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INDUSTRIAL AND ENGINEERING CHEMISTRY
bulky substance, are much cheaper than barley for the production of malt. Likewise, the duration of the process for the preparation is much shorter for moldy bran than for malt. For plant-scale use it should be possible to prepare the moldy bran without difficulty in equipment similar to the pneumatic malting drums now in common use. The product can then be ground wet and used like green malt, or dried and used like cured malt in the saccharification of the starchy mashes. The problems which are always encountered in going from the laboratory to the plant scale are now being investigated with regard to the production of the’moldy bran. I n the laboratory an investigation of the use of moldy bran for saccharification of starchy substrates other than corn is now in progress.
Acknowledgment The above investigation was financially supported by, and largely carried out a t the alcohol plant of, the Bailor Manufacturing Company (now Atchison Agrol Company), Atchison, Kans., during the summer of 1937. The authors wish to ex-
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press their appreciation to Leo M. Christensen for making this study possible and for his helpful suggestions during the course of the investigation.
Literature Cited Am. Soc. Brewing Chemists, Official Methods, 1936. Anderson, J. A., and Sallans, H. R., Can. J . Research, 15C, 70 (1937). Assoc. Official Agr. Chem., Methods of Analysis, 4th ed., 1935. Galle. E.. 2.anoew. Chem.. 36. 17 (1923). Oshima, K., a n i Church, M., IND.‘ExG.’CHERI., 15, 67 (1923). Owen, W. L., Ibid., 25, 87 (1933). Shaffer, P. A,, and Hartmann, A. F., J . Bid. Chem., 45. 365 (1921). Smyth, H. F., and Obold, W. L., “Industrial Microbiology”, Chap. 32 (1930). Takamine, J., J. IND. ENQ.CHEW,6, 824 (1914). Takamine, J., U. S. Patents 525,819-25 (1894); 525,971 (1894); 562,103 (1896) ; 826,699 (1906) ; 975,656 (1910) ; 991,560-1 (1911); 1,054,324 and 1,054,626 (1913); 1,148,938 (1915); 1,263,817 (1918); 1,391,219 (19’20); 1,460,736 (1921). Thaysen, A. C., and Galloway, L. D., “Microbiology of Starch and Sugars”, Chap. I1 (1930).
Evaluation of Nitrocellulose Lacquer Solvents S
EVERAL factors must be taken into consideration when a nitrocellulose solvent is evaluated. These factors vary in their relative importance according to the type of lacquer and the use to which it is applied. When contemplating the adoption of a certain solvent or solvent mixture for lacquer formulation it first becomes necessary to consider such items as the viscosity per unit of solids, hydrocarbon tolerance, cost, evaporation rate, flow-out characteristics, blush, and a number of others. However, the first threeviscosity, hydrocarbon tolerance, and cost-are of almost universal importance, regardless of the type of lacquer or its intended use. The object of this paper is to describe a method for nitrocellulose solvent evaluation by means of which a single value may be assigned to the combined viscosity characteristic and diluent acceptance of the solvent, and which, in turn, may be used to relate this combined solvency value to the cost of application. Baker (1) in 1913 first advanced the use of viscosity of solutions as an indication of the solvent strength of the mixture for nitrocellulose; Sproxton (7) in 1920 used the tolerance of the solution for hydrocarbons for the same purpose. These two procedures have been employed extensively in the industry for comparing the ability of solvents to dissolve nitrocellulose, and no satisfactory method has been advanced to replace them up to the present time. The viscosity and hydrocarbon dilution ratios of a lacquer solvent are commonly classed together under the heading of its “solvency characteristics”, but only recently has any material appeared in the literature which attempts to interpret the two sets of data and correlate them into a more flexible and usable form. Doolittle (.2) approached the problem by the utilization of phase diagrams which provide an evaluation of solvent strength by combining the two. It has been recognized for some time (5,6) that there are cases where dilution
Comparison by Means
of a Constant Viscosity Procedure V. W. WARE AND W. 0. TEETERS E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
ratio and viscosity actually furnish conflicting indications. Of still greater importance in this connection is the fact that whether they are considered separately or together, they not only fail to supply a satisfactory basis for comparison, but in some cases they tend to exaggerate the differences which exist between two or more solvents or solvent combinations and to minimize them in others. Thus it is both difficult and confusing to attempt to assign a definite solvency value to one solvent as compared with another by considering separately viscosity, on the one hand, and hydrocarbon tolerance, on the other. That there is a real need for a simple means of correlation of viscosity and dilution values becomes more evident when we consider the drawbacks associated with each of the two methods. The viscosity of a nitrocellulose solution alone in a pure solvent or solvent-coupler mixture does not serve as an adequate indication of solvent strength because costs depend largely upon the extent to which the solution may be diluted with cheaper hydrocarbon. On the other hand, dilution
JUNE, 1939
INDUSTRIAL AND ENGINEFRINO CHEMISTRY
739
ratios as such are not a dependable criterion of solvency because they furnish information concerning the behavior of a nitrocellulose solution a t the point of precipitation only and indicate nothing regarding its properties through all the intermediate stages of dilution until that point is reached. The fact that the end point in hydrocarbon titration is ill defined presents still another disadvantage. This paper deals with a method, referred to hereafter as the constant viscosity procedure, for simultaneously determining the combined
The constant viscosity procedure as outlined gives a complete picture of the effect of diluent on the action of a nitrocellulose lacquer solvent and at the same time eliminates the use of dilution ratios. The data obtained by the constant viscosity procedure may be extended to the calculation of the relative costs of solvents or diluents for actual lacquer application at spray viscosity, and an example of this method of comparison for two solvents with a typical diluent is given in detail.
l di I-
7
8
9
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0 . NITROCELLULOSE PER 100 CC. BASE LACQUER I 1
7 8 9 IO II I2 FIGURE1. VISCOSITY-COMPOSITION CURVESFOR SOLVENT A DILUTIONS (above) AND SOLVENT B DILUTIONS (below)
viscosity and dilution effect in such a way that the separate study of the two is eliminated. It affords a direct and simple means of comparing the solvency for nitrocellulose of one material with another a t any hydrocarbon dilution over the entire range of spray viscosity under conditions which approach those of actual commercial application. It has the added advantage of not demanding any titration with hydrocarbon; the latter analytical method has been beset with many difficulties, some of which are still not under satisfactory control (3). The new method replaces the qualitative “dilution ratio” with a quantitative figure.
Constant Viscosity Procedure Briefly, the constant viscosity procedure for measuring the power of solvent and solvent-diluent mixtures to dissolve nitrocellulose involves viscosity determinations of nitrocellulose solutions in three or more concentrations in the range of spray viscosity. From these data curves are drawn by plotting viscosity against weight of nitrocellulose per 100 cc. of base lacquer. The exact concentration of nitrocellulose a t any viscosity within the chosen range may be obtained from the curve Curves may be set up from experimental data in this way for any number of solvent-diluent mixtures, extending from the pure solvent under test through various degrees of dilution to the point where a cloudy solution is obtained (Table I, Figure 1). The values for nitrocellulose concentra-
1. 100 parts solvent 2. 80 solvent-20 diluent 3. 60 solvent-40 diluent 4. 50 solvent-50 diluent 5. 40 solvent-60 diluent 6. 30 solvent-70 diluent
tion a t a standard viscosity as obtained from the curves (Table 11) are in themselves an accurate means of comparing the solvency of two or more solvent mixtures; they show the amount of nitrocellulose that will dissolve over a range of dilutions to give a constant viscosity, and thus serve to combine in one set of values all of the information which has previously required both a viscosity determination and a dilution ratio. The above information is sufficient for ordinary solvent comparison purposes, but its use may be extended further. By plotting the solvent-diluent composition against the concentration of nitrocellulose at any desired viscosity as obtained from the first set of curves, a second curve (Figure 2) is obtained from which the ratio of solvent to diluent which will dissolve a given amount of nitrocellulose a t that viscosity may be read. Then, when the apparent values of the diluent and of the solvent in use as standards are known, the comparative value of the solvent strength of any new solvent composition offered to the trade may be established, whether or not its market price is known. For example, assume that the values of the diluent and solvent A used in a lacquer are 30 and 62 cents per gallon, re-
INDUSTRIAL AND ENGINEERING CHEMISTRY
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VOL. 31. NO. 6
solvent-diluent ratio of 55 to 45 for solvent A and 45 to 55 for solvent B. At this point it is possible to set up three separate comparisons: (1) The point of minimum cost for solvent A -Grams Nitrocelluloae/lOO Cc. Base LacquerQmay be compared with the solvent B-diluent mixture con-Composit,ion6 7 8 9 10 11 12 Solvent Diluent aec. 880. sec. 8ec. aec. sec. sec. taining the same weight of nitrocellulose; (2) the point of minimum cost for solvent B may be compared with solvent Solvent A A-diluent a t the same weight of nitrocellulose; or (3) the two 100 0 .. . . 44 24 .. 00 55 24 .. 59 767.2 90.2 .. .. 80 20 .. 1 . 4 100.3 minimum points may be compared with each other. The 60 40 .. 38:O 4 7 . 3 62.1 8 6 . 0 . . .. 50 50 40.0 51.6 7 0 . 5 100.5 .. .. broken lines in Figure 3 indicate these three possibilities. 40 60 36:O 4 6 . 0 6 3 . 3 9 6 . 7 .. .. .. If course 3 is adopted and the two solvents are compared Solvent B at their points of lowest cost, a labor cost factor is introduced .. .. .. 444.7 2.9 5 1 . 2 6 4 . 4 85.5 100 0 immediately since the same total volume of the two bases is .. .. 55.1 71.8 .. 20 80 .. .. 40:3 51.9 63.5 91.0 .. 40 60 not required to apply a given weight of solids. The only ex.. 43.0 53.7 71.7 .. .. 50 50 ception would be the entirely fortuitous case in which the two .. 38:8 47.9 63.9 88.0 . . . . 40 60 .. 4 5 . 2 63.2 9 2 . 7 . . *. .. 70 30 mixtures dissolved identical quantities of solid at the miniVisooaity in No. 7 cup at 25' C. mum point. Hence such a comparison may be removed from further consideration in this paper. The constant viscosity procedure recognizes the importance of, and to a large extent TABLE11. NITROCELLULOSE CONCENTRATION AT VARIOUS excludes, the labor cost variable by offering either or both of DILUTIONS AND CONSTANT VISCOSITY the two firsbnamed methods of comparison in preference t o Grams Nitrocellulose/lOO Co. Base Lacquer5 the third. In either of these two the ultimate value on which Parts Parts w-cost comparisons are based is the ratio of solvent to diluent Solvent Diluent Solvent A Solvent B necessary to give a lacquer solution containing a standard 10.1 11.3 100 0 9.9 10.9 80 20 amount of solids per 100 cc. of solution a t a viscosity most 9.4 10.4 60 40 8.9 9.9 50 50 applicable to the problem a t hand. It should be pointed out 8.3 9.2 40 60 that a change in the cost of any of the volatile ingredients may .. 8.2 30 70 change the solvent-diluent ratio a t which minimum cost is oba At 70-seoond viscosity (No. 7 oup at 25' C.). tained, but no additional experimental details would be required in such a case. I n order to complete the comparison of the two solvents, spectively, and that the manufacturer offers a new solvent B reference is again made to Figure 2. Here the solvent Bwith essentially the same evaporation rate as solvent A a t the diluent ratio which gives the same solvency performance a s same price of 62 cents. Assume also that this lacquer is the minimum-cost solvent A-diluent ratio of 55 to 45 (e. g., applied a t a viscosity of 70 seconds. Table I1 indicates that dissolves 9.2 grams of nitrocellulose) is 40 to 60. I n the same a t a viscosity of 70 seconds an 80-20 mixture of solvent A and way the solvent A-diluent ratio which corresponds to the diluent will dissolve exactly the same weight of nitrocellulose minimum-cost solvent B-diluent ratio of 45 to 55 (e. g., disas a 50-50 mixture of solvent B and diluent-that is, 9.9 solves 9.6 grams of nitrocellulose) is found to be 65 to 35. grams. However, an accurate comparison cannot be made After the correct ratios of solvent to diluent have been thus on this basis since there is no assurance that either the 80-20 mixture in one case or the 50-50 in the other is the most economical under the circumstances. Hence the solvent-diluent mixture of minimum cost for each solvent is established by calculating the relative costs of several different dilutions as obtained from Figure 2 and shown in Table 111. These costs 90 are then plotted against nitrocellulose content in each case to obtain cost curves (Figure 3) from which the most economical mixture, or mixture of minimum cost, may be obtained for each solvent. TABLEI. VISCOSITY-NITROCELLULOSE CONTENTAT VARIOUS DILUTIONS
Q
'ooR=Y=L4
TABLE 111. COST VALUESOF SOLVENTAND DILUENTFOR CONSTANT VISCOSITY AT CERTAIN NITROCELLULOSE CONTENTS AND CORRESPONDING DILUTIONS
-
Grama Nitrocellulose/ 100 Cc. Base
..
a
'
+
Solvent: Cost of Solvent DiluentQ Diluent Ratio Solvent A Solvent B 1oo:o $0.15399 SO. 13676 0.12742 0.14103 80:20 0.13177 60:40 0.12115 0.13041 55:45 0.11700 0.13048 50:50 0.11660 0.11633 0.13054 45:55 40 :60 0.11726 0.13058 30:70 0.12300 nitrocelluloae at 70-second viscosity.
Solvent B 11.3 10.9 10.4 10.1 9.9 9.6 9.2 8.2 To dissolve 100 gram8 of
Solvent A 10.1 9.9 9.4 9.2 8.9 8.6 8.3
E! 70
.....
As the proportion of lower priced diluent is increased, the cost of the solvent mixture decreases until such a point is reached where the decrease in nitrocellulose solubility overcomes this factor. Figure 3 shows this point to lie close to a nitrocellulose content of 9.2 grams in the case of solvent A and 9.6 grams for solvent B. Figure 2 shows a corresponding
I
I
9
I
IO
I
II
I
0 . NITROCELLULOSE PER 100 CC. BASE LACQUER
FIQURE2. SOLVENT-DILUENT NITROCELLULOSE SOLUBILITY CURVES AT 70-SECOND VISCOSITY
INDUSTRIAL AND ENGINEWUNG CHEMISTRY
JUNE,1939
.established in each case, the true value of solvent B in relation to the standard solvent A at the points of minimum cost for each solvent is merely a matter of calculation (Table IV). At a nitrocellulose content of 9.2 grams, solvent B has an increased value over solvent A in the ratio of 62 to 74 cents per gallon, and a t 9.6 grams in the ratio of 62 to 76.2 cents. As mentioned previously, the comparative value of a new solvent may be established by means of this procedure even though the market price is not definitely known, or the manufacturer may make use of it in setting a tentative value on a new product intended for solvent purposes. I n addition, a similar procedure may be followed for the evaluation of a diluent or a solvent coupler simply by comparing its effect on the solvent strength of the solvent to be used with the effect of a diluent of known value on the same solvent.
741
mixtures made up in various proportions will dissolve to give 100 cc. of base lacquer a t a viscosity of 70 seconds on the Parlin No. 7 cup a t 25” * 0.1’ C. (4). This is an efflux type of viscometer in which the time in seconds required for 50 cc. of material to flow through an orifice 0.07 inch in diameter is used as a measure of the viscosity. This method was chosen because of its simplicity and because this type of viscometer is generally used in the lacquer industry.
Conditions of Testing Since the constant viscosity procedure was devised primarily as a method of comparing the solvent power for nitrocellulose of the numerous solvents now offered for lacquer formulation under conditions approaching those of actual application, an effort was made to simplify the experimental details as much as possible and still maintain high accuracy. For this reason all of the work has been carried out on a volume rather than a weight basis; that is, all nitrocellulose concentrations are in grams per 100 cc. of solution, and all solvent.diluent ratios refer to percentage by volume. This method has the added advantage of being in agreement with the usual plant practice where thinning is done by volume and with actual film application where the important consideration is pounds of solid per gallon of lacquer.
0 . NITROCELLULOSE PER 100 CC. BASE U C Q U E R
FIGURB3. SOLVENT-DILUENT COST CURVESAT 70-SECOND VISCOSITY OF VALUBOF SOLVENT B IN TERMS TABLEIV. CALCULATION OF SOLVENT A ON A GALLON BASIS4
Solvent A Nitrocellulone/lOO cc., base lacquer, grams 9.2 Solvent A-diluent ratio 55:45 1 3.5 Value of diluent in mixt. at 30 cents/ al., cents 34.1 Value of solvent A in mixt. at 62 cents/kgal., cent6 Value of 1 gal. of mixt., cents 47.6 Solvent BTdiluept ratio 40:60 18.0 Value of diluent in mirt. at 30 oents/gal., cents Value of solvent B in mixt., oents 29.6 Value of 1 gal. of solvent B, cents 74.0 62 :74 Comparative value, solvent A to solvent B 4 Based on minimum cost points of solvent plus diluent.
Solvent B 9.6 65:35 10.5 40.3 50.8 45:55 16.5 34.3 76.2 62 : 7 6 . 2
A single lot of standard, dry, ’/z-second nitrocellulose was used throughout; since the weights were in the range of 6 to 12 grams, all weighings were made to within *0.02 gram of t h e desired amount. For greatest accuracy the weighed nitrocellulose was dissolved in an amount of solvent necessary t o make somewhat less than 100 cc. of solution; after the nitrocellulose had dissolved completely, enough additional solvent was added to make the total volume up to exactly 100 cc. All volumes were measured a t 25” C. An examination of a number of lacquers made in this manner showed that for the range of concentration employed (6 to 12 grams in 97 to 94 cc. of solvent mixture) the nitrocellulose dissolved to occupy a volume in. cubic centimeters of solution equal to half of its numerical weight in grams. This observation was checked closely, found not to affect the accuracy of the results seriously, and adopted. By its use the procedure was simplified considerably in that with a given weight of nitrocellulose the volume of solvent necessary to form 100 cc. of solution could be calculated and added at the beginning (e. g., 10 grams nitrocellulose 95 cc. solvent mixture = 100 cc. base lacquer). In this paper the experimental data involve the determination of the quantity of nitrocellulose which solvent-diluent
+
Viscosity values are obtained for three or more nitrocellulose concentrations with each mixture, and the quantity of nitrocellulose is chosen so that at least one value is below and one value above 70 seconds. However, in a later paper which will deal with the constant viscosity procedure as applied to specific solvents diluted with toluene, the viscosity values cover the entire range of practical spraying and demand a larger number of determinations. All samples were tumbled a t an identical rate for 24 hours to ensure complete solution. The viscosity measurements were made within 48 hourq after the ingredients had been mixed. The recorded viscosity in seconds for the three or more nitrocellulose concentrations with each solvent-diluent mixture is plotted against grams of nitrocellulose, and the curves so obtained are used to express the results as grams of nitrocellulose per 100 cc. of solution a t any viscosity common to all the mixtures-in this case, 70 seconds. By using the above curve and choosing viscosity values a t random for purposes of checking the accuracy of the method, it has been established that for nitrocellulose concentrations of 6 to 12 grams per 100 cc. the values obtained are within 0.1 gram of the correct value. Thus in no case can the error be considered to be greater than 2.0 per cent.
Literature Cited (1) Baker, J . Chem. Soc., 103, 1653-75 (1913). (2) Doolittle, IND.ENQ.C H E M . ,30, 199-203 (1938). (3) Doolittle, P a i n t Oil Chem Rev.,99, 26-8 (1937). (4) Gardner, “Physical and Chemical Examination of Paints, Varniahes, Lacquers and Colors”, 8th ed., p. 585 (1937). (5) McBain, J. Phys. Chem., 30, 312-52 (1926). (6) Mardles, J. SOC.Chem. I n d . , 42, 2 0 7 - l l T (1923). (7) Sproxton, Brit. Assoc. Advancement Sci., Colloid Rept., 3, 82-9 (1920).
PRESENTED at the 96th Meeting of the American Chemical Society, Milwaukee. Wis.
