-sealed vessels showed no loss in electrical and stability properties over those reacted at 20 °C in the presence of air. Energy dispersive spectroscopy (EDS) results confirm the existance of excess bromine and chlorine in the iodine interhalide GICs, which is predicted by the oxidation mechanism proposed for this class of intercalation reactions.

A heater made from graphite composite material for potential deicingapplication

A surface heater was developed using a graphite fiber-epoxy composite as the heating element. This heater can be thin, highly electrically and thermally conductive, and can conform to an irregular surface. Therefore it may be used in an aircraft's thermal deicing system to quickly and uniformly heat the aircraft surface. One-ply of unidirectional graphite fiber-epoxy composite was laminated between two plies of fiber glass-epoxy composite, with nickel foil contacting the end portions of the composite and partly exposed beyond the composites for electrical contact. The model heater used brominated P-100 fibers from Amoco. The fiber's electrical resistivity, thermal conductivity and density were 50 micro ohms per centimeter, 270 W/m-K and 2.30 gm/cubic cm, respectively. The electricity was found to penetrate through the composite in the transverse direction to make an acceptably low foil-composite contact resistance. When conducting current, the heater temperature increase reached 50 percent of the steady state value within 20 sec. There was no overheating at the ends of the heater provided there was no water corrosion. If the foil-composite bonding failed during storage, liquid water exposure was found to oxidize the foil. Such bonding failure may be avoided if perforated nickel foil is used, so that the composite plies can bond to each other through the perforated holes and therefore lock the foil in place.

Material Damping in Aluminum and Metal Matrix Composites

The material damping in beam-like specimens of aluminum and metal matrix com posites was measured. A unique apparatus to determine damping by free decay while the specimens are in free fall in a vacuum was used. The specimens tested include 2024-T3 and 6061-T4 aluminum, and unidirectional graphite/metal matrix specimens with P55 and P100 fibers and 6061 Aluminum and AZ91C Magnesium as matrix materials. Tests were conducted to determine the dependence of damping on frequency and stress level. For the aluminum specimens, the material damping followed the Zener model at very low stress levels. Below the Zener relaxation frequency, a strong dependence of damping on stress was found for even moderate stress levels. Damping for the aluminum matrix materials was slightly above that predicted by the Zener model for a homogeneous bar of the matrix aluminum. For the magnesium matrix specimens, damping significantly above the Zener prediction for the homogeneous matrix material was observed.

Effects of milling brominated P-100 graphite fibers

Preliminary procedures have been developed for the ball milling of pristine and brominated P-100 graphite fibers. Because of the lubricative properties of graphite, large ball loads (50% by volume) are required. Use of 2-propanol as a milling medium enhances the efficiency of the process. The fibers, when allowed to settle from the milling medium, tend to be preferentially aligned with rather few fibers standing up. Milled, brominated P-100 fibers have resistivities that are indistinguishable from their pristine counterparts, apparently because of loss of bromine. This suggests that bromine would not be the intercalate of choice in applications where milled fibers of this type are required. It was found that brominated graphite fibers are stable in a wide variety of organic solvents.

Thermal conductivity of pristine and brominated highly graphitized pitch based carbon fibers

The thermal conductivity of brominated and pristine Union Carbide P-100 graphite fibers in the 30–160°C temperature range was determined by measuring the thermal conductivities of graphite fiber epoxy composite samples and then excluding the epoxy contribution. A comparative thermal conductivity instrument was used to measure the thermal conductivity of the samples containing fibers. Results showed that the thermal conductivity values were 225–370 W/m-k and 215–340 W/m-K for pristine and brominated fibers respectively. Furthermore, the thermal conductivity ratio of brominated to pristine P-100 fibers was 0.89, 0.91 and 0.92 at 55–80°C, 108 and 130°C respectively. Such a decrease in thermal conductivity results almost entirely from the 10% increase in the fiber cross-sectional area due to bromination. This result suggested that bromination effects on P-100 fiber structure is small and that some structural changes (presumably the sharp-angled domain wall becomes less sharp) occurred in the 80–108°C temperature range.