Oxidative Stabilitv of Cellulose J
Derivatives HEAT STABILITY OF ETHYLCELLULOSE LANE F. MCBURNEY Hercules Powder Company, Wilmington 99, Del. The heat degradation of ethylcellulose is shown to be an oxidation reaction brought about by the oxygen of the air. Peroxide formation is the primary result of oxygen attack; secondary reactions such as viscosity drop, ethoxyl loss, and carboxyl development result from peroxide decomposition. A mechanism has been proposed to explain the course of the degradation reaction and the degradation reaction has been shown to be inhibited by compounds such as secondary aromatic amines, and substituted phenols and hydroquinones, and to be retarded by primary aromatic and aliphatic mercaptans (thiols).
T
HE cellulose ethers, of which ethylcellulose is the most im-
viscosity achieved. Thirdly, it is conceivable that the products of decomposition will also influence the rate of oxidation. Therefore, the ultimate viscosity would be dependent upon whether such materials could or could not escape from contact with the cellulose derivative. As the assumption t h a t the degradation reaction is a n oxygen oxidation seemed most reasonable in the light of previous work on ether stability, it was decided t o measure the rate and volume of oxygen absorbed b y a sample of ethylcellulose under optimum conditions, and t o use these results as a measure of stability. Such a method would also permit a correlation between oxygen absorbed and chemical and physical changes undergone by the ethylcellulose during this treatment.
portant, are distinguished by their great stability toward MEASUREMENT OF OXYGEN ABSORPTION chemicals, such as alkali and salt solutions, and toward water. However, upon being exposed t o oxygen at high temperature A line drawing of the apparatus used to measure the volume Qf (9,11) they show considerable embrittlement. oxygen absorbed by ethylcellulose is shown in Figure 1. The I n commercial practice it is customary t o incorporate antioxireaction apparatus consisted of a 150-ml. Pyrex bulb connected by means of a ground joint t o a mercury seal stirrer. This bulb was dants (1,.5, 6, 10,1 2 ) into ethylcellulose formulations in order t o connected, by a spherical joint, to the gas measuring buret. An prevent excessive degradation and t o prolong their plastic life. outlet tube was also sealed into the Pyrex bulb and could be conThe effectiveness of such materials, in preventing breakdown of nected to a trap which was cooled by dry ice for the purpose of the plastic, is measured in terms of the per cent of viscosity recondensing any volatile reaction products. One leg of a manometer was sealed into the oxygen inlet system and the other leg tention obtained under a given set of conditions of heat and air or was connected to a barometric compensator located in the conoxygen availability. However, up to the present time, no standstant temperature bath. The barometric compensator had a ard heat test has been agreed upon within the industry. I n fact, volume approximately equal to the total volume of the reaction it has been difficult t o obtain any degree of reproducibility in any and gas measuring systems. The stopcock, in the compensator one individual test. This lack of agreement can be attributed t o several factors. First, viscosity retention has been used as the criterion of stability. Although this factor is important from commercial aspects, viscosity changes are a result of the degradation reaction and are not a direct measure of the reaction bringing about degradation. For this reason i t cannot be relied upon completely. For example, if decomposition could occur so t h a t cross linking took place, either the viscosity would remain in the same relative range or in the extreme case i t could be greater after the test than before. Secondly, as it can be assumed that the degradation reaction is a n oxygen oxidation, on the basis of the structure of ethylcellulose and upon the abundant literature ( 4 , 8, 9, 6 - V TRANSFORMER 16)relative t o ether oxidation, the oxygen availability during the test llOV A C will greatly influence the ultimate Figure 1. Apparatus for Measuring Oxygen Absorption of Ethylcellulose
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I
I
I
I
I
I
Vol. 41, No. 6
I
T UE
Figure 2. Rate of Oxygen Absorption by Various Types of Ethylcellulose a t 90' C.
side of the manometer, Iyas used to adjust the pressure to a known value (atmospheric) before beginning a series of runs. Constant pressure \vas maintained in the reaction flask at all times during the oxidation of ethylcellulose, by a n automatic pressure equalization in the gas measuring buret. T T Vcontacts ~ were sealed into the manometer; one was permanently in contact with the mercury and the other was in contact only when absorption of oxygen resulted in a slight decrease in pressure in the reaction system. The contacts were connected through a Serfass electronic relay to an electrolyt,ic cell. The cell was connected to the top of the bulb which acts as a reservoir for the dibutyl phthalate used as qmeasuring fluid in the gas buret. Upon excitat,ion of the relay, current flowed through the electrolytic cell, thus producing gas. This gas then forced the dibutyl phthalate up into the buret until the pressure had been returned t o its original value, at which point contact was broken and no further current passed through the cell. For relatively slow rates of oxidation, such as were observed with ethylcellulose, this system was capable of maintaining the pressure constant to within 1 mm. of mercury. The temperature in the constant temperature bath was maintained to *0.1" C., and the reaction mixtures mere stirred at a constant rate of 500 r.p.in. A saturated solution of hydrazine sulfate was used as the elcctrolyte in the elect.rolytic cell and evolved nitrogen and hydrogen as products of electrolysis. Before each experiment the reaction apparatus was cleaned with soap and wat,er, then filled with cleaning solution and allowed to stand for several hours. The cleaning solution was removed, the flask was rinsed with distilled water, washed finally with distilled acetone, and dried in an oven a t 100" C. for 1 hour. After the above treatment the reaction flask was connected as shown in Figure 1 and oxygen allowed to pass through it for at least 45 minutes. The apparatus was t,ested for leaks before Oxidation was initiated by placing it under 10 min. of mercury pressure. If t'he system held this pressure unchanged for 30 minutes, it was assumed that the apparatus was ready for the experiment. The ethylcellulose sample to be oxidized mas then added through the stirrer neck, while a slow stream of oxygen mas admitted through the oxygen inlet tube. The stirrer neck x a s closed arid the system allowed to come to thermal equilibrium with stirring. Zero time was taken when the pressure became constant. The pressure increased when the flask was closed owing to the heating of the oxygen which was introduced into the flask. PREPARATIOIV OF SAMPLES
The ethylcellulose samples were dissolved in sufficient 70 to 30 rat,io of benzene to alcohol, with stirring, to make a 10% solution by weight. This solution was poured into a large dish and the solvent allowed to evaporate to dryness. The film which resulted from this evaporation was dried a t 70' C. in a vacuum oven after being stripped from the glass tray. The film was then cut int,o small pieces and ground, along with dry ice in a Wiley mill, through a 20-mesh screen. The dry ice served a dual purpose; it kept the temperature low enough t o prevent degradation, and also provided a n inert atmosphere during this operation. After grinding, the sample was again dried for I hour a t 100" C. in a vacuum oven and was ready for the oxidation studies. I n the ex-
, HOURS
Temperature Dependence of Rate of Oxygen Oxidation of Ethylcellulose
Figure 3.
periments in which the effect of stabilizers on the rate of oxidation of ethylcellulose was studied, the stabilizers vere introduced into the 10% solution in benzene-alcohol. By this technique, they were evenly distributed throughout t,he ethylcellulose and thereby exerted a uniform effect on the over-all rate of oxidation. The ground film was oxidized, as such, in t,he absence of any solvent. The use of solvents in this system had tlvo major disadvantages. First, because of t,he viscosity characteristics of the ethylcellulose, it was necessary t80use dilut,e solutions which involved large quantities of solvent and complicated attempts to determine the oxidation products. Secondly, over long periods of time all the solvents investigated were affected by the peroxides formed during oxidat'ion and it x a s not possible t o ascertain how much of the oxygen absorption was due to ethylcellulose and how much was due to peroxide-catalyzed solvent oxidation. Reproducibility of results was satisfactory using ground film. This is illustrated in Figure 2 by curves 1 and 2 which represent duplicate runs on the same sample of ethylcellulose. PEROXIDE DETERMIN.4TIOiY
The peroxide content of ethylcellulose ITas determined by heating a sample, dissolved in alcohol-benzene mixture, with potassium iodide and titrating the liberated iodine rq-ith standard thiosulfate solution. A 2-gram sample of ethylcellulose was dissolved in 100 ml. of 70 to 30 2B alcohol (ld)-benzene solvent. N'hen solution was complete, nitrogen \\-as bubbled through the solution for 1 minute. A blanket of nitrogen was maintained over the solution as 1 ml. of a saturated potassium iodide solution and 5 ml. of glacial acetic acid were added. During the addition the solution was swirled constantly. The resulting solution was placed on a water bath at 50' C. for 45 minutes. ht the end of this time, the solution was titrated immediately with 0.01 A' thiosulfate solution. I t was found advisable to run blanks on each new batch of solvent as it was prepared. CARBOXYL DETERMIWATIOX
The carboxyl content of ethylcellulose was determined by the pot,entiometric titration of a sample dissolved in alcohol-benzene mixture. A Beckman pH meter, laboratory model G, was used in conjunction with a glass electrode. The end point was determined from a plot of apparent p H versus milliliters of alkali, and was chosen as the point of maximum slope. The electrode response in some cases was not too rapid, arid it was found advisable to maintain a nit,rogen blanket over the solution at all times to prevent interference by the carbon dioxide of the air. A 1-gram sample was dissolved in 100 ml. of a 70 to 30 2B alcohol-benzene solvent mixture. The resulting solution was stirred mechanically and titrated with 0.05 N sodium hydroxide solution, while a nitrogen blanket was maintained over the mixture. -45-ml. microburet graduated in 0.01-ml. subdivisions was used for these titrations in order t o increase the accuracy of measurement. A blank t,itrat,ionwas run on each batch of mixed solvent as it was prepared. This blank should not exceed 0.025 ml. of 0.05 iV sodium hydroxide.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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pressed in this fashion in order to permit the comparison t o be made on one graph; for that reason, the curves give no indication of the reaction mechanism.
F T H O X I L CONTENT
OXYGEN A 8 S O P B E D I N MILLIATOMS PER GLUCOSE
Figure 4.
s
UNIT
Chemical Changes Accompanying Oxygen Oxidation of Ethylcellulose at 90' C. VISCOSITY DETERMINATION
Viscosity determinations on ethylcellulose were made in 70 t o 30 benzene-2B alcohol solution using a Ubbelohde (IS) viscometer. The individual viscosities were determined at concentrations of 1, 0.75, 0.50, and 0.25%. The intrinsic viscosity was determined by extrapolating the logarithm of q s p / C versus C t o zero concentration, according to Martin's (7) equation, where C is expressed as the concentration of the ethylcellulose in grams per 100 grams of solution.
Curve 1 is the rate of absorption at 108' C. I n this case a very short induction period was observed and the oxidation reaction was rapid over the range of measurement. Curve 2 is the corresponding rate at 90" C., curve 3 at 80" C., and curve4at 69 O C. I n all these cases the ethylcellulose samples were identical. The effect of the lower temperature was dual: i t reduced the rate of oxidation, and it increased the induction period. For example, if the induction period can be assumed t o be complete with a n absorption of 20 ml. of oxygen per 15 grams of ethylcellulose, then the induction period increased from 1.8 hours a t 108" C. t o 70 hours at 69 C. By drawing tangents t o these curves at points of equal oxygen absorption, i t is possible t o obtain initial reaction rates. When the logarithms of these rates are plotted against the reciprocal of tfheabsolute temperature, the rates at 90 ', 80 ', and 69 ' C. all fell on a straight line. However, the rate of 108O C. was off the curve and considerably below where it would have been if calculated from the values at the other three temperatures. This indicated that either of two possibilities was occurring. First, that at a point between 90" and 108" C. diffusion was becoming the rate controlling step in the reaction. Secondly, that some other reaction was becoming rate controlling over t h a t operating between 69" and 90" C. By calculating a n ener y of activation from the temperature coefficient plot, a value of 25,000 calories was obtained for the reaction between 90' and 69' C. Since this value is at least five times the value which would be expected if the rate being measured was one of diffusion, i t seemed reasonable t o assume t h a t oxygen absorption in this range would be truly representative of the oxidation of ethylcellulose. On the basis of these facts, 90" C. was chosen as the temperature at which all further work would be conducted, as i t satisfied the two requirements previously set forth. CHEMICAL CHANGES ACC02MPANYING OXIDATION
INFLUENCE OF ETHOXYL SUBSTITUTION, VISCOSITY, AND TEMPERATURE ON ETHY LCELLULOSE OXIDATION
I n order t o establish the general nature of the ethylcellulose oxidation reaction, it was necessary to show whether differences in chain length and the degree of substitution of the chains would cause differences in the character of the oxygen absorption curves. Figure 2 shows a representative group of curves resulting from the above investigation. The ethylcellulose samples used to obtain these data varied from a low of 44% ethoxyl and 50-centipoise viscosity in 570 concentration to a maximum of 49,270 ethoxyl and 1000-centipoise viscosity. Thus the useful range of both substitution and viscosjty has been covered. Inspection of the curves shows that while there is a very considerable variance in induction period from sample to sample, the general rates of oxygen absorption are similar after the reaction has been initiated. Curve 5 in Figure 2 shows the longest induction period although it is the most highly substituted sample. Curves 1 and 2 show the least induction period and regresent samples of the highest viscosity, while not differing very greatly in degree of substitution from sample 5 . These results led to the conclusion that the rate of oxygen absorption and the length of the induction period are not a function of the degree of substitution or of viscosity within the commercially useful ranges. The effect of temperature on the rate of oxygen absorption by ethylcellulose was of paramoun importance. I n order to make such a study possible, a sufficiently high temperature had t o be chosen so that an appreciable rate of oxygen absorption would occur in a reasonable time. Also it was necessary to establish the fact that the rate being measured was actually that of oxidation and not merely the rate of diffusion of oxygen into the cellulose granules. I n order to establish these points, oxygen absorption rates Were measured a t temperatures between 69" and 108" C. This series is illustrated by the curves in Figure 3 in which the volume of oxygen absorbed by 15 grams of ethylcellulose is plotted against the logarithm of time. The time scale was ex-
In order to measure the chemical and physical changes ethylcellulose undergoes during oxidation, samples were oxidized to definite levels of oxygen absorption. These samples were then analyzed for carboxyl content, peroxides, and total ethoxyl. Figure 4 shows the results of these runs graphically. The peroxide content shows a n immediate development with oxygen absorption and then goes through a maximum a t a n absorption of 320 xnilliatoms of oxygen per glucose unit. The carboxyl content also increases but does not show a similar maximum; instead, it continued t o rise throughout the entire range of measurement. The ethoxyl content did not change for a low absorption of oxygen but it then decreased rapidly from approximately 48 t o 45%. This was followed by a much slower decrease in ethoxyl which continued throughout the entire reaction. The nature of the peroxide formation curve is probably the most significant of these results. It indicates an initial attack of 0.91
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3 40
3.00
5
5 -*c
260e
O3
i
4
'2
0.4
2 20
rc x z
$
I 8 0
-
1.40
0
40
Figure 5.
BO 120 160 BOO 240 280 320 OXYGEN ABSORBED IN MILLlATOMS/GLUCOSE UNIT
360
1.00 400
Heat Degradation of Ethylcellulose a t 90" C.
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the oxygen t o form peroxide; furthermore, once these peroxides are formed, they undergo a simultaneous decomposition. The maximums in the curve are then accounted for by the fact that the rate of decomposition is such that peroxides are breaking down faster than they are being formed: thus, there is a decrease in the total concentration of the peroxides present. I t can be deduced further that the decomposition of the peroxide is accompanied by a loss of ethoxyl by the ethylcellulose, and, as would be expected, the loss of ethoxyl should lag slightly behind peroxide formation. Carboxyl formation can be occurring on the chain a t the point of peroxide decomposition. The carboxyl measurements can be complicated by the formation of some acetic acid from the acetaldehyde although none was actually isolated from the oxidized products. REACTION OF OXYGEN WITH ETHYLCELLULOSE
On the basis of these findings it is possible t o deduce a tentative mechanism of the oxidation which is illustrated in the following: INITIATION
H-
bI -0CH1CH3
K1 + R. + H-
bI -0CH-CH3
PROPAGATIOS
H-
(4I OCH-CH3 + O=O . I b
-O-CH-CH,
I
-OCH2-CH3
H-(!-OCH-CH,
I
4I
c:
+ H-
H-4-OCH-CH,
9I
Kz
+H-
1
i
+ RH
+ H-
x I
K3
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only minute traces of oxygen have been absorbed. This early stage is then followed by a period of autocatalysis. This change in rate is caused by the decomposition of peroxides to form more free radicals which then initiate nen- oxidation chains. As can be seen from the above sequence of reactionb, the paths by which a hydroperoxide may decompose are numerous and in all probability all are followed to some extent. For example, deconiposition may occur so as to generate free hydroxyl radicals. They are highly reactive and would be expected to be excellent reaction initiators. Another decomposition would result in the formation of acetaldehyde. This type of decomposition actually does occur, as acetaldehyde was isolated from the oxidation reaction and identified as its 2,4-dinitrophenylhydrazone. The cellulosic radical left after the formation of acetaldehyde may undergo a number of reactions. It can act as a n initiator by removing a hydrogen from an adjacent ethoxyl group or it can initiate the oxidation of acetaldehyde by removal of hydrogen. The cellulosic free radical can be converted to a carbonyl group by reaction with a free hydroxyl radical or it can act as a chain terminator by reaction with any other of the radicals present. I n the oxidation of rubber, the presence of a free radical on the chain causes scission to be greatly favored. I n a similar manner the cellulosic radical would be expected to bring about a certain amount of chain rupture. Figure 5 shows the rate of viscosity drop and fluidity change with oxygen absorption. The viscosity drops rapidly initially and then tends to level off, whereas the fluidity is a linear function of the oxygen absorbed, over the range of measurement. This indicates t h a t the chain scission mechanism probably is operative. However. chain scission could be the result of another reaction which can be illustrated as follows:
--+
bI -0CH-CH3
0
I
H
H
DECOMPOSITION I
H-&OCH-
I i i!
-CH,
K4
+
.OH
0
b
I
0
H
I
!
H
0 I
H-&-OH
+ R.( R H = acetaldehyde
or ethylcellulose)
Ks
I t is possible that such a reaction occurs along with the oxidation of the ethoxyl groups, but it has not been possible to measure its extent in the present series of experiments. The postulated mechanism requires the formation of hydroperoxides and their decomposition. The latter is accompanied by a corresponding loss of ethoxyl. From such a reaction sequence i t is possible to deduce the following kinetic expression:
H-C--OR Chain scission
II
On the basis of the above mechanism the initial reaction between the ethylcellulose and oxygen is one of hydroperoxide formation, In the uncatalyzed state, this reaction is very slow and is represented by the early portion of the induction period. However, during this time peroxides are being formed although
where P = hydroperoxide concentration, k 2 = rate of peroxidation, lcl = rate of initiation, and k = rate of chain breaking. A rigorous mathematical solution of such an equation is not possible in this case as it would necessitate the separate evaluation of the individual reaction rates. For example, the rate of
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tion. This lack of mobility would increase the probability for two such radicals to combine to terminate a chain. On the other hand, it is not likely t h a t such active points would influence chains other than those which are very close neighbors. Because of this, i t is difficult t o see how any kinetic expression would adequately describe the oxidation over its entire course, for such equations are developed for solutions in which complete mobility is assumed as a prerequisite.
TIME
, HOURS
F i g u r e 6 . Calculated us. M e a s u r e d Functional Group Development chain breaking would be a composite of all the possible mechanisms by which the chains could be terminated and each would have to be evaluated separately. Another factor would be the dependence of the oxidation rate upon the partial pressure of the oxygen present. The literature ( 3 )is inconclusive relative t o this factor and such dependence would have to be established experimentally for this reaction. However, through some simplifying assumptions i t is possible to set up equations which appear to fit the experimental points fairly well, a t least over the portion of the ethylcellulose oxidation that was followed. Equation 1 shows the reac3tion velocity to be primarily dependent upon the rate of peroxidation whereas the terms within the bracket account only for the rate of initiation and termination of the reaction. By considering the term within the bracket t o remain essentially constant, although the individual rates themselves may change, i t is possible to treat the formation of peroxides and loss of ethoxyl as a simple simultaneous process from which the concentration of the peroxide can be represented by:
where P = peroxide concentration, K: = rate of peroxide formation, K: = rate of peroxide decomposition, and CO = initial ethoxyl concentration. The two velocity constants were evaluated by choosing a single set of values and calculating K1 directly from them, since the peroxides present plus the ethoxyl loss will be a measure of the total peroxide formation up to t h a t time. From the value of K: i t is possible t o determine K i graphically. The agreement between the calculated rate of ethoxyl loss and peroxide formation and that found experimentally is remarkably good (Figure 6 ) despite the simplifying assumption involved in the calculation. The calculated rate is represented by the smooth curve, and the observed rate is shown by the circles. Furthermore, because the agreement is so good, any future mechanism will have to account for the kinetics as found in these calculations. Attempts to give a complete kinetic evaluation of polymer reactions, such as oxidations, are further complicated by the nature of the polymer system, especially in the absence of any dispersing agent. For example, the mobility of a reactive center on a long chain is greatly reduced over what i t would be in a corresponding short-chain molecule, so that its potential sphere of influence is greatly restricted. This would tend to retard the separation of free radicals which are produced in close conjunc-
TIME, HOURS
Figure 7 . Initiation of Oxidation of Ethylcellulose 1, 45% ethoxyl; 2, 45% ethoxyl, initiators removed; 3, 4 5 p ethoxyl, initiator removed, plue 0.1 o oxidized ethylcellulose; 4, 45% ethoxyl, initiators removed plus 0.1 yo paraldehyde
Another requisite of this proposed mechanism would be the ability of peroxides or similar materials t o catalyze the rate of oxidation. Ethylcellulose is subject t o such a catalysis as can be seen from Figure 6 . Curve 1 of Figure 7 is a typical oxygen absorption curve of a n ethylcellulose sample. By treating this material in such a fashion to remove low ends, peroxides, and metallic impurities, it is possible t o reduce its r*"e of reaction t o that shown by curve 2. If a small amount (O.lyo) of a n oxidized ethylcellulose, containing peroxides, is added t o sample 2, a very definite catalysis is observed as shown by curve 3. A similar effect can be observed by adding a trace of paraldehyde as shown by curve 4. Although not shown on the graph, materials such as benzoyl peroxide also show a catalytic effect similar to that of oxidized ethylcellulose under the same conditions. OXIDATION INHIBITORS AND RETARDERS
As i t appeared fairly well established t h a t the proposed mechanism is actually operative, a study of inhibitors was undertaken. Their effectiveness was measured by following the rate of oxygen absorption for a period of time and comparing the observed rate with a control of the same ethylcellulose sample without inhibitor present. The program under consideration would involve the comparison of a number of substances with regard to their ability t o inhibit or retard the oxidation of ethylcellulose. For that reason i t was necessary t o determine the concentration of antioxidant t o be used in all of these comparisons. This ratio was established by noting the effect on the oxidation rate obtained by varying the concentration of the hydroquinonemonobenzyl ether. The results obtained in this series are illustrated in Figure 8. A very marked retardation is observed with a sample containing only 0.026% of hydroquinonemonobenzyl ether. When the concentration is increased t o 0.33%, t h e material is very effective and be-
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Vol. 41, No. 6
DIP-EVTCMI~E
‘0
8
IS
32
24
40
48
16
64
72
T I M E , -(OURS
Figure 9. Figure 8.
Effect of Inhibition on Oxidatiori of Ethylcellulose a t 90” C.
Inhibitory Effect of Hydroquinonemonobenzyl Ether on Ethylcellulose Oxidation
haves more as a n inhibitor than as a retarder. This inhibitory effect is even greater at’a concentration of 5yo,although very little difference is observed in the oxygen absorbed over a period of 48 hours between 0.33 and 57% antioxidant concentration. On the basis of the above results, a concentration of 1% antioxidant was chosen as a standard for all the future mork. Figure 9 illustrates the effectiveness of several different conipounds in prcventing oxidation of et’hylcellulose. As can be seen, secondary aromatic amines such as diphenylamine are most effective, as illustrated by curve 5 . This same curve was obtained when substituted phenols were used such as p-menthylphenol, Belro phenol lactone, and similar compounds. I n all these cases, oxidation was completely surpressed for almost 36 hours and t.hen progressed only very slowly over the entire range of measurement. Mercaptans (thiols), on the other hand, showed somewhat peculiar results. For example, the sample containing p-nitrothiophenol as an inhibit,or (curve 4)showed a n initial rapid upt’alte of oxygen followed by a period of no absorption after oxidation was resumed. A similar behavior was shown by 2-thionaphthol. It mas postulated that this initial rapid reaction might represent Oxidation of t8hemercaptan of disulfide, and that the latter was acting as a chain breaker. T h e tcndency for aromatic disulfides t o exist as free radica,ls lends further support to such a hypothesis. However, upon the addition of di(p-nitrophenyl) disulfide to ethylcellulose, very little effect was noted, as can be seen from curve 2, Figure 9. Although cont.rary to expectations, this result might be explained by the fact that since the disulfide has poor solubility in the alcohol-benzene solvent used t o incorporate it into the ethylcellulose, it might not have been
properly diatributed in the film Primary mercaptans were found to be far more effectivo than secondary; in fact, the latter showed practically no inhibitory action. LITERATURE CITED
Bass, F. L., Rauner, L. A , , and Lipkeph, P. H. (to Dow Chemical C o . ) , U. S. Patent 2,383,361 (May 5, 1943). Berl, E., and Rueff, G., Cellulosechemie, 14, 44-7 (1933). Bolland, J. L., and Gee, G., Trans. F a r a d a g SOC.,42, 230 (1946)
Clover, J . A m . Chem. SOC.,44, 1107 (1922). Kline, G. M., Xoc. of Plastics Ind. Conference, Los Angeles, Feb. 23.1943.
Koch, 1%‘. W.(to Hercules Powder Co.), U. S. Patent 2,389,370 (Nov. 25, 1943); 2,333,577 (Nov. 2, 1943).
hlartin, Arthur, and O t t , E., “Cellulose and Cellulose Derivatives,” High Polynier Monograph, Vol. 5, p. 966, New York, Interscience Publishers. 1943. Milas, N . A., J. A m . Chem. SOC.,52, 739-63 (1930); I b i d . , 53, 221-33 (1931).
Moureu, C . , and Dufraisse, C., Chem. Revs. 3 , 113 (1927); J . Sac. Chem. I n d . , 47, 819,848 (1928).
Sharphouse, J. H., and Downing, J . , (British Celanese, Ltd.), Brit. Patent 578.286 (June 21, 1946) ; I b i d . , 580,369 (Sept. 4, 1946). Staudinger, H.. Stockand, H., and Doemisch, K. I?., M e l l i a n d Teztilber., 22, 620-1 (1941).
Tinsley. J . S. (Hercules Powder Co.), U. S. Patent 2,337,508 (Dee. 21, 1943): 2,275,708 (May 18, 1942). Ubbelohde, L., IND.EXG.CHEX,ANAL.ED.,9, 85 (1937). U. S. Treasury Dept., Bur. of Internal Revenue, appendix to Reg. No. 3, “Formulae for Completely and Specially Denatured Alcohol,” 1942. Willard and Wingler, Ann., 431, 317 (1923). RECEIVEDOctober 2, 1947. Presented before the Division of Cellulose Chemistry a t the 112th Meeting of the b ~ n n r c a h -CXEMICAL Sociz,w, New York, N. Y.
(Oxidative Stability of Cellulose Derivatives)
ULTRAVIOLET LIGHT STABILITY OF ETHYLCELLULOSE EVAN F. EVANS ANI) LANE F. RlcBURNEY, Hercules Powder
C
ELLULOSE derivatives exposed to outdoor weathering are known t o degrade more readily than can be accounted for by simple heat-catalyzed oxidation at the prevailing temperatures. This difference is undoubtedly due largely to the ultraviolet radiation of sunlight. Accelerated weathering tests, involvirlg exposure of the sample to ultraviolet light in the presence of air, have been devised for the evaluation of cellulose derivatives. The stability of the
Company, WiZmington 99, Del.
sample I S deteiniined by measuring the pel cent ietrntion of thc original viscosity of the sample. I n the preceding paper of thiq series ( d ) , the heat stability of ethylcellulose was shown t o be related to the stability toward oxidation. Factors influencing the rate of thc heat-catalyzed oxidation were studied and a mechanism for the oxidation was discussed. This mork was extended to a n investigation of the effect of ultraviolct light on the oxidation of ethylcellulose.
