INDUSTRIAL AND ENGINEERING CHEMISTRY
large number of brown spots whereas the Vinylite VYNW-di-Ca Oxo alcohol phthalate blend is almost free of these spots and also shows little color change. This advantage was not confirmed in Florida exposure tests. Table V presents results on Vinylite VYNW plasticized with bri-C8 Oxo alcohol phosphate and tri-%ethyl hexyl phosphate. The results show t h a t these two plasticizers are equal in plasticizer performance at a concentration of 50 parts of ester per 100 parts Vinylite VYKW. These blends have good tensile values, good elongation, and interesting processing properties. Laboratory studies proved t h a t the C8 Oxo alcohol phosphate formed a flux on a mill with Vinylite VYNW a t 150" C. in 2 minutes while the tri-%ethyl hexyl phosphate required a temperature of 160' C. t o obtain a flux in 2 minutes. These plasticizers are excellent in their low temperature properties-for example, at -15' C. the blends in Table V have a stiffness of 16,200 and 17,100 pounds per square inch and a break point of -62.2'C. Table VI gives the results obtained with a Vinylite VYNW blend and a VYPTW-Paracril 35 NS 90 blend plasticized with Oxo nonyl alcohol phthalate. A comparison of Tables I11 and V I indicates that the CS Oxo alcohol phthalate and the CS Oxo alcohol phthalate are about equal in these compounds in plascicization efficiency. Only in the brittle point test is the CS Oxo alcohol phthalate better than the CSalcohol ester. However, in general, when other compounds are evaluated, the trade rates Cp Oxo alcohol phthalate as 10% less efficient than the CS Oxo alcohol phthalate.
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RESULTS ON P A R A C R I L C O M P O U N D S Tables VI1 and VI11 give results on Paracril blends plasticized with dioctyl phthalate, both C8 Oxo alcohol phthalate and di-2-ethyl hexyl phthalate, as well as the phosphate esters of these alcohols. These data show, based on tensile, 1 0 0 ~ o modulus, ultimate elongation, crescent tear, brittleness, etc., that the plasticizers used impart the same physical properties to the same base compound. Results in Paracril blends show that the structure of the octyl alcohol phthalate and phosphate to be of minor importance as reflected in the check physical properties of the final cured blends. The tensile, 100% modulus, and elongation values obtained on the blends show differences for the test ester plasticizers that the authors believe are less than the over-all accuracy of the test methods. ACKNOWLEDGMENT The advice, encouragement, and assistance of A. Voorhies, Jr.. J. J. Owen, C. E. Rlorrell, B. M. Vanderbilt, L. A. Wlikeska, B. E Hudson, Jr., and P. V. Smith, Jr. during the course of this work are greatly appreciated,
LITERATURE CITED (1) Reed, M. C., ISD. ENG.CHEM.,35,896 (1943). (2) Young, B. W., Burkly, D. J., Newberg, R. G., and Turner, L. B., Ibid., 41,401(1949). (3) Young, D. W., Newbwg, R G , and Howlett, R. M., Ibid.. 39 1446-52 (1947). RECEIVEDJuly 8, 1948.
LAVERNE E. CHEYNEY' Battelle M e m o r i a l Institute, Columbus, O h i o
Natural and synthetic rubbers may be grouped into two broad classes-polar and nonpolar. Dipole linkages are involved in the plasticization of the polar group, hence they possess certain resemblances to the polar thermoplastics in this respect. Plasticizers are employed with such polymers for two general purposes: increasing plasticity of the uncured rubber; and increasing flexibility OP corresponding effects in the cured material. Plasticization of the polar rubbers is a complex problem because of: structural variations inherent in diene polymers and copolymers; the vulcanization process; and effects of other
additives-for example, carbon black. Available data are extremely confusing because of these factors and the faci that much of the information reported is meager. Many of the materials which have been employed may be grouped into a few broad chemical classes. The effects of these vary widely among a given class because of structural variations and differences in physical properties. It is possible to generalize concerning a few- types of effects, but more and better data are required before an adequate picture of the plasticization of the polar synthetic rubbers will be available.
N E of the most useful methods of compounding natural or
Commercial materials of this general type were identified for many years merely as softeners. Many of the products employed in the rubber industry were complex chemical mixtures, often of varying composition. Until the advent of neoprene synthetic rubber, there was little need for softeners or plasticizers, as they began t o be known, which would be especially s u i t a h l ~for URC with a particular polymer. The development of plasticizers, particularly the ester typeu, for use with the newer thermoplastics has taken place largely within the past 10 years. The commercial application of several types of synthetic rubbers of varying chemical structure and of specific physical and chemical properties has paralleled the plasticizer development. The successful utilization of these special-purpose synthetic rubbers for many product applications
synthetic rubbers has been by the use of auxiliary materials known as plasticizers. These materials have been employed in rubber compositions for two broad, general purposes: T o facilitate processing of the uncured rubber stock by softening the composition, increasing its plasticity, decreasing nerve, etc.; and t o alter the properties of the final cured product by decreasing hardness, lowering brittle temperature, improving rcsistance t o tear, or other effectsof similar character. These two effects of plasticizer addition are corollary. However, certain specific groups of materials have pronounced effects on one type, but only minor influence on the other group of properties. 1 Present
address, Poliook Paper Corporation, Middletown, Ohio.
INDUSTRIAL AND ENGINEERING CHEMISTRY
has been determined by the availability of the correct plasticizers which would so modify the properties of the original polymers as to make them suitable for the particular uses in question.
INFLUENCE O F P O L Y M E R Types of Synthetic Rubbers. There are several methods of classifying natural and Synthetic rubbers, depending on the particular problem involved. For the purposes of this discussion, it has been found convenient t o group these polymers into two general classes: those containing essentially no polar centers, and those containing significant proportions of polar groups or atoms. The nonpolar group would contain natural rubber as well as the synthetic hydrocarbon polymers-polyisoprene, polybutadiene, Butyl rubber, GR-S, etc. The polar group would contain the chloroprene polymers and copolymers (neoprene), the nitrile rubbers (acrylonitrile-diene copolymers, etc.), acrylatediene copolymers, chlorostyrene-diene copolymers, and numerous other polymers and copolymers containing polar atoms or groups such as GI, CN, COOR, and F. The mechanism of plasticizer action may involve either polar or nonpolar portions of the molecule, where both are present. Where only a nonpolar polymer is involved, the mechanism of plasticization is much simpler from thermodynamic considerations, inasmuch as secondary dipole linkages are not involved. For this and other considerations, it has been deemed wise to limit this treatment of the subject t o those polymers possessing original polarity-that is, in the uncured.state. It should be borne in mind that the vulcanization process as normally carried out produces dissymmetry (polarity) in the molecule, so that there are essentially no nonpolar polymers in the vulcanized state. Polymer Structural Variations. There are some regions of similarity in plasticization of the polar synthetic rubbers and the analogous polar thermoplastics. However, some structural modifications are possible in the synthttic rubbers which are not possible in the simpler polymer molecules, and therefore it is natural t o expect that the problems associated with plasticization would be somewhat more complex. The actual degree of polarity of the polymers will be determined first by the selection of the polar group and second by the fractional occurrence of this group in the molecule. Where the polar group is present in the monomer-for example, acrylonitrile-its occurrence in a copolymer will depend on the relative rates of polymerization of the monomers and the degree of conversion of the combined monomers. The series of commercially available butadiene-acrylonitrile copolymers has a range of starting butadiene to acrylonitrile ratios from 85 to 15 to 55 to 45. Other structural factors which will determine t o a great extent the behavior of the rubber with plasticizers are: molecular weight distribution of the various polymer species; degree of linearity of the polymer-for example, 1,2 against 1,4 addition-and resulta n t crystallinity in the case of certain synthetic rubbers such as neoprene; separation of chains by bulky substituents such as .methyl groups, benzene rings, etc.; and combination in the polymer chain of residues from certain polymerization ingredients (catalysts, chain transfer agents). It is also possible to introduce polar centers a t various points in the polymer structure by aftertreatment with various reagents such as halogens. I n addition t o the structural features inherent in the original polymer, there are effects produced by various additives to the compounded rubber stock. The most outstanding of these is the , effect produced by carbon black in reinforcement of the rubber. The mechanical effects produced by this type of material are pronounced and they determine in many cases the need for plasticizer as well as its specific effects. The vulcanization process introduces additional structural changes into the polymer molecule. The exact character of these changes has been the subject of a large amount of research. It is believed by many that the primary reaction is one of cross linkage between adjacent polymer chains and that the effects on mechani-
I I 30 40 w PLASTICIZER- PARTS BY WEIGHT I 20
FIGURE I. EFFECT OF TYPICAL PLASTICIZERS ON PLASTICITY OF A NITRILE RUBBER
oal properties are the result of the extent of cross. linkage. This general belief is substantiated by the excellent work of Flow (If) on Butyl rubber. On the other hand, Farmer has shown with materials of greater unsaturation (IO)that cyclization can occur readily. The work of Stiehler and Wakelin ( d 7 ) led them to the belief that the introduction of polar centers into the polymer molecule was the primary effect and that the mechanical properties of the vulcanized product were the result of polar bonding between adjoining polymer molecules. Although the exact nature of the vulcanized rubber structure may still not be clanfied completely, it can at least be stated that the vulcanized rubber consists of a network of tangled polymer chains, which are bound together in some fashion at various points of contact. The effectiveness of a plasticizer will be a measure of the degree t o which it modifies this network structure. The effects of oxidation and other factors involved in the aging of a rubber product also are important in determining the apparent effects of plasticizers after such aging has taken place. This factor is one which has been overlooked by many workers in this field.
EFFECTS PRODUCED BY PLASTlelZERS Effects in Uncured Rubber. The effectiveness of plasticizers in uncured rubber stocks may be exhibited in several different ways: Increased plasticity may allow milling or mixing operations t o proceed more smoothly. Typical effects on plasticity are shown in Figure 1. I n many instances i t is difficult t o incorporate pigment into the stock without the assistance of plasticizer. In other cases the nerve of the rubber is reduced so t h a t it can be banded on the mill. An economic effect produced by plasticizers is a reduction in power consumption and often in mixing time, Alteration of the elastic-plastic deformation ratio has significant effects in processing operations such as extrusion or calendering. It is ossible by suitable lasticization t o control such items as s p e e a o f extrusion, calenfer shrinkage, grain, dimensional sta-
INDUSTRIAL AND ENGINEERING CHEMISTRY
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turn are dependent on certain specific characteristics of the plasticizers themselves. Such properties as vapor pressure, viscosity, melting point play an important part in determining ultimate behavior. Molecular weight and molecular structure of the plasticizer rn 54 are important as original determinants for some of these prop5 X = DIBUTYL PHTHALAT erties. The shape of the plasticizer molecule, especially the shape which it assumes in the plasticized composition, is also an important characteristic (26). Another type of property which is essentially derived from com- binations of the above direct properties of the plasticizer, but which also reflects the character of the polymer, is usually referred to as PLASTICIZER - PARTS BY WEIGHT PLASTICIZER-PARTS ay WEIGHT compatibility, sometimes as misciFIGURE 2 EFFECT OF VARIOUS P L A S T I C I Z E R S ON T E N S I L E STRESS A N D H A R D N E S S O F bility (16, 1 6 ) . I n other words, V U L C A N I Z E D N I T R I L E RUBBER compatibility is not an absolute property of either polyiner OK plasbility, etc. Many of these processing operations can be carried ticizer, but is a result of t h e specific combination of materials. out at lower temperatures v i t h plasticized stock, thus minimizing is another property which has been considered in detail t h e effectsof scorch (precure). for certain plsstic compositions, but which has been largely overhlodification of the deformation characteristics of the looked in the synthetic rubber literature. This is the matter of has a profound influence on the molding characteristics of the stock, especially when intricate mold designs are involved or efficiency which has been discussed in excellent fashion by Boyer when knitting of the rubber stock is a problem. and Spencer ( 9 ) . Both compatibility and efficiency are indicated The thixotropic character of cements and doughs may be influby their treatment to be ultimate functions of temperature coeffienced t o a great extent by the presence of specific plasticizers. cient of viscosity. General Effects in Cured Rubbers. The plast,icizer remaining in the rubber stock after vulcanization has been completed MECHANISM OF PLASTICIZER ACTION exhibits its effects primarily because it modifies the original netConsiderable attention has been devoted in the technical literawork structure of the vulcanizate. The specific effects are deterture t o problems associated with the mechanism of plasticizer mined by the individual plasticizers involved. action, but relatively little attention has been devoted t o the class Many of the plasticizers which are employed for their effect of -polymers being- considered here, probably because of the comon the uncured rubber stock have little or no effect on the s i m d e plexities previously noted. mechanical properties of the vulcanizate. Those materials which Numerous workers in the field of plasticization have attempted affect the finished product will in general: Decrease hardness and elastic modulus. Increase elongation (this is true only within certain practical limits). Produce a variable effect on tensile strength, resilience, tear resistance, and permanent set. Produce a variable effect on the rate of cure. Influence aging properties (the volatility of the plasticizer and its tendency toward oxidation are important factors). Improve low temperature flexibility in some cases and harm i t in others (a limiting factor is the polymer in this instance). Have variable effects on swelling properties of the composition. Some of these properties are illustrated in Figures 2 t o 4. Specific Properties of Plasticizer. Plasticizers are usually evaluated in terms of the effects which thcy produce. However, these in
P L A S T I C I Z E R -PARTS BY WEIGHT
PLASTICIZER- PARTS B Y WEIGHT
FIGURE 3 EFFECT OF VARIOUS P L A S T I C I Z E R S ON TENSILE STRENGTH A N D ELONGATION OF A VULCANIZED N I T R I L E R U B B E R
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
of dilution ratio measurements of the type employed by Doolittle (6) or even the swelling measurements used by D o t y a n d Zable (7) to determine the p values (polymer-plasticizer interaction constant) for a series of polyvinyl chloride plasticizers. Direct swelling measurements of vulcanized polymer in plasticizer are possible, as shown by Jones and Chadwick (15, 16), but calibration of the polymer itself is difficult unless suitable solvents are available for osmotic pressure measurements of polymer solutions. However, i t is possible to secure an evaluation of the system by indirect means ( 8 , I i ) . Swelling results have been reported by Jones and Chadwick (16,16) for vulcanized Hycar OR-15, a typical butadiene-acrylonitrile rubber. I n a series of n-alkyl phthalates, the swelling decreased regularly as the length of the alkyl chain increased, until a minimum was reached at the n-hexyl derivative, after which the swelling again increased. The parallel with the M value data reported by Doty and Zable (7) for polyvinyl chloride and with viscosity measurements on the same polymer reported by Frith (IS) is strong indication that a common effect must be occurring. The similarity of these effects is illustrated in Figure 5. In connection with swelling measurements the means by which the plasticizer enters the polymer molecule is important in determining the physical character of the resulting product. Table I shows data t o illustrate this point.
MATERIALS EMPLOYED AS PLASTICIZERS Available Information. The literature of plasticizers for the polar synthetic rubbers is extensive, b u t much of it is of relatively little value to those seeking to determine general relationships. PLASTICIZER -PARTS BY WEIGHT FIGURE 4. EFFECT OF VARIOUS PLASTICIZERS ON RESILIENCE VULCANIZED NITRILE RUBBER
TABLE I. EFFECTO F OIL IMMERSION ON PHYSICAL CHARACTERISTICS O F NITRILE-TYPE SYNTHETIC RUBBER Tensile 100% to group together all plasticizers for thermoplastics into two Strength, Stress Elongation, Lb./Sq. In. Lb./Sq. 'In. % broad classes-solvents and nonsolvents. This classification has been useful, but i t is obviously inapplicable directly t o the system Control (calculated on original dl2100 1350 200 mensions) of vulcanized rubbers, simply because there are few solvents for Control (calculated on final dimen1840 1180 200 sions) these materials. Plasticized stook (40 parts plasti1850 300 360 Jones and Chadwick (16, 1 6 ) have attempted to relate the becizer giving no volume change) havior of typical plasticizers in a vulcanized butadiene-acrylonitrile rubber t o the viscosities of the plasticizers. The data presented are limited and i t is believed that further 90 study of this particular factor would show that the indicated simple relation is not general. 96 Zhurkov and Lerman (18) reported * cdata for combinations of solvents with ul 102 butadiene-acrylonitrile polymers; these E tended t o support the senior author's 0 previous hypothesis that all plasticizers u108 (or sohents) are equivalent on a molar a In basis. Boyer and Spencer (8)have stated their belief that Zhurkov and Lerman's II 4 work was based on too few observations. Furthermore, it is extremely doubtful that theke generalizations could be 12.0 extended to the vulcanized state. I82 268 324 390 192 258 324 390 192 258 324 390 Methods of studying the entire polyMOLECULAR WEIGHT mer-plasticizer system employed by others FIGURE 5. EFFECT OF INCREASING CHAIN LENGTH OF N-ALKYL PHTHALATES ON for determination of the fundamental (01 PLASTICIZER ABSORBED BY A VULCANIZED NITRILE RUBBER [DATA OF characteristics of such systems cannot JONES (E)] be applied in unmodified form t o this (b) POLYMER- PLASTICIZER INTERACTION CONSTANT FOR POLYVINYL CHLORIDE DATA OF DOTY AND ZABLE ( 7 ) ] system, for reasons given earlier. This (c) VISCOSITY OF POLYVINYL CHLORIDE SOLUTION IN PLASTICIZER- SOLVENT BLENDS would be especially true in the case , [DATA OF FRITH t13)]
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No, 4
Strangely enough there is no simple standard procedure in use
TABLE 11. TYPESOF MATERIALSEMPLOYED AS PLASTICIZERSfor estimation of relative flexibility of various specimens. Most FOR POLAR SYNTHETIC RUBBERS observers rely on hardness (which is not a n accurate measurement A.
Hydrocarbons Coal tar distillates (chiefly aromatic hydrocarbons) Asphaltic fluxes Unsaturated hydrocarbons Polybutenes Cyclized or isomerized rubbers Resinous diolefin-styrene copolymers Terpene resins
B. Resins and polymers (not listed in A) Factice Vinyl resins Phenolic resins Alkyd resins Rosin and its derivatives Coumarone-indene resins
Esters Esters of dibasic acids (phthalates, adipates, sebacates, succinates, maleates, pelargonates, carbonates) Esters of monobasic acids (benzoates, ricinoleates, stearates, oleates) Esters of dihydric alcohols (triethylene glycol and other polyethylene glycol derivatives) Esters of tribasic acids (phosphates, citrates, aconitates) hliscellaneous esters
D. Miscellaneous chemical types Nitriles Ethers Amides Carbamates Halogen compounds Thiophenols Phenols Sulfides Nitro compounds Amines Ketones
Patents in this field are numerous and there are several extensive plasticizer studies in the trade literature (2, 4,5, 8, 9, 12, 14-29, ?&I 25). Several points become apparent when a n a t t e h p t is made t o study the available information. Several screening-type studies have limited themselves t o comparative evaluations of a series of plasticizers in a single concentration with a standard recipe. Such a procedure is of value in eliminating materials which are incompatible, highly volatile, or otherwise objectionable and in establishing the relative degree of efficiency. I t s use in arriving at broad, general conclusions concerning relative effectiveness of widely diversified types of materials is hardly justified, however. It is the author’s belief t h a t all materials of definite interest should be evaluated over the entire useful range and should be compared with one another on the basis of efficiency-for example, other properties can be compared t o compositions of the same flexibility or hardness. This practice has been followed in the case of vinyl and i t is encouraging t o note that a n effort chloride plastics (M), has been made t o do something similar with the nitrile rubbers (8, 22) and t o a limited extent with neoprene. The effort of Patton and Smith (22) t o establish a graphical method of evaluation in which the relations of several variables can be seen simultaneously is a step in the right direction and should be encouraged by all means. Much of the available information is based on single tests, even though these may have been carried out in duplicate or triplicate. Many of the standard tests which are employed in various laboraLories suffer from this deficiency. Any test which depends for its net result on a series of measurements is advantageous in this respoct, even though i t may be less convenient t o employ. A good example of the desirable type of test is the A.S.T.M. procedure for determination of Young’s modulus st low temperature ( 1 ) . Relatively little information obtained with this test is available in the literature (.4] 18),especially concerning plasticizer concentration, although it might be assumed that, the general trend of low temperature properties indicated by Boyer and Spencer ( 3 )would be observed. This procedure is rather tedious and kime-consuming.
with standard durometers) and simple stress determinations a t a predetermined elongation, such as 200%. It is impossible to estimate small differences by either of these methods and extrapolation of results with a single plasticizer concentration t o those at some other concentration might lead t o large errors. Examination of available information reveals that certain chemical types of materials have been employed as plasticizers for this class of synthetic rubbers. A few general statements may be made concerning their effects, although many of the data are too limited to permit more than tentative conclusions and many others have been obtained with procedures having large experimental errors, so that small differences lose their significance. The general groups of materials employed may be classified as in Table 11. It should be borne in mind t h a t many of the compounds employed possess more than one functional group and consequently would be found in more than one place in a classification such as this.. Analysis of Literature. The specific effects of the various types of materials for which information is available may be summarized as follows: COMPATIBILITY.Ethers, ether-esters, nitriles, and unsaturated compounds are highly compatible with all polymers of this class. Limited compatibilit depending both on the specific plasticizer structure involveJ’and on the particular polymer, is shown by saturated hydrocarbons, compounds possessing free hydroxy groups, and by esters containing hydrocarbon chains of greater than 8 to 10 carbon atoms in length. Aromatic materials a r e in general more compatible than the analogous alilshatic structures. EFFICIENCY. Materials of low molecular weight and especially those of low viscosity are highly efficient. Poor plasticizing efficiency is shown by materials of high molecular weight, especially when this factor is coupled with high visrosity. Resins are almost always inefficient. Those materials which possess limited Compatibility are usually inefficient within their comlsatible range. EFFECT O S PROCESSIXG CHARACTERISTICS. Most plastiCiZerS assist processing in some fashion. T h e most outstanding include certain amides, certain carbamates, many resins, some esters, some aromatic hydrocarbons, certain phenols, many amines, and numerous sulfur compounds. EFFECTO K CURE. This effect is difficult t o evaluate, inasmuch as the particular curing recipe involved will determine the specific results. Some amines are known t o accelerate cure and retarding effects have been reported for many resins (especially coumaroneindene resins), unsaturated compounds, acidic materials, phenols, and some of the esters of longer chain alcohols. PmirAmrvcE. Polymeric and resinous materials and various processed natural oils are t h e most permanent, possibly because of their low mobility. The least permanent materials are thdse which combine high vapor pressure, low viscosity, and high diffusion rate in the polymer. Materials of low compatibility are usually nonpermanent, provided they possess sufficient mobility to migrate to the surface and sufficient vapor pressure t o evaporate at t h a t point. Rate of diffusion in the polymeric composition is a n important property, but unfortunately quantitative data are lacking. AGING. It is almost impossible t o generalize concerning the
P R O D U C E D B Y PLASTICIZER ON TABLE 111. VhRIABLE EFFECTS SWELLING OF NITRILE-TYPE SYNTHETIC RUBBERIS HYDROCARBON
Plasticizer (50 Parts/ 100 Polymer) None (control) Castor oil Dibenzgl ether Dibutyl sebacate Diisobutyl adipate Asphalt Brown factice Light process oil Coumarone-indene resin Selected alkyd resin
Volume Swell in Hexane, r0 G.l 12.5 -17.4 -10.8 -12.5
12.5 -10.8 14.1 17.4
INDUSTRIAL AND ENGINEERING CHEMISTRY
effects of plasticizers on the aging of rubber compositions. A few have definite inhibitory effects on oxidation; some amines and phenols are outstanding in this respect. SWELLING IN HYDROCARBON FLUIDS.Swelling of the rubber composition in hydrocarbon fluids is increased by the presence of materials of high viscosity, which presumably cannot be extracted readily by the fluids. Resins and natural oils are outstanding examples of this class. Swelling is decreased in some instances by the presence of materials of low viscosity and high degree of efficiency, including certain nitriles, esters such as dibutyl sebacate and diisobutyl adipate, and certain coal t a r distillates; these materials presumably are extracted by the fluid in question. Typical data illustrating these effects are shown in Table 111. WATERRESISTANCE. Although many plasticizers are relatively insoluble in water, practically all have a deleterious effect on water resistance of the vulcanized rubber composition. The worst in this respect are those which are water sensitive themselves, such as those containing ether or hydroxyl groups. An exception t o this general effect has been noted in the case of neoprene (1%). EFFECTON STRESS-STRAIN PROPERTIES. A few plasticizers show reinforcing effects in the rubber compositions. These are chiefly resinous materials which function a s processing aids and a part of their effect may be simply t h a t of facilitating the fabrication of a more homogeneous composition. A few materials exhibit a weakening effect on the rubber; examples are acidic materials, halogen compounds, and materials of low compatibility. EFFECT ON RESILIENCE. Those materials which have the most outstanding effects i n improving resilience of the rubber composition are chiefly low viscosity liquids, including some esters and ethers and a few nitro compounds. Low TEMPERATURE FLEXIBILITY. The most outstanding materials in improving this characteristic are those of low molecular weight and low viscosity, including especially some ethers, nitriles, and esters containing relatiyely ehort hydrocarbon chains. Poor low temperature flexibihty 1s Imparted by cyclic materials, many resins, halogenated compounds, and phenols. There are many other properties of interest and importance, but the available information is both limited and confusing. It can safely be stated t h a t there is room in this field for extensive additional work. Many of the principles and general observations are similar to those of the plasticized thermoplastics and any advances in general knowledge will assist in elucidating some of the puzzling problems existent in t,he field of plasticized polar qmthetic rubbers.
LITERATURE CITED (1) Am. SOC.Testing Materials, Designation D 797-44T (1944). (2) Baker Castor Oil Co., “Baker Plasticirers for Synthetic Rub-
bers” (1945). (3) Boyer, R. F., and Spencer, R. S., J . Polymer Sci., 2, 157 (1947). (4) Conant, F. S., and Liska, 3. W., J. Applied Phys., 15, 767 (1944). (5) Crossley, R. H., and Cashion, C. G., Rubber A g e (Ar. Y.), 58,197 (1945). (6) Doolittle, A. K., J . Polymer Sci., 2, 121 (1947). (7) Doty, P., and Zable, H. S.,Ibid., 1 , 90 (1946). (8) du Pont, E. I. de Nemours and Co., Inc., Rept. BL-53, (Nov. 6, 1942). (9) Ibid., Rept. BL-79 (Feb. 10, 1943). (10) Farmer, E. H., and Shipley, F. W., J . PolymerSci.,.l, 293 (1946): Rubber Chem. and Technol., 20. 341 (1947). (11) Flory, P. J., IND. ENG.CHEM.,38,417 (1946): Rubber Chem, and Technol., 19, 552 (1946). (12) Fraser, D. F., Neoprene and Rubber Compounding Report 41-2. E. I. du Pont de Neinours & Co. (1941). (13) Frith, E. M., Trans. Faraday Soc., 41, 90 (1947). (14) Goodrich, B. F., Chemical Co., Hycar Blue Book (1944). (16) Jones, H., Trans. Inst. Rubber I n d . , 21, 298 (1946); Rubbep Chem. and Technol., 20,184 (1947). (16) Jones, H., and Chadwiok, E. C., J. Oil & Coolour Chemials” Assoc., 30,199 (1947). (17) King, G. E., IND. ENG.CHEM.,35, 947 (1943). (18) Liska, J. W., Ibid., 36, 40 (1944). (19) Moll, R. A., Howlett, R. M., and Buckley, D. J., Ibid., 34, 1284 (1942). (20) Morris,’R. E., Hollister, J. W., and Seegman, I. P., Rubber Age ( N . Y.), 56, 163 (1944). (21) Patton, T. C., and Smith, M. K., I n d i a Rubber World, 116, 643 (1947). (22) Patton, T. C., and Smith, M. K., Ibid., 115, 666 (1947). (23) Reed, M. C., IND.ENG.CHEM.,35, 896 (1943). (24) Stanco Distributors, Inc., Perbunan Compounding and Processing (1942), (25) Starkweather, H. W., and Walker, H. W., I n d i a Rubber World, 96,43 (1937). (26) Stickney, P. B., and Cheyney, L. E,,J . Polymer Sci., 3, 231 (1948). (27) Stiehler, R. D., and Wakelin, J. H., IND. ENQ.CHEX.,39, 1647 (1947). (28) Zhurko;, S. N., and Lerman, R. L., Compt. rend. acad. sci., U.R.S.S., 47, 106 (1945). RECIBIVEDJuly 8. 1948.
PLASTICIZERS IN VINYL CH LORIDE-ACETATE RESINS M. C. REED AND JAMES HARDING Bakelite Corporation, Bound Brook, N. J.
Results of the evaluation of 64 plasticizers in a vinyl chloride-acetate copolymer resin are presented. The test methods are discussed briefly. Tensile strength, elongation at break, extensibility at 25” C., brittle temperature, low temperature stiffening characteristics, volatile loss, oil and water resistance, and compatibility with the resin are tabulated. Supplier, molecular weight, specific gravity, refractive index, viscosity at two temperatures, boiling range under reduced pressure, and color are given for most of the plasticizers. The migration of plasticizers from vinyl sheetings into surface coatings is discussed, and a test method for evaluating this property is described. Test results for seven plasticizers and four types of surface coatings are given. The migration of four plasticizers into polystyrene was studied. Polymeric plasticizers are surveyed briefly.
WIDE variety of nonvolatile or high boiling materials has
been used for the plasticization of vinyl chloride-acetate copolymers. T h e physical and chemical properties essential to satisfactory performance have been discussed at length in earlier papers in this series and by other writers. Sales promotion literature now frequently contains much useful information, such as chemical composition, boiling range or vapor pressure, and physical properties of vinyl compounds containing the plasticizers being offered for sale. One of the objectives of the present paper is t o list a group of plasticizers, not previously discussed, together with the p r o p erties and behavior of these plasticizers when used in vinyl chloride-acetate copolymer resins. A resume of high molecular weight materials used for the plasticization of vinyl polymers fa also included.