As-manufactured polymeric fibers are oriented semi-crystalline structures in which the macromolecules are rarely in their equilibrium state. Further instabilities are imparted when the fibers are converted to yarns and the yarns to fabrics. Heat setting is an important industrial process, since it rids them of their instabilities. This review article first considers aspects that are relevant to the broad area of heat setting, viz., the origin of instability, the durability of set, thermal and dynamic mechanical transitions, thermodynamic basis of setting, shrinkage and shrinkage stress, and characterization of the degree of set. The heat setting of major thermoplastic fibers, viz., polyester, polyamide, polyacrylonitrile, polypropylene, and polyethylene has been described in terms of the conditions of heat setting, the structural and morphological changes that occur on heat setting, and the changes in their physical properties. It is shown that heat setting affects such important properties as stress-strain and recovery behavior, dye-uptake, optical properties, and thermal properties. The structural and morphological changes have been described in terms of changes in crystallinity, crystal size and their size distribution, crystal defects, crystal orientation, the nature of the amorphous phase and its orientation, the coupling of the crystalline and amorphous phases, etc. The structural basis of property changes is then discussed.
Alkaliphiles are interesting groups of extremophilic organisms that thrive at pH of 9.0 and above. Many of their products, in particular enzymes, have found widespread applications in industry, primarily in the detergent and laundry industries. While the enzymes have been a runaway success from the industrial point of view, many more products have been reported from alkaliphiles such as antibiotics and carotenoids. Less known are their potential for degradation of xenobiotics. They also play a key role in biogeocycling of important inorganic compounds. This review provides an insight into the huge diversity of alkaliphilic bacteria, the varied products obtained from them, and the need for further investigations on these interesting bacteria.
SYNOPSISA mathematical model that includes crystallization in the spinline and the effect of crystallization on the extensional viscosity and the various physical properties of polypropylene has been developed and used to help in identifying the various factors that can affect the spun yarn characteristics. The model is used to simulate effects of spinning parameters on fiber physical properties, temperature, and stresses. The experimental observation of a minimum in density of the spun yarn at high throughput rates, when density is plotted as a function of takeup velocity, has been investigated in some detail. It has been found that all conditions which can substantially affect the rate of cooling and the orientation of the polymer in the spinline, viz, throughput rate, spinning temperature, and spinning speed have an important bearing on the temperature range in which crystallization can take place in the spinline and thus affect the density. It is suggested that in addition to these factors, the formation of different crystal modifications at different spinning speeds could also contribute to the reduction in density of these samples. The model cannot reflect the observation of density changes occurring due to the formation of different crystal modifications. Nevertheless, it can be of use in understanding the effects of various process conditions on the cooling rate and the orientation of the polymer in the spinline. INTRODUCTIONThe density of fibers spun from nylon 6, nylon 6,6, and poly (ethylene terephthalate) has been shown to increase with increase in spinning apparently because of orientation when the spun fiber is amorphous and orientation and crystallinity when it is semicrystalline. In polypropylene, which is a fast crystallizing polymer, the density is reported to show an increase with increase in spinning speed4 or a decrease followed by an i n c r e a~e .~ Jinan et a1.2 obtained experimental data which showed that at spinning temperatures of around 250 to 290"C, the crystallinity of the as-spun yarns gradually decreased with increase in spinning speed, reaching a minimum at a spinning speed of around 600 to 800 m/min before increasing again. The minimum did not appear at lower spinning temperatures and it * To whom correspondence should be addressed. was observed that in addition to spinning temperature, the melt flow index of the polypropylene sample also affected it. The authors suggested that the competing effects of cooling-dominated crystallization and orientation-induced crystallization were responsible for the minimum. The authors also argued that in the low stress regime in which crystallization is dominated by cooling rates, the spun fiber crystallinity decreases with increasing spinning speed until the orientation effects begin to enhance the rate of crystallization and lead to an increase in the spun fiber crystallinity with further increase in spinning speed. Simulation work carried out by them indicated a similar trend at all spinning temperatures starting from 210 to 290°C. During o...
The main features of the wide angle X-ray patterns in wool are': meridional a-arc associated with group of reflections at about 0.51 nm (28 = 17.8"), the equatorial spot at 0.465 nm (28 = 19" ) associated with @-form, and the equatorial spot at 0.98 nm (28 = 9") common to both a-and @-forms. The various reflections observed in the X-ray patterns indicate good crystallite orientation in the direction of fiber axis.Wools of different biological origin are known to show differences in their properties, which, in turn, are related to differences in the structure and morph~logy.~-~ The birefringence values of three different wools, namely Merino, Chokla, and Lincoln, have been shown to correlate well with their morphology and various physical pr0perties.3.~ Birefringence in wool arises predominantly from its crystallites, and their orientation is therefore of considerable interest. However, there is hardly any reported study on the changes in crystallite orientation as related to such differences. In the present work, the X-ray diffraction
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