Fiber formation techniques

Fibers with unique sensual characteristics, such as color, appearance, feel, bulkiness and texture, are commonly referred to as aesthetic fibers. Aesthetic fibers are highly fashionable and expensive, and their production process and advanced technology are also costly. Materials that may require 

5 Thermotropic liquid-liquid crystal polymer spinning 

Fibers with very high strength and modulus can be fabricated from polymers that have a molecular structure in which the chains are packed in small cross-sectional areas with strong bonds and low elongation. However, some of these aromatic polymers have melting points that are higher than their decomposition temperatures due to the rigidity of their molecules. It is therefore impossible to process them in thermotropic liquid crystal form. 

It has been shown that this can be overcome by a slow introduction of flexible alkyl groups into the main chain, by introducing substituents into the individual aromatic ring in the main chain, by co-polymerization of more than one rigid molecule, or by the introduction of non-molecular structures. 

Combinations of these techniques have been shown to provide a means of creating thermotropic LCPs that can be injection-molded or melt-spun. The chemical structures of thermotropic LCP fibers are varied and based on the original polymer material characteristics and conditions. The choice of synthesis process is therefore the key to achieving the desired end product characteristics and qualities. The current challenge, however, in the spinning of thermotropic LCPs is to improve cost effectiveness through performance process optimization. 

---

Apart from the above-mentioned fiber formation techniques, biomaterial fibers may be produced by other techniques. Among these, biospinning plays an important role. Biospinning is defined as the process of direct fiber drawing from the spinning glands of various insects such as silkworms and spiders [37]. Biospun fibers, eg, from Bombyx mori silkworms, have been traditionally used as suture material [38]. 

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. 

Detailed time course analysis of NM fiber formation provided insight into the mechanism of nucleation (Serio et al., 2000). Specifically, a series of biochemical probes and microscopy techniques were used in concert to determine if preformed NM fibers acted as nuclei for con-... 

Despite the simple basic setup and its versatility, it has to be considered that the ES process is influenced by numerous interacting parameters [36]. To date, the complex mechanism of fiber formation has not been thoroughly understood. While ES is well suited for producing thin layers or membranes with large surfaces and small pore sizes, the technique is not suitable for producing thicker films due to the long production time resulting fiom the small fiber diameters. 

Chemical reaction, though present, is not generally an important factor in fiber formation. This is in direct contrast to nature, where the chief mechanism in forming fibers by spiders, silkworms, and ant lions is chemical reaction [77]. All these creatures, in essence, eject or spin a prepolymer, which then reacts and forms the final polymeric material. Attempts have been made from time to time to emulate the reaction-spun fibers formed by the spider, silkworm, and ant lion. For example, in the early days of World War II, spiderweb fibers were used to construct the cross hairs for bomb sights. There was, at that time, an effort to reproduce these fibers by laboratory techniques. 

Reviews of specimen preparation methods for fiber microscopy and instrumental techniques applied to fibers were published during the early 1970s [14-16]. This section contains applications of microscopy to the understanding of fiber microstructures used in the industrial laboratory for modification of fiber formation processes to... 

In addition to the single fiber formation, the alumina and/or zirconia fiber mats having web-like microstructure were produced by using the centrifugal spinning technique (Venkatesh et al., 1999 Chatleijee et al., 2002a). 

---