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(162) M cBee, E. T., and Welch, Z. D. (to Purdue Research Foundation), U. S. Patent 2,443,630 (June 22, 1948). (163) M acNair, R., Metal Znd., 73, 206-8, 247-9 (1948). (164) M ahla, E. M., and Nielsen, N. A., J. Applied Phys., 19, 378-82 (1948). (16.5) M anler, M., Metal Finishing, 45, No. 11, 62-6; No. 12, 82-8 (1947). (166) M ann, C. F. A., Diesel Progress, 14, No. 11, 44-5 (1948). (167) M ariner, T., and Bleakney, W.,Rev. Sci. Instruments, 20, 297303 (1949). (168) Meijering, J. L., Proc. Pittsburgh Intern. Conf. Surface Reactions, 101-4 (1948). (169) Miller, G. L., Iron and Steel Inst., Symposium on Powder Metallurgy, Special Rept. 38 (1947). (170) Misch, R. D., and MacDonald, H. J., Wire and Wire Products, 23, 221-6, 260-4 (1948). (171) Mond Nickel Co., Brit. Patent Appl. 28,168/47 (Oct. 21, 1947). (172) Morris, A. L., Sowter, G. A. V., Melville, W. S., Jarkson, D., Fletcher, F. H.. Chirnside, H. S., and Robertb, M .W.F., BZOS Final Rept. 682 (November 1947). (173) Morton, B. B., Corrosion, 4, No. 7, 1-3 (1948). (174) Morton, B. B., J . Znst. Petroleum, 34, 1-68 (1948). (175) Naidu, D. S.,J . Proc. Znst. Chemists ( I n d i a ) , 18, 13-43 (1946) (176) Ned, L., Rev. met. 45, 475-80 (1948). (177) Nelson, J. H., Metal Ind., 73, 343-5, 369-71, 373 (1948). (178) Parmley, T. J., and Moyer, B. J., Phys. Rev., 72, 746 (1947). (179) Pattison, F. R., Dairy Inds., 12, 329-37 (1947). (180) Pattison, F. R., Metallurgia, 39, 269-71 (1949). (181) Paul, J. M., and Beard, G. V., J.Phys. Colloid. Chem., 52, 750-3 (1948). (182) Phillips, E. M., S . A . E . Journal, 56, 66-7 (1948). (183) Pray, H. A., and Igelsrud, H. (to Battelle Development Corp.), U. S. Patent 2,446,060 (July 27, 1948). (184) Pray, H. A., Peoples, R. S., and Dalrymple, R. S., A m . Gas ASSOC. Monthly, 30, N03. 7, 8, 19-23, 59, 60 (1948). (185) Raub, E., and Engel, A., Metallforschung, 2, 11-16 (1947). (186) Rhines, F. N., Corrosion Material Protection, 4, No. 2, 15-20 (1947). (187) Richelson, M., Chem. Eng., 55, No. 9, 114 (1948). (188) Rocard, Y., Rev. sci., No. 3267, 195-204 (Fob. 15, 1947); Engineers Digest ( A m . Ed.), 5 , No. 4, 180-2 (1948). (189) Roehl, E. J., Plating, 35, 452-5, 478 (1948). (190) Rosen, E., Materials and Methods, 27, No. 6, 107 (1948). (191) Rosen, E., and Black, G., Zbid., 27, No. 6, 105 (1948). (192) Rowan, M. J., A m . Machinist, 93, No. 10, 107-18 (1949). (193) Rowley, L. N., and Skrotzki, B. G. A,, Power, 91, 681-96 (1947). (194) Rudge, A. J., Chemistry & Industry, No. 16, 247-53 (1949). (195) Sanderson, L., British Steelmaker, 14, 518-19 (1948). (196) Schempp, R., Office of Military Gov. for Germany (U. S.), Office Tech. Services, PB 80,356, F I A T Final Rept. 1148 (June 3, 1947). (197) Schlecht, L., BIOS Final Rept. 1575 (November 1947). (198) Schreiner, N. G., and Tippett, M., Welding J . , 27, 431-7 (1948). (199) Schwarzkopf, P., Powder Met. Bull. 4, No. 2, 28-56; No. 3, 64-111 (1949).
Vol. 41, No. 10
Scott, R. B. Chem. Eng. News, 27, 545 (1949). Scott, R. B., Petroleum E n ~ t . 19, , No. 3, 148 (1947). Shaw, A. E., Phys. Rev., 75, Second Series, No. 2, 331 (1949). Shaw, J., Product. Eng., 19, No. 6, 158-63 (1948). Shirai, S., Proc. Phys. Math. SOC.Japan, 25, 637-8 (1943). Siegle, L., and Brick, R. M., Trans. A m . Soc. Metals, 40,813-69 (1948). (206) Silsbee, N. F., Aero Digest, 58. 44-6 (May 1949). (207) Spencer, E., Chem. Eng., 55, No. 10, 110-13 (1948). P h w . , 20, No. 1, 1-8 (1949). (208) Stahl, H. A . . J . Applied .. Ibid., pp. 8-14. Stauffer, R. A., Chemistry &Industry, No. 41, 519-526 (Oct. 9, 1948). Strutz, C. R., Welding J., 28, No. 4, 329-34 (1949). Taylor, A. D., Plating, 36, 239-45 (1949). Teeple, H. O., Steel, 121, No. 18, 134 (1947). Teeple, H. O., Yearbook of Am. Pulp and Paper Mill Supts. Assoc., 29th Annual Ed., 73-9 (1948). Toerge, W. F., Steel, 123, N o . 21, 72-8, 80, 111-12, 115 (1948). Tolley, G.. Metallurgia, 37, N o . 218, 71-4 (1947). Treseder, R. S. (to Shell Development Co.), U. S. Patent 2,382,753 (.4ug. 14, 1945). Treseder. K. S., axid Wachter, A., "Corrosion in Petroleum Processes Employing Aluminum Chloride," Natl. A4ssoc. Corrosion Engrs., Cincinnati, April 11 to 14, 1949. Turner, E. E., Jr. (to Submarine Signal Corp.), U. S. Patent 2,444,967 (July 13, 1948). Van Dusen, M. S., and Dahl, A. I., J . Research S a t l . Bur. Standards, 39, 291-5 (1947) : Research Paper 1828. Wagner, C., and Zimens, K. E., Acta Chem. Scand., 1, 547-65 (1947). Wakefield, J. E., Iron A g e , 163, No. 11, 81-5 (1949). Way, K., Sucleonics, 2, KO.5, Part 2, 122-3 (1948). Weber, C. H., Jr., Znd. Heating, 14, 1635-6, 1638, 1640, 1642 (1947). Weinhaum, S.. J . Applied Phys., 19, 897-900 (1948). Welter, G., Metallurgia, 38, 287-92, 328-30 (1945); 39, 13-17 (1949). Ibid., 158-90, 253-6, 313-15 (1949). Wernick. S., and U'illetts. F., Machinist, 91, 903-7 (1947). Wesley, W. A , , and Copson, H. R., J . Electrochem. Soc., 95, 226-41 (1949). White, E. D., C h e n . Ens., 56, No. 4, 91-3 (1949). Williams, A. E., Mining J . , Ann. Review S o . 41, 43, 45, 47 (1948). Williams, R., J r . , Chem. Eng., 5 5 , No. 8, 96-8 (1948). Kohlfarth, E. P., Proc. Roy. Soc., A195, 434-63 (1949). Wood, R. L., and Von Ludwig. D., Iron A g e , 161, No. 19, 72-8; SO. 20, 90-4, 140-2 (1948). Woodhouse, H . , Aero Digest, 57, 74, 76, 117 (August 1948). Zander, J. M., Better Enameling, 19, 6-8 (1948). Zapffe, C . A., Trans. A m . SOC.Metals, 40, 315-54 (1948). Zarubina, 0. V.. Zhur. Priklad. Khim., 21, 362-71 (1948). Zeeh, C . J., Metal Progress, 52, 824, 824B, 825 (1947). Ziels, N. W.,and Schmidt, UT.H., Oil & Soap, 22, 327-30 (1945). (200) (201) (202) (203) (204) (205)
KECLXVED August 11, 1949.
PLASTICS G. &I. KLINE,
NationaE Bureau
of Standards, Vashington, D .
T.
C.
IE great expansion in the range and volume of application of plastics since 1941 can be attributed in part t o the effort which was expended during the war period t o obtain engineering data on the properties and performance of plastics. The designer, engineer, and manufacturer will use more and more plastics when the background of knowledge and experience regarding their behavior under service conditions instills confidence in their reliability. This survey reviews recent developments and new informatiox which has been published concerning the use of plastics as chemic31 engineering materials of construction.
ACRYLIC RESINS
Cast methyl methacrylate sheet of the heat-resistant type is now fusion welded to form cells, tanks, tank liners, cradles, and baskets for the electroplating and chemical industries. These are reported to be satisfactory for use with acids and alkalies up to 50% by volume concentrations a t temperatures up to 228" F. (96).
I n the new Fisher-Stern ultracentrifuge the rotor and cells are made of polymethyl methacrylate. At the top speed of the rotor, 20,000 r.p.m., liquid samples are subjected to a centrifugal force
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26,000 times as great as that of gravity. The acrylic rotor weighs less than a pound, whereas a metal rotor t,he s8me size would weigh about 7 pounds ( 1 2 ) . ETHYLENE POLYMERS
Production capacity for polyethylene more than tripled during the year, going from 15,000,000 to approximately 55,000,000 pounds. Pipes and fittings made of polyethylene for use in chemical plants are insoluble in all common solvents a t temperatures up to 50" to 60" C., but are attacked by chlorinated solvents and aliphatic and aromatic hydrocarbons a t elevated temperatures. The threaded fittings are reported to withstand pressures up to 50 pounds per square inch a t normal temperatures without leakage (15). Buckets and jugs (20) for holding corrosive liquids, such as acids, and a large aircraft battery ( 5 ) are molded of translucent polyethylene. A centrifugal casting process is being used in Great Britain to produce large pieces of chemical plant equipment with greater strength, stability, and accuracy than can be obtained by forming from sheet material. The method consists of charging a cylindrical metal mold with polyethylene granules, rotating a t sufficiently high speed to form a powder lining, and applying heat to fuse the granules in place. Tanks of circular section in capacities up to 500 gallons have been successfully lined with polyethylene sheeting using a hot gas torch for welding joints (98). Packings of polytctrafluoroethylene (Teflon) in braided form on spools or in rings are being marketed for packing valves, centrifugal and rotary shafts, and reciprocating rods. The packings are not affected by any solvents, acids, or caustic solutions a t temperatures up to 690' F. Their nonadhesive property prevents excessive wear of reciprocating rods, shafts, and valve stems (17 ) . Polymonochlorotrifluoroethylene, mentioned briefly in last year's review, is now available conimercially under the trade name Kel-F. This material was originally developed during the war as a gasket and valve seat material for use in highly corrosive fluorine atmospheres and has proved to be very satisfactory for such service. One form of considerable interest to the chemical industry is lay-flat tubing with wall thicknesses ranging from 1 to 10 mils. This tubing is useful as protective liners or fuel bags for such highly corrosive materials as white fuming nitric acid and hydrogen peroxide. The material in this form also lends itself for protective coating applications on metal or wooden surfaces (10, 55-57). Polymonochlorotrifluoroethylene products are being produced under the trade name Fluorothene for use by the various Atomic Energy Commission installations and other government agencies. Among the standard items lyhich are being molded by compression, injection, and extrusion molding are sheets, tubes, rods, flare fittings, and laboratory ware (29). Tests (82, 100) have shown that the material is impervious to the action of inorganic agents except molten alkali metals. Concentrated solutions of alkalies and acids, including nitric, hydrochloric, hydrofluoric, and sulfuric, and fluorine and metallic fluorides do not attack it. Organic solvents may swell the material but will not react chemically. There is no known solvent for this plastic. I t has a I o n rate of heat conductivity, escellent electrical resistance, high tensile strength, and exceptional resistance to shatter under impact (Figure 1). Fahricntion of the chlorofluoroethylene plastic sheets is best accomplished a t 300' to 305' C. in a hydraulic press equipped with chrome plated ferrotype plates. Transparent sheets can be produced up to 0.25 inch thickness and translucent sheets up to 3.5 inches thickness. Special heating equipment is required for estrusion molding tubes and rods. Machining is easily accomplished with ordinary wood or metal viorking tools. Punch press operation is possible on sheet, stock up to 0.15 inch thickness. Tubing made of this material can be flared (on warming) with the standard flaring tool used for copper tubing. Thick wall tubing can be threaded with standard pipe threaders.
COURTESY CARBIDE A N D CARBON C H E M I C A L S CORPdRATION
Figure 1. Fluorothene Coil for Studying Gas Flows and Condensation on a Refrigeration System -4mong the important uses of this plastic in chemical engineering are: gaskets and valve seats in high vacuum and pressure systems for handling corrosive chemicals such as hydrous and anhydrous hydrofluoric acid, and all concentrations of fluorine; valve bodies and diaphragms in all chlorofluoroethylene plastic systems consisting of tubing, flare fittings, and reactors for corrosive chemical processes; bearings and pump seals when filled with graphite or other forms of carbon; and windows (sight glasses) and manometers with inert fluorocarbon oil as a manometer fluid on reactors involving highly corrosive chemicals. The lower polymers of polymonochlorotrifluoroethylene are excellent lubricants for applications in which the lubricant is exposed to corrosive gases and liquids-for example, this fluorolube oil has been used extensively in vacuum pumps and compressors for handling hydrofluoric acid and fluorine. The intermediate polymers are blended to make an excellent stopcock grease. FURAN RESINS
A pro'ective coating based on a partially polymerized furfuryl alcohol (Durez resin ) has proved to be a valuable aid agtin:-t corrosion by acids and alkalies in chemical plants. It, has been used effectively on steel structures in the acid areas of the Celnnese Corporation of America's Celriver plant a t Rock Hill, S. C. Thc prepared resin may be applied directly to clean wood surfaces. Since it contains sulfuric acid catalyst, metal surfaces must fir:it be given a coat of a rust-inhibiting primer. hlasonry must be coated with a primer sealer. An equal volume of acetone is used to thin the proprietary rcsin; the use of alcohol as a thinner leads to inferior acid resistance. The catalyst is 2q7, by volume, based on the diluted resin, of a 33% by volume aqueous sulfuric acid. The catalyzed resin
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has a pot life of about 4 hours. Application may be made by brush or dipping; spraying has been unsuccessful. Two coats are necessary to ensure complete coverage, free of pinholes. The finished coating is black, hard, smooth, and glossy. I t may be sanded, machined, and polished without chipping. It Iazks flexibility and cannot be used on surfaces subject to bending. Heating above 150" F. causes cracking of the coating, due to thermal expansion stresses. It resists caustic in all concentrations, glacial acetic acid at ordinary temperatures, and esters and acetone (104). Another application of furan-type resins is illustrated by Nukem all-purpose resinous cement, designed to cope with the chemical conditions encountered in battery plants, dairies, dye plants, food processing, oil refineries, ordnance works, pickling houses, pulp and paper mills, rayon plants, soap factories, and steel processing mills. It is used as a mortar in installing brick or tile for floors, pits, sewers, vats, walls, towers, flues, and constructions where high temperatures and alternate acid-alkali processes are involved. It is immune to high concentrations of practically all acids (except chromic and nitric), alkalies, salts, and solvents and is resistant to temperatures up to 350' F. (75). ISOBUTYLENE POLYMERS
Increased activity in the use of isobutylene as a raw material for making plastics was evident (71). The properties of polyisobutylene blends with polyethylene (72) and waxes ( I ) mere described. LAMINATES
An investigation of eight phenolic laminates immersed in various aqueous chemical solutions for 6 months showed that the glass fabric and asbestos-filled materials are best for field conditions involving weak acids, weak oxidizing agents, and conditions such a> are found in the rayon-spinning industry. Where alkaline field conditions are involved, the cotton fabric laminates can be expected to offer the best resistance. Strongly acid conditions led to losses in strength of 30 to 40% for glass fabric laminates and over 50% for all other grades (99). LOW DENSITY PLASTICS
Many types of installations require materials with low thermal and sound conductivity, lory moisture absorption, and low specific gravity. Foamed plastics made from polystyrene (38, 64) and phenolic resins (45)are available; these are considerably more efficient 1%-ithrespect to these factors than many of the insulating materials used heretofore, such as cork, fiberboard, and rock wool. They are also useful as a buoyant material in flotation devices. NYLON
hylon moldings are belng Tvidely Lised for cams, bearings, fastening devices, and other industrial mechanical parts, many of which are buried within operating mechanisms. The type commonly employed is FAI-10001, which is form-stable even above 400" F., although it becomes appreciably more flexible above this tcmgerature. It does not become brittle at temperatures as low as -70" F., but it does increase in stiffness as the temperature is lon wed. I t is resistant to impact, abrasion, and the usual lacquer solvents including hydrocarbons and chlorinated hydrocarbons. It is soluble only in phenols and formic acid. Mineral acids attack it fairly rapidly, but strong alkalies have a negligible effect
(4). l l a n y parts are now molded of nylon for testile machinery because of its abrasion resistance, l o x coefficient of friction, oilless operation, durability, and a cost n-hich is about one sixth that of parts machined from steel or brass. Nylon roller rests are operating a t 1500 r.p.m. in centerless wet grinding of aluminum tubing. Sheet, fiber used previously had a tendency to pick up particles, \year fast, and mar the stock bcing ground. The nylon rollers are
Voi. 41, No. 10
replaced only once a 67 aek, after approximately 30,000 feet, of aluminum tubing have heen processed ($1). -1LIC04ES
The production a i d vdriety of applications of silicone poll nlers increased during the past year (2, 8, 49, 50, 68). Silicone resins available for formulating heat stable coatings are supplied a t 50 to 60% solids content in suitable solvents. These silicone enamel> have excellent weather and moisture resistance as iiidicated by complete freedom from yellowing, chalking, and checking. Modified silicone aluminum coatings are currently about 30% more expensive t o apply than organic aluminum coatings but they normally protect hot metal surfaces two to three times as long as organic aluminum finishes (78), The remarkable heat-stability of silicone (Class H) insulation enables design engineers to increase the power per pound ratio in electric motors, transformers, generators, and solenoids by 50 to 100%. Increased production schedules in a chemical plant, for example, made it necessary to pump more cooling water to a battery of distillation columns. That problem was solved without any lost time by installing larger pump impellers and casings and by rewinding the pump motors n i t h silicone insulated wire to increase pumping capacity by 50%. Cost was $2900 below the cost of a new installation (36). Silicone ball bearing greases remain serviceable over a temperature span of about 400" F. h low temperature silicone grease, for example, is recommended for use a t temperatures of -100' to 300 'F. A high temperature, low speed silicone grease used extensively in oven conveyer systems has a useful temperature range of -20" to over 400" F. A typical application is in the bearings of a core oven conveyer system which are exposed t o peak oven temperatures of 700" F. for 2 out of 4 hours, 24 hours a day. A third type of ball bearing grease is recommended for use a t temperatures from -40" to 350" F., and a t speeds up to a t least 20,000 r.p.m. This silicone grease is used as a permanent Iubricant in sealed bearings. I n open or shielded ball bearings it ha5 many times the life of high quality petroleum greases (33). Silicone rubber is made from high polymer silicones compounded with inorganic fillers. Over twenty different stocks are available for special applications. The newest Silastic stocks have brittle points in the range of -150' F., and withstand continuous exposure to temperatures of 300" to 350' F. or more limited exposure to temperatures of 500" F. and upwards. Special stocks for gasketing applications are more resistant to permanent compression set a t high temperatures than any other resilient gasketing material. -111 types of silicone rubber are useful a t temperatures well above and below the limits of organic rubber. I n gcnera1 they have excellent dielectric properties and high resistance t o weathering, oxidation, lubricating oils, and to a variety of chemicals. They can be molded, extruded, calendered, sheeted, laminated, or coated. Principal applications are in the electrical industry aq a heat-stable resilient insulating material and in the aircraft, automotive, and chemical industries as high and low temperature, oil-reqistant gasketing and sealing material (52, 5Q) STYRENE RESINS
Styrene-Lutadiane copolymers made with high styrene conwnt are providing a new series of high impact strength plastics. A product known as Plio-Tuf (3,90) consists of a blend of such 5 high-styrene-butadiene copolymer (Pliolite S-6) with any of the natural or synthetic rubbers. The resultant mixture displays excellent impact resistance, lorn water absorption, and good moldability and machinability. Some of the industrial applications for Plio-Tuf include textile spools, chemical buckets, photographic trays, chemical piping, and other uses where hard rubber was formerly employed. More recently it has been found that natural rubber Pliolite (cyclized rubber) when blended with GR-S produces a compound.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
2135
I t is highl? resistnnt to impact b l o w down to 20" F.,but should be handled with moderate care a t lower temperatures. It can be Jrilled and tapped by standard iron pipe techniques (Figure 2). VINYL R E S I X S
COURTESY
Figure 2.
U
5
RUBSLq COMPANY
Uscolite Plastic Pipe Carries Acid
I t is resistant to most corrosive chemicals and is tough and easy to thread and bend
Pimilar t,o the usual Plio-Tuf, but having a heat distortion point about 40' F. higher-that is, approximately 173" F. This co~lipound is of particular interest in applications such as battery bases. New copolymers of styrene and isobutylene produced by lorn temperature polymerization have been announced (71). They exhibit rubberlike elastic properties in addition to their thermoplastic characteristics. They have a broad softening range, mix Tell x i t h waxes, are easily processed on conventional equipment, and have l o v permeability to moisture and gases. Polystyrenes with improved light stability, toughness, and h a t resistance were marketed during the past year (11, 102). The impact strength of the new tough styrene-type resiii is three t o five times greater and the elongation ten times greater than the corresponding values for regular polystyrene. The increase in heat resistance of one type of polystyrene is attributed to more precise control of molecular chain forms in the polymer as a result of the application of principles discovered in the course of fund:*mental research (105). A styrene-base copolymer thermo$astic molding material witL I n impact strength in the high ccllulo?ic range was introduced in May 1949 under the name Plesene T.1. Its resistance to battery acids m d gtsoline and its dimensional stability make it suitable for battery cases and parts, toti' li~~s~:.;, freezer lids, and general intiuitrisl applications ( I S ) . A rigid plastic pipe nhich i d 1 handle most of the corrosive chemicals used industrially is made of a modified styrene copolymer, trade named Uscolite (101). It shorn negligible distortion a t 180' F. but can be bent easilv \\-it,houtflattening by heating it, t,o 2SO" F. and bending it slorvly around a form of proper radius.
Research on polymers of various vinyl derivatives (19, 82, 23, 28, 65, 8 6 ) continued to provide a foundation for future progress in this sector of the plastics industry. Polyvinyl resin latex (7'6) that Kill form a strong coherent film or coating nithout plasticizer by simply drying a t or near room temperature is further evidence of the increasing importance of synthetic elastomeric latices, organosols, and plastisols in industrial operations (79). Special techniques were described for compounding and curing of butadiene-acrylonitrile copolymers with high molecular weight polyvinyl chloride acetate copolymers and vinylidene chloride polymers. Products which had excellent thermal and light stability, toughness, and chemical inertness were made with blends containing 13 to 25% of the nitrile synthetic rubber (108). The .:ffects of plasticizers (85) and fillers (69) on the properties of vinyl plastics were reported. Further data were presented on the properties of the copolymer of vinyl chloride and acrylonitrile which is used to make fibers for filter fabrics and dust fume bags (83). The chemical resistapce of vinyl plastics (37) has been put to use in linings for steel pipe and fittings and for tanks holding corrosive liquids. In making one such tank liner 10 feet in length and 2 feet in diameter, two pieces of vinyl sheet 0.040 inch thick were electronically welded (9). Tests by a British firm have shown that industrial gloves made Kith polyvinyl chloride paste and a fabric base have five to twenty times the life of those made with leather, moleskin, or rubber for use in chemical plants. The gloves were found to be particularly satisfactory for handling sodium hypochlorite, hydrofluoric acid, acetylene, and aniline. In sodium plants their useful life is reported to be seven t o eight times as long as rubber gloves. Polyvinyl alcohol is used as a flexible diaphragm in the HillsMcCanna packless valves for use in contact with organic solvents and hydrocarbons. I t is pressed down on a transverse seat to stop 90w. Printing plates were made of this same material, during the past, year, for use with the new hydrocarbon inks for printing on plastics, taking advantage of the inherent resistance of Compar to organic liquids. Another type of Compar has been formulated to impart a minimum tendency to swell and disintegrate due to the action of water. GENERAL APPLICATIONS
In the packaging machinery field there has been an increasing use of plastics for both structural and functional purposes. In some cases the plastics do a mechanical job better than other maw & & ; in other cases chemical resistance and freedom from rust and corrosion are factors in their favor. Parts on a machine for packaging hydrogen peroxide are mads from polymethyl methacrylate and saran (6). I n a bottling machine a rotary star wheel made of phenolic laminate has reduced breakage 40% and permitted a 30% increase in speed of operation. The problem of corrosion by salt and fats has been met in weighing and packaging potato chips by the use of acrylic plastic parts; in the nen' machine the potato chips do not come in contact Yith any material other than acrylic pla from the time they !cave tile storage hopper until they reach the bag (14). Other reported applicstions of plastics involving :esistance to chemicals pertained to film developing tanks made of polystyrene, ethyl cellulose, and cellulose acetate butyrate (IS), battery cases of polystyrene (16), strippable coatings of vinyl resins ( 5 5 ) , and bearings of fabric base laminates (49, 67). PROTECTIVE COATINGS
A large variety of high polymers in the form of lacquers, organosols, plastisols, aqueous emulsions, and hot melts have been used
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INDUSTRIAL AND ENGINEERING CHEMISTRY
as protective coatings (47, 97). Providing the metal surface has been properly prepared and the deposited film is continuous, some degree of protection from fumes and spray may be secured from thin films but a minimum thickness of 0.1 inch is required for plastic membranes subjected to actual contact with corrosive liquids. If the temperature exceeds that a t which the plastic will flow or lose its bond to the metal surface and if unusual abrasive conditions exist, the lining must be protected by a tile or brick sheathing. Whenever possible, metal surfaces should be sand- or shotblasted and preferably passivated (34),but such techniques are generally considered as impractical for maintenance work. Some corrosion engineers have secured fair service from coatings applied to wire-brushed surfaces but such procedures often lead to disappointments in which the protective coating rather than the method of application is considered to be a t fault. During the war years, the tedious step of surface preparation was sometimes replaced by the use of vinyl-base wash primers containing phosphoric acid and zinc chromate. Such preparations yield good adhesion to steel, galvanized iron, aluminum, copper, and stainless steel ( 3 5 ) and when a properly formulated topcoat is applied, CYcellent service may be secured under mild conditions of corrosion (76, 89). Baked and modified phenolic coatings have given reasonably good service under mild corrosive conditions for many years. These coatings are not resistant to alkalies or oxidizing acids and are not readily adaptable to field application but are resistant to vesicant acids (48).Some improvement has been made by condensing substituted phenols such as cashew nutshell oil with formaldehyde (30) and by condensing bisphenol with epichlorohydrin. Some improvement has also been noted when vinyl chloride copolymers are blended with phenolic resins since the hydrochloric acid evolved during the baking process aids in setting the phenolic resin (81). Because of the resistance of the cured coatings to alkalies as well as to acid, furan derivatives have received considerable attention. The corrosive resistance of these films is said to be improved by the addition of wax (87) but because of the jet-black color of the base material it is difficult to produce products in a wide range of colors. In 1949, a new furan-base coating was introduced which could be used directly over a wash primer without a baking operation. These jet-black coatings have found ready acceptance by those corrosion engineers who have previously found it impractical to sandblast metal surfaces and to place their equipment in baking ovens. Rubber derivatives such as rubber hydrochloride (74), chlorinated rubber ( l o g ) , and neoprene based lacquers ( 6 1 ) are used widely as protective coatings. Prior to the recent war, cyclized rubber was used to protect concrete but its use has been replaced in part by copolymers of styrene and butadiene in which the former is the major constituent ( 2 7 ) . Copolymers of vinyl chloride still enjoy wide use as protective coatings on metal, concrete, and wood providing the temperature< are not too high and abrasive conditions do not exist ( 4 6 ) . The adhesion to metal of nonbaked vinyl-base coatings has been improved by the use of primers containing maleic anhydride copolymers (31, 7 0 ) . Vinyl chloride copolymers may be applied in the form of plastisols (26) providing the coated product may be heated to 350' F. and aqueous emulsions may be used directly on steel in the presence of alkali phosphates (84). Polyethylene has been flame-sprayed and also applied in various hot chlorinated solvents (106). However, it is difficult to secure adhesion of polyethylene to inside corners and it is said to lack resistance to acetir acid (96). Some improvement has been noted when polyethylene is blended with polyethylene sulfide ( 4 4 ) or polyisobutvlene (63). Even M hen stabilizers are added, there is some degradation of molten polpethvlene and polyisobutylenc (91). Because of their extreme chemical inertness and solvent resistance, polytetrafluoroethylene and polymonochlorotrifluoroethyl-
Vol. 41, No. 10
ene have been the subject of considerable experimentation (40, 107) but to date attempts to secure adhesion to metal surfaces have been unsuccessful. Some interest has been displayed in copolymers of tetrafluoroethylene (66) and other fluorinated products such as polyvinylidene fluoride (@), but none of these products is commercially available. There has been a revival of interest in polysulfide coatings (88)and a t least one firm is contemplating the introduction of coatings containing polysulfide in the near future. Claims for superior products containing stainless steel powder have been made (25) and there have been renewed attempts to polymerize monomeric materials in situ on metallic surfaces (39). Interesting results have also been secured by use of polymerizable unsaturated polyesters in the presence of catalysts and promoters. LININGS
Many of the flexible protective coatings can function as linings when used in sufficient thickness ( 5 4 ) . Soft rubber has been used widely by itself or in conjunction with ebonite. Continuous rubber linings can be applied in the field when specially compounded latices are sprayed in multiple layers on the surface to be protected. A thickness of 0.125 inch is considered a minimum for rubber, but this should be increased to a t least 0.25 inch if abrasive conditions are present. Rubber is not satisfactory for use with chlorine or hydrochloric acid unless sufficient material is present to permit reaction to take place on the surface to form a resistant layer (6%). Aqueous dispersions of natural and synthetic rubber may be sprayed or electrodeposited (103) over selfhardening compositions containing mutual solvents (60) or polymethyl methacrylate (34). Polymethyl methacrylate has had limited use as a tank lining because of its low softening point and lack of solvent resistance, but these deficiencies have been overcome in part by surface reactions of its copolymers (93). Fabric-reinforced plasticized polyvinyl chloride has been used for many years as a nitric acid-resistant tank lining and more recent,ly vinylidene chloride copolymers have been used to line steel pipe. When vinylidene chloride copolymers are plasticized with butadiene-acrylonitrile copolymers, the resulting product can be used in sheet form as an acid resistant tank lining. Polyisobutylene ( 4 5 ) ,Butyl rubber, and copolymers of isobutylene and styrene (S polymers) ( 3 2 ) when properly compounded have served as acid resistant bases. Likewise, polyethylene has been applied as a melt over polyethylene sulfide ( 5 1 ) . Srperior linings and coatings based on polymethyl methacrylate (92)have been obtained by the incorporation of silica sols. Polystyrene has been used as a tank lining for the transportstion of strong alkaline solutions for several years but some applications have failed due to t,he low softening point. This has been overcome in part by forming copolymers with p-chloro-a-methylstyrene (68). Flexible linings, having good adhesion to steel, h,tve been obtsined by the plasticization of copolymers of styrene, acrylonitrile, and maleic anhydride (94). A tank lining mzterial mzde of phenolic resin is described in a report on German thermosetting resins (7). After almost a decade of investigation, fursn-base resins ( 7 7 ) have been applied successfully as acid and alkaline resistant linings, In the most successful technique, a woven Fibcrglzs textile is imbedded in a chemical setting carbon-furan resin mortar applied by troweling over a thermosetting neoprene-base primer. Another trowel coat is applied above the textile, and the entire surface is then coated with a plasticized furan solventless lacquer. Some success has also been claimed for cashew nutshell-base resins when used as tank linings (80). ACKNOWLEDGMENT
The sections on Protective Coatings and Linings were written by R. B. S q m o u r , l t l a s Mineral Products Comnnny. The author gratefully acknowledges assistance received from the following individuals in the preparation of this review: I. G. Callo-
October 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
mon, National Bureau of Standards; R. E. Dodd, Durez Plastics and Chemicals, Inc.; W. C. Goggin, Dow Chemical Company; E. 0. Hausmann, Continental-Diamond Fibre Company; W. B. Humes, Carbide and Carbon Chemicals Corporation; W. C. Kirschner, Goodyear Tire and Rubber Company; H. E. Krebs, Resistoflex Corporation; hl. Scott Moulton, B. F. Goodrich Chemical Company; R. V. Keuhaus, Nukem Products Corporation; J. J. Pyle, General Electric Company; L. C. Rubin, M. ?T. Kellogg Company; L. L. Stott, Polymer Corporation; J. Allen Wheat, Celanese Corporation of America; and A. ?*I.York, U. 8. Rubber Company. Anyone who has information pertaining to the use of synthetic resins and plastics as chemical engineering materials of construction is invited to send it to the author for incorporation in the next annual review. LITERATURE CITED
(1) (2) (3) (4) (5) (6) (7) (8) (9)
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2137
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