Fiber structure effect

In an earlier study (44) on the effect of viscosity ratio on the morphology of PP-LCP blends we found that the viscosity ratio is a critical factor in determining the blend morphology. The most fibrillar structure was achieved when the viscosity ratio (i7lcp i7pp) ranged from about 0.5-1. At even lower viscosity ratios the fiber structure was coarser, while at viscosity ratios above unity, the LCP domains tended to be spherical or clusterlike (Fig. 1)=... 

Polk et al. reported27 that PET fibers could be hydrolyzed with 5% aqueous sodium hydroxide at 80°C in the presence of trioctylmethylammonium bromide in 60 min to obtain terephthalic acid in 93% yield. The results of catalytic depolymerization of PET without agitation are listed in Table 10.1. The results of catalytic depolymerization of PET with agitation are listed in Table 10.2. As expected, agitation shortened the time required for 100% conversion. Results (Table 10.1) for the quaternary salts with a halide counterion were promising. Phenyltrimethylammonium chloride (PTMAC) was chosen to ascertain whether steric effects would hinder catalytic activity. Bulky alkyl groups of the quaternary ammonium compounds were expected to hinder close approach of the catalyst to the somewhat hidden carbonyl groups of the fiber structure. The results indicate that steric hindrance is not a problem for PET hydrolysis under this set of conditions since the depolymerization results were substantially lower for PTMAC than for die more sterically hindered quaternary salts. 

The main difference between titania nanotube and the ID nanostructures discussed before is the presence of an hollow structure, but which has significant consequences for their use as catalytic materials (i) in the hollow fiber nanoconfinement effects are possible, which can be relevant for enhancing the catalytic performance (ii) due to the curvature, similarly to multi-wall carbon nanotubes, the inner surface in the nanotube is different from that present on the external surface this effect could be also used to develop new catalysts and (iii) different active components can be localized on the external and internal walls to realize spatially separated (on a nanoscale level) multifunctional catalysts. 

Although chemically modifying DNA have distinctive implications for chromatin transitions and fiber structure in the presence of HI [250], in vivo these effects appear to work in concert with chromosomal proteins. 5 -Methylcytosines are specifically bound by members of the MBD (methyl-CpG-binding-domain) family, such as MeCP2 (Methyl-Cytosine binding Protein 2) and MBDl. These proteins have been shown to interact with HDACs and provide a casual link between DNA methylation, histone deacetylation and transcriptional repression [251-253]. 

Histone acetylation is without a doubt one of the most thoroughly characterized post-translational modifications of histones where both the functional (see Section 3.1) and structural implications for chromatin have been explored. In the sections that follow we are going to summarize the major structural effects of this post-translational modification as they pertain to the nucleosome and the chromatin fiber. 

The major structural effects of histone acetylation that affect both the nucleosome core particle and the chromatin fiber are schematically summarized in Fig. 13. 

The insight from AFM images may be greatly boosted by sophisticated image analysis. Fritzsche and Henderson [30,31] have extracted cross-sections of nucleosomes at half-maximum height and have fitted them to virtual ellipsoids. These ellipsoids had relatively smooth perimeter and an aspect ratio of 1.2 1.4 moreover, the orientation of the ellipsoids was correlated with the direction of the fiber axis, with more than 50% of nucleosomes aligned with the axis. While this orientation effect may result from surface interactions, as discussed by the authors themselves, it may also represent an actual, and structurally important, feature of fiber structure. Ellipsoid-shaped nucleosomes have been reported in electron EM studies [32,33], and have been predicted in models of chromatin... 

The foregoing indicates that much remains to be learned concerning the effects of fiber on the metablic influences of xenobiotics. Very little has been done to elucidate influences of types of fiber and to relate them to fiber structure. The sex differences observed have not been exploited to learn what there is about the male-female difference (hormones, blood chemistries) which could be used to make dietary fiber a more effective protective agent in males. 

Measurements on Reinforced Plastics (Structure Effect). Polymeric substrates (Poly-butylterephthalate PBT) with different amount of glass fibers were painted with a typical coating system for plastics. The complete coatings... 

Displacement of peak of fusion on curves DTA in area of smaller temperatures specifies that in the modified fibres crystals have mainly morphological form II (the extended circuits of polymers incorporated into crystallites) while in initial PETP crystals mainly have morphological form I (folded structure). Therefore for initial PETP it is observed endothermic effect at temperature 269°C - speaking by fusion flat folded crystallites (morphological form I). At modified PETP - fibers this effect is observed at temperature 245 - 263°C, it speaks fusion of spherallite (the morphological form II). 

One of the chief difficulties in attempting to relate the physical properties of the fiber to its chemical structure is the nonspecific nature of many chemical treatments applied to the fiber. Frequently, effects ascribed to the modification of one residue are explained equally well in terms of side reactions with other amino acid residues. 

Effect on Fiber The effect of extrusion on fiber is related primarily to its bulk density. As a result of the mechanical action, grinding, and attrition, the hollow structure of fibrous materials is crushed, thus changing the bulk density. High fiber ingredients are normally low in moisture and take on moisture slowly, which requires some type of preconditioning prior to extrusion. 

Another method to improve the structural order of CMs is the conversion of the precursors to fibers prior to the pyrolysis step [377]. The precursor polymer may be stretched in addition. Carbon fibers are manufactured in large quantities as reinforcements in composite materials, after Bowen [403] and Fitzer [404]. Surface and bulk activation can be accomplished by anodic oxidation in dilute aqueous electrolytes (cf. Besenhard et al. [405, 406]). But carbon fibers with various degrees of graphitization have also been employed recently in rechargeable batteries [407-411] and in electrochemical double layer capacitors [18, 412-416]. This takes advantage of two fiber specific effects, namely... 

Empirical permeability predictions are not as effective in fibrous materials as in packed beds due to wider variations in pore morphology. The Carman-Kozeny equation is used at times, in which case kcK and must be inferred from what is known about the particular fiber structure or from available experimental data. 

The mechanical properties of PAn differ considerably between the electrochemi-cally prepared polymer and that produced from solvent casting. As described earlier, electropolymerized emeraldine salts are highly porous and, consequently, have low mechanical strength. Freestanding films may be prepared electrochemically, but their poor mechanical properties limit their usefulness. In contrast, the polymers made from solution are much less porous and are widely used as freestanding films and fibers. The effect of polymer structures and morphology on PAn mechanical properties are described in the following text. 

It is a mistake, however, to ascribe deviations from the results expected by Darcy s law to weakness of the experimental technique. A more productive point of view is to assume that Darcy s law holds for the ideal gelled grease structure and to interpret deviations from predicted behavior as informative of the actual structure. For instance, Brown and Ewbank [15] proposed that permeation takes place predominantly through the larger pores of the grease structure and cited evidence that only about 25-50% of the oil held by a grease can be made to flow out of the structure. Persistent retention of the oil can be ascribed to physicochemical interaction with soap fibers, the effect of which is... 

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