The Emulsifying Powers of Bentonite and Allied Clays derived from

T H E EMULSIFYING POWERS OF BENTONITE AND ALLIED CLAYS, AND OF CLAYS DERIVED FROM THESE BY BASE EXCHANGE AND BY HYDROLYSIS BY R. M. WOODMAN AND E. MCKENZIE T A n O R

In a previous paper of this series1the character and properties of bentonite were discussed, and it was demonstrated to consist mainly of sodium clay. Thus its suspension in water yielded free sodium hydroxide by hydrolysis; it will be shown here, among other things, that the sodium can be replaced by other metals by the process known as base exchange, or by hydrogen as a result of hydrolysis. A 7 percent. aqueous bentonite suspension was shown to be an efficient emulsifying medium for many oils and non-aqueous liquids, but one result was rather singular: bentonite was found to be capable of promoting both types of emulsion with cresylic acid and water.’ Such a result warrants further investigation, as it might have an important bearing on theories concerning the mechanism of emulsification, “as it is at present understood that a given emulsifying agent only promotes one type of emulsion with any two given liquids to be Moreover Weston3 states that “colloidal clay” is capable of forming the dual types with (fixed) oils and water; no details as to the type of clay under experiment were given, the term “colloidal clay” evidently being thought sugcient. The present work is concerned mainly with attempts to cause specified clay-containing substances to promote the dual types of emulsions with water and fixed oils. The character, properties, modes of preparation (where necessary) and occurrence of the clay-containing substances (usually designated somewhat broadly in emulsion literature as “colloidal clays” or “clays”) are discussed in their separate sections.‘ Woodman and hlcK. Taylor: J. SOC.Chem. Ind., 48, 121T(1929). Clayton: “Emuleions and Their Technical Treatment,” 31 (1928). Weston: Chem. Age, 4, 604,638 (1921). 4 It should be understood that natural clays such as bentonite and the so-called soil clays, usually, (although designated as sodium clays, calcium clays, acid clays, etc., in virtue of replaceable sodium calcium or hydrogen), contain other replaceable elements besides that specifically menkioned in the name. Thus a natural sod~umclay may also contain re laceable calcium, magnesium, hydrogen, etc., being a mixture of aluminosilicates. I n ad&ion to the clay proper of a natural clay, there is commonly contained other material: silt (silica), organic substances such aa alkali-soluble humus, free chalk (calcium not replaceable), alumina, iron oxide, etc. Thus a so-called clay is not a true clay, but is a clay-containing substance. Agriculturally, clay is defined aa that portion of a soil which will remain in suspension in a de th of 8.&cm. of yater,for 24 hr., (Le., has articles less than 0.002 mm. in diameter). The f a h y of t s d e h t i o n is a t once a parent even if coarse non-clay material is sedimented by this process, it is possible &at much k e silica, alumina, iron oxide, organic matter, etc may still be in suspension either because of fineness of division, or because of the protec$ve action exerted by the clay itself and by the organic matter. 2 J

&,

R.

M.

WOODMAN AND E. MCKENZIE TAYLOR

Experimental The method of experiment was as follows: an aqueous suspension of the clay emulsifier, ground to I O O mesh to the inch,’ was made; in all cases the suspensions, unless specially mentioned to the contrary, were one percent. This comparatively low concentration was adopted because in the previous experiments with bentonite* a 7 percent. suspension seemed to yield primarily OW typesJ3which might very probably have been due to the comparatively large amounts of free sodium hydroxide (produced by the hydrolysis of so much bentonite) favouring this type. Thus it is conceivable that, in a one percent. aqueous suspension of, say, a fully-saturated sodium clay, the whole of the replaceable sodium is present in solution as the result of hydrolysis in the form of sodium hydroxide a few minutes after making; removal of the hydroxide, e.g., by chemical interaction with the non-aqueous liquid component of the emulsion system, should then allow the residue of the clay-variously styled a “completely-unsaturated,” “hydrogen” or “acid” clay, and often supposed to be chemically inert-to exert its emulsifying action alone, and a WO type might result. It will be seen later that these “inert” clay residues are possibly very chemically active in certain emulsion systems, even though a true acid clay be obtained by removal of all replaceable metals and replacement by hydrogen. The aim was to make the dual types of emulsion in a given system by any means. For this reason the phase-volume ratios employed were altered greatly, as a certain preponderance of a given phase tends to make that phase the continuous one if dual types are a t all po~sible.~Different mechanical treatments during preparation were also employed, as mechanical treatment has often a great effect, especially if the phase-vdume ratio selected happen to be that common to both types.* Standing various emulsions, followed by reshaking of different kinds, was also employed as a possible artifice for obtaining the dual types.4 The oils employed were: I , oleic acid (pure “frozen out”); 2 , linseed oil (R. D. H. Oleum Lzni Opt., guaranteed in accordance with the I?. P. (1914)~ a t w o year old sample kept in a blue bottle and possessing an acid value 0 . 7 3 in terms of percent. of oleic acid5); 3, the same linseed oil plus free oleic acid (labelled hereafter “acid” linseed oil), so that the acid value was 5.8 percent. oleic acid5; 4, olive oil, (a two year old sample stored in a brown bottle, possessed of an acid value 1.20 percent. oleic acid5, and labelled “B. D. H. This, therefore, includes particles much greater than those of clays. McK. Taylor: loc. cit. 3 0 W means, throughout, the oil (or non-aqueous liquid)-in-water type; WO the reverse. Woodman: J. Phys. Chem., 30, 658 (1926); 33, 88 (1929); Woodman and Gallagher: ibid., 33, 1og4(1929).Woodrnsn: J. Pomol.Hoi-t. Sci.,4, 18 (1925). I t has been found that the age of the emu1s:fying medium, and of an emulsion wkch is to be re-shaken, often influence the type formed by subsequent shaking. In these papers the influence of the relative densities of the phases on the character of the cream, and the connection between character, amount of cream and emulsion type are fully discussed. Fryer and Weston: “Oils, Fats and Waxes,” 2, 125 (1920).

* Woodman and

‘

EMULSIFYING POWERS OF BENTOKITE AND ALLIED CLAYS

301

Obum Olivae, ‘Cream’,’’ guaranteed genuine olive oil; 5 , B. D. H. liquefied phenol; 6 , B. D. H. cresol (mixed isomers or cresylic acid), guaranteed in accordance with the B. P. (1914); 7 , hexalin (cyclo-hexanol); 8, methylhexalin; and, 9, B. D. H. petroleum ether, boiling range IOO-I~O~C., guaranteed

to conform to the standards of purity given in “The B. D. H. Book of A. R. Standards.” This last oil was used as a kind of control which should indicate the type of emulsion actually favoured by the emulsifier, for the petroleum ether was “inert” and neutral, whilst it is conceivable that the free sodium and calcium hydroxides derivable from certain clays by hydrolysis with water might react with free fatty acids and phenols. The suspensions and the oils were pipetted into 50 C.C. cylinders (the less dense phase slowly and carefully on to the other’), and the type of emulsion formed was judged by appearance, drop tests and observations on the character and quantity of the cream;‘ the results are given in the tables under the respective sections, the times indicating in every case the age of the suspension used in making, or on re-shaking, an emulsion’. I n previous experiments two methods of preparation were chiefly used:’ I , immediate vigorous or vigorous intermittent shaking (labelled hereafter IVS), and, 2 , gentle partial rotation (equivalent to very gentle, “languid” shaking followed by vigorous shaking) , labelled henceforth GPR. The vigorous shaking was from the elbow down, the elbow acting more or less as the pivot on which the lower portion of the arm was swung for the shake. A third method of shaking was also employed in the present experiments; this was immediate and vigorous long arm shaking (labelled LAS) and consisted of vigorous and continuous long shakes, the whole arm being kept stiff and swung as freely as possible from the shoulder. This third method was adopted as a result of accidental observations; had it been used before it might have been responsible for an extension in the ranges of phase-volume ratios over which dual types were possible in certain systems.’

Notes, Results and Discussions: Preparation and Properties of Clays used The abbreviations employed in the tables are as follows: OW = oil-inwater, and WO = water-in-oil, types of emulsion; FO = free or unemulsified oil in an OW type, and FW = free or unemulsified water in a WO type; P = perfect; S = stable; U = unstable; SU = slightly unstable; VU = very unstable; CG = coarse-grained; IVS, GPR and LAS represent the methods of shaking discussed previously in the text (the third method was not used throughout as it was apparently unnecessary for some systems) ;s = creaming upwards to give a “supernatant” cream less dense than the excess continuous phase, and u = creaming downwards to give an “undercream” denser than the excess continuous phase’; the columns of Table I are numbered so that headings in subsequent tables can be given briefly by reference to these numbers. Woodman: loc. cit.

R . M. W O O D U AND E . MCKENZIE TAYLOR

302

8 4vo

10

1010

I

b10

W

2

I-

EMULSIFYING POWERS OF BENTONITE AND ALLIED CLAYS

B B B B B 3 0 3 0 3 m

m

m

m

m

m m 7

7

1

1

E

Lo

v.

m

m

e

%

- rN o b N ,

Lo",

N

I N

03

I

N h

b

c i *

303

R. M. WOODMAN AND E. MCKENZIE TAYLOR

304

vi

N C--

no!suadsns a p o l u a q .bo . + n a i a d I ---+


r=l 0

s

10

h

i

P.

R o

!-

+++E plI4plk

10

N

t -

uo!suadsns a p o p a q .be .?uawad I ---+

305

3 06

R. M. WOODMAN AND E. MCKEXZIE TAYLOR

Bentonite and Derived Clays: Bentonite: The composition, character and properties of this substance were investigated previously.’ The clay portion of bentonite (about 80 percent.2), mainly consists of sodium clay; calcium clay is also present, and, without doubt, hydrogen clay as a result of hydrolysis. By submitting the bentonite to the action of salt solutions it is possible to produce saturated clays with only one replaceable base present. I t is also possible to produce a completely-unsaturated clay (i. e., an acid or hydrogen clay) by the complete hydrolysis of the sodium and calcium clays in the bentonite. Results3 illustrating the use of bentonite as an emulsifier are given in Tables I and 11. These tables demonstrate clearly that both types of emulsions are possible in various systems when bentonite is the emulsifier. In those systems where the common phase-volume ratio was sought, it was found to be 15/5 in favour of the oils (oleic acid, linseed and “acid” linseed oils), dual types being possible here according to the mechanical preparation given, LAS (the most vigorous shaking possible by hand) yielding the OW type (results I O , 26, 2 8 and 2 9 ) , GPR (the gentlest treatment) giving the WO type (results I I 2 7 and 50) and IVS (intermediate mechanical treatment) giving both types apparently fortuitously when tried for oleic acid ( 4 ) 5 ) 6 and 9). At this common ratio, re-shaking an OW emulsion after standing some time, caused inversion ( 5 , 9, IO, 26, 28 and 2 9 ) , though the WO, on standing, did not invert by re-shaking (result 6). The re-shaking necessary to*cause inversion to the WO type was sometimes quite long (e.g., about 5 min. vigorous shaking for 9 and I O for oleic acid), and indications were obtained .that GPR alternating with vigorous shaking was beneficial (9 and I O ) , just as it was the surest method of preparing the WO type initially at this ratio. No other phase-volume ratio in the systems just discussed gave dual typesJ4 even by inversion on re-shaking after long standing of emulsions ( 2 , 31 7 1 8, 2 4 and 2 5 ) . Points of general application can be illustrated from the oleic acid series. I n the first place LAS favoured, a t the common ratio, the OW type. This is the reverse of the behaviour noted in the system water-gelatine-cresylic acid (or pure cresols), where GPR favoured this types. Moreover the inversion on re-shaking an aged emulsion was from ON7t o WO, again different from the Woodman and McK. Taylor: loc. cit. Twenhofel: “Treatise on Sedimentation,” 206 (1926). 3 OW emulsions with sodium clay aa the main emulsifier were invariably found to be much slower-creaming than those made with other clay emulsifiers. Suspensions of sodium clay were also slow to settle (“deflocculated”) compared with suspensions of other clays, and were much harder to make, owing to a tendency to clog together in m m e a impermeable to water. It should be perfectly understood that a phsse-volume ratio yieldin both types not a definite pmnf,but more probably one of the arbitrarily chosen ratios w&ch happena to be included in a range of ratios giving the two types; it is quite likely that ratios a little t o either side of that discovered might show this phenomenon. (Two comparatlvely mdelyseparated common ratios have been discovered in another system). 5 Woodman: loc. cit.; Woodman and Gallagher: loc. cit.


307

previous system'. These two observations were soon found to be of general application throughout the whole of the present experiments, and the first leads to a rule which holds for every system examined here, and, in fact, for all systems yielding dual types examined in this respect excepting that of water-potassium oleate-hexalin (and, possibly, methyl-hexalin) 2 : the most vigorous treatment (LAS, and, in general, IVS), predisposes t o an OW type, and the gentlest treatment (GPR etc.) to a WO type, if the oil is less dense than the aqueous phase, and vi@-versa. The caution should be added that this rule was not tested for the phenols with clay emulsifiers, where common ratios were not sought. The rule was true for fixed oils and fatty acids, however, and considerably eased the experimental work necessary to prove the existence of dual types in these systems and to fix the common ratio: when determining whether a system would yield dual types, a phase-volume ratio well in favour of a particular type was chosen and treatment favouring that type was given, in accordance with the rule; similar treatment, mutatis mutandis, favoured the opposite type-if it existed-in the system. If the system gave two types, the following method was found expedient for fixing the phase volume ratio common to both types, saving both time and materials: a ratio was chosen, say Io/Io, and the phases subjected to G P R treatment, which, according t o the above rule, in the present systems favoured the WO type. If the emulsion formed were WO, then the next convenient ratio in favour of the aqueous phase was chosen, and that method of treatment favouring the WO type again given; the process was repeated until that ratio (in favour of the water) which yielded an OW type by treatment predisposing t o a WO type was found. This was one of the two limits between which the common ratio lay. The ratio was next altered in favour of the oil, and treatment opposing the WO, and in favour of the OW type, given, until a ratio was similarly found yielding the WO type only; this was the other limit. The two limits were usually close, the intervening ratio or ratios being tested out as the common ratios. If the original emulsion at Io/io ratio were OW, similar treatment, mutatis mutandis, was given; reshaking emulsions in various manners was also used as a method of fixing the common ratio. Another point of general interest is that during G P R treatment, whenever the favoured WO type was subsequently formed, the aqueous phase was seen t o break up in large part or in whole to distinct small globules in the less dense oil phase in every case; the G P R given in these systems was not, for some reason, necessarily so gentle as in previous systems examined: a much larger arc, more quickly described, apparently being advantageous. Emulsions 26 and 28 call for special mention; the presence of dual types was amply demonstrated in the system water-bentonite-linseed oil, but these Woodman: loc. cit.; Woodman and Gallagher: loc. cit. Woodman: J. Phys. Chem., 33, 88 (1929). *Woodman: loc. cit.

1

308

R. M. WOODMAN AND E. MCKENZIE T A n O R

two might be at the common ratio. They were formed by LAS with absolutely no discontinuity in the shaking (about I O shakes), as even one vigorous shake immediately afterwards caused the WO type (result 28). Drop tests in water could not be relied on to fix the type: the drops formed small irregularlyshaped globules (indicating WO, but of a somewhat yellowish linseed oil colour, and not large, well-shaped opaque globules, similar to the true WO drops in water). I n addition, these globules creamed upwards in the water in which the drop test wa’s done, the “cream” being a mass of small globules compressed together, unlike a true cream. I n view of the fact that GPR at this ratio gave perfect WO types (result 2 7 ) and that re-shaking 26 and 28 caused the WO emulsion, it is obvious that this ratio, if not common to both types, is very near the common ratio; probably the difficulty of emulsifying 7 5 % of oil (without adopting the “mayonnaise” system)’ prevented the formation of a true OW type, the most vigorous shaking by hand2 possibly partially forming the emulsions only. No. 2 I (water-in-methyl-hexalin) was also a doubtful case; flocculent stringy masses were observed, which settled downwards. Addition of water to the emulsion caused cracking of these masses, tending to prove that the water was dispersed as irregular masses, addition of free dispersed phase favouring de-emul~ification.~ I n an investigation on the use of finely-divided solids as emulsifiers made by Bechold, Dede and rei ne^,^ “clay” was experimented on as an “inert” solid emulsifier (presumably), and grain size and quantity of “clay” were given as the features influencing the powers of “clay” as an emulsifier (to give one type only, the OW). Again, a North African argillaceous earth6 is quoted as an emulsifier which can replace soap in the emulsification of oils, the inertness of clay as an emulsifier being therefore stressed once more. This is no doubt correct for the mineral oils they used, though the present results, demonstrating that clays are not inert solid emulsifiers merely, but can undergo hydrolysis (to give sodium hydroxide and calcium hydroxide), and other chemical changes (see later), according t o the type of clay utilized, should materially modify even this. The present results are in accord with Weston’s> for his “colloidal clay” (the only particular mentioned being that it came from Messrs. Catalpo, Ltd.,) gave dual types with water and various fixed oils. Weston gave no explanation of these strange results, and Clayton,’ obviously perplexed by Weston’s results, states that one emulsifier cannot form both types of emulsions with any two given liquids to be emulsified.

’ Woodman: J. Pomol. Hort. Sci., 4,95 (1925).

* I n view of the marked differences in results obtained by the three methods of shaking1

it is probable that a more powerful man (possibly with a longer arm) than the experlmenter concerned might have effected emulsification in these two instances. Stirling: J. Inst. Petrol. Tech., 6,382 (1920); Clayton: loc. cit., p. 212. Bechold, Dede and Reiner: Kolloid-Z., 28,6 (1921). ‘Pharm J.: 6,1228 (1898). Quoted from Clayton: loc. cit., p. 28. 8 Weston: loc. cit. Clayton: loc. cit., 31 (1928).

EMULSIFYING POWERS O F BENTONITE AND ALLIED CLAYS

309

If clays are regarded not as inert solid emulsifiers but as compounds capable of undergoing a diversity of chemical reactions, experimental data can be brought into accord with the usual theory of emulsifiers as enunciated by Clayton. Moreover a successful explanation for these systems would give hope of similar explanations for other systems where great doubt and perplexity now exist.’ As a tentative explanation of the results of Tables I and 11, it can be suggested that the bentonite, containing most of its clay as sodium clay, gives, by hydrolysis, some or all of the free sodium hydroxide possible by the action of water. The emulsifier is, therefore, liable to change, and hence alternative emulsifiers are possible in the systems, providing Clayton’s contention with weight at the start. The hydroxide then combines with the oleic acid and the free fatty acids of the fixed oils, (or the phenols), to form sodium soaps (or phenolates),2 and the sodium soaps thus formed act, either alone or in conjunction with other emulsifiers present, as oilin-water emulsifiers for the oleic acid and for the fixed oils (just as alkalies emulsify fixed oil because of soap formation with the free fatty acid impurities).3 The bentonite possessed 69.9 milligram equivalents of replaceable sodium per IOO gm. of material;4 calculations of the sodium hydroxide obtainable by hydrolysis from I C.C. of a 1% suspension demonstrate that in every experiment tried there was a large excess of free fatty acid after conversion of the whole of the hydroxide possible to sodium soap, even in the case of the linseed oil, which possessed the lowest acid value, 0.73% “oleic acid.” Weight is given to the above notion that the fixed oils are wholly or in part emulsified to OW types in virtue of their free fatty acid content by the facts that, a t the common ratio I S / S in favour of the oils where dual types are possible, the oleic acid and the “acid” linseed oil gave definite OW types easily ( 5 , 9, I O and 29), whilst the linseed oil of low acid value gave indefinite results (26 and 28, see previous discussion on these). These results tend to prove the desirability of a great acid value, although theoretically there is already a large excess of free acid in the linseed oil i t ~ e l f . ~ But the systems also yield WO types: it will be noticed that bentonite contains calcium clay, having a replaceable calcium value of 23.9 milligram equivalents per IOO gm. of bentonite;6this calcium clay yields calcium hydroxide by hydrolysis in water (see preparation of calcium-saturated bentonite later), and hence it is possible for water-insoluble soaps t o be formed with part of the oleic acid (or the excess fatty acid of the oils), these soaps then Seifria: J. Phys. Chem., 29, 834 (192j). No data were known concerning the part layed by phenolates in emulsification, and hence the argument is mainly developed from t f e sodium soap side. Donnan: Z. physik. Chem., 31, 42 (1899). Woodman and McK. Taylor: loc. cit. EmuLsion 31 also illustrates this; it was much stabler than the corresponding emulsions for linseedoil at this ratio (24and 2 5 ) , &s was shown by standing the emulsions side by side for a period of a week. a Woodman and McK. Taylor: loc. cit. 2

310


acting as WO emulsifiers.' An excess of suspension in the chosen ratio should favour water-soluble sodium soaps and consequently OW types (less free fatty acid then present, greater smashing action of the aqueous phase, and, though the replaceable sodium and calcium are always present in the s u e pension in the ratio 311, a much greater absolute difference in the amount of sodium and calcium soaps present, which last fact is probably of great importance); excess of oil in the chosen ratio should similarly favour oil-soluble maps and WO types. At the phase-volume ratio common to both types an equilibrium of the opposing soap emulsifiers can be assumed, and the methods of shaking employed will entail striking differences. Gentle treatment (e.g., GPR for a minute or so, etc.) should first favour the formation of all the sodium soaps possible, (without, however, attempting to utilize them as emulsifiers), and then the formation of calcium soaps, subsequent vigorous shaking giving the WO type a t this ratio 15/5 on the oil side. Grounds for this statement are not wanting, for it is known (see later, preparation of calcium-saturated bentonite) that a sodium clay hydrolyses much more quickly in water to give sodium hydroxide than a calcium clay to give calcium hydroxide; moreover, it is likely that hydrolysis of calcium clay does not commence or is not very advanced until all or most of the free sodium hydroxide has been removed. Immediate and very vigorous shaking at the common ratio, of course, would tend to cause utilization of the sodium soaps formed first as emulsifiers at once, and hence OW types would results. Re-shaking of an aged OW type to a WO type can be explained somewhat similarly: result 5 shows definitely that time must elapse before this change, results 5, 9 and IO that traces of oil (and, therefore, of free fatty acid as well) are probably necessary, and results 9 and IO that some gentle' treatment is possibly an aid. Taking these facts in conjunction, it seems possible that in the case of OW types the oil is emulsified (and therefore prevented from participating in chemical action) by sodium soaps, and only on ageing of the emulsions accompanied by slight cracking to produce free oil (free fatty acid) is the formation-aided, as seen, by gentle treatment-of that amount of calcium soaps necessary to accomplish inversion brought about by combination of free fatty acid and the calcium hydroxide obtained as a result of hydrolysis. The immediate re-shaking to WO types at this ratio for linseed oil (26 and 28), is linked up yith this: here it has been assumed (see previously) that complete OW emulsification has not occurred; hence the system is not nearly so viscous as a perfect 7 5 percent. OW emulsion, and free oil is present. Consequently one re-shake allows thorough contact of the oil and the calcium hydroxide which has developed, giving the WO type. The long shaking sometimes necessary to cause inversion, and the favourable influences of gentle treatment, are no doubt due to the fact that the stiffness of the usual 75 percent. OW types (practically semi-solid masses) prevents 1 With phenols etc., calcium phenolates etc. may be formed; these-presumably insoluble-might tend to be water-in-oil emulsifiers.

E Y U L S I F T I S G P O W E R S O F B E N T O S I T E AND ALLIED CLAYS

311

contact of calcium hydroxide and the traces of cracked oil, vigorous shaking tending to re-emulsify these traces by sodium soap solution. So far as it goes, the foregoing hypothesis of the emulsifying action of bentonite seemed quite feasible, but other considerations of great note had to be taken into account. Besides the emulsifiers present by hydrolysis and subsequent chemical action, other emulsifiers were taking part : thus there were the non-clay portions of the bentonite ( 2 0 percent.) composed of such substances as fine silt (silica), unaltered felspars and biotite,’ etc., and the often supposedly-inert hydrogen clay (completely unsaturated) present to some extent initially in the clay portion, and presumably obtained in increasing amounts by the hydrolysis of the sodium and calcium clay and the utilization of the alkali and calcium hydroxide so formed to give soaps. I n addition, the questions as to whether pure hydrogen, sodium and calcium clays acted as one-type emulsifiers, and, if so, which type of emulsion each yielded, or whether the hydrogen clay, perhaps in virtue of wettability and increasing quantity, opposed the emulsifying actions of the sodium or calcium soaps obtained from the sodium or calcium clays b y hydrolysis and subsequent chemical action, demanded attention.2 To aid in the solution of these questions, completely unsaturated bentonite (the clay portion being all hydrogen clay) was made by hydrolysis, and specimens of sodium-saturated and calcium-saturated bentonite were prepared by base exchange; other natural clays from soils, coal-mines, oilwells, etc., were also procured and derivatives made. They were tested as emulsifiers for fatty acids and fixed oils, and their properties, preparation (where necessary) and the results of emulsion tests are given later.3 Before proceeding to these, however, it will be found convenient to review briefly some conclusions made previously with regard to the possible uses of bentonite itself. I n a former paper4 attention was drawn to the possible uses of bentonite as an emulsifier in the preparation of insecticidal emulsions for plants, and as a water-softener in cases of permanent hardness. The first question was investigated more fully, and it was shown that because of the impermeability t o water of bentonite (due to the sodium clay content), the preparation of “smooth” aqueous suspensions of bentonite (and, consequently, of spraying emulsions which would not choke the spray nozzles) should not be left to the actual sprayer, but should be undertaken by spray manufacturers possessed Twenhofel: loc. cit. Judging b y the results for petroleum ether, and for other oils such as decahydronaphthalene, etc., (loc. cit., footnote 41, which are non-reactive to clays and their breakdown products, so that the clays may then be re arded merely &s inert solid emulsifiers, it would seem that clays are OW emulsifiers only. f n these petroleum ether experiments, emulsions were made by a “mayonnaise” method L e . , the emulsions were gradually built up by addition of 5 cc. lots of the oil with emuLkification by vigorous shaking between each addition. a I n many instances phaae volume ratios common to both types of emulsion were not sought. The existence of dual types in a system, however, necessarily presumes such a common ratio. Woodman and McK. Taylor: loc. cit. 1

2

312


of efficient mixing machinery. Now if an emulsion is to be transported economically, it should contain as much dispersed phase as possible, and such concentrated spraying emulsions, intended for dilution with water by the sprayer a t the place of spraying, are called “stock” emulsions.’ It was shown* that 67 percent. stock emulsions of various oils, including phenols and hydrogenated phenols (other than cresylic acid), oleic acid and fixed oils could be easily made with 7 percent. bentonite suspension, and the ,~ reasons for doubt use of bentonite was advocated to some e ~ t e n t though were already entertained, and further investigation was deemed necessary. The present experiments demonstrate clearly, for I percent. bentonite suspensions at least, that the absolutely useless water-in-oil type of emulsion (regarded from the viewpoint of the sprayer’) is liable to occur when the concentration of the fatty acid, fixed oil, phenol or hydrogenated phenol reaches about 7 j percent of the system. Even were advantage taken of the possibility of preparing (approximately) 7 j percent. emulsions of these oils by very vigorous treatment, the jolting received during subsequent transport would probably cause inversion to t,he undesirable type of emulsion for spraying; and to reduce the amount of oil (a spray manufacturer usually aims at sending out a non-creaming emulsion, which, therefore, contains more than 7 5 percent. of oil’) would mean uneconomic transport and packing. I n the circumstances it would be far better to reserve the use of bentonite as a spray emulsifier for such oils as tetra- and decahydronaphthalene, where 80 percent. emulsions of the correct oil-in-water type could be made2 because of the non-reactivity of these oils to the products of the hydrolysis of sodium and calcium clays. The possible utilizat,ion of other natural clays than bentonite, and of derivatives of these and of bentonite as spray emulsifiers deserves some attention, and the following preparations and experiments were made for the dual purposes of investigating this and the previously-proposed problems. Preparation of bentonite saturated with sodium: Hissink’s method‘ for the

determination of replaceable bases was used to prepare the sodium-saturated bentonite. Twenty-five gm. of bentonite, ground to pass the IOO sieve,5 were suspended in IOO C.C.of normal sodium chloride solution for 24 hr. The suspension was filtered and the residue washed with 400 C.C.of normal sodium chloride solution; the residue was then well washed with 50 percent. aqueous alcohol until free from chlorides. The object of washing with the 50 percent. alcohol instead of with water was to prevent hydrolysis of the sodium clay (which would have resulted Woodman: loc. cit.; J. Agric. Sei., 17, 44 (1927);J. Pomol. Hort. Sci., 6,313 (1928). McH. Taylor: loc. cit. See also, in this connection, English: J. Economic Entomol., 18, 513 (1925). 4 Hissink: Internat. Mitt. Bodenkunde, 12, 81 (1922). 5 All grinding WVBSdone out of contact of metals; the products made by base exchange and by hydrolysis were re-ground to roo mesh previous to making suspensions for emulsification purposes. 1

* Woodman and

J

EMULSIFYING POWERS OF BENTOKITE AND ALLIED CLAYS

373

in t,he formation of hydrogen clay), as it had previously been found that sodium clay does not hydrolyse in alcohol of that concentration.‘ The sodium-saturated bentonite was dried a t 3ooC. This sodium-saturated bentonite produced an alkaline solution of suspension in water, and possessed the characteristic properties on a sodiuni clay. The alkaline reaction of the suspension in water is due to the production of free sodium hydroxide as a result of hydrolysis? Estimation of replaceable sodium was not done, though, as the sodium hentonitewas saturated, it must have been equal t o the sum of the replaceable sodium,3 calcium3 and hydrogen of t,he original bentonite sample. Emulsification results are given in Table 111. Preparation of calcium-saturated bentonzte: The calcium-saturated bentonite was prepared in a similar manner to the sodium-saturated bentonite. the replacing solution being normal calcium chloride solution. The calciunisaturated bentonite, after being filtered off, was washed with j o percent alcohol to remove excess of calcium chloride4and was then dried a t 30OC. The calcium-saturated bentonite had a pH value5 of 7.4, Its physical properties contrasted strongly with those of the sodium-saturated bentonite; It did not set to a hard mass, but mas granular and also readily permeable to water. On hydrolysis in water it yields a solution of calcium hydroxide and a residue of hydrogen clay; the process of hydrolysis being much slower than that of sodium-saturated bentonite. The results of emulsion formation with this substance as emulsifier are given in Table 111. Preparation of Completely-unsat~Lrated bentonite: Bentonite, ground to pass the I O O sieve, was suspended in Y / I O hydrochloric acid and the suspension filtered through a porous candle under reduced pressure. The residue was again washed with ?;/IO hydrochloric acid, the washing being repeated until the filtrate was free from calcium. The residue-an “acid” or hydrogen claymas then washed with distilled water until the filtrate was free from chloride and was finally dried at 3 0 T . The pH value of the clay was 2 . 4 . Emulsion results are given in Table 111: The results for sodium-saturated bentonite as emulsifier are very similar to those for bentonite, a phase-volume ratio common to both types being indicated by the re-shaking experiment 39 at the same ratio I j ’5 in favour hIcIi. Taylor: unpublished data. 1IcK. Taylor: “Cotton Research Board Fourth hnnual Rpt.”, (Cairo), I Z I ( 1 9 2 3 ) . 3 JVoodman and McK. Taylor: loc. cit.; a simular remark also applies to all fully-saturated clays derived by base exchange. 1IcIi. Taylor: Fuel, 6 , 3j9 ( 1 9 2 7 ) . The authors adopted the following method in all cases for determining p H values of ciais and soils: I O gm. of 100 mesh air-dried clay or soil were shaken with j0c.c. of distilled HzO; after leaving 30 min. with occasional shaking the pH of the clearest portion of the suspension was determined colorimetrically. 1

R. M. WOODMAN AliD E. MCKENZIE TAYLOR

dd

m m 7 7

m m m s m

1

a v i 0 mv. m ) 3

loo 0 0 3 3 -

EWJLSIFYING POWERS O F BENTONITE AND ALLIED CLAYS

0

c--

- apoquaq pa~elnqesun-iCIa~aiduroo ----------+

30 no!suadsns

.bE

315

3 16

R. M. WOODMAN AND E. MCRENZIE TAYLOR

of the oleic acid.’ As sodium was the replaceable base present, and as, therefore, no calcium soaps were possible, it was reasonable to assume that sodium bentonite would form simple one-type oil-in-water emulsion systems; this assumption gathered weight from the results for the “inert” oil petroleum ether.* The systems containing oleic acid and fixed oils, however, gave dual types, despite the well-proven fact that sodium soaps, possible in these cases, are known to yield OW types with such oils. The only hypothesis possible at this st>ageto explain the phenomena was that the completely-unsaturated clay, obtained by full hydrolysis of the sodium-saturated bentonite in water and utilization of the sodium hydroxide so got to form sodium soaps, favoured the WO type. If the sodium-saturated bentonite were expected to form OW types, calcium-saturated bentonite would be expected, similarly, to give WO types only; and if the completely-unsaturated clay obtained by full hydrolysis and subsequent Utilization of the calcium hydroxide so formed to give oilsoluble calcium soaps were a R O emulsifier, as reasoned above, this expectation should be strengthened. “Inert” petroleum ether, however, yielded OW types only, the ot,her oils giving dual types (Table 111). I t is true that the phase-volume ratio common to both types for oleic acid had shifted from the usual I j/s in favour of the acid to between I O / : I O and IO/ j for this system, but this could be taken to demonstrate the absence of all sodium soaps and the presence of greatly increased amounts of calcium soaps, and affords no solution for the actual occurrence of OW types. The only explanation possible at this stage was that the completelyunsaturated bentonite-which should be identical with that got similarly from sodium-saturated bentonite-was an emulsifier favouring O X types, a conclusion diametrically opposite to one preceding. Harmony between these two conclusions was only possible if it were assumed that the hydrogen clay could act as an emulsifier for both types of emulsions, and this was found to occur (Table 111),for, though only the OW type was given by “inert” petroleum ether even at 83 percent. of oil, dual types were formed with the other oils, the common ratio in the case of oleic acid being between I 5 1 I O and I 5,’s in favour of the acid. Now completely-unsaturated or hydrogen clays are often thought to be chemically inert to a large degree, pardonably so in view of the fact that they apparently represent the end product of complete hydrolysis. If, however, they are regarded as being chemically inert, so that they act as emulsifiers simply in virtue of grain size and quantity, they should not react with 1 S o . 39 was similar to nos. 26 and 2 8 , I O shakes with no discontinuity in the shaking being given to form the pasty OW (tested]. Practically immediate reshaking caused inversion, as shown in Table 111. A duplicate (not given) to 39, evidently inverted during the LAS preparation to the WO type, judging by the change in the feel of the cylinder (the WO type is less wscous a t this common ratio I j / j in favour of the 0’1, and hence the cylinder’s contents respond to shaking more). * I . e . , “inert” as regards chemical reaction to the products of the hydrolysis and breakdown of clays.


317

fatty acids, and the results could only be explained by the presumption that one emulsifier could form dual types with water and fatty acids (or fixed oils containing fatty acids). If this were so, then dual types might also be expected with petroleum ether, a result contrary to that found. Hence it was assumed that hydrogen clays are not inert, and evidence of this was gathered from the literature:' Thus Gedroizz stated that when the (clay) complex is saturated with hydrogen ion (Le., when a completely-unsaturated or hydrogen or "acid" clay is present) its resistance to the decomposing effect of water is lowered, which may result in the disintegration of the anion portion of the complex into its constituent oxides; this is sometimes shown b y the accumulation of the free ~ examination hydrate of alumina in podzol soil^;*^^ moreover, M a g i ~ t a d ,by of a number of soil solutions from natural soils, showed appreciable quantities of soluble aluminum to be present in the solutions lying outside the limits5 of pH 4.7 and 8.0, and Kelley and Brown6 found that every neutral or alkaline soil examined gave extracts containing appreciable amounts of silica (as much as 0.1percent of the soil), so that the stability of the complex ion in every clay is open to question. The decomposing effect of water on completely-unsaturated clays (especially) afforded a solution to the problem raised in the section on hydrogen bentonite as an emulsifier, for it could be assumed that the soluble aluminum present by this disintegration combined with free fatty acid to give aluminum soaps, which would favour the R O type of emulsion; the OW type would be formed by the clay ztself, or its breakdown products, silica and alumina (which are O b 7 emulsifiers'), in virtue of grain size and quantity present. Nile szlt containing sodium clay: The naturally-occurring alkaline soil used in these experiments was obtained from Halq el Gamal, Lower Egypt. The material originally consisted of normal Sile silt, a calcium clay, derived from the igneous rocks of the Abyssinian Plateau. It had been deposited during the Nile flood in that portion of the Kile Delta situated below a sixmetre contour. The sub-soil water in this area contains sodium chloride 'The present systems differ from others examined minutely in view of the occurrence of dual types (loc. cit.) because the emulsifiers are not soluble in either or both phases to any great extent presumably, as the other emulsifiers were, and hence partition of emulsifier cannot be supposed to play a leading role; the explanations given in the present instances raise the hope that other systems d l , in the future, be brought strictly into line with the existing emulsion theories. Gedroiz: "The Theory of the Absorptive Power of Soils." (monograph) ( 1 9 2 2 ) . J. Expl. Agronomy ( 1 9 2 4 ) ; see also Tiurin: Acad. of Sei. of the USSR: Russian P e d o l o g h Investigations, 4 ( 1 9 2 7 ) . Hemmerling: Rept. 5th. hfeeting of Soil Scientists of USSR ( 1 9 2 6 ) . hlagistad: Soil Science, 20, 181 ( 1 9 2 j ) . This factor, of course, might directly play an important part in the formation of WO types with alkaline clam of pH value greater than 8.0 (e.g. bentonite and sodium-saturated bentonite), the soluble"a1uminium forming aluminium soaps (see the reasoning following for the formation of dual types with hydrogen clay). Completely-unsaturated bentonite gives a solution of pH 2 . 4 (see preparation). 'Kelley and Brown: Vniv. of California Publicns., Tech. Paper 1 5 ( 1 9 2 4 ) ; see also Joseph and Hancock: J. Chem. Soc., 125, 1888 ( 1 9 2 4 ) for a discussion on the reactivity of clays, including bentonite. Pickering: J. Chem. Soc., 91, 2001 ( 1 9 0 7 ) .

3 18


in solution. Owing to the intense evaporation of water from the surface of the soil during the summer months, a crust of sodium chloride forms on the surface of the soil, and, during the subsequent flood period, the salt is washed out of the soil, which then becomes a typical “black alkali” soil because of its sodium clay content. The properties of this soil have been discussed previously.l The soil contained 4.4 percent. of ‘‘free” calcium carbonate, and its pH value was 9.8; the following replaceable bases were present: sodium 47.5 and calcium 3.6 milligram equivalents per IOO gm. of soil. Emulsion data are presented in Table 11‘. Preparation of Nile silt f u l l y saturated with barium: Barium-saturated N l e silt was prepared from the alkaline Nile silt discussed above by replacement of replaceable sodium, calcium and hydrogen by means of barium from barium chloride solution. The excess barium chloride was removed by washing with 50 percent alcohol. I n its physical properties barium clay closely resembled calcium clay, having a granular structure and being permeable to water. I t is uneuitable for plant growth, however, for though germination is normal the plants are dwarfed. Emulsification results are given in Table IV. Calcium clay ( L o n d o n clay f r o m Rettendon, Essex, England): As an example of a calcium clay, a subsoil of the London clay at Rettendon was selected. It contained no calcium carbonate; its p H value was 7.2 and i t contained 16.5 milligram equivalents of calcium per IOO gm. of soil, having no replaceable sodium. Emulsion data are given in Table IV. Preparation of completely-unsaturated (hydrogen) clay f r o m Rettendon London clay subsoil: A hydrogen clay was prepared from the London clay subsoil from Rettendon. The subsoil was suspended in normal ammonium chloride solution for 24 hr. to produce a saturated ammonium clay. The ammonium clay was washed with water, the filtration being carried out by means of a porous candle. On removing the excess of ammonium chloride, the soil became almost impermeable and was alkaline, the ammonium clay behaving similarly to a sodium clay. Continuing the hydrolysis, the alkalinity disappeared, the final p H value of the soil being 4.2. The washing of the ammonium clay was continued until no further ammonia could be detected in the washings b y Nessler’s solution. Results illustrating the emulsifying power of this hydrogen clay are given in Table IV. Table IV demonstrates the fact that with the Nile silt as emulsifier, both types of emulsion were possible with linseed oil and oleic acid; with olive oil, doubtless because of “specificity” of oi1,2 the WO type alone seemed possible, results 81 and 86 most probably signifying non-emulsification, the oil being merely turbid with water. With petroleum ether, (dilute) OWtypesonly were 2

.McK. Taylor: Fuel, 5, 195 (1926) Woodman and McK. Taylor: loc. cit.


3‘9

noted; but, despite this fact, Xile silt, though good for the preparation of WO emulsions, was poor as an OW emulsifier even in 5 percent aqueous suspension. I n this connection, however, it must be remembered that, in dealing with soil clays, quantities of silt (silica) present as comparatively large particles are probably not particularly effective as emulsifiers, though they favour the OW type. Other substances associated with this clay, such as free chalk, magnetite (typical of Egyptian sedimentsL),etc., also probably masked the OW emulsifying action of the clay through being poor emulsifiers. The barium-saturated Nilt silt was also an unsatisfactory O W emulsifier; the presence of replaceable barium, however, favouring the production of oilsoluble barium soaps by combination of free fatty acid and the barium hydroxide liberated by hydrolysis, would tend to make it worse than N e silt itself for this purpose. London clay subsoil in I and 5 percent aqueous suspension tended generally to give good WO and poor OW types also; the completely-unsaturated derivative of this subsoil was much more definite in both types of emulsion (Table IV). Aczd shale formzng roof of a coal seam: This specimen was obtained from the roof of a Tertiary bituminous coal seam a t S o . 15 mine, Nazira Colliery, Dhanbad, Assam.z The pH value of the specimen was 4.2;a determination of replaceable bases gave the following: Calcium, 0.6, sodium, 6.6 milligram equivalents per I O O gm. of shale. Since the replaceable sodium was in excess of the replaceable calcium it indicated that the clay in the shale had undergone base exchange with solutions of sodium chloride. As the shale was acid, the hydrolysis of the sodium clay must have proceeded to such an extent that the dominant clay type finally present was a hydrogen clay. The specimen consisted, therefore, of hydrogen clay together with small quantities of unhydrolysed sodium and calcium clays. Emulsion data are given in Table V. Lignitic clay: The specimen of lignitic clay used was from the roof of the lignite seams in Czecho-Slovakia; as with the roofs of other lignite seams, it had not undergone base exchange with sodium salts3 I t consisted of a mixture of calcium and hydrogen clays, the pH value of the specimen being 6.8; it contained 12.7 milligram equivalents of calcium per 100 gm. of material. Emulsification results are given in Table T’. “ C a p rock” of oil sands: The shales forming the cap rocks of oil-bearing strata have been shown to contain large quantities of sodium clay.4 The clays in these rocks have undergone base exchange with sodium chloride solu-

3

Mosseri: BullInst. d’Egypt, 1, 151 (1919). McK. Taylor: Paper read a t 16th. Indian Science Congress (Madras 1929 McK. Taylor: Fuel, 7, 227 (1928). McK. Taylor: J. Inst. Petrol. Tech., 14,82j (1928); 15, 207 (19zgi.


E J K L S I F T I S G POWERS O F B E S T O S I T E AXD ALLIED CLAYS

v, w, vi v. vi vi -

-

i

vi w, v, w, vi vi -

.

-

i

321

R. M. WOODMAN AND E . MCKENZIE TAYLOR

v;

10 10 10 10 vi H

C

v. 3

w,

w 1

Y

vi vi Y

w e

- +++

lz? 10 vi

10 10


f.

B

”

m E

C

m

T &

L

vivivivi

vi c

H

- -

++++

Lnvirnvivi~vivi

4.

vi

E

.2

3 0

--

spuss 110 30 dw,, 30 noTsuad -sns ‘bs ObS

“VOJ

N

Y

-

x x x

N c

323

324

R. M. WOODMAN AXD E . McKENZIE TAYLOR

tions, and some subsequent hydrolysis of the sodium clay has taken place in fresh water. The specimen used was obtained from the Guapo Field, Trinidad Central Oil Fields, and occurred a t a depth of 1485 ft. It was non-calcareous (z.e., had no free chalk), and possessed a pH value of 9.0. I t contained some free petroleum, perceptible to the smell, and it was found impossible to estimate replaceable sodium because of the non-wettability by normal aqueous ammonium chloride, the particles clinging together in clusters. This was the case, to some extent, on attempting to make a suspension of the material in water; vigorous shaking, however, caused an even suspension, no doubt because the cap rock acted as an emulsifier (in the presence of sodium hydroxide obtained by hydrolysis in water) for the traces of petroleum causing non-wetting. Emulsion details are given in Table V. Much the same as the results obtained for Nile silt and London clay subsoil were those observed for the roof shale of the Nazira Colliery, Assam, and the cap rock of the Guapo oil sands (Table V). The tendency to form the OW type was slight and doubtful, and was in no case similar to the pronounced tendency of bentonite and its derivatives. This bias in favour of the WO type reached its limit in the case of the lignitic clay, the small clay portion of which consisted of calcium and hydrogen clays. I n no instance was the OW type prepared with a fixed oil or with fatty acid, though with petroleum ether this was the sole type; it is, therefore, very probable that this substance acts as a simple one-type emulsifier in most systems, the type yielded in any particular instance depending mainly on the character of the oil. With the lignitic clay, it was noticed that xhere non-emulsification , particles in the aqueous suspensionoccurred (results 114, 116, I I ~ ) the even the coarsest-were transferred to, and intermingled with as a kind of “slime,” the layer of oil, leaving practically clear water in the underlayer. This was quite different behaviour from that noted with any other clay emulsifier, and evidently denoted preferential wetting by the oil phases, with a tendency, therefore, to yield WO types only. These results seem to demonstrate some analogy between the partition of a solid emulsifier and of one soluble (like soaps and gelatine) in one of the liquid phases a t least, between the liquids of an emulsion system;’ an infinite partition of the solid particles takes place in favour of the oils because of the preferential wetting, one-type systems resulting. Emulsion 120, that with petroleum ether (OW), was also peculiaron adding sufficient oil to cause cracking, for the solid matter gathered as a thick layer a t the interface of the liquids, which were both quite clear (in all other cases the breakdown of the petroleum ether emulsions by addition of excess oil resulted in a clear layer of oil over a thin OW emulsion, the aqueous medium also retaining the suspended matter). 1

Woodman: loc. cit.


325

The results of Tables IV and V demonstrate that the clays tested last were of no use whatsoever in the preparation of concentrated stock emulsions of the oils experimented on for spraying. With bentonite and its derivatives (Tables 1-111) moderately concentrated and stable OW emulsions were at least possible, and risks of inversion were the main drawback; here, even dilute OW emulsions cannot be prepared in a stable form, the main tendency being to form the WO type, which is undesirable from a spraying standpoint. Thus a large number of clays from diverse sources and of diverse kinds was entirely unsuitable in the preparation of spraying emulsions containing oils which might interact chemically with products obtained from clays either by hydrolysis or by the cleavage of the clay complex. -S The contention of Weston (loc. cit.) that a clay can promote both types of emulsion in certain cases has been proved correct. Clay-containing substances of diverse kinds and from diverse sources, and derivatives prepared from these by base exchange and by hydrolysis, have been demonstrated, in the main, to give the dual types of emulsions. Clays give dual types of emulsions with fatty acids, fixed oils containing free fatty acids, and with phenols and hydrogenated phenols. The hypothesis advanced is that this is due to chemical interaction of the fatty acids, etc., with sodium and calcium hydroxides, etc. obtained by hydrolysis of the clay when in aqueous suspension, or with breakdown products of the clay itself. The original emulsifier thus undergoes change and soaps are introduced into the system. The changes taking place in the original emulsifier and the different emulsifiers present can easily be made to afford sufficient explanation of the fact that dual types are formed; the clays, as such, are not responsible, and the results are brought strictly into line with the usual emulsion theory as enunciated by Clayton (loc. cit.) that one emulsifier cannot promote two types of emulsion with any two given liquids to be emulsified. Clays of all kinds are unsuitable AS emulsifiers in the preparation of spraying emulsions containing free fatty acids, fixed oils and phenols because of the Iiability of the formation of the undesirable water-in-oil type. Even if moderately concentrated oil-in-water stock emulsions are possible as with bentonite and its derivatives, jolting received during subsequent transit would probably cause inversion. The results of this extended study of clays modify to some extent the conclusions to be drawn from the previous study of bentonite. An example is given-"lignitic clay"-where water-in-oil emulsions only are possible with fatty acids and fixed oils, and where the suspended material is completely withdrawn from the aqueous phase. Horticultural Research Statim, Cambridge University, England.

June 17. 19.99.

The Emulsifying Powers of Bentonite and Allied Clays derived from

Recommend Documents