Fibers surface area

There are two mechanisms of PAN-based carbon fiber oxidation dependent on oxidation temperature ((67,68). At temperatures below 400°C, oxygen diffuses into the fiber and attacks at pores resulting in significantly increased fiber surface area. At higher temperatures impurities catalyze the oxidation reaction. 

A PET microfiber is loosely defined as one with a decitex (see Section 5 earlier) per filament less than one. This translates to a fiber diameter of 10 xm or less. In fabric form, such fibers provide a very soft hand and a non-shiny appearance. They can also make moisture-repellant fabrics without sacrificing comfort or air porosity, ideal for sportswear. The larger fiber surface area also can be useful for filtration applications. 

Another approach to exploit the properties of nanocarbons consists in integrating them in standard fiber-reinforced polymer composites (FRPC). The rationale behind this route is to form a hierarchical composite, with the nanocarbon playing a role at the nanoscale and the macroscopic fiber providing mainly mechanical reinforcement. This strategy typically aims to give FRPCs added functionality, improve their interlaminar properties and increase the fiber surface area. The first two properties are critical for the transport industry, for example, where the replacement of structural metallic... 

In cottonseed oil mills, GNB and leaflike trash are partitioned when linters are removed from the seed. Linters from oil mills and even cleaned linters used by garnetters contained about one order of magnitude more GNB than that found on seeds and on seed hulls (Table I). Linters also contained more leaflike trash than delintered seed and seed hulls. Presumably GNB are found in greater numbers on linters than on delintered seed in oil mills because of larger amounts of leaflike trash entrained in linters and/or because of the relatively huge fiber surface area available on linters for bacterial attachment. 

Formulation Requirements. In order to penetrate the mass of fiber at one end of the bundle, the formulation must have sufficiently low viscosity to move easily through the bundle completely wetting all fiber surface area. Typically, formulations of viscosity less than 8000 poises have been successful. Too low viscosity or too rapid delivery of the formulation can result in the occlusion of air and the ultimate development of voids with loss of mechanical integrity. Our process demands that formulation be delivered and partially cured to an intermediate plateau termed green state. This requires a minimum pot life of 30 minutes after blending of resin and curative. The physical chemistry of the composite membrane requires that the initial exotherm not exceed approximately 150 C. 

There are substantial changes in fiber surface area with associated variations in rugosity depending on the oxidative treatment medium. 

The Kubelka-Munk theory of diffuse reflectance is a good description of the optical properties of paper. The two parameters of the theory, absorption and scattering coefficient, are purely phenomenological, but are closely related to basic properties of paper. The absorption coefficient is approximately a linear function of the chrcmgphore concentration in the paper. The scattering coefficient is related to the nonbonded fiber surface area in the paper, or the area "not in optical contact," and the Fresnel reflectivity of that surface. 

Figure 2.9 Fiber surface area per unit volume versus fiber diameter, d.

Equation (2.5) says that the fiber surface area, for a given fiber volume, varies inversely as the fiber diameter. Figure 2.9 shows a plot of the fiber surface area... 

The carbon fiber surface areas were previously determined by BET krypton adsorption to be 0.62 0.01 m g-1 and 0.74 0.01 n g-1 for T-300 and P-55, respectively. The molecular area of krypton was taken as 0.195 nm2. Prior to these measurements, the fibers were degassed at 300°C for 15 h. The elution of a characteristic point method of finite concentration IGC was used to determine the Isotherms for a series of n-alkanes. Approximately 15 to 20 Injections were used for each Isotherm. The hand-drawn curve through the peak maxima was digitized for Integration and subsequent data handling. 

Increases In qm and C values with the Increase In temperature of column conditioning Indicates the presence of micropores. Carbon fiber surface areas, calculated with Groszek s values for... 

Irreversible Adsorption on Oxide-Free Carbon Fiber3 (Union Carbide VYB fiber, surface area 240 m /g)... 

Variation of Fiber Surface Area with Diameter... 

For a given weight of hair, the fiber surface area is inversely proportional to the fiber diameter. Table 8-17 shows how the calculated fiber surface area varies with diameter for 1 g of hair (assuming it is a right cylinder). 

FIGURE 35.2. Increases in the ratio of CNT surface area to carbon fiber surface area as a function of the CNT diameter. Two typical carbon fiber diameters are compared. 

For filtration, a special profiled fiber 4DG attracts industry s attention. 4DG fiber has deep groves and channels along its longitudinal axis, as shown in Fig. 2.14. These deep grooves can provide higher fiber surface area and improve the transition of water or air along the longitudinal axis of the fiber. Also, the fiber that can serve as ducts to... 

At a given location within an artificial lung, the gas exchange rate (y) per unit fiber surface area (A) can be described in terms of an overall mass transfer coefficient, K. For Oj and COj, these relationships are... 

---