Cork flow

N. El Kissi and J.-M. Piau, The diiferent capillary flow regimes of entangled poly-dimethylsiloxane polymers macroscopic slip at the wall, hysteresis and cork flow, J. Non-Newtonian Fluid Mech., 37 (1990) 55-94. 

During the extrusion of polymers different defects and flow instabilities occur at very low Reynolds numbers. The commonly known ones are sharkskin, melt fracture, slip at the wall and cork flow. These defects are of commercial importance, since they often limit the production rate in polymer processing. Many researchers have been interested in the subject, and thorough reviews on flow stability and melt fracture have been written in the last 30 years [1-4]. More recently, two review papers deahng with viscoelastic fluid mechanics and flow stability, were published by Denn [5] and Larson [6]. However, although much work has been done in the field of extrusion distortions, controversy still exists regarding the site of initiation and physical mechanisms of the instabilities. 

It should be noted that this second zone of instability had already been demonstrated with similar polymers [35]. However, the authors assume the existence of another area of cork flow, i.e., an area where the polymer adheres to the wall, even at these high regimes, which is in contradiction with the analysis of... 

In (d) the side arm outlet extends a short distance into the long neck of the flask, thus preventing any vapour which has been in contact with cork or rubber stoppers from condensing and flowing down the side arm. 

Cork compositions 250 Low cost. Truly compressible materials which permit substantial deflections with negligible side flow. Conform well to irregular surfaces. High resistance to oils good resistance to water, many chemicals. Should not be used with inorganic acids, alkalies, oxidizing solutions, live steam. 

The low conductivity of heat insulating materials, such as cork, glass wool, and so on, is largely accounted for by their high proportion of air space. The flow of heat through such materials is governed mainly by the resistance of the air spaces, which should be sufficiently small for convection currents to be suppressed. 

Closure liners of pulpboard or cork, unless specially treated with a preservative, foil or wax coating, are often a source of mould contamination for liquid or semi-solid products. A closure with a plastic flowed-in linear is less prone to introduce or support microbial growth than one stuck in with an adhesive, particularly if the latter is based on a natural product such as casein. If required, closures can be sterilized by either formaldehyde or ethylene oxide gas. 

Standardization of Na Og with Cu. To prevent air oxidation of iodide in the acidic solution, use a 180 mL tail-form beaker (or a 150 mL standard beaker) loosely fitted with a 2-hole stopper. One hole serves as inlet for a brisk flow of N2 or Ar that leaks out the side of the stopper. The other hole is used for the buret. Pipet 10.00 mL of standard Cu solution into the beaker and flush with inert gas. Remove the cork briefly to add 10 mL of water containing 1.0-1.5 g of freshly dissolved KI and begin magnetic stirring. Titrate with Na2S2Os from a 50 mL buret, adding 2 drops of starch just before the last trace of I2 disappears. Premature addition of starch leads to irreversible binding of I2 to the starch, and makes the end point harder to detect. 

Sephadex G-50 has been prepared for your use. The dry beads have been preswollen in water for several hours, fine particles that may slow column flow have been removed, and the gel has been equilibrated in Tris buffer. If chromatography columns are not available, one can easily be constructed from a glass tube (2.5 X 40 cm), cork stoppers, Tygon tubing, a screw clamp, and small glass tubing as shown in Figure E4.4. With the screw clamp closed, add 10 to 15 mL of Tris buffer and insert a small piece of... 

The apparatus consists of a flow through extraction system that can be operated at pressures up to 400 bar and temperatures up to 200°C. This apparatus was described elsewhere (2). Its main piece is a 19 cm3 reactor, where 4-5 g of 40-60 mesh milled cork were placed between two G3 fritted glass discs. The reaction mixture is expanded into a series of three 35 cm3 precipitation traps. A dual-head high pressure liquid pump was used to compress the solvent. One pump head was cooled with ice to pump liquid C02 while the other pump head was used for 1,4-dioxane. 

Figure 2 FT1R spectra of a - extractive-free cork, b - residue of extraction carried out at 170 bar, 170C with dioxane with a mass flow rate of 1.38 g min-1 and c - extracts obtained from high-pressure dioxane extractions.

However, on account of the cork-like character of the flow in the channel the error of the design scheme is great, whilst the reproducibility of the results may unsatisfactory because of friction losses in the punch-and-die mating in the chamber. Other shortcomings of this method are due to difficulties of extracting the specimen, a long preparatory period prior to testing. 

Tube ends can be made to fit cork or rubber stoppers by reaming them out to approximately the same taper as the stopper. When the reinforced rim has been made, as described above, the tube is put back into the flame with slightly reduced air-flow. Heating is continued until about 2 cm of the tube length is plastic. The glass is taken out of the flame and the same heated tool inserted so that the point touches the inside wall (Fig. 6.12a). 

---