i Antioxidant Influence of
ormaldehyde inseed ~ i l ' i the n Presence af~ c, C . VERNON AND w. w. Rim HE phenomenon known as drydouble bonds particularly susceptible ing of eertain u n s a t u r a t e d University of LouisvilIe, Louisville, Ky. to polymerization. This study was polymerizable oils has been long limited to unbodied oil, and the results attained should not be compared to those where bodied oils known. Many factors govern this drying, and many substances when mixed with oil accelerate or retard it. Many were used. theories have been proposed in an effort to explain thjs behavio;. Method I t is generally recognized that oxidation and polymerizaAfter a study of the limitations of such methods as ultimate tion nre t h e principal factors involved in the process. The analysis, volumetric measurement of oxygen absorption, and oxidation is believed to be confined to addition of oxygen to blowing with conditioned air, the simple gain-in-weight unsaturated carbon atoms of those acids whose esters commethod was chosen. prise the major part of a drying oil. T h e gain in weight folThis method gave only the apparent rate of oxygen absorplowing such addition of oxygen provides an approximate tion, but in a study such as this one where conclusions were criterion of the rate of oxidation, despite the fact that volato be drawn from a comparison of data collected under identile products are cvolved during the drying process, espccially tical experimental conditions, it was considered adequate. a t the end of it. It hnd the further advantage of rapidity, making possible hloureu and Dufraisse (6) proposed a theory relntive to many readings in the time avnilable. inhibition of nutoxidation processes in general, which has been helpfuI in planning this study and which hns indicated The resin-oil solutions were prepared in concentrations calsome of the procedures followed. This theory holds that culated as per cent by wei ht. Each constituent was weighed antioxidants are thcmselvcs oxidixnble substnnces with the to 0.5 mg. on an annlyticnl%alance; for each gram of oil in the solutions, 0,0427 gram of naphthenate nritioxygenic property localized in drier was included, the metal content the oxidizable part of the molecule. of which is @ w n in the section headed Prominent m o n g the antioxidants "Materials. The m i x t u r e w a s hcatcd to 150' C. for 5 minutes to of Moureu nnd D u f r n i s s e a r e This investigation, using ensure complete dispersion, seulcd in phenols, which arc used in thc proviala, and stored in a dark cabinet 2 commercial m a t er i a 1s , duction of many synthetic resins. dnys before use. The mixture so reSeveral investigators (4,9,10) Imw showed that the six phenolic pnred was then spread on slig!tly shown that phenolic compounds ctched tared glass lates so that an resins tested increased the nrcn o i approximatery 95 sq. cm. was inhibit the oxidation of linseed oil induction period in the oxyexposed. These plates were weighed during the induction period. Other immediately and at timed intervala gen absorption of unbodied investigators (I, 8) have inferred t h e r e a f t e r ; t h e intervals were linseed oil in the presence of poverned by the rn idity of drying. the presence of free phenols in synrho initial wei hts orthe films so prethetic resins. Careful tests of the driers, in direct proportion pnred varied from 0.1OOO to 0.2580 samples used in this investigation, to the a m o u n t of resin grnm, depending on the thickness of using diazotized p-nitroaniline RS the film which, in turn, was governed present. The behavior of by the viscosity of the original soluwell as ferric chloride, showed the the oil after the induction tion. No nttem t was made t o govern abscnceof any considerable amounts the thickness o r t h e films, except to period was a p p i n t l y unof u n r e a c t e d simple phenol left kccp it within the limits prescribed by idfected, since it eventually there from the manufacturing procWise nnd Duncan ( 1 1 ) who showed that reasonable variation did not apess. In one instance a somewlint dried completely. Mixtuws pyeciably affect the rsto of oxidntion. complex phenol was detected anti of synthetic resins with ester Ihe present writers' experience in removed. securing checks with films of t h e same gum had the same effect as Synthetic resins have been used rcqin mixture but varying in weight the pure resins, but t o a less nnd thercforo thickness, confirmed in the manufacture of varnishes tlrc finding of these investigators. degree since the proportion for some time. Such v a r n i s h Since temyerature ( 6 , f O humidity have rlricd satisfactorily, althougli of resin was less. Treatment 7), and li it (9) nll in ucnco the the cffcct of the rcsins on such dryh y i n g or ois, it was nccossary t o carry of two of the three resins out the experiments undcr conditions ing hay vnricd. This behavior must t h a t s h o w e d t h e most such that tlieso factors wcre as nenrly not be confused with tlic results constnnt as possible. During thr day marked antioxidant effect reportcd for this study. The oil the films wcro exposed to diffused with an oxidizing agent reuscd in the rnanufncture of thcsc light, nnd tho temperntun, variation for tho test periods was hcld within varnishw w:rs heat-bodied to Login sulted in a diminution of 2" C. limits. The h u m i d i t y was with , bccnmc hcrrt-bod icd tl uri ng t h b effect. much more diflicult to contml but it the procc.qs, or elso wna t1iti.g oil t v ~ sfound tlrnt data collcctcd wtwn uIiich ti:w :i c o n j t i p t c t l yntwii of tho Irwnitiity vnricd Imm 50 to 60
d
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VOL. 29, NO. 12
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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agreed within the l i m i t a of rxpf~iiiientaIerror. Most of the dStS were collected at nn average of 55. Wei hings were made over a riod of 180 hours, the intervals being konger after Go hours. $e most satisfactory agreements were secumd during the first 15 houm, after which time uncontrollable factors cawed sonic variation.
Y
Materials The resins invrstignted met the usual industrial specificat ions and contained thc amount of phenolic resin indicated in tlie folIon-ing table. The diluerlt for those resins specified as less thsn 100 per cent phenolic was ester gum. The numbers given provide the key for reference in the discussion: Resin
No. I 2 3
.-\ppror. PheApprox. Phenolic Resin Tert lor Resin nolic Keain Con- Test lor Content. yo Free Phenol No. tent, yo Free Phenol 4 45 100 45 20 100 6 14 100
.-
T!ie alkali-refined Iinsecd oil used had the following values: Iodin:,No., \Vijs method Arid .YO. Snponification vnlue Specific gravity
’I‘tie metal content of the nnphtliennte drier used was 0.30 p r cent cobnlt, 0.30 per ccnt iiianpsne~e,nnd 4.60 per cent I c ~ d ;the specific pi-nvity of the drier wvns O.Sli.5.
Consideration of Curves The curves prcsentrd rcprcscnt the pcrccntngc gain in weight of the oil i n the rcsin-oil mixtures, riot that of tlic entire niistrire. I t WRS shown i n prcliiiiinnry studies that tliin filiiw of tlie resin, sprcad from ether suspcnsions or solutions, did not gnin in weiglit when cxposctl to air untler thc ~sperimcntalconditions wliic*h prcvnilctl during this study. The nrnount of oil prcscnt i n m y given sarnplc I V ~ Scnsily tlcterinincrl from the original weight of thc film nntl tlie ~ ) c r ccntngc cunipositioii of ttic solution. Tlir “raw” cI:its wwc all recnlculstecl hy the iisc of nn npproprinte conversion factor so that the new dntn showed thc pcrcentngc giLiii in weight < I f the oil. The coriclusions \vercl drawn by coriipnring tlic curvcs for the rcsin-oil mixtures with ctirves for linseed oil without resin; both curves werc froin dntn collectcrl untlcr idcnt,ical experimental coiiditions. This rnctliod hncl the ndvautrigc that the inherent tlcfects of the gain-iii-~wightnicthocl were eliminated. Each of t l i c x CIII’\’CS represents rlnt:i collected in several runs under similtir contlitions nnci iigrceing within the usunl experinicnttrl liniits. In ntldition to crirves representing the resin-oil niisturts is the cirrve sliowin~tlic bchnvior of linseed oil (I’igurc 2 , I) and n curve (Figure 5 , I) showing tlic behavior of ester gum, tlie tiiluctit for resins 4, 5 , nnd 6. ?‘lie data for these curves were collcctcd rrntlcr the cspcrimcntnl conditions picvniling ciurinl: this study nntl ttic cirrvcs hnve been incliitled for cornpnrison with tlic resin-oil curvcs. The curves for the I 0 0 per ccnt I)hcnolic resins (Figures 1, 2 , and 3) show thnt each of these iind antioxidant influence, in direct proportion to the amount of resin Iireserit. This effect ivns confined for the most prirt to thc iiiduction period. Thcrc wris n low i i i weight after tlic iriitinl wcighing i n the higher conccntrritiorin of resin 1 nntl i n all concentrations of resin 3. ’I‘his portion of thc curves W R B clicckecl many times i n a n effort ~ C J dctcrriiinc thc eniiw. I t WRX founrl ttist ticntinK the wcighecl sninplc of rcsiii to incipicrit fusion iintlcr R vacut~iri l ~ r f o r ciiicory~orntion i i i tile litisectl oil reni~lterli n the climiriritiori of this behnvicv, \vitliout nffccting th(3 rcst of the curve. J3oiling wcigl~cdsrirnples of resin in water, clryirig, and incorporntitiK with oil hat1 Imciscly the w n c effect. Natrrrnlly, thcre wns IL low i n weight of resin t);v troth of thwe trc*atmetit. Soiric volritilc wntcr-solirblc
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srrbstancc w w cliiiiiristed by these treatrncnts, b u t it could not be identified with certainty, although occluded or adsorbed formaldehyde WRR suspected. Eini (2) noted a simiInr initial loss of weight in the drying of trilinolenic glyceride, which of course WRY not due to formaldehyde. I n order to tcst thc applicnbility of hIoureri and Dufraisse’s thcory to the work in l i ~ n d4.0 , grams of resins I and 3 n ~ n ! oxitlizetl for onc hour with GO cc. of 30 per ccnt hydrogen pcrosidc. After thorough washing and drying, these wrnplcs wcrc spread and ivciKliect in tlic usus1 nianncr. Although the antioxygenic propertics were not completely climinnted (Figurc I , I, and Fijpre 3, f ) , tlicy were sufficicntly dccmcd to sribntnritinte the tlicory. This sninc nntiosirlant cffcct WRS noted when coniincrcid resins rnndc up of rnisturcs of pllcnolic w i n s nnd cstcr gum nwc tcstctl (I‘iKures 4, 5 , nnti 6). ISstcr gutn itsclf nns found slightly oxitlisnlilc, K n i i i i n K 1 .i pcr c c n t in wight nftcr
.INDUSTRIAL AND ENGINEERING CHEMISTRY
DECEMBER, lq37 13 12 I1
io
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I 5 7. SOLUTION II 102 SOLUTION (BOILED)
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1395
to 260" was identical with that heated to 150" within the limits of experimental error, and therefore was not included. An interesting point concerning resin 4 was that it yielded, on prolonged treatment with boiling water, 19.93 per cent of 4,4-dihydroxydiphenylmethane. When this substance had been removed, the dried residue, incorporated in oil and spread in the usual manner, showed markedly less antioxidant effect (Figure 4, 11). The other resins when so treated did not show any change in their antioxidant effect. With resin 3 an initial loss of weight was eliminated by this treatment, as has already been mentioned. The increased viscosity of the solutions containing the larger amounts of resin was undoubtedly a factor in the rate a t which the oil in the mixture absorbed oxygen, in that the diffusion of oxygen was rendered more difficult. KOway of eliminating this was found. Then, too, there was less oil exposed at the surface of the more concentrated solutions, which would tend to slow up the oxygen absorption. It was believed that the slope of the curves representing more concentrated solutions was due a t least in part to these factors.
Conclusion The six phenol-formaldehyde resins and mixtures of these resins with ester gum studied in this investigation showed marked antioxidant effect on pure alkali-refined linseed oil in the presence of driers. This effect was specific for each individual resin, and was confined to the induction period. This antioxidant effectwas partially due, in two cases, to some oxidizable part or component of the resin, since it was markedly decreased when the resin was treated with oxidizing agents. This last fact was in accord with the theory of Moureu and Dufraisse (6) relative to antioxygens, and indicated a possible treatment of such resins should their antioxygenic properties be undesirable. The resins studied were apparently free from simple phenols used in their manufacture, although one of the resin-ester gum mixtures yielded a considerable amount of a complex phenol. The presence of free formaldehyde could not- be demonstrated; yet in one case a behavior was noted which indicated the possibility of its presence. The results of this investigation must not be compared to those attained with heat-bodied oils, since the oil used here was not heat-bodied. Neither must it be concluded that these resins prevented the complete drying of the oil, for the oil did dry eventually. The results of interest are those shown during the induction period of oxygen absorption.
Acknowledgment
120 hours when spread as a film from an ether solution. It did not, however, show antioxidant properties when incorporated in linseed oil and treated in the usual manner (Figure 5 , I). The synthetic resins did not gain in weight when treated in the same manner as the ester gum. The amount of synthetic resin actually present in these solutions was less than the percentage given for the curves in the figures. Thus a 30 per cent solution of a 20 per cent phenolic resin-ester gum mixture actually contained but 6 per cent phenolic resin. Curves for such mixtures can scarcely be compared to 6 per cent solutions of purely phenolic resins, since the amount of oil exposed at the surface interface of the former was much less than that exposed in the latter case. The temperature required to disperse resins 4 and 5 was 260"rather than 150" C. The curve for the linseed oil heated
This work was made possible by a fellowship granted to W. W. Rinne, the junior author, by the Louisville Oil, Paint, and Varnish Production Club. The authors wish to express their deep appreciation, not only for the fellowship, but also for the generous cooperation of the members of the club in furnishing materials and helpful suggestions.
Literature Cited (1) Bradley, R.,IND.ENQ.CHEM.,Anal. Ed., 3, 304 (1931). ( 2 ) Elm, A. C., IND. ENQ.CREM.,23, 881 (1931). (3) Long, J. S.,Rheineok, A. E., and Ball, G. L., Ibzd., 25, 1086 (1933). (4) Morrell, R.S.,J. Oil Colour Chem. Assoc., 10,278 (1927). (5) Moureu, C.,and Dufraisse, C., Chem. Rev., 3, 113-62 (1927). (6) Rodgers, W., and Taylor, H. S.,J. Phys. Chem., 30,1334 (1926). (7) Schmuta, F.C., and Palmer, F., IND. ENQ.CHEM.,22,84 (1930). (8) Seebach, F.,U. S.Patent 1,891,455(Deo. 20, 1932). (9) Tanaka, Y.,and Nakamura, M., J . SOC.Chern. Ind. Japan, 33, 126 (1930). (10) Wagner, A. M., and Brier, J. C., INDENQ.CHEM.,23,40(1931). (11) Wise, L. E.,and Duncan, R. A,, Ibid., 7, 203 (1915). RECEI~BD December 14, 1936. Abstracted from a thesis presented by W. W. Rinne t o the faculty of the Graduate School, University of Louisville. In partial fulfillment of the requirements for the M.S. degree, June, 1936.
