The Pendulum as a Source of Energy for Plasticity Measurements J
IRA WILLIAMS, E. I. du Pont de Nemours & Company, Wilmington, Del.
A
should be measured only after DVANCEMENT in methA pendulum of known potential energy is compression of the rubber to a ods for studying the conused to produce a definite, rapid deformafixed thickness. The general sistency of rubber during the usefulness of the arallel-plate tion in a plastic material. The damping last 10 years has been confined p l a s t o m e t e r has !,en greatly effect produced on the pendulum is a measincreased by the mathematical largely to various modifications treatment of Peek (IS) and Scott ure of the energy expended to produce the of previous tests and to better (15). interpretation of the data obdeformation. The elastic recovery followA third type of plastometer, tained. consisting of a disk which rotates ing the rapid deformation is much greater in compressed rubber while the The extrusion plastometer inthan that obtained with the ordinary paralresistance t o shear is measured, troduced by Maraetti ( 1 1 ) has has been described by Mooney lel-plate instrument. The actual measurebeen modified by Rehre ( 1 ) t o (1%. grovide a battery of instruments, ment of the energy consumed and elastic y Dillon and Johnston (5) t o recovery requires less than 1 minute. General Considerations provide more simple apparatus capable of operating a t increased Samples should be brought to a uniform Manufacturing d if f io ul t i e s rates of shear, and by Dillon (4) temperature by preheating €or at least 10 to provide an i n s t r u m e n t for are more often due to the elasrapid control work. The parallelminutes at the temperature of the test. ticity of r u b b e r t h a n to its plate p l a s t o m e t e r (16) has reresistance to flow. M a t e r i a l s ceived numerous modifications of form. DeVries ( 2 ) modified the plates t o provide a constant such as lead are easily extruded or rolled into a form which area of contact with the rubber. This modification was used by is retained. On the other hand, rubber, after being devan Rossem and van der Meyden (14) who stressed the necessity formed, never retains its shape perfectly and careful control f d F following the elastic recovery as well as the rate of compresis required to prevent excessive and sometimes irregular defsion. Karrer (8) pointed out the need for controlling the time factor during compression and recovery and has described an inormation. strument (9) with which each measurement requires about 30 The volume flow per unit volume of a material is unlimited. seconds. The balance plastometer, which employs parallel If the flow takes place in an orderly manner, such as that plates, was described by Hoekstra (7) and is well adapted to folresulting from compression between parallel plates, the total lowing the elastic recovery after the rubber has been compressed under any conditions of thickness and time. A parallel-plate displacement and shear can be determined. If the flow takes instrument with interchangeableparts t o provide various methods the form of internal rearrangement without change of external of applying pressure and following recovery was described by shape, the shear and displacement usually cannot be deterLefeaditis (10). The relation between compression and the exmined. An example of the latter type of flow is the mixing tent of recovery has been considered by Diilon @),who concluded that the measurement of either the compression or the elastic of a rubber cement by a paddle immersed in the cement. recovery as obtained with the usual parallel-plate plastometer Both types of flow are unlimited in extent and produce either was sufficient if the comparison was confined to a number of thorough mixing or very great changes in shape. batchesof a given stock or type of rubber. He also pointed On the other hand, the amount of elastic strain in rubber is out that elastic recovery depends on the speed of the previous deformation. Hoekstra (e), after considering some of the facdefinitely limited and is a direct result of shearing resistance. tors involved in plastic flow, concluded that elastic recovery The frictional resistance between either elastic particles or plastic and elastic particles in relative motion causes the elastic particles to be strained. The strain increases for any I rate of shear until the resulting stress is equal to the frictional resistance, after which no further strain can be produced. The elastic strain will then reach a maximum after sufficient shear has taken place, the exact amount being a function of the elastic properties and resistance to flow of the rubber. Since recovery depends on the residual elastic strain a t the time flow ceases, it follows that elastic recovery will also be some function of the resistance to flow of the rubber. The consistency of rubber would then seem to be determined equally well by measuring either the resistance to flow or the recovery. This may be approximately true if only one grade of rubber is considered. When different types of compounded or uncompounded rubber or other types of material are considered, the relationship between resistance to flow and elastic strain does not remain constant. For this reason, it is necessary to determine both resistance to flow and elastic recovery in each case. The measurement of elastic recovery should be made only after shear sufficient to produce an equilibrium stress. I n order to produce a reliable index to the working quality of the material, the deformation should produce a rate of shear comparable to that existing in service. FIGCRE1. DIAGRAM OF APPARATUS 304
JULY 15, 1936
ANALYTICAL EDITION
305
Heavy paper requires a large amount of energy for the defThe energy required to proormation and produces irreguduce a definite deformation can larly projecting wrinkles. Thin, be supplied by a p e n d u l u m porous paper stretches and slips which will also control the time against the plates during comwithin limits. The quantity of pression by an amount which energy required can then be varies with the resistance of the determined from the damping rubber and disturbs the type of efiect produced on the penduflow produced. If paper is used, lum. The general form of such the type must be standardized, an i n s t r u m e n t is shown in and unmarked cigaret paper Figure 1. A p e n d u l u m , W , should probably be preferred. of known potential energy is Clean test pieces, without paper, brought to rest in a horizontal talc, or other lubricant, unless p o s i t i o n . When released, it excessively tacky, cause no diffiactuates a cam, C, which serves culty. Materials such as asphalt t o compress the rubber between and wax which adhere to metal parallel plates, P. After the should be run against removpendulum reaches the lowest able thin metal plates, since point the cam rapidly releases the resistance to flow of these the upper plate in order that materials a t high rates of shear is the elastic r e c o v e r y may be sufficient to tear paper. followed. The pendulum conThe amount of compression tinues its swing and is mainadopted was shown by experitained in position a t its maximent to produce sufficient flow mum height. The amount of to provide a maximum elastic energy consumed in the cycle recovery for most samples of is proportional to the cosine of rubber. V e r y s o f t r u b b e r FIGURE 2. PHOTOGRAPH OF INSTRUMENT the angle which the pendulum tested a t 70" C. gave a maxidescribed in its upward swing. mum r e c o v e r y if compressed from any thickness greater than 2.5 mm., while tough'rubber The instrument which has been designed is shown in Figure 2. required compression from a height of a t least 6 mm. down to The pendulum consists of two weights of 2630 grams each, the center of gravity being on a radius of 7.3 cm. Each weight is the final thickness of 1.25 mm. attached to a balance wheel of 3710 grams, the combined moment of inertia of which gives the system a period of 0.6 second for a TABLEI. CHANGE IN CONSISTENCY OF RUBBER WITH MILLINQ complete vibration. The shaft connecting the two balance Pendulum Plastometer, Parallel-Plate Plastometer, wheels carries the cam which actuates the upper plate, a ratchet 70; C. 70' C. for maintaining the position at any point on the upswing, and a Available Thickness Thickness Recovered Minenergy reafter thicknessa cam which works against a dash-pot and lowers the system to the utes concovRe5 after 1 Recorrect starting position. The driving cam can be replaced by Milled sumed ereda covery minutes minute covery others of different shape for special work, The weight of the % Mm. % Mm. Mm. % upper plate assembly, under which the recovery must take place, 5 55.6 6.85 548 5.35 7.12 33.1 is 300 grams. To compensate for the mechanical inefficiency of 53.8 6.40 512 the system, the pendulum is dropped from 2' above the hori54.5 6.82 546 zontal position and a complete cosine scale is inscribed on the face 10 51.0 5.15 410 4.27 5.47 28.2 50.2. 4.95 396 of one balance wheel to cover the upswing from the low point to 52.0 4.98 399 2" below the horizontal. The wheels rotate with the top moving 15 48.6 4.57 366 3.95 4.96 25.6 toward the rear. 50.0 4.34 347 Operation is as follows: The instrument is enclosed in an oven 49.0 4.65 372 49.0 4.52 361 which maintains the desired temperature. A forward position of 20 46.7 2.73 218 3.71 4.50 21.3 the weights permits the upper plate t o be raised sufficiently for 46.8 3.10 248 inserting the test sample, which is 1 cc. in volume, approxi48.0 2.96 237 mately 10 mm. long, and should be approximately cylindrical. 30 46.7 1.55 124 3.30 3.81 15.5 The sample should be preheated for at least 10 minutes before 45.8 1.64 131 45.7 1.55 124 being tested. The weights are then raised t o the highest position 46.7 1.49 119 from which they lower slowly under control of a cam and dash45 44 8 0.92 73 2.82 3.26 17.0 pot to the starting position. During the descent of the weights 44.8 0.96 77 to the horizontal, the sample is compressed to a thickness of 7 a Thickness recpvered is the increase in thickness from the thickness of mm. The weights are then released. During the next 45" rotagreatest compression. Recovered thickness is the total thickness of the sample. tion the sample is compressed to a thickness of 1.25 mm., at which thickness it is held for an additional 45" before being reThe amount of energy available for compressing the rubber leased. The cosine of the angle of upswing is read and the recovered thickness is recorded after equilibrium is reached, which depends on the shape of the cam. The cam described comoften requires less than 15 seconds. Highly elastic materials presses the rubber during only the first 45" rotation of the show a slow elastic creep toward the end of their recovery which pendulum, which limits the amount of energy available to the amounts to a few per cent of the total, In this case the recovery cosine of 45" times the potential energy of the pendulum a t is usually read after an arbitrary time. the starting position or to a reading of 70.7 on the instrument scale. The substitution of a cam which compresses the rubThe energy consumed should vary with duplicate samples ber through an angle of 90" would make available the total by not more than *l per cent and the recovery should fall potential energy of the system. within = t 5 per cent of the actual recovered height. The enclosure of the test sample between sheets of paper Experimental Part can be the cause of nonuniform results. The sample after compression adheres tightly to the paper and must deform The type of results obtained with the pendulum plastometer the paper in order to recover any portion of its former shape. is illustrated by the following experiment. Two thousand
Description of Apparatus
IYDUSTRIAL AND ENGINEERING CHEMISTRY
306
grams of pale crepe rubber were milled on a 45 X 20 cm. mill, khrough which water a t 50" C. was circulated. The temperature of the rubber was approximately 70" C. during the milling. Samples were removed a t intervals for test. The consistency of the rubber was followed by means of both the pendulum plastometer and the parallel-plate plastometer (16). The results are shown in Table I. Several sets of data are shown with the pendulum instrument, in order to illustrate the degree of duplication. The samples run in the pendulum plastometer were in direct contact with the metal plates. TABLE11. ENERGY CONSUMPTION AND ELASTIC RECOVERY Available Thickness Energy ReConsumed covered Recovery
Material Rubber 100, mineral oil 30 Rubber 100, mineral rubber 60 Mineral rubber (0.5-00. sample) Tire tread stock Balata
%
Mna.
%
24.8
0.53 0.41 0.07 4.03 0.54
41.4 32.8
37.5
68.0 67.0 57.3
5.6
322.0 42.1
The data obtained with the two instruments are directIy comparable only in regard to the elastic recovery. The pendulum instrument shows not only a much higher recovery, but a much greater difference between the extremes. The thickness index of the parallel-plate plastometer, while not indicating a quantitative energy relationship, has a greater percentage spread than the energy consumed by the pendulum instrument. The thickness index is probably satisfactory for following the uniformity of a given material. The energy consumed should, however, be a more reliable index for a Comparison of various rubber compounds or other materials. While a more or less definite dependencJ7exists between the elastic recovery and energy consumed by different samples of the same rubber, this relationship varies considerably when
VOL. 8, NO. 4
different rubber compounds or other substances are considered. This is illustrated by the data in Table 11, which shows the results of tests on various compounds and substances. The early stages of vulcanization are detected with the pendulum plastometer by the rapid change in the elastic recovery. I n many cases the elastic recovery will double before a noticeable difference is found in the energy consumed.
Literature Cited Behre, J., Kautschuk, 8, 2 (1932). DeVries. Arch. Rubbercultuur.. 8. . 223 (1925) Dillon, J. H., IKD. ENG.CHEM.,26, 345 (1934); Rubber Chem. Tach.. 7. 718 (19.74). _ _ . . , _ , . - ...~, Dillon, J. H., Physics, 7, 73 (1936). Dillon, J. H., and Johnston, N., Ibid., 4, 225 (1933); Rubber Chem. Tech., 7, 249 (1934). Hoekstra, J., Chem. Weekblad, 31, 745 (1934); Rubber Chem. Tech., 9, 55 (1936). f Hoekstra, J., Physics, 4, 285 (1935); Rubber Chem. Tech., 7, 136 (1934). Karrer, E., IND.EKG.CHEM.,Anal. Ed., 1, 158 (1929); Rubber Chem. Tech., 2, 601 (1929). Karrer, E., IND.ESG.CHEM.,Anal. Ed., 2 , 9 6 (1930). Lefeaditis, G. D., Trans. Inst. Rubberlnd., 9, 123 (1933). Marzetti, Ciorn. chim. ind. applicata, 6, 277, 567 (1924) ; India RubberJ., 66,417 (1923). Mooney, IND.ENG.CHEM.,-4nal. Ed., 6, 147 (1934); Rubber Chem. Tech., 7, 564 (1934). Peek, J.Rheol., 3, 345 (1932). Rossem, A. van, and Meyden, H. van der, Rubber Age (N. Y . ) , 23,438 (1928). Scott, J. R., Trans. Inst. Rubber Ind., 10, 481 (1935); Rubber Chem. Tech., 8, 587 (1935). Williams, I., IND.EKG.CHEM, 16, 362 (1924). ~
RECEWBD April 22, 1936. Presented before the Division of Rubber Chemistry at the 9lst Meeting of the American Chemical Society. Kansas City, Mo., April 13 to 17, 1936. Contribution No. 32 from the Jackson Laboratory, E. I. du Pont de Nemours & Company.
The Preparation of Naphthidine STUART COHEN AND RALPH E. OESPER, University of Cincinnati, Cincinnati, Ohio
S
TRAKA and Oesper ( 8 ) showed that naphthidine
(4,4'-bi-l-naphthylamine) is a satisfactory oxidationreduction indicator, particularly as an internal indicator in the volumetric determlnation of iron and chromium by means of dichromate. None of the methods hitherto available (1, 2,SJ6,7)for the preparation of naphthidine has been found satisfactory, for they are either laborious or yield only small specimens of this compound. A simple and practicable procedure has now been worked out, and the preparation of naphthidine in adequate quantities is here described. The starting materials are cheap, the time required is reasonable, and the yield of the finished product is good. The procedure may be divided into two stages: (1) the preparation of azonaphthalene, and (2) the reduction of the azonaphthalene to hydrasonaphthalene, which is not isolated but immediately rearranged t o naphthidine (Figure 1).
Preparation of Azonaphthalene The following modification of Lange's (5)method was found most suitable for the preparation of azonaphthalene: Thirty-five grams of a-naphthylamine hydrochloride are stirred into 500 cc. of water in an 800- to 1000-cc. beaker, 17.5 cc. of concentrated hydrochloric acid are added, the mechanical stir-
rer is started, and the solution is cooled in an ice bath to about 0'. Cold diluted sulfuric acid (21 cc., sp. gr. 1.84, plus 200 cc. of water) is then stirred in. The suspended amine salt is diazotized (by vigorous stirring, with customary precautions as to temperature) by slowly adding a cold solution of 14 grams of sodium nitrite dissolved in 80 t o 100 cc. of water. The reddish brown solution of the diazonium salt is allowed to stand 5 minutes (good cooling),and filtered at the pump, the filtrate being received in B precooled filter flask surrounded by an ice bath. The cold filtrate is transferred t o a 2-liter beaker (ice bath), the stirrer started, and a cold solution of 66 grams of anhydrous sodium acetate in 300 cc. of Tater slowly added, the temperature being kept between 0" and 5 . -4cooled solution of 31 grams of sodium sulfite in 200 cc. of water is then run in slowly, a vigorous evolution of nitrogen ensues, and 1,l'-azonaphthalene begins t o separate. After the addition of the sulfite solution has been completed, the stirring is continued for 5 minutes. The suspension is then taken out of the ice bath, and warmed on a water bath, and the tan or orange precipitate is filtered off, washed, and dried on a porous plate. The average yield of crude azonaphthalene, melting a t 180" to 184" C., is 31 grams (calculated 27.5). Pure azonaphthalenemelts a t 186" (S), 188" to 189" (4). The product obtained by the present procedure can be used for the preparation of naphthidine without further purification; in fact, the moist filter cake can be carried directly into the next step.
