Asbestos fiber reinforcements

One of the interesting properties of PBPCP [187] was its fast heat dissipation characteristics and so it was tested by the well-known oxy-acetylene panel test (ASTM 285-70) for ablative materials. Figure 13 shows the survival of a flower for 100 s. kept on the 6.35-mm asbestos fiber-reinforced hexamine-cured panel. The ablation rate value of this material was 3.2 x 10 in/s in comparison with 3.6 x 10 in/s for asbestos-phenolic. As the char content of PBPCP was only 27% compared with 60% for conventional phenolics, mechanisms involving transpiration processes rather than heat blocking by char formation might be playing a greater role in this case [188]. 

AFK asbestos fiber reinforced plastic ANM acrylate rubber... 

Asbestos fiber reinforced plastic Elastomeric terpolymer from tetrafluoro-ethylene, trifluoronitrosomethane, and a small amount of nitrosoperfluorobntyric acid nitroso rubber (ANSI/ASTM) see also CNR... 

Pulp-like olefin fibers are produced by a high pressure spurting process developed by Hercules Inc. and Solvay, Inc. Polypropylene or polyethylene is dissolved in volatile solvents at high temperature and pressure. After the solution is released, the solvent is volatilised, and the polymer expands into a highly fluffed, pulp-like product. Additives are included to modify the surface characteristics of the pulp. Uses include felted fabrics, substitution in whole or in part for wood pulp in papermaking, and replacement of asbestos in reinforcing appHcations (56). 

Fiber-Reinforced Cementitious Material. Use of asbestos (qv) has been legally restricted in Europe and the United States as being ha2ardous to health. In asbestos cement, which had consumed 70—80% of total asbestos, PVA fiber has been used in large amount as a replacement for asbestos. PVA fiber has a strength of at least 0.88 N/tex (9 gf/dtex) and can therefore provide the necessary reinforcement for cement the fiber has excellent adhesiveness to cement (qv) and alkaU resistance, and is not a health ha2ard. 

Other. Vinyl acetate resins are useful as antishrinking agents for glass fiber-reinforced polyester mol ding resins (165). Poly(vinyl acetate)s are also used as binders for numerous materials, eg, fibers, leather (qv), asbestos, sawdust, sand, clay, etc, to form compositions that can be shaped with heat and pressure. Joint cements, taping compounds, caulks, and fillers are other uses. 

The reinforcing capacity of asbestos fibers in a cement matrix constitutes another key criteria for the evaluation of asbestos fibers. This property is assessed by preparing samples of asbestos —cement composites which, after a standard curing period, are tested for flexural resistance. The measured mpture modub are converted into a parameter referred to as the fiber strength unit (FSU) (34). 

The main characteristic properties of asbestos fibers that can be exploited in industrial appHcations (8) are their thermal, electrical, and sound insulation nonflammabiUty matrix reinforcement (cement, plastic, and resins) adsorption capacity (filtration, Hquid sterilization) wear and friction properties (friction materials) and chemical inertia (except in acids). These properties have led to several main classes of industrial products or appHcations... 

The reinforcing properties of asbestos fibers have been widely exploited in asbestos—cement products mosdy for the constmction industry and sanitation (sheets, pipes). Into the 1990s, asbestos—cement products represent by fat (f 70%) the largest industrial consumption of asbestos fibers. 

Asbestos fibers have likewise been used in reinforcement of plastics such as poly(vinyl chloride), phenoHcs, polypropylene, nylon, etc. Reinforcement of both thermoset and thermoplastic resins by asbestos fibers has been practiced to develop products for the automotive, electronic, and printing industries. 

Finally, the combined reinforcing effect and high absorption capacity of asbestos fibers have been exploited in a variety of appHcations to increase dimensional stabiHty, typically in vinyl or asphalt tiles and asphalt toad surfacing. Figure 9 summarizes, as of 1984, the various classes of application for asbestos fibers in combination with other materials. The diagram shows that in recent years, most industrial appHcations have evolved towards composite materials where the fibers are bonded within an organic or inorganic matrix. 

The primary constituent of practically ah. asbestos—organic friction materials was asbestos fiber, with smah quantities of other fibrous reinforcement material. Asbestos was chosen because of its thermal stabhity, its relatively high friction, and its reinforcing properties. Because asbestos alone did not offer ah of the desked properties, other materials cahed property modifiers were added to provide desked levels of friction, wear, fade, recovery, noise, and rotor compatibihty. A reski bkider held the other materials together. This bkider is not completely neutral and makes contributions to the friction and wear characteristics of the composite. The more commonly used kigredients can be found ki various patents (6—9). 

Asbestos Cement Asbestos-cement pipe is seamless pipe made of sihca and portland cement, compacted under heavy pressure, uniformly reinforced with asbestos fiber, and thoroughly cured. The interior surface is smooth, does not corrode, and does not tuberculate. Under normal conditions of operation, asbestos cement will handle... 

Plienoplasts manufactured on tlie basis of thermoreactive plienolfornialde-hyde resin, liarden on licaling up to 120-170°C and tlien become insoluble. Tlicy are usually reinforced with asbestos fiber. 

Table 12 Typical Properties of Anorin-38 Based Asbestos Short Fiber Reinforced Brake Linings...

For firewater, steel pipes are used but corrosion products can block sprinklers. Cement asbestos pipes are utilized but pressure limitations restrict their use. For critical applications, including offshore oil installations, cupronickel alloys and even duplex stainless steels are used. Fire-retardant grades of fiber-reinforced plastics are now available. 

Asbestos fibers are found worldwide in many products as reinforcement in cement water pipes and the inert and durable mesh material used in filtration processes of chemicals and petroleum, for example. However, asbestos is not the only inorganic fiber in use today. Synthetic inorganic fibers abound. Glass fibers have replaced copper wire in some intercontinental telephone cables. Fiberglas (a trade name) has become the insulation material of choice in construction. Carbon and graphite fiber composites are favored materials for tennis racket frames and golf clubs. Fibrous inorganic materials have become commonplace in our everyday lives. 

Phenoplasts manufactured on tlie basis of thermoreactive phenolformalde-hyde resin, harden on heating up to 120-170°C and then become insoluble. They are usually reinforced witli asbestos fiber. 

Fillers. Inert inorganic substances such as calcium carbonate, clay, silicates, and asbestos are often utilized in vinyl compositions where clarity is not a requirement. While the carbonates and clay are used ostensibly to reduce cost, beneficial results are forthcoming. The carbonates produce a dry, matte surface and are claimed, because of their alkaline nature, to benefit heat and light stability. Clay improves electrical insulation. Silicates enhance surface dryness. Asbestos fibers provide the reinforcement necessary for dimensional stability in floor tile. Antimony oxide, per se or as a surface coating on an inert carrier, provides flame retard-ance. Their only major adverse effects are to reduce tensile strength and elongation and require an increase in plasticizer level to compensate... 

Since ancient times, natural fibers have been used to reinforce brittle materials. For example, thousands of years ago, Egyptians began using straw and horsehair to reinforce and improve the properties of mud bricks. In more recent times, large-scale commercial use of asbestos fibers in a cement paste matrix began with the invention of the Hatschek process in 1898. However primarily due to health hazards associated with asbestos fibers, alternate fiber types have been investigated and introduced throughout the 1960 s and 1970 s. 

Currently glass fiber is the overwhelmingly dominant reinforcement (90-95% ) used for thermoplastics. Various other materials make up the remaining 5-10% with perhaps asbestos running a far distant second. The use of synthetic, organic fiber reinforcements on the other hand has been very limited. Although isolated applications document their utiliza-... 

Procedure. Specimen Fabrication. The reinforcements were mixed into the polystyrene melt on a Farrell two-roll mill at 320°F. It was necessary to dry the asbestos fibers for 24 hr at 250°F prior to mixing to ensure the breakup of bundle aggregates. The milling/fluxing time was held to 8 min for all samples. The sheets obtained in milling were cut, crossplied, and compression molded in an open frame on a Wabash press. After they reached the platen temperature the material was held at 330 °F and 2000 psi for 6 min. The frame was then transferred to a cold press, and the sample was cooled under the same pressure. The test specimens were cut from ys-inch thick plates prepared in the foregoing manner. 

Carbon fibers are also of interest as replacements for asbestos fibers in friction materials, such as brake shoes (221. This move was initially driven in order to avoid the health hazards associated with asbestos. In comparison to asbestos reinforced brake formulations, isotropic carbon fibers have been shown to provide much higher friction performance and superior wear resistance, together with many advantages in operating characteristics. These advantages translate to other friction materials, such as clutch plates, and to a much broader range of applications in which carbon fibers are used as reinforcing or filler materials in various matrices. Carbon fibers in the forms of mats, felts, and paper insulation also present viable replacements for asbestos fibers. 

The most important fiber-reinforced inorganic-based product i,s asbestos cement, which has been used in the building indu,stry since 1900, Asbestos nbers (normally chrysotile) are bonded by Portland cement and the mixture sets to a fiber-rein forced material with 10 to 20% asbestos, which has excellent properties (Eternit , Fulgurit etc,)... 

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