DETERGENT ACTION Mechanical Work as a Measure of Eficiency of Surface Active Agents in Removing Soil OSBORNE C. BACON AND J. EDWARD SMITH Fine Chemicals Division, E. I . d u Pont de Nemours & Compuny, Inc., Wilmington, Del. T h e purpose of this paper is to establish the existence of a quantitative relationship between the concentration of a surface active detergent in water and the mechanical work required in removing soil in a detergent process. In addition to accomplishing this purpose, a method of calculating the per cent of colored soil removal from reflectance data is presented. A n equation of the curves relating the per cent soil remoial and the factors of detergent concentration, applied force, and time at a given temperature is developed also. The principles established provide a basis for developing a comprehensive method for the evaluation of detergents in the removal of soil.
T
HE subject of the mechanism of detergent action and deter-
gent evaluation has received considerable attention and much theoretical and experimental work has been done. The topic has been reviewed very well by McBain ( I O ) , Robinson ( 1 4 ) , Valko ( I O ) , Fall (ti), and Chwala ( 3 ) . Factors which have received considerable attention in the past include such properties as surface and interfacial tension changes, adhesion tensions, suspending power, emulsification, micelle structure, sudsing, and adsorption of detergent. h variety of methods for evaluating detergents are discussed in the literature. These methods include standardized washing procedures using soiled fabrics, measure of emulsifying and suspending power, foaming action, and surface and interfacial tension. I n the opinion of JTilliams, Brown, and Oakley (19) the only adequate measure of detergent efficiency is some sort of detergent test with dirty cloth There have been numerous investigations of detergent action involving standardized washing tests. The status of the tests is illustrated by the work of Shukow and Shestakow (1.5), Rhodes and Brainard ( I S ) , Gottc ( 7 ) , Crowe (4), and Bacon ( 1 ) . Six general variables affecting detergent action in aqueous syqtems are: 1
2 3.
4
5. 6.
Detergeiit IIechanlcal force Time Temperatuie Eafie of soil removal Soil suspension and redeposition
The variables studied in this paper are the detergent, the mcchanical force, and time. The temperature and ease of soil removal are not varied. Soil suspension as measured by redeposition is eliminated by experimental conditions, since it is difficult to study soil removal and redeposition in the same experiment. For the purposes of this paper a detergent is defined as a substance which, when dissolved in water, increases the inherent detergent power of water. Ordinary solvent action and chemical reaction involving the soil are not included in this study. The importance of mechanical action as controlled by force and time in cleansing operations is widely recognized on a qualitative basis. The use of mechanical force dates back to antiquity. Even today in many parts of the world where detergents are not abundant, cleansing operations with water are still carried out by rubbing or beating the object to be cleaned. The use of soap and more recently, newly developed synthetic detergents,
has enormously decreased the amount of work required in detergent processes. Reduction in the amount of mechanical work is of great importance in reducing the destructive effects of abrasion, flexing, stretching, and pounding. Rhodes and Brainard (13) considered the effect of mechanical action in a wheel type washer but detected only negligible differences. Morgan (11) expressed the opinion that revolutions per minute are equally as important as the supplies used in washing. Despite the obvious importance of mechanical action in detergent processes, studies of its quantitative significance have been neglected. The general problem of &dying mechanical work as a factor in detergent action may be divided into three parts: preparation of a standard soiled fabric, the scouring operation, and interpretation of the results. The problem of preparing a standard soiled fabric may be subdivided into two main parts, the selection of a fabric and the selection of a soil. The soiled fabric must be uniform from one lot to another and remain essentially unchanged over the period of time that it is stored prior to use. The cotton sheeting used In this investigation represents a standard commercial fabric which is readily available and presents the same type of surface on both sides. This fabric also shows a minimum of crease marks after scouring. The selection of a soil is a more difficult problem. Van Zile (I?) has surveyed the literature and lists a wide variety of materials which have been used, There is no doubt that different soils vary in the ease with which they can be removed from cotton. However, soils 15 hich are soluble in water may be disregarded when evaluating detergents that are designed to add to the inherent detergent power of mat Soils which are solubilized by reaction with the alkalies commonly used in washing formulas may also be eliminated from consideration. Examples of such materials are fatty acids and easily saponified materials. This leaves for consideration a variety of soils which may be classified as nongreasy and greasv soils. Common examples of nongrrasy soils are rust, charcoal, coal, soot, starches, clays, and sand Examples of greasy soils arc vegetable and animal fats and oils, mineral oil, and hydrogenated vegetable oils. A method of evaluation by measuring the mechanical work replaced by the detergent should apply to both types of soil or t o a *combinationof both, a$ the mrchanical force required to remove ‘&%oil is dependent primarily on the magnitude of the forces holding the soil rathei than the nature of the forces. A combinaljy of lamp black, a mineral oil, a hydrogenated vegetable oil, larid starch is the soil used throughout this work. The formula used is taken from the Bureau of Ships ( 2 ) . A suitable washing machine and procedure for use in studying the mechanical work equivalence of detergent action must be selected for accurate control of mechanical action over a range of known relative forces. A practical procedure should permit making a number of deteiminations a t one time. A standard Launder-Ometrr (standard washing machine of the American Association of Textile Chemists and Colorists, manufactured by the Atlas Electric Devices Company, Chicago, Ill.) slightly modified to obtain more accurate and variable speed control, fulfills these requirements. T h r mechanical foice of a LaunderOmater can be varied by changing the number or siz? of the
2361
2362
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T.R Y
steel balls in the jars, and by varying the speed of rotation. Twenty individual tests may be made a t one t,ime and the machine is easily loaded and unloaded. Published methods of interpreting experimental dat.a obtained by scouring standard soiled fabrics under varying conditions have not been entirely satisfadory. R.esults of washirig experiments may be expressed by plotting the change in reflectance or might, of soil removed against variations in the detergent, concentration or time of scouring. There is no accepted st,andard method for interpreting the curves obtained. It has been general custom t o employ reflectance-concentration curves to compare detergent,s. A partial interpretation of such curves has been obtained by cornparing the concentrations or times, giving the same degree of soil removal as measured by reflectance, with two different, detergents under the same conditions of washing. HOTever, this method can be applied only belony the maximum of t,he curve for the poorer detergent. Vaughn, \%tone, and Bacon (18) concluded that reflectivity is not a linear function of the Tyeight of soil present on soiled fabric. They describe a method for determining the weight' of soil removed by comparing the turbidity of the detergent bath, after the scour, with a similar bath containing a known n.eight of. the soil. On a theoretical basis, Vaughn et al. (18) also derived an equation rclating the weight of soil removed and t,he time involved by means of empirical constants. There is no disclosure in the literature of any attempt to measure directly, by a washing procedure, the amount of work done by a detergent. Data adapted LO such an interpretation should compare detergents on a direct and practical basis. The present investigation was carried out t o attain this objoct,ivp. EXPERIM EVT 4 L PROCEDURE
I n order t o establish a general DESCRIPTION OF DETERGENTS. relationship between the soil removing power of a detergent and the mechanical work required, it is necessary that the relationship established should hold for a variety of detergent types Accordingly, work -'as carried out with the f o l l o ~ i n gfour types of detergents: Detergent A is a commercial soap containing 9470 fatty acid sodium salt, 1% inert material, and 5% Imter. The fatty acid content consisted of 85% tallow acids and 15% coconut oil acids. Detergent 13, the sodium salt of technical lauryl alcohol sulfate, contains approximately 90% active ingredient and 10% inorganic salts. Detergent C i s a product containing 35y0 of the sodium salt of a hvdrocarbon sulfonate and in addition 27% of tetrasodium pyrophosphate as a builder. Detergent D is a product containing 35% of the sodium salt of a hydrocarbon sulfonate, the remainder of the product being inorganic salts.
PREPARATION OF STASDARD Sorr,m, FABRIC.The preparation of t,he soiled material, the method of storage, and the basic procedure for washing in the Launder-Ometer have been described by Bacon ( 1 ) . For convenience, these procedures are briefly outlined here. Cotton sheeting, having 48 warp and 48 filling threads per inch, 40 inches wide, and measuring 2.85 yards per pound, was soiled with a nlixt,ure of 60 grams of lampblack, 180 grains of Crisco, 258 grams of Nujol, and 120 grams of wheat starch (200 mesh) in carbon tetrachloride. The mixture !vas applied by immersion and passage between squeeze rolls follox-ed by drying in a current of air. Apparatus similar to that employed by Van Zile (17) was used for applying the soil. Soiled material was prepared on days when the relative humidity was between 40 aiid 507.. (Van Zile used heat to prevent the condensation of moisture on the fabric which is cooled belox the dew point by evaporation of the carbon tetrachloride.) The air-dried material was heated for 30 minutes in a current of air, at 170" F., cooled, and stored in a desiccator containing calcium chloride. This method of storage is necessary because exposure to the atmosphere during storage causes radical changes in the ease of removal of the soil by scouring as reported by Racon ( 1 ) . Van Zile ( 1 7 ) noted that the condensat>ionof moisture
Vol. 40, No. 12,
on the fabric during the drying step adversely affected the keeping qualities of soiled fabrics but gave no details as t,o t,he effects. The soiled fabric used in this r o r k showed a reflectance ol 22 to 245%relative to magnesium oxide. The soiled fabric contained 1.7 * 0.1% of oil and Criseo combined, as determined by extractions made with freshly distilled carbon tetrachloride iii a Soxhlet extractor Containing a fat extracted thimble.
ITASHIKG PROCEDURE. X Launder-Ometer equipped with a temperature control and a preheating bath for the pint jars containing the detergent solution was used. The standard driving mechanism TYas modified to permit two speeds of operation, 42 and 59 r.p.ni. A chain drive was used in place of a belt to ensure uniform speed. Cniforni speed is very important, because the capacity of the machine to do work is proportional to the square of the angular velocity. Leather belts tend to slip and the amount of slippage will vary with the tensions on the belt, changes in frictional characteristics, arid the load in the machine. The load in the machine varies viit,h the number of jars used and the level of the water in the heating bath. With proper care a belt drive can be used, Even with the chain drive in use, the r.p.m. was checked periodically in case other mechanical defects should develop. Rubber stoppers were used in place of t,he usual glass tops of the Launder-Ometer jars to provide greater ease of manipulation. The mechanical work performed by the washing machine was controlled by using two speeds of 42 and. 59 r.p.m. and by varying t,he number and the mass of the balls of two diameters in t,he jar. Absolute measurement of the work involved is not possible, and fortunately, not necessary to compare detergents on a work pcrformance basis. I n order to set up a scale of work or force factors for the Launder-Ometer it was assumed that the viork performed in this machine is directly proportional to the mass of t,he balls in each jar and to the square of the r.p.m. within the prescribed limits. This assumption is based on the rr-ell-known relationships between work, mass, acceleration, and velocity. The experimental result's to be described demonstrate the validity of these assumptions. For the purpose of t,his paper, an arbit'rary force scale was est,ablished based on the force imparted by five 0.25-inch stainless steel balls, each weighing 1.134 grams, a t a Launder-Ometer speed of 32 r.p.m. An arbitrary scale of force values, ranging from 1 to 48, and the means of attaining them, arc given in Table I. The masses of the 0.375- and 0.25-inch steel balls used are 3.459 and 1.134 grams per ball, respect,ively. This isamass ratio of 3.05 to 1. A mass ratio of 3 to I was used in calculating the relative forces given in Table I. The ratio of the squares of the t v o speeds are as follows: 42 squared equals 1764 and 59 squared equals 3364. The ratio of these numbers is 1.97 to 1. A ratio of 2 to 1 was employed in preparing Table I. The 1.5% error involved is considered negligible lor t,he purposes of this paper.
Speed, R.P.M.
Ball Dinmeier,
In.
----
5
10
S u m b e r of Ba.118 per Jar15 20 25 30
7
35
40
Tests madc in the Launder-Ometer over this range of forcc factors showed that force values above 30 do not give proportionate effects. This is probably due to the overcrowding effect of too many balls or too great a centrifugal force. T'isual observation of the action in the Launder-Omctcr jars indicates negligible mechanical action on the fabric,in the absence of balls. A clear view of the jars was obtained b y building a cross section of the Launder-Onietcr and studying slow niutiori pictures of it rotating a t various speeds. The pictures were
December 1948
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
42 r.p.m.; 0.25-inch balls
59 r.p.m.; 0.25-inch balls
42 r.p.m.; 0.25-inch balls
2363
42 r.p.m.; 0.375-inch balla
59 r.p.m.; 0.25-inch balls
59 r.p.m.: 0.375-inch balls
Figure 1. Cross-sectional View of the Launder-Ometer taken a t the rate of 128 frames per second. At 42 r.p.m. the water in the jars almost maintains its natural level with practically no turbulence. At 59 r.p.m. the water level is appreciably affected and more turbulence occurs as the jars pass from positions corresponding to 11 and 1 o'clock. Squares of soiled fabric in the jars merely float about in the water when the machine is in motion. When the steel balls are placed in the jars, and the machine set in motion, their mechanical action on the soiled fabric is evident. The balls strike the fabric while it is suspended in the water and when it is in contact, or in near contact, with the jar. The balls do not have an exact periodic motion all the time, neither has the fabric; however, the average motion over a period of 20 minutes at 42 and 59 r p.m. proved to he reproddcible on a statistical basis. Figure 1 shows the crosssectional view of the Launder-Ometer. The r.p.m., 42 or 59, and the ball size used, 0.25 or 0.375 inch, are indicated. The presence of detergent is indicated by foam. The period of the scouring operation was controlled with an interval timer. The temperature of operation was controlled a t 120" F. by means of a thermostat. Each jar contained a selected number of stainless steel balls to provide the desired mechanical action. I n studying detergent action in aqueous systems, it is necessary to consider the detergent effect arising from the water alone. In order t o compare added detergent, the detergent effect of water alone must either be measured separately or canceled by the experimental procedure. I n carrying out washing experiments u i t h detergent solutions, the swatches of standard soiled fabric were given a prerinse in water. Water plus the mechanical action of the Launder-Ometer, without any steel balls in the jars, removes considerable soil from the standard soiled fabric. The addition of steel balls increases the amount of soil removed.
As will be seen by the experimental results obtained by varying the mass of the steel balls, the work done by the machine is almost entirely due to the action of these balls. We, therefore, must conclude that either the soil removed by a rinse without balls is loosely held initially or the forces holding it are entirely eliminated by the detergent action of water. The reflectance values obtained by rinsing at various force factors (Table I) are shown in Table 11. Let us consider the case where a detergent is added t o wat,er and prerinsed soiled fabric is washed in the solution under the same conditions of mechanical action, time, and temperature as used in the prerinse. The increase in soil removal over the amount removed in the prerinse must be proportional to the effectiveness of the added detergent in reducing the forces holding the soil on thc fabric, and to the equal and opposite mechanical force acting t o remove the soil. The relative decrease in mechanical force required t o remove soil under these conditions must be inversely proportional t,o the effectiveness of the added detergent.
TABLE11. REFLECTANCE V A L U E SOBTAINED ~ B Y RINSING IN \T'ATER FOR 20 MINUTESAT 120 F. AND VARIEDFORCE VALUES O
Reflectance relative t o MgO % Soil reAoved, %(based on original reflectance of
Double Water Rinse
28
29.8
25 34 Values are averages of 6 determinations.
24%) a
Water Rinse
Water Rinse Followed by Rinse with Balls to Give Force Levels of 4 12 24 36 30.7
32
33
33
37
42
46
46
INDUSTRIAL AND ENGINEERING CHEMISTRY
2364
Two squares of soiled fabric each weighing approximately 1 grain and measuring 3 X 3 inches were used in each jar during the scouring operation. Each jar contained 200 ml. of detergent solution or water. The standard practice in this work was to prerinse all specimens of soiled fabric in vater before scouring. Except where noted the prerinse vias conduct,ed under the same conditions of t'ime, teniperat'ure, and mechanical action as in the. subsequent scour. In each Launder-Ometer load, one extra square \vas placed in each of t\w jars, during the prerinse, to be removed for use in determining the reflect,arice obtained iu the prerinse. Experiments showed that four squares may be placed in each jar during the prerinse without measurably affect,iiig the prerinse value or the subsequent scour. Hoxever, the number of squares in the jars during the scouring operatiori n-ith added detergent vias always two. REDEPOSITION ELIMINATE:U BY Tmrr COSDITIOSS.Itedeposition must be eliminated in any soil-removal test, based on rcflectance values, because redeposited soil does not necessarily give the same reflectance as the sanic weight of soil applied the method used in the preparation of the original soiled fabric; it is thus impossible t o interpret t,he reflectance valucs. T for redeposition vicre made by including two piorcs of w fabric in each jar with the two pieces of soiled fabric. and operating a t the higher force level--that is, 24F. A11 four detergents showed no measurable redeposition in the range of coriceritrations report,ed in this paper. The white fabric eniployed was the same as used for preparing the soiled fabric: and had a reflectivity ol 76Yc relative to magnesium oxide. ;\11 redeposition test pieces had a reflectivity of 76 to 777" due t o a slight, cleansing action. This does not mean that very slight redeposition which might be objectionable in laundry practice does not take place in sonic. instances. It does mean that, the tests, as performed, measure soil removal without the interference of a significant amount of redeposition. It was found that increasing the number of soiled squares from two to six resulted in nieasurable redeposition xhen the prerinse was omitted. AIEASIJREnIENT O F ~ E F L E f T A X C X . The reflcctiVit,J' Of test specimens >vasdetermined by means of a Lange universal photoelectric photometer, calibrated to read brightness relative to magnesium oxide. This was accomplished by using :I series of standards calibrated by use of a General Electric spectrophotometer operating at, a wave lengtli ol 458 millimicrons. The standards included two porcelain plates and 8 Munsell standards. The brightness of these standards in pcr ceul relative to magiiesiuni oxide is given in the following tablc. hIunael1 Standard Suinber N/ X/ N / N/ Plat,e 5 . 0 6.0 6.5 7.0 7.5 1 . 6 5 1 9 . 2 2 5 . 2 30.8 3 6 . 8 4 3 . Q 4 9 . 9 , . 18.0 2 5 . 5 3 0 . 5 3 7 . 5 43.5 50.0
Instru- Blark
inent G.E. Lnnge
XI
K/ 8.5
N/ miiite 8 . 0 8 . 5 Plate 55,G 6 1 . 8 7 9 . 1 66.0 62.0 .. N/
The tllarli and white platea \$ere used to set the photometer before ure. Reflectance nieasuremerits were a h ays made 011 two test pieces using one piece as a background for the othei. hleasurements showed that tv,o test pieces selected from the upper range of reflectivity involved (about 60V0)gave identical readings M hen placed on the white standard (79.175 reflectivity) as mhen placed on the black standaid (1.65c/o reflectivity). CALCULATION OF PER CEWT SOIL REMOVAL FROM REFLECTIVITY MEA SUR EWENT S
The folloviing method was de\ eloped to calculate the per cent of the original quantity of black present on the fabric after rinsing and bcouririg operation-. The method is based 011 the assumption that the colored solid iemaining onafabric after scouring has the same reflectivity characteristics as before scouringflocculation or deflocculation on the fabric does not occur. Change of reflectivity is not a linear function of colored soil iemoval. It i q ohviouq that rrflectivitr nirawienientS take into
Vol. 40, No. 12
account, only the colored coinponcnts of a soil and the various components may not be removed a t the same rate. How:ver, n-here combined soils are removed a t essentially the sanic: rate, or in the case of single colored soils, a method of determining the per cent soil removal from reflectivity is of considerahle value. The method is based on the equation reported by Kubelka and bIunk (8). This equation has been used by Solan (12) and Foote ( 6 ) in connection with color problems on papc'r and by 1.aughlin ( 9 ) for measuring color strengths on textiles. Thc equation states that
\vh(.rci
h-
=
S H
=
=
roc~ficiento f rclflectivity coefficient of light scattering observed rrflectivity for monochroinatic light
Although this relationship holds only for monochromatic reflectivity, it can be applied t o the calculation of t,he amount of lamp black present on a fabric, since the light reflected by lamp black, as measured by a spectrophotometer, is the same a t all wave lengths in the visible spectrum. Therefore, the visible light reflected by lamp black is the equivalent of monochromatic light \\-hen using a photometer. The soiled fabric uscd in this work reflected t'he same amount of light a t all wave lengths in the visible spectrum within the range of 207" reflectivity for the original soiled fabric to 60Tc for the scoured fabric, the readings being relative to magnesium oxide. The reflectance values involved in this work are all below 607" relative to magnesium oxide and the use of the Kubelka-Munk equation is valid in this range. K I S values are a linear function of the amourit of black on the experimental soiled fa,bric,as shovin by the folloxing expcrirnent. Two lots of vihite cotton bat,ting were soiled by inirriersiori i n a mixture of the soil in carbon tetrachloride, extracted, and dried. By varying the concentration of t'he treating bat,h, reflectance values of 11 and 3070 relative to .magnesium oxide \yere obtained on the tvio lots. The soiled cotton was carded to make it uniform and placed under a glass plate in a box. A piece of black paper was placed over the glass. -1suitable hole in the paper permitted reflectivity readings to be made. This met,hod was used t o Beep the samples flat and to prevent light from entering the photometcr cell by way of the glass plate. Excellent reproducibility of readings was obt,ained in this v a y . K I S values were applied in the following manner t'o calculate the fraction of each lot required to give a mixture having any reflectivity drsired. The ratio required f o give a reflectance of 22% was calculated as follows: IJet X = fraction of X (reflectivity 11%,K j S 3.6) Let I ' = fraction of R (reflectivity 30%, K j S 0.82) Then X 2.' = 1 and 3.6 X 0.82 Y = 1.38( K I S for 2295 reflect ivity ) SubstitutingX = 1 - Y 3.6 - 3.6 Y 0.82 Y = 1.38 Y = 0.8 x' = 0.2
+
+
+
A mixture vas preparod by blending 1 parts of I3 with 1 part, of A and carded for reading on the photomet,er. The reflect,ance reading was 22%. By use of K / S values it is possible to calculate the per cent black removed between any trvo values of reflect,ivity hg means of the following equation: per cent K / S for soiled fabric -_K_, S for scoured fabric X 100 = black K / S for soiled fabric - K ' S for unsoiled fabric reinovrd 111 ordcr to eliminate repeated calculations, a familv of curve^ a a s constructed to give the per cent soil removcd a t any reflectance betx-een soiled values of 20 to 45L70, and 757,, the rcflcrtivity of the unsoiled fabiic. The range 20 to 45cG C O W I S all prerinse values encountered in this tyork. The cuivcs arc' given in Figure 2.
December 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
2365
I n order to establish a general relationship between the mechanical force and detergent concentration, whilc maintaining time and tempera90 ture constant, it is necessary that the relationship should hold for different types of detergents 80 Therefore, three different types of detergents (A, B, and C) mere selected and reflectance values a t 70 different concentrations and force levels were determined by the procedures previously described The concentrations and force levels used, and the 60 reflectance values obtained, are given in Table 111. -I 24 The time of scouring was 20 minutes, and the 2 50 temperature 120" F. The prerinse in wateI nab L also for 20 minutes a t 120" F. a t the force level $40 employed. PRECISION OF D4T4 The experimental data given in Table I11 are representative data. The 30 data for detergents A and B were obtained from several lots of dirty material and represent the 20 work of more than one operator over a period of one month The data for detergent C were ohtained by one operator, on one lot of dirty ma10 terial in a period of 3 dags. The standard deviation values for detergents A and B are therefoie 0 20 40 50 60 70 larger than for detergent C. Standard deviation REFLECTANCE RELATIVE TO Ma0-9: values for each averaged reflectance value given in Figure 2. Relation of Soil Removal to Reflectance Relative to MgO Table 111 were calculated and the average of these values for each of the curves shown in Figures 3, 4, and 5 are given in the following table: The folloning example illustrates the use of Figure 2. 100
Reflectance of soiled fabric = 22 Reflectance of prerinsed fabric = 32
Foire 4 8 12 16 24
The amount of soil removed by rinsing is 50%. This result is obtained from the chart by erecting a perpendicular line from 32% reflectivity and reading the per cent soil removal figure opposite the point of intersection with the curve originating a t a reflectance ot 22%.
RELATIONSHIP BETWEEN DECONCENTRATION AR'D > h 2 H A i i I C A 4 L \vORK I N DETERGEKT ACTION. The experimental data given in the following paragraphs show that in a detergent process the concentration of detergent required is inversely proportional to the mechanical force applied when the degree of soil removal, time, and temperature are kept constant. While the drtcrgent may act to decrease the forces holding soil on the fabric, practical experience teaches us that mechanical work a3 well as detergent is required in laundry practice. Mechanical work is required unless the detergent acts to reduce the forces holding the soil to zero or negative values. The amount of mechanical work required in the removal of soil obviously is related to the forces holding the dirt particles.
19 2 0
Detergent C 0 0 1 1
1 7 2 1
7 7 0 6
Figures 3, 4, and 5 shov the data of Table 111 plotted with the concentrations of detergent as abscissas and the reflectances of
*
EXPERIZl Eh T A L RESULTS
TERGENT
Standaid De7 iation Values Detergent I Detergent B 1 6 1 8 2 0 2 0
( R ) AND TABLE 111. REFLECTANCES
P E R C E N T SOIL REMOVAL (8)"OBTAINED WITH DIFFERENT DETERGENTS AT VARIEDFORCE LEVELS
?rerinse
R
33.0
S
R S R
33:5 3712
S
R
36:6
R S
33.0
s
R s R S
R
s
R S
R S
R
s
R
Y
..
3d:O 3611 3810
..
Concentration,
%5 Active Ingredient 0.10 0.12 0.14 Detergent A b 45 47 49 54 60 65 52 49 52 72 57 78 74 81 63 GO 62 89 91 86
0.02
0.04
0.06
0.08
37 22 41 40 45 54 47 60
38 27 44 50 46
40 36 46 57 48 62 55 78
42 44 48 62 50 67
37 22 38.5 29
38 27 42 44 42 44 46 57
38.5 29 43
41 40 46 57
46 57 50 67
50
41
40 43 45
57 51 69
45
58 83
67 56 80
E!
Force Level ________
0.16
0 , 2 5 - 0,375inch inch 0.18 Force balls balls R.P.M.
51 69
51
54
53 74 .58 83 64 92
;; ;;
Detergent Bb 41 43 45 40 47 54 51. 47 49 60 65 69 49 50 53 65 67 74 58.5 59.5 GO 84 85 86
90
60 86 43 48 49
0.05
0.06 43.5
20
.. ..
42
20
42
20
59
42
59
24
4
20
..
8
20
..
59
12
..
20
42
24
..
20
59
.,
8
20
..
59
..
12
..
10
59
16
10
10
59
..
24
,
.
20
50
65 52.5 73 69
GO
Detergent C c 0.10 0.16 .. .. .. 31.0 40,; 45.5 46.5 .. .. ,. 45.5 55 62 64 3i:5 40 44.5 48 51 52 .. .. .. .. .. .. 44 58 67 73 75 ,. .. 321.5 42 45.: 50 52 54.5 .. 50 61 71 75 79 .. .. .. .. .. .. 33:O 43.5 50 51 54 55 .. 55 71 73 79 80 .. .. .. a Based on reflectance obtained a t a force of 4 f o r dotergents A and B and b Data are average of G runs made over a period of one month. C Data are average of 4 runs made over a period. of 3 days. 0.02 37 31.5
20
8
.. ..
42 45 51 69 51 69
84
4
69
12
86
.. .. .. , .
8 for detergent C.
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
2366
I
1
.02 .04
35Y 30 0
.02
.C4 .06
.08 .IO GONG. %
.I2
.I4
.I6
.I8
-DETERGENT
35v 1
.02
\
1
I
.06 .08 .IO .I2 GONG.-%
1
.I4
I
.I6
.I8
I
Figure 5. Reflectance Relative to MgO us. Concentration of Detergent C at Varied Force Levels
Figure 3. Reflectance Relative to MgO CY. Concentration of Detergent A at Varied Force Levels
301 0
I
Vol. 40, No. 12
I
.04
I
06
/
.08
I
.IO
!
I2
!
I
I4
.16
I
1
I~EIATIOSSHIP BETWEEK TIMEA N D DXTERGEX~T CONCENTRATime is also a variable which is quantitatively related t'o detergent concentration and mechanical force in removing soil by a detergent process. The experimental dat,a given in t'he folloxing paragraphs sholT that the time of scouring and the detergent concentration required are inversely proportional when the force, degree of soil removal, and temperature are kept constant. The physical definition of work is the product of force and the distance through xhich the force acts. hccording tothis dcfinition, work is doubled when either the force or distancc is doubled. We have assumed that the average distance each particle of dirt is moved is the same, and that t'he force involved is the variable. As the steel balls cannot act on all the particles of dirt at' once, thc amount, of soil removed should be a function . of the time as long as soil removable a t the force level involved is available. ,4study of the effect. of time on the degree of soil removal in the detergent process was made by cxrrving out teak with product TION.
TABLEIv. PRODCCTS O F DETERGENT CONCENTRATIONS ASD CORRESPOVDIXG FORCDS ARC EHSEKTIALLY CONSTAI~T TVITHIN LIMITSOF EXPERIMEKTAL ERROR Detergent
B
.I8
GONG %
1.
Figure 4. Reflectance Relative to MgO vs. Concentration of Detergent B at Varied Force Levels
the scoured fabrics as ordinates. Each figure b h o h i h a family of curves for four different force levels. The numerical values indicated on the curves are interpolated values and shoJ5 the concentration of detergent required t o obtain selected levels of reflectance in the range 40 to 51 corrcsponding to the removal of 44 t o 7170 of the soil based on the lowest prerinse value. Euamination of the curves shows, that for a selected level of reflectance in this range, the products of the detergent concentrations and corresponding forces are essentially constant, within the limits of experimental error, as summarized in Table IV. When the ratio of change in ieflectance to the corresponding change in concentration is small, as shown by leveling off of the curve, the experimental error in determining constants may be large.
R
Per Cent Soil Concn Force Reflec- Removal, Detergent, Factor, tance, Yo Sa C F 40 36 0.06 4 0.028 8 45 54 0 007 4
4 .j
54
R
50
67
c
30
71
A
.?I
1
69
0.048 0 030 0 014
8 12 24
0 076 0.053
8 12
0.026
24
0.103 0.048 0.08 0.06 0.04 0.12 0.087 0.040
12 24 12 16 24
8 12 24
CF 0.24 0.22 0 39 0 38 0 36 0 34 0 61 0.63 0.62
1.24 1.15 0.96 0.96 0.96 0.96 1.04 0.96
Average 0.23
(I
37
0.61
1 20 0 Hb
0.98
Prerinse reflectance used in calculation; detergent d 33%, detergent B 3370, detergent C 31%. a
December 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
2367
TABLE VI, RELATIONSHIP BETWEEN CONCENTRATIOX (C) AND TIME( T ) AT SAMEPERCENTSOILREMOVAL (8USINGDETERGEKT D AT A FORCE LEVELOF 8 Reflectance,
3 v)
401-
301I d
a
Figure 6. Study of Effect of Time on Degree of Soil Removed in Detergent Process
D a t varied concentrations in solution. The force level employed was 8 as obtained with 0.25-inch balls a t 59 r.p.m. The temperature was 120" F. Prerinses in water identical in conditions to the scours were employed. The data obtained are given in Table V and plotted in Figure 6. The numerical values given on the curves are interpolated values to show the time required to obtain levels of reflectance in the range 40 to 53% corresponding t o the removal of 30 to 70% of the soil based on the lowest prerinse value (10 minutes). Examination of the curves shows that for a selected level of reflectance in this range, the products of the detergent concentrations and corresponding times ( C T ) are essentially constant as summarized in Table VI. RELATIONSHIP BETWEEN TIME AND MECHANICAL FORCE, From the relationships already established between concentration and force and concentration and time, it is obvious that time and force are related in the same manner. The relationship between F and T may be derived as follows:
%
Sa
T
40
38
10 20
44
52
10 20
47
61
48
63
C 0.044% 0.022 0.12 0.06 0.025 0.10
40 20 40 60 20
0.05
0.032 0.125 0.06
40
60 0.04 Per cent soil removal based on 10-minute prerinse.
CT 0.44 0.44 1.20 1.20 1.00 2.0 2.0 1.92 2.50 2.40 2.40
Average 0.44 1.13 1.97
2.43
detergent was included in the prerinse, as it was not varied in this experiment and the prerinse value determines the origin of the force- or time- reflectance curves. The scouring tests were carried out using 0.15% detergent B a t varied times and with varied numbers of 0.375-inch balls to obtain varied force levels a t 59 r.p.m. The data were obtained from the average of two runs made a t 120" F. The product of time and force a t the same degree of soil removal is obtained from interpolated values from the curves in Figurc 7 These values are listed in Table VIII.
TABLEVII. REFLECTANCES OBTAINED AT VARIEDTIMESAND FORCES~ J S I N G 0.15% DETERGENT B IN PRERINSE AND SCOTJR Ti me, Min. 10
20 40
__
Force Factor
Prerinse 41.5 43.0 46.0
6 47
12 bo 2 .54. J
49
52.5
24 54
18
53 59 62
.i8
58 62.5
TABLEVIII. RELATIONSHIP BETWEEN TIME(T)AND FORCE ( P ) AT SAMEPERCENTSOILREMOVAL (8)USING0.15% DETERGENT B IN PRERINSE AND SCOUR Reflectance.
CF = Ki CT = Kz
%
Sa
T
56
65
40 20
16
20 10
12
F 8
TF 320 320
62
By multiplication we get
( C F ) ( C T ) = ( K J (Kz) (Ki) (Kd FT = ____
50 a
44
6
120 120
Based on a 10-minute prerinse.
(2%
when C IS kept constant, then FT = K I 651
The dcrivation in tho previous paragraph shows that in a detergent process the time of scouring required is inversely proportional to the applied mechanical force, when the degree of soil removal, detergent concentration, and temperature are held constant. Experimental proof of this relationship was obtained with detergent B. The experimental data are given in Table VI1 and are plotted graphically in Figure 7. The prerinse values were obtained for 10, 20, and 40 minutes using 0.15y0 detergent B and omitting the balls from the jars. The
TABLEV. REFLECTANCES OBTAINED AT VARIEDCONCENTRATIONS AND TIMES USINGDETERGENT D AT A FORCE LEVELOF 8 Minutes 10 20 40 60
Concentration, Per Cent Active Ingredient Prerinse 0.01 0.03 0.09 0.12 36.5 38.5 43.0 44.5 34.5 46.5 47 35.5 37.5 40.5 50.5 52 45 38.0 42.5 39 53.0 53.5 43 46
I
I
I
/
1
20 MIN.
IO MIN.
Y
E
0
w
DETERGENT B 46
0.15% IN RINSE AND SCOUR
Figure 7. Reflectances Obtained at Varied Times and Forces Using Detergent B in Prerinse and Scour
2368
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 40, No. 12
c
90
DETERGENT 8
Figure 8. qc Soil Removed us. Concentration nf Detergent C a t 1 aried Force Levels I)ISCUSSION
C o ~ c e s ~ x ~ ~ Fr cr m u c~~, , .&SI>TIXE Rsi2ariossHu%. Tho experimental data present,ed in the previous sections S ~ O T I -that the concentration of detergent, mechanical force, and time are quantitatively related to each other in bringing about t,he removal of soil in a detergent process. I t is obvious t,hat these relationships arp limited t o a range above the point, of very loapercentage soil removal and below the point, of total available soil removal. -1pproximately 90% of the soil remaining after the prerinse is available wit,h the standard soiled fabric, usod iri this TT-ork. This figure was arrived a t by increasing the t,irne of scouring until the rate of soil removal became very slow and not measurable by the methods employed. It is possible to remove all of the available soil in the standard time of 20 minutes by using an efficient detergent a t high force levels. This is illustrated in Figure 3 where t,he curve a t 24F levels off at about 637" reflectance or 86% soil removal based on a 377" reflectance prerinse value. The increase in soil removal x i t h increasing concentration of detergent a t constant force and time is not uniform aiid reaches a maximum (provided the variables of force and time are insufficient to remove all the available soil) which is peculiar to each detergent. The increase in soil removal wilh increasing force values continues until either the available soil i s removed or the limitations of the machine prevent, utilization of further attempts t o increase the force, The increase in soil removal with increasing time continues until the available soil is removed. As thc detergent Concentration is increased, rho drgree of soil removal increases up to a limiting concentration beyond which further increase in detergent concentration is without a measurable increase in soil removal. When the point of total available soil removal has not been approached, it is interesting to speculate as to t,he reason for this leveling off. I t appcars probable that this limit on concentrat,ion is related to an equilibrium betsveen the soil on the fabric and adsorbed detergent. The term saturation may be applied t o .the condition where adsorption of detergent does not increase n.hen the concentration in solution is increased. Tf we assume that detergent p o ~ e is r related to the adsorbed detergent, the efficiency of a detergent depends upon the quantity and quality of the adsorbed detergent. The quant,ity of detergent adsorbed determines a t which concentration a curve will level off while the quality of the adsorption determines the maximum soil removal obtained.
Figure 9. Sui1 Keino\al vs. Relative Force Level at Varied Concentrations of Detergent H
O n the basis of work repoi,tctl iii the literature together with t h t s experimental data presented in this paper it appears logical to assume that a drtcrgcnt functions iri a cleaning process alo~ig the following lines. The addition of a dctergeut t o tlie water aocelerates the wetting Ketting of the fabric and soil is accompanied by adsorption of t,he d e k g e n t resulting in reduction of the forces acting betL7een the soil and tde fabric. The reduction in the attractive forces is a function of tlie concentration of detergent in t.he bath up io the point that adsorption on the particles of soil has reached sa,turation. ht, greater concent,rations of detergent,, the excess detergent is of value only if it improves t,he nsion of removed soil \\-ith accompanying reduction in reition. Ketting and adsorption can occur with or without niechanical action. However, it is only in except'ional ca.scs thal u.ater-insoluble soil is removed without rncchanical action. The quantity of soil removed will depend on t h r extent t o which the forces holding the soil on the substrat,e hnvc: boen reduwtl and 1 o the amount of mechanical n~orkemployed. of tlie fabric and the soil.
EQUkTTON FOR DETERGENCY CURVES
The mathematical equation relating the independent variables of detergent concentration, mechanical force, and time, with the
I
I
1
,
CON_CC_OF DETERGENT D 0
0 a I
20
30
40
1
002% 004% 008% 1
J
5 0 60 70 BO
T-MIN
Figure 10. Plot of Soil Removal us. Time at Varied Concentrations of Detergent 1)
December 1948
I
INDUSTRIAL AND ENGINEERING CHEMISTRY I
I
I
I l / l l l
I
I
20-
1
0
0.04%
0
o.oa%
1
I
4 ,
,
I
/
9
/ I
I?
detergent C. Logarithmic concentration curves for detergent A and B are given in Figure 13. The equations for the linear portions of the logarithmic detergency curves are derived by intergrating the differentrial equations as follows:
I
X
-
log
'
C
log
%
REL. FORGE-F
100
I
1
, ,
24
2369
= n1 (the constant slope)
s
= n1 log
c + log K ,
S = KiCnl Also
S = K2Fm and
S = KsTnj
I-
where S represents per cent soil removal, C conccntration of detergent, F the relative mechanical force, and T the time of washing. The constants K I , Kz, and Ks include the factors of F and T , C and T , and C and F , respectively. We have shown that values of C, F , and T are interchangeable, and their product is constant in that portion of the detergency curve where increased detergent concentration is accompanied by increased soil removal. Therefore, at a given degree of soil removal in this region we may write the equation
20
I
I
I
I
,
I I I I I
I
l
l
Figure 11. qo Soil Removal us. Relative Force a t Varied Concentrations of Detergent B, and % Soil Removal us. Concentrations of Detergent C a t Varied Relative Force
dependent variable of per cent soil removal is of the type Y = K X n . This relationship holds over the range in which the curves
S = K (CFT)n
obtained by plotting these variables are straight lines on logarithmic scale graph paper. The relationships between the independent variables of detergent concentration, mechanical force, and time and the dependent variable of per cent soil removal are illustrated graphically on rectangular coordinate plots (Figures 8 to 10) and on logarithmic coordinate plots (Figures 11 to 13). The plots are based on data given in Tables I X to XI, inclusive. The values for per cefit soil removal given in the tables are calculated by means of the curves in Figure 1 from interpolated reflectance values taken from the curves in Figures 3 to 6,inclusive.
The significance of K and n in relation to detergent is the subject of current investigation. As the value of n is always positive and less than 1, the above equations represent parabolic formulas. These equations represent a horizontal parabola when n = 0.5 and the general X. The values of K and IL will vary formula becomes Y z = (K*) for different detergents and different soiled fabrics. COMPARISON OF DETERGENTS. It appears logical to assume that the adsorbed detergent functions in removing water-insoluble soils by reducing the forces of attraction holding the soil on the substrate. As a result, the soil is more readily removed by mechanical action. In view of the essential role played by work in detergent processes, it is necessary t o includethis factor in any comprehensive evaluation of detergent effectiveness. I t is obvious that in comparing detergents on the basis of concent r a t i o n-r e flectance curves obtained a t the same work level, the comparison must DE'T.A be made on the basis of the relative concentra100tions required to give equal reflectance at the same work levcl. This method cannot be used for comparisons above the maximum soil re. m o v a l of t h e .OI .02 .03 .04 .os .oa .I .2 .3 poorer detergent GONG.-%-DETERGENT and is therefore Figure 13. "0 Soil Removed us. limited t o the Concentration of Detergent A and lower concentraB at Varied Force Levels in 20 tions covering a Miniites at 120" F.
I
4
55L
I
I
,
DETERGENT D-
-
35$/
i 0.01 l
I
0.03
0.06
GONG. %
I
0.09
I
0.12
1J
Figure 12. Reflectance us. Concentration of Detergent D at Varied Times and at Force 8 and 120" F.
The independent variables of force and time give straightline graphs in the range plotted. The concentration curves are essentially straight at the lower concentrations but are curved at, the higher concentrations. The curvature is believed to be caused by the nonuniform variation in efficiency of the detergent as the concentration increases. Detergents A and B give straight line logarithmic curves over a wider range of concentrations than
1
Vol. 40, No. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
2370
TABLE IX. PERCEXTSOILREMOVED AT VARIED FORCX LEVELS ASD COKCESTRATIONS OF DETERGEKT 11:20 MINUTES AT 120 O F.
24
Concentration of Detergent, % Active Ingredient 0 . 0 6 0 . 0 8 0 . 1 0 0 . 1 2 0.14 0 . 1 6 Detergent A 27 37 43 52 58 62 67 69 48 61 71 78 83 86 87 87
4 24
20 30
Detergent B 36 40 63 72
41 77
47 81
49 81
8 12 16
Detergent C 3 1 . 5 45.5 5 5 , 40 58 66 ., 50 04 70 .. 58 70 75 ..
62 73 75 80
.,
, ,
.,
, ,
..
,
Force 4
24
0 . 0 2 0.04
29 48
.
.,
19 81 64 75 77.5 82
. ..
s.
TABLE P E R CENT SOIL REVOVED AT V A R I E D F o n c E LEVELS AND CONCENTRATIONS O F DETERGENT B I N 20 hlISUTES A T Concn., % Active Ingredient
The c,oncentratioii of detergent required is inversely proportional to the mechanical force applied \\-hen the degree of soil removal, time, and temperature are kept constant. The time of scouring and t h e detergent concent,ration required are inversely proportional wlicn tho degree of soil removal, force, and temperature are kept const,ant,. The time of scouring and the force are inversely proportional when concentration, temperature, and dcKi.ee of soil removal are kept constant,. An equation relating detergent action with concentration of detergent, mechanical force, and time has been derived for that portion of the detergency curve m-here increased detergent ooncentration is accompanied by increased soil removal. method for calculating the per cent colored-soil renioval from reflcctance data has been developed.
120’F ~~. -. Force F a c t o r 8 12
4
LITERATURE CITED 21
0.04 0.08
0.12
XI. P E R CENT SOIL REMOVED AT VARIED T I X E S AND CONCEKTRATIONS O F DETERGEXT D hT FORCE 8 AXD 120’ E’.
TABLE
Concn., % Active Ingredient 0.02
concentrat’ion is accompanied by iuc shown that:
10
Time, in Minutes 20 40
, 60
0.04 0.08
range appreciably below the point a t which the concentiationreflectance curve becomes flat. The relative effectiveness for removing soil of two detergents a t different reflectance levels is determined directly by increasing the force or time of scouring for the detergent giving the lower reflectance value until the reflectance values for both detergents are equal a t equal concentrations of t h e product. The ratios of the forces or times required to give the same degree of soil removal with both detergents is a measure of the relative efficiency of the two detergents. This method makes possible compari‘sons of detergents over the entire concentration range used, including concentrations a t which maximum soil removal (below the total available soil on the fabric) has been reached. I n the range of lower concentrations where the reflectance-concentration method is applicable, the results obtained by either method should be the same. However, it does not necessarily follow t h a t the efficiency ratio of detergents a t higher concentrations will be the same as a t these lower concentrations to which comparisons were of necessity limited in the past. Time of washing is the most flexible means of varying the work in comparing detergents, since this variable remains uniform over any desired range. Variations in relative force are not so flexible as variation in time, since force is limited according to the type of machine used. The effect of changing concentration is limited by the inherent properties of the detergent substance. The use of logarithmic graph paper for plotting soil removal against time or relative force minimize8 the number of points required to construct an accurate curve. The products of concentration and force or concentration and time may be used to comparc detergents a t the same degree of soil removal. Inasmuch as these products Rill vary with differences in soiled fabric, a uniform and reproducible standard soiled fabric would be requircd in order to cst,ablish absolute values of C F and CT. SUMMARY
Over the range of Concentration and mechanical work variations studied in a detergent process and where increased detergent
Baeoii, 0 . C., Am. Duestup Reptr., 34, 556 (194.5). Bureau of Ships Ad I n h i m Specification, 5 1 S 4 7 ( I K T j , “Soap, Salt-Water, Powdered (for Cse in Soft, Nard, or Sea W a t e r ) ,” April 1, 1944. C h n d a , A., “Textilhilfsmittel. 1hr.e Cbemie, Kolloid-chcmir i ~ n d Anwendung,” Vienna, Julius Springer., 1939. Crowe, J. B., Am. D y e s t u f R e p t r . , 32, 237-41 (1943). Fall, P. H., J.Phys. Chew., 31,801 (1927). Foote, W. J., Tech. Assoc. Papers, 22, 397 (1939). G o t t e , E., KoZZoid-Z., 64, 222, 327, 331 (1933). K u b e l k a , P., a n d Munk, F., Z . tech. P h y s i k , 12, ,593 (1931). Laughlin, E. R., A m . Dyestuf Reptr., 34, 280 (1945). MoBain, J. W., Adaances in Colloid Sci., I, 99 (1942). Morgan, 0 . M., Can. J . Research, 6 , 292 (1932). Nolan, P., Paper T r a d e J . , 1 0 5 , 4 2 (1937). Rhodes, F. H., a n d B r a i n a r d , S. W., IND. Eric;. CHmi., 21, 80 (1929). Robinson, C o n m a r , Wetting and DeteTyency Sgmposium, F e b . 1920, 1937, Brit. Sect. Intern. Soc. Leather Trades’ Chem., 25-30. Shukow, A. -4., and Bhestakow, P. I. E., Chew.-Ztg., 35, 1027 (1911). Valko, E., “Kolloidchemische Grundlagen der Textilvercdlung,” Berlin, Julius Springer, 1937. Van Zile, B. S.,Oil &. S o a p , 20, 56 (1943). Vaughn, T. H., V i t t o n e , A , , J r . , and Bacon, L. Et., ISD. ENG. CHEM., 33, 1011 (1941). Williams, E. T., Brown, C. B., and Oakley, H. B., Wetting and Detergency Symposium,Feb. 19-20, 1937, Brit. Sect. Intern. Soc. Leather Trades’ Chem., 163-74. t i E r ! F I Y E D April 26, 1947. Presented before the Division of Colloid Cheniist r y a t the 111th Meeting of the .%MERIC.%N CHEMICAI, SOCIETY, .\f,lant,rc City, S . J.
Thermochemistry of S Q ~ ~ U Carbonate IXI and Its Solutions-Addendum In the oiiginal article [ISD ESG.CHs2v 40, 99-102 ( l Y 4 Y ) l Table V, column 4, gives the heat capacity as calories per gram of sodium carbonate decahydiate dissolving during heating. Because the two temperature rangps used, 20 O to 26 and 26 to 32”, are identical these values chcck well. For use over other temperature ranges the heat capacil y should bc expres3cd in calories per centigrade degree per gram of sodrum carbonate derahydrate disqolving Thcw values qhould bc inc1udc.d in Table V. Cal./O
Run 16 18
c./o.of
Na*COa.lO€I20 Dissolved during Heating 11.3
15 20
Av.
10.5 10 9 10.7 10.9
3 4
I ~ E A X E.$, ~ HKOBEAND
THOAI4S
hI. SHEEHY
