1054
ANALYTICAL CHEMISTRY
blue, and the end point is then indicated by the sudden reappearI ance of the bright yellow of the lead iodide. Procedure 2A. A conventional constant-volume type of Warburg respirometer is used for measurement of carbon dioxide produced. Detailed descriptions of the apparatus and its manipulation are given by Umbreit et d.( 7 ) . The reaction temperature in the author’s experiments was 27” C. One milliliter of oxidizing solution (10 mg. each of lead tetraacetate and potassium acetate in 90% acetic acid) is added to the vessel and 0.2 ml. of the formic acid solution (0.1to 0.5 mg. of formic acid in 90% acetic acid) is placed in the side arm. A blank is run simultaneously with 1 ml. of oxidizing solution in the vessel and 0.2 ml. of 90% acetic acid in the side arm. The vessels are equilibrated for 10 to 15 minutes, the contents are mixed, and the change in pressure is observed until a constant value is attained (20 to 25 minutes). The apparatus is calibrated in the same manner by oxidizing known quantities of formic acid, or compounds such as glycerol and erythritol which yield known quantities of formic acid when oxidized by lead tetraacetate. Since the carbon dioxide produced is proportional to the change in pressure, the formic acid content of the unknown solution is determined by reference to the manometer calibration. Procedure 2B. The apparatus is a gas train consisting of the reaction vessel provided with a gas-inlet and gas-outlet tube and a separatory funnel, a dry ice trap, a scrubbing bottle containing concentrated sulfuric acid, and a carbon dioxide adsorption tube containing Ascarite. I n a typical experiment 10 ml. of 90% acetic acid containing 21.5 mg. of formic acid are added to the reaction vessel. The inlet tube is closed and the oxidizing solution, 25 m]. of 90% acetic acid containing 1 gram each of lead tetraacetate and potassium acetate, is introduced through the
separatory funnel. When the reaction has proceeded a t room temperature for 30 to 40 minutes, the inlet tube is opened and a stream of carbon dioxide-free nitrogen is slowly flushed through the apparatus for 30 to 40 minutes, the reaction vessel being shaken owasionally. Carbon dioxide evolved is measured by the increase in weight of the ascarite tube. A blank determination is also made using the lead tetraacetate reagent and 90% acetic acid. ACKNOWLEDGMENT
The technical assistance of J. Giroux is gratefully acknowledged. LITERATURE CITED
(1) (2) (3) (4) (5) (6)
Ahlh, L., and Samuelson, O., ANAL.CHEM.,25, 1263 (1953).
Auerbach, F., a n d Zeglin, H., 2. physik. Chem., 103, 161 (1923). Cordner, J. P., a n d Pausacker, K. H., J . Chem. SOC.,1953, 102. Grosheints, J. A I , , J . A m . Chem. SOC.,61, 3379 (1939). Rlosher, W. A., and Kehr, C. L., Ibid., 75, 3172 (1953). Perlin, A. S., presented before the Division of Carbohydrate Chemistry at the 124th Meeting of the AMERICAN CHEMICAL SOCIETY,Chicago, Ill. (7) Umbreit, W. W., Burris, R. H., a n d Stauffer, J. F., “hIanometric Techniques and Tissue Rletabolism,” Minneapolis, Burgess Publishing Co., 1949. (8) Vogel, A. I., “Practical Organic Chemistry,” p. 195, New York, Longmans, Green and Co., 1948. RECEIVED for review December 14, 1953. Accepted February 23, 1954. N.R.C. No. 3276.
Analysis of Alkyd Resins Modified with Vinyl Chloride-Acetate Copolymer MELVIN H. SWANN and GEORGE G. ESPOSITO Paint a n d Chemical Laboratory, A b e r d e e n Proving Ground,
W
HEN alkyd resins are modified with vinyl chloride-
acetate copolymer, they dry more rapidly and possess increased chemical and abrasion resistance. As in other types of modified alkyd resins, control is needed on the alkyd resin content as well as on the amount of modifying resin. Analysis for vinyl resins based entirely on total chlorine content does not prevent the substitution of other chlorinated resins and is affected by chlorinated plasticizers and solvents. The alkyd resin content of enamels has always been controlled by analysis for the phthalic anhydride present. All methods for determining phthalic anhydride begin with saponification of the resin with alcoholic potassium hydroxide. Vinyl chloride-acetate resins decompose during saponification and form products tvhich prevent determination of the phthalic anhydride content of the alkyd resin by any existing method. This characteristic of vinyl resins necessitates an analysis based on separation of the vinyl resin from the alkyd. Alkyd resins are soluble in glacial acetic acid and aromatic hydrocarbons and partially soluble in ethyl alcohol, but vinyl chlorideacetate resins are insoluble in these materials.
Use Of aromatic for separation give a medium suitable for direct saponification of the alkyd resin, but consistent results could not be obtained in separations with this class of solvents. When the vehicle of the enamel was properly diluted with glacial acetic acid, then added dropwise to an excess of acetic acid, follomd by considerable mechanical agitation, good quantitative separations could be obtained, ex?ept with alkyds modified with raw soybean oil. Ethyl alcohol is an excellent precipitating medium for the separat,ion
KO. 1
Md.
of the vinyl resins, but alkyd resins are only partially soluble in ethyl alcohol a t room temperature. If alkyd resins are first dissolved in a small amount of dioxane or methyl isobutyl ket’one, they will not separate from solution when poured into alcoholic potassium hydroxide, even a t low concentrations of alkali. Vinyl resins are decomposed by alkali, but a solution of 0.125N potassium hydroxide in absolute ethyl alcohol precipitates the vinyl chloride-acetate resin without decomposition in the time required to effect separation, retaining the alkyd in solut’ion. The separated vinyl resin must then be dried a t a low temperature, since decomposition may occur a t temperatures above 80” C. The alkyd resin is then present in a suitable saponifying medium for further analysis. The vinyl chloride-vinyl acetate copolymers are available in varying proportions of the chloride to the acetate. A copolymer,
Alkyd Castor oil, modified
Table I.
Results of .4nalyses
Vinyl Chloride-
Acetate Copolymer by Gravimetric Separation, % Theoretical Found
Vinyl Chloride by Chlorine Analysis, % Theoretical Found
Phthalic Anhydride, % Theoretical Found
32.1
32.5 32.3
29.4
29.5 29.4
23.8
23.8 23.8
33.2
33.2 33.5
30.4
30.1 30.6
15.7
15.7 15.6
modified
34.2
33.1 33.0
31.3
31.6 31.61
...
...
Coconut oil, modified
33.2
34.0 33.5
30.4
31.7 31.7
...
...
2
Soybean oil, modified (low phthalic anhydride)
3
Linseed oil,
4
1055
V O L U M E 2 6 , NO. 6, J U N E 1 9 5 4 known as a medium acetate copolymer, having 89.5 to 91.5 parts of vinyl chloride combined with 2.5 to 5.5 parts of vinyl acetate (5.3 to T.0 parts of vinyl alcohol), has the compatibility properties that make it best suited for use in vinyl-alkyd blends. The chlorine content of the vinyl chloride is known to vary, therefore, the total chlorine content of the resin serves only as an estimation of the composition of the copolymer. However, this analysis is desirable for quality control. The vinyl chloride resin ran be estimated from its chlorine content, either on the enamel vehicle or on the isolated copolymer. Many methods for determining chlorine are available; most of those used with organic materials either involve special equipment or are time-consuming. T o find a rapid, accurate, and simple method for total chlorine determination, suitable for routine testing and specification use to control the acetate length of the vinyl copolymer, a technique used to determine polystyrene in epoxy resins ( 2 ) was tested. This method, which involves fusion with potassium hydroxide, is not rapid, requires very little attention, and with slight modification, has proved satisfactory. PROCEDURE
Determination of Vinyl Chloride-Vinyl Acetate Copolymer. A dry 50-ml. Erlenmeyer flask is provided with a cork stopper and weighed. From 1 to 2 grams of the clear enamel vehicle (0.1 to 0.2 g a m of vinyl resin) are poured into the flask, which is then stoppered and reweighed. Five milliliters of 1,Cdioxane are added, the sample is dissolved, and the flask is reweighed. The sample solution is poured very slowly into 200 ml. of 0.125N alcoholic potassium hydroxide made with absolute ethyl alcohol contained in a 500-ml. glass-stoppered Erlenmeyer flask. The small sample flask is stoppered and revxighed, and the 500-ml. flask is shaken constantly for 5 minutes, preferably in a mechanical agitator. Without delay, the alkallne solution is filtered through a weighed fritted-glass crucible of coarse porosity, previously prepared with a mat of asbejtos. Khen all of the filtrate has drained through, it is set aside for phthalic anhydride analysis. then the washing and transferring of the precipitate are continued with 9570 ethyl alcohol. The crucible is given a t least tm-o washings &ith water followed by additional washing with 95% ethyl alcohol. It is then dried in an oven a t 60' C. to constant weight (2 t o 4 hours) and the vinyl resin content calculated on a solids basis. yovinyl chloride-acetate copolymer = weight of precipitate X 10,000 weight of sample x yo nonvolatile The actual weight of the sample used may be calculated in the following manner: If A = weight of empty flask (stoppered) B = weight of flask plus sample plus dioxane (befoie pouring) C = weight of flask plus residual sample (after pouring) B - c the actual sample weight = _ _ X original sample weight
B - A
Chlorinated paraffin or chlorinated diphenyl, if present in the original sample, is not precipitated by the alcohol and is present in the filtrate. Chlorinated rubber, if present, is precipitated and will appear in the crucible n i t h the vinyl resin. It can be removed by washing lvith warm xylene (60" C . ) immediately after the vinll resin has been xashed with ethyl alcohol; the vinyl resin is insoluble in xylene. Determination of Phthalic Anhydride in the Alkyd Resin. The filtrate contains the alkyd resin. I t is transferred, washing with absolute ethyl alcohol, to a 500-ml. Erlenmeyer flask and refluxed under a condenser for a t least 1 hour in a water bath. The sample is allowed to cool to a comfortable temperature for handling, about 50" C., filtered while warm through a weighed fritted-glass crucible of medium porosity, washed, and dried in the usual manner. Potassium carbonate may precipitate with the dipotassium phthalate and be a source of error. A correction is made by dissolving the weighed precipitate in about 50 ml. of distilled water that has been neutralized to the phenolphthalein end point. If the solution is alkaline to phenolphthalein, it is titrated with 0.1N hydrochloric acid. Weight of potassium carbonate = ml. of HCl X normality X 0.1382. Deduct the weight of potassium carbonate from the weight of dipotassium phthalate and calculate the phthalic anhydride, on a solids bask:
% phthalic anhydride
=
corrected weight of dipotassium phthalate x 6110 weight of sample X yo nonvolatile The actual weight of the sample used was determined in the analysis for the vinyl resin. If chlorinated paraffin was present in the original sample, potassium chloride is formed during saponification and affects the phthalic anhydride analysis. Its presence is indicated by dissolving the dipotassium phthalate precipitate in water and testing for chlorides by adding 6 s nitric acid followed by an aqueous silver nitrate solution. Chlorinated diphenyl has no effect on the phthalic or vinyl determination. If the dipotassium phthalate contains chlorides, the phthalic anhydride should be determined by precipitation a-ith lead acetate ( I ) , using aliquots estimated to contain 30 to 45 mg. of phthalic anhydride. Determination of Vinyl Chloride in Chloride-Acetate Copolymer. The enamel vehicle or the isolated copolymer separated from the alkyd resin may be used for the chlorine analysis. If there is no evidence of other chlorinated resins or plasticizers present, the determination can be made more conveniently from the vehicle of the enamel. From 1.0 to 2.0 grams of vehicle are weighed into a nickel crucible of 30-ml. capacity. Six grams of potassium hydroxide pelletc: are added and the contents of the crucible dried in an oven a t 110' C. for 3 hours. The fusion of the dried sample is conducted as for the analysis of styrenated epoxy resins ( 2 ) ) with the following modification: After 45 minutes of fusion, the cover is removed and the temperature gradually increased a t 15-minute intervals until the fusion is complete. R7ithout cooling, the crucible is transferred to a 400-ml. beaker and the contents are poured into the bottom of the beaker. When cool, sufficient \v-ater is added to cover the crucible completely, and the contents are boiled for 15 minutes. The sample is filtered through a double thickness of filter paper of medium porosity into a 600-ml. beaker, and the crucible and rod are scrubbed and washed with water. The filtrate is neutralized with 6 N nitric arid and an excess of 5 nil. of acid added for every 100 ml. of mater volume. While stirring vigorously, 20 ml. of a 5% silver nitrate solution are added, and the sample is heated to boiling. When cool, it is filtered through a Gooch crucible which has been heated t o 200" C., cooled, and weighed. Transfer of the precipitate and washing are done with 2% nitric acid. The crucible is dried a t 110" C. for an hour folloived by 15 minutes of additional drying a t 200" C.
% vinyl chloride
=
weight of AgCl X 4360 weight of sample X yo nonvolatile
If preferred, the volumetric method for determining chloride may be used. If a vinyl chloride-acetate copolymer of the medium acetate length was used, the vinyl chloride content of the sample should equal 89.5 to 91.5% of the copolymer found. DISCUSSION
A vinyl alkyd resin made according to specification was used as a known sample. Resin vehicle, Number 1 in Table I was made b y blending 32.1 parts of Vinylite VAGH and 67.9 parts alkyd resin (nonvolatile basis). The nonvolatile content of the finished vehicle was 30.7%. The vehicles tested were also pigmented lvith the same formulation was used in Federal Specification TT-E485b, then separated without difficulty by the usual high-speed centrifuging. The vinyl chloride content of Vinylite VAGH, the copolymer used to formulate these enamels, was also determined by the fusion method. This resin, believed to contain 89.5 to 91.5y0 vinyl chloride, was analyzed to be 91.5 and 91.6%. ACKNOWLEDGMENT
The authors appreciate the advisory assistance of C. F. Pickett, Myer Rosenfeld, and H. L. Ammlung of the Paint and Chemical Laboratory. LITERATURE CITED
(1) Swann, hI. H., ANAI..CHEM., 21, 1450 (1949). (2) Ibid., 25, 1735 (1953). RECEIVED for review February 3, 1954.
Accepted April 7, 1954.
