ASPHALT-POLYBUTENE PAINTS
H. C. EVANS', D. W. YOUNG, AND R. L. HOLMES2
Accelerated weathering and normal weathering tests have been conducted on seventy experimental asphalt-polybutene cutbacks, with and without fillers, and the results are critically discussed. Results indicate that polybutene reduced or completely eliminated the tendency of the several asphalts to alligator, slightly reduced the tendency to check, reduced surface hardness, and increased the length of time before dusting began.
Standard Oil Company of New Jersey, Elizabeth, N. J.
ECENT work on the general subject of petroleum asphalt-polybutene blends has followed two general lines, the first being a study of the effect of polybutene on the physical properties of asphalt as determined by standard laboratory instruments. It has been found that, in general, the softening point, penetration, ductility, and similar standard asphalt tests are influenced not only by the molecular weight of the polybutene but also by the type of asphalt in which it is blended. These observations prompted the second portion of the program. This work is more practical and is a study of the effect of low concentrations of polybutene on the weathering and surface consistency characteristics of several asphalt films.
R
EFFECT OF POLYBUTENE ON COLLOIDAL STRUCTURE
The effect of the addition of polybutene on the colloidal structure of asphalt raises several problems. A number of them were previously discussed by Thomas et al. (9). Limited quantities of polybutene will dissolvein the oily medium without destroying the colloidal structure of the asphalt. It is thought that viscosity can be raised in this manner enough to decrease markedly the loss of oily constituents by evaporation and the leaching action of water. Since the medium's resistance to oxidation will be improved by the polybutene addition, oxidation as an accelerating force in the loss of the oil phase will be lessened, and the retention of the medium will be more dependent upon resistance to volatilization and moisture permeability. Both the latter should be improved by the addition of polybutene. This has been borne out by an actual weathering comparison of a straight asphalt and an asphalt-polybutene coated on a roof and exposed for 210 days. While the straight asphalt coat became brittle and showed cracking, the polybutene blend remained soft and pliable; this behavior indicated successful retention of the oil components by the latter. The stability of the colloidal system itself will be profoundly influenced by the addition of polybutene. Surface tension and absorption effects will play decisive roles in this consideration. ' Research with rubber indicates that small amounts of rubber powder blended into asphalt produce changes in the properties of the asphalt due to the selective absorption of the lighter hydrocarbons from the bitumen; a disperse system of swollen grains of rubber is thus formed in an asphaltic bitumen of the same type as the original but harder. High-molecular-weight polybutenes might be comparable to rubber in this respect; but those of lower molecuf
3
lar weight (less than about 30,000 as determined by the Staudinger method, I ) will be so much more soluble in the oil phase that the system will remain a two-phase system of asphaltene micelles, now dispersed in an oil-polybutene medium. It seems likely that the addition of polybutene will result in lowering the interfacial tension of the medium micelle. This will tend to produce positive absorption or a concentration of the polybutene a t the interface as the concentration of polybutene in the solution increases. Flocculation of the disperse phase would be the ultimate result if the concentration of polybutene in the oil phase was increased to the proper point. It can also be postulated that selective absorption of the resinous protective bodies of the micelles by the polybutene may also result in destruction of the micelles and precipitation of the asphaltenes. From theoretical considerations, therefore, it would seem that the concentration of polybutene of a given molecular weight in solution will be limited by the extent of solubility as well as by absorption and surface tension effects. If optimum improvement in weathering properties made desirable the incorporation of polybutene above the limit of compatibility, it would be still essential to protect the stability of the colloidal system. This might be effected artificially by the addition of a fluxing agent, possibly one of the cheaper resins of the desirable softening point and toughness. In high concentrations the polybutene would bloom to the surface in the form of a thin film, and would protect the asphalt by its own qualities from the action of oxygen and water. The surface, however, would be far too tacky for practical application; a t any rate, such high proportions of polybutene, even if dried by the use of fillers, is getting out of the paint range into that of tapes and mastics. Certain finely divided mineral fillers might profitably be added, nevertheless, to the asphalt-polybutene solution, both to stabilize the solution and to increase hardness and lessen tackiness. EFFECT OF POLYBUTENE ON PHYSICAL PROPERTIES
Since such physical properties of asphalt as softening point, penetration, and ductility are closely related to viscosity, it is apparent that such a substance as polybutene, known to have a profound effect on the viscosity-temperature of oils, should considerably affect the properties of asphalt. Work has been done on the solubility of polybutene in asphalts, and the extent of compatibility has been found to be a function both of the molecular weight of polybutene and the origin of the asphalt. Table I lists the results obtained from seventy-four experiments on asphalt-polybutene blends. Ninety-four steel panels were coated with asphalt-polybutene paints. Coating from solution instead of applying as a
Present address, Stanoo Distributors, Inc., New York, N. Y. Present address, Rsybestos-Manhattan, Ino., Stratford, Conn.
481
INDUSTRIAL AND ENGINEERING CHEMISTRY
482
Vol. 35, No. 4 WEATHERING TESTS
I.
ASPHALT-POLYBVTEKE BLENDS
Mixtures of 5, 10, 15, and 20 per cent polybutene of -Penetrations L Ductility S,usoeptibility --PolybutenType of Softening d Factor , 77' F. 115' F. a t 77O F . e 70 Mol. w t . Asphalt Pointa, OF. 32O F. 6000 and 15,000 molecular 1.69 0 weight in asphalts of 110" F. Oxidized Columbian, 176 :1 3 . 2 0 S. P. 160-180' F. 165 1;ioo 0.5 4.25 164 4 1.0 1,500 softening point (S. P.), 1602.83 6 165 1,500 2.0 180" F. S. P. oxidized, 1801A 9 2.86 1,500 5.0 2.07 150 15 1,500 10.0 200" F. S. P. oxidized, and 1.96 142 2.5 . ._ _. 1,500 16.0 1.91 137 35 1,500 20.0 220-235" F. S. P. oxidized 1 . 5 3 Oxidized Columbian, 190 15 0 were made up a t about 1.44 S. P. 180-200° F. 190 16 0.5 1:ioo 1.44 (36% oil. 29.5 resin, 190 16 1,500 1.0 100" C. in the laboratory 1.44 34.7 asphaltene) 191 16 1,500 2.0 1.33 191 21 Baker-Perkins kneader1,500 5.0 1 . 3 9 193 23 1,500 10.0 mixer. Visual observations 1.07 209 41 1,500 20.0 of brightness and homo15 loo+ 6.60 S. P. 110' F. 108 99 300 + 0 11 9.46 104 3004loo+ geneity of t h e resulting 108 0.5 1;r;oo Same 7.47 112 15 106 1004300 + 1,500 1.0 panels, as a rough criterion 6.85 130 100 + 104 300+ 19 1,500 2.0 9.00 207 23 loo+ 300 499 5.0 1,500 of solubility, bore out the 5.9+ 51 300+ 94 300 + loo+ 1,500 10.0 1.11 119 125 300 + 31, 50,71 previously determined limits 107 1,500 20.0 (Table 11). However, above 3.00 4 12 37 2L/n Steam-reduced, S. P. 171 0 3.00 5 15 41 .. 160-170° F. 176 0.5 1;500 the limit of actual solubility 3.00 176 5 15 43 .. 1,500 1.0 2.33 6 14 39 .. of polybutene in asphalt, 179 1,500 2.0 2.38 166 8 19 55 .. 1,500 5.0 there may be intermediate 1.82 164 11 20 61 1 1,500 10.0 stages of incompatibility 1.69 0 1.80 above which compatibility 15;OOO 0.5 1.69 1.0 15,000 again occurs, but where the 1.81 15,000 2.0 1.50 15,000 5.0 asphalt simply acts as a filler 1.19 15,000 10.0 .. in the polybutene and no 15,000 20.0 actual solution of polybutene 1.53 0 1.40 0.5 15:dOO in asphalt occurs. Yet when 1.37 15,000 1.0 1.50 enamels were made up in 15,000 2.0 1.36 15,000 5.0 2-20 per cent concentrations 1 . 2 6 15,000 10.0 of polybutene from the 6.60 6 . P. 110° F. 108 15 99 300C lOOC 0 6.36 blends, the solubility seemed 109 14 89 3004100+ 0.5 15;OOO Same 9.45 9 85 300t 1004110 15,000 Cracking-coil tar 1.0 to follow a straight-line de7.33 88 E : 21 12 112 110 15,000 Wax tailings substitute 2.0 5.34 108 15,000 Same 5.0 crease with increasing poly3.94 15,000 Same 112 35 138 300+ 67 10.0 butene concentration. This 3.6483 3004300t .. 86 15,000 Same 20.0 would indicate, therefore, 3.00 0 3.00 15;OOO 0.5 that during the period in 2.40 15,000 1.0 which the solvent is evapo2.33 15,000 2.0 3.00 15,000 5.0 rating, there is a breakdown 2.83 15,000 10.0 3.17 15,000 20.0 of the colloidal structure of the film which is partially 15 23 1.53 Oxidized Columhian, 190 38 0 1.50 24 40 16 S. P. 180-200° F. 204 40:OOO 0.5 inhibited a t high concentra23 1.53 15 215 38 40,000 1.0 1.18 22 26 214 44 40,000 2.0 tions of polymer where the 25 1 . 5 6 41 234 16 40,000 5.0 viscosity prevents this ag0.74 30 27 20 " 265 40,000 10.0 1.06 46 32 34 285 40,000 20.0 gregation. 6.60 0 Though not the best solvent 9 . 2 0 40:dOO 0.5 for asphalt, Varsol No. 2 was 2.75 40,000 1.0 2.14 2.0 40,000 first used for cutting back 1.95 40,000 5.0 1.75 40,000 10.0 the highly viscous kneaderformulated mixtures. After 3.00 0 2.40 40:dOO 0.5 several methods were tried 2.16 40 000 1.0 3.50 40:OOO 2.0 for mixing the polymer1.73 40,000 5.0 asphalt blend with light 1.40 40,000 10.0 hydrocarbon solvents, mea By ring and ball method ( A . S. T. M. D5-25). chanical shaking for 8 hours a t A. 9. T. M. method D113-39. 6 A. S. T. M. method D36-26. d Ratio of penetration a t 77' t o penetration at 32' F. room temperature in the laboratory shaker was found the simplest means for obtaining a homogeneous paint. I n Varsol there was some trouble with thixotropic gel formahot melt or enamel has been the practice; slight improvement tion, but stirring was ample to break the viscosity. This was could be more easily noted and any definite improvement especially noticeable in the higher polybutene concentration. of coat would more easily justify polybutene addition, since, No attempt was made to control the viscosity of the cutin general, poor weathering results are obtained with asphalt backs; in each case sufficient solvent was added to give satisin thin films. Seventy-six of the panels were tested for accelfactory paint consistency. Actually, in painting the panels, erated weathering in a Weather-ometer. Sixty-eight of the two-coat applications were found to be 0.003-0.005 inch samples were also tested on steel in the 45" southern exposure thick for a wide range of consistencies. weathering racks on the roof of the General Engineering Steel panels (12 X 6 inches) were coated with the paints Building a t Bayway, N. J. T.4BLE
PHYSICAL PROPERTIES O F
7
C
April, 1943
INDUSTRIAL AND ENGINEERING CHEMISTRY
483
OF POLYBUTENE ON PHYSICAL PROPERTIES OF ASPHALT-POLYBUTENE PAINTP TABLE 11. EFFECT
Physical Property Softening point Penetration
Ductility Susceptibility factor, penetration a t 77' F./penetration a t 32" F. Solubility 6
0
b
Mol. Wt. of Polybutene 1,500 15,000 40,000 1,500 15,000
Cracking-Coil Tar, 110' F. S. P. Lowers No effect Raises Raises Raises slightly
Steam-Reduced Asphalt, 160-170° F. 8. P. Lowers Raises Raises Raises Raises slightly
40,000
Raises at 32', lowera at 115' F. Lowers Lowers Lowers Lowers Lowers Lowers
Approx. unchanged a t 32' and 1 1 6 O F. Lowers Raises (1) Raises (?) Lowers Unchanged Lowers
1,500 15,000 40,000 1,500 15,000 40,000 1,600
15,000 40,000
;YO
0.5%
$2
0.5%
Oxidized Columbian Asphalt, 160-180O F. 9. P. Lowers Raises Raises Raises Raises a t 3 2 O ers a t 115' blow-
..... ..... Lowers .....
... ... ...
Oxidized Columbian As halt, 180-200° F. P. No effect Raises Raises Raises Raises a t 3Z0, remains same a t 115' F. Raises a t 3Ze raises slightly a t li5O F. Lowers
E.
.....
Lowers Lowers Lowers Lowers
.....
5% 0,5%
Physical properties determined on blends of 0.5. 2, 5 , 10, and 20% polybutene. As determined by visual observation of homogeneity.
and submitted to a slippage test. Lines are drawn parallel to the 12-inch side, 1 inch apart. The panels are placed vertically on their 12-inch sides in an oven a t 160" F. for 5 hours, and the increase in distance between lines is measured. By this method all paints containing 110' F. S. P. asphalt were discarded as too soft; the 160-170" F. S. P. steam-reduced asphalt was substituted for it in later work. Examination of the panels made for the above test showed that, upon standing, the tendency of the polybutene to bloom to the surface of the 10, 15, and 20 per cent blends left the films with a blotched appearance; this indicated a breakup of the asphalt-polybutene colloidal structure during solvent evaporation. As these films were characterized by extreme tack, it was decided to withhold weathering tests on the mixtures until a more general study could be made of solvation and evaporation. Twenty-eight sets of panels were then painted with 0,1,3, and 5 per cent polybutenes of 6000 and 15,000 molecular weight in four asphalts: 220-235' F. S. P. oxidized, 180-200' F. S. P. oxidized, 160-180" F. S. P. oxidized, and 160-170' F. S. P. steam-reduced. Test panels were placed on the southern exposure racks of the General Engineering Building, and in accelerated conditions in a vertical position in the Atlas Weather-ometer. Results on the accelerated tests are listed in Table 111. Each cycle of the Weather-ometer consists of 16-hour exposure to a carbon arc light and finally 2 hours of
tap water spray a t room temperature. Although this test does not give satisfactory quantitative results for asphalt coatings, i t shows qualitative results for comparison. COATINGS IN ACCELERATED TESTS
After two cycles, all of the coats had lost their original luster and all showed checking except the 1,3, and 5 per cent 6000-molecular-weight polybutenes in 220-235' F. S. P. oxidized asphalt, and the 5 per cent 15,000-molecular-wei@;ht polybutene in 220-235" F. 8. P. oxidized and in 160-180' F. S. P. oxidized asphalts. Checking was particularly bad in the 160-170" F. S. P. steam-reduced asphalt paints, some of which had started t o alligator. All blanks had suffered more than their corresponding polybutene blends with the exception of the 160-180" F. S. P. oxidized asphalt. The 220235' F. S. P. oxidized asphalt paints were, in general, noticeably superior to those of the other asphalts. After four cycles all samples were marked by considerable dusting, except for the 5 per cent 15,000-molecular-weight polymer blends where the condition was, a t most, merely incipient. Many coats had begun to alligator, and a t the end of six cycles, this alligatoring had reached a maximum. The three 5 per cent 15,000-molecular-weight blends in the oxidized asphalts were, i s general, the best. The steam-reduced asphalt blends showed bad flow failures. At ten cycles all samples were dusting badly, with the exception of the 5 per cent 15,000-molecularweight blends, b u t checking and alligatoring had begun to disappear. By t h i r t y - e i g h t cycles there had been a general leveling off in the appearance and character of the paints that continued throughout the rest of the test. At this point the 160-180' F. S. P. oxidized asphalt blends showed a slight advantage over the others. All the 160170" F. S. P. steamreduced asphalt panels Sample 91-66, asphalt paint (note oheoking) Sample 91-6E, asphalt-polybutene paint had failed except for the Figure 1. Comparison of Weather-ometer Test on Asphalt Paints, with and without 3 and 5 per cent 15,000Polybutene (Table 111)
INDUSTRIAL A N D ENGINEE-RING CHEMISTRY
484
TABLE 111. Sam le Num%er 91-6A 6B 0c 6D 6E a 6F 6G a
Type of Asphalt Oxidized, S. P. 220-235O F.
91-7A 7B
Oxidized, S. P. 180-200° F.
1 3 5
1 3 5
7D 7E 7F
..
7G
91-8A 8B 8C 8D 8E 8F 8G
Oxidized, S. P. 160-180° F.
91-9A
Steam-reduced, 8. P. 160170' F.
QB 9c 9D 9E 9F 9G
Polybutene Mol. wt. 1 6,000 3 6,000 5 6,000 1 15,000 3 15,000 5 15,000
1 3 5 1
a
5
.. 1 3 5 1 3 5 ,.
Solvent Name Varsol 2
..
..
7c
56.5 58.3 60.0 56.5 60.0 60.0 60.0
PAINTS
Appearance a t End of Test Checking Rusting Condition Chalking Yea Fair I n mots Y es Slight None Good Yes Slight Slight Good Yes Yes Good Y es Slight None Yes Good Yes None Slight Gopd Yes Large checks Fair Slight Yes
Varsol 2
52.0 52.0 52.0 52.0 52.0 52.0 62.0
0.0038 0.0036 0.0036 0.0038 0.0038 0.0038 0.0038
63 63 63 63 63 63 63
Yes Yes Yes Yea Very alight Very slight Yes
On corners Slight Sl.ight Slight None Slight Yes
Good Good Good Good Good Good Good
Yes Yes Yea Yes Y e8 Very slight Yes
6.000 6,000 6,000 15,000 15,000 15,000
Varsol 2
52.0 62.0 52.0 52.0 52.0 52.0 52.0
0.0038 0.0038 0.0036 0.0038 0.0038 0.0038 0.0036
63 63 63 63 63 63 63
Large checks Fine checks Slight Yes Large checks None Large checks
Yes Slight Slight Yes Y es None Yes
Fair Good Good Poor Good Good Poor
Yes Very little Very Yes little
6,000 6,000 6,000 15,000 15,000 15,000
Varsol 2
..
63 63 63 63 63 63 63
Slight Y e8 Wide checks Wide checks Slight Large checks Deep
Yes Y e8 Slight Slight Yes Slight Y es
Fair Poor Poor Poor Fair Poor Poor
Yes Yes Y es Y es Yes Y es Y e8
..
..
Oxidized 230° F 230° F: Oxidized 190' F Oxidized: 170' F: Steam-reduced, 165' F.
'8
6,000 15,000 15,000 15,000 15,000
Solvesso 3
5 5 5
91-16Fb 16G h 16H b 161 b 16J b
Oxidized 230' F Oxidized' 230' F' Oxidined' 190' F' Oxidized' 170° F: Steam-rehuced, 165O F.
10 5 5 5 5
6,000 15,000 15,000 15,000 15.000
91-17A 17B 17C 17D
Oxidizcd 230' F Oxidized: 230' F: Oxidized 170' F. Steam-r:duced, 165' F.
10 5 5 5
91-18A 18B 18C 18D 18E 18F
Oxidized, 9. P. 220-235" F.
1 1 3 5 10 20
5
%
Thickness of Coat, No. of In. Cycles 63 63 63 63 63 63 63
6,000 6,000 6,000 15,000 15,000 15,000 15,000
91-16Ab 16B b 16C b 16D b 16E b
Oxidized:
TESTON ASPHALT-POLYBUTENE
RESULTS O F WEATHER-OMETER
Vol. 35, No. 4
54.5 54.5 54.5 62.0 52.0 52.0 52.0
.... . I
..
....
..
Yes Very slight Yes
50.0 50.0 60.0 50.0 40.0
.. *.
....
50 50 50 50 50
None Y e8 Y e8 Yes Slight
None None None None None
Good Good Good Good Good
Y e8 Y es Yes Yes Yes
Varsol 2
62.5 60.0 60.0 53.5 50.0
.. .. .. .. ..
50 50 50 50 60
None Yea Slight Yes Yes
Very slight Yes Slight Yes Y e8
Good Fair Fair Poor Poor
Yes Yes Yes YE% Yes
6,000 15,000 15,000 15,000
Solvesso 3
53.5 50.0 50.0 40.0
50 50
None Slight Faint Very little
None None None Slight
Good Fair Good Good
Yes Slight Y e8 Yes
87,590 87,590 87,590 87,590 87 590 87:590
Solvesso 3
.. .. .. .. .. ....
Fair Fair Good Good Good Good
Yes Yes Yes Yes Slight None
50.0 50.0 50.0 60.0 68.67 73.0
.. ..
Figure 1.
50
50 50 50 50 50 50 50
Yes Yes None
None _ ."_._
None Large & small checks
b Plus 5% sodium sulfonate or "BI" soap.
TABLE Iv.
GIVINGPROTECTIOK ACCELERATED WEATHERING TEST
COATINGS IN EXPOSURE TESTS
ASPHALT-POLYBUTEKE PAINTS IN
Steel panels painted with paints 91-6A to 6G and 91-7A to 7G, inclusive, were placed on the General Engineering Building on April 17, 1940. Panels painted with paints 91-8A to 5 5 3 5 3 5 15,000 6000 15,000 6000 15,000 6000 8G and 91-SA t o 9G, inclusive, were a180 exposed t o the weather on the same roof on April 22, 1940. On September 200-235 200-235 180-200 180-200 160-180 160-180 s* 3, 1940, most of the paints had failed to give adequate protec60 52 52 58.3 52 52 Varsol 2, % tion. The paints formulated without polybutene had failed completely in every case. The samples all showed a great deal of weathering, but the paints that gave the best protection PAINTS GIVINQ PROTECTION TABLE V. ASPHALT-POLYBUTENE are listed in Table V. IN NORMAL WEATHERING TEST(IN VARSOL2) Shortly after the above panels had been placed under test, Order of s. P. of Polybutene Sample General Oxidized work was instigated t o stan'dardiEe the mixing procedure and % Mol. wt. Number Appearance Asphalt, OF. t o develop the best solvent for use in polybutene-asphalt 91-7FO 1 180-200 5 15,000 paints. Blends of the following were made up in Solvesso 5 3 6000 91-6Ba 2 220-235 91-8C 3 160-180 5 6000 (aromatic solvent) : 5 6000 91-7Cn 4 180-200 Code No. Polybutene Per cent Mol. wt. asOxidized
91-6B
91-0F
91-7C
91-7F
220-235
1
91-8B
91-8F
Ft
91-6A
5
6000
a Sample gave good results in accelerated test.
Paint Number 1 2
molecular-weight blends. All coatings were dusting considerably, and the 220-235" F. s. P. oxidized asphalt paints had assumed a brownish tinge while the steam-reduced asphalt paints were definitely brown. At the end of the accelerated test, the six panels of series 91-6 to 9, inclusive, were found to give good protection and have the best appearance (Table IV).
8 4
---PoIybuteneYo Mol. wt. 10 6000 5 15,000 6 15,000 5 15,000
,
S. P.,
F. 220-235 220-235 160-170 160-180
Asphalt Type Oxidized Oxidized Steam-reduoed Oxidized
These blends were submitted to the best mixing procedure and panels were coated. The coatings showed higher luster and homogeneity than the corresponding Varsol paints. Also, in the course of twenty-three cycles of accelerated weathering there was far less checking than with the Varsol equiva-
485
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1943
Figure2 (Left). Difference between Alligatoring and Checking in Asphalt Films after 63 Cycles in the Weatherometer
Figure 3 (Below). Effect of Polybutene on Weathered A s p h a l t Paints with Red Lead Primer (Table VIL) Checking
Alligatorins
Circles indioate inspeotion points.
ients and no alligatoring. Moreover, the 160-170" F. s. P. steamreduced asphalt sample showed no flow tendencies in contrast to the similar Varsol paint. To further improve mixing, samples of the above paints were given a thorough treatment in a colloid mill and painted out for comparison. Paints 1, 2, and 3 gave no evidence of improved mixing; paint 4 suffered a large drop in viscosity, The film of this paint was soft and tacky. However, during the time before a viscosity determination could be made (24 hours), the viscosity had returned to the original, and a later painted film showed no signs of breaking down. This m a y have been due Sample 91-20-H, with polybutena
Sample 91-20-C,without polybutens
TABLE VI. WEATHER-OMETER TESTON FILLED ASPHALT-POLYBUTENE PAINTS Sam le Numger
%5
Polybutene Mol. wt.
Solvesso z % b y Wi.
2oc
20D 20E
0 0 0 0 0
.. .. .. .. ..
60 60 60 60 60
91-20G 20 H 201 205 20 K
5 5 5 5 5
15 000 15:OOO 15.000 15,000 16,000
60 60 60 60 60
91-20A 20B
Filler Name
%
No. of Cycles
Checking
Oxidized Aaphalt, Softening Point 160-180° Mica 15 50 Slate flour 35 Silica powder 15 25 Talcum owder 50 Marble Jour 15 50 Mica Slate flour Silica powder Talcum owder Marble Jour
15 35 15 25 15
50 50 50 50
Appearance a t End of Teat Rusting Condition
Chalking
F. Yes Slight Y e8 Yes Yes
Y e6 I n s ote slig%t Slight Slight
Poor Fair Fair Fair Fair
Yes Yes Y e8 Y e8 Yea
Slight Slight Slight Slight Slight
No No No No
Good Good Good Good Good
Slight Slight Slight Slight Slight
Good Good Good Fair Good Good
Slight Slight Slight Slight Slight Slight
NO
Steam-Reduced Asphalt, Softening Point 160-170° F.
91-21Gb 21H 21Ib 215
21Kb
:
5 5 5
15,000 15 000 15:OOO 15,000 15,000 15,000
215 4- 1La 5 a Calculated on asphalt. b Paints t h a t gave beat protection.
50 50 50 50
;; I
Mica Slate flour Silica powder Taloum owder Marble four Talcum powder Ilmenite
16 35 15 25
15
25 101
50 50 50
50
No Slight
h.0 Slight
NO
NO
NO
NO No Slight NO
NO
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
486
Red lead primer
Figure 4.
No primer
Effect of Primer on Weathered Asphalt Paint 2 1 4 (aboze) and on Asphalt-Polybutene Paint 21-J-IL (below)
Circles indicate inspection points; note rusting around edges of panels without primer.
Vol. 35, No. 4
91-16.4 to 16J, inclusive (Table 111). During the first twenty cycles these paints showed definite promise; there was far less checking and alligatoring on the painted panels. However after fifty cycles there was no great improvement, but slightly less rusting was noted when the sodium sulfonate was used. Higher molecular weight polybutene mixtures have also been studied. Five paints containing 1 , 3,5,10, and20per centpolybutene of 87,590 molecular weight were tested in the Weather-ometer (Table 111,samples 91-18A t o 18F, inclusive). Paints containing polybutene of this molecular weight contain lower solids content for comparable consistencies. This may be shown by the fact that for 1 per cent polybutene of 87,590 molecular ITeight, 50 per cent Solvesso 3 is required t o give a consistency similar to 20 per cent polybutene of 87,590 molecular weight in 73 per cent Solvesso 3. Polybutene of this molecular weight is also considerably less compatible iyith asphalts. The resulting composition should be classed as a mastic and for that reason a discussion of compatibilities may be irrelevant. The blends of 87,590-molecularmeight polybutene after fifty cycles have shown the best results of any tested to date. Slight dusting was noticed in the 5 and 10per cent blends, but no dusting a t all with the 20 per cent blend. Samples formulated with more than 1 per cent high-molecular-weight polymer were almost free from
to the thixotropic characteristics of plastic oxidiEed asphalt and the polybutene. I n an attempt to improve the bond of the paints t o steel and to improve the compatibility of polybutene in asphalt, sodium sulfonate or sodium alkyl s u l f o n a t e (molecular weight about 450) 1
0
R-$--O--Na I
.
ti was added to asphaltpolybutene paints
Figure 5. Weathered Asphalt-Pokybutene Mica-Filled Paint The tear ooourred in removing the sample from the roof: the circle shows a section magnified 25 times.
INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1943
487
TABLE VII. TWO-YEAR WEATHERING TESTON FILLED ASPHALT-POLYBUTENE PAINTS Sam le Nuder
%a
Polybutene Mol. wt.
Solvesso 2, % by Wt.
....
60 60
Mica Slate flour Silica powder Talcum owder Marble l o u r
Yes Slight Slight None None
Yes Slight Heavy Slight Heavy
Fair Fair Poor Fair Fair
Oxidized Asphalt, Softening Point 160-180° F. Mica 15 No None Slate flour 35 No Yes Silica powder 15 No Slight Talcum owder 25 No Slight Marble l o u r 15 No
Slight Slight Yes Slight Extreme
Slight Slight Slight Heavy Heavy
Poor Fair Poor Fair Failure
60 60 60 60
Mica Slate flour Silica powder Talcum owder Marble l o u r
None None None None None
Slight Slight Slight Heavy Heavy
Fair Good Good Good Good
.. .. ..
50 50 50 50 50
Steam-Reduced Asphalt, Mica Slate flour Silica powder Talcurn owder Marble t o u r
Softening Point 160-170° F. 15 No Y ee 35 No Yes 15 No Y e8 25 No Y e8 16 No Slight
Yes Yes Slight Yes Y e8
Heavy Yes Yes Very heavy Heavy
Poor Good Poor Poor Poor
.... .. *. ..
50 50 50 60 50
Mica Slate flour Silica powder Talcum owder Marble l o u r
15 35 15 25 15
None None None Slight Slight
Slight Slight Slight Slight Slight
Fair Good Good Fair Fair
15,000 15,000 15,000 15,000 15,000 15,000
50 50 50 60 50 50
Ye8 Yes Slight Slight Slight Slight None None None None None None
Slight Slight Slight No Slight Slight Slight None None None None Slight
Fair GoFd Frtir Good Good Fair Good Excellent Excellent Excellent Excellent Good
91-20G 20H 201 205 20K
5 5 5 5 5
15,000 15,000 15,000 15,000 15,000
60 60 60 60 60
91-20G 20H b 201 205 20K
5 5 5 5 5
15,000 15,000 15,000 15,000 15,000
60
0
..
0 0 0
91-21Aa.d 21B 21c 21D 21E
0 0 0 0 0
91-21GC 21H 211 215 21K 215 1La 91-21G c 21Hee 211 21Jee 21K 215 f 1Ld
5 5 5 5 5 5 5 5 5 5 5 5
+
0
Condition
Very poor Poor Poor Poor Failure
0
91-21A%J 21B 21c 21D 21E
General Appearance Peeling Chalking Heavy Heavy Y es Y e8
0 0 0 0
Checking
Yes Y e8 Moderate Extreme Extreme
91-20A 20B 2OC b 20D 20E
0
Red Lead Primer
76"
Oxidized Asphalt, Softening Point 160-180° F. Mica 15 No Yes Slate flour 35 No Yes Silica powder 15 No Yes Talcum powder 25 No Yes Marble flour 15 No Yes
.. .. .. .. .. .. .. .... ..
0 0 0 0
91-20A 20B 2oc 20D 20E
Filler Name
..
60 60 60
60
60
60 60
60
15 35 15 25 15
Yes Yes Yes Yes Yes
Y es Yes Yes Yes Yes
...
15
Yes Yea Yes Yes Yes
35
15 25 15
Yes Yes Yes Yes Yes
Slight None None None None
Slight None None None Slight
Softening Point 160-170' F. 15 None No 35 None No 15 Slight No 25 Y es No 15 Slight No $ ~ ~ ~ e ~ ~ $ d25e r No None 15 Yes None 35 Yes None 15 Yes None 25 Yes None 15 None Y e8 25 Yes None 10
Steam-Reduced Asphalt, Mica Slate flour Silica powder Talcum owder
I
Calculated on asphalt. b See Figure 3. Average thickness of paint film of series 91-21A to 215. approximately 0.0076 inch. d See Figure 4. a Paints that gave best protection. a 0
checking or any other types of failure. These paints were not tested under normal weathering conditions. Several filled asphalt-polybutene paints were prepared in the laboratory kneader and tested for weathering characteristics. Two coats of each paint were placed on steel, and the plates were tested in the Weather-ometer and on the roof of the General Engineering Building. Some tests were also conducted with the paints over steel that had been given a primer coat of red lead. The experimental paints did not brush so easily over red lead as over the clean polished steel. Table VI lists the composition of each paint and results observed in the Weather-ometer. They indicate that polybutene reduces the chalking and improves the surface consistency of filled asphalt paints. It appeared desirable t o compare a filled asphalt-polybutene blend with other commercialasphalt and coal-tar roof coating. Therefore, an asphalt-polybutene mica-filled blend was formulated and placed on roofing paper covering a portion of the Pipe Trench Building a t Bayway. At the same time eight other well-known commercial products, some with a guarantee of ten years, were also placed on a part of the same building. After thirteen months the asphalt-polybutene mica-filled product was rated first, based on durability, application, and cost to the company by a disinterested neutral observer (Figure 5 ) . All of the products tested showedsome evidence of chalking.
Of considerable interest is the two-year actual weathering lL, inclusive. The retest for filled paints 91-20A to 215 sults are listed in Table VII. It is evident that the presence of a red lead primer coat gives improved protection to metal when asphalt-polybutene paints are used. Also 5 per cent of 15,000 molecular weight polybutene increased the weathering resistance of a number of the experiment'al filled asphalt paints. The improved weathering property of asphalts conditioned with polybutene may be due in parts to the ability of this stable polymer to plasticize the product film and, therefore, to eliminate so-called structural hardaess (3).
+
CONCLUSIONS
1. Less than 10 per cent polybutene of 6000-15,000 molecular weight in oxidized and steam-reduced asphalts reduced or completely eliminated the tendency of the asphalts to alligator, slightly reduced the tendency to check, deduced surface hardness, and increased the length of time before dusting began. 2. Films having better appearance and resistance to weathering were formed from cutbacks containing highly aromatic solvents than from cutbacks containing highly paraffinic solvents. 3. Polybutene of 6000-15,000 molecular weight also improved the weathering resistance of inert filler-asphalt films.
INDUSTRIAL AND ENGINEERING CHEMISTRY
488
With fillers steam-reduced asphalts were more favorable than oxidized asphalts; without fillers the reverse was true. 4. All coatings on red lead primer were superior to those on polished steel. 5. I n general, the improvement was proportional to the polybutene content, the polybutene film of higher molecular weight having better physical properties; but films containing over 10 per cent polybutene were either too tacky, for the low-molecular-weight polybutene, or too viscous for easy application in the case of the polybutene of higher molecular weight.
Vol. 35, No. 4
ACKNOWLEDGMENT
The advice, encouragement, and assistance of G. W. Oxley during the course of this work is greatly appreciated. LITERATURE CITED
(1) S t a u d i n g e r , H., "Der A u f b a u der hochmolekularen organisohen Verbindungen", 1932. (2) T h o m a s , R. M., Zimmer, J. C., T u r n e r , L. B., Rosen, R., a n d EXG.C H E M . ,32, 299-304 (1940). Frolich, P. X., IND. (3) Traxler, R. N., a n d Coombs, C. E., Proc. A m . SOC.Testing Materials, 37, 11, 549 (1937). PRESENTFAD before the Division of Paint, Varnish, and Plastics Chemistry a t the 104th Meeting of the AMERICAN CHEMICAL Socxnry, Buffalo. N. Y .
Brittle Temperature of
Rubber under Variable Stress A. R. KEMP, F. S. MALM, WINSPEAR
AND G. G.
Bell Telephone Laboratories, Murrab- Hill, N.J
HE projected use of synthetic elastomers on a large scale for outdoor service presents a pressing need for information dealing with their properties a t subzero temperatures. Under extreme cold weather conditions insulation, cable jackets, tires and tubes, and many other items must be capable of being (repeatedly) flexed without failure a t temperatures of -50" C. or lower. I n a previous paper (25) a method was presented for determining the critical temperature of fracture where the sample is bent rapidly through an angle of approximately 90". Although this test provides an excellent technique for the comparison of various rubber compositions, it was realized that the procedure should be revised to include the effect of varying the magnitude of stress as well as the rate of bending in order t o simulate more closely certain types of service. The present paper does this and also reviews some of the work already carried out in the field of low-temperature rubber testing. Early investigation (21) showed that crude rubber inoreased in tensile strength a t low temperatures. Le Blanc
T
~~
and Kroger (17) described this phenomenon as cold vulcanization. The observation that rubber which had been elongated and cooled in liquid air could be disrupted into fibrous fragments was reported by Hock (11). Mark and Valko (19) associated this phenomenon with brittleness and conducted experiments which showed that, under given test conditions, the "critical point" of raw rubber was -67" C. Ruhemann and Simon (89) observed that a sharp rise in the specific heat of smoked sheet rubber occurred in the range -65" to -75" C. Bekkedahl (1) found that a t -70" C. a sharp change of slope occurs in the temperature-volume curve with both supercooled amorphous and crystalline raw rubbers. This observation is important because it demonstrates that the state of brittleness develops at the same point independently of the existence of either physical state. Differences in the brittle points of crystalline and amorphous smoked sheet rubber, as determined by the fracture method described in the previous work (25),were found to be slight. Aside from the fracture method ( I S , 16,2626)other procedures used in investigations of rubber at low temperatures may be grouped according to the method of test into three general types involving deflection (15,18),penetration (go), and elastic
~
This paper supplies the need for a method to determine the temperature at which rubber and similar materials fracture under variable bending stress. Although the brittle temperature is sharply defined under high-speed bending through a sharp angle, it is lower as the speed of application or the magnitude of the stress is reduced. In some instances decreases of more than 28' C. in brittle temperature resulted from
reductions in bending stress such as might be encountered in service. Vulcanized pure gum natural rubber and plasticized polyvinyl chloride-acetate copolymer showed the largest changes, whereas the compounded and vulcanized natural and synthetic rubbers involved in this study exhibited a reduction in brittle temperature from 5' to 10' C. in going from the highest to the lowest stress employed.
