August, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
865 I
Behavior of Various Clays with Crude and Reclaimed Rubber' H. A. Winkelmann and E. G. Croakman PHILADELPHIA RUBBERWORKSCo., AKROA, OHIO
The maximum and minimum variations produced the highest of which conHE emphasis which is by a large number of commercial clays in crude and tained 0.164 per cent alkali placed on uniformity reclaimed rubber have been determined. Their effect as sodium carbonate. and ease of processing on both the uncured and the cured products have been of rubber compounds makes Microscopic Examination studied. The chemical analysis gives but little init necessary to evaluate raw formation regarding their behavior in crude or reMicroscopic examination materials on the basis of claimed rubber. Clays show wide variation in plasof the c l a y s showed t h a t both the uncured and cured ticity, retentivity, and softness in crude and reclaimed there was a large variation properties of the compound. rubber. They vary widely in their effect on the physiin particle size f r o m o n e This study was made to show cal properties of crude and reclaimed rubber. Bomb sample to a n o t h e r . T h e the variation produced by a aging is an important test for differentiating between minimum a n d maximuni large number of samples of various clays. In comparing samples of clays it is effects produced by the clays commercial clays in crude and desirable to note their effect on the uncured as well as on the various physical tests reclaimed rubber. I t w a s the cured properties of a compound. may be predicted on the basis observed that the properties of the uncured s t o c k s i n of particle-size measurements. many cases showed much greater variation in hardness, feel, The fineness of subdivision of a clay determines its influence on and processing than was predicted from the physical tests of the properties of both the cured and uncured compounds. The the cured products. The influence of the clays in several finer the clay the greater is its stiffening power and reenforcing cases was more marked in the uncured stock than in the effect. A microscopic examination is one of the most iniportant tests which can be applied to clays, since it enables cured compound. It is the purpose of this paper to show the variations in one to make a quick classification of the material. The crude and reclaimed rubber produced by the various clays following table gives microscopic measurements of repreon the basis of plasticity, retentivity, physical tests, oven sentative samples: and bomb aging, and chemical examination. The maximum MAXIMUM MIXIXUX AVERAGE and minimum limits as well as the average results of the P P P 0 2 1 12 samples of clay examined are graphically shown. A micro0 2 1.5 25 0 5 3 10 scopic examination of the clays was made to show the relation0 5 S 50 ship between particle size and physical tests of the crude or 1 0 15 75 reclaimed rubber compounds. The results obtained bring Reclaimed Rubber out the maximum effects produced by clays and indicate the emphasis which should be placed on these effects in the Twenty parts of clay were refined with 80 parts of a standexamination and evaluation of a clay for rubber compounding. ard alkali whole-tire reclaim. Four parts of sulfur were subsequently added on a mixing mill and slabs cured for Chemical Examination 15, 30, 45, 60, and 75 minutes a t 141.6" C. Analysis of Clays PLAsTrcITY-Plasticity of the uncured stocks was deMAXIMUM MINIMUM on the Williams plastometer a t 27" and 100" C. termined Silica 94.2 37.46 Alumina 46.48 2.6 The clays are arranged in Figure 1 in order of decreasing Iron oxide * 0.1 3.0 plasticity a t 100" C., the control containing no clay is the Lime 2.2 None Magnesia 3.24 Trace most plastic and No. 27 is the least plastic. It was found Potash 1.35 0.13 Soda 1.63 0.05 that the plastometer readings a t either temperature failed Titania i 56 0.44 to show the actual variations in consistency observed in the Total alkalinity as NazCOa 0.164 0.005 Total acidity as HzSOr 0.07 0.002 hand tests. The plasticities a t 27" C. are lower than a t There was no relationship between iron oxide content and 100" C., as would be expected, and are in less agreement color of the clays. ru'either was there any relationship be- with hand tests than the readings a t 100" C. The plasticitween iron oxide content and oxygen bomb or oven aging in ties a t 27" C. show greater variation and a less gradual decrude or reclaimed rubber. The samples containing the crease in plasticity than a t 100" C. A comparison of the plasticities taken after 30 days with lowest and highest amounts of silica gave soft uncured stocks and the stress-strain curve of the cured products showed about both the Goodrich and Williams plastometers shows a much the same reenforcing effect. Irrespective of the chemical wider variation in the case of the Goodrich plastometer. composition of the clays, the behavior in rubber is largely (Figure 2) The classification of the clays according to determined by fineness of subdivision. The fact that some plasticity with the Goodrich plastometer corresponds very clays shorn acid reaction while others show an alkaline re- closely with the hand tests. A comparison of fhe original action should be kept in mind when using clay in different plasticity with that taken after 30 days with the Willianis types of compounds. Some clays were found to give an plastometer shows that there is a gradual "setting up'' on acid reaction the highest of which gave an acidity of 0.07 per standing. I n the case of the Williams plastometer the lower cent as sulfuric and others were decidedly alkaline in reaction, the K value the softer is the stock, while with the Goodrich plastometer the lower the value the tougher is the stock. 1 Received April 15, 1930. Presented before the Division of Rubber This should be kept in mind in observing Figure 2, since the Chemistry a t the 79th Meeting of the American Chemical Society, Atlanta, Ga , April 7 t o 11, 1930 units used for expressing plasticity do not correspond for the
T
INDUSTRIAL AND ENGINEERING CHEMISTRY
866
VARIOUS CLAY^ INRECLAIMED RUDDER
Vol. 22, No. 8
IN RECLAl NED PI.ASTICITY
VARIOUS CLAYS
WlLLIFlM3 PhASTOMETER
RUBBER
IO
t
0'
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5
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SAMPLE NUM6ER
I
Figure 1
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25
20
SAMPLE NUMBER Figure 2
VARIOUS CLAY5 IN RECLAIMED Ru~~ER Rh5TICITY- RETENTIVITY5OmNES5
COOPRICH FLA~TOMETLR
60
I
C
5
1.5
IO
,
I
20
25
SAMPLE NUM6ER Figure 3
VARIOUS CLAYS I N
RECLAIMED Rueem
TENSILE -ELONGATION
1
15
'
TIME
30
45
60
75
IN MINUTE5 AT 141.6'C. Figure 4
two plastometers. Plasticity as measured on the Goodrich plastometer takes into consideration both softness and retentivity, while on the Williams plastometer no account is taken of retentivity. The important fact brought out in this comparison is that the Goodrich plastometer is more sensitive in measuring differences in plasticity of clays in reclaimed rubber. PL.4STICITY-RETEXTIi I T Y 4 O F T K E S e - 4 Comparison Of these properties taken on reclaimed rubber containing various clays indicates a diminishing value for retentivity and softness as the plasticity decreases. (Figure 3) The clay which shows the highest plasticity, retentivity, and softness has an average particle size of 15 microns, whereas the clay showing the lowest plasticity, retentivity, and softness has an average particle size of 1 micron. The coarser clays give softer stocks, because there is less rubber consumed than is the case with a fine clay. TEXSILEAND ELoscmIos-Because of the number of clays tested, it would have been both impractical and confusing to attempt to show individual curves for each clay. I n order to simplify the presentation of results, i t was therefore deemed advisable to show only maximum and minimum results which by comparison with the average and control (in which no pigment was added) will indicate clearly the trend of the intermediate curves. (Figure 4) The tensile varies from 74 kg. per sq. cm. on the maximum to 49 kg. per sq. cm. on the minimum, which shows even lower tests than are obtained in the case of the control which contains no pigment. An average of all the tests produces a curve which falls midway between that of the control and the maximum. The elongation curves fall in the same order as those of the tensiles but, as would be expected, do not show so much variation between the individual curves. The clay showing the highest tensile strength and elongation has an average
VASIOUSCLAYS \ N RECLAIMED Ruse~R AGEING
1
I5 30 45 60 75 T i r n E l ~MINUTESAT I41.6'C. Figure 5
0
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10
IZ
INDUSTRIAL A N D ENGINEERING CHEiVISTRY
August, 1930
particle size of 1 to 1.5 microns, whereas the sample showing the lowest tensile strength and elongation has an average particle size of 15 microns. Mo~uLus-Practically the same relationship holds true for the modulus, as was shown in the comparison of the tensile strength curves. The minimum curve falls below the control, although the average in this case is somewhat closer to the results obtained with the control. (Figure 5) The smaller the particle size the greater is the reenforcing effect. A G I N d v e n - a g i n g tests were obtained using the 45minute cure. (Figure 6) The maximum decrease in tensile strength is from 68.5 kg. per sq. cm. to 47.5 kg. per sq. cm. The average aging, however, is considerably better and the curve is, of course, higher than that obtained with the control or the minimum. The curve showing the minimum decrease has the least variation and is almost a straight line. The initial tensile strength, however, is considerably lower than in the case of the clay showing the maximum decrease on aging. BOMBAGING--brnples of the 45-minute cure were aged for 48 hours in the oxygen bomb. The results shown on Figure 7 indicate good aging for most of the clays tested, since there is very little difference between the aging curves for the average and minimum decrease in tensile strength. This is also indicated on the graph showing elongations (Figure 8), since the curves showing maximum and minimum decrease in elongation also coincide. Crude Rubber
Twenty-two samples of clay were incorporated into a compound of the following formula:
4Q
VARIOU5CLAYS IN
RECLAIMEP fflJ66ER TENSILE
Parts 100
Pale crepe
D.P.G.
1.57 3.91 2.38 8.75 40.70 1.54
Sulfur Hvy. magnesium oxide Zinc oxide Clay Stearic acid
158.85
The compound was designed to give its maximum tensile strength in 30 minutes. Cures were made for 15, 30, 45, 60, 75, and 90 minutes at 141.6’ C. This compound was chosen because the compounds in which clay is most gefieralIy used are designed for a short cure. PLASTICITY-RETENTI\ITY~OFTNESS-chYS in crude rubber compound give an uncured product showing a wide variation in plasticity, retentivity, and softness (Figure 9), as indicated by the Goodrich plastometer. Except for minor variations, the retentivity and softness curves follow the trend of the plasticity curve very closely. TENSILE STRENGTH AND ELONGATIox-The variation in tensile strength shown in Figure 10 is very appreciable. The average tensile-strength curve corresponds more closely with the minimum curve. The elongation (Figure 11) of both the maximum and minimum curves shows reversion, whereas the average curve does not. The finest clay gives the highest and the coarsest clay the lowest tensile strength. STRESSSTRAm-Stress-strain curves of the 15-minute (Figure 12), 30-minute (Figure 13), and 75-minute (Figure 14) cures show but little variation in reenforcing effect. The average and maximum curves correspond very closely in all three cures. There are a few samples which show poor reenforcing properties. The minimum curve for the 75-minute cure (Figure 14) is low, owing to reversion. Here again the
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Figure 8
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SO
25
Vol. 22, KO.8
IXDUSTRIAL A-VD ENGTNEERING CHEMTSTRY
868
VARIOUS CLAYSIN RUBBER STRE55 STRAIN
15 MINUTE CUKE /
w
1000
7a3
doff
200
100
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600
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Figure 13
Figure 12
VARIOUS CLAY5 IN RU65ER
VARIOUS CLAYS IN
RUBBER STRESS STRAIN
75 MINUTE. CURE flhXlMUM
TEAR
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MINUTES CUKE AT Figure 15
Figure 14
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0
48 HOURS
0
IN mM6
Figure 17
smaller the particle size the greater is the reenforcing effect of the clay. RESISTANCE TO TEAR-The resistance to tear was measured both transversely and longitudinally and an average was made of the two tests. The Winkelmann tear test was used. Compounds containing clay generally show low resistance to tear. Some clays (Figure 15) are much better than others, although the average of all clays is not much above the minimum. The smaller the particle size the better is the resistance to tear. ABRASION Loss-The resistance to abrasion as determined by the Grasselli abrador measures loss in cubic centimeters
46
L
0
40 0 H O U R 5 IN mM0
48
Figure 18
per horsepower hour. It is shown (Figure 16) that the average loss is but little more than was obtained with the best sample. Some samples of clay show poor resistance to abrasion compared with the average. Owing to inconsistent results, it is impossible to draw any conclusions regarding the effect of particle size on resistance to abrasion. BOMBAcrxc-Samples of the 15- and 30-minute cures were aged in the oxygen bomb for 48 hours. (Figure 17) The variation in the decrease in tensile strength and elongation on the &minute cure is very slight and there is hardly any difference between the average and minimum decrease curves. The 30-minute cure shows the importance of bomb
August, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
aging, because on this cure there is considerably more variation between the minimum and maximum decrease curves for tensile strength. (Figure 18) Conclusions
1-The chemical analysis of clays gives but little information regarding their behavior in crude or reclaimed rubber. Acidity or alkalinity should be determined for effect on rate of cure. Color of the clay is no criterion of its purity. 2-Clays show wide variations in plasticity, retentivity, and softness in crude and reclaimed rubber. 3-Commercial clays vary widely in their effect on the physical properties of crude and reclaimed rubber. I n general,
869
the effect of the clays is the same in reclaimed as in crude rubber. There is not quite the percentage variation in tensile strength in reclaimed rubber t h a t there is in crude rubber. The alkalinity of the reclaim may have decreased the variation. 4-Bomb aging is an important test for differentiating between various clays. &The uncured as well as cured properties of a compound should be noted in compounding and processing various samples. 6--Microscopic examination of clays makes it possible to. predict their effect on the uncured and cured properties in both crude and reclaimed rubber.
&Methyl-1,3=Pentadiene’ Harry I,. Fisher and F. D. Chittenden GPINERAL LABORATORIES, UNITED STATES RUBBERCOMPANY, PASSAIC, h-. J.
A new set of reactions is given for preparing 3-methylARRIES, in his book, step. The f o l l o w i n g con ‘LInvestigations o n 1,3-pentadiene. Ethyl methyl ketone and acetaldesideration also seemed imNatural and A r t i f i hyde are aldoled to form 3-methyl-4-hydroxy-2-pentan- portant. 1,3-Butadiene, isocia1 Varieties of R u b b e r ” one, and this keto alcohol is then catalytically hydrogprene, and p i p e r y l e n e , on (d), wrote that further sysenated to the corresponding glycol, which on being being polymerized, give syndehydrated forms the 1,3-diene. NO l,2-diene can thetic rubbers which have t e m a t i c work on t h e innumerable homologs a n d form during the dehydration. Attempts to polymerize better practical p r o p e r t i e s analogs of butadiene would the U-diene to rubber-like products were only parthan those obtained from 2,3tially successful. The additional evidence given shows dimethyl-1,3-butadiene (6). doubtless produce substances which could easily be polymthat the polymerization of l,%-dienesto rubber-like I n view of the structural relaerized to rubber-like prodproducts does not depend solely on the presence of a tionships of these hydrocaru c t s . H e himself h a d vinyl group. bons worked chiefly only on 1,3butadiene or erythrene, @-methylbutadiene or isoprene, CH3 H3C CHa CH.CH? CH1:C. CH.CHz CH3. C H : C H . CH:CHa CHz:C. C:CHa a-methylbutadiene or piperylene, and p,y-dimethylbutadiene. CH2:CH. Butadiene Isoprene Piperylene 2,3-Dirnethyl1,3-butadiene The patent literature, he says, cites many others that could be polymerized to rubber under the usual conditions, but he adds that the possibilities may be quite limited, because, it was thought that the vinyl grouping, C H : CH2, present for example, he has found that a,a-dimethylbutadiene (2- in the first three, might be responsible for this difference in the rubber polymers, and therefore that the diene should contain methyl-2,4-pentadiene), such a grouping. The hydrocarbon chosen was 3-methylCH3. 1,a-pentadiene. It had already been prepared by Abelmann C: CH. CH:CH2 ( I ) , who used the following reactions: CHI’
H
“presents difficulties in polymerization to a rubber,” and similarly with a-phenylbutadiene (l-phenyl-1,3-butadiene), CJ&,.CH :CH.CH: CH,. Macallum and Whitby (10) also discuss this subject, stating : “It would appear that methyl substitution in the terminal positions of butadiene has, compared with such substitution in the middle positions, an unfavorable effect on the ease of polymerization,” and “that increase in the number of methyl substituents in butadiene diminishes the ease of polymerization.” They prepared a new derivative-namely, a,p,y,d-tetramethylbutadiene (3,4-dimethyl-2,4-hexadiene)and showed that it has “little or no tendency to undergo thermopolymerization” to a rubber. The writers undertook to prepare a simple homolog of butadiene which could easily be obtained pure and in good yield, and then to test its polymerization possibilities, especially to a rubber-like product. It was decided to form the double bonds in the final compound by a dehydration process and therefore to prepare a glycol in the previous 1 Received April 15, 1930. Presented before the Division of Rubbu‘ Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga., April 7 to 11, 1930.
CH3 CHaMgI and hydrolysis CHI Concd. HCl CH3.CH:C.CHO-----------f CHz.CH:C. C H ( 0 H ) . CHI Tiglic aldehyde 3-Methyl-4-hydroxy-2-pentene
+-
CHa Quinoline, at 180’ C. CHs CHz.CH:C. CHCI. CHa-----------fCHz. CH:C.CH:CHz 3-Methyl-4-chloro-2-pentene 3-Methyl-l,3-pentadiene
The position of one double bond is fixed by the starting product, and the position of the other one can only be as shown, provided no rearrangements have taken place. Abelmann apparently did not try to polymerize it. The writers’ method consists in aldoling ethyl methyl ketone and acetaldehyde to form the keto alcohol, 3-methyl4-hydroxy-%pentanone, CH3 CHI. CO . CH . C H ( 0 H ) .CHI
reducing this catalytically to the corresponding glycol, 3methyl-2,4-pentanediol, 7H3 CH,. CH(0H). CH. C H ( 0 H ) .CHI
