Mechanical Processing of Carbon Blacks Resultant Effects in GR-S Compounds
T pubIicatioii> , 13) conccriiing r l I ' 1wli:iyior of carbon black it1 (i1t-Q compouud, dim.,.l.it)cer, ~l~~ largP lumps Tvere brrls~led tllrollgh a so. 28 r. s, Standard sieve, The ~ , , ~ l k density after sieving L,.:lq 18.4 pounds per cubic i;)ot, I n a second expcrimtsnt 2 pounds of the origin:il fluffy blnck vxre millcd with flint 1)cbt)lc.~Ior 3 lioiii,., 'rlii. hiilk tlensitj- :it tht, end of this time \vas 19.1 po~uids1)i'r cubic foot. Firidly, halt' of this dense pebble millcd black \vas subjected for 90 minutes to the mrchanical pelletizing nctioii of x qtnndard Spheron process :ipparatus (f5). S m d l , firm pellets w r e formed in this operation, ranging in sieve size betn-ecii 28 and 60 mesh. These pellets had R bulk density of 23.1 pounds per cubic foot. Thus, three samples were prepared with bulk densities of 18, 19, ;ind 23, respectively, as contrastrd n-ith t h e original dciisity ( i f 2.8 pounds per cubic foot. This change \vas accomplished by .straight application of prcssiirc' :ind by vigorous and continued mccli:inical artion.
'l'hc effect of mechanical treatment o f carbon block, of the type it might enrolinter in densification or pelletization, Tias studied. It \vas found that the properties of "structure" blacks shol+ the greatest response to mechanical action. The effect of mechanical action may be noted by a loss in smoothnesr; of the uncured GR-S stock at normal tread stock loading, coiisiderahle loss in modulus. and a decrease i n electrical conductivity of the cured stock. So loss in ultimate tensile strength was observed. Lit& effect was noted using carbon with lesser structural tendencies. The effect of mechanical action, therefore, was related to an alteration of strrirtiire units or chainlike ~ p r e e a t e of s carboll particles.
c t riiclui.e-forming
tmdt,iic.it+ --that is, t o the ability 1 1 1 tlita c:ii,t)oii i):ii,ticlesto ni:iiiit;iiii :Icliaiiil i k ~ .gi,ouping (illustr:iti.il i n F'igui.t. 1 :IS a secoiitlary :I yregate) ii I ~ Itlisprrsed I in r i i l ~ l x ~nictli;c, i~ i i i c ~ ~ n t r a e t eto d nor triicturc til:irsks, which tend to ili-pci'se :is single discreet particlt,.. Tlli. -ti,ricture of the primary p:ii,ticle was thoroughly defined hj. s-i'aj. !liffr;iction studies (.;). S o theoretical interprrtation h:i$ bwn cltfeid to describe rigidly the contribution of structure ti) n d u [ h i < : it was found necessary to introduce :t particle-shapct i':ictor t i l ;ii,count,for modulus c1iar:icteristic. of c:irbon b l a r k , ~(,v). Sharrinigan acetylc.iic' black is :i commercial ciirt)oii 1)I:ick I .;hibiting high moduIii~-wliich ti:i,. been :ittrihntcd til :I higli - t ructure tendency. Hon.cxver, it seems reasorinhlc ti) :issum tliat .structure is not :L property unique t o a n y *ingle tyl)c of I :irl)on black but is pu ed to ,wmcdegree by all black.. Modu111- properties of a blncak m a y be tnken as some indii-:ition of t h c x (,\;tent of structure. I t is difficult to demuiistratc the cxistence of this struct,ural tt,ndency. The electron microscope offers the best direct evidence tlic chainlike grouping of pnrticles (IO). The most striking v\-itlrnce of this type has been demonstrated with acetyli.nc black T h e fact that acetylene blnek resists compression :iiid ii ilifticult to densify or pellctizc is further evidence of tht, c~xi;.tc*nt.c~ ( l i wcoiidary aggregates in this material. It Y i x d of iiitriwt, t Iicwforc, to deteminc whether mcchanical trcatnic*iit voultl ::Iter or destroy thi. nssociation among individual pxticIe.* I t.qmiisible for structurv, and thus permit densificatioii 01' pcllrti>:ition of the black. Furthermore, it was hoped thnt i f .siirli + i , c ~ ~ t m ccould n t bc (.orrelated witli I iihhcr properties. i t might off(,r !ieetedout on the roll mill, they showed a definite and progrcqsive decrease in both length and relative smoothness with extent of nicchnnical treatment,. This effect is illustrated in Figure 5. 1Iieroscopic examination of the rubber stocks employing the .illen squeeze-out technique shon-ed no difiereiices in gross dispersion of the black. Cures were made a t 292" F., and, a t the end of each cure, the samples were quenched in a water bath and alloived t o age in air overnight a t 80" F. before testing. Rubber test data are presented in Table IT. The modulus values a t full cure s h o a~ definite and progressive decrease relative to the extent of mechanical treatment. Ultimate tensile strength, however, ihons no significant rhange. The electrical resistance values of the cured stock a t 60-minute cure show a progressive increase with extent of mechanical treatment. Thus it is evident that all changes in t,he properties of compounded GR-S, believed to be related to the presence of secondary aggregates, were substantially altered by straightfornard mechanical lvork on the carbon black. This change in structure tendency is further substantiated h y .similar esperiments with a second commercial carbon, Philblack. Philblock is similar to acetylene black in its smooth-out and high modulus characteristics. Figure 6 s h o w the effect of mci~linnicnlaction on length and smoothness of stocks compounded rvith Pliilblack. Table V shows that a loss in modulus for Philhlnck occurred with mechanical processing, although ultimate tcnqile Ftrength does not change. In mother experiment, a Cabot experimental HAIF black, liclieved to have structure tendency to a lesser degree than acetylc,n(> hlnck or Philhlack, v a s wbjected to mechanical pelletizing :action for nn extended period. The density wai thus increased
'
TREITIIEST L ox ASALYTICAL T IBLI: I. EFFECTOF M E C H ~ S I C A PROPERTIES OF CARBOSBLACK Density, Sample Lb./Cu. Ft. Fluffy iiretylene hlack 2.8 Heavy compressed 18.4 Rnll-milled 19.1 Ball-milled and pelletized 23.1 rr.i.BI.I
s S PROPERTIES OF SRF BLACK
30 Modulus
”aniooth-out” modulus and electrical conductivity of c*ompoiinded ruhh(br stockr.
OK RUBBERPROPERTIES OF 813.4\TISXG.XS A C E T Y L E S E RIAC‘K
EFFECT O F
4 80 450
67
410 530 490 480
70 8A Gi 88
I~T~HHER
R a w Material Comyreaaed t o Density, 12.5 Density of l.h./Cu. F t . 20.3 Lb./Cu.Ft. 1860 1880 2710 2640 2660 2680 2540 2680 700 700 1300 1300 1580 1500 l5GO 1550 1090 1080 1900 1870 2260 2180 2220 2210
... ...
G!I
Vol. 38, No. 11
0,0!IO
( l j -‘lmon, F.. and Eatelow, It., I s u . 12s~.
0 : iil:
CHEM.,24, 579 (1932>. ( 2 1 . t i n . SOC. Tebting ll:~tc14;i13,Stand-
...
a d s , D281-28T. !:i) Henson, G., Riiblicr
.Iuc, 58, 4(iI (1936). (4) Biscne, J., ani1 IVarreii, B., J . A p p l i e d Phyyicu, 13, 381 (1942’ ( 5 ) Brunauer, P., :ind Enimet,tt, Teller, .I. A m . C h e m . Soc.. 60, X X I
(19.38).
(6) C‘iLbot, Godfrey L., Inc., BUZZ.,“Xigroinetcr”, 1931.
(7) I b i d . , Bull., “3Ieasuring BlaFkness”, 1938. (8) Guth, L,R u b b e r C h e m . Tech., 18, 396 (1945j. ( 9 ) Hall, R., Buckley, B., and Griffit,h, T., Can. C’hcm. I’IYXLBSI / [ A . , 29, 587-90 (1945). (10) Ladd, W., and Wiegand, W., Rubber A y e , 57, 399 (1945). (11) Parkinson, D.. Rubber Chem. Tech., 19, 100 (1946). (12) Smith, IT-., Thornhill, F.,and Bray, R., I s n . I k G . CHEM., 33, 1303 (1941). (13) TViegand. W., Cun. Chenz. Process Inds., 28, 151 (191d;). (14) I b i d . , ISD. ENG.CHEM.,29, 953 (1937). (15) Billing and Offutt, C. 8.Patent 1,957,314 (May 1, 1931). before t h e Division of Rubber Cheinistry a t t h e 109th IICetitlZ of t h e A V E R I C A N CHEMICAL SOCIETY, Atlnntic City, N..J. I’REsEsTED
c s of c~:~rhon hlarki. They appear t o be of of the structure prop sufficient, interest t o he brouglLt t o tlie :Ittention of those studying reinforcement. Data available nt prment do not permit an interprrt:ition d’t,hv coiitrihntion of structure t o properties of
b
iTrNsiie-
2500-
!
I /./-&--
Os
!
\I
I
.SO
52
I
I
10
Fluffy Black
Ball-Milled and Pelletized
Figure6. Effect of Rlechanical Treatment on Length and Smoothness of Uncured Calendered Stocks of Philblack in GR-S
I
10
20
22
24
26
Pellet Density, Lb./Cu.
28
Ft.
Figure 7 . Effect of Continued 3Iechanical .kction in Pelletization 3lachinery on a n Experimental HhIF Black (1TnpeIletized Raw- >laterial)
