V O L U M E 22, NO. 1 2 , D E C E M B E R 1 9 5 0 bility (1). The values given in Table I1 for Sos. 4,5, and 7 shoN that there is a large difference between initial (short-interval) and steady-state permeability. These data were taken from Figures 7 and 8, which clearly show the transitions observed in long-r:inge tests on the modified General Foods gas permeability cell. Thev show also that the data of Doty, Aiken, and Mark are high (arid closer to vapor cup results) because the latter are taken i n the initial period of the test. Further evidence of the essential steady-state nature of the results for 3 0 s . 4 and 5 of Table I1 is the final permeability constant comparison: P = 0.0003 X lo-* for 0.0005-inch film and P = 0.0004 X lo-* for 0.0028-inch film, an exceptionally good check for films of such widely different thicknesses and treatment. CONCLU ?JON
Widely different test apparatus and technique for determining water vapor permeabilities for synthetic films result in widely different transmission values. In the case of saran films the data from different techniques are riot so divergent as f i s t appears when due consideration is given the over-all conditions, and the time interval involved in making the determination. For practicnl purposes, therefore, it is necessary to know to what condi-
1545 tions the film sanipleb \%ill kw rsposed befort. choosing :i test method that will give applicable results. Keither the evacuating nor the nonevacuating method give. conditions universally encountered in film packaging. If film packaging with desiccant is employed, water vapor rates derived from nonevacuating techniques (such as the cup method) should be employed. If film packaging without desiccant as in food and meat packaging is employed, the evacuating methods or lower rates should be considered. In other words, the specific application to which the film material is put should dictate the test nwthod for rates of water vapor transmission, LITERATURE CITED
(1) Doty, P., J. Chem. Phys., 14,244 (1946). (2) Doty, P. M., Aiken, W. H., and Mark, H., IND.ENQ ( : H E M ANAL.ED.,16, 686 (1944). (3) Elder, L. W., ModernPackaging, 16,69 (1943). (4) Noll, A., Papierfabr. Wochbl. Papierfabr., 5, 151 (1944). (5) Sarge, T.W., ANAL.CHEM.,19,396(1947). (6) Shuman, A. C., IND.ENG.CHEM., ANAL.ED.,16,58(1944). 17) Southwick, C.A., Jr., M o d m i Packaging, 19,No.11, 137 (1 $146). l i a c t i r r i i Srpteinl)ri 12 lq40
Impact Resilience as a Brittleness Test for Polyvinyl Plastics GERARD FRIEDLANDER D r . Rosin Industrial Research Co., Ltd.. Wembley, Middlesex, England
l h e paper deals w-ith Lupke impact resilience of plasticized polyvinyl chlorides. The impact resilience temperature curve passes through a minimum which defines the transition from ordinar) to rubberlike elasticity. The position of this minimum with regard to temperature is characterized by the percentage concentration and type of plasticizer used. .it temperatures lower than the re-
T
HE loss of flexibility of polyvinyl sheets which occurs :it lo\\
dience minimum-i.e., in the absence of rubberlike elasticity-polymer compounds which give rise to high resilience are not capable of large viscous deformation during the short time of impact. In this temperature region impact resilience can be used to classify then1 according to their tendency toward brittleness. Merits of the method are discussed and compared with other hrittleness tests.
temperatures and the consequent brittleness have been a serious drawback in the application of these plastics for articles for out-of-door use, such as handbags. Various test methods have been proposed and tentatively introduced to establish a brittleness standard for these materi;ils. The two best known ones are the A.S.T.R.I. test ( 2 ) , which measures the temperature a t ufhich a plastic test sample ce to be brittle when subjected to a certain impact, and the flex temperature test (S), which measures the temperature at which a certain torsional deflection is attained when a test strip i.; subjected to a constant torsional moment. The A.S.T.M. test suffers from the disadvantage that thv so-called tirittleness temperatures determined by it are far lower than the temperatures the plastic has to withstand in actual practice and therefore cannot give an adequate representation of the behavior of a plasticized polymer under actual working conditions. For instance, many failures due to brittleness have occurred with polyvinyl rhloride handbags at teinpernturcs
temperat'ures of plttsticixed polyviiiyl chloi,ides are appr affected by changes in the rate of deform:tlion. The Clash and Berg method does not measure brittleness but loss of plasticity or increase i n rigidity modulus as a function of temperature. The so-called flex temperature of the Clash and Berg test is defined as the temperature a t which n specimen of standard dimensions is twisted through an ai'c of 200" under a fixed torque of 5.68 X lo6dyne-cm. which is applied for 5 seconds. These specifications lead again to low test temperatures which for H niisturc. having an .LF.T.XI. hrittlentw temperature of - j O " C. are below -20" C. Though the Clash and Berg test is c:rrried out over a relatively short time interval ( 5 seconds), thtj r;:impIe probably undergoes other than purely elastic deformation. hiltrn ~t al. in their paper on creep behavior of plasticized T'iriylite ( 1 ) conclude that in a test lasting only a fraction of a second B trioctyl phosphate plasticized sample of T'inylite may be several times as flexible as R tricresyl phosphate one, though its "5-second stiffness" is the same.
:il~oundo o A further disadv:rntage of t h e tmt i* its dependence on the rat? of' impact. Iienip et nl. ( A ' h : i w reported that brittle
The tendency to brittleness in a plastic is characterized by the :tbsence of rubberlike elasticity aud by a low plasticity-i.c~.. low
c.
THEORY
ANALYTICAL CHEMISTRY
1546
capacity for viscous deformation. When it is subjected to a quick strain, sufficient stress relaxstion cannot take place and the material cracks. A test which would permit the determination of the viscous and elastic properties under rapid deformation and in a practical temperature range should be a good indication of brittleness tendency. Impact resilience as used in rubber technology gives a measure of the elasticity and of the internal viscous friction-Le., energy loss when a material is quickly deformed. Application of this test to plasticized polyvinyl chloride leads a t first sight to apparently contradictory results. While high resilience in rubber is a desirable property, polyvinyl chloride samples which exhibit high resilience a t low temperature are very prone to brittleness. On closer examination, however, i t is seen that the same laws obtain far both rubber and plastics when the right temperature soale is used.
Figure 1. Test E q u i p n i e n t
It is h o a n from rubber research that the resilience of rubber, which decreases with reduction in temperature, undergoes n marked change when a sufficiently low temperature has been reached. Below this temperature the resilience increases again from 4% at -40" C. to values as high as 70% at -100" C. (7). As the temperature is reduced, beyond the point of minimum resilience, the materid begins to show the rigidity and resilience of a solid body. The lowering of resilience is characteriaed by B rapid rise in stiffness of the rubber and when the paint of minimum resilience has been passed the material becomes very brittle. The high elasticity component (the pardlel spring-dashpot element of the Burgess model) ( I d ) is gradually frozen in Nhen the temperature is reduced, and beyond the minimum point resilience is only a measure of Hooke's elasticity (which is not capable of supporting large deformations) and of the viscous component. This is shown by the high permanent set of rubber a t low temperatures (11). The point of minimum resilience, which for mtural unvulcanized rubber lies between -40" and -70' C., marks therefore the lower temperature limit of tho rubberlike state. Above this temperature high resilience indicates high rubberlike elasticity, low internal viscosity, and low Young's modulus. Below this temperature high resilience is to be associated with a high Young's modulus and tendency to brittleness. The resilience-temperatue curve8 of plasticized polyvinyl chlorides show a minimum (though not as sharply defined as that of rubber) which occurs in the region between 0" and 30" C.Le., at a far higher tempemture than is the case with rubber (see Figures 4 and 6). Plasticized compounds which have a good low temperature flexibility exhibit this minimum a t a lower temperature than those compounds h a h g high flex tempers, tures (see Figures 4, 6, and 8). It is known that plasticiaers of
low viscosity confer low flex temperatures (9) and one would therefore expect a relatively low resilience for compounds possew ing good low temperature flexibility, as visoous deformation can take place during the time of impact. High resilience-Le., mainly elastic deformation (Hooke's elasticity)-is shown by compounds made from plasticizers of high viscosity. However, a t temperatures higher than the minimum point of resilience there occurs a crossing over of the curves (see Figures 4,6, and 8) and the higher resilience is exhibited by the compound which has good low temperature flexibility. In this region the rubberlike state prevails and low internal viscosity confers greater resilience, whioh may be expressed according to the formula
if the impact is considered as a single half cycle of free vibration, where R is the ratio of height of rebound t o height of fall of pendulum, ooq the hysteresis index, n the internal viscosity, and En the effective dynamic Young's modulus. An analogy between electrical and mechanical properties leads to an identification of the mechanical (viscous) energy loss with the dieleotric loss. Now the mechanical energy loss which is equal t o (100 - resilience) X energy input/100 is a t its maximum when resilience passes through its minimum value. Busse et al. (4) in their paper on the dielectric properties of plasticized polyvinyl chloride have shown that the dielectric loss-temperature curve has a maximum which is shifted to lower temperatures for greater plasticieer concentrations. Similarly, an increase in plasticiaer Concentration shifts the resilience minimum to lower temperatures, as shown by Figure 4. Fuass et al. (8) have reported that with increasing plastioiser concentration the dielectric loss factor goes through a maximum and explain this in terms of internal viscosity which when lowered allows an increasing movement of the molecular dipole segments. The maximum in the loss factor occurs when the greatest phase difference between the movement of the dipole and that of the imposed electrical field exists. Further decrease in internal viscosity reduces this phase difference and gives a lower loss factor.
Figure 2. Test Equipment
1547
V O L U M E 2 2 , NO. 12, D E C E M B E R 1 9 5 0 Figure 5 is in good agreement with Fuoss's findings, the resilience curve going through a minimum when the plasticizer concentration is increased (at constant temperature)-i.e., when the internal viscosity of the compound is reduced. Rider et al. (IO)found that a change in plasticizer concentration produces a marked change in the impact resilience. Their experiments were carried out a t a constant temperature of 70" F. and show a prcnounced resilience minimum in the range of 30 to 50% plasticizw content-i.e., a t concentrations mostly used in practice. The
the sample a t an even temperature in the range from -12' +30" C. The details of the pendulum are as follows: Suspension Length of suspension Distance between points of suspension parallel to striker Distance between points of suspension normal to striker Weight of striker
Radius of spherical end of striker Height of fall of striker Length of striker
RLFRIGERATOR
AIR HOL ES
to
4 filar 1 meter 12.5cm. 45 cn1. 176 grams 0.6cm.
6 cm. 32. 7 CIIL,
The striker is rather long; this is necessary, as it has to enter the refrigerator throu h a small opening in the front panel. In order to keep the weigtt down, the striker is made of Duralumin. It is weighted in the center by a brass sleeve to give it greater stability after impact. Both ends of the ram are made from mild steel. The striker is released by an electric magnet. The cabinet is a refrigerator of the normal 4 cubic foot capacity type. In order to ensure an efficient cooling of the test sample a 9-inch electric fan (having a totally enclosed motor) is mounted inside the lower compartment of the refrigerator. The air circulation is so arranged that the fan blows the air past the cooling coils of the refrigerator onto the sample holder. For conditions above room temperature, warm air is blown into the cabinet and temperature control is effected by altering the rate of flow o i air.
1 --SCALE
PfNOUL UM
MAGNET
Figure 3.
Test Equipment
higher the brittleness temperature of the plasticized compound the greater is the plasticizer concentration at which this minimum resilience occurs, and a loweiing of plasticizer content results in a rapid increase of resilience. When compared a t low plasticizer content the compounds containing plasticizers like tricresyl phosphate and Paraplex G25 (which are known t o confer poor low temperature flexibility) show the greatest resilience. The opposite is the case when the critical plasticizer concentration is exceeded. The curves cross over to the right of the minimuin (as has been found for the resilience-temperature dependence) and tricresyl phosphate and Parnplev compounds exhibit the lowest resilience. A summing up of all these facts leads to the conclusion that in the absence of rubberlike elasticity-Le., a t temperatures below the point of minimum resilience-polymer compounds which give rise to high resilience are not capable of a large viscous deformation during the short time of impact, and that impact resilience can be used to classify them according to their tendency to brittleness. APPA RATU 9
The test equipment consists of a Lupke-type pendulum (13) and a temperature-controllrd cabinet capable of maintaining
Figure 4.
Percentage Resilience us. Temperature Plasticizer, dioetyl phthalate
The sample to be tested is mounted on a holder which moves with a sliding fit in a cylindrical sleeve. A strong cylindrical spring inside this sleeve keeps the holder in position and ensures that the sample is pressed firmly and with a constant force against a steel anvil. The possibility that the spring might set up vibrations when the sample is hit by the pendulum and thus interfere with the rebound has been checked. Springs of different wire gage and different number of coils gave the same resilience values. The temperature of the test saniple is measured by a springloaded needle-tip thermocouple n-hich projects slightly from the
1548
ANALYTICAL CHEMISTRY
steel anvil and embeds itself in t,he sample when this is pressed against the anvil. The rebound of the pendulum is measured in the following way: A fluorescent light, tube throws the shiidow of a pointer which is attached to the striker onto a glass screen, graduated in centimeters. Superimposed on the glass screen is a movable transparent scale with millimeter graduation. One or two rebound rcadings are taken to find the range on t,he scale. Thcl movable scalr is then put into position and the correct rehound measured. l>iguv(,s1 , 2. : t i i d :3 show t,he test equipment,. TESTING PROCEDURE
' l h samples to be tested a,re cut into strips 3 cni. wick, arid 9 c:m. long. I n order to minimize the influence of such variables as radius of spherical end of st,riker and height of fall, it is usually considered advisable to use test samples 0.5 inch thick. However, as t'he testing equipment, had been primarily designed for a large scale commercial user of polyvinyl chloride sheeting, it proved inipracticable to go to such thick samples. The finished commercial product usually has a thickness of 0.020 to 0.025 inch and four t o five pieces can be used to build up a sat,isfactory test sample. I t has consequently been decided to standardize the test, for t: sample 0.10 inch thick. If the thickness of thcx sheets is between 0.020 and 0.025 inch, tests are ma.de wit ti samples consisting of four and fivr i)irws (iindrr :Inti above 0 . I O inch) and themean result is taktw.
Figure 6. Percentage Resilience us. Temperature Samples plasticized with mixtures of tricresyl phosphate and diocty 1 phthalate
ture was found to give repeatable results. Conditioning may he progressively shortened with increasing test temperatures. EXPERIMENTAL RESULTS
Hefore commercial polyvinyl chloride sheets were tested, vxtcnsive experiments with specially prepared samples were conducted. These tests covered a wider temperature range than is proposed for commercial samples.
Figure 5. Percentage Resilience us. Plasticizer Concentration at Various Temperatnres Plasticizer. dioctyl phthalate
To eliswe accurate test iesults it is very iiiiportant that the sample be properly conditioned. For temperatures as low as - 12' C. it was found necessary to leave the sample for 15 hour= at this temperature before taking measurement. Rider ct al. (IO)report a similar experience when using the A.S.T.M. brittleness test for compounds plasticized with Paraplex G25. I n their opinion it is the slow velocity of crystallization of G26 which makes these long conditioning times necessary. With plasticizers having low melting points, shorter conditioning may bc sufficient. Commercial samples are not tested a t temperatures loxcr than - 3 " C. and conditioning for 2 hours at this tempera-
The test sheets were made in a 6 X 6 inch frame mold compressed between highly polished stainless steel plates in a laboratory static press. The temperature of cure was 155" C., and the pressure 0.5 ton per square inch. The sheets were cooled under pressure. The polymer used for the sheets was polyvinyl chloride Corvic grade P.M., as supplied by the Imperial Chemical Industries, Ltd. Lead stearate was taken as stabilizer in quantities of 2% by weight on the polyvinyl chloride content, The plasticizer content is in all cases stated as a true percentage-e.g., in the case of a 40% plasticized sheet 100 parts by weight of the finished product contain 40 parts of plasticizer and 60 parts of polymer. The plasticizers used were tricresyl phosphate, trixylenyl phosphate, butyl acetyl ricinoleate, dioctyl phthalate, and Flexol T.O.F. (trioctyl phosphate). The thickness of the sheets was 0.060 inch and two test pieceb (cut from the center of the sheet) were clamped together to make up a sample 0.12 inch thick. The results are shown in Figures 4 to 9. Figure 4 refeis to aamples plasticized with various amounts of dioctyl phthalate: percentage resilience is plotted against temperature. Figure 5 refers to the same samples, but here resilience is plotted against percentage plasticizer content with temperature as parameter. Both figures show that an increase in plasticizer concentration lowers the resilience at temperatures which are below the point of minimum resilience and increases the resilience a t higher temperatures. Furthermore, higher plasticizer concentration
V O L U M E 22, NO. 1 2 , D E C E M B E R 1 9 5 0
1549
vinj 1 chloride sheetings, the exact composition and pel centage plasticizer content of \\hich nere not given to the author. Their thickness \\as 0.050 inch niid t\vo sheets mere clamped together to make up a sample 0.10 inch thick. Figure 10 refers to miytures for \$ hich ttniple prac~tlrale\pc'l II I I I Y ~ h n i betw :~vail;thl~
OOP
yo coumsirm OF PI ASTICIXR MIXTUM
DOP
Figure 7 . Percentage Resilience us. Percentage Composition of Tricresyl Phosphate and Dioctyl Phthalate Mixture Total plasticizer conteni 45%
shifts the point of minimum resilience toward lower teiiipwtures. Figures 6 arid 7 refer to mixtures of tricresyl phosphate and tlioctyl phthalate, the total plasticizer content being 45%. Starting with a sample having 45% tricresyl phosphate, part of the tricresyl phosphate is being replaced lvith dioctyl phthalate, the last sample containing 45% dioctyl phthalate only. In I'igure 6 resilience is plotted against temperature, whereas Figure 7 shows :t plot of resilience against plasticizer mixture concentr:ition. The results are essentially the same as for Figures 4 :inti %--Le., the replacement' of a plasticizer which has bad low temperature properties by one which confers good low temperature Hexibility has the same effect as increasing the o~er-all plasticizer concentration. 111 Figure 8 mixtures \vith five different plasticizers art' conip;ir(ad, all samples having it plasticizer content of 4570. The well kno\vii difference in low temperature flexibility between tricrrsyl phosphate a r i d trioctyl phosphate is brought out b). their respective lesiliencc, valut~s. Whereas the point of minimum iwilirrice for the tricresyl ~)hosphi~te itrid trisylenyl phosphate samples is just being reached ut +28" C., the mininium of the trioctyl phosphate curve occurs bcsloa - 12 O C. Over the Irholt. temperature range from -12' to +28" CI. the trioctyl phosphate sample eshibits rubberlike elasticity, as shown by the positire gradient, of its resilience temperature curve, whereas the negative gradient of the t,ricresyl phosphate curve proves the absence of rubherlike elasticity in this tcmperat,ure range. Figure 9 gives a comparison of butyl acetyl ricinoleate, dioctl--l phosphate, and a mixture of butyl acctyl ricinoleate and trioctyl phosphate, for a total plasticizer concentration of %Yo. Figures 10 and 11 refer to test samples of commercial poly-
Figure 8 .
l'rrcwntage Resilience os. 'l'eniperat l i r e I'lartiI10 t u --liOO
->.-IC
(,
t o -,;.io
('
.-, ( '.
- I,
0
They do not place the speciiiiens in thc s:tnw ortl(*i. as the: resilience tests, in particular with regard to sanipl~s T I and Tt. Percentage elongation tests for a stress of 1000 pounds per square inch applied in 45 seconds xt 0" C. give better agreement and are given in Table I t,ogether with the British Standard Specification 903 hardness number at 20" C. (r.longntion and hartlness mere measured hj- the makers of the stirsets).
ANALYTICAL CHEMISTRY
1550 Table 11.
Effect of Increased Plasticizer Content Y0~,1Rvzilimre at 0' C .
o&
Elongatiori a t 0' C. 13.3 17 1 22.5 21i 0
Table 111.
-3.7 -2,fi
-1 ti -0 ti -0 '7 T1.0 +2.0 -2.7 c3.3
XO.
4" 11
Reproducibility of Tests
TraI.! ~.~ 'pe~np., C. Itrsilirncr ~
Hardnesq a t 20' C . 32 37
Test 2
-
~~
~
38.2 37.0 3.i. 8 33.2 3 4 , .i 33 8 32.7 32.7 3:?, 1
Tettip.. O C.
-3.5 -2.2 -1.G -0.7 0 0 0 9 +1 9 +2 3 f 3 0
Resilirnw
37 30 3(i 33 33 33 33 32 32
i
7
4 0 $1
7 0 2 1
C.
TEMPERATURE
Figure 10. Percentage Resilience us. Temperature for Commercial I'olyinyl Chloride Samples
7EMPERATURi * C
Figure 9. Percentage Resilience us. Temperattare Plasticizer concentration 35%
The TI sample, which at 0 " C shows a higher resilience arid smaller elongation, is actually softer a t room temperature than the T2sample. Figure 11 and Table I1 show the effect on resilience of increasing the plasticizer content. Though there seems t o be a good correlation between per cent elongation and resilience at 0" C. for these four samples, this no longer holds good when elongation and resilience of T,, TI, and T, are compared with the figures obtained for the T C samples REPRODUCIBILITY OF TESTS
If the thermocouple is fixed in such a way as to give a true temperature reading of the sample, the reproducibility of the test is within *0.3% resilience. Table I11 and Figure 12 give a comparison of two tests carried out with the same sample. After completion of test 1 the samplr was taken out of the refrigerator and kept a t room temperature for 1 hour. Before starting test 2 the sample was conditioned for 3 hours at -4" C. Impact resilience is rather sensitive t o sample thickness. A standard thickness of 0.10 inch built up from four 0.025-inch thick sheets shows a lower resilience than one made up from two O.OB(Xnch sheets. This is a drawback which this method shares
TfMPfRATURL
'C
Figure 11. Percentage Resilience CS. Temperature for Conimercial Polyvinyl Chloride Samples Ha-ticizer concentration increasing from TCI to TC4
wit11 other brittleness tpsts. The disadvantage could be overconie by using samples ut I w a t 0.5 inch thick, as is done for the rrsilience testing of rubber. Figure 13 shows a plot of impact resilience against sample thickness a t a constant teiiiperature of 0" C. The different thicknesses \yere made up from 0.020-inch commercial sheetings. The curve flattens oyt a t approximately 0.200-inch thickness. I t is, however, difficult t o ensure uniform contact pressure between anvil and sample when the latter is made up from a great number of single strips.
V O L U M E 2 2 , NO. 12, D E C E M B E R 1 9 5 0
1551
cannot manifest themselves to such an extent as with creep and elongation tests. Resilience is not a fundamental physical property like viscosity and stiffness but a composite of both. This, however, does not make it less valuable as a tool for assessing the properties of a material. The minimum in the resilience-temperature curve clearly defines the transition point from ordinary to high elasticity in so far as short time deformations are concerned. 4 t lower temperatures stress and stress relaxation are a function of the combined properties of ordinary elasticity and macroscopic viscosity, of which resilience is a measure. ACKNOWLEDGMENT
Figure 12. Reproducibility of Test 0 X
Test 1 Test 2
Polyvinyl chloride sheeting used for handbag manufacture is very often embossed with a surface pattern. It was found that the pattern had no influence on the resilience values. Test simples with embossed surface gave the same pendulum rebound when the pattern faced either the anvil or the striker.
The investigations were carried out for AIarks and Spencer, Ltd., as part of a quality testing program, and the author wishes to thank them for permission to publish the paper. Thanks are also due to V. E. Yarsleys’ Laboratory for the preparation of the experimental test samples and to John Beresford-Hunt for the design of the equipment and collaboration in obtaining the experimental results. In conclusion, the author wishes to thank P. 0. Rosin for his encouragement and constructive suggestions in this development. BIBLIOGRAPHY
(1) .liken,
W.,Alfrey, T., Janssen,
A., and SIark, H., J . Polgmer
Sci., 2, 178 (1947).
DISCUSSION OF RESULTS
The experiments have shown that polyvinyl chloride sheetings \\ hich have failed in cold weather or mixtures which by virtue of their plasticizer composition are known to have poor low temperature flexibility give higher resilience values for the iiegative gradient branch of the resilience temperature curve than those which have good low temperature properties. Small changes in plasticizer content are readily detected by the resilience test. While there exists some correlation between resilience and per cent elongation a t the same temperature, this rule does not hold generally, especially when mixtures which have different plasticizer compositions are being compared. In the resilience test the sample is deformed during a very short time interval, and delayed elasticity and viscous effects 52
(2) Am. SOC. Testing Materials, D 746-44T. (3) Clash, R. F., and Berg, R. M., I n d . Eng. Chetn.. 34, 1218 (1942). (4) Davies, T. M.,Miller, R. F., and Busse, W.F., J . Ani. C h a . Soc., 63,361 (1944). ( 5 ) Dillon, T. H., Prettyman, I. 13.. and Hall, G. L., J . dpplied Phys., 15, 320 (1944). (6) Kemp, A. R., Malm, F. S., and Kinspear, G. C., I n d . Eng. Chem., 35,488 (1943). ( 7 ) Lewis, W. K., Squires, L., and Broughton, G., “Industrial Chemistry of Colloidal and Amorphous Materials,” p. 422, New York, RIacmillan Co., 1942. (8) Mead, F. D., Tichenor, L. R., and Fuoss, R. M., J . Am. Chem. Soc.. 64, 283 (1942). (9) Reed, R‘I. C., and Connor. L., I n d . Eng. Chem., 40, 1415 (1948). (10) Rider, K. D., Sumner, J. K., and Myers. R. J., Zbid., 41, 709 (1949). (11) Sagajllo, M., Bobinska, T., and Saganorski, hL, Proc. Rubber Tech. Conf. (London),1938, 749. (12) Tuckett, R. F., Chemistry and Industry, 62, 430 (1943). (13) T’anderbilt Co., R. T..Vnnderbilt News, 3, Xo. 6 (1933). RECEIVED September 29, 1949.
50
Merck Graduate Fellowship 48
46
k
5 44
$
8 42 40
38 ,020
,060 ,100 ,140 ,180 THICKNfSS OF SAMPLE IN INCHES
,220
Figure 13. Percentage Resilience z‘s. Sample Thickness Temperature, 0‘ C.
Applications are being received for the Mewk Graduate Fellowship in h a l y t i c a l Chemistry, financed by LIerck & Co., Inc., and administered by the .hfERICbN CHEMIC 4 L SOCIETY.The annual stipend is 52500. The place of study must be an institution whose undergraduate course of instruction in chemistry is approved by the Societx or, in Canada, by the Chemical Institute of Canada. The fellowship d l be an-arded to the applicant believed capable of contributing most to the advancement of the theory and practicae of analytical chemistry during the fellowship and in the future. I t will be contingent upon the candidate’s obtaining acceptance from the institution and professor selected for the study program proposed. Application blanks may be obtained from the AMERICAS CHEMICAL SOCIETY, 1155 Sixteenth St., N.W., Washington G, D . C. They should be completed and returned to the Merck Fellowship Committee R ith letters of recommendation and transcripts of credits. Deadline date for receipt of all material is February 15, 1951.
