Synthetic “Natural” Rubber
...
Polymer Structure and Properties: S. E. Horne, Jr., J. P. Kiehl, J. J. Shipman, V. 1. Folt, C.
E. A.
Processing and Vulcanization: Tire Testing:
Willson, E.
F.
Gibbs
B. Newton
M. A. Reinhart’, E. A. Willson
B. F. Goodrich Research Center, Brecksville, Ohio
T
HE important observation, made by Katz ( 6 ) in 1925 using x-ray diffraction technique, showed that the mere stretching of crude or soft vulcanized Hevea rubber caused a t least a portion of the polymer to undergo crystallization. This and the subsequent experiments of Hock ( 4 ) emphasized the point that ~uccesafulattempts to synthesize a polymer resembling Hevea rubber mould have to take regularity into account. The situation is complicated in isoprene polymers by the variety of ways the monomer can enter the growing polymer chain. The four isomeric forms of polyisoprene are shown in Figure 1. Since head-to-tail orientations must be considered because of the asymmetry of the isoprene molecule, there are eight possible arrangements of the units that can occur in polymerized isoprene. Sodium, potassium, emulsion, and alfin polyisoprenes have been shown to contain all four forms of the repeating units (8). All of these uncured polymers have poor tack and their pure gum vulcanizates shorn poor physical properties. They do not crystallize when stretched or cooled. It has long been recognized that polymers of conjugated hydrocarbon dienes would have to be very regular in structure before their properties would approach those of Hevea rubber. Looking back over the last 15 to 20 years, there has been a elow development, almost iniperceptible a t first, of catalyst systems m-hich produce polymers that in some degree shox- an oriented structure. This orientation could result if the monomer, during the propagation phase of the polymerization, is held in a definite position with respect to the growing chain, as by cybotactic forces where polymerization is initiated a t the melting point of the monomer or as by adsorption of the monomer onto a solid surface-perhaps to the surface of the catalyst itself. The woik reported here deals primarily mith the properties of a rubber made by directed polymerization. POLYMER STRUCTURE AND PROPERTIES Catalyst. Catalyst systems, based on polyolefin information purchased from Karl Ziegler, hare been applied to isoprene mononler systems. and modifications have been developed such that either cis-1,4-polyisoprene or trans-l,4-polyisoprene can now be prepared a t n 111 Infrared Absorption Spectra. The effect of one of these catalyst modifications was first recognized when a modified olefin polymerization yielded an isolable unstabilized rubbery component n~liichshowed an infrared absorption spectrum (2- to 25micron range) almost identical to that of Hevea rubber except for peaks due to oxidation a t 2.8, 5.6, and 5.8 microns and, additionally, a slightly higher intensity in the peak a t 11.25 microns. Subsequent samples of this rubber, a cis-1,4-polyI
The B. F. Goodrich Go., Tire and Equipment Division, Akron, Ohio.
isoprene, now called Ameripol SN,when protected by age resistors did not show these oxidation peaks (Figure 2). Infrared absorption spectra indicate low ma,ximum concentrations of 1,2- and 3,4- addition products in Bmeripol SN. For these two isomeric units the discrimination in the presence of cis-1,4-polyisoprene units is good, being of the order il%. The discrimination of small amounts of trans-1,4- units in the presence of a large concentration of cis-1,4- units is not good, for, if we add by common solvent technique 5 parts of balata to 100 parts of Hevea rubber, detection of the added balata is very difficult. In the region from 8.0 to 10.5 microns where the spectrum of amorphous balata is most unlike that of Hevea rubber, the spectra of Hevea rubber-balata mixtures are practically superimpnssible on that) of Hevea rubber alone. At least 10 parts of balat,a per 100 parts of Hevea rubber are required for detection (Figure 3). Single isolated trans-1,4-polyisoprene units would not necessarily have the 3ame set of absorption bands as totally trans-1,4- polymer chains. At least four trans-1,4- units in a block are required to produce a spcctrum resembling that of balata. These Iimitations on the infrared absorption technique apply to both synthetic. and natural polyisoprenes. Since it has been noted in this ~ o r l as r well as in the previous work of Richardson and Sacher (8j and of Binder and Ransaw ( 2 ) that infrared absorption techniques do not, offer sufficient discrimination for accurately measuring the concentration of trans1,4- isomer in predominately cis-1,4- Eamples of polyisoprene, we concluded that such a quantitative analysis for characterizing a material having less than 1Oyo trans-1,4- units was not feasible a t this time. Instead, a e estimated the maximum possible amounts of each isomeric impurity from the infrared spectra. The spectrum of the Ameripol SIT protected with an antioxidant duplicates that of the natural product except. for the slight increase in intensity at 11.25 rnicroiis which may be attributable to the presence of about 1% more 3,4- addition product than is present in Hevea rubber. To the best of our knowledge, the origin of the 11.25-micron peak in the spectrum of Hevea rubber has not been established. Salomon arid Van der Schee (9) say it is tempting to assign the 11.25-,Apeak to 3,4- addition structure, but they foiintl it survived ozonization. The spectra of ilmeripol SY and of Hevea rubber in the region around 10.9 microns are very much the same, indicating very lit’tlc differcnce in 1,2- addition product concentration. Thiis the amount of side chains formed by 1,2- addition is estimated to be less than 1% for both Hevea rubber and for Ameripol SX. It is not knoan what the differences in the infrared spectra of cis-l,4- head-to-tail polyisoprene and of cis-l,.i- head-to-head polgisoprene aould be like because polymers of the latter type are
784
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
April 1956
not available. It appears safe t o assume that some of the skeletal vibrations would be affected, producing differences in the spectra. Since no differences except those already mentioned are apparent,
cq3 ,C=CH CH3
p z TRANS 1-4
,C=CH
(BALATA) II 95
\
CHz-CHz ,CHz-
,CHz-C\"z
F= C H
CH3
c H3
\
CIS 1-4 (HEVEA RUBBER\
11.95p
Figure 1. The four isomeric forms of isoprene and characteristic infrared absorption peaks
it is reasonable to say that no great differences in head-to-tail orientation exist between Ameripol SN and Hevea rubber. Examination by Phase Microscopy. Crystalline and amorphous balata are insoluble in Hevea rubber and Ameripol SN.
Concentrations as low as 270 of balata in either of these polymers are detectable by phase microscopy in the mixtures. Since gelfree fractions of Ameripol SN and Hevea rubber hydrocarbon show a single phase by this method, we conclude that each contains less than 2y0 of trans-1,4 polymer chains. This technique is applicable only if all the trans-1,4- units are in separate polymer chains. If the trans-1,4- units are distributed along predominately cis-1,4 polymer chains, insolubility would not result and detection by this means would be impossible. X-Ray Diffraction Patterns. Ameripol SN crystallizes when cooled as does Hevea rubber. The initiation period for Ameripol SN a t -26' C. is much longer than that for acetone-extracted Hevea. This is believed t o be due to the absence of impurities which furnish nuclei for crystal growth. Seeding with stearic acid greatly reduces the initiation time. The rate of crystal growth in Ameripol SN a t -26' C. was slower than in the acetone-extracted Hevea rubber used. Crystallization rate is also affected by impurities. Figure 4 shows the x-ray diffraction patterns of unseeded Ameripol SN and of acetone-extracted pale crepe. The pale crepe was cooled a t -26' C . for 24 hours and held a t this temperature during exposure. The Ameripol SN was cooled a t -26' C. for 140 hours and then photographed a t this temperature. These ring diagrams are typical of nonoriented, finely divided crystals. The slightly mottled appearance of the rings is due t o the Styrofoam frost shield used during the experiment. The ring diameters are the same in the two patterns, indicating identical crystal structures, The ratio of ring intensity to halo intensity is not quite the same in both patterns-the degree of crystallinity being somewhat higher in the Hevea rubber sample. Hevea rubber shows its maximum rate of crystalliza-
PROTECTED SAMPLE C*LCIUY
785
-
AMERIPOL
FLUORIDE
SOOIUY
SN CHLORIDE
POTASSIUM BROMIDE
I
1;;
14 15
PURIFIED HEVEA RUBBER
CALCIUM FulORlDE
SODIUM CHLORIDE
11'11 POTASSIUM BR
I
I
Figure 2.
I(
17 I8
Comparison of the infrared spectra of Ameripol SN and Hevea rubbers Films on potassium bromide disks
19 20 2,
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 48, No. 4
Intrinsic viscosity m e a s u r e ments were made at 25.00" f 0.01" 6. over a concentration range and were extrapolated to zero concentration to obtain the limiting intrinsic viscosity value which is designated by the symbol [?lo. Cannon-Fenske type viscometers (50 Series) were employed for the viscosity determinations. Using the toluene solutions of the polymers, osmotic pressure L m e a s u r e m e n t s were made a t 25 00" f 0.01" C. Regenerated cellulose film was employed as the semipermeable membrane. I t is of interest to compare a -G few of the polymer properties of 9cr QP SS rubber with Hevea rubber. Figure 3. Infrared absorption spectra of Hevea rubber- -refined balata mixtures Some of the pertinent data relating to polymer propel ties such as gel content, swelling index, tion ( I O ) a t -26' C., hence this temperature was used for these ill, (number-average n:olec~llar n-eight), -Vu(viscosity-averagp experiments. It is not yet known whether Ameripol SN S h 0 ~ 3 molecular weight), [v!o anti values are summarized in Table I. its maximum rate of crystallization a t this same temperature, l'ulcanixates of Ameripol SPI' and Hevea rubber crystalll~e when stretched. Figure 5 shows the x-ray diffraction patterns of Table I. Polymer Properties of Ameripol S\the stretched vulcanixates a t room temperature. The spot [ q l o = limiting intrinsic viscosity value diagrams are essentially identical, indicating the same crystal A I n = number-average molecular weight illw = viscosity-average molecular weight structure and about the same degree of crystallinity in each caw PL = memure of degree of solvation The agreement here is as good as for two different sample. cf of polymer molecules b y solvent molecules Hevea rubber. The fact that the two materials form cryst'ils of identical structure precludes any large differences in head-to.ImerigolSS 6.3 126 3.80 230,000 658,000 2.86 0.398 tail orientation, It is impossible for head-to-tail oriented pol! Ameripol S S 0 ., 1.32 77,200 135,000 1.75 0.406 ixer of isoprene to form crystals of the same type and dimensions hlilledualecreue 0 ,. 1 , 4 7 118.700 157.700 1.33 0 . 4 3 1 C n n i i l k i pale as a head-to-head polymer even though the repeating unit. :iic Crepe 11.6 127 8 30 838.000 2 , 1 2 0 , 0 0 0 2 . 2 0.431 otherwise identical. From the infrared data, phase microscopy examination, aiitl the x-ray diffraction data, we conclude that Anieiipol S S an
-T-TT-'-l
-*
---
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1956
187
A comparison of the pi values of the rubbertoluene systems is of interest. The pl value is a measure of the degree of solvation of polymer molecules by solvent molecules. For the binary system of natural rubber-toluene a t 27' C. a p1 value of 0 . 4 3 was reported by Huggins ( 5 ) . The high and the low molecular weight Ameripol S N rubber samples yielded p i values of 0.406 and 0.398 a t 25.00" C. Unmilled pale crepe and milled pale crepe had pl values of 9 . 4 3 4 and 0.431, respectively, a t 25.00' C.; this represents agood check on the value of 0.43 reported by Huggins. At the present time, it is believed that the difference in the values of Ameripol SN and Ameripol SN rubber Hevea rubber (acetone-extracted) Hevea rubber is real. These data imply that Figure 4. X-ray diffraction patterns of frozen but unstretched specimens the Hevea rubber molecules are less solvated by toluene than the Ameripol S N rubber molecules. This may be due to the presence of a more highly branched structure in the Hevea molecule as compared to the SN molecule, or it may be a reflection of the Table 11. Stabilization of Ameripol SN Rubber Qualitative Screening Test presence of a small amount of nonrubber constituents in the 9 8 0 (0.5% in Hevea samples. parts/ Toluene) Solvents having solubility parameter values of 8.6 1.35 100 Heated Parts Un8 hr. a t appeared t o be good solvents for both Ameripol SN rubber and Stabilizer Rubber heated l o O D C. milled pale crepe rubber. Carbon tetrachloride was the best Diphenyl-p-phen lenediamine 3.39 2.51 solvating agent for both materials. Other good solvents were 2 :5 Di-tert-butylxydroquinone (Santovar 0) chloroform, cyclohexane, carbon disulfide, chlorobenzene, toluene, Bis(dimethylthiooarbamy1) disulfide (Tuads) 0.2 3.40 1.08 and benzene. 2.87 1.02 0.2 Mercaptobenzothiazole (Captax) Stabilization of Ameripol SN. Freshly made polymer must be 0.2 2.68 1.30 Bis(2-benzothiazyl) disulfide (Altax) stabilized to protect it from degradation and softening by atmos0.2 3.04 1.08 Sulfur pheric oxidation. Illustrative of some of the early r e d t s of Polymerized trimethyldihydroquinoline 1.0 3.27 1.20 (AgeRite resin D) screening tests are the examples in Table 11. Aliquots of a poly1,2-Dihydro-2,2,4-trimethyl-6-phenylquinoline mer charge were mill mixed (eight passes) with the materials (85%) 1.0 3.04 1 84 Dip henyl-p-phenylenediamine 15% shown and exposed as 0.015-inch-thick sheets both a t room (Santofiex BX) temperature (unheated) and (heated) in a circulating air oven for sy?n-Di-,%naphthyl-p-phenylenediamine (AgeRite white) 0.5 3.43 2.34 8 hours a t 100" C.; specific viscosities (at 1/2yo concentration Diphenyl-p-phenylenediamine 0.25 in toluene) were then determined. 4 s one would expect, son-e sum-Di-P-naphthyl-p-phenylenediamine materials and combinations were more effective than others in ' 2.60 1.92 (AgeRite white) 2,5-Di-tert-butyl hydroquinone (Santovar 0) stabilizing the raw polymer. The effectiveness of the stabilization of some of these Ameripol SN rubber samples prepared by the addition of the more promising commercial stabilizers or antioxidants was further determined by measurements of the rate a t The curves of oxygen consumed versus time were all of an autowhich various polymer samples reacted with oxygen a t elevated catalytic nature, oxidation rate increasing with time. Two temperatures. An apparatus that permitted measurements of parameters can be obtained from such curves: The first is the the volume of oxygen consumed a t constant pressure and teminitial rate of oxidation, designated yo, and the second is a factor perature was employed. All measurements were made a t a temdesignated by k which is a measure of the autocatalytic nature or self-acceleration of the oxidation: Table I11 shows typical 0.2' C. and a t approximately 760 mm. of perature of 100" data from a series of oxidation rate measurements. Decreased mercury pressure. values of ro, of course, correspond to more efficient stabilization as do decreased values of k . For this series, AgeRite white is the most efficient stabilizer, Santovar 0 being next. Both AgeRite white and the combination of AgeRite white and Santovar 0 shown have stabilized the Ameripol SN t o a degree equivalent to or better than that shown by pale crepe. The unstabilized Ameripol SN polymer is quite susceptible t o oxidation a t 100' C. The addition of stabilizers decreased the initial rate of oxidation by a factor of approximately 20, whereas k was decreased by a factor of almost 100.
+
g:y}
1
0": )
*
Ameripol
Figure 5.
SN
rubber
Hevea rubber
X-ray diffraction patterns of pure gum vulcanizates at 1000% elongation
PROCESSING AND VULCANIZATION
Ameripol SN, as ordinarily made, looks and handles much like masticated Hevea rubber.
INDUSTRIAL AND ENGINEERING CHEMISTRY
788
Table 111.
Stabilization of Ameripol SN Rubber Oxygen Absorption at 100" C.
ro = initial rate of oxidation, mole Oz/gram -1 min. - 1 k = measure of autocatalytic nature of oxidation, min.-l
Polymer Aineripol S N Anieripol SS Aii~eripolS N Anieripol
SN
Stabilizer None 2,5-Di-tert-butyl ii droquinone (Santovar 61,0.3% on rubber Diphenyl p phenylenediamine, 0.2'70 on rubber s y n Di 0 - naphthyl p phenylenediamine (AgeRite white), 0.5yo o n rubber
k
TO
5 0
x
10-7 0 . 2 5 X 10-7
x x
SF 6 3
10-1
10-4
- -
-
-
-
.inieripol SN
Hevea pale crepe
Iione added
0.10
x
10-7
0.19
x
10-7
-0
2 2
Table IV. Physical Properties of \'ulcanizates-Gum (Room temperature tests) Ameripol SN Hevea Rubber so plus 1.5 T e c h Classified Grades addi- parts of Red Yellow Blue tive additi\-ea 0 0 0 Tensile, Lb./Sq. Inch Cure, min. a t 280' F. 15 Nooure 2840 800 2540 2900 3530 2680 3150 30 1400 3970 3440 2970 3850 45 2030 3810 60 2380 3200 3090 3450 4000 90 2250 3210 3110 3600 3730 15 30 45
60
sn
15 30 45 60 90
13007~hlodulus, Lb./Sq. Incli260 380 500 700 550 790 970 700 1110 800 1200 800 930 1280 1320 700 1040 1400 1520
.. 120
m
i90
Elongation a t Break, 870 890 820 800 790 780 750 760 750 820 750 700
280 350 430
910 860 800
930 8.50 880
x
10-4
Stock
Tpbt Blelill
Vol. 48, No. 4
canizates-antioxidant for polymer stabilization, nonrubbey constituents (such as ash, protein, and protein decomposition products), and fatty acid material xhich affect the state oi vulcanization. These deficiencies are corrected by additions of suitable materials. The antioxidant is added a t once to every lot of the freshly made polymer accordingly as a nonstaining or staining type polymer is required. Addition of fatty acid and a material simulating the nonrubber constituents is made by t h r compounder as required. Some buffer material ('7) is needed to help adjust the rate of cure of Ameripol SN, and in the tests reported the additive, soybean lecithin (95Yo) with triethanolamine (TEA) ( 5 7 0 ) ,was used (I1/>parts of this mixture to 100 parts by weight of polymer). Othenvise, Ameripol S N is conipounded and handled like Hevea rubber. Pure Gum Stocks. Ameripol SN with additive s h o w gooti properties in the ACS I1 test recipe (Table IV), approximating thoqe shown by the Hevea rubber trqt blend of ribbed smoked sheets and pale crepe. In a IOT sulfx, pure gum recipe, (Tablr T'), Ameripol S S containing both additive and extra fatty acid gives a vulcanizatc quite comparitble t o that of the Hevea rubber control. Heavy-Duty Tire Stocks. I t was a natural anticipation that this new polymer, dnieripol S S , so much like Hevea rubber in chemical structure, milling, compounding, and vulcanizing characteristics, should show low hysteresis values, as well, in heavy-duty truck tire stocks. Evtendrd tests have amply borne this out.
2490
3410 3210 3670 3620
T a b l e V.
Physical Properties of VulcanizatesLow-Sulfur Gum Compound (Room temperature tests) Ameripol
380 790 950 1170 1240
SNO
Hrvea Rubber6
%--------860 830 760 770 750
910 830 790 760 760
Lecithin (95%) and TEA ( 5 % ) . ACS 11 Recipe: Rubber 100, zinc oxide G , stearic acid 4, Captax 0.3 sulfur 3.5; ACS tensile sheets.
600% ZIoduliis, Lb./Sq. Inch 10 20
30
40
800"; . \ I o ~ : I ~ LLb./Sq. Is. Inch 10 20 30 40
It has excellent tack and good "tooth." The ;\looney viscosity ( M L - 4 ' at 212" F.) of the polymer is in the 50 to 7 5 range. Processing Properties. Ameripol S S requires no preliminary breakdown and bands smoothly on a laboratory mill by the time the rolls have made three or four revolutions. This is partly due to the excellent natural tack of the polymer. Like natural rubber, Ameripol SN breaks donn rapidly on a cold mill, so mill mixing is usually carried out at temperatures around 180" F. Compounding ingredients then added are accepted as readily and dispersed as well as they would be in Hevea rubber Laboratory Banbury mixing is usually run a t 220" to 260" F. n here the stocks handle xell, but batches have been discharged satisfactorily a t 325' F. Factory Banbury mixing presented no problem and Ameripol S S stocks processed well on factory calenders and in extruders. In fact, extruded treads s h o m d less linear shrinkage and less extrusion porosity than ordinary Hevea rubber treads. The carcass plies and the treads handled v-eli in the factory tire-building operation, and the building tack of the A4meripol S N was equivalent to that of similar Hevea rnbber stocks. Compounding. Freshly made Ameripol S S lacks three kinds of materials (naturally present in Hevea rubber) that are Irnonn to have an important influence on the technical quality of vul-
4i0 500 3 50
iiio
1900 1550
Elongation a t Break, % 930 860 9iO 830 900 40 860 980 Recipe: Rubher 100, zinc oxide I , .lgeRite White 0.5, f a t t y acid activator 2.5, Captax 0.4, Xltax 0.55, s u l f u r 1.3; ACS tensile sheets. a Additives: 1 part stearic acid: 1 . 5 paits lecithin plus TEA. b Additive: 1 part rosin oil.
in
20 30
Two different lots of Ameripol SX, labeled I and 11, differing somewhat in gel content and in swelling index of the gel (determined on the unmilled polymer) were compounded in a typical carcass stock and in a tread stock along with a Hevea rubber test blend (ribbed smoked sheets and pale crepe) as a control. The recipes in each case are identical except for the lecithin-triethanolamine additive (1.5 parts/100 parts of Ameripol SN) and extra stearic acid (1 part)100 parts Ameripol SN) to approsimate the amount naturally present in Hevea rubber. Comparative data on physical properties of the carcass stocks are shown in shoxn in Table T'I and in Figure 6; those on the tread stocks are shown in Table T-I1 and in Figure 7 . The stress-strain properties a t rooin temperature, at 212' F., and after aging are very similar on all the stocks and so ale the Gehnian low temperature moduli
April 1956
789
INDUSTRIAL AND ENGINEERING CHEMISTRY Table VI.
Physical Properties of Vulcanizates-Carcass Ameripol S N
I Gel, % Swelling index
[?I
Mooney viscosity, ML-4' a t 212' F. Carcass recipe, Parts Polymer Zinc oxide Steari! acid A eRite powder (PBNA) H%F black (Statex 93) Pine tar T E A (5%) Lecithin Altax Sulfur B. F. Goodrich plasticity, 85' C. (on compounded stock) Mooney scorch, 260' F. (large rotor) I.V., initial viscosity Vm. min. viscosity T,, scorch time min. T.(T. T A S ~ ) ' cure time, min. T&o, min. for io-point viscosity increase Gehman low temperature modulus (cure 30 min., 280' F.), O C.
+
+
T? ~.
Ts Freeze point
14 83 3.17 75 100.0 3.0 2.0 1.0 40.0 5.0 1.5 1.0 2.5 72.8 36 26
20.9
27.6 6.7 -33 -48 -58
I1 31 59 3.45 75
100.0
3.0 2.0 1.0 40.0 5.0 1.5 1 .o 2.5 66.4 42 32 17.3 21.3 4.0
-32 -48 -58
.. .. ..
.. 100.0
3.0 1.0 1.0 40.0 7.0
i:o
2.5 72 8 34 25 16.9 20.5 3.8 -34 -49 -59
400% Modulus, Lb./Sq. Inch 200 630 360 780 1650 880 1260 1370 1080 1300 1340 1040 1160 1220 Elongation at Break, % 940 660 640 720 680 690 710 630 670 670 610 640 650 470 610
10 15
30 60 150
Ameripol S N I11
I
Rubber
Stress-Strain a t Room Temperature Tensile, Lb./Sq. Inch Cure, min. a t 280' F. 150 680 1820 10 1070 2260 2930 15 2840 2880 3580 30 2910 2650 3240 60 2420 1500 2720 150 10 15 30 60 150
Stocks
H~~~~
and freeze points. The heat rise in the B. F. Goodrich flexometer a t both 0.175- and 0.225-inch strokes are likewise comparable. The Graves angle tear tests a t 212' F. are somewhat lower than those for the Hevea stocks, but, on the other hand, the Ameripol SN stocks in the DeMattia flex crack-growth (initiated) tests appear on the whole t o be more resistant than do those of the H w e a stocks. Summary. The results of the laboratory comparative evaluation tests on pure gum carcass and tread stocks indicate a virtual identity in the performance of Ameripol SN rubber and of Hevea rubber. The comparative data suggest that Ameripol SN heavyduty tires will perform as well as similar Hevea rubber tires. T I R E TESTING
The possibility of using Ameripol SN rubber to replace Hevea rubber completely in the tread and carcass stocks of heavy-duty bus and truck tires has undergone extensive testing. The results reported here deal with a lot of sixteen 11.00 X 20 heavy-duty express tires which required about 1 ton of Ameripol SN for manufacture. The procedure for evaluation of test tires is divided into three programs-namely, indoor wheel tests, where tires are run to destruction; test truck operation, where conditions such as speed, load, and inflation are closely regulated; and mileage contract busses, where tire maintenance is a t a high level, but service conditions on the highways are very severe. Indoor Wheel Test. Tires are run on smooth 67-inch-diameter wheels in an ambient temperature of 100' I5"F. at a speed of
xevea
Rubber
Stress-Strain a t 212O F. Cure, min. a t 280° F. 10 15 30 60 150
Tensile, Lb./Sq. Inch 230 1200 900 1650 2180 1620 1500 2290 1330 1300 1920 1320 1220 1820 400% Modulus, Lb./Sq. Inch 220 iio 400 620 740 830 560 700 800 750 700 780 660
10 15 30 60 150
Elongation a t Break, % 1000 940 1040 800 900 660 790 850 610 760 700 700 600 800
10 15 30 60 150
Aged in Teat Tubes 24 Hours a t 212O F. in Air; Streas-Strain a t Room Temperature Cure, min. a t 280° F. Tensile, Lb./Sq. Inch 10 1770 2500 , 2680 15 2220 2800 3140 2450 2540 a080 30 60 1880 2230 2780 150 2030 2100 2380 400% Modulus, Lb./Sq. Inoh 700 1000 1800 800 1200 1840 1050 1440 1650 1280 1620 1480 1080 1320 1120
10 15 30 60 150
Elongation a t Break, % 650 650 510 680 640 590 640 560 600 520 500 600 600 570 620
10
15
30 60 150
Graves Angle Tear (212O F.) Cure, min. a t 280' F. 15 30 60
-Lb./Inch60 130 210 190 190 170
180 220 220
B. F. Goodrich Flexometer (212O F.): 5.j-Lb. Load: BO-Min. Cure, 280° F. Stroke 0.175 inch Shoie A hardness A T OF. Perkanent set % Static compredsion a t 55 lb., % Duration of test, min. Stroke 0 225 inch Shoie k hardness AT OF. Per'manent set % static compre&ion &t55 Ib., % Duration of teat, min.
48 27 10.4 28.8 25
52 25 6.7 24.3 25
49 25 7.5 27.3 25
47 52 15.3 30.1 25
41 8.5 24.7 25
52
48
45 10.6 29.3 26
50 miles per hour. This is a continuous 24-hour-per-day test with the load increased in increments amounting to 20% of the rated load capacity each 24 hours. The test is started at SO% of standard Tire and Rim Association load. This is a very severe accelerated test and usually is terminated by a carcass blowout due to heat build-up. Hysteresis of compounds used is a strong influential factor of the mileage obtained to failure. The heat build-up in Ameripol SN rubber tires, as measured by thermocouple needle and air pressure build-up in the tire, was slightly less than that in the Hevea rubber control tires. Tires evaluated by this method are always run to destruction. The mileages run by the Ameripol SN tires to failure were comparable to those shown by the Hevea rubber controls (Table VIII). Resistance t o cut growth (standardized cuts are made in the tread grooves before the test is started) was somewhat better in the Ameripol S N tires (an average of 1270 increase in cut growth) than in the
INDUSTRIAL AND ENGINEERING CHEMISTRY
790
Table VII. Gel % Swdlling index [?
1
hlooney viscosity, IIL-4' a t 2 1 2 O F. Tread recipe, Parts Polymer Zinc oxide Stearic acid AgeRite powder (PBK.4) BLE-25 ISAF black Fine t a r TEA ( 5 % ) Lecithin Santocure Sulfur B. F. Goodrich plasticity, 85' C . (on compounded stock) hlooney scorch, 260' F. (large rotor) I.V.0
+
Vm
TS To
TAW Gehman low temperature modulus (cure 30 min., 280' F.), C.
TI Ts
Freeze point
Physical Properties of Vulcanisates-Tread
Ameripol SN I 1114 31 83 59 3 17 3 45 75 75 100.0 3.0 4.0 1.0 1.0 42.0 2.0 1.5 0.6 3.0 44.8
52 35 12.8 15.0 2.2
lie\ea Rubber
100.0 3.0 4.0
100.0 3.0 3.0
1.0
1.0 1.0 42.0
1.0 42 0 2.0 1.5 0.6 3.0 38.4
56 40 11.3 13.4 2.1
4.0
..
0.6
3.0
50.3 i G 36 12.25 13.8 1.55
Stock
Ameripol S N I IJ Rubber Aged in Test Tubes 24 Hours a t 212' F. in Air; Stress-Strain a t Koom Temperature Cure, min. a t 280° F. Tensile, Lb./Sq. Inch 15 3120 2990 2050 30 2890 2710 2810 45 2570 2510 2620 75 2120 2110 1880 150 1430 1360 1550 400% Modulus, Lb./Sq. Inch 1900 2780 2640 2100 2400 2660 .. 2340 2570
15 30 45 75 150
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..
.. ..
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Elongation a t Break, r0 600 530 460 470 440 550 400 380 450 380 330 300 270 290 280
15 30 45 1%
Graves Angle Tear (212" F.) -33 -48 -58
-32 -48 -58
-34 -49 -59
Stress-Strain a t Room Temperature Cure, min. a t 280° F. Tensile, Lb./Sq. Inch 15 3810 3820 4040 30 3810 4230 4160 3900 3730 4080 45 76 3840 3700 3920 150 3150 3490 3540 15 30 45 75 150
400% Modulus, Lb./Sq. Inch 1580 1890 2110 2010 2300 2550 2250 2460 2570 2170 2360 2450 1900 2010 2200
15 30 45 76 150
Elongation a t Break, % 690 640 630 650 580 570 570 600 560 600 560 580 630 570 560 ,Stress-Strain a t 212' F.
Cure, min. a t 280' I'. 15 30 45 75 150
Vol. 48, No. 4
Tensile, Lb./Sq. 2700 2480 2460 2100 2220 2120 2210 2000 2170 1830
Inch 2860 2480 2490 2480 2400
15 30 45 75 150
400% Modulus, Lb./Sq. Inch 1120 1140 880 1370 1290 1150 1300 1500 1420 1290 1380 1500 1150 1280 1220
15 30 45 75 150
Elongation a t Break, % 840 690 770 580 600 700 570 600 620 eo0 520 GOO 600 520 650
Hevea rubber control tires (an average of 26y0 increase in cut gron th). Test Truck Operation. This is also an accelerated service test but of lew severity than the indoor wheel test The test trucks are operated in the Kerrville, Tex , area, on a 24-hour-per-day basis a t 45 miles per hour. Tires ale rotated to the four wheel positions at 700 mile intervals. Test conditions such as loads, speeds, and inflation pressures are closely regulated. The test is operated at standard Tire and Rini Association load for 2800 miles, followed by 2800 miles at 130y0rated load, and then run to failure or completion of 19,600 miles ( v hichever occurs first) a t 150% rated load. The Ameiipol SK rubber tires made a very creditable shoning. Tread wear was %To that of the standard Hevea control tires. (These particular .41neripol SN rubber treads were 1 e i u n
