Soiling and Soil Retention in Textile Fibers SUSPENDING POWER OF SURFACTANTS JACK COMPTON AND W. J. HART Institute of Textile Technology, Charlottesville, V a . R
I
R
where B
N AN earlier paper of this series ( 2 , 5 ) it was shown that the chopped fiber technique yields quantitative information concerning the efficiency of various surfactants in preventing soil deposition from aqueous solutions on textile fibers. The present investigation deals with the extension of this suggestion to a studg of “suspending power” of surfactant sySterns as defined by ~~~l~~ and Weatherburn ( 1 ) . The term “surfactant” includes any substance which when introduced into a heterogeneous system will act upon the interfaces of the system in such a manner as to produce changes of a property, or properties; of the system. The systems studied are limited t o greasefree carbon black as the soil and cotton fibers as the substrate.
= reflectance of sample after soiling in the carbon
black surfactant dispersion B, = reflectance of sample after soiling in carbon black dispersion alone BO = reflectance of unsoiled chopped cotton fiber The suspending Power values were found generally to be reproducible t o =!=2%. All determinations were run in duplicate. RESULTS
Variation of Suspending Power of Surfactants and Their Mixtures. SINGLE COMPONENT SYSTEMS. The materials tested cover a wide range of chemical types and structures. The first group considered are single component systems. I n many cases, these materials are neither pure nor nearly pure chemical entities, but are of commercial importance and readily available for use in this study. This group of materials is subclassified on the basis of structure as follows:
EXPERIMENTAL METHOD
The experimental technique was similar t o that described in preceding papers of this series ( 2 , 8). Desized, kiered, and bleached cotton print cloth (80 X 80) was chopped in a Wiley mill. Five grams of the chopped fiber was added to 200 ml. of a 1% carbon black dispersion with primary particle size of 30 mp prepared by diluting a commercial carbon black paste, Aquablak B (35y0 solids) with a n aqueous solution containing 1.5 grams of Daxad 23 per liter. The slurry was agitated for 30 minutes in a closed jar on a reciprocating table shaker which has a 3-inch motion and a
Structure Cellulosic derivatives Other high polymer surfactants Anionic surfactants (low mol. wt.) Nonionic surfactants (low mol. wt.)
tt;
resultsobtained ~ ~ ~ ~ i !i ~ ?~ , c , o~ , ~ i t~ , ~ r o‘~ ~ ,~ ~ ~~ ~ ~ ~$~ The ~ ~~ $ ~ using ~ thevarious surfactants included in the four classes are summarized in Tables I, 11, 111, and IV. T h e
decanting until a clear supernatant liquor was obtained. The slurry was then poured into a Waring Blendor, with an operating speed of 10,000 to 12,000 r.p.m. After dilution with t a p water (the t a p water used in all the tests described in this paper contalned 26 p.p.m. dissolved solids; total hardness as calcium carbonate, 10 p.p.m.; and a pH value of 6.9) the slurry was stirred for 10 seconds, allowed t o stand for 10 seconds, and then stirred again for 20 seconds. The classification of the slurry by decantation was then repeated until a clear supernatant liquor was obtained. The fiber slurry was then made into a pad by filtratio? on a 3-inch diameter Buchner funnel. The pad was dried a t 105 C. in a n oven and reflectance readings were made using a Photovolt reflectometer, Model 610. At least three readings were made on each side of the pad and the average reflectance value obtained. The reflectometer was calibrated a t frequent intervals during the observation process using standard reflectance plates obtained from the National Bureau of Standards. I*
cellulosic derivatives show uniformly high suspending power except for low viscosity sodium cellulose sulfate. This may be due to the relatively low chain length of this cellulose derivative. The other high polymei surfactants do not behave like the cellulose derivatives, with the single exception of polyvinyl alcohol,
TABLE
~~~~~~~~~~~~~~~~1~~~~~~~~~~
Carboxymethylhydroðylcellulose Methylcellulose water soluble Sodium cellulosd sulfate OW vis. sodium cellulose sulfate: med- vis* a Based On active ingredients* TABLE
‘I.
DERrvaTIVEs
OF (Concentration 0.5%Q)
Material Sodium carboxymethylcellulose, low vis. Sodium carboxymethylcellulose med. vis.
I n evaluating the suspending power of the surfactant systems, known quantities of the materials t o be tested were added to the 200 ml. of carbon black dispersion. The amounts added were sufficient t o give the specified percentages of active ingredient. The soap used was a high-grade commercial neutral sodium soap which was taken to be 100% active ingredient. The mixture was then agitated in the Waring Blendor for 1 minute t o ensure dispersion or solution of the surfactant, allowed t o stand 30 seconds, and again stirred for 1minute. When a heavy foam was produced, the dispersion was allowed t o stand until the foam broke prior to the addition of the chopped cotton fiber. All tests were run at room temperature except where otherwise noted. The function “suspending power” is defined by the BayleyWeatherburn equation Suspending power (SP), % =
I.
Active Ingredient, % 99 5 99.6
.
99 5
95 99 95 99 99
vis.
OF
Suspending Power, %
41 51
52 52 46
43 -3 36
OTHER
SURFACTANTS (Concentration 0 . 5 % a )
B - B, rB; (1)
Q
597
Suspending Material Power, Yo Carboxymethyl starch (99% active ingredient 6 Condensation product of a n aryl sulfonate w i d formaldehyde 6 Oxidized starch which had also been sulfated 0 Carrageenin 10 Polyvinyl alcohol 61 3 Sodium lignosulfonate Unless otherwise specified the active ingredient was assumed t o be 100%.
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
598
Vol. 45, No. 3
cellulosic derivatives was evaluated in combination with three surfactants of other types, Table 11, which had shown superior suspending power. (Concentration All but one of the binary combinations gave higher suspending Active IngreSuspending power values than those of the constit'uent materials. The excepPower, % Material dient, % tion mas the carboxymethylcellulose-cetyl alcohol-polyoxyalkylSodium N-methyl-N-oleoyl taurate 76 36 Sodium alkyl aryl sulfonate 100 17 ene condensate mixture which was intermediate in value between Sodium fatty acid soap 99 17 the 0.5% concentrations of its constituents. Sodium metasilicate 100 - 16 TERXARY MIXTURES. The suspending powers of ternary a Based on active ingredients. mixtures of surfactants are given in Table VI. The total concentration of the surfactants was again held consttmt, a t 0.50;1,. Four cellulose derivative surfactants were tested in conjunction The marked difference in behavior of cellulose and starch derivawith t'he fatty alkylolamide and a third component. High BUStives would indicate that this is attributable to fundamental pending power values were obtained in most cases, some even differences in the structure of these polymers. approaching the theoretical limit (100%). The nonionizing Of the low molecular weight surfactants, the fatty allrylolarnide cellulosic derivatives were found t o be definitely inferior t'o the and the cetyl alcohol polyoxyalkylene are outstanding. Sodium anionic derivat,ives, carboxymethylcellulose (Chf C ) and sodium N-methyl-N-oleoyl taurate has good suspending power while soap cellulose sulfate (SCS), in those combinations. The concentraand alkyl aryl sodium sulfonate have only moderate suspending tion series run with CMC, Tahle VI (the first three experiments) power. shows that relatively sinall percentages of other components such as polyvinyl alcohol or fatty alkylolamide can greatly increase POWER OF Low MOLECULAR W E ~ G H T the suspending power value of a primary component. Butyl TABLE IV. SUSPENDING NONIONIC SURFACTANTS Cellosolve and alkyl aryl sodium sulfonate lowered the suspend(Concentration o.5'%a) ing power value. The two alkaline inorganic salts, sodium metaActive Suspending silicat'e and sodium pyrophosphate, showed significant off ect on Material Ingredient, % Power, % the suspending power of the CMC-fatty alkylolamide (compare F a t t y alkylolamide 100 68 Cetyl alcohol polyoxyalkylene Table V), condensate 100 68 Diethylene glycol monostearate 100 2 Effect of Surfactant Additives on Suspending Power of Three Commercial Detergents. GENERAL.After studying a range of a Based on active ingredients. materials and combinations which gave high suspcnding power, it WCI'BRof interest to test' these in conjunction with surfactants accepted as good detergents in order t o find, if possible, formulaBINARYMIXTURES. The data obtained with binary mixtures tions of superior action in the prevention of soil redeposit. Three of surfactants are summarized in Table V. For purposes of detergentmewere chosen which represent a high percentage of the comparison, the total surfactant concentration was held constant tot,al ainount of detergents manufactured: a t 0.5%, with each of the constituents present in equal amounts, O.25Vc. I n this series, the suspending power of two of the anionic 1. A commercial fatty acid soap (Ivory Snow) 2. Sodium N-methyl-N-oleoyl taurate ( C ~ T H & O N C H ~ C ~ H ~ SOaNa) POWER OF BINARY MIXTURES OF TABLE V. SUSPENDING 3. h i alkyl aryl sodium sulfonate SURFACTANTS TABLE 111. SUSPENDING P O W E R O F L O W hIOLECULAR WEIQHT ANIONICSURFACTANTS
~~
~
~
(Ratio 1: 1; total surfactant ooncn., 0.5%)
For these studies the technique previously described was slightly modified. Master batches of 2 to 4 liters of 1% Aquablak B dispersion were prepared by adding 0.570 active ingredient Component B % of the dry detergent and stirring until solution was complete. Polyvinyl alcohol 84 Cetyl alcohol polyoxyalkylene condensate 59 To aliquots of the master batches sufficient quantities of 1% Fatty alkylolamide 77 solutions of the surfactant additives were introduced to give the Polyvinyl alcohol BO Cetyl alcohol polyoxyalkylene condensate SO specified concentrations given in Tables F a t t y alkylolamide 87 VII, TIII, and IX. After stirring the final mixture, the chopped cotton fiber MIXTURESOF SURFACTANTS TABLE VI. TERKARY was added and processed as previously Materials Suspending described. Component C Power, % Yo . Component B % % COMNERCIAL FATTY ACIDSOAP(IVORY 0.125 95 Polyvinyl alcohol Fatty 0.125 0.25 SNOW).The results obtained are sumalkylolamide marized in Table VII. The total surfactant additive present was 5% on the 0.10 92 0.10 0.30 0.05 85 weight of the detergent, or 0.025y0 in the 0.40 0.05 0.126 0.125 84 0.25 slurry. The change in suspending power (ASP) is the difference between the S P 0.125 0.126 64 0.25 0.128 75 0.125 value for the detergent alone and that 0.25 0.125 75 0.125 0.25 for each of the detergent-additive compyrophosphate 0.125 Alkyl aryl sodium sul- 0.125 64 0.25 binations. fonate 0.125 0.26 57 0.125 CMC, SCS, and polyvinyl alcohol 0.125 Polyvinyl alcohol 0.126 61 0.25 were found t o be the most effective 0.125 Cetyl alcohol poly- 0.125 51 0.25 additives for soap. The binary surfactoxyalkylene 0.125 Polyvinyl alcohol 0.125 59 a n t combinations do not show the 0.125 93 0.125 marked superiority as small percentage additives which was displayed when they were tested a t higher concentrations. Materials
Component A Sodium carhoxymethylcellulose (med. vis.) Sodium cellulose sulfate (med. vis.)
Component A Sodium carboxymethvlcellulose, (pled. VlS.)
Hydroxyethylcellulose
Suspending Porver,
-
March 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE VII. EFFECT OF ADDITIVES ON SUSPENDINQ POWER FATTY ACIDSOAP Formulation with 0.5% Soap
%
Additive Soap only Sodium carboxymethylcellulose (rned. vis.) H ydroxyethylcelluloee Carboxymethylhydroxyethylcellulose Sodium cellulose sulfate (med. vis.) Methylcellulose Gum tra acanth Gum ara%io Polyvinyl alcohol F a t t y alkylolamide Cetyl alcohol polyoxyalkylene condensate C M C (med. vis.) Cetyl alcohol polyosyalkylene condensate C M C (rned. vis.) F a t t y alkylolamide C M C (rned. vis.) Polyvinyl alcohol Sodium cellulose sulfate (med. vis.) Cetyl alcohol polyoxyalkylene condensate
0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.025 0.0125 0.0125 0.0125 0.0125 0.0125 0.0125 0.0125 0.0125
SCS (rned. vis.) F a t t y alkylolamide SCS (rned. vis.) Polyvinyl alcohol Polyvinyl alcohol
0.0125 0.0125 0.0125 0.0125 0.0125
Cetyl alcohol polyoxyalkylene condensate Polyvin 1 alcohol F a t t y aYkylolamide
0.0125 0,0125 0,0125
.. 0.025
OF
ChangeJn Suspending Suspending Power, Power, % ASP 17 41 24 36 19 36 44 27 19 34 17 31 24 l4 7 51 34 12 -5 24 7
..
41
24
34
17
44
27
39
22
34
17
44
27
39
22
41
24
The fatty alkylolamide showed antagonism as a n additive which would hardly be expected from its intrinsically high SP value, Table IV. SODIUM N-METHYL-N-OLEOYL TAURATE (SMOT). The results obtained using this detergent are summarized in Table VIII. A pronounced antagonism is shown by the nonionic cellulosic derivatives, while the fatty alkylolamide is inert. The ionizing cellulosics, the natural gums, and polyvinyl alcohol are about equal in increasing the suspending power of SMOT, whereas the polyoxyalkylene is somewhat inferior. The binary combinations containing SCS are slightly superior in suspending power to any of the single component additives.
OF ADDITIVES O N SUSPENDING POWER OF TABLE VIII. EFFECT SODIUM N-METHYL-N-OLEOYL TAURATE
Formulation with 0.5% Sodium N-methyl-N-oleoyl Taurate Additive % SMOT only 0.025 C M C (med. vis.) 0.025 Hydroxyethyl cellulose 0.025 Carboxymethylhydroxyethylcellulose 0.025 Sodium cellulose sulfate fmed. vis.] 0.025 Methylcellulose 0.025 Gum tragacanth 0.025 Gum arabic Polyvin 1 alcohol 0.025 F a t t y agylolamide 0.025 Cetyl alcohol polyoxyalkylene condensate 0.025 C M C (rned. vis.) 0.125 Cetyl alcohol polyoxyalkylene condensate 0.125 C M C (rned. vis.) 0.125 F a t t y alkylolamide 0.125 C M C (rned. vis.) 0.125 Polyvinyl alcohol 0.125 SCS (rned. vis.) n. 125 Cetyl alcohol polyoxyalkylene condensate 0.125 SCS (rned. vis.) 0.125 Fatty alkylolamide 0.125 SCS (med. vis.) 0.125 Polyvinyl alcohol 0.125 Polyvinyl alcohol 0.125 Cetyl alcohol polyoxyalkylene Condensate 0,125 Polyvinyl alcohol 0,125 F a t t y alkylolamide 0.125
Change j n Suspending Suspending Power, Power, % ASP 37 51 14 -3 40 49 12 47 10 17 20 49 12
-
ALKYL ARYL SODIUM SULFONATE .(AASS). The results obtained with this detergent are summarized in Table IX. The ionizing cellulosics and polyvinyl alcohol markedly increase suspending power while the low molecular weight fatty alkylolamide and polyoxyalkylene are inert or possibly antagonistic. The binary combinations of high polymer surfactants are equally as effective as their single components a t equivalent total additive concentration. Effect of Temperature on Suspending Power. METHOD. I n order to observe the effect of temperature differences on suspending power, the technique of soiling the chopped cotton fiber was modified as follows. Twice the usual quantity of fiber-soil-surfactant slurry was prepared and thoroughly mixed. This was divided in two parts and one portion heated to 60' C. while the other was held at room temperature. The usual 30minute period of fiber soiling was carried out while maintaining the slurries a t tmhe specified temperatures. The slurries were then diluted tenfold with water at 20' C., and the final classification procedure completed as described.
TABLE IX. EFFECT OF ADDITIVES ON SUSPENDING POWER OF ALKYLARYLSODIUMSULFONATE Formulation with 0.5% Alkyl Aryl Sodium Sulfonate Additive
Suspending Power,
%
%
C M C (rned. vis.) 0.125 Cetyl alcohol polyoxyalkylene con0.125 densate C M C (rned. vis.) 0.125 Fatty alkylolamide 0.125 C M C (med. vis.) 0.125 Polyvinyl alcohol . 0.125 SCS (rned. vis.) 0.125 Cetyl alcohol polyoxyalkylene condenBat e 0.125 0.125 SCS (rned. vis.) 0.125 Polyvinyl alcohol
AN
Change in Suspending Power, ASP
25
11
29
15
37
24
25
11
37
23
RESULTS. The effect of temDerature differences on sumending power of the various systems studied are summarizid in1 Table X. Soap, both with and without additives, showed a, large negative temperature coefficient of suspending power. The ionizing cellulosics greatly enhanced the suspending power of soap a t both temperatures.
..
-
49
599
TABLE X. EFFECT OF TEMPERATURE ON SUSPENDING POWER OF DETERQENTS AND DETERGENT-ADDITIVE MIXTURES
12 ._
47 37 44
10 0 7
46
9
42
5
46
9
54
17
54
17
53
16
48
11
53
16
Formulation Soap C M C (rned. vis.) SCS (rned. vis.) Sodium N-methyl-N-oleovl taurate 3 M C (rned. vis.) SCS (med. vis.) Alkyl aryl sodium sulfonate C M C (rned. vis.) SCS (rned. vis.)
0.5 0.025 0.025
5 34 34 31
14 52 51 34 ..
- 18
0.025 0.025
51 49 14 44 36
51 51 15 36 36
0 -2 -1 8 0
0.025 0.025
-9
- 17 -2
The synthetic detergents SMOT and AASS, with and without additives, proved insensitive to temperature changes except in the case of the AASS-CMC system, where a positive temperature coefficient was found. Changes in Suspending Power of Surfactants Induced by Changes of Concentration and by Sodium Metasilicate. The
INDUSTRIAL AND ENGINEERING CHEMISTRY
600
effects of concentration changes of the detergcnt alone and of changes in additive concentration a t fixed detergent concentration were next investigated. Suspending power curves for the detergent-additive formulations were run in the presence and absence of sodium metasilicate which was chosen as a representative alkaline detergent builder.
Vol. 45, No. 3
the builder concentration low with this detergent. Buspending power is, however, only one of the important factors involved in detergency and thus for the best action in service all factors must be taken into consideration and rated according t o their relative importance. DISCUS SIOK
The phenomenon of redeposit of soil has long been recognized as a major factor in textile detergency. When a technique was developed which could evaluate the effect of surfactants on the formation of soil-fiber complexes, it was obvious that a n investigation in this field would be of interest. I n considering soil redeposition on fabrics two distinct mechanisms are in operation during laundering, namely:
i 1. Distribution of suspended soil between the liquor adherent to, or interpenetrating, the fabric and the remainder of the detergent bath. 2 . kttachinent of soil particles to the fiber surfaces.
WEIGHT
%
SOAP
Figure 1. Effect of Soap Concentration on Soil Suspending Power The change of suspending power with concentration of soap is shown in Figure 1. Little suspending power is evident for concentrations of soap of 0.1% and less. The critical micellar concentration of soap is reported to be a t about 0.10% and this may be related to suspending power. The change of suspending power of soap with increasing concentrations of added CMC in the presence and absence of sodium metasilicate is given in Figure 2 . This builder depresses the suspending power of soap a t CMC concentrations below 0.025%, whereas, et this concentration and above, the enhancement of the suspending power by CMC overcomes the depressing action of the sodium metasilicate. Of interest is the fact t h a t increasing the CMC concentration above 0.005% adds little or nothing to the suspending action of unbuilt soap, but that with built soap the suspending power increases as the CMC concentration increases so t h a t eventually i t is equal t o t h a t of the soap-CMC systems-i.e., a t CMC concentrations of 0.03% and above. A similar study was made using a synthetic detergent, sodium AT-methyl-N-oleoyl taurate, in place of soap (as in Figure 1). The change in suspending power with concentration is shown in Figure 3. Below a concentration of 0.05y0 there is little suspending action, whereas, abovc this concentration there is a rapid increase in suspending action until a concentration of 0.2 to 0.3Yc is reached, At concentrations in excess of the latter values the increase in suspending action is very small. The change in suspending power of SWOT with increasing concentration of CMC in the presence or absence of sodium metasilicate is shown in Figure 4. The situation here is different from t h a t found when soap was used, Figure 2 . The antagonistic action of sodium metasilicate on the suspending power of SMOT is evident, b u t the addition of CMC does not overcome this effect even a t high concentrations as in the case of soap. The addition of more than 0.00570 to 0.0170 CMC causes little or no change in the suspending power of SMOT whether in the presence or absence of sodium metasilicate. I n the absence of metasilicate, SMOT gives much greater suspending action with C M C ; thus it should be advantageous from this point of view to keep
It is believed that the presence of surfactants in the wash liquor can do little or nothing to reduce soil redeposit by the first mechanism, because this would require the establishment of equilibrium concentration gradients in colloidal systems. Some evidence obtained in this laboratory does indicate that some of the high polymer surfactants, when adsorbed on the soil particles and/or the substrate fiber, can reduce, or prevent, the diffusion of small soil particles into the finer capillaries of the fiber and fabric structure. I n most fabric structures, however, this will not be a major factor so far as distribution is concerned.
-I
F i 20
WEIGHT
%
CARBOXYhlETHYLCELLULOSE
Figure 2. Effect of Carboxymethylcellulose on Suspending Power of Soap, w-ith and without Sodium Metasilicate Alkaline Builder On the other hand, the addition of a strong stabilizing and peptizing agent to the wash liquor during laundering may cause a reduction in the average particle size of the suspended soil and lead t o a greater decrease in the subsequent fabric reflectance for a given weight of soil redeposited. I t must be assumed that the soil distribution in the fabric in the two cases is similar. This is equivalent to increasing the light absorption coefficient, K , in the Kubelka-XIunk equation ( 4 ) by increasing the specific surface of the light absorbing pigment: - R)2 (Kubelka-Munk equation restated) R = S(12K
where R = reflectance K = light absorption coefficient S = light scattering coefficient
(2)
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
March 1953
P
The principal role of surfactants in prevention of soil redeposition, however, lies in their ability to decrease the probability of soil particles becoming attached to fiber surfaces-i.e., by affecting the second mechanism of soil redeposition set forth above. Lambert and Sanders (6) have pointed out the difficulties of obtaining reproducible detergency tests and of translating laboratory results to predictions of commercial laundry behavior. This objection t o small scale tests would apply to all methods of determining soil redeposit so far proposed. Mankowich (6) has recently emphasized the desirability of isolating the “prime factors,” or processes, of detergency and the consequent need t o obtain quantitative data on such processes. It is suggested t h a t the chopped fiber technique does precisely this in the study of surfactant effects on soil redeposition. The fiber surfaces are exposed t o the soiling dispersion under easily controlled conditions. This eliminates variables which might arise from the fabric structure and a t the same time avoids the necessity of extrapolating sedimentation data to soil-fiber complex formation. A quantitative index of soil redeposition involving attachment to the fiber surfaces is thus afforded for a given system using the techniques described in this paper. This does not mean, however, that a determination of suspending power for a given surfactant with a given soil and ~1given fiber under specified conditions of temperature, concentration, agitation, etc., will provide a general index of suspending power for all soils, fibers, and conditions, It is highly improbable that a single determination or single index adequately describing t h e behavior of a large variety of such systems will be found. The suspending power of surfactant or surfactant combinations is the resultant of the interaction of a large number of factors involving the surfactant, soil dispersion, and substrate fiber. The interaction is, in general, neither additive nor linear. Within reasonable limits, the techniques employed in t h e present investigation offer a valuable index of suspending power which, thus far, has given satisfactory correlation with commercial laundry practice. The low molecular weight surfactants have the power of greatly depressing surface tension, and therefore are superior wetting agents, but neither appear to be the strongest suspending agents, nor to increase suspending power when added in small percentages to other detergents. Wetting action, therefore, does not seem to be a prime factor in suspending power. High polymer materials have also been studied as primary surfactants and as additives to detergents. The ionizing cellulose derivatives are outstanding examples in this group, in t h a t
t P
WEIGHT
%
SODIUM
N-METHYL-N-OLEOYL TAURATE
Figure 3. Effect of Sodium N-Methyl-N-Oleoyl Taurate Concentration on Soil Suspending Power
601
0 sWcthoY1 Malo S i l i C O I e 50
t LO
0.02
0.01
WEIQHT
%
0.03
CARBOXYMETHYLCELLULOSE
Figure 4. Effect of Carboxymethylcellulose on Soil Suspending Power of Sodium N-Methyl-N-Oleoyl Taurate, with and without Sodium Metasilicate Alkaline Builder Sodium N-methyl-N-oleoyl taurate (SMOT) 0.5%
they have high suspending power alone as well as when present in small percentages as additives to detergents. Polyvinyl alcohol also proved to be very interesting in this respect. The use of alkaline builders with detergents is a widespread commercial practice. The results obtained in this study indicate, however, that unless detergent formulations are carefully a n d thoroughly tested, i t is possible that redeposit values might rise t o a level which would lead to unsatisfactory performance in multicycle laundering. The general problem of the solid-solid interface and of solidsolid interaction is one of the most difficult and obscure problems in all collloid chemistry, and the present work emphasizes the need for further investigation of these questions. CONCLUSION
A theoretical analysis of the mechanisms of soil redeposition during laundering has been made and a technique for the evaluation of the effect of surfactants in such systems is presented. High polymer surfactants are found t o have the highest suspending power as a group, both individually and in combination with detergents. This was also found t o be the case when the amount of additive was small relative to the detergent. Of t h e surfactants tested, the anionic cellulose derivatives and polyvinyl alcohol are outstanding in this respect. Either synergism or antagonism usually results from combinations of surfactants. T h e interactions of these Combinations are in general nonlinear and nonadditive. Addition of alkaline builders to detergents decreases the suspending power of the detergent but this effect can be overcome by the addition of small amounts of high polymer suspensants which show synergism. The amount of suspensant required varies with the detergent and amount of builder present, A negative temperature coefficient for soil deposition on cotton fiber was found for fatty acid soap alone and in the presence of the additives, sodium cellulose glycolate and sodium cellulose sulphate, whereas a zero or positive temperature coefficient was found for the synthetic detergents, sodium N-methyl-N-oleoy] taurate and analkylaryl sodium sulfonateunder similar conditions. These phenomena may be of practical importance in detergency. The complexity of interaction in surfactant systems makes i t impossible a t present to predict their behavior. More work in this field is needed.
602
INDUSTRIAL AND ENGINEERING CHEMISTRY ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of William R. Musick i n obtaining the experimental data and the helpful suggestions and interest of W. F. Busse. LITERATURE C l T E D
(1) Bayley, C. H., and Weatherburn, A. S., Testile Research J . , 2 0 ,
510 (1950).
(2) Compton, Jack, and Hart, W. J., IND.ENG.CHEM.,43, 1564
(1951).
(3) Hart, W. J., and Compton, Jack, Ibid.,44, 1135 (1952).
Vol. 45, No. 3
(4) Kubelka, P., and Munk, F., 2.tech. Phys., 12, 593 (1931). (5) Lambert, J. M., and Sanders, H. L., IND. ESG.CHEM.,42, 1388 (1950). (6) Mankowioh, A. M., Ibid., 44,1151 (1952). RECEIVED for review December 11, 1951. .bxePrm October 30, 1982. Presented a t the X I I t h International Congress of Pure and Applied Chemistry, New York, September 1951. Report of work done under contract with the U. 6. Department of Agriculture and authorized by the Research and Marketing Act. The contract is being supervised by the Southern Regional Laboratory of the Bureau of Agricultural and Industrial Chemistry. The mention of trade products in this paper does not imply their endorsement by the Department of Agriculture over similar products not mentioned.
Relation of Smoke Molecular Structure RUSSELL A. HUNT, JR. Research Department, Standard Oil Co. (Indiana), Whiting, Znd.
S
MOKE points have been used since about 1930 as a measurement of quality of kerosene used as a n illuminating oil. Smoke point is defined as the height in millimeters of the highest flame produced without smoking when the fuel is burned in a specified test lamp. A standard method of test was described ( 7 ) before the World Petroleum Congress in 1933. Kewley and Jackson ( 3 ) showed t h a t the smoke points of organic compounds varied widely and decreased for pure hydrocarbons in the order: alkanes, cycloalkanes, aromatics. Minchen (6) amplified this work and developed a n empirical equation with which he calculated smoke points for some of the members of several homologous series. The Factor lamp, which was developed by Davis during the early 1920's, was modified so that smoke points could be determined with accuracy (6). Clark, Hunter, and Garner ( 1 ) used a modified smoke-point apparatus to screen organic compounds for use in incendiary bombs. This apparatus differed from a smoke-point lamp i n that no wick was employed, but burning occurred a t the surface of a pool of liquid. With this apparatus a group of 25 hydrocarbons and 80 compounds containing oxygen and nitrogen were investigated. On the basis of the work with the 25 hydrocarbons, Clark made several basic observations on the relation of smoke point to molecular structure: Straight-chain alkanes have the highest smoke points. Branching decreases the smoke point markedly, but the position of the branches on the molecule makes little difference. Addition of a n olefinic linkage to an n-alkane appreciably lowers the smoke point. Cycloalkanes have about the same smoke points as highly branched alkanes; apparently the number of carbon atoms in the cycloalkane ring has little effect. As with alkanes, the introduction of a double bond drops the smoke point markedly. Aromatics have low smoke points, irrespective of the configuration of aliphatic side chains. Clark concluded t h a t the compactness of the hydrocarbon molecule is responsible for smokiness. Compounds of oxygen and nitrogen had smoke points as high as or higher than the corresponding hydrocarbons. In a n investigation of combustion processes in a standardized pot-type space heater, the amount of soot formed on the walls of the burner pot when a given amount of fuel was consumed was found in this laboratory to correlate with the smoke point of the fuel. A high smoke point indicates a heating fuel of better quality in the same manner t h a t a high smoke point for kerosene indicates better illumination properties. Smoke point thus provides a general means for studying the combustion properties of individ-
ual compounds which might occur in virgin petroleum distillates boiling in the range of 160' to 330' C. Compounds were selected for test from types known to be present in the distillates. The main constituents of these fuels are alkanes, cycloalkanes, and aromatic hydrocarbons; alkenes and even alkynes are sometimes present in untreated distillates in minute quantities, and compounds of oxygen, nitrogen, and sulfur are generally present as impurities. With the exception of oxygen compounds, which were thoroughly studied by Clark ( I ) , representatives of these classes of compounds were included in this study. The 108 compounds studied are listed in Tables I, 11, and 111, along with observed and literature values for refractive index as a n indication of the purity of the compounds. I n order to study as broad a molecular-weight range as possible, and because of the unavailability of individual isomers of the higher molecular weights, many compounds boiling below the range of the distillates being considered were included, EXPERIMENTAL PROCEDURE
The smoke-point apparatus used was an improved Factor lamp (6) having a 0.25-inch nick tube and a cylindrical glass chimney 7 inches long with an outside diameter of 1 inch. In order to test small samples in the lamp, a 12-ml. glass vessel that could be filled to the depth of oil normally used in the lamp font was placed in the 4-ounce font for this study. The 0.25-inch white felt wicks (No. D-187, Complete-Reading Electric Co., Inc., 100 South Jefferson St., Chicago 6, Ill.) used are superior to either x-oven or sewn wicks, in that they are uniform in quality and easy t o trim. The wicks were cleaned in a Soxhlet extractor -first with benzene or benzene-ethyl alcohol, then with hexane. After most of the solvent was removed by evaporation, the wicks were dried overnight in an oven a t 200' F. A 4-inch length of wick was prepared for use by cutting one end square with a small device resembling a guillotine and singeing from the freshly cut surface small protruding fibers that might cause uneven burning. After the lamp was assembled, filled with material to be tested, and lighted, the wick was adjusted t o give a nonsmoking flame, not over 10 mm. in height, and allowed to burn 10 minutes t o establish eauilibrium. The flame was then turned UTI until a smoky tail appeared a t the top, and was turned down b t i l the smoky tip just disappeared. The height of the flame in millimeters at this point was taken as the smoke point ( 2 ) . Each smoke point was determined by two observers independently. If the readings differed by more than 2 mm., they were repeated until a point agreed upon by both observers was obtained.
As various modifications of the test lamp and procedure have been used, a quantitative comparison of the results of various
