Evaluation of Nitrocellulose Lacquer Solvents Ester Activation bv Alcohols and the Use of ALohols as Lacquer Diluents’
V. W. WARE AND W. M. BRUNER E. I. du Pont de Nemours 8. Company, Inc., Wilmington, Del.
that will dissolve more nitrocellulose a t any given viscosity than will an equal volume of the solvent alone. Actually, as far as the theoretical aspects of this increase in solvency are concerned, it seems possible that they may be explained on the basis of some form of hydrogen bonding similar to that used by Copley, Zellhoefer, and Marvel ( I , 2) in the correlation of solubility data on solutions of halogenated hydrocarbons in solvents of different types. However, the object of this paper is to present certain data of a more or less practical nature in such a form that it may be of value to the solvent manufacturer and user; any theoretical discussions concerning the cause of these phenomena will be reserved for a later communication. In spite of the frequent mention in the literature of the increased solvency for nitrocellulose of the ester-alcohol couple, little effort seems to have been macle toward a systematic examination of the conception and of the conditions and limits which govern it. The constant-viscosity procedure which has been applied to the investigation of nitrocellulose lacquer solvents (’7) and diluents (6) is particularly suited to a n examination of the general problem of the behavior of esters in the presence of alcohols when they are used as nitrocellulose solvents. The examination has been extended somewhat beyond this point to where it may be considered as a study of the use of alcohols, not only as solvent activators, but as lacquer diluents as well. For this purpose eight commercially available aliphatic esters were chosen: ethyl acetate, methyl propionate, npropyl acetate, ethyl propionate, isobutyl acetate, isobutyl propionate, amyl acetate, and a still higher acetate designated as B-23. (B-23 acetate is prepared from B-23 alcohol which is a mixture of seven- and eight-carbon-atom primary and secondary branched-chain alcohols in about equal proportions, and is obtained in the high-pressure hydrogenation of carbon monoxide.) The reaction of the nitrocellulose solutions of these esters to dilution up to 70 per cent by volume with various alcohols was examined by the constant viscosity procedure. Five alcohols (ethyl, n-propyl, isobutyl, amyl, and the still higher B-23 alcohol) were used with each ester. In the case of isobutyl acetate three additional alcohols (isopropyl, tert-butyl, and n-butyl) were utilized to establish the differences in solvent action which might be attributable to the differences in structure of alcohols with the same molecular weight. Additional data not included here indicate that for all practical purposes the reactions of isobutyl and n-butyl acetates to alcohol dilution are the same; this is true also of isopropyl and n-propyl acetates. Hence n-butyl and isopropyl acetates are given no further consideration since their inclusion would involve essentially a duplication of the values and curves for the two isomers which are included. Previous papers (‘7) gave a complete description of the procedure employed in these evaluations.
Little attention has been given to the study of alcohols as nitrocellulose solvent diluents. Beyond recognition of the fact that certain ester and alcohol mixtures possess greater solvent action than the ester alone, little effort has been made to define the limits of this phenomenon or to subject it to critical study. The constant viscosity procedure is admirably suited to such a study. It gives a complete picture of the “activation” or 6 6 coupling action’’ of alcohols on esters. The esters whose solvent action is improved by alcohols, the alcohols which cause this improvement, and the extent to which it is applicable are defined. The study has been extended to dilutions as high as 70 per cent and to a point where it may be considered as an evaluation of alcohols as nitrocellulose lacquer diluents. Eight esters are compared in the reaction of their solvent strength to dilution with each of eight alcohols. The possibility of establishing a new type of lacquer solvent balance in which the present hydrocarbon diluent content is reduced to the minimum necessary to obtain resin and oil compatibility is pointed out.
A
COMBINATION of ethyl ether and ethyl alcohol is a more active nitrocellulose solvent than either material alone. The same is true of certain mixtures of ethyl acetate and ethyl alcohol or of any of the unsubstituted alkyl esters which find common use as lacquer solvents. A number of references may be found in the literature (3, 4,6) to the socalled “activating effect” of alcohols on the nitrocellulose solvency of alkyl esters, and this property is quite generally taken advantage of in commercial formulation. I n such cases reference is often made to the “ester-alcohol couple” or to the alcohol itself as a “coupler”. For the purpose of this discussion a solvent “activator” or “coupler” may be defined as a nonsolvent which, added in limited amounts to a nitrocellulose solvent, forms a mixture 1 Previous papers in this series appeared in June and September, 1939 and in January. 1940.
519
INDUSTRIAL AND ENGINEERING CHEMISTRY
520
TABLE I. VISCOSITY-NITROCELLULOSE CONTENTFOR Alcohol Diluent
Ester: NitrocelluAlcohol -Viscosity (No. 7 CUP, 2.5' C.), Set.- lose at 50 Ratio 5 g.0 6 g. 7 g. 8 g. 9 g. 10 g. Sec., Grams
THE
ESTERSAT VARIOUS ALCOHOL DILUTIONS
Alcohol Diluent
Ester: NitrucelluAlcohol -Viscosity (No. 7 Cup, 25' C.), S e c . 7 lose a t 50 Ratio 6 g.a 7 8. 8 g. 9 g. 10 g. 11 g. Sec., Grams
Isobutyl Acetate
..
Kone
1oo:o
.,
Ethyl
9O:lO 70:30
. . . . . .
. . . . . . . . ., ..
50 :50
30:70 n-Propyl
1soprop> 1
9O:lO 70:30 50:50 30:70
9.5 9.3 8.8
Ethyl
90:10 70:30 5 0 :50 30:70
8.0
Isobut~l
30:70
9.0 8.7 8.2 7.2
9O:lO 70:30
. . . . ., ..
8.6 8.3 7.7 6.7
4my1
8.6
B-23
90:10 70:30 30: 70 9O:lO 70:30 50 :50 30:70
90:10 70:30
.
.. . . . . . .
. . . ...
..
..
42.0 53 8 69.8 3k:7 46.6 59:3 , . 43.3 53.6 70.0 43:7 54.1 72.6
..
___ .
. . . .
42.5 5 5 . 1 72.7 39:3 47.7 60.9 .. 43.9 54.6 74.0 . . 44:455.875.1 . . . .
. . . .
:
. . . . .. ,.
43.3 5 6 . 5 74.7 40:O 48.7 63.9 , . 46.4 61.4 85.9 .. 37:2 47:s 62.3 . . ,. ,.
. . . .
. . . .
50:50
B-23
100:00
40.2 49.5 64.2 . . . . 42.0 54.0 7 0 . 5 .. 39.1 48.4 6 0 . 1 . . 38:4 48.3 60.2
90:10 70:30
50:50
Amyl
. . . . . .
None
n-Propyl
30:70
tert-ButS1
37.9 45.0 57.1 . . 38.8 46.6 59.0 42.5 52.6 64.0 39:s 5 0 . 0 62.5 , ,
8.5
9.0 8.6 8.1 7.1
50 : 50
Isobutyl
,,
40.5 50.0 65.3 41.2 52.7 6 8 . 8 39:9 49.4 61.6 , . 39.0 44.4 62 2 ,. ,
5 0 : 50
n-Butl I
Methyl Propionate
37.2 44.2 57,2
. . . .
..
46.1 60.2 82.8 4Q.4 51.8 65 3 .. 47.5 63.8 8 1 . 2 ..
. . . . . .
30:70
3910
90:10 70:30
48.0 63.2 83.1 43.'8 57.3 87.0 .. 42:7 65.3 88.4 _. ., 43:s 66.7 94.1 . . . . . .
50:50
30:70
50:3 6 5 . 5
. . . .
..
8.2 7.6 6.5
None Ethyl
n-Propyl
Isopropyl
1oo:o 90:10 70:30 50 : 50 30:70
9 g.
10 g.
. . . . 44.6 . . . . . . . . . . .. 48:s ,
.
11 g. 50 5
49.2 51.4 60.0 48:2 56.7 71.8
12 g. 13 g. 60.5 .. 56.1 69.3 59.5 69 4 66.5 81:O 83.9 . .
. . . .
8.3 7.8
7.1 6.0 7.3 6.4 5.3
. . . . . .
30:70
Amyl
B-23
9O:lO 70:30 50 : 50 30:70 9O:lQ
70:30 50 :50 30:70 90:10 70:30 50:50 30:70
.,
.,
,.
41.6 46.1 52.2 43.5 50.7 59.2 43,'O 53.9 70 0 . . 3912 49:4 66.0 93.0 . . . .
. . . .
.,
.,
40.7 45 5 54.7 . . . . 43.9 53.0 65.7 4410 56.0 71.2 40:l 4918 69.3 . . . . . . ,,
..
. . . . ..
40.8 47 6 57.3 39:O 46.5 58:5 . . 40:2 49 3 62.3 . . . . 45:l 5 8 . 8 86:9 . . . . . .
30:70
None
10o:o
Ethyl
90: 10
11.1 10.8
G r n m nitrocellulose per 100
00.
70:30 50 : 50
30:70 n-Propyl
90:10
70:30 50:50 30:70 90:10 70:30 50:50
30:70 Amyl
10.2 9.2
90:10 70:30 50:50
30:70 B-23
9O:lO 70 : 30 5 0 : 50 30:70
38.0 45.5 . . . . . . 38.6 46.0 . . . . 42.3 50.2 . . . . 40:9 49.0 61.5 . . . . . . 40.3 47.5 . . . . 42.9 31.1 .. 4i:9 49.2 62.0 . . 42:3 52.7 68.9 . . . . . . 41.1 5 0 . 1 38:2 45,5 57.1 . . 39:047.457.5 . . 41:7 56.0 73.6 . . . .
. . . .
39:s 46.7 59.0 39:s 49.8 61.7 . . 42:6 5 9 . 7 79.5 . . . .
. . . . .. 42:O
. . . . .
..
10.6 10.0 9.1
59.0 62.7
10.3 9.9
,.
9 .I 7.8
61.0
10.0
. .
. , ..
9.5
. .
8.3 6.6
64.5
9.9 9.3
.. . .
. .
. . . . . .
8.0
6.4 9.7 9.0 7.7 6.1
n-Propyl Acetate 7 g. 8 g. 9 g.
. . . . . .
. . . . .
10.0 10.7
43.0 53.3 63.8 4i:i 50.3 6 5 . 0 .. 52.4 71.2 . . . .
4817 62.5 9 8 . 0
. . . . .
. . . . . . . . 44:2 . . .
.. ,. ,. 4610 . . . . ..
10 I'. 1 1 x . 44.859.273.2
9.4
42.052.860.0 4 1 5 5 3 . 8 68.5 47.2 5 5 0 76.2 55.2 71.3 . .
9.7 9.4 8.6
45.055.577.5 46.5 89.9 81.8 47:O 56 5 73.8 , . 5 6 . 5 73.9 . . ,,
4 0 . 0 57 ;I 77 8 4i:7 3 2 . 9 67.6 , . 4i:551.777.7 , . ,. 43:O 57.7 85.8 . . . . . ' '
. . . .
..
47.0 42:8 5 5 4
4i:8 54.2 78:s 44:O 5 6 . 7 80.2 . ,
78.2 74.1 , . SS.5
. . . .
,.
,
,
. . . . 47.3 61.8 78.4 46:2 56.3 77.3 ,. 37:O 45:3 63.4 . . . . . . 45.4 73.8 99.3 . . . . . . 6g.5
8.0 10.7 9.9 8.7 7.1
Ethyl
10.5
1oo:o
7 g.
8g.
. . . . . . . . . . . .
9 6. 10 g. I1 8. 46.557.274.0
30: 70
. . . . . . . .
41.3 . . 41.6 44.5 41:6 51.6
n-Propyl
90:10 70:30 50350 30:70
. . . . . . .... . . 44:6
37.0 38.5 43.2 55.2
Isobutyl
9O:lO 70:30
.,
9O:lO
70:30 50 :50
9.7 8.6
7.0
50:50
8.1
6.6
of base lacquer.
B-23
9.9
9.6 9.4 8.4 7.5 9.5 8.8 7.9 6.6 9 3
86 7.7 6.5
92 8.5 73 6.2
. . . .
..
49.8 62.8 50.4 59.8 54.8 70.4 65.6 . .
.. 43.0 53.1 46.5 59.0 54.0 70.3 . . 74.0 . . . .
..
39.5 44.8 55.8 41.9 48.1 67.5 4i:849.463.3 . _ 54.5 75.2 . . . .
..
.. ..
. .
9.4 10.0
10.0 9.6
8.9 9.7 9.4 8.7 7.6
9.5 9.2 8.1
30:70
4316
90:10 70:30 50 :50 30:70
,.
39.5 47.7 5 9 . 6 43.5 52.5 69.1 42:5 5 1 . 7 65.5 . . 4410 58.3 79.7 . . . .
.. ,. . .
9.2
. .
7.8 6.5
90: 10
.. 42.6 48.2 61.7 .. . . . . 37:9 45.5 5 5 . 5 38:5 45.5 66.8 .. 52.7 68.6 ( 3 9 . 8 a i 5 g.)" ..
9.2 8.5 7.3 5.9
70:30 50 :50 30:70
Experimental Procedure The experimental details are identical with those described i n previous papers (7) with the exception that a different lot of l/rsecond nitrocellulose was used. The behavior of this lot was almost identical with that of the previous one a t low dilutions and low solids content, but as the dilution and percentage of nitrocellulose increased, there was a noticeable de-
4 2 . 0 80.5
..
64.1 53.6 84.6 62.5
Ethyl Propionate
10.5 9.5
10.3 9.3
41.0 5 0 . 3
. . . . . .
6 g.a
Amyl a
90:10 70.30 50: 50
None Isobutyl
90:10 70:sO 50:.,0
10.9
11.1
. , 43.1 49.0 56.7 47.2 5 5 . 7 65.2 76,'4 46:s 55.2 66.4 8 6 . 0 .. 5012 62.8 89.3
..
90: 10 70:30 30:50
30:70
Isobutyl
.,
9O:lO 70:30 50:50 30:70
30: 70
8.2
11.1 10.4 9.4 7.9
44.8 49.6 58.5 48.0 56.5 65.8 8O:l 47:O 56.5 68.4 84.2 . . 5Q:8 62.1 83.4 . . . . . .
.SO: 50
7.3 6.2
..
90:10 70:30 50 : 50 30:70
90:10 70: 30
. . . . . .
8.5 8.1
Ethyl Acetate
8 g,a
VOL. 32, NO. 4
I .
,
.
6.7 8.8
viation in the viscosity readings of the two lots. For this reason the data contained in this paper are not strictly comparable with those previously given. Dry nitrocellulose was used, and the viscosity measurements were made on the Parlin No. 7 cup a t 25 * 0.1' C. All samples were tumbled a t an identical rate for 24 hours to ensure complete solution. The recorded viscosity for the three or more solids concen-
INDUSTRIAL AND ENGINEERING CHEMISTRY
APRIL, 1940
TABLE I (Continued) Alcohol Diluent Xone
Ethyl
n-Propyl
Isobutyl
Amyl
B-23
Ester: Alcohol Ratio 1oo:o
Amyl Acetate 36.2 43.0 54.5
..
90: 10 70:30 50:50 30:70 90: 10 70:30 50: 50 30: 70 90: 10
,0:30 RO:50 30:70
9O:lO 70:30 50: 50 30: 70 go: 10 70 : 30 50 : 50 30:iO
~
-Viscosity (No. 7 Cup, 25' C.), Sec.5 g , a 6 g. 7 6. 8 6. 9 6. 10 g.
..
,
..
,. ,.
,: .. .. ,,
38:s
.. -, ,
42:O
.. 36:5 45.6
. . . .
36.4
42.0 50.1 40.6 49.0 41.6 5 0 . 1 39:446.558.4
..
5910 63.2
..
44.7 45.4 49.9 60.9
53.7 55.0
..
3i:4 40.0
37.7 38.2 41.2 47.7 39.3 41.6 47.8 66.6
47.0 50.2 60.0
56.8
3,i:7 39.2 49.8
..
38:6 42.5 51.9
42.5 44.5 51.2 68.4
5 0 . 2 65.6 53.2 .. 65.8 ..
30:7 44.7 62.0
43.7 45.4 55.9 91.1
52 7 57.2
..
. . . . . . . . ,,
. . . .
. . . . . .
Nitrocellulose at 50 Sec., Grams 7.6 9.0 9.1 9.0 8.3 8.6 8.4 8.0 7.2 8.3 8.0 7.2 6.0 8.0 7.7 6.9 5.8
. . . .
..
66.7
. . . .
. . . . . .
. . . .
7.7 7.4 6.5 5.4
Isobutyl Propionate
5 g.
4 E.0
None
1oo:o
Ethyl
90: 10 70:30 50: 50 30 : 70
n-Propyl
90: 10 70:30 50:50 30:70
Isobutyl
Amyl
B-23
None Ethyl
n-Propyl
Isobutyl
Amyl
B-23
90: 10 70: 30 5 0 : 50 30: 70 90: 10 70: 30 50:50 30:70 90: I O 70:30 50:50 30: 70
1oo:o
. . . .
. . . .
. . . .
::
3k:l
. . . .
..
36:l 40.0
34:O
. . . . ..
35:4 42.5
34:4
... . . .
38'6 4816
3;:3
6 g. 7 R . 8 g. 3 7 . 4 4 5 . 8 63.0
9 0. 87.9
7.3
390 36.7 38.2 38.6
45.6 43.0 44.3 48.0
58.4 53.8 53.2 58.5
8.4 8.7 8.6 8.2
41.2 40.0 4.5.1 51.4
50.0 49.9 57.0
68.8
8.0 8.0 7.5 6.9
43.7 43.8 53.0
53 7 57:5
74.4
43.0 44.8 55.5
56.3 59.1
3i:6 37.5 41.8 3f:O 41.6 50.8
37.0 37 6 4218 55.8
. . . . . .
. . . . . .
90: 10 70:30 50: 50 30:70
. . . .
90: 10 70:30 50 :50 30: 70 90: 10 70:30 50:50 30:70 90: 10 70:30 50 : 50 30:70
.
.
.
,.
. . . . . . . . . . .
..
..
36:O
. . . . "
36:O
38:4 44 2
. . . .
..
34:s 40 0
,.
6.0
.. ..
7.5 7.4 6.6 5.6
.
7.4 7.1 6.2 5.1
,.
8 a. 83,O
7.7 7.6 6.8
. . . . , , , ,
. . 9
e.
..
6.5
46.0 41.3 40.5 39.8
59.2 75.6 4 8 . 3 64.2 47.0 61.1 4 6 . 8 59.6
7.4 8.1 8.2 8.3
47.7 45.8 47.1 74.8
64.1 58.7 62.5
, ,
7.2 7.4 7.3 6.2
. .
6.8 7.0 6.3 5.4
,.
4 1 . 6 5 2 . 7 68.7 4 0 . 8 5 0 . 8 69.8 47.5 62.4 ,. 64.2 . . . . 42.7 42.0 48.5 62.1
ts4.0 73 8 5 2 . 6 75 0 59.0 ..
45.0 38'7 47 8 $2 7 .56 7 a7 1 X.i fi
5 6 . 5 77.5 65.4 , .
38'0 3&:7 4 6 . 0
..
39:O 47.8
.
..
36.5 45.4 57.7 40 1 4 9 . 0 6 7 . 9 47'2 62.2 .. 6713 . . . .
90:lO 70: 30 50: 50 30: 70
.
. . . .
B-23 Acetate 4 5 x. 6 g. 7 a. . . . . 4 4 . 1 59.1
88.3 72.1 ,.
,.
6 7
.
6.8 6.2 5.2
, .
6.5 6.1 5.6
. . . .
.
Ester Ethyl acetate Methyl propionate n-Propyl acetate Ethyl propionate Isobutyl acetate Amyl acetate Isobutyl propionate B-23 aaetate
, .
A 7
trations with each ester-alcohol mixture is shown in Table I. These viscosity values were plotted against grams of nitrocellulose, and the curves obtained are shown for isobutyl acetate. The esters used in this work were obtained or prepared in an essentially alcohol-free condition, as indicated by the following analytical values:
521 -4aDonificarion No.-Founb Theoretical 641 1 637. 1 637. 1 642 0 346 8 lj49 7 549 7 548.3 483.3 481.5 431.2 426.6 431.2 431.0 282 0
Hvdroxvl
..
NO.
0.3 0.0 1.1 0.0 1.9 2.7 0.0 3.8
The amyl acetate was prepared from the amyl alcohol fraction obtained in the high-pressure alcohol synthesis. The B-23 alcohol used in the preparation of B-23 acetate was obtained from the same source; the alcohol has a boiling range of 150-160" C. and the acetate a range of 160-170" C. The other alcohols, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and amyl, were 99 per cent pure or better.
Viscosity vs. Nitrocellulose Content The experimental viscosity values for solutions of nitrocellulose (Table I) are expressed as grams per 100 cc. of base lacquer. The alcohol dilutions are expressed on a volume basis and in every case extend from the pure ester through 90:10, 70:30, 50:50, to a final ester-alcohol composition of 30:70. Table I also gives the grams of nitrocellulose that each ester-alcohol mixture will dissolve to form 100 cc. of sohtion a t a viscosity of 50 seconds. The latter values are obtained by plotting curves of the experimental data as shown in Figure 1. From these curves the exact weight of nitrocellu lose which will dissolve in the various mixtures a t any desired viscosity may be read; a viscosity of 50 seconds has been chosen as the standard reference point in this work Little discussion is required for the experimental data curves. They are included as an example in the case of ifiobutyl acetate (Figure 1) and omitted with the other seven esters. For purposes of comparison the curve for the purr. ester is shown in each chart. Figure 1.4 gives the isobutyl acetate curves for 10 per cent alcohol dilution; the curves for ethyl alcohol, the propyl alcohols, and the butyl alcohols are to the right of the curve for pure ester, and thus show an increased solvent action. The two higher alcohols act simply as diluents and show no activation whatever. In Figure 1B for 30 per cent dilution the situation relative to the pure solvent has changed somewhat in that the curves for n-,iso- and tert-butanol have now moved across to the left with the two higher alcohols; this indicates that the point of optimum dilution of this ester with either of the three alcohols lies between 90 and 70 per cent ester content. At 50:50 alcohol dilution in Figure 1C both of the propanols show poorer solvent strength than the pure ester. Only ethyl alcohol is left on the right side as possessing better solvent strength a t 50 per cent alcohol content than the undiluted material; even this curve is considerably closer to that of the pure ester than a t lower dilutions. The pure ester is a more active solvent (Figure 1D) than any of its mixtures a t a 30:70 dilution with any of the alcohols used.
Volatile Composition DS. Nitrocellulose Content a t Constant Viscosity Figure 2 deals with the change in nitrocellulose content as the alcohol content of the ester is increased. The grams of nitrocellulose which will dissolve in the various mixtures to give 100 cc. of solution with a viscosity of 50 seconds (as obtained from the last column in Table I) are plotted against the composition of each corresponding ester-alcohol mixture. From these curves it is simple to calculate the cost of any solvent mixture required to apply a unit weight of solids; hence further discussion will be confined to the curves themselves. In Figure 2B ethyl acetate is considered with six aleohols. The increase in solvent strength with ethyl alcohol is noticzable; it reaches the same point with the propyl alcohols but drops off much more rapidly than with ethyl alcohol. The three higher alcohols do not activate ethyl acetate, and their
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
522
function would resemble that of a diluent in such a composition, except that the solids content is higher than would be obtained with an equal volume of any hydrocarbon diluent.
70
60-
I
I 100% ESTER
2 90 3 90 4 90 5 90 6 90
E S T E R - 1 0 8-23 ALCOHOL ESTER-IO A M Y L ALCOHOL ESTER-IO TERT-BUTANOL ESTER-IO ISOBUTANOL ESTER-IO n - B U T A N O L
90 ESTER-IO I?-PROPANOL 8 90 ESTER-IO ISOPROPANOL 7
G
NITROCELLULOSE
PER
I00 CC
CONTENTFOR FIGURE 1, VISCOSITY-NITROCELLULOSE
VOL. 32, KO. 4
Consideration of the alcohol dilution curves for methyl propionate in Figure 2C in comparison with B indicates that, whereas the solvent action of pure methyl propionate is weaker than that of pure ethyl acetate, the propionate is activated much more than the acetate by all of t h e a l c o h o l s . This increase is outstanding in the case of both ethyl and propyl alcohol where the relative activation of the propionate is not only greater but does not drop so low as it does with the acetate; thus while the difference in grams of nitrocellulose dissolved is 0.9 between the pure esters and 0.4 a t 30 per cent ethanol 3 70 ESTER- 30 A M Y L ALCOHOL content, the pro4 7 0 ESTER- 30 TERT'BUTANOL pionate still has a 5 70 ESTER- 30 ISOBUTANOL superiority of 0.2 6 7 0 ESTER- 30 r\-BUTANoL gram a t an ethanol 7 70 ESTER- 30 n-PROPANOL content of 50 per 8 70 ESTER- 30 ISOPROPANOL cent. T h e two esters are not so close i n s o l v e n t strength with the higher a l c o h o l s , but in every case t h e solvency is better relative to pure propionate than to pure ace2 50 ESTER - 50 8 - 2 3 A L C O H O L tate. 3 5 0 ESTER - 50 A M Y L ALCOHOL n - P r o p y l ace4 50 ESTER - 50 TERWUTANOL . tate (Figure 2D), 5 50 E S T E R - 5 0 ISOBUTANOL similar to the more 6 5 0 ESTER - 50 n-BUTANOL volatile esters dis7 5 0 E S T E R - 5 0 n-PROPANOL cussed above, is 8 5 0 E S T E R - 5 0 ISOPROPANOL activated by both ethyl and propyl alcohols but is unlike them in that there is a small increase in solvent strength with isobutanol. In the propionate series the ethyl ester has an evaporation rate or volatility similar to that of n-propyl acetate. C o m p a r i s o n of these two esters (Figures 2 0 and E) shows that relaBASE LACQUER tionships resembling those pointed ESTER-ALCOHOL COMPOSITIONS
APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
523
524
INDUSTRIAL AND ENGINEERING CHEMISTRY
out in the next lower member of each series exist here also. Although the solvent strengths of pure n-propyl acetate and pure ethyl propionate are identical, the propionate in general accepts alcohol to form a mixture which will dissolve more nitrocellulose than a corresponding alcohol mixture with n-propyl acetate. Alcohols higher than butyl show no increase in solvency with ethyl propionate or with propyl acetate. Certain points of interest in connection with the effect of alcohol dilution upon the solvent action of isobutyl acetate are pointed out above in the discussion of the viscosity-nitrocellulose content curves, but the derived curves in Figure 2.4 serve to illustrate these tendencies in a much clearer manner. The butyl alcohols have a gradually decreasing efficiency as the chain becomes more branched until the tertiary alcohol imparts an action which resembles that of amyl alcohol almost as much as it does n-butyl alcohol, especially at high dilutions. On the other hand, although the differences between the two propyl alcohols are hardly greater than the experimental error, the branched-chain isopropyl alcohol forms a more efficient couple than the normal alcohol. That this differential is a true one is borne out by the consistency of the results and the fact that the values obtained in the case of ethyl acetate are corroborative. The relationships which exist here for the various isomeric alcohols with isobutyl acetate have been found to be generally applicable t o all of the esters considered in this paper. Hence, in order to simplify the presentation, data and curves for isopropyl, n-butyl, and tert-butyl alcohols have been omitted from the consideration of the other esters. Ascending in the acetate and propionate series t o the next two important esters, amyl acetate (Figure 2F) and isobutyl propionate (Figure 2G), the point of greatest solvent strength has moved down to about a 70-30 ester-ethanol mixture, an 80-20 ester-propanol mixture, etc., until even the high-boiling B-23 alcohol shows some slight activation up to about 10 per cent alcohol. With the higher B-23 acetate and ethyl alcohol (Figure 2H) there is a continuous increase in the amount of solids which the mixture will dissolve up to the point of incompatibility. At 70 per cent ethanol content the mixture will actually dissolve to form a clear solution almost 30 per cent more solids than the pure ester alone. The increase in solvency with the addition of propyl alcohol is also quite pronounced with this and other higher esters. The behavior of amyl and isobutyl alcohols is not greatly dissimilar, and any improvement by the use of B-23 alcohol with its own acetate is so small as to be of little practical value. Slthough the “coupling action” as defined previously actually demands an improved solvent action over that of the pure ester upon the addition of limited amounts of diluent, the alcohols as a class are more efficient diluents than the hydrocarbons. Even the higher alcohols which show no activating effect under the conditions described here invariably allow the incorporation of more nitrocellulose when they are used as the diluent than do either toluene or naphtha. The advantage of alcohols over hydrocarbons as lacquer diluents is particularly noticeable at ester contents of 70 per cent and lower, and it would be erroneous to conclude that the activating effect discussed here is a complete measure of the total differences in solvent value between the two types of diluent. This work has been confined entirely t o the viscosity and solids content of the material in solution or “at the gun”. Although little or no attention has ever been given the matter in the literature, it is possible that a clearer understanding of lacquer behavior might be obtained if more attention were paid to the composition after it has left the gun and if the changes occurring from that point on were studied thoroughly, It also seems possible that an entirely new and un-
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expected solvent balance might result from the use of only enough hydrocarbon diluent to disperse the resins and oils t o obtain a mutually miscible formulation, and that by replacing the remaining unnecessary hydrocarbon with alcohol of the desired volatility, an increase in solids content great enough to compensate for differences in cost of hydrocarbon and alcohol might well be obtained. Such a balance would result not only in better solvency as mentioned above, but also in improved flow, smoothness of application, and blush resistance within certain recognized limits. It may be demonstrated that the blushing tendencies of the more volatile solvents increase as the proportion of hydrocarbon diluent, parbicularly gasoline, is increased. Moreover, with the excep tion of methyl and ethyl alcohols, much larger proportions of alcohol than of a hydrocarbon of corresponding evaporation rate may be used without inducing blush in the film. Although aliphatic hydrocarbons show the same general effect on solvency, regardless of the boiling range of the fraction (true t o a lesser extent of the aromatic hydrocarbons), the data shown above indicate the greater versatility of the alcohols in this connection in that they not only offer a wide range of volatility but a range of solvency as well.
Summary A study of the utilization of alcohols as lacquer diluents and their activating effect on the solvent strength of nitrocellulose solvents of the aliphatic ester class has been presented. . The activating effect or coupling action of alcohols with esters, as defined by an increase in the solvency of nitrocellulose in the mixture over and above that observed in the pure solvent, becomes more and more evident as the volatility of the ester becomes less than that of the alcohol. The point of maximum solvent strength also tends to move in the direction of greater alcohol content as the ester decreases in volatility relative to the alcohol. Thus ethyl alcohol with ethyl acetate shows an increase in solids content of about 2.5 per cent, and the point of maximum solvency is a t an alcohol content of approximately 12 per cent; the same alcohol with the less volatile B-23 acetate allows a solids increase of 30 per cent, and this point is located a t an ester-alcohol ratio of 30-70. Although ethyl acetate is activated by no alcohol higher than propyl, amyl acetate and isobutyl propionate react t o all alcohols up to and including B-23. The propionates are in general somewhat different from the acetates; although the pure propionate possesses somewhat lower solvent strength than the pure acetate of corresponding volatility, they are activated to a considerably greater extent by alcohol than are the acetates. Thus the increase in solvent strength from the pure ester to the point of optimum ethanol dilution is 2.5 per cent for ethyl acetate and 8.0 for methyl propionate, 4.5 per cent for propyl acetate and 7.5 for ethyl propionate. Similar relations may be observed with the other alcohols as well. The possibility of establishing a new solvent balance and the advantages which might be gained from a consideration of this information in actual lacquer formulation has been pointed out.
Literature Cited ( 1 ) Copley. Zellhoefer, and Marvel, J . A m . Ckem. Soc., 60, 2665
(1938). (2) Ibid., 60, 2714 (1938). (3) Doolittle, A.K., IKD. ENG.CHEM., 30,189 (1938). (4) Keyes, D.B.,Ibid., 17,1120(1925). (5) Schwara, Caoutchouc & gutta-percha, 12,3859(1914). ( 6 ) Ware and Bruner, IND. EKG.CHEM.32,78 (1940) (7) Ware and Teeters, Ibid., 31, 738,1118 (1939). PREBENTED before the Division of Paint and Varniph Chemistry at the 98th Meeting of the Americbn Chemioal Society. Boston, Msss.
