Fiber drawing temperature

FIGURE 3.46 Relation between draw ratio and average orientation in polypropylene fibers and film (O) film, draw temperature 135°C (x) film, draw temperature 110°C ( ) fiber, draw temperature 90°C (A) fiber, heat-set. (From Samuels, R.J. Structured Polymer Properties, John Wiley Sons, New York, 1974. With permission.)... 

In the sol-gel process, ceramic polymer precursors are formed in solution at ambient temperature shaped by casting, film formation, or fiber drawing and then consolidated to furnish dense glasses or polycrystalline ceramics. The most common sol-gel procedures involve alkoxides of silicon, boron, titanium, and aluminum. In alcohol water solution, the alkoxide groups are removed stepwise by hydrolysis under acidic or basic catalysis and... 

The optimum draw ratio is close to the micropore saturation level (if any), since further drawing would lead to an undesirable embrittlement of the fiber without substantial gains in the amount of microvoids. By analogy with the results obtained with stretched films, a maximum of micropores is expected for drawing temperatures around 80-110 °C [128,129]. However, no incontestable experimental evidence has been provided up to now to support this assertion. 

Equation (7.3) states that the rate at which the fiber (or sheet) becomes thinner is proportional to the applied force, not the applied stress. This means that thinner and thicker regions suffer cross-sectional reduction at an equal rate. This expression also informs us that, for a given load, as the viscosity ri increases, the axial strain rate, e, decreases. This has very important implications in fiber drawing. In order to understand these implications, we need to examine the temperature dependence of viscosity. The temperature dependence of viscosity is given by the Eyring equation... 

Silicate melts suitable for fiber production have to fulfill many requirements first a sufficient fiber drawing potential, which is dependent upon the ratio of surface tension to viscosity. Fixing of the molten filament in the form of a fiber is a consequence of the increase in vi.scosity with decreasing temperature. Got)d fiber formation requires a viscosity-temperature dependence which is relatively flat. The glass must also not exhibit a tendency to crystallization. 

---