Oven and Bomb Aging of GR-S at Corresponding Temperatures ;ittempts to correlate oxygen t>onit>a r i c ~air oieii aging gctierall? proic urisati-factory, particularl: with GK-S. tc*tiiallj, a direct correlation should not be expected since .I -irnultatieou- change i n temperature aiid o x ~ g e nconcentration is itiiolietl i+ hen the, are conipared under t h e c.onieiitioria1 conditions for each test. The eflect of temperature arid of o x ? grn concentration ha\ e been separatel? eialuatecl 13, comparing the results of both oien and bomb ayiiig a t 80" and 100" C . Increased temperature i t a s foiind to increase the rate of deterioration in both t?pes of aging, but t h e effect appears to be more marked in t h e ox?peti bomb. Reaction of o x ? g e t i with GR-S, which re+ults i n hardening (cross liiihiiig). appear- to be \irtualI> iridepe~identof o x ~ g e i eoncentratioti i aboie t h a t in air aiid i b the predominant reaction i n t h e air oieri. Reaction of o\>geri with GK-S which leads to chain sciasion is inc-rea.cc1 t): 01, gen concentration aiid is t h e predoniinant reac tiori iii t h e o\?gen bonib. Chain scission is reflected in hot11 tensile breahdown .ind in a loiter niodulus t h a n i + o t i l t l other\+ibe be ohtaiiied since the shortcniiig of t h e chairis ~ o u l dh a i e a softeiiirig effect: thi- accwunts for t h e inidler iiiotldiis increase obseri ed i+ i t h bonil) agitig ant1 for t h e re\ersioii of the riioditlii- obseriecl 'it 100" C .
.ill
s:iiii~)l!- \voii>
cured
50
iiiiilutc3i
7
8 10
.. ,. ... .,
2970 29.30
ti
..
2770 2680 '320 2300
0
3220 2.370 2420 lj70 1.;30 1:13e1
I (IS0
1:350
1140 1310
13-10
Air
L
:i130 3160
1400 1:330 l(i10 1ii00 li(i0 1790 "010 2060
.1000 2800
"80 2860 Hurdol (softener)
F a t t y acid
Charinel black
5.0 1.5 50.0
L
R , i l i ~1 ,
aged i n rectangular strips; t e s t strips.
RUES2 , :teed a s
1133
!ii0
1010 1130
..
poi0
3,0 1 2 2.0
lOi0
13.50 1.300
3000
Zinc oxide Santucure (accelerator) Sulfur
IIcc
t.
1
100.0
1;.
forced circulation typo and was opcratod so th:rt tlic rn:i\iiiiiiiii amount, of fresh air was introduccil. Triplicntc: s&n1[)lc,q\\ ~ I ' C removcd aftcr 1, 2, 4 , 6, 8. arid 10 days at, 80" C , :inti :it il:tiih- i n t e r v a i up to 3 days at 100" c'. Tcnsile strips irew cu: i i , i i t i i tlic n g i d sarnp1i.s for testiiig. Tliis prcxedure was e~iii)loyi,! I O :tvoid the possibility of niore extensive deterioration along thr ( , v l y i ~of tensile strips cut before aging. IIo~\-ever,compari-oii oi 1 lie' TI?sults with a duplicate set of samples aged a t 100" C.iii tlii. iiwtii of trn?ilc Pti.ips shoired that this precaution was no1 e s c i i I1 The tensile strength, elongation a t break, nnii tiiw Iwth 200 arid 300% elongation n-ere determined. The, ported in the graplis represent the averagc tL'3t s t r i p for the data a t 80°C.; t h e data pr thc average of two indcpcritlcnr dc'tc.rniiti:it triplicate samples. The actual test i h t a arc end 11.
4
r: I{-s
:it 2%'
baniplc.~cut 1'roin tciiiile shei.13 w i r e agi!d in the tisygell 300 pouiids per square incii s t both 80" :tnd 100" Ci. aiiii : i I w iii the air oven a t the saiiie tc~nilicraturcn. The air ovc'ii n;t> ( 1 i the
test strips c l l t o u i
. J ! I P ~ngiug.
. 1134
INDUSTRIAL AND ENGINEERING CHEMISTRY COMPARISON OF AGING DATA
Figure 1 shows the change in ultimate elongation brought about by heating a GR-S vulcanizate at 80" and at 100" C. in both the air oven and oxygen bomb. At the lower temperature the oven is the more severe, b u t a t the higher temperature the oxygen preseure test produces a greater change after the first day. T h e temperature coefficients per 10" C. from the data of Figure 1 arc
Vol. 39, No. 9
a t both 200 and 300y0 elongation increased in h j t h bomb and oven during the first day. During the second day the niodulus continued t o increase in the air oven although a t a > l l J \ V C r rate. The drastic reduction in t,ensile strength in the I i n i i i ~ ) ,I I O I ~ C V C ~ I . , continued through the second day, with the result tli:it, tlic: (ah:iitiscission reaction predominated over the hardening rcm:rion :tnd the nct offcct on the modulus TY:LS a decrcase. T1it~ri~:iItt~t~ tliia iciisil(x curve for the bomb aging levcaled off \rliile t l i c b liaril(:tiiriy reaction, as measured in the oven, conliriucil and tiit' ZOOc; $ t i once mort: started to increase in t,he osygcn IjoiiitJ. ' l ' i i t b qI~)pc t.hc ciirvc' from this point (second t o fourth day of nyini: i. c'ssentislly tile samc as that of the corresponding curve for t i i t , < I I , I , ~ S at 200'c elongntion in the o v ~ n . Since the effect nf cliiiiii v,ibsion rras sninll during this period, as sho1v-n by thc teiisile c i i i , \ . i - ~t,his , slope represerits primarily the hnrdeiiiiig reactioii :inrl tleinonstratcs that it is virtually independent of osggc~riconcetitration above t h a t in air. I t i
