Formulation of Nitrocellulose Lacquers - American Chemical


tion rose enough to touch the drum, men started to brush the surface vigorously with steel wool to preventrusting until platingstarted. Then the surfa...
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July, 1928

I N D U S T R I A L A N D ENGINEERING CHEMISTRY

r. p. m. The generator was started and water run into the tank through a fire hose. As soon as the level of the solution rose enough to touch the drum, men started to brush the surface vigorously with steel wool to prevent rusting until plating started. Then the surface was brushed with steel brushes every 15 minutes for the first 24 hours and every half hour thereafter. By observing the surface during rotation, it was possible to detect any spots that were not plating and a little extra rubbing here soon gave a complete coat of zinc. Since about one-fifth of the drum's surface was submerged, it was only plating one-fifth of the time. Based on the amperes flowing, it was calculated that the zinc was plating a t the rate of 0.0001456 inch in thickness per hour. The specifications called for inch, so the electroplating was carried on for 100 hours. Of course, any shutdown would have been disastrous. To meet emergencies, pump connection to pump out the solution quickly, fire hose to wash the drum surface, etc., were provided, but fortunately these were not brought into use. During the plating, the solution was checked by taking pH readings and adjusted from time to time by the addition of salts. At the end of the 100 hours, the solution was pumped out of the tank and the drum was kept rotating. The amperage dropped as the level of the solution went down, and as soon as contact of the liquor with the drum surface was broken

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the ammeter indicated zero. The drum was immediately washed with water and steam, then quickly wiped and dried, and finally the finished surface was wire-brushed. Careful examination showed the galvanizing had been put on evenly, heavy, hard (not spongy) and, in general, was a satisfactory job. Calculation of Weight of Deposit

A final check on the thickness of the coating gave the following interesting figures: (1) The actual zinc deposited as determined by loss in weight of anodes less tares, etc. = 169 pounds ( 2 ) Area of cylindrical surface of drum = ?r (' 5 ) 2 lo 67 = 285squarefeet 4

(1) + ( 2

(3) Pounds deposited per square foot, i e

=

= 0.593 pound

285 Specific gravity of zinc = 7.14

Weight of 1 square foot of zinc l , =

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inch thick

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x 62 12 X 64

7 14

0.582 pound

Therefore, the hourly depositing rate as figured by the current flow checked very closely with the actual deposit as calculated from the weight of zinc used.

Formulation of Nitrocellulose Lacquers' H. E. H o f m a n n a n d E. W. Reid MELLON IXSTITGTE

O F INDUSTRIAL

RESEARCH, UNIVERSITY O F

PITTSBURGH, PITTSBURGH, P A

I t is t h e purpose of this paper to develop a s y s t e m a t i c c o n s t i t u e n t s among themH E formulation a n d m e t h o d of lacquer formulation, based on the use of selves remains constant, but manufacture of nitroexperimental d a t a scientifically obtained a n d reprethe ratio of the volatile to the cellulose lacquers is a sented graphically by m e a n s of the t r i a n g u l a r con o n - v o l a t i l e varies as the part of our growing chemical o r d i n a t e chart. An a t t e m p t is m a d e t o show how the former evaporates. Likewise, industry which has not been properties of both the volatile a n d non-volatile porthe ratio between the solvents, subjected t o such accurate t i o n s of a lacquer m a y be studied, a n d their variation the alcohol, and the hydrochemical or scientific control w i t h changes in composition is recorded d i a g r a m carbon, changes during the as is warranted by its impormatically. It is also i n t e n d e d t o indicate how t h e s e drying period. For this reatance. As the industry has d a t a a n d charts m a y b e used to f o r m u l a t e new lacquers son it is essential, not only grown and the competition or to Predict Propertiesthat a proper balance of the has become keener, the need volatile constituents be presfor scientific formulation of ent initially, but that this balance be maintained throughout lacquers has become more urgent. A number of methods of testing lacquers have been given in the literature, but scientific the drying period. The various steps in lacquer formulation are not clearly procedures of formulation are lacking. The methods offered in this paper are given as suggestions for a systematic scheme defined since they are interdependent, and it is somewhat of lacquer formulation and are accompanied by a correlation difficult to show them in a logical or definite sequence. These of experimental data. It is believed that methods of this steps may be divided as follows: nature will aid in materially increasing the efficiency and (1) Determination of the properties desired in the finished decreasing the tedium and intricacy of lacquer formulation. product. A nitrocellulose lacquer consists essentially of two parts(2) Determination of the ratio of non-volatile constituents. (3) Selection of the non-volatile ingredients to be used viz., the volatile and non-volatile portions. The non-volatile (4) Selection of the volatile ingredients. part consists of nitrocellulose, resin, and plasticizer (the pig( 5 ) Determination of the composition of the volatile portion ment will be treated as an auxiliary component). The volatile portion consists of the nitrocellulose solvent, an Properties alcohol, and a hydrocarbon. This division includes all types of lacquers and is shown diagrammatically in Figure 1. The properties of a lacquer will depend upon how and for In the formulation of a lacquer, it must be considered that what purpose it is to be used. An automobile lacquer must the composition varies continuously from the moment it be hard but not brittle, durable. have good adhesion, and leaves the container until it is thoroughly dry as a film on the capable of being rubbed to a high gloss. The nature of the surface to n-hich it is applied. The ratio of the non-volatile solvent is of minor importance, except where applied over an old finish. Presented before the Division of Paint and Varnish Chemistry A household brushing lacquer should brush easily, have at the 75th Meeting of the American Chemical Society, St. Lours, hio April 16 t o 19, 1928 fair gloss and hardness, but need not have as great durability

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as an automobile lacquer. The solvent is of importance since a strong or disagreeable odor is undesirable. It should not "lift" old paint or varnish and the solvents should evaporate quite slowly since this factor contributes to the brushability. A furniture lacquer should possess a fair gloss, be somewhat flexible, yet hard enough to permit sanding and polishing. Lacquers for other special purposes will have different properties. It is not possible to obtain all of the desired properties in one-lacquer, and the ideal lacquer has not been found. 1

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Note-All materials used were of ordinary commercial grade. Unless otherwise specified, all solvent compositions are b y volume and all other proportions are by weight.

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widely. All the lacquers were pigmented, since the majority of commercial lacquers are used in a pigmented form. The pigment used in all tests was of the same nature and composition, and was present in the ratio of 1 : 2 (by weight) to the non-volatile vehicle. EXPERIMEKTAL PRocmwRE-In order to prepare a series of mixtures of varying composition, it was necessary to have available solutions or mixtures, each containing only one non-volatile ingredient. The solvent used throughout these experiments had the same composition, which was as follows: toluene, 70; Ansol, M.L., 5; ethyl acetate, 15; Cellosolve, 5; Cellosolve Acetate, 5 per cent.

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An illustration of this fact is shown in Figure 2. This is a triangular coordinate chart2 representing the system nitrocellulose-resin-plasticizer. It is known that an increase of the nitrocellulose content improves the toughness of the film but decreases the gloss; an increase of the resin improves the gloss but also produces a more brittle film; an increase of the plasticizer adds to the flexibility but detracts from the hardness. These facts are shown graphically in the diagram, where any composition of nitrocellulose, resin, and plasticizer may be represented by a point. It is obvious that this point cannot be in the region of maximum hardness and maximum adhesion or some other region a t the same time. With the materials a t present available to the lacquer technologist it is not possible to prepare a lacquer which will have the maximum of all the properties desired. Determination of Non-Volatile Composition The composition of the non-volatile part of the lacquer will depend primarily upon the properties selected above as being m o s t important. I n almost all cases a compromise must be made in certain respects, but t h e f i n a l composition s h o u l d represent the highest degree of each property attainable. I n order to explain clearly the method used to achieve this result, it will first be n e c e s s a r y t o t a b u l a t e the various P L * T I I r i s p r o p e r t i e s , or attributes, considered in lacFigure 2 q uer formulation and then to study the effect on each of variation in the composition of the non-volatile portion. For the purpose of this paper the following lacquer properties may be mentioned: gloss, adhesion (to metal), flexibility, hardness (printing), ease of sanding and polishing, durability (out-door exposure), blushing, lifting (of varnish) and brushing properties. The experimental data obtained to show the effect of the non-volatile composition on the properties are presented in Figure 3. They are obtained on a series of lacquers having the same solvent composition and the same solid ingredients, but the ratios of the latter to one another varied NlTRDCllLUiOIL

9 For the use of these charts in lacquer technology, see Hofmann and Reid, IND. END.CHEM.,20, 431 (1928).

The nitrocellulose solution consisted of 20 per cent (dry weight) of 'lrsecond R. S. nitrocellulose in the above solvent. The resin solution was 50 per cent dewaxed dammar in the above solvent. The dewaxed resin was prepared by dissolving Batavia dammar resin in 90 per cent commercial benzene, then adding a double volume of denatured alcohol ( c o m p l e t e l y denatured, formula No. 1) to precipitate the wax. When the wax had settled, the clear solution was placed in a d i s t i l l i n g flask and most of the solvent removed. The thick r e s i d u e was poured into shallow pans and placed in a v a c u u m oven for about 8 hours a t a temperature of 60' to 75' c. and a Figure 3-Properties of Nitrocellulose pressure Of to 2o In all lacquers theLacquers pigment equals 33I/a per cm. of mercury. cent of non-volatile content The plasticizer used was commercial dibutyl phthalate. Since nitrocellulose is the only ingredient common to all the mixtures, the pigment paste was ground in a nitrocellulose solution of the following formula: h src H 8 ~ a ~ i r r i u i a r r

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Parts b y wt. Nitrocellulose (dry), l/r-second Special solvent mixture Zinc oxide Prussian blue Bone black

150 2200

700 400

100

Per cent by wt. 4.3 62.0 19.7 11.2 2.8

This paste was ground in a pebble mill for 75 hours. A medium blue color was chosen as being fairly representative, and permitted such properties as gloss and blushing to be easily noted. The compositions of the test lacquers are given in Table I. Gloss. The gloss of all the panels, both bare and surfaced, coated with the above test lacquers, was practically the same throughout the series. Readings were made on the Ingersoll Glarimeter and all lacquers gave values between 55.5 and 57.0 on the Ingersoll scale. This may be expected from the fact that the percentage of pigment in the nonvolatile residue was the same in all cases. It is thought, however, that a number of commercial lacquers having the same pigment and other solids, but varying in the proportion of each, would give films of widely differing gloss. Besides giving the same readings with the Glarimeter, all the panels in the above series appeared to have practically the same gloss when observed visually. Adhesion. So far no satisfactory methods have been developed for the measurement of this property. The pro-

July, 1928

I N D U S T R I A L ALVDENGINEERING CHEMISTRY cedure used in this work was essentially that proposed by Sub-committee XXV of Committee D-1 of the American Society for Testing M a t e r i a l s . A moderately heavy double coat of each lacquer was sprayed on a steel panel, 10 by 15 em.; and, while still wet, a strip of good quality crepe de chine, 3.76 by 20 cm., was stretched and placed firmly upon the lacquer film, the ends of the cloth being pulled down slightly beyond the ends of the panel. The panels were allowed to dry in a horizontal position, and were observed after standing for 24 hours. The results of this preliminary test were negative, the strips of cloth being very easily lifted from the panels, having absorbed the lacquer, and leaving a well-defined bare strip on the metal. In a repetition of this test two methods were adopted. One coat of lacquer was sprayed on a clean bare metal panel as before, and allowed to dry. A second coat was sprayed on, and, while wet, a strip of the silk cloth placed on the film, similar to the procedure in the first series of tests. h second strip of cloth was then placed on the film when it was nearly but not quite dry, so that very little material was absorbed by the cloth, but the latter would yet adhere to the lacquer. I n the second series it was found that the strips of cloth which were placed on last-that is, those that were not saturated with the lacquer -gave the best results. The method needs considerable i m p r o v e m e n t , however, and the observations are only approximate. On Figure 3 the dotted lines show approximately the divisions containing the combinations exhibiting good, fair, and poor adhesion to bare metal (steel). As expected, the adhesion varies inversely as the amount of n i t r o c e l l u l o s e present. Flexibility. There are some objections to the method for testing the flexibility of the lacquers on the basis that the property tested may not be entirely flexibility but may also depend upon adhesion. The test is easily made, however, and the results are of interest. Two coats of each lacquer were sprayed on a piece of tin plate which had been previously sandpapered and cleaned thoroughly with solvent. After drying for 2 days, the tins were tested by quickly bending them double over a 0.5-cm. iron rod a t a temperature of 25" C. The lacquers were then divided into two groups, those that cracked upon being bent double and those that did

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not. These are indicated in Figure 3, and a line has been drawn separating the more flexible combinations from the less flexible. It must be understood that the values obtained in this series of experiments are only approximate, and are not applicable when a different resin or a different plasticizer (such as an oil) is used, but the general trend of variation will be similar. It is advisable for the individual investigator to study in this manner the properties of the nonvolatile ingredients he intends to use. When a series of charts similar to those being described in this paper has been prepared, a lacquer may easily and quickly be formulated for any given purpose with the assurance that it will have the desired properties when finished. Other properties, as humidity resistance, settling of pigments, resistance to extreme temperature changes, resistance to ultra-violet light, outdoor durability, and, in the case of data intended for brush lacquer formulation, the brushing properties, may be quantitatively determined and plotted on an appropriate triangular chart, against the non-volatile composition. Selection of Non-Volatile Ingredients

The choice of the non-volatile ingredients to be used in a lacquer does not appear to rest on any easily recognizable scientific basis, but seems to be more or less arbitrary. The chief considerations are price and availability. The lowviscosity, or 1/2-second, nitrocellulose is the most widely used member of its class, since it may be used in greater amounts without unduly increasing the viscosity of the lacquer solution. This results in greater film thickness, hence greater gloss and more protection per coat, which are desired in most present-day lacquers. I n certain cases where a thin film is particularly wanted, or where gloss and depth of film are not so important as strength, the higher viscosity types of nitrocellulose are used. It will be seen that the choice of the types of this fundamental ingredient is really restricted by the use to which the material is to be put. In the common use of the term "nitrocellulose lacquer," whether an automobile, a household brushing, or an architectural lacquer, it is generally understood that l/Z-second R. S. nitrocellulose is involved in the formulation. This type has become a fairly well-defined article of commerce. The choice of plasticizers is almost as limited as that of nitrocelluloses. From the standpoint of commercial availability, the dialkyl phthalates and the triaryl phosphates are the only ones of major importance. The properties of dibutyl and diamyl phthalates and tricresyl phosphate make them the most popular members of these groups. There seems to be little real difference in their merits and the price is usually the deciding factor. From time to time various compounds are proposed as lacquer plasticizers, some of which appear to have considerable merit, but their widespread adoption is usually restricted by their high price, inadequate supply, or some undesirable physical or chemical property. The oils now being used advantageously in nitrocellulose lacquers include castor oils, both raw and blown, rapeseed, and blown linseed oil. Of all the commercially available oils these seem to possess the most desirable properties for this use. Tung oil is objectionable on account of its odor and its tendency to "crystallize;" raw linseed and other ram oils, such as corn oil, cottonseed oil, etc., are too thin, and cannot be used except in very limited quantities. In general, the drying oils tend to become hard and brittle with age, thus changing the nature of the lacquer film. This leaves the non-drying oils of the castor oil type holding the preferred place for this particular use. Contrary to the relatively narrow choice in the cases of nitrocellulose and plasticizer, there is a bewildering array of resins from which to choose. A discussion of the properties

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Selection of Volatile Ingredients

The solvent ingredients to be used in any lacquer composition will depend chiefly upon the mode of application and the nature of the non-volatile components. For ex; Note-The authors prefer t o use the term “solvent” to include a n y liquid used in the volrtile part of a nitrocellulose lacquer. The fact t h a t “non-solvents” for nitrocellulose (also called “diluents”) are always good solvents ior some other ingredient of the lacquer renders the latter terms misleading and not scientifically accurate.

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which they are used, than the natural resins. D a m m a r resin is used in p r o d u c t s where good adhesion, good gloss, and pale

ample, if the lacquer is to be sprayed, the solvents used will be more volatile than if it is to be a brushing lacquer. Likewise, if a brushing lacquer is being designed, the solvents must be chosen with agreeable odor and minimum lifting action on old varnish and paint films. Furthermore, if the resin used is of the alcohol-soluble type, the solvent may not contain more than a certain limited amount of hydrocarbons; and if the lacquer contains one of the hydrocarbon-soluble oils, the presence of large quantities of the lower alcohols (which contain water) is precluded. Also, certain properties desired in the finished product indicate certain solvent ingredients, such as blush resistance and flowing properties, which require the presence of slowly evaporating solvents for nitrocellulose. There are a number of empirical practices well known to most lacquer technologists and used by lacquer manufacturers, which may be mentioned in connection with the choosing of solvents for a lacquer. A study of Figures 4, 5, and 7 will give some definite information as to why butyl alcohol, or any of the ordinary aliphatic alcohols in general, is often a desirable addition to a lacquer solvent. The data in Figure 4 were obtained by adding a non-solvent C c i i o s o ~ r cASCTATC mixture of the composition indicated by the abscissas to 10 grams of a 20 per cent solution of l/psecond R. S. nitrocellulose in normal butyl acetate. The number of grams of non-solvent added before the nitrocellulose was precipitated is given by the ordinate. It will be seen 9 5 2 ~ i L c a l a L by referring t o t h i s Figure 5 figure, as well as to Figures 5 , 6 , and 7 , that some mixtures of butyl alcohol and toluene, or, in fact, of any alcohol and any hydrocarbon, are better diluents than either the alcohol or the hydrocarbon alone. A further example of this phenomenon is given in Figure 5, where point A represents a mixture of 25 per cent Cellosolve Acetate and 75 per cent toluene, which iq not a solvent for nitrocellulose (point A ) . If, now, alcohol is added until the composition is 20 per cent alcohol, 20 per cent Cellosolve Acetate, and 60 per cent toluene (point B ) , the mixture is a good solvent for nitrocellulose. Another illustration will show the reason for the effect of the addition of an alcohol on improving the compatibility of certain resins with nitrocellulose. Figure 7 represents a mixture of equal parts of nitrocellulose and bleached shellac in the solvent system butyl acetate, butyl alcohol, and 5” xylene. Point A on this figure represents a solvent mixture composed of 50 per cent xylene, 20 per cent butyl alcohol. and 30 per cent butyl acetate. -4s indicated by its position on tho diagram, this point represents a mixture which produces a turbid film (although the solution is clear). If butyl alcohol is added to change the composition to that T.L“C“C

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able lifting action on varnish. This may be seen by referring to Figures 9 and 10, which represent the same systems, except that in Figure 9 the hydrocarbon is toluene and in Figure 10 a petroleum fraction with comparable boiling points. Although the petroleum product may be lower in price, it will be seen that a mixture which will dissolve nitrocellulose, and which has a moderate amount (5 to 10 per cent) of the high-boiling component, ecrrri< will cost more when petroleum is used than when the hydrocarbon is toluene. All this may be changed somewhat if the prices vary considerably from those given in the diagrams. Figure 11indicates the influence of petroleum hydrocarbons on the viscosity of a nitrocellulose solution or of a lacquer. The hydrocarbons used were xylene as the aromatic and a petroleum (straight-run) distillate boiling a t approximately 130-165O C. as the aliphatic hydrocarbon. The data show that up to 50 or 60 per cent of the hydrocarbon content S.&"il*C mav consist of Detroleum hvdrocarbon before Figure 6 Figure 7 the increase in viscosity is appreciable. C o m p a t i b i l i t y ChaFt o = turbid film. As suggested, there appears to be some reX = clear 6!m. Equal parts l/i.second nitrocellulose and bleached shellac. lation between the viscosity of a solution (of rating mixtures of different compositions from, but analogous nitrocellulose) and the wetting power of the solvent, but this to, the constant-boiling mixtures a t higher temperatures. has not been thoroughly investigated. It is known, however, Since xylene is a rather slowly evaporating compound, the that petroleum hydrocarbons in general have poor wetting mixture denoted by A (above) becomes, upon evaporation, power, even less than the aromatic hydrocarbons. -4 relaricher in hydrocarbon than is desirable for the formation of tive indication of the wetting power of these materials may a homogeneous film. Therefore, the addition of more alcohol, be gained from the following figures, which represent the capable of forming a constant-evaporating mixture with the quantity of liquid required just to wet 100 grams of French hydrocarbon, will remove it from the film, and a clear solid process zinc oxide: toluene 71 and petroleum naphtha (80130' C.) 82 cc. solution of resin and nitrocellulose will result. Thus, by methods The experimental basis for this theory is represented in Figure 8, which shows evaporation curves of xylene, butyl similar to those dealcohol, and a mixture of 70 per cent xylene and 30 per cent s c r i b e d , it may be butyl alcohol. The data from which these curves were possible to correlate plotted were obtained by evaporating 400 grams of each experimental data in liquid in wide, shallow pans placed in a circle a t equal dis- such a way as to extances from an oscillating fan. The purpose of the fan was plain clearly the acto increase the speed of evaporation. The pans and con- tual reasons for what tents were weighed a t regular intervals. Several mixtures are often hit-or-miss of the two ingredients were tested, but all gave curved lines procedures. when plotted, except the 70:30 mixture, which gave a straight I n T a b l e I1 a r e line, as shown. The evaporation was stopped when 95 per presented some of the cent had evaporated, and the residue analyzed by treating more important propwith several volumes of sulfuric acid. The portion insoluble e r t i e s of a l a c q u e r in the acid (xylene) closely approximated 70 per cent of the solvent residue. A number of other alcohols and bye- w h i c h depend upon the solvent, with the carbons form constant-evaporating mixtures of this type. As a final example of the use of systematic experimental commercially a v a i l data in the selection of solvent ingredients for a, lacquer, able products which mention will be made of petroleum us. aromatic hydrocarbons. meet the conditions Figure 8 There is no doubt that the former are very desirable in imposed. brushing lacquers, but this discussion will only concern Determination of Compositien of Volatile Portion the use of petroleum spirits in commercial spraying lacquers. The petroleum hydrocarbons have less solvent power (or smaller dilution ratios) than the aromatic hydrocarbons, It is in the proper adjustment of the solvent composition but are cheaper in price. Other things being equal, they pro- that the greatest changes may be made in the nature and duce nitrocellulose solutions of higher viscosity than when behavior of a lacquer, as well as the greatest differences from the aromatics are used. They are therefore not very satis- practical and economic standpoints. Since the solvent comfactory in thinners, which may also be surmised from the prises from 60 to 90 per cent of the total lacquer, it may fact that their wetting power is less than that of toluene and readily be seen that it offers the greater possibilities for savits homologs. I n connection with the first of these topics ings in cost of materials. it may be said that, at present prices, there is no marked When the nature and composition of the non-volatile part advantage in the use of petroleum hydrocarbons in ordinary of the lacquer, and the solvents that are to be used, have been spray lacquers or thinners, except in cases where it is desired determined, the behavior of this particular mixture of solids to take advantage of their mild odor or their lack of appreci- should be studied in all combinations of the solvents chosen.

shown a t B-viz., 45 per cent xylene, 30 per cent butyl alcohol, and 25 per cent butyl acetate-the lacquer will now give a clear film. Shellac is an alcohol-soluble resin: and if the lacquer does not give a clear film, alcohol is added until it does. The real reason for the behavior noted above seems to be that certain alcohols and hydrocarbons form constant-evapoB"7"L

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If there are more than three solvents, the procedure is lengthened somewhat, but generally certain arbitrary adjustments may be made, SO as to divide the solvent ingredients into three parts so that their behavior may be investigated by means of a triangular coordinate chart. A few of these arbitrary adjustments will be mentioned. (1) If it is intended to use a petroleum and an aromatic hydrocarbon together, the proper proportions may be determined by means of a chart similar t o Figure 11, and this mixture considered the hydrocarbon component. (2) If i t is desired t o use two esters-for example, a mixture of ethyl acetate and amyl acetate, or ethyl acetate and butyl propionate, instead of butyl acetate, or other single substancethat mixture having the same evaporation time (weight for weight) as the material which it is to replace may be used as a single component on the chart. The same substitution may be made in the case of alcohols. (3) Certain other combinations may be selected as single components for the purpose of studying their behavior systematically, such as equal parts of Cellosolve and Cellosolve Acetate, equal parts of ethyl alcohol and ethyl acetate, etc. Table 11-Solvents

a n d Relation to Properties of Lacquers NITROCELLULOSE T Y P E OB SOLVENT SOLV~NT ALCOHOL HYDROCARBON Good odor Cellosolve Ethyl isopropyl Petroleum (straight ~~- o~ run) Quick evaporation Ethyl acetate Ethyl isopropyl Benzene Isopropyl acetate Petroleum (low b. D.) Xylene‘ Butyl Slow evaporation Amyl esters Ethyl benzene Cellosolve Acetate Amyl Turpentine Butyl Cellosolve Petroleum (b. Cyclohexanol 17(t26Oo C.) Diacetone alcohol Non-lifting of varPetroleum Low-boiling esters Ethyl isopropyl nish, etc. Cellosolve Acetate Butyl Blush resistance Any b . >looo C. Butyl propionate Amyl Cyclohexanol Amyl acetate High tolerance of Cellosolve hydrocarbons Ethyl lactate High degree of Cellosolve All primary alAll except turstability pentine Butyl Cellosolve cohols PROPERTY

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Before the experimental method is described, a few examples of the type of chart referred to above will be given, in order to illustrate their construction and method of use. I n Figure 12 the non-volatile composition is equal parts of 1/2-second nitrocellulose and ester gum, and the solvents are butyl acetate, butyl alcohol, and xylene. The portion of the chart above the broken line includes all the mixtures of these three solvents which will dissolve nitrocellulose. It will then be seen that all combinations which will dissolve nitrocellulose are divided into two parts, those which produce a clear film (not merely s, clear lacquer solution) with the solid ingredients under investigation and those which do not. The latter are included in zone B, within the curved line at the right of the chart. All points in zone A , then, represent satisfactory solvent formulas for the lacquer in question and the final choice will then depend upon other considerations, as will be noted later. It is interesting to observe that when the hydrocarbon is toluene instead of xylene the zone of turbid films is absent and any solvent mixture above the nitrocellulose-solubility limit may be used. This is due to the difference in volatility between the two hydrocarbons, and disproves the belief sometimes held that various hydrocarbons may be substituted for each other a t will. I n Figures 6 and 7 the same solvents are used as above, but with a different resin-namely, bleached shellac. In Figure 6 the hydrocarbon component is toluene, and in Figure 7 it is xylene. As before, zone A represents satisfactory solvent compositions, and zone B those that produce turbid films with equal parts of llrsecond nitrocellulose and bleached

Vol. 20, No. 7

shellac. The difference caused by the substitution of xylene for toluene in this case is easily noted, but is not so marked as it was in the first example. The charts shown in Figures 9 and 10 represent the type obtained when two of the three components are solvents for nitrocellulose. The region in which the nitrocellulose is insoluble is then in the corner adjacent to the non-solvent and its extent depends upon the solvent or diluting power of the latter. It will be seen that the non-solvent zone in Figure 9, where toluene is the non-solvent component, is much smaller than in Figure 10, where a petroleum fraction was used. I n Figure 9 is also included a curve showing the zone compatibility of the non-volatile composition: 2 parts nitrocellulose (l/t second), 2 parts ester gum, and 1 part dibutyl phthalate. Solvent mixtures represented by points below the line M N therefore produce clear films with this combination. When the nitrocellulose, ester gum, and dibutyl phthalate are present in equal parts, they are compatible over practically the entire chart. EXPERIMENTAL PROCEDURE-The method of obtaining the experimental data for the construction of these compatibility charts is rather simple, especially when something is known regarding the general behavior of the substances being investigated. A solution is prepared (as concentrated as convenient) of the non-volatile ingredients under consideration, taken in the proper proportions, in a s o l v e n t composed of equal parts of each of the t h r e e s o l v e n t comp o n e n t s . A small p o r t i o n of t h i s is tested by flowing on a glass plate, allowing to dry, a n d n o t i n g whether the resulting film is clear or turbid. If clear, the point is noted r e p r e s en t i n g 33l/3 per cent of each Figure 9 liquid, or, if turbid, it is noted w i t h some o t h e r characteristic s y m b o l . To a weighed quantity of the base solution is then added one of the pure components, and the’ solvent composition will vary along a l i n e connecting the center point with the v e r t e x representing the component being added. The mixture is tested a t intervals Figure 10 by placing a drop or two on the glass plate (as above) and marking the chart with the appropriate symbol at the point representing the composition of the solvent when each test was made. The addition of each liquid should continue until the film changes from clear t o turbid (or vice versa) or until the nitrocellulose is precipitated. Besides adding each pure component, mixtures of 50 per cent each of two components (represented by points at the centers of the sides of the triangle) may also be used. After proceeding with part of this experiment, it may become obvious that certain additions are super-

I N D U S T R I A L A N D ENGINEERING CHEMISTRY

July, 1928

fluous, in which case they may be omitted. Figure 12 is an example of the application of this method. The mixtures of the three solvents giving clear films are marked with an 1: and those giving turbid films by an 0, and a "line of demarcation" is drawn between the two zones in the most probable position. I n order to obtain points on one side of the triangle, it will be necessary to start with a solution in the two components represented at the ends of the side-usually 50 per cent of each. This method of observing the lacquer film after drying, instead of the solution, gives information regarding the

I ,

aYI"/

.,'D.SL

Pl*
/*

W"OI(OC*IICOhS

Figure 11

behavior of such a composition in actual use. A large number of lacquer troubles due to incompatibility of the ingredients just as the final film is deposited would be obviated by a study of this kind, instead of making tests on a new formula in the pigmented form. Another practice which often leads to erroneous or disastrous results is that of adding a pigment paste ground in an oil or a resin solution to a finished clear lacquer. A heterogeneity may result which will be obscured by the presence of the opaque pigment and is only manifested by a lack of gloss, durability, or adhesion in the resulting film. Too much cannot be said in favor of investigating the behavior of the non-volatile ingredients i n the proportions in which they will exist in the film, minus the pigment. Application of the Method

I n order to show that these charts are of some practical value, the data contained on one of them (Figure 9) were used to formulate a commercial lacquer. It was desired to prepare a spray lacquer for interior finishing which would be as free as possible from residual odor. The solvents chosen were Cellosolve, denatured alcohol (free from pyridine), ethyl acetate, and toluene. The solvents should contain no homologs or impurities of strong or unpleasant residual odor, such as are frequently present in the aromatic hydrocarbons. Since ethyl acetate and ethyl alcohol are used in equal parts, they may be considered as one solvent ingredient. On Figure 9 there is a zone showing the region of suitable solvent mixtures, composed of these ingredients which give clear films with the solids: 12 parts 1/9-second nitrocellulose, 12 parts ester gum, and 6 parts dibutyl phthalate. It was accordingly decided to use this same combination in the odorless lacquer. The next step was to decide which of the many possible solvent combinations to use, and in this connection the price was the deciding factor-excepting, of course, the fact that there should be an appreciable percentage of the high-boiling solvent, Cellosolve, present. Two combinations were tested in the clear form, those designated as A and B in Figure 9.

693

It will be noted from the chart that the raw material cost of solvent A is about 59 cents per gallon and that of solvent B approximately 51 cents. The test lacquers contained 12 grams dry */2-secondnitrocellulose, 12 grams ester gum, and 6 grams dibutyl phthalate in 100 cc. of a solvent mixture composed as follows: B

4

Toluene Denatured alcohol Ethyl acetate Cellosolve

cc.

cc.

70 10 10

80 7 5 7 5

10

0

Solvent A produced a very satisfactory clear smooth film, but B tended to give a wrinkled film of a cellular nature. It was therefore decided to use mixture A as the solvent in the lacquer, and mixture B as a thinner, for reducing the lacquer to spraying consistency. The final lacquer, then, had the following composition before being thinned for spraying: 10 per cent nitrocellulose, 10 per cent ester gum, 5 per cent dibutyl phthalate, 10 per cent Titanox pigment, B u n i Acrrrrr and 65 per cent solvent mixture A (Figure 9). It gave a film which was practically odorless 30 m i n u t e s after a p p 1i c a t i o n , s i n c e t h e slowest evaporating ingredient was the Cellosolve, w h i c h is practically odorless. Assuming that the general properties of ester gum do not differ 12-Compatibility Chart greatiifrom those of EqualFigure parts l/z-second nitrocellulose and ester dewaxed dammar, the . .. gum. X clear film. 0 = turbid film. non-volatile composition of this lacquer would be represented by point M on Figure 3, and would have good adhesion, hardness, and moderate flexibility. ALEo*oL

-

Acknowledgment

The authors are indebted to E. A. Stoppel, of Valentine & Company, New York, for permission to reproduce certain of the diagrams accompanying this paper.

Determination of Ammonia in Sulfonated Oils' Geo. Lang ST. L O U I S

COLLEGE OF P H A R M A C Y ,

ST. LOUIS,M O .

0 the emulsion produced in a distilling flask by adding 10 to 15 grams of the oil to 50 cc. of water, add with constant shaking 100 cc. of 4 per cent sodium hydroxide solution. With continued shaking now add 100 cc. of 8 per cent calcium chloride solution. A gummy calcium soap precipitates, and the ammonia can be rapidly distilled off without any Iiumping or frothing into a measured portion of standard acid solution. This method yields results in close agreement with the more tedious method of shaking out an ethereal solution of the oil with successive portions of sulfuric acid as described in the works of Lewkowitsch, Holde, and Mueller. 1

Received M a y 4, 1925.

I N D U S T R I A L A N D ENGINEER1 NG CHEMISTRY

694

Vol. 20, No. 7

Catalysts for the Formation of Alcohols from Carbon Monoxide and Hydrogen‘ I-Decomposition

of Methanol by Catalysts Composed of Copper and Zinc Per K. Frolich, M. R. Fenske, and D. Quiggle

DEPARTMENT OF CHEMICAL ENGINEERING, hfASSACHUSETTS INSTITUTE

HIS paper is the first in a series dealing with studies on the fundamental nature of catalysts employed in the synthesis of methanol from carbon monoxide and hydrogen. Inasmuch as considerable information has already been procured concerning the synthesis of methanol from these gases using high pressure and diverse catalytic material,2 it was deemed advisable to make a thorough investigation of the reverse reaction-i. e., the decomposition of the alcohol-in the presence of the same type of contact substances. A study of the decomposition permits operation a t atmospheric pressure where the experimental procedure is greatly simplified, it being justifiable to suppose that the catalyst mixture giving the maximum decomposition into carbon monoxide and hydrogen will be particularly suitable for the synthesis of methanol from these same gases under pressure. Indeed, the early researches of Sabatier3 on the catalytic decomposition of methanol served as a guide in the search for catalysts for the methanol ~ y n t h e s i s . ~ This paper is limited to a discussion of catalysts composed of copper and zinc.

T

Previous Work

OF

TECHNOLOGY. CAMBRIDGE, MASS.

t h a t zinc oxide alone was a good catalyst. Patart, however, obtained better results with mixed catalysts. For example, his experiments showed that a catalyst containing 90 per cent metallic copper and 10 per cent zinc oxide was more effective than one consisting entirely of zinc oxide. Similarly, a British patent12 on the synthesis of methanol from carbon monoxide and hydrogen mentions the use of a catalyst prepared from ten molecular proportions of copper nitrate t o one of zinc nitrate. In contrast with this, other [email protected] specify that in a mixture of two oxides it is essential that the more basic be present in preponderating quantity. A large number of patents relating t o the synthesis of methanol and similar oxygenated organic compounds mention copper,14 zinc oxide,15and mixtures and alloys of zinc oxide and copper16 as catalysts. One patent,” moreover, states that zinc oxide, supposedly a non-reducible oxide, is reduced in the presence of copper, an observation which has been verified by Rogers.ls Preparation of Catalyst

The catalysts were prepared by adding ammonia to 1 mol of a mixture of chemically pure zinc and copper nitrates dissolved in 3 liters of distilled water. The solution was kept a t a constant temperature of 85” C. and thoroughly agitated by a motor-driven stirrer. Ammonia, 1 part by volume of concentrated chemically pure ammonia of specific gravity 0.89 to 2 parts of distilled water, was added a t a constant rate of 20 cc. per minute until the end point was reached, zinc and comer hydroxides being pre&itatld together.

Considerable work has already been done along these lines. Sabatier,a the pioneer in the field, studied the decomposition of methanol by copper as well as by zinc oxide. Others, as for example G h ~ s h ,Hara,6 ~ A s t u d y of the catalytic decomposition of methanol and Mannich and Geilman,’ have studied the catalytic at 360” C. a n d a total pressure of 1 a t m o s p h e r e w i t h effect of copper on the same mixtures of zinc a n d copper oxides in varying proporr e a c t i o n , while Palmer,8 t i o n s shows that the m a x i m u m decomposition a n d Rideal,@ and Constable1ohave f o r m a t i o n of carbon monoxide occur when t h e zinc investigated the decomposition of ethanol by the same oxide i s present in excess. catalyst. Patart4instudying Between 40 a n d 50 m o l per c e n t zinc oxide, the mols the decomposition and syntheof carbon monoxide f o r m e d per mol of m e t h a n o l sis, and Fis’cher,ll the syntheincrease a b o u t 350 per cent. sis of methanol, both found T h e addition of a small a m o u n t of zinc oxide to 1 Received April 23, 1928. copper oxide markedly increases the decomposition 2 Lewis and Frolich, I N D . of methanol. A catalyst composed of 3 m o l per cent END. CHEM.,20, 285 (1928). 8 “Catalysis in 0r g a n i c zinc oxide a n d 97 m o l per c e n t copper oxide decomChemistry,” pp. 234 a n d 2 4 0 poses 26 per cent of the m e t h a n o l , while p u r e copper (1923); Sabatier and M a i h I e , decomposes only 9 per c e n t u n d e r otherwise c o n s t a n t Compl. rend., 146, 1376 (1908); conditions. 148, 1734 (1909); Sabatier and Sanderens, Zbid., 136, 921 (1903). A similar p r o m o t e r effect is observed w h e n a s m a l l 4 Lormand, IND.ENG. CHEM., a m o u n t of copper oxide is added to zinc oxide. That is, 17, 430 (1925). a m i x t u r e c o n t a i n i n g 98.6 m o l per c e n t zinc oxide a n d 6 Ghosh and Chakravarty, J . 1.4 m o l per cent copper oxide decomposes 41 per cent Indaan Chem. Soc., 2, 142 (1925); Ghosh and Baksi, I b i d . , 3, 415 of the m e t h a n o l , whereas p u r e zinc oxide decomposes (1926). 33 per c e n t u n d e r parallel conditions. 0 Mem. Coll. Sci., Kyoto I m p . Copper promoted w i t h zinc oxide especially favors Unis., 9, 405 (1926). the f o r m a t i o n of m e t h y l f o r m a t e , while carbon m o n 7 Ber., 49, 585 (1916). 8 Proc. ROY. SOC. (London), oxide f o r m a t i o n i s favored by zinc oxide promoted w i t h 98A, 13 (1920); 99, 412 (1921); copper. 101, 175 (1922); 103, 444 (1923); The r e s u l t s are interpreted in l i g h t of the i n f o r m a t i o n 106, 250 (1924); 107, 255 (1925). available as to the activity of the same t y p e of catalysts 0 Zbid., 99A, 153 (1921). 10 I b i d . , 107, 270, 279 (1925). in the high-pressure synthesis of m e t h a n o l f r o m carbon 11 “Conversion of Coal into monoxide a n d hydrogen. Oils,’’ New York, 1925; IND.ENG. CHEM.,17, 574 (1925).

12 British Patent 237,030 (July 23, 1925). ISU. S. Patent 1 , 5 5 8 , 5 5 9 (October 27,1925); French Patent 571,354 (January 3,1924); British Patent 227,147 (Applied for May 23, 1924). 14 British Patent 27 1,538 (January 20, 1927). German Patents 2 9 3 , 7 8 7 (March 8, 1913); 295,202 (May 31, 1914); 415,686 (July24, 1923), British Patents 20,488 (Applied for March 9, 1914); 227,147 (Applied for May 23, 1924); 2 3 8 , 3 1 9 (August 20, 1925); 255,127 (July 12,1926); French Patents 468,427 (April24,1924); 571,354 (January 31, 1924); 581,816 (October 3, 1924); U. S. Patents 1,201,850 (October 17, 1916); 1,558,559 (October 27, 1925). 16 B r i t i s h Patents 229,715 (February 23, 1925); 2 2 9 , 7 1 4 (February 23,1925); 237,030 (July 23, 1925); 254,819 (July 9 , 1926); 240,955 (Applied for February 26, 1925); 254,760 (Applied for Octo ber 24, 1925) : French P a t e n t s 571,356 (January3,1924); 585,169 (December3,1924); U. S. Patent 1,569,775 (January 12, 1 9 2 6 ) ; Canadian Patent 271,569 (June 14, 1927). 17 British Patent 237,030 (July 23, 1925). 18 J . Am. Chem. Soc., 49, 1432 (1927).