Applications of polyurethane elastomers today and in the future

Direct Uses of Latex

Latex is compounded by introducing the ingredients in the form of very fine aqueous dispersion, colloidal where possible. Compounding is carried out in pebble mills, and also in special pieces of equipment known as colloidal mills. Generally speaking, the same ingredients are added to latex as to rubber; it should be noted that reinforcing fillers do not affect latex. It has been found desirable to add a certain number of special ingredients, the principal ones being as follows:

a) Dispersing agents, which prevent agglomeration of the colloidally - dispersed particles.

b) Stabilisers, to prevent coagulation during processing of the latex.

c) Thickeners, for increasing the viscosity of the mix as required.

d) Wetting agents, to reduce the surface tension of the latex thus enabling it to penetrate more easi1y into materials to be impregnated with it.

Various processes exist for the working up of latex mixes. In the dipping process a former (usually ofporcelian, aluminium or glass) is dipped into the mix, and then withdrawn, the thin layer of latex adhering to it being then dried. An article of the desired thickness is obtained by repeated dripping. Electrodeposition is the process by which rubber is deposited from the latex when an electric current is passed through the bath, the particles of rubber being deposited on an anode in the form of the object to be reproduced. Latex may be used for impregnation and rubberising, not only of textiles but of many other materials, e.g. paper, leather fibres, and horsehair. Goods may also be made by moulding with latex. The field in which latex finds widest application is that of cellular goods mattresses, pillows – made of latex foam, usually obtained by beating the mix, then gellifying as in the case of moulding, followed by drying.

Vocabulary List

dispersion – дисперсия;

compounding – смешивание;

pebble mills – галечные мельницы;

dispersing agents – диспергатор, диспергирующий агент;

agglomeration – скопление;

colloidally-dispersed particles – коллоидные дисперсные частицы;

coagulation – коагуляция;

thickener – сгуститель, агент сгущения;

viscosity – вязкость;

impregnate – пропитывать;

impregnation – пропитка;

dipping – окунание, макание;

electrodeposition – электроотложение;

rubberising – прорезинивание;

moulding – формование, формирование;

cellular – ячеистый, клеточный;

foam – пена;

gelify – затвердевать.

Text 17

The high performance properties make polyurethane elastomers the material of choice for an endless assortment of mechanical and manufacturing goods, including gaskets, casters, hammerheads, elastomer-lined pipe, oil pipeline pigs, cable jacketing and cone dischargers used in taconite mining. They are also used in electrical potting, farming equipment, recreational goods including golf carts and snowmobiles, golf ball covers, swim fins, bicycle tires, football helmet liners, bowling balls and pins, and pour-in-place running tracks. Medical equipment uses include antishock trousers and artificial heart chambers.

Now let us look at some examples.

Conduit to life. The disposable tubing used in heart/lung machines in the well over 100,000 open heart and coronary bypass operations performed yearly used to be made entirely of PVC. Now, a PVC tube lined with polyurethane elastomer provides improved compatibility with blood and better resistance to the abrasion caused by the continuous rolling of peristaltic pumps. Because polyurethane elastomers can be fabricated without plasticizers, there is no danger of these toxic compounds migrating into the blood.

TPUs get the boot. Polyurethane elastomers provide strength, stiffness and flex properties demanded of a ski boot at subzero temperatures. Light weight and superior comfort, acceptable cycle times, consistent color and a long-lasting, hard, high gloss finish are other advantages TPUs bring to this application.

Chopper protector. The Army wanted a one-piece helicopter cover to keep copters weather-safe and action-ready. The covers had to be flexible, yet tough, as well as abrasion, weather and fuel resistant and repairable in the field. They also wanted covers in different colours to distinguish various models of aircraft. Polyurethane elastomers filled the bill.

Tags iron out herd management. Manufacturers of the millions of ear tags made yearly for domestic use and export need a material that resists degradation by moisture, oxidation, tearing and abrasion; that remains flexible even at low temperatures; and is lightweight It also helps if the material can be pigmented and even impregnated with insecticide. Polyurethane elastomers fit these criteria, offering cattle owners an excellent aid to herd management

And what about future applications of elastomers?

Tomorrow may see additional applications for polyurethane elastomers in space. Chances are good that the high performance characteristics of these materials will also be used to expand the horizons of telecommunications, electronics and other burgeoning technologies.

Whatever chapters the next decade or so adds to the history of elastomers, one thing is certain: new opportunities to exploit the inherent and unduplicated versatility and performance of these materials will continue to arise in the marketplace - and polyurethane producers will continue to respond.

Text 18

Дата добавления: 2014-10-17