Smaller fiber diameter

Activated carbon fibers (ACF) and nano fibers (ACNF) are a relatively modem form of porous carbon material with a number of significant advantages over the more traditional powder or granular forms. Advantages include high adsorption and desorption rates, thanks to the smaller fiber diameter and hence very low diffusion limitations, great adsorption capacities at low concentrations of adsorbates, and excellent flexibility [18, 19]. 

The small gain in the selective mechanical properties sometimes cannot make up the higher cost of finer diameter of fiber glass. More important to the molders is the increased melt viscosity associated with smaller fiber diameter (Fig. 9.14). At 20 wt% of glass content, the melt flow decreases from 1.9 to 1.35 g/10 min. 

Empirical observations [9] indicate that smaller fiber diameters are obtained using low flows of material. Experimental considerations show that the viscosity greatly affects the diameter of the fibers. With increasing viscosity, the drop of material to be submitted to the electric field changes from a semi-spherical shape to a conical shape, and the length of the jet increases to a steady/laminar flow. The diameter of the fibers increases with increased viscosity, proportionally to the length of the jet. 

Alkali treatment of natural fibers, also referred to as mercerization, is an old and most widely used method for modifying ceUulose-based natural fibers [30-36]. The most favorable alkali solution for mercerization is sodium hydroxide (NaOH) aqueous solution. The effect of alkali treatment on the properties of the composite as well as on the natural fibers strongly depends on alkali solution type, alkali concentration, treatment time, treatment temperature, and treatment tool. Alkali treatment may cause fibrillation of pristine natural fibers, resulting in the breakdown of individual fibers with smaller fiber diameter. This phenomenon can not only increase the aspect ratio of reinforcing natural fibers but also roughen the fiber surfaces. As a result, the fiber-matrix interfacial adhesion may be enhanced and the... 

Many of the potential uses for nonwoven fabries eomprised of nanofibers are expeeted to take advantage of the large speeifie surfaee area, high porosity and small pore size of these fabrics. Both theoretical models and experimental studies have indieated that fiber diameter strongly influences the pore diameter in the fabrie, with smaller fiber diameters resulting in smaller pores. For some applieations, however, it would be interesting to... 

Kaur and co-workers discussed the influence of electrospun fiber size on the separation efficiency of thin-film nanofiltration composite membrane [92], The experimental results indicated that the separation of salts increased with decreasing electrospun nanoflber diameter, with a corresponding decrease in the flux. So, the best combination was to decrease the thickness of the ENM layer, together with smaller fiber diameter the desired result of an increase in the flux together with a high salt rejection should be feasible. For practical water treatment applications, the pore size and thickness of the ENM layer could be adjusted to achieve the desired combination of rejection and flux. 

Nozzle diameter also is an important operational parameter in controlling the fiber diameter. A decrease in nozzle diameter typically leads to smaller fiber diameters and fewer beads. However, if the nozzle diameter is too small, it may not be possible to extrude the spinning solution through the nozzle to form nanofibers. 

Air Flow— During centrifugal spinning, a snction force often is nsed to collect nanofibers onto a porous substrate (Figure 13.5B). Sometimes, air also is blown onto the liquid jet to assist the spinning process. In both cases, the air flow may enhance the elongation of the liqnid jet and lead to smaller fiber diameter. 

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