Polythene

The reaction is carried out in a lead retort one suitable for the laboratory can be made from a piece of lead piping, bent like a retort and closed at the shorter end. This is charged with fluorspar and the acid and heated, and the hydrogen fluoride is distilled into a polythene vessel. 

Aqueous hydrogen fluoride is a weak acid (see above) and dissolves silica and silicates to form hexafluorosilicic acid hence glass is etched by the acid, which must be kept in polythene bottles. 

Lithium aluminium hydride if carelessly manipulated may be dangerous for two distinct reasons. The material is caustic, and should not be allowed to touch the skin it is particularly important that the finely divided material should be kept away from the lips, nostrils and eyes, and consequently pulverisation in a mortar must be carried out with the mortar in a fume-cupboard, and with the window drawn down as far as possible in front of the operator. This danger from handling has however been greatly reduced, for the hydride is now sold in stated amounts as a coarse powder enclosed in a polythene bag in a metal container this powder dissolves readily in ether, and preliminary pulverisation is unnecessary. 

Ethylene. Under the influence of pressure and a catalyst, ethylene yields a white, tough but flexible waxy sohd, known as Polythene. Polyethylene possesses excellent electric insulation properties and high water resistance it has a low specific gravity and a low softening point (about 110°). The chemical inertness oi Polythene has found application in the manufacture of many items of apparatus for the laboratory. It is a useful lubricant for ground glass connexions, particularly at relatively high temperatures. 

McClellan s and Hamsberger s survey, which embraced a considerable variety of solids including carbons, metal oxides and organic polymers such as polythene, arrived at a mean value of 20-2 A, with a standard deviation of 1-6 A. Other more recent results, likewise based on = 16-2 A, ... 

Fig. 11.9. Polythene forms o stable neck when it is drown out drown polythene is very strong.

Polythene shows a kind of necking that does not lead to fracture. Figure 11.9 shows its (T /e curve. At quite low stress... 

Finally, mild steel can sometimes show an instability like that of polythene. If the steel is annealed, the stress/strain curve looks like that in Fig. 11.10. A stable neck, called a Luders Band, forms and propagates (as it did in polythene) without causing fracture because the strong work-hardening of the later part of the stress/strain curve prevents this. Luders Bands are a problem when sheet steel is pressed because they give lower precision and disfigure the pressing. 

Fig. 1.6. The titanium alloy implant for a replacement hip joint. The long shank is glued into the top of the femur. The spherical head engages in o high-density polythene socket which is glued into the pelvic socket.

Crystalline Olefin Polymers (Eds. raff, r. a. v. and doak, k. w.). Interscience, New York (1964) Polythene—the Technology and Uses of Ethylene Polymers (Eds. Renfrew, a. and Morgan, r), Iliffe, London, 2nd Edn (1960)... 

Although poly(vinyl fluoride) resembles PVC in its low water absorption, resistance to hydrolysis, insolubility in common solvents at room temperature and a tendency to split off hydrogen halides at elevated temperatures, it has a much greater tendency to crystallise. This is because the fluorine atom (c.f. the chlorine atom) is sufficiently small to allow molecules to pack in the same way as polythene. 

Use only apparatus strong enough to withstand the considerable force which may arise due to movements of mercury (e. rigid pvc or polythene)... 

PVC, polythene and PTFE if moist gas is used Stainless steel, copper, nickel. Monel, brass, aluminium for dry gas <200°C. Borosilicate glass for low pressures. For moist gas, copper and polyvinylidene chloride plastics Monel and nickel Monel and nickel Most common metals so long as gas is dry... 

Rubber or plastic gloves, face shields or goggles, rubber boots or over-shoes, face masks and an all-purpose respirator Household dustpan (rubber or polythene), brush and large bucket (preferably polythene), an ordinary steel shovel, stiff bristle brush and a soft brush, for sweeping up and containing broken glass, and industrial cotton mops, plastic foam mops or squeegees... 

Fairly resistant to chemicals treated with polythene disposable underwear... 

Polythene Hygienic Low abrasion resistance Suitable for disposable... 

Example 5.2 In a plunger-type injection moulding machine the torpedo has a length of 40 mm, a diameter of 23 mm and is supported by three spiders. If, during moulding of polythene at ITO C, the plunger moves forward at a speed of 13 mm/s, estimate the pressure drop along the torpedo and the shear force on the spiders. The barrel diameter is 25 mm. 

Example S3 The output of polythene from an extruder is 30 x 10 m /s. If the breaker plate in this extruder has 80 holes, each being 4 mm diameter and 12 mm long, estimate the pressure drop across the plate assuming the material temperature is 170°C at this point. The flow curves in Fig. 5.3 should be used. 

Example 5.10 During the blow moulding of polythene bottles the parison is 0.3 m long and is left hanging for 5 seconds. Estimate the amount of sagging which occurs. The density of polythene is 760 kg/m ... 

Polythene is passed through a rectangular slit die 5 mm wide, I mm deep at a rate of 0.7 X 10 w /s. If the time taken is 1 second, calculate the natural time and comment on its meaning. 

Polythene at 170°C is used to injection mould a disc with a diameter of 120 mm and thickness 3 mm. A sprue gate is used to feed the material into the centre of the disc. If the... 

A polythene tube of outside diameter 40 mm and wall thickness 0.75 mm is to be extruded at a linear speed of 15 mm/s. Using the 170°C polythene flow curves supplied, calculate suitable die exit dimensions. 

The exit region of a die used to blow plastic film is shown below. If the extruder output is 100 X 10 m /s of polythene at 170°C estimate the total pressure drop in the die between points A and C. Also calculate the dimensions of the plastic bubble produced. It may be assumed that there is no inflation or draw-down of the bubble. Flow data for polythene is given in Fig. 5.3. 

Dry A filter manufactured from cotton wool, glass-fiber fabric, pleated paper, foamed polyurethane, cellular polythene, or other suitable materials. As the name suggests, the filter is dry in nature and has no oil coating. 

Even more important is the stereoregular catalytic polymerization of ethene and other alkenes to give high-density polyethene ( polythene ) and other plastics. A typical Ziegler-Natta catalyst can be made by mixing TiCU and Al2Eti in heptane partial reduction to Ti " and alkyl transfer occur, and a brown suspension forms which rapidly absorbs and polymerizes ethene even at room temperature and atmospheric pressure. Typical industrial conditions are 50- 150°C and 10 atm. Polyethene... 

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