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
LITERATURECITED (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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