146
INDUSTRIAL AND ENGINEERING CHEMISTRY
prevent flooding of the check valve with the hydraulic oil. However, when pumping perfectly dry gases it has been found that a drop of oil in the check valve helps its operation. What might in some cases be construed as a drawback iri pulsating the use Of such a pump lies in the fact that a gas flow is obtained. One method to decrease this tendency is kt use surge drums and line constrictions. Another suggestion by Gibson e' a'. ( 1 )is to use a pair of bellows pumps out of phase with each other-i.e., one is at compression while the other is a t
Vol. 42, No. 1
extension. Only the former method has been used by the authors. LITERATURE CITE11
(I) Gibson, J., Heron, J., and Nicholson, G. A , J. Sci. Instruments, 24, 273 (1947). RECEIVEDApril 25, 1949. Presented before the Division of Petroleum Chemistry a t the 116th Meeting of the ~ m m o A Nc H ~ \ ~ I C A LSOCIETY, San Franoisco, Calif
Reactions of Resins with Drying Oils P. 0.POWERS, Battelle Memorial I n s t i t u t e , Columbus, Ohio
N
Drying oils react with resins either by acid, alcohol, o r ATURAL and synever, alkyd resins will not be ester interchange or by addition reactions at the double considered in any great dctail thetic resins are often incorporated in the production bond. The occurrence of the ester reactions is well esin this discussion, but the emphasis will be placed on of varnishes and other preptablished and is often the basis of the formation of alkyd the resins which are usually arations for protective coatresins. Ester-type resins combine with the drying oils by ester interchange, and while quantitative measure of added in the varnish kettle. ings. I n some cases, as with the alkyd resins, the chemithe extent of this reaction cannot readily be obtained, I n the drying oils, there are cal reaction is well underdefinite indications of the reaction have been obtained two positions in the molecule which are readily susceptible by marked changes in the solubility of the resin on heating stood and is carefully controlled in the manufacture with the drying oil and by changes i n the viscosity. These t o chemical reaction. The effects are most pronounced with resins of high viscosity of the preparations. With ester group can readily enter many other resins, the extent into acid interchange, alcohol and low solubility. Reactive phenolic resins are known interchange, and ester interof the reaction with the oil to combine with the drying oils, particularly the conjuchange. This type of reacis not known and could be gated type, but this reaction must be regarded as seconddetermined only with diffition occurs frequently and is ary to the polymerization reaction, and the unreactive exceedingly important, parphenolic resins usually used with drying oils give little culty. I n some cases, it has ticularly with the acid- and evidence of any appreciable chemical reaction with the not been clearly shown ester-type resins. The fatty whether a chemical reaction oil. Hydrocarbon resins, in general, do not combine acid in the glyceride structure occurs or, when there is with drying oils. can readily be replaced by evidence of combination, what rosin acids. natural resin type of reaction takes place. Chemical combination between the resin and the drying oil is acids, and a wide variety of synthetic acids, The glycerol in the recognized as a desirable occurrence. Resins which are soluble ester structure also can be replaced by other polyhydric alcohols &nd by synthetic resins containing hydroxyl groups. Esters of in drying oils without chemical reaction are limited in number, resin acids readily interchange with the drying oils, forming mixed and they often do not possess the most desirable properties. fat-rcsin glycerides. In many cases, resins of the same series of higher molecular The unsaturated groups are not so readily combined with weight have much better properties but cannot be used because resinous materials. This type of addition is often postulated of their insolubility in the drying oil. A resin which does not even when there is no definite proof of such combination. Rereact with a drying oil can act only by dilution of the properties cently, there has been considerable study of the formation of of the drying oil. Thus, many of the qualities of both the resin addition products of hydrocarbon monomers with the drying and the oil may be apparent. With extensive combination oils effected by polymerization in the presence of the drying oil. between the resin and the oil, a new structure is formed which In this case, it is apparent that more desirable results are obtained may be superior to that of either component. when some degree of combination of the hydrocarbon resin and TYPES OF REACTIONS the drying oil is achieved. Proof of Combination of the drying oil and resin is not always While the idea that a reaction does occur is widely accepted, readily obtained, and it will be shown later that certain types of the type of the reaction is not always fully understood. In behavior which have been taken as evidence of chemical commost cases, the extent of this reaction has not been measured in bination are not necessarily proof of such combination. quantitative terms because such measurement, frequently, can
be made only with great difficulty. I n many cases, no serious attempt has even been made to measure the extent of the combination of the resin with oil. The alkyd resins, however, do not fall in this classification, because, in this case, the type of reaction is well understood and the extent of the combination of the polyester structure with the drying oils is, in most cases, rather accurately controlled. How-
REACTIONS WITH THE ESTER GROUP
It has been long known that rosin, when added to tung oil, retards gelation of the oil. If enough rosin is used, gelation is prevented. This effect is not due t o dilution of the oil alone, since neutral diluents do not prolong the gelation in such a manner but the effect of the rosin results from combination with the
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950
141
275" C. This (19) cloud point determination was found to be >
EQUAL WEIGHT
- RESIN AND OIL
2 PARTS OIL- I PART RESIN
J
110
+-
?a
3 70
\
0.5
0
10 TIME, HOURS
I S
2 0
Figure 1. Rosin-Modified Phenolic Resin and Linseed Oil
glyceride structure of the oil and reduction of the extent of cross linking. The McNicoll method of determining resin acids in the presence of fatty acids is well suited to a measurement of the extent of the combination of the resin and the oil. Linseed oil was heated with rosin a t 275" C., and samples were taken at 0.5,1, and 2 hours. CHzOOCF AHOOCF
CHzOOCR
+ RCOOH-bHOOCF
CH200CF I Linseed oil
very useful for a wide variety of varnishes. It can be made on preparations containing solvents but often is more readily determined on the unthinned varnish. Also, the ratio of mineral oil to varnish may be varied to obtain cloud points in a convenient range. Often, fifty parts of mineral oil to one hundred parts of varnish give cloud points in this range. However, if cloud points are too low for ready determination, the addition of more mineral oil will result in higher cloud points. Also, more paraffinic mineral oils may be used with the more soluble resins. I n this experiment, the resin acidity was again followed by the McNicoll method. Substantially the same rate of exchange between the resin and the oil was found as with rosin. Figure 1 shows that the cloud point drops rapidly as the resin and oil combine. This increase in solubility is most rapid during the first hour of heating during which the most combination of the resin with the oil occur^. In many cases the cloud point goes through a minimum; this minimum is occasioned by the polymerization of the drying oil, since the bodied oil is a much poorer solvent for the resin than the unbodied oil. As seen above, there is always a certain amount of the resin which does not combine with the oil at equilibrium conditions; this is probably about 50% of the added resin when equal amounts of resin and oil are used. However, if a larger excess of oil is used, the amount of uncombined resin will be proportionally reduced and if five parts of oil are used with one part of resin, only about 16% of resin added would remain uncombined at equilibrium. Thus, resins tend t o be more completely dispersed when long oil lengths are employed.
+ FCOOH
IC
hH200CF Rosin
Fatty acid
These samples were refluxed with methanol containing ptoluenesulfonic acid ; the decrease in acidity measured the amount of fatty acids present and the amount of rosin acids was determined by the difference from the total acidity. The results of these (18) determinations are shown in Table I. After 2 hours, nearly half of the rosin present had entered into the linseed oil structure as an ester, and an equivalent amount of fatty acids had been liberated in the process. The theoretical equilibrium point, assuming the free energy of rosin ester formation is the same as of the formation of the fatty ester, would be reached when half of the rosin acids had entered the oil structure. This value was approached a t the end of 2 hours.
v)
!. ::
E
TABLE I. ACIDINTERCHANGE OF ROSIN WITH OIL Time,
Hr. 0 0.5
1
2
%
Rosin 50 41
36 30
%
Fatty Aoids 1 10 14 20
I 2
Figure 2.
Since no method was available to measure the amount of ester interchange occurring when an ester-type resin was heated with the drying oil, studies were made to see if solubility relationships could be employed. I n order to determine if the solubility behavior paralleled combination of the resin with the oil, the behavior of a rosin-phenolic condensate was studied when heated with linseed oil. This resin is made by condensing a phenolaldehyde resin with rosin, and it is not readily soluble in drying oils, except on heating. The solubility of the resin in the oil was measured by determining the temperature at which a mixture of the oil-resin varnish and a paraffinic mineral oil clouded after the rosin-phenolic condensate and linseed oil were heated a t
I
I
4
6
T I M E , HOURS
Rate of Bodying Linseed Oil and Resins Linear soale
Undoubtedly, many of the acidic natural resins (17) also combine with the drying oils. It would seem t h a t the running of natural fossil resins could be obviated or some means of effecting interchange between the carboxyl groups with the oil structure could be achieved, because these resins are believed t o be dibasic acids. However, their low solubility in the oil before running has prevented such a n operation. Recently, varnishes have been formulated using both (11) natural and synthetic resins to form gels which are dispersed by further heating. ALCOHOLINTERCHANGE. The ester group in the drying oil
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148
molecule can be replaced with alcohols just as the acid groups can be replaced by a variety of acids. This operation is principally employed in the alcoholysis step in the formation of alkyd resins. Glycerol is largely employed here, although pentaerythritol and other polyhydric alcohols have also been employed. Also, the formation of polyhydric alcohol esters of the drying oils acids has resulted in the formation of synthetic drying oils with improved properties.
'oar----" 1
--9
80
Vol. 42, No. I
indication of the reactivity of a resin with the oil (16). The bodying rate of ester gums and a phenylphenolic varnish resin, A , a t 75 gallons' oil length ( 1 ) is compared with linseed oil in Figure 2. The viscosities are plotted here on a linear scale against time and the sudden upsaeep of viscosity suggests an accelerated rate of polyrnerization caused by the resin, However, i t is doubtful if the phenolic resins combine to any appreciable extent ~ i t linseed h oil If one takes the same results and plots them on a logarithmic scale, an entirely different argument can be derived. Figure 3 s h o w that the slope of the rurve in the three cases is substantiall) the same and the resins do not change the slope of the viscosit3 increase. I n other words, thr most viscous resins have mere11 resulted in a greater viscosity of the starting oil, which then bodies a t the expected rate It has been established empirically that the logarithm of viscosity increases linearly with time Thus, increased rates of bodying cannot be attributed to an? combination of the resin in oil unless a definitely steeper slope of viscosity on a logarithmic scale can he observed EXI'ERIME.NI'AI
A I 0
I
2
4
J 6
T I M E , WURS
Figure 3.
Rate of Bodying
Logarithmic scale
The introduction of synthetic I wins with alcoholic groups has also been used to reinforce drying oils. By using high temperatures, ethyl cellulose does form esters by alcohol interchange with the drying oils (a). In this case, it is apparent that only a few of the hydroxyl groups in the ethyl cellulose are esterified, and the improved solubility of ethyl cellulose is due, in part, to depolymerization. However, formation of cellulose fat acid esters also is a factor in the improved solubility, The presence of cellulose fat acid ester might Tell improve the miscibility of the oils with ethyl cellulose and serve as a coupler. Polyvinyl acetate, on heating with rosin and acidic resins, undergoes a certain amount of acid interchange, and a resin which is soluble in drying oils can be obtained in this manner
Alkali-refined Linseed nil and two commercial r,)sin-niodified phenolic resins were used. Resin B melted a t 130" C and Resin C a t 175" C These resins were chosen as examples of the readily soluble and less solulile resins of this type. The resin6 and oil were heated with stirring in a glass 3-necked flask under carbon dioxide a t 280" C. Twenty minutes were required to reach this temperature. Samples were taken when the temperature reached 280" C. and a t 1, 2 , 4 , and 8 hourd, thereafter. Viscosity of the samples wab taken in Gardner-Holdt tubes and the cloud points were determined by heating equal weights of unthinned varnish and a paraffinic mineral oil of 126' C. aniline point. The mixture was heated until clear and allowed t o cool slowly in a test tube. The temperature where the solution became opaque was recorded as the cloud point. When no cloud occurred a t room temperature, the determination was made at higher mineral oil content (60 to 70%). Results are plotted in Figures 4 and L From Figure 5 , it is apparent that both resins become much more soluble on heat bodying.
(id). Alcohol groups present in the drying oil within the glyceride structure as mono- or diglycerides or in the fatty acid structure as in ricinoleic acid esters undergo chemical reaction with urea formaldehyde and other synthetic resins (4). Polyacrylate esters may be combined with mono- or diglycerides of the drying oils. The resulting polyacrylate-drying acid-glyceride formed from linseed oil dries very rapidly (8). This type of reaction occurs when an ESTERINTERCHANGE. ester resin is heated with a drying oil. Methods of measuring the extent of this reaction have not been achieved, although it is probable t h a t a random distribution of the fat and resin acids in the ester group is reached a t equilibrium. Solubility determinations are useful in confirming the occurrence of ester interchange, However, it has not been possible to make these results quantitatively, since, as seen earlier, the drying oil itself alters in its solvent properties during the heat treatment. It has often been shown that the speed of heat bodying is greatly increased by the presence of certain varnish resins and it is readily observed that the time to reach a certain viscosity may be greatly reduced by such additions. This behavior may be an
30
0
\
I 2
, 4
6
a
T I M E , HOURS
Figure 4.
Solubility of Resins on Heating at 280" C.
The more soluble resin, B, does not cloud after 2 hours' heating under the conditions employed; however, resin C is much less soluble and its cloud point was taken a t a much lower mineral oil content. In the case of resin C, the solubility went through a minimum, reflecting the poorer solvent power of heat-polymerized linseed oil. When the viscosity of these varnishes was measured, a surprising difference between the two varnishes was observed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
January 1950
Resin B exhibited the behavior characteristic of many varnish resins and a progressive increase of viscosity was noted. However, the behavior of resin C was unexpected. Figure 6 shows that the viscosity of the varnish a t early stages of the cooking decreased quite rapidly. This effect, it is believed, is a very good evidence of ester interchange. I n this case, however, the resin is highly polymerized and, since the uncooked oil has a fairly simple structure, the ester interchange results in a simplification of the structure and an attendant decrease in viscosity. However, as polymerization of the drying oil segments in the molecule proceeds, the viscosity increases rapidly and, in over-all behavior, is much faster than the low-viscosity resin employed. This behavior of high-viscosity resins containing the ester structure was observed in several other cases and is observable in long oil preparations, although the effect is most noticeable with highly polymerized resins and a t short oil lengths.
149
PHENOLIC RESINS. Phenol-formaldehyde resins have been used with the drying oils for many years. The high degree of chemical resistance of these resins suggests their use in paints and varnishes. The first use wm in the rosin-modified phenolics where rosin became the solubilizing agent. The authors have already considered the reactions of some of these resins with the drying oils. The introduction of the unmodified resins soon followed. Cresols were used to form relatively low molecular weight resins. Also substituted phenols such as butyl-, amyl-, phenyl-, octyl-, and terpinylphenols were condensed with formaldehyde t o give oil-soluble resins, The alkyl groups prevented gelation and also improved the oil solubility of the resulting resins. Whether phenol-formaldehyde resins react with drying oils is apparently still a subject of controversy (a). Recently, there has been more discussion than there has been experimental work on this point. It is felt that the reactive phenolic resins do combine with the drying oils. Hilditch (9) has studied the condensation of the methyl esters of palmitic, oleic, linolenic, linoleic, and eleostearic acids with 2,6-dimethylol-p-cresol. There was little evidence of any appreciable condensation with the saturated ester or with methyl oleate, although a slight formation of an ester of the resin was suggested. There was evidence, however, of some degree of combination with linolenic and linoleic ester, although, in this case, it was apparent that the principal part of the resin had not combined with the oil. In the case of methyl eleostearate, there was an indication of much more combination with the phenolic resin than in any other case. In this case, 34% more unreacted esters were recovered in a blank experiment than when the phenolic resin was added. In a study of the behavior of the dimethyl01 cresol with linseed oil and tung oil, the indication again was clear that tung oil combined much more readily than did linseed oil. 2
2
0
4
6
I!
TIME, HOURS
Figure 5.
Viscosity of Varnishes L)
A reduction of viscosity as a highly polymerized ester is combined with a low molecular weight ester has been observed by Flory (6). The equilibrium point is the same as that obtained by random polycondensation. Linseed oil polymerized under the conditions of the experiment, resulting in the rapid increase in viscosity after the resin was dispersed. Rosin-maleic esters are widely used in the preparation of varnishes. These consist of the glycerides of rosin and the rosin-maleic adduct. Since these resins have a high ester content, they might well be expected to disperse readily in the drying oils, and this was found to be the case. The behavior (19) of a rosin-maleic-linseed varnish is shown in Figure 6. It will be noticed, however, that the resin does not disperse readily until temperatures above 250' C. are reached. This, it is believed, reflects the relative insolubility of the resin.
i
z
---+ I
I!
a
0
v
I
2
I TIME,
Figure 6.
HOURS
Rosin-Maleic Resin in Linseed
Oil REACTIONS WITH DOUBLE BOND
The double bond in the drying oil is responsible for the increase in viscosity of the oils on heating and of the drying properties of the varnish films. However, the double bonds apparently are not especially active with the usually employed varnish resin. Phenolic resins are believed to combine a t the unsaturated groups. Also, certain hydrocarbon resins add to the drying oils at the double bond but monomers are much more effective (7').
More recently, the reactivity of phenolics with the drying oils has been studied by Runk (14). I n this case, p-terkbutylphenol was used as the source of the resins, and its greater solubility, as compared with p-cresol, was reflected by the complete solubility of the butylphenol condensates in linseed oil. However, when phenol was added with butylphend in the starting material as a cross-linking agent, less soluble resins were
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
150
obtained, and, if 30% phenol is present in the mixture with butylphenol, resins are formed on condensation with formaldehyde which become insoluble in tung oil when they are heated with it. These results indicate t h a t the phenolic resins tend to polymerize much more readily with themselves than they condense with the drying oils. It is also apparent that the difference between tung oil and linseed oil, while noticeable, is not great. Therefore, the evidence does seem t o indicate t h a t the methylolphenols and other reactive phenolics do combine with the drying oils but that this reaction is secondary to the polymerization proress.
.I---
D
1
Vol. 42, No. 1
as its viscosity increases. Therefore, no appreciable combination of the resin with the oil is indicated, since improved solubility would be expected t o result from any such combination. HYDROCARBON RESINS. Many hydrocarbon resins, such as the coumarone-indene resins, give little evidence of any combination with the drying oils. Low molecular weight polystyrene also gives little evidence of chemical combination. The results of measurements of solubility by the cloud point of several resins in linseed oil are shown in Figure 7. Two nonheat-reactive unmodified phenolic resins, low molecular weight polystyrene, and a coumarone-indene resin were heated ( l a ) with linseed oil. Polystyrene increased in cloud point as the time of heating was continued. This indicates t h a t no chemical combination has occurred, the reduced solubility reflecting the poorer solvent power of linseed oil as i t polymerizes. The coumaroneindene resin does become somewhat more soluble as heating is continued. However, i t should be noted that the solubility behavior is entirely different than t h a t observed with ester resins where combination is known t o occur. I n this case, the cloud point does not decrease greatly in the first hour’s heating, but only on prolonged heating, whereas with the ester-type resins, solubility increased very rapidly a t first, and, on continued heating, the resin may become less soluble. I t is felt, therefore, t h a t better solubility of the coumarone-indene resin reflects a depolymerization resulting in a more soluble resin. The possibility remains t h a t conditions can be established whereby a hydrocarbon resin can be depolymerized and the active fragments formed can be combined with the linseed oil molecule. Such conditions, in general, have not been established; although, when dicyclopentadiene (6) does combine chemically with the drying oils, i t is believed that dicyclopentadiene depolymerizes t o cyclopentadiene which then combines with the drying oil.
3
TI ME, HOURS
Figure 7 . Phenolic and Hydrocarbon Resins in Linseed Oil
The structure of the methylolphenol-drying oil condensation products has not been established. It has been shown that when styrene or the rosin acids condense with the saligenin, a phenol chromane is formed. This is believed to be formed by the addition of a quinone methide, formed by the dehydration of the methylolphenol, which adds to the double bond of styrene (IO, 16). Apparently, a second double bond or a conjugated structure of double bonds is not essential t o this addition. However, it is apparent that the phenol alcohols combine much more readily with rosin, and reactive phenolic resins of this type are condensed with rosin to produce the modified phenolic resins. However, they are seldom condensed with drying oils, except for special varnishes, because they foam badly in the varnish kettle, and, in general, must be carefully formulated. Phenolic resins which do not contain reactive groups have been used widely with the drying oils. In this case, there is no clear-cut evidence for any chemical reaction between the resin and the oil. As seen earlier, the increase in viscosity on heat bodying which has been suggested as proof of such combination cannot be regarded as such. Figures 2 and 3 show that the increase in viscosity, when plotted on a linear scale, dors indicate a measurable change in the rate of viscosity increase. Further indication that chemical reaction does not occur is shown by the solubility of resins of this type of heat bodying in linseed oil. Two commercial unmodified phenol-formaldehyde resins were heated to 275” C. and samples mere taken periodically. T h e results are shown in Figure 7 and it will be seen that the solubility of the resin, reflected by the cloud point, becomes progressively poorer as heating is continued. This decrease in solubility has been observed before and is caused by the polymerization of the linseed oil which has poorer solvent properties
LITERATURE CITED
Bakelite Synthetic Resin Formulations, Bakelite Corp., New York, 1940. Bass, S. L., and Sherk, J. L., in Mattiello, J. J., “Protective and Decorative Coatings,” Vol. I, p. 797, New York, John Wiley &Sons, 1941. Charlton, W., and Perrins, L. E., J . Oil & Colour Chemists’ Assoc., 30,No. 324, 185 (1947). Chatfield, H. W., “Varnish Constituents,” p. 175, New York, Interscience Publishers, Inc., 1944. Flory, P. J., J. Am. Chem. Soc., 64, 2205 (1942). Gerhart, H. C., and Adams, L. M., U. S. Patent 2,397,601 (April 2, 1946). Hexvitt, D. H., and Armitaae. F., J . Oil & Colour Chemista’ Assoc., 29, No. 312, 109 (1946). Hewitt, D. H., and Armitage, F., U.S. Patent 2,441,068 (May 4. 1948). Hilditch, T. P., and Smith, C. J., J. soc. Chem. I n d . , 54, ll1T (1935). Hultzsch, K., J . prakt. Chem., 158, 275 (1941). Krumbhaar, W., U. S.Patent 2,471,629 ( M a y 31, 1949). Powers, P, O., IND.ENG.CHEM.,ANAL.ED.,14, 387 (1942). Powers, P. O., C . S. Patent, 2,371,065 (March 6, 1945). Runk, R. H., IND.ENG.CHEM.,submitted for publication. Shuev, R. C., Ibid., 32, 925 (1940). Singer, J., Kem. Maanedsblad, 23, 49 (1942). Sleightholme, J. J., “Varnish Making,” p. 94, New York, Chemical Publishing Co., 1940. RECEIVED July 18, 1949. Presented before the Division of Paint, Varnish, and Plastics Chemistry at the 116th Meeting of the AMERICANCHXMICAL SOCIETY,Atlentic City, N. J.
