504
INDUSTRIAL AND ENGINEERING CHEMISTRY
laurate (Table I) which causes it to be by far the hardest of the group. It be pointed Out that soaps as manufactured contain considerably more water than the present samples and, hence, might give somewhat different results. LITERATURE CITED (1) Bodman, J. W., U. S. Patent 2,215,539 (Sept. 24, 1940). (2) Bowen, J. L., and Thomas, R., Trans. Faraday Soc., 31, 164 (1935). (3) Carothers, W. H., and Hill, J. W.,J. Am. Chem. Soc., 54, 1579 (1932). (4) Darke, W. F., McBain, J. W.,and Salmon, C. S., Proc. Roy. SOC.(London), A98, 395 (1921). (5) Ferguson, R. H., Oil & Soap, 26,6 (1944).
(6) Ferguson, R. H., Rosevear, F. B., and Stillman, R. C., ISD. ENQ.CHEX.,35, 1005 (1943). (7) Fryer, P. J., and Weston, F. E., Technica! Handbook of Oils, Fats and Waxes, Vol. 11, p. 92 (1939). (8) Houmink, R., “Elasticity, Plasticity and the Structure of
Matter”, p. 14, Cambridge Univ. Press, 1940. (9) Ibid., pp. 109.f. (10) Lederer, E. L., Handbuch der Kolloidwissenschaft, VOl. V, P. 16, Leipzig, Th. Steinkopf, 1932
Vol. 37, No. 5
(11) Lyon, L. L., and Vold, R. D., accepted for publication by IND.
ENG.CHEW,ANAL.ED.
(12) McBain, J. W., J . Chem. Education, 6,2115 (1929). (13) McBain, J. W., and Lee, W. W., Oil & Soap, 20, 17 (1943). (14) McBain, J. W., Vold, R. D., and Gardiner, K., Ibid., 20, 221 (1943). (15) McBain, J. mi.,Vold, M. J., and Johnston, S., J . Am. Chem. Soc., 63, 1000 (1941). (16) McBain, J. W., Vold, M. J., and Porter, J. L., IND. ENQ.CHIW., 33, 1049 (1941). (17) McBain, J. W.9 Void, R. DVand Void, hf. J., J. Am. ChemSOC.,60, 1869 (1938). (18) McBain, J. w., and Watts, 0 . o., J . Rheol., 3 , 4 3 7 (1932). (19) MacLennan, K., J . SOC.Chem. Ind., 42, 393 (1923). (20) Mark, H., !L?an5. Faraday SOC.9 29, 6 (1933). (21) Marton, L., McBain, J. W., and Vold, R. D., J . Am. Chem. SOC.,63, 1990 (1941). (22) Mills, v., u. 8.Patent 2,295,594 (1942). (23) Scott’s Standard Methods of Chemical Analysis, Vol. I, p. 870 (1939). (24) Thiessen, P. A., and Spychalski, R., Z. physik. Chem., A156, 435 (1931). (25) Vold, R. D., Soap, 16, 31 (1940).
.
PRESENTED in part before the Division of Colloid Chemistry at t h e 108th Meeting of the AMBRICAN CHEMICALBOCIFITY in Pittsburgh, Pa.
Resinous Plasticizers from Sebacic Acid IC. K. FLIGOR AND J. IC. SU-MNER
Resinous Products and Chemical Company Philadelphia, Pa.
T
HE development of plasticizers has closely paralleled the growth of both the plastic and the rubber industries. The use of camphor in nitrocellulose is a n early example of a plasticized composition in the plastic industry; the use of modifiers, such as mineral and vegetable oils, waxes, resins, and tars in natural rubber,is probably as old as the industry itself. I n recent years the tremendous expansion of the plastic and synthetic rubber industries has increased many fold the volume usage of plasticizers over that of only a few years ago. I n many present-day plastics and synthetic rubbers the function of the plasticizer is second in importance only to that of the base material. The increasingly important role played by plasticizers has imposed more exacting and severe serviceability requirements on them. These demands could not always be met by available materials. This condition stimulated plasticizer research rather generally, until today there are on the market materials with resistance toward heat, chemicals, and other deteriorating influences that would have been thought impossible several years ago. Plasticizers are used in many plastics and in natural and synthetic rubbers chiefly for two reasons: (1) to aid processing and (2) to impart desirable and specific properties to the finished products. As processing aids, plasticizers reduce power consumption on mills, calenders, extruders, and other equipment, as well as cutting down the time necessary for such operations. Higherquality products result from the greater smoothness and good definition of the formed surfaces of compounds containing plasticizers. I n the case of many plastics the use of plasticizing agents is mandatory in order to reduce processing temperatures to a practical level. With synthetic rubbers, the contribution of the property of building tack by plasticizers is invaluable.
The inherent toughness and resistance to breakdown of some synthetics is largely overcome by the use of plasticizers. Plasticizers impart to plastics and to synthetic rubbers properties that are generally desirable in the finished product such as appearance, smoothness, and feel, but in addition, certain other specific properties may be obtained by the proper choice of plasticizing agent. Flexible, rubberlike compositions are produced when plasticizers are incorporated in certain rigid plastic materials. The degree of hardness and flexibility obtained is a function of the concentration and type of plasticizer employed. Such compound designing involves a knowledge of the functions of the various classes of plasticizers, as well as those of the individual members of these classes. Some specific properties that may be desi.gned into a compound by means of plasticizers are low-temperature flexibility, resilience, varying degrees of roomtemperature flexibility or modulus, and resistance to hardness gain on aging at elevated temperatures. GENERAL REQUIREMENTS O F A PLASTICIZER
PLASTICIZING EFFICIENCY. This term refers to the ability of a material to plasticize the rubber or plastic to produce softness for easier processing or flexibility in the case of the elastomeric plastics. The nature of the plasticizer must be such that this is accomplished a t no sacrifice of other general requirements. This property is the first and most important requirement of a plasticizer. Coiw.mIBILITY. I n order to be generally useful, a plasticizing material must be completely compatible under all conditions (especially of temperature) likely to be encountered in service. PERMANENCE (Low VOLATILITY).This property is desirable in order that the beneficial effect of the plasticizer may persist throughout the useful life of the base material. WATER RESISTANCE.Since most plasticiaed compositions come in contact with water more or less frequently during their
May, 1945
INDUSTRIAL AND ENGINEERING CHEMISTRY
A sebacic acid polyester plasticizer has been developed which shows good compatibility with polyvinyl chloride, vinyl chloride-acetate copolymer, Buna N (oil-resistant type), GR-S, GR-M, and nitrocellulose. When compounded in typical formulations, this plasticizer exhibits outstanding qualities of permanence, heat stability, oil and gasoline resistance, nonflammability, water resistance, and nonmigration to adjacent plastics, combined with plasticizing efficiency and low-temperature properties equal in some cases to those of the monomeric-type plasticizers. Since the polyester chosen for this work is only representative of a large class of materials, proper choice and combination of suitable raw materials, molecular weight, and polymer modification should yield other polymers whih may have other desirable properties.
serviceable life, this property is also important. A plasticizer must be stable toward, and essentially nonextractable by water. CHEMICALINERTNESS. A plasticizer must be chemically stable a t room, processing, and service temperatures, must be inert toward materials with which it is likely to come in contact in service, and must be inert toward the base material in which it is used, so as not to accelerate the decomposition of the latter. EASEOF INCORPORATION. I n factory practice there is a practical limit to the time and temperature needed to incorporate a plasticizer, and for this reason ease of incorporation is important. FREEDOM FROM ODOR. An obnoxious odor in a plasticizer would be objectionable in most applications. Resistance to extraction by oil and solvents is desirable, but this requirement is specific for given applications. Many specific requirements, such as light stability, good electrical characteristics, and nonflammability, may become necessary or of paramount importance in special applications, and most of them can be met by judicious choice of plasticizer or combination of plasticizers.
-
*
CLASSIFICATION OF PLASTICIZERS
Plasticizers in general fall into one or the other of the two following classifications, although there may be some borderline cases: (1) monomeric, exemplified by the esters, amides, and others; (2) polymeric or resinous, exemplified by some alkyd resins, urea-formaldehyde alkyd combinations, and linear polyesters. The monomeric types are characterized by their good efficiency-i.e., low plasticity imparted to synthetic rubbers and low modulus imparted to vinyl plastics, good resilience, low-temperature flexibility, and low hardness of the compounds containing them. They suffer in varying degrees from the disadvantage of being nonpermanent (volatile), having characteristic odors, poor resistance t o solvents, oil, and gasoline, and of being inflammable; the latter property carries over into the compounds containing them, to a greater or less degree. The properties of the polymeric types are, to some extent, complementary to those of the monomeric type. Thus, many of the former are permanent (nonvolatile), oil, solvent, and gasoline resistant, nonflammable, heat stable, nonmigratory from a compounded stock, and water resistant. Certain of the poIyesters however, combine to a remarkable degree the good qualities of the plasticizers of both broad classifications. Thus, they impart low-temperature flexibility (bendbrittle point) and plasticizing efficiency equal to those of some monomeric types. An additional advantage is the possibility of their being “tailor-made” to meet predetermined requirements by adjusting the molecular weight level and by proper choice of raw materials. The effect of molecular weight on the properties of certain polyesters is known. The effect of various polyhydric alcohols and polybasic acids on the properties of the polyesters
505
is also known, and this approach offers wide latitude in the choice of raw materials from which t o make a polyester with desired properties. Of the polyester plasticizers prepared to date, those derived from sebacic acid have shown most promise, and one has been found t o have more general utility as a plasticizer than most of the others. The data presented in this paper have been collected principally on this plasticizer (Paraplex G-25). The use of the sebacic acid polyesters as plasticizers and rubbery materials has recently assumed great importance with the advent of the synthetic rubbers and some of the newer plastics. MATERIALS AND FORMULATIONS
The sebacic acid polyester, as well as several other typical widely used plasticizers, was evaluated in the following three types of commercial polyvinyl chloride: copolymer of %yo chloride and 5% acetate, copolymer of 90% chloride and 10% acetate, and 100% polyvinyl chloride. Most of the work reported here was carried out on the 95-5 copolymer. The formulation used for the copolymer batches was as follows: Polyvinyl chloride-acetate copolymer Basic lead carbonate Stearic acid Plasticizer
63.6% 1.0 0.5
35.0 100.0
With 100% polyvinyl chloride the amount of plasticizer was increased from 35% to 40%, based on the compound. Basic lead carbonate was used as a stabilizer, and stearic acid as a milling aid. The amount of plasticizer in this formulation was chosen as being fairly typical of that used in commercial practice. figments were purposely omitted so that the modifications effected in the properties of the finished compound would be due only to the plasticizer. Samples for evaluation were prepared by methods to be described later. For the evaluation of the plasticizers in synthetic rubber, a typical oil-resistant Buna N was used in the following formulation: Buna N (oil-resistant type) Zinc oxide Stearic acid Benzothiazvl disulfide Sulfur Medium-processing channel black Plasticizer
100 parts 5
1
1.6
1.6 60.0 30.0
The batch was milled and vulcanized by methods to be described later. Tests were carried out on both cured and uncured samples. Tests on the cured stock were made on specimens from the optimum cure. Plasticizer compatibility was the only study made with GR-S, GR-M, and Thiokol FA. These elastomers were milled in the following typical formulations: GR-S, 100 parts; semireinforcing furnace black, 50; zinc oxide, 5.0; mercaptobenzothiazole, 1.5; diphenylguanidine, 0.2; sulfur, 2.0; plasticizer 10, 20, or 30. GR-M, 100 parts; &ne thermal black, 100; zinc oxide, 5.0; neozone A, 2.0; stearic acid, 0.5; extra light-calcined magnesia, 4.0; plasticizer, 25.0. Thiokol FA (master batch), 100 parts; zinc oxide, 10; stearic acid, 0.5; plasticizer, 10, 20, or 30; S R F black, 60. Thiokol FA master batch: Thiokol FA, 700 parts; benzo-” thiazyl disulfide, 2.1 ; diphenylguanidine, 0.7. These batches were milled and vulcanized by standard methods, and compatibility tests were run. Compatibility studies were also made with the plasticizer, and lacquer grades of nitrocellulose, cellulose acetate, cellulose acetate-propionate, cellulose acetate-butyrate, ethylcellulose,
506
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 37, No. 5
elongation was computed to unit stress and called ' ' l O O ~ o modulus". The dumbbellspeci100% Heat Sta- BendHeat Modulus, bility, Brittle % Extraction Loss in: Volatile piamma- Defermens were cut from A.S.T.M. Lb. per Hr. a t Temp., Aromatic Loss a t bility, % ' mation, molded sheets. Plasticizer 8s. In. 150' C. ' C. Water Oil gasoline 60' C. Burned % Sebacic acid polyester 1650 6 -50 0.1 0.1 19.0 +1.0 7 15 HEATSTABILITYwas judged Tricresyl hosphate 1440 3 -30 0.1 1.8 28.0 +1.0 0 ' 23.4 by the time required to proDioctyl pgthalate 1060 3.5 -50 0.1 8.4 +1.2 100 24.3 Trioctyl phosphate 820 2 -70 0.2 22.4 .... 3-0.2 12.5 .. duce significant discoloration of Dibutyl sebacate 540 5 -70 0.3 24.6 ., -9.8 100 37 the compound a t 150" C. BEND-BRITTLE TEMPERATURE, TABLE 11. DATAON THREEPLASTICIZERS IN VIKYLPOLYMER was t h e temperature below which specimens from the molded stocks could not be flexed Hnot 100% StaBend without shattering when bent through 180" over a rod a/* inch Rfodulus bility Brittle % Extraction Volatile FlammaLb. per' Hr. a i Temp., in: Loss a t bility % in diameter. The samples were preconditioned by storing in Plasticizer Sq. In. 150' C. C. Water Oil 60' C. BurAed air a t -30" C. for 24 hours before testinn. After meconditionI n 90% Vinyl Chloride-10% Vinyl Acetate Copolymer ing, the samples were quickly transferred to a dry ice-methanol Sebacic acid bath a t -40" C. The bath temperature was changed 5' C. at polyester 1560 2.5 -20 . .. 0.1 +0.8 7.5 Dicapryl a time and the samples tested until break occurred, after being phthalate 665 3 -40" 0.3 5.0 4-1.5 58 stored for 5 minutes at each temperature. The bend-brittle Dibutyl sebacate 222 3.5 -60 0.5 24.3 -10.5 47 point was taken as that temperature 5" above the maximum at I n 100% Polyvinyl Chloride which the sample broke. Sebacic acid EXTRACTION TESTS.The methods were essentially those of polyesterb 1050 8+ -40 ... -0.2 $ 0 . 6 31 Reed' except that samples 0.010 inch thick and 30 square inches Dicapryl phthalate 1210 8 -40" 0.1 18 $1.5 100 in area were used. Dibutyl sebacate 550 5-8 -60 0.5 24 -11.6 100 VOLATILITY TEST. The method used was also that of Reed' except that samples 0.010 inch thick and 24 square inches in area 5 A proximately. b TEis batch contained the polyester plasticizer in a concentration of were used in a simpler oven. 4OyG,based on the compound. FLAMMABILITY was determined by A.S.T.I
