14. SYNTHETIC RESIN PRICES, PROPERTIES, AND USES

Synthetic resins as substitutes.

Any new material will in the course of time be applied to the uses for which it has special advantages, displacing older materials which formerly served those purposes. The resulting product may sometimes be used in the same manner as before, or the properties of the substitute material may widen the usefulness of the finished product, or even make possible a product almost wholly new.

Before the development of molded synthetic resins, electrical plugs and sockets were usually made of porcelain or molded of marble dust and shellac. In this use substitution has been almost complete. Wall plates for electric switches and outlets were usually of brass. Today molded tar-acid or molded urea resins are substituted in part. In neither of these examples has the substituted material any important effect upon the use of the product.

An example of a substitute material widening the usefulness of the product is afforded by a new computing scale, where a molded urea resin casing (substituted for metal in the older model) has aided in decreasing the weight and has improved the appearance. Another example is the use of laminated synthetic resin coil forms in radio frequency transformers which, because of their better electrical properties at high frequencies, have aided in the design of more compact units.

Examples of synthetic resins making possible a wholly new product are more difficult to find, but the following will serve as illustrations: Cast acrylate sheets to form curved cockpit enclosures for airplanes; molded acrylate buttons for reflecting road markers; and new special coatings, which make possible the use of metal cans for preserving foods and beverages hitherto impossible to can without loss of flavor.

Motives for substitution.

One of the most important reasons why a manufacturer may decide to substitute a synthetic resin for another material is the resulting economy in the sense of economy in total costs. As a rule, the synthetic resin will be more expensive pound for pound than the material for which it is substituted; but frequently the manufacturing cost is enough lower to more than make good the difference in material cost, because the resin part will come from the mold almost in finished form, whereas the part made of wood or metal will require considerable fabrication. In some cases there may be a saving in marketing costs. For example, the shades for large office fixture lights are now made of synthetic resin as well as of opal glass. The resin shades are less expensive to ship because they are lighter and require less expensive packing.

Another incentive toward substitution is to give novelty, and hence sales appeal, to an old product. In many cases the use of synthetic resins fits in with the present tendency to redesign an old-style product so that it will be more compact, have more pleasing lines, and more color.

Still another incentive toward substitution is to give the product greater usefulness, or lower costs in use. The great expansion in the use of synthetic resins in surface coatings has come about because, with these materials, coatings can be developed to fit special purposes, and dry rapidly, which means an important saving to those who use them.

Materials displaced by synthetic resins.

The wide range of uses to which synthetic resins are now applied implies that the materials displaced are numerous. For example, cast or wrought iron or steel is displaced in timing gears and in many small machine parts, such as cradle-type telephones; nonferrous metals in small machine parts and novelties, such as inexpensive bracelets; glass in lamp shades and in cosmetic containers; natural resins in lacquers; plastics, such as cellulose acetate in safety glass or cellulose nitrate in colored lacquers; other adhesives in bonding plywood; and cork or metal in bottle closures.

In general, the quantity of material displaced is a very small part of that material’s total market. Frequently, however, industries producing the finished product have had to make substantial changes in their equipment in order to use synthetic resins. This has been true in the button industry, in the bottle closure industry, in the varnish and lacquer industry, and in the various electrical supply industries; and readjustment is now proceeding in the fancy container industry and in the safety glass industry.

Competition between synthetic resins.

Any particular synthetic resin must compete for its market with other synthetic resins, as well as with other materials. The basis of choice or substitution will be the same as that which has already been briefly discussed in connection with the displacement of other materials by resins. As between a number of resins with properties fitting them for a particular use, the total costs of using each will be compared and the choice will go to the least expensive; but where a resin has special advantages in a particular use it may win out over a less expensive resin.

It should be emphasized that this battle of materials for markets is a never-ending one. The fact that a specific synthetic resin has achieved a certain position is no guarantee that it may not lose it wholly or in part to some newer resin or other material. Thus cast phenolic resin was for a time the only resin available in light colors but urea resins became available in pastel shades and more recently water-clear polystyrene and acrylate resins have come on the market. Until recently tar-acid resins were without competition in laminating, but urea resins now are used to some extent for the surface laminae and the tar-acid resins now face a potential threat in a new product offered to laminators. If the use of this cellulose sheet, which looks much like blotting paper and which has lignin incorporated in it to act as a binder in the press, should materially decrease the cost of laminated sheets, it will mean serious new competition for the tar-acid laminating resins.

The general effect of the increase in number of types of synthetic resin has been to modify the market outlook of the producers of each type. They are now more inclined to view the market as being limited by the price at which they can supply their product and by the physical properties of each resin rather than attempt to exploit it as a universal resin for all purposes.

Resins classified by cost.

At present the resins produced in largest volume are the alkyd resins for use in surface coatings; the tar-acid resins for molding, laminating, and surface coatings; the urea resins, chiefly for moldings; and the cast phenolic resins. Roughly, the price per pound of pure resin material[12] for these various resins may be compared as follows:

Type of resin: Average sales price
of net resin, 1937
(per pound)
Cast phenolic $0.41
Tar-acid:
For molding .18
For laminating .13
For coatings .17
Alkyd .20
Urea .45

Because the cost of the filler is less per pound than the cost of the resin, the cost of the tar-acid and urea molding powders will be less than the figures given for the pure resin. On the other hand, wholesale prices paid by consumers will include transportation and distribution costs not included in the figures of manufacturers’ sales.

Vinyl resins, acrylate resins, and polystyrene resins are at present produced in much smaller volume than those just listed. If and when the volume of production is increased the price may be decreased. In 1937, the price per pound of pure resin[12] was as follows:

Type of resin: Average sales price
of net resin, 1937
(per pound)
Vinyl $0.69
Acrylate 1.66

Early in 1938, acrylate resins were being offered for sale at 85 cents per pound for molding powder and $1.25 per pound for the cast material; polystyrene resins at 72 cents per pound.

Petroleum resins, in 1937, sold for an average of 2 cents per pound net resin content.[12] This low price puts them beyond competition of the other synthetic resins in the uses in laminating and coating to which they are adapted.

The physical properties of a resin and its uses.

A more expensive resin will be used in preference to a cheaper one, only if the higher cost is more than offset by some physical property, such as color, which makes it more desirable in a particular use. The most common molding resin at present is the tar-acid type, but it is available only in the darker colors and therefore has been at a disadvantage, where a light color is desired, in competition with cellulose nitrate (celluloid) and cellulose acetate plastics or with urea and cast phenolic resins. In recent years the production of cellulose acetate molding compounds and of urea resins has increased rapidly, largely under this stimulus. The desire for color also promises well for the future of the acrylate and polystyrene resins which are produced in water-clear grades or colored with dyes or pigments.

Table 17.Synthetic resins and other plastics: Properties that affect appearance

Type Machining qualities Clarity Color possibilities Burning rate Effect of age Effect of sunlight Refractive index No1
Synthetic resins:
Tar-acid—Formaldehyde:
Molded, wood flour filler. Fair to good. Opaque Limited Very low None Light shades discolor
Molded, mineral filler. do do do Nil do do
Molded, fabric filler. do do do Approximately nil do do
Laminated, paper base. Fair to excellent. do do Very low Improves mechanical and electrical properties. Lowers surface resistance.
Laminated, fabric base. do do do do do do
Laminated, asbestos cloth base. do do do Approximately nil do
Cast Excellent Transparent, translucent, opaque. Unlimited Very low Hardens slightly Colors may fade 1.5-1.7
Tar-acid—Furfural:
Wood flour filler. Fair to good Opaque Limited do do Light shades discolor
Mineral filler. do do do Nil do do
Fabric filler. do do do do do do
Urea—Formaldehyde. Fair Translucent, opaque Unlimited pastel shades Very low do None 1.54-1.6
Vinyl, unfilled. Good Transparent, translucent, opaque Unlimited pastels to black Nil Strength unaffected Darkens 1.53
Vinyl, filled. Excellent (organic filler). do do Approximately nil None Discolors
Acrylate Very good Transparent (95% light transmission). Unlimited Slow do None 1.49
Polystyrene Poor to good Transparent, translucent, opaque. do do do Yellows 1.67
Other plastics:
Shellac compound. do Opaque Limited, pastels excluded High (wood filler) None
Cold molded:
Nonrefractory. Poor do Dark colors only Nil
Refractory. do do Gray do
Rubber compounds:
Chlorinated rubber. Translucent, opaque Unlimited do Slight embrittlement Darkens 1.56
Modified isomerized rubber. Good Transparent do Slow None Slight surface crazing
Hard rubber. Fair Opaque Limited Medium do Discolors surface, resistivity decrease.
Casein Good Translucent, opaque Unlimited Very low Hardens slightly Colors may fade
Cellulose compounds:
Ethyl cellulose do Transparent, translucent, opaque do Slow Slight Slight 1.47
Cellulose acetate sheet do do do do do do 1.49-1.50
Cellulose acetate molding do do do do do do 1.47-1.50
Cellulose nitrate do do do Very high Slight hardening Discolors and becomes brittle 1.50

1 Specified refractive degree.

Note.—The values for the properties in this table are based upon maximum and minimum figures submitted to Modern Plastics by a number of manufacturers of each type of material. Differences in test procedures and sizes of test specimens may lead to erroneous conclusions in some cases if direct comparisons are attempted. Special grades of materials are often available which excel in one particular property.

Source: Modern Plastics, vol. 15, no. 2, opp. p. 120. October 1937.

Table 18.Synthetic resins and other plastics: Molding properties

Type. General molding qualities Compression molding temperature Compression molding pressure Injection molding temperature Injection molding pressure Compression ratio Mold shrinkage Effect on metal inserts
°F. Pounds per
square inch
°F. Pounds per
square inch
Inches per inch
Synthetic resins:
Tar-acid—Formaldehyde:
Molded, wood flour filler Excellent 280-360 1,600-4,500 275-375 2,000-10,000 2.5-3.0 0.006-0.010 Inert.
Molded, mineral filler Excellent to fair 270-350 1,600-6,000 275-350 2,000-15,000 2.2-7.1 .002-.006 Do.
Molded, fabric filler Good to fair 270-330 3,000-8,000 2.5-11.0 .003-.007 Do.
Laminated, paper base 250-365 1,000-3,000 1.5-3.0 Do.
Laminated, fabric base 250-365 1,000-3,000 1.5-3.0 Do.
Laminated, asbestos cloth base 250-325 1,000-3,000 Do.
Cast Do.
Tar-acid—Furfural:
Wood flour filler Excellent 330-400 1,000-3,000 250-290 300-5,000 2.5-3.0 .005-.009 Do.
Mineral filler do 330-360 1,000-3,000 250-290 300-5,000 2.5-6.0 .002-.006 Do.
Fabric filler Good to fair 300-360 1,000-3,000 250-290 300-50,000 4.0-15.0 .0025-.006 Do.
Urea—Formaldehyde (alpha cellulose filler) Excellent 290-325 1,500-6,000 3.0 .007-.011 Do.
Vinyl, unfilled Good 240-275 1,500-2,000 2.0 .001 Not used.
Vinyl, filled Excellent 250-300 2,000-2,500 1.5-3.5 .000 Inert.
Acrylate do 285-315 1,500-5,000 325-475 3,000-30,000 2.0 .002-.003
Polystyrene Good 280-325 300-2,000 300-375 3,000-30,000 2.5 .002-.0025
Other plastics:
Shellac compound do 240 1,000-1,200 .002 Do.
Cold molded:
Nonrefractory Fair 4,000-12,000 2.5 .000-.022 Do.
Refractory do 4,000-12,000 3.5 .000 Do.
Rubber compounds:
Chlorinated rubber do 200-225 2,000-5,000 2.0-3.0
Modified isomerized rubber Good 260-300 1,200-4,000 3.0 .000 Do.
Hard rubber Fair 285-350 1,200-1,800 180-220 2,000-5,000 4.0-6.0
Casein Poor 200-225 2,000-2,500
Cellulose compounds:
Ethyl cellulose Excellent 212-300 1,000-5,000 2.2-2.9 .0003-.0007 Do.
Cellulose acetate sheet do 210-320 500-5,000 (1) Do.
Cellulose acetate molding do 250-350 500-5,000 300-440 3,000-30,000 2.0-2.8 (1) Do.
Cellulose nitrate Good 185-250 2,000-5,000

1 Positive and injection 0.002-0.003; semipositive 0.005-0.007; flash 0.008-0.009.

Note.—The values for the properties in this table are based upon maximum and minimum figures submitted to Modern Plastics by a number of manufacturers of each type of material. Differences in test procedures and sizes of test specimens may lead to erroneous conclusions in some cases if direct comparisons are attempted. Special grades of materials are often available which excel in one particular property.

Source: Modern Plastics, vol. 15, No. 2, opp. p. 120. October 1937.

Table 17 lists the properties which affect appearance and gives in addition to the color range, the clarity, material, the burning rate, the effect of age and sunlight, the refractive index, and the machining quality of each synthetic resin.

Table 18 lists molding properties of synthetic resins. Of special interest are the possibilities of using a resin in injection molding. The thermoplastic resins and plastics (see softening point in table 20) are generally preferred to the thermosetting materials for injection molding because they permit the reuse of material otherwise wasted.

Table 19 lists the strength properties of the synthetic resins; table 20 the heat properties; table 21 the electrical properties; and table 22 the resistance to acids, alkalies, and solvents. All of these qualities are important in some uses and each quality may be paramount in a few. Each material has its limitations and its special advantages and the consuming industry must choose the one best suited to its purposes. The tie-up between specific properties and particular uses is exemplified by vinyl resins, which because of their great elasticity at low temperatures, are used in safety glass, and by the polystyrene resins, which because of their electrical properties at high frequencies, are used in laminated electrical parts. As production of the various resins increases new uses will probably be found for most of them.

Table 19.Synthetic resins and other plastics: Strength properties

Type Tensile strength Elongation Modulus of elasticity Compressive strength Flexural strength Impact strength1 (foot pounds) Hardness2
Pounds per
square inch
Percent Pounds per
square inch
× 10³
Pounds per
square inch
Pounds per
square inch
Brinell No
Synthetic resins:
Tar-acid—Formaldehyde:
Molded, wood flour filler 6,000-11,000 10-15 16,000-36,000 8,000-15,000 0.10-0.28; I, N 30-45
Molded, mineral filler 5,000-10,000 10-45 18,000-36,000 8,000-20,000 0.11-0.36; I, N
Molded, fabric filler 6,500-8,000 7-12 20,000-32,000 10,000-13,000 0.4-2.4; I, N
Laminated, paper base 6,000-13,000 5-20 20,060-40,000 13,000-20,000 0.4-1.2; I, N 24-40
Laminated, fabric base 8,000-12,000 5-15 20,000-44,000 13,000-20,000 0.8-5.2; I, N 30-45
Laminated, asbestos cloth base 9,000 18,000-40,000 17,000
Cast 5,000-12,000 5-15 15,000-30,000 0.1-1.5; I, N 30-45
Tar-acid—Furfural:
Wood flour filler 5,000-12,000 10-25 28,000-36,000 10,000-16,000 0.08-0.52; C, N 335-40
Mineral filler 4,000-12,000 10-45 24,000-36,000 8,000-14,000 0.08-0.48; C, N 344-46
Fabric filler 5,000-10,000 7-12 26,000-30,000 10,000-16,000 1.6-3.1; C, N 330-35
Urea—Formaldehyde 8,000-13,000 16 24,000-35,000 13,000-15,000 0.7-1.5; C, U 448-54
Vinyl, unfilled 8,000-10,000 3.5-4.1 10,000-13,000 0.3-0.6; I, N 15-25
Vinyl, filled 6,000-12,000 3.5-8.5 0.1-0.7; I, N 15-25
Acrylate 7,000-9,000 1.0 6 8,000 15,000-17,000 0.25-0.5; C, N 418-20
Polystyrene 5,500-7,500 1.0 4.6-5.1 13,000-13,500 6,500-8,000 0.16-0.25; I, N 20-30
Other plastics:
Shellac compound 900-2,000
Cold molded 6,000-15,000 5,300-7,500 0.4; C
Nonrefractory } 16,000 6,000 0.4; C
Refractory
Rubber compounds:
Chlorinated rubber 3.0+; C, U
Modified isomerized rubber 4,300 0.013 4.7 8,500-11,000 7,000-9,000 2.6-6.2; I, N 585-90
Hard rubber 4,000-10,000 8-15 5.3 8,000-12,000 0.5; I 31
Casein 7,600 5.1-5.7 1.0; I 23
Cellulose compounds:
Ethyl cellulose 2,000-7,000 2.8 1-4; I, N (per in. sq.)
Cellulose acetate sheet 6,000-11,000 20-55 1-3 4,000-16,000 2-7; C, N (per in. sq.) 66-11
Cellulose acetate molding 3,500-10,000 10-48 2-4 11,000-16,000 5,200-8,800 3-12; C, N (per in. sq.) 66-7.5
Cellulose nitrate 5,000-10,000 10-40 2-4 3-12; C, N (per in. sq.) 68-11

1 ASTM D256-34T. C = Charpy; I = izod; N = notched; U = unnotched.

2 2.5 mm ball; 25 kg. load unless otherwise noted.

3 50 kg. load.

4 10 mm. ball; 500 kg. load.

5 Shore.

6 10 kg. load.

Note.—The values for the properties in this table are based upon maximum and minimum figures submitted to Modern Plastics by a number of manufacturers of each type of material. Differences in test procedures and sizes of test specimens may lead to erroneous conclusions in some cases if direct comparisons are attempted. Special grades of materials are often available which excel in one particular property.

Source: Modern Plastics, vol. 15, No. 2, opp. p. 120; October 1937.

Table 20.Synthetic resins and other plastics: Heat properties

Type Thermal conductivity Specific heat Thermal expansion Resistance to continuous heat Softening point Distortion under heat Tendency to cold flow
10⁻⁴ calories
per second per
square centimeter
per 1°C. per
centimeter
Calories per
°C. per gram
10⁻⁶ per °C. °F. °F. °F.
Synthetic resins:
Tar-acid—Formaldehyde:
Molded, wood flour filler 4-12.2 0.35-0.36 3.7-7.5 350 None 240-285 None.
Molded, mineral filler 8-20 0.25-0.35 2.5-4 450 do. Do.
Molded, fabric filler 3-5 0.30-0.35 2-6 250-350 do. Do.
Laminated, paper base 5-8 0.3 -0.4 2 212-300 do. 320 Do.
Laminated, fabric base 5-8 0.3 -0.4 3 212-350 do. Do.
Laminated, asbestos cloth base 2 400-500 do. Do.
Cast 3-5 0.3-0.4 2.8 160
Tar-acid—Furfural:
Wood flour filler 3.5-5 0.3-0.4 3 280-400 Chars 450 268-288 Do.
Mineral filler 10-20 0.3-0.4 2 350-500 Chars 550 277-297 Do.
Fabric filler 5-8 0.3-0.4 4.5 280-350 Chars 400 Do.
Urea—Formaldehyde 7.13 1.5 160 None 260 Do.
Vinyl, unfilled 4 0.244 6.9 130-160 140-150 Slight.
Vinyl, filled Varies Varies Varies 130-160 140-158 Do.
Acrylate 4.3-6.8 0.45 8.5 170-235 158 Do.
Styrol 1.9 0.324 10.2 110-200 185 Do.
Other plastics:
Shellac compound 150-190 150 Do.
Cold molded:
Nonrefractory 500
Refractory 1,300
Rubber compounds:
Chlorinated rubber 175-230 140 Do.
Modified isomerized rubber 2.6-2.9 7-8 165-220 167-221 Do.
Hard rubber 3.2 0.33 8.0 150-190 Do.
Casein 8 200
Cellulose compounds:
Ethyl cellulose 210-266
Cellulose acetate sheet 5.4-8.7 0.3-0.4 14-16 140-180 140-230 122-212 Do.
Cellulose acetate molding 5.4-8.7 0.3-0.45 14-16 140-180 145-260 122-212 Do.
Cellulose nitrate 3.1-5.1 0.34-0.38 12-16 ca. 140 160-195

Note.—The values for the properties in this table are based upon maximum and minimum figures submitted to Modern Plastics by a number of manufacturers of each type of material. Differences in test procedures and sizes of test specimens may lead to erroneous conclusions in some cases if direct comparisons are attempted. Special grades of material are often available which excel in one particular property.

Source: Modern Plastics, vol. 15, No. 2, opp. p. 120. October 1937.

Table 21.Synthetic resins and other plastics: Electrical properties

Type Volume resistivity
(50 percent relative
humidity) (ohm = cms)
Breakdown voltage,
60 cycles
(volts per mil
(instantaneous))
Dielectric constant Power factor
60
cycles
10³
cycles
10⁶
cycles
60
cycles
10³
cycles
10⁶
cycles
Synthetic resins:
Tar-acid—Formaldehyde:
Molded, wood flour filler 10¹⁰-10¹² 300-500 5-12 4-8 4.5-8 0.04-0.30 0.04-0.15 0.035-0.1.
Molded, mineral filler 10⁹-10¹¹ 250-400 5-20 4.5-20 4.5-20 0.10-0.30 0.10-0.15 0.005-0.1.
Molded, fabric filler 10⁹-10¹¹ 300-450 5-10 4.5-6 4.5-6 0.08-0.30 0.08-0.20 0.04-0.1.
Laminated, paper base 10¹⁰-10¹³ 400-1,300 4-6 0.02-0.05.
Laminated, fabric base 10¹⁰-10¹² 150-600 4.5-7 0.02-0.08.
Laminated, asbestos cloth base 90
Cast 10⁹-10¹⁴ 300-450 5-10 5-7 0.025-0.20 0.005-0.08 0.01-0.045.
Tar-acid—Furfural:
Wood flour filler 10¹⁰-10¹² 400-600 4-8 6-7.5 0.04-0.15 0.035-0.1.
Mineral filler 10⁹-10¹¹ 200-500 4.5-20 5-18 0.1-0.15 0.04-0.1.
Fabric filler 0.4 × 10¹¹ 200-500 4.5-6 5-7.5 0.08-0.20 0.035-0.1.
Urea—Formaldehyde (2-2.8) × 10¹³ 650-720 6.6 6 0.034 0.01-0.03.
Vinyl, unfilled 10¹⁴ 400-500 4 0.0143 0.0175.
Vinyl, filled 10¹¹ 350-400 4.7 4 0.02-0.15 0.02-0.065.
Acrylate 10¹⁵ 480 4-6 2.8 0.06-0.08 0.02.
Polystyrene 10¹⁷-10¹⁸ 500-700 2.6 2.65 2.7 0.0003 0.0001 0.0001.
Other plastics:
Shellac compound 100-400
Cold molded:
Nonrefractory 1.3 × 10¹² 85 15 6 0.20 0.07.
Refractory
Rubber compounds:
Chlorinated rubber 2,300 ca. 3 0.003
Modified isomerized rubber (5-7) × 10¹⁶ 2.7 2.68 0.006 0.0016.
Hard rubber 10¹²-10¹⁵ 250-900 2.8 3 0.003-0.008.
Casein 400-700 6.15-6.8 0.052.
Cellulose compounds:
Ethyl cellulose 1,500 3.72 0.011
Cellulose acetate sheet (5-30) × 10¹² 800-2,500 5.1-7.5 4.2-5.3 0.025-0.07 0.038-0.091.
Cellulose acetate molding (4.2-6.2) × 10¹² 800-850 5.8-6.0 4.4-4.6 0.042-0.058 0.038-0.042.
Cellulose nitrate (2-30) × 10¹⁰ 600-1,200 6.7-7.3 6.15 0.062-0.144 0.074-0.097.