Glass fibers drawing conditions

TABLE 2. Typical drawing conditions for forming glass fibers. 

Unlike nylon, which in the as-spun state contains a high amount of crystalline component, PET fibers are essentially amorphous as spun. In order to secure a usable textile yam or staple fiber, this product must be drawn under conditions that will result in an increase in both molecular orientation and crystallinity. This is done by drawing at a temperature well above the glass transition point, T, which is about 80°C. Conditions of rate ana temperature must be selected so that the amorphous areas are oriented, and crystallization will take place as the temperature of the drawn... 

A polymer normally used as a fiber may make a perfectly good plastic if no attempt is made to draw it into a filament. Similarly, a plastic, if used at a temperature above its glass transition and suitably cross-linked, may make a perfectly acceptable elastomer. In the following text, a brief account of some of the more common plastics, fibers, and elastomers is given. The classification is based essentially on their major technological application under standard working conditions. 

Under most conditions oxide glasses behave as Newtonian fluids, i.e., the strain rate, dbildt, is a linear function of the applied shear stress, t. An important consequence of this behavior is that when we draw glasses, such as during the formation of optical fibers, the cross section reduces at a constant rate. In other words, we do not get necking of narrow sections of the fiber. At high stress levels non-Newtonian behavior, which is common in polymers, may be observed in oxide glasses. 

Similar to other polyesters, PLA displays crystal polymorphism and four different crystal modifications have been identified so far, named a-, P-, y-, and e-forms. The a-form of PLA grows upon melt- or cold-crystallization, as well as from solution [18-25]. Hot-drawn, melt-spun, or solution-spun PLA fibers of a high-draw ratio show the P-form [21-23]. The y-form is obtained via epitaxial crystallization on hexamethylbenzene substrate [24] and the s-modification is a crystalline complex formed below room temperature in the presence of specific organic solvents such as tetrahydrofuran and Af,Af-dimethylformamide [25]. Besides these four main crystal polymorphs, two disordered modifications of the a-form, named a and a , were recently proposed for PLA. The a -crystals grow via melt- or cold-crystallization below 110 °C [21, 26-29], whereas the a"-form develops upon crystallization under special processing conditions, below the glass transition temperature and in the presence of carbon dioxide [30]. 

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