Properties of Plasticized Polyvinyl Chloride Compositions D. K . RIDER', J. K. SUMNER2, AND R. J. MYERS Resinous Products Division, R o h m & Haas Company, Philadelphia, Pa.
19 number of plasticizers have been studied over wide ranges of concentration in polyvinyl chloride and in copolymerized vinyl chloride-vinyl acetate resin. Properties of the plasticized compositions have been plotted as functions of plasticizer coricentration. A method of molding test slabs was developed which produced slabs free of shrink marks and other imperfections and with a minimum of residual strain.
T
HE importance of a plasticizer in polyvinyl chloride and in
copolymerized vinyl chloride-vinyl acetate resin is second only to that of the base material. The kind and amount of ip1astic;zer to a large degree determines the properties of the plasticized composition. For these reasons it is of great interest to a compounder of such compositions t o have available a backlog of knowledge on the effects produced on compound properties by various kinds and amounts of plasticizers. The object of this work was to collect data on vinyl chlorideacetate copolymer compositions (copolymer, as used in this paper, designates the copolymerized vinyl acetate-vinyl chloride resin) plasticized with a number of widely varying types of plasticizers, over a range of concentrations; the results are presented in the form of plots of compound properties against plasticizer concen; tration. The data cover a wide range of concentration a t close intervals so that deviations from expected normal behavior are disclosed. A somewhat less comprehensive program was carried out using polyvinyl chloride resin. During the course of the work a method of molding was developed which produced slabs more satisfactory for test purposes than the method formerly used.
did not prove reliable enough t o produce consistently satisfactory molded specimens for test purposes. The slabs frequently showed shrink marks and invariably were strained to a greater or lesser degree depending on the kind and concentration of plasticizer. Molding method B, however, gave slabs with nearly perfect surfaces and with a minimum of residual strain. The amount of strain was found by experiment (annealing) to be low enough so as not to affect the results by more than the amount of probable experimental error, Thus the molded slabs were used directly, without annealing t o relieve strain. The effect of annealing (measured by 1 0 0 ~ modulus) o t o relieve strains in samples made both by methods A and B is shown in Tables I and 11. The following properties of the plasticized compositions were determined: 100% modulus; tensile strength; ultimate elongation; Lupke resilience; Shore durometer hardness; and brittle temperature. The ranges of concentrations over which the various tests were carried out for the several plasticizers were originally planned to be those which produce compounds with 100% moduli from about 500 t o 2000 pounds per square inch. With some of the plasticizers, however, the ranges were extended
TABLEI. EFFECT OF
loo'%
Modulus, Condition Lb. per Sq. In. Strained 1365 Annealed 1230 Paraplex AP-27b Strained 1785 Annealed 1610 Paraplex G-25 Strained 1745 Annealed 1635 4 All stocks contain 35% plasticiaer. b Experimental resinous type plasticizer, Plasticiaera Dicapryl phthalate
POLYVINYL CHLORIDE-POLYVINYL ACETATE COPOLYMER
The copolymer chosen for the first part of the work was 95% -vinyl chloride and 5% vinyl acetate (Vinylite VYNW, supplied by Carbide and Carbon Chemicals Corporation, New York, N. Y.). The generalized formulation (100 parts by weight) was as follows: copolymer, 98.5 - X ; basic lead carbonate, 1.0; stearic acid, 0.5; and plasticizer, X . Fillers were omitted from the formulation so that the compound properties would be a function only of the kind and amount of plasticizer used. The basic lead carbonate was used as a stabilizer and the stearic acid as a mill-release agent. The amounts of these two latter materials were kept constant for the same reason khat fillers were omitted. Moreover, heat stability and milling behavior were of no particular interest in this work. The plasticizers studied were: dibutyl sebacate; dibenzyl aebacate; dioctyl (2-ethyl hexyl) sebacate; plasticizer 35 (amide of long chain fatty acid); plasticizer 36 (amide of long chain fat acid); dicapryl phthalat#e; dioctyl phthalate; tricresyl phosphate; and Paraplex G-25 (polyester type). Physical data o n these plasticizers have been described previously ( 8 ) . The batches were prepared and milled as follows: Two molding techniques (A and B) were tried. Method A 1 2
STRAIN
(Molding method A) Decrease in Modulus on Annealing, Lb. per Sq. In. 133 175 110
TABLE 11. EFFECT OF STRAIN (Molding method B) 100% Decrease in l O O q Modulus Modulus on Anneal&:, Condition Lb. per Sq. 'In. Lb. per Sq. In. Strained 720 Annealed 675 45 Dibenzyl sebacate Strained 970 Annealed 990 20 Dioctyl sebacate Strained 1020 Annealed 985 35 Dicapryl phthalate Strained 1350 Annealed 1285 65 Plasticizer 35 Strained 705 Annealed 670 35 Strained 750 Plasticizer 36 Annealed 725 25 Paraplex G-25 Strained 1785 Annealed 1725 60 Paraplex AP-27 Strained 1730 Annealed 1700 30 Diootyl phthalate Strained 1175 Annealed 1130 45 Trioresyl phosphate Strained 1500 Annealed 1425 75 a All stooka oontsin 35% plasticizer.
PlasticizerQ Dibutyl sebacate
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Present address, Bell Telephone Laboratories, Inc., Murray Hill, N. J. Present address, Chicopee Manufacturing Corporation, Milltown, N. J.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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20 c
G-25=Paraplex G-25
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DCP=Dicapryl Phthalate
1800 DOS-Dioctyl Sebacate D8zS:Dibenzyl Sebacate
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Figure 2
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1 Plasticizer 25
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Concentration. Weiaht Pe; Cent
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Figure 1. Plasticizer Concentration us. 100% Modulus
a t both ends in an attempt to obtain a more complete picture, which it was hoped would provide an explanation of the unexpected results obtained. The ranges of concentration actually used in the tests are shown in the plots. After this work had been completed, it became evident that the resilience curve of the tricresyl phosphate stocks was different From that of the other monomeric types in that it had the lowest minimum and the greatest displacement to the right (Figure 4), To find out whether this was typical of the phosphate group, which is relatively more closely packed, or spherical, than the straight chain groups of the other plasticizers examined, trioctyl phosphate was used a t several different levels in the copolymer, and Lupke resilience of the stocks was measured. The results of this work with trioctyl phosphate are sho-m in Figure 3. Milling Procedure. The ingredients were weighed and dryblended by hand. Batch (400grams) was charged to a 6 X 12 inch laboratory rubber mill heated with steam to about 300" F. After the resin was fluxed, it was allowed to mill with a rolling bank for 5 minutes with occasional cutting. The batch was then sheeted off the mill a t 0.06 or 0.10-inch thickness, depending on whether molding method A or B was to be used. Molding Method A. This operation was carried out in a standard A.S.T.M., four-cavity mold (D 15-41) yielding slabs 6 X 6 x 0.075 inch. Two plies of stock 0.06-inch thick and approximately 5 inches square were used. The molding cycle was 10 minutes a t minimum ram pressure a t 150" C., then 10 minutes a t 900 pounds per square inch a t 150" C. The stock was charged to a cold mold. The samples were cooled under pressure in the mold. Molding Method B. Squares 6 X 6 X 0.100 inch were used in the same mold as above, one piece to each cavity. Each was carefully enclosed in cellophane before placing in the mold cavity. Here again, the stock was charged to a cold mold. The temperature was regulated to a given point (from 141O to 168" C., depending on the softness of the stock), and the mold charged to the press. Minimum rain pressure was applied for 10 minutes, then full pressure (900 pounds per square inch) for an additional 10 minutes. The mold was cooled slovly under full pressure until it was cool enough to be handIed with bare hands. Test for Strain. Samples of molded slabs were laid on glass plates and exposed to a temperature of 120" C. for 30 minutes
in an oven. They vere then examined for dimensional changes. warping, and roughness. 100% Modulus. This property was determined on a Scott tester Model IP-4. Temperaturr and humidity of the room were controlled to 70" * 2" F. a t 65 * 2% relative humidity, respectively. Samples were conditioned a t least 16 hours before testing. The rate of loading varied mith several factors but averaged 200 pounds per minute (10,600 pounds per square inch per minute, on initial cross-section) Dumbbell-shaped specimens (A.S.T.U. D 41231, die C) were used. The 100% modulu8 was the load recorded at 100% elongation and computed to nominal unit stress. Tensile Strength and Ultimate Elongation. These properties were determined on a Model DH-2 Scott tester under the same temperature and relative humidity conditions as were used with the 1 0 0 ~modulus o test and with the same type of samples. The rate of jaw separation was 12 inches per minute. For measurement of elongation, the specimens were bench-marked with a 0.5-inch die, the grips adjusted a t zero load 0.75 inch apart, and the elongation measured by means of a decimal scale held close t o the specimen. The limited maximum jaw separation of about 10 inches on this particular machine made the use of the normal self-tightening clamps impossible. This was also the reason for the use of 0.5-inch bench marks for measuring elongation instead of the customary 1-inch marks. Lupke Resilience. The Lupke impact resiliometer ( 3 ) way used. The target was attached rigidly to a solid wall, and independent of the frame, so that no energy was lost as vibration transmitted to the frame. The samples were disks 1.625 inch diameter by 0.25 inch thick. TTO disks in close contact mere used in each determination. Samples were conditioned a t the test temperature (70" * 2' F.) a t least 16 hours before testing. Shore Durometer Hardness. These values were obtained using the Shore A durometer (A.S.T.M. D 67644T). Rlultiple readings were taken on each specimen, Samples were conditioned a t least 16 hours a t 70" * 2 " F. and 65 =t 2% relative humidity before testing. Brittle Temperature. The instrument used to determine these values was that described under A.S.T.M. D 746-43Twith the minor differences that the breaker bar was located across the top of the box instead of beneath the surface of the liquid coolant (methanol), and a toggle-screw clamp was fixed on the quadrant to hold the specimens. The specimens were allowed 2 minutes t o reach equilibrium temperature in the bath prior to sets of Paraplex G-25 samples were tested. The testing, TTTO first set was preconditioned in methanol for 1.5 hours a t - 15' C., and the second set was preconditioned in air for 15 to 18 hours a t - 15 C. The longer conditioning time with the samples containing Paraplex G-25 was necessary to obtain consistent equilibrium values, and to study the time effect. ~
DISCUSSION OF RESULTS
Effect of Strain. The results in Table I show that wherr molding method A was used, the effect of annealing the samples
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
45 1 0 0 ~ omodulus by an appreciable amount. Moreover, the annealed stabs were usually so misshapen aqd rough 40 that they were unfit for further testing. In 35 Table I1 a comparison of the moduli of strained m d annealed slabs molded by molding method B shows that there was no substantial ad30 vantage to be gained by annealing. For this reason it was decided t o conduct all tests on 25 unannealed slabs molded by method B-that is, slabs taken directly from the mold with no 20 further treatment before testing. Method B had the further advantage of producing slabs 15 .with no shrink marks. 1 0 0 ~ oModulus. Figure 1 shows that all 10 the plasticizers tested behaved similarly in the copolymer VYSW; the only difference was in 5 their relative plasticizing efficiencies. Between 25 and about concentration, 100% modulus changes rapidly. Tensile Strength. Except for the posslble existence of plateaus in the curves of Figure 2 it could be said that within the limits studied, tensile strength is inversely proportional to concentration. Lupke Resilience. The curves of Figures 3 and 4, generally speaking, are concave upward, and the least resilient stocks are those with moderate amounts of plasticizer. The minima on the curves, representing stocks of maximum hysteresis, occur a t the plasticizer concentrations most commonly used, The major dips on the curves, occurring in the range of 30 t o 50% plasticizer, are reproduced in miniature a t about 5 to 10% plasticizer. At high plasticizer Concentrations it would be expected that after maximum resilience had been reached, the values would fall off again finally to zero. Although the minima on all the curves occur over a limited range of plasticizer concentration, there are important differences among the various plasticizers. Thus, the dioctyl sebacate and trioctyl phosphate curves have the highest minima, indicating that they are the most generally useful plasticizers, as far as resilience is concerned, over the most common range of concentration. For maximum resilience a t moderately high plasticizer concentration, plasticizer 38 is outstanding. Paraplex G-25 and tricresyl phosphate do not impart good resilience except a t low concentrations. The minimum resilience value for the tricresyl phosphate stocks is the lowest of any of the stocks tested. The practical value of high resilience is obvious in those applications wherein the polyvinyl compound is replacing rubber. In an attempt to explain the character of the resilience curves, the values were plotted against molal c o n c e n t r a t i o n of p l a s t i c i z e r (not shown). The minima fall together somewhat, with the important exceptions of tricresyl phosphate and Paraplex G-25. The molecular weight of the latter is so high in comparison with those of the other plasticizers that in order to get its curve on the same plot, an effective molecular weight of 500 had to be assumed. Justification for this assuniption is based on the fact that, judged by a number of its properties, Paraplex G-25 behaves as a plasticizer of much lower molecular weight. This suggests that Paraplex G-25 functions as a plasticizer a t more than one position in its molecule. The minimum for the tricresyl phosphate curve fell considerably to the right of the others. As previously
711
was to lower the
Figure 3
mentioned, to find out whether this peculiarity of the tricresyl phosphate resilience curve was characteristic of the phosphate group, another series of stocks was mixed, using trioctyl phosphate a t three concentrations. The results, as presented in Figure 3, indicate that the phosphate group probably does not account for the unique position occupied on the plot by the tricresyl phosphate curve, in spite of the fact that the phosphate molecule is relatively closely packed and more nearly spherical than the straight chain molecules of the other plasticizers tested. Six of the plasticizers can be grouped in pairs, as far as resilience is concerned. Both members of each pair have resilience curves which are similar, and quite close together. These pairs are plasticizers 35 and 36; dicapryl phthalate and dioctyl phthalate; and dioctyl sebacate and trioctyl phosphate. Concerning the lateral position of the minima on the resilience curves (Figures 3 and 4), those plasticizers generally considered t o be good solvents of polyvinyl chloride or copolymer give curves whose minima appear a t lower plasticizer concentrations, and the known poor solvents for the resin-namely, tricresyl phosphate and Paraplex G-25-produce stocks whose curves lie a t the other extreme. There is a tendency also for the minima t o become flatter when they fall a t the higher plasticizer concentrations. Dioctyl sebacate and trioctyl phosphate are possible exceptions. At any rate, whatever effect takes place in the resin as plasticizer ccuncentration increases, takes place a t a rate approximately proportional to the soIvent power of the plasticizer. The miniature
Figure 4
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INDUSTRIAL AND ENGINEERING CHEMISTRY
dips at low plasticizer concentrations may be a resonance effect due to the low molecular weight fractions in the resin. It was thought that the back anvil effect of the target on the resiliometer might account for the high values obtained a t the higher plasticizer concentrations, since with these softer stocks i t might be expected that the target would contribute the major portion of the resilience values. That this assumption was not correct, however, was shown by a blank test on the target; this gave a resilience value of only 20%.
IO
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Figure 5
The shape of the resilience curves is not characteristic of the particular instrument used because exactly similar curves (not shown) were obtained on several of the compounds, using a Yerzley oscillograph (4). I n this latter instrument the sample is under compression continuously during the test. The Lupke resiliometer is of the rebound type. Shore Durometer Hardness. The curves shown in Figure 6 indicate that for all practical purposes a straight line relation exists. The lines are essentially parallel except at the extreme ends of the durometer scale, where the accuracy of the instrument is questionable. At any given plasticizer level the hardness of the stocks falls in the order of the plasticizing efficiency (lOOyo modulus) of the various plasticizers, the less efficient giving the harder stoclrs. Hardness then might well be used as a rapid measure of plasticizer efficiency. Brittle Temperature. I n Figure 6 also, there is almost a straight line relation, but there is a slight concavity upwards in all the curves. The excellent low temperature properties of dibutyl sebacate, dioctyl sebacate, and plast,icizer 36 are clearly shown, as well as the poor p r o p erties of tricresyl phosphate. The curve for p&ticizer 35 is flatter than the others, undoubtedly because of the limited compatibility of this plasticizer at low temperatures. Thus during immersion in the liquid coolant prior to testing, the plasticizer that has spewed out to the surface of the sample is dissolved off, and the brittle value obtained is that for a sample containing less than the nominal amount of plasticizer. If the reciprocal of the brittle temperature is plotted against the square root of the polymer concentration (Figure 7), good linear relation is shown, similar to the findings of Boyer ( 1 ) on other plasticized polyvinyl chloride systems. The empirical reFigure 6 lation derived by Boyer, form-
Vol. 41, No. 4
ing basis of this method of plottingis .\/Wi= D - (E/B?'m) where W Z = weight fraction of the polymer in the compound; D, B are constants; E = energy of activation for viscous flow and Trn = brittle temperature.
POLYVINYL CHLORIDE The work wit'h polyvinyl chloride, for the most part, was carried out using the same plasticizers as with the copolymer, and similar tests were run, using identical test methods. The material chosen for this work was Geon 101, supplied by The B. F. Goodrich Company, Akron, Ohio. The generalized formulation was the same as for the copolymer. Milling and molding techniques also were the same, and full advantage was taken of the improved molding procedure developed during the course of the work with copolymer. I n an attempt bo correlate the anomalous behavior of some of tJhe plasticizers in polyvinyl chloride with thermodynamic changes, specific gravity measurements were made on a series of dioctyl sebacate compounds, and the values plotted against plasticizer concentration. A Kraus balance was used for the specific gravity determinations. Addit,ional work also done with polyvinyl chloride and not with the copolym&-was the determination of certain electrical properties (dieleckic constant, power factor, and loss factor, all a t 60 cycles, 1 kilocycle, and 1 megacycle per second, and arc resistance and dielectric strength), on a series of dioctyl sebacate compounds. Dielectric constant and power factor a t the three frequencies were plotted against plasticizer concentration. The methods used were as follows: Dielectric constant and power factor, A.8.T.M. method D 1BO-44T. Dielectric strength, A.S.T.M. method D 149-44: temperature, 25' C.; electrodes, 2inch diameter under oil; rate of rise of voltage, 1 Idovolt per second; sample thickness, 0.075 to 0.085 inch. Arc resistance, A.S.T.M. method D 495-42. DISCUSSION OF RESULTS
100% Modulus. The curves of Figure 8 arc similar to those obtained for the copolymer compounds. The fiexibilizing action of Paraplex G-25 is practically equivalent to that of tricresyl phosphate. Dibutyl sebacate stands out as the most efficient plasticizer tested. The curves for plasticizers 35 and 36, dioctyl sebacate, and dioctyl phthalate are drawn as broken lines b e cause only two points were available to determine these curves. Tensile Strength. The dip in the dioctyl sebacate curve (Figure 9) at, 35% concentration makes t#his plasticizer excep-
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Temperature,
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713
tional, but this is in keeping TENSILE STRENGTH O F COPOLYMER-PLASTICIZER COMPOSITIONS TABLXI 111. ULTIMATE with certain other irregularities Ultimate Tensile Strength, Lb./Sq. In. noted with this ester. Its tenPlasticizer, Dibutyl Dibenzyl Dioctyl Diaapryl Plasticizer Plasticizer Paraplex Diootyl Tricresyl sile strength would make it apsebaoate sebacate sebacate phthalate 30 36 G-25 7' phthalate phosphate pear to be an efficient plasti50 ... ... ... ... ... 1605 ... ... ... 1885 ... 45 ... 1625 cizer of the order of dibutyl 1925 2080 it320 42.5 ... ... ... ... ... sebacate and the amides. I t s 1540 1970 2'1'60 i465 40 ... 1490 2340 2000 2480 ... ... ... 37 ... 2655 ... 2780 efficiency, however (as shown 2520 2310 1990 1950 35 2705 is35 2575 2655 2955 ... ... ... 33 ... ... by Figure 9), although good, is ... 2940 ... ... 2880 ... . . . 32.5 . . . ... 3150 not so extreme as the best of the 2625 32.0 2965 ... ... 2790 ... 2455 2985 2GO 2750 ... 31.0 ,.. ..* series. 2485 2970 2725 ... ... 29l.O 30.0 ... 3390 if395 29.0 . . . ... . . . 2695 Whether the inflection in ... ... 3305 ... ... 28.5 ... ... 3300 ... the dioctyl sebacate curve is 2960 ... ... . . . . . . ... 28.0 ... ... 2790 ... 27.5 ... 3390 really a dip, or a plateau, is 2625 3290 2530 3245 27.0 3370 ... ... 3300 ... open to question, and can be 3225 ..* ... ... ... 25.0 ... 3115 3040 3040 3700 ... . . . 24.0 . . . . .. decided only by testing a num3430 3330 3470 22.5 ... ... ... ber of additional stocks varying over small intervals of plastiTENSILESTRENGTH AND ELONGATION OF PLASTICIZER-POLYVINYL TABLEIV. ULTIMATE cizer concentration. At any C H L O R I ~COMPOSITIONS E rate the inflection represents a Ultimate Tensile Strength, Lb./Sq. In. and Elongation, %' deviation from normal beDioctyl Plasticizer Plaaticizer Diootyl Plasticizer, Dibutyl Dibenzyl Dicapryl Paraplex Tricresyl G-25 sebacate 35 36 phthalate phosphate havior, and is as yet unexl % sebacate sebaoate phthalate ... ... 1635-360 ... ... ... 50 ... plained. ... ... 1585-345 1980-335 ... ... ... ... 45 The curves for plasticizers 35 , . . ... ... 202;-345 44.5 ... ... 40 1580-i 15 201'0-345 2 030-3 15 2390-350 1570-260 ... 2375-295 and 36 are drawn as broken 1725-260 ... ... ... . . . ... 37.5 ... ... lines because only two points ... ... 2630-8 10 1375-'160 ... ... ... ... 37 ... 2015-360 2480-315 2515-265 2800-335 { 1600-200 2005-270 1945-895 2495-326 2910-270 35 determine each of them. The ... ... 2850-280 2855-355 ... 33 ... ... data from which the curves ... 2100-200 ... ... ... ... ... 32 have been constructed are 2840-265 ... ... ... ... 31 . .. 3025-280 ... . . . 2895-285 242';-270 . . . 30 ... given in Table IV. ... 2660-275 . . . 3200-250 ... ... 28 ... 3260-250 ... ... 28a'0-280 27b:d-iQO ... ... 2730-280 27.5 Ultimate Elongation. Fig... ... ... 26 ,.. ure 10 shows exceptions to ex... 2910-240 ... ... ... ... 2890-255 3466-220 25 ... ... ... ... .,. 3000-255 ... 23 pected normal behavior y i t h ... 3180-240 ... ... ... ... ... ... 22.5 Paraplex G-25 and with dioctyl First figure is ultimate tensile strength; second figure is elongation. sebacate, especially the latter. The minima in both the elongation and tensile curves for diplace. Curves over a range of temperatures might show a temoctyl sebacate occur a t the same plasticizer concentration. The perature below (or above) which such behavior does not occur. data for the curves appear in Table IV. To a somewhat lesser degree, the curve for Paraplex G-25 It may be that the plasticizer-resin relation with dioctyl shows a similar dip. sebacate is different in some ways from that of the other plasBrittle Temperature. The dioctyl sebacate curve of Figure 11 ticizers, with the possible exception of Paraplex G-25. From the gives further proof of the abnormal behavior of this plasticizer peak of the dioctyl sebacate curve to the minimum point, inin polyvinyl chloride. It is apparent that t o gain the full benefits creasing amounts of plasticizer operate t o lower the elongation, of its good low temperature properties, it is necessary t o use it in whereas beyond the minimum point the opposite effect takes amounts exceeding 36 or 37%. A 3575 dioctyl sebacate stock exhibits anomalous behavior in regard to all three properties thus far discussed with 100% polyvinyl chloridenamely, brittle temperature, tensile, and ultimate elongation. ..I
.
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Figure 8
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Figure 9
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Figure 10
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 41, No. 4
low plasticizer concentrations, similar to those obtained with the Brittle Temperature, e C. copolymer stocks. The indiPlasticizer. Dibutyl Dibenwl Dicapryl Paraplex Dioctyl Plasticizer Plasticizer Dioctyl Tricresyl cated drips &*erenot drawn in 0-25 sebacate sebacate sebacate phthalate 35 36 phthalate phosphate % because of lack of sufFicient data. 37 Below - 78 ... ... . ~ * 50 ~~' ,.. -39.5 28 45 Below - 7 8 ... .. In Figure 14 the effect of tem. . . . . . . . ... 44.5 ... ... -17.5 perature on resilience is shown - 41 - 35 -23 -77' -74.5 40 . . ~ ... .. .. .. - 9.5 ... .. - 72 ... ... 37.5 ... ~ . . ... for a stock plasticized with di- I9 ... , . . ... ... 37 ... . . . -27.5 - 19 -'id -28 - 47 35 - 40 -55.5 -'30 - 0.5 benzyl scbacate. Similar results - 14 ... ... .(. ... 33 ... .. . .. ~ . . . .i. were obtained with other plasti- 24 - 45 ... ... 32 ... ~ . . -io.5 ... ... 31 . . ~ ... cizers. The most interesting -60.5 .. -'ii ... -'ii.5 30 ,.I ..l ... -17 - 42'. 5 ... ... 28 ... ... ... ... feature of these wives is the '13 5 7 , 5 . . . . . . 27.5 ... ... crossing over at the minimum .. ... ... ... - 32 -41 26 ... . . . -i ... - 35 -51 .., 25 . ~ . ... ... points. In the region to the left ... - 47 ... ... 23 ... ... .., ... -.19. . 22.5 .~~ ... ... of the crossoyer, the temperature coefficient of resilience is negative, whereas to the right i t is positive. This may indicate t>hat a t the niininiuni point a change in resin-plasticizer relation is taking place so that the type of resilience is different, on either side of the minimum. The point of intersection of the 'tn-o resilience curves may be t,aken as the arbitrary dividing line: to the left, of it lie compositions Fhose plastic properties are predominant, and t>othe right lie compositions whose elastic properties are predominant. A more obvious explanation of this data might be that a temperahre change merely results in a shift of the curve such as would be obtained by changing the plasticizer content -"by a small amount a t any given temperature. Resilience curves a t a number of t,emperatures would show whether they intersect Figure I1 at the same plast,icizer concent,ration. The plasticizer 35 curve is flatter than the others, again inSpecific Gravities of -25 dicating plasticizer spew a t the low temperatures. Dioctyl Sebacate Tmperotbre, 'C. Stocks. I n Figure 15 Over the ranges of concentration used, the curves for the other plasticizers are essentially straight lines, with approximately the resilience and elonequal slopes. With plasticizers 35 and 36, however, only two gation curves are inpoints determine the lines. The data are given in Table V. cluded with the specific. Effect of Preconditioning Time on Brittle Temperature. Paragravity curve for complex G-25 is a resinous material which nevertheless exhibits a tendparison. Although L x e r Cancentrotion, I weigi.1 l Per Cent l ency to crystallize. The rate of crystallization is slow, and the there is indication of a 30 35 41) 45 50 brittle temperature of a stock containing this plasticizer is a funcplateau in the specific tion of the degree of crystallization of the Paraplex G-25. The gravity curve a t 23 to Figure 12 highest (poorest) brittle temperature is obtained when crystallization of the plasticizer is complete. The curves in Figure 12 illustrate the dependency of brittle temperature on preconditioning time, for stocks containing slowly crystallizing plasticizers such as Paraplex G-25, Experience has sholyn that even 16 hours a t -15" C. is not time enough for crystallization to become complete, but these conditions have been adopted as standard in this laboratory because the results thus obtained seem to be reproducible to a satisfactory degree. Lupke Resilience. The curves in Figure 13 are of much the same nature as those obtained with the copolymer stocks, and similar comments apply. The curves are complete only for four plasticizers. The data showed indications of the presence of miniature dips at Figure 13
TABLE v. BRITTLETERfPERa4TURES O F
PLASTICIZER-POLYVINYL
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I
CHLORIDn COMPOSITIONS
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INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1949
718
25% plasticizer, which might be interpreted as evidence of a change of state in the plasticized composition, rigorous proof of such a change cannot be offered at this time. More accurate specific gravity data are needed for the series of stocks in question as well as for the series containing other plasticizers. Specific gravity curves (not shown) for some of the other series of plasticized stocks did not all show significant changes of slope in the region where anomalies occur. Moreover, Figure 15 shows that the lowest dip in the resilience curve does not occur a t the plasticizer concentration corresponding t o the indicated plateau in the specific gravity curve.
M y v i n y l Chloride with Dlcctyi Sebncnte
30
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PIost~clzer Concentrnticn, Weight Per Cent
0
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55
Figure 14
Figure 16
Electrical Properties of Dioctyl Sebacate Stocks. Electrical properties of these stocks were measured to find out whether any would exhibit sharp changes a t plasticizer concentrations where such changes were noted in resilience and elongation. However, no unexpected electrical phenomena manifested themselves in this study. The dieiectric constants at the three frequencies (Figure 16) show a general increase with increasing plasticizer content. This would be expected in view of the polar nature of dioctyl sebacate and of polyvinyl chloride. The shift of the maxima of the dielectric constant curves to the region of higher plasticizer concentrations as frequency is increased also is in agreement with expected normal behavior. The power factor curves also proved to be of littlesignificance i n e x p l a i n i n g the 20 25 30 35 40 Plasticizer ConCentrntiM, Weight Percent anomalies found in this work. The existFigure 15 ence of maxima and their shift to higher plasticizer concentrations as frequency is increased may be explained on the basis of the dipole theory and the effect on the dipoles of frequency and viscosity of the medium. The slight fluctuations in dielectric strength and arc resistance with plasticizer concentration were not significant, and indicated nothing of value in the attempt to correlate physical and electrical properties. The values were not plotted because the curves were essentially horizontal straight lines. With reference t o the anomalous behavior of certain plasticizers, especially dioctyl sebacate, in all the compounds studied in this work, only one pfabticixer was present in each.compound. In actual practice i t is customary t o use two or more plasticizers in each stock, in which case the properties of any one of them are masked in proportion to the amount of the others present.
COMPARISON O F DATA In regard to 1 0 0 ~ modulus, o without exception the copolymer required less of any given plasticizer to attain a given modulus than did the 100% polyvinyl chloride. This may be ascribed to internal plasticizing action of the acetate group or accounted for on the basis of differences in molecular weights of the resins. With most of the plasti,cizers, the copolymer stocks had better tensiles than the corresponding polyvinyl chloride stocks. This was particularly true with dioctyl sebacate. There were two exceptions, however, plasticizer 36 and Paraplex G-25. It might normally be expected that the more effectively plasticized stocks (copolymer) would have more polymer-polymer contacts broken and thus be weakened to an extent detectable in tensile data, but this seemed not to be the general rule. Although there were several exceptions, there seemed t o be a general trend toward higher elongations with copolymer than with 100% chloride. The most notable exceptions were plasticizers 35 and 36, and Paraplex (2-25. The unexplained dip in the elongation curve of the dioctyl sebacate-polyvinyl chloride stock was not present with copolymer. The brittle temperatures of the stocks seemed to depend more on the plasticizer than on the resin. Five of the plasticizers gave lower brittle temperatures in straight polyvinyl chloride than in copolymer, whereas the remaining four plasticizers gave better results in copolymer. No generalization can be made as t o which of the two types of plasticized resin has the better resilience. The effect of temperature on resilience of copolymer stocks was not studied. ACImTOW LEDGRl ENT All electrical tests were carried out by the Physics Laboratory of Rohm & Haas Company, Bristol, Pa. Acknowledgments are also due W. F. Bartoe and E. A. Taylor of Rohm & Haas, Philadelphia, Pa., and t o Wilfred Gallay, consulting chemist, of Ottawa, Ontario, Canada, for their helpful critical comments.
LITERATURE CITED S.,“Advances in Colloid Science.” Vol. 11, New York, Interscience Publishers, 1946. ( 2 ) Rider, D. K., and Sumner, J. K., IND. ENQ.CESM.,ANAL.ED., (1) Boyer, R. F., and Spencer, R.
17, 730 (1945). (3) Vanderbilt, R. T.,Co., Vanderbilt Newr, 3, No. 6 (1933). (4)Yerzley, F. L., Proc. Am. SOC.Testing Materials, 39,1180 (1939). RECEIVED May 28, 1946. Presented before Division of Paint, Varnish, and Plastics Chemistry at 110th Meeting, AMERICANCHEMICAL SOCIETY, Chicago, Ill.
