14
R; C . WILHOITAND MALCOLM DOLE
from their metallic alcoholates two staiinic oxide crystal sizes wece detected at the compositions of 10% alumina and 9Oy0stannic oxide, 20% alumina and 80% stannic oxide, and 30% alumina and 70% stannic oxide. The sample 20% alumina and 80% stannic oxide, contained the maximum amount of the larger type crystals indicating that 20% alumina had a markedly enhancing effect on the growth of larger stannic oxide crystals. This phenomenon was not observed in the work of Weiser, Milligan and Mills. Heat Treatment at 1000°.-A preliminary study was made on the system heated to 1000". The results were very similar to the results obtained after the 800" heat treatment with the following exceptions : (a) the amorphous area had completely disappeared; (b) all the samples gave much sharper X-radiograms; (e) titania was completely transformed to its most stable forni, rutile; (d) the zones of mutual protection previously observed at the lower temperature levels were not detectable. The results obtained in the ternary system A1203Sn02-TiO2 are in agreement with the general conclusions concerning the existence of multiple composition zones of mutual protection against crystallization which have been set forth in earlier papers.
DISCUSSION .hoN.-Did you make any particle sise messuremeiits in the amorphous regions? W. 0. MILLIGAN.-I\'e made no attempt to do so. We were working with nearly 300 samples and could not study cstensively each individual one. Such measurements would be of value. The question as to whcther these mxtcrials are poorly crystalline or truly amorphous would
'
VOl.
57
have to be considered. Some of our patterns did appear to be of the truly amorphous type. ANON.--I am on your sidc! I believe you do havc amorphous regions. W,0. ~IILLIGAY.-I have been on both sides a t different times. i\xo~.--\Vhen you hydrolyzed the alcoholates did you Ixoceed nelt merely to heat the wet oxide sample mixtures? IT, 0. ~IILLIGAN.--~\To. The samples were washed successively with water and acetone and finally with water, nnd were then air-dried, prior to heat treatment at elevated temperatures. ANoN.-Did the nature of this treatment, and other factors, suoh as gH value, affect the location of the zones of mutual protection? u'. 0. hhmGAN.-Although such systematic studies have not been made, we would expect all such factors to influence the results. ANON.--IS there any evidence of a relation between tllc zones of mutual protection and stoichiometric ratios of the oxides? W.0. RhLIcm.--Certainly no simple relation exists. A. L. IlilCCLELLAN.--Why are two amorphous zones observed hi the +&08-Sn02 leg of the triangle and not in the other two legs? jv. 0.hIILLIaG.-& 800" temperature level, t v 0 amorphous zones were found in the A1208-Sn02leg, whereas in the other two legs, all of the samples were crystalline, a t least in part, and two zones of mutual protection were detected, in which the degree of crystallinity was markedly decreased. R. D. VoLD.-Did you carry aut any studies of the effect of different r%tes of cooling on the properties of these materials? Iv. 0. 1IIrJrdGAs.-In our work, all such variables wcre held Rtrictly constant. However studies of the type YOU mention would be of great interest.
SPECIFIC HEAT OF SYNTHETIC HIGH POLYMEBS. 11. POLYHEXAMETHYLENE ADIPAMIDE AND SEBACAMIDEl BY R. C. WILHOIT~ AND MALCOLM DOLE The Chemical Laboratory of lVorthwestem Uniuersity, Evanston, Illinois Receh,ed J u l y 6% I866
Data are given for the specific heat of ribbons and of undrawii and drawn filaments of 6-6 Nylon as well a8 of annealed 6-6 Nylon from room temperature to 280". The results of a similar ntudy of 6-10 Nylon in ribbon form are also included a8 well as data for three monomeric analogs of Nylon. No heats of transition can be detected at the temperature of the secondorder trbnsitiooli, 47", but a slight heat of transition of the order of 1 cal. g.-1 has been observed for the crystal structure change a t 165 . By estimating the heat of fusion of perfectly crystalline Nylon from the data on the monomeric analogs, it was possible to.calculate the degree of crystallinity of the different forma of Nylon over the whole temperature range. The undrawn filaments were the least crystalline nitd the annealed Nylon the most crystalline at room temperature, but a t 220",the drawn filaments were more crystalline than annealed Nylon. The crystallinity increases from about 160 to 220 a t which temperature i t passes through a masiinum.
Introduction The data on two polyamides and three monomerir aiialogs contained in this paper represent the secoiid contribution in a series devoted to the measurement and interpretation of specific heat data on synthetic high polymers. The first paper,s on ( 1 ) Presented before the twenty-sixth h'atioiial Colloid Syriipoaium whioh was held iinder the ampices of the Division of Colloid Cheniistry of the American Clieinioal Soviety i i i Los Angeles, California, June 1618, 1952. (2) A . E. C. Predootoral Fellow, 1949-1961. (3) A I . Dole, W. P. Hettinger, Jr., N. Larson and J. A. Wctliington, Jr., J . Chern. Phys., 90, 181 (1952).
polyethylene, contained in additioii to the thermal measurements, calculations of the degree of crystsllinity and a statistical theory of crystallite length. Maglie, Portas and Walteham4 determined the average specific heat of Nylon over the temperature range -4.5 to +28.5" with an estimated average error of about 1% (actual fluctuations in several cases amounted t u 3 to 5% from the mean). These authors also refer to an average value of 0.555 for the specific heat over the temperature range 20 to (4) F. C. Magne, H. J. Portas and H. Wakeham, J . Am. Chew. Soc., 69, 1896 (1947).
L
I
Jan., 1953
SPECIFIC HEATOF SYNTHETIC POLYHEXAMETHYLENE ADIPAMIDEAND SEBACAM~DE15
250'. None of these results shows in detail how the specific heat changes with change of temperature. The time-temperature cooling curves of a number of polyamides were studied by Baker and Fuller5 but such measurements are too crude to calculate from the data the finer details of changes in the specific heat. Furthermore, super-cooling enters in to complicate any attempted interpretation of the results. It was to fill a significant gap in knowledge of the thermodypamics of Nylon that this research mas undertaken.
Experimental Materials.-The various samples of 6-6 and 6-10 nylon, polyhexamethylene adipamide and polyhexamethylene sebacamide, in the form of ribbons, undrawn and drawn filaments were kindly supplied to us by Dr. C. E. Black of the Rayon Technical Division, E. I. du Pont de Nemours and Company in 1947. The following information accompanied the samples. 6-6 Nvlon. batch V-432 ~.~ RelatiGe viscosity, poises 25.1 NHz ends/l06 g . 24.0 COOH ends/106 g. 113.1 Number av. mo1,wt. 11,000 Stabilizer . 1 mole % acetic acid 6-10 Ndon, batch V-431 Absolute viscosity (phenol), poises 141 NHz ends/l08 g. 21.0 COOH ends/l06 g. 159.6 Number av. mol. wt. 9,250 Stabilizer 1 mole % acetic acid. 6-6 Nylon undrawn filaments. Batch V-432 rapidly extruded from the melt and cooled in the order of one second. Each yarn contains 23 filaments and weight is 400 denier. 6-6 Nylon drawn filaments. The above undrawn yarn was hot-drawn. Weight of yarn produced 80 denier, tensile strength was 6.5 g. per denier and elongation a t break 14.3%. The nylon samples were used as received except for drying. They were stored in a desiccator before use and after placing in tho calorimeter, the samples were evacuated for several hours bctore filling the void spaces of the calorimeters with helium. Considerable difficulty was expericnced with thermal deconiposition of 6-6 nylon at temperatures above thc melting point. Pockets of gas formed which caused the nylon to swell and to spill over into the calorimeter which after cooling and solidification produced a hard ma88 which led to much damage to the calorimeter in taking it apart. ;Innealed nylon could not, therefore, be prepared in the calorimeter. It wasmade by heating the 6-6 nylon in a purificd nitrogen atmosphere in a glass flask umil the nylon melted and then by cooling it slowly during 8 hours from 270 to 200" and during 120 hours from 200' to room temperature. After breaking the glass, the nylon was removed from the flask and broken up into lumps for insertion into the trays of the calorimeter. Threc monomeric analogs of the polyamides S,S'-di-,cticxyladipamide, N,N'-di-n-hexylsebacamide and N,N'di-ji-propyladipamide, were also studied in thc: hope oi obtaining information on thc specific heat arid heat of fusion of the 10070crystalline polymer. The first t w o monomers were kindly made for us by Dr. J. G. f'anOot of thc Carothers Research Laboratory, E. I. du Pont de Semours and Company while the third was synthesized by us by first preparing adipyl chloride from adipic acid and thionyl chloride, then making the propylamine hydrochloride and finally converting to the amine by treatment with potassium hydroxide. We are indebted to Professor C. D. Hurd for suggesting the use of this compound as an analog and for preparative details. The product was recrystallized from a solvent containing 80% and 20'30 alcoho;, maximum rnelting point 178.5", mclting range 173-179 . The maximum ~
e
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.
melting points and melting ranges of the N,N'-di-n-hexyladipamide and sebacamide were, respectively, 159', 145These melting ranges were esti159' and 142'. 115-142 mated from plots of the enthalpy as a function of temperature; the visual melting ranges were only about two degrees. Measurement of the Specific Heat.-The apparatus used for the measurements has been described in detail elsewhere,6 but modifications in operating procedures had to be introduced because of the higher temperatures required for the nylon measurements as compared to those on polythene. A very careful and detailed study was made of the temperature distribution about the inner surface of the adiabatic jacket and methods and equations developed for kee ing heat exchange to a minimum and calculating thermaflosses. We shall not describe these methods in erlenso as we are now in the process of building a new and more symmetrically designed calorimeter and adiabatic jacket in which temperature inequalities during the heating should be considerably reduced. I t is sufficient to say that every attempt was made to adjust the temperature controls, the heating currents and the air-cooling rates, to values such that heat transfer was reduced to a minimum. More thermocouple systems were installed so that a record could be made of temperature differences between the center of one side, the center of the bottom, the edge of the top of the adiabatic jacket and the center of the bottom of the calorimeter. Corrections due to heat transfer between these points were applied to the data, as well as the corrections described in our previous papers.6 The total corrections in any one specific heat measurement amounted to about 1-2% of the heat added on the average. Table I gives a list of the average fluctuations of the specific heat data from a smooth curve.
.
TABLE I AVERAGEDEVIATIONOF THE OBSERVEDSPECIFICHEAT DATAFROM SMOOTH CURVES,CAL. G.-1 0.002 , 6 - 6 Nylon annealed .004 6-6 Nylon drawn .004 6-6 Nylon ribbon .009 6-6 Nylon undrawn filament .004 6-10 Nylon ribbon ,0017 N,N'-Di-n-hexyladipamide ,0012 N,N'-Di-n-hexylsebacamide .003e N, N'-Di-n-propyladipamide I n the case of the crystalline monomers which exhibit no peculiarities in their thermal behavior and which melt a t lower temperatures than the polymers, the fluctuations are less. It is apparent that some of the observed deviations result from the non-crystalline and fluctuating properties of the polymers themselves. Although we are currently attempting to improve our experimental accuracy by the construction of a new calorimeter and adiabatic jacket, it would appear that the very nature of the polymer is such that a limit to the significant accuracy of the work will soon be reached-unless, of course, the study of the fluctuations becomes important.
Experimental Results There are three temperature regions of especial interest in the case of 6-6 nylon, 40-50' where at 17 to 49" nylon is said to pass through a second-order transition point,7 in the neighborhood of 165" where the crystal structure of nylon changes from triclinic to a pseudohexagonal close packed system and the region of the melting point, 263'. Specific heats of 6-6 nylon in the form of ribbons, undrawn filaments, drawn filaments and of annealed nylon (@(a) M. Dole, W. P. Hettinger, Jr., N. R. Larson, J. A. Wethington, Jr., and A. E. Worthington, Rev. Sei. Instruments, 22, 812 (1951); (b) M. Dole, N. R. Larson, J. A . Wethington, Jr., and R. C. Wilhoit, ibid., 22, 518 (1951). (7) R. F. Boyer and R. 5. Spencer, J . Applied P h y ~ .15, , 398 (1944). "Adrsnres i n Colloid Srience." Vol. 11, Interscience Publishers, Inc., New Yorh, N. Y.,1940, 11. I .
.
R. C. WILHOITAND MALCOLM DOLE
16
1
SPEC/f/C H€AT
.30 .40
.40 .30
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240 90
260 110
280 130
o DRAWN
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4.0
2.0
0
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200 50
Fig. 3.-Specific 25
50
75
heat of polyhexamethyleneadipamide.
AND
0 20 40 60
.Sa.70
80
.92
.48, -60
.82
-50
.?2
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.62
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Fig. Z.-Specific
HEATOF ANNEALED DRAWN 6-6 NYLON AND 6-10 NYLON RIBBONS
Temp., OC.
1.02
140
180
TABLE I1
SMOOTHED VALUES OF THE SPECIFIC
68
100
heat of polyhexamethyleneadipamide. .
T,"C. Fig. 1.-Specific
220 70
T, "C.
4
0
*
220
2F0
T, "C. heat of polyhexamethyleneadipamide.
in these three temperature ranges are illustrated in Figs. 1, 2 and 3. As the curves for the drawn and annealed nylon are the most regular and as these are the two most interesting forms of nylon, specific $eat values for the drawn and annealed nylon a t rounded-off values of the temperature are given in Table 11. Data for 6-10 nylon ribbon are also included as this was the only form of 6-10 nylon studied.
,
100 120 140 160 180 200 220 240 250 260 270 280
6-6 Nylon Annealed Drawn
0.311 .333 .367 ,424 .468 .505 .548 .583s .642 ,620 .G46 ,664 .80
1.13 2.75 1.30 0.75
0.302 .345 ,376 .420 .458 .479 ,503 .528 .542 ,560 .582 .567 .67F 1.55 6.5 1.35 0.75
6-10 Nylon ribbons
0.327 .373 ,420 ,486 ,512 ,518 .531 .561 .592 .588 .686 1.95 0.737 .639 ,627 .632 .639
Table I11 includes smoothed specific heat values for three monomeric analogs of 6-6 and 6-10 nylon as well as the heats of fusion of each of these substances as determined from an enthalpy plot. Interpretation of the Data Heats of Transition-Possibly the most interesting question which comes to mind with respect to the thermal behavior of nylon is, can a latent heat or heat of transition a t 47 or 165" be observed? In Fig. 4 we have plotted the enthalpy of the four forms of nylon for both of these temperatures. It readily can be seen that no break in the enthalpy corresponding to a latent heat exists a t 47". On the contrary, in the case of the undrawn filaments, the break, if any does occur, seems to be in the negative direction; that is, if the enthalpy below 40' is extrapolated to temperatures above 40°, the extrapolated values lie slightly above the enthalpy
Jan., 1953
SPECIFIC HEATOF S Y N T H E T I C P O L Y H E X A M E T H Y L E N E
ADIPAMIDE AND SEBACAMIDE
17
occur, however, on' annealing a t 200'. Unfortu TABLEI11 nately, no quantitative estimates of the extent o SPECIFIC HEATS AND HEAT OF FIJMON OF MONOMERIC crystallinity were given by Fuller, Baker and Pape. ANALOGS OF NYLON Specific h a t s , cal. g.-' T-' Other studies of the effect of temperature on poly-. Temp., QC.
N.N'-nHexyl: adipaniide
N,N'-nHexylscbacaniide
0.69 .596 0.493 .524 .523 .634 .542 ,812 .610 Melting 0.68* 79 Melting .641 .646 0.658 ,652 .640 .642 .G57 .642 .663 .G69 G42 cal. g.-l ' Heats of fusion, 31.2 34.8 142 Max. m.p., "C. 159
GO 80 100 120 130 140 150 160 170 180 190 200 210
I
N,N'-nPropyladipaniide
0,490 .5oi .505 .504 .511 .63 Melting 0.642 .656 .657 37.8 179
amides are those of Clark, Mueller and Stott'o who studied nylon in bulk form; Brillll who discovered the cryst.al structure change of nylon at 165' and the effect of water vapor on promoting crystallization at 100'; Hess and Kiessig12 who studied the change with temperature of the long period in nylon; and WallnerI3 who discussed methods of determining crystallite dimensions from the X-ray data. Turning now to the enthalpy effects in the neighborhood of 165', it can be seen that a slight latent heat probably does exist here, particularly in the case of annealed nylon, but the latent heat is extremely small, of the order of 1 cal. g.-I, or about one-thirtieth of the heat of fusion actually observed over the melting range. It is uncertain from the specific heat data whether a transition has occurred in the case of the drawn nylon; there is a maximum at 195' and a dir, in the curve a t 210' but this may be due to crystailization occurring during the measurement.14 Transition heat effects in un-
observed, but by less than 1 cal. g.-'. The undrawn filaments were cooled more rapidly from the melt than any of the other forms and con75, 70 55, 45 tain in all probability a greater fraction of amorphous nylon. Langkammerer and Catling in their study of spherulite formation in 6-6 nylon demonstrated that transparent filaments of nylon containing no 80, 70 100, 95 spherulites could be formed by rapidly quenching molten nylon. They could detect no formation of spherulites by annealing in the solid phase. However, there is no evidence that formation of spherulites 105, 95 125,120 influences the specific heat, the lack of spherulites suggests only that such nylon F, would probably be less crystalline than A ! $ nylon containing spherulites. If a very d small fraction of the amorphous content 135, 130 165, 155 of the undrawn filaments, say 1 to 2%, 4 should crystallize in the neighborhood of :r I 40°, the enthalpy above 40' would be less @ by the latent heat of crystallization of this l(jo, 155 amount of the nylon. Fuller, Baker and 190,180 Papeg made a comprehensive study of the -. effect of heat treatment on 6-6 and 6-10 nylon, using X-ray diffraction measurements and observing changes in Young's 185, 180 215,205 modulus and shrinkage in length as indica130 155 180 205 220 tions of the structural changes occurring 0 25 50 75 90 during the heat treatment. In brief they T, "C. found that the Of the 'lid Fig. 4.--Enthalpy of polyhexamethyleneadipaIni~~The lower set Polymer depended most critically 011 the of four curves covers the temperature range 0 to 90 ; the upper set rate of cooling from the melt and to a lesser 130 to 220". The numbers on the ordinates give the enthalpy values extent on annealing a t 2000 after solidifica- for the different curves: the arrows between curves show how much the A sample scale is changed. The scale for the undrawn filaments should have 4.2 tion at a lower cal. g.-1 added to it. of 6-10 nylon, about 0.5 mm. thick, quenched at 20' on a metal plate did not crystallize drawn and ribbon nylon are barely perceptible; on annealing a t ZOO" to the same extent as a sample (io) G. L. Clark, M. H. Mueller and L. L. stott, ~ n dEng. . Chen.9 originally cooled slowly to 200' (over about 40 42.831 (1950). (11) R. Brill, J. prakt. Chem., 1 6 1 ~ 4 9(1942). minutes) from the melt. Some crystallization did (12) I
