P
p 4 qn-s
0
GEORGE R. VILA Naugatuck Chemical Division, United S t r t a Rubber Company, Naugatudc, Conn. Viscosity or plasticity measurements bear a direct relation to the power required and the heat generated while tubing GR-S but d o not correlate with tubing rates. The latter, in turn, depend upon worm speed and the surface condition of the mixed compound, smoother surfaces tending to give faster speeds regardless of vlrcosity. The increase i n cross-sectional area upon tubing also bean a direct relation to surface smoothness, smoother compounds exhibiting less swell. It i s possible, therefore, to predict tubing characteristics with a reasonable degree of accuracy from the plasticity or vlscosity of the finished compound in conjunction with an estimate of its relative surface smoothness. The latter quality may be achieved by
hot breakdown, increasing softener ratios, or increastpg pigment ratios. Thus the faster tubing rate and smoother appearance resulting from Gordon plastication i s explained by the higher temperatures developed during breakdown. High-temperature plasticatioe however, exerts a deleterious effect on the physical properties of the vulcanizate. There Is evidence that a higher degree of benzene solubility in the raw polymer may result i n a more favorable processing history, but additional examples are required before conclusions are justified. When working with normal OR-S, cold milling I s found to increase benzene solubility whereas hot milling or Gordon plastication reduces it and, presumably, results i n a gelled polymer.
N RESEARCH on polymers and their compounds it is often assumed that, in general, the viscosity or plasticity of the mixed compound is a direct measure of its processing characteristics. (In this paper the term “viscosity” is used in lieu of “plasticity”, low viscosity implying high plasticity and vice versa.) It was observed, however, that c?mpounds formulated from GR-8 which had been treated in a Gordon plasticator invariably tubed faster and smoother than similar compounds made from cold milled polymer although the compounded viscosity of the former frequently was higher. Inasmuch as these observations were at variance with laboratory predictions, it was decided to inveetigate the plastication and processing of GR-S in an effort to disoover interrelations among the phenomena involved. The experimental runs may be grouped into five series of treatments, set forth in Table I. In each run the raw polymer was subjected to the indicated type of plastication and then compounded on a laboratory mill. After a rest period of several days the compounds were remilled and tubed in a laboratory unit (made available for this study through the kindness of W. B. Dunlap, Jr., of the Lee Tire and Rubber Company). This a p paratus has already been described (4). It measures extrusion rates and the average power consumed while tubing. The worm speed may be varied, and the temperature of the tubing chamber and head is rigidly controlled.
Following plastication, a standardized procedure (3) was adhered to during the laboratory mixing operations with reference to mill openings and the addition of compounding ingredients. All mixing was effected on a 6 X 12 inch laboratory mill. Finally, batches of each of the compound variations listed in Table I were vulcanized and subjected to certain physical testa in order to determine the effect of the different treatments on ultimate product quality. These testa included modulus, tensile strength, elongation at break, rebound, hysteresis, and flex crack growth. The procedure for the last named test was described in a former paper (6). Mooney viscosity determinationh were made on the uncompounded and compounded polymers during the successive stages of plastication, mixing, and tubing. Benzene solubility was also determined on the raw and plasticated polymers by a technique not yet described in the literature (6). This method provides for the extraction of sol. The movement of the solvent in relation to the mass of the polymer is very gentle, and agitation is purposely avoided although some weak gel structures may be destroyed becauxe of the relatively high temperature of the benzene.
9
Table 1. Series I, Polymer X 88. Polymer Y A C
OR-Spplymer X
... ......
COMPARISON BETWEEN TWO PRODUCTION LOTS
Series I compares two lots of GR-Sfrom current production designated RS pplymers X and Y,respectively. It is evident from
Polymer Treatments and Compound Formulations
Seriea 11 Cold Breakdokn 08. Gordon Plastication A B
... ... .. .. .. .. .. .. .. .. .. .. .. ..
Series 111, Cold Breakdown 08. Hot Breakdown C F O H
Beriea IV Inwearing Ratioa dt Softener C D F :
Series V Increaaing Ratios of darbon Black I J C K
.. .. .. .. .. .. .. .. .. .. .. ..
...
. . . . . . . . . . . . . . . . . . . . . . .
... .. .. .. .. .. .. . . .
100 . . . .100 .. .. .. .. ... ... ... ... ...
IO-min. cold breakdown 100 100 3 pasaes, Gordon plssticrator 100 OR-Spolymer F IO-min. cold breakdown” 100 100 100 10-min. hot breakdown b ibb 1:: 20-min. hot breakdown 100 iob 40-min. hot breakdown ci .‘i 6 6 6 6 6 6 6 BRT No. 7 Carbon black 60 60 60 60 60 SO 60 60 60 Zinc oxide 6 6 6 6 6 6 5 6 6 Sulfur 2 2 2 2 2 2 2 2 2 Mercaptobenrothiarole 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.5 1.6 Polymer broken down on 6 X 12 inch laboratory mill with cooling water circulating through rolls. b Polymer broken down on 6 X 12 inch laboratory mill with steam circulating through rolls.
... ......
.. . . . . . .
Q
1113
:::
.....
. . . . . . . . .
10 50 6
2 1.6
20
60 6
2 1.6
100 .. .. .. ..100.. .. .. 100 .. .. .. .. ..
100
INDUSTRIAL AND ENGINEERING CHEMISTRY
1114
Series No. Polymer Compound Feature
7 1 -
X
-11-
Y
A C ,-Polymer10 rnin..
Plastication
Table II. Comparative Propertier r I11
x
cold mill
10 rnin., 3 passes
cold mill
Gordon Dlast.
Y
Y
X
Y
Y
.
F 0 Breakdown
H
10 min.,
10 rnin., 20 rnin.,
40 min..
cold mill
hot mill
hot mill
-1v-
Y
.
C
A B -Breakdown-
Vol. 36, No. 12
C -BRT 5
hot mill
Y
Y
10
20
*
D E No. 7-
10 rnin., cold mill
V-
Y
Y
20
35 60 10 min.,
I J -Carbon
I'
Y
K
C black
65.
cold mill
Bencene aoly., % Before lastication 74.2 82.4 74.2 74.2 82.4 82.4 82.4 82.4 Allas in compound After pfastication .. 99.7 .. 56.3 99.7 70.7 62.9 55.2 Mooney viscosity" 62 62 62 62 Unplasticated 67 62 67 67 62 62 62 62 36 35 Plasticated 35 35 37 35 37 44 35 33 30 24 80 75 68 52 Compounded 100 80 100 106 80 84 82 83 72 69 72 82 69 61 57 63 69 64 59 44 Remilled 3 min. Net increase in Mooney viscosity 34 29 24 9 when compoundedb 35 34 35 38 34 28 27 39 Relative tubing speed, compound C equated to IOOC 94 100 94 102 100 93 112 140 112 97 100 107 Relative power consumption during tubing,.compound C equated to 100: 106 100 106 112 102 100 96 97 100 100 95 93 lnorease in area of tubed rod, % 230 230 230 214 230 199 293 184 230 233 253 171 5 4 $ y a r a n c e of mixed stockd 5 2 5 5 5 5 6 3 8 1 ysical roperties of vulcaniaate c1iref6O min. at 292O F: Modulua at 3 0 0 7 lh /sq. in. 910 900 910 1100 900 910 1000 1240 900 830 680 300 3200 3200 3250 Tensile atrength.Pb./&. in. 3200 3250 3250 3500 3390 1400 3010 2750 2390 Elongation % 610 560 603 610 610 603 603 666 706 685 540 453 Rebound. % 32.0 31.0 32.0 32.0 32.0 31.0 27.8 42.0 32.0 31.8 29.0 28.8 Torsional hysteresis ce +v '*no _ . I log. decrement 0.190.19 0.19 0.20 0.19 0.20 0.21 0.22 0.19 0.24 0.30 0.08 Flex crack growth thousandths inch per kc. flexing 2.65 2.35 2.65 4.76 2.35 3.77 3 65 7.92 2.35 3.70 2.28 0.59 a All Mooney viscosity values taken 4 min. after starting rotor following a 1-min. preheating period at 212O F. (large rotor used). b Mooney viscosity value of remilled compounded stock minus viscosity of raw polymer after plastication. C See Table V. d Arbitrary scale: 0 infinite smoothness; 10 = infinite roughness.
t"g$]
C+ 62 35 71 55
62 35 136 103
62 35 80 69
20
34
68
104
100
109
102 248 6
100 230 6
119 210 4
600 2580 630
900 3250 603
38.0
32.0
1770 3376 490 27.0
"V"
0.12
0.19
0.23
1.33
2.35
5.01
-
Table I1 that, both materials are nearly comparable with reference to the various properties developed. Figure 1, series I, traces their processing histories through the successive stages of plastication, mixing, remilling, and tubing. Polymer Y exhibits a faster rate of breakdown during the early stages of plastication, although comparable values are obtained at the end of 10 minutes. Polymer X tends to show a higher degree of stiffening during the mixing operation, but this differential is again substantially eliminated upon remilling 3 minutes following a 24-hour resting period. Investigation has shown that Mooney viscosity values tend to drop off at a sharply decreased rate after the first remill, as shown in Table 111; consequently additional remillings were not considered necessary. The relative tubing characteristics and power consumption during tubing are also depicted in Figure 1. The jagged edges of Table 111. Decrease in Moone Viscosity of GR-S Compound with Successive 3-Minute Remiling Periods at PCHour Intervals (Compound C) Change in No. of Remills Mooney Viscositya Mooney Viscosity
..
80 69 2 68 87 3 .. a 4-minute reading, large rotor, 212' F. 0
i
Series No. Compound Feature Worm Speed, R.P.M. 36 40 46 60 78
the bars representing tubing speeds are designed to indicate the relative smoothness or roughness of the tubed rod. The breadth of these bars is also approximately proporiional to the diameter of the tubed rod. It is evident that the degree of smoothness and the increase in diameter or swell are comparable for both stocks. Compound C (polymer I") did extrude 6% faster and consumed 6% less power than did compound A (polymer X). These figures are bssed on the averages of data obtained a t several worm speeds, as shown in Table IV, and are probably real. There may be a causative relation between the lower benzene solubility of unplasticated polymer X and its slower rate of breakdown, slower tubing speed, and higher power consumption. The data are not sufficiently extensive to draw valid conclusions although the subject is under further investigation. The slower breakdown rate of polymer X is set forth in detail in Table V. The over-all rate may be expressed for convenience as a coefficient of breakdown, which is defined arbitrarily as the decrease in Mooney viscosity upon milling 300 grams of polymer 3 minutes on a 6 X 12 inch laboratory mill with the cooling water on, divided by the original unmilled Mooney viscosity figure:
- M3
Coefficient of breakdown = Mo
Mo where Mo = Mooney viscosity of unplasticated polymer Ma = Mooney viscosity of polymer milled 3 minutes
-11 - 1 - 1
Table IV. Tubing Speed and Power Consumption (IS a Function of Worm Speed 7 1 7 1 1 I11 IV A C A B C F G H C D E -Polymer-Breakdown-BRT No. 7-Breakdown X Y Cold Gordon Col!, Hot 5 min. 10 min. 20 min. 10mm. 10 min. 2 0 m i n . 40 min. Tubing Speed, Grams per Minute
.
I
.
P
I J -Carbon 20
35
32.6
V
C K Black50
65
I
28.8
38.8
6y.6
31.3 34.4 40.3 54.0 65.5
28.8
31.2
31.3
29.6
33.8
38.8
41.5
38.6
46.0
61.6
...
40.5
66.9
65.5
59.9
74.9
480
500
450
530
570
830
Si0
...
...
...
c
36 480 40 ... 46 530 60 ... 78 830 a This figure ia low, probably
450 470 510 640 780
... ...
...
...
440
,510
520
490
780
790
740
...
31.3
34.5
30.9
40.3
41.0
45.6
40.2
65.5
65.9
74.4
t..
...
31.4 I
.
.
...
Average Power Consumption While Tubing, Watts 460
...
42.0 48.2 58.3 72.4 92.4
...
...
...
440 460 490 600 750
... ...
...... ... ...... 61.6 ...
450
460
430
430
510
510
480
480
780
770
730
700
...
...
...
,..
because of incipient vulcanization while tubing due to excessively high heat generation.
...
...
31.3
33.3
40.3
61.8
65.5
62.'Oa
457
450
. . . . . . . . . . 810 .. ... 510 620
:::
780
9bQ
December, 1944
INDUSTRIAL A N D ENGINEERIN G CHEMISTRY
1115
Teble V.
Comparative Breakdown Rates of Polymer X vs. Polymer Y MiIIin Period, Mooney Viscosity din. X Y
Examination of several commercial lots of
GR-Shas disclosed that breakdown rates are not necessarily uniform, and a specsc coefficient of breakdown appears to be a fundamental characteristic. These, in turn, might be used as a basis for selecting polymers for blending operations, Further investigation is required, however, to establish a quantitative relation between coefficient of breakdown and plastication on a factory scale. The benzene solubility of polymer Y increased with cold breakdown on an open mill from 82.4 to 99.795. Figures are not available for polymer X in this respect although in all probability it, too, increased by a comparable degree. Other work in this laboratory and elsewhere has established the fact that milling at comparatively low temperatures usually has the effect of increasing benzene solubility of standard GR-S,presumably disaggregating any ordinary gel structure introduced during polymerization effected in a normal manner. The physical properties of the ultimate vulcanizstes from compounds based on polymers X and Y are seen from Table I1 to be substantially identical. It is evident, therefore, that differences noted in the gel contents and breakdown coefficients of the raw polymers have not apparently been reflected in the end product, a t least under the conditions prevailing in the present experiments. Had the variations between the two raw polymers been of greater magnitude, it is possible that their influence might have been felt a t the latter stage. However, slightly better resistance to flex crack growth was observed for the polymer exhibiting lower gel. This suggests a correlation, but significance cannot be ascribed to the single observatiog reported. COLD BREAKDOWN AND QORbON PLASTICATION
Figure 1.
Prosming History of Various Series
The comparative effects of cold open-mill breakdown and Gordon plastication are listed in series 11, Table 11, and the processing characteristics are shown graphically in Figure 1. Three passes in a Gordon plasticator have not reduced the Mooney viscosity of the plrtsticated polymer to so low a level as was realized after a 10-minute cold breakdown on an open mill. Thereafter, however, the viscosities run parallel during the mixing and remilling stages. In spite of a higher compounded viscosity level, however, compound B, based on the Gordon plasticated polymer, exhibited an 8'3% faster tubing speed; and as indicated in Figure 1, series 11, the appearance of the tubed
INDUSTRIAL AND ENGINEERING CHEMISTRY
1116
rod wm noticeably smoother. This observatioii is typical of those which instigated the present investigation. Examination of the mixed compounds revealed that compound B was noticeably smoother than A, a proof that this quality did not originate in the tuber. The relative increase in the diameter of the tubed rod was slightly less which suggested that the enhanced smoothness of B may have been the result of a reduced degree of shrinkage or nerve. The power consumed by compound B during tubing was somewhat higher than by A, the increase in this respect paralleling the higher compounded Mooney viscosity.
Vol. 36, No. 12
The slight differences in the viscobity valueb obviously are not sufficiently extensive to explain the tubing characteristics observed. The explanation therefore must lie, a t least superficially, in the surface condition of the compound-that is, the degree of smoothness in the mixed stock. Such an explanation is consistent with the resylts observed in the case of Gordon plastication. This line of reasoning points to the conclusion that surface smoothness is a major factor in tubing performance. It has already been noted that the surface appearance in the mixed compound persists in the tubed ro& The data also show that hot breakdown has caused a progressive decrease in benzene solubility. It will be recalled t h a t the same trend was noted for Gordon plastication. The physical properties of the vulcanizates also deteriorate in proportion to the time of hot breakdown. This, too, confirms the trend noted for Gordon plastication although the relative deterioration is much greater for the longer periods of hot breakdown. INCREASING SOFTENER R A T I O S
SMOOTH +
-
ROUGk
The results obtained with increasing ratios of a coal tar type softener are set forth in series IV (Table 11), consisting ol compounds C, D, and E, containing 5, 10, and 20 parts of BRT No. 7, respectively. Figure I , series IV, depicts their processing history. Plastication of the basic polymer was identical for all variations--namely, a IO-minute cold breakdown. The softener was added a t the compounding stage with the remaining ingredients. Inspection of Figure 1 reveals that the increase in viscosity upon compounding becomes progressively less with increasing ratios of softener. This differential persists after remilling, all of the compounds decreasing approximately ten points. Relative surface smoothness and tubing speeds increased with higher softener ratios: whereas power consumption tended to decrease.
'
The properties of the vulcanizates showed an undesirable effect from Gordon plastication, exhibiting higher moduli. lower elongation, lower rebound, higher hysteresis, and somewhat poorer flex crack growth. I n general, the quality was noticeably poorer in all respects in comparison with compound A. Another interesting observation resulting from Gordon plastication was the decrease in benzene solubility. This is in sharp contrast to the increase already noted during cold breakdown. I t is apparent that the case of Gordon plastication introduces many apparent anomalies, in so far as faster tubing speeds are obtained a t higher Mooney viscosity levels, and superior processing characteristics are achieved concomitant with lower benzene solubility. The poorer physical properties developed also require explanation.
0
°
0
1
900 Z
0
i-
800-
a
2 3 invi700 -
gr 5
600-
3
2
500 -
C O L D AND HOT B R E A K D O W N
Cold breakdown os. hot breakdown is examined in series I11 involving compounds C, F, G, and HI all based on polymer Y . Breakdown was effected on a laboratory mill with either cooling water or steam circulating within the rolls. The treatments applied and the results obtained are summarized in Table I1 and Figure 1. It is evident that hot breakdown has served to produce compounds which tube faster and smoother, the improvement in these respects being proportional to the breakdown up to 40 minutes. Compound C (cold breakdown) exhibits a surface which might be described as medium rough. By contrast, compounds G and H (prolonged hot breakdowh) exhibit surfaces which approach a smoothly calendered vulcanized sheet in appearance. Compound F (10-minute hot breakdown) was barely distinguishable from the cold milled blank, an indication that prolonged treatment is required.
4001
1
4 40
60 '/IOONEY
80 100, VISCOSITY
Figure 3. Reidtion of Viscosity of Compounded Stocks to Power Requirements during Tubing
These observations are consistent in so far as they indicate progressively faster tubing rates occurring simultaneously with a higher degree of surface smoothness. It is not clear whether the lower viscosity values also contributed to the faster tubing speeds. The parallelism between declining viscosity and reduced power consumption should be noted. It appears, therefore, that the beneficialeffects of a smooth swface may be realized by increased quantitim of an adequate
December, 1944
INDUSTRIAL A N D ENGINEERING CHEMISTRY
softener as well as by hot breakdown of the polymer as observed in series I1 and 111. I n the vulcanizate the added softener had the effect of reducing moduli and increasing breaking elongations. Tensile values improved somewhat, but rebound and hysteresis were affected adversely. Flex crack growth remained substantially unchanged. These observations, of course, would not necessarily apply to all types of softeners and should be interpreted with this limitation in mind. INCREASING RATIOS
1117
IC00
HARD
OF C A R B O N BLACK
Series V consisted of compounds I, J, C, and K, containing 20, 35, 50, and 65 parts of carbon black, respectively. The basic polymer in all cases received a 10-minute cold breakdown. The results obtained are 4001 shown in Table I1 and Figure 1, series V. I . The compounded viscosity levels increase progressively with increasing loadings of carbon black, and the differences persist Figure 4. during the remilling phase. Tubing speeds varied but slightly and were somewhat faster for the compound containing the highest amount of carbon black. Power consumption also increased with higher black loadings. As the pigment ratio was increased, there was a pronounced transition from a relatively rough to a relatively smooth surface, the improvement in this respect being in proportion to the carbon black loading. This is typical of the so-called smoothing out effect characteristic of high loadings of most compounding ingredients. The properties of the vulcanizates varied in the expected manner with increased loadings; modulus, tensile strength, rate of flex crack growth, and hysteresis ascended while elongation and rebound descended. The highlight of this series is the observation that the tubing speeds of the four compounds did not dBer by more than la%, whereas the compounded Mooney viscosities varied from s minimum of 43 to a maximum of 103. The compound containing the highest ratio of carbon black and exhibiting the highest viscosity actually gave the maximum tubing speed, presumably because of its smoother surface. It seems clear, therefore, that tubing speed is essentially independent of viscosity and that the latter cannot be used to predict the former. SURFACE APPEARANCE AND INCREASED DIAMETER O F TUBED R O D
The data in Table I1 reveal an inverse relation between relative increase in tubed cross-sectional area and surface smoothness. The latter property was rated visually on an arbitrary scale in which 0 and 10 represent the extremes of smoothness and roughness, respectively. On this scale the standard War Production Board test recipe (compound A or C) utilizing a cold mill breakdown is described as medium rough and is assigned a rating of 5. The surface condition of the mixed compound was found to carry over t o the tubed rod, a series of stocks being rated in the same order a t either stage. In Figure 2 the appearance ratings are plotted as a function of percentage increase in cross-sectional areas. The former were made independently of the latter, the degree of correlation being remarkable in view of the subjective nature of the appearance ratings. The increase in area, therefore, may be interpreted as a quantitative measurement of relative surface smoothness. It is well known that roughness in a sheeted compound is proportional to shrinkage which takes place upon removal from a mill. It appears, therefore, that swelling which occuro upon tubing is the
WORM
SPEED
-
RPM.
Generalized Relations between Worm Speed and Other Facton
direct result of a longitudinal contraction of the stock as i t emergers from the die. EFFECT OF W O R M SPEED
Table IV exhibits data relating tubing speed and power consumption to worm speed. Each figure recorded is the average of three determinations. It is evident that both properties increase progreasively with increasing worm speed. It has already been observed that the virscosity of the cornpounded stock bore a relation to power requiremenfs during tubing. This is set forth in greater detail in Figure 3 where power consumption at three diEerent worm speeds is plotted as a function of viscosity for compounds A to K, inclusive. The relation between power and viscosity is substantially linear a t any worm speed, the slope becoming progressively greater as the speed of the worm increases. This relation may be approximated mathmatically by the equation:
-
+
+
P = 131 4.83s 0.05565 X M power consumption, watts S = worm speed, r.p.m. M = Mooney viscosity of compounded stock after remilling
where P
It should be possible to develop similar equations relating any specific tubing unit to viscosity or plasticity measurements given sufficient basic data to compute the required constants. A more generalized relation between worm speed, power consumption, and compounded viscosity is portrayed in the left-hand half of Figure 4,which is derived, in turn, from Figure 3, plus additional data from Table IV. These factors are direct functions of one another, an increase in any one being reflected in a simultaneous increase in the remaining two. During the tubing testa it was observed that a greater degree of heat resulted from the more viscous compounds or at higher worm speeds. This, of course, is an expected relation, leading to the well known principle that knowledge of the viscosity of a compound allows one t o predict the temperature level at which i t will tube a t a given worm speed, other things being equal. TUBING SPEED
It has already been noted that tubing rates were found to be essentially independent of viscosity but dependent upon worm speed and the condition of the surface. The precise relation i s shown in Figure 5 where tubing speed is plotted as a function of
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
1118
surface smoothness at different worm speeds. Increase in crosssectional area is also indicated on the abscissa in addition t o surface smoothness, as these properties were found to bear a constant relation to each other regardless of worm speed. Figure 5 indicates that surface condition exerts a relatively negligible effect in the rough to medium rough range but becomes more important as progressively smoother surfaces come into play. If tubing rates were expressed as volume rather than weight per unit time, the extreme right-hand point on each curve of Figure 5 would have been approximately 6% higher as they are based on compound I, which has a somewhat lower specific gravity than the others. Under these conditions the right-hand portion of each curve might be expected to turn up slightly although the evidence is not conclusive. The generalized relation between worm speed, tubing speed, and surface smoothness is portrayed in the right-hand half of Figure 4, which is derived from Figure 5 and Table IV. The two halves of Figure 4, taken together, present a comprehensive picture of the interrelation between the various elements studied and provide a basis for predicting processability from a knowledge of the viscosity of the compound in conjunction with a n estimate of its surface smoothness. It is assumed that a high degree of smoothness increases tubing speeds because of reduced frictional resistance as the compound is propelled along the tuber barrel and slips through the die.
what faster and to consume slightly less power than X. More examples will be required t d establish a causativerelationalthough the present data show a better processing history for the polymer exhibiting the higher benzene solubility.
PLASTICATION
POLYMER
cp
unplasticated asses qordon plasticator
IO' hot breakdown
30'
1
7
-
1)
~~~
i
7 -
L I
0
The benzene solubilities of the various polymers, before and after plastication, are summarized graphically in Figure 6. The difference between polymers X and Y in this respect has already been discussed. When compounded, Y was found t o tube some-
25
50
75
IO(
% SOLUBLE
Figure 6.
Benzene Solubilities, before and after Plastication
The effect of breakdown on benzene solubility is also portrayed in Figure 6 , reiterating the observations that low-temperature plastication increases and hot plastication decreases solubility. The benzene-insoluble portion of the unplasticated polymer is assumed t o represent a cross-linked network which originates during the latter stages of polymerization (Y, 2 ) or during postpolymerization processing such as drying. Frequently such gel structures are relatively weak and subject to disaggregation by comparatively gentle agitation, such as stirring the suspension with a glass rod. It is not surprising, therefore, that these weak gels disintegrate when the polymer is milled, provided the mill is maintained at & sufficiently low temperature t o prevent a concomitant formation of gel in situ. It should be borne in mind that the foregoing remarks apply to normal G'R-5. Under adverse conditions polymer might be formed in which the gel structure was sufficiently dense to resist disaggregation upon cold milling. Likewise, the gelation which appears upon hot milling or Gordon plastication has been found to be sufficiently dense t o resist subsequent cold millings (7).
78 R.P.M. 60-
BENZENE SOLUBI LlTY soluble insoluble ~~
BENZENE SOLUBILITY
I
VoI. 36, No. 12
A
CONCLUSIONS
On the basis of data accumulated in this investigation the following conclusions appear justified with reference to the plastication and processing of GR-5:
30 2 4 SMOOTH +------SURFACE 775
200
225
% INCREAkE
figure 5.
6
250
a
-
275
ROUGF
3
IN AREA
Effect of Worm Speed and Surface Condition on Tubing Rate
1. Viscosity measurements on the com leted compound bear a direct relation t o the heat generated a n a the power consumed during tubing but do not correlate with tubing speeds. 2. Power consumption and heat generation during tubing increase directly with increasing worm speed. 3. Tubing speed is a function of worm speed and the surface condition of the compound, hi her degrees of surface smoothness resultin in faster tubing speedps. 4. &e relative increase in cross-section+ area of degree of swell of the tubed rod vanes inversely with relative surface smoothness of the compound; that is, smoother compounds exhibit a lower degree of swell.
INDUSTRIAL A N D ENGINEERING C H E M I S T R Y
December, 1944
6. The tubing characteristics of a compound may be predicted with a reasonable degree of accuracy from knowledge of the viscosity or the plasticity of the finished compound in conjunction with an estimate of ita relative surface smoothness. 6. Surface smoothness may be achieved b hot breakdown, ncreasing softener ratios, or increasing ratios o f carbon black. 7. High-temperature plastication tends to exert a deleterious effect on the physical properties of the subsequent yulcanizate, 8. Further investigation is re uired to estabhsh a relation between the relative benzene sdubility of the unplasticated polymer and ita processing characteristias. 9. Plastication at low temperatures tends to increase benzene solubility of the olymer, whereas plastication at hlgh temperatures tenas to re&ce it.
1119
LITERATURECITED (1) Baker, W. O., and Mullen, J. W., 11, unpub. rept. on "Solubility
Relationships in G R S Polymer". Flory, P. J., J. Am. Chem. Soc., 63, 3083 (1941). (a) Naugatuck Chemical Div., U. 8. Rubber Co., Synthetic Rubber Compounding Bull. 2, 4 (Oct., 1942). (4) Nellen, A. H., India Rubber World, 96, No. 0, 4 3 6 , 62 (Sept., (2)
1937). (5) Tingey, E[. C., unpub. rept. (0) Vila, 0. R.,IND. ENG.CBEM.,34, 1209 (1940).
(7) Vile,0;. R., unpub. data.
Passsmsr, before the fall meeting of the Diviaion of Rubber Chemiatry. AMlaarcAN CEmmic& SOCIETY. in New York, N.Y.. 1943.
PURE HYDROCARBONS from
PETROLEUM Development of Laboratory Pilot-Plant Screen-Plate Fractionating Columns JOHN GRISWOLD, J. W. MORRIS, AND C. F. VAN BERG* University of Texas, Austin, Texas BEVELLED
WIRE
O V E R FLOW 8/10"
IN
SCREEN
SYALL LOWER
END
ASSEMBLY
" Y
LL 0
HIS article describes the development and performance of screen-plate columns that have been used for generalpurpose hydrocarbon fractionations and in pilot-plant processes for separating pure hydrocarbons from petroleum* i n the University of Texas laboratories during the past several years. Laboratory fractionating columns may be classified as packed, h - t y p e , and plate-type. With the exceptions of Stedman embossed packing (I) and single-turn helices (4), high-efficiency film-type packings have been successful only in smaller sizes of laboratory columns. The efficiency of such columns is often sensitive t o throughput and even to the operator's technique. These considerations led to the development of screen-tray columns having the desirable characteristic of relatively constant plate efficiency over a wide range of liquid and vapor velocities. Bruun developed a 1-inch (25-mm.) diameter, all-glass bubbletray column @) that has found extensive use. Oldershaw reported comparable performance data on all-glaw perforatedplate columns (6). Because of the complexities of constructional
T
PIPE
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Development and performance of three designs of allmetal screen-plate fractionating columns for general laboratory and pilot-plant use are reported. The characteristics of six different screens were determined, and performance of 1.5-inch and 2-inch diameter columns are given with plate efficiency-rate data on n-heptanemethylcyclohexanea t total reflux. The features of these columns are ruggedness, ease of construction, and relatively high capacities, with maintenance of efficiency at high rates characteristic of plate-type columns. Maximum boil-up rates are 73 ml. per minute (1.2 gallons per hour) for a 1.5inch column and 250 ml. (4 gallons) for a 2-inch column. Maximum HETP occurs a t maximum boil-up, and the corresponding values are 1.8 and 3.2 inches, respectively.
I
I STEEL
PIP6
address, Grasselli Chemicals Department, Oak Ridge, Tenn. Present address,+Iumble Oil and Refining Company, Baytown, Teur. Previous articles of this series appeared in Volume 35, pages 117-19, 247-61,8b4-7 (1948). 1 Present
Figure 1. Details of Construction of Experimental Column for Wire-Screen Plates (No.1)
