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Measurement of film-breaking ability of antifoaming agents
Measurement of Film-Breaking Ability of Antifoaming Agents HIDEKI TSUGE, JUNKO USHIDA,t AND SHIN-ICHI HIBINO Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Yokohama 223, Japan Received October 19, 1982; accepted December 2, 1983 The characteristics of an antifoamer added to prevent difficulties caused by the foaming of liquid are divided into the film-breaking action and the foam-preventing action. In order to measure quantitatively the film-breaking ability of an antifoamer, a new pop test is presented, which is a modified version of the pop test proposed by S. Ross and J. W. McBain (Ind. Eng. Chem., 36, 570, 1944). The film-breaking ability determined using the new pop test is expressed in terms of the film-breaking factor Fp, which is shown not to be affected by the experimental temperature and the relative humidity. The properties of antifoaming agents, that is, the film-breaking ability and foam-preventing ability, are measured by the new pop test, the film-breaking test, and the Ross-Miles method, and their relationships are discussed. INTRODUCTION
lution in the foaming column, the foam is formed in the column. The foam height immediately after that shows the foam-preventing ability of the antifoamer, while the foam height after 5 min shows the foam stability. The details of the experimental procedure are shown later. This method has been used in the development of new antifoamers by Abe et al. (3, 4).
In order to prevent various difficulties caused by the foaming of liquids, two methods have been adopted: (1) physical or mechanical methods: usage of heating elements, temperature change, or centrifugal force, etc.; (2) chemical methods: addition of antifoaming agents.
(2) Japan Industrial Standard (JIS) method for determining foaming characteristics of peWhich method should be used is decided by troleum products (5). The air is fed through a considering the physical properties of the liquid, the operating conditions, the cost, and so on. With the development of excellent silicone antifoaming agent in recent years, the chemical method has come to be applied widely. The performance of an antifoamer or a foam preventer is divided into the film-breaking action and the foam-preventing action. In order to examine the performance of antifoaming agents, the following methods have been used:
(1) Ross-Miles method (1, 2). When a constant volume of a foaming solution containing an antifoamer is dropped into the same soi" Deceased.
diffuser stone into a foaming solution containing an antifoamer in a 1000-ml measuring cylinder for 5 min, and the foam heights immediately and after 10 min are measured, which show the performance of the antifoamer and the stability of the foaming agent.
(3) Deutshe Industrie Norm (DIN) method (6). A perforated plate 55 mm in diameter is moved up and down 30 times during 30 sec in a 200-ml sample solution in the measuring cylinder and the foam height is measured after 30 sec to assess the performance of the antifoamer.
(4) Pop test by Ross and McBain (7). A platinum wire ring, on which the foaming film is formed, and another platinum wire ring, previously dipped in the antifoamer to be ex-
175 0021-9797/84 $3.00 Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
Copyright © 1984 by Academic Press, Inc. All rights of reproduction in any form reserved.
176
TSUGE, USHIDA, AND HIBINO
amined, are gently touched. The performance of the antifoamer is classified qualitatively in terms of film breaking.
(5) Tests of film breaking and foam preventing by Okazaki and Sasaki (8). (a) Filmbreaking test: The foam height is measured after an antifoamer drop is added to the foam formed by bubbling air. (b) Foam-preventing test: A foaming solution and an antifoamer are poured in a glass tube and shaken at constant frequency and amplitude, and the foam height is measured subsequently. Among the methods described above, methods 1-3 are industrial standards so that quantitative measurements are possible by using the apparatus and procedure described in detail. On the other hand, in method 4, the details of making the contact of the two platinum rings are not specified so that only qualitative data are possible. Method 5 is semiquantitative in nature. To measure the film-breaking ability of an antifoamer, the pop test (method 4) is the most favorable because of its simplicity. By modifying it, a quantitative method for measuring the film-breaking ability can be developed. The objectives of this paper are to discuss the modified version of the pop test (7), that is, the "New Pop Test," and to present the quantitative data on the film-breaking ability of some antifoamers. The results obtained using the new pop test are compared with the experimental results obtained by the filmbreaking test similar to method 5a and the foam-preventing ability data obtained by method l, Ross-Miles method. 1. MATERIALS
An aqueous solution of reagent grade sodium dodecyl benzene sulfonate (DBS) (0.12 wt%) was used as the anionic foaming solution. Its critical micelle concentration (CMC) is 0.071 wt% (11). The following were used as, antifoaming agents: 2-butyl octane- 1,2-diol which was produced and purified by Abe et al. (3) (designated 12D); silicone emulsion-type antifoaming agent K_M-73, produced by Shin-etsu ChemJournal of CoUold and Interface Science, Vol. 100, No~ I, July [984
ical Company (designated KM-73); 2-ethyl hexanol; tri-n-butyl phosphate (designated TBP); ethanol; and ethyl acetate. All were reagent grade except KM-73. Their chemical structures and solubilities in 0.12 wt% DBS solution and water are given in Table I. In the new pop test, the antifoamers were dissolved in 0.12 wt% DBS solution. 2. APPARATUS AND PROCEDURES
2.1. New Pop Test Figure 1 shows the schematic diagram of the experimental setup for the new pop test. Platinum ring 6, composed of 0.8 mm wire, was fixed horizontally and the ring diameter was 20 mm. Holder 4 with plastic cup 7 and injector 2 were connected to the movable apparatus and they moved simultaneously up and down. Injector 2 was 10 cm in length and 1 mm in diameter, and its point was fused. Two plastic cups (25 mm in height and 45 mm in diameter) were used, one (7A) for ethanol as the cleansing agent and another (7B) for the foaming agent. Each liquid depth in the plastic cup was 17 mm. The light from lamp 5 converged at the rim of the platinum ring, being reflected by the foaming film, but reached directly to the phototransistor by the film break, so that the film duration time described below could be determined by detecting, with the phototransistor and two electronic counters 9 and I0, the changes in light intensity caused by the film breaking. To avoid the effect of wind, the whole apparatus was covered with vinyl sheet hood 1. Vibration was also avoided as far as possible. The room temperature, liquid temperature, and relative humidity were measured by thermometers and Assman's aspiration psychrometer, and their averaged values were used. Initially the moment of film breaking was photographed with a 16-mm high-speed camera (HIMAC 16M) for two or three cases. The experimental procedure was as follows: (1) Platinum ring 6 was immersed and cleansed in ethanol in cup 7A placed on holder
177
FILM BREAKING BY ANTIFOAMING AGENTS TABLE 1 Solubilities of Antifoamers Antifoamer
Solubility[wt%]
Chemicalformula C4H 9 ~
12D
/CH2OH
0.2-0.35 (25°C) a
C C6HI3/
KM73
0.1-0.2 (25°C) a
~OH CH3
[ CH~
CH3
i
/l!
I
CH3-- Si--O[-- Si-- 10-- Si--CH3
i
|l/
I
CH3
L_ C H ~
CH3
H "-, C / C H 2 O H 2-Ethyl hexanol
0.013 (25 °C) b C4H9/
~C2H5
TBP
Insolubleb
(C4H90)3P=O
Ethanol
Infinitely solubleb
C2HsOH
Ethyl acetate
7,86 (20°C) b
CH3COOC2Hs
Solubility in 0.12 wt% DBS solution was obtained from visual observation. b Solubility in water was obtained from Ref. (9).
4 for 20 sec, and the tip of injector 2 was cleansed by ethanol. Ethanol attached to the platinum ring was evaporated by blowing hot air over it for 20 sec. (2) Cup 7A was replaced by cup 7B and then ring 6 was immersed in DBS solution in cup 7B placed on holder 4 for 30 sec. Holder 4 was lowered at constant speed and DBS film was formed on the ring. The time necessary to form the film is tF, film formation time. The time from film formation until film breaking (duration time of base film), to, was monitored. F--
I
"7
FIG. 1. Experimental setup for the new pop test: (1)
hood, (2) injector, (3) clamp, (4) holder, (5) lamp, (6) platinum ring, (7) cup, (8) phototransistor, (9, 10) electronic counter.
(3) Ring 6 was again immersed in DBS solution in cup 7B for 30 sec by translating holder 4 upward. A 9-~1 drop of DBS solution was placed on the tip of the injector, and then holder 4 was lowered at constant speed until the drop was attached to ring 6. tB, the time from film formation until addition of a drop (blank time), and tD, the time from addition of a drop of foaming agent until film breaking (DBS film duration time), were monitored with the phototransistor and electronic counters. (4) After the residual drop on the tip of injector 2 was wiped with a paper towel, a 9~1 antifoaming agent drop was attached to the injector tip. After the platinum ring was immersed in DBS solution for 30 sec, holder 4 was lowered at constant speed and the DBS film was formed on the ring. The holder was further lowered to add a drop to the film on the ring. Then tB and t, the time from addition of a drop of antifoaming agent to the film until film breaking (film duration time), were measured with the phototransistor and electronic counters. Journal of Colloid and Interface Science, Vol. 100,No. 1, July 1984
178
TSUGE, USHIDA, AND HIBINO
After the foaming film broke, the residual drop of the antifoaming agent at the injector tip was wiped with a paper towel. (5) Procedures 1 to 4 were repeated 15 times for a given concentration of the antifoaming agent. (6) Procedures 1 to 5 were carried out for several concentrations of six antifoaming agents in DBS solution.
~7 11,5 .
r'-"
6
--3
2.2. Film-Breaking Test The experimental procedure was as follows: (l) The air was blown at a constant flow 2 rate through a glass nozzle with an air pump into 0.01 mole/liter DBS solution (1 ml) in a test tube 24 cm long and 14 m m in diameter. When the foam was formed up to the upper end of the tube, the air blowing was stopped. Immediately after, a drop of 0.01 mole/liter DBS solution (6/zl) was gently added to the top of the foam and the decrease in foam height, ho, was measured after 30 sec. (2) Procedure 1 was repeated using a drop of antifoaming solution (6 #l) instead of a drop of the DBS solution and the decrease in .z_--I foam height, h, was measured after 30 sec. This measurement was repeated 10-15 times at a given concentration of antifoaming solution. (3) Procedures 1 and 2 were carried out for FIG. 2. Experimental setup of Ross-Miles method: (1) several concentrations of six antifoaming pipete, (2) foaming column, (3) constant temperature water jacket, (4) hole, (5) rubber stopper, (6) tip nozzle, (7) agents in DBS solution.
tl
stopcock 1, (8) stopcock 2,
2.3. Ross-Miles Method Figure 2 is a schematic diagram of the experimental setup of the Ross-Miles method (1, 2). The foaming column 2 is 50 m m in diameter and 90 cm long, and is jacketted by column 3, in which water was circulated at constant temperature (30°C); 1 is the removable pipet and the tip nozzle 6 is 2.9 m m in diameter and 10 m m long. The experimental procedure was as follows: (1) The inside wall of the foaming column 2 was rinsed with water and then with the DBS solution containing antifoamer to be examined. Journal of Colloid and Interface Science. Vol. 100, No. 1, July 1984
(2) Stopcock 2 (8) was closed and the 50ml sample solution was run down the inside wall of column 2. (3) Pipet 1 was filled with 200 ml of the sample solution and placed on rubber stopper 5 at the head of column 2. When stopcock 1 (7) was opened and the solution came down, the foam was formed in the column and the foam height, lo, was measured immediately after the pipet 1 was emptied, and after 5 min the foam height, Is, was again measured. (4) Procedures 2 and 3 were repeated three times at a given concentration of the given antifoaming agent.
FILM BREAKING BY ANTIFOAMING AGENTS (5) Procedures 1 to 4 were carried out for several concentrations of ethanol and ethyl acetate. The data for other antifoamers were obtained from the experimental results (40°C) by Abe et aL (3, 4, 10). 3. DEFINITIONS OF FILM-BREAKING AND FOAM-PREVENTING FACTORS
Lo
=
I
- lo/ In
[3l
L5
=
I
- ls/lo
[4l
where lo is the foam height when the sample solution does not contain an antifoamer, that is, only 0.12 wt% DBS solution. Lo is considered an indicator of foam-preventing ability, whereas L5 indicates the foam stability.
3.1. F i l m - B r e a k i n g Factor by the N e w Pop Test
4. RESULTS
Film-breaking ability is represented in terms of the film-breaking factor, Fp, which is defined as Fp = (to - t)/tD = 1 -- t/tD
179
[ll
where tD was measured in order to cancel out the increase in film thickness owing to the addition of an antifoaming agent to the film by adding a drop of foaming agent to the film, so that the dimensionless derivative of t is introduced as defined in Eq. [ 1]. Fp shows the extent of film breaking by an antifoaming agent, that is, when the film breaks immediately after adding the antifoaming agent to the film, t = 0 and then FI, = 1 from Eq. [1], which means the film-breaking ability of the antifoaming agent is at a m a x i m u m . On the other hand, when t = tD, that is, Fp = 0, the antifoamer has no film-breaking ability.
4.1. N e w Pop Test 4.1.1. P r e l i m i n a r y experiments. Initially three factors affecting film-breaking ability were examined: 1. F o r m a t i o n t i m e o f f o a m i n g f i l m , tF.
The formation times of foaming film, tv, described in procedure 2 in Section 2.1, were 0.1, 1.0, and 7.9 see, so that its effect on the base film duration time, to, could be examined. Figure 3 shows the relation between to and tF and the arrows in the figure show the standard deviations of to. In the cases where tv = O. 1 and 1.0 sec, the holder was lowered by hand so that the scatter in to would be large; on the other hand, in the case where tv = 7.9 sec, the holder was lowered at a constant speed using a m o t o r so that the scatter in to would be relatively small. It shows that when the formation time of a foaming film is long, the
3.2. F i l m - B r e a k i n g Factor by the F i l m - B r e a k i n g Test
The film-breaking factor, FB, is defined in terms of the film-breaking test as
8o
FB = 1 - (ho - h)/(ho - hD)
6O = (h - ho)/(ho - ho)
[2]
where ho is the foam height when the air is blown, hD was measured to compensate the effect of addition of a drop of antifoaming agent on foam height and film thickness.
v
~o
20
3.3. F o a m - P r e v e n t i n g Factor by the Ross-Miles Method oi;
Foam-preventing factors Lo and L5 represent the foam-preventing ability and are defined as
o'.s i
tF
(S)
~
;o
FIG. 3. Relation between base film duration time, to, and formation time, tF, of foaming film. Journal of Colloid and Inte~ace Science, Vol. 100, No, 1, July 1984
TSUGE, USHIDA, AND HIBINO
180
film becomes thinner by the drainage of the foaming film and is liable to break down
1.0
sooner.
Figure 4 shows the relation between t and concentration, C, of 12D, the antifoaming agent, as a function o f tF, where the drop volume was constant at 9 ~tl. The arrows in the figure show the standard deviations of t. When C is equal to 0, t is equal to DBS film duration time, which corresponds to the case in which a drop of DBS solution was added to the DBS film. As the film formation time tv decreases, t increases at C = 0, which agrees with the tendency of the base film duration time to increase owing to less drainage when tF is short as shown in Fig. 3. On the other hand, film duration time t decreases as film formation time t F decreases in the case of addition o f an antifoaming drop, which corresponds to C > 0 in Fig. 4. This is explained on the grounds that the antifoaming agent immerses easily into the film surface owing to the nonuniform distribution of foaming agent on the film surface when the film formation time is short, so that film breaking is facilitated. Figure 5 shows the relation between Fv and concentration of 12D, which is a replot of Fig. 4. The arrows in the figure show the standard deviations o f Fp. The shorter the film formation time, the larger the Fp value. This means that it is necessary to measure Fp at constant film formation time, and the follow-
0.~
0.2 0
0
01
C (wt %)
0.2
FIG. 5. Relation between the film-breaking factor determined by the new pop test and the concentration
of 12D. ing experiments were conducted at a constant film formation time, tF, of 1.0 sec.
2. Drop volume of anti foaming agent. The effect of the drop volume of the antifoaming agent on Fp was examined and the drop volumes used were 7, 9, and 1 t #1. Fp decreases slightly with an increase in drop volume of the antifoaming agent irrespective of the concentration of the antifoamer, because when a larger drop is added, the film thickness increases slightly, so that the film duration time becomes longer and Fp decreases. So the following experiments were conducted at a constant antifoaming agent drop volume 9 ~l.
3. Effects of environment (temperature, humidity). (a) Effect of temperature: Figure 6 shows the relations between temperature and base film duration time, to, DBS film duration time, to, film duration time, t, and film-break-
(
801
6( < ~ _ _
40
-
20 ~ ,'
e
to ,~
'
'
"
~
~ " " ~
4[
j. 0.6
;O t (0.025wt%12D~
o e~(
22
..
2/-,:
T O~ ta-a 26
,
,
28
Temperature (°C)
o
~
o:~
c (~t °/o)
0:2
FIG. 4. Relation between film duration time, t, and concentration of 12D. The drop volume was 9 el. Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
FIG. 6. Relations between temperature and base film duration time, DBS film duration time, and film duration time. Relative humidity, 57.0-58.8%.
FILM BREAKING BY ANTIFOAMING AGENTS B0
v
(b) Effect of humidity: Figure 7 shows the relations between to, tD, t, and Fp, and relative humidity at nearly constant temperature, 20.3-22.0°C. to, tD, and t (for 0.1 wt% TBP) increase with an increase in relative humidity. The film breaking is concerned with the solvent evaporation from the film, so that the film is difficult to break owing to the retardation of evaporation and as a result the film thickness remains constant when the relative humidity is high. As the relative humidity has roughly the same effect on tD and t, the effect of relative humidity on Fp is relatively small. The arrows in the figure show their standard deviations. By analyzing Fp factors using other antifoaming agents at the same temperature but at different humidity, it was found that Fp is not very affected by relative humidity. From the results described above, the effects of temperature and relative humidity on Fp are small though the experimental ranges were limited.
60
G
0.8
~ 0
•
.~, F(
40
"
)
.
,~, .... u_a_ .
.
.
181
04
50 6U " Relative humidity (%)
FIG. 7. Relations between relative humidity and base film duration time, DBS filmduration time, filmduration time, and Fp. Temperature, 20.3-22.0°C.
ing factor Fp when the relative humidity was relatively constant, that is, 57.0-58.8%, and 0.025 wt% 12D solution was used as the antifoaming agent. Throughout this experiment, the liquid temperature was nearly equal to the room temperature, so that the effects of room and liquid temperatures were considered at the same time. to, tD, and t decrease with an increase in temperature, because the surface tension and the viscosity decrease with an increase in temperature, and as a result the film becomes slightly unstable. But F_p is not influenced by the temperature because the effects of temperature on t and tD compensate each other. The arrows in the figure indicated standard deviations.
4.1.2. Relation between film-breakingfactor and concentration of antifoaming agent. According to the preliminary experiments described above, measurements of the filmbreaking factor were conducted under the following conditions, that is, the film formation time tF = 1.0 sec and the volume of the antifoaming drop V = 9 ~I. Figures 8A and B show the relations between the film-breaking factor Fp and the concentration of antifoaming agents, where the keys and arrows show the average values of
1.01
o51
"°- 0
-04 •
, ,l !'+: '
, ITBP' ~ KM73 , 12Ethylhex°n°ll-,-'~'--l~2D
0.5
c (w t'/o)
I'-0-'
I--"'¢)-:-l.O
ol
I0
c (wt%)
20
30
FIG. 8. (A, B) Relation between film-breaking factor Fp and concentration of antifoaming agents. Journal o f Colloid a n d Interface Science, Vol. 100, No. 1, July 1984
182
TSUGE, USHIDA, AND HIBINO
experimental results and their standard de- those after 20 sec, but their tendencies were viations. The results for 12D, KM73, and TBP very similar. In the following FB values after are very similar and show very good film- 30 sec are discussed. breaking ability. The standard deviations in 4.2.2. Relation between Fs and concentraFp value for KM73 below 0.25 wt% are greater tion ofantifoaming agent. Figures 9A and B than those for 12D and TBP. 2-Ethyl hexanol show the relation between FB and the conshows a weak film-breaking ability compared centration of antifoaming agent. The keys and with the other three antifoaming agents de- arrows show the average values of experiscribed above and conversely it stabilizes the mental results and their standard deviations. film below about 0.1 wt%. The distribution FB values also depend on the concentration of its Fp values above 0.2 wt% is very broad and kind of antifoaming agent. FB values for and the standard deviations of the Fp values ethanol and ethyl acetate are much smaller are large. than those for other antifoaming agents. FB Ethyl acetate as well as ethanol do not show values for TBP, KM73, and 2-ethyl hexanol film-breaking ability until the concentration increase with an increase in their concentrabecomes high. The Fp of ethyl acetate changes tion and afterward reach constant values, abruptly around 7.5-8.0 wt%. The solubility whereas the FB value for 12D changes in two of ethyl acetate is 7.86 g/100 g H20 (at 18°C), steps in this experimental range. so it can be said that the film-breaking ability 4.3. Ross-Miles Method of ethyl acetate becomes excellent in the region Figures 10A and B show the relation beof supersaturation. tween L0 and the concentration of six anti4.2. Film-Breaking Test foaming agents. KM73 shows the best foam4.2.1. Preliminary experiments. (1) The ef- preventing ability, whereas ethanol and ethyl fect of the drop volume of antifoaming agent acetate show very weak ability. Figures I 1A on foam height was examined by using dif- and B show the relation between L5 and the ferent volumes: 6, 10, and 15 ~1. With an concentration of six antifoaming agents. By comparing Fig. 10 with Fig. 11, KM73 increase in drop volume, the FB value increased especially when the concentration of is shown to possess excellent foam-preventing the antifoaming agent was high. In the fol- ability. 2-Ethyl hexanol and TBP make the lowing the drop volume was maintained at foam unstable, so that their foam-breaking ability continues for a relatively long time. 6 ~1. (2) The effect on FB of the time from adThe standard deviations of L0 and L5 are dition of an antifoaming drop until measure- so small that they are not shown in the figures. Table II shows the relative evaluations of ment of the decrease in foam height was also examined. From measurements of the de- film-breaking ability by the new pop test and creases in foam height after 20 and 30 sec, FB by the film-breaking test, and of foam-prevalues after 30 sec were slightly higher than venting ability by the Ross-Miles method. I [-(A)
,
0~.
[
C (wt */,)
.
04l Ethanol 1"--'49--- " / Ethyl Acetate I ---~---I
2LcB
'
0
I0
'
..-'S ........... 20
+. 30
C (wt*/,)
FIG. 9. (A, B) Relationbetweenfilm-breakingfactorFBand concentrationof antifoamingagents. Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
" L
40
183
FILM B R E A K I N G BY A N T I F O A M I N G AGENTS
~----0-
1.0
'(3'
01.0 (B)
'
"
, 10
, I Ethyl Acctcttel-" 49- - 20 C (wt*/,) 30 40
9
0.5
O~~. o 0 ~..~., -0.2
(A) IKM73 --'-O---- TB'P .... e ..... 12D 05 C (wt*/,)
~
(
,12Eihythextano
1.0
-0.'
"'~---~
P3G. 10. (A, B) Relation between L0 and concentration of antifoaming agents.
5. DISCUSSION
The moment at which film breaks in the new pop test was photographed with a highspeed camera. The drop of antifoamer was observed to force its entry into the foaming film and the film began to break from the point where the drop attached. So the new pop test can indicate whether an antifoamer forces its entry into the foaming film, which is considered to be the most fundamental property of an antifoamer. Whereas the filmbreaking test examines both the spreading ability and the entering ability of antifoamers. Lo by the Ross-Miles method shows foampreventing ability and it is said that in this case the antifoamer need not be spread in the foam, but it is necessary that it be insoluble in the foaming agent. L5 by the Ross-Miles method shows foam stability, which is related to the continuation of foam-preventing ability and the spreading ability of antifoamer. From Table II, there seems to be a correlation between film-breaking ability FB measured by the new pop test and foam-preventing
ability measured by the Ross-Miles method in this experimental range. Based on the results of the tests described above, the characteristics of each antifoamer are summarized as follows: (1) KM73: It does not have a hydrophilic group and as a result has no spreading ability, but it has strong film-breaking ability and foam-preventing ability, which persist for a long time. Okazaki and Sasaki (8) showed that the film-breaking ability of a saturated silicone solution is weak, but a heterogeneous silicone solution shows strong film-breaking ability. As KM73 is an emulsion-type antifoaming agent, hence a heterogeneous solution, our results agree with that of Okazaki and Sasaki (8). (2) TBP: It has a phosphoric group, and has strong film-breaking ability, spreading ability, and foam-preventing ability. (3) 12D: It has strong film-breaking ability, has a hydroxyl group, but not necessarily good spreading ability.
1.0
0.5
0.5
i/ ,,.,~i7.'/ (A) IKM'~3 --'-O--'- TgP "~"~, , [2 E'thyl hexcmo - - - 8 - - - 12D 0.5 C (wt*/,)
' ~
' 1O
/
~ OF "~ -0
, 10
1Ethanol I ~ ~ Ethyl Acetate I---~---40 2'0 C (wt*/,) 30
FIG. 1 1. (A, B) Relation between L~ and concentration of antifoaming agents. Journal of Colloid and Interface Science, Vol. 100,No. 1, July 1984
184
TSUGE, USHIDA, AND HIBINO
hD Foam height decrease 30 sec after a drop
TABLE II Properties of Antifoaming Agents Filmbreaking ability,Fp
Agent
Filmbreaking ability,FB
Foampreventing ability,Lo
h0 Lo
[3] L5
KM73 TBP 12D 2-Ethyl hexanol Ethanol Ethyl acetate
Ea E E M I I
M E M M I I
VE E E M I I
a VE, very excellent; E, excellent; M, moderate; I, inferior.
(4) 2-Ethyl hexanol: It does not have strong film-breaking ability, but it has a hydroxyl group and good spreading ability. (5) Ethanol: The weak film-breaking ability and foam-preventing ability observed were also observed by Okazaki and Sasaki (8). (6) Ethyl acetate: Film-breaking ability and foam-preventing ability are not shown in the soluble range, but are shown remarkably in the region of supersaturation, which was also observed by Okazaki and Sasaki (8). CONCLUSIONS
It is shown that film-breaking ability can be measured quantitatively by the new pop test. The film-breaking factor Fp presented here is not affected by the experimental temperature and relative humidity. The film-breaking properties of six antifoaming agents were measured by the new pop test, the film-breaking test, and the RossMiles method, and were compared as shown in Table II. Heterogeneous solutions of antifoaming agents showed generally excellent film-breaking ability and foam-preventing ability. APPENDIX: NOTATION
C Fa Fp h
Concentration of antifoaming agent Film-breaking factor defined by Eq. [2] Film-breaking factor defined by Eq. [ l] Foam height decrease 30 sec after a drop of antifoaming agent was added to the foam
Journalof Colloidand InterfaceScience.Vol. 100,No. 1, July 1984
of DBS solution was added to the foam Foam height when the air is blown Foam-preventing factor defined by Eq.
lD l0 /5 N t
ta to
tF to V
Foam-preventing factor defined by Eq. [4] Foam height when the sample solution does not contain antifoamer Foam height immediately after addition of sample solution Foam height at 5 rain after addition of sample solution Frequency Time from addition of a drop of antifoaming agent to the foaming film until film breaking; film duratiom time Time from the film formation until addition of a foaming drop; blank time Time from addition of a drop of foaming agent to the foaming film until film breaking; DBS film duration time Time to form the film at the ring; film formation time Time from the film formation until the film breaking; base film duration time Volume of a drop ACKNOWLEDGMENTS
The authors express their thanks to Professor Y. Abe and Dr. S. Matsumura (Keio University) for suggesting this problem and for their intelligent discussions and for providing 12D, and also to Mr. N. Akusawa (Japanese National Railways), Mr. K . Ueno, and Mrs. K. Endo (Keio University) for providing experimental assistance. REFERENCES I. Ross, J., and Miles, G. D., Oil Soap 18, 99 (1941). 2. Japan Industrial Standard (JIS)-K3362 (1978). 3. Abe, Y., Matsumura, S., and Yamanoi, K., Yukagaku 26, 470 (1977). 4. Abe, Y., Matsumura, S., and Shibuya, Y., Yukagaku 28, 276 (1979). 5. Japan Industrial Standard (JIS)-K2518 (1967). 6. Duetsche Industrie Norm (DIN) 53902 Teil 1 (1981). 7. Ross, S., and McBain, J. W., Ind. Eng. Chem. 36, 570 (1944). 8. Okazaki, S., and Sasaki, S., Tenside3, 115 (1966). 9. "Handbook of Chemistry" (Kagaku Benran). Maruzen Co., 1975. 10. Matsumura, S., private communication (1980). 11. Abe, Y., and Matsumura, S., Yukagaku 26, 416 (1977).
lution in the foaming column, the foam is formed in the column. The foam height immediately after that shows the foam-preventing ability of the antifoamer, while the foam height after 5 min shows the foam stability. The details of the experimental procedure are shown later. This method has been used in the development of new antifoamers by Abe et al. (3, 4).
In order to prevent various difficulties caused by the foaming of liquids, two methods have been adopted: (1) physical or mechanical methods: usage of heating elements, temperature change, or centrifugal force, etc.; (2) chemical methods: addition of antifoaming agents.
(2) Japan Industrial Standard (JIS) method for determining foaming characteristics of peWhich method should be used is decided by troleum products (5). The air is fed through a considering the physical properties of the liquid, the operating conditions, the cost, and so on. With the development of excellent silicone antifoaming agent in recent years, the chemical method has come to be applied widely. The performance of an antifoamer or a foam preventer is divided into the film-breaking action and the foam-preventing action. In order to examine the performance of antifoaming agents, the following methods have been used:
(1) Ross-Miles method (1, 2). When a constant volume of a foaming solution containing an antifoamer is dropped into the same soi" Deceased.
diffuser stone into a foaming solution containing an antifoamer in a 1000-ml measuring cylinder for 5 min, and the foam heights immediately and after 10 min are measured, which show the performance of the antifoamer and the stability of the foaming agent.
(3) Deutshe Industrie Norm (DIN) method (6). A perforated plate 55 mm in diameter is moved up and down 30 times during 30 sec in a 200-ml sample solution in the measuring cylinder and the foam height is measured after 30 sec to assess the performance of the antifoamer.
(4) Pop test by Ross and McBain (7). A platinum wire ring, on which the foaming film is formed, and another platinum wire ring, previously dipped in the antifoamer to be ex-
175 0021-9797/84 $3.00 Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
Copyright © 1984 by Academic Press, Inc. All rights of reproduction in any form reserved.
176
TSUGE, USHIDA, AND HIBINO
amined, are gently touched. The performance of the antifoamer is classified qualitatively in terms of film breaking.
(5) Tests of film breaking and foam preventing by Okazaki and Sasaki (8). (a) Filmbreaking test: The foam height is measured after an antifoamer drop is added to the foam formed by bubbling air. (b) Foam-preventing test: A foaming solution and an antifoamer are poured in a glass tube and shaken at constant frequency and amplitude, and the foam height is measured subsequently. Among the methods described above, methods 1-3 are industrial standards so that quantitative measurements are possible by using the apparatus and procedure described in detail. On the other hand, in method 4, the details of making the contact of the two platinum rings are not specified so that only qualitative data are possible. Method 5 is semiquantitative in nature. To measure the film-breaking ability of an antifoamer, the pop test (method 4) is the most favorable because of its simplicity. By modifying it, a quantitative method for measuring the film-breaking ability can be developed. The objectives of this paper are to discuss the modified version of the pop test (7), that is, the "New Pop Test," and to present the quantitative data on the film-breaking ability of some antifoamers. The results obtained using the new pop test are compared with the experimental results obtained by the filmbreaking test similar to method 5a and the foam-preventing ability data obtained by method l, Ross-Miles method. 1. MATERIALS
An aqueous solution of reagent grade sodium dodecyl benzene sulfonate (DBS) (0.12 wt%) was used as the anionic foaming solution. Its critical micelle concentration (CMC) is 0.071 wt% (11). The following were used as, antifoaming agents: 2-butyl octane- 1,2-diol which was produced and purified by Abe et al. (3) (designated 12D); silicone emulsion-type antifoaming agent K_M-73, produced by Shin-etsu ChemJournal of CoUold and Interface Science, Vol. 100, No~ I, July [984
ical Company (designated KM-73); 2-ethyl hexanol; tri-n-butyl phosphate (designated TBP); ethanol; and ethyl acetate. All were reagent grade except KM-73. Their chemical structures and solubilities in 0.12 wt% DBS solution and water are given in Table I. In the new pop test, the antifoamers were dissolved in 0.12 wt% DBS solution. 2. APPARATUS AND PROCEDURES
2.1. New Pop Test Figure 1 shows the schematic diagram of the experimental setup for the new pop test. Platinum ring 6, composed of 0.8 mm wire, was fixed horizontally and the ring diameter was 20 mm. Holder 4 with plastic cup 7 and injector 2 were connected to the movable apparatus and they moved simultaneously up and down. Injector 2 was 10 cm in length and 1 mm in diameter, and its point was fused. Two plastic cups (25 mm in height and 45 mm in diameter) were used, one (7A) for ethanol as the cleansing agent and another (7B) for the foaming agent. Each liquid depth in the plastic cup was 17 mm. The light from lamp 5 converged at the rim of the platinum ring, being reflected by the foaming film, but reached directly to the phototransistor by the film break, so that the film duration time described below could be determined by detecting, with the phototransistor and two electronic counters 9 and I0, the changes in light intensity caused by the film breaking. To avoid the effect of wind, the whole apparatus was covered with vinyl sheet hood 1. Vibration was also avoided as far as possible. The room temperature, liquid temperature, and relative humidity were measured by thermometers and Assman's aspiration psychrometer, and their averaged values were used. Initially the moment of film breaking was photographed with a 16-mm high-speed camera (HIMAC 16M) for two or three cases. The experimental procedure was as follows: (1) Platinum ring 6 was immersed and cleansed in ethanol in cup 7A placed on holder
177
FILM BREAKING BY ANTIFOAMING AGENTS TABLE 1 Solubilities of Antifoamers Antifoamer
Solubility[wt%]
Chemicalformula C4H 9 ~
12D
/CH2OH
0.2-0.35 (25°C) a
C C6HI3/
KM73
0.1-0.2 (25°C) a
~OH CH3
[ CH~
CH3
i
/l!
I
CH3-- Si--O[-- Si-- 10-- Si--CH3
i
|l/
I
CH3
L_ C H ~
CH3
H "-, C / C H 2 O H 2-Ethyl hexanol
0.013 (25 °C) b C4H9/
~C2H5
TBP
Insolubleb
(C4H90)3P=O
Ethanol
Infinitely solubleb
C2HsOH
Ethyl acetate
7,86 (20°C) b
CH3COOC2Hs
Solubility in 0.12 wt% DBS solution was obtained from visual observation. b Solubility in water was obtained from Ref. (9).
4 for 20 sec, and the tip of injector 2 was cleansed by ethanol. Ethanol attached to the platinum ring was evaporated by blowing hot air over it for 20 sec. (2) Cup 7A was replaced by cup 7B and then ring 6 was immersed in DBS solution in cup 7B placed on holder 4 for 30 sec. Holder 4 was lowered at constant speed and DBS film was formed on the ring. The time necessary to form the film is tF, film formation time. The time from film formation until film breaking (duration time of base film), to, was monitored. F--
I
"7
FIG. 1. Experimental setup for the new pop test: (1)
hood, (2) injector, (3) clamp, (4) holder, (5) lamp, (6) platinum ring, (7) cup, (8) phototransistor, (9, 10) electronic counter.
(3) Ring 6 was again immersed in DBS solution in cup 7B for 30 sec by translating holder 4 upward. A 9-~1 drop of DBS solution was placed on the tip of the injector, and then holder 4 was lowered at constant speed until the drop was attached to ring 6. tB, the time from film formation until addition of a drop (blank time), and tD, the time from addition of a drop of foaming agent until film breaking (DBS film duration time), were monitored with the phototransistor and electronic counters. (4) After the residual drop on the tip of injector 2 was wiped with a paper towel, a 9~1 antifoaming agent drop was attached to the injector tip. After the platinum ring was immersed in DBS solution for 30 sec, holder 4 was lowered at constant speed and the DBS film was formed on the ring. The holder was further lowered to add a drop to the film on the ring. Then tB and t, the time from addition of a drop of antifoaming agent to the film until film breaking (film duration time), were measured with the phototransistor and electronic counters. Journal of Colloid and Interface Science, Vol. 100,No. 1, July 1984
178
TSUGE, USHIDA, AND HIBINO
After the foaming film broke, the residual drop of the antifoaming agent at the injector tip was wiped with a paper towel. (5) Procedures 1 to 4 were repeated 15 times for a given concentration of the antifoaming agent. (6) Procedures 1 to 5 were carried out for several concentrations of six antifoaming agents in DBS solution.
~7 11,5 .
r'-"
6
--3
2.2. Film-Breaking Test The experimental procedure was as follows: (l) The air was blown at a constant flow 2 rate through a glass nozzle with an air pump into 0.01 mole/liter DBS solution (1 ml) in a test tube 24 cm long and 14 m m in diameter. When the foam was formed up to the upper end of the tube, the air blowing was stopped. Immediately after, a drop of 0.01 mole/liter DBS solution (6/zl) was gently added to the top of the foam and the decrease in foam height, ho, was measured after 30 sec. (2) Procedure 1 was repeated using a drop of antifoaming solution (6 #l) instead of a drop of the DBS solution and the decrease in .z_--I foam height, h, was measured after 30 sec. This measurement was repeated 10-15 times at a given concentration of antifoaming solution. (3) Procedures 1 and 2 were carried out for FIG. 2. Experimental setup of Ross-Miles method: (1) several concentrations of six antifoaming pipete, (2) foaming column, (3) constant temperature water jacket, (4) hole, (5) rubber stopper, (6) tip nozzle, (7) agents in DBS solution.
tl
stopcock 1, (8) stopcock 2,
2.3. Ross-Miles Method Figure 2 is a schematic diagram of the experimental setup of the Ross-Miles method (1, 2). The foaming column 2 is 50 m m in diameter and 90 cm long, and is jacketted by column 3, in which water was circulated at constant temperature (30°C); 1 is the removable pipet and the tip nozzle 6 is 2.9 m m in diameter and 10 m m long. The experimental procedure was as follows: (1) The inside wall of the foaming column 2 was rinsed with water and then with the DBS solution containing antifoamer to be examined. Journal of Colloid and Interface Science. Vol. 100, No. 1, July 1984
(2) Stopcock 2 (8) was closed and the 50ml sample solution was run down the inside wall of column 2. (3) Pipet 1 was filled with 200 ml of the sample solution and placed on rubber stopper 5 at the head of column 2. When stopcock 1 (7) was opened and the solution came down, the foam was formed in the column and the foam height, lo, was measured immediately after the pipet 1 was emptied, and after 5 min the foam height, Is, was again measured. (4) Procedures 2 and 3 were repeated three times at a given concentration of the given antifoaming agent.
FILM BREAKING BY ANTIFOAMING AGENTS (5) Procedures 1 to 4 were carried out for several concentrations of ethanol and ethyl acetate. The data for other antifoamers were obtained from the experimental results (40°C) by Abe et aL (3, 4, 10). 3. DEFINITIONS OF FILM-BREAKING AND FOAM-PREVENTING FACTORS
Lo
=
I
- lo/ In
[3l
L5
=
I
- ls/lo
[4l
where lo is the foam height when the sample solution does not contain an antifoamer, that is, only 0.12 wt% DBS solution. Lo is considered an indicator of foam-preventing ability, whereas L5 indicates the foam stability.
3.1. F i l m - B r e a k i n g Factor by the N e w Pop Test
4. RESULTS
Film-breaking ability is represented in terms of the film-breaking factor, Fp, which is defined as Fp = (to - t)/tD = 1 -- t/tD
179
[ll
where tD was measured in order to cancel out the increase in film thickness owing to the addition of an antifoaming agent to the film by adding a drop of foaming agent to the film, so that the dimensionless derivative of t is introduced as defined in Eq. [ 1]. Fp shows the extent of film breaking by an antifoaming agent, that is, when the film breaks immediately after adding the antifoaming agent to the film, t = 0 and then FI, = 1 from Eq. [1], which means the film-breaking ability of the antifoaming agent is at a m a x i m u m . On the other hand, when t = tD, that is, Fp = 0, the antifoamer has no film-breaking ability.
4.1. N e w Pop Test 4.1.1. P r e l i m i n a r y experiments. Initially three factors affecting film-breaking ability were examined: 1. F o r m a t i o n t i m e o f f o a m i n g f i l m , tF.
The formation times of foaming film, tv, described in procedure 2 in Section 2.1, were 0.1, 1.0, and 7.9 see, so that its effect on the base film duration time, to, could be examined. Figure 3 shows the relation between to and tF and the arrows in the figure show the standard deviations of to. In the cases where tv = O. 1 and 1.0 sec, the holder was lowered by hand so that the scatter in to would be large; on the other hand, in the case where tv = 7.9 sec, the holder was lowered at a constant speed using a m o t o r so that the scatter in to would be relatively small. It shows that when the formation time of a foaming film is long, the
3.2. F i l m - B r e a k i n g Factor by the F i l m - B r e a k i n g Test
The film-breaking factor, FB, is defined in terms of the film-breaking test as
8o
FB = 1 - (ho - h)/(ho - hD)
6O = (h - ho)/(ho - ho)
[2]
where ho is the foam height when the air is blown, hD was measured to compensate the effect of addition of a drop of antifoaming agent on foam height and film thickness.
v
~o
20
3.3. F o a m - P r e v e n t i n g Factor by the Ross-Miles Method oi;
Foam-preventing factors Lo and L5 represent the foam-preventing ability and are defined as
o'.s i
tF
(S)
~
;o
FIG. 3. Relation between base film duration time, to, and formation time, tF, of foaming film. Journal of Colloid and Inte~ace Science, Vol. 100, No, 1, July 1984
TSUGE, USHIDA, AND HIBINO
180
film becomes thinner by the drainage of the foaming film and is liable to break down
1.0
sooner.
Figure 4 shows the relation between t and concentration, C, of 12D, the antifoaming agent, as a function o f tF, where the drop volume was constant at 9 ~tl. The arrows in the figure show the standard deviations of t. When C is equal to 0, t is equal to DBS film duration time, which corresponds to the case in which a drop of DBS solution was added to the DBS film. As the film formation time tv decreases, t increases at C = 0, which agrees with the tendency of the base film duration time to increase owing to less drainage when tF is short as shown in Fig. 3. On the other hand, film duration time t decreases as film formation time t F decreases in the case of addition o f an antifoaming drop, which corresponds to C > 0 in Fig. 4. This is explained on the grounds that the antifoaming agent immerses easily into the film surface owing to the nonuniform distribution of foaming agent on the film surface when the film formation time is short, so that film breaking is facilitated. Figure 5 shows the relation between Fv and concentration of 12D, which is a replot of Fig. 4. The arrows in the figure show the standard deviations o f Fp. The shorter the film formation time, the larger the Fp value. This means that it is necessary to measure Fp at constant film formation time, and the follow-
0.~
0.2 0
0
01
C (wt %)
0.2
FIG. 5. Relation between the film-breaking factor determined by the new pop test and the concentration
of 12D. ing experiments were conducted at a constant film formation time, tF, of 1.0 sec.
2. Drop volume of anti foaming agent. The effect of the drop volume of the antifoaming agent on Fp was examined and the drop volumes used were 7, 9, and 1 t #1. Fp decreases slightly with an increase in drop volume of the antifoaming agent irrespective of the concentration of the antifoamer, because when a larger drop is added, the film thickness increases slightly, so that the film duration time becomes longer and Fp decreases. So the following experiments were conducted at a constant antifoaming agent drop volume 9 ~l.
3. Effects of environment (temperature, humidity). (a) Effect of temperature: Figure 6 shows the relations between temperature and base film duration time, to, DBS film duration time, to, film duration time, t, and film-break-
(
801
6( < ~ _ _
40
-
20 ~ ,'
e
to ,~
'
'
"
~
~ " " ~
4[
j. 0.6
;O t (0.025wt%12D~
o e~(
22
..
2/-,:
T O~ ta-a 26
,
,
28
Temperature (°C)
o
~
o:~
c (~t °/o)
0:2
FIG. 4. Relation between film duration time, t, and concentration of 12D. The drop volume was 9 el. Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
FIG. 6. Relations between temperature and base film duration time, DBS film duration time, and film duration time. Relative humidity, 57.0-58.8%.
FILM BREAKING BY ANTIFOAMING AGENTS B0
v
(b) Effect of humidity: Figure 7 shows the relations between to, tD, t, and Fp, and relative humidity at nearly constant temperature, 20.3-22.0°C. to, tD, and t (for 0.1 wt% TBP) increase with an increase in relative humidity. The film breaking is concerned with the solvent evaporation from the film, so that the film is difficult to break owing to the retardation of evaporation and as a result the film thickness remains constant when the relative humidity is high. As the relative humidity has roughly the same effect on tD and t, the effect of relative humidity on Fp is relatively small. The arrows in the figure show their standard deviations. By analyzing Fp factors using other antifoaming agents at the same temperature but at different humidity, it was found that Fp is not very affected by relative humidity. From the results described above, the effects of temperature and relative humidity on Fp are small though the experimental ranges were limited.
60
G
0.8
~ 0
•
.~, F(
40
"
)
.
,~, .... u_a_ .
.
.
181
04
50 6U " Relative humidity (%)
FIG. 7. Relations between relative humidity and base film duration time, DBS filmduration time, filmduration time, and Fp. Temperature, 20.3-22.0°C.
ing factor Fp when the relative humidity was relatively constant, that is, 57.0-58.8%, and 0.025 wt% 12D solution was used as the antifoaming agent. Throughout this experiment, the liquid temperature was nearly equal to the room temperature, so that the effects of room and liquid temperatures were considered at the same time. to, tD, and t decrease with an increase in temperature, because the surface tension and the viscosity decrease with an increase in temperature, and as a result the film becomes slightly unstable. But F_p is not influenced by the temperature because the effects of temperature on t and tD compensate each other. The arrows in the figure indicated standard deviations.
4.1.2. Relation between film-breakingfactor and concentration of antifoaming agent. According to the preliminary experiments described above, measurements of the filmbreaking factor were conducted under the following conditions, that is, the film formation time tF = 1.0 sec and the volume of the antifoaming drop V = 9 ~I. Figures 8A and B show the relations between the film-breaking factor Fp and the concentration of antifoaming agents, where the keys and arrows show the average values of
1.01
o51
"°- 0
-04 •
, ,l !'+: '
, ITBP' ~ KM73 , 12Ethylhex°n°ll-,-'~'--l~2D
0.5
c (w t'/o)
I'-0-'
I--"'¢)-:-l.O
ol
I0
c (wt%)
20
30
FIG. 8. (A, B) Relation between film-breaking factor Fp and concentration of antifoaming agents. Journal o f Colloid a n d Interface Science, Vol. 100, No. 1, July 1984
182
TSUGE, USHIDA, AND HIBINO
experimental results and their standard de- those after 20 sec, but their tendencies were viations. The results for 12D, KM73, and TBP very similar. In the following FB values after are very similar and show very good film- 30 sec are discussed. breaking ability. The standard deviations in 4.2.2. Relation between Fs and concentraFp value for KM73 below 0.25 wt% are greater tion ofantifoaming agent. Figures 9A and B than those for 12D and TBP. 2-Ethyl hexanol show the relation between FB and the conshows a weak film-breaking ability compared centration of antifoaming agent. The keys and with the other three antifoaming agents de- arrows show the average values of experiscribed above and conversely it stabilizes the mental results and their standard deviations. film below about 0.1 wt%. The distribution FB values also depend on the concentration of its Fp values above 0.2 wt% is very broad and kind of antifoaming agent. FB values for and the standard deviations of the Fp values ethanol and ethyl acetate are much smaller are large. than those for other antifoaming agents. FB Ethyl acetate as well as ethanol do not show values for TBP, KM73, and 2-ethyl hexanol film-breaking ability until the concentration increase with an increase in their concentrabecomes high. The Fp of ethyl acetate changes tion and afterward reach constant values, abruptly around 7.5-8.0 wt%. The solubility whereas the FB value for 12D changes in two of ethyl acetate is 7.86 g/100 g H20 (at 18°C), steps in this experimental range. so it can be said that the film-breaking ability 4.3. Ross-Miles Method of ethyl acetate becomes excellent in the region Figures 10A and B show the relation beof supersaturation. tween L0 and the concentration of six anti4.2. Film-Breaking Test foaming agents. KM73 shows the best foam4.2.1. Preliminary experiments. (1) The ef- preventing ability, whereas ethanol and ethyl fect of the drop volume of antifoaming agent acetate show very weak ability. Figures I 1A on foam height was examined by using dif- and B show the relation between L5 and the ferent volumes: 6, 10, and 15 ~1. With an concentration of six antifoaming agents. By comparing Fig. 10 with Fig. 11, KM73 increase in drop volume, the FB value increased especially when the concentration of is shown to possess excellent foam-preventing the antifoaming agent was high. In the fol- ability. 2-Ethyl hexanol and TBP make the lowing the drop volume was maintained at foam unstable, so that their foam-breaking ability continues for a relatively long time. 6 ~1. (2) The effect on FB of the time from adThe standard deviations of L0 and L5 are dition of an antifoaming drop until measure- so small that they are not shown in the figures. Table II shows the relative evaluations of ment of the decrease in foam height was also examined. From measurements of the de- film-breaking ability by the new pop test and creases in foam height after 20 and 30 sec, FB by the film-breaking test, and of foam-prevalues after 30 sec were slightly higher than venting ability by the Ross-Miles method. I [-(A)
,
0~.
[
C (wt */,)
.
04l Ethanol 1"--'49--- " / Ethyl Acetate I ---~---I
2LcB
'
0
I0
'
..-'S ........... 20
+. 30
C (wt*/,)
FIG. 9. (A, B) Relationbetweenfilm-breakingfactorFBand concentrationof antifoamingagents. Journal of Colloid and Interface Science, Vol. 100, No. 1, July 1984
" L
40
183
FILM B R E A K I N G BY A N T I F O A M I N G AGENTS
~----0-
1.0
'(3'
01.0 (B)
'
"
, 10
, I Ethyl Acctcttel-" 49- - 20 C (wt*/,) 30 40
9
0.5
O~~. o 0 ~..~., -0.2
(A) IKM73 --'-O---- TB'P .... e ..... 12D 05 C (wt*/,)
~
(
,12Eihythextano
1.0
-0.'
"'~---~
P3G. 10. (A, B) Relation between L0 and concentration of antifoaming agents.
5. DISCUSSION
The moment at which film breaks in the new pop test was photographed with a highspeed camera. The drop of antifoamer was observed to force its entry into the foaming film and the film began to break from the point where the drop attached. So the new pop test can indicate whether an antifoamer forces its entry into the foaming film, which is considered to be the most fundamental property of an antifoamer. Whereas the filmbreaking test examines both the spreading ability and the entering ability of antifoamers. Lo by the Ross-Miles method shows foampreventing ability and it is said that in this case the antifoamer need not be spread in the foam, but it is necessary that it be insoluble in the foaming agent. L5 by the Ross-Miles method shows foam stability, which is related to the continuation of foam-preventing ability and the spreading ability of antifoamer. From Table II, there seems to be a correlation between film-breaking ability FB measured by the new pop test and foam-preventing
ability measured by the Ross-Miles method in this experimental range. Based on the results of the tests described above, the characteristics of each antifoamer are summarized as follows: (1) KM73: It does not have a hydrophilic group and as a result has no spreading ability, but it has strong film-breaking ability and foam-preventing ability, which persist for a long time. Okazaki and Sasaki (8) showed that the film-breaking ability of a saturated silicone solution is weak, but a heterogeneous silicone solution shows strong film-breaking ability. As KM73 is an emulsion-type antifoaming agent, hence a heterogeneous solution, our results agree with that of Okazaki and Sasaki (8). (2) TBP: It has a phosphoric group, and has strong film-breaking ability, spreading ability, and foam-preventing ability. (3) 12D: It has strong film-breaking ability, has a hydroxyl group, but not necessarily good spreading ability.
1.0
0.5
0.5
i/ ,,.,~i7.'/ (A) IKM'~3 --'-O--'- TgP "~"~, , [2 E'thyl hexcmo - - - 8 - - - 12D 0.5 C (wt*/,)
' ~
' 1O
/
~ OF "~ -0
, 10
1Ethanol I ~ ~ Ethyl Acetate I---~---40 2'0 C (wt*/,) 30
FIG. 1 1. (A, B) Relation between L~ and concentration of antifoaming agents. Journal of Colloid and Interface Science, Vol. 100,No. 1, July 1984
184
TSUGE, USHIDA, AND HIBINO
hD Foam height decrease 30 sec after a drop
TABLE II Properties of Antifoaming Agents Filmbreaking ability,Fp
Agent
Filmbreaking ability,FB
Foampreventing ability,Lo
h0 Lo
[3] L5
KM73 TBP 12D 2-Ethyl hexanol Ethanol Ethyl acetate
Ea E E M I I
M E M M I I
VE E E M I I
a VE, very excellent; E, excellent; M, moderate; I, inferior.
(4) 2-Ethyl hexanol: It does not have strong film-breaking ability, but it has a hydroxyl group and good spreading ability. (5) Ethanol: The weak film-breaking ability and foam-preventing ability observed were also observed by Okazaki and Sasaki (8). (6) Ethyl acetate: Film-breaking ability and foam-preventing ability are not shown in the soluble range, but are shown remarkably in the region of supersaturation, which was also observed by Okazaki and Sasaki (8). CONCLUSIONS
It is shown that film-breaking ability can be measured quantitatively by the new pop test. The film-breaking factor Fp presented here is not affected by the experimental temperature and relative humidity. The film-breaking properties of six antifoaming agents were measured by the new pop test, the film-breaking test, and the RossMiles method, and were compared as shown in Table II. Heterogeneous solutions of antifoaming agents showed generally excellent film-breaking ability and foam-preventing ability. APPENDIX: NOTATION
C Fa Fp h
Concentration of antifoaming agent Film-breaking factor defined by Eq. [2] Film-breaking factor defined by Eq. [ l] Foam height decrease 30 sec after a drop of antifoaming agent was added to the foam
Journalof Colloidand InterfaceScience.Vol. 100,No. 1, July 1984
of DBS solution was added to the foam Foam height when the air is blown Foam-preventing factor defined by Eq.
lD l0 /5 N t
ta to
tF to V
Foam-preventing factor defined by Eq. [4] Foam height when the sample solution does not contain antifoamer Foam height immediately after addition of sample solution Foam height at 5 rain after addition of sample solution Frequency Time from addition of a drop of antifoaming agent to the foaming film until film breaking; film duratiom time Time from the film formation until addition of a foaming drop; blank time Time from addition of a drop of foaming agent to the foaming film until film breaking; DBS film duration time Time to form the film at the ring; film formation time Time from the film formation until the film breaking; base film duration time Volume of a drop ACKNOWLEDGMENTS
The authors express their thanks to Professor Y. Abe and Dr. S. Matsumura (Keio University) for suggesting this problem and for their intelligent discussions and for providing 12D, and also to Mr. N. Akusawa (Japanese National Railways), Mr. K . Ueno, and Mrs. K. Endo (Keio University) for providing experimental assistance. REFERENCES I. Ross, J., and Miles, G. D., Oil Soap 18, 99 (1941). 2. Japan Industrial Standard (JIS)-K3362 (1978). 3. Abe, Y., Matsumura, S., and Yamanoi, K., Yukagaku 26, 470 (1977). 4. Abe, Y., Matsumura, S., and Shibuya, Y., Yukagaku 28, 276 (1979). 5. Japan Industrial Standard (JIS)-K2518 (1967). 6. Duetsche Industrie Norm (DIN) 53902 Teil 1 (1981). 7. Ross, S., and McBain, J. W., Ind. Eng. Chem. 36, 570 (1944). 8. Okazaki, S., and Sasaki, S., Tenside3, 115 (1966). 9. "Handbook of Chemistry" (Kagaku Benran). Maruzen Co., 1975. 10. Matsumura, S., private communication (1980). 11. Abe, Y., and Matsumura, S., Yukagaku 26, 416 (1977).