Determining Plasticizer Content of Cellulose Esters B. S. BlGGS
AND
R. H. ERICKSON, Bell Telephone Laboratories, N e w York,
N. Y.
the joint. The temperature is held at 256" C. by boiling Dowtherm and the heat input is controlled so that the Dowtherm refluxes about halfway up the column. The exact point reached by the condensing vapor is easily determined by passing a damp cloth along the outside of the pipe. A glass plug in the top of the dome seals the hole and a t the same time serves as a convenient handle. The other pieces of apparatus required are standard items and are clearly indicated by the diagram.
Plasticizer content is determined b y the vacuum distillation of the plasticizer from the sample. Dry samples of 1 gram or less are placed in weighing bottles on the floor of a special vacuum still heated with Dowtherm. The sample is quickly converted to a film b y action of a solvent and heating is continued for 1.5 hours. The loss in weight is due to plasticizer plus a slight decomposition of the cellulose ester. The latter is determined on a blank but i s usually small enough and uniform enough that a fixed value may b e assumed For it. Plasticizer content is given within about 0.3%.
PROCEDURE
Samples of approximately 1 gram in any form-Le., film, powder, or lump-are weighed into tared wide-type Pyrex welghing bottles (50 X 30 mm.), which are placed, with covers off, in a vacuum desiccator over fresh phosphorus pentoxide. The pressure is reduced to 5 mm. and the samples are dried overnight. When the desiccator is to be opened dry air from a calcium chloride tower is admitted. The bottles with covers on are reweighed and the weight of the dried sample is thus obtained. To each sample are added 3 cc. of acetonyl-acetone (Eastman Kodak Co., boiling point about 193' C.) and the bottles, without covers, are placed in the apparatus which has previously been carefully cleaned. The flange is cleaned before each run vtith fine Carborundum paper held against a flat metal disk to assure a vacuum tight joint. The acetonyl-acetone is st powerful solvent for cellulose esters and in 3 or 4 minutes the sample dissolves. As soon as the solvent begins to boil the glass dome is set in place, care being taken to see that it makes a good joint, and with the stopcock open the vacuum pump is started. The stopcock is slowly closed, the operator keeping his hand on it while watching the samples to see that they do not boil over or splatter. If the boiling is too vigorous the vacuum is released slightly till the boiling subsides. In this way the full vacuum is applied as rapidly as possible, the usual period being about 10 minutes from the time the samples were placed in the apparatus. As the solvent evaporates, the cellulose ester is left in a thin foamy layer from which the plastizicer can readily escape. As soon as the full vacuum is applied the operator seals the flange joint with a good sealing compound and the pressure in the system should then be 1 mm. or less. After exactly 1.5 hours from the time full vacuum was applied the stopcock is opened, the vacuum pum is shut off the glass dome is removed, and the samples are liftedgy means 01 tongs and quickly placed in a desiccator to cool. After half an hour the bottles with covers on are reweighed. The dry samples should not be exposed to the air uncovered before weighing, since dry cellulose esters absorb water rapid1 . The weighing bottles can be cleaned for re-use very convenient& after being soaked in acetone for a few hours. The loosely adhering ester is wiped off, and the bottles are rinsed in acetone, wiped dry with a cloth, and finally gently ignited and left t,o cool in a desiccator.
THE
determination of the plasticizer content of cellulose ester plastics has always been a slow operation, usually requiring large volumes of solvent and sometimes resulting in ambiguous values. The principal methods used have been (1) the extraction method, in which the sample is converted to a film,weighed, and extracted with ether, and either the extracted film or the extract is weighed, and (2) the precipitation method in which the weighed sample is dissolved in a small volume of solvent, the solution is poured into a large volume of nonsolvent, the precipitated cellulose ester is removed by filtration, and the plasticizer is recovered and weighed. While these methods, in the hands of a careful operator, can be used successfully, they are liable to serious error a t several points. One source of trouble is the great tenacity with which cellulose esters cling to acetone and even to ether. Another is the obvious difficulty in removing the solvent quantitatively from the plasticizer without loss of the latter when many plasticizers have appreciable vapor pressure at the temperature required. The method described in this paper consists of the removal of the plasticizer from a weighed sample of plastic by distillation under controlled ronditions of temperature and pressure, and was developed as a result of an observation by IT. 0. Baker of these laboratories that additional plasticizer could be removed by vacuum distillation from a sample which had already supposedly been freed of plasticizers by ether extraction. Ryan and Ratkins ( I , @ have used a method based on distillation of the plasticizer, but their sample (500 grams) was prohibitively large for an analytical method. The method developed here is fast and accurate, the technique is simple, it does not call for large quantities of solvents, arid it requires only 1 gram or less of material. APPARATUS
DETERMINATION OF BLANK
The apparatus required, illustrated in Figure 1, can be made in any laboratory shop. The still itself consists of a steel double boiler, the top chamber of which has a 2.5-cm. (1-inch) flange or Lip around the edge ground like a desiccator flange to fit the glass dome of a standard vacuum distillation apparatus (Corning Glass Co. No. 3480 EESHF). T e apparatus is conveniently made of standard 0.6-cm. tO.25-inch) seamless steel tubins, 15 cm. (6 inches) in inside diameter. by welding on the-flange, the partition, and the bottom. The partition, which constitutes the floor of the vacuum chamber, has a groove around the edge to collect any distillate which does not leave the chamber. The reflux column and vacuum line are, respectively, 0.5-inch and 0.375-inch iron pipe. Magnesia pipe lagging serves as the insulation. After being welded in place the flange should be turned as smooth as possible on a lathe, and when the whole apparatus is finished the flange must be ground to a perfectly plane surface. This is very important, since the satisfactory operation of the apparatus depends on maintenance of a good vacuum in the vacuum chamber. When the joint is properly ground an ordinary laboratory vacuum pump should be able to reduce the pressure in the apparatus to less than 5 mm. with no sealing compound in
The loss in weight of the samples put through the procedure described above represents plasticizer plus a certain amount of decomposition of the cellulose ester.
n
Figure I. Vacuum Distillation Apparatus
93
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
94
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much more nearly the actual deconiposirioii low of 1 he sample itself. The authors use a correction of 0.4% for acetate butyrates ran ing from 0 to 15% in plasticizer content. For very exact one can either make an absolute correction without regard to plasticizer, or determine the blank for the range of plasticizer content of t.he samples to be studid.
Table 1. Cellulose AcetateButyrates
Determination of Plasticizer Cellulose Acetate% % Plasticizer Lab. I I,ab. 1 Lab. 2 8.5 9.5 8.4 9.5 8.5 8.6 8.6 8.6 8.5 8.5 8.8 8.7 8.8
1
2 3 4 5 6 7 8 9 10 11 12 13
8.6 9.3 8.3 9.4 8.7 8.7 8.4 8.5 8.5 8.6 8.7 8.5 8.7
14
15
Celluloae acetates
war%
I,ab.
12.4 15.7
12.4 15.7
26,1
25,9
16 17 18 19 20 21
26.2 26'1 25.2
2:
26.2 26'o 25.3
22 23 24
24.9 25.5 25.2
25.0 25.5 25.0
The method has been used in these laboratories on cellulose acetate samples varying in plasticizer content from 18 to 40% and on acetate-butyrate samples from 2 to 20% with excellent results. The plasticizers which these samples contained were diethyl phthalate, dibutyl phthalate, dibutyl sebacate, and butyl stearate, and no difficulty was encountered with volatilizing any of them. One would expect difficulty with the very high boiling
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materials such as dixenyl cresyl phosphate and similar compounds. The method is particularly useful for routine control, where large numbers of samples are to be run, since one operator over a period of several days can run in duplicate an average of six to eight samples per day. The method has also been used for following plasticizer distribution by analyzing single particles of molding powder or fractions of molding powder separated by flotation methods. The reproducibility of the method is illustrated by Table I, results obtained on identical samples in two different laboratories with different stills. Each result is an average of duplicate runs. The precision of the method is illustrated by the following analyses of samples, all taken from a single molded object and all analyses being run by the same operator.
In order to determine the latter, dry samples of unplasticized cellulose ester of the type to be analyzed are put through the standard procedure, an approximately normal amount of plasticizer being added along with the acetonyl-acetone to make the conditions comparable. The result can be calculated either on the plasticized or unplasticized weight of cellulose ester. The former is usually more convenient. For example, if samples under examination contain about 25% of plasticizer, for the blank, one takes 0.73 gram of unplasticized ester, adds about 0.25 gram of plasticizer, and determines total weight loss in per cent. The blank correction representing decomposition is: Weight loss of sample (not including plasticizer) X 100 Weight of sample plus plasticizer This figure, which for cellulose acetate is usually about 0.3% is directly applicable to plasticized samples and when subtracted from per cent total weight loss gives the correct plasticizer oontent. In the authors' experience, cellulose acetate-butyrate samples have a slightly greater initial loss in weight than the acetate but the curve of the decomposition with time a t 256' C. is much flatter after this initial loss than it is with acetates. Furthermore, acetate-butyrates usually contain considerably less plasticizer t,han acetates, and t,herefore the correction factor is
Vacuum- J acketed
Vol. 16, No. 2
Ground-GIass
Sample 1
% Plasticiser
Sample
25.16 24.95 25.01
4
2
a
s
% Plasticicer 24.94 24.99 25.07 Av. 25.01
LITERATURE CITED (1) Jeanny, M., Rev. ~ 6 %mat. . plastiques, 10, 151-3 (1934). (2) Ryan and Watkins, IND. ENG.CHEM., ANAL.ED..5, 191 (1933).
Joi nt For
High-Vacu um Dis t iIlat ions
at Elevated Temperatures CHESTER M. McCLOSKEY, ROBERT L. SUNDBERG,
AND
GEORGE H.C O L E M A N
State University of Iowa, Iowa City, Iowa
MOST
packed or specially prepared distilling columns are surrounding the distilling column and is thus out of conattached to the boiling flask by means of a standard taper tact with the distilling vapors. The vacuum jacket is exground-glass joint. High-vacuum distillatended for a short distance below the joint tions at elevated temperatures through with an enlargement which approaches the .,.,~_ these columns become difficult when the sides of the neck of the boiling flask and lubricant used on the tapered joint is ex. __.. serves as a baffle. This minimizes heating tracted or rendered too fluid to be effecof the joint and prevents extraction of the tive as a seal, owing to continued high lubricant from the joint by the refluxing temperatures. Prolonged heating distorts liquid. the joint and if special precautions are not observed, the inner and outer members beAPPARATUS. Figure 1 shows the modified come frozen together upon cooling. These inner member alone and the inner member undesirable features have been largely in position in the boiling flask. Tube A eliminated by a modified vacuum-jacketed is 8 mm. in diameter and is ring-sealed to joint, by means of which the joint is a 24/40 standard taper joint (Ace Glass, kept a t a sufficiently low temperature to Inc., Catalog KO.7640) 3 cm. below the taper, C. The outer tube is enlarged impermit the use of ordinary high-vacuum mediately above the ring seal as illustrated. lubricants. Good seals have been mainWhen this member is placed in position in tained in distilling with bath temperatures as the boiling flask the distance between the high as 300 O C. enlarged portion and the neck of the i3ask / The column is so constructed that the is about 1.5 mm. The drip joint, D,is about 2 cm. below the ring seal, B . Figure I tapered joint is part of the vacuum jacket
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