September, 1927
II1’DUSTRIAL AA’D ENGINEERING CHEMISTRY
was distinctly helpful in protecting the wood. In two cases there was no choice, and in one (19 and 20) the panel with the aluminum primer was distinctly worse, although the difference in the grain of wood could readily explain this. I n these exposure tests the paint coatings having the highest initial moisture-proofing efficiency proved the most durable and gave the best protection; these were the aluminum paint coatings. The next in order of moisture-proofing efficiency, as well as durability, were the combinations of a prime coat of aluminum paint with top coats of white. That aluminum paint may have high moisture-proofing efficiency after 18 months’ severe exposure is shown by other tests (Table 111), where there were observed values of 70 to 80 per cent. The white paint exposed a t the same time was badly deteriorated and the checking of the wood indicated failure in its moisture-proofing power, which according to the writers’ measurements was only about 10 to 20 per cent.
977
Heat-bodied (kettle-bodied) linseed oil, diluted with about 40 per cent mineral spirits or turpentine and with added drier, makes the most generally satisfactory vehicle for aluminum paint for protecting wood. Varnishes should only be used when they are exceptionally long in oil-say, an 80-gallon varnish, or better. Conclusion These tests show that moisture-proofing efficiency and wood protection go hand in hand. It is important also that relatively high impermeability be maintained if the protection is to continue. Checking and cracking of the wood resulting from failure of the moisture-proofing power of the paint film must accelerate the mechanical disintegration of the overlying paint film. Disintegration of the paint film further accelerates wood weathering, and so a vicious cycle is established. In a very practical sense, therefore, protected wood helps preserve the paint.
Dilution Ratios of Nitrocellulose Solvents‘ By J. G. Davidson and E. W. Reid CARBIDEA N D CARBON CHEMICALS CORPORATIOS, NEWYORK,N. Y.
A conti?zuatiovt
of previous work2 discussing, i i z addition to the usud aromztic hydrocarbon diluetits, a aumber of
experiments carried out xith uarious types of gasoliue.
T
HE dilution ratio of a nitrocellulose solvent is a measure of its solvent power and is obtained by dividing the
volume of diluent that must be added to cause incipient precipitation of the nitrocellulose by the volume of solvent in which the nitrocellulose is dissolved, or -‘Vd_ - D. R T 7n where Vd = volume of diluent Vn = volume of solvent
It therefore corresponds to the solvent-power numbers of Mardles,3 who defines them as “the volume of the liquid (diluent) in cc. required to begin precipitation from 1 cc. of a 5/100 concentration sol.’’ Determination of Dilution Ratios The dilution ratio (D. R.) will vary with the following factors: (1) solvent, (2) diluent, (3) temperature, (4) type of nitrocellulose, and (5) concentration of nitrocellulose. For the purpose of this paper variables (3) and (4) hare been eliminated by using the same type of nitrocellulose and by working with all solutions a t a temperature of approximately 20” C. The influence of variable (5) is described briefly a t the end of the paper. but with this exception all solutions from which data were derked contained the same concentration of nitrocellulose. The procedure was approximately the same as reported before,* although the concentration of nitrocellulose mas somewhat greater for these experiments. It consisted siniply in dissolving 2.5 grams of dry l/e-second nitrocellulose in 7.5 grams of solvent. After solution was complete the diluent was carefully added with vigorous stirring until precipitation of nitrocellulose was just evident. Some investigators maintain that results determined in this manner are subject t o error because the solutions become 1 Presented by J. G . Davidson under the title “Diluents and Dilution Ratios” as a part of the Symposium on Lacquers, Surfacers and Thinners before the Section of Paint and Varnish Chemistry a t the 73rd Meeting of the American Chemical Society, Richmond, Va., Aprll 11 to 16, 1927. 2 THISJOURNAL, 18, 669 (1926). 8 J . SOC.Chem I n d , 42, 129T (1923).
supersaturated and there is considerable lag in the appearance of the precipitate even though the true dilution ratio has been exceeded. In order to obtain a true measure of the solvent power it is proposed to start with nitrocellulose and a diluent to which mixture solvent is gradually added with stirring until the nitrocellulose just dissolves. Another advocated method involves the production of various mixtures of solvent and diluent. The solvent power of each mixture is determined and the composition of the mixture which is just able to dissolve the nitrocellulose is noted. The ratio of the diluent to true solvent in this mixture may also be called the dilution ratio. The authors have experimented with all three methods and find no great difference in the results. Certainly the relative rating of the various solvents by each method is the same. Results Table I shows that the ethers of the glycols have in general better dilution ratios than the butyl esters with respect to benzene, toluene, and xylene. Figure 1 expresses the same information in a graphic manner. The numbers in the tables and a t the bottom of the charts correspond with the numbers shown opposite the list of compounds below: KUMBER TABIX I 1 2 3 4 5 6 7 8 9 10
FOR
11
12 13 14 15 16 17
NUMBER CHARTS 1 1 2 2 3 3 4 5 5 6
FOR
Methyl ether of ethylene glycol Methyl ether of propylene glycol Ethyl ether of ethylene glycol Ethyl ether of propylene glycol Propyl ether of ethylene glycol Propyl ether of propylene glycol Isopropyl ether of ethylene glycol Butyl ether of ethylene glycol Butyl ether of propylene glycol Isobutyl ether of ethylene glycol Isobutyl ether of propylene glycol Isoamyl ether of ethylene glycol Isoamyl ether of propylene glycot Ethylene glycol monoethyl ether acetate Butyl acetate Secondary butyl acetate Butyl propionate, commercial
6
7 7 8 9 10
11
On the charts, the dotted lines represent the ethers of propylene glycol and the numbers refer to the same alkyl
978
I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol. 19, No. 9
8
< b
'!I? Figure 1-Dilution
Ratio with Toluene
!
J ' j ' J ' ! ' ! ____
Figure 5-Dilution
'
E7./Le5 O F PrnPYL€rn€ GLYCOL 8 9 /o //
Ratio w i t h Vapor-Phase Cracked Gasoline (50-221O C.)
? d
BP
8
Figure 2-Dilution
Ratio w i t h 80-120° C. Gasoline Figure 6-Variation of Dilution Ratio w i t h Boiling Range of Gasoline-25 Per Cent Nitrocellulose Solution
F
B
B 2 P
Figure 3-Dilution
R a t i o w i t h Turpentine
2 CTMYL€"C GLYca MONO PRoPrL f T * m
urn Acmm fOnU€NTPrT/ON
Figure 7-Effect
50%r MX6
/osxr Figure &Decrease
?5%r
75%0
i n Dilution Ratio a8 Gasoline Is Added
group as in the case of ethylene glycol. For example, point 5 on the dotted line represents the dilution ratio for the monobutyl ether of propylene glycol. Variation in Solvents
McBain4 and his co-workers maintain that the value of a solvent can be determined by the apparent viscosity of the J. Phrs. Chem., SO, 312 (1926).
W
NITQOCCILULOSE /N % 81 WE/GHT
of Nitrocellulose Concentration o n t h e Dilution Ratio
solution produced by dissolving cellulose nitrate in the solvent. He defines the apparent viscosity as "the logarithm of the viscosity of the (cotton) solution divided by that of the solvent calculated per gram of nitrocotton in 100 grams of solvent." The present writers have not yet investigated the solvent power of the glycol ethers by this method, but certain observations have convinced them that neither this generalization nor the following, to which both Mardles and McBain subscribe-"Within any homogeneous series the lower the molecular weight the greater the solvent power"-will fit all cases set forth in this paper. Table I bears out in general the assumption that the higher members of any homologous series are poorer solvents than the members of lower molecular weight. For example, when the dilution ratio with respect to toluene is taken as a criterion, ethylene glycol monobutyl ether is a poorer solvent than ethylene glycol monoethyl ether, and in turn propylene
I N D U S T R I A L A N D ENGINEERI-VG C H E M I S T R Y
September, 1927
T a b l e I--Dilution R a t i o s of N i t r o c o t t o n S o l u t i o n s 1 2 3 4 5 6 7 8 9
Diluent
979 11
10
12
13
14
15
16
17
AROMATICS
Benzene Toluene Xylene Turpentine
4.3 3.8 2.4 0.4
3.7 4.8 4.4 5.2 3 . 5 4.0 1.5 1 . 9
(1) (2) (3)
0.2 0.2 0.2 0.2 0.6 0.2 0.2 0.2
0 4 0.5 0.5 0.5 1.0 0.5 0.4 0.5
0.1 0.2
0 . 5 0 . 5 0 . 7 1 . 0 0 , s 0 8 1 . 1 0.6 0.6 0.8 1.0 1 . 6 0,r 1.1 1.5 0.6
0 6
0.3 0 3
1.2 0 4 1 . 2 0.4
0.4
0.9
2.7 2.8 2.8 1.4
3.0 3.4 3 6 3.0
3.2 3.5 2.8 3.3
0.8 0.8 0.8 1.5 0 . 9 1.4 1.4 2.1 0.8 1.2 0.2 0.7 0 I 0.9 1.3
1.4 0.6 0.9 0.7 1.0 1.0 1.6 0.7 0.9
2.6 3.0 2.8 2.8
1 2 1.5 1.4 2.0 1 . 5 2.0 1.1 1.4
1 . 2 2 . 2 2.4 1.5 2.4 1.4 2.2 1.3 1.4 0 8 2 5 0.9
2.6 1 . 5 2.5 1 6 2.4 1.5 3 . 5 2.2
1.3
1.A
1.4 1.0
GASOLINES
Straight-run Pennsylvania Straight-run midrontinent A. N o . 1 gulf (4) Coastal naphtha (5) Vapor-phase cracked (6) Venezuela naphtha (7) California naphtha (8) 500 type pressure still distillate (435' F., 224" C.) (9) 300 type pressure still distillate heavy (435' F., 2240 C . ) (10) Straight-run (80-120' C.) 25y0 Toluene 75% Gasoline (10) 5 0 0 Toluene 50% Gasoline (10) 75Y0 Toluene 25% Gasoline (101
1
1 1
0
0 6 0.6 0.6 0.6 1.3 0.5
1 . 6 1 . 3 2.0
0.9
1.8 2.6
2.7
3.5 4 . 5 2.7
glycol monobutyl ether is a poorer solvent than ethylene glycol monobutyl ether. B superficial observation of the relative viscosities of the test solutions leads to the same conclusions. K i t h turpentine or gasoline as the diluent the results are much more erratic. The glycol ethers then vary greatly among themselves, but even under these conditions the normal propyl and butyl ethers of ethylene glycol have dilution ratios that are equal to or better than the ratios for the butyl esters (Figures 2 and 3 ) . Certainly-at least as far as the dilution ratios with gasoline are concerned-the normal propyl and butyl ethers are better solvents than the ethers of lower molecular weight, and in the case of the methyl and ethyl compounds the ethers of propylene glycol are better solvents than the ethers of ethylene glycol. These results are opposed to the assumption that in a homologous series the compounds of higher mol'ecular weight are the poorer solvents. It should also be noted (Figure 2 ) that the secondary ethers are poorer solvents than the normal ethers. The dilution ratios with the gasolines are almost invariably smaller than with the aromatic hydrocarbons. For the glycol ethers the differences are more pronounced than for the butyl esters. Figure 4 shows the decrease in dilution ratios, starting with 100 per cent toluene as a diluent and proceeding to 1OG per cent gasoline. Since the dilution ratio may be taken as a measure of solvent power, all other factors being discarded, the value of a diluent is proportional to the dilution ratio in which it plays a part. Thus in the case of the monoethyl ether of ethylene glycol, which has a dilution ratio of 5.2 for toluene and 0.8 for gasoline, the toluene is worth about six times the price of gasoline as a diluent. When butyl acetate is the solvent chosen, toluene is worth only about twice as much as gasoline, for the respective dilution ratios are then only 2.5 and 1.5. This is important in the production of thinners for automobile base lacquers. If the thinner used is not a true solvent for nitrocellulose, drowning of the base lacquer with the thinner will result in the precipitation of small aggregates of nitrocotton that will not quickly go into solution again and are liable to interfere with the action of the spray gun or mar the lacquered surface on which they are deposited. Variation i n Gasolines
Attention should also be drawn t o the great variation in the dilution ratios of a given solvent with different types of gasoline. Thus, the dilution ratio of the monoethyl ether of ethylene glycol is 1.3 with respect to a vapor-phase cracked gasoline, while it is only 0.6 for a straight-run Pennsylvania
1.9 2.4 2.9
1.2 0.4 0.5 1.4 0 . 5 0.7 0 . 3 0.9 0 . 4 1.4 0.5 0.4 1 1 0.4 1.9 0.8 0.9 0.5 1.4 0 . 5 1.4 0.5 0.3 1 . 1 0.4 1.3 0 6 1 . 0 1.6 0 . 6 0 . 8 0.4 1.2 0 . 5
0.9
1.3 1.3 1.4 1.5 2.0 1.5 1.3
0.8
1.0 0.9 1.3 0.9
1.2 1.2 1.4 1.2
1.5 1.0
1.2
1.3 0.9 1.5 1.1
1.0 1.2
1.1 1 . 5 2 . 2
0.9
1.1 0 . 5
1 . 7 0.6
1.7
1.4
1.3
1.3 2.3
2.4
1.0
1 . 3 0.7
1.8
2.1
1 5
1.4
1.8 2 5
2.4
1.4
1.6 0.9
1.9 0.9
2.3 1 7
1.5
0.8
gasoline of the same approximate boiling range (Table I). The obvious explanation seems to be in the high content of aromatic hydrocarbons in the vapor-phase cracked gasoline (Tables I1 and 111). Many of the cracked gasolines have very pronounced odors which militate against their use in lacquers, and even though straight-run gasolines are inferior from the standpoint of dilution ratios, they will no doubt continue to be used owing to their lack of obnoxious odor. T a b l e 11-Distillation Gasoline 1 Barompier, mm. 749 Initial O C . boiling point 48
2
3
4
R a n g e s of G a s o l i n e s 5
7
6
8
9
1
0
-I-.
749 OC.
45
743.9 743.9 743.9 7 4 6 . 8 746 8 746 8 745.7 745.7 O C . 'C. ' C . "C. "C. O C . O C . OC, 52
71
50
58
63
58
85
83 96 109 122 135 150 I66 182 198 216.5 221
95 109 119 128 137 147 157 169 185 199 211
135 '149 159 167 174 181 189.5 198 209 219 229
94.3 115 144 163 179 190.6 200 208 218 228 237
78
7c 0.f 10 20 30 40 50 60 70 80 90 95 98
80 91.5 101 109.5 119 129.5 141.5 158 186.5 218 221
87 74 101 88 115. 5 100 112. 127 137. 5 125 138.5 148 152 159 1 6 5 . 5 171. 5 1 8 3 . 5 190 205 201 213 218
102 110 118.5 128.5 142 155.5 166.5 179 194 206.5 218
160 83 189 84 206. 5 86 220 87.5 232. 5 90 240. 5 9 1 . 5 250 94 26 1 97 276. 5 102 280 107 121.5
T a b l e 111-Comparison of D i l u t i o n R a t i o s of S t r a i g h t - R u n and Cracked Gasoline Fractions DILUTIONRATIOS 7570 Ethylene glycol BOILINGRANGE monoethyl ether 75% Butyl acetate OF FRACTION 25% Nitrocotton 2370 Nitrocotton I
c.
STRAIGHT-RUN G A S O L I N E
27 to 80 to 130 to 180 t o
80 130 180 E. P.
27 t o 80 to 130 t o 180 to
80 130 180 E. P.
0.8 0.7 0.5 0.4
1.4 1.4 1.2 0.9
CRACKED GASOLINE
0.9 0.8 0.7 0.9
1.5 1.4 1.3 1.5
I n general, it will not be possible to use gasolines with heavy ends, as they will not only slow down the rate of drying in a lacquer film but, as gasoline is not a solvent for nitrocellulose, they will unbalance the solvent mixture toward the end of the drying period, with consequent precipitation of the nitrocellulose. Gasoline 10 (Table 11) is a low-boiling fraction of straight-run gasoline having a boiling range between 80" and 120" C., which seems to approximate the type of gasoline usable in lacquer work. This gasoline gave most of the solvents a better dilution ratio than was obtained with a gasoline of higher boiling range. Tests were therefore conducted with various fractions of gasoline, and in general the lower boiling fractions were found to work out better from the standpoint of dilution ratios (Figure 6).
Vol. 19, No. 0
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
980
Effect of Concentration of Nitrocellulose
The figures in Figure 7 are of interest in connection with the influence of the nitrocellulose concentrations upon the dilution ratio. The dilution ratio of a concentrated soiution of nitrocellulose is much lower than that of a dilute solution, confirming the observations of Mardles, who reached the same conclusion with respect to cellulose nitrate dissolved in acetone. Conclusions
1-The dilution ratio is a reasonably accurate measure of solvent power.
2-Other conditions remaining the same, the dilution ratios of nitrocellulose solvents are greater with respect to the aromatic hydrocarbons than to gasolines. 3-The glycol ethers have better dilution ratios with respect to the aromatic hydrocarbons than the butyl esters. With respect t o gasoline the ratios are approximately equal. 4-Cracked gasolines are better diluents than straight-run gasolines of the same boiling range. 5-The lower boiling fractions of a given gasoline are better diluents than the higher boiling fractions. 6-The dilution ratio decreases as the concentration of nitrocellulose is increased.
The Effect of Thinners upon the Consistency of Nitrocellulose Solutions' By P. E. Marling and J. M. Purdy LOWEBROTHERS COMPANY, DAYTON,OHIO
HE purpose of these experiments was to determine the
T
effect of the addition of different thinners and various amounts of the same thinner upon the consistency of nitrocellulose solutions. These nitrocellulose solutions contained 25 per cent nitrocellulose and 75 per cent solvent. The solvent was 50 per cent ethyl alcohol and butyl acetate, and 50 per cent toluene, by volume. The addition of the thinners was based on the volume of the original solution. Thus, GO cc. of thinner were added to 600 cc. of the original solution, for a 10 per cent addition of thinner. Increasing amounts of thinner were used until the nitrocellulose precipitated out of solution and would not go back into solution upon stirring. I n the case of butyl acetate, thinner, which is a solvent for the nitrocellulose and therefore does not precipitate the nitrocellulose, the percentage was carried t o
50. The consistency was measured with a mobilometer as described by Gardner2and Parks. The weight of the plunger of the mobilometer was 151 grams and the measurements were made using additional weights (50, 100, 200, and 500 grams) which were placed on top of the plunger. The experiments were made in a constant temperature room a t 25" C. Tables I, 11, and I11 show the effect of adding different percentages of turpentine, toluene, xylene, and butyl acetate to 4-, and IO-second nitrocellulose solutions, respectively. 1 Presented as a part of the Symposium on Lacquers, Surfacers, and Thinners before the Section of Paint and Varnish Chemistry at the 73rd Meeting of the American Chemical Society, Richmond, Va., April 11 t o 16, 1927. 2 Paint Mfvs.' Assocn. U . S., Tech. Civc. 265; see also THISJOURNAL, 19, 724 (1927).
Figures 1 to 4 show in a graphic manner the effect of adding the same percentage of turpentine, toluene, xylene, and butyl acetate to 1/2-second nitrocellulose solution. The turpentine could only be carried to 35 per cent; therefore this thinner is not shown in Figure 4. These curves are representative of the results obtained with 4- and 10-second nitrocellulose solutions when thinned in the same proportion as the second nitrocellulose solution. Summary
(1) The consistency of I/*-, 4-, and 10-second nitrocellulose solutions is reduced by increasing the amounts of thihner. KO exceptions to this general rule were observed. (2) Butyl acetate, which is a solvent for the nitrocellulose and was used as a blank to compare the results of the turpentine, toluene, and xylene, has the greatest effect in reducing the consistency of the solutions. (3) Turpentine has the least effect in reducing the consistency and not more than 35 per cent could be added to any of the original nitrocellulose solutions. (4) Toluene and xylene are very similar in their effect on reducing the consistency of the nitrocellulose solutions. Percentages from 5 to 40 of xylene with '/Z-second nitrocellulose solution reduced the consistency more than the same percentages of toluene. The opposite effect was observed with 4-second nitrocellulose solution as 5, 20, 30, 40, and 45 per cent of toluene reduced the consistency more than the same percentages of xylene. The 10 per cent addition of thinner was an exception to this observation in the 4-second nitrocellulose solution. The consistency of the 10-second nitrocellulose solution was reduced more with xylene than
A
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