Surface properties resistivity, polymer electricity

Many polymer items are designed specifically to make contact with other materials. Where surface contact is concerned, two key properties are coefficient of friction and abrasion resistance. Polymers used in such applications include ultra high molecular weight polyethylene, polyacctal, fluorinated polymers, and natural and synthetic rubbers. Examples that we routinely come across include furniture upholstery, bushings and gears in office equipment, and bicycle tires. Industrial uses include the outer cover of electrical cables, and pipes that convey abrasive liquids such as slurries and powders. 

It is through the solid state characteristics of polymers that we - as users - primarily interact with them. For convenience, we can divide the principal properties of polymers into five categories mechanical, optical, surface contact, barrier, and electrical. Weather resistance is a sixth category that can influence each of the other five categories. In order to understand these properties we must be able to quantify them. In this chapter we shall concentrate on measurement techniques, since it is through these methods that we learn how a polymer will behave during use. 

We can define the principal electrical properties of polymers in terms of four characteristics electrical resistance, capacitive properties, dielectric strength, and arc resistance. We can change the surface characteristics of a polymer by subjecting it to a corona discharge generated by a strong electrical field. Lastly, we must also consider the influence of other physical properties on the application of polymers in electrical applications. 

Fluorinated polymers are considered high value-added materials, due to their outstanding properties which open up various applications [1-9]. Such polymers exhibit high thermostability and chemical inertness, low refractive index and coefficient of friction, good water and oil repellence, low surface energy and valuable electrical properties. In addition, they are non-sticky and resistant to UV, ageing, and to concentrated mineral acids and alkalies. 

When exposed to an electrical discharge, the surface of some polymers may become carbonised and conduct current the arc resistance, a measure of this behaviour, is an important property in the application as insulating material in engine ignition systems. 

Prpcedures for Studying the Fundamental Frictional Properties of the Polymers. To study the fundamental frictional properties of the heat resistant polymers, a steel sphere of 2.38 mm in radius was slid on flat polymer plates at a low speed of 0.25 mm/s under variotis loads ranging from 1 N to 8 N and at various teinperatures up to 300 C, and the frictional force was measured. The temperature of the specimen polymer surface was controlled by thermocouple and electric heater. 

Employing atomic composition data, obtained by XPS, one is, however, led to believe that the atmosphere may affect the type of oxide that forms. Co/O ratios for dry and moist air cured films are 1.7 and 0.9, respectively whereas, Sn/0 ratios are 1.6 and 1.7. Thus, the electrical properties are apparently influenced by both the type of oxide formed during the thermal cure and by the spatial distribution and amount of metal oxide within the surface of host polymer. The thickness of both the oxide layer and polymer overlayer also appear to be very important here in achieving improved surface electrical resistivity. 

Even with resistant polymers, the surfaces of products can be contaminated by microorganisms if they become roughened or pitted, and they then remain moist for long periods. Also, they become discoloured if constituent additives are vulnerable. Other symptoms include black or pink staining, odour, and changes in electrical or mechanical properties. Affected plastics products attract and retain dirt more than unaffected ones. 

As Dr. Plunkett mentioned, all of the initial product from the pilot plant at Arlington, New Jersey went to the Manhattan Project. After World War II, the polymer became available for critical industrial uses A comb ination of extreme resistance to chemicals, excellent resistance to very high temperatures, superb electrical properties, and unique surface properties indicated a promising future for this new material Plans for commercial production led to construction of a full scale plant at the new DuPont facilities at Parkersburg, WV where operations started in 1950. Since then there have been almost continuous expansions within DuPont and the other companies that now manufacture PTFB. Table ill lists various manufactures with the trademark each uses. 

Over the past decade, polymer nanocomposites have attracted considerable interests in both academia and industry this is because of the outstanding mechanical properties like elastic stiffness and strength which can be achieved with only a small amount of the nanoadditives. This is caused by the large surface area to voliune ratio of nanoadditives when compared to the micro- and macro-additives. Other superior properties of polymer nanocomposites include barrier resistance, flame retardancy, scratch/wear resistance, as well as optical, magnetic and electrical properties. 

Metal finishing is the name given to a wide range of processes carried out in order to modify the surface properties of a metal, e.g. by the deposition of a layer of another metal or a polymer, or by formation of an oxide film. The origins of the industry lay in the desire to enhance the value of metal articles by improving their appearance, but in modern times the importance of metal finishing for purely decorative reasons has decreased. The trend is now towards surface treatments which will impart corrosion resistance or particular physical or mechanical properties to the surface (e.g. electrical conductivity, heat or wear resistance, lubrication or solderability) and, hence, to make possible the use of cheaper substrate metals or plastics covered to give them essential metallic surface properties. 

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