Comparison of experimental results obtained by fat splitting in a n autoclave and by the Twitchell process shows the similarity of the reaction mechanism in both. The reaction rate increases with temperature and with amount of reagent, and changes with its nature, and the reaction is limited only by the ratio of fat to water. Fat hydrolysis is mainly homogeneous because a n appreciable amount of water is dissolved i n t h e oil phase. The splitting reagents increase the solubility of water in the oil phase: and make this water more active by liberating hydrogen ions in i t . Action of splitting reagents is due to their highly hydrated and ionizing functional groups.
REVIOUB work ( 4 )showed that, in spite of tration, which would actually accelerate splitting LuCIo LASCARAY catalytically, juqt as hydrogen ions activate the most commonly held theories, to which the Vitoria, Spain author also contributed (3),the fat-splitting rereverse reaction of esterification. This theory cannot be supported, sincc zinc action by the autoclave process is not, heterogeneoxide and magnesia, the most effective fat-splitous. This r e d i o n occurs in a homogeneous ting reagents, are insoluble in water and cannot perceptively inmedium (the fat itself) due t o t,he fact that water is slightly crease the hydroxyl ion concentration, whereas strong electrolytes, soluble in fats, particularly in acid fats and in fatty acids. such as the caustic alkalies, are poor reagents. Because of their As the author showed in the case of autoclave splitting, heteroinsolubility in water, zinc oxide and magnesia are rapidly transgeneous hydrolysis in the int,erface, which is aided by factors that formed into metal soaps during the first period of the reaction, and tend to increase emulsifying act,ion,has slight importance in relapass into t’he oil phase without exerting any particular influence tion to the more active homogeneous reaction in fat. I n the early on the concentration of hydroxyl ions in the aqueous phase. stages of the reaction, when little acid has been produced, stable The aut’hor has shown experimentally t h a t t,he various reagents and finely dispersed emulsions are formed, and the hydrolysis increase t,he solubility of water in the oil phase in the same (contrary to what might be expected according to current ideas) proportion as they accelerate hydrolysis. The conclusiori progresses slowly. After a period of time, coinciding 17-ith the follows, then, that the degree of activity of a reagent is in direct breaking of the emulsions, the reaction is strongly accelcratcd and proportion to the degree of hydration and to the valence of its goes forward quickly a t a practically constant rate. During t’his metal ion. The reagent,s dissolve in t,he fat and draw with them period fat and water are no longer emulsified, but are only mixed an aqueous “envelope” around the metal ions; this comes into and kept in a coarse dispersion by the stirring motion. When this direct contact with the glyceride molecules, and they then split stops, the two distinctly defined layers, fat and water, separate into both glycerol and fatty acid. The valence of the ion exerts immediately and completely. some kind of influence, since, for an equal degree of hydration These tests in the autoclave indicate that, as long as. eniulsions and consequently for an equal proportion of dissolved watcr, thc form, hydrolysis is slow, whereas when they disappear, the period bivalent ions are more active than the monovalent. This may of quick reaction is reached. This fact is not compatible with be due to the fact t h a t the metal ion within it,saqueous envelope previous theories that attribute greatest importance to t’heheteroincreases the electrolytic dissociat,ion of wat>erby t>heattractive geneous reaction in the interface. Thus, it seems evident that, of action that this ion exerts on the hydroxyl ions. As a congreater importance compared to the slow heterogeneous reaction, sequence, the activity of the hydrogen ions in the aqueous layer is a much more active homogeneous reaction takes place in t’he oil increased. From this theory it follows that the hydrolysis of phase, which is produced by the solution in this phase of small fats in the autoclave, like the esterification reaction, is catalyzed quantities of water. These tests show t h a t water is far more soluby hydrogen ions and not by hydroxyl ions. The well known ble in fatty acids or in acid fats than in neutral fats. This exrule is again confirmed that bhe agents t h a t catalyze a reaction plains why the reaction, in its early stages, is ma,inly heterogenealso catalyze the reverse reaction. ous, because neutral fats or partially acid fats are much more easTo summarize: ( a ) The rate of hydrolysis increases with ily emulsified than fatty acids, owing t o the strongly hydrophilic temperature, with t’he amount of reagent (to which it is in direct action of the glyceryl radical. B s the reaction progresses and proportion), and with the degree of hydration and with the these radicals are sepamting from the fat moIecules, emulsificavalence of the metal ion of the reagent; this rate, however, is tion becomes more difficult; but as the solubility of the water in independent of the amount of water used. ( b ) The reaction the partially hydrolyzed fat increases simultaneously, t’heheterolimit depends only on the ratio of fat t o wat,er; it is independent geneous reaction is progressively supplanted by the homogeneous of temperature and of the quantity and nature of reagent. reaction in the oil phase, and then hydrolysis reaches its greatest, Therefore, velocity and limit of reaction are to some extent velocity. This is kept, up almost constantly during the major part antagonistic, for the factors that influence one of them have no of the process, until it reaches a limit; then the decrease in glycereffect on the other. ides and the increase in glycerol concentration, which aids the opposing reaction, lead t o a n expected final decrease in velocity. TWITCHELL PROCESS Accordingly, three reaction periods are defined, for which the author proposes the names “emulsive hydrolysis,” ”rapid hydrolyThe Twitchell process differs from the autoclave process in that sis,” and “terminal hydrolysis.” During the first period, usually the reaction takes place in a n open vessel a t 100” C. in an acid short, the reaction is heterogeneous; during the other two, it is medium and with a reagent, usually a n alkylarylsulfonic acid. essentially homogeneous. The work t o be described was carried out t o determine whcthrr To accelerate splitting in the autoclave, the industry uses rethe above observations regarding the hydrolysis mechanism in agents such as zinc oxide, magnesia, and lime. These react’ with an autoclave might also be applied to the Twitchell process: fatty acids t,o form metal soaps insoluble in water but readily soluble in fatty acids, The activity of these substances was previRound-bottom flasks of I-liter capacity are closed with a cork pierced by two glass tubes, One tube, 1 em. in diameter and 80 ously considered to be due to the increase in hydroxyl ion concen-
786
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
100
$80 Lj 0 a a 60
% kbo W w
g 20 n
4
0 Figure 1.
8 TIME
12 16 20 IN HOURS
24
Effect of Reagent on Hydrolysis
em. long, serves as a reflux condenser. The other tube is thinner and reaches the bottom of the flask; the upper end is closed by a rubber tube fitted with a clip, By means of a pipet a sample of the boiling mixture can be removed without interrupting boiling. The flasks are submerged in oil baths heated by electricity to 115' to 120 C. I n each-flask are placed 300 grams of fat and the desired quantities of distilled water, reagent, and 60" BB. sulfuric acid. Small fragments of porous porcelain kee the boiling steady, and its intensity is regulated so t h a t about Ralf of the reflux condenser is hot. Fat, water, reagent, and acid are introduced into the flasks, previously heated t o 100' C. Evaporated water, condensed in the air cooler, flows back into the flask. The weight loss after 48-hour boiling is negligible, ranging between 0.5 and 2.0 grams. Periodically, without interrupting boiling, samples of about 10 ml. are withdrawn. The fat ik separated ahd washed twice with distilled hot water. After rapid drying, the acid and saponification numbers are determined. The degree of hydrolysis = (100 x acid number) /saponification number. Since the error in this simple calculation is relative, the conclusions are not affected by it. Unless otherwise specified, good quality beef tallow was used, with a n acid number of 0.6 and a saponification number of 201. Distilled water was generally used. The reagents were the commercial products Divuslon, Pfeilring, and Neokontakt (designated D, P, and N), and a reagent made according t o Twitchell's formula (designated Tw). The sulfuric acid concentration was 60" BB. (78% HeS04). The amounts of water, reagent, and acid were based on 100 parts of fat. O
The curves representing the progress of the reaction as a function of time have the S-shape typical of all splitting reactions. T h e curves rise at first and then straighten out until they reach the maximum velocity, which is kept almost constant during the major part of the process. Finally they approach asymptotically a limit value of the degree of hydrolysis, which is the equilibrium position of this reversible reaction under the conditions of the experiment. I n contrast to what happens in the autoclave, the two phases do not completely emulsify a t the beginning. The separations into two.layers is easy, although both of them are turbid, which indicates the presence of secondary emulsions. A mFhite foam forms a t once, similar t o the foam produced in an aqueous solution of the reagent. This shows t h a t the latter dissolves in water. T h e reagents are not soluble in neutral fat. When melted fat and Twitchell reagent are mixed, the reagent falls t o the bottom of the flask or remains as a coarse dispersion. On the contrary, with fatty acids the reagent is completely dissolved and a transparent solution is obtained at once. This behavior explains what happens during the hydrolysis of fats. At the beginning the reagent acts exclusively in the aqueous phase, where it decreases the surface tension, produces foam, and emulsifies, b u t the reaction is slow. This is the initial period of L'emulsive hydrolyr sis." As the reaction goes fdrward, t h e formation of foam decreases and soon stops. At the same time the velocity of the
787
reaction has increased, and when ebullition stops for a moment, the layers t h a t separate immediately are less turbid than they were before. During this period t h e reagent has been passing from the aqueous phase t o the oil phase, and when this transition is completed, the maximum speed of reaction is attained. The reagent dissolved in fat loses its emulsifying properties but acquires its greatest activity. The heterogeneous reaction of the first period gives way t o a homogeneous one, which has t o be in the oil phase where the reagent is dissolved. T h e period of rapid hydrolysis has been reached and is characterized by an almost constant speed. During this period emulsification plays a n insignificant part. Slight stirring keeps t h e water saturated in the oil phase and removes from it, by washing, the glycerol produced. However, t h e increase in the glycerol concentration in the aqueous phase and the decrease is triglyceride concentration in the oil phase finally effect a rapid decrease in t h e velocity of the fat-splitting reaction which approaches a limit, depending entirely on t h e amount of water present. T h e limit is not affected by the quantities of reagent ormlfuric acid used. This is the "terminal hydrolysis" period. HYDROLYZING ACTIVITY
Figure 1 and Table I show the hydrolyzing activity of the different reagents. It is difficult t o establish a relation between this activity and the composition of t h e reagents, because they are ill-defined mixtures of different components. However in each reagent t h e sulfonic group, SOaH, is joined t o a long chain of fatty hydrocarbon and t o a n aromatic ring. T h e long hydrocarbon chain makes the reagent soluble in t h e fat, and the strongly hydrated and ionizing SOaH group brings t o this solution the water necessary for hydrolysis. The aromatic ring gives stability to the molecule by acting as a bond between the SOaH group and the hydrocarbon chain. The emulsifying power of the reagent is not a factor, since the curves of Figure 1 show t h a t the most effective reagents have the shortest emulsive hydrolysis period. T o shorten this initial period and increase the activity of the reagent, its solubility in water must be reduced. Figure 2 and Table I1 show t h a t the addition of sulfuric acid improves the reagent activity. Tvhis effect has not been explained satisfactorily b u t is generally attributed t o the increase in hydrogen ion concentration produced by the acid. However,
TABLE I. DEGREE OF HYDROLYSIS (IN PERCENT)WITHVARIOUS REAGENTS
-
-
(Distilled water, 60%; reagent, 0.5%; 60' BB. sulfuric acid, 0.2%) Time, Hydrolysis Hr. D N Pa Tw
a
~
Reagent many years old.
TABLE 11. DEGREE OF HYDROLYSIS (IN PERCEXT) WITH DIFFERENT QUANTITIES OF SULFURIC Acrn Time, Hr.
-
(Distilled water, 60% ; reagent, 0.57c,) 60' BB. Sulfuric Acid-0 . 0 % 0 2% 0 . 4 % 0 . 6 % 0 . 8 % l.OY0 1 . 5 % 2 . 0 7 0 Reagent D
5 8 24
28.0 46.0 84.5
41.0 62.0 89.5
5 8 24
33.0 48.0 80.5
.. .. ..
5 8 24
11.3 24.5 71.5
24.0 42.0 84.0
55.0 72.5 90.0
59.0 76.0 90.5 Reagent N 50.5 68.5 , .: 89.0 Reagent T w 28.0 32.5 52.5 61.0 87.5 89.0
.. .
61.5 78.0 90.0
66.0 81.0 90.0
66.0 79.0 90.0
71.0 82.5 90.0
54.5 73.0 89.5
.. ..
56.0. 74.0
. . .
.. .. ..
36.0 61.0 89.5
41.0 63 0 89.5
40.5 61.5 88.5
..
90.0
INDUSTRIAL AND ENGINEERING CHEMISTRY
788
the curves of Figure 2 show that the effect of the acid is far from being proportional to the hydrogen ion concentration; the first addition of 0.3% of acid produces approximately the same acceleration as a further addition of 1.7%. Thc curves also show that sulfuric acid shortens the emulsive hydrolysis period, which almost disappears. This action is connected t o the property of the sulfuric acid of decreasing the water solubility of the reagent.
TABLE IV.
Vol. 41, No. 4
PER CENT HYDROLYSIS WITH VARIOUSOII~WATER RATIOS (Tw reagent,
Time, Hr. 5 8
0.5%: sulfuric acid in water, 0.75%)
Hydrolysis 60% HzO 28.0 52.0 87.0
r--
20% Hz0
34.0 51.5 78.6
24
TABLE v.
INFLUENCE O F OIL-JVATER
HYDROLYSIB
.-
100% Hz0 19.0
51 .O 93.0
RATIOON
IiIhlIT O F
( F a t , palm kernel oil; T w reagent, 1.2%; sulfuric acid in water, 0.75% boiling time, 48 hours) Degree of Degree of H10, Hydrolysis, Concn. of HnO, €Iydrolysis. Concn. of % % Glycerol, % % % Glycerol, %
600 100 40' 20 15 13
97.8 92.5 86.0 72.5 70.3 66.7 65.6
12
0
8 I2 16 20 24 TIME IN HOURS Figure 2. Effect of Various Amounts of Sulfuric Acid o n Hydrolysis 0
4
Addition of a little sulfuric acid t o an aqueous solution of Twitchell reagent makes the solution turbid if it was clear or more turbid if it was turbid already, until the reagent separates into droplets. In the presence of acid fat,, which tends t o withdraw the reagent from the water, the sulfuric acid action is stronger, and the reagent goes more quickly and more completely into the oil phase; therefore the reaction is more active, since it takes place almost exclusively in the oil phase. Thus, the action of sulfuric acid may be considered due to a decrease in the solubility of t h e reagent in water. As a rule it may be assumed t h a t all factors t h a t decrease the reagent's solubility in water increase its activity.
OF HYDROLYSIS (IN P E R CEXT) TABLE 111. DEGREE FERENT QUANTITIES OF REAGENT
(Distilled water, 60%) Tw 1.0% Tw, Hr. 0.2%'HzSOr 0.4% HzSO4 48.5 a 5 27.0 66.5 8 44.5 89.0 24 84.0 After 2 hours, 9.5. Time,
,
0.57
WITH
DIF-
38.4 38.6 33.9 21.1
14.6 16.7
limit. As fat hydrolysis has no heat of reaction ( 2 ) , this curve possesses, for a given fat, an abjolute value which is influenced neither by temperature nor by reagent. I t s h o w t h a t to obtain a high degree of hydrolysis the final glycerol concentration must be kept very low. For example, in the case of palm kernel oil, t o attain 98% splitting, the final glycerol concentration must bc only 2% a t most. The widespread practice of prolonging ebullition for many hours increases the degree of hydrolysis in the mass only a3 water condenses. The same effect can be obtained in a shorter time by using a greater amount of water. Best industrial practice is t o replace the glycerol-water phase by pure water as boon as the rapid speed of hydrolysis declines. As Figure 5 shows, systematic enriching of the glycerol-water phase in splitting vats, such as sugar diffusers, may raise the glycerol concentration to about 35 to 40%. It is surprising that such a method has not get been employed. Table VI shows how the hardness of the water decreases the reagent activity Hard water is very detrimental when the reagent is used alone, but has little effect in the presence of sulfuric acid. The reagent probably reacts with the hardness of water to yield magnesium and calcium salts. Since these salts are more soluble in water than is the reagent, they pass with more difficulty into the oil phase; therefore substantial amounts of reagent are kept away from the splitting action. Sulfuric acid limits or prevents t>histransformation.
2.0% Tw 54.0 74.5 91 .o
The influence of the quantity of reagent is shown in Figure 3 and Table 111. The curves indicate that the reaction rate increases with a n increase in the concentration of reagent, but all of them tend to reach the same limit. Therefore the reagents act as catalysts and increase the velocity of the reaction without changing its limit. As Figure 4 and Table Is' show, Fater acts in the opposite way. When the amount of water increases, the rate diminishes a t first, but the curves, after crossing, tend t o reach a higher limit in accord with the law of mass action. Table V shows, for palm kernel oil, the effect of water on the equilibrium of the reaction; the degree of hydrolysis after 48-hour boiling (the practical reaction limit) is shown to be a function of the initial amount of water. Figure 5, drawn from data in the last column of Table T', shows the influence of glycerol concrniration on the reaction
64.7 60.3 57.9 48.5 43.2 42.0
11 10 8 3 5 4
2.03 10.6 20.4 33.0 37.0 38.6 39.2
-
100 r-
0 e
r 1 --
8
12
16
20
TIME IN HOURS Figure 3. Effect of Various Amounts of Twitchell Reagent on Hydrolysis
24
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
April 1949
TIME F i g u r e 4.
IN HOURS
Effect.of V a r i o u s R a t i o s of Fat to W a t e r o n Hydrolysis
MECHANISM O F FAT HYDROLYSIS
The foregoing experimental results indicate a complete analogy in regard to the reaction mechanism of bo@ the autoclave and Twitchell processes. I n both, the main reaction is carried out in the oil phase and is helped by the dissolution of appreciable amount of water in this phase. Water solubility in fats, especially in fatty acids, increases greatly with temperature. Above 200' C. and a t pressures sufficient to maintain water in a liquid state, the water solubility in the oil phase may become considerable. I n the Victor Mills continuous hydrolytic process (1), the fatty acids leaving the top of the column a t about 250' C. contain 15 to 20% dissolved water. This explains that a t high temperatures hydrolysis may be possible with water alone, whereas a t lower temperatures i t is necessary to use reagents t o stimulate the reaction and obtain acceptable rates. Suen and Chien (6) also infer, from values obtained in splitting with sulfuric acid, that acid hydrolysis is carried out in the oil phase.
789
greater part of the metal oxide remains in suspension in the aqueous phase. I n this stage hydrolysis progresses slowly, aided by the emulsifying power of the metal soap formed. As the reaction progresses, the metal oxide is being neutralized and passes as metal soap into the oil phase. When this process is finished, homogeneous hydrolysis in the fat reaches a maximum and becomes the only reaction, as the increasing quantities of fatty acid produced make emulsification more difficult. Twitchell reagents, easily soluble in water, are insoluble in neutral fat. They remain, therefore, in the aqueous phase a t first and catalyze emulsive hydrolysis. Nevertheless, on account of the solubility of the reagents in fatty acids'as the reaction advances, they pass to the oil phase. Stirton, Hammaker, Herb, and Roe ( 5 )studied the reagent distribution between the aqueous and oil phases, and found that the reagent concentration in the nonaqueous phase increases as hydrolysis advances. With a sufficient 'amount of fatty acid, all of the reagent goes into t h a t phase, emulsification disappears, and hydrolysis progresses as a homogeneous reaction. I n this way the reagents of the Twitchell process carry into the fat the strongly hydrated SOaH groups, which increase water solubility in fat. At the same time, these groups liberate hydrogen ions, and the water molecules activated by these ions are in the best condition to produce glyceride hydrolysis. I n a similar way the'basic oxides of the autoclave process dissolve in fat as metal soaps and draw around the metal ions an aqueous cover which produces an increase in the solubility of water in fat. T h e metal ion, which partially ionizes the water covering it, fixes hydroxyl ions around it, The ionic equilibrium is displaced and the concentration of hydrogen ions increased. This explains why alkali hydrates are poorer reagents than zinc or magnesium oxides. The alkali ions cannot fix hydroxyl ions as strongly as zinc or magnesium ions, and so the hydrogen ion concentration in the aqueous cover is less. I n both processes the water molecules, carried by the reagent into the oil phase and activated by the hydrogen ions, are those which promote hydrolysis. For hydrolysis with pure water, without reagents, much higher temperatures are needed to increase both the water solubility in fat and the electrolytic dissociation of this water. By means of reagents the sameteffect may be obtained a t much lower temperatures-hence the widespread use of reagents in fat splitting. CONCLUSIONS
'
1. Splitting reactions in the autoclave and in the Twitchell process function according t o the same mechanism. The reaction is chiefly homogeneous and is carried out in the oil phase, under the influence of the water dissolved in thi$ phase, activated by
TABLE VI. U L U "0 10 20 30 40 %GLYCEROL
The different reagents used in the autoclave and Twitchell processes .act in exactly the same manner. Those used in the former process are inorganic and basic; in the latter, organic compounds giving an acid reaction. Kevertheless, both increase the water solubility in the oil phase and activate this dissolved water by liberating hydrogen ions in it. Basic oxides of the autoclave process are not the actual reagents, but the metal soaps they produce on combining with fatty acids. I n the first stages of the reaction, assuming the fat t o be slightly acid, the
HYDROLYSIS (IN PERCENT) (60% water, 0.5% reagent)
Without HzSOa
Time,
Hr.
F i g u r e 5. Influence of Glycerol Concentration on Hydrolysis Limit
INFLUENCE OF TYPEOF WATER=ON DEQREE OF
A
C
B
0.4% 60' BB. H z S O r A B C
Reagent D 21.5 55.0 53.0 44.0 69.0 61.0 31.0 72.5 68.0 90.0 90.0 88.0 Reagent N 5 33.0 24.0 10.3 50.5 39.5 35.5 8 48.0 35.5 13.8 58.0 52.5 68.0 24 80.0 68.0 32.5 89.0 .. ,. Reagent Tw 6 11.3 19.2 8.5 28.0 28.5 21.0 * 8 24.2 33.5 10.7 62.0 52.5 42.0 24 71.5 75.5 28.3 88.0 84.0 87.5 A = distilled water; B = sprin water, 9 French degrees total hardness (3.5O temporary, 5.5O permanent): = well water 40 French degrees hardness (21° temporary, 19O permanent). One Frenili degree is equivalent t o 10 parts per million.
5 8 24
(I
28.0 46.0 84.5
33.5 48.5 85.0
8
790
INDUSTRIAL AND ENGINEERING CHEMISTRY
hydrogen ions. The heterogeneous hydrolysis in the interface takes place only in the initial stage. I t s speed is low compared with that of the homogeneous reaction. 2. The reagents of both processes act similarly-that is, by dissolving in the oil phase as the reaction goes on, increasing the water solubility in it, and activating the water by liberating hydrogen ions. The requirements for a good reagent are strong solubility in fats and weak solubility in water, and the presence in the molecule of ions or functional groups which are strongly hydrated and capable of producing free hydrogen ions directly or indirectly. 3. The rate of hydrolysis increases with temperature and amount of reagent. It also depends on the nature of the reagent, 4. The reaction limit depends exclusively on the ratio of fat to water; it is greater when the proportion of water increases.
Vol. 41, No. 4
It is independent of temperature and of amount or nature of reagent used. LITERATURE CITED
(1) Anon., ~ o a pP,e r f u m e r y , and Cosmetics,20, 1090 (1947). 44, 105 (2) Kaufmann, H. p., and Keller, M. C., Fette U . Setfenen, (1937). (3) Lascaray, Lucio, Seifensieder-Ztg., 51, 755, 895, 915 (1925) ; Anales SOC. sspcin., f f s . y qulnz., 25, 332 (19271, (4) Lascaray, Lucio, Seifensieder-Ztg., 64, 122 (1937); Fette u. S e i f e n , 46, 828 (1939); Analesfis. quam., 41, 878 (1945). (5) Stirton, &4.J., Hammaker, E. M., Herb, S.F., and Roe, E. T., Oil & Soap, 21, 148 (1944). (6) Suen, T.-J., and Chien, T.-P., IND. ENG.C H E ~ 33, ~ . ,1043 (1941). RECEWED riugust 28, 1947.
Emulsion Polvmerization of Acrvlic d
e
inyl Monomers
Esters an
W. C. MAST AND C. H. FISHER Eastern Regioltal Research Laboratory, Philadelphia 18, P a . T h e previousIy reported study of emulsion polymeriaation of acrylic esters was extended. It was demonstrated that many types of latex containing various acrylic polymers and copolymers can be prepared and that the eniulsifying system has a profound effect on their properties. Emulsions containing 60y' resin were prepared satisfactorily. The emulsifying systems and conditions developed for acrylic esters, which differ in several respects from those recommended for dienes, are suitable for the polymerization of certain other vinyl-type monomers.
STUDY of the preparation of resin emulsions or dispersions from certain monomeric alkyl acrylates and the effect, of various ingredients in the emulsion was reported previously ( 1 9 ) . This study was extended because of the importance of resin einulsions as such in several applications and the fact t h a t emulsion po1,ymerization affords a convenient method for converting monoiner into polymer. In the study reported here,'attention was directed toward (a)use of additional types of emulsifiers, ( b ) preparation of high-solids latices by direct polymerization, (c) preparation of 2-chloroallyl alcohol copolymers in high- and low-solids latices, ( d ) polymerization and copolymerization of the higher alkyl acrylates, ( e ) use of various organic peroxides a s polymerization initiators, (f) continuous polymerization, and (0) use of emulsifying systems found to be suitable for acrylates in the polynierization of certain other vinyl monomers. Because of the possibility that acrylic esters might hydrolyze during the emnlsion polymerization and yield polymers or copolymers of acrylic acid, the resistance of certain alkyl a ~ r y l n t ~ teos hydrolysis under appropriate experimental conditions was investigated briefly. The observations made in studying these several points are concerned with several factors that are important in determining the properties of resin emulsions (4,19). These factors include the constitution of the film absorbed around the dispersed particles, the nature and particle size of the dispersed phase, solids concentration, pH, and relat,ive specific gravities of the t w o phases. EXPERI3IENTA L
The procedure most frequently used in this laboratory for 'the routine preparation of a vide variety of polymers and copolymers is described below. Since the ,same procedure iyas used also t o
prepare the ernulsions of the present work (except when otherwise indicated) a detailed account of the method is given. Parts by Weight
Water Triton 720 (based on monomer)a Tergitol paste S o . 4 (based on monomer) J l o n o m e r (ethyl acrvlate) Ammonium persulfate (sufficient t o produce polymeriaation at refluxing temperatures) Q
Chemical nature of emulsifying agents used
IS
200 O5to1 1 to 2 100
0.005
givon in Table I1
Water and the water-soluble ingredients were charged into a round-bottomed, three-necked, ground-glass joint flask fitted with a stirrer, reflux condenser, and thermometer well. The solution was stirred nit,h anchor, paddle, or half-moon-type stirrers a t 50 t o 150 r.p.m. The monomer and any remaining ingredients were then added, and the flask was heated until refiuxing occurred. Flasks ranging in size from 200 ml. to 12 liters were used, and were generally filled Do 60% capacity. Heat was applied intermittently, if needed, t o induce polymerization. If the polymerization did not start within 10 minutes after refluxing first occurred, additional ammoniuni pcri;ulfate was added. If excessive quantities of catalyst mere requlred, the monomer was not considered to be of the proper purity. The reaction usually proceeded a t a rat,e sufficient t,o cause refluxing without external heating for 15 to 30 minutes without flooding the condenser. Heat was t,hen applied, and the refluxing temperature raised t o 93 t o 95' C. for completion. The emulsion was then steam distilled for 15 t o 30 minutes. To obtain the polymer, the hot emulsion was run slowly int,o twice its volunie of hot (approximately 90" C.), rapidly stirred 3 t o 570 sodium chloride solution. The precipitated polymer in the form of discrete particles was washed with hot water until free of salt and dried. Polymers prepared in this manner were soluble in organic solvents such a3 toluene, benzene, ethyl acetate, acetone, and dioxane, whereas those made with substantially larger amounts of catalyst were not. I€ the emulsion itself was desired, i t was cooled and poured into storage vessels. Some polymerization initiators are capable of cross-linking soluble polymeric alkyl acrylates (18). It is of interest t o compare the proportion of persulfate used by the authors with the larger quantities (approximately 1%) employed by other workers (19) in the copolymerization of butadiene with various vinyl monomers. Redistilled monomers were used and in general precautions previously described (19) regarding elimination of detrimental impurities were observed. I n the present, report, low- and high-solids refer to emulsions containing 30 to 45Vo and 45 to 60% internal phase, respectively. The percentage of total solids was determined b y evaporating volatile matter from a known quantity of emulsion.
