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very weakly basic and magnesium L on the border line. It is a well-known fact that the salts of the weaker bases are more easily hydrolyzed than those of the strong bases. Thus, even though lithium, sodium, and calcium perchlorates are hydrated, they are sufficiently strong bases to withstand the action of the water. The basic strength of magnesium, iron, and aluminum, however, is not sufficient t o prevent hydrolysis. The results obtained in the quantitative decomposition of the perchlorates bear out even more conclusively the two types of decomposition. If the above explanation is valid, one would expect chlorides in the case of lithium, sodium, potassium, and calcium, and oxides from magnesium, iron, and aluminum. As the results indicate, this is a fact, except in the case of calcium. However, the weight of residue obtained from the ignition of Ca(ClO&XH,O corresponds very nearly to the empirical formula CaO.20CaCl*, which has no particular significance.
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Obviously, calcium is just on the border line between the two types of decomposition but is still predominantly of the first type. LITERATURE CITED
(1) Carnelly and O’Shea, J. Chem. Soc., 45,409 (1884). (2) Honda, K.,Sci. Repta. Tbhoku Imp. Uniu., 4,97,215 (1915). (3) Noshida, J . Chem. SOC.Japan, 48,520 (1927). (4) Orosco, E.,Miniaterio trabalho ind. com., I m t . nad. tee. (Rio de Janeiro) 1940. (5) Richards and Cox, J. A m . Chem. SOC.,36, 819 (1914). (6) Richards and Willard, Ibid., 32,4 (1910). (7) Saito, Heikichi, Sci. Repta. TBhoku Imp. Univ., 16, 37-200 (1927). (8) Scobai, 2.physikal. Chena., 44,319 (1903). (9) Somiva. J . Cham. SOC.J a m n . 31. 217 (1910). (10) Yamanoto, Bull. Dept. A&&d Chena.’W&da Univ. (Japan), 9,12 (1929). PUBLICATION 98, Research Laboratory of Inorganic Chemistry.
Ring and Ball Softening Points OF Resins A Constant-Temperature Air-Bath M e t h o d VICTOR E. GROTLISCH
AND
HAROLD N. BURSTEIN
Naval Stores Section, Cotton and Fiber Branch, Office of Marketing Services, U. S. Department of Agriculture, Washington, D. C.
A method of determining softening points of resins is described, in which the wmple is heated in an air bath immersed in a liquid bath held at a constant temperature. A scheme and tentative formula are presented for correlating the varying observed softening points of a resin obtained when different liquid bath temperatures are used, together with 4 basis for selection of the bath temperature suitable for making the test.
Tis
H E suitability of many resinous products for particular uses often related to the softening point-that is, the temperature a t which the material reaches some specified degree of fluidity. The temperature range within which such fluidity is to be maintained-that is, the softening point limits-is frequently incorporated in specifications. However, this softness or fluidity (softening point), as determined by the usual test methods, is a function not only of temperature but also of the duration of the exposure of the resin to the heat. It is also affected by the medium by or through which the heat energy is conducted to the resin. Therefore, all numerical values depend cntirely on the purely arbitrary and empirical procedure used in their determination, and must be identified with the name or description of the method. Perhaps the best known method for determining softening points is the A.S.T.M. ring and ball method, first adopted as a tentative method in 1916 for use with bituminous materials, and now designated as A.S.T.M. D36-26 (I). In order to adapt the method to resinous materials, Walker (6) proposed certain modifications, principally a change in the design of the ring in which the sample is molded. On recommendation of Committee D-17 on Naval Stores of the American Society for Testing Materials, this method was adopted as a new tentative standard in 1936,and is now known as A.S.T.M. E28-42T ( 2 ) . Although this method has proved satisfactory and is often specified as the test method when the softening point is incorporated in specifications for rosins and related resins, several features have limited its usefulness. One is the time required to run a large number of samples, as must be done in some plant control laboratories. Another is the provision that, for softening points up to SOo C., water shall be used as the bath medium, while
for softening points above that temperature glycerol shall be used. For resins softening at or near SO”, the bath medium must be stated, since these softening points may differ according to the bath liquid used. Finally, in some cases the hot glycerol has a softening or plasticizing effect on certain synthetic resins that soften in the higher temperature ranges. One of the projects of A.S.T.M. Committee D-17,through its Subcommittee I on Softening Point of Rosin, is the survey or d e velopment of new methods and modifications of present methods for determining the softening point, with the view of developing, if possible, a method that will be better adapted to the needs of the industry. Five requirements have been set (4): 1. Apparatus to be of simple design and low cost 2. Procedure to be more rapid than the present one 3. Results to have good reproducibility within * 1.0” C. 4. Method to be applicable to a wide range of softening points 5. Results to have close correlation with present ring and ball softening point values
This paper describes a method of test, in which the sample is heated in an air bath immersed in a liquid bath held a t a constant temperature. The method is believed to meet the above requirements and also to overcome the objections to the present method, E28-42T. A scheme for determining the proper bath temperature a t which any resin is to be tested is also presented, together with the experimental data and theory upon which the temperature selection is based. Several air-bath methods are already in use. A method developed by the Bakelite Company has been included in Navy Department S ecification 52R 10b for p-phenylphenol-formaldehyde fesins (67 In addition to employing a different size ball and ring, it retains the feature of a rising temperature for the heating bath. Both the General Electric Company and Hercules Powder Company have methods for bituminous materials and rosins, using the so-called “thermometer drop” principle. These methods employ a specified wei ht of sample that is molded onto the bulb of a thermometer, an8 placed in a preheated air bath until it forms a tear drop which falls slowly from the thermometer bulb. These two methods, although satisfactory when used by experienced plant control chemists, have not been considered suitable for collaborative study and standardization for a d o p tion as A.S.T.M. methods. Another constant-temperature method is that of Hershberger
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August, 1945
477
sorbing. The resin with the higher heat capacity is not given sufficient time t o absorb' enough heat before the final temperature reading is taken. If a thermocouple were inserted in each mold, it might show not only that neither of the two resins WM at the temperature of the bath, but also that they were not at the same temperature internally. Again, 'the bath medium may greatly affect the softening point because of the difference in heat capacities. These constants for water, glycerol, and air at 100" C. are, respectively, 1.006, 0.669, and 0.240 calories per gram (cp for air in 15" 0 -INOICATES TIME AND TEMPERATURE calories). This difference accounts for the fact that AT W H I C H SOFT€NING OCCURRED the softening point of a resin may vary by as much aa 10" C. in a rising temperature method, depending on whether a water bath or an air bath is used. The true softening point could be determined only by placing a thermometer or thermocouple in the sample itself, and then heating the bath ['I TIME IN MINUTES I I I I I I . slowly enough to keep the temperature of the bath-and the mold practically equal until the Figure 1. Curve Types Time vs. Temperature resin reached the arbitrarily selected degree of fluidity. This would entail a very slow rate of and Overbeck (S),in which the ring and ball tests are run on heating and be too time-consuming for a practical method of petroleum asphalts, at one of three specified temperatures, setest. lected according to the nature of the material. The correspondAn alternative would be to heat the sample very rapidly a t ing softening point is obtained from a table, and depends on the first, until it is a few degrees below its softening point, and observed time required to reach the prescribed softening point then to slow the temperature rise of the sample, so as to allow it fluidity. This is merely a modification of the present ring and ball method, as i t is still a liquid bath method. sufficient time to absorb enough heat from the surrounding bath to reach the dropping point. It is necessary to select the conditions best suited to bring about this result, in order that the THEORETICAL CONSIDERATIONS test procedure may be kept practical. The time lag would have Although the use of a bath at a constant temperature is still t o be limited, so that the observed softening point would reflect an arbitrary method of determining softening points, in such a the condition of the resin when brought to a similar temperature procedure there are certain inherent fundamental advantages. in actual use, as in a varnish kettle. The theoretical ring and ball softening point of a resin may be exThe optimum conditions for making the test, conditions which pressed by : approach the theoretical requirements previously discussed, are h obtained by using an air bath a t some predetermined constant S.P. = IC x t temperature, reasonably close to the final softening point, since in which this permits the sample to heat up rapidly a t first, after which the temperature rise or heat intake levels off as the observed softIC = a numerical correction factor based on the difference in heat conductivity of the resin, ring, and bath ening point is approached. It also eliminates the need for h = total heat in calories supplied to the sample, ignoring any closely controlling the rate of heating or timing of the operation. latent energy of fusion, which latter may be assumed to be the The best practical conditions under which to make a test can same for resins of approximately equal softening points perhaps be brought out by a series of curves showing the timec = real heat capacity of amount of resin in ring t = initial temperature of sample temperature increment on resins run a t varying temperatures above their softening points. Thus, the true boftening point should depend only on the charIn Figure 1, curve 1 represents the results obtained when too acteristics of the resin, and be free from outside influences. All high a bath temperature is used. The softening point occurred transition points are best measured by having the process occur before the resin had had opportunity to absorb heat slowlya t constant temperature, so that the temperature of transition that is, it occurred during the rapid rise in temperature. Curve is not confused with extraneous temperature rises within the 2, although it represents the best conditions for taking a softening point according t o theory, is nevertheless an unacceptable type, system. An approximation to such conditions is represented by since the time required to reach the softening point was entirely curve 2 in Figure 1, in which the softening point occurs almost at too long,and thus slowed down the test. The slope of an acceptconstant temperature. I n this case it is obvious that the resin able type of curve should therefore lie somewhere between 1 and air-bath temperatures are equal. and 2. Such a curve is represented by curve 3, in which the soft.4s obtained by the A.S.T.M. ring and ball method, as well as ening point was reached a short time after the rate of temperature increase began to slacken. The bath temperature in this by other methods that employ a rising temperature bath, the case mas IO" C. above the recorded softening point. softening point is primarily a measure of the temperature of the bath and depends largely on the rate a t which the bath temperaEXPERIMENTAL WORK ture increases. The experimental work in this study consisted of running a A hypothetical example may serve to illustrate the point. Two series of softening point tests on a selection of gum and wood resins may have different true softening points and still show the rosins, treated rosins, and rosin-base synthetic resins, under same observed softening point when tested by a rising temperature method, if their heat capacities are different. Assuming various conditions, in order to determine what conditions of test that the heat conductivity is equal in both cases, it will require a would best meet the points of practicability brought out in the longer time for the resin with the higher heat capacity to absorb theoretical discussion, and what correlation might be expected the amount of heat needed to cause a specified temperature rise. between air-bath softening points and those obtained by the In the meantime, the temperature of the bath is increasing a t a iteatiy rate, independent of the amount of heat the resin is ahpresent E 2 8 4 2 T ring and ball method.
+
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Figure 2.
Figure 4.
Original Apparatus
Softening Point Assembly
SYNTHCTIC RES!
MODIFIED ROSIN
0 MIOICATES TIME AN0 TEMP€RATURE
,
_.rwo a n o n
AT W H l c x S O f TENlNG OCCURRED T,'IME
ROUNOHE40 SCREWS! TO SERVE ns EXTRA
UNDERSfOE VIEW OF BOTTOM
ETEAMINQ THE
Figure 3.
4
Figure 5.
Time
VI.
6
!* M I N U T E S 8
? ,/
10
Temperature Curvei. above S.P.
SO,
IO',
14
and 15' C.
Ring Holder
Briefly stated the method used in running the air-bath softening points c o & e d of placing the sample, previously poured into a standard shouldered ring mold, in an aw-bath vessel immersed in a liquid bath (large beaker containing glycerol) maintained a t a constant temperaturd above the softening point. The standard steel hall is placed an the sample in the usualmanner. The observed softening point is the reading of the air-bath thermometer at the instant when the softened resin drops the usual distance of 2.5 em. (1 inch) below the bottom of the nng. The general over-all design of the apparatus used for these tests is shown in Figure 2. It was submitted t o the members of Subcommittee I on Softening Point of Rosin of A.S.T.M. Committee D-17 on Naval Stores, as a result of a report covering a survey of methods in use for determining softening point by a special group of tlie subcommittee, headed by its chairmzn, C. E. Kinney of the Hercules Powder Company. Improvements recom-
15" C. above the known ring and ball
