Effect of Solvents upon Solid Organic Plastics JOHN DELMONTE Plastics Industries Technical Institute, Los Angeles, Calif.
the need for a simple analytical tool t o make rapid comparisons of various solvents. The most obvious practice of determining the effect of solvents is t o weigh out known quantities of material and place them in contact with certain amounts of solvents for a long interval of time and then comment on the effect. Effect of solvents upon methacrylic esters were reported in this way (H), as were solvents on natural resins (17), cellulose derivatives and natural resins (11), ethylcellulose ( i d ) , miscellaneous plastics ( W ) , and casein (S2). More work has been done upon the effect of solvents upon nitrocellulose than for any other plastic material. The toluene dilution ratio technique has, for example, been a useful analytical tool (3, 4, 6, 8, 10, 13, 16, 18, 19, 21, 24, 69, 66). Solubility based upon precipitation methods has also been applied to other plastics such as polystyrene
Solvents are classified according to the degree with which they reduce the shear strength of plastics. Complete loss in strength accompanied by formation of a smooth solution identifies a true type A solvent. Nonsolvents are classified into three groups-those which weaken and swell the plastic, those which only weaken it and those which have no effect. Solvents which exhibit the greatest initial rate of penetration of a solid are also the fbst to dissolve the plastic completely. Quantitative data are given for the effect of fourteen representative solvents upon six commercial plastic materials in relation to rates of dissolution. An equation is derived for the solvent power of an organic solvent upon a plastic,
(30)*
Another useful analytical tool is the determination of a known weight of plastic material in solution. The method was first proposed by Baker (2) for nitrocellulose and used frequently in analyzing the effect of solvents (14, 17, 18, 26, 27, 60, 33, S4). However, compositions giving minimum viscosity do not necessarily coincide with maximum dilution ratio (7). When true solutions of plastics are not obtained, other methods for determining the effects of solvents such as observations of the changes in weight and physical dimensions have been employed (1, 9, 16, 20). However, even these methods do not give the entire picture arid are subject to weighing errors in measuring volatile solvents. A still further approach to evaluation of the effect of solvents upon plastics is an examination of the physical properties of plastics in the presence of solvents. Sakurada ($8) observed for cellulose ester films that the greater the solvent
where I< is an arbitrary value which is constant for a given solvent upon all types of plastic, R is a resistance coefficient, t is the time, and x the thickness. The effects of conditioning, temperature, and material thicknesses are expressed in separate curves. The usefulness of the punch and die as a rapid analytical tool for evaluating the effect of solvents on plastics is emphasized.
2
I+
d12,000
$ ;
HE effect of solvents upon organic plastics influences many activities in the field of plastics. Preparation of lacquers and enamels; varnish solutions for impregnating purposes; cements and adhesives; formulation of moldable compositions, etc., are some of the processes relying upon the aid of solvents. Aside from the practical interpretations, the penetration of solvents into solids reveals data on the too little known structures of solid polymers, through certain swelling phenomena and diffusion rates. While many data have been published upon the effect of solvents upon plastic materials and related bodies, much of this information has been qualitatively reported as insoluble, partly soluble, or soluble. In lieu of other information the value of these interpretations is not underestimated, but quantitative methods of comparison would be more useful. Perhaps the lack of adequate data may be explained by
T
54 8,000 6 ar U
W
x
v,
y,ooo 20 40 GO 80 PERCENT RELATIVE: HUMIDITY
FIQURE TION OB
loo
STRENGTH OF SAMPLES AS FUNC1. SHEAR
HUMIDITY AFTER
% W E E K CONDITIOKING
1. Laminated phenolic (grade C) a t 60' F. 2. Laminated phenolic (grade XX) at 20° F., 1 hour after conditioning
3. Laminated phenolic (grade XX) a t 68' F. 4A. Cellulose acetate a t 20° F., 20 days after conditioning 4B. Cellulose acetate a t 20° F., 1 hour after conditioning 5. Cellulose acetate a t 6S0 F.
764
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1942
765
in the. curve sheets to follow, ordinates are represented as per cent of original shear strength. When these values are 100 per cent, there is no solvent action. Likewise, when there is a definite slope toward the axis under 10 per cent of original shear strength, complete dissolution has probably taken place. Where results extend over many hours, as for nonsolvents, semilog graph paper is more convenient to show data. The following plastic materials were included in this investigation :
TfMElN
MINUTES
FIGURE 2. EFFECTOF PRECONDITIONINQ UPON Loss OF STRENQTH OF CELLULOSI ACETATESHEETIMMERSED IN ACETONEAT 70" F. A.
Conditioned 1 week in water B. Conditioned 1 week i n a desiocator over oalcium chloride
power, the smaller the tensile strength and the greater the elongation. Peierls (26) determined the effect of solvents upon polyvinyl alcohol by the loss in tensile strength after prolonged immersion in the solvent. Physical properties of films cast from solvents are frequently studied (11, I d , 2.2, 26) but, less frequently, the properties of the plastic in contact with the solvent.
Method of Test and Materials Examined In these tests the method was to determine the physical property of the plastic, resistance to shear, at intervals during more or less prolonged contact with an organic solvent. The load required to force a small punch and die through a given thickness of material was determined. This technique applied to evaluating physical properties of plastics was described in a recent paper (6). The method is extremely simple and a complete test can be performed in several seconds. The procedure was as follows: Strips of various plastics approximately 1/16 inch thick, 1/2 inch wide, and 3 inches long were placed in small glass vials (11.1 ml. capacity) averaging about 0.700 inch inside diameter. Solvent was poured into the vial to a depth of roughly 2 inches, and time of immersion was observed to the nearest second. After various intervals the samples were removed and given a punch test, usually within the space of 10 seconds, and reimmersed. When tests were extended over several days or weeks, the vials were corked to prevent evaporation of solvents. After each test the punch and die were carefully wiped clean. In this manner the apparent shear strength of the plastic material could be determined as a function of time of immersion in a given solvent under controlled conditions. Shear strength can be determined from the load in pounds to produce failure, divided by shear area. This may be expressed in terms of the following equation: shear strength
=
W
rdt
where W = load to produce failure pounds d = diameter of punch, inches t = thickness of specimen, inches
Data are reported as the percentage change in strength because this represents the effect, of the solvent action. Thus,
Cellulose acetate sheet, clear, 0.065 in., Monsanto Chemical Co. Cellulose nitrate sheet, white, 0.063 in., Celluloid Corp. Cellulose acetate-butyrate, 0.068 in., Orange 8567MX, Tennessee Eastman Corp. Polyvinyl chloride acetate, 0.062 in., Cream VS3300, Carbide & Carbon Chemicals Corp. Polystyrene, 0.067 in., clear, Molded A-100, Dow Chemical Co. Polymethyl methacrylate, 0.059 in., clear, Rahm and Haas Co. Laminated phenolics, 0.048-0.050 in.
Sheet stock of a thickness as near inch as available was obtained from commercial sources so as to reduce the number of variables in the test. For special thicknesses the stock was press-polished between highly polished plates to the thickness required. The following solvents were included in the scope of these tests, simply on the basis of their being representative of a large number of types of solvents: Carbon tetrachloride, pure n-Butyl acetate, 88-92% Chloroform, 0. P. Methanol, A. C. S. grade Butyl alcohol, 0. P. Celloaolve Ethylene dichloride
Acetone, 0. P. Ethyl acetate, 85% Toluene, pure Benzene, pure Denatured alcohol Amyl acetate Methyl ethyl ketone
In addition, the effect of contact with water was observed, as well as the effect of binary combinations of solvents. Two extra solvents were included in a limited way in the testenamely, methyl acetate for testing cellulose acetate and methyl methacrylate monomer with the polymer.
20
40
60 80 100 T I M E IN M I N U T E S
FIGURE 3. EFFECTOF TEMPERATURE ON ACTIVITYOF ACETONEAS SOLVENT FOR CELLULOSE ACETATESHEET
CONDITIONING OF SAMPLES.All samples were preconditioned before immersion in the solvent by placing them in an oven with air circulation a t 122" F. for 48 hours, because it was established that the intensity of solvent action or chemical attack was dependent upon this treatment. Figures 1 and 2 show some of these relations. I n Figure 1 the relative humidity of conditioning was varied from 0 to 100 per cent (complete immersion in water), samples being maintained for 2-week intervals. Upon removal they were tested either
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 34, No. 6
100
ao 60
40
20
r
5
100
Y t
rx
*
80
5 z
i
60
-
g + o
b
r
5
20
Y
a
100
80
60
40
20
20
40
80
60 TIME
IN
/00
I20
/YO
160
MINUTES
.s
/
5
IO
50
100
500
IO00
TIME. I N HOURS
Effect of nonsolvents Effect of type A solvents FIGURE 4. EFFECT OF SOLVENTS AND NOXSOL~ENTS ON SHEARSTRENGTH OF PLASTICS a t room temperature (68" F.) or 20" F. in the cold room. The results of tests on only two materials are shown-cellulose acetate and laminated phenolics-though other plastics followed similar curves except that the slopes were not so marked as for cellulose acetate. An explanation of one of the results for cellulose acetate is that exposure to the cold (20" F.) for 20 days changed only one point on the curve (due to dehydrating action), indicated by a dotted line. Otherwise the effect of preconditioning was not altered by exposure to 20" F. In Figure 2 the greater activity of acetone upon cellulose acetate exposed to wet conditioning is clearly demonstrated. While only a few tests of this character were performed, it seems reasonable to expect a definite influence when the solvent is soluble in water. However, for standardization in other tests, a dry atmosphere was adopted for conditioning purposes.
TEMPERATURE O F TESTS. Most O f the tests, except as otherwise noted, were performed a t room temperatures varying from 68" to 75" F. Temperatures were read frequently during the course of tests and for all short-time tests were within this range. However, the effect of temperature upon the activity of solvents is well known, and a group of tests "ere conducted upon conditioned cellulose acetate immersed in solvents a t various temperatures (:Zoo, YO", and 100' F.). The retarding influence of lower temperatures is clearly indicated in Figure 3.
Solvents and Nonsolvents Complete quantitative data for all of th.e solvents are presented in Figure 4. The curves for each type of plastic material are divided into two groups:
June, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
767
Effect of nonsolvents
Effect of type A solvents FIQURE4 (Continued) The left-hand graphs are plotted upon Cartesian coordinates and the per cent loss in shear strength is shown as a function of the time of immersion. In this group only the effects of true solvents are shown. The true solvents are referred to as type A and form a true solution of the plastic in the course of time. Instead of presenting absolute shear strength measurements, the comparison or evaluation of penetration of solvent was made on the basis of the change in shear strength. The right-hand graphs are plotted upon semilog paper inasmuch as some of the tests were conducted for several hundred hours and longer. The effects of materials described as nonsolvents are shown. There are two definite groups among the nonsolvents-those which produce a loss of shear strength and those which have no effect. I n some cases considerable time must elapse before the loss of strength is apparent-for example, butyl alcohol upon cellulose acetate. However, in all cases of penetration by nonsolvents
the shear strength falls to a fixed and definite percentage of the original. Some prolonged tests of a few thousand hours showed no change in this new value of shear strength, and it may be assumed that when the curve has flattened out for a particular solvent, it will remain that way indefinitely. CELLULOSE NITRATE.The ketones are apparently the most active solvents, followed in turn by the esters. Among the nonsolvents only carbon tetrachloride had no effect. The rapidity with which the shear strength falls off when cellulose nitrate is immersed in acetone is considerably sharper than for most of the other plastics and indicates the greater activity of acetone upon cellulose nitrate. POLYMETHYL METHACRYLATE. In general, the effect of the solvents was much slower for this plastic. In fact, the results for toluene, benzene, amyl acetate, and butyl acetate are shown with a longer available time axis. Many solvents are apparent for polystyrene POLYSTYRENE. and all showed a marked degree of actmity. The four nonsolvents hsted had no effect on the shear strength.
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Vol. 34, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEI. EFFECTOF SOLVENTS UPON PLASTICS~ Butyl Amyl Ethyl Butyl Methyl Carbon Ethylene EthMeth- AceAceAoeAlcoAceEthyl ToluBenTetraDiCello- Chloromol ancl tate tate tate hol tone Ketone ene zene chloride ohloride solve form Cellulose nitrate 7A SD 4A 5A 3A 9D 1A 2A 13D 12D 14E 10D 6A 11D SD 4A 13D 1A 3A 12D 11D 14E 5A 2A 6D 9D 10D Cellulose acetate 7D 10D 6A 7A 4A 13D 1A 3A 11C 9C 14D SA 8A 2A Cellulose acetate-butyrate 12D 6B 7B 5B 14E 1A 2A 8D 9D 14E 14E 4A 10D 3B Polyvinyl chloride-acetate 14E 5A 14E 1A 3A 4A 14E 8A SA 7A 106 BA 14E 2A Polystyrene 14E SA 9A 4A 14E 3A 5A 6A 7A 11D 12D 13D 2A 10A 1A Polymethylmethaorylate oExplanation of symbols: Most rapid in effect No. 1. next rapid 2. least rapid 14 A complete dissolving of plastio whioh enters solution: B 3 aomplete disintegration of plastic with loss of a!1 s d e y stringth; C Lu6stantial sweiling, aooompanied by loss of shear strength to a constant value; D o loss of shear strength to a oonstant value, no dissolution; E no effect at all.
-
- -
There was a tendency for POLYVINYL CHLORIDE-ACETATE. some of the solvents tested t o delaminate polyvinyl resin sheet, which was prepared from thinner members calendered together. Figure 4 indicates an end oint of the curves for butyl and amyl acetate with a complete deLrnination of the polyvinyl resin. CELLULOSE ACETATE-BUTYRATE. Pronounced softening occurred for alcohols, benzene, and toluene. The material became rubberlike in the last two nonsolvents. While the strength was only a small fraction of the original, indefinite exposure did not alter it. The removal of the plastic from the nonsolvent was accompanied by a gradual regain of shear strength upon evaporation of the volatile matter. CELLULOSE ACETATE. Not so many solvents are indicated for this plastic as for the other cellulose derivatives. The long time delay before butyl alcohol shows up as a nonsolvent is unusual. To indicate the further usefulness of observing shear strength in analyzing solvent action, Figure 5 demonstrates an analysis of a typical binary solvent combination. Neither methyl alcohol nor ethylene dichloride has any effect alone in dissolving cellulose acetate, though they will weaken its shear strength, but in combination they produce a true solvent action. The optimum results are observed for 70 parts of ethylene dichloride to 30 parts of methyl alcohol. Similar analyses can be carried out upon any type or combination of materials. Table I lists the effects of the organic solvents; the relative reactivity of solvents upon plastics was determined from group A solvent curves (Figure 4). Those with the steepest slopes are the most active. For example, acetone and methyl acetate are obviously the most active for cellulose acetate. Another type of action appears in a few examples, notably for polyvinyl chloride acetate, where a complete loss may occur with no smooth solution forming but rather disintegration with complete loss of structure. The solvents producing this action are classified as type B. Type C, D, and E solvent actions are described in Table I and are reported as nonsolvents.
Discussion of Solvents
It is not unreasonable to assume that the loss in physical strength is a measure of the penetration and effectiveness of the solvent action upon the plastics. An insufficient number of solvents were included in these tests to allow an interpretation of solvent action upon high polymeric substances in terms of their polar or nonpolar characteristics. However, for type A solvents relations expressing the solvent power may be derived. Loss in a physical pr6perty such as shear strength can be explained by the disassociation of the long-chain molecules from its immediate neighbors, due to a solvent which counteracts those intermolecular forces keeping the substance together as a physically strong body. For true solvents the dissolved molecules should be free to move within the solvent, the degree of mobility depending upon the relative proportion of the two because plastics and type A solvents are miscible in all proportions. The activity of the solvent can be assumed t o be directly related to the rate at which the plastic material loses its shear strength. Many factors have a bearing upon this
activity, such as relative movement of solvent and plastic (which was stationary in these tests), nature of impurities, temperature effects (illustrated in Figure 3), past history and conditioning of samples, and physical dimensions of the material being dissolved. The activity of the solvent as determined by its rate of penetration into a solid and measured by loss in the shear strength of that solid can be expected to grow progressively slower, the deeper the penetration. This is definitely indicated for all solvents upon all plastics, and is explained by the formation of a solid saturated layer of dissolved plastic which retards penetration and diffusion of solvents to those regions of the plastic which have not been reached. The fact that the curves for shear strength us. time of immersion do not cross one another in the great majority of cases for type A solvents leads t o the general conclusion that solvents which exhibit the greatest initial rate of penetration of a solid will also be the first to dissolve the plastic completely. This is correct for true type A solvents. Figure 6 demonstrates the effect of material thickness upon rate a t which shear strength is lost. Obviously the initial rate of penetration of the solvent should not depend upon total material thickness. Nevertheless, inasmuch as the per cent loss in shear strength is determined by the total thickness of the plastic, the slope curve for loss in shear strength us. time of immersion may be shown to be some logarithmic function of over-all thickness. These relations may be expressed mathematically a8 follows: where S Q t
S = dQ/dt (1) dissolving power per cent loss in strength as plastic is dissolved by solvent = time of immersion = =
Another useful relation expressing the solvent action upon plastics may be written as follows:
s = K -RQ/X where K = arbitrary activity coefficient of solvent, dependent upon chemical and physical properties and constant at a certain temperature R = resistance t o penetration of solvent X = thickness of solid being dissolved Expressed another way, solvent power may be said to depend not only upon initial activity of the solvent but also upon the increased resistance offered to it as the layer of saturated solid grows thicker. This relation can be put in terms of a differential equation as follows: (3)
Solving for Q and rememberng that Q = 0 at t = 0, Q =
Kx (1
-
es)
(4)
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INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1942
required for polymethyl methacrylate or half the time required for cellulose acetate. Some approximation can be made of the comparative solvent power of various solvents by the slope of the shear strength vs. time curves. I n the case of polymethyl methacrylate, acetone is not the most active solvent. Chloroform and ethylene dichloride are more rapid in effect. Both of these materials are preferred as solvents for the acrylates, particularly for cementing operations.
Discussion of Nonsolvents O IO
E
8
Y
6
Y
8 2
The unusual effect of certain solvents upon plastics is manifested by loss of shear strength, sometimes accompanied by swelling but without the plastic being reduced to a solution. Even though shear strength may be reduced by nonsolvents to a small fraction of the original strength, once the curve of strength us, log time has straightened out, the plastic can be left in contact with solvent indefinitely without further changes.
10
0
6ETHYLE PIE DlCHLORl DE
FIGURE 5. EFFECT OF SOLVENTCOMBINATIONS ON CELLULOSE ACETATE SHEET , A . 20-minute immersion B. BO-minute immersion
20
vo 60 ao T l M E I N MINUTES
io0
FIGURE6. EFFECTOF THICKNESS OF CELLULOSE ACETATESHEETON RATE AT WHICHSHEAR STRENGTHIs LOST IN ACETONE
One explanation of the partial loss in strengi is the fact that the solvent may affect only one of the ingredients in a formulation and not the others. For example, Figure 7 shows that acetone will dissolve out part of the phenolic resin which has not been fully cured and leave the remainder of the material still with substantial strength. However, in the case of homogeneous materials such as polystyrene and polymethyl methacrylate the effects are different. There are no nonsolvents for polystyrene which weaken the material, but several for the polymethyl methacrylate. These effects are not necessarily accompanied by swelling. In general, materials referred to as nonsolvents have little or no apparent effect on the plastic for a period ranging from one to several hours or more; then a rapid
Differentiating this equation again and solving for S, (5)
Thus a t zero time, solvent power equals K/R,and at infinite time, solvent power equals zero. From Equation 5 we would expect the value K to be a oonstant for a given solvent and independent of the material being tested, and R to be a variable measuring resistance to penetration of solvent. The curves for the six samples of plastics tested were used in determining values of K and R for the solvent acetone. The results of these calculationsshow the following constants for acetone: Plastic Cellulose acetate-butyrate Cellulose nitrate Cellulose acetate Polyvinyl chloride-acetate Polymethyl methacrylate Polystyrene
K 20.6 23.2 22.0 22.6 25.5 25.2
R 4,730
4,010 8,060 8,360
43,200 6,620
!
These values bear out the conclusions arrived a t for Equation 5. No explanation is offered for the higher constants for polymethyl methacrylate and polystyrene; insufficient samples were available for a recheck. On the other hand, the values of R allow a comparison to be made of the activity of acetone upon various plastics. Thus it may be said that acetone will dissolve cellulose nitrate in one tenth the time
o
5 a
$
I
60
10
0’
s?
I
too
I loo0
TIME I N HOURS
FIGURE 7. EFFECT OF ACETONEON LAVINATED PHENOLICS A. B.
Fabric base 0 050 inch thick Paper base,’0.048 inch thick
INDUSTRIAL AND ENGINEERING CHEMISTRY
770
change in shear strength will occur until it falls to a k e d value where it remains indefinitely. While the shear strength is changed, outward physical appearance may remain the same. On the other hand, for nonsolvents such as benzene and toluene on cellulose acetate-butyrate, the loss in shear strength is accompanied by swelling, and the reason may be that swelling is due to increase in intermolecular distances with a decrease in molecular-cohesion forces.
Literature Cited (1) A. S. T. M. Specification D543-39T, Resistance of Plastics to Chemical Reagents. (2) Baker, J. Chem. SOL, 103, 1653 (1913). (3) Brunkow, IND. ENG.CHEW.,22, 178 (1930). (4) Davidson, Ibid., 18,670 (1926). (5) Delmonte, Modern Plastics, 19,63 (Sept., 1941). (6) Doolittle, IND.ENG.CHEM.,27, 1169 (1935). (7) Ibid., 30, 189 (1938). (8) Durrans, “Solvents”, London, Chapman & Hall, 1930. (9) Fermazin, Chem.-Ztg., 54, 605 (1930). (10) Frazier, IND.ENG.CHEW.,22, 607 (1930). (11) Gardner and Sward, “Physical and Chemical Examination of Paints, Varnishes, Lacquers and Colors”, p. 440, Washington, Inst. of Paint and Varnish Research, 1939. (12) Houwink, “Elasticity, Plasticity and the Structure of Matter”, Cambridge Univ. Press, 1937.
Vol. 34, No, 6
(13) Jordan, “Technology of Solvents”, New York, Chem. Pub. Co., 1QR8.
and Bass, IND.ENG.CHEM.,30, 74-9 (1938). (15) Keyes, Ibid., 17,505 (1925). (16) Kline, Rinker, and Meindl, 44th Ann. Meeting A. S. T. M., June 24. 1941. (17) McBain, J. Phys. Chem., 30,239 (1926). (18) McBain, Grant, and Smith, Ibid., 38, 1217 (1934). (19) McBain, Harvey, and Smith, Ibid.. 30, 312 (1926). (20) Mantel1 and Allan, IND.ENG.CHEW.,30, 262 (1938). (21) Mellan, “Industrial Solvents”, New York, Reinhold Pub. Corp., 1939. (22) Meyer and Fordyce, IND.ENG.CHEW.,32, 1053 (1940). (23) Ostwald, Kolloid-Z., 59, 25 (1932). (24) Park and Hofmann, IND.ENG.CHIDW., 24, 132 (1932). (25) Peierls, Modern Plastics, 18,53 (Feb., 1941). (26) Reinhart and Kline, IND.ENG.CHEM.,31, 1522 (1939). (27) Sakurada and Shojino, J. SOC.Chem. Ind. J a p a n , 37, Suppl. Binding, 603 (1934). (28) Sakurada and Watanabe, Ibid., 39,Suppl. Binding, 50-1 (1936). (29) Sproxton, 3rd Colloid Rept., p. 82, Brit. Assoc. Adv. of Sei., 1920. (30) Staudinger and Heber, J. Phys. Chem., A171, 129-80 (1935). (31) Strain and Kennelly, IND. ENG.CHEW.,31, 382-7 (1939). (32) Surtmeister, “Casein and Its Industrial Applications”, p. 150, New York, Reinhold Pub. Corp., 1939. (33) Ware and Teeters, IND. ENG.CHEU., 31,738-41 (1939). (34) Ibid., 31, 1118-41 (1939). (35) Wilson, Ibid., 21,592 (1929). (14) K ;;;
CORRESPONDENCE Viscosity Pole and Pole Height ( V p ) of Ubbelohde SIR: This note is written because t h e pole height, W p , of Ubbelohde (9) was recently used in INDESTRIAL AND ENGINEERING b y Neyman-Pilat and Pilat (8) without any indicaCHEMISTRY tion of how the function is calculated and without a clear reference as t o where this information can be obtained, Pole height has been extensively used by German petroleum chemists but has received little notice in American or English journals. The concept of viscosity pole (Viskosit(itspoE) is based on t h e fact t h a t if viscosity-temperature curves are plotted on A. S. T. M. type viscosity paper (1, 2, 3) for a series of cuts from one crude, these lines will converge, a t least approximately, toward a point. This point is characteristic of t h e crude and is called the “viscosity pole”. The vertical height of this point above t h e base line corresponding t o zero viscosity is defined as t h e “pole height” (Polhdhe). This constant is characteristic of t h e crude type in much the same way thatviscosity-gravity constant ( 7 ) and viscosity index ( 4 ) are characteristic of crude types. For calculation of pole height, Ubbelohde recommends t h e following equations: 11 w, = (log TI - 2410 + - WI) = pole height (; - 0.19,) m
m
=
W1 =
(1)
+
Wi Wz log Tz - log Ti log log (Vl
+ 0.8)*
(3)
where TI,TZ = absolute temperature, K. Vi, VI = kinematic viscosity, centistokes Pole height is somewhat similar t o viscosity-gravity constant and viscosity index. Roughly, a paraffin base oil will have a pole height of about 1.0 t o 2.0, and a naphthenic oil, a pole height of about 3.0 t o 4.0. A pole height of 10 corresponds roughly t o 0.900 viscosity-gravity constant. T h e d a t a available indicate t h a t i t is probably not practical t o establish a conversion curve between pole height and either viscosity-gravity constant or viscosity index, even though they are alternative ways of measuring the same general effect. It should be noted t h a t pole heights calculated for different temperature intervals do not always check, and t h a t TIused b y Ubbelohde is 323’ K. (50” C.).
Bibliography (1) Am. Soc. for Testing Materials, Procedure D-341-32T (1932). (2) Ibid.. D-341-39 (1939). (3j Barnard, D. P.‘in “Science of Petroleum”, Vol. 11, p. 1079, London, Oxford University Press, 1938. (4) Dean, E. W., and Davis, G. H. B., Chem. & M e t . Eng., 36, 618 (1929). (5) Docksey, P., in “Science of Petroleum”, Vol. 11, p. 1091, London, Oxford University Press, 1938. (6) Geniesse, J. C., private communication. (7) Hill, J. B., and Cootes, H. B., IND.ENG.CHEM.,20, 641 (1928). (8) Neyman-Pilat, E., and Pilat, S., I bid., 33, 1382-90 (1941). (9) Ubbelohde, L., “Zur Viskosimetrie”, 2nd ed. rev., pp. 9-18, Leipsig, S. Hirzel, 1936.
S.S.KURTZ,JR.
* A modulus of
0.8 was used prior t o 1937 in preparing t h e A. S. T. M. charts (1,9). Sinoe 1937 a modulus of 0.6 has been used above 1 . 5 centistokes (8, 6).
SUNOIL COMPANY MARCUB HOOK, PEKNA.
