Fibers heat effects

For fabrics of thermoplastic fibers, permanent effects are obtainable if heat and pressure are appHed to soften the material. Processes dealing with carpets, nonwovens, and chemical modifications or additions that occur before the fiber is formed are not discussed herein (see Nonwoven fabrics). 

These results provide clear evidence for the existence of selective heating effects in MAOS involving heterogeneous mixtures. It should be stressed that the standard methods for determining the temperature in microwave-heated reactions, namely with an IR pyrometer from the outside of the reaction vessel, or with a fiber-optic probe on the inside, would only allow measurement of the average bulk temperature of the solvent, not the true reaction temperature on the surface of the solid reagent. 

Muller (1959) and co-workers have made many interesting and important studies of heat effects during the mechanical stretching and relaxing of polymeric fibers. However, Dole (1959) in reviewing calculations of the enthalpy differences between drawn and undrawn fibers and annealed samples as computed from specific heat-temperature data could find no differences that could not be explained on the basis of the extent of crystallinity of the samples. 

It has been confirmed that when undergarments produced from the PVC fiber are worn, the fibers become negatively charged and the concentration of calcium ions in the blood increases [153]. The fiber also has an excellent heat-retaining property. Because of these factors, it has been shown that the PVC fiber is effective for the treatment of neuralgia or rheumatism. 

Creep Behavior of Non-Oxide Fibers and Effects of Heat Treatment, Oxidation, and Aging... 

The unexpected transition in the electrical conductivity was attributed to the interactions between the MWCNTs and the CPs inside the fiber due to an annealing effect of the PANl/PEO matrix from the thermal dissipation of the carbon nanotubes (CNTs). It was also related to the self-heating effect of the MWCNTs incorporated into the CPs, which will be very helpful in enhancing the electrical properties of nanoscale conducting composite fibers. 

Temperature is one of the processing parameters which has a pronounced effect on the failure strength of carbon fibers. This effect is quite different for MP based and PAN based fibers. As the heat treatment temperature (HTT) is raised, the strength of a mesopitch based fiber, tested at room temperature, progressively increases [3] [38] [54-55]. Conversely, that of most PAN based fibers undergo a maximum at about 1300-1500 C (Figure 12). 

The current requirements for the surface treatment of HM fiber are relatively high and there is an appreciable heating effect, which necessitates cooling of the electrolyte in order to control the rate of treatment. Also, with some electrolytes, cooling is essential to avoid thermal decomposition. 

Table 5.11 The effect of gage length on the tensile strength of carbon fibers heat treated to 2500°C.

Figure 5.46 Apparent crystallite size against heat treatment temperatures for three levels of stress. Source Reprinted with permission from Ozbek S, Isaac DH, Carbon fiber processing Effects of hot stretching on mechanical properties. Mater Manuf Process, 9(2), 179-197, 1994. Copyright 1994, CRC Press, Boca Raton, Florida.

Chen et a/ (1981) [201] studied the effect of decolorizing with NaOCl (5.25% available chlorine) on partly or fully stabilized acrylic fibers, heated for various times at 220-250°C. With lightly stabilized fibers, decolorization takes place in two steps—an incubation period with slight decolorization followed by a further incubation period and then gradual decolorization, whereas, with the fully stabilized fiber, the two processes occur simultaneously. 

Tsai J-S, Wu CJ, Exothermic heat effects on polyacrylonitrile and carbon fibers during continuous... 

The concentration of the electrolyte in water must be sufficient to enable the electrolytic process to take place and further electrolyte must be added during the run in order to allow for depletion in the bath due to fiber take-up. A suitable cathode material is a graphite block which is best covered with a fabric bag to prevent the carbon fiber (anode) shorting out. Faraday s laws will apply and the current should be adjusted to provide the correct level of treatment. Type A fiber is readily attacked and a surface dross, akin to colloidal graphite, is formed on the surface of the bath, whereas in order to provide sufficient treatment for a Type HM fiber, relatively heavy currents are required, accompanied by a substantial heating effect, which in turn necessitates cooling. 

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