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fr/Ecl Materials of Construction Review
Plastics by Raymond B. Seymour, Su2 Ross State College, Alpine, Tex.
The continued growth of this nation’s multibillion dollar plastics industry is testimony to technical achievement, quality conciousness, and responsibility. Plastics as materials of construction alone now exceed all plastics applications of two decades ago
AMERICA’S
plastics industry reached full maturity in 1960. I n addition to producing 6 billion pounds of quality product, it demonstrated responsibility by developing new standards, tests, and specifications and by publishing new information on application of plastic materials. Some of its severest critics recognized this maturity and accepted plastics along with more conventional materials of construction. Plastics continue to set the pace in the chemical process industry. Its growth factor is 5070 greater than that of the entire chemical process industry. T h e value added by manufacture for all synthetic high polymers excluding elastomers exceeded 53 billion. This industry is continuing to make an unprecedented investment in scientific investigation. I t employs more than 2000 scientists and is spending approximately $100 million annually on technology. New commercial products, improved formulations, and creative applications of plastics are now accepted as routine. Over 200 new test methods and standards have been promulgated by the American Society for Testing Materials (ASTM) Committee D-20, the International Standardization Organization, the Society of the Plastics Industry (SPI), the Society of Pldstics Engineers (SPE), and the U. S. Department of Commerce. The cooperation among these groups and industry approaches perfection. Annual reviews continue to record impressive advancements on all fronts. Most significant has been progress in the reporting of information in media available to design engineers and architects. ‘Three types of products are now being produced a t a n annual rate in excess of 1 billion pounds, and production capacity for these materials (polyethylene, vinyl
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polymers. and styrene plastics) is being increased significantly. The industry is confident that polypropylene will join this select billion-pound club by 1965 and that the production of at least one or two other products will increase to 2 billion pounds a year. S e w books, now being published at an unprecedented rate, are supplying much needed application information in language understood by the design engineer. The third edition of “Plastics Engineering Handbook” is now available. Plastics nomenclature is being analyzed critically. General terms such as high polymers, plastics, resins, and kunststoffe are often used synonymously. This self-examination is concerned principally with minimizing the possibility of future confusion. Fortunately, the intelligent architect and design engineer are becoming better informed. A special issue, “Plastics in Architecture,” appeared in June 1960. Plastics exhibitions and symposia a t Dusseldorf, Olympia, Utrecht, and Wiesbaden attracted record numbers of interested spectators. Attendance records were also set at national, regional, and divisional meetings of SPI and SPE. T h e latter society has reported considerable progress by its professional activities group 011 plastics in building. This subject was keynoted a t the ninth semiannual conference of the Manufacturing Chemists’ Association and at a special meeting sponsored by the Building Research Institute a t iVew York. Symposia on sealants, end use markets. and post-irradiation effects were held a t Los Angeles, Chicago, and San Francisco. Education in the field of plastics is now an actuality a t eight schools. “Plastec” (Plastics Technical Center) was established at Picatinny Arsenal to
INDUSTRIAL AND ENGINEERING CHEMISTRY
provide technically evaluated design information on plastics to all government agencies. Considerable progress has also been reported on attempts to establish the Plastics Institute or Amer ica. This facility will be affiliated with a college and will serve as a central agency for education, research, and technical information on plastics.
Design and Engineering Many reliable reports on long time behavior, based on short term tests, have developed considerable additional confidence in plastics. While some agencies await actual 20-year performance tests, breakthroughs are occurring in the use of plastic as functional components of structural units on many fronts. Because the technical data were considered reliable, these applications were not delayed. Probably most important, superior plastic materials will certainly be developed to replace most of the products now under long term tests. Fortunately, informed engineers in the building field have confidence in case history data and today‘s technology. Almost one half billion pounds of plastics were used in structural applications during the past year. This use will increase as more sophisticated methods of evaluation are developed and as load bearing characteristics of plastics are better understood. T h e relationship between stability and chemical structure of plastics was discussed by Achhammer ( 7 ) . Boor ( 9 ) has investigated hardness and resistance to abrasion and wear. Data on available standards have been compiled by Reinhart (72). The physicist’s viewpoint in the evaluation of plastics as structural materials
a n ) F u Materials of Construction Review was presented by Hellwege ( 3 9 ) . Timedependent properties have been compared by Maxwell (59). Progressive stress studies have been used to develop data on endurance limits of plastics (54). Brittle failure has been induced by applying axial stress on extruded shapes (30). As might be anticipated, extrapolated long term data are being confirmed by practical results. Plasticity theories, of course, can be applied only when yielding occurs at failure ( 6 ) . The structural behavior of laminates has been predicted from a study of stress-strain relationships of individual layers ( 2 7 ) . A general formula describing creep and rupture stresses for polyethylene, polyacetals, and reinforced plastics is available ( 3 2 ) . Information is also available for the creep behavior of transparent plastics at elevated temperatures (57). All-plastic rockets with strength to weight ratios in excess of 1 million have operated the equivalent of 75,000 miles. A vast amount of data on the design of ablative materials has been developed. A recent study of the relationship of structure and dynamic mechanical properties has been published ( 6 3 ) . Information on flame resistance of plastics has been tabulated. Additional information on the fabrication of plastics has been published (96). The relationship of safety and structural plastics is being studied by the Southwest Research Institute.
Structural Applications of Plastics Past attempts to imitate conventional building materials have hampered growth. Future growth in all applications will depend on the utilization of plastics as functional materials. Progress in such applications is related to technical effort and knowledge a t the user level. The successful construction of honeycomb sandwich structures with diameters approaching 150 feet has suggested that 15-story plastic buildings would be substantial and practical. Smaller transparent igloos have been used to exclude air from titanium structures during welding. The U. S.pavillion at Moscow, consisting of 630 premolded parts, was assembled by inexperienced Russian workmen. This type of design, as well as the use o i plastic pans as forms for concrete waffle floor sections, should catalyze additional creativity in the building field. Plastic shipping containers capable of transporting a 20ton pay load are available ( 74). Large plastic grids for cooling towers and molded phenolic plastic bubble caps are performing well. Large vacuum-type leaf filters and huge roof ven-
tilators, constructed from reinforced plastics, are now commonplace. Likewise, massive sea gates, bumpers for the protection of large diameter pipe, long plastic missile cylinders, and even pontoons for small craft harbors or buoys are considered conventional applications of plastics. Other unique applications of plastics are flat springs, magnets (60), foundry patterns ( 4 5 ) , gasoline bricks, semiconductors, and thermoplastic recorders ( 9 2 ) . The latter process utilizes electrons for recording a tremendous amount of data. Polymerization of monomers to plastics on exposure to light is the basis for a new photopolymeric procexs.
methyl methacrylate has been recommended by Smith (87). Various reinforcing agents and resins have been evaluated by Schmidt (78). A report on the control of variables has been published by the U. S. Department of Commerce. Perry (70) has supplied considerable information on adhesive bonding of plastics. Rocket motors with a hoop stress of 120,000 p.s.i. have been constructed by the filament winding of glass impregnated with epoxy resin and an anhydride catalyst (65, 88). Nondestructive quality control tests for reinforced plastics have been developed ( 7 7 ) . Considerable test data were presented at an ASTM-sponsored symposium on reinforced plastics at San Francisco.
Reinforced Plastics Some of these unique applications are unconventional. Yet, the investment in the development of the last two mentioned processes exceeds $10 million. In contrast, the plastic fabricator has had little money available for development. These factors have plagued the reinforced plastics industry and retarded its growth. Yet, the potential of reinforced plastics has been great enough to assure a growth rate which exceeds that of the entire plastics industry. Production of reinforced plastics during the past year was 15 times greater than in 1946. A 5 0 7 increase is predicted for 1965. This. growth has been favored by thinking that is not oriented toward conventional metallic structures. Colson (78) has advocated a comprehensive understanding of the anisotropic nature and physical characteristics of reinforced plastics. coupled with assurance of adequate reproducible quality through the elimination of hand skill. The sensitivity of fibers to damage by abrasion has been emphasized by Parrott (67). Heebink (38) has demonstrated the absence of deterioration of reinforced plastics at relative humidities below 65%. The replacement of styrene by
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High Temperature Applications Advancement in the space age requires lightweight, heat-resistant materials. The U. s. Government has already invested over $30 million in the development of improved heatresistant plastics. Some of the newer polymers contain A1 and Zn. Chelated compounds, Si copolymers, and fluorinecontaining plastics have been considered. The progress of research and problems associated with short and long term heat resistance tests have been discussed (4, 77, 40). Graphite fibers, resinbonded quartz sheet, and glass fibers have been studied. The necessity for controlling all variables has been emphasized by Sonneborn (82). Reinforced plastic laminates of special design have been described by Miglarese (69). Various heat resistant plastics were rated (33) by studying surface decomposition at elevated temperatures.
Plastic Film and Sheet Studies on space travel within the earth’s atmosphere are also directed toward lightweight, high strength materials. The availability of clear ori-
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ented and unoriented film based on several different plastics has made many new designs practical. Some of the developments on multiaxially stretched films have been described by Fortner (28), Longstreth (56),and Richard (73). Film with controlled shrinkage a t elevated temperatures has been produced by stretching irradiated film in two directions. Heavier gage flexible sheet and reinforced film has been used for the construction of tanks, dams, and moisture barriers. The use of film for bags and as liners for pails is increasing. Many liquids are now packaged in plastic bags (25). These bags may be collapsible pillow tanks on flat bed trucks or sausage shaped “dracones“ towed behind tug boats (20). The size is limited by the power of the tug; 200-foor-long “dracones” capable of transporting 300 tons of liquid are practical. Similar containers can be used for stationary storage on land or under water. The thermoplasrics structures division of SPI is compiling a design manual describing techniques used in the fabrication of sheet plastics. Over 1.5 million pounds of these materials were used last year. Five tons of rigid pol\-(vinyl chloride) was used for the fabrication of ducts and the like in an airline maintenance building. Two new books describing plastic welding were published (35, 95). U1trasonic energy (40,000 cycles per second) has also been used to weld plastic sheets. A control method based on hardness tests has been proposed for evaluating the quality of welded plastics (66). Polyethylene has been compounded with starch, which is removed after extrusion, to produce a water repellent, vapor transmitting film. Polyethylene sheet has been used for neutron shielding. New developments in vinyl-metal laminates have been discussed (8). The use of this type of material increased about 1570 during the past year. I t is expected that the annual usage of
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vinyl-metal laminates will be about 20 million square feet in the near future (90).
Cellular Plastics About 100 million pounds of polyurethane foam was produced during the past year. Annual consumption of this type of cellular plastic is expected to double during the next five years. Polystyrene foam has been used to form inexpensive, paperlike sheets. The properties of various cellular products were compared by Davall (21) and Khawam (47). Recipes for one shot formulations have been published (58),and the use of organotin compounds in these compositions has been investigated (43). The importance of proper catalyst selection has been discussed (37). The use of volatile organic liquids as foaming agents has been considered (48). Nonsolvent hydrocarbons with moderate boiling points are incorporated in polystyrene to provide heat-expandable products of various densities ( 7 6 , 8 3 ) , Sheets of expanded polystyrene are being used in large quantity as insulation in building. Flame-resistant modifications are available. Carved pieces serve as expendable molds for casting metals. Hydrogen peroxide and azodiisobutyrodinitrile (37) have been used as expanding agents for poly(viny1 chloride). Sheets produced with the latter agents should be aged before use to reduce toxicity. Techniques are available for determining the average cell volume (36) and for measuring dynamic resilience (46). Cellular plastics based on epoxy, phenolic, and urea resins have excellent resistance to heat and solvents.
P l a s t i c Pipe The plastic pipe market now exceeds $50 million a t the user level. The attainment of the potential, which exceeds 10 times this volume, depends on
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a continued demonstration of quality consciousness and adherence to standards by all members of the industry (77, 77, 97). Plastic pipe for use in cold water service, outside drainage, and vent pipes has been approved by five states. Difficulties heretofore considered inherent in ships’ plumbing have been eliminated through the use of plastic pipe. An ingenious device consisting of interlocking plastic rods has been used to install hundreds of miles of clcctrical cable in underground ducts. One mile of mandrel-wrapped, glass mat plasticimpregnated 3.25-foot pipe is now in service. Approximately 10,000 miles of ABS pipe in smaller sizes have been installed successfully. Approximately 2 miles of this type of pipe were used in the construction of a research center for Republic Steel. Plastic pipe is performing satisfactorily for all types of service in research houses and apartment houses. Plastic sewer mains are also providing satisfactory performance. A 4-inch water main was prefabricated and laid under difficult conditions in England. A 100% increase in the use of plastic pipe for gas service was reported by the Public Service Co. of Colorado. Considerable information on predicting service life of plastic pipe is available ( 6 4 ) . Exposure to fire has been added to practical tests for plastic pipe conveying petroleum products (55). In spite of the unqualified success of plastic ball and socket joints and rubber ring-polyester joints in clay pipe and solvent wclded and mechanical joints, the interest in other joining techniques continues. The assembly techniques for toys have stimulated creativity in more practical applications. I n one technique the pipe end is heated to form a bell which is joined to another length by use of a rubber ring. Reheating causes contraction to a tight seal which eliminates the need for expansion joints. Proprietary stainless steel couplings and cemented molded sockets for pressure pipe have been described (84). Because the perfect joint is rhat found in a continuous jointless section, there is considerable interest in on the job extrusion. I n addition to processing of thermoplastics, continuous production of reinforced plastic pipe has been reported in France and by Armour Research Institute. Case hisrories describing over 10 years of successful service with saranlined pipe are not uncommon. Comparable service data are being developed for steel pipe lined with poly(viny1 chloride), polyfluorocarbons ( 8 6 ) , and polychloroether. An annual savings n excess of $500,000 was reported by
anb 4one H F plant through the use of polyfluorocarbon-lined pipe. Pipe with superior physical properties for hot water service has been obtained by extruding blends of poly(viny1 chloride) and chlorinated polyolefin or blends erroneously described as vinyl dichloride polymers (16). Plastic pipe has been strengthened by the application of wrappers of reinforced plastics or spiralled polyethylene. Helical winding with steel tape has been used to produce pipe capable of withstanding high pressures. One 4-inch pipe of this design is used to convey oil from the Gulf of Mexico at a pressure of 2000 p.s.i.
Plastics vs. Corrosion T h e most obvious advantage of plastics over conventional materials of construction is their characteristic resistance to salts, alkalies, and acids. Because of his training as a metallurgist, the average corrosion engineer often overlooks the characteristic advantage of nonmetallic materials. However, progressive corrosion engineers have recognized the importance of plastics as materials of construction and have reported their observations (5, 13, 75, 23, 29, 79, 80). An accelerated test for evaluating reinforced plastics in the chemical industry has been proposed. T h e importance of degradation in outdoor exposure has also been recognized (24). The importance of surface preparation and proper selection of plastic coatings continues to be emphasized. Today's emphasis is on fluidized coatings (68). This process also makes possible large, economical plastic objects (26). Regardless of the application technique each plastic has inherent characteristics which govern its use in the battle against corrosion.
Plastic Materials
Polyethylene. Finely divided polyethylene has been applied by the fluidized process and as an aqueous dispersion. Regardless of the application technique, adhesion of polyethylene can now be assured through a CuO undercoating. Polymethylene, now available, serves as a standard in determining characteristics such as degree of branching Polyethylene has been irradiated and compounded with flame retardants. Cross linking has been accomplished by irradiation and by compounding with peroxides. Electrical discharge has been used to improve receptivity to printing. High density polymers have been used as fibers, pipe, sheet, and moldings. Polyethylene sheet can be joined by a n automatic welding process. Perform-
ance characteristics have been predicted by immersing specimens in a n aqueous solution of surface active agent and plotting the log of the melt index against log of cracking time (69). Polypropylene. Several up-to-date reviews on the present status of polypropylene have been published (53). High and low pressure polymerization techniques have been investigated. Fiber and biaxially oriented film are of great importance. Vinyl Chloride. Blending with acrylic resins has improved the processing characteristics of rigid poly(viny1 chloride) (47). The addition of poly(ethy1ene glycol dimethacrylate) and irradiation have caused cross linking; HZS treatment has also reduced thermoplasticity (51). Polystyrene. Because styrene polymers account for almost 20% of all plastics produciion, capacity for the production of monomer and polymer has been increased considerably. The processing of polystyrene from crude oil and its applications have been reviewed (3). Polyfluorocarbons. The annual production of 10 million pounds of polyfluorocarbons appears insignificant if one disregards the dollar volume, which exceeds many of the common plastics. This phase of the industry continues to grow and is strengthened by the introduction of clear, weather-resistant poly(viny1 fluoride), poly(viny1idene fluoride), trifluoronitrosomethane copolymers, and copolymers of fluoropropylene and tetrafluoroethylene. This type of product is used for lubricants and oilfree bearings, Adhesion to metal surfaces has been improved by vapor blasting and copolymerization. Fluorocarbon plastics have been utilized as windows in nose cones, piston rings for compressors, pipes, tanks, and linings. New information on the chemical resistance of polytrifluoromonochloroethylene is available (87). Polyacetals. Recent price reductions, coupled with inherent physical properties, have stimulated the use of polyacetals in place of die-cast metals. I n addition to long fatigue life, acetals are resistant to solvents and weak corrosives. They, like other polymers of formaldehyde, are attacked by strong acids and strong alkalies ( 2 ) . Polyesters, Polycarbonates are now produced by two different American firms. These inherently stiff polymers possess high impact resistance, transparency, dimensional stability, and good low temperature properties (34). Polycarbonates have been adopted for photographic products and will find many other applications in the future. T h e growth of styrene-unsaturated ester mixtures continues. T h e annual
Materials of Construction Review consumption of polyester putties exceeds that of polyfluorocarbons. Mixtures of this type have been used for maintenance in chemical plants (7, 85) and as coatings. Flame resistant (74) and conductive flammable formulations are available. Additional data have been published on metal and peroxide accelerators as well as on the chemical resistance of polyesters. Clear polymers of diallyl phthalate have been proposed as overlays for plastic laminates. The chemical resistance of polyesters has been improved through the use of bisphenol A or isophthalic acid. Epoxy Resins. Epoxy resins represent about O.5y0ofthe total production of plastics. Nevertheless, this segment of the industry continues io grow and is described in a large number of publications and in various trade journals. New resins based on peracetic acid and epoxidized polyolefins are available. Toxicity problems continue to plague this segment of the industry. Sensitization and allergic rhinitis of exposed workers have been reported. Organophosphorus epoxides, flame resistant products. foams, laminates, molding powders, castings, tooling, cements, and potting compounds are available. T h e relationship of structure to high temperature performance (94) and the change of electrical properties during polymerization were studied (22). Polyurethanes. Urethane polymers, which were developed as a n alternate for nylon, were introduced in this country in 1948 as cellular products. Interest in foams continued, but the use of these products for lining pipe and as potting compounds is also of considerable interest. Belts and hoses of polyurethane retain their physical properties a t -90" F. The effect of reactants and conditions on the properties of this type of product have been studied (12, 19). Silicones. One of thr most interesting recent developments is a room-temperature curing silicone composition ( 8 9 ) . This product, which is produced by two different firms, has been used as a mold for casting plastics and metal and for the production of cellular products (75). Polyamides. Both nylon 6 and nylon 6,6 are being produced by several firms in this country. Large sections of nylon 6,6 weighing u p to 400 pounds are now commonplace. Nylon has been used for fluidized coatings, film, reinforced plasIntics, and with MoSz bearings. formation on creep characteristics and properties of nylon film has been published ( 4 4 ) . Miscellaneous. Chlorinated polyether is now produced commercially at a reduced price. I t has lived u p to expectations in industrial applications and has VOL. 52, NO. 12
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been approved by the YTational Sanitation Foundation (62). Over 200 gallons of polyolefin sulfide caulking cement was used in the construction of the American Airlines building a t the New York International Airport. Bornego (70) has provided a n up-to-date report of this type of material. Copolymers of styrene and a-methylstyrene with methyl methacrylate are available. Considerable information on acrylic plastics has been supplied ( 4 2 ) . Polymers of 2,3-diphenylbutadiene have been described, and polymers of 1-butene, isoprene, and butadiene are in commercial production. A copolymer of butadiene and acrylic acid has been proposed as a base for solid propellants. Polymers of furfuryl alcohol formed in situ continue to be of interest. Many different polymers based on phosphorus have been studied (50, 52). Polymers based on cyclohexene dioxime and chloromethyldiphenyl oxide have been reported. Information on organotin polymers ( 4 9 ) and reaction products of poly(a1kylene oxides) and poly-(carboxylic acids) has been published. Low profit margins have provided little incentive for investigations of ordinary thermosetting compounds. These products continue to be used as “work horse” plastics and also as glamor plastics in adhesive (93) and missile applications. Literature Cited
ern Section, SOC. Plastics Ind., Palm Springs, Calif., April 1960. ( 1 9 j Cooper, W:, Pearson, R. W., Drake, S . , Znd. Chemist 36, 121 (1960). (20) Cronan, C. S., Chem. Eng. 67, No. 13, 62 (1960). (21) Davail, C. R., S P E Journal 15, 955 (1959). (22) Delmonte, J., J . Appl. Polymer Sci. 2, 108 (1959). (23) Dewar, W., Delmonte, J., 16th Ann. Conf., Natl. Assoc. Corrosion Engrs., Dallas, Tex., March 1960. (24) Dolezel, B., Korose, O., Ochrana Materiales 3. 59 (1 959). (25) Doyer, L., Doyer,’ L., U. S. Patent 2,927,410 (March 8, 1960). (26) Engel, T., 2nd. plastiques mod. (Paris) 11, 38 (1959). 127) Fischer, L., Modern Plastics 37. No. 10. ’ f 2 0 (1960). (28) Fortner, C. P., Dalton, P., Materials i n Design Eng. 50, No. 7, 94 (1959). (29) Gabel, A. R.? Schmidt, H. W., Chem. Eng. Progr. 55, No. 11, 39 (1959). (30) Gisolf, J. H., Van Goudoever, H., Kunstsfoffe49. 264 (1959). (31) Grnztes, G. T., Grub&, E. E., Joseph, R. D., S P E Journal 15, 957 (1959). (32) Goldfein, S., Modern P1astic.s 37, No. 8: 127 (1960). (33) Gruntfest, J., Chem. Eng. 66, No. 11, 134 (1959). (34) Hagedorn, M., Chemiker-Ztg. 83, 643 ( 1 959) -~ , ’ (35) Haim, G., “Manual for Plastic Welding, Chemical Publishing Co., New York, 1959. (36) Harding, R. H.. Modern Plastics 37, No. 10, 156 (1960). (37) Hawkins, J. G., U. S. Patent 2,901,446 (Aug. 25, 1959). (38) Heebink, B. G., Stevens, G., SPE Journal 16. 39 11960). (39) Hellwege, K . H., K u n s t s t g e 50, 3 (1 960). (40) Hertz, J., Western Plastics 7, No. 5, 25 (1960). (41) Hopkins, R. P., SPE Journal 16, No. 3, 304 (1960). (42) Horn, M. B., “Acrylic Resins,” Reinhold, New York, 1960. (43) Hostetter, F., Cox, E. F., IND.ENG. CHEM.52, 609 (1960). (44) Hughes, R. L., Simpson, D. G., Plastics Technol. 5, No. 11, 41 (1959). (45) Johnson, T., 15th Ann. Conf., Reinforced Plastics Division, SOC.Plastics Ind., Chicago, February 1960. (46) Jones. R. E.; Hersch, P., others, Plastics Technol. 5, No. 6, 55 (1 959). (47) Khawam, A., Ibid.: 5, No. 6, 31 (1 959). (48) Klesper, E., Rubber Age (A‘. Y.) 84, (1959). (49) Kochkin, D. A., Krotrelev, V. N., others, Vysokomolekul~.’arnyeSoedinenba 1, 482 (1959). (50) Kolesn:kov, H. S., Rodinova, E. F., Federova, L. S., Ibid., 1, 367 (1959). (51) Krahnstover, M. J., Sauerwald, F., J . Prakt. Chern. 141 8, 353 (1959). (52) Krause, I
