Flexibility

Eng2;r

Compounding Acry lonitrile-T y pe Rubber for l o w Temperature

Flexibility

ing

Process development I

RICHARD A. CLARK AND JOHN B. DENNIS BATTELLE MEMORIAL INSTITUTE, COLUMBUS, OHIO

5

T h e object of the research was to improve the low temperature flexibility and oil resistance of AN-P-79 type hydraulic pacldngs. The choice of vulcanizing system had only a small effect on low temperature flexibility. The higher the carbon black loading, the higher was the hardness and the poorer the low temperature flexibility. In stocks of equal hardness, MT, SRF, and MAF blacks were best, HAF black intermediate, and EPC black poorest in low temperature flexibility. The addition of both plasticizer and carbon black tended to improve low temperature flexibility. This improvement fell off with hardness, and became negligible at a hardness of about 85 durometer. Differences in low temperature flexibility between stocks, varying in composition but the same in hardness, were substantially reduced by aging in a petroleum-base hydraulic fluid. Data presented should be useful to those interested in low temperature flexibility and/or oil resistance. It is recommended that minimum levels of plasticizer and carbon black be used in seeking a compromise between hardness, swell, and low temperature flexibility.

T

temperature flexibility are often temporary, because, when highly plasticized compositions are immersed in oil or gasoline, the plasticizer may be lost. The loss of plasticizer is not serious when the immersion medium is absorbed and contributes a significant amount of plasticization itself. The amount of such plasticization depends on both the nature of the immersion medium (5, 7, 14, 20) and the composition of the rubber employed. The higher the resistance of the base polymer to the particular oil, the less significant is the plasticization which can be expected from this source. These are some of the factors which should be taken into consideration in selecting the base polymer. Three commercial-type polymers have been found suitable for many applications involving both low temperature flexibility and oil resistance : Paracril 18-80 (formerly Perbunan 18),Butaprene NF, and Neoprene Type FR. Although this paper is limited to studies with Paracril 18-80, some of the discussion may apply to other polymers as well. The effects of type of vulcanizing system on low temperature properties have been studied (?',l.d,18). However, because optimum cures of two stocks, differing only in vulcanizing system, may exhibit marked differences in physical properties, these data are difficult to compare on the basis of a common property, such as a t equal hardness. Carbon blacks have been reported to impair low temperature flexibility (10, 11, 18). This appears logical, since stocks which contain carbon black are harder and stiffer at normal temperatures, and would be expected to show greater stiffness a t low temperatures. On this basis, stocks containing different carbon blacks, but loaded to the same hardness, might be expected to

HE literature on compounding oil-resistant rubbers for low temperature service considers a variety of subjects, such a8 the effect of base polymer, plasticizer, carbon black, and vulcanizing system on flexibility, oil resistance, and other physical properties. Efforts to improve one physical property have invariably resulted in a loss in a t least one other. This is particularly well demonstrated in studies on the effect of type of polymer on low temperature flexibility (2-4, 6-8,11,1~,1.d,16,1~,sl). Improvements made in the low TABLEI. COMPOUNDING RECIPESIN PARTSBY WEIGHT t e mp e ra t u r e f 1e xi b i 1i t y of butadiene-acrylonitrile copoly-Recipe Type KO. Source 1 2 3 Ingredients mers by increasing the ratio of Paracril 18-80 Enjay Co. butadiene have resulted in a Zinc oxide Phenyl-@-naphthylamine loss in oil resistance. It has Vulcanizing svstems also been found that polymers Vultac-l%Lds Vultac No. 3 Sharples Chemicals 6 ... which have good low temperaTetramethylthiuram disulfide R . T. Vanderbilt Co. 0.5 ... Santooure-Tuads ture properties obtain this N-Cyclohex 1 2 benzothiazole sulfenamide Monsanto Chemical Co. .. . 3 ... Tetramethyr ihiuram disulfide R. T. Vanderbilt Co. ... 1.5 ... property a t a sacrifice of tensile Tetraethyl thiuram disulfide ... 1.85 ... strength (2). Tetrone A-Tusds Dipentameth lene thiuram tetrasulfide Du Pont Co. . . . . . . 1.5 Starting with a butadieneTetramethylt%iuram disulfide R . T . Vanderbilt Co. .. . ... 1.5 acrylonitrile copolymer high in Sulfur-Altax Sulfur ... acrylonitrile, low temperature Benzothiaz 1 disulfide R . T . Vanderbilt Co. .. . ... ... Plasticizer Tgiokol TP-95 Thiokol Corp. 0,20c 20 20 flexibility may be obtained by Carbon bldoks (varied separately) 0-240 0-240 adding relatively large amounts R. T. Vanderbilt Co. 0-320 M T (Thermax) 0-160 0-160 Witco Chemical Go. 0-180 S R F (Continex SRF) of plasticizer, but other physi0-130 0-160 Phillips Chemical Co. 0-130 M A F (Phjlblack A) 0-130 0-140 HAF (Philblack 0) Phillips Chemical Co. 0-130 cal properties are compro0-130 0-120 J. M. Huber Corp. 0-140 E P C (Wyex) mised (3, 9, 12, 14, 15, 19). CureQ min. (" C.) ..... 20 (160) 30 (160) 32gA043) 30-90 30-90 Approx. range durometer hardness (Shore A) ..... Moreover, gains made in low

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a

Time of cure based on optimum stress-strain results.

b Durometer hardness, instant, determined a t room temperature.

Present address, Johnson Rubber Co., Middlefield Ohio. 1

c

30 and 40 parts plasticizer also used with S R F black.

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1.5 1.5 20 0-240 0-160 0-130 0-130 0-130

%>~~o)

INDUSTRIAL AND ENGINEERING CHEMISTRY

112

SANTOCURE-TUADS

Vol. 43, No. 3

SULFUR-ALTAX

0

0

40

80 120 160 TETRONE A TUADS

200

-

240

A MAF BLACK

0

Figure 1.

40

80

120

160

200 240 0 40 80 PARTS OF CARBON BLACK BY WEIGHT

160

200

240

Effect of Type and Amount of Carbon Black and Type of Vulcanizing System on Hardness

show similar low temperature flexibility. However, sufficient data are not available t o make satisfactory comparisons on the same hardness basis. Because much of the compounding of butadiene-acrylonitrile copolymers for lo^ temperature flexibility and oil resistance is aimed a t making a product of a definite hard-

TABLE 11.

120

P H Y S I C A L PROPERTIES O F

ness, information on the same hardness basis was desired. Therefore, the object of this study was t o approach the compounding of Paracril 18-80 by comparing stocks of varying composition, but of equal hardness, for low temperature flexibility and oil resistance, with particular emphasis on low temperature flexibility.

70-DUROMETER STOCKS

BEFORE .\Xi3 AFTER A G I N G I N

-Qf-VV-0-366B FLUID

[Base recipe (parts b y weight) : Paraoril 18-80 (Enjay Co.), 100. zinc oxide 5. phenyl-@-naphthylamine, 2; S'ultac No. 3 (Sharples Chemicals).5; tetrah e t h y l t h i u r a m hisulfide, 0.51 No. 5 KO.6 No. 7 S o . 8 S o . 9 N o . 10 No. 11 KO.12 No. 13 KO. 1 4 No. 15 NO. 16 NO. 17 T'ariables SRF black (Witco Chemical Co.) 80 100 120 140 160 100 120 140 160 100 120 160 TP-95 (Thiokol Corp.) .. 10 20 30 40 ... .. . . 140 ... G-E 2557 (General Electric Co.) .. .. .. 10' 20' 30 40 .. .. ... Paraplex G-25 (Rohm b- Haas Co.) .. .. .. . . . 10 20 30 40

..

Plasticity No., 3 min. a t 80' C. Durometer hardness (Shore A) A.S.T.M. compression set, Yo A.S.T.M. permanent set, % ' Stiffness temperature, O C. Stress a t 100Yo elongation, lb./sq. inch. Tensile strength, lb./sq. inch. Elongation, % PHYSICAL Determined on dumbbell specimens Volume changea, Stress a t 100% elongation, lb. sq. inch Tensile strength, lb. sq. inch Elongation, %

.

.. ..

... ...

..

...

..

. I .

INITIAL PHYSICAL PROPERTIES

516 495 466 465 72 70 69 70 70 76' 70' 21.8 20.3 19.0 22.0 16.1 21.2 20.2 3 3 3 1 3 .. , . -38 -44 -50 -52 -53 -46 -42 450 760 750 900 950 575 400 2550 2475 1950 2075 1775 2425 1750 295 265 210 195 190 290 255 A F T E R AGINGI N BS-YV-0-366B HYDRAULIC OIL 7 DAYS ,

..

70' 20.0

..

-39 475 1500 210 AT 70'

68''

20.2 ,.. -39 GOO 1475 195

530 71 12.9 1 -40 450 2200 275

530 72 14.2 3 -35 825 1825 180

536 75 14.2 Broke -26 650 1575 170

562 77 20.5 Broke -15 900 1225 120

20.3 500 1600 200

18.5 650 1375 160

17.0 925 1425 130

16.4 650 1000 140

-54 62 23.7

-52 63 20.2

-50 64 19.8

-48 65 20.4

20.0 14.7

17.9 8.3

16.2 3.2

14.8 -1.0

c.

5.4 12.5 8.7 2.7 17.1 22.6 10.6 6.3 16.1 900 625 600 975 400 625 475 560 700 1625 1450 1600 2025 1650 1575 2150 2125 1600 190 170 230 280 255 190 160 260 180 DETERXISED O N YOch'G'S bxODULUS SPECIMENS -52 -51 -54 -53 -53 -50 -6-1 -55 -53 Stiffness temperature, C. 65 63 64 60 70 75 63 63 66 Hardness 13.4 18.8 1 5 . 2 4.9 22.5 28.9 18.4 9.7 14.3 Volume changeb, % THEORETICAL VOLUXIE CHANGE, BASEDO N 22.6% SWELLFOR UNPLASTICIZED STOCKC No plasticizer extracted, o/o 22.6 19.9 17.8 16.1 14.7 19.9 1 7 . 8 16.1 14.7 22.6 14.3 7.8 2.6 -1.8 14.4 7.9 2.7 -1.7 Total plasticizer extracted, % a A.S.T.M. designation D 471-46T (increase in weight method). b Based on linear measurements of thickness, converted t o volume. 0 Assumption made t h a t swell is proportional t o volume of base polymer in these stocks.

March 1951


773

ature stiffness t e m p e r a t u r e (temperature a t which Young’s 0 1 I Y I I modulus reached lo4 pounds per square inch) with amount of carbon black for these four vulcanizing systems. Tetrone A-Tuads and Vultac-Tuads v u l c a n i z i n g s y s t e m s gave better low temperature flexibility than the other two, when compared on an equal 80 120 160 x)O 240 hardness basis. However, not w VULTAC- TUADS TETRONE A-TUADS all the differences found between these vulcanizing systems can be attributed directly and solely to the vulcanizing system. As Figure 1 shows, different amounts of carbon black were required to produce stocks of equal hardness for these various vulcanizing systems. I t w a s e x p e c t e d that better low temperature 0 40 80 120 160 200 240=100 40 o flexibility would be obtained PARTS OF CARBON BLACK BY WEIGHT for those vulcanizing systems which r e q u i r e d t h e l e a s t Figure 2. Effect of Type and Amount of Carbon Black and Type of Vulcanizing System on Stiffness Temperature amount of a given carbon black to reach a given hardness. This was approximately The procedures folloned in the experimental work were: Samtrue for the thiuram-type cures but did not hold so well for the ple preparation, A.S.T.M. Designation D 15-41; plasticity, sulfur-type cures. The difference in stiffness temperature obA.S.T.M. D 926-47T; tension testing, A.S.T.M. D412-41; duromtained for these vulcanizing systems was not large but is consideter hardness, A.S.T.M. D 676-47T (Shore A); compression ered significant. set, A.S.T.M. D 395-47T (Method B); immersion in oil, A.S.T.M. D 0 471-46T (increase in weight method); -10 Young’s modulus in flexure, A.S.T.M. D 797-46; stiffness t e m p e r a t u r e , -20 t e m p e r a t u r e a t w h i c h Young’s -30 modulus reaches lo4 pounds per -40 square inch (6, IS). The materials, with sources, are -50 listed in Tables I and 11. -60 SULFUR- ALTAX

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-20

EFFECT OF VULCANIZING SYSTEM

c

a

A comparison was made of four different vulcanizing systems (Table I). The systems are described as Santocure-Tuads, Tetrone A-Tuads, Vultac-Tuads, and sulfur-Altax. The first three vulcanize b i t h o u t the use of elemental sulfur and are all thiuram in type. Three examples were selected because of the superior compression-set properties reported for this general type of vulcanizing system (3). The fourth employs a conventional sulfur vulcanizing system. Each of these systems was used in formulations in which 20 parts of plasticizer were employed, and five different carbon blacks varied to give hardness ranges from approximately 30 to 90 durometer. Figures 1, 2, and 3 show variations of hardness and low temper-

p-

-30

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-40

-50

p

-60

Y

-30

;-20 U

Z IL

’

VULTAC-TUADS

-40

-50

-60 -10

SULFUR- ALTAX

-20 -30

-40 -50 -60

MT SRF MAF HAF EPC 50

Figure 3.

MT SRFMAF HAF EPC

M T SRFMAF HAF EFC

60 70 DUROMETER HARDNESS (SHORE)

MT SRF M4F HAF EPC

so

Effect of Vulcanizing System on Stiffness Temperature

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Vol. 43, No. 3

ner, demonstrate that in highly loaded stocks of equal hardness, E P C black had the poorest low temperature flexibility, HAF black was intermediate, and MT, SRF, and MAF blacks were best. These differences were more pronounced in the series of stocks containing plasticizer. In contrast to these Young’s modulusdata, brittle point data by Crossley and Cashion (71, in which they compared SRF, EPC, FT, and MT blacks, showed that E P C black was superior in low temperature resistance. This is probably only an apparent discrepancy, however, because ,the higher tensile strength and elongation results obtained by these investigators for EPC black may account for its greater resistance to an impact type test. Brittle point temperatures are usually lower and do not necessarily correlate 0 40 80 120 160 200240 280320 0 40 80 120 I 6 0 200 0 40 80 I20 160 200 PARTS OF CARBON BLACK BY WEIGHT with stiffness temperatures. The stiffness temperatures reported here Figure 1. Effect of Carbon Black on IIardness of Pnracrill8-80 Stocks are, therefore? conservative estimates of the minimum temperature a t which these various stocks can be useful EFFECTOFCARBONBLACK Comparison of the Young’s modulus curves of Figures 6 to 13 indicates that the slope decreases with hardness and is less for The study on vulcanizing systems brought out some differences stocks containing plasticizer. At equivalent hardness levels the among the carbon blacks. These differences were investigated curves for stock8 containing plasticizer did not show appreciably further with one of the more promising vulcanizing systemslower Young’s modulus until temperatures were reached below Vultac-Tuads. Variable amounts of the same five carbon blacks, the range of -20’ to -30‘ C . Strangely, this temperature range and two levels of plasticizer (0 and 20 parts of TP-95) were emapproximately coincides with the stiffness temperature of the 85ployed (recipe type 1 in Table I). Figure 4 shows plots of harddurometer stocks previously discussed. Butadiene-acrylonitrile ness against parts of carbon black for these stocks. The low copolymers, lower in butadiene content, probably would show temperature stiffness temperatures of these same stocks are plotted similar effects a t higher temperatures. against hardness in Figure 5. These data and those of Figure 3 show that in the lower hardness range the choice of carbon black Co’fBIYAT1oN EFFECTS OF BLACK *”’ PLASTICIZER has little effect on stiffness temperature. The contribution to low It has been shown that, when the hardness of Paracril 18-80 temperature flexibility made b y the addition of plasticizer destocks reaches about 85 durometer, the presence of a plasticizer creased with increasing hardness and became negligible at about 85 durometer hardness. The stiff. . ness temperature for both plas0 ticized and unplasticized stocks at -10 this hardness is in the range of -25” to -30” C., which is in-20 sufficient for most military re-30 quirements. Additional plasticizer -40 studies will be discussed later. -50 While stiffness-temperature data provide information on an arbitrary LT -60 3 lower limit of serviceability, they -70 do not tell much about relative a w flexibility a t intermediate temperaB ti0 tures, such as are shown in plots Iof Young’s modulus against tem2 w o perature. Families of surh plots U z & -10 were desired for various hardness m + levels, without the need for com-20 pounding stocks to exact hardness -3J requirements. This was done by -40 first plotting Young’s modulus -50 against durometer hardness for the various Young’s modulus test tem-60 1 SRF BLACK I 1 1 HAFIBLACK at intervals of peratures-i.e., -70 30 40 50 60 70 80 90 30 40 50 60 70 80 90 30 40 50 60 70 80 90 10’ C.-and then replotting these DUROMETER HARDNESS (SHORE) data on a common hardneas basis. Figures 6 t o 13, obtainedin this manFigure 5. Relation of Hardness of Carbon Black Stoclrs to Stiffness Temperature

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1

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INDUSTRIAL A N D ENGINEERING CHEMISTRY

March 1951

-60

-50

TEMPERATURE, e C.

-40

715

-30

- 20

-10

0.

TEMPERATURE,*C.

Figure 6. Flexibility at Various Temperatures of 50-Durometer Stocks Containing No Plasticizer

Figure 7. Flexibility at Various Temperatures of @-Durometer Stocks Containing No Plasticizer

does not help lower the stiffness temperature. This conclusion was based on only two series of stockB, one without plasticizer and one with 20 parts of TP-95. Because greater amounts of plasticizer might have improved the low temperature flexibility of high hardness stocks, stocks containing 30 and 40 parts of TP-95 were prepared and compared with the data previously obtained for 0 and 20 parts. Figures 14 and 15 show the data for these amounts of TP-95 in a Paracril 18-80 type recipe containing various amounts of SRF black. These data confirm previous observations that a t higher hardness levels the effect of a plasticizer on low temperature flexibility becomes negligible. It is interesting to note that a t lower hardness levels a greater incremental lowering in stiffness temperature was obtained with 20 parts than with 30 or 40 parts of plasticizer. While there is a limit as to how

much plasticizer can effectively be used in improving low temperature flexibility, the requirements for processibility and other physical properties may alter the picture.

Id I -60

I I I -50

I II

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II

II

-30 -20 TEMPERATURE, OC.

-40

OIL RESISTANCE

Table I1 presents data on a number of stocks which contain increasing amounts of both carbon black and plasticizer, in such ratios as to maintain a hardness of approximately 70 durometer. One carbon black, SRF,was used in combination with three different plasticizers, TP-95, G-E 2557, and Paraplex G-25. These three were selected t o illustrate the general effects of plasticizer permanence on low temperature properties, after aging in a typical hydraulic oil (1).

I I t

-16

I

0

Figure 8. Flexibility at Various Temperatures of 70-Durometer Stocks Containing No PlaBticizer

-60

-50

-40

-

-30 20 TEMPERATURE.OC.

-10

0

Figure 9. Flexibility at Various Temperatures of 80-Durometer Stocks Containing No Plasticizer


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-40 -33 TEMPERATURE,

- 10

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KEY: TYPE BLACK

-20

Vol. 43, No. 3

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-60

-50

'C.

1 -40

I

- 30I

-20

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1

- 10

n I

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TEMPERATURE ,OC

Figure 10. Flexibility at Various Temperatures of 50-Durometer Stocks Containing 20 Parts of Plasticizer TP-95


The relative permanence of these plasticizers is shown by comparing the change in volume of their stocks after oil aging. This change in volume, or swell, is primarily a function of the polymer and plasticizer contents of these stocks (14). Thus, the higher the carbon black-plasticizer loading, the less polymer is present to swell and the more plasticizer to be extracted. The stocks containing TP-95 and G-E 2557 show volume changes approaching that which is theoretically possible for total plasticizer extraction. On the other hand, the data indicate that Paraplex G-25 was not extracted. This also has been substantiated by infrared examination of the extracting media for evidence of Paraplex G-25. The type of specimen had some influence on swell, as shown by differencesobtainedfor Young's modulus and dumbbell-type speci-

mens, Final equilibrium swell was not obtained for either type of specimen, inasmuch as other work indicated that equilibrium is not obtained even after months of immersion (6). Figure 16 gives plots of stiffness temperature against parts of plasticizer for the stocks of Table 11, both before and after oil aging. The results before oil aging show that TP-95 was effective in lowering stiffness temperature, G-E 2557 had relatively little effect, and Paraplex G-25 raieed stiffness temperature. However, after oil aging, the type of plasticizer had relatively little influence on stiffness temperature. Furthermore, concentration of plasticizer had only a small influence on stiffness tempcrature. The TP-95 stocks had only a, slight edge on the other stocks and reached a minimum stiffness temperature of -55' C.

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-60

-50

-40

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-30 -20 TEMPERATURE,"C.

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LEY TYPE BLACK

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1 -10

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- 60

~

50

- 40

- 30 20 TEMPERATURE, OC. ~

-10

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Figure 13. Flexibility at Various Temperatures of 80-Durometer Stoclis Containing 20 Parts of Plasticizer TP-95


March 1951

777

0

bj U

-10

W”

g -20

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RECIPE TYPE I

-30

m

m W

E

-40

v)

-50

0

40

SO

120

160

200

240

280

PARTS SRF BLACK BY WEIGHT

Figure 14. Effect of Various Amounts of SRF Black and TP-95 on Hardness

i

P;

at 20 parts of plasticizer. The slight impairment in stiffness temperature, noted for higher amounts of plasticizer, may be associated with the higher hardness values obtained for these stocks after oil aging. The extraction of plasticizer was greater for the more highly loaded stocks, and tended to alter the original balance of carbon black and plasticizer, which controlled hardness. Obviously, the loss in hardness and improvement in low temperature flexibility for the more lightly loaded stocks were largely the result of swell and plasticization by the hydraulic oil. A concentration of 20 to 30 parts of TP-95 appears to offer the best compromise for swell, low temperature flexibility, and hardness. Table I1 shows the stress-strain results on these same stocks, before and after aging. As might be expected, a simultaneous increase in carbon black and plasticizer tended to increase modulus and decrease tensile strength and elongation, both before and after oil aging. Oil aging tended to lower both tensile strength and elongation, but no definite pattern was found for modulus. High tensile strength and high elongation are usually desired for most applications, and favor low carbon black-plasticizer levels. Processibility, as judged by plasticity measurements, did not appear to be greatly influenced by increased loadings of the type described here. Combining the various factors discussed for various loadings of carbon black and plasticizer, the general conclusion can be drawn that it is desirable t o h d , first, a level of carbon black-plasticizer which will meet the minimum limit for hardness and the maximum limit for swell. Then a minimum amount of additional carbon black and plasticizer should be used to meet the low temperature flexibility requirements. If it appears difficult or impossible t o meet the desired low temperature flexibility in this manner, it is suggested that consideration be given to sacrificing hardness to obtain the desired low temperature flexibility. The limits of low temperature flexibility and swell are both very dependent upon the type of immersion media (6,14). Hence, there is a different problem for each type of immersion media. However, the same general effect, but differing widely in magnitude, may be expected for applications involving other immersion media. SUMMARY

A study has been conducted on the effect of the type of vulcanizing system, type and amount of carbon black, and various ratios of carbon black and plasticizer on the low temperature flexibility of Paracrill8-SO stocks. Also, the effect of immersion in AN-VV0-366B hydraulic oil has been investigated. The choice of vulcanizing system had only a small effect on results obtained. The higher the carbon black content, the higher the hardness and the poorer the low temperature flexibility. In

-60

-

20

30 ?

40

50

60O

70

80

90 7

DUROMETER HARDNESS ( S H O R E )

Figure 15. Effect of TP-95 Content on Stiffness Temperature of SRF Black Stocks

highly loaded stocks of equal hardness, carbon blacks of fine particle size produced increased stiffening a t low temperatures. A number of stocks with varying amounts of carbon black and plasticizer are compared. Results show that the improvement in low temperature flexibility contributed by the addition of plasticizer decreased with increasing hardness and became negligible a t about 85-durometer hardness. In stocks of equal hardness, the presence of a plasticizer was shown t o contribute appreciably nothing to flexibility, until temperatures below -20” to -30” C. were reached.

-60

’ IO

20

30

40

PARTS PLASTICIZER

Figure 16. Effect of Oil Aging on Stiffness Temperature

A number of stocks of the same hardness, but varying widely in carbon black and plasticizer loading, were aged in AN-VV-O366B hydraulic oil. Wide differences in low temperature flexibility were obtained for these stocks before oil aging, but these differences became relatively small after oil aging. For applications involving exposure t o both low temperature and oil, it is suggested that the amounts of carbon black and plasticizer be adjusted as follows: Find the minimum amounts of these materials which will meet the hardness and swell requirements, and then


778

add only sufficient additional carbon black and plasticizer (in such a ratio as to maintain constant hardness) to meet the low temperature flexibility requirements. ACKNOW LEDGiMENT

The data reported in this paper were obtained in connection with a research project sponsored by the United States Air Force, Air Materiel Command. The authors are grateful to the Air Materiel Command for permission to publish this work. Any opinions expressed here are those of the authors and not necessarily those of the sponsor. LITERATURE CITED

(1) Army-Navy Aeronautical Specification AN-VV-O-366B, Oil, Hydraulic, Petroleum Base, April 19, 1943. (2) Borders, A. M., and Juve, R. D., IND. ENQ. CxEhf., 38, 1066 (1946). (3) Cashion, C. G., Rubber A g e ( N . Y.),65,307 (1949). (4) Chatten, C. K., Eller, S. A., and Werkenthin, T. A., Ibid., 54, 429 (1944). ( 5 ) Clark, R. A., and Cheyney, L. E., Ibid., 65, 531 (1949). (6) Conant, F. S., and Liska, J. W., Rubber Chem. & Technol., 18, 318 (1945); J. Applied Phys., 15, 767 (1944). (7) Crossley, R. H., and Cashion, C. G., IND.ENG.CEIEM.,36, 55 (1944).

Eng$nyring

Vol. 43, No. 3

(8) Enjay Co., Tech. Rept. BP-3 (Aug. 15, 1949). (9) Garvey, B. S., Juve, A. E., and Sauser, D. E., IND.ENG.CHEM., 33,602 (1941). (10) Gehrnan, S. D., Woodford, D. E., and Wilkinson, C. S., Jr., Ibid., 39, 1108 (1947). (11) Greene, H. E., and Loughborough, D. L., Rubber Chem. & Technol., 18, 587 (1945); J. Applied Phys., 16, 3 (1945). (12) Kemp, A. R., Malm, F. S., and Winspear, G. G., IND. ENG. CHEM., 35, 488 (1943). (13) Liska, J. W., Ibid., 36, 40 (1944). and Buckley, D. J., Ibid., 34, 1284 (14) Moll, R. A., Howlett, R. M., (1942). (15) Morris, ’R. E., Hollister, J. W., and Seegman, I. P., Rubber A g e ( W . Y . ) ,56, 163 (1944). (16) Morris, R. E.. James, R. R., and Evans, E. R.. Rubber Chem, & Technol., 18, 192 (1945); I n d i a Rubber W o r l d , 110, 529 (1944). (17) Morris, R. E., James, R. R., and Werkenthin, T. A., IND.ENG. CHEM.,35,864 (1943). (18) Selker, M. L., Winspear, G. G., and Kemp, A. R., Ibid., 34, 157 (1942). (19) Stickney, P. B., and Cheyney, L. E., J. Polymer Sci., 3, 231 (1948). (20) Wilson, G. J., Chollar, R. G., and Green, B. K., Rubber Chem. & Technol., 18, 182 (1945); IND.ENG.CHEM., 36, 357 (1944). (21) Yerzley, F. L., and Fraser, D. F., Rubber Chem. & Technol., 15, 605 (1942); IND.ENG.CHEM.,34, 332 (1942).

RECEIVED June 5. 1950.

Extraction of lactic Acid from Water Solution

pocess development

I

BY AMI NE-SOLVENT MIXTURES

WILLIAM P. RATCHFORD, EDWARD H. HARRIS, JR., C. H. FISHER. AND C. 0. WILLITS EASTERN REGIONAL RESEARCH LABORATORY, PHILADELPHIA 18, PA.

Although lactic acid can be made by fermentation from inexpensive raw materials, it is at present fairly costly, partly because of the costs of recovery and purification. The present study was undertaken to investigate a process which might reduce these costs. The results suggest that it will be commercially possible to extract the lactic acid from the aqueous fermentation liquor by neutralizing the acid with an organic tertiary amine and then extracting the lactic acid-amine salt with an organic solvent. Triamyl- and trioctylamine were effective amines, and chloroform and alcohols were good extraction solvents. Tertiary amine-chloroform mixture extracted more than an equivalent amount of lactic acid. Alcohols are of interest because of the possibility of making the lactic acid ester directly from the salt. An efficient and low-cost extraction process for the recovery of lactic acid from crude dilute aqueous solution would materially enhance the position of lactic acid as a large-volume chemical intermediate.

A

LTHOUGH lactic acid is readily made by fermentation of inexpensive carbohydrates (11, 12) and is relatively inexpensive in the crude grades, the price of the refined acid is high. Thus, 44% technical grade acid costs 25 cents a pound (100% basie), whereas 85% National Formulary grade costs 81 to 85 cents a pound (100% basis) (1). This large spread in cost between the crude and refined grades suggests that any improve-

ment in production or recovery methods leading to a reduction in costs would materially improve the position of pure lactic acid as an industrial raw material (7). The possibility of one such improvement, through esterification of the crude acid, has been pointed out by several workers (6,6,14,19).Still another possibility is the esterification-extraction process of Dieta, Degering, and Schopmeyer ( 3 ) . Extraction of lactic acid from water by solvents has also received attention from several investigators, who studied isopropyl ether (9), isoamyl alcohol (IO),amyl alcohol ( l a ) , nitroparaffins (I?’), and several other solvents (11). Some refined lactic acid has been produced in this way ( l a ) , with isopropyl ether (9) as the solvent. Solvent extraction in general, however, is handicapped by unfavorable distribution coefficients ( 1 1 ) and, in the case of isopropyl ether, by the danger of fire or explosion (16). It occurred to the authors that an improved recovery method might be based on extraction of the aqueous acid with a waterinsoluble solvent containing an organic base. This view was supported by the work of Smith and Page ( 1 5 ) , who extracted several acids, including lactic, from water solution with organic solutions of tertiary amines. The authors have found that tertiary amines in water-insoluble organic solvents, including chloroform and alcohols, extract lactic acid from water solution more effectively than does solvent extraction alone. Tertiary amine-chloroform systems extracted more than enough acid to neutralize the amine.

Flexibility

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