Resistance: abrasion

Resistance to abrasion is defined as the ability of a material to withstand mechanical action that tends to progressively remove material from its surface. Abrasion resistance of polymeric materials is a complex subject. The resistance to abrasion is closely related to other factors such as hardness, resiliency and the type and amount of added fillers and additives. Resistance to abrasion depends on factors such as test conditions, type of abradant and development and dissipation of heat during the test cycle. This all makes abrasion a difficult mechanical property to define as well as to measure adequately. 

A material s ability to resist abrasion is most often measured by its loss in weight when abraded with an abrader. The Taber abrader is widely used to measure abrasion resistance. In the Taber abrasion test, the test specimen is placed on a revolving turntable with a suitable abrading wheel imder a set certain dead weight. The weight loss after a large number of revolutions (at least 5000 revolutions) is measured. For softer materials, less abrasive wheels with a smaller load on the wheels may be used. 

Wear may be high when reinforced parts are in contact with unreinforced parts. This situation could lead to excessive wear of unreinforced parts. Use of lubricated reinforced grades may reduce wear when in contact with the unreinforced component. 

LDPE is easily marked by a thumbnail, HOPE is scratched in this way with difficulty, but PP is marked little, if at all. Hardness is defined as the resistance of a material to deformation, particularly permanent deformation, indentation, or scratching. Hardness is a relative term and should not be confused with wear and abrasion resistance. Many tests have been devised to measure hardness. Rockwell and Durometer hardness test are commonly used. 

A few case histories of the use of rubber lining in anti-abrasive applications are given below. 

F%ar 456 Reiailoa between fiber content and polymer Cesicat ratio and relative impact strength of steel fil ef remforced PAE-m( ified concretes. 

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Polybutylene exhibits high tear, impact, and puncture resistance. It also has low creep, excellent chemical resistance, and abrasion resistance with coilability. 

The abrasion resistance of ionomers is outstanding, and ionomer Aims exhibit optical clarity. In composite structures ionomers serve as a heat-seal layer. 

Its principal advantages are high resilience and good abrasion resistance. 

It possesses resistance to oils up to 120°C and excellent abrasion resistance and adhesion to metal. 

Spandex fibers are available as fine as 1.1 tex (10 den), and the finest extmded latex thread available is about 16 tex (140 den). The availabihty of spandex fibers in such fine sizes and their unique properties compared to mbber, eg, dyeabiUty, high modulus, abrasion resistance, and whiteness, has allowed extensive penetration into hosiery and sportswear markets. 

From 1910 onward waste filament yam had been chopped into short lengths suitable for use on the machinery designed to process cotton and wool staples into spun yams. In the 1930s new plants were built specifically to supply the staple fiber markets. During World War II the production of staple matched that of filament, and by 1950, staple viscose was the most important product. The new spun-yam oudets spawned a series of viscose developments aimed at matching the characteristics of wool and cotton more closely. Viscose rayon was, after all, silk-like. Compared with wool it lacked bulk, residence, and abrasion resistance. Compared to cotton, it was weaker, tended to shrink and crease more easily, and had a rather lean, limp hand. 

In the sheeting market, the low density polyethylenes are less important than the high density resins. The high density resins have excellent chemical resistance, stress-crack resistance, durabiUty, and low temperature properties which make them ideal for pond liners, waste treatment faciUties, and landfills. In thicker section, HMW-HDPE sheet makes good containers, trays, tmck-bed liners, disposable items, and concrete molds. The good durabiUty, abrasion resistance, and light weight are critical elements for its selection. 

Cellular mbber has been used extensively as shoe soles, where its combination of cushioning abiUty and wear resistance, coupled with desirable economics, has led to very wide acceptance. In this case the cushioning properties are of minor importance compared with the abrasion resistance and cost. Other significant cushioning appHcations for cellular mbbers and latex foam mbbers are as carpet underlay and as cushion padding ia athletic equipment. 

Catalysis is usually accompHshed through the use of tertiary amines such as triethylenediamine. Other catalysts such as 2,4,6-/m(/V,/V-dimethylaminomethyl)phenol are used in the presence of high levels of cmde MDI to promote trimerization of the isocyanate and thus form isocyanurate ring stmctures. These groups are more thermally stable than the urethane stmcture and hence are desirable for improved flammabiUty resistance (236). Some urethane content is desirable for improved physical properties such as abrasion resistance. 

The abihty of organically modified ceramics based on alumina, zkconia, titania, or siUca (and mixtures of each) to function as abrasion-resistant coatings has also been studied (62). Eor example, polycarbonate, when coated with an epoxy—aluminosihcate system, experiences a significant reduction in the degree of hazing induced by an abrader, as compared to uncoated polycarbonate. 

Some amorphous copoly(ether—sulfone) fkms have been prepared (117) with Ts around 130°C with no loss in weight up to 400°C in ak or N2. Other backbones iavestigated in this class of polymers are copoly(ether—amides) (118) and copoly(ether—ketones) (119). These polymers show good mechanical properties, flow characteristics, and abrasion resistance. 

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