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2-The members of a given series show marked similarity in crystal form. 3-The broad types of crystal form may be given as plate, needle, and mal-crystalline, the last-named group being characterized by lack of any definite recognizable form. &The general crystal form of a given pure wax is an inherent property of the compound, and is independent of factors such as viscosity of the solvent. Marked changes in the chemical character of the solvent may change details of the shape of the plate, but they do not destroy the general plate characteristics. %Both needle and mal-crystalline waxes have marked powers of impressing their form upon plate waxes, the latter apparently being the most powerful. Neither type of wax, fiowever, is capable of affecting the form of plate waxes unless the solubility relationships are such that the needle or malcrystalline waxes may separate from solution simultaneously with the plates.
Val. 23, No. 6
Acknowledgment
The authors are indebted to J. M. McIlvain for very careful work in the determination of molecular weights, and to K. 0. Brown for assistance in carrying out the long series of fractional crystallizations. Literature Cited (1) Buchler and Graves, IND. ENG. CHEX, 19, 718 (1927). (2) Carothers, Hill, Kirby, and Jacobson, J . Am. Chcm. Soc., 61, 5279 (1930). (3) Ferris, Cowles, and Henderson, IND. ENG.CHEM.,21, 1090 (1929). (4) Gurwitsch. "Scientific Principles of Petroleum Technology," pp. 15 and 450, Chapman & Hall, 1926. (5) Hetley and Padgett. Presented before the Division of Petroleum Chemistry at the 73rd Meeting of the American Chemical Society, Richmond, Va.. April 11 to 16, 1927. (6) Katz, J . I n s f . Petroleum Tech., 16, No. 86, 870 (1930). (7) Rhodes, Mason, and Sutton, IND. ENG.CHEW,19, 935 (1927). (8) Ruzica et al., Helv. Chim. Acta, 11, 496 (1928). (9) Tanaka, Kobyashi, and Ohno, J . Faculty Eng., Tokyo I m p . Univ., 17, No. 15 (1928).
Rate of Deposition of Latex on Porous Molds' H. W. Greenup FIRESTONE TIRE & RUBBERCOMPANY, AKRON,OHIO
The effects of pressure, rubber concentration of H E m a n u f a c t u r e of to 3p, with some of u l t r a latex, temperature, and hydrogen-ion concentration rubber articles by dipmicroscopic size. As the upon the rate of deposition of latex on porous molds ping porous forms in average pore size of an ordiare described. Pressure, rubber concentration, and latex was first described by nary grade of filter paper is temperature were found to be negligible factors in Condamine (5). He reported 3 . 3 , ~ (16), l a t e x passes comparison with hydrogen-ion concentration. By to the Paris Academy in 1736 through unchanged until a adjusting the pH of the latex to 6.1 it was found possible t h a t t h e n a t i v e s in South sufficient number of particles to obtain aggregation of the latex particles and a America made such articles as have been adsorbed on the marked increase in rate of deposition. shoes and bottles, using clay Pore walls to cause stowage. molds which, after drying of This is not t h e case w i t h the deposited layer, were shattered and removed. The idea of unglazed porcelain filters of the Chamberlain type, where the making articles by a process of this sort, instead of by coagu- size of the largest pores is from 0.2 to 0 . 4 ~(16). It would lating the latex, milling, and then shaping the milled rubber, seem that filtration would be fairly rapid a t first, but would appeals to the imagination. Increased tensile strength and become slower with increasing resistance to flow of serum improved aging have been claimed (10) for articles made di- through the deposited layer. Undoubtedly, some of the ultrarectly from latex, and their remarkable resistance to tear, ob- microscopic particles would be drawn into the pores and, being tained under certain conditions, is well known. adsorbed on the walls, contribute to the decrease in the rate of I n more recent years there has been a revival of interest filtration. Another factor to be considered, especially when in this method of manufacture, t o judge by the number of working with pressure, is the deformability of the latex parpatents issued. Ditmar (2) and also Hopkinson ( I d ) have ticles. I n view of the fact that the literature offers no detailed patented a process for making articles such as surgeons' gloves, inner tubes, etc., by deposition on porous forms. information as to the effects of pressure temperature, rubber Venosta (20) used concentrated latex to lessen the number of concentration, or hydrogen-ion Concentration, the effect of dips necessary with a non-porous mold. The Dunlop Com- these factors on latex deposition on porous molds was inpany (3) has attempted to hasten deposition by using a vestigated. porous mold filled with a coagulant-containing gel, while the Experimental Procedure Anode Rubber Company ( 1 ) has impregnated the mold with a coagulant which diffuses outward through the still perThe apparatus illustrated in Figure 1 was used. It conmeable, coagulated layer. Hauser (3) has used atration sisted of a 24-inch (68.5-em.) piece of galvanized 4-inch (10.15through porous ceramic filters as a method of concentrating cm.) pipe, A, closed a t each end with caps, B. A 0.25-inch latex, but he states (8) that there are too many drawbacks to (6.35-mm.) pipe, C, led from a vacuum line through the permit its being used commercially on the plantations. bottom cap to the porous mold, D,to which it was joined However, Stevens (18) is of the opinion that systematic by means of a rubber stopper, E. A 0.25-inch (6.35-mm.) experiments with differently prepared collodion filters might side pipe, F , permitted the entrance of air either at atyield a method of quickly and cheaply filtering, and thereby mospheric or higher pressure. When working above room concentrating, latex. temperature the water jacket, G, was added. Latex usually contains particles varying in size from 0.5 The porous molds were alundum extraction thimbles of medium porosity. They were 45 mm. in diameter and 127 1 Received April 6, 1931. Presented before the Division of Rubber mm. in length. Thimbles of coarse porosity allowed some Chemistry at the 81st Meeting of the American Chemical Society, Indianlatex to pass through, but those of medium porosity did not. apolis. Ind., March 30 to April 3, 1931.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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689
They were relatively uniform, would stand an external pressure of a t least 35 pounds per square inch (2.46 kg. per sq. cm.), and could be easily cleaned by ignition in a mufflch furnace. In performing the experiments the mold was first wet with water to prevent the formation of an impermeable, dehydrated layer, the latex added, and the top cap screwed on. After deposition the top cap was unscrewed, the latex poured out, and the bottom cap and connected mold removed. The deposited layer was dried a t 60” C. and its thickness determined. Suction was applied to give pressure differences up to 7.5 pounds per square inch (0.52 kg. per sq. cm.) and above that air pressure was also used. All pressure differences were recorded as “pressure” whether due to a partial vacuum in the mold or a partial vacuum and air pressure on the latex. Ammonia-preserved latex, containing 1 per cent ammonia and 35 per cent rubber (by coagulation>l, was used unless otherwise stated.
(2.46 kg. per sq. cm.) did not increase the rate of deposition sufficiently to bring it into the range of practical applicability.
Time Required for Deposition
B -
Effect of Rubber Concentration of Latex
I n determining the effect of rubber concentration, the latex was prepared by dilution with distilled water; thus there was no change in the ratio of rubber to non-rubber constituents. The results are shown in Table 111. There was no change in speed of deposition upon dilution of the latex. Some experiments were made with latex mixtures of higher rubber content, with the result that thicker deposits were formed. The latex was concentrated by the Hauser evaporation process to a rubber content of 68 per cent. It contained 0.75 per cent potassium hydroxide and 0.75 per cent potassium-coconut oil soap. This was attributed t o the increased viscosity of the mixtures and corresponding tendency for increased thickness of what might be termed “the undeposited but adhering” layer.
A preliminary experiment to determine the time necessary to obtain a deposit of appreciable thickness was first made. The results are shown in Table I.
F
Table I-Effect of Time on Thickness of Deposit Pressure. 7 Ibs per sq. in. (0 52 kg per sq. cm.) TIME THICKNESS O F DEPOSIT hlinules Mm. 30 0 3
--
n
A6
5.i
1.38 1.5
840 1020
These preliminary tests demonstrated that deposition of this sort is too time-consuming to be considered commercially feasible. As expected, the rate of deposition was more rapid a t the start than later, a deposit of 0.55 mm. being formed in the first 45 minutes, while the increase in thickness was only 0.12 mm. between 840 and 1020 minutes.
D
n
Effect of Pressure
The effect of pressure was first determined in attempting to hasten deposition. The pressure was first kept a t 5 pounds per square inch (0.35 kg. per sq. cm.) for 3 minutes and then increased the desired amount. This prevented latex particles from being forced into the pores of the mold a t the start, a condition which would have decreased deposition considerably. The results are shown in Table 11. Table 11-Effect of Pressure on Deposition Time, 30 minutes PRESSURE THICKNESS O F DEPOSIT Lbs./sq. in. Kg./sq cm. Mm. 7.5 0.52 0.3 12.5 0.88 0.2 17.5 1.23 0.5 2.46 35 0.5 Table 111-Effect of Rubber C o n t e n t of Latex on Deposition Pressure, 35 Ibs. per sq. in. (2.46 kg. per sq. cm.) ; time, 30 minutes RUBBERCONTENT THICKHESS OF I3EPOSIT
%
Mm.
10
0.25
25 35
0.25 0.3
_15_
n
2.5
A pressure of 17.5 pounds per square inch (1.23 kg. per sq. cm.) caused an increase in thickness of the deposited layer of about 60 per cent over that obtained with a pressure of 7.5 pounds per square inch (0.52 kg. per sq. cm.), but a further increase to 35 pounds per square inch (2.46 kg. per sq. cm.) did not cause a corresponding increase in thickness. One trial was started a t a pressure of 50 pounds per square inch (3.5 kg. per sq. cm.), but was interrupted by the breaking of the mold. Pressures up to 35 pounds per square inch
Figure 1-Deposition
G
Apparatus
Effect of Temperature
As increased tempexature ordinarily has a considerable effect upon the rate of filtration of liquids owing to decreased viscosity of the liquid, it seemed logical to assume that this would be the case in the filtration of latex. A water jacket was added to the apparatus (Figure 1) and experiments were made a t different temperatures. The water jacket was heated with a gas burner and, after the latex had reached pressure I), was applied. The the desired temperature (% results are shown in Table IV. Table IV-Effect of Temperature on Deposition Pressure, 27.5 lbs. per sq. in. (1.93 kg. per sq. c m . ) ; time, 30 minutes TEMPERATURE THICKKESS OF DEPOSIT O c. hlm. 26 0.3 3s 0.4 49 60 71
0 5
0.5 0.5
It was evident that decreased viscosity of the serum resulting from higher temperatures did not increase the rate of deposition sufficient to merit further consideration. Experiments a t temperatures higher than 71” C. were made, but difficulty was encountered due to the formation of a dried
June, 1931
I N D UXTRIAL 24ND ENGIXEERING CHE*MISTRY
or similar materials a less complete aggregation may be accomplished. The filterability of the treated Revertex was not so great as that of the aggregated latex. It has been found that considerable difficulty may be encountered in obtaining the exact degree of aggregation and consequent filterability when repeating experiments, especially if latices are used which have been obtained from different sources or from trees tapped shortly after a rest period. The addition of pigments will in some cases cause marked increase in the degree of aggregation. In view of these factors, the development of a process which always yields a latex in a definite state of aggregation would seem to be a difficult problem. Acknowledgment
The writer wishes to acknowledge his indebtedness to N. A. Shepard for his helpful suggestions and willing counsel during the course of this work.
69 1
Literature Cited Anode Rubber Co., British Patent 252,673 (1927). Ditmar, British Patent 214,224 (1924). Dunlop Co., Ltd., British Patent 285,938 (1926). Dunlop Co., Ltd., Canadian Patent 284,565 (1928). Hauser, “Latex,” p. 3, Steinkopff. Hauser, Zbid., p, 94. Hauser, I h i d . , p. 95. Hauser, Ibid., p. 121. Hauser, German Patent 412,060 (1923). Hauser, M. I. T.Lectures, 1928. Hazell, British Patent 295,700 (1929). Hopkinson and Gibbons, U. S. Patent 1,542,388 (1925). Hopkinson and Gibbons, U. S. Patent 1,632,759 (1927). McGavack and Rumbold, IND.ENG.CHEM.,Anal. Ed., S, 94 (1931) MacKay, I n d i a Rubber J . , No. 10 (1930). Ostwald, Fischer’s Handbook of Colloid Chemistry, p. 263, Blakiston. Smith, U. S. Patent 1,678,022 (1928). Stevens, “Latex,” p. 21, British Rubber Growers Assocn. Stevens, Ibid., p. 9 . Venosta, British Patent 233,458 (1924).
Effect of Storage on Milled Crude Rubber’ C. M . Carson THE
GOODYEAR TIRE82 RUBBER COMPANY.
AKRON, OHIO
Smoked sheets which have been milled to different months which the p r e s e n t U R k n o w l e d g e of degrees of plasticity and stored in bale form for periods paper attempts to cover. cured rubber, aged for up to 9 months show a decided increase in modulus, various periods of time Experimental Methods plasticity, and recovery values. The increase in reis fairly extensive. The fact covery value is the most noticeable, the change being Smoked sheets were milled that uncured rubber also un180 per cent of the original, if the rubber is baled at under definite procedures to dergoes certain changes, even 40-50” C. and stored at 10-20” C. for 9 months. produce four different plasover short storage p e r i o d s When the aged, milled rubber is mixed in a tube ticity grades ranging f r o m ranging from a few hours to stock and processed on a tubing machine, the stock is slightly to thoroughly plastiseveral days, is also known rougher and the speed of extrusion is slower than a cized rubber, and stored a t in a g e n e r a l way. It was similar stock containing freshly milled crude rubber. considered i n t e r e s t in g to two temperatures (10-20’ C.) The plasticity of stocks which are subjected to tubing and a t 55” C., for periods up s t u d y t h e effect of l o n g e r operations is shown best on an extrusion type plasto 9 months. For convenaging periods along this same tometer in preference to the compression type. line. ience in handling, the rubber Milled crude rubber “freezes” at temperatures below was baled, 225 pounds per TThen p l a s t i c i z e d or so0’ C. and thaws at room temperature of 15-25’ C. bale, using pressures of 60 to called broken-down rubber It may be permanently frozen by being placed under 70 p o u n d s per square inch is not used within a reasonslight pressure for several months, freezing temperato exclude air; and in order a b l e p e r i o d , it r e g a i n s a ture being unnecessary. In either sheet or milled not to overlook any effect of certain amount of “nerve” form this type of frozen rubber requires a temperature original t e m p e r a t u r e , the and b e c o m e s more difficult of about 50’ C. to thaw, whereas temporarily frozen bales were prepared with rubto handle in ordinary facrubber will thaw at room temperature. ber a t three temperaturestory processes. This p a p e r 43”, 72”. and 100” C. deals Drimarilv with the effect Plasticity values are based on the Williams plastometer of stoiage a t “different temperatures on milled crude rubber, in an attempt to translate the general term “nerve” into defi- under the following testing conditions: a 1-cc. pellet, under nite physical properties such as plasticity, modulus, and rate 10 kg. pressure for 3 minutes a t 70” C . , the compressed height of cure. This investigation was conducted on a factory scale being expressed in millimeters times 100. The regain or in order to permit comparisons between typical factory recovery value is based on a 1-minute recovery expressed operations and these physical properties, and a total amount in the same way. The four plasticity groupings used in of 40,000 pounds of rubber was used. this work were 390,350,325, and 275. The first was obtained The literature contains a number of articles dealing with by one breakdown on an 84-inch mill, the second by one breakchanges taking place in rubber a t certain definite tempera- down on a 60-inch mill set a t a somewhat tighter gage, the tures. Among these is an article by Griffiths ( 1 ) appearing third by remilling 390 rubber, and the fourth by remilling 325 in 1926, in which he evaluated “nerve” in terms of extrusion rubber. plasticity. He showed that the plasticity figure did not Results increase for periods up to 30 hours after the rubber had been cooled below 55” C. He did not continue his experiment beyond 30 hours, and it is this longer period extending into The effect of storage is most noticeable in the recovery value with but slight change in the plasticity figure, except for 1 Received March 16, 1931. Presented before the meeting of the the longest storage periods. The recovery value increases Akron Rubber Group of the American Chemical Society, February 19, 1931. consistently under all conditions inyestigated up to 9 months,
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