Surface area treated fibers

From SEM studies, it can be observed that the untreated sisal fiber has a network structure and includes waxes and other low molar mass impurities whereas sisal fiber gets thinner after treatment. It is possible that treatment leads to microfiber fibrillation. The surfaces of the treated sisal fiber become smoother as compared to those of untreated sisal fiber. The effective surface area of fiber available for contact with the matrix also increases in composites while also reducing the diameter of sisal fibers and thereby increasing their aspect ratio. This may offer better fiber-matrix interface adhesion and improve stress transfer. These will give rise to improvement in mechanical properties [78]. 

Figure 3 shows the water-vapor adsorption isotherms measured on the silane-treated fibers along with those obtained on the untreated fibers. A complete discussion of the water adsorption isotherms of the untreated fibers has already been reported [8]. Here, two new features are immediately evident. First, the presence of the silane overlayer has greatly enhanced the water adsorption capacity of the fibers, and, second, the silane-treated fibers that contain 4% and 6% B,0, adsorb significantly more water than the 0% B20, fibers. It is important to note that these data have been normalized to the specific surface areas of the... 

The water adsorption capacity of the silane-treated fibers—at low pressure where only the most reactive sites are sampled—was 5-10 times the specific surface area. It is proposed that the excess water adsorption capacity of the silane-treated fibers is associated with sites within the silane overlayer. These may be hydroxyls, strained siloxanes, boroxanes, free volume, or microporosity. These sites provide a mechanism for physical and chemical adsorption, swelling, and rearrangement of the adsorbed silane in the presence of water. These observations are consistent with the idea that the adsorbed silane is a chemically... 

Methods which enploy liquid phase treating liquors (spray, transfer rolls and belts, etc.) share a cannon difficulty stemming from the lew volume of liquor in relation to the large surface area of the fibers conprising the substrate to be treated. This difficulty is acerbated when aqueous liquors are to be applied to hydrophilic fibers. Foam coating methods enploy stable foams which allow the thickness of the liquid-air mixture to be controlled by a doctor blade or roll. Conparatively low add-ons can be achieved by virtue of the low density of the foam layer, but the stable nature of such foam, and its immobile liquid phase, inhibit rapid, uniform distribution through the substrate. 

Because of differences in surface area. For example, a sample in powder form derived from BHQ/MHQ/DPT/DPC (50/50/55/45) with reduced viscosity of 1.97, can be treated to give a product with reduced viscosity of 4.19 at 240°C for 6 hours, while a sample in fiber form, spun from a sample of the same viscosity, became insoluble in the same solvent after it was treated under the same conditions. 

Since the consequences of mechanical energy uptake were disaggregation of fiber bundles, shortening of fiber length and reduction of DP, it is plausible to consider that new surface areas were also created. Accordingly, the change of accessibility of mechanically treated fibers may be observed. The accessibility of mechanically treated fibers was evaluated based on the iodine absorption techniques. Results are shown in Figure 5. 

Recent studies on the use of ammonia-treated activated carbon fibers or cloth for the catalytic removal of SO2 have shown that the activity increases with the amount of basic nitrogen groups present [104-106]. In particnlar, it was fonnd that the more basic pyridinic groups are the most active for the catalytic oxidation of SO2 both into SO3 and H2SO4 [107], and a linear correlation between the activity (normalized by the BET surface area) and the concentration of pyridinic groups was obtained, as shown in Fignre 6.7. 

A 10 and A 15 are activated carbon fibers treated with NH3 at the temperatures (in °C) indicated, for 10 or 60 minutes. The ACFs were produced industrially from Kymol, a phenol-formaldehyde fiber with a surface area of 730 m /g (A 10) or 1585 m /g (A 15). 

Plasma-induced hydrophobization of cottonfabric in conjunction with increased specific surface area leads to an interesting and practically important effect. Water droplets are able to effectively remove dirt particles from the surface of the cotton fabric. This phenomenon is illustrated in Fig. 9-29 for the case of HMDSO-plasma-treated cotton fabric (Hocker, 2002) and is usually referred to as the Lotus effect. Thus, the highly hydrophobic plasma-treated surface of cotton with specific plasma-modified surface topography is extremely dust- and dirt-repellant in contact with water. As an important consequence, the plasma-treated surface also becomes repellant to bacteria and fungi. The effect is relevant not only to cotton fiber but to some other materials as well. 

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