Sample J76 from "Survey of foamed plastics" Modern Plastics Encyclopedia, edited by Joel Frados. New York: Plastics Catalogue Corporation, 1961. Pp. 390-393, of Vol 39, No. 1A. 0010-1940 A part of the XML version of the Brown Corpus2,064 words 2 (0.1%) quotes 2 symbolsJ76

"Survey of foamed plastics" Modern Plastics Encyclopedia, edited by Joel Frados. New York: Plastics Catalogue Corporation, 1961. Pp. 390-393, of Vol 39, No. 1A. 0010-1940

Arbitrary Hyphens: hydroxyl-rich [0660, 0720] free-blown [1810] air-cell [1160]Typographical Error: mid [0530]

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Within only a few years , foamed plastics materials have managed to grow into an integral , and important , phase of the plastics industry -- and the end is still not yet in sight . Urethane foam , as only one example , was only introduced commercially in this country in 1955 . Yet last year's volume probably topped 100 million lb. and expectations are for a market of 275 million lb. by 1964 . Many of the other foamed plastics , particularly the styrenes , show similar growth potential . And there are even newer foamed plastics that are yet to be evaluated . As this issue goes to press , for example , one manufacturer has announced an epoxy foam with outstanding buoyancy and impact strength ; ; another reports that a cellular polypropylene , primarily for use in wire coating applications , is being investigated .

On the following pages , each of the major commercial foamed plastics is described in detail , as to properties , applications , and methods of processing .

It might be well to point out , however , some of the newer developments that have taken place within the past few months which might have a bearing on the future of the various foamed plastics involved . In urethane foams , for example , there has been a definite trend toward the polyether-type materials ( which are now available in two-component rigid foam systems ) and the emphasis is definitely on one-shot molding . Most manufacturers also seem to be concentrating on formulating fire-resistant or self-extinguishing grades of urethane foam that are aimed specifically at the burgeoning building markets . Urethane foam as an insulator is also coming in for a good deal of attention . In one outstanding example , Whirlpool Corp. found that by switching to urethane foam insulation , they could increase the storage capacity of gas refrigerators to make them competitive with electric models . Much interest has also been expressed in new techniques for processing the urethane foams , including spraying , frothing , and molding ( see article , p. 391 for details ) . And in meeting the demands for urethane foam as a garment interlining , new adhesives and new methods of laminating foam to a substrate have been developed .

New techniques for automatic molding of expandable styrene beads have helped boost that particular material into a number of new consumer applications , including picnic chests , beverage coolers , flower pots , and flotation-type swimming toys . Two other end-use areas which contributed to expandable styrene's growth during the year were packaging ( molded inserts replacing complicated cardboard units ) and foamed-core building panels . Extruded expandable styrene film or sheet -- claimed to be competitive price-wise with paper -- also showed much potential , particularly for packaging . Sandwich panels for building utility shelters that consist of kraft paper skins and rigid styrene foam cores also aroused interest in the construction field .

In vinyl foam , the big news was the development of techniques for coating fabrics with the material ( for details , see P. 395 ) . Better `` hand '' , a more luxurious feel , and better insulating properties were claimed to be the result . Several companies also saw possibilities in using the technique for extruding or molding vinyl products with a slight cellular core that would reduce costs yet would not affect physical properties of the end product to any great extent .

Readers interested in additional information on foams are referred to the Foamed Plastics Chart appearing in the Technical Data section and to the list of references which appears below .

Urethane foams Since the mid 1950s , when urethane foam first made its appearance in the American market , growth has been little short of fantastic . Present estimates are that production topped the 100-million-lb. mark in 1960 ( 85 to 90 million lb. for flexible , 10 or 11 million lb. for rigid ) ; ; by 1965 , production may range from 200 to 350 million lb. for flexible and from 115 to 150 million lb. for rigid . The markets that have started to open up for the foam in the past year or so seem to justify the expectations . Furniture upholstery , as just one example , can easily take millions of pounds ; ; foamed refrigerator insulation is under intensive evaluation by every major manufacturer ; ; and use of the foam for garment interlining is only now getting off the ground , with volume potential in the offing . Basic chemistry Urethane foams are , basically , reaction products of hydroxyl-rich materials and polyisocyanates ( usually tolylene diisocyanate ) . Blowing can be either one of two types -- carbon dioxide gas generated by the reaction of water on the polyisocyanate or mechanical blowing through the use of a low-boiling liquid such as a fluorinated hydrocarbon .

The most important factor in determining what properties the end-product will have is quite naturally the type of hydroxyl-rich compound that is used in its production . Originally , the main types used were various compositions of polyesters . These are still in wide use today , particularly in semi-rigid formulations , for such applications as cores for sandwich-type structural panels , foamed-in-place insulation , automotive safety padding , arm rests , etc. . More recently , polyethers -- again in varied compositions , molecular weights , and branching -- have come into use at first for the flexible foams , just lately for the rigids . The polyether glycols are claimed to give flexible urethanes a spring-back action which is much desired in cushioning .

Although the first polyether foams on the market had to be produced by the two-step prepolymer method , today , thanks to new catalysts , they can be produced by a one-shot technique . It is possible that the polyether foams may soon be molded on a production basis in low-cost molds with more intricate contours and with superior properties to latex foam .

The polyester urethane foam is generally produced with adipic acid polyesters ; ; the polyether group generally consists of foams produced with polypropylene glycol or polypropylene glycol modified with a triol . One shot vs. prepolymer In the prepolymer system , the isocyanate and resin are mixed anhydrously and no foaming occurs . The foaming can be accomplished at some future time at a different location by the addition of the correct proportion of catalyst in solution . In one-shot , the isocyanate , polyester or polyether resin , catalyst , and other additives are mixed directly and a foam is produced immediately . Basically , this means that simpler processing equipment ( the mixture has good flowing characteristics ) and less external heat ( the foaming reaction is exothermic and develops internal heat ) are required in one-shot foaming , although , at the same time , the problems of controlling the conditions of one-shot foaming are critical ones . Properties Most commercial uses of urethane foams require densities between 2 and 30 lb. / cu. ft. for rigid foams , between 1 and 3 lb. / cu. ft. for flexible foams . This latter figure compares with latex foam rubber at an average of 5.5 lb. / cu. ft. in commercial grades . Compression strength : Graph in Fig. 1 , p. 392 , indicates how the ratio of compressive strength to density varies as the latter is increased or decreased . The single curve line represents a specific formulation in a test example . By varying the formula , this curve may be moved forward or backward along the coordinates to produce any desired compression strength / density ratio . Thermal conductivity and temperature resistance : In flexible urethane foams , we are referring to the range between the highest and lowest temperatures under which the materials' primary performance remains functionally useful . In temperature resistance , this quality is usually related to specific properties , e.g. , flexural , tensile strengths , etc. . Thermal conductivity is directly traceable to the material's porous , air-cell construction which effectively traps air or a gas in the maze of minute bubbles which form its composition . These air or gas bubbles make highly functional thermal barriers . The K factor , a term used to denote the rate of heat transmission through a material ( B.t.u./sq. ft. of material/hr./*0F./in. of thickness ) ranges from 0.24 to 0.28 for flexible urethane foams and from 0.12 to 0.16 for rigid urethane foams , depending upon the formulation , density , cell size , and nature of blowing agents used . Table 1 , , p. 394 , shows a comparison of K factor ratings of a number of commercial insulating materials in common use , including two different types of rigid urethane foam . Flexural strength : This term refers to the ability of a material to resist bending stress and is determined by measuring the load required to cause failure by bending . The higher-density urethane semi-rigid foams usually have stronger flex fatigue resistance , i.e. , the 12 lb. / cu. ft. foam has 8 times the flexural strength of the 3 lb. / cu. ft. density . Note that flexural strength is not always improved by simply increasing the density , nor is the change always proportional from one formulation to another . Where flexural strength is an important factor , be sure that your urethane foam processor is aware of it . Tensile strength : This property refers to the greatest longitudinal stress or tension a material can endure without tearing apart . ( like compression strength of urethane foams , it has a direct relationship to formulation . ) Exceptional tensile strength is another of urethane foam's strong features . Figure 2 , above , shows the aging properties of urethane foams as determined by the percent of change in tensile strength during exposure to ultra-violet light . Processing urethanes There are many ways of producing a foamed urethane product . The foam can be made into slab stock and cut to shape , it can be molded , it can be poured-in-place , it can be applied by spray guns , etc. .

Slab stock is still one of the most important forms of urethane end-product in use today . Basically , the foam machines that produce such stock consist of two or more pumping units , a variable mixer , a nozzle carriage assembly , and , in many cases , a conveyor belt to transport and contain the liquid during the reaction process and until it solidifies into foam . The ingredients are fed from tanks through a hose and into the mixer at a predetermined rate . The mixing head moves back and forth slowly across the width of the receptacle . It only takes a few minutes for the foaming action to be completed and after a short cure , the material can be cut into lengths as desired .

Much has been done in the way of ingenious slitters to fabricate the slab stock into finished products . Profile cutting machines are available which can split foam to any desired thickness and produce sine , triangle , trapezoid , and other profiles in variable heights , dimensions , etc. . The convoluted sheets can be combined to attain certain cushioning effects mechanically rather than chemically . Also available is a slitter which `` peels '' the inside of a folded block of foam and can be used to slit continuous sheets up to 300 yd. in length , down to 1/16 in. thick .

The low cost and ease of fabrication of the dies for three-dimensional foam cutting plus the wide variety of shapes , dimensions , and contours that can be tailor-made to customer requirements has made the technique useful for producing case liners , materials handling containers , packaging and cushioning devices , and such novelties as soap dishes , toys , head rests , arch supports , and gas pedal covers . Molding Although slab stock appeared first , it soon became apparent that for the production of cushions with irregular shapes , crowned contours , or rounded edges , the cutting of slab stock is a wasteful and uneconomical process . Only by resorting to molding techniques can the cushion manufacturer hope to compete satisfactorily in the established cushion market .

The closed molding of flexible urethane foams has been a problem ever since the introduction of the material ( molding in open molds was more feasible ) . Satisfactory methods for polyester foams and even prepolymer polyether foams were never fully achieved . Closed molding generally resulted in parts weighing more ( because of higher density ) than parts fabricated from free-blown foams . This counteracted the gain from having no scrap loss . In addition , there were difficulties with the flow and spreading of the foam mixture over the mold surface , trouble with lack of gel strength in the rising foam , and problems of splits . The introduction of one-shot polyether foam systems , aided by the development of new catalysts , helped to alleviate some of the problems of closed molding . While there are still many bugs to be ironed out , the technique is fast developing . Other techniques Simple systems are available that make it possible for urethane foam components to be poured , pumped , etc. , into a void where they foam up to fill the void . In a typical application -- the making of rigid urethane foam sandwich panels -- an amount of foam mixture calculated to expand 10 to 20% more than the volume of the panel is poured into the panel void and the top of the panel is locked in place by a jig .