Fiber Formation and Structure

During the cooling process the fiber is subjected to a draw-down force, which introduces the orientation. Additional orientation may be introduced later by stretching the fiber to a higher draw ratio. 

In wet spinning, the polymer solution is spun into a coagulant bath. An example is a 7% aqueous solution of sodium cellulose xanthate (viscose), which is spun into a dilute sulfuric acid bath, also containing sodium sulfate and zinc sulfate (160). The zinc ions form temporary ionic cross-links between the xanthate groups, holding the chains together while the sulfuric add, in turn. 

Polyamide Polyester Polyethylene Polypropylene PVDC Cellnlose acetate Cellnlose triacetate Acrylic Modacrylic Aramid Elastane PVC Vinylal Acrylic ModacryUc Aramid Elastane PVC Viscose rayon Cupro 

For the purpose of X-ray analyses, the samples should be as highly oriented and crystalline as possible. Since these are also the conditions required for strong, high-modulus fibers, basic characterization and engineering requirements are almost identical. 

Because of the imperfect orientation of the polymer in the fiber, arcs are seen, rather than spots. The variation in the intensity over the arcs can be used, however, to calculate the average orientation. 

---

Despite the fact that the electrospinning technique is relatively easy to use, there are a number of process parameters that can greatly affect fiber formation and structure. Listed in order of relative impact to the electrospinning process, the most important parameters are applied voltage, polymer flow rate, and capillary-collector distance. All three parameters can influence the formation of nanofibers with bead-like defects. 

Other additional phenomena may contribute to the progressive enrichment in /(-sheet structure. For example, silk glands produce multiple proteins and the interactions of these proteins facilitate fiber formation and contribute to the size and amounts of crystallinity (Craig, 2003 Lee, 2004 Sehnal and Zurovec, 2004 Sponner et al., 2005b). Furthermore,... 

These thermotropic cellulose derivatives are of course of interest from the viewpoint of their structure and properties and might be considered for such applications as chiroptical filters. However, they are unlikely to be considered for fiber formation and certainly not for regenerated fibers, as essenti dly they are ethers of cellulose and desubstitution woiild be difficult. Pawlowski et al. (I2fi) prepared a series of cellulose derivatives, namely phenylacetoxy, 4-meflioxyphenyl-acetoxy-, and p-tolylacetoxy cellulose and tnmethylsilyl cellulose that... 

In addition to the process parameters, a number of system parameters play an important role in fiber formation and the obtained structure. System parameters include molecular weight, molecular weight distribution, polymer architecture, and solution properties. Solution properties play a particularly important role. In relation to their impact on the electrospinning process, these factors can be ranked as follows polymer concentration, solvent volatility, and solution conductivity. 

BNC is biosynthesized by several species of bacteria, most importantly G. xylinus (Klemm et al., 2005, 2006, 2009). This biosynthesis process was first discovered by Brown (1886). Systematic and comprehensive research of recent years has given broad knowledge about the formation and structure of the BNC. The formation of BNC by fermentation opens up new vistas for the in situ shaping of nanocellulose. This bioshaping allows the production of flat pellicles, beads, fibers, and hollow bodies with high effectiveness by changing the conditions of the bacteria cultivation (Klemm et al., 2006, 2009). Stationary fermentation gives pellicles of BNC, while as a result of nonstationary conditions mainly the beads can be obtained. 

The T-protein is represented in neurons under normal conditimis. It is involved in the incorporation of tubulin into microtubules, stabilizing them, and affecting transport in axons [14]. Intracellular NFTs, consisting of paired helical fibers of paired helical filaments, arise within the course of AD. The main component of these fibers is hyperphosphorylated x-protein [15] that disrupts the formation and structure of tubulin and induces destabilization [16]. The influence of cyclin-dependent kinase 5 (CDK5) and glycogen synthase kinase 3p (GSK-3p) is a significant factor of hyperphosphorylation [17]. Recent... 

It is too early to describe the structural requirements for fiber formation. Further work is needed to see if there are structural requirements for fiber formation and what those structural requirements are. 

A. Coulsey and S. B. Smith, The formation and structure of a new cellulosic fiber . International Man-Made Fiber Conference, Austria, 1995. 

Peebles, L. H., Carbon fibers from acrylic precursors. In Carbon Fibers Formation, Structure, and Properties. CRC Press, Boca Raton, FL, 1995, pp. 7 26. 

In addition, it was found that the blends with highly fibrillar structure exhibited a significantly lowered viscosity. Increased shear rate caused slight changes in the blend morphology but did not enhance the fiber formation. Thus, in addition to shear, elongational forces are needed to achieve a well-fibrillated blend structure and significant mechanical reinforcement. 

The development of the internal orientation in formation in the fiber of a specific directional system, arranged relative to the fiber axis, of structural elements takes place as a result of fiber stretching in the production process. The orientation system of structural elements being formed is characterized by a rotational symmetry of the spatial location of structural elements in relation to the fiber axis. Depending on the type of structural elements being taken into account, we can speak of crystalline, amorphous, or overall orientation. The first case has to do with the orientation of crystallites, the second—with the orientation of segments of molecules occurring in the noncrystalline material, and the third—with all kinds of structural constitutive elements. 

One of the important aspects of the development of P-plastomers was the expectation that these materials were amenable to plastics processing such as fiber and film formation and yet would yield soft elastic fabrication. This combination was hitherto unknown [24]. The formation of nonwoven fabrics including spun-bond and melt-blown nonwoven fabrics as well as their laminated forms has been documented. Similarly, cast film operation to form elastic monolithic films or composite structures which are not only amenable to these processes, but also to a variety of postfabrication processes have been described. 

PE, the united atom model. We considered a sufficiently long PE chain made up of 5000 united atoms under periodic conditions in each direction. The initial amorphous sample prepared at 600 K was quenched to 100 K and drawn up to 400%. The sample was then quickly heated to various crystallization temperatures, and the molecular processes of fiber formation were monitored in situ via the real-space image and its Fourier transform, the structure function S3d([Pg.79]

However, 2 also affected the regulation of actin stress fiber formation [19]. Rho proteins are involved in the regulation of various cytoskeletal structures, and RhoB is believed to be one of the prime targets of FTase inhibitors. Rho B is apparently both geranylgeranylated and farnesylated [20, 21]. If cells were treated with 2, vesicular localization of Rho B was inhibited. Thus 2 may also inhibit the farnesylation of Rho B, thereby interfering with actin stress fiber formation [22]. 

The structural and sequence studies have highlighted two interesting prerequisites to fiber formation. First, the animal must control the size and... 

Fig. 3. Solubility of silk proteins in solution as a function of time. Low solubility corresponds to protein aggregation. The fast and slow aggregations are observed in vitro (Dicko et al., 2004a), whereas the stable helical conformation (storage structure) is observed in vivo (Dicko et al., 2004b,d). This illustrates the inherent instability of silk protein in solution and shows the /(-sheet polymorph structure as the most stable form. In other words, the spiders actively control and modulate the unavoidable silk protein aggregation prior to fiber formation.

---