A N A L Y T I C A L CHEMISTRY Kay, K., Reece. G. If.,and Drinker, P., J . I n d . Hyg. Tozicol., 21, 264 (1939). Kent, J. W., and Beach, J. Y., ANAL.CHEM.,19, 290 (1947). Lecomte, J., Ann. phys., 15, 258 (1941). Lecomte, J., Bull. soc. chim. France, 12, 706 (1945). Lecomte, J., C'ompt. rend., 196, 1011 (1933). Ibid., 204, 1186 (1937). Lecomte, J., J . phys. radium, 8 , 489 (1937). ENG.CHEM.,ANAL.ED.,7, 428 (1935). hIalisoff, W.51., IWD. hIartinek, 51. J., and Marti, W.C., Ibid., 3, 408 (1931). IIoskowitz, S., and Burke, 11.' J., Ind. Bull. A'. Y . State Dept. Labor, 17, 168 (1938). Nielsen, J. R., and Smith, D. C., IND.ESG. CHEY.,ASIL. ED., 15, 609 (19431. Kuckolls, -1.H., "Comparative Life, Fire, and Explosion Hazards of Common Refrigerants," Alliscellaneous Hazards No. 2375, Chicago, Underwriters' Laboratories, 1933. Olsen, J. C., Smyth, H. F., Jr., Ferguson, G. E:, and Bcheflan, L., IND.EXG.CHEY.,ANAL.ED., 8, 260 (1936). Patty, F. h.,"Industrial Hygiene and Toxicology," Vol. 11, Chap. 25, New York, Interscience Publishers, 1949. Patty, E'. d..Ychrenk, H. H., and Yant, W. P., ?NO. ENQ. CHEY., .%S.4L. E D . , 4, 259 (1932).
(46) Rogers, G. K., and Kay, B. K.. J . I n d . Hug. Tozicol., 29, 229 (1947). (47) Ruigh, w. L., IND.ENG.CHEY., ANAL.ED., 11, 250 (1939). (48) Silverman, L., Reece, G. >I., and Drinker, P., J . I n d . Hyg. Toxieol., 21, 270 (1939). (49) Smith, C., personal communication. (50) Stair, R., and Coblentz, W.W., J . Resoarch Natl. Bur. Standurds, 15, 295 (1935). (51) Tebbens, B. D., J. I n d . Hug. To.cicol., 19, 204 (1937). (52) Thompson, H. W., and Torkington, P., Trans. Faraday SOC.,42, 432 (1946). (53) Timmis, L. B., J . SOC.C h e m Imi. (London), 63, 380 (1944). (54) Torkington, P., and Thompsori. H. W.,Trans. Faraday Soo., 41, 184 (1945). (55) Webb, F. J., Kay, I(. K., and Sichol, W. E., J . I n d . Hug. Tozicol., 27, 249 (1945). ( 5 6 ) Winteringham, F. P. W., J . Soc. Chern. Id.(London), 61, 186 (1942). (57) Wright, Norman, IND.ESG. CHEM., AN.AL.ED., 13, 1 (1941). (58) Wu, T.-Y., Phys. Rev., 46, 465 (1934). RECEIVED for review August 27, 1931. Accepted December 26, 1951
Ozone Deterioration of Elastomeric Materials Preliminary Results of a Study by Infrared Spectroscopy A. R. ALLISON AND I. J. STANLEY Muterial Laboratory, New York .Vaval Shipyard, Naval Base, Brooklyn 1 , N . Y . The work described consists of exploratite studies with the ultimate objective of developing an accelerated ozone aging test for elastomers based primarily on compositional changes rather than on the conventional variation in physical characteristics. Infrared spectrographic techniques were found to be admirably suited for the reflection of accumulation or depletion of specific structural linkages in pol?mer molecules undergoing ozonization. Purified gum specimens of He, ea, GR- S, nitrile rubber, neoprene, and GR-I were dissolved in chlorinated hydrocarbon solvents such as ethylene dichloride or o-dichlorobenzene, and subjected to a stream of ozonized ox? gen containing approximatel) 50 p.p.m. of oAone. Infrared spectrograms of films cast from the treated solutions show progressire intensification of clearly defined absorption bands a t 2.9 and 5.8 mu, reflecting the functional groups hydroxyl and carbon?1, respectivelj llethods for quantitating these changes by calibration against reference compounds are described. A means is available for following ozone degradation of pollmers in terms of specific \ariations in molecular structure. Basic information of this nature is potentially useful in the development of a n accelerated ozone aging test correlatable with aging under conditions of actual service.
the accelerated evaluation of ozone aging of elastomer conipounds. I n this paper, the initial results preaented are concerned exclusively with the examination of the various elastomers in the crude, or raw gum, state. T h e polymers were ozonized by the 100 r
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.
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HE isolation and identification, by conventional chemical methods, of the products of ozone attack of natural and synthetic rubberlike materials have been intensively investigated by several workers (1, 8, 9). T h e procedures involved are generally intricate and long-drawn-out. T h e present studies were undertaken t o explore the feasibility of employing the relatively simpler method of infrared spectroscopy t o determine compositional changes effected by ozonization of materials of this t.ype. T h e ultimate objective is the development of a practical method, more fundamental in nature than those currently in use (d), for
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Figure 1. Relative Effects of Ozonization and Oxygenation of 1% Solutions of Hevea (Smoked Sheet) in Ethylene Dichloride
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Figure 2. Relative Effects of Ozonization and Oxygenation of 1% Solutions of GR-S (41' Polymer) in o-Dichlorobenzene
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6 8 10 12 WAVE LENGTH, MICRONS
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Figure 3. Relative Effects of Ozonization and Oxygenation of 1% Solutions of Nitrile Rubber (F'aracril 26 N) in o-Dichlorobenzene
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Figure 4. Relative Effects of Ozonization and Oxygenation of 1% Solutions of Neoprene Type W in o-Dichlorobenzene
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Figure 5. Relative Effects of Ozonization and Oxygenation of 1% Solutions of Butyl Rubber (GR-I) in o-Dichlorobenzene
ANALYTICAL CHEMISTRY
632 solut,ion method (1, 9), and were prepared for infrared spectrographic analysis by the technique developed by Dinsmore and Smith ( 5 ) . Essentially, the procedure followed \vas: Purification. The s p t + n e n \viis extracted with acetone (when not c,xcessively gelled bl- that solvent) and 9SCh ethyl alcohol to rr'move antioxidant and residual emulsifying or polymerization agents. Solution. The pui,ificd polymei~n-us dissolved in a chlorinated hydrocahon solvent. Ethylene dichloride and o-dichlorobciizrrle \vert>found satisfactory. The latter, being l ( w volatile, n-as preferred. The conceiitixtion of thr, solution, before ozonization, \\-as adjusttld to coiit:iin 1 gram of polymer per 100 nil. of solvcnt. Ozonization. Ozonized oxygc:n, containing approximately 50 p.p.m. of ozone as determined by periodic iodonietric titration was bubbled at the rate of 0 . j liter pcr miiiute througli 100 nil. of the polymer solution at rooni trrnperature. T h e ozone n-as generated by passing c-onimercial tank oxygen over an ult.raviolet lamp (Hanovia Safe-T.lire type). The resultant oxygen-ozone mixtuie \vas led directly through glass tubing 0.5 mm. in insidediamrter into the 1,od:- of the solution. T h e
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Figure 8. H u t ? I Ricinoleate in I'etrolatuni
use of absorption aids, such 9s bubble towers, fritted disks, etc., was purposely avoided to minimize decomposition of t'he ozone. .kt regular, predetermined intervals, aliquots of the solution cont,inuously undergoing ozonization xere removed for treatment as described helow, Evaporation. I\-ht:re imall amounts of prwipitate formed during ozonization, these were Iemoved by careful clec~nntation. T h e clear solution !vas gently n.:niiied just below the h i l i n g temperature of the solvent, until a sirupy, vi+ cous concentrate of the ozonized elastomer \vxs obtained. Film Spreading. ; ifilm ~i the ionized product rvas cast by spreading a layer of the concentrate on a rock salt plate and evaporating t,o a solrtnntfree state in a vacuum oven a t 50'' C. Filni- of increased thickness could be obtained by se\c,raI such depositions on a single plate. Spectrographic Examination. Spectral tiatn on the films thus cast were obtained in the 2- to 15-micron region, using a Beckman Model IIt-2 infrared recording sprctrophotometer.
Figure 6.
01
For purposes of ConipariEon, spectrogrnnis were also obtained on films from the polymer solutions prior t o ozonization, and on films in Isohut?l 4lcohol in Eth5lerie Dichloride the preparation of which t h e ozonizat,ion step n-as replaced by treatment with unozonized oxygen. I.'igures 1 to 5, inclusive, show results oi application of the :tl)ove procedure to Hevea (smoked sheet) : GR-S (cold rubber, 41 O polymer); nitrile rubber (Paracril 26 S ) ; Seoprene Type IT-; and Butyl rubber (GR-I). .Ilthough a m i e s of a t least six aliquots n a s examined for each polymer solution during a 24-hour ozonization period, the tw-o ozonization speetra selected shon- the trend of t.he gross changes observed. T h e arrows point, to significant ahsorption bands. At 2.9 microns, absorption is generally considered to reflect hydroxyl (OH) group content. I n t,he region of 5.8 microns, absorption indicates carbonyl (C=O) group, n-hether of carboxylic, aldehyde) or ketone origin. I t higher n-ave lengths, the arrows, ivhere present, designate bands that are characteristic of t8hepolyIS0 BUTANOL INETHYLENE DICHLORIDE mer at the double bond. I n Figures 2 , 4, and 5 , the dotted line curvw are spectra yielded hy reduced film thickness. On the basis of the spectra presented in Figures 1 to 5 , inclusive, tlic. following general ohservations may he made: 02 03 04 05 WT (OH1 - MG. /CM*
Figure 5 . Beer's Law Curl-e for Hydroxyl 2.9-mu band
Oz>piiation i ~ l o n e ,under the conditions described, yields a product, the infrai,ed spcctrd characteristics oi q-hich are prartically identical with thow of the untrented pol?-mer film. This
V O L U M E 24, NO. 4, A P R I L 1 9 5 2
633 The spectral changes noted parallel somewhat those
of Cole and Field (4), Ivho reported qualitative effects of air oxygenation at 100" C., and ultraviolet irradiation a t 40" C., on specimens in the solid state, of various polymers and copolymers of isoprene, butadiene,
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and styrene. I n the present Xvork, t o estimate the quantitative extent of the variations observed in hydroxyl and carhonyl content, as a result of ozonization in solution at room t,emperature, the families of curves sho1T.n in Figures 6, 8, and 10 rr-ere obtained. In selecting the component pairs on which these curves are based, no ntt,eiiipt mas made to simulate actual ozonization prodB U T Y L RICINOLEATE IN P E T R O L A T U M ucts. T h e deciding factors m r e functional group content and suitability for spectral study, from the stantipoint of forming clear, homogeneous solutions or films. Variation of functional group concent.ration was ohtained by preparing a series of solutions or mixt,ures of 0 05 0 IO 0 I5 0 20 0 25 0 30 W T (OH)- MGM /CM2 accurately weighed or meiiaured proportions of parent conipound to diluent,. In Figure 6, the concentrttFigure 9. Beer's Law Curve for ZEj-droX? 1 tions tahulated v ere computed from the knon-n coni2.9-mu band positions of the respective solutions, and the cell thic-kness (0.03 mm.), of the single ahsorption cell I 1 I I I 1 used. 111 Figures 8 anti 10, the concentrations shown were calculated froin filni iveights and the supporting area of the rock salt plat'e, using the method of differential wighing, as described by Hunt et a/.( 7 ) . In computing absorliurice, as used in this paper, so called "bascline" trnnsmittance value?, o1it:iiiied graphically irom per cent transniittance curves, Tvere employed. The lxise-line techniqur, as originally tiescribed b y \Trigkit (IB), facilitutes the preaentat,ion of quantitative dnta l ~ l compeiisating for iwckground variations and minor differences in film thickness, :inti I )!. >-ielclinganalytical curves origirmting a t zero. In Figure 6, a displacenieiit towiirtl higher w . v e lengths with iricreasiiig isobutyl alcohol content is olwervcd for the 2.4micron band. This is verified by the relative constancy of tlie 3.4-miD =0.02255 cron ("-H stretching band. In dilute solutions of isol)ut8plalcohol F = 0.07170 in ethylene dichloride, tlie relatively shallow band a t about 2.77 U W micron3 m i ! : be considered :is reflect,ing free. or unaesociated, hydroxyl. .It higher concentrations of the alcohol, hydrogen I 1 I I I I bonding occurs, causiiig :I shift of the hydroxyl ahsorption peak 54 56 58 60 6.2 64 WAVE LENGTH - MICRONS t,oward 2.95 microns. I n Figure 7 , the deviation from Beer's 1:iw caused by this shift Figure 10. Oleic Acid in Petrolatuni ~~
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holds ronsistently for a11 the, pol>-mer t,ypes esamined, and indic:itrs that no major structural change is effected by t h e oxygrii treatment, even though coiit,iiiued for 24 hours. Introduction of 50 p.p.m. of ozone into the osygen stre:ini effects several clearly defined c1i:tnges iii the polymer i,esitlue. Hydroxyl and cwhoiiyl groups show R progressive increase, while olefinic structure, ivlicre i)i,esent, exhibits a concomitant deterioration. Of the elnstoiiieis studied, But)-l (CR-I) differs in t w o major respect.s on ozonization. The in-1 content is relatively negligible, dec.reuse in transmittance a t Tvave leiigths e,l)ove 7.0 microns, seen in common in t h e spectra of t h e ot,her elastomers, does iiot inodidevelop. This s o u l d imply less st~ruct~ural fication of the Butyl polymer :is :I result of ozonization. It is interesting t o note, in all the spectra, t h e absence of clearly defined bands in t h e 11- t o 12-micron region which could be ascribed t o hydroperoxides and epoxy linkages, in accordance with t h e work of Shreve et al. (10, 11). It may be assumed therefore, t h a t products of this type are not present in appreciable amounts in the films examined.
Figure 11.
Beer's Law- Curve for Carbonyl 5.S-mu hand
ANALYTICAL CHEMISTRY
634 is clearly seen. The dotted line represents a hypothetical curve for hydrogen-bonded hydroxyl, assuming that a t the highest isobutyl alcohol concentration shown the hydroxyl groups are completely associated. The deviation from rectilinearity shown by the plotted data is a function of the ratio of “free” t o “hydrogenbonded” hydroxyl in this system. I
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Figure 12.
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WAVE LENGTH - MICRONS
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I n Figure 10, the absorption nxiuima at 5.86 microns, due to carbonyl, show a tendency t o shift to loxer wave lengths with increasing concentrations of oleic acid. The plotted data of Figure 11 shon substantially good agreement iyith a straight line. The curves of Figures 7, 9, and 11 may be used to estimate percentage concentration of the respective functional groups in the ozonized polymers. The spectral data of Figures 1 t o 5 are utilizable, provided the weights of the polymer films are known. These reights may be determined by direct weighing, or by optical methods. Figures 12 and 13 illustrate a n optical procedure for determining film weights of GR-S. The measurements are based on variations of absorbance a t 6.7 microns. This band reflects the phenyl ring of the styrene component, and is apparently unaltered on ozonization. The sixteen points of Figure 13 are derived from four families of curves, in which is included that of Figure 12. It may be assumed from Figure 13 thxt, within reasonable limits, absorbance a t 6.7 microns is a specific linear function of GR-S film weight. Utilizing this optical method for determination of film 71 eight, Figures 14 and 15 show the rate of accumulation, percentagewise, of hydroxyl and carbonyl groups in GR-S undergoing ozonization. Figure 14 indicates that hydroxyl accumulates a t a relatively uniform rate, whereas in Figure 15 it is seen that the variation of carbonyl content is more compley. Francis (6) has shown that \I hile the integrated intensity of the band at 5.8 microns, associated with C=O stretching, is relatively constant for coinpounds of the same type, an increase of as
GR-S F i l m Weight us. Absorption a t 6.67 RIu
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Figure 8 illustrates the variation in absorption due t o hydroxyl concentrat,ion in a system differing widely from that of Figure 6. Here, the hydroxyl is attached t o the central portion of a longchain olefinic radical in an ester, as contrasted t o attachment to a four-carbon aliphatic radical. Kevertheless, the Beer’s law curve of Figure 9 approsimat,es that, of Figure 7. The relationship between absorbance and the quantity of a functional group is appnrent.ly relatively independent of the structure of the re mainder of t,hemolecule t,o which the functional group is attached. Previous confirmation of this has been reported by Anderson and Seyfried (S), who m-orked with petroleum hydrocarhons.
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Figure 14. Per C e n t Hydroxyl 13s. Ozonization T i m e for GR-S G u m
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Beer’s Law Curve for GR-S F i l m Weight
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The interspersion of the shoulders a t 2.7 and 3.2 microns in the curves of Figure 8 is due t o deliberate, appreciable variations in film thickness. The reotilinearity of the major part of Figure 9 plot demonstrates the effectiveness of the base-line technique.
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Figure 15.
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V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2 much as 70% is observed in the integrated intensity of this band for esters as compared t o the corresponding value for ketones. This would indicate that the failure of the curve of Figure 15 to extrapolate through zero may be due t o either a more rapid init’ial build up of carbonyl content, or an initial preponderance of a structural environment of the C 4 group different from that prevailing in the period from 2 t o 16 hours of ozonization. Severtheless, in the lat,ter period, a good approach t o a straightline variation is observed. FUTURE WORK
This investigation is continuing. Curves similar to those of Figures 14 and 15 for GR-S are being obtained for the reniaining crude polymers. I t is intended t o include vulcanizates of known formulation in this study, to determine the applicability of the procetluiw described to coinpounded and cured elastomer stocks. ACKNOWLEDGMENT
The authors are indebted t o Morris Alpert, and Alvin D. Delmail for valualile assistance in the experimental phases of this work.
635 LITERATURE CITED
(1) Alekseeva and Belit&a>a. Rubber Chem. & Technol., 15, 693 (1942); J . Gen. Chem., U.S.S.R., 11, 358 (1941). (2) -\m. Soc. Testing Materials, Committee D-11, “Standards on
Rubber Products. ” (3) .hiderson. J. .I.,Jr., and Ycyfried, W. D.,,ANAL.CHEM.,20, 998 (1948). (4) Cole, J. O., and Field E., I u d . Eng. Chem., 39, 174 (1947). ( 5 ) Dinsinore, H. L., and Smith, D. C., A N ~ L CHEX, . 20, 402 (1 948). 16) Francis, S. -\., J . Chem. Phbs.. 19, 942 (1951). (7) Hunt, .J. M., Wisherd, 31. P., and Bonham, L. C., i l ~ a r .CHEM., . 22, 1478 (1950). (8) Marvel, c‘. S.,and Light, R. E., J . -4m. Chem. SOC.,72, 3887 (1960). (9) Rabjohn, N., et d., Ibid., 69, 314 (1947). ( 1 0 ) Shreve. 0. D., et u l . . B s ~ I . CHEM., . 23, 277 (1951). (11) Ihi’d.. p. 283. (1’2) \Vright, S . ,IND.ESG. CHEX.,ANAL. ED., 13, 1 (1941).
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RECEIYED for review February 2 , 1951. dcoepted January 16, 1952. Pre sented before t h e S t h iiieeting of the Division of Rubber Chemistry, AYERIC A S C n E m c . 4 L SOCIETY, Washington, D. C., March 2, 1951. Opinions and a-sertions a r e those of the authors and are not t o be construed ao reflecting t h e vie\vs of tlie I)epar.tment of t h e S a v y or the Naval Service a t large.
Infrared Absorption Spectra of Aluminum Soaps WARREN W. HARPLEI, STEPHEX E. WIRERLEI’, AND WALTER H. BAUER Rensselaer P o l y t e c h n i c I n s t i t u t e , Troy, 5. Y . This investigation was undertaken to determine the structure of aluiiiinuin soaps by means of infrared spectroscopy. Infrared absorption spectra have been obtained on one series of aluminum soaps prepared bj an aqueous metathesis method from a-ethylcaproic acid and lauric acid with \ arj ing fatty acid-aluminum ratios and on a second series of aluminrun soaps prepared with a constant fatty acid-aluminum ratio approxinlating Lhat of a disoap from caproic, eiianthic, caprylic, pelargonic, capric, lauric. m y ristic, palniitic, and stearic acids. The presence of a fatty acid band was e\ident onlj i n soaps containing fatty acid extractable with cold iso-octane, indicating that trisoaps of the higher fatty acids do not exist as cheniical comporinds. The spectra of snaps of disoap coniposition contain a free hydroxyl h i i d , Nherear those approaching a monosoap composition contain bonded h j ~ N J X >1 groups.
I
?;FR..IRED spectroscopy has been applied to the stud?- of
the structure of aluminum soaps by several workers, but has not received sufficient emphasis. The following work is reported by Gray and Alexander ( 3 ) : Absorption spect,ra were obtained for the “mono” and “di” aluminum stearates formed by aqueous precipitation, and also for stearic acid, various samples of alumina, covalent’ stearates euch as t,he mono-, di-, and tristearates of glycerol, and ionic stearates such as potassium stearate. Conclusions reached were: (1) Aluminum soaps are definite chemical compounds, as the spectra contain features not present in st,earic acid and alumina. ( 2 ) The structure is predominantly covalent. (3) S o obvious difference bet.ween t h e spect,ra of “mono” and ‘,di” stearates w:ie noted. I n a more recent paper apparently referring t o the same work. Alexander and Gray ( 1 )state, “Aluminum mono- and distearates, prepared by a n aqueous precipitation method, give essentially identical spectra in the 3- t o 8-micron region. Comparison with sodium stearate (an ionic compound) and with glycerol stearates (covalent compounds) suggests that the linkages in aluminum soaps are probably covalent in nature.” To the authors’ knowledge no other work of this nature has been reported in the literature. 1
Present address, Allegheny-Ludlum Steel Corp., Brackenridge, Pa
Thercx is ciisagreemenl in tlie literature concerning the nature of aluininurn soaps as t o whether mono-, di-, and trisoaps all exist a s distinct compounds. It is generally stated that preparation of a reproducible aluminum soap is difficult,. English authors ( I ) have ymerally held to a nonaqueous double decomposition reaction such as that between a n aluminuni alkoiide and a fatty acid in order t o control the influence of water. Commercial aluminum soaps are made by an aqueous precipitation process (coiumonly called the aqueous metathesis method) which is sinipler than tlie previously mentioned procedure. PREPARATION O F ALUiMINUiVl SOAPS
The soaps used in this investigation were prepared by a n aqueous metathesis process as follows: The f:Ltt,v acid (nielt,ed, if a solid a t room temperature) \ Y ~ R treated wit‘li a 20% by weight sodium hydroxide solution and sufficient dist.il1t.d water t o yield a 10% by weight sodium soap solution. T h e amount of sodium hydroxide used varied from 0 to 200% “excess” sodium hydroxide over that required to inake a neutral sodium soap from t’he fatty acid, depending upon the composition of the soap desired. The solution was stirred and heated if necessary t o dissolve all the sodium soap until clear. The temperature was maintained between 5 ” and 10’ C. above the ready solubility temperat.ure where isotropic soap solutions are stable. For acids cont,aining from eight t o twelve carbon
