Colloid Chemistry of Drying Oils LASZLO AUER John D. Lewis, Inc., Mansfield, Mass.
I
in their physical state. The dispersed phase is an aggregated form of the dispersion medium. There are two types of colloidal solutions-(a) the lyophobic, of which the sulfur-water dispersion is a good example, and (b) the lyophilic, of which the gelatin-water dispersion is a typical example. The fatty oils are lyophilic colloids, but here chemically similar compounds-i. e., the mixed triglycerides-are playing the role partly of the dispersed phase and partly of the dispersion medium. The dispersed phase is in the aggregated state, and this is the part which forms the gel skeleton in the sol-gel change. It is generally known that, when lyophilic sols are coagulated by electrolytes, the coagulated dispersed phase adsorbs a part of the coagulating ions. I n such cases a so-called threshold concentration of the electrolyte must be reached before coagulation will take place. Electrolytes influence also the sol-gel change of lyophilic colloidal systems; to explain the above experimental facts, it has been assumed that gases behave in the same way in the drying of fatty oils as electrolytes on certain aqueous lyophilic colloidal systems. A certain threshold concentration of the coagulating oxygen must be present to bring about the sol-gel change-i. e., film formation. As the sol-gel change progresses, the adsorptive capacity of the gel towards the gelatinizing oxygen increases in a similar degree. In the vacuum desiccators, for example, the threshold concentration necessary for the sol-gel change is present, and therefore the drying process (i. e., 61m formation) takes place a t normal speed. As film formation progresses, the gel formed takes on a certain adsorption power for the oxygen; since the equilibrium of adsorption in the case of solids vs. gases (or liquids vs. gases) is reached within a few seconds, the adsorptive power is saturated during the short time the glass plates have been placed on the balance for weighing purposes. The adsorbed oxygen is very active chemically, and for this reason secondary chemical action may take place. However, when we consider the form of the curves showing the relation between time and increase in weight, and the fact that film formation is independent of the amount of oxygen adsorbed, the vacuum experiments show that the colloid changes occur fist, followed by oxidation (if any), and then by the sol-gel change. Not only do the gases act as a coagulating medium, but they also aggregate the dispersed phase of the isocolloid system and increase the concentration of the dispersed phase, and thus simultaneously decrease the concentration of the dispersion medium which is chemically similar. The threshold concentration of oxygen seems to be below 10 mm. and above 10-6 mm. mercury pressure. I n t.he case of other gases than oxygen-for example, carbon dioxide-the threshold concentration of gas necessary for film formation may be much higher than it is for oxygen, and the drying velocity-i. e., the velocity of film formation-may be quite different too.
N CARRYING out systematic, desiccator experiments to determine the action of water vapor on the drying processes of fatty oils, a model experiment, originally designed as a control of the other experiments, showed that drying and semidrying fatty oils dry in vacuum desiccators under 10 to 16 111111. mercury pressure. The desiccators contained a calcium chloride charge to exclude any possible humidity in the atmosphere under reduced pressure. Similar film formation was observed in air-tight desiccators, charged with calcium chloride, in atmospheres of carbon dioxide a t normal pressure. In both cases increase in weight occurred simultaneously with film formation. In the vacuum desiccator experiments the increase in weight was in some cases larger than the amount of oxygen present in the desiccator. In other cases it was larger than the amount of oxygen adsorbed in the desiccator but less than the total amount of oxygen present. In the latter experiments the increase in weight was followed by gravimetric determination, whereas the amount of adsorbed oxygen in the desiccator was determined volumetrically by the aid of an attached mercury manometer. The phenomenon of larger increase in weight than the oxygen adsorbed in the desiccator was also observed by other investigators who checked the above experiments. This phenomenon occurred in mercury-sealed vacuum desiccators whose internal pressures were reduced to 16 mm. mercury. The glass plates holding the thin coatings and the metal support holding the glass plates were weighed after every fourth day, and the air was evacuated to 16 mm. mercury pressure after each weighing. These experiments were described in detail in previous publications (1, 3 , 4 , 6,7,8,9,11). I n other experiments the desiccators were not opened until the seventy-ninth day. The pressure was held a t 16 mm. mercury for 30 days, and the pressure increased gradually until it reached 94 mm. on the seventy-ninth day. In a nitrogen atmosphere saturated with water vapor and having a pressure of 16 to 93 mm., a distinct step towards film formation could aIso be observed but a print-free film was found only in 1 case in 16. Experiments under oil-pump vacuum of approximately 1 mm. mercury pressure also showed film formation, whereas high-vacuum experiments under a mercury pump vacuum of 10-8 mm. pressure showed no evidence of film formation after 3 or 4 weeks of exposure. In different experiments,weight increases of 13.45,7.81, and 3.82 per cent were observed as the average for sixteen panels, and in other cases 22 per cent and still higher increases in weight were observed for individual panels in low-vacuum experiments. In all cases, regardless of the increase in weight, dry print-free films resulted. To explain these findings, a new theory of the drying process-the gas coagulation-has been developed. Gas Coagulation Theory
The fatty oils are isocolloids in which the dispersed phase and the dispersion medium are chemically similar but different 466
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The term “isocolloid” was originated by Wolfgang Ostwald. We can illustrate i t by the case of styrene. Stobbe and Posnjak (16) originally thought that the solidification of styrene is a polymerization process. However, during the solidification process they were able to flocculate the dispersed phase of the isocolloidal system of styrene by adding alcohol to a benzene solution of the solidifying styrene. This flocculated styrene phase forms with unchanged styrene as well as with other chemically different dispersion-medium gels of different hardness. The solidification of the styrene may be affected by influences which do not comply with stoichiometric proportions, and therefore this solidification of styrene cannot be considered a polymerization process, but is a sol-gel change-i. e., gelatinization of an isocolloidal sol. Since the styrene sols are lyophilic in nature, they cannot be separated by electrophoresis or by ultrafiltration. Since both the dispersed phase and the dispersion medium are chemically identical, their refractive indices are similar, and neither of the two phases is visible in the ultramicroscope. The degree of dispersion is greatest in the sol stage, whereas it is more limited in the gel form. The gels may be considered to be partially coagulated. The gels may be separated into the two phases by syneresis in which case the coagulated dispersed phase forms the xerogel and the serum the dispersion medium. The flocculation of metastyrene from the benzene solution by means of alcohol completed the separation of the two phases of the isocolloidal styrene before the sol-gel change could have occurred-i. e., before gelatinization. If the fatty oils are isocolloidal, there should be a coagulating agent for them as alcohol is for the styrene sols. Concentrated formic acid was found to be the coagulating agent for the isocolloidal systems of the fatty oils (2).
Formic Acid Flocculation If one part by volume of concentrated formic acid is thoroughly shaken with one part of fatty oil in a separatory funnel, three layers may be observed after separation which may take several days. The bottom layer is the formic acid, which dissolves only the impurities and sometimes the coloring matter of the oils. The top layer is the dispersion medium of the isocolloid system of the oils, and the medium layer contains the coagulated dispersed phase, together with a small amount of the coagulant and of the dispersion medium. If various fatty oils are treated according to the above method, quantitative differences between them may be observed. China wood oil contains the largest amount of dispersed phase. The other oils follow in the order: linseed oil, sunflower oil, poppyseed oil, walnut oil, olive oil, castor oil. It seems, therefore, that the amount of dispersed phase is in direct relation with the drying velocity of the drying and semidrying oils. The medium layer is generally similar to an emulsion, and the dispersed phase may be entirely separated from the small amount of formic acid and dispersion medium by centrifuging the medium layer a t high speed for a long period. It has been found that the dispersion medium always has a decreased iodine number when compared with the original oil, and that its solubility in acetone is also reduced. The boiled oils, containing metal soaps as driers, show an interesting picture. The boiled oils have a higher amount of dispersed phase than the corresponding raw oils, and further, the driers sensitize formic acid flocculation. The separation of the flocculated dispersed phase is much faster in the case of boiled oils. The metal soaps (driers) flocculate from the oils together with the dispersed phase. For this reason formic
467
acid can be used to determine the amount and nature of driers present in a boiled oil. Besides centrifuging, the dispersed phase may be separated from the attached dispersion medium parts and from the formic acid by fractionation. The acetone-insoluble pure dispersed phase has a decreased iodine value and is capable of forming drying oils when mixed with nondrying oils, such as olive oil or mineral oils. Table I compares mixtures of raw China wood oil and mineral oils with mixtures of China wood oil dispersed phase and various mineral o h . Table I also shows the behavior of mixtures in various concentrations from ten parts of mineral oil and ninety parts of fatty oil up to ninety parts of mineral oil and ten parts of fatty oil. The flocculated China wood oil dispersed phase has a definite action on the drying properties of such mixtures. Raw China wood oil has far more dispersed phase than any other drying oil. If the amount of the dispersed phase increases, centrifuging does not give good results within a short time, and it is more advisable to separate the dispersed phase by fractionation. The heat-bodied oils and the blown oils have a larger content of dispersed phase than the raw oils. For example, a heat-bodied linseed oil may contain more dispersed phase than a raw China wood oil. The slower drying of heat-bodied oils does not seem to be in agreement with their higher content of dispersed phase and with the above observation that the higher the amount of dispersed phase, the faster the film formation. However, this is not really a contradiction, as the gas coagulation theory explains the situation. To obtain a film-i. e., a sol-gel c h a n g e t h e coagulating minor gas particles have to penetrate to the; bottom layer of the oil coat. Where a more viscous bodied-oil film exists, the gases may reach the bottom layer more slowly. The higher concentration of dispersed phase brings about faster drying, only when oils of similar viscosity are compared. The gases may increase the concentration of the fatty oils of the dispersed phase. This occurs when a fatty oil is airblown as well as during the drying process (film formation). This statement has been proved by determining the drying velocity of the dispersion medium phase of a formic-acidcoagulated boiled linseed oil. The dispersion medium which was separated from the dispersed phase and from the metal soaps (the drying agent) dried more slowly than the original linseed oil from which it was prepared by heating the raw linseed oil with metallic soaps. The fact that it dried, however, proves that the air produced a certain amount of a new dispersed phase in the system. However, a longer time was needed for drying, as the dispersed phase had to be formed anew. Heat bodying also increases the concentration of dispersed phase. However, it is probable that small amounts of adsorbed gases, such as oxygen, are responsible for this action. The adsorbed oxygen is slowly driven off from the oil; since the upward moving oxygen particles are more active electrically (electricity is evolved because of friction during the upward movement), they cause the increase in dispersed phase concentration. This theory is substantiated by the experimental observation that petroleum-ether-insoluble acids are formed when oils are heat bodied in vacuum as well as when they are blown by oxygen. The petroleum-ether-insoluble acids are considered to be oxyacids. The heat-bodied oxyacids are similar to the oxyacids obtained in blowing processes, but chemically they contain less oxygen. Their oxygen content is somewhat lower than that of the original fatty acids, showing that the formation of petroleum-ether-insoluble fatty acids, usually considered as oxyacids, in the case of heat bodying is not connected with chemical oxidation. The following table
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TABLE I. COMPARISON OF MIXTURES Coatingo Clear (unpigmented)
Raw China Cylinder Wood Oilb Oil
%
%
10
90 67
33 66 90 100
Zinc oxide
10 33 66
Ochre (French)
Red lead
Red iron oxide (Spanish)
34 10
..
90 67
34
90 100
10
10 33 66 90 100
90 67
10 33 66 90
90 67
34 10
..
34 10
100
..
10 33
90 67
66
90
Set Days
.... .. .. .. .. .. ..
.. .. .. .. .. .. .. .. .. .. .. ..
Tacky Day8
.. .. ..
.. .. .. .. .. ..
Zinc oxide
100
*.
10 33
90 67
66 90 100
Ochre (French)
10 33 66 90 100
..
.. .. .. ..
..
.. .. 2 2 ..
..
.. ..
.. ..
.. .. ..
.. .. ..
.. ..
.. .. .. ..
..
..
.. .. .. .. ..
100
Clear (unpigmented)
.. .. .. .. ..
.. .. ..
..
34 10
China W,ood Oil Cylinder Dis ersed oil PEase 10 90 33 67 66 34 90 10
Tackfree and Dry Days
Thoroughly Dry Days
.. .. .. .. ..
.. .. .,
..
.. .. .. .. *. .. 14 14
....
..
Hard dry Hard' dry Soft 'dry Dry: somewhat taoky Wet
2 2 4 4
Hard dry Hard' dry soft 'dry Soft: dry (perspires) Wet Soft dry Soft' dry Soft' dry Soft: dry (perspires) Wet
..
..
.. .. ..
..
..
..
90
..
..
2 2
4 4 4 4
10
..
.. .. .. .. .. .. .. .. ..
'2
2
..
Soft, dry Soft, dry Wet Wet Wet
2 14
,.
34
Wet Wet Wet Wet Wet
'4 10 10
..
67
Wet Wet Wet Wet Wet
.. .. .. ..
..
..
..
Wet Wet Wet Wet Wet
.. .. .. .. ., ..
34 10
..
Condition after 14 Days
'2 2
..
.. .. .. .. ..
..
Wet Wet Wet Wet Wet
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place on the liquid-gas interface. According to Warburg, all reactions a t such interfaces may be influenced by capillary active substances. In most cases the action of capillary active substances is retarding. To investigate this point, etheric oils, known as capillary active substances, were added in small p r o p o r t i o n s (around 1per cent) to the fatty oils, and the drying of these oils was checked. Anethol, e u g e n o 1, and isoeugenol were tried. In all cases film formation was greatly retarded and the increase in weight was reduced. This action was similar t@ the retarding action of urethane on the assimilation process. The capillary active substances do not reduce the surface tension on the whole surface to an equal degree, and the lack of uniformity of this reducing action between neighboring portions causes turbidity in the films. This turbidity in linseed and sunflower oil a m s is similar to t h e turbidity of China wood oil filmsLe., to the gas checking of China wood oil in cases where the wrinkle formation is o n l y m i c r o s c o p i c . Under the microscope these turbid films of linseed oil appear hazy because of fine distribution of small globules in the films.
Effect of Electrolytes on Fatty Oils
Before classifying t h e v a r i o u B f o r m s of s o l s a n d gels of fatty 66 34 '2 oils, we have to deal with new kinds 90 10 2 .. 100 .. .. .. .. of fatty oil jellies which are pro10 90 .. .. 2 . . Medium hard dry Red iron oxide (Spanish) duced by dissolving inorganic salts 33 67 .. .. Medium hard: dry .. 2 in the isocolloidalsystem of fatty oils 66 34 .. Soft, dry ... 2 90 10 Soft, dry .. 6 with the aid of heat. 100 . . ' .,. .. ..2 Wet .. .. A weak gelatin hydrosol is divided China into three parts; to one is added B Wood Oil Floor Dispersed small percentage of sodium sulfate, Oil0 Phase to the s e c o n d is a d d e d a small 90 .. 10 .. 14 Dry, soft Zinc oxide .. 14 lo 67 .. 33 . . Tacky percentage of potassium chloride, Wet 66 34 .. .. .. .. . . Wet and the third is kept for compari90 10 .. .. 100 .. .. .. .. Wet son. The sodium sulfate increases 10 90 .. .. .. 2 Dry, hard Red lead the rate ,of g e l a t i n i z a t i o n of t h e .. 2 Dry hard 33 67 .. system as well as the melting point of' 66 34 .. .. Dry: soft . . 4 90 10 .. 14 Tacky .. the jelly formed, as it has a solidify100 .. .. .. .. .. Wet ing action. P o t a R s i u m chloride The coatings were made without driers, and the proportion of pigment to vehicle was 1 to 1. retards the gelatinization, lowers the b Heavy mineral oil. e Mineral oil with a specific gravity of 0.885. melting point of the jelly formed, and shows, therefore, a liquefying action. The author has found (6) that, if suitable different electrolytes shows the oxygen content of the acids of China wood oil before are dissolved in fatty oils with the aid of heat, the gelatinizaand after gelatinization (in per cent) : tion velocity may be increased or decreased. In the case of 17.5 A. Total aoida of raw China wood oil fatty oils the measurement of gelatinization velocity is very 15.9 3. Total acids of oil A after gelatinization by heat difficult, and the simplest method is to follow the change 14.7 C. Petrolgum-ether-insoluble oxyacids of gelatinized oil B in the melting points of the reaction products. Sodium sulfate, which h a l a solidifying action on-gelatin-water jelly, also Capillary Active Compounds had a solidifving effect on the oils. Potassium chloride, on If the gas coagulation theory is correct, the adsorption of the other haid, Lad a liquefying effect on gelatin-water jelly oxygen and the coagulating action of the oxygen must take and also liquefied the isocolloidal system of the oils. Red lead
10 33
90 67
..
2 2 4 6
1 .
Hard dry Hard' dry Soft 'dry Soft: dry Wet
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Just as it does during the heating process, which is used for dissolving the electrolytes, the raw oil thickens without the addition of any material to a thick stand oil; the so-called liquefied products are actually thicker than the original starting material, but the liquefaction can be easily observed if the product is compared with a stand oil obtained by heating under similar conditions in the absence of)any electrolyte. The anions as well as the cations have a distinct role in the process. The role of the cations seems, however, to be slightly more important. Products with different viscosities result from the reactions of chemically equivalent amounts of different electrolytes having the same anion. If the products are arranged in the order of their viscosity, the order of the cations is practically the same as that observed in many other similar tables arranged according to observations on other phenomena of colloid chemistry. LYOTROPE CATION SERIES. Different carbonates in quantities chemically equivalent to 3 per cent sodium sulfate were dissolved in linseed oil, and the viscosities of the products were compared by means of an EngIer viscometer a t 145” C. The viscosities are expressed as the time required for 50 cc. of the oil products to flow through the viscometer, as follows: Min.:sec.
Li+ 22:28 A I + + + 18:51 F e + + 6:55
> > >
Min.:sec.
Na’
10:45
>
Ba++ 16:37 >
Zn++
6:35
. .
M i n :sec K + 9:35 > Ca++14:30 >
Min.:sec. NHd+ 4:35 Sr++ 7:35
Under the same conditions 50 cc. of raw linseed oil required only 16 seconds to flow through the viscometer. If, on the other hand, chemically equivalent amounts of different electrolytes having the same cation are dissolved, anion series are obtained which are similar to those observed in other investigations of colloid chemistry. LYOTROPE ANIONSERIES. In this series the same conditions were present as were described for the cation series, except that the cation is always sodium and the anion is variable : Min.:sec. Min.:sec. M in. :sec. Min.:sec. (COO)z-- 18:27 > SaOa-- 17:35 > SOs-- 14:50 > HCOa1 2 ~ 0 4> COa-10:45 > SO1-9:55 > NOe9:40 > BrOa9:25 > 5-8:52 > B&-8:36 > NOaI- 7:4 > CHaCOO- 6 ~ 4 5> c15:45 > Br5:25 > Sz04 4:50 > I4:45 > HPOI-4:40 > C N 3:30 > CNS2:51
Thus t,he nature of the chosen electrolyte is one of the most important factors of the reaction. Further factors influencing the reaction are the concentration of dissolved electrolyte in the final product, the duration of heating, and the state and kind of gases present in the reaction chamber. It has been found, for example, that in vacuo the results differ from those obtained a t ordinary atmospheric pressure, and that under increased pressure the results are again different. After a certain maximum is reached, the solidifying action changes into a liquefaction process and the viscosity decreases. This action seems to be caused by the gases present in the reaction chamber, and with a further slight addition of electrolyte the liquefaction process can be again changed into a solidification process. The viscosity changes are probably due to changes in the electrical structure of the material. Oils solidified by the aid of electrolytes may show consistencies varying between those of vaseline and of common rosin. If the applicability of different fatty oils for this process is studied, it is found that the different oils give different results under the same reaction conditions. For example, the viscosities of solidified oils containing 5 per cent sodium bicarbonate decrease in the following order : China wood oil > castor oil > linseed oil > rapeseed oil > &h oil > sunflower oil > olive oil. When the solidified oils containing inorganic electrolytes
469
are used for making varnishes, they yield faster drying products than similarly heat-treated fatty oils which do not contain such electrolytes. If the solidified oils are vulcanized with sulfur, the resulting factice, when applied in rubber compounding, has much better properties than a similar factice not containing the electrolytes. The rubber mixes containing such factices show high tensile strength and improved elongation and aging properties.
Aggregation and Polymerization The isocolloidal fatty oils form various types of sols and gels. The relation between these different types of sols and gels is seen more clearly after consideration of the conception of aggregation and polymerization. The terminology of aggregation and disaggregation was suggested by Harries and Nagel (10) in connection with the properties of shellac resin. This resin is composed of two different solid phases existing in different physical states but having similar chemical constitutions. The two phases form a special type of colloidal system termed “isocolloidal.” Such a system may exist either in a solid jellylike gel state or in a liquid sol state. The change from sol to gel-via., gelatinization-is supposed to be a type of coagulation, which in the case of isocolloids may be accompanied by a change in the concentration of the dispersed phase. Aggregation is also a type of coagulation in which the sol-gel change does not necessarily occur. In other words, a liquid isocolloidal system may be aggregated and yet remain liquid, and a solid isocolloidal system may also be aggregated. In the case of aggregation, the degree of dispersion decreases and the particles coalesce to form coarser particles. Aggregated products show small chemical activity and solubility, and differ from chemically polymerized products in that they may be peptized to an increased degree of dispersion by simple treatment with dispersing agents ; chemical polymers are not depolymerized by such treatment. Ordinary shellac resin may be aggregated with ether containing hydrochloric acid, and this aggregated product may be peptized with the aid of fatty acids of low molecular weight-. g., formic acid. The best example of the difference between a polymerized product and an aggregated product is distyrene and metastyrene (12). Distyrene is formed by treating styrene with hydrochloric acid at high temperatures and is a liquid product having the properties of a definite chemical compound. It distills unchanged (boiling point, 312’ C.), adds two atoms of bromine to form a bromide with a deiinite melting point, and cannot be separated by physical methods into two or more different phases. It is a polymer of styrene. When acted upon by light or heat, however, styrene forms solid products with consistencies ranging between jellylike and glasslike materials. When these products are dissolved in benzene and then precipitated with alcohol, they yield a white powdery product, metastyrene, which does not show any lowering of melting point or raising of boiling point when dissolved in solvents, and does not have the properties of a definite chemical compound. In the opinion of the author, metastyrene is the most typical example of an aggregated product. Metastyrene powder forms the disperse phase in the isocolloidal system of the jellylike solidified styrene, whose hardness depends on the concentration of powdery metastyrene in the system. With increasing concentration of metastyrene the jelly becomes harder and harder, and the melting point increases. Stobbe and Posnjak also found that metastyrene forms jellies with various organic solvents, which are similar to those it forms with unchanged liquid styrene; this shows that an isocolloidal system-for example, styrene-metastyrene-is quite similar to the colloidal system benzenemetastyrene. Thus it is evident that hard glasslike jellies
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may be built up from, and contain, liquid components and may constitute a two-phase system. No formation of distinct chemical polymers of fatty oils could be proved. Compounds of fatty oils or fatty acids which would be equivalent to distyrene have not been found. The so-called polymerized oils or their acids do not contain stoichiometrical polymers and have no constant boiling points or melting points, and their molecular weights vary according to the solvents in which their molecular weight determinations are made. Their molecular weights are not constant. Therefore, it is incorrect to call the heat-bodied oils (‘polymers.” They are aggregated forms of the original oil and differ from the raw oils in two respects: (a) The concentration of dispersed phase is increased and ( b ) the dispersed phase micellae are aggregated when compared with the raw oil micellae. The fatty acids which are insoluble in petroleum ether are the acids of the aggregated dispersed phase. If aggregation occurs in the presence of oxygen, the aggregated acids may contain a large amount of adsorbed oxygen. If, however, the amount of oxygen present during aggregation (e. g., in case of heat bodying under vacuum) is limited, the aggregated petroleum-ether-insoluble acids show no increase in oxygen content when compared with the acids of the raw oil. In the section on “Formic Acid Flocculation” above, experiments were mentioned where the petroleum-etherinsoluble acids had less oxygen content than the original acids of the raw oil. Since vulcanization is a parallel and equivalent process to
aggregation in the presence of oxygen, experiments were carried out to determine the sulfur content of the various acid fractions of factices (in per cent) : Unsaponifiable matter, sol. in petroleum ether Total acids sol. in ether Acids sol. in petroleum ether Acids insol. in petroleum ether (by difference) Acids insol. in petroleum ether (direct detn.) Total sulfur in: Total acids Acids insol. in petroleum ether
0.40 77.0 24.4 52.6 57.4
0.39 76.1 24.2 51.9
16.6 18.3
15.5 17.5
These results are similar to those found for oxygen when linoxyn or any gelatinized oil, prepared by air blowing and heating, is examined. The increase in saponification number is also a mutual characteristic of oxyns and factices. The saponification number of the raw oils is increased in both cases with 100 to 200 units, as the saponification values are between 260 and 400 and sometimes still higher, instead of 180 to 200 as usual. The amount of oxygen, however, is unimportant in film formation, and it has been shown that in vacuo films-i. e., oxyns-may be formed with as low an increase in weight as 3 per cent. Also such films are infusible, insoluble in organic solvents, and nonthermoplastic. It has been possible to vulcanize electrolyte-solidified fatty oils with as little as 1.45 per cent total sulfur; the analytical results of a sample made with 1.45 per cent sulfur are as follows (in per cent) : Unsaponifiable matter sol. in petroleum ether 0.50 0.54 Total acids 91.0 90.6 Acids sol. in petroleum ether 71.4 70.4 Acids insol. in petroleum ether (by difference) 19.6 20.2 Acids insol. in petroleum ether (direct detn.) 18.6 20.0 Total sulfur in: Vulcanized sample 1.45 1.43 Total acids 1 . 5 3 1.01 (probably Acids insol. in petrolow) leum ether 1.70 1.70
All of t h e s e experimenh show that heat bodying (incorrectly design R t e d ‘ ‘p o 1y m e r i z a t i on ’’) , film f o r m a t i o n (incorrectly designated ‘ ( o x i d a t i o n ” ) , and vulcanization (factice formation) are chemically similar colloidal processes and yield similar produots.
Forms of Fatty Oil Sols and Gels The different kinds of isocolloidal gels of fatty oils are best i l l u s t r a t e d by styrene. Figure 1 shows the various forms of isocolloidal sols and gels. Into the first group of isocolloidal sols fa11 the freshly prepared styrene and the raw fatty oils. These sols contain only a small amount of dispersed phase. The action of gases, heat, ultraviolet irradiation, electrolytes, or sulfur results in isocolloidal sols with an increased proportion of dispersed phase. To this group belong the bodied oils (heat-bodied or air-blown), ultraviolet-irradiated oils, and electrolyteor sulfur-treated oils being still in the liquid stage.
sols and O I L - S Ol L + OIL-GEL I
I
GELLED OILS on OILFILMS
23
I
XEROGEL TREATED
m
OIL-SOL WALTON-MASS BECOMING LIQUID E 8
FURTHER SOLIDIFIED GELS. HARD B A K E D ORHARDLNED
T W O PHASES
O N STORAGE
SOLSAND GELS FIGURE 1. TYPESOF ISOCOLLOIDAL
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471
CAUSED BY G A S E S , HEAT; U L T R A - V I O L E T
! I
Q U I D . S O L U B L E IN OR-
GANIC S O L V E N T S .
-. __ - --
__ - -- -- -.
. S O L U B L E IN ORGANIC 5 0L V E NTS
ACTION O F S U L F U R
C---------r---------
ui
5
e )..
-
STYREN L J E L L I E S - U _ ~ ~ ~ ~ ' / ' p _ L _ E _ T _ ~ -~ -~- ~- D W ~ IAT -HTS~M~A~L _L M E T A S T Y R E N E CONCENTRA OR H E A T T R E A T M E N T
h
0
-. 4
I N S O L U B Le SHELLAC S O L U B L E . A . L S 0 PREPARED 8 Y T R E A T M E N T W I T H FORMIC ACID FROM INSOLUBLE SHELLAC
Th isocolloidal gels may also be divided into two definite classes--namely, reversible and irreversible. When the reversible isocolloidal gels are heated, they form sols; i. e., they undergo a gel-sol change. When cooled, the sols revert again to the same gel form that existed before heating was started. These reversible gels are always soluble in organic solvents. Styrene jellies with small metastyrene concentrations are part of this class; the above-mentioned electrolytes, which contain solidified fatty oils, are soluble in organic solvents, and are thermoplastic, also fall into this class. The solidified oils may be prepared directly from the raw oils as well as from the various bodied oils. Into the same class fall the partially vulcanized solidified oils and partially vulcanized raw oils which are soluble in organic solvents but are solid at room temperature. In commercial practice, before the final factice is obtained, a product may be separated which is soluble in organic solvents, is liquid when hot, and is solid and pasty when cold. Into the class of irreversible gels fall the linoxyn and other oxyns obtained from fatty oils by the action of gases; they include the dry films of drying oils as well as irreversible jellies obtained by blowing air or oxygen into the fatty oils (hot or at room temperature). To the same class belong the heatgelatinized oils, such as gelatinized China wood oil or heatgelatinized linseed oil. Into the same class belong the factices (vulcanized oils) obtained by the action of sulfur which act similarly to oxygen in forming irreversible gels. The irreversible gels belong to the so-called considerably aggregated class of irreversible gels; the styrene films, formed by the action of ultraviolet rays and gases on thin layers of styrene, are equivalent to this group. These gels are infusible and insoluble in solvents without decomposition. Besides these irreversible gels which are considerably aggregated, another type of irreversible gel exists-namely, the moderately aggregated gels. The styrene jellies which contain a high proportion of metastyrene are an example.
__
P RE P A R F n FROM .
NATURAL SHELLAC 4
BY TREATMENT - W I T H E T H E R CONTAINING HCI
Fatty oil equivalents to this group are not known to the trade. Figures 1 and 2 show the various forms of isocolloid sols and gels.
Summary Fatty oils are isocolloids which form solid f3ms in thin layers as a result of the action of gases. In film formation the gases behave as electrolytes in coagulating lyophobic colloids. A certain threshold concentration must be reached. The coagulating gases are adsorbed by the films. Such adsorption is a secondary process and is not essential for film formation. If adsorbed oxygen is the coagulating gas, chemical processes may result, but such processes are not essential for f ilm formation. The amount of adsorbed gas is unimportant in film formation. The film formation-i. e., gas coagulation-occurs in the gas-liquid interface, and it may be influenced by certain active capillary additions. Etheric oils retard film formation and metal soaps accelerate it by sensitizing the colloidal system for the gas coagulation. The action of driers is a parallel sensitizing action to that of accelerators in vulcanization. Fatty oils may be separated into two phases by formic acid, and the dispersed phase is capable of forming jellies with the dispersion medium of the oil as well as with nonfatty dispersion mediums. When electrolytes are dissolved by the aid of heat in fatty oils, they form reversible, fusible, and soluble gels. Heat bodying, bodying by air blowing, film formation, and vulcanization are parallel processes, and the colloidal structures formed are physically and chemically similar in nature. Fatty oils form various types of sols and gels. The gels may be classified as reversible and irreversible. Films, oxyns, factices, and heat-gelled oils are irreversible gels which are
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infusible and insoluble in organic solvents without decomposition. The application Of theprinciples Of colloid chemistry Opens wide possibilities in the protective coating industry.
Literature Cited (1) Auer, L.,Chem. Umschau Fette, Ole, Wachse Harze, 33,18 (1926). (2) Ibid., 35,9,27 (1928). (3) Auer, L.,Farben-Zto., 31,No. 22 (1926). (4) Auer, L.,Kolloidchem. Beihefte, 24,No. 5/9,268 (1927).
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(5) Auer, L.,Kolloid-Z., 40,334 (1926). (6)Ibid., 47,38(1929). (7) Ib
