Cooling extrusion temperature

The extrusion temperatures of the polymer far below the melting point of the drug. Upon cooling of the extruded fibers, dissolved drugs may either recrystallize or remain soluble, which results in a supersaturated state. The amount of the dissolved drug can be correlated to the release properties. The state in which the drugs are left after extrusion determine their properties of permeation. 

Cooling of Extruded PE Wire5 Consider a copper conductor, 0.16 in in diameter, coated by extrusion to a 0.62-in insulated wire (first transatlantic cable core wire). The conductor is preheated to the extrusion temperature 412°F, and... 

Extrusion temperature of the PVDF/PMMA was in the range of 220°C-240°C. The preferred drawdown ratio of the first bubble was in the range of 10 1 to 15 1, and 2 1 to 3.75 1 forthe second bubble. The desirable blowup ratio ranged from 1.5 1 to 1.75 1. A cooling air temperature of 10°C-20°C was required while the hot air temperature, before the second bubble, varied from 120°C-140°C. The film can be dimensionally stabilized by an annealing process at 120°C for 5 minutes. 

Most of the membranes listed in Table 5.20 are formed through phase separation processes, i.e., melt extrusion or coagulation of a polymer solution by a nonsolvent. In melt extrusion, a polymer melt is extruded into a cooler atmosphere which induces phase transition. The melt extrusion of a single polymer usually gives a dense, isotropic membrane. However, the presence of a compound (latent solvent) that is miscible with the polymer at the extrusion temperature but not at the ambient temperature, may lead to a secondary phase separation upon cooling. Removal of the solvent then yields a porous isotropic membrane. Anisotropic membranes may result from melt extrusion of a dope mixture of polymers containing plasticizers. 

FIGURE 3.34 Relation between birefringence and take-up velocity at various extrusion and cooling air temperatures for polypropylene. (From Shimizu, J. Toriumi, K. Imai, Y. Sen-i Gakkaishi, WTl, 33, T-255. With permission.)... 

The increase in take-up velocity and the extrusion temperature results in the increase of the cooling rate. Consequently, the crystallization temperature moves toward lower values. The crystallization starts at lower temperature and then quickly, by further cooling, moves below the critical temperature for the formation of p crystals. Then, the smaller part of the material crystallizes at conditions favourable for the formation of the P form. At the beginning of the crystallization process p crystals are formed. During crystallization temperature decreases into the range below the critical temperature and remaining crystallisable material crystallizes at a lower temperature, forming a crystals. 

The precursor is melted in an extruder which pumps the melt into a die head equipped with a filter and a multihole spinneret [5-6] [24]. As the precursor fibers exit the spinneret holes they cool and solidify, and are drawn before windup. The window for achieving successful and continuous fiber formations is small. The temperature dependence of the viscosity is large and the failure strength of the mesophase pitch fibers is low (30-40 MPa). Thus, the extrusion temperature must be precisely controlled. 

Rubber extruders used to be heated quite frequently with steam because of the relatively low extrusion temperatures. Today, many rubber extruders are heated like thermoplastic extruders with electrical heater bands clamped around the barrel. Oil heating is also used on rubber extruders and the circulating oil system can be used to cool the rubber. Many rubber extruders use water cooling because it allows effective heat transfer. 

The value of the approach using dichroic ratios coupled with a knowledge of the assignments of peaks is further illustrated by measurements on plain polyethylene films [2]. The production process leads to a rather complex orientation pattern. The molten polymer is extruded as a thin, hollow cylinder, in what may be termed the machine direction. It is simultaneously expanded in a plane perpendicular to the machine direction by the application of internal pressure. Additional variables are the extrusion temperature and the rate at which the blown film has been cooled. The resulting orientation behaviour is best studied by x-ray diffraction pole figure measurements [3,4,5] but the infrared approach provides a relatively simple means for obtaining a useful amount of information, particularly for the behaviour of chains in amorphous regions. 

For certain alloys, the hot rolling or extrusion temperatures are on the same level as the solution heat treatment temperatures. If the critical quenching rate is suflhciently low, it may be possible to quench immediately after hot working. This is current practice for several extrusion alloys of the series 6000 (6060, 6005A, 6106) that are press-quenched by forced air-cooling or water spray. These tempers are referred as T1 (quenched and naturally aged) and T5 (quenched and artificially aged). 

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