Document M47Zoz91VVJa4798kQO2X1Nx

By Robert E. Byrne, Jr. "Reprinted by permission of Modern Plastics Encyclopedia, McGraw-Hill, Inc." Asbestos is a commercial term used for six naturally occurring "asbestiform" minerals that are fibrous, hydrated metal silicates. They include the fi brous form of serpentine, known as chrysotile, and five minerals of the am phibole group: anthophyllite, crocidolite, actinolite, tremolite and amosite. Chrysotile is the most plentiful and useful form of asbestos. Of the more than 2 billion lb. of asbestos used each year by the plastics industry, about 93% is chrysotile. Its positive surface charge, softness and flexibility, and its low re fractive index set it apart from other as bestos. Chrysotile's fiber diameters, less than 0.03 micron, are the smallest among commonly known fibers, and the material has exceptional mechani cal strength. Commercial products based on chrysotile have been introduced which, by chemical modifications of the nor- *Area Manager, "Calidria" Asbestos, Market ing and Technology, Mining and Metals Div., Union Carbide Corp., P.O. Box 579, Niagara Falls, N.Y. 14302 mal chrysotile fiber, have novel surface properties. These materials are used mainly for viscosity control in antisag and thixotropic applications. Compared to chrysotile, amphibole fibers are larger in cross-section, harsh, and hard. The amphibole asbestos min erals are anionic in surface charge, and are more resistant to acids than is chrysotile. Anthophyllite fibers usually occur as fibrous masses containing randomly oriented cubic blocks of fiber up to an inch in length. They are generally used in insulating materials, as filtering me dia, and as fillers in plastics, paints, and asbestos-cement products. Crocidolite, or blue asbestos, is found principally in South Africa. Needle-like in structure and possessed of exceptionally high mechanical strength, it is used in plastics, where its pronounced color is not detrimental. Tremolite and actinolite are very similar, except for the higher iron con tent of the latter. Both are in relatively short supply, and are used mainly as filter media or fillers. Amosite is a long yellowish-brown fiber that is harsh and brittle, and is used mainly in thermal insulation. Low cost, exceptional mechanical strength, and heat resistance account for much of the increasing usage of as bestos in plastic products. It has re cently been recognized that the unit chrysotile fibril is a naturally occurring reinforcing whisker. Because of its high strength, stiffness, and aspect ratio, it provides excellent whisker reinforce ment. Maximum utilization of these reinforcing potentials, however, re quires a high degree of fibril liberation and the absence of extraneous gangue material. Some caution is necessary in selecting a product providing the opti mum in these characteristics. Asbestos is usually graded on the basis of fiber lengths separated by dry screening. While the different grades cannot be precisely characterized by a specific length, grades 2 and 3 are the UCC 016389 ASBESTOS products ^ Economical plastics^ ^ High Purity sfc High Brightness % Low Moisture ^ Less Dust CALIDRIA Asbestos RG-244 a chemically modified, high-purity fiber with a mineral coating CALIDRIA Asbestos RG-144 a high-purity asbestos fiber without coating for maxmum thickening efficiency and thixotropy in polyester spray-up and hand lay-up laminating resins and gel coats. effective thickener for plastisol and organosol adhe sives, coatings, mastics, and sealants as well as epoxy and phenolic adhesives. Advantages: Permits high viscosity at low loadings, reducing costs. Wets out quickly and disperses easily. Improves shelf life, reduces settling. Does not add color or opacity at normal loadings. Reduces dusting from material-handling operations. efficient, low-cost thickener and thixotrope for epoxy, vinyl, and phenolic resins; butyl, polysulfide, and other sealants; and casein adhesives. excellent reinforcer for rigid vinyl, nylon, polysulfone, and similar compounds. Advantages: Thickens both epoxy resins and amine hardeners at 1/6 the cost of pyrogenic silica. Wets out quickly and disperses easily. Has no shear sensitivity. Improves shelf life, reduces settling. Reduces dusting from material-handling operations. Eliminates need for viscosity build-up or thixotropic stabilization additives (except for low viscosity, cyclo aliphatic epoxides). For further information on this "new approach" to thickening and thixotropy, contact your nearest Union Carbide sales office, listed on the back cover. UNION CARBIDE THE DISCOVERY COMPANY UCC 016390 i Table I. Comparative properties of asbestos minerals Properties Chrysotile Anthophyllite Crocidolite Composition Mg3Si205(0H)4 Mg7Si8022 (OH) 2 Crystal habit Color Fine, easily separable fibers White, gray, greenish Prismatic crystals and fibers Gray-white Texture Flexibility Hardness, Mohs Fiber dia., A Tensile strength, p.s.i. Modulus of elasticity, p.s.i. Fusion pt., F. Specific heat, Btu/lb./ F. Surface area BET, mVg. Specific gravity Refractive index (mean) pH Electric charge in aqueous slurry Resistance to acids Resistance to alkalis Soft to harsh, also silky Very good 2.5-4 180-300 300,000800,000 23.2 x 10* 2770 0.266 10-60 2.4-2.6 1.51-1.55 9.5-10.3 Positive Poor Good Harsh Poor 5.5-6 600-900 <4,000 2675 0.210 7 2.8-3.1 1.61 9.4 Negative Very good Good Na2F esF e2Sis O22 (OH) 2 Long brittle fibers Blue Soft to harsh Good 4 600-900 400,000600,000 27.1 x 106 2180 0.201 10 3.2-3.3 1.7 9.1 Negative Good Good Actinolite Ca2Fe5Si8 O22 (UH) 2 Prismatic crystals and fibers Green Harsh Poor 6 600-900 <1,000 -- 2540 0.217 3.0-3.2 1.63 9.5 Negative Fair Good Tremolite Mg5Ca2Sig 022(0H)2 Prismatic crystals and fibers White, gray-white, greenish Harsh Poor 5.5 600-900 1,000-8,000 __ 2400 0.212 2.9-3.2 1.61 9.5 Negative Good Good Amosite (Fe,Mg)7Si 022(0H)2 Prismatic crystals and fibers Ash gray or brown Harsh Good 5.5-6 600-900 100,000200,000 23.6 x 10" 2550 0.193 9 3.1-3.3 1.64 9.1 Negative Good Fair UCC 016391 Table II. Typical changes in resin properties with asbestos reinforcement* % change Material Flexural modulus Flexural strength Tensile strength Impact notched Izod HDT, F. ABS Nylon 6 Phenolic Polyethylene Polyphenylene sulfide Polypropylene Polystyrene + 130 +170 + 120 +320 +60 +360 +110 -20 + 100 +50 +30 +100 -- +50 -5 +85 -- +20 + 10 -4 +20 Optimum reinforcement usually requires 20-40% short fiber asbestos. -60 +20 +5 0 + 100 + 125 -40 +16 +200 -- +72 +35 +25 +18 longest fibers and grade 7 is the short est. In general, the longer fibers are more expensive. One of the few important nonmetallic minerals imported into the U.S. from foreign sources is asbestos. About 10% of our annual usage is pro duced from domestic sources with a value of over $10 million. The remain der comes mainly from Canada. Asbestos selection Asbestos short fiber is normally used for reinforcement, heat resistance, and flow control of plastics, while the longer grades are used for reinforce ment and heat resistance in the form of fibers, yarns, or textiles. Chrysotile, as noted previously, is normally chosen for most applications because of its plentiful supply and product uniformity unless the special advantages of an other mineral are required. For ex ample, anthophyllite has been em ployed for reinforcing polypropylene because it allows easier heat stabiliza tion. Recent reports, however, show that this disadvantage of chrysotile can be overcome. One of the amphiboles may be selected also where the poor re sistance of chrysotile to acids presents a problem. The use of short fiber asbestos in plastics products requires adequate dis persion to achieve optimum results. Melt processing is most satisfactorily accomplished in high-intensity mixers such as the Banbury. Dispersion in liq uid resin systems also requires high shear devices and maximum viscosity to allow the resin/asbestos mix to ab sorb maximum energy. The masterbatch technique should be employed wherever practical. Asbestos use The largest uses for asbestos in plas tics are vinyl/asbestos floor tile and in phenolic compounds. It is also used in myriad other areas including poly propylene, polyesters, nylons, mela mines, epoxies, silicones, and vinyls. It is used in product types, including fric tion materials, heat resistant and elec trical components, sealants, and mas tics. The applications for asbestos are a balance of some combination of these effects. For example, short fiber chryso tile is used in vinyl asbestos floor tile to improve heat strength and dimen sional stability, but requires that par ticular attention be given to heat stabi lization of the resultant product mix during processing. Since 1965, the consumption of as bestos-reinforced polypropylene by the automotive industry has increased rapidly. This trend toward the use of short fiber products for reinforcement is dependent on the inherent strength and fibril geometry of asbestos. The volume of short fiber chrysotile used in mastics, sealants, and adhesives of various types is increasing. From 5 to 60% asbestos is used in adhesives to reduce crazing, shrinkage, and em brittlement. Asbestos also reduces cost, increases bulk, and provides controlled penetration and resistance to heat in such adhesives as phenolics, urea, res orcinol, epoxy, nitrile and reclaimed rubber, and silicones. In mastics and sealants, asbestos provides toughness, flow, and penetration control, as well as reduced cost. The colloidal grades of chrysotile are reported to contribute additional performance and handling improvements. Polyester premixes used to fabricate automotive parts, tractor and marine engine housing, and materials-handling bins and containers often contain short fiber chrysotile to provide flow control, improve surface appearances, reduce shrinkage, and lower cost. The new low-profile systems utilize asbestos for controlled shrinkage, improved me chanical strength, and heat resistance. The amount of asbestos needed varies with the particular resin system and the fiber length, and degree of openness of the asbestos. Each system has an optimum level for maximum mechanical strength. For example, in phenolics about 25% is typical for as bestos floats, or as low as 5% colloidal chrysotile. Asbestos content may vary up to 60%, however, depending on the levels of chemical, thermal and impact resistance, and the electrical properties desired. Asbestos-filled phenolic and urea formaldehyde resins find use in many electrical applications where heat resistance is required. Asbestos-filled polyester and diallyl phthalate com pounds are also used in electrical appli cations. The asbestos-containing com pounds enable molding with excep tional accuracy, molding-in metal in serts easily, and mass producing in tricate shapes difficult to fabricate from other dielectric materials. Phenolic/asbestos laminates used for rocket flame tubes are one example of the increased demand for asbestos-rein forced systems brought about by space age requirements for heat, chemical, and shock resistance. UCC 016392 Any of our offices below will be glad to give you complete information on properties, applications, and orices of "Calidria" asbestos. fahdrtaasbestos Marketing and Technical Center Niagara Falls, New York 14302 Plant King City, California 93930 Sales Offices P. 0. Box 579 P. O. Box K 716-285-3311 408-385-5961 Atlanta, Ga. 30329 17 Executive Park Dr. Baltimore (Moorestown, N. J. Sales Office) Boston, Mass. 02194 300 First Ave., Needham Hgts. Buffalo (Cleveland, Ohio Sales Office) Charlotte (Atlanta, Ga. Sales Office) Chicago, III. 60606 120 South Riverside Plaza Cincinnati, Ohio 45227 3814 West St. Cleveland, Ohio 44114 1300 Lakeside Ave., N.E. Clifton, N. J. 07012 935 Allwood Rd. Dallas, Texas 75207 2710 Stemmons Freeway Detroit (Southfield, Mich. Sales Office) Houston (Dallas, Texas Sales Office) Indianapolis (Cincinnati, Ohio Sales Office) Kansas City (Chicago, III. Sales Office) Los Angeles, Calif. 90058 2770 Leonis Blvd. Memphis (Atlanta, Ga. Sales Office) Minneapolis (Chicago, III. Sales Office) Moorestown, N. J. 08057 Route 38 and Pleasant Valley Rd. New York, N.Y. Philadelphia (Moorestown, N. J. Sales Office) Pittsburgh (Moorestown, N. J. Sales Office) St. Louis (Chicago, III. Sales Office) San Francisco (Los Angeles, Calif. Sales Office) 404-633-6161 301-944-8211 617-444-5400 716-837-6450 704-364-1400 312-822-7000 513-272-0206 216-621-4202 201-778-2900 214-631-0010 313-354-0800 713-621-1000 317-255-3181 913-362-2200 213-583-3061 901-396-5375 612-927-4221 609-235-6200 212-551-3763 215-923-3200 412-922-5700 314-726-0324 415-765-1000 UNION CARBIDE CORPORATION MINING AND METALS DIVISION 270 PARK AVENUE, NEW YORK, N. Y. 10017 THE DISCOVERY COMPANY F-72-0061 3/72-1 M UCC 016393 "Calidria" and "Union Carbide" are registered trade marks of Union Carbide Corporation. Printed in U.S.A.