Fiber fusion

The stabilization process is crucial for the quality of the final carbon fiber. Fusion and other damages to the fiber have to be avoided by applying a carefully balanced regime of time and temperature gradient. For most commercial carbon fiber precursor fibers, stabilization is a time-consuming and costly procedure. 

With regard to carbon fiber stabilization. Table 1 and Figure 3 clearly show that the vinyl halides depress the melting point considerably less than more voluminous monomers such as methyl acrylate, methyl methacrylate or vinyl acetate, at comparable molar level. It can be concluded that fiber fusion will be less of a problem with the former, as compared with the latter. Figure 4 illustrates this point for copolymers AN/VBr as compared to AN/VA. The melting points are calculated using Eq. (2),... 

To stabilize PAN based fibers in a reasonable time (say one hour or less), higher entrance temperatures are required, and this inevitably dictates limitations concerning the type and the concentration of the comonomer. Evidently, a compromise between the beneficial influences of the comonomer with regard to the oligomerization reaction, and the danger of fiber fusion, has to be looked for. 

Co., Ltd, Tokyo, Japan) [64], An increase in the A,A-dimethylfomianiide (DMF)/ tetrahydrofuran (THF) ratio led to fiber fusion and a decrease in fiber diameter, leading to lower compliance values. An increase in rotational speed led to stiffer, less compliant tubes. Another study confirmed that an increase in the DMF/THF ratio significantly increased fiber bonding and elastic modulus [65]. 

However, if the distance is too great, this causes failure of the fiber formation. If the distance is too short, the solvent may not be completely evaporated, resulting in a larger fiber diameter. Reducing the distance also can increase fiber fusion and adherence to the collector surface [15]. 

Fusion reactors Fusion temperatures Fuzz fibers... 

The thermal protection system of the space shutde is composed mainly of subliming or melting ablators that are used below their fusion or vaporization reaction temperatures (42). In addition to the carbon-carbon systems discussed above, a flexible reusable surface insulation composed of Nomex felt substrate, a Du Pont polyamide fiber material, is used on a large portion of the upper surface. High and low temperature reusable surface insulation composed of siHca-based low density tiles are used on the bottom surface of the vehicle, which sees a more severe reentry heating environment than does the upper surface of the vehicle (43). 

Thermal Theory. The thermal approach to flame retardancy can function in two ways. Eirst, the heat input from a source may be dissipated by an endothermic change in the retardant such as by fusion or sublimation. Alternatively, the heat suppUed from the source maybe conducted away from the fibers so rapidly that the fabric never reaches combustion temperature. 

The use of steam is generally limited to polypropyleae and polyethylene fusion because impractical pressures are required to reach the temperature levels, eg, >200° C, required for bonding polyesters. In general, greater temperature control is required for area bonding polypropylene than for other polymers because the temperature difference between the matrix and biader fibers can be only 3°C (26). 

Applied Sciences, Inc. has, in the past few years, used the fixed catalyst fiber to fabricate and analyze VGCF-reinforced composites which could be candidate materials for thermal management substrates in high density, high power electronic devices and space power system radiator fins and high performance applications such as plasma facing components in experimental nuclear fusion reactors. These composites include carbon/carbon (CC) composites, polymer matrix composites, and metal matrix composites (MMC). Measurements have been made of thermal conductivity, coefficient of thermal expansion (CTE), tensile strength, and tensile modulus. Representative results are described below. 

Zell-verschmel2ung, /. cell fusion, -wand, /. cell wall. -woUe, /. staple fiber, staple rayon artificial wool. 

The heat of fusion of the rotator phase in n-paraffms is 38-40 cal/g, while AHo- m for PE irradiated with 1000 Mrad is about 29 cal/g. The corresponding value of AHo->m for hexagonal PE at high pressure (500 MPa) is only around 15 cal/g. Thermograms of constrained PE fibers showed similarly low heats of fusion of the hexagonal phase. 

Skeletal muscle is made up of many muscle fibers (Figure 1) each of which is a multinucleated cell that was formed during development by the fusion of many cells (myoblasts). Skeletal muscle is formed from precursor myoblasts which arise... 

Figure 1. Muscle development. A skeletal muscle fiber is formed by the fusion of many single cells (myoblasts) into a multinucleated myotube. Myotubes then develop into the muscle fiber (see text). Sarcomeres form in longitudinal structures called myofibrils. The repeating structure of the sarcomere contains interdigitating thick and thin filaments.

---