Extraction and Determination of Plasticizers from Cellulose Acetate Plastic! GERALD C. WIIITNACK AND E. ST. CL ical Chemistry Branch, U. S. Naval Ordnance Tea
A mixed solvent, consisting of 50 parts of Skellysolve B and 50 parts of itbsolute ethyl alcohol, was used as the extraction solvent. The Skellysolve B had 8. 146" to 156' F. boiling range and was purchased from the Skelly 011 Co.
PROCEDURE that would recover a t least 98% plasticiaer A from cellulose acetate plastic in short time, and would determine avariety of plasticizers (either alone or in combination), a
was desired.
The extraction and determination of plssticizers found in cellulose acetate plastics have been studied by numerous investigators (8-7). Many solvents, procedures, and types of apparatus were recommended in these studies; however, none appeared entirely satisfactory for the authors' problem. A comparative study of procedures of microextraction was made hy Batt and Alber (f). From their work, the accuracy of a semimicro-Soxhlet extractor, calculated from 28 determinations, was found to be f1.85%. I n addition, the important advantages of the semimicro-Soxhlet extractor over the conventional macro-Soxhlet extractor ( I ) warranted the application of a semimicro8axhlet extractor t o the authors' problem. This report describes the apparatus, operation of this appamtns, and the method developed for the efficient extraction and precise determination of several plasticizers in cellulase acetate plastics.
PROCEDURE
APPARATUS AND MATERIALS
Apparatus. A semimicro-Soxhletextraction apparatus (Figure 1) wss used in all the extraction studies. The extraction flask was 30-ml. capacity and included a T 12/18 joint. The extractor unit was 6 inches long, with S 19/22 and T 12/18 joints. An Allihn-typ! condenser, 9 inches long and fitted with a T 19/22 joint, wasloined t o theextractor unit. Extractions were performed on a six-unit Vari-heat apparatus manufactured by the Precision Scientific Co., Chicago, Ill. A steam bath and Cenco Hyvac vacuum pump were used in the removal of solvent from the extracted material, An intermediate model Wiley mill was used to prepare the plastic samples for extraction and a Sargent polarograph (Model XXI) was used in testing the efficiencyof the extractions. plasticiaers and mixtures of plasticieers were subjected t o extraction by the proposed method. Data presented in Table I1 show an average of 99.5% recovery of plasticizer with a 0.95% standard deviation. To study the reproducibility error, a few experiments were made on samples of plastic containing dimethyl phthalate as the plasticiser. The results (Table 111) indicate that &n average deviation of 0.83% with a standard deviation of 0.42% may be expected on duplicate extractions of cellulose acetate plastic. Before obtaining the mem and standard deviation values (Table 111, the data were first subjected t o a statistical analysis of variance. From this i t can be shown that (1) the variation in mean per cent recovery, from 98.2 to lOO.Z%, is insignificant relative t o the experimental error in a single extraction, and (2) despite the variation in the differences between the per cent recovery, from 2.1 t o O.Z%-for example, the variation in the differences between per cent recoveries of glycerol triacetate and the mixture of triethyl citrate, N-ethyl ptoluene sulfonamide, and dimethyl phthalate-the variation is insignificant and the experimental error can be expected t o be the same for all the plasticizers considered. Figure 1. Semimicro ~~~~~~~i~~
Each valueis average of t,wo extractions: 500 mg. of plasticized oellulose *cetateuBed for each ertraction.
Materials. Sheets of cellulose acetate, plasticized with different plasti&ers were prepared by premixbig crllulo% I I C C I S ~ C powder n n d Ihkticizer wirli w sigma blade mixer. 'I'hc mix W S blerrdcd with :(I$ 8-inrb dilierenti:xl sucrd roll 8i.d I ~ P Uiormed IO the desired thickness bv use of a h e c o d a t e hvdraulic mess. Thepress wssequipped&thadieform. One hundred parts of Eastman Kodak cellulose acetate A-48 (39.5% acetyl content) were mixed with 35, 55, Bpd 75 parts of plasticizer. The plasticizers used were not repunfied, and they were as follows: Dimethyi phthalate, Monsanto Chemical Co., boiling point 263' C. Diethyl phthalate. Monssnto Chemioal Co.. boiling paint 295" C. Methyl phthelyl ethyl glycollate (Ssnticieer M-17). Monsanto Chemioill Co.. boiline mint 189- C. a t 5 mm. of I m r C U N . cal Co.. eryslalline d i d . G R O C . minimum cryatdliziug puint. Triethsl eitraw. Charles Pfiser nnd Co., Inc.. boilinc point 150° C.
I)ISCUSSION
sl3mrn.ofrnrirurv.
Triphew1 phosihate. Monsanto Chemical CO., hoiling point 245'C.,meItingpoint49.O0C.
Glyoerol triacetate, Esatmen Kodsk Co., beat grade, boiling point275' to280° C.
several solvents were tried extraction media, including methylene chloride, alcohol, and SkellYSoive B. The 1 t o 1 mixture of absolute ethyl alcohol and Skellysolve B \%-as ~
1060
1061
V O L U M E 2 4 , NO. 6, J U N E 1 9 5 2 the only solvent that gave satisfactory data with all plasticizers investigated. Skellysolve B appeared to extract the phthalic acid derivatives as efficiently as the mixed solvent of absolute ethyl alcohol and Skellysolve B; however, if phosphoric acid derivatives such as triphenyl phosphate are present, the alcohol is needed to ensure a 99% recovery of the total plasticizer in 20 hours. For example, the mixture of diethyl phthalate and triphenyl phosphate (Table 11) gave only about 60% recovery of total plasticizer in a 20-hour extraction with Skellysolve B alone; however, with the 1 to 1 mixture of absolute ethyl alcohol and Skellysolve B, an average recovery of 99.8% plasticizer was obtained in a 20-hour extraction. On continuous heating, methylene chloride dissolved the cellulose acetate. Benzene gave sat'isfactory data for dimethyl phthalate plasticizer but was not investigated further. Table 11. Recovery of Plasticizer from Cellulose Acetate Plastics Plasticizer, % Present Found Recovery 35.48 35.30 99.5 35.48 35.80 100.9 35.48 35.58 100.3 35.48 35.46 99.9
Dimethyl phthalate Diethyl phthalate Diethyl phthalate plus phosphate"
triphenyl
Diethy phthalate plus triphenyl phosphatea Methyl phthalyl ethyl glycollate Glycerol triacetate Methyl phthalyl ethyl glycollate Dimethyl phthalate Diethyl phthalate
25.00
24.91
99.6
25.00 35.48 35.48 35.48 35.48 42.85 42.85 42.85 42.85 42.85 42.85
25.03 34.96 34.71 35.37 34.63 43.08 42.85 43.05 42.77 42.63 43.00
100.1 98.5 97.8 99.7 97.6 100.5
Table 111. Reproducibility of Duplicate Extractions Plasticizer Founda, Difference, % Abs. Wt. % 24.95 24 99 0.04 33.98 33.54 0.44 34.12 33.91 0.21 35.30 35.80 0.50 41.84 41.50 0.34 43.05 42.77 0.28 42.63 0.37 43 .OO a Dimethyl phthalate in all cases. Actual difference mean 0.31% abs. Standard deviation,s 5 0.24% abs. deviation mean = 0.83%. tandard deviation, 8 = 0.42%.
100.5 99.8 99.5 100.3
Triethyl citrates plus N-ethyl p toluene sulfonamide plus dimethyl phthalate
+
It is important to keep the drops of solvent falling from the condenser into the extraction thimble during the 20-hour extraction period. Low results will occur if the thimble is tilted. The drop rate did not appear to be significantly important in the 20hour extractions. A setting of 30 on the Vari-heat apparatus gave a steady drop rate and kept the loss of solvent to a minimum. If good connections between the extraction units are made, no appreciable loss of solvent will occur in a 20-hour extraction period. No grease is used on the T joints. To test the effect of the mixed solvent on cellulose acetate under the conditions of the extraction, 500-mg. samples of powdered cellulose acetate (Eastman Kodak Co., E-13, 39.0% acetyl and A-48, 39.5y0 acetyl) were extracted for 20 hours with the mixed solvent. Less than 1 mg. of extracted material was found in the flask. Blanks were determined for the extraction media and thimbles. The amount of residual material in the flask at the end of a 20-hour extraction was negligible. The loss of plasticizer, during the removal of solvent, was investigated. About 200 mg. of diethyl phthalate was placed in an extraction flask with the mixed solvent. The solvent was removed under the conditions of the analysis and the amount of plasticizer then determined. Less than 0.3 mg. of the plasticizer was lost in the procedure. To test the efficiency of the extraction further, several cellulose acetate residues from the extractions were dissolved in ace-
% ' Deviation between Duplicate Samples
I
z
100.0
25.92 25.52 98.5 25.92 25.59 98.7 a 4 parts diethyl phthalate 4- 1 part triphen 1 phosphate. b 11 parts trieth 1 citrate +12 parts N-et$l p-toluene sulfonamide 12 parts dimethylp&halate. Mean,& = 99.5% (best estimate). Standard deviation of single extraction = 0.95% (best estimate).
tone and subjected to a polarographic test for the presence of plasticizer. The test showed that less than 0.1% of plasticizer remained in the cellulose acetate after a 20-hour extraction with the 1 to 1 mixture of Skellysolve B and absolute ethyl alcohol. The samples chosen for this study contained only phthalic acid derivatives, as these plasticizers give a characteristic currentvoltage curve at the dropping mercury electrode.
0.16 1.30 0.82 1.41 0.82 0.65 0.86
-
In the preparation of the sheets of cellulose acetate plastic, a cellulose acetate with a 39.5% acetyl content was chosen because this acetyl value is representative of most commercial cellulose acetate. However, the results might be altered if cellulose acetates of widely varying content were employed. The cellulose acetate used in preparing the plastic contained 1.6% moisture. Water was added to the mix in the blending process and the final material after pressing contained about 1% moisture. As the authors were interested only in a method that would recover a t least 98% plasticizer from cellulose acetate plastic in a short time, the plastic was weighed on a wet basis. Plasticizers with varying volatilities were used in the preparation of the plastic. Since the plasticizers had rather high boiling points, it is doubtful that a significant amount of plasticizer was lost at the temperatures of 180' to 190" F. for 2 minutes during the blending operation. The agreement of the data substantiates this feeling. ACKNOWLEDGMENT
The authors wish to express their appreciation to the Solid Propellants Branch a t the Kava1 Ordnance Test Station, Inyokern, for the samples of cellulose acetate plastic used in this investigation and to E, L. Crow and D. s. Villars for advice on statistical treatment of the data, This paper is published with the permission of L. T. E. Thompson, technical director of the U. S. Naval Ordnance Test Station. LITERATURE CITED
(1) Batt, W. G., and Alber, H. D., ISD. ENG.CHEM.,ANAL.ED., 13, 127-32 (1941). (2) Biggs, B. S., and Erickson, R. H., Ibid., 16, 9 3 4 (1944). (3) Elliott, M. A., Jones, A. R.,and Lockhart, L. B., Ibid., 19, 10-15 (1947).
(4) Goldman, I., Dubinskaya, E., and Moksimova, N., Kinofotokhim Prom., 4,47-50 (1939). ( 5 ) Ryan, J. D., and Watkins, G. B., IND.ENG.CHEM.,ANAL.ED., 5,191-2 (1933). (6) Thames, F. C., Ibid., 8, 418-19 (1936). (7) Yokhel, A. L., Plasticheskie Massy, 2 , 40-1 (1935). RECEIVEDfor review August 27, 1951. Accepted March 3, 1952. Presented before t h e Pacific Southwest Regional Meeting of t h e AMERICAN CHEMICAL SOCIETY,Whittier College, Whittier, Calif., April 28, 1951.
