INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Yol. 23, No. 1
Some Studies in the Fat-Liquoring of Chrome Leather Effect of Hydrogen-Ion Concentrations upon Oil Adsorption' Edwin R. Theis and Frank S. H u n t ENGINEERING, LEHIGHUNIVERSITY, DEPARTMENT OF CHEMICAL BETHLEHEM, PA., AND RESEARCH LABORATORIES, HUNT-RANKIN LEATHER co., PEABODY, MASS.
Characteristic fat-adsorption curves were obtained (2) Fat l i q u o r s of the XPERIMENTAL work for various oils used in t h e fat-liquoring of chrome same type as used above were with relation to the leather. It is shown that t h e pH value of both t h e fundamentals of fatadjusted to varying pH conskin and t h e fat liquor is important and results in ditions and pieces of chromed liquoring of leather has been varying t h e amounts of oil being adsorbed by t h e skin (pH 4) fat-liquored for rather meager. Wilson and skin over a pH range. It is further shown that each 1 hour a t 100" F. (36" C.). his co-workers have given type of oil has its own characteristic adsorption curve (3) Various fat liquors in the leather chemist about over this range. Addition of another oil t o a control general use in the leather inthe only information that is oil results in various modifications of t h e characteristic dustry were adjusted to pH available. Wilson has adcurves of either pure oil. The relation of strength of values ranging from 1 to 12 vanced theories to account leather to fat liquor and to oil adsorbed is shown. and chrome skin (pH 4) for the many peculiarities The adsorption of the oil is shown as "oilation" by fat-liquored for 1 hour a t that occur during the fatmodified by means of t h e dilatometer as originally 100" F. (38" C.1, liauorinz of skins and has Theis and Neville. (4) It was early evident di'scuss4 the effect of many that the strength of the fatvariables. T h e s e variables liquored skin was dependent upon the fat liquor used and may be summarized as follows: upon the pH value of the fat liquor. Accordingly, experiThe effect o f fineness and stability of the emulsion. (1) ( a ) A very unstable fat liquor precipitates oil on the surface ments were made to determine if in general the strength was in any way related to the pH value of the fat liquor of the leather. ( b ) A highly dispersed fat liquor gives a very pliable leather used. but tends to Droduce looseness, especially in the flanks. (5) In all cases where triethanolamine was added to the (2) Fat is not absorbed by leather from fat liquor in direct system the leather showed a lessened fat take-up but a greater proportion to fat content of liquor. (3) The effect of time. Absorption increases up to 4 hours, pliability and even ragginess. For this reason some of the but penetration does not increase much since oil deposits chiefly in the outer layers. C (4) The effect of pH value. The hydrogen-ion concentration plays very little role with regard to the quantity of oil taken up.
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Figure 1-Effect of Skin Acidity u p o n Percenta g e of Oil Taken U p by Chrome S k i n
It seemed to the writers that the pH value of the fat liquor should have some effect upon the amount of oil taken up by the skin, and the following experimental work was started in order to determine definitely any such effect. Experimental Procedure
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Figure 2-Effect of Hydrogen-Ion Concentration of Fat Liquor u p o n Oil Taken U p by Chrome Skin A-System sulfonated neat's-foot-raw neat's-foot-water. B - S y s t e m sulfonated neat's-foot-raw neat's-foot-triethanolamine.
(1) Chromed skin after shaving was placed in solutions of varying pH and allowed to remain thus until the skin had attained the set pH wanted. This acidity or alkalinity was obtained by the addition of hydrochloric acid or sodium hydroxide. The pieces were then placed in fat liquor a t 100" F. (38' C.) for 1 hour. Two types of fat liquor were used-sulfonated oil-raw oil and sulfonated oil-raw oiltriethanolamine (Figure 1). 1 Presented by E. R. Theis under the title "Some Studies in Fat-Liquoring" before the Division of Leather and Gelatin Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930.
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Figure 3-Percentage of Oil in Chrome Leather When Various F a t Liquors Are Used a n d When p H of Fat Liquor I s Varled
IIVDUSTRIAL A S D ENGINEERING CHEMISTRY
January, 1931
51
two exceptions: (1) less oil is taken up with decidedly greater pliability, ( 2 ) on the very acid side (pH 1 to 2) more oil is taken up and less detannizing takes place. Even though less oil, in general, is taken up, much greater pliability is obtained, in some cases too great a pliability leading to ragged flanks as though over-fat-liquored. The addition of the triethanolamine leads to greater dispersion of the oil in water and therefore to a more stable emulsion-thus this condition in fat-liquoring. Effect of Varying pH of Fat Liquor
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work indicated that there was a contraction in net rolume of the system when chromed skin was placed in a fat liquor. Small pieces of the skin were placed in the dilatometer and the bottles filled with a standard fat liquor. The contraction in volume was measured at constant temperature. Sulfonated neat's-foo t oil was compounded with various percentages of moellon and with various percentages of sulfonated cod oil, the pH value of the resulting oil adjusted and the fat adsorbed by chrome leather determined. I n all cases, the oil used in
If, instead of varying the pH of the chromed skin, the hydrogen-ion concentration of the fat liquor is adjusted to varying pH, an entirely different picture results, as shown in Figure 2. Curve A shows the system raw oil-sulfonated oil-water adjusted to a pH range of 1 to 12. I n the range 3 to 7 there is little difference in the oil take-up, whereas above pH 7 there is a gradual increase to pH 10, when there is a sharp decrease. I n the range of 1 to 3 there is a very low oil take-up, due in all probability to the instability of the fat-liquor emulsion. As the pH value of the system increases up to pH 10, the leather becomes more pliable, but beyond this it takes on a rubbery appearance and feel. When the system raw oil-sulfonated oil-triethanolaminewater was adjusted to varying pH values and then used as the fat liquor, the data as shown by curve B of Figure 2 were obtained. It is seen that as the pH values of the system increase there is a very gradual increase in the oil take-up until a pH value of 10 is reached, after which there is a decrease. A comparison of curves A and B a t pH 1 and 2 shows that the high acid content at this pH (0.1 to 0.01 A-) affected very little the oil take-up of the system represented by curve B, while that represented by A was drastically affected. The increased oil take-up a t the higher pH values (9 to 10) is undoubtedly due to the soap formed in adjusting the pH values of the fat liquors, this soap acting as an additional emulsifier. Beyond p H 10, however, the alkaline condition of the emulsions causes a decided plumping of the leather. Curve C shows the increase in thickness of the leather fat-liquored at higher pH ralues.
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Figure 6-Effect
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Several fat liquors in general use in the industry were adjusted to varying p H values, and it can be seen from Figure 3 that each fat liquor has its own characteristic curve over this range of pH values. For the system raw neat'sfoot-sulfonated neat's-foot oils there is little difference in oil adsorption in the range pH 3 to 7 , beyond this point there is a gradual increase in oil adsorption with an increased pliability; a t pH values greater than 10 there is a sharp decrease in oil adsorption. For a moellon fat liquor, over
INDUSTRIAL AND ENGINEERING CHEMISTRY
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This fact was also observed for all other fat liquors tried, This experiment carried over into the practical field yielded the information that skin fat-liquored a t pH 6 or 7 was much stronger (tear test) than that processed a t pH 3 or 4. This work is being continued and will undoubtedly be reported at some later date.
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Figure 7-Effect of Fat Li uor upon Chrome Leather System Neat's-Foot 01-Sulfonated Oil-Water Volume contraction indicates absorption of oil.
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Effect of Adding Triethanolamine to System
Figure 5 shows the distribution of oil throughout the skin for the two systems oil-sulfonated oil and oil-sulfonated oil-triethanolamine, This work was only done a t the natural pH of the fat liquor, but is a t least indicative of the distribution for the two systems. Here again the triethanolamine systems show a less adsorption of oil within the leather but a greater pliability. It is also seen that the systems using no triethanolamine tend to drive the oil in from the flesh, whereas the triethanolamine systems have an equal tendency to drive the oil in either from the grain or flesh. This work is being carried further with regard to penetration and distribution of oil within the leather for fat liquors of varying pH value.
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of Composition upon Characteristics of FatLiquor Curves A-Sulfonated neat's-foot oil B-76 sulfonated neat's-foot oil 4- 25 moellon C-5Og sulfonated neat's-foot oil 4- 5 0 2 moellon D--25% sulfonated neat's-foot oil 75 moellon E-0% sulfonated neat's-foot oil 4- 100% moellon
Figure 8-Effect
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a range of pH 1 through 4, practically no oil is taken up by the leather; from pH 4 to 6 there is a decided increase in oil adsorption; from 6 to 9 the oil adsorption remains more or less constant with a sharp decrease beyond pH 9. For sulfonated cod oil there is a very gradual oil adsorption from pH 1 through pH 9, beyond which the oil take-up decreases sharply. Sulfonated cod oil shows the greatest adsorption of all fat liquors used over the range pH 1 to 5. Moellon gives the greatest fat adsorption in the range pH 6 to 8, which may account for its "filling" effect and mellowness of the fat-liquored leather. Figure 3 also shows the characteristic curve for a commercial fat liquor.
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Figure 9-Detailed Effect of Composition upon Characteristics of Fat-Liquor Curves For Notations A, B, C, D, E, see Figure 8.
Figure 4 shows the relation of pH value of the fat liquor to strength of the fat-liquored skin. It is seen that over the range pH 1 to 4, the skin has very little strength (using moellon fat liquor); beyond pH 4 the strength constantly increases to pH 6, when a further decrease is noted. It would seem from such results that the strength of the leather is dependent upon the oil adsorption by the leather, as the strength curve follows very closely that of the oil adsorbed.
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Figure 10-Further Effect of Fat Liquor. Composition u p o n Per Cent Oil Taken Up by Chrome Leather A-Sulfonated neat's-foot oil B-Sulfonated neat's-foot oil C--507, neat's-foot and 50% cod oil
Vhen triethanolamine is used for making the emulsions, much less oil is needed to cause complete fat-liquoring of the skin, and with proper control of the pH value of the skin, fat liquor, and the right concentration of oil, the skin can be better processed than without the addition of triethanolamine. It is absolutely necessary, when using triethanolamine as a dispersing agent in the fat liquor, to use less oil, or the skins will be over-fat-liquored and will tend toward ragginess, softness, and tenderness. The emulsification properties of triethanolamine are more effective in a sulfonatedraw oil mixture if the raw oil has a higher acid value. With regard to penetration alone, triethanolamine rapidly shortens the period of fat-liquoring, causing equilibrium between the skin and liquor to take place much more rapidly. Effect of Adding Egg Yolk to Fat Liquor
Rlerrill points out that when egg yolk is incorporated with a sulfonated neat's-foot oil fat liquor the total fat adsorbed by the leather increases. The work of the present writers in some instances shows the same facts, but in other instances does not. When a system sulfonated neat's-foot oil-egg yolk is varied with respect to pH value and chrome skin fat-liquored with this emulsion, the writers find that from pH 1 to 4.5 the total fat adsorbed by the leather is considerably less than that adsorbed when the system contains only sulfonated neat's-foot oil. However, beyond pH 4.5 the total oil adsorbed becomes greater than with the sulfonated oil until pH 6.75 is reached, when the percentage oil take-up again decreases decidedly below that for sulfonated neat's-foot oil alone. The curve for the system sulfonated oil-egg yolk in Figure 6 again illustrates the
January, 1931
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
fact that, over the pH range used, each system has a characteristic curve peculiarly its own. Effect of Fat Liquor on Volume of System
Figure 7 shows the contraction in net volume of the system when chromed skin is fat-liquored. During the first hour there is a very rapid decrease in net volume, attaining a practical equilibrium a t the end of l l / z hours. This rapid contraction would indicate a selective adsorption of the oil by the leather and would tend to strengthen the theory as advanced by Wilson that there is a chemical combination between the leather and oil.
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Effect of Composition of Fat Liquor
Figures 8, 9, and 10 show the effect of the composition of fat liquor on the curves. Figures 8 and 9 show how the curve characteristics change when sulfonated neat's-foot oil is compounded with various amounts of moellon. Figure 9 shows the detailed changes in characteristics. These curves indicate that the moellon has the predominating influence. Figure 10 shows the influence of sulfonated cod oil upon the characteristic curve of sulfonated neat's-foot oil. The resulting curve for a 50 per cent mixture of the two oils in no way resembles the curves for either of the unadulterated oils.
Studies in the Drying Oils XIV-Rate of Oxidation of Linseed Oil at 160" C.' J. S. Long and H. D. Chataway2 LEHIGEUNIVERSITY, BETHLEHEM, P.A.
The rate of oxidation of drying oils at 160" C. deX I D A T I O N plays a for the gas through the pump. creases as an almost straight-line function of the degree vital role in a t least Jvithin the central tube is the first stage of setof oxidation until gelation takes place. a glass plunger filled with Gelation ensues when a certain size or degree of soft-iron wires, and fitting tjng of drying oils and in paints, varnishes, and other complexity or of polarity of the molecule has been closely outside the central p r o t e c t i v e coatings. The reached. It is only indirectly a function of the degree tube are two electromagnetic of oxidation. oxidation of drying oils, both coils. Current is passed alterin bulk and in thin films has In the case of glycerol esters of unsaturated fatty nately through these, whereacids gelation or setting occurs when one ethylene upon t h e p l u n g e r within therefore been studied by many investigators (1 to 7 , linkage on each molecule of acid in the ester has taken moves rapidly back and forth, up sufficient oxygen to form a peroxide group. thus operating the valves at 9). In a previous paper by Chataway (1) earlier work The loss of carbon and hydrogen from drying oils either end and causing an along the same line is deby oxidation at the elevated temperature of 160" C. almost c o n t i n u o u s circulaamounts to only 2 to 3 per cent up to the point of t i o n of g a s t h r o u g h scribed. The present paper deals setting or gelation. the a p p a r a t u s . The rate of c i r c u l a t i o n m a y b e with oxidation of linseed oil and related substances by blowing oxygen through the oil in varied over a wide r a n g e b y varying t h e current bulk. A temperature of 160" C. was chosen, first because passing t h r o u g h t h e coils. Some difficulty was at this temperature the oil can be oxidized to the gel point encountered in the construction of the valves and finally within a working day; second, because it is low enough to the design of these was slightly altered (Figure 2). In minimize effects due to heat bodying alone. Thus linseed making such a valve the grinding in is done before the outer oil can be heated a t 160" C. in an inert atmosphere for many tube is sealed on. The valve is then completed with little days without gelling. Incidently it is approximately half difficulty, way between room temperature and 293" C. (560" F.). The oil to be studied is placed in the bubbler, A , a Pyrex glass container 38 mm. in diameter fitted with a groundApparatus , and ts. glass cap holding the inlet and outlet tubes, t ~ tz, A diagram of the apparatus is shown in Figure 1. It The outer wall of the container which projects above the will be seen that the whole forms a complete circuit open can is necessary to afford a means of supporting the conto the air a t no point. It is filled with oxygen which is con- tainer and also to hold the mercury required to make the tinuously circulated by means of the circulating pump, joint air-tight, The gas circuit may be "shorted" across E. The original pump was one described by Chatterji the outlet and inlet tubes by means of the three-way stopand Finch (Z),but the rate of circulation maintained by this cock, a. This is an essential feature to prevent frothing pump proved to be extremely irregular over short periods. For of the oil over the sides of the container while filling the this reason and also in order to avoid the possibility of apparatus with oxygen. Such frothing would lead to surcatalyzing the reaction by mercury vapor from the valves,' face drying as well as bulk oxidation of the sample and the pump was replaced by an all-glass electromagnetic one this would impair the value of the results. The outlet designed by Funnel and Hoover (7). This pump consists tube, tz, leads to sulfuric acid and soda lime (ascarite was of a central tube terminating a t each end in an upper and finally used and found to be satisfactory) a t B1 and BP, lower valve, each pair of valves constituting a passageway respectively. About 4 inches (10 cm.) of platinum wire are sealed into the apparatus a t Bz. This is maintained a t 8 1 Received September 19, 1930. Presented under the subtitle before red heat, just as in Orsat combustion pipet, in order to burn the Division of Paint and Varnish Chemistry at the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. the considerable quantities of organic compounds which * Archer-Daniels-Midland and William 0.Goodrich Fellow a t Lehigh are found to be untouched by the sulfuric acid. The water University. and carbon dioxide SO formed are absorbed by the soda lime a The danger of this was pointed out in a private communication by J. (or ascarite) in BB. L. Buchan of the Goverrnent Laboratories London, England.
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