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lower temperatures this point could be checked consistently to within *0.5" C., while a t the higher temperatures it could be checked consistently to *0.25" C. The saturation points, of course, are for the least soluble components of the waxes in the solvents used. However, it was observed that once precipitation had set in it increased rapidly with further decrease in temperature. Data and Discussion
The solubility data are given in Table
I1 and Figures 1 to 4. It is evident that solubility curves (l),(a),(3),and (4) all lie relatively close together, with ( 5 ) some-
Method of Making Tests
Solubility tests \yere made by Tveighing illto a 100+,. ~~l~~~~~~~flask the desired amounts of and solvent, sealing the flask with a cork a Centigrade thermometer graduated in degrees, heating the flask and contents under the hot water tap until all wax was in solution, and then determining the point a t which the wax began to precipitate on cooling with constant agitation. With the flask properly oriented against a strong light the point a t which precipitation began could be determined closely. At the
what lower. At lower t e m p e r a t u r e s Solvenol, No. 22 Thinner, and turpentine are all better solvents for the waxes tested thanV. M. &- P. naphtha, while a t the higher temperatures the latter is the best solvent. C u r v e s m a r k e d (6) show that sulfonated castor oil is a relatively poor solvent for the waxes. Yet it is known t o be a good emulsifying agent in the dewaxing of textile fibers. Mixtures of pine oil and sulfonated castor oil are coming i n t o e x t e n s i v e use for such purposes; curves marked (7) partly explain why such mixtures are increasing in favor. c: The addition of pine oil increases the solubility of the wax without appreciably decreasing the emulsifying power of sulfonated castor oil, since pine oil itself is a good emulsifyillg agent* Acknowledgment
The author acknowledges his indebtedness to J. H. Wallace and John S. LIoore for obtaining part of the data in Table 11.
Time and Temperature-Plasticity Relations for Crude Rubber as Measured with the Goodrich Plastometer' E. 0. Dieterich THER. F. GOODRICHCOXPASY, A K R O N ,
ARRER ( 2 ) has presented the fundamental principles guiding the quantitative measurement of plasticity of materials, and has described a plastometer ( 1 ) whose design and operation incorporate these basic principles. The simple relationship between softness, permanent set, and plasticity, when the time interval of compression is kept short, was pointed out. This relationship makes it an easy matter to interpret the results obtained by the use of this instrument and to make intelligent comparisons of different materials, or of the effects of different kinds of treatment of the same material. The reshlts recorded below, all of which refer to crude
K
1 Presented before the Division of Rubber Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass., September 10 t o 14, 1928.
OHIO
rubber, and which are typical of rather extensive data, illustrate the applicability of the plastometer to the requirements of the rubber industry, and their bearing on progress in rubber technology is indicated. The plasticities have not been expressed in absolute units, since relative values, based on the changes of dimensions of the sample during compression and recovery, are entirely adequate for factory control work. Multiplying these values by the factor 0.01876 gives the absolute plasticity in kilogram-centimeter-second units. Change of Plasticity of Crude Rubber with Time of Milling
~IASTICATION OF DIFFERENT KINDSOF RuBBER-The data in Table I, which are plotted in Figure l a , were obtained during the course of some mastication tests and refer
IA-DCSTRIAL 24A-D ESGIAISEERISG C H E X I S T R Y
August, 1929
to 200-pound (91-kg.) batches milled on a 24 by 84 inch (61 by 213 cm.) smooth roll mill. The mill roll setting was kept constant a t 9/30 inch (7 mm.) and the cooling water regulated to give the same rate of temperature rise in each batch so that milling conditions might be as nearly as possible alike for all batches. Comparisons TTere made of pale crepe, smoked sheets, and latex-sprayed rubbers.
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practically equal, in 90 minutes, to that of a 60-pound batch a t the end of 60 minutes, the former having been cut through the mill 50 per cent oftener. Table 11-Relative Plasticities of Pale Crepe at looo C. i n Different B a t c h Sizes for Various Periods of Mastication 60-LE. ( 2 7 . ~ ~ ) 9 0 . ~ ~(41-sc.) . TIM^ O F MASTICATION BATCH BATCH Miniites
A satisfactory linear relationship between plasticity and period of mastication is again observed in this case, although the latter is 11/2 hours. I n fact, we have noted this proportionality for milling times as long as 2 hours. Such a simple relationship between milling time and plasticity does not hold for any other type of plastometer, and the ease of calculating milling time in terms of equivalent plasticities is clearly evident. Temperature Coefficient of Plasticity
Unless stated otherwise, all measurements were made at 100" C. and, whatever the temperature, the samples were preheated for 20 minutes before they were put into the plastometer. Plasticities at 100' C. of Different Kinds of Rubber for Various Periods of Mastication SMOKED SHEETS LATEX-SPRAYED >IASTICATION P A L E CREPE No. 1 so. 1 Minrifes 2 9 1.1 !
Table I-Relative
TIMEOF
10 15 20 2.5 30
Final batch temperature
::: z, ..,3
8.5 9.1 227' F. (1090 C . )
.; ;
8.8 9 . (i
lo,?
13.0 14.9 227' F. (1090 C . )
2.8 3.1 4.3 4.i 4.9 6.3 283O F. (112" C . )
It is evident that the rates of breakdown of these three varieties of rubber differ enormously. There is considerable scattering of the experimental values, but this is to be expected when small samples are taken from large batches-i. e., the deviations are due to variations in different parts of the batch. The personal factor introduced by cutting the bank through the mill also influences the regularity of the results. For small batches, as illustrated in Figure l b , tho scattering is much reduced. A straight line fits the points as well 2s any other smooth curve, which means that the rate of mastication of rubber, for relatively short intervals a t least, is uniform and directly proportional to the time of milling. This linear relation, unquestionably, does not hold for very long masticating periods, and is related to the batch size and the method of manipulation on the rolls. EFFECT OF BATCH SIZE-Some typical results are shown in Table I1 and Figure l b . These data relate to 20 by 60 inch (51 by 152 em.) smooth roll mills operated a t '/*-inch (3mm.) opening. A 60-pound (27-kg.) batch on these rolls gives a fairly small bank, the greater part of which is rolling. A 90-pound (41-kg.) batch, on the other hand, produces a bank which is largely stationary. Theoretically, the extent of mastication is directly proportional to the number of times the rubber passes between the rolls, so a 90-pound batch should require 50 per cent more cutting back and forth and a 50 per cent longer time on the rolls to reach a plasticity equivalent to that attained by a 60-pound batch a t any given time. This is verified to a satisfactory degree by the experimental data, the final plasticity of the 90-pound batch being
References in the literature to the effect of temperature upon the properties of rubber leave the impression that in the neighborhood of 70" C. the plasticity undergoes a sudden change and that above this temperature rubber is, in fact, a different material in this respect than it is a t lower temperatures. T h u s , V a n Rossem and Van der Neyden (3) speak of rubber as being "fully plastic" at 70" C., but only "partially plas- t tic" below this tem- ,, p e r a t u r e . Table I11 4 and Figure 2 illustrate 4 the manner in which ( temperature affects the plasticity of masticated f s m o k e d sheets, and these data are typical of m a n y m e a s u r e ments. In no case has ircmprrrturrs ," 'C a d i s c o n t i n u i t y , or abrupt change, been found in plastic properties a t or near 70" C.; the variation with temperature is of degree rather than of kind.
-
Plasticities of Masticated S m o k e d S h e e t s at Various Temperatures TEMPERATURE L-0 SOFTENER ADDED SOFTENER ADDED
Table 111-Relative
c.
30 50 75 100
6 4
I4 1 24 9 56 2
14 24 49 101
0 3 0 0
As shown by the curves, the temperature coefficient of plasticity gradually increases as the temperature is raised. In the first case the temperature coefficients arc' found to be 0.35, 0.75, and 1.50per degree Centigrade for the temperature intervals of 30-40", 70-80", and 90-100" C., respectively. In the other instance, in which a softener was added, the corresponding values are 0.42, 1.50, and 2.45. This change in the temperature coefficient of plasticity is a confirmation of the desirability of lowtemperature mastication, for a t temperatures below, say, 60" C., the internal stresses set up in the rubber are high and rapid breakdown occurs, while at higher temperatures the internal resistance to deformation rapidly decreases, and little permanent softening of the rubber results.
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I S D CSTRIAL A S D EXGI~VEERIA$~G CHE-MISTRY
The instrument has proved a powerful tool in the study of mastication, mixing, calendering, and tubing problems, some of the results of which, it is hoped, will be published in the near future. I n speed and simplicity of operation it leaves little to be desired. The fact that the true plasticities, as measured with the instrument, are directly proportional to the figures which express them-a plasticity of 20, for example, indicates a material which is exactly twice as plastic as one for which the figure is 10-makes it possible to set up a
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convenient scale which is easily understood by machine operators with no technical training. This is of immense importance in factory control and can be accomplished a t the present time by no other plastometer. Literature Cited
:;
Karrer, IND ~
CHEM.,
f:&trzi
~ ~ ~ Testing Materials, 1927.
Ed ~ ~~
‘ 9
~
158 (1929). ~of ~ International n ~ l s ~ Congress $ ’~ for
Meaning and Measurement of Plasticity’ E. Karrer THEB F GOODRICH COMPANY, AKRON, OHIO
A
LTHOUGH the word “plasticity” is widely used in the arts and sciences, it has no definite quantitative meaning ( 6 , 7 ) ,yet the plastic properties of matter are of enormous importance in many industries. As scientific study of materials has increased, it has become more and more desirable to attain to a clearer idea of what is involved in this concept, to the end that plasticity may ultimately be quantitatively defined and measured. The emergence of the word from common usage into the realm of technical words with well-defined meaning for quantitative considerations has been accompanied by considerable difficulty and confusion. Plasticity does closely relate to other properties of materials and the phenomena wherein plasticity may be an important factor are so varied that the role it plays may be overshadowed by and confused with the interplay of elastic and hardness phenomena on the one hand, and permanent set and viscous flow on the other. Reference to a few comments found in the literature will convince anyone of this. Van Rossem and Van der Meyden ( 1 4 ) have pointed out that plasticity involves more than deformationthat the amount of recovery is an essential element. Some seem to indicate that plasticity is synonymous with softness (If), or permanent set (f4).Frequently the flow involved in the deformation is the all-engaging aspect and considerable confusion with viscosity has resulted (1, 2, 16). Inverse flow, or recovery, or “revertibility” is also to be considered. Loose and contradictory usage of the term exists in the rubber industry (22, 1.4, 15). A few attempt to use the term with the usual common-sensical meaning (5, 8). It does not help matters much to call plastic strain or plastic flow one of the three types of strains which are referred to as elastic, plastic, and pseudo-elastic (3). When the element of time is considered, all three of these classes merge into one another, since in the first there is quick and complete recovery, in the second no recovery, in the last slow recovery. The amount of deformation effected by a given force per unit area may have any value. The retention of the deformation may take place to any extent. Recovery may occur from perfectly complete to none; and from instantaneous to grossly and indefinitely slow. Whenever any property of matter, such as plasticity, that involves any of these factors is to be defined and measured, the quantitative definitions, the units, and the methods of measurement must allow for a gradation of the property from practically nil to an indefinitely great amount. Therefore, boundaries such as these for classification are difficult to set up and must remain diffuse. When a substance lies within the 1 Presented before the Division of Rubber Chemistry at the 76th Meeting of the American Chemical Society, Swampscott, Mass , September 10 t o 14, 1928
diffuse boundary region, as rubber does, it becomes of paramount importance to analyze clearly definitions and concepts. Within such regions and with such substances are to be found the severest tests for quantitative definitions and methods of measurement. It is desirable to consider plasticity as an integral property of material and to base the quantitative definition and units and methods of measurement upon the integrated aspect of the phenomena involved in this property just as is done in practice in respect to viscosity and many other complex properties of materials. It is purposed to attempt this for plasticity if for no other reason than that it is extremely desirable to come to a clear and universal understanding regarding the definitions of certain mechanical properties of materials such as plasticity, softness, hardness, and permanent set, so that the concepts may become more serviceable and such properties be better controlled in the arts and industries. Preliminary Definition
As an introductory and general definition more suited to the present purpose may be given this: Plaslicilg is the susceptibility to and the retentivity of deformation. The first aspect of plasticity refers to softness, the second to permanent set. Plasticity by historical connotation refers somehow to the characteristics of matter that have to do with the receiving and the holding of form. I n practice one must distinguish between two substances which, although equally soft and yielding with equal ease to the molding pressure, yet differ in the fidelity with which they hold shape when taken out of the mold. One may retain the mold contour accurately and permanently. The other may, within some interval of time, more or less prolonged, resume to a considerable extent its original or some other shape, determined by surface tension and other forces, quite unlike that which was impressed upon it. The first is said to mold better-that is, to be more plastic than the second. The question is thenWhen any quantitative definition of plasticity is tentatively set up, how much should a substance be penalized in its degree of plasticity by virtue of the fact that, although it is not more stubborn in taking a new shape, it shows more variability and fickleness in holding it? Degree of plasticity may be tested by means of sensations directly. One may judge the plasticity of a pellet of sculptor’s clay or other plastic somewhat as follows: The pellet is held between the tips of the thumb and the forefinger and made to undergo some change of shape by pressure with the fingers. The force necessary to make any slight deformation is judged by the muscular effort in the fingers. The
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