Factors Influencing Fiber Characteristics

In general, the process of electrospinning may be affected by several parameters, among which the main ones are characteristics of polymer viscosity and conductivity of the polymer solution, surface tension, electric field, distance between the capillary and the collector object, the form of the collector and environmental conditions. 

In practice, a mixture of the above mentioned factors can influence the properties of the fibers. The main achievements in the production of fibers by electrospinning are control of the fiber diameter, fibers free of defects, control of the surface of the fibers, aligned fibers and continuous fibers. 

Several process parameters controlled the fibers diameter during the electrospinning process [27-29] the viscosity of the polymer solution, the concentration of the solution, which is proportional to viscosity, and the voltage used during electrospinning. 

The non-uniform diameter fibers and defects such as beads are among the most frequent problems (Fig. 4.3). Demir et al. [14] dmnonstrated the effect of temperature on the uniformity of the fibers. Higher temperatures for polymer solutions with the same concentration result in more uniform fiber diameters. A higher concentration of polymer solutions leads to a deaease in the number of beads. It has been observed that the addition of salts to a polymer solution can decrease the formation of beads. The reason for this has been attributed to the existence of higher surface charge densities of the jet of the solution. 

---

Other Fiber Deformations. Deformations such as bending, torsion, shear, and compression are of practical importance in textile apphcations. Bending and twisting of yams, both influential in the development of bulk and stretch in filament yams, are also important in the production of staple yams. Bending characteristics are important in cmsh resistance in carpets. Bending and shear are factors that influence the hand and drape of apparel fabrics, whereas compression influences the recovery of fabrics after such processes as winding. 

A very unusual characteristic of mesophase pitch is the extreme dependency of its viscosity on temperature [19,34,35]. This factor has a profound influence on the melt-spinning process (described above), as a mesophase pitch fiber will achieve its final diameter within several millimeters of the face of the spinnerette, in sharp contrast to most polymeric fibers. 

For typical filament winding applications, the fiber reinforcement provides the stiffness and strength required to maintain structural integrity. Thus, material characterization for filament wound structures focuses on characterizing the fiber dominated stiffness and strength properties of the composite. The stiffness of fiber reinforced plastics (FRPs), in the fiber direction, is dominated by the fiber stiffness characteristics. The strength will be influenced by a number of factors, however, and not all of them are related to the fiber, including ... 

The proportions of fibers within a muscle are determined by a combination of genetic and developmental factors and by the pattern of recruitment of the muscle unit. Due to this latter influence, the twitch and enzyme characteristics of muscle fibers are somewhat malleable, being influenced by training (especially endurance training) or by detraining (as in bed rest). 

Polymers for use in biotextiles should possess three specific properties. The first is their ability to be spun. This is the most important characteristic for the production of fibers. The second property is their elasticity. This is fundamental when a variation of the shape and/or the dimension of the DDS is required during its application. The final property is their biocompatibility. Tliis is vitally important for the preparation of oral DDSs, implantable DDSs, etc. Fibers for TDDSs are derived from all types of filament-forming polymers and natural fibers, and because of this they are used ex v/vo. A number of other factors must be taken into account, including how polymers influence a drug s properties, drug delivery routes and desired drug release profiles. ... 

The crystallization of isotactic polypropylene (iPP) is affected by many factors, such as macromolecular characteristics [82], crystallization conditions (temperature, cooling rate), and stress (shear, elongational fields) [83-85]. In fiber reinforced iPP matrix composites, the crystalline morphology of the polymer is influenced by the fibers that can act as nucleating agents affecting the crystallization process [86-88]. TranscrystaUinity is a well-known structural feature in pol rmers, which occurs as the result of dense nucleation of the semi-... 

---