FIRE-RETARDANT PAINTS Role of Pigment Volume, Antimony Oxide, and Chlorinated Parafin LEON S. BIRNBAUM AND MORRIS MARIIOWITZ1 Industrial Test Laboratory, Philadelphia Naval Shipyard, Philadelphiu, P a .
obvious that any paint which tends t o flash or flame, when the steel on which it is applied is quicklv heated to a high temperature, M ould be hazardous. The purpose of this paper is t o present data concerning factors involved in formulating fire-retardant paints of this second category-that is, paints which are fire retardant of themselves but which are not necessarily designed to protect a combustible substrate. The test is based on steel as the substrate, and the results are not beclouded by considerations of possible variations in substrate, as would be true if a combustible material, such as wood, had been used. The results therefore may be presented as strictly representing the behavior of the paints, rather than representing the behavior of the system paint-substrate. A similar study was reported by the Kew York Paint and Varnish Production Club (16). S o attempt was made to restrict formulations to those compositions which would be considered practical, although accepted paint ingredients rrere used. Rather, the plan followed was to vary each selected factor in such fashion that basic information would be obtained. The information merely delineates the area within which the practical formulator must work if he wants to achieve a degree of fire retardance acceptable under the test method used in this investigation. To transform such information into a practical paint requires the selection of materials which will supply the necessary fire retardance and the compounding of these materials in such a fashion that the finish will also bc acceptable to the user as to color, covering power, drying time, and similar properties. The factors selected for study include pigment volume (ratio between the volume occupied by the pigment and the total volume of the pigment and the nonvolatile portion of the vehicle), chlorine concentration (per cent chlorine by weight of the nonvolatile portion of the total vehicle), and presence or absence of antimony oxide in the pigmentation (ratio between the volume occupied by the antimony oxide and the total volume of pigment). Increasing the pigment volume entails decreased organic matter in the dried film and should be expected to increase fire retardance. Chlorinated materials, especially in conjunction with antimony oxide, are widely used for imparting fire retardancy (6). The presently specified Navy fire-retardant paint (24) utilizes the features of high pigment volume and antimony oxide to achieve fire retardance. Battle damage reports have Figure 1. Thermoelectric i n d i c a t e d t h a t t h e f i r e r e t a r d a n c e has Tester
T h e principle of the test method selected for this investigation is based on the transformation of electrical energy into heat energy by short-circuiting, across the test specimen, the current delivered by a motor generator. This causes a rapid heating of the test specimen; the same test conditions can be reproduced reasonably well for each test run. In order to evaluate the fire-retarding effectiveness of antimony oxide and organically combined chlorine, a total of 101 paints was prepared and tested. Results showed both agents to be effective and indicated that their relative efficiency is dependent upon the amount of organic matter in the dried film (indicated by pigment volume). The results are presented primarily as a guide to practical formulation of fire-retardant paints for use over noncombustible substrates, such as steel.
M
A S Y combustible materials may be rendered less hazardous by proper attention to procedures intended to render them f i e retardant. (The term “fire retardant” as used in this paper describes materials which may be destroyed by exposure to flame but which do not further the spread of fire.) Interest in such materials is widespread, and a considerable number of patents covering such coatings or impregnants has been issued both in the United States and foreign countries. Primary emphasis in fire retardance has been directed to coatipgs or impregnants which will protect a combustible substrate. A familiar example is a fire-retardant preservative compound for canvas (13). Canvas, after impregnation with this compound, although charred and destroyed by direct application of flame, will not burst into flame or continue burning after the flame has been removed. Likewise some studies have been made of paints designed to protect wood in a similar fashion (4,7 , 17). The interests of the United States Navy Department, however, have been concentrated on paints which were fire retardant per se without any consideration of whether such paints would protect a combustible substrate. This follows from the fact that steel bulkheads are used to separate compartments in the interior of ships. These steel bulkheads must be painted to prevent corrosion. The only factor which necessitates the use of a fire-retardant paint in this case is the prevention of the spread of fire from one compartment to adjacent compartments. It is Present address, 1809 North 33rd St., Philadelphia 21, Pa.
400
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March 1948
59"
H
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Figure 2.
40 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
Wiring Diagram for' Thermoelectric Tester
A, voltmeter range 0-100 volts d.c.; B , ammeter, range 0400 amperee d.c.; C: speeimen holder electrodes; D , shunt, 400 amperes, 50 millivolts; E, snap switch, two-pole single throw; F, d.c. contactor, 400 amperes, and coil, 110 volts a.c. or d.c.; G, souree of power, 110 volts a.c. or d.c.; H , conductors to welding generator, 3/0 stranded
been satisfactory in service. However, the high pigment volume induces other unsatisfactory properties, such 8s poor resistance to staining and high humidity.
of the steel specimen, the rate of heating being dependent upon such factors as initial current, dimensions of the test panel, and time. However, by controlling these factors, the sam conditions of test can be reproduced reasonably well for each test run. Figure 1 shows the testing device with a panel in position for determining fire retardance. A wiring diagram of the apparatus is given in Figure 2. The panels were mild steel of the dimensions shown in Figure 3. The test paints were applied to both sides of the test panels to yield a dry film about 3 mils (0.003 inch) thick per side (corresponding to about two or three coats as normally applied). Automatic spraying equipment was used. and the actual film thickness was measured and recorded for each test result. The steel panels were coated not only over the narrow (constricted) area, but also for a distance of about 2 inches beyond this area. The initial conditions of test were a current of 300 amperes and an open circuit voltage of 78 volts. When the circuit was closed the voltage across the constricted area of the bare (unpainted) metal panel fell to less than 1 volt and rose to approximately 7.5 volts a t the end of the 30-second test period. During this time the amperage fell approximately 10%. The temperatures developed during the run were 1700' F. a t 10 seconds, 2100' F. at 20 seconds, and 2300" F. at 30 seconds as determined by an optical pyrometer. This represents a severe condition of test, but was selected after study of temperatures attained in large scale fires by utilizing simulated ship structures at the Philadelphia Naval Base Fire-Fighters' School. Maximum temperatures of 2000' F. were obtained in these structures 2.5 to 3 minutes after starting an oil fie. Tests performed by the Naval Research Laboratory (9) indicate that combustion temperatures ranging from 1300' to 2000' F. arc reached in a burning fuel-oil tank. Actual test conditions somewhat more severe than those noted in simulated ship structures were deliberately chosen to provide a satisfactory safety factor. To determine the fire retardance of a paint, test panels were prepared by automatic spraying as described. These panels were allowed to air dry for a period of at least 1 week, The test apparatus was then properly adjusted to give the desired conditions, the painted panel inserted, and the current switched on for a period of 30 seconds. During this period the constricted portion of the panel was rapidly heated to glowing. The paint on this area charred and finally completely disintegrated. The paint on the wider areas of the panel a t either end of the constricted area was closely observed for any tendency to flash or flame. If flaming occurred, the flame height was estimated from guide lines (1 inch apart) on the instrument board of the apparatus, and the time at which initial flaming occurred was recorded. I n all cases those paints which showed no flaming a t the end of 30 seconds did not ignite even though the current was permitted to continue considerably beyond this period. Only these latter paints were considered to be f i e retardant. This provided an adequate estimation of differences in f i e retardance. Flashing and flaming generally were observed only on the wider (and thus cooler) areas of the panel. Only when paints were extremely poor in fire retardance did flaming occur on the constricted area. This method of test is considered to be ideal in
APPARATUS AND PROCEDURE
A wide variety of test procedures appeai in the literature (1, 3, 3,6, 8,10, 18, 19, $0). The procedure selected for this investigation utilizes a device developed by H. R. Moore of this laboratory (6). The principle of this method is based on the transformation of electrical energy into heat energy by short-circuiting, across the test specimen, the current delivered by a motor generator. This causes a rapid heating
I
4
Ca.6. taooos-
Figure 3.
Diagram of Test Panel
402
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 40, No. 3
ment volume; the second represents the chlorine content (per cent by weight) of the nonvolatile vehicle; and the letter identifies the pigmentation used. For example, 40-0-A indicates 40% pigment v0lume-07~ chlorineantimony oxide present (7.8% by volume), whereas 30-35-2 indicates 30% pigment volume-35% chlorine (nonvolatile vehicle, 50% chlorinated paraffin, 50% alkyd resin)-antimony oxide absent. Paint 40-0-Z Paint 40-0-A Maximum flame height was used as an index of combustibility, and the flame rating scheme given in Table 111 was followed in reporting result,s. The results of test presented in Table IV represent the averages of four determinations. The data in Table IV indicate that susceptibility to flaming and height of flame decrease as the pigment concentration (pigment, volume) increases. Fire retardance is not achieved with pigmentation Z even at 70% pigment volume. With pigmentation 8 , howPaint 60-0-2 Paint 60-0-A ever, fire retardance is reached a t 50% pigment volume: this indicates that Figure 4. Role of Antimony Oxide in Fire Retardancy antimony oxide contributes to fire retardance. However, as the pigment volume is decreased, the effect of the antimony oxide a p respect to naval use, since it is expected that paint will be depears to be overshadowd by the increasing amount of comstroyed on areas immediately above extremely hot spots, but it is important that paint surrounding this glowing area does not bustible material. SERIES B. Table IV shows that, with pigmentation A , begin t o flash or flameand thus augment the spreading of a fire. fire retardance is lacking at or below a pigment volume of 40%. Figures 4 and 5 show examples of the type of flame behavior obIt was therefore considered advisable to study further the effect served. (The flame which is bright and fairly well defined on the of antimony oxide. A second series of paints was prepared at photograph should not be confused with the smoke which is hazy. 40% pigment volume in which the amount of antimony oxide The first guide line represents the zero level. For example, in was increased from 20% to 100% by volume of the pigment porFigure 4, paint 60-0-2 illustrates a flame height of 1 inch, wheretion in steps of 20%. This was accomplished by removing aluas paint 60-0-A shows smoke but no flame. Paint 40-0-A illusminum stearate, magnesium silicate, titanium calcium pigment, trates a flame height of 3.5 inches with considerable smoking.) and zinc oxide (in that order) from pigmentation A , and replacing them by an equal volume of antimony oxide in such EXPERIMENTAL RESULTS amounts as to yield the proper percentage of antimony oxide. SERIESA. -4 preliminary study was made of the effect of (20% Sb203is pigmentation B, 40% SbzOJ is pigmentation C, antimony oxide and pigment volume on fire retardance, using etc., to 100% SbzO3, pigmentation P.) Five replicas of each the presently specified Savy fire-retardant paint (14) as a control. paint were run. Since results appeared inconsistent with exThe formulation of this paint is given in Table I. Two pigmentations were used in this series and are given in Table 11. Pigmentation A is as presently specified in the Navy fire-retardant paint and contains 7.8% antimony trioxide by volume. PigOF PAINTS WITH A N D WITHOUT TABLE11. PIGMENTATION mentation 2 is similar, except that antimony trioxide has been ANTIMONYOXIDE replaced by an equal volume of zinc oxide. Each pigmentation Pigmentation Z Pigmentation A Wt., % by Vol., Wt., % by Vol., was formubted into paints a t various pigment volumes using Pigmentation lb. wt. gal. Ib. wt. gal. alkyd resin (15)as a vehicle. Titanium dioxide 250 29.3 7 . 7 2 250 29.4 7.72 All paint formulations reported in this paper may be identified Titanium calcium pigment 235 27.5 8 . 6 7 235 27.6 8.67 Zinc oxide 170 20.0 3 . 6 6 2 6 7 . 5 3 1 . 4 5.75 by the following scheme: The first number represents the pigMagnesium silicate Antimony oxide 'Aiuminum stearate Total
90 100 8.5
gj3.j
10.5 11.7 1.0
3.79 2.09 1.03
90
10.6
... 8.6 i:O 1oo.o 26.96 851.0 1oo.o
3.79
1:03 26.96
TABLE I. 52P22 FORMULA (6OY0PIGMENT VOLUME) Total pigment (pigmentation A) Alkyd resin (70% solids) Petroleum spirits Lead naphtHenate drier Cobalt naphthenate drier Manganese naphthenate drier Total
W't. for 100 Gal., Lb. 853.5 229 281 7.8
a Figure in parentheses refers t o volume
1.0
0.5 1372.8
of vehicle solids.
vel., Gal. 26,96 29.00 (18.46)a 43,05 0.81 0.12 " 0 06 100.00
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TABLE 111. FLAhIE-RATING SCHEME Max. Flame Height, In. 0
Flash T o 6/a a/,to
la/,
I'/z to 2'/3 2'/4 to 27/3
Flame Rating
Max. Flame Hripht, In. 3 t o 35/s 33/4 t o 4 3 / 8 4'/z t o 5'/3 5'/4 to 5 7 / 8 6 and over
Flame Rating
4 3 2 1 0
March 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
Fire-retardant paints consistently show no burning and, again, are as well evaluated by one test panel as by many, Borderline paints n p t be replicated and may give inconclusive results even when the test i s highly replicated. It is therefore evident that it is necessary to run replicate tests on each paint for satisfactory results. Table V does indicate, as does Table IV, that antimony oxide contributes to fire retardance, since paints containing 20 to 100% antimony oxide are definitely less flammable than those containing either none or 7.8% antimony oxide. A more important conclusion, however, is that antimony oxide alone does not possess a sufficient degree of efficiency to produce a fire-retardent paint (as defined by the test method used) at the 40y0 total pigment volume level. Tables IV and V together show that antimony oxide may be used as the sole fire-retardant agent to produle satisfactorily fire-retardant paints only a t pigment volumes of boy0 and above. According to Troutman (111, the pigment tolume of flat paints may fall anywhere within the range of 71.5 to 52.5%; that of semigloss and gloss paints within the range of 52.5 to 33%; and that of enamels within the range of 33 to 20%. Thus, the use of antimony oxide as the only fire-retardant agent is generally limited to the formulation of flat paints. SERIESC. Since it had been established that antimony oxide alone could not be used to produce fire-retardant paints a t 40% total pigment volume or lower, a third series of paints was prepared ip which organically combined chlorine was investigated, either alone or in conjunction with B fixed amount of antimony oxide. Chlorine was introduced into the vehicle of these-paints in the form of a resinous chlorinated paraffin (12) containing 7070 chlorine by weight. Ninety paints were prepared in which the per cent chlorine by weight in the vehicle (nonvolatile portion) was varied in 5y0 steps over the range 0 to 70% by mixing alkyd resin and chlorinated paraffin. Paints were prepared a t three pigment volumes (20, 30, and 40%). At each pigment volume level, two parallel series of paints were studied, one series containing 7.8% by volume of antimony oxide in the pigmentation, the other series being without antimony oxide. These paints are identified, as previously described in this report, with notations that indicate pigment volume, per cent chlorine, and presence or absence of antimony oxide. Results of test given in Table VI represent averages of four determinations. These results again show the existence of paints falling into the three general categories previously described as flammable, borderline, and fire retardant. Increasing chlorine content results in increasing fire retardance, and the amount of chlorine necessary is dependent upon pigment volume (amount of combustible material) and presence or absence of antimony oxide.
TABLEIV. EFFECT OF PIGMENT CONCENTRATION ON FIRE RETARDANCE IN SERIES A, CHLORINB-FREE ALKYD RESIN VEHICLE Pigmentation A Flame Film thickness, mils rating 3.4 0 3.2 1 4 4
Pigment Concn., VOl. %
in
Pigmentation Z Flame Film thickness, mila rating
..
3'. i
.41.
3'. 6
TABLEV. EFFECTOF ANTIMONY OXIDE CONCENTRATION ON FIRERETARDANCE IN SERIESB, CHLORINE-FREE ALKYDRESIN VEHICLE,TOTAL PIGMENT VOLUMB 40% SbtOa Concn., VOl. % 0 7.8 20
Pigmentation
Z
A B
C
40 60 80 100
D E F
Film Thickness, Mils 3.5 3.2 3 0 3.1 3.0 3.0 2.9
Flame Rating 4 4 9 9 9 9 9
pectations, an additional four replicas were prepared and tested. The results are given in Table V. It may be advisable to discuss the data forming the basis for Table V in some detail. All panels prepared from those paints which contained either no antimony oxide, or 7.8% antimony oxide by volume, were flammable, and all replicate panels prepared from them behaved in a consistent manner. However, this was not true of the remaining paints. For exdmple, nine panels were prepared with the paint containing 20% antimony oxide by volume. Of these, three showed no burning, four exhibited a momentary flashing but no continued burning, and two showed continued flames about 1 inch high. Thus, it is at once evident that a single test panel cannot be relied upon in all cases. In some cases, as in the case of paint Z, the relative flammability of the paint is as well measured by testing a single panel as it would be if a number of panels were used. In other cases, as in the case of paint B, an erroneous conclusion might result if only a single test panel were used. Further experience with the test method confirmed this erratic behavior, which was associated with paints that are considered to be borderline cases relative to fire retardance-that is, all paints tested were found to fall into three general categories: flammable, borderline, and fire retardant. Flammable paints consistently burn in the test and are as well evaluated by one test panel as by many,
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TABLE VI. EFFECTO F CHLORINE CONCENTRATION ON FIRERETARDANCE I N SERIES c , CHLORINATED PARAFFIN-ALKYD RESIN VEHICLE 7
Chlorine Concn., Wt. %
20% pigment vol. Pilm thickness, Flame mils rating
3 4 4
4 7
8" 8"
8" 80 10 10 10 a
Borderline paints.
Antimony Oxide Present 30% pigment vol. Film thickness, Flame mils rating 4 2.9 5 2.9 6 2.9 6 3.1 8" 2.9 8" 3.0 2.9 9" 94 2.9 9a 3.2 3.1 9Q 10 3.2 10 3.3 10 3.4 10 3.4 10 3.7
40% pigment vol.
Film thickness, mila 3.2 2.8 g.0
3.1 3.4 2.8 3.0 2.9 3.1 3.2 3.3 3.1 3.4 3.2 3.6
Flame rating 4 8" 9" 80 9" 10 10 10 10 10 10 10 10 10
10
20% pigment vol. Film thickness, Flame mils rating 3.3 3.0 -3.2 3.2 3.3 3.3 6 3.1 8" 3.0 9a 3.0 9a 3.5 9a 3.6 10 3.5 10 3.4 10 3.6 10 3.4
-Antimony Oxide Absent 30% pigment 40% pigment vol vol. Film Film thickthickness, Flame ness, Flame mils rating mils rating 4 4 2.6 2.9 4 6 2.9 2.9 4 6 2.8 3.1 6 5 3.0 2.9 80 5 2.9 2.5 7 8" 3.2 2.9 8a 9" 3.0 2.7 10 3.0 2.8 9" 10 3.1 2.6 90 10 9" 3.9 2.7 10 10 2.5' 4.0 10 10 4.0 2.6 10 10 4.0 2.7 10 10 2.5 3.8 10 2.6 10 3.8
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INDUSTRIAL AND ENGINEERING CHEMISTRY
404
Vol. 40, No. 3
Paint 20-0-2
Paint 30-0-2
Paint 20-10-2
Paint 30-10-2
Paint 40-10-2
Paint 20-35-2
Paint 30-35-2
Paint 40-35-2
Paint 30-io-2
Paint 40-70-2
Paint 20-70-2
Figure 5.
Paint 40-0-2
Role of Pigment Volume and Chlorine Content in Fire Retardancy
DISCUSSION
The foregoing section indicates that fire-retardant paints to be used over noncombustible substrates may be formulated by simplv using the antimony oxide as part of the pigmentation only when dealing mith flat (high pigment volume) paints. If enamel or semigloss paints are desired, organically combined chlorine must constitute a part of the vehicle, and concurrent use of antimony oxide is sometimes advantageous. Thus, the formulator will be well advised to begin by selecting the highest
permissible pigment volume. This may allow the omission of chlorine-containing materials entirely, and if so will eliminate concurrent problems connected with the possible presence of hydrogen chloride or phosgene (or other lachrymatory or toxic vapors) in the fumes evolved at high temperatures. Although it is known that such fumes may be avoided by the use of calcium carbonate in the pigmentation, it has not yet been established whether the use of calcium carbonate will reduce the fire-retarding efficiency of the chlorinated material
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1948
405
LITERATURE CITED
Additional studies covering this point are planned, together with studies to determine whether results similar to those reported here are obtained when other sources of chlorine are utilized, such as chlorinated alkyd resins, vinyl resins, or chlorinated rubber.
Am. Wood Preservers Assoc., ”Fireproofing,” Rept. of Com-
mittee 9 (1944). Brit. Standards Inst., No. 476 (1932). Bryan, J., and Doman, L. S., Wood, 21, 19 (Jan. 1940). C. D. I. C. Club, Oficial Digest Federation Paint & Varnish Production Clubs, 262, 512-17 (1946).
CONCLUSIONS
Clayton, E. C., and Heffner, L. E. (to W. E. Hooper & Sons Co.), U. S. Patent 2,194,690, (April 25, 1933). Gardner, H. A., and Sward, G. G., “Physical and Chemicd Ex,amination of Paints, Varnishes, Lacquers, and Colors,” ‘10th ed., pp. 386-9, Bethesda, Md., H. A. Gardner Laboratories, Inc., 1946. Forest Products Lab., Madison, Wis., Bull. R-1280 (Sept. 1942). Landt, G. E., and Hausman, E. O., IND.ENG.CHEM.,27,288-91
By the use of a thermoelectric tester, based on the principle of transformation of electrical energy into heat energy by short. circuiting, across the test specimen, the current delivered by a motor generator, it was possible to evaluate the role of pigment volume, antimony oxide, and chlorinated pariffins in fire-retardant paints. 1. Both antimony oxide and organically combined chlorine are of value as agents to impart fire retapdance. 2. Antimony oxide, used as the sole fire retardant, is effective only when the amount of organic matter in the dry film is smallthat is, only at pigment volumes of 50% or more. 3. The amount of organically combined chlorine necessary to achieve fire retardance depends on the amount of organic matter in the dry film and, t o a lesser extent, on the concurrent presence or absence of antimony oxide.
(1935)
MoElroy, J. K., Natl. Fire Protection Assoc. Quarterlg, 39, 4 , 307 (1946).
MoNaughton, G. C., and Van Kleeck, A,, Forest Products Lab., Madison, Wis., Bull. R-1443 (Jan. 1944). Matiello, J. J., “Protective and Decorative Coatings,” Vol. 3, pp. 353-4, New York, John Wiley BE Sons, 1943. Navy Dept. Bur. Shipsspecification52P63(INT) (Oct. 10,1943). Navy Dept. Specification 52C26 (March 1.5, 1946). Ibid., 52P22a (June 15, 1946). Ibid., 52R13a (Aug. 15, 1945). N . Y. Club, Oficial Digest Federation Paint & Varnish Production Clubs, 250, 408-20 (1945). Ibid., 262, 575-615 (1946). Schlyter, R., Statens Provningsantalt, Stockholm, Medd., 62, 1-41
ACKNOWLEDGMENT
The authors wish to express their sincere appreciation to W. W. Cranmer for his advice and criticism, both on the progress of the work and the finished paper, and to M. Alpert and M. Goldberg for their assistance in the preparation of paints and test specimens. The opinions expressed in this paper are those of the authors and do not necessarily represent the opinion of the Navy Department.
(1939).
‘Schulte, E., Oficial Digest Federation Paint & Varnish Produc,
tion Clubs, 214, 123-34 (1942). Truax, T . R., and Harrison, C. A , Proc. Am. SOC.Testing Materials, 29, 973-89 (1929).
RECBIVED July 10, 1947. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 112th Meeting of the AMERICAN CHEMICAL SOCIETY, New York, N. Y.
Suitability of Gasolines as Fuel J
EFFECT OF CONTAMINATES EXTRACTED’ FROM SYNTHETIC VULCANIZATES ROBERT R. JAMES AND ROSS E. MORRIS Rubber Laboratory, Mare Island Naval Shipyard, Vallejo, Calif.
A test procedure is described which will enable determination of the gum-forming tendencies of contaminates of gasoline. I t has been demonstrated that extractable plasticizers can contaminate gasoline sufficiently to cause gum deposit in an internal combustion engine, and that contamination of leaded gasoline by phosphaterbqaring plasticizers will cause serious losses in octane rating.
P
. .
LASTICIZERS in considerable proportion are added t o nitrile rubbers for the purpose of improving the processing characteristics of the raw mixes and increasing the resilience and softness at normal and low temperatures of the vulcanizates. As most of these plasticizers, unfortunately, are extractable by gasolines, users of hose, gaskets, tanks, etc., which are lined or constructed with nitrile rubber vulcanizates and are in gasoline service, must beware the effects of the extracted plasticizers on the suitability of the gasoline as fuel. The purposes of the investigations described herein were twofold: to develop a method for evaluating extractables which would reflect truly the gum-forming tendencies of fuel contaminates, and t o determine the effect of extracted plasticizers on the performance characteristics of aviation-type fuels.
.
GUM-FORMING CHARACTERISTICS OF EXTRACTIONS
The practice has been for purchasers t o specify a maximum amount of nonvolatile matter which may be extracted from a standard-size specimen cut from the article in question. The extraction fluid is generally gasoline or a synthetic test fuel. The amount of material extracted by the gasoline is determined by evaporating t o dryness on a water bath or electric hot plate, followed by further drying of the residue in an air oven a t moderate temperature (6). This procedure has two disadvantages: It is frequently impossible to evaporate the gasoline t o dryness on a water bath because many of the extracted plasticizers are high boiling liquids, and the vapor pressure of gasoline is reduced t o such an extent by the extracted material that the high boiling constituents in the gasoline are not removed by this treatment. Thus, the residue usually ‘consists of most of the extracted materials (part having been lost by evaporation) and the highest boiling fraction of the gasoline. The extracted material would presumably consist of plasticizers, sulfur, fatty acid, zinc salts of accelerators, antioxidants, and other miscellaneous compounding ingredients. Besides the uncertainty of this determination, the idea of accepting the total extraotables as being harmful to an engine is
