Isolation and Identification of the Resinous Binder in Water Paints ROBERT W. STAFFORD, American Cyanamid Co., Stamford Research Laboratories, Stamford, Conn.
The typical water-emulsion paint is usually composed of the following phases:
An analytical procedure for the isolation and identification of the resinous binders used in water-emulsion paints is outlined and discussed. Three general methods for the separation of the binder are recommended for use either separately or together. The determination of characteristic physical and chemical properties is outlined. Particular emphasis is placed on the analysis of alkyd- and rosin-type resins. A procedure is given for the separation of an alkyd resin into its dibasic acids, polyhydric alcohols, and modifiers, and methods are suggested for identifying most of the probable members of each group. Rosin resins are included in some detail. A suggested method for the detection of rosin adducts by ultraviolet spectroscopy is outlined.
CONTINUOUS AQUEOUSPHASE,including the protective colloids or emulsifying agents, “dissolved” by the application of suitable solubility aids (such as alkalies). Buffers and preservatives are also included in this phase. EMULSIFIED OIL PHASE, including the water-insoluble resinous binder, the driers, and usually small proportions of high-boiling volatile solvents for the driers. SUSPENDED PIGMENTPHASE,treated to produce water nettability. The present discussion is limited to the isolation and identification of the resinous binder, the “oilJJ of the oil-inwater emulsion. The resin may be any one, or a combination of available resins, selected to give optimum results in the specific application desired. Although a wide variety of resins, both natural and synthetic, may conceivably be present in water paints, those most commonly encountered by the author have been resins of the alkyd type-i. e., reaction products of polyhydric alcohols and organic polybasic acids and their anhydrides. These resins possess good adhesion, toughness, and pigment-binding qualities, and represent materials which generally have been developed especially for water paint formulation. Hitherto less common, but of increasing importance, are the rosin-type resins. Methods for the identification of these two types will be considered in particular. Modifying possibilities will be discussed briefly in passing.
T
HE modern water paint, which is essentially a pigmented, stabilized oil-in-water emulsion, is the logical extension
of the old-type, relatively simple aqueous dispersion such as
Isolation of the Resinous Binder
casein pigmented with whiting. Water-wettable pigments of greater opacity have been introduced, resins and varnishes have been incorporated as water-resistant binders, and various protective colloids have been added as emulsifying agents and stabilizers. The modern water paint differs from the oil paint, not because it contains water, but because it contains water as the continuous phase. Water paints are economical and nonflammable, and are characterized by outstanding brushing ease and spreading rate. They permit a wide variation of the solids-viscosity ratio, and are characterized by a degree of penetration which may be readily varied as desired. They dry rapidly, generally setting-to-touch in less than 2 hours after application, and unlike ordinary oil paints may be applied to moist or wet surfaces without detriment to the eventual dried film. It is usually true that the water resistance of the dried film from the water paint is less than that of a dried film of the same resin from an oil paint, owing to the retention of the emulsifying agent in the water-paint film. This disadvantage may be a t least partially overcome by the selection of an emulsifying agent which is irreversibly dehydrated, during the drying of the film. Water paints have been used extensively for interior coatings, and have been approved for this purpose by Federal Specification TT-P-88 (December 27, 1940). I n addition, they have found considerable application for exterior coatings, particularly masonry. I n the latter instance, the reaction of the casein usually present in the paint with the calcium in the surface coated produces increased water-impenetrability. Additional remarks on the versatility of water paints may be found in ( l a ) .
Before the resin or mixture of resins present as the paint binder can be analyzed, separation from the other constituents is essential. This is often a rather difficult procedure, because of the complexity of the mixtures and wide variations of the ingredients, so that no general procedure is applicable to all water paints. However, the use of the following general procedures, either singly or in combination, usually results in the separation of the various constituents in a state sufficiently pure to permit identification of the resin. The first two methods discussed were devised during the analyses of emulsions over a period of 7 years, with constant modification due to the introduction of new constituents. Method C is a modification of the procedure introduced by Bradley (3) for the analysis of oil paints and lacquers. These methods have been devised for the majority of cases. There have been, and probably always will be, instances where further modifications are in order. Some of these are suggested in their proper places. It cannot be emphasized too strongly, however, that each sample presents an indiFI E 1. vidual challenge to the ingenuity of the M oD IFIED analyst. DEAN STARK A . BESZENE DISTILLATION.ApproxiMOIBTURE APPARATus mately 10 grams of paint emulsion as
dr -
694
September 1.5, 1942
ANALYTICAL EDITION
n received are weighed into B 500-cc. flask equipped with a graduated water trap and a reflux condenser (Dean-Stark moisture determination apparat u s , Figure 1). Roughly 250 cc. of anhydrous benzene are added and the mixture is heated until the water level in the trap is constant. The following fractions result: 1. Volatile benzeneimmiscible liauids. retained in the trap. This fraction will consist of water, together with any water-soluble volatile solvents present. 2. Benzene-soluble ON F L A S K material, consisting of the resinous binder and benzene-soluble waterinsoluble solvents. 3. Nonvolatile benzene-insoluble material, including the protective colloids, soaps, and other dispersing agents, bulk FIGURE2. COLD SEPARATION FILof the driers, inorTRATION APPARATCS ganic salts, benzeneinsoluble resins (such as cellulose ethers and esters, unalkylated urea resins, etc.), pigments, and dyes. Benzene is substituted for the xylene or toluene usually employed (%'$), because it also is an excellent solvent for most resins generally found in the average water paint, and because, being more volatile than toluene, it is easier to separate from the resin. An additional advantage is the relative insolubility of most alkali metal soaps in anhydrous benzene, preventing contamination of the resin fraction by such possible ingredients. Toluene has been found to dissolve some soaps under the conditions described. Nitrogenous base, alkaline earth, and heavy metal soaps are generally soluble in benzene, but these would be present only in small amounts, if a t all. If subsequent analytical procedures indicate the presence of benzene-insoluble resinous constituents of the binder, these may be isolated from the benzene-insoluble fraction by extraction with suitable solvents, such as alcohol for cellulose ethers, acetone for cellulose esters, and water for unalkylated urea resins. The major proportions of any shellac present will also be found in this fraction, and may be isolated by extraction with alcohol. B. COLDSEPARATION WITH ALCOHOL AND BENZEKE. Occasionally, a water paint will contain ingredients which react with each other in the boiling benzene solution, or become occluded. As an example of the latter instance, the resin may be so coated with benzene-insoluble protective colloid that portions of it remain in the benzene-insoluble fraction even after prolonged extraction. In such cases, quantitative separation is seriously affected. When this situation occurs, separation may be expedited by the following procedure: A small sample of paint is weighed into a tared Alundum thimble of medium porosity (Norton Alundum 5811 R A 360). A glass rod (for stirring) is included in the tare. After dilution with an equal volume of water, the mixture is stirred thoroughly, and the emulsion is broken by the addition of glacial acetic acid, or, if necessary, concentrated hydrochloric acid. The thimble containing the broken emulsion is then placed in the apparatus diagrammed in Figure 2, and the aqueous liquid is drawn off under suction. The material remaining in the thimble is thoroughly washed with water and the washings added to the original filtrate. This procedure yields (1) aqueous filtrate containing water-soluble salts (and possibly a small amount of protective colloid), and (2) precipitate in thimble, consisting
695
of water-insoluble materials, such as the binder, protective colloids, etc. The thimble is transferred to a second suction funnel and washed with 2B alcohol, to remove remaining water droplets, and finally with warm benzene until all the resin has been dissolved. Evaporation of the combined alcohol and benzene wash liquors leaves the resinous binder as residue. The protective colloid remains in the thimble, available for further examination. The use of an Alundum thimble has been found advantageous because of its greater filtering surface. I t may also be used in a Soxhlet extractor if such a step is thought necessary, and can be easily cleaned for reuse, either with chromic acid or by ignition. In addition, the insoluble residue remaining in the thimble can be dried and reweighed with good accuracy. C. COLDSEPARATION WITH ACETONE,BENZENE, AND PETROLEUM ETHER. In other instances, it has been found advisable to use the method of Bradley (S), in which the binder is isolated from the other constituents by dilution with acetone, followed by concentration and then dilution of the acetone solution with benzene to precipitate cellulose esters. The benzene solution is then evaporated, and the residue thoroughly extracted with etroleum ether to separate natural resins and plasticizers (solub e ) from synthetic resins (insoluble) Since the above method was deJised for the analysis of oil paints and lacquers, a few changes are required before it can be applied to water-emulsion paints. Addition of acetone to the original emulsion causes the precipitation of hydrophilic bodies, including methyl cellulose. Filtration of the broken emulsion gields a filtrate that not only contains the acetone-soluble binder, ut also water-soluble constituents dissolved in the water associated with the acetone. The filtrate must therefore be evaporated to dryness and extracted with acetone. The resulting solution is treated as described. In carrying out the remaining procedure, it must be borne in mind that not all natural resins are soluble in petroleum ether-e. g., shellac-nor are all synthetic resins insoluble-e. g., rosin-esters, etc. Particularly resistant mixtures may necessitate supplementing the methods discussed above with those described by Biffen and Snell (8). Whatever the method used to separate the vehicle dissolved in a suitable solvent, care should be taken in the evaporation of the solvent. Carrying out this step on a steam bath, in a vessel through which is passed an inert gas, such as nitrogen, has been found both rapid and free of objectionable oxidation of the resin. Standard-joint flasks, equipped with a 45' sidearm tube, are suitable vessels available for this purpose (Figure 3).
Identification of the Separated Resin or Resins After isolation in a reasonably pure, unoxidized condition, the resin or resins may be considered an organic unknown, and analyzed according to the usual procedures of organic analysis. These procedures include : physical examination, determination of physical and chemical constants, elementary
n
FIGURE 3. SOLVENT DISTILLATIOX APPARATUS analysis, solubility tests, classification tests, and preparation of a derivative. I n the case of resins, the usual methods for the identification of pure organic compounds are necessarily subject t o many modifications, some of which are discussed in the following paragraphs.
PHYSICAL EXAMINATION. The physical state, the relative degree of hardness, the homogeneity, color, and odor, are noted. Microscopical examination for possible dispersed phases, crystals, etc., should be included. The determination of the behavior
INDUSTRIAL AND ENGINEERING CHEMISTRY
696
.of the resin during its ignition in a platinum spoon may yield valuable clues. Odors evolved during this procedure may include: Odor Acrolein Formaldehyde Acetaldehyde Phenols Amines
Resin Indicated Alkyd resins (glycerol? and glycols) Urea and phenolic resins Glycols, vinyls, or acetaldehyde resins Phenolic, resins Urea resins
then
Dt
=
c - a (h-a) - (d-C)
Vol. 14, No. 9
XD
The density of the OT solution is practically equal to that of water alone. The density of less solid resins is determined directly by the use of the pycnometer. Great care must be exercised in all cases to exclude air bubbles.
Table I includes refractive indices and densities determined Many other characteristic odors evolved during the ignition on a number of resins of the alkyd and rosin types. Unless are indicative to the experienced analyst. otherwise noted, the refractive indices were determined by It is advisable to supplement this procedure with destructive the immersion method, and the densities by the pycnometric distillation of the resin, both alone and intimately mixed with methods. All these resins have not been encountered by the crushed sodium hydroxide. This determination may be readily carried out in a Pyrex test tube, with some arrangement for author in the analysis of water paints, but they represent absorbing the volatile decomposition products in water. Detersome of the possible variations which may be present. minative tests applicable to this solution are discussed under LLClassificationReactions”. The appearance of a white subliAcid and Saponification Values. These values are generally mate on the walls of the test tube during the destructive disbest determined by treatment of an alcohol-benzene solution of tillation of the resin alone is generally indicative of a phthalate the resin with 0.5 N alcoholic potassium hydroxide. Acid resin. numbers are obtained by cold, direct titration to a phenolphthalDETERMINATION OF PHYSICAL AND CHEMICAL COY I STANTS. ein end point. Saponification is effected by refluxing the solution The most common physical and chemical constants include with excess potassium hydroxide and back-titrating to a phesoftening range, refractive index, density, acid numbers, and nolphthalein end point. Difficultly saponifiable materials may saponification values. be refluxed with a 1 N solution of potassium hydroxide in diethylSoftening Range. Since none of the resins have sharply deene glycol (62, 27). However, the solvent used will probably fined melting points, the softening range is determined instead. have an effect on the saponification value (28). In general, if The two principal methods are the mercury bath method (11) the saponification value exceeds 200, it is probable that the and the ball and ring method ( S I ) . Softenin points are not resinous binder contains an alkyd resin. If a sublimate of phthalic particularly determinative for synthetic resins, %ecause of overanhydride has been detected during fusion, and the saponifilapping among various classes and intentional variations within cation value of the resin is less than 200, the presence of uneach class. They may be valuable, however, when used in consaponifiable modifying materials (such as phenolic resins) is junction with other data. indicated. Refractive Index. The Abbe refractometer is most commonly used with liquid resins, but is also applicable to solid resins ELEMENTARY ANALYSIS(27). Ultimate analysis by fusion ( I , 52). . Immersion methods, however, are more generally used with solid resins. In the latter instance, a small fragment of the with metallic sodium permits the detection of sulfur, nitrogen, resin is immersed in aqueous standards of known refractive chlorine, and phosphorus, and therefore the inclusion or index, and this constant of the resin is determined by the Becke exclusion of resins known to contain these elements. Mark line method (7). Aqueous solutions of potassium mercuric (20) in discussing the physical-chemical examination of high iodide, containing a small proportion of a suitable wetting agent, and varying in 0.01 step, are recommended standards. Aquepolymers, includes several useful tables permittipg classifious standards are used to prevent dissolution of the resin. The cation of resins according to nitrogen, sulfur, chlorine, and presence of the wetting agent facilitates the wetting of the resin phosphorus content (and also saponification values). fragments by the aqueous media. Refractive indices have been SOLUBILITY TESTS. The solubility of the resin in benzene, found particularly useful in differentiating natural and synthetic resins, and in establishing their identity ( 3 ) . Table I includes and perhaps in acetone and petroleum ether, has already the refractive indices of a number of alkyd- and rosin-type resins, been observed during isolation of the resin. Other solvents the types most common in water paints. which may add pertinent information include ethanol, ethyl Densify. The density may be determined by water-displaceacetate, butyl acetate, Cellosolve, turpentine, and naphtha. ment, sink-or-float, or pycnometer methods. When sufficient resin is available, a 4- to 5-gram fragment may be suspended on a fine wire and the density measured on the analytical balance by displacement of water or other TABLEI. DENSITIESAND REFRSCTIVE I N D I C E S O F RESINS nonsolvent liquid of known density. Alkyd-type resins D25/4 hT2.50 With small amounts of resin, a less accurate method consists of density de1.3890 1.5750 Reayl 10 (glycerol phthalate) termination by sink-or-float methods in 1.3520 1.5705 Reeyl 337-1 (ethylene glycol phthalate) salt solutions of known density. A more 1.3900 1.584a Pentaerythritol phthalate 1.210= 1 5730 Resyl 11 (nondrying alkyd) accurate method with relatively small 1.014 1.5005h Rezyl 7906 (drying alkyd) amounts of material consists of determi1.112 1.535 Rezyl 775-1 (phenolic modified drying alkyd) 1.160 1.526 Beetle 592-8 (amine modified nondrying alkyd) nation of the density by use of a small 1.179 1.4744b Rezyl 7019 (unmodified alkyd) (1.5 to 2 cc.) pycnometer. The pyc1.197 1.4840b Rezyl 7020 (unmodified alkyd) nometer is weighed empty, and weighed 1.160 1 550 Melmac 599-8 (amine modified drying alkyd) again filled with water at room temperaRosin-type resins ture. A 20- to 40-mesh fraction of resin (consisting of particles not too large for 1 082 1 54s Rosin (Grade S wood) 1.077 1 546 Rosin (G gum) the stem of the pycnometer, but too large 1.103 1 549 Ester gum No. 6 (glycerol ester) to float out through the overflow capil1.038 Abalvn imethvl abietate) 1 5288b lary) weighing 0.2 to 0.5 gram, is weighed 1.030 Hercblyn-(rneihyl dihydroabietate) 1 5179b 1,071-1.074c 1 . 5361-1 5363c Flexalyn (diethylene glycol diabietate) into the dry pycnometer and the vessel 1,099 Pentalyn (pentaerythritol abietate) 1.546 is then filled Rith nater containing a 1,069 Poly pale resin (polymerized abietic acid) 1.546 small proportion (0.1 to 0.5 per cent) of 1.222 1-insol resin (oxidized rosin fr,actions) 1 614 1.112 Galex (principally dehydr,oabietip acid) 1.544 Aerosol OT (to faci!itate wetting the 1.063 Staybellite (tetrahydroabietic +cid) 1.529 resin particles) and weighed. The density 1.113 Phenac 622N (modified phenqlic) 1 555 is calculated as follows: 1.145 1.541 Teglac 2152 (dibasic a,cid-rqsin ester type) 1.124 1,542 Teglac 161 (dibasic acid-royn ester type) If a = weight of pycnometer 1.162 1.532 Teglac 127 (dibasic acid-rosin ester type) h 3 weight of pycnometer filled with a Reported b y Bradley ( 3 ) . Reayl775-1, Beetle 592-8, and Melmac 599-8 are available comqeroially water as 50% solutions Above results were determined on films t h a t had been dried t o constant weight in c = weight of pycnometer plus sample ZnCuO b Abbe refraddmeter. d = weight of pycnometer plus sample Hercules bulletin, refractire index determined a t 20’ C. plus OT solution D = density of water a t f Q C
September 15, 1942
ANALYTICAL EDITION TABLE
11. CLASSIFIC.4TION
COLOR
Test L i e b e r m a n n - S t o r c h (StorchMqrawski in Europe) for rosin
Procedure Dissolve a small fragment of resin in hot acetic anhydride; cool. Add 1 drop of His04 (sp. gr. 1.53) t o soln. in spot plate or small porcelain crucible
Halphen-Hicks for rosin (confirmatory)
Two reagents: A. 1 volume of phenol i n 2 volumes of CCh; B . 1 volume of bromine in 4 volumes of CCla. Add 1 t o 2 cc. of soln. A t o particle of resin in depression in porcelain spot plate. Stir. Fill adjacent cavity with soln. B. Cover with inverted watch glass and note color development in A. H e a t 0.29 t o 1 gram of resin with 2 t o 3 times this amount of pure resorcinol t o boiling point of latter. Extract with boiling water, dilute, and render alkaline. Heat 1 gram of resin with 2 t o 3 grams of pure phenol and 10 drops of concd. HnSOa until formation of orange or brownish-orange melt. Cool, extract with boiling water, dilute, render alkaline. 4 d d 2 t o 3 drops of 156 aqueous suspension of dibromoquinone chlorimide t o 10 cc. of ,aqueous extracts of resin. Carefully neutralize by adding 0.1 .V NaOH dropwise (to p H ca. 9.4)
Resorcinol test for phthalates. Bradley ( 5 ) modification of Holde, Bleyberg, and Aziz test (14) Phenol test ( 5 ) for phthalates (phthalate confirmatory test)
Gibb's indophenol for phenols (18) (applicable t o KaOH fusion residue or t o destructive distillation products in aqueous solution) Millon's reagent for phenols (metallic mercury dissolved in concd. HKOs, diluted with equal volume of water)
Coumarone test for coumaroneindene resins
Add 2 drops of reagent t o 5 t o 10 cc. of aqueous soln. of products of destructive distillation. Shake, heat just t o boiling.
Dilute 1 cc. of 10% soln. of resin in C H C h to.6 cc. with C H C h and add 1 cc. of glacial acetic acid, Shake. 4 d d 1 cc. of 10% soln. of bromine in CHCla. shake, allow t o stand.
Miscibility is generally determined at 60 per cent concentration. Viscosity determinations of some solutions may also be helpful. The solubility and viscosity data of Van Heuckeroth (SO) should be consulted. Comparison with known materials is advisable in all cases. CLASSIFICATION TESTS. Most of the resin classification tests are color reactions applicable directly to the solid resin. Others may be applied to the water solution from destructive distillation. Table I1 includes some of these tests. Other tests include testing the p H of the water solution of the decomposition products. If alkaline, condasation products of aldehydes with urea, melamine, aniline, or proteins are indicated. If acid, the acidic anions (and likewise the resins from which they are derived) may be detected by the addition of silver nitrate, barium chloride, nitron sulfate, etc. The author has found that identification of the various anions is facilitated by carrying out the tests b y microscopical methods (8) which permit the use of very small samples (of necessity or for rapidity). Microscopical methods also permit more absolute identification of the precipitates obtained during the tests. The combination of the information derived from the various procedures discussed above gives an excellent idea of the physical-chemical nature of the resin or resins isolated from the paint. PREPARATIOX OF A DERIVATIVE. The preparation of derivatives is limited to those of individual constituents of a resin-i. e., dipotassium phthalates, etc. Their use may be employed wherever the analyst decides t h a t addit'onal information is required for absolute identification of a particular resin constituent.
Additional Analytical Methods As has been stated above, the most common resins that the author has encountered in water paints have been: alkyd resins, usually oil-modified, and rosin esters or rosin adducts.
RE.iCTIOhX Coloration Transient blue-violet Red Rose red
697
Observations
Bluish green Deep purple or deep indigo blue
Indicated Resin Rosin, ester gum, etc. Coumarone (31, rosin adducts Cyclohexanone a n d cyclohexanone-CHnO (5) Vinyl resins (5) Rosin (10)
Greenish-yellow fluorescence of fluorescein
Phthalates. Also applicable t o phthalate plasticizers. Other dibasic acids may interfere.
Red coloration of phenolphthalein in alkaline solutions
Phthalates
Blue t o wine
Phenol,
Purple blue
p-tert-Butylphenol a n d p - t e r t amylphenol ( 8 1 ) Reagent p-phenylphenol gives no color (21) Phenol, cresols, a n d xylenols (91) p-Phenylphenol (81)
Faded purple Deep red t o brown Distinct lavender t o purple; sediment in tube IS edged with blue or purple on standing. Rose Permanent red color
cresols, and xylenola
(Z1)
p-tert-Butylphenol a n d amylphenol (21) Coumarone resin (10)
p-tert-
MODIFIEDALKYDRESINS. Alkyd resins may be modified by oiis and/or other resins. The presence of modifying oils will have been indicated by the softening point, the refractive index, and the density of the resin. These determinations, as well as the other general procedures discussed, will also have supplied information as to the presence and identity of modifying resins. I n either case, additional information concerning the composition of the alkyd resin, including the percentages of dibasic acids, polyhydroxy alcohols, and modifying agents may be readily determined by a suitable saponification procedure. Two common methods for the determination of phthalic anhydride in alkyd resins are available: (1) Kappelmeier method, and (2) Kavy Department method. Sanderson (26) described both these methods in detail in a report on the results of a cooperative test program, and recommended the adoption of the Kappelmeier procedure as a tentative A. S. T. M. method. Weigh a quantity of the vehicle equivalent to 2 to 3 grams of solid content into a 500-ml. soil-digestion flask, fitted with a ground-glass air-cooled reflux condenser 32 inches in length. Add 10 ml. of benzol and warm until a homogeneous mixture is obtained, and then add 150 ml. of 0.5 N potassium hydroxide in absolute alcohol. The alcohol may be denatured 2B grade, but must be absolute. Warm on the steam bath for 1 hour at 60" C. and then gently reflux for 3 hours. Cool, allow to stand for 1 hour, and wash donm the sides of the flask with 50 ml. of absolute ether. Filter at room temperature, using a Gooch crucible with asbestos mat, and wash the precipitate with 50 ml. of a mixture of equal parts of absolute alcohol and ether, using five 10-ml. portions. Do not allow air to suck through the crystals, as they are st,rongly hygroscopic and may absorb water from the air. Dry for 10 minutes in an oven heated to 60" C. and then to constant weight over sulfuric acid in an evacuated desiccator. One gram of the precipitate, the potassium alcohol salt of phthalic acid, is equivalent to 0.513 gram of phthalic anhydride. Application of this procedure results in the breakdown of the alkyd resin into its original constituents, and permits the
698
2.0
I.5
1.0
2
2
k
y
Vol. 14, No. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
0.0
a ul
0 0
-1 -0.5
-1.0
-1.5
2800
3000
3200
3400 3600
MOO
4000
4200
4400
WAVENUMBER (MK’)
FIGURE 4. STANDARDS FOR ULTRhVIOLET CONJUGATION A SSlY S 1. Double conjugation. 10.12-linoleic acid, CHs(CHz)r(CH=CH)1(CH2)sCOOH 2. Triple conjugation, a-eleostearic acid ( 8 ,CHa(CHn)a(CH=CH)a(CHz);COOH uadruple conjugation, parinaric acid ( 1 7 ) . CHsCHZ(CH=CH)v z);COOH
TABLE 111. REFRACTIVE INDICES Salt Dipotassium alcohol phthalate Dipotassium maleate Dipotassium fumarate
>Vl
1.557 1.610 1.530
N 1
1.466
1.513 1.420
separation of bhe insoluble potassium dibasic acid salts from the soluble potassium soaps of the oil fatty acids and the soluble unsaponifiable materials. Potassium Dibasic ilcid Salts. If phthalic acid is the only dibasic acid present, the precipitate will be composed of dipotassium phthalate, containing one molecule of alcohol of crystallization. Because of the increasing shortages of phthalic anhydride, however, the presence of other dibasic acids is also possible. Maleic and fumaric acids are usually the most common of these possibilities. Both acids form dipotassium salts which are insoluble in absolute alcohol. The author’s attempts to detect the presence of these salts mixed with the phthalate salt have thus far been unsuccessful. Refractive indices, determined in two extinction directions on the individual salts, are data which permit identification of the various acids when present alone (Table 111). This method apparently is not applicable to the coprecipitated salts since the results obtained on mixtures precipitated from solutions of 3 to 1 and 1 to 1 molar ratios of phthalic anhydride, and maleic and fumaric acids were not determinative. In fact, they closely resembled the results obtained on dipotassium alcohol phthalate alone. X-ray diffraction methods also proved unsuccessful. The application of ultraviolet absorption methods has shown some promise, but has not been developed sufficiently to warrant publication at this time. Other possible methods are also being investigated. Unsaponijables. After removal of the precipitate of potassium dibasic acid salts, the alcohol-benzene solution is concentrated on the steam bath, dilut’ed with several volumes of distilled water, and extracted with ether. The ether extraction may be carried out Ti-ith a set of separatory funnels (avoid violent shading to prevent emulsions) or by use of the Knapp (18) continuous extractor. In either case, the ether extract
must be thoroughly washed Tvith dilute alkali t o catch any fatty acids that might have passed into the ether layer by hydrolysis. The ether-extract-residue represents the unsaponifiable material and should not exceed 1 per cent if the fatty oil is the only modifying agent. Much higher proport,ions suggest t,he presence of ether-soluble unsaponifiable resins, which should be identifiable by the procedures previously described. Fatty Acids. The aqueous layer from the ether extraction contains the potassium soaps of the oil-acids and also the polyhydric alcohols. Acidification with 6 N hydrochloric acid causes the precipitation of the free oil acids, which are removed by ether-extraction and dried t o constant weight in an inert atmosphere. The water layer containing the polyhydric alcohols is reserved. The most commonly reported physical constants for oil fatty acids include melting point, acid value, and iodine value (19). Refractive index, usually determined on the oil, is also generally included. In a great many instances, however, these constants are not sufficient to identify the source of the acids, particularly when the oil has been treated t o alter its natural properties, or when the acids are derived from a mixture of two or more oils. Ultraviolet absorption analysis, first applied to the esters of the acids ( E ) , has also been found to give excellent results with acids separated from resins modified with known oils and mixtures of oils. In some instances, a quantitative estimation of the relative proportions of dehydrated castor, soy, and linseed oils has been found possible by the ultraviolet absorption analysis of mixed acids from these sources. The identification depends on the presence of conjugated unsaturation. In general, the presence of more than 20 per cent conjugated unsaturation strongly indicates either dehydrated castor oils or alkali-isomerized oils (6). Ten to 20 per cent conjugation indicates the presence of dehydrated castor oil or alkali-isomerized oil diluted with a less conjugated oil such as soybean oil. With less than 5 per cent conjugated unsaturation, it is safe to assume that dehydrated cast’oroils are absent. The conjugation mentioned above refers to two conjugated double bonds. Varying proportions of three (or more) conjugated double bonds may be equally characteristic for other oils such as tung, oiticica, or isomerized linseed oils. It must be borne in mind, however, that the conjugation of all oils is changed (generally increased), owing to the effect of elevated temperatures during resinification (I). (The most highly conjugated oils show a decrease.) Figures 4 and 5 serve to illustrate the ultraviolet absorption spectra of the basic conjugated acids (Figure 4) and some common oils illustrating their occurrence (Figure 5). Soy, perilla, and oiticica oils were not plotted because of their resemblance to linseed, linseed, and tung, respectively (Table IV). Polyhydric Alcohols. The polyhydric alcohols originally present in the alkyd resin may be isolated and identified by neutralization of the acidified aqueous layer from the fatty acid extraction, followed by evaporation to dryness. It is advisable to divide the solution into two fractions of known volume before evaporation. Fraction 1 is evaporated to dryness and the residue extracted with tert-butyl alcohol. The extract is filtered, and the filtrate evaporated to remove the solvent. The highboiling alcohols remaining (usually glycerol or ethylene glycol) may be identified by refractive index, specific gravity, and the TABLEIs’. Oils Castor Cottonseed Linseed Oiticica Perilla Soybean Tung
TYPICAL CONJUG.iTIOS . k S . i Y S FATTY ACIDP
FOR
SOXE OILS
AND
% Acids with Conjugated Double Bonds Two 0.23 0.41 0.69 0.0 0.50 0.79
0.0
Three 0.024 0.06 0.12 75.8 0.23 0.12 84.5
Four
0.0025 0.0 0.04
0.36 0 06 0 02 0 38
F a t t y Acids 28.4 0.A9 0.06 De!iydrated castor 32.6 6. I 0.16 Isonerized linseed 37.8 1.9 0.07 Isomerized soybean a Figures are based upon t h e assumption t h a t all observed absorption is due t o the presence of conjugated acids. Xote t h e marked increase in t h e triple Conjugation of isomerized linseed oil, a s compared t o t h a t of isomerized soybean oil. I n general, oils known t o contain linolenic acid (which has three nonconjugqted doub!e bonds) will show substantial amounts of triple coniugated acids a f t e r isomerization. Soybean oil contains little linolenic acid.
September 15, 1942
ANALYTICAL EDITION
application of color tests such as those of Hovey and Hodgins (16).
After qualitative identification of the polyhydric alcohol present, its proportion may be determined quantitatively on fraction 2 by application of several rocedures. General methods include the acetin process (15) a n j t h e bichromate process (15). A suggested improvement of these methods is that of Shaefer (E),which is applicable t o a dilute solution from which oxidizable impurities and chlorides need not be removed.
ROSINESTERSOR ROSINADDUCTS.The presence of a rosin-containing binder will have been detected during the general analysis. Rosin resins found in water paints may be divided into rosin esters, present as abietic or modified abietic acid esters of mono- and polyhydric alcohols, and as polyhydric alcohol esters of rosin-dibasic acid (usually maleic or fumaric acid) adducts. Both types are esters, but application of the Kappelmeier procedure does not yield the usual separation, because both the potassium salts of rosin and of rosin adducts are alcohol-soluble, and therefore are not readily isolated as a precipitate (as are the potassium salts of the dibasic acids alone). I n addition, rosin esters are generally rather difficult to saponify, particularly monohydric alcohol esters; so the Kappelmeier procedure often results in partial saponification a t best, necessitating more rigorous conditions. If the classification reactions have indicated the presence of rosin, the resin may be either of the above types. Rosin esters are not too difficult to identify by chemical methods (saponification and titration of the liberated rosin acids) but chemical procedures for the analysis of rosin adducts are very few (24). Ultraviolet absorption analysis, however, offers a method which appears to be both rapid and reasonably accurate, although it does not permit identification of the dibasic acid. Rosin gives a characteristic ultraviolet absorption pattern, due to the conjugated unsaturation present. An unknown
2.0
1.5
I.o
z
8Z
05
W X
2 J 0.0
W
In
x
-1-0.5
-1.0
-1.5
2800
3000
3200
3400 3600 3800 WAVENUMBER (MM-1)
4000
FIGCRE3. ULTR.4VIOLET ABSORPTIOXCURVES FOR CAL OILS
4200
4400
SOME
TYPI-
T u n g oil (largely t r i le conjugation) Isomerized linseed oip (mixed triple and double conjugation) Dehydrated castor oil (double conjugation) 4. Linseed,.oil (little conjugation) 1. 2. 3.
699
resin containing rosin which gives the usual pattern is either rosin or an untreated rosin ester. d decrease or abnormal change in the characteristic rosin absorption, however, indicates that the rosin has been hydrogenated, an adduct has been formed, or a diluent transparent to ultraviolet light is present. Hydrogenated rosins usually contain disproportionation products with their own characteristic ultraviolet absorption (23’). If this particular absorption is absent, the resin is either an adduct or diluted rosin. Diluents are detectable by the general methods of analysis. There is another possibility-i. e., an adduct plus an oil containing sufficient conjugated unsaturation to give a normal rosin absorption in the usual range. Since such oils show characteristic absorption over a wide range of wave lengths, their presence may be readily detected.
Acknowledgments Much of the material presented in this discussion has been accumulated during the analyses of many samples of widely varying types, over a period of years. The author wishes to acknowledge the contributions and suggestions of his colleagues T. F. Bradley, R. P. Chapman, Helen L. Clapp, A. G. Houpt, C. H. Parker, Jr., D. Richardson, and T. G. Rochow. Credit is also due to the American Cyanamid Company for permission to publish this material.
Literature Cited (1) Bhattacharya, G. N., I n d i a n J . Phys., 14,237-46 (1940).
(2) Biffen, F. M., and Snell, F. D., IND. ENG.CHEM.,ANAL.ED., 7, 316-19 (1935). (3) Bradley, T. F., Ibid., 3,304-9 (1931). (4) Bradley, T. F., and Johnston, W. B., IND. ENG.CHEM.,32,802 (1940). (5) Bradley; T. F., and Richardson, D., Ibid., 32,936 (1940). (6) Ibid., 34, 237 (1942). (7) Chamot, E. M., and Mason, C. W., “Handbook of Chemical Microscopy”, Vol. I, 2nd ed., p. 362, New York, John Wilev & Sons, i938. (8) Ibid., Vol. 11,2nd ed., pp. 314-92, 1940. (9) Dingwall, A., and Thomson, J. J., J . Am. Chem. SOC.,56, 899 (1934). (10) Gardner, H. A,, “Physical and Chemical Examination of Paints, Varnishes, Lacquers, and Colors”, 9th ed., pp. 332-3, Institute of Paint and Varnish Research, 1939. (11) Ibid., p. 326. (12) Gibbs, H. D., J . Biol. Chem., 72, 649-64 (1927). (13) Gill, P. H., Am. Paint J.,24,51, 54, 56 (May 27, 1940). (14) Holde, Bleyberg, and Aaiz, 2. angew. Chem., 42,283-4 (1929). (15) Holde, D., and Mueller, E., “Examination of Hydrocarbon Oils and Saponifiable Fats and Waxes”, 2nd English ed., pp. 4536, New York, John Wiley & Sons, 1922. (16) Hovey, A. G., and Hodgins, T. S.,IND.ESG. CHEM.,A x . i L . ED., 9, 509 (1937). (17) Kaufmann, H. P., Baltes, J., and Funke, S., Fette u. Seifen, 45, 302 (1938). EXG.CHEM.,AivaL. ED.,9,315 (1937). (18) Knapp, I. E., IND. (19) Lange, N. A., “Handbook of Chemistry”, 2nd ed., pp. 518-25, Sandusky, Ohio, Handbook Publishers, 1937. (20) Mark, H., and Raff, R., “High Polymeric Reactions”, 5’01. 111, pp. 37-46, New York, Interscience Publishers, 1941. (21) Moore and Catlow, Mattiello’s “Protective and Decorative Coatings”, Vol. I, p. 317, New York, John Wiley & Sons, 1941. ( 2 2 ) Redemann, C. E., and Lucas, H . J., ISD.ESG. CHEM.,.%SAL. ED., 9,521 (1937). (23) Richardson, D., private communication. (24) Sadolin, Eric, IND. ENG.CHEM., -4saL. ED., 11, 608 (1939). (25) Sanderson, J. McE., A . S. T. M . Bull. 107,15-16 (Dee. 1940). (26) Shaefer, W.ii., IND.EXG.CHEM.,As.4~.ED., 9, 449 (1937). ( 2 7 ) Shriner and Fuson, “Systematic Identification of Organic Compounds”, 2nd ed., pp. 112-18, N e w York, John Wiley & Sons, 1940. (28) Smith, W. c.,IND. ESG. CHEM.,ANAL.ED., 9, 469 (1937). (29) T. A. P. P. I. Standard T 3 M-34. (30) Van Heuckeroth, Paint Mfrs. Assoc. U. S., Tech. Circ. 369 (1930). (31) Walker, P. H., U. S. Bur. Standards, Research Paper 142,Feb. 1930. (32) \vest, c. D., IXD. ENG.CHEM., -4N.4L. ED., 10,627 (1938). PRESENTED before the Division of Paint, Varnish, and Plastics Chemistry CHEMICAL SOCIETY, Buffalo, N. T. a t t h e 104th Meeting of t h e AMERICAN
