Freeze-line distance

In the tubular process a thin tube is extruded (usually in a vertically upward direction) and by blowing air through the die head the tube is inflated into a thin bubble. This is cooled, flattened out and wound up. The ratio of bubble diameter to die diameter is known as the blow-up ratio, the ratio of the haul-off rate to the natural extrusion rate is referred to as the draw-down ratio and the distance between the die and the frost line (when the extrudate becomes solidified and which can often be seen by the appearance of haziness), the freeze-line distance. 

Figure 10.14. Effect of freeze-line distance and other operating variables on the haze of low-density polyethylene film. (Reproduced by permission of ICI)...

FIG. 87 Effect of freeze-line distance on gloss (curve 1), relative haze (curve 3), and transmission (curve 2) of film of PE. (From Ref 12.)... 

Figure 13.4 Illustration of the freezing point, as shown by the variation in diameter and birefringence with distance from the spinneret for (a) branched, and (b) linear (IV, 0.66) PET samples spun at 5400m/min [13]. From Some effects of the rheological properties of PET on spinning line profile and structure developed in high-speed spinning, Perez, G., in High-Speed Fiber Spinning, Ziabicki, A. and Kawai, H. (Eds), 1985, pp. 333-362, copyright (1985 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc.

The dashed line represents an idealized process in which all solid is heated to the freezing point and then all the sample is melted isothermally. The two lines, QO and OS, are thus separate specific-heat and melting components for the actual process. The flat line, OS, represents the melting of the two substances, solvent and solute, with different heats of fusion. However, for most substances studied, the amount of solute is always small so that on the central part of the curve, which is used for analysis, the fraction of material melted is proportional to the distance along OS. 

Free radical brominations in conventional solvent. An appropriate quantity of alkylaromatic and 10 mL solvent were placed in a 30-mL Pyrex pressure tube (equipped with an 0-ringed Teflon needle valve and Teflon-coated magnetic stir bar). An appropriate HBr scavenger (1,2-epoxybutane) was added, and the solution was degassed 4x by the freeze-pump-thaw PT) method. Bromine was FPT degassed and distilled (via vacuum line) into the reaction mixture at -196 C. The pressure tube was sealed and the reaction mixture allowed to equilibrate at the desired reaction temperature in total darkness. The reaction mixture was irradiated with a 400 W medium-pressure mercury arc lamp at a distance of 2 ft through two Pyrex layers. Complete discharge of Br2 occurred in less than 5 min. Afterward, the solution was analyzed by GLC vs an appropriate internal standard. 

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