IXDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1931
When the extraction plant was first put into operation the length of t h e for steaming varied from 3 to 6 hours. This was an excessive length of time for the evaporation of 300 gallons (1134 liters) of benzene. By the use of hot washes and wire screen lining instead of cloth, the average time of steaming was cut to about 60 minutes. Applications of Products
The two products obtained during the extraction process from uncured tire ply scrap are cotton, containing about 0.5 per cent rubber, and a 6 per cent rubber cement in benzene. From 1000 pounds (454 kg.) of scrap were obtained 1200 gallons (4536 liters) of cement and about 400 pounds (181 kg.) of cotton. The first problem was to dispose of the rubber cement. A rubber cement of about the same composition as the cement obtained from the tire ply scrap, but with a higher rubber content, is used in the impregnation of fabric. The problem resolved itself into producing a heavier cement from the 6 per cent extracted cement. The original process called for a still, or evaporator, which would concentrate the cement to the required rubber content, However, this idea was abandoned when it was realized that in evaporating the rubber cement the thin film of rubber next to the heating surface would be cured, and also the low conductivity of the rubber cement itself would make evaporation very difficult. The concentration of the cement was therefore increased by adding fresh stock in the cement mixer. Aside from a small application in rubber compounding, the cotton may be utilized in paper manufacture and as a filler in cheap felt compositions. It may also be finely ground and used as cotton floc, since the 1 per cent rubber it contains is not detrimental. Economics of Process
The actual cost of recovering the rubber and cotton by the extraction process is only 30 per cent of the cost of acid re-
703
claiming. I n addition the cotton is saved and can be sold, thus increasing the savings effected. The cotton and rubber are both completely reclaimed without suffering any deterioration. I n the other methods for reclaiming uncured ply scrap, either a depreciated product results (acid process) or an incomplete separation of the rubber and cotton may occur (washing process). The power consumption and the labor cost of extracting with solvent are both low. Limitations of Process
There are several limitations to the extraction process, however. Scraps containing appreciable amounts of reclaim are unsuitable, because cement made from them cannot be used for fabric impregnation. Another difficulty is that it is not practical to mix scraps containing different accelerators, owing to the rapid set-up of the cement under the combined effect of certain accelerators. The process must therefore be operated on one kind of scrap a t a time. I n order economically to dispose of the cement produced, the extraction of the uncured scrap must operate in conjunction with fabric impregnation. In plants which do not do this the process would have limited applicability. Acknowledgment
Acknowledgment is made to N. A. Shepard, who initiated the process, and to F. W. Stavely and R. R. Jones, who, with the writer, developed it. Literature Cited (1) Chandeysson, British Patent 157,792 (Jan. 10, 1921); C Q O U ~ C 6’ ~O~C guffa-percha,19, 11, 195 (1922). (2) Dunlop Rubber Co., French Patent 637,211 (July 7, 1927); Rev. gtn. caoutchouc, 6, No. 43, 25 (1928). (3) Furness, U. S. Patent 1,321,200 (Nov. 11, 1919). (4) Penfold, I n d i a Rubber J., 77, 337 (1929). (5) Weber, “Chemistry of Rubber Manufacture,“ Gri5n. p. 265 (1926).
An X-Ray Diffraction Study of Chicle’*z Charles W. Stillwell DEPARTMENT OF CIIEMISTRY, UNIVERSITY OF ILLINOIS, U R B A N AILL. ,
A comparative study of the x-ray diffraction patterns for whole chicle, both crude and refined, and for the several fractions into which it may be conveniently separated, brings out the following facts: (1) Whole crude chicle is a mixture of at least three crystalline constituents-the gutta, the resin, the “benzene insolub1e”and one or more amorphous fractions. (2) Refined chicle is essentially the same in structure as crude chicle, except that the gutta is probably highly dispersed and amorphous.
(3) Calcium oxalate monohydrate exists in chicle as such and is the crystalline constituent of the benzeneinsoluble fraction. (4) Chicle gutta is identical with gutta-percha and balata, its exact nature depending on how one interprets the facts relating to the last two. (5) The structural units of chicle do not assume a preferred orientation under tension, and chicle differs in this respect from rubber.
...... ..
v
ERY few data as to the nature of chicle are available in the literature. An average analysis is as follows (1): %
%
Water-soluble: Arabin., . . . . . . . . . 1 0 . 0 Calcium.. . . . . . . . 9 . 0 Sugar.. . . . . . . . . 5 . 0 Calcium salts. . . . 1.O
Alban . . . . . . . . . . . . . . . 33 75 Fluavil.. . . . . . . . . . . . 2 2 . 5 0 Gutta., . . . . . . . . . . . . . . 18.75
25.0
75 00
__
__
1 Received January 17, 1931. Presented by C. W. Stillw-ell and G. L Clark before the Division of Rubber Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931. 2 This investigation was supported by the Beechnut Packing Co.
Dannerth ( 2 ) lists a typical analysis of chicle, and hazards the opinion that the chewing qualities of any gum are a function of the resin content and the melting point of the resin. The gutta is apparently polymerized isoprene, alban is a mixture of two or three compounds, and fluavil may be a mixture of two compounds. Separation into Fractions
Both crude and refined chicle were studied in the present investigation. Each was separated into the customary gutta and resin fractions as follows: The whole gum was dissolved
INDUSTRIAL A N D ENGINEERING CHEMISTRY
704
WHOLE CRUDE CHICLE
d
d.)
I
Table I - D i f f r a c t i o n Data for Whole Chicle and the Several Fractions of Chicle 1 = intensity; vs = verystrong; s = strong; m = medium; w = weak: vw = very weak WHOLE BENZENE-INSOLUBLE CHICLEGCTTA CRUDE REFINED CRUDEAND CRUDEAND CHICLE CHICLE REFINED CHICLE REFINED GUTTA d (.+I.) T I d (A,) I d (A,) I d (‘4.) SPACINGS OBTAINED WITH C U K,
16.3
10.4
6.56
m (blur) S
16.3 6.50
10.4
m
4.68
VS
s
5.70
vs
3.93
S
vs m
3.80 3.65 3.33
VR
3.01
S
3.00
vs
W W
2.69 2.53 2.38 2.28
m
2.09
m
2 01 1.96
1.870
S
m
W
W W W
1.815 1.755
W
1.655
VW
1.605
4.97
VW
2.68 2.53 2.37 2.27
2.09 2.01
1.96 1,860 1,810 1,745 1,695 1.645 1.600
vw VS
3.65 2.99
2.50 2.37 2.27
m s
m
2.08 2.00 1.948 1.860 1.805 1.745 1.700
m w w w vw w
m
W W W W W VW
vw vw
s
4.66
s
4.07
m
4.75
m
I m W S
3.93
s
3.91
vs
3.33
s
3.33
vw
2.93 2.72
m w
2.93 2.75
m
2.37
VW
2.36
2.12
w (blur)
1.895
vw
1.640
vw
5.70
S
4.67 4.38
W
3.80
m
3.33 3.08
m
2.68 2.48
m
2.18
W
1.99
m
VS
vs
W
d.1
RADIATION
vs
m s
REFINED
d
16.3 10.4 6.48
(blur)
vs
S
3.65 3.34
2.92
6.00
CHICLE CRUDE RESIN AND
RADIATIOX
m SPACINGS OBTAINED WITH M O E ,
5.70 4.97
Vol. 23, No. 6
m
W
W
W
W
vw
in benzene and the solution decanted off an insoluble residue. To the hot concentrated benzene solution hot acetone was added, precipitating the gutta. This was filtered off and washed with hot acetone. The resin was obtained by allowing the acetone-benzene filtrate to evaporate spontaneously. The original residue, that portion of the gum which is insoluble in benzene, was also studied and is designated below as the “benzene-insoluble” fraction. To obtain the water-soluble fraction the chicle was immersed in boiling water for an hour and then filtered. The addition of alcohol to this filtrate precipitated a gum, which was filtered, washed with alcohol, and dried. This gum, according to Allen, should constitute less than half of the water-soluble portion, but the present writer failed to get any appreciable residue when the alcohol filtrate was evaporated to dryness. Diffraction Data
X-ray (Debye-Schemer) diffraction patterns were obtained for specimens of both the crude and refined whole chicle and for the gutta, resin, benzene-insoluble, and water-soluble fractions. Molybdenum K , radiation and the General Electric multiple-diffraction apparatus were used. The beam was defined by a narrow slit and was transmitted through a sheet of the sample about 1mm. thick. For many of the samples patterns have also been recorded using copper radiation and defining the beam by a pinhole. It should be noted that in some cases the patterns do not give the sharp lines characteristic of highly crystalline materials. They are sharp enough, however, to permit sufficient accuracy of measurement to support all the conclusions which are drawn from the data. Figure 1 illustrates the sort of pattern from which the data were taken. The diffraction data for all the specimens are arranged in Table I. Where two specimens give the same pattern that fact is indicated a t the head of the column. Two diffraction patterns are given for chicle gutta and their relation is explained below. The water-soluble fraction produced no diffraction pattern, indicating that it is amorphous. The interplanar spacings obtained with copper K , radiation agree reasonably well with those obtained with molybdenum radiation, considering the nature of the substances involved,
and only the larger spacings needed to complete each pattern are included in the table. The error in the determination of the long spacing is comparatively large. The ring corresponding to the largest spacing i s very sharp on the resin pattern (Figure 2) and its diameter may be measured to within 0.2 mm. a t least; hence the maximum error in the final value ford is 0.5 A., and t&e actual error is probably only half that. The spacing 10.4 A. for gutta-percha and chicle gutta is calculated from a badly blurred maximum in which the error of measurement may be as much as lomm. This would lead to a maximum error of about 0.65 A,, making the correct which does not check too well with von value 10.4 0.32 i., Susich’s longest spacing for gutta-percha (S), No great reliance can be placed on this value, however, and it is quite likely that the discrepancy has no significance. The resin spacing of 16.3 1.is of interest inasmuch as it is the longest spacing of a substance of this nature which has yet been detected by the pinhole method and gives a very sharp maximum. One would like to identify it as the length of one of the long molecules in chicle, but the exact chemical nature of chicle resin is so much in doubt that such a conjecture would be of little value.
+
Interpretation of Data
A consideration of Table I brings out several interesting relations. It may be seen, first, that the patterns for crude and refined chicle are identical, except that the former contains a few extra lines. These extra lines correspond exactly to the strongest lines of the chicle gutta pattern, indicating that the gutta is present as a crystalline constituent in crude chicle but not in refined chicle. On the other hand, it is known that the gutta is not removed from the chicle during refining, or changed permanently in crystal structure, since a pattern has been obtained for the gutta extracted from refined chicle w-hich is identical with crude chicle gutta. The refining process consists essentially in melting the chicle, filtering it, and allowing it to solidify, so that there is no reason why the gutta should be seriously altered. Two alternatives present themselves. The gutta may go into solid solution. To check this possibility the patterns for both crude and refined chicle were taken on the same film under carefully controlled conditions. These are the
INDUSTRIAL A N D EArGl'NEERK.VG C'HEMISl'liY jiiipnis iised in 1~'igure1. 'l'ltere is no
