Polyethylene friction

The material in use as of the mid-1990s in these components is HDPE, a linear polymer which is tough, resiUent, ductile, wear resistant, and has low friction (see Olefin polymers, polyethylene). Polymers are prone to both creep and fatigue (stress) cracking. Moreover, HDPE has a modulus of elasticity that is only one-tenth that of the bone, thus it increases the level of stress transmitted to the cement, thereby increasing the potential for cement mantle failure. When the acetabular HDPE cup is backed by metal, it stiffens the HDPE cup. This results in function similar to that of natural subchondral bone. Metal backing has become standard on acetabular cups. 

This is a standard friction problem. A glance at Fig. 25.5 shows that, when polymers slide on metals and ceramics, x can be as low as 0.04. Among the polymers with the lowest coefficients are PTFE (Teflon ) and polyethylene. By coating the ski or sledge runners with these materials, the coefficient of friction stays low, even when the temperature is so low that frictional heating is unable to produce a boundary layer of water. Aircraft and sports skis now have polyethylene or Teflon undersurfaces the Olympic Committee has banned their use on bob-sleds, which already, some think, go fast enough. 

Slip membrane serves to reduce friction between the slab and sub-base to minimize subsequent slab cracking. This is normally a polyethylene sheet. It may also serve as a damp-proof membrane ... 

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. 

Figures 8 and 9 show the dependence of the self-diffusion constant and the viscosity of polyethylene melts on molecular weight [47,48]. For small molecular weights the diffusion constant is inversely proportional to the chain length - the number of frictional monomers grows linearly with the molecular weight. This behavior changes into a 1/M2 law with increasing M. The diffusion...

Fig. 8. Self-diffusion coefficients of polyethylene chains as a function of molecular mass. The measurements were carried out at the same value of the monomeric friction coefficient. (Reprinted with permission from [48]. Copyright 1987 American Chemical Society, Washington)...

The insulation was 3.5-in.- (90-mm-) thick, unfaced, glass-fiber insulation (friction-fit). Walls with insulation also had a 4-mil clear polyethylene vapor barrier on their interior side. All wood and gypsum materials were conditioned at 23°C and 50 percent relative humidity, resulting in moisture content of 9 to 10 percent in wood materials. Figure 1 is a diagram of the wall frame construction. The hardboard siding was on the exterior side of the 5/8-in. (16-mm) plywood (not shown). 

Liquid-liquid solvent extraction, 21 399 Liquid lithium, 15 131 Liquid low density polyethylene, 20 205 Liquid lubricants, for extreme environments, 15 256 Liquid lubricated system, coefficient of friction in, 15 209 Liquid magnesium, 15 336 Liquid manometers, 20 646-647 Liquid MDI, 25 462. See also MDI [4,4 -methylenebis(phenyl isocyanate)] Liquid melamine resins, 15 773 Liquid membrane extraction, 10 766 Liquid membranes, 15 800, 814-815 supported, 16 28... 

Friction factors for turbulent flow of dilute solutions of polyethylene oxide Source R. W. Patterson and F. H. Abernathy, Journal of Fluid Mechanics, 51, pp. 177-85(1972)... 

High density and UHMW polyethylenes are used to make antifriction parts. The coefficients of friction are low but the moduli, hardnesses and softening temperatures are weak, which limits the loads and PV factors. 

Spalding, M.A. and Hyun, K.S., Coefficients of Dynamic Friction as a Function of Temperature, Pressure, and Velocity for Several Polyethylene Resins, Polym. Eng. Set, 35, 557 (1995)... 

G. Deamaley and J. Lankford, Jr., Ultra high molecular weight polyethylene components treated to resist shearing and frictional wear, US Patent 6171343, assigned to Southwest Research Institute (San Antonio, TX), January 9, 2001. 

Polyolefins. Ultra-High-Molecular-Weight Polyethylene.TIus is easily made by conventional low-pressure coordination polymerization. Hercules Hi-fax 1900 has a molecular weight of 2.5-5.0 million. Its outstanding properties are low coefficient of friction (0.11) abrasion-resistance superior to nylon, polyurethane, and steel unbreakable in the Izod notched impact test and high resistance to most inorganic and many organic chemicals. 

Gold PI, Amar PK, Swaidan BE (1973) Friction reduction degradation in dilute polyethylene oxide) solutions J Appl Polym Sci 17 333... 

Generally speaking, the 3M taggants do not sensitize expls to impact or friction even with unencapsulated melamine-alkyd cores. With a more highly cross-linked and consequently harder core there was evidence of sensitization. As an added safeguard, it is desirable to encapsulate even the soft taggants in polyethylene... 

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