Thermal Degradation of Unvulcanized and Vulcanized Rubber in a Vacuum SIDSEY STRAUS AND S. L. MADORSKY National Bureau of Standards, Washington 25, D . C .
T
HE history of distillation of rubber under various conditions of temperature, pressure, and atmosphere goes back more than a century (1). As far back as 1860, Williams ( 1 4 ) distilled
vacuum, using techniques and apparatus that were previously developed by the authors in connection with an extensive study of thermal degradation of a number of polymers (6-8).
rubber in an iron retort at relatively low temperatures and obtained some 557, crude isoprene. I n 1922, Staudinger and Fritschi (11) distilled rubber a t 278" to 320" C. at 0.1- to 0.3-mm. pressure and obtained 3.17, isoprene. I n 1926 Staudinger and Geiger ( I d ) distilled rubber below 300" C. a t ordinary pressure in an atmosphere of carbon dioxide and obtained 4.3% crude isoprene. Distillation of rubber a t higher temperatures and under atmospheric pressure ( 2 , 10) yielded as much as 58% isoprene. I n addition to isoprene, dipentene and higher terpene compounds were also identified in the distillation products of natural rubber. More recently, distillations of pure synthetic polyisoprene ( a mixture of cis- and trans-polyisoprene), purified natural rubber (cis-polyisoprene), and purified gutta hydrocarbon (transpolyisoprene) were carried out by the present authors (9, I S ) in a vacuum under conditions of molecular distillation. The volatile products were fractionated and analyzed both qualitatively and quantitatively, using the mass spectrometer for the lighter fractions. The volatiles consisted of about 3 to 47, isoprene and 13 to 207, dipentene, the rest being large terpene fragments of average molecular weight of about 600. The present paper describes an investigation of the effects of various additions to natural rubber, with or without subsequent vulcanization, on the degradation process during pyrolysis in a vacuum, with the view that such a study might throw some light on the structure of vulcanized rubber. I n addition t o pyrolysis, a study was also made with unvulcanized and vulcanized rubber of the rates and activation energies of thermal degradation in a
Table I.
MATERIALS U S E D
A good grade of pale crepe natural rubber, containing 0.36% ash, was used in the experiments described here. On acetone extraction this rubber lost 3.77, of its weight. Composition of the various samples employed, before vulcanization and acetone extraction, and the treatment xhich they received are shown in Table I. APPARATUS AND EXPERIMENTAL PROCEDURE
Pyrolysis. I n earlier work on pyrolysis of synthetic polyisoprene (9) and purified natural cis- and trans-polyisoprene (IS), a Dewar-like molecular still was used. The polymer sample was placed in a tray in the form of a benzene solution. After the solvent was evaporated, the sample remained as a thin film which made good contact with the tray. The tray was then placed on an electric heater in the vacuum apparatus. I n the present work some of the samples were not completely soluble in any suitable solvent because of vulcanization and the presence of zinc oxide and carbon black, and were used without solvents; this made contact between the sample and the heated tray poor. For this reason an apparatus of a different design was employed in this work. I n Figure 1, A is a borosilicate glass tube 4.5 cm long, 6 mm. in inside diameter, and closed a t one end. This tube fits into a borosilicate glass tube, R, which is closed a t one end, and attached to the rest of the apparatus by means of a ball joint.
Composition of Rubber Samples
Composition before Vulcanization and Acetone Extraction, Partsa
Sample KO.
1 2 3 4
5 t3
7
8 9 10 11
Pale crepe
Sulfur
Zinc oxide
Stearic Carbon JIBTS acid PBNB black
..
..
i:5 2.5 2 7 2.7 3.0 3.0 2.5
.. 1.5 1.5 1.0 1.0 1.5
..
..
..
'1' 3 3 2
300 220 40 40 40
liih
140 140 140 140
Acetone Extraotion NO Yes Yes Yes Yes Yes Yes
60
140
Yes
..
.. ..
.. .. .. 1 1
.. , .
1.6
V dcanization Conditions Temp., Min. C.
..
.. 40 40 40 40
..
N o t vulcanized
..
. I
..
Combined Sulfur, % b
0 0 2.0 0.9 2.2 2.2 2.1
NO
1'.6
N O
No
a Filler, standard NBS channel black; accelerator, benzothiazyl disulfide ( M B T S ) ; antioxidant, phenyl-&naphthylamine (PBKA). I Combined sulfur in vulcanized acetone-extracted samples determined by chemical analysis.
1212
July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
1213
The apparatus can be evacuated to about 10-6 mm. of mercurv bv TO McLEOO GAGE E means of a mechanical pump and a large mercury diffusion pump, not shown in the figure, aided by a liquid nitrogen trap, C. A sample weighing about 20 to 50 mg. was given a preliminary heating in a vacuum a t 100' to 150' C. in order to remove any volatile material. In most cases there was no appreciable loss of weight due to this treatment. The sample was then placed in tube A a t D' and the system was evacuated to 10-6 to 10-6 mm. of mercury. A tube furnace wound with Nichrome wire was first preheated to the temperature required in the experiment and then moved into position so that W the sample inside tube A was approximately in the center of the Figure 1.. Apparatus for thermal degradation of rubber furnace. The temperature was read by means of a platinum-platinumrhodium thermocouple, D,which was attached to tube B below the the sample, it also improved the method of collecting fractions sample. The relation between the thermocouple reading and the V--80 and V25, as compared with the Dewar-like molecular still temperature inside tube A was checked by determining the melting used previously (9, I S ) . The introduction of trap F made the points of silver nitrate (212' C.), potassium perchlorate (368' C.), collection of combined fractions V-80and V Z S and their subsequent and potassium dichromate (398' C.), placed in the tube a t D'. separation more efficient and complete. It ordinarily took about 5 minutes before the required temperaFraction V,,, volatile a t the temperature of pyrolysis but not ture was attained. The heating was continued then for 30 a t room temperature, condensed inside tube B a t f, between the minutes, and the furnace was removed a t the end of this period. end of the furnace and a barrier in the tube near the ground The temperature was constant to within f 1 ° C. joint. I t was collected by dissolving it in benzene. The solution The following fractions were collected: was then evaporated in a weighed platinum crucible and the residue weighed. However, determination of the weight of 1. Residue, not volatile a t the temperature of pyrolysis. fraction V,,, was made only in a few experiments. In most 2. Fraction V,,,, volatile a t the temperature of pyrolysis, cases its weight was determined by subtracting the sum of the but not a t 25" C. 3. Fraction VZ,, volatile a t 25' C but not a t -80' C. weights of fractions V--190,V-80, and V26 from the total loss sus4. Fraction V-80, vofatile a t -8d'. C., but not a t -190" C. tained by the sample. 5. Fraction V--190,volatile a t -190" C. Preliminary experiments showed that complete pyrolysis could [In previous work in this laboratory on pyrolysis of polymers be obtained in this apparatus in 30 minutes a t about 390' C. (6-9, I S ) , these five fractions were designated as fractions I, 11, All the pyrolysis experiments were, therefore, carried out a t IIIB, IIIA, and IV, respectively.] about this temperature. In experiments with samples not conDuring pyrolysis, stopcock E was kept closed. The volatiles taining carbon black, the residues were dark-brown and glasslike. condensable a t -190" C. remained in the system to the right In the case of samples that contained carbon bladk the residues of this stopcock and were condensed in the liquid nitrogen trap, were black and porous. F . Any part of the volatiles not condensable a t the temperature The residues were weighed on a semimicrobalance, and those of liquid nitrogen was removed from the vacuum system on the from samples that contained zinc oxide and carbon black were right of stopcock G by means of a small mercury diffusion pump, flamed in a porcelain crucible in air with a h4eker burner. A HI capable of holding a pressure of about 25 mm. At the end white material remained, which weighed slightly more than the of pyrolysis, stopcock G was closed and the pressure of the nonzinc oxide in the original sample because of the ash content of the condensable gas was measured by means of a McLeod gage. A rubber, the carbon black, and the other ingredients. sample of this gas was sealed off in tube I a t point J and was anThe gaseous fraction, V-lgo, was in all cases less than 0.1% alyzed in the mass spectrometer. From a previous determination by weight of the original sample. Mass spectrometer analysis of the volume between stopcocks G and E, from the pressure deshowed it to consist of carbon monoxide. veloped in the apparatus during pyrolysis, and from the mass Rates. The apparatus and experimental procedure employed spectrometer analysis of the gaseous fraction V- lse, the total in this phase of the work have been described previously (4, 5 ) . weight of this fraction could be calculated. Briefly, this apparatus consists of a vacuum system with an The condensate in trap F was separated into two fractions. enclosed, sensitive, tungsten-spring balance. A 5- to 6-mg. Fraction was collected in a previously weighed tube, IC,, sample in a small platinum crucible is suspended from the spring by placing dry ice around trap F and liquid nitrogen around k,. and the loss in weight of the sample during pyrolysis is noted a t After 30 minutes the tube was sealed a t point Zl. Fraction Vz5was various time intervals by gbserving the change of position of a collected next by bringing trap F to room temperature, placing crossline on an extension of the spring. liquid nitrogen around the weighed tube, kz, for 60 minutes, and The rates of volatilization for any particular rubber sample then sealing off this tube a t Z2 as in the case of tube kl. Tubes were studied a t several temperatures. Cumulative loss in weight kl and ks were weighed to an accuracy within 0.02 mg., and their and also the logarithm of residue weight a t any time, t , were contents were then analyzed in the mass spectrometer. plotted separately us. time for each temperature. If the reaction Aside from the fact that the new design of pyrolysis apparatus rates are of first order, then the plots of logarithm of residue weight employed in this investigation made it unnecessary to dissolve us. time would be straight lines whose slopes represent the rate I
> :&
"
INDUSTRIAL AND ENGINEERING CHEMISTRY
1214
Table 11. Fractions Obtained by Pyrolysis of Rubber
1
Experiment No. a
2
a
Sample NO.
b
b
Temperature, O C. 396 400 Ar. 378 392
a
4
a
5
a
6
a
7
a b
b
c
8
a
b
10
4.9 4.5 4.7
AV.
4 6 4 5 5.8 5.1
Av.
3.8 4.5 4.0 4.3
Av.
3.8 3.6 2.6 2.3 1.7 2.2
Av.
2.1 3.6 2.9
406
3
V-80
387 380 390 390 390 389 390 392 385 390
Recovered, VN 16.5 16.6 16.5 17.4 16.6 20.0 18.3 9.5 10.3 12.3 11.3 10.2 10.6 9.5 6.8 7.3 7.9 7.1 7.5 7.3
BY
Diff .,
%a
Residue' 1.8 1.5 1.7 4.5 2.0 1.1 1.6b 8.8 7.4 8.2 7.8
Vpyr,!%"
7.9 7.8 33.5 33.3 32.4 33.1 34.4 32.3 33.3
78.1 78.0 54.4 57.6 58.6 56.8 56.4 56 6 56.5
76.8 77.4 77.1 77.5 78.9 73.1
75.0 77.9 77.7 75.4 76.6
390 3.9 11.5 34.0 50.6 11 a 390 4.0 14.3 8.1 73.6 a I n per cent of original weight of specimen. b Result,s of 2, a , not included in average values because of low pyrolysis temperature. a
constants. In the case of rubber the reaction was found not to be of first order. Hovever, when the rates of volatilization in per cent of residiies a t any given time, t , are plotted against percentage volatilization, the plots are straight lines for lower amounts of volatilization, and in some cases up to about 40% volatilization. The intercepts of these lines represent the apparent initial rates. To obtain the activation energies, the logarithms t o the base 10 of the initial rates for various temperatures were plotted against the inverse of absolute temperatures. The slopes of the straight lines thus obtained, multiplied by 2.303 X R (where R is the gas constant, 1.99), represent the activation energies. RESULTS O F PYROLYSIS STUDIES
Results of the pyrolysis experiments are shorn in Table 11. The fractions are expressed in per cent of the weights of the samples. Fraction V-lso was omitted from the material balance because of its small reight-less than 0.170 of the weight of the sample. Compositions of the residues are shown in Table 111. The percentages of zinc oxide and carbon black are calculated from the original composition as given in Table I, taking into consideration the acetone-extracted portions. It can he seen that
Table 111. Composition of Residues Sample NO.
A r . Total Residue,
Av. for samples 1 and 2 Av. for samples 3 t o 11 a In per cent of original weight of specimen. b D a t a from Table 11.
the residues fall into three groups. In the case of rubber samples 1 and 2 , whish did not contain zinc oxide, the residues are due t o the ash content in the rubber and to a small amount of carbonization of the rubber during pyrolyeis. I n samples 3, 4, 5, 6, and 11, zinc oxide is the additional constituent of the residue; in samples 7, 8, and 10, zinc oxide and carbon black are the additional constituents. In samplee 1 and 2, consisting of raw and acetone-extracted rubber, respectively, without additives, the amount of carbonized rubber plus ash is conderably less than it is in the other samples. Evidently more of the rubber becomes carbonized in the presence of zinc oxide. Because composition of the samples varies considerably, one can obtain a better picture of the distribution of the volatile V-sDJand T,', if they arc represented in per cent fractions, T,' of the total volatilized part of the samples. The nonrubber volatilizable constituents-natural resins, fatty acids, proteins, sulfur, benzothiazyl disulfide, phenyl-p-naphthylamine, and stearic acid-add up to a few per cent of the total volatile or volatilizable material. These constituents, not being volatile a t room temperature, appesr as part of fraction VpF. Distribution of the three fractions calculated on this basis is shown in Table IT', which also shons that the amount of fraction Vz. falls off sharply (from about lSV', to about 11y0)when sulfur is added t o the sample. Fractions V-80 and S ' Z s vere analyzed in the mass spectrometer. Results of the analysis of fraction T7-so are shovn in Reight per ceiit in Table V. Values for samples 1, 2, 4, 7, and 8 are averages of duplicate analyses and those for 3, 6, 6, 10, and 11 are single analyses. Fraction V- mas Peparated from the other volatiles ' have at -80" C. Because the components given in Table 1 vapor pressures of 1 mm. in the temperature range from -36" t o -160" C , it v a s found that 30 minutes was a sufficient time for their complete separation, using liquid nitrogen for their condensation. Fraction V25 mas removed from trap F at room temperature after fraction V--80 had been removed One hour was sufficient for a complete collection of T-25, using liquid nitrogen for its condensation. Mass spectrometei analysis shomd that this fraction consisted of a mixture of terpenes, such as dipentene and its isomers, of the general formula CloHle-i.e, dimers of isoprene, Fraction VDITconsists of the residual volatiles after fractions \--so and 1-25 have been removed. This fraction, judging from the work on pyrolysis of synthetic polgisoprene and of czsand trans-polyisoprene (9, I S ) , has an average molecular weight of about 600. Fraction Vpyrfrom rubber sample 1 was vaporized directly into the ionization chamber of a Sier-type mass spectrometer so that high molecular masses could be scanned. RIass spectra were recorded a t several temperatures. The larger peaks in these spectra correspond to mass of the formula C6nHs,+li e , of ions of multiples of the isoprene monomer, where n varies from 2 to 16. Although the relative abundance of the various
Table IV.
Components in Residue, % a Carbonized Zinc Carbon rubher oxide black ash
+
1.6 3.2
Vol. 48. No. 7
Sample KO.
Distribution of T-olatile Fractions as Function of Sulfur Conteut of Samples Total Combined Sulfur
Fractions, % rprr
v- so
VZK
a Sulfur added in form of benzothiazyl disulfide. 1, Sulfur added partly as free sulfur and partly in form of benzothiazyl disulfide.
July 1956
INDUSTRIAL AND ENGINEERING CHEMISTRY
1215
ions a t any given temperature Table V. Mass Spectrometer Analysis of Fraction V-SO" was thus obtained, no quantiAverage Values for Experiments, Wt. % tative conclusions as to the Components 1 2 3 4 5 6 7 8 10 11 actual amounts of the various ... ... ... . . . ... 0.07 0.03 0.01 ... 0 01 m o l e c u l a r s p e c i e s could be ... ... 0 . 0 1 0 . 0 2 0 . 0 5 0 . 0 2 0 . 0 6 0 06 0 . 0 3 O . C % 0.02 0.35 0.13 0.37 0.19 ... ... 0 25 0 09 0 39 d r a w n b e c a u s e of lack of 0.20 0.23 0.20 0.41 0.09 0.44 0.53 0.28 0.10 0 36 spectra of the individual frag4.82 3.93 4.56 3.20 2.97 4.62 3.89 2.02 3 04 4.07 0.01 0.05 ... 0.07 0.06 0.05 0 11 0.07 0.05 0.06 ments in the literature. A 0.04 0.04 ... ... ... 0.02 0.01 ... ... ... more detailed description of ... ... ... ... 0 15 , . . ... . . . . . . . . . . . . . . . . . . . . . ... 0 03 the analysis is given by Bradt .. ,. .. ... ... ,.. 0.14 0.16 and Mohler ( 3 ) . T;BCB 0.03 ,.. ... Trace ... N o attempt was made to ... 0 Trace 0.21 0.30 0.34 0 15 ... Total 4 . 8 5 . 1 4 . 1 4 . 6 4 . 1 3 . 9 3 . 2 4 3 5 . 8 4 .4 analyze fraction V,, from coma All percentages expressed in terms of total volatilized part of specimen. p o u n d e d vulcanized or unvulcanized rubbers in the mass spectrometer, because i t would not be possible to interpret the complicated spectra. This fraction, in addition to fragments teristic of most polymers except when they contain a certain amount of low molecular weight chains (4)or degradation accelfound in fractions Vpyr from uncompounded rubber, includes erators such as benzoyl peroxide ( 5 ) . Beyond about 5 to 10% some of the organic additives. volatilization, all the rate curves, except that a t 325" C., rise Infrared analysis of rubber sample 1 was made, using a sodium chloride prism, in the 2- to 15-micron region on thin films in straight lines to about 42y0 volatilization. Beyond this point cast from benzene solution. Similar analysis was made of fracthe rates drop gradually. Extrapolation of the st,raight portions tion Vpyrfrom rubber sample 1. The two spectra are similar of the curves to the ordinate gives the apparent initial rates of in the main features, Some dissimilarities of detail may be due to the increased number of ends in fraction V,, as compared with the original rubber, or, perhaps, to different types of ends produced by pyrolysis. These results are in agreement with the Table VI. Sulfur Material Balance0 conmass spectrometric analysis, indicating that fraction ,,'l Sulfur after Sulfur Recovery, % Vulcanization sists niainly of fragments of the original rubber. Sample and Acetone As H& No. Extraction, % in V-80 Vpyr Residue Total Sulfur in the vulcanized acetone-extracted samples, as well as in fractions ITpyrand the residues, was determined by chemical 2.2 0 ,.. ... ... 1.0 Trace 0.63 0.30 0.93 analysis. Sulfur in fraction V-,o, in the form of hydrogen sulfide, 0.21 2.4 ... 2.4 0.30 1.39 0.51 2 , '20 was determined in the mass spectrometer. A sulfur material 3.2 0.34 ... balance is shown in Table VI. 2.4 ... ... Sulfur appeared as hydrogen sulfide in fraction V - - 8 to ~ the exAll values are expressed in per cent of total volatilized part of specimen. tent of about 1Oyoof the total sulfur content of the sample. Most of the rest appeared in fraction,,,T' and in the residue. A comTable VII. Rates of Volatilization plete material balance is shown only for rubber samples 4 and 6. Apparent ActivaIn these cases the sulfur recovery was 93 and 92%, respectively. Duration Total Initial R a t e tion Ternof ExperiVolatdof VolatdEnergy, I n fraction Vpyrsulfur appears most likely in combined form as Sample perature, ment ieed, isation, Kcal./ part of the rubber chain fragments. In the residue it could be No. 0 c. Min.' % %/Min. Mole in the form of zinc sulfide or as sulfides of metals found in the ash. I n the case of samples 4 and 6, a complete conversion from oxide to sulfide mould require about 2.0% sulfur in terms of the 3 310 210 55 0 455 rubber content. Actually the residues from samples 4 and 6 58 315 180 62 0.700 contained only 0.3 w d 0.5y0sulfur, respectively, so that most of 4 310 240 54 0 275 the zinc apparently remained as oxide. 315 230 65 0.416 56 . I .
I
.
.
. . t
(1
~~
R E S U L T S OF RATE STUDIES
Experimental conditions and summary results of measurements of rates of thermal degradation of six unvulcanized and vulcanized rubbers are shown in Table VII. Details of the rate studies are shown plotted in two sets of curves. I n one set, Figures 2, 4, 6, 8, 10, and 12, the results are plotted in terms of cumulative percentage volatilized us. time, and also as log,, of residue us. time. In the other set of curves, Figures 3, 5, 7, 9, 11, and 13, the rates in per cent of residues are plotted against percentage volatilization. The first set of figures shows in all cases several per cent volatilization at zero time. This is due to the fact that, when the hot furnace is brought into position to heat the sample, some of the material vaporizes during the 15 minutes or so required to reach the temperature of the experiment. The zero time for rate observation was counted from the time this temperature was reached. Results for unvulcanized acetone-extracted rubber sample 2 are shown in Figures 2 and 3. The curved interrupted lines a t the top of Figure 2 indicate that the reaction is not first order. The rates, as shown in Figure 3, are a t first low. This is charac-
5
6
~
320
200
73
0.630
310 315 320
280 220 150
52 58 59
0.240 0.385 0.606
64
310 315 320 325
250 260 200 140
57 68 70 73
0,255 0.430 0.655 1.070
65
9
305 340 54 0,210 310 240 55 0.340 64 315 220 64 0.540 a Apparent initial rate a t 325O C. could not be obtained b y extrapolation (see Figure 3).
Table VIII.
Maxima on Rate Curves
(Comparkons made on basis of 310° and 315O C. rate curves) Volatilization Sample VulcanizaRange of Maxima, tion NO. % N O 42 t o 43 Yes 24 to 33 Yes 25 to 26 Yes 26 to 28 Yes 20 to 30 Yes 18 to 24
INDUSTRIAL AND ENGINEERING CHEMISTRY
1216 100
2 .o
90
1.8
80
1.6
2 70
1.4
a w N I-
90
1.8
--_
*-.-__ - - _
-
a
3 0
' 60 w
u)
-I
0
W W
-I
W
a
I-
50
1.0
70
$
I 6
--.3 1 5 O
80
1.2 a
a
3
Vol. 48, No. 7
t
] I 4 1.2 ;
0
LT W
LL
0
a
40
0.8
LL
0 W
3 z
30
0 -6
20
0.4
IO
0.2
Y
d 4
E:
W
a
0 0
50 100 150 200 250 300 TIME FROM START OF EXPERIMENT, MINUTES
0 350
0
0
I
I
I
I
I
50
100
150
200
250
TIME F R O M S T A R T
Figure 2.
Thermal degradation of unvulcanized acetone-extracted rubber sample 2
volatilization shown in Table S'II. Yo rate studies were made of nonacetone-extracted rubber (sample l), because samples 1 and 2 gave similar results on pyrolysis, as shown in Tables I1 to V. Figures 4 and 5,pertain to rubber sample 3, which contained sulfur and zinc oxide. This rubber was vulcanized a t a higher temperature and for a longer period of t,ime than the other vulcanizates. Judging from the high initial rates of volatilization in Figure 4,the rubber has undergone considerable degradation during the vu1caniz:tion process; this results in low molecular weight polymer ;fragments. After these low molecular
Figure 4.
lo 300
CF EXPERIMENT, MINUTES
Thermal degradation
meight, fragments have vaporized, the rate curves generally follow the same pattern as in the case of pure rubber, except that the breaks occur a t a lower percentage volatilization. I n Figure 4, the plot,s of log,, of residue cs. time are curved lines similar to those for pure rubber. This is also true for all the other rubber samples in t,his investigation. Results of rate studies on vulcanized samples 4, 5, G, and 9, containing various ingredients, are shown in Figures G to 13, inclusive. The volatilization and rate curves are all similar t o those for unvulcanized rubber, except that the maxima on the rate curves appear at lower pcrccntages of volatilization. Table VI11 0.9 I l l I / I I I I I I I I 1 gives positions of the maxima. The extrapolated apparent initial rates for all these samples are shown in Table VII. A coniparison of initial rates of 310" and 313" C. s h o w that the rates are considerably higher for sample 3, d i i c h had undergone a drastic vulcanization at a higher temperature and for a longer period of time than the other vulcanizates. The rates a t these two temperatures for all the other vulcanizatee, though lower than for sample 3 , are still higher b y about 5557 than for unvulcanized rubber, sample 2. In order to determine the effect, of milling on the rate of thermal degradaOb 1 I I I 1 I I I I I I I I I tion of rubber, the same pale crepe 0 5 IO 15 20 25 30 35 40 45 50 55 6 0 65 70 75 rubber v a s milled for 3 to 4 niiriutes at PERCENTAGE VOLATILIZED room temperature and then acetoneextracted. h specimen of this material Figure 3. Rates of volaLilination of unvulcanized acetone-extracted rubber n-as heated in the pyrolysis apparatus sample 2
1NDUSTRIA.L A N D E N G I N E E R I N G C H E M I S T R Y
July 1956
0
5
IO
15
20
25 30 35 40 45 50 PERCENTAGE VOLATILIZED
Figure 5.
Rates of volatilization
55
60
65
1217
70
Vulcanized rubber sample 4 0
z
Figure 6.
0.9
5 0.8
E
3
0.7
3 0.6
Residue
t u 7
a w
6 ," 0.5 > O
0.4
1.8 77.3 17.8 4.9
These results are similar to those obtained for nonmilled acetone-extract>ed, pale crepe, sample 2, a, b, and c, Table 11. Specimens were also pyrolyzed in the rate apparatus a t 310" and 315" C.
2= E 0.3 5a
The following frac-
%
W
&g
300
Thermal degradation
a t 390" C. for 30 minutcp. tions were obtained:
2-(I Z
100 150 200 250 TIME FROM START OF EXPERIMENT, MINUTES
50
0.2
0.I 0 0
5
IO
15
20
25 30 35 40 45 50 PERCENTAGE VOLATlLlZIlC
Figure 7.
55
60
65
70
Rates of Volatilizatiion n
Vulcanized rubber sompIe 5
-
70
2
60
1.4 3 W
5
0 1.2
g
LA
tL A
W
5
1.0
;
2
4
50
ce 0
0 L.
2
40
0.8
30
0.6
20
0.4
10
0.2
f3
0 J
n
O.0
t , , , , , , , , , , , l 0
5
IO
15
Figure 9.
20
25
30
35
40
45
50
55
60
L 8
0
0 0
PERCENTAGE VOLATILIZED
50 100 150 200 250 T I M E FROM START OF EXPERIMENT, MINUTES
Rates of volatilization
Figure 8.
Thermal degradation
300
s
INDUSTRIAL AND ENGINEERING CHEMISTRY
1218
Vof. 48, KO. 7
Vulcanized rubber sample 6
r .O
0
0.4
15
IO
5
30 35 40 45 5 0 PERCENTAGE VOLATILIZED
20 25
Figure 11.
0.2
--i---1
--_r
i
1.8
55
6 0 65
70
Rates of volatilization
0 0
50 100 150 200 250 TIME FROM START OF EXPERIMENT, MINUTES
Figure 10.
300
Vulcanized rubber sample 6
Thermal degradation
100
90
n
80
w
3
N
t
70
1.4
> 0 w 6o J
5
o)
50
0 LL
w
0
2
0 4c
0 U
I
I
I
I
I
I
I
5
IO
I5
20
25
30
35
I
'
40 45 PERCENTAGE VOLATILIZED
'
I
I
50
55
60
69
W
s
w
E
0
3c
Figure 13.
Kates of volatilization
P w
2(
I(
