Boric Acid-Alcohol Treatment of Cotton Batting' John P. Madacsi,' Julius P. Neumeyer, and Nestor 6. Knoepfler Southern Regional Research Center,2 New Orleans, Louisiana 70 179
Boric acid effectively imparts smolder resistance to cotton batting. Mattresses made from the batting pass the Mattress Flammability Standard FF 4-72. A problem in impregnating cotton batting is the limited solubility of boric acid in water at 20-25'C. To achieve an 8-10% dry add-on from a wet pickup of about 100% by weight of the cotton being processed, water at about 7OoC must be used. A major drawback to using hot water is the excessive boric acid deposited on the fiber surfaces as the water cools. Solvents such as 2-propano1, methanol, ethanol, and glycerol, which dissolve higher ratios of boric acid than water, were used to impregnate cotton batting with boric acid. This paper describes effects of the solvents on properties of the products and on mattresses made from the treated batting when subjected to the FF 4-72 test.
Introduction Implementation of Mattress Flammability Standard FF 4-72 (1973) concentrated attention on the problems of imparting smolder resistance to cotton batting products destined for use in mattresses. Phosphorus flame retardants such as urea phosphate, tetrakis(hydroxymethy1) phosphonium chloride (Thpc), Thpc-amide, and phosphoric acid do not provide adequate smolder resistance to cotton batting in mattress structures (Neumeyer e t al., 1972). Boric oxide donors such as ammonium pentaborate and boric acid render cotton batting sufficiently smolder resist a n t to pass the Mattress Flammability Standard FF 4-72. These salts form boric oxide glasses a t about 325OC which soften and flow a t about 5OO0C, coating the fibers during pyrolysis (Gay-Lussac, 1821). The boric oxide glasses are thermally stable up to temperatures above 750°C (Koenig e t al., 1973). Thermoanalytical (Koenig e t al., 1973) and other data (Knoepfler e t al., 1974) have shown that borax-boric acid treatments for cotton batting are less effective in inhibiting smoldering combustion than boric acid alone. The lower efficiency can be attributed to catalytic effect of the Na+ ion on char oxidation (Walker, 1968). I t appears, therefore t h a t boric acid is the most effective treatment t o comply with FF 4-72. Depending upon the method of application, an add-on of about 8-10% by weight of the cotton is needed (Knoepfler et al., 1974). In wet processing, one of the problems in treating cotton batting with boric acid is the limited solubility of the acid in water at room temperature (20-25OC). T o obtain an 8-10% dry add-on of boric acid from a 100% wet pickup, water a t about 70°C must be used. At this temperature, boric acid is deposited extensively on the surface from crystallization as the fibers cool (Knoepfler e t al., 1974). Some alcohols that dissolve boric acid in higher concentrations than water does are methanol, ethanol, and glycerol. 2-Propanol, also included in this study, solvates boric acid to a limited extent, having the unusual characteristic of being a solvent for boric acid yet being intolerant of water. Addition of water to solutions of boric acid and isopropanol immediately precipitates crystalline boric acid. The alcohols become more interesting as solvents for This research was carried out under a cooperative agreement between the U S . Dept. of Agriculture and the National Cotton Batting Institute, and under a Memorandum of Understanding with the Textile Fibers and ByProducts Association and with the National Cottonseed Products Association. One of the facilities of the Southern Region, Agricultural Research Service, US.Department of Agriculture.
boric acid in the wet processing of cotton batting when their effect on swelling of the fibers is considered. At room temperature (20-25OC), methanol, 2-propanol, and glycerol all efficiently swell cotton, whereas ethanol shows very little swelling action (Rebenfield, 1965). Better penetration of t h e boric acid into the fibers should be effected by swelling. Because of its solvating action on cotton wax, ethanol should improve wettability.
Experimental Section Cotton batting rawstock used in this study was a blend of 60% first-cut linters and 10% each of fly, sweeps, motes, and picker from textile mill wastes. The rawstock was opened, cleaned, and formed into picker laps of uniform fiber content. The laps had a nominal weight of 16 oz/yd2 and were cut into strips about 1 2 in. wide for processing. Treatments were applied to the rawstock by padding the prepared picker laps to about 100% wet pickup, using two dips and two nips, in a laboratory padder. T o control the wet pickup, samples were weighed before immersion, after the first nip, and after the second nip. Alternatively, the rawstock was treated by spraying the webs formed in garnetting before they were lapped into batts, using a laboratory sample card equipped with garnett wire and air dispersion type spray nozzle. Throughput of treating formulation was regulated by a rotameter to obtain a wet pickup of approximately 100% by weight after spraying. Products from both padding and spraying were dried in a forced-draft laboratory oven a t a temperature of 6OoC for 1.5 hr, then allowed to equilibrate for 24 hr before being mechanically processed into batts. The treated rawstock was analyzed before and after garnetting to obtain an indication of how much boric oxide is lost in mechanical processing. Approximately 5-g samples of the treated cotton batting were extracted by refluxing for 2 hr with boiling water in a Soxhlet apparatus. Boric oxide content was determined by titration (Kemp, 1956; Liepins, 1970; Steinberg and Hunter, 1957; and Van Liempt, 1920) with mannitol to enhance acidity of the extracting solution. For evaluating the products by F F 4-72, mini-mattresses were constructed as shown in Figure 1 (Knoepfler et al. 1974). T h e mini-mattresses measure 5 X 11 in. and consist of untreated 7.5 oz/yd2 standard gray and white cotton ticking, three pads or layers of filling material, and a metal base covered by YIG-in. thick asbestos. Each pad has an average nominal density of 2.0 lb/ft3. The base pad (D in Figure 1) was a control flame-retarInd. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976
71
,
FLAME RETARDANT
4 I N D E R CLIPS
Figure 1. Typical mini-mattress construction and cigarette test location.
do -____
Severity of test (increasing order) 1
2 3 4
I
eo
I 30
I 50
I
I
60
m
I d
eo
90
100
Figure 2. Solubility of boric acid in aqueous-organic solvent mixtures.
1 cigarette on bare surface 1 cigarette between 2 sheets 2 cigarettes side by side 2 cigarettes between 2 sheets
Table 11. Immersion Application of 5.7% Boric Acid from Solvent Systems Boric oxide, -_
dant-treated Cotton Flote (Knoepfler e t al., 1965; Knoepfler and Koenig, 1971) 1.5 in. thick. The middle, top, and edge layers A, B, and C were made from the material to be tested. Layers B and C were each 0.75 in. thick; edge pad A was 0.25 in. thick. The finished mini-mattress has a thickness of 13&in. a t the roll edge and l:y4 in. a t the center of the crown. The Standard employs a lighted cigarette as the ignition source. The cigarette is placed on the mattress surface and allowed to burn completely. The mattress passes the test if the char does not extend beyond 2 in. in any direction on the surface from the nearest point of the cigarette. Additional tests are made with a cigarette placed between two sheets on the mattress surface. Previous research showed that the most easily ignited location on a mattress is the rolled edge (Knoepfler et al., 1974; Neumeyer e t al., 1972). For this reason, in all cigarette ignition tests, lighted cigarettes were placed in the valley between the roll edge and the flat surface of the bare mattress and also between two sheets a t the same location shown in Figure 1. FF 4-72 is a “go-no-go” type Standard. Our research showed that additional information can be obtained by testing mattresses with two cigarettes placed side by side in the valley between the roll edge, both on the bare surface and between two sheets. The relative severity of the cigarette test is shown in Table I. Samples that passed the test with a single cigarette on a bare mattress surface were successively subjected to the more severe tests. For use as solvent systems, four alcohols were chosen to increase the boric acid that could be deposited in cotton batting. Figure 2 shows solubility curves for boric acid in methanol-water, ethanol-water, glycerol-water, and 2-propanol. Similar data have been reported by others (Linke, 1958). Anhydrous methanol dissolved the greatest amount of boric acid. The saturation value for methanol is 27.3 g/100 g a t 27OC. The lowest solubility is the 6 g/100 g saturation value for anhydrous 2-propanol.
Results and Discussion Immersion Techniques. Table I1 shows the boric oxide content of a series of samples impregnated with various solvent systems, each containing 5.7% by weight of boric acid. 72
I 40
WEIGHT PERCENT OF ALCOHOL IN SOLVENT MIXTURE
Table I. Cigarette Testing of Mattresses
_________-
I
io
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15,No. 1, 1976
Solvent
Prea
Boric acid, % --__-
%
Post*
Pre
Post
Garnett loss, 70
Water (control) 2.42 2.18 4.29 3.86 4.21 6.41 3.62 2.38 2-Propanol 5.51 4.16 2.35 20% Methanol 3.11 3.86 2.18 6.27 20% Ethanol 3.54 4.48 2.53 4.14 10% Glycerol 2.34 a Pre = before garnett process. b Post = after garnett cess.
9.8 34.2 24.4 38.4
-
pro-
A control, impregnated by a water system containing 5.7% boric acid by weight, is shown for comparison. The boric oxide and boric acid values in the columns marked “pre” were obtained on rawstock after drying and equilibration for 24 hr. There was a wide spread in boric oxide and boric acid add-on when different solvents were used, ranging from 2.34% boric oxide for 10% glycerol to 3.62% for 2-propanol. The columns marked “post” indicate boric oxide and boric acid contents after treated rawstock was garnetted. A large loss of boric oxide and a corresponding loss of boric acid occurs during garnetting. Boric oxide loss was 9.8% for the water system and as high as 38.4% for the 20% ethanol system. As a general observation, losses of boric oxide and boric acid that accompany garnetting usually result from dusting off of material deposited on the surface by mechanical manipulation of the fibers. Table I11 shows the results obtained when batts prepared from rawstock impregnated with boric acid from various solvent systems were assembled into mini-mattresses and tested with lighted cigarettes. The control mattress failed the test where a cigarette was placed between two sheets. In contrast, mattresses containing batting from rawstock impregnated with boric acid dissolved in solvent systems passed both tests with the cigarette on the bare surface and between two sheets. Although products of the 20% ethanol and the water systems both had identical boric oxide and boric acid contents after garnetting, the sample impregnated with the 20% ethanol solvent system passed the cigarette tests, whereas the water-impregnated sample failed. The apparently greater efficiency of the solvent systems may be due to their solvating effect on the waxes present on the fiber surfaces, improved wettability, and concomitantly better penetration of boric acid into the swollen fibers.
Table 111. Cigarette Ignition Results on Mini-Mattresses Ignition test of mini-mattresses
Solvent
5,5r 5.0L
Cigarette(s) ~
1
a
Water (control) Na N 2-Propanol N 20% Methanol N 20% Ethanol N 10% Glycerol N = no ignition. b I = ignition.
1 + sheets
2
Ib N N N N
-
I I I I
Table IV. Glycerol Solvent System
2.0
Boric oxide. Glycerol Boric % acid %
%
Boric acid, %
Garnett Prea Postb Pre Post loss, % 6.98 3.94 80 10.5 5.83 3.29 70 8.4 5.40 3.05 60 6.9 10 5.7 2.34 2.53 4.14 4.48 0 5 5.7 2.27 4.85 4.02 17.1 2.74 4.11 23.1 2.32 5.37 2.5 5.7 3.03 3.96 9.8 0 5.7 2.18 4.29 2.42 a Pre = before garnett process. b Post = after garnett process.
c
Y*OH
1 0
I
25
I
50
----___---
Methanol concentration was varied from 100% to 20% of the total solvent system. Boric acid concentration was 5.7% in all of the mixtures. In the solvent systems where methanol ranged from 80% to 20% by weight, boric oxide and boric acid deposited in the cotton fibers remained practically constant a t about 3% and 5.3%, respectively. When 100% methanol was used as solvent, the add-on of boric oxide decreased to about 1.65%. This 45% reduction in boric oxide add-on between the anhydrous methanol and methanol-water systems can be attributed to formation of methyl esters of boric acid a t ambient temperature in the absence of water (Ethridge and Sugden, 1928; Stasinevich and Polyakova, 1965; Steinberg and Hunter, 1957), which contributes to the rather high solubility of boric acid in 100% methanol compared to that observed for methanolwater systems. Methyl borate esters have high vapor pressures (Arquet, 1936; Schlesinger e t al., 1953); therefore, significant losses of boric oxide occur during drying. Losses in boric oxide that accompany drying for a water system, a 75% methanol system, and a 100% methanol system are shown in Figure 3. For these tests, boric acid content in the impregnating bath was held a t 10%. Each 100-g sample of rawstock was padded t o 100% wet pickup and dried in a forced-draft laboratory oven. Drying temperatures varied from 25 to 150OC for different samples. It is apparent that cotton impregnated by the 100% methanol system loses boric oxide much more rapidly than that treated by water and 75% methanol systems. The shape of the loss curves for the three systems is interesting. Batting treated with boric acid dissolved in 100% methanol lost boric oxide quite rapidly a t all of the temperatures investigated. In contrast, samples treated with the water system or the 75% methanol system lost little boric oxide until drying temperature reached about 75OC. Between 75OC and about 125OC, boric oxide loss from the water and the 75% methanol systems increased, hut remained only about 1/4 of that experienced with the 100% methanol system. These findings emphasize that methyl borates in the 100% methanol system contribute to a rapid loss of boric oxides during drying, even a t temperatures as low as 25OC. Where water is present, for example, in the other two systems,
I
I
75
100
I
I 125
I50
1
I 175
200
DRYING TEMPERATURE, 'C
Figure 3. Deposition of boric acid on cotton batting. Table V. Glycerol Solvent System Glycerol
Boric acid %
%
Ignition test of mini-mattresses Cigarette(s)
1
1 +Sheets
NO 80 10.5 N 70 8.4 N 60 6.9 N 10 5.7 N 5 5.7 2.5 5.7 N 0 5.7 N a N = no ignition. b I = ignition.
N N N N N N I
2
2 +Sheets
N N N I I I I
N Ib I
-
-
-
Table VI. Boric Oxide Add-on from Saturated Methanol-Water Systems as a Function of Alcohol-Water Ratio Treating solution
-___
-
Post garnetting ___-_ Boric acid
Methanol
Water
Boric acid Boric oxide
%
%
%
%
%
100 80 60 50 40 20 0
0 20 40 50 60 80 100
21.4 13.6 9.1 7.7 7.0 6.3 5.9
5.87 5.10 3.63 2.92 2.55 2.33 1.95
10.40 9.04 6.43 5.17 4.52 4.13 3.45
methyl borates are hydrolyzed to methanol and boric acid and the material deposited is boric acid. Glycerol solvent systems increase deposition of boric oxide in the cotton fibers, as shown in Tables IV and V. Where the glycerol-water (10/90) system is used, loss of boric oxide is significantly reduced during garnetting. At higher glycerol concentrations, i.e., 60% or more, it becomes difficult to garnett the treated rawstock because of interfiber adhesion. The products, when installed in mini-mattresses, pass FF 4-72. Table VI shows how boric acid concentration in methanol and methanol-water systems affects the add-on of boric oxide. Saturated solutions were used for each system. Boric oxide deposited on and within the cotton fibers during impregnation increased as concentrations of boric acid and methanol in the solvent system increased. I t appears t h a t there are certain limits t o the deposition of boric oxide for given water-methanol ratios. Deposition of boric oxide increased gradually for methanol-water ratios from 20/80 to 50/50. Greater increases occurred when the methanolInd. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976
73
Table VII. Methanol Solvent System
Meth- Water anol % %
Boric oxide %
Ignition test of minimattresses Cigarette(s) Boric acid %
0 10.40 5.87 20 9.04 5.10 40 3.63 6.43 50 5.17 2.92 60 4.52 2.55 80 4.13 2.33 100 1.95 3.45 N = no ignition. b I = ignition.
100 80 60 50 40 20 0 0
N N N N N N N
Ignition test of mini-mattresses
_-
2+ 2 sheets
1+ 1 sheets NU N N N N N N
Table IX. Spray Application of 5.7% Boric Acid from Solvent Systems
N N N N N Ib I
N N N N N -
Table VIII. Cigarette Evaluation of Mini-Mattresses Containing Cotton Batting Treated with a 5.7% Boric Acid Solution Applied by a Spray System
Solvent
Boric oxide content Solvent
%
Ignition test of minimattresses Cigarette(s) __-__
Boric acid %
6.66 3.76 8.29 2-prop an 01 4.68 20% Methanol 3.19 5.65 6.11 20% Ethanol 3.45 10% Glycerol 6.41 3.62 a N = no ignition. b I = ignition. Water (control)
1+ 1 sheets Na N
N N N
N N N N N
2
N N Ib I I
2+ sheets
N N -
Ind. Eng. Chem., Prod. Res. Dev., Vol. 15,No. 1, 1976
Cigarette( s)
-
1+ 1
sheets
2
NU
N N N I N
Ib I I
~
37.1 40.4 20.4 31.9 18.8
N N N N
I
Table X. Comparison of Application Methods
Solvent Water (control) 2-Propanol 20%Methanol 20% Ethanol 10% Glycerol
Boric oxide, % Garnett loss, % ____ ImmerSpray + Immersion Spray garnett sion Spray 2.18 2.38 2.35 2.18 2.53
3.76 4.68 3.19 3.45 3.62
2.39 2.79 2.54 2.35 2.94
9.8 34.2 24.4 38.4 -
37.1 40.4 20.4 31.9 18.8
-
-
water exceeded 50/50. Large increases in the amount of boric acid in the treating formulation are required, however, if boric oxide deposition is to be increased. Results obtained when samples of cotton batting treated as noted in Table VI were evaluated by the cigarette tests are shown in Table VII. Products of the 20/80 methanolwater system passed the requirements of F F 4-72; the 40/60 methanol-water system yielded products that passed the two-cigarettehwo-sheet test. The improvement is due solely to the increased boric oxide deposited in the fibers. These data confirm that the amount of alcohol above 40% of the total solvent present in the system has little effect, if any, on performance of mini-mattresses evaluated by cigarette tests. The critical minimum boric oxide needed to pass all tests had been exceeded in all samples where 40% or more methanol was used. Spray Techniques. For this work, rawstock picker lap was garnetted, and the in-process webs were sprayed with boric acid dissolved in a variety of solvent systems. Wet pickup was controlled to about 100% by weight of the cotton being processed. The boric acid concentration was kept a t 5.7% in all spray formulations. Table VI11 shows that add-on of boric oxide was approximately 45% higher with the spray system application than with the immersion treatments (Table 11). In all cases, the alcohol-water system formulations applied by spraying yielded products that passed FF 4-72. Treated products from the 2-propanol system and from the water system passed both the two-cigarette and the twocigarettehwo-sheet tests. Although the saturation capacity for boric acid was nearly identical in both these systems, cotton batting treated with 2-propanol had a greater boric oxide content. This may be due to solvation of the wax in cotton fibers by the alcohol, permitting better wettability and penetration of the treatment solutions. Data on performance of the water system application indicate that it may be more efficient than the alcohol systems by providing a 74
Boric acid % Garnett post loss garnett %
Water (control) 2.39 4.23 2-Propanol 2.79 4.94 20% Methanol 2.54 4.50 20% Ethanol 2.35 4.16 10%Glycerol 2.94 5.21 a N = no ignition. b I = ignition.
Batting
_____-__
Boric oxide % post garnett
safety factor exceeding that required by FF 4-72, whereas 20% methanol, 20% ethanol, and 10%glycerol do not. Table IX shows results when products from Table VI11 were regarnetted to obtain an index of the ease of removing the treatment by mechanical manipulation of fibers. The product from the water-spray application lost 37.1% of its boric oxide content when it was regarnetted. This loss is considerably higher than the 9.8% observed for the product of water-immersion treatment followed by drying and garnetting (Table 11). Analysis of the data in Table IX points to the possibility that a large amount of boric acid is deposited on the surface when water is used. In actual practice, surface deposition would be highly undesirable because boric acid would be dusted off when the fibers are flexed in use, and there would be a rapid loss of boric acid from the surface during storage (Knoepfler et al., 1974). All of the products as shown in Table IX passed F F 4-72 after regarnetting, with the exception of those from the 20% ethanol system. A more detailed comparison of the effectiveness of the immersion treatment technique vs. the spray treatment technique is given in Table X. Spray application consistently deposits a larger amount of boric oxide than does the immersion system under the conditions chosen. The larger add-on indicates that it may be possible to employ only an 80% instead of a 100% wet-pickup, and still achieve sufficient add-on of boric acid to pass FF 4-72, using the spray technique. The higher add-on for the spray systems may be attributed to evaporation of solvent from the fine droplets of the spray, resulting in surface deposition of crystalline boric acid. Products from the spray process would have a tendency to lose boric oxide on flexing; losses in some cases would be greater than for products from the immersion process.
Summary The use of alcohols, with boric acid as the oxide donor, was investigated in systems for imparting smolder-resistant properties to cotton batting for mattresses. Four alcohols and two methods of application were examined. Results indicate that alcohol-water solvent systems can be utilized
successfully either in (a) a pregarnett immersion application, or (b) a postgarnett spray application. The treated products, with boric oxide contents of about 2.2%, pass FF 4-72, the Mattress Flammability Standard. The pregarnett immersion application confirmed the better efficiency of the alcohol-water over the water system, in both add-on and performance in cigarette tests. When treatment is applied from an aqueous system, 4.11% or greater boric oxide content is needed to consistently pass FF 4-72. A range of 2.18% to 2.53% boric oxide was necessary with alcohol-water systems. Alcohol immersion systems for rawstock show large losses of boric oxide on garnetting. In the postgarnett spray process, boric oxide deposits as much as 45% greater with the immersion treeatment were observed. With spray application, both the water and the 2-propanol systems yielded products that well exceeded requirements of FF 4-72, passing the most severe test of two lighted cigarettes between two sheets. Garnetting samples after the spray process demonstrated that a large proportion of the acid is deposited on the surface of the fibers, as indicated by boric acid lost in this mechanical processing.
Flammability Standard for Mattresses DOC FF 4-72 (1973). Federal Register 38(110), 15095-15101 (June 8 , 1973); 38(149), 20935-20937 (Aug 3, 1973). Gay-Lussac, J. L.. Anal. Chem., 18 (2), 211-217 (1821). Kemp, P. H.. "The Chemistry of Borates, Part i.," pp 14, 15 Borax Consoiidated Limited, London, S.W., 1, 1956. Knoepfler. N. B.. Gardner, H. K., Jr., Vix, H. L. E.,US. Patent 3181225 (May 4, 1965). Knoepfler, N. B., Koenig, P. A,, U.S. Patent 3626052 (Dec 21, 1971). Knoepfler. N. B., Neumeyer. J. P., Madacsi, J. P.. Flammability, 1, 240-264 (1974). Koenig, P. A.. Neumeyer, J. P., Knoepfler. N. 8.. Vix, H. L. E., Abstracts, Division of Organic Coatings and Plastics Chemistry, 165th National Meeting of the American Chemical Society, Dallas, Texas, No. ORPL 72, 1973. Liepins, R., J. Appl. Polym. Sci., 14, 2594-2599, (1970). Linke, W. F., "Solubilities of Inorganic and Metal-organic Compounds," 4th ed, D. van Nostrand Co. Inc., Princeton, N.J.. 1958. Neumeyer, J. P., Koenig, P. A., Knoepfler, N. B., "Preventing Cigarette Ignition of Mattresses," Proceedings of the Twelfth Cotton Utilization Research Conference, ARS 72-98, 55-64 (1972). Rebenfield, L., "Systematic Investigation of Nonaqueous Swelling Agents for Cotton Cellulose," ARS 72-33, U S . Department of Agriculture, 1965. Schlesinger, H. I., Brown, H.C., Mayfield, D. L., Gilbreath, J. R.. J. Am. Chem. SOC.,75, 213-215 (1953). Stasinevich, D. S..Poiyakova, N. Ya., Zh. Neorgan. Khim., 10(9), 2170--2174 (1965). [Huss. J. lnorg. Chem., 10(9), 1180-1183 (1965).] Steinberg, H.,Hunter, D. L., lnd. Eng. Chem., 49, 174-180 (1957). Van Liempt, J. A. M.. Rec. Traw. Chim., 39,358-370 (1920); Delft 2. Anorg. Algem. Chim., 111, 151-166 (1920). Walker, P. L., Chem. Phys. Carbon, 4, 292 (1968).
Literature Cited Received for review J u l y 21, 1975 Accepted September 22, 1975
Arquet, M., Bull. SOC.Chim., 5 (3). 1422-1424 (1936). Ethridge, J. J., Sugden, S..J. Chem. SOC.,1, 989-982 (1928)
Pigment-Binder Interaction in Paints' Karel Rehacek Paint Research lnstitute, Prague, Czechoslovakia
The simultaneous and competing physical interactions among dissolved polymer molecules (and aggregates) with pigments are defined and analyzed for typical conditions in liquid paints. The nature and composition of the adsorbed layers on several pigments are identified with reference to properties such as stability, flow, and sedimentation. The adsorbed layer of solvated polymer on pigments is independent of the system solvent ratio over a range of concentrations. Such adsorption values are relatively constant among pigment types but are greatly changed by polymer composition. The pigment surface holds a high ratio of the contained solvent. The properties of the dispersed phase of solvated polymer on pigment determine some characteristics of the liquid paint and polymer coating.
1. Introduction In the study of the interactions between the components of paints, it is our aim to characterize the interactions between the elementary particles, Le., the smallest independent particles of the systems, such as the pigment particles, the binder globules (associates), and the molecules of the solvent. The forces developed and the processes occurring due to the interactions between these particles are slight, but in their aggregate they significantly affect the paint and the coatings. For example, if a coating film 50 F (microns, i.e., 2 mil) thick contains 20% by volume of titanium white having a particle size of 0.25 microns (Le., 0.01 mil), an area of 1 cm2 contains roughly 60 billion pigment particles. The surfaces of the particles are separated by the minPresented a t t h e 51st A n n u a l M e e t i n g o f t h e Federation of Societies for P a i n t Technology, held in Chicago, Ill., Nov. 14-17, 1973. A t a meeting of FATIPEC (European Societies f o r Coatings Technology) in Florence, I t a l y , t h e a u t h o r was awarded F i r s t Prize in t h e competition of 1972.
Ute distance of about 0.1 (i.e., roughly 0.005 mil) (Rehacek, 1973). Under these circumstances, even comparatively small forces of attraction developed between the particles are able to produce important changes in the paint being applied. These changes are significant enough to affect the appearance of the final coating. In a 1-1. can of contemporary paint, the total area o f t h e pigment-vehicle interface is of the order of 10,000 m2. In view of the enormous extent of the area, even a small change in the phase interface must, of necessity, affect the properties of the paint. In a pigmented paint, which is a complex polycomponent system, we generally witness a number of interactions between the components, as represented schematically in Figure 1. We are faced on the one hand with interactions between individual components of different kinds, Le., with interactions between pigment, binder and solvent; on the other hand, consideration must be given to the interactions between particles of the same kind, i.e., pigment-pigment, binder-binder, solvent-solvent interactions. In this paper we shall focus our attention on the pigment-binder (P-B) Ind. Eng. Chem., Prod. Res. Dev., Vol. 15, No. 1, 1976
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