INDUSTRIAL AND ENGINEERING CHEMISTRY
22'76 I'Hl
S l ( : 4 L PHOPEHTIES OF COAGULhTED POLYMERS
:I numhrr of the latices described in earlier sections of thii report have been coagulated and the dried polymer compounded in a tread recipe. Coagulation was effected with a 10% solution of sodium hydroxide after the addition of a n acid dispersion of phenyl-2-naphthylamine t o the lates. The rcsults of physica! tests on curcad tread stovks are presented in Table VIII. T h e v polymers did not show a great deal of variation from GR-S. [n one case (run 7) normal tensile value: were superior t o GR-S" in the others they were equal or slightly inferior. Eficiencies were in general inferior t o GR-S nhile cut growth was about e q t d Aftor aging 4 days a t 212' F., the experimental polymer was superior t(J GR-S in all properties tested. .i comparison oi runs 7 and 7 1 indirates the desirability of stopping polynierizat,ion a t 70 t o 75% iv)nversion, if guod physical properties arc t n hi 1,btained. Thus in I ~ i t i i i lit-? cxmuisifier-free lariws a i d the pulyiiie~a coagulated t'roni them one find. a riumher of unique properties which shoulrl ~ ~ r r : t I i lthese ~: riiaterials t o find practical appliratilm. 4CKVOW LEDG\IEVT
rile writer wishes to acknon ledge the kind assistance uf E. 32 H a n w n nnrj 1 , . 4 n'ohler in nhtaining part; of the data rnntaintvi
Vol. 41, No. 10
herein. Thanks are a1.1~ due. Thv FirtAnturie Tire B Rubber Company for permiwion to piihli.;h this papcr
Rt:cr.n.ED Sovernher 16. 1948. I're..-nieii bciorr the fall merting d f the Division of Rubber Cheniistrh , A \ i > . R I i .4s C R E ~ I C A L SOCIETY,Detroit Wich., S o r e m b e r 1918. This wiirli was carried o u t under the sponsorship of the Office of Ruhber Reserve Reconstruction Finance Corporation in r,nnnrrtinr wit11 the g n v c r n m P n t ci ~ t h tic c rubber program.
SOLUBILITY OF GEON FILMS R. H. Ill\\lCH
m - R. ~ L. S-4YAGE
R a t t r l l e Ilenzorial Institute, Columbus, Ohio
'I'hv nerd f o r qaarititdti\r ddld un the solubilit? of Geun films in sacral liquids, especial13 for amounts as small as a few parts per million, led to the development of methods
active carbon in the polynier itself bui neii her the material nor the time was a v d a b l r for thi. study.
for such determinations. The methods used and results obtained are described. Solubilities of not more than 1 part per million of Geon 31X films in distilled water, sodium hjdroxide solution (pH 9 5 ) , and lactic acid solution (pH 3.5) were measured bj chlorine anal?sis of the solutions. No effect by change in pH was obsened. Solubilities of not more than 6 parts per million in lard oil and in peanut oil were measured b> nephelometric analjsis of the oils after 1-. $-, and % w e e k test periods.
LXTR*( TIO\ YIEDIA
T
HE applicatiuii uf such marerials as Geon (vinyl chloride! resins in food packaging has made necessary a study of the solubility and toxicological properties of these rcsinj. Informacion in t l ~ eliterature indicated t h a t these polymers were r e h tively unaffected by a large number of solvcntu, lint quantitarire data, especially for amounts of the order of :t few parts pcr million. were unavailable, and mcans had to he del-eloped for such dvierrnina;ions. Thrl methods used and results obtained :irg~ drscrillcd in this papi'r. Initial attack on this problem involved the determination of the increasc in chlorine content of aqueous solutions and oils. A microgravinietric method of analysis, having a n accur:] cy of 0.02 parts per million (p.p.ni.1 proved to be acceptable fur the aqueous solutions. T h e oxidation procedure used on t h c s peariur and lard oils indicated that chlorine determinations would not be sufficiently sensitive to detect solubilities of less than 150 p.p.in. T o report solubilities of the oils niorc accuratdv. altcrnative met hods were considered. A nephelometric determination was found to be suitable and was used for this phaw of the work h promising apprnarh was through the we u! rei1il+
The rnedia selected for a study of the solubilitv of Geon 31X films consisted of peanul 011, lard oil. distilled water and sodium hydroutle a n d lactic acid Eolutions. The lactic acid solution mas prepared by adjusting ili*tilled water to a pH of 3.5 by the addition of 8E17~lactic acid: the sodium hydroxide solution Fa? preparcJd by the addition of 5 % sodium hydroxide solution to distillcd water to give a pH of 9.5. An edible grade of peanut oil and a conipairhle grade of lard oil n-ere used. Iwii'.mAm)\
OF FILMS
T h e Geon 3 1 5 utilized in this investigation consisted of a water dispersion composed of approximately 49% of a vinyl clil(,ride-vinvlidenc chloride type copolymer containing 65%, vhlorine. The, original reFin dispersion was found to be unsatisfactory f o r ea+tiiig films I,ecarisc thc films invariably developed many irregu1ai.itie-i during the initial dq-ing period. This difficulty was comicred by the addition of 0 . ~ 1of7 carhosymethyl ~ cellulose :I' a 2Yc water solution. The thickened disper-ion produced wiooth and regular films which Terr considered to l i e acceptable. Films were cast on a plate-glass panel which had been careiuily clcbaned by immersion in a sulfuric acid-sodium dichromate bath followed hy a a-ash x i t h distilled IT-ater and mrthyl ethyl kctone. .Ipproximately 2 ml. of Geoii 31X were then poured (Into the glass panel nest to a l l a y e r bar constructed with 12-mil stainless steel wire. The l I a y e r liar was dran.n across the panel forming a thin film \\Liirli rovered the surface. The glass plate r~mtsiningthe wet film was drier1 for 3 minutes on a hot plat+
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
October 1949
2277
~~
Figure 1.
Effect of \'ariation in Oven-Baking Time at 210" F. on Film Shrinkage
which wap heated with steaiii at a pressure of 10 pounds per 3quare inch; after this it was transferred to a n oven for a 15minute baking period. Shrinkage of some uf the firht films after the oven-drying sitated a determination u i the optimum oven baking time. X series of plate-baking periods was investigated; the bakings varied from a minimum of 2 to a maximum of 15 minutes. The films were then rernovcd from the plates, supported on glass frame., and baked an additional 10 minutes to observe the shrinkage. The film shrinkage effects are s h o ~ v nin Figure 1, which indicates the results of four plate-haking periods. This filni shrinkage may be exuplairid by incomplete fusion of the rc4n micelles during the shorter baking periods. Fur the solubility tests, the films v-ere allov-ed to cool t u room temperature, and a strip I 1 x 3 inches was taken from tiit. plate. Thcse strips w w rollcd u n glass rods, after placing a paper backing nt.xt t o the film, :tnd then transferred t o the clean glass frames vht're tile loose C I L & \'.-ere heat-sealed to the frame. The frames were placrd in covcred Pyrex battery jars containing 450 mi. of each of the previously iiientioned test liquids. The jars were then placed in a n C J T ' ~a~t 100" F. for periods varying from 2 days to 8 week*, So loss by evaporation \vas ol~srrverl. I M ~ I E K * I C ) \ c:o\i)tric)vy
An early observatiori That the &on latex had a n appreciabIt. content of ioniznble chlorine introduced a modification in til.. immersion schedule. BeeauFc the methods of determining the solubility of the Geon 3 1 5 films in aqueous ,elutions rrere based on a determination of the iiirrcwc in chlorine cqntent of the exrraction media, i t vas considered newssary either t o determine the Initial amount of chlorine or t o rcmove it by a preliminary l ~ a c h ing. This chlorine initially prve-rit in the latex was fourid T O 1~ inorganic, and a check on the history of tlie polymerization reaction discloxd that i t was prol)a\,lJ. due to a nicasurable &111(~11llT of hydrogen chloride e\-olutioii during r he pol>-merizatioii.
The removal of the initial chlorine from t.he latex was accomplished by 1-hour immersion of the dried films, supported on glass rods, in three successive portions of distilled water. T h e chlorine content dropped from 6 p.p.m. in the first leaching solution t.o less than 0.5 p.p.m. in the second and third solutions. SOLCBILITY DETER\IINTIO'I BY CHLORINE .4NALYSI$
T h e v-ater solutions !yere analyzed for chlorine by well known rriicrogravimetyic methods which gave a sensitivity of 0.02 p.p.m For the oils the method of analysis was the same as for the n-atcr solutions after initially burning a small quantity in a nickel bomh with sodium peroxide. T h e sensitiveness of t,hk method Fur determining chlorine in oils was found to be 150 p.p.m. which was of little value for this investigation. Ta1,le I s h o w the results of the chlorine analyses on the various extraction media for 2-day, 1-week, and 1-month film inimeriioii periods. .In analysis of the 1-week test solutions showed no gain in the inorganic chloride content which had h e n decreased from approximately 6 p.p.m. for the fir$t, 1-hour leach to less t h w 0.5 p.p.ni. for the second hour of leaching. Thcre was, also, no appreciable gain in tlie total chlorine content of the n-ater solutions during this period. The analyses on rhe 1-month test solutions, which Irere not sulljected t o the leaching procedure, show values of the inorganic chloriiie conterit to be the same as the values for the total chlorine. Khen the chlorine contents of the 1-month test solutions weie compared x i t h the first leaching period of the l-~veck iists, close agreement was noted. This indicated that, for the water solutions? there lyas no appreciable increase in the chlorine content :iftt,r t.he first hour of immersion. Since this chlorine was inorg:mi[*, it evidently was a result of the initial ioniznhle chlorine contrnt of the Geon 3 1 s eniulsion. The inorganic and total chlorine anal>-ses for the 2-day immersion period ncw also in loit it^ agrcvmient viith the data of the other test periods. All C.+t*oii3 1 s films n-hirh entered \vater solutioris r:ipitily lost their
I - T e e k Film Immersjon Inorganic chlorine, ~~
S o Filiii Iiiiinersion
Bxtraction Media a n d Component Solutions Distilled water
PH 5.5
Inorganic chlorine. D.P.I~ u ,2
Sodium hydroxide
9.5
0.3
Lactic acid
8.3
Peanut oil Lard oil Carboxymethyl cellulose Geon 31X
... . l .
...
8.4
I)
2
... ~. . suo0
..approx.
Total chlorine, P.P.~.
0.2
?-Day E iliu
Immersion Inorganic Total chlorine. chlorine, p .I,. m p .p.111. 3 x
0.2
3
0.2
4
150
130 ''5 6.5%
3
I _ _
~
First l-hoi~r lrach
Second
Inorganic chlorine, p.p.ni.
Total chlorine,
0.5 0.5 0.5
0.5
0.5 0.5
0.5 0.5 0.8 0.9 0.9
0.3
0.5
...
0.6
...
1.50
...
...
l-tiwir
lrach 0.5 0.5
0.5 0 5
I
1-Month Film
11.1i.m.
... 1..
...
...
. I
c1.p. I l l .
I niniersion -__~_ Inorganic chlorine, p.p. m. 4
..
Total chlorine, p .I).in. 4
1 1
1
1 1 1
150
..
.\Ian. hrnt. Dissolved Filrn, P.P.hl.
...
...
2278
Fipiire 2.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41, No. 10
F i l m - a f t e r Removal f r o m Varioiiq Extractinn %rediaFollowing 2-Day Period of I m m e r s i o n at 100' F.
,.quuiizccl by rlic ailditiur, #,i :qJpropi,iaLe amounts
J O L U B ~ ~ . ~ 1T ~Y ~ : 1 ~ ~ ~ 1 1 . ~ .BY ~ ~ THE 1 - 1 0AEPHELOVF 3 r w
Two nephelonietric methods for the determination of the soiubility of Geon 31X films in peanut and lard oils were developed One method was based on the use of a n oil-miscible solvent R hich could he used to form a solution to introduce known quarltitirs of film into the oils and could then be removed by evaporation. Methyl ethyl ketone was satisfactory for this procedure. The, second method required the use of a n oil-miscible film ~ Y ~ T I n-hich could be used to introduce known quantities of film into the oils and then the addition of sufficient oil-miscible noiisolvent t,o precipitate the film from the oil. A similar method wa+ utilized by Erbring ( 1 ) who precipitated high molecular tveight materials from solution by the addition of alcohols. 1)iosanc and petroleum ether (boiling point 35" to 60" C . ) were suitahli. for this procedure, T h e soiubility of the film in the pcanut, oil was so low that the addition of the petroleum pther ns precipitant. was unnecessary, but no turbidity developed after the additioo .If diosane solutioiis t o lard oil until the petroleum ether w a ~ Y rlded . Apparatus. Tllr rwptielometer asaenibly consisted of the uephelometer, a ITariac and a constant-voltage transformer. The nephelometer contained light source, a tube, which was blackened on the inside, for holding samples, and a light-meter iunit having a n electronic circuit such as n-as used by .Hald?;; Wright, and Todd ( 2 ) . Operatioii of this assemnb!y t o give reproducible results depended on srveral factors. It was essential that the light-meter unit be given sufficient time to attain a temperature equilibrium, the value of which was dependent on the atmospheric temperatures. Compensation for this variation could be made by modilying the electronic circuit. Thia instrument was found io give reproducible results nithin 9 F. in the room temperature. A systema,t ic method of cleaning the Kessler tube consisted of rinsing trike with acetone, twice with petroleum ether, and wiping the outside carefully with paper cleansing tissues, After filling the Sessler tube with the test sample, it, n-as placed in the sample holder, and the relative transmission measured as the meter reading for the light transmitted through the tube and oil, +QZI compared to a meter reading of 100 for the amount, of light transmitted through the Sessler tuhe. Analysis of Oils. Standard film solutions were prepared from films cast in the manner previously described. The methyl ethyl ketone solution of Geon 3 1 s film contained 1.30 grams of 6lm per liter and the solution of film in diosane containrd 2.28 gram? per liter. Calculated amounts of the methyi ethyl kctone solution were added to a number of samples of peanut oil and lard oil to cover B range of concentrations from 6.5 to IO4 p.p.m. of resin. Tables I1 and I11 s h o data ~ on these samples. The dilution effect was
I
01
rnathvl
t,t!iJ.l kctone. After additioii irf the dcsired quantities of film wlution to the oil, the samples w r e placed in an oven at 212" F f o v a period of 17 hours. This resulted in the evaporation o! tile methyl ethyl ketone leaving the desired Geon 31X in the oil. The samples were allowed t o cool to room temperature prior to the determination of their t,urhidity. The precipitation method servrd ti- a clirck on the turbidity of the peanut and lard oils contairiiiig ( h n 31X introduced by the methyl et,hyl krtone solutioiic. This method consisted of Adding known quantitice of f i l i i i , dissolved in diosane, t o 50gram samples of oil, cowring a range of film concentrations from 5.7 t o 102.6 p.p.m. and precipitating with a definite amount of nonsolvent. Required amounts of pure dioxane were added t o make the saniples comparative in volume. Thirty ml. of petroleum ether wrre pipetted into each sample as the precipitant complete data on t,heTe sanrples are t o be found in Tahlw TT' snd 1'. Calibration Curves for Peanut and Lard Oils. The relative ransmission of light through the oil samples containing known concentrations of dissolved film was determined on each of the peanut and lard oil samples after evaporation of the methyl ethyl ketone. The transmission was found to vary from 70. f o r the peanut oil containing no Geon film. to 42 for peanut oil inraining 104 p.p.ni. of film, and from a n initial value of 76 to a l a h e of 52 for lard oil containing 10-1- p.p.ni. of film. There ria^ Iio changc in the light trsnsiiiissioii or' the peanut rJil after f
(21
>ampie Yo.
5Iethgl Ethyl Ketone Film Solution MI.
P.P.51. None 6.5 13.0 26.0 52.0
3.u 4.0
78.0 104.0
FlI~il
so.
Geon 31X Film,
;";one 1 .lJ 1.0 2.0 2.0
hfethyl Ethyl liet nni' dau~ple
I-liii'
Solution Concn.. C+./hf 1.
Solution. hI1.
f11~1~ 5olurinu Concn., i;/. lIl.
Geon 31X Film, P.P..\I.
Relstivr Trapsmission
Relative
TFans-
mss1on
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
heating for 17 hours a t 212' F. However, there was an increasc in light transmission for the lard oil after heating for 17 hours at 212" F. KO data on changes in the physical or chemical properties of the oil were recorded to show correlation with this change. HoFever, knowing the extent of the variation in relative transmission, it was possible t o compensate for the change in the test samples. T h e calibration data indicated a straight-line relation within the concentrations of film investigated. These data were the average values of duplicate samples which showed maximum Jpreads of one division on the dial scale between samples containing the same quantity of film. This indicated that an error of more than one scale division would cause a n error of 5 p.p.m. in the determinations. T h e transmission data for peanut oil and lard oils are presented in Tables I1 and 111. I t was observed that some turbidity developed on the addition uf dioxane-film solution t o the peanut oil. For this reason, nephelometer readings were taken on a series of samples containing various amounts of the dioxane-film solution; Figure 3, curve 1, s h o w the results. This observation suggests that no solubility occurs above 6 p.p.m. of film since differences in tiirhidity were noticed for film conrr>ntrations 2s Inn. 2.y .i.T
2279
-
-
t-
2 PEANUT OIL CONTAINING DIOXANE SOLUTION PRECIPITATED WITH P E T R O L E U M ETHER 3 L A R D OIL CONTAINING DIOXANE l o - F I L M SOLUTION PRECIPITATED WITH PETROLEUM E T H E R
20
- FILM
0
l
"--'
--
,
I
!
l
I
!
I
1
,
I
l
10
20
30
40
5C
60
70
80
90
FILM
Figure 3.
--
1 - --
-f
o
--------I
00
110
1%
CONCENTRATION, P P M
Effect of i d d i n g Geon Film to Peaniit 1,arrl Oil9
niid
p.p.iii., without the addition of petroleurii ether as a precipitaui. 'The peanut oil itself apparently caused a precipitation of G w n (Concentratiun of t h e film solution used v a s 0.0005iO gram per ml.: 30 ml. of petroleum ether were added t o each samulp: each samule contained 50 grains of oil)' Dioxane -Relatire Transmlsaion Film Pure Geon 31X Average. Film, Each four Sample Solution, Dioxane 511. KO. 511. P.P.hI sample sarnpl?* 85 84 h'one e Kone 84 84.2 32 84 78 33) 34 I 77 0.5 8.5 5.7 78 78. r. 79 371 1.0
8.0
7.0
1'
47 48 49
51 52 53
E:]
5.0
4.0
1
6.0
3.0
9.0
0.0
56
11.4
22.8
45.6
68.4
102.6
76 75 78 76 66 67 07 66 53 52 54 51 45 43 42 41 29 28 30 29
76.2
66 5
.i2, n
42.5
29.0
31); film from the dioxane solution. Values of the relative transniissioii also were determined f o ~ peanut oil samples containing Geon 315 precipitated with pt.1 rrlleum ether. Figure 3, curve 2 s h o w a variation from 81 for thr sample containing no film to 29 for the sample containing 102 p.p.m. The change of light, tranamii+im rvith film concentrativrl was different from the case of oil containing only Geon 31X. after evaporation of the methyl ethyl kctone. This change resulted froin t,he dilution by the dioxane and petroleum ether a.nd caused a deviation from a straight line. In using this type o f curve where the slope decreased with an increase in film coiic~11tration, greater accuracy may be obtained for low film concenirations since greater errors in dial readings can be made with lrsr effect on the film concentration. Kephelometer readings were taken on a series of lard oil sarnples containing Geon 31X film precipitated with petroleum ethrr to establish the calibration curve. The readings were found 1,o vary from 85, for the samples containing no film, to 28, for , 1 1 1 .amples containing 102 p.p.m. The data are shown by Figurv 3. curve 3. Results of Peanut and Lard Oil Measurements. After the calibrating curves were established, relative transmissions werc. determined for 1-week, 1-month, and 2-month immersion tzs: oils. Values were obtained on the oils, as removed from thy oven, and after subjection to the precipitation method. Thest data are given in Tables VI and T'II. The light transmissions iIrJ
TABLEV. TL-RBIDITY OF LARD OIL COST.IISING Ksonw hrocms
OF
PRECIPITATED GEOS 3 1 5 F I u r
(Concentration of film solution w'as 0.000570 gram per ml.; 30 ml. of petroleum ether were added to each sample; in all cases 50 grams of lard oil were utilised) Dioxane ~ i l pure ~ ~ G~~~ 31r; Relatire Transmission Sample Solution, Dioxane, Film, Each KO. $11. hll. P.P.11. sainple Arerage 57 None 9 Sone 87 58 Sone 9 h'one 84 85.6 59 0.5 8 5 5.7 83 60 0 5 8.5 5.7 82 82.5 61 1.0 8.0 11.4 80 62 1 .o 8.0 11.4 78 79.0 63 2.0 i,0 22.8 73 64 2.0 7.0 22.8 72 72 5 65 4.0 5.0 45.6 57 66 4.0 5.0 45.6 56 56.5 67 6.0 3.0 65.4 44 69 9.0 0 0 102.6 28 70 9.0 0.0 102.6 28 28.0
! d a i u i i l ~ . aconsistrd of 450 nil. each:
Sample SU.
il
7% i3
i4 -_ I J
76 77 75 79 80 81 82
d a t a indicate a solubility of lew t h a r , 6 p.p.in. of Gtson tilm) Type Immersion T e l c Relative Oil Period Transmission Lard Sone 7G One w x k 78 One week 79 One month 83 One iiiontli 83 80 Two rnonttis T w o montlis 81 Peanut \-one 70 One week O n e aerl,
One niontli One inontti Two months ' h o inonths
7n
io
70
io
69 7 !I
2280
i N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY -0
TABLEVII. PRECIPITATI~S OF GEOS 3 1 1 SAMPLES
F I L I I FROX
TEST
,Added 9 ml. of pure diovane to each sample: added 30 nil. of petroieniii other t o each sample; each sample contained 50 qranis of oil. d a t a i n d l c a t e a solubility of less t h a n 6 p.p.m. 07 Geon filrnj Sample Immersion Test Relatire No. T y p e Oil Period Transmissinn 89 Peaniit Vane 84 83 I Teeh 84 84 1 Week 81 85 I Month 84 86 1 Xonth 8-1 87 2 RIonths 83 88 2 Months 81 96 Lard None 84 90 i Veek 8i 91 I Week 80 93 92 I Month 93 1 1Ionth 92 94 2 Month90 9; 2 Months 90
all the peanut oil tests, on removal from the oven, xvere found tu be 70, which corresponded to the value of the original peanut oil. The data on the lard oil immersion tests, on removal from the oven, mere rather surprising in that the relative transmission increased t,hrough a maximum value, as shovm by Figure 4. The peanut oil immersion tests, after subjection to the petroleum ether precipitation method, Tvere found to have a relative t,ransinission of 84, which corresponded to the value obtained by this method for the original peanut oil. The lard oil immersion tests, treated to precipitate Geon 315, were found to increase through a masimum in the same manner as the ~rontrolsample of oil r~mol-rtl from the oven. Since the readings on all of the ~wmpleswere negative---tliat is, the relative transmissions ivere all as high as for the control J B ~ I ples-and since the method was shown by the calibration curves to be sensitive to as little as 6 p,p.m. of film in the oil, it was concluderl that there 11-as no solubility of the film a t more than 6
5
__--
1
Vol. 41, No. 10
7-7-
I T E S T OILS 2 TES- CILS T R E b T E D TO PPECIPITA-E G E O N 31 I
70 1 0
3
2
4
S
I,
1
I
1
6
7
e
---
-7--
1
MKERSION TIME. W E E K S
Figure 4.
Variation in Light Transmission for Lard Oil
p.1j.m. in the oils after the designated t,est periods of u p to 2 ninii t lis. CONCLUSIOriS
Based on the results of the total chlorine analyses of thr leached solutions, the solubility of thoroughly dried Geon filme in aqueous solutions was found to be less than 1 p.p,m. This corresponds to less than 1.48 mg. per square foot of film surface Variations in the pII of the test so.utions from 3.5 to 9.6 had no effect on this result. The solubility in edible-grade lard or peanut oil n-as no greater than 6 p.p.m. .iCKNOWLEDGMEST
The assistance of 11.K. Loftfield, formerly of Batt,elle IIemorial Institute, who contributed to the development of a technique for handling the cast films, is acknorledged. LlTERATURE CITED
(1, Crhring, H., Kolloid-Z., 90,257 (1940). ( 2 ) Haldy, K. L., Wright, J . H., and Todd, F. C . , J . A m . C e m m Soc., 30,153 (1917).
RECEIVED August 26, 1948.
Oxygen Absorption of Vulcanizates A MEANS OF EVALUATING AGING RESISTANCE LOUIS R. POLLACK, ROBERT E. A\ICELWaAIN,AND PAUL T. WAGNER Industrial Laboratory, Mare Island !Yaval Shipyard, Vallejo, Cal;,f. Rates of oxygen absorption have been measured for tw-o natural and six synthetic rubber stocks. In addition, the course of aging in the oxygen bomb and air oven was followed by means of the changes in tensile strength and ultimate elongation for the same eight stocks. Correlation between oxygen absorption rates and deterioration of physical properties is close enough to justify substitution of a rapid oxygen absorption measurement for longer standard prwedures in evaluating aging characteristic* of rubber stocks.
I
T IS recognized (4,10) that the principal cause of deterioration
of rubtwr I& an oxidative one. The present study confirms previous itifilriri+rioti t o rhe effect that rates of oxygen uptake by a rubber s t o r k t i i i v be vorrelated, a t least roughly, with the e\-
tent of deterlor t o o t i raused by accelerated aging and by natural aging. Beraux! (11 natural deleterious effects other than by o ~ y -
gen (such as by stretching, ozone, ultraviolet light, heat, and pressure), no rapid aging method can be expected to do more than a p p r o ~ i m s t ethe reaction of a rubber stock to its service environment. Despite the nonquantitative nature of rapid evaluations of ~ P I ’ V I C life, ~ such tests are of value to compounders, purchasers, and research workers because of the basis rvhich they provide for comparison of similar stocks. In view of the lack of correlation between standard aging procedures ( 1 7 , 18), the question may ell arise as to which method to use. I n the absence of a compelling reason to choose one procedure over another, bomb aging has been used most co~nnionlybecause of i t s advantage of rapidity. The purpose of this paper is to show that routine volumetric measurement of rates of ovygen absorption of vulcanizates can give comparisons which, for control purposes, are a t least as adequate as those provided by standard procedures and are a considerable saving of time and apparatus.
