Fibers static friction

Static friction decreases with an increase in load, and the static coefficient of friction is lower than the dynamic coefficient. The tendency to creep must be considered carefliUy in FEP products designed for service under continuous stresses. Creep can be minimized by suitable fillers. Fillets are also used to improve wear resistance and stiffness. Compositions such as 30% bronze-fiUed FEP, 20% graphite-filled FEP, and 10% glass-fiber-filled FEP offer high PV values ( 400(kPa-m)/s) and are suitable for beatings. 

The proportionahty constant (p) is called the coefficient of friction, and the frictional coefficient is generally independent of the area of contact. However, at low loads, the fiber is often deformed changing the true area of contact and thereby affecting the coefficient of friction. The force necessary to initiate movement determines the coefficient of static friction (p ), and the force necessary to maintain movement determines the coefficient of kinetic friction (p ). p is generally less than p. ... 

Robbins [121] has also developed a procedure for determining dry static friction at low load (in the milligram range) by modification of the incline plane fiber loop method of Howell and Mazur [124]. This procedure attempts to measure those intimate fiber-fiber interactions associated with hair body and style retention, by determining the angle of slip for a small hair loop sitting on two parallel hair fibers. Above a 1-mg load, the frictional coefficient decreases very slowly with increasing load. However, below a... 

It can be seen that the curves for both the woven and knitted fabrics follow similar trends. Intra-yam or inter-fiber friction (a) is most influential at the origins of both curves, starting out as the static friction that needs to he overcome to initiate the sliding of long fibers past one another. 

Because fiber frictional properties are so important in the conversion of staple yams to spun yams, ASTM D2612 has been designed to measure the cohesive force encountered in the drafting or fiber alignment of sHver and top under static conditions. This frictional force is affected by surface lubrication, linear density, surface configuration, fiber length, and fiber crimp. 

Fibers emerging from the spinneret are cooled under controlled conditions, passing over guides and rollers to a take-up spool or bobbin. Often a finish is applied before windup to control static electricity and friction (Stevens 1993). Large-scale production machinery produces fiber at a rate of thousands of feet a minute. A schematic diagram of a melt-spinning apparatus is drawn in Figure 8-10. 

Microemulsions (<150 nm) can penetrate into the yarn and deposit onto the fibers. They deliver a dry lubrication and feel. They probably reduce the static coefficient of friction. 

Polymer emulsions (150 to 250 nm) deposit on the external surface of fabrics and on fibers. They improve the softness and the ease of ironing since they reduce both static and dynamic coefficients of friction. 

The importance of frictional properties largely exceeds the area of domestic fabric softeners. They are also key in the textile industry, as they condition the slipping of fibers over each other in all mechanical processes [20], Friction causes breakage of threads and generates static electricity. More generally, softened fabrics are pressed and sewed more easily, as there is less resistance to the metal movement. They also relax more quickly at the dry state since fibers slide over one another more easily. However, it is more difficult to cut fabrics with scissors as the blade slips over the fibers and fewer fibers are tom during cutting [20],... 

All surfactants develop an antistatic activity. Their efficacy relies both on their ionic character and their capacity to bind water [23], However, the most efficient antistatic agents are cationic softeners, because of their high affinity for fabrics [20], Moreover they also reduce the generation of static electricity by lubricating fibers and reducing interfiber friction [10]. 

The difficulties encountered by the textile industry are even greater. The friction of hot air moving along fibers produces static electricity. Besides electric shocks, the problems caused by static electricity are twofold it may cause malfunctions in the operation of electronic equipment and it generates sparks that may be hazardous in the presence of flammable vapor [20], Here also, softeners are extremely efficient in fighting static charges on fibers. 

GeoDeck composite deck boards often utilize HDPE with the density of 0.955 g/cm Its coefficient of friction is about 0.15. However, when rice hulls and a granular blend of calcium carbonate/kaolin and delignifled cellulose fiber are incorporated into the plastic matrix, the static coefficient of friction increased to 0.53, that is, to 350% compared to the initial HDPE. 

Fillers in composite materials, such as wood fiber and (if any) mineral fillers, are natural friction enhancers, though, strictly speaking, they typically increase abrasion, not friction. It is not important, though, for this consideration is aimed at safety, and it is not an academic discussion about differences between molecular interactions and abrasiveness. As it was described above, neat HDPE is characterized by a low value of coefficients of friction, and the higher the density (specific gravity), the lower the static coefficient of friction. For HDPE density between 0.915 and... 

Another important classification that will be referred to routinely is single fiber and fiber assembly properties. The more important single fiber properties are elastic deformations, friction, cross-sectional area (diameter), static charge, luster or hair shine, and cohesive forces. 

Cross-sectional shape, friction, density, and static charge are described as other important physical properties, and hair shine, combing ease, body, style retention, manageability, and hair conditioning are the primary important consumer assessments described in this chapter. A new section describing normal variation that exists in the cross-sectional shape of hair fibers and a few examples are given describing how these variations influence both the physical and the chemical behavior of the fibers. 

As indicated earlier, wet friction for human hair is higher than dry friction (see Table 8-18). In addition, both static and kinetic friction and the differential friction effect increase with increasing relative humidity. These same phenomena have been observed for wool fiber [126,127]. 

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