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I n the dynamic test the two vehicles were again fastened together and their speed synchronized a t 20 miles per hour. With the chain taut, the brakes on the skid dynamopeter truck were slorvly applied until the rear wheels on the car started spinning, Relative ratings obtained as a result of these tests are also given in Table 111. The test surface vias glare ice with the sun shining brightly and the temperature varying from 14 O t o 25 F. The control tires were tested frequently so t h a t each experimental tire was compared with a control tested shortly before or afterward.
ments and G. L. Hall who made the internal friction measurements reported. The cooperation of B. G. Labbc in the use of the cold room at the Government Evaluation Laboratory is gratefully acknowledged. The continued interest of F. W. Stavely in the project is appreciated as is also the permission of the Firestone Tire &: Rubber Company to publish these results. LITERATURE CITED
Bird, G., and Miller, R. A., “Studies in Road Friction, 11,” Department of Scientific and Industrial Research and Ministry of Transport Road Research, Technical P a p e r , 2, (1937). Bird, G., and Scott, W. J. O., Degt. Sci. Ind. Research (Brit.), BUZZ.1 (1936). Committee on Winter Driving Hazards, Rept. t o Street and Highway Traffic Section, Natl. Safety Council, Inc., 1940. Conant, F. S., and Liska, J. W., J. A p p l i e d Phys., 15, 767
CONCLUSIONS
The laboratory test method described is capable of indicating a fair degree of accuracy the tractive ability of a tire tread compound on ice. Coefficients of both dynamic and static friction are important in determining the resistance t o slide of a tire. The base polymer in a tread compound is the principal factor affecting the coefficients of friction. Among compounds based on different polymers, the coefficients of friction on ice are not closely related t o either the stiffness or hardness of the stock or to its hysteresis. The coefficients of friction of stocks based on a single polymer, however, are greatly influenced by the type and amount of softener and by the type and amount of black. x ith
ACMVOWLEDGMENT
The authors wish to thank various members of the Firestone technical organization for their cooperation in this work, particularly J. IT. Liska for his many helpful suggestions and com-
‘gT J
of
VoI. 41, No. 1
(1944) .
Dillon, J. H., Prettyman, I. B., and Hall, G. L., I b i d . , 15, 309 (1944). Gustafson, F. B., Natl. Advisory Comm. Aeronaut., Rept. L-245 (1942).
Liska, J. SV., IND. ENG.CHEM.,36,40 (1944). Moyer, R. A , , Iowa State Coll., Eng, E x p t . Sta. BUZZ.No. 120 (Aug. 8, 1934). Roth, F. L., Driscoll, 1%.L., and Holt, TV. L.. J. Research it’atl. Bur. Standards. 28. 439-62 (1942). Snedecor, G. W., “Statistical ’Methods,” Chap. 7, Ames, Iowa, Iowa State Coll. Press, 1940. Stinson, K. W., and Roberts, C. P., Proc. 14th Ann. Meeting of Highway Research B o a r d , December 1934. RECEIVED June 10, 1947. Presented before the meeting of the Division of Rubber Chemistry, AMERICAN CHEXIICAL SOCIETY, io. Cleveland, Ohio, M a y
1947.
J
Y J
r ‘ h e solubilities of two daniples of conimercial low-molecular-weight polystyrene have been nieasured in n-decane and n-octadecane and in mixtures with toluene between 20’ and 110’ C. The resins are soluble in the alkanes in a limited range, n-decane being the best solvent. Addition of about 30% toluene has little effect, but larger amounts of toluene with the alkanes greatly increases the solubility. Above 80% toluene with n-octadecane, the more highly pol) merized resin i s soluble at all concentrations at room temperatures. SolLability has been plotted at 20°, S O ” , 80’, and 110” C. for the two resins in decane-toluene and octadecane-toluene mixtures. These results are in general agreement with the expected behavior for polymersolvent systems except that the critical concentration occurs in several cases at above 50% resin concentration. ‘Fhe behavior is believed to be characteristic of resin-plasticizer systems. Exudation of plasticizer in a relatively pure form is consistent with the less readily miscible systems.
HIS study is a continuation of work on the solubility of lowmolecular-weight polystyrenes in the normal alkanes ( 7 ) . I n the present study two samples of more highly polymerized polystyrene Tere used, and since these are soluble in only a narrow range in the normal alkanes, solubility was measured in mixtures of decane or octadecane with toluene, which range from very poor t o good solvents.
Two commercial samples of low-molecular- eight polystyrene were used. The unfractionated resins were studied t o establish ranges of solubility. The samples were sufficiently different in average degree of polymerization to show pronounced difference in solubility. A sample of commercial low-molecular-weight polystyrene was obtained from Pennsylvania Industrial Chemical Corporation (resin A) and from the Don. Chemical Company (resin B). Decane, tetradecane, and octadecanc werc obtained from the Connecticut Hard Rubber Company, and density, refractive index, and aniline point were determined for each. Since these values were reasonably close to the constants for the pure materials, these solvents were used without further purification; C.P. toluene was used. Solubility was determined by heating a weighed sample of resin and solvent in a one-inch test tube in a glycerol bath t o solution. The bath was then cooled with a thermometer immersed in the solution until the mixture became opaque. At low resin concentrations a solution of the polystyrene in toluene of known content was titrated with decane or octadecane until a definite haze was formed at 25” C. An excess of precipitant was then added, the mixture heated to solution, and the temperature of precipitation determined on slowly cooling. The aniline point was determined by heating weighed mixtures of aniline, decane, or octadecane, and toluene until clear, and determining the temperature of separation on slowly cooling with qtirring.
January 1949
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INDUSTRIAL AND ENGINEERING CHEMISTRY
However, it was soon found that excessively high temperatures were required t o bring the resins into solution below 50% resin concentration (Figures 1and 2). At temperatures above 250' C. the resin depolymerizes. Also, it was not possible t o determine the amount of resin in large amounts of alkane. This solubility is much less than 1%. Solvent power decreases in the order decane, tetradecane, octadecane, and the more highly polymerized resin B is appreciably less soluble (Figure 3) than resin 8. A LKANE-TO LUENE MIXTURES
7oRESIN A
Figure 1.
Solubility of Resin A in Alkanes
Molecular weights of the polystyrene samples were determined by measuring the viscosity in toluene at 0.5, 0.25, and 0.125 gram per 100 ml. of solution, and by depression of the freezing point of solutions in pure benzene:
Resin s Resin B
Intrinsic Visoasity 0.51 1.53
ANILINE POINT. Since the alkanes were not sufficiently good solvents t o explore solubility relationships at all resin concentrations, i t was decided to measure solubility in mixtures with toluene. A study of the systems aniline-decane-toluene and aniline-octadecane-toluene was made (Figures 4 and 5 , and Table I). The aniline point (critical solution temperature) of the mixtures was then determined (Figure 6) t o see whether the solvent power of decane with toluene or octadecane with toluene was measured by this aniline point. Although the aniline point serves as a useful index of solvent power, it apparently does not, give a quantitative measure of the behavior of the mixtures,
2601
1
Mol. Wt. (Cryoscopic) 1130 7G50
SOLUBILITY IN ALKANES
It was hoped that the solubility of the polystyrene samples could be measured over all concentrations of resin, in decane, tetradecane, and octadecane, as had been done in Che earlier work.
100
RESIN B
Figure 2.
80
60 %RESIN
Solubility of Resin B in Alkanes
Figure 3. Solubility of Resins in Octadecane
% OCTADECANE
Fignre 4.
System Decane-Toluene-Aniline
Figure 5.
Sys tern Octadecane-Toluene-Aniline
128
INDUSTRIAL AND EN G INEERING CHEMISTRY
Vol. 41, No, 1 n
90
Ec a/o
Figure 6.
20
Figure 8.
40
ALKAUE
D
1
Aniline Points of Ultane-Toluene Mixtures
cn
% TOLIJEUE
% TOLUENE
Figure 7 . System Resin A-Decane-Toluene
60
20
f
System Resin 4-Octadecane-Toluene
since mixtures of octadecane and toluene'do not have the same solvent power as mixtures of decane and toluene of the same aniline point. SOLUBILITY OF POLYSTYRENE. The precipitat.ion temperature of mixtures of resin A and resin B with mixtures of decane or octadecane with toluene \vas determined a t resin concentrations from about 90 t o 1%. The toluene content was varied from 10 to 80% of the solvent mixture (Table 11). Precipitation temperatures were plotted on triaxial diagrams, and isotherms (20 ', 50", SO", 110" C.) were drawn from these values. The curves (Figures 7 to 10) show the trends already noted-namely, that resin A is more readily soluble than B and that decane is a better solvent than octadecane. It is also apparent that toluene is a much better solvent for polystyrene than the alkanes. The results were redrawn (Figures 11 to 15) by plot,ting precipitation temperature against resin concentration a t various ratios of alkane t o toluene in the solvent. The numbers on the ourves are the percentage of toluene in the alkane-toluene mixture. The Line marked zero measures the solubility in the pure alkane.
40 TOWENE
Figme 9. System Kesin H-Decane-Toluene
T~~~~~1. iiNILINE poINTsOF D~~~~~ AxD TOLCENE ~~IIXTURES ___
7% by Weight
Aniline 80 70 60 50 40 33 25
20 12 83 83 83 71 71 71 63 63 62 55 56 55 50
Decane Toluene 20 ,. 30 40 .. .
50
60 67 75 80 78 12 8 17 20 14 26 22 31 l9 26 22 35
I
.. , .
..
% by Weight T ~ ~ ~ . , OctaC. Aniline decane Toluene 77 78 78 78 77 72
, .
..
5
7
9 12 9 15 11
15 19 14 18 22 15
o ~ ~ , ~
47 49 40 33 47 55 41 56 45 38 54 42 31 52
80 70 60 50 40 33 25 20 12 83 84 72 72 67 63 63 62 56 F6 06 50
20 30 40 50
60 67 75 80
78 10 8 17 14 23 26 22 31 26 22 33
.. .. .. .. .. .. . I
.. '7 8 11
14 10 11 15 19 13
18 22 15
TZI?.,
98 102 103 102 98 94
87 81 63 75 67 77 69 84 86 73 65 81 69 60 77
INDUSTRIAL AND ENGINEERING CHEMISTRY
lanuary 1949
129
R
TABIXTT. SOLUBILITY O H I'OLYS~~YRENE yo by Weight Resin A
90 80
E 77
72 67 67 67 50 50 50 33 16.6 14.3 13 5 12 9 10.6 9 9 9 2 8.7 8 2 5.3 4.7 4 3 4.1 1.7 1.6 1.5 1.4
The first additiun of toluene up t o 20-309$ has but little effect on the solvt>iit power of the mixture. Beyond this poiiit the addition of toluene greatly increases the solubility of polystyrcne. Further addition of toluene results in solubility a t all concentrations a t rooin temperature. Further concentration of toluenes required varies with the resin usctl and ~ i t the h aUlaiio bctwecri 50 to 80% of thc solvent. The effect of incre:tsing toluenc concentration and the effect of temperature are in the same direction. Most of the plots were made against temperature. Solubility isotherms (Figures 16: and 17) were drawn agaiiist the concentration of toluene, showing the aniount necessary to bring polystyrene into solution rtt a given temperature and resin concentration. These curves are comparable to those sliown above, but the maxima are often at a diffrrent rwiri conoentrittion. 1)ISCUSSIO"I Of: RESULT3
T1-\(IsoIubility of polystyrene a t ordinary temperatures has bcen
90 80
::
83 83 77 77 72 72 72 67 67 67 50 50 40 33.3 25.0 20.4 16.9 12.8 11.2 0.1 5.2 1.9 1.7
1.5
% by Weight
Decane Toliienr 40 20. 30 .. .. 50 6 18 6 22 7 26 13 20 20 13 40 10 20 30 30 20 27 40 44.5 38.0 33.2 52.5 31 . O 55.5 57.2 29 . 9 42.2 47.2 50 5 39.6 37.3 63.5 34. s 56.5 !32.R 59 5 47.0 46.8 41 .8 53.5 56.6 39.2 59.0 36.9 55.8 42.5 51.3 47.1 47.8 50.7 44.0 54.0
..
Octadecane 10 20 30 50 10 14 14 18 11 17 22 13 20 26 10 25 30 33.3 37.5 32.0 43.8 35.3 43.6 38.7 48.5 38.3 43.7 48.5
DECANE-TOLIJL:\ I: MIXTURES
IN
AND OCThl)E(. \ N E - T O I . U E N E
..
c.
Resin
B
Decane
5 43 71
90 80 70 77 77 67 67 67 72 72 50 50 50 33 19.2 17.3 16.1 14.9 12.0 11.1 10.2
10 20
'kml).
135
35 51 64 23
