CELLULOSE A C E T A T E BUTYRATE PLASTICS H i g h Temperature Evaluation of Plasticizers by the Parallel Plate Plastometer W. M. GEARHART AND W. D. KENNEDY Tennessee Eastman Corporation, Kingsport, Tenn.
plasticizer. The polymer dissolves in diethyl phthalate a t 90 to 110" C., in dibutyl sebacate a t 125" t o 135" C., and in di-2ethyl hexyl adipate at 160" to 170" C . Diethyl phthalate will slowly dissolve cellulose acetate butyrate a t room temperature. The above figures are only approximate and are run in test tubes a t as closely the same rate of heating as is conveniently possible. Each of the above plasticizers was processed into plastic granules in varying percentages from 0 t o 20%, the usual limits for this plastic in commercial use. These granules were compression molded into sheets 0.40 inch thick and right cylinders of 0.375 or 0.625 inch in diameter were cut from the sheet using plug cutters. I t was found necessary to dry these pills thoroughly to avoid bubbling a t the higher temperatures. The usual technique was to dry the pills over phosphorus pentoxide for a t le&&3 days before using them. The principle of the parallel plate plastometer is shown schematically in Figure 1. The specimen, in the form of a right circular cylinder of initial height ho, volume V , is placed between two smooth steel plates. The upper plate is attached to a vertical member through which the load is applied; the lower plate is fixed. Between specimen and plate are placed sheets of thin aluminum foil. By means of a lever and sliding weights, a load W is applied to the specimen, and by means of a dial gage, the height, h, of the specimen is read as a function of time, t . All measurements were taken on a parallel plate plastometer obtained from the Tinius Olsen Testing Machine Company. I n early experiments temperature control of t h e apparatus was based on a
The viscosity of cellulose acetate butyrate as a function of nature and amount of plasticizer, and of temperature, was measured by means of a parallel plate plastometer. These data were used to assess numerical values for plasticizer efficiency, applying to the range of temperatures associated with molding, extruding, etc. The efficiency so found was discovered to be somewhat different at some temperatures from that determined by plasticizer solvent power, and at other temperatures, similar to it. The connection between the measurements of principal viscosity and molding conditions appears to be well established. The consequences of too low a molding temperature are clearly shown in terms of sharply increasing viscosity and onset of viscoelastic processes which may be responsible for permanent strains in molded pieces. A four-element mechanical model consisting of springs and viscous dashpots appears to fit these high-temperature phenomena quite w d l . All constants of this system are decreased as either temperature or plasticizer content increases.
O
N IMPROVED type of parallel plate plastometer has been
A
shown by Dienes and Klemm (4)to yield deformation-time curves from which the true absolute viscosity of a plastic specimen can be calculated. They showed that viscosities of polyethylenes of various molecular weights determined in this way a t elevated temperatures were in harmony with those determined (for materials of lower molecular weights) by the falling ball and capillary viscometers, and in addition, reported melt viscosity measurements on plasticized vinyl chloride polymers. In a later paper, Dienes (I) described further experiments with the parallel plate plastometer, using plastiiized vinyl chloride polymers, polyethylene, and a plasticized cellulose acetate butyrate. In a recent paper, Spencer and Dillon (7) report measurements of melt viscosities of polystyrene, determined in a capillary extrusion plastometer. Dienes (3) measured the viscosities of samples of the same materials a t some of the same and higher temperatures by means of the parallel plate plastometer, and was able t o show that viscosities determined by the two widely different methods were in good agreement. I t can be concluded on the basis of all of this work that the parallel plate plastometer is a reliable instrument by means of which the flow properties of plastics a t elevated temperatures may be evaluated. I n particular, in the present researches, the relative efficienciesof three plasticizers for cellulose acetate butyrate were studied by this means. For this study cellulose acetate butyrate (12% acetyl and 37y0 butyryl) was used as a base polymer. Three plasticizers of different solvent power were used: diethyl phthalate, a good solvent; dibutyl sebacate, a medium solvent; and di-2-ethyl hexyl adipate, a nonsolvent type. This classification is rather empirical but convenient in roughly classifying the plasticizers. The same comparison may be made by observing the temperature of solution of 1 gram of cellulose acetate butyrate in 9 grams of the
THERHDHZTEll DIAL GAUGL_
-\
\
LOADINO WLIGYT
RETRACTABLL LOADINS
LLVELINO
Figure 1.
695
5CRLW5
Parallel Plate Plastometer
INDUSTRIAL AND ENGINEERING CHEMISTRY
696
y
= F =
HEIGHT, CM
V
VOLUME,
h
I
9 =
I
0
Figure 2.
CW?
VISCOSITY. POISES
=
TIME, SEC.
m =
S L O P E , CW-'
w =
LOAD, K G
t
ELASTlclrV
FORCE, D Y N E S
SEC-'
Schematic Deformation-Time Curve
plots in this way. No model representation of the polymer structure is necessary; the formula rests on assumptions of NPwtonian viscosity. Investigation of the meaning of the elastic and viscoelastic regions of the curve requires a model of some kind, and reference has been made frequently t o a mechanical structure containing Hookean springs and Newtonian viscous elements, or dashpots. The four-element niodel whose response to applied force duplicates qualitatively t h a t of a polymer is shown in Figure 3. The open spring, whose force-constant is GI, accounts for true elasticity; the parallel spring (G2)-dashpot ( ~ 2 )combination, for viscoeldsticity; and the open dashpot (Q)for purely viscous flowv. The extension of the viscoelastic element (Gz, 72) under constant load is of a negative exponential type, with a time constant T Z , such t h a t 72
thermometer and thermostat inserted in the air of the interior chamber, but data obtained in this manner tended t o be somewhat erratic. I t \+-as found t h a t a thermocouple inserted in the upper platen produced considerable improvement. All data taken in these measurements were based on constant load experiments; the load on the plastometer may be varied from 0 to 60 kg. The desired test load is applied to the test specimen inserted betm een the platens of the parallel plate plastometer. Test specimens were 0.4 inch (1 cm.) in-height and 0.375 or 0.625 inch in diameter. Temperature of the apparatus was vaiied from 120' t o 195" C. in the course of these tests. The deformation-time curve obtained with this device is shown schematically i? Figure 2. For reasons which will appear later, the variables plotted are l / h 4 and t , measured in and seconds, respectively. There are three parts to this curve which are generally recognized to be associated with true elasticity, delayed elasticity or viscoelasticity, and viscous florr, respectively. The truly elastic part is instantaneously achieved and as quickly recovered on removal of the load; the viscoelastic part is completely recoverable deformation provided sufficient time is alloived. The viscous deformation is not recoverable a t all. Dienes ( 4 ) has shown t h a t for flow in the viscous region, the deformation-time function has the form as follows:
Vol. 41, No. 4
=
E
-4s was shown by Dienes ( 1 ) the equation describing the
G2'
extension of the four-element model under the conditions of t,he constant-load parallel plate plastometer test is:
where K is a normalization factor: I
K =
T'2
x
The first term is t h a t relating t o true or instantaneous elasticity, the second to viscoelasticity or delayed elasticity, and t h e third t o viscous flow. T h e constants GI,Gz,72, q~ (and Q) are evaluated as follows (Figure 4): The original observations are plotted in the form l / h 4 against t , and the straight line portion of the curve, with slope m extended t o intercept the axis of ordinates at !he value I . T h e point-by-point differences (D) between the observed curve and this straight line are computed and are plobted on semilogarithmic paper, on which they form nearly a straight line which, when extended to the axis of ordinates, intercepts it in the value DO.The values of the constants are computed as follows: qa
=
1/Km 72
where F is the force in dynes and
r)
is the viscosity in poises. The
TF 3v2
slope of this straight line is m = 8 -
is expressed in kilograms,
r)
=
. n'
and, if the load W
10-6
8.21 W
GI= 1 / K ( I -Do)
1 = tatD=;Dd
qz .=
G2q
If the original experimental data are plotted in the form of K / h 4 against time, normalized curves are obtained. T h e curves
8.21 X 10EW
mv*
.
T h e viscosity q is obtained from the slope, m, of the l/h4 against t
/
+ l t 73
/
2y
LOG DI
,VISCOELASTIC
;li E,
[ / I
J . & 73 I
i
Figure 3 .
v,s~ous
+
GI=
FORCE C O N S T DYNES/GM?
G ~ =FORCE CONST. DYNES/CM? 72
=
VISOOSITY, POISES
93s
VISCOSITY. P O I S E S
z,=
Titdl CONSTANT, SEC.
Four-Element Mechanical M o d e l
Do+j 0
Figure 4.
f
t
Evsluation of Constants of Four-
Element Model
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
697
1/T where T is the temperature in O K. I n Figure 5 where the results for the dibutyl sebacate are given, Dienes' results (I) are also plotted. A part of the disagreement might be due t o differencee in the base esters used, but this seems inadequate t o account for all of the discrepancy. I n a private communication, Dienes has told us that a further source of uncertainty in his measurements may have been variations in moisture content of the specimens; the importance of this was not recognized at t h a t time. I n subsequent and as yet unpublished work, Dienes has obtained good agreement with the present work, using dried specimens of a material identical to one used in this work. I n the range of temperatures over which it is feasible to measure viscosities by means of the plastometer (120' to 212" C.), the log Ta against 1/T curves are not straight lines throughout, but only at higher temperatures. At lower temperatures, the curves rise steeply. At still lower temperatures, the log 1 3 against 1/T curves must again level off to lower slope. The region of steep slope which is only partly covered by the present measurements is possibly associated with the second-order transition range of temperatures in which a partly crystalline structure is formed. The linear, less steep region begins when the viscosity has decreased t o lo7 t o 108 poises. I n Figure 6, there are a few points on the low-temperature ,+x lo3 DEG:' KELVIN ends of the curves for cellulose acetate butyrate plasticized with di-2-ethyl hexyl adipate; these may indicate Figure 5. Principal Viscosity vs. Reciprocal of Absolute Temperature that the curves level out at lower temperatures. It may Cellulose acetate butyrate plus dibutyl rebacate be possible t o study this question by investigating the secondary creep of these materials at temperatures in the neighborhood of room temperature and somewhat higher. The second-order transition has not been investigated are such that all experimental data involving one material at one for these materials, but the hypothesis that the region of abruptly temperature (but in which various loads and specimen volumes changing viscosity is to be identified with a second-order transiare involved) should be represented by a single curve. This serves as a partial internal check on the applicability of the plastometer theory t o the materials in question, as well as a check on internal consistency of the data. In the experiments discussed here, on the whole, the data normalized properly, although in many cases, inconsistencies were observed. tfs against
EXPERIMENTAL PROCEDURE AND RESULTS Tests were run to determine the effect of preheating the pellets at test temperature before testing. As shown in Table I, periods of preheating did not greatly affect the principal viscosity. I n the usual run the test pellet was preheated for at least 20 minutes. It seems logical that the preheating time would have more effect on the delayed elasticity portion of the curve than the portion where completely viscous flow has started. Another source of error might be the loss of plasticizer, particularly at the higher temperatures. However, cellulose acetate butyrate plastics have such a degree of internal plasticization of the base polymer t h a t fairly low amounts of high boiling plasticizers are required t o produce the desired range of physical properties in the commercial flow range. Weight measurements were taken on the pellets before and after the high temperature runs and no loss in weight of higher than O.lyowas encountered. To check possible heat degradation of the polymer, intrinsic viscosities were measured on several runs of unplasticized cellulose acetate butyrate before and after testing with no appreciable change being noted. The principal viscosities determined for acetate butyrates plasticized with the three plasticizers in various proportions are shown in Figures 5, 6, and 7 plotted as loglo
0
kT x lo3 D E C ' Figure 6.
KELVIN
Principal Viscosity vs. Reciprocal of Absolute Temperature Cellulose acetate butyrate plus di-2-ethyl hexyl adipate
INDUSTRIAL AND ENGINEERING CHEMISTRY
698
Vol. 41, No. 4
I O'O
lo9
IO8
c: IO7
0
FLOW TEMPERATURE, 'K.
6
IO
Figure 8.
Temperature vs. Flow Temperature VI
-
10' poises
Ios IO8 1
2
1
2.50
2.40
2.30
pTx lo3 Figure 7.
DEG:'
I
2.20 KELVIN
I
I
2.10
2.00
I o7
Principal Viscosity vs. Reciprocal of Absolute Temperature Cellulose acetate butyrate plus diethyl phthalate
tion could be tested in a number of ways. Figuie 7 shows the basic data for the third of the plasticizers tested. In Figure 8, the absolute temperature a t a fixed viscosity of 10' poises is plotted against the flow temperature for the three materials. For the sebacate and adipate plasticizers, the correlation of flow temperature with temperature a t viscosity of 107 poises is fairly good. However, this is not true for the diethyl phthalate, whose effect in reducing flow temperature is greater than its reduction of viscosity. This discrepancy might be due to differences in shear rate in the two types of test, but it might a130 be due to residual effects of elasticity and viscoelasticity in the Rossi-Peakes test. Piech and Gloor (6) have shown t h a t the viscosity (of cellulose acetate) a t the flow temperature determined in the Rossi-Peakes flow tester is about l o 7 poises. It is reasonable to suppose that molding temperatures should be sufficiently high that the viscosity lies in the linear part of the log qa against 1 / T curve; since the linear part lies in the range lo' to 108 poises and lower, molding temoeratures should be rouahlv determined from these Dlastometer results. I t is true that, in the plastometer experiments, a low shear rate is used, wit,h pressures less than about 100 pounds per square inch. With t8heflow t'ester, Piech rand Gloor showed that Lhe apparent viscosity decreased about twofold over the pressure range from 300 to 1500 pounds per square inch. Allowing for t,he high shear in molding, it might be predicted that the optimum -
c? IOb
IO5
I ol;
Figure 9.
173
vs. Per Cent Plasticizer at 170° and 1 90° C.
I
molding range of temperatures would correspond t o those which give, in the plastometer, say,10* to IOQpoises and lower viscosities. Following Dienes' suggestions (2) the logarithms of the viscosities ( 1 1 3 ) mere plotted as a function of per cent plasticizer at each of two selected temperatures, 170" and 190" C. The points are well represent,ed (except for those a t zero plasticizer) by st,raight lines (Figure 9). This implies:
OF PREHEATIKG ON MECHAKICAL CONSTANTS TABLEI. EFFECT
(Cellulose acetate butyrate Preheat TemperaTime, ture 1,s, OC.' Poises hlinutes 5 163 1.96 X 10' 10 163.8 2.06 X lo7 20 163.8 2.76 X lo7 40 163.8 2.10 X lo7 80 164.2 1.91 x 107
containing 4.9% di-2-ethyl hexyl adipate.) GI
Gz
I
V?, ~ynks/ Dynes/ Sq. Cm. Sq. Cm. Poises 8.92 X 106 5 . 3 6 X l o 5 5 . 4 5 X 10' 1 . 0 6 X 107 2.68 X 106 6.06 X lo4 7 . 6 0 X 1 0 6 2 . 5 5 X 106 6 . 3 8 X 104 1 . 6 9 X l o 7 2 . 6 3 X 106 5 . 4 4 X 106 1.00 x 107 2 . 6 2 x 1 0 5 5 . 3 7 x 1 0 6
72.
Seconde 160 175 120 310 180
q3 = Be -w
where P is the per cent plasticizer and band H are constants. The constant b has been used by Dienes t o express plasticizer efficiency. In Table 11, t>hevalues of b so calculated are given as a r e some determined by Dienes for other plastic materials. In four of the six cases, the plasticizer efficiency decreases with increasing temperature;
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April 1949
The data for Gz,and particularly for GI, 72, and T Z are subject to considerably more error than are those for q3 which have been discussed thus far. Accordingly, comparisons of activation energies, etc., are less reliable than are those for qs, The general character of the curves of log 72, log GI, log GZagainst 1 / T is similar to those for log v3. In Figure 12 the reciprocals of the absolute temperature are plotted against the plasticizer content, at constant GI and Gg equal to 106dynes per square cm. I n contrast t o the efficiencv of plasticizing of 73, the diethyl phthalate is the most efficient in plasticizing Gz,di-2-ethyl hexyl adipate the least. On the other hand, the order of plasticizing efficiency for GI appears to be like that for 73. Because of the scatter of measurements of GI, it is difficult to determine whether or not there is a difference in the plasticizing efficiency of dibutyl sebacate and di-2-ethyl hexyl adipate on GI. In Figure 13 the logarithms of the retardation times, TZ, are plotted against per cent plasticizer a t the fixed temperature 162" C. Within the rather large scatter of the data, there appears to be no difference in plasticizing efficiency among the three plasticizers for TZ. However, the variation of n~ with temperature may be somewhat different for the diethyl phthalate from that for the other two, which were indistinguishable. This is shown by Table IV, which gives the activation energies for TZ for the three plasticizers in various amounts. The data were such that differences within each plasticizer and between dibutyl sebacate and di-2ethyl hexyl adipate n'ere not significant, and the lower activation
2.SC
241
h
n)
0
z
231
3
w
-
Y
b
w
2.2.21
2 IC
% = A P + C 2.0
699
,
Z
4
6
E
IO tZ
14
16
PERCENT PLASTICIZER
Figure 10. Reciprocal of Absolute Temperature vs. Per Cent Plasticizer at Constant Viscosity
In two cases-namely, the di-2-ethyl hexyl adipate and the Santicizer M-17-the value of b was unaffected or increased, with Increasing temperature. At these conditions of elevated temperature, among the three plasticizers studied the dibutyl sebacate is the best and the diethyl phthalate the poorest (using this method of expressing plasticizer efficiency), which is not related to the order of solvent power. However, a t higher temperatures, the di-2-ethyl hexyl adipate becomes indistinguishable from the dibutyl sebacate, and, at still higher temperatures, presumably the order of plasticizer efficiency is the inverse of the order of solvent power. An alternative method of expressing plasticizer efficiency, which has the merit of being related to molding conditions, is a comparison of the temperatures a t which a given constant viscosity is obtained for various percentages of plasticixer. In Figure 10, the reciprocal of the absolute temperature is plotted as a function of plasticizer content for each of the plasticizers a t each of three viscosities. The straight lines represent the points quite well, and can be expressed:
1/T
=
AP
TABLE 11. PLASTICIZER EFFICIEXCY
18 20 42 24 26 28
+C
where A and C are constants dependent on the materials. A can be taken to be a measure of plasticizer efficiency. Table I11 shows A , calculated from these straight lines. Under the conditions of this test, the order of plasticizer efficiency is again, the sebacate best and the phthalate poorest. This is not the inverse order of solvent power. In Figure 11, in which the activation energies which were obtained from the slopes of the log 73 against 1 / T curves are plotted as funcMons of plasticizer content, it can be seen that the slopes (a)are in the order of solvent power. High solvent power, In these polar substances, implies strong attraction for solvent and solute. Thus, the activation energy curves imply that the more tightly bound the plasticizer and polymer molecule, the lower the energy barrier hindering flow.
(?a
= Be-bP)
Temperature,
Base Eater or Resin Cellulose acetate butyrate
Plasticizer Dibutyl sebacate
Cellulose acetate butyrate
Di-2-ethyl hexyl adipate
Cellulose acetate butyrate
Diethyl phthalate
Cellulose acetate (8)
Dimethyl phthalate
Cellulose acetate ( d )
Santicizer M-17
Vinyl chloride acetate (VYNS) ( 8 ) Dioctyl phthalate
oc.
b
170 190 170 190 170 190 170 190 170 190 160 170
0.32 0.28 0.28 0.28 0.24 0.18 0.35 0.30 0.22 0.23 0.23 0.20
TABLE 111. PLASTICIZER EFFICIENCY (1/T = A P
Plasticizer Dibutyl sebacate Di-2-ethyl hexyl adipate Diethyl phthalate
-
10' 1.12 1 .OO 0.62
+ C)
A
(x
10-9
101
1.24 1.10 0.85
IO' 1.34 1.22 1.09
TABLEIV. ACTIVATION ENERQIES FOR VISCOELASTICITY (72) Plasticizer, %
AE* Kcal.
Dibutyl sebacate 0 2.0 7.8 12.7 20.0 Mean
35 33 32 34 34 33.6 Di-2-ethyl hexyl adipate
0
41 32 32 31 33 38 34.5
1 4.9 7.8 15.0 20.8 Mean
Diethyl phthalate 1
4.8 9.1 13.0 16.7 Mean
31
26
31 26 28.5
INDUSTRIAL AND ENGINEERING CHEMISTXY
700
phthalat,e will give t,he highest surface hardncss, highest tensilc and flexural strengths a t 77" F., and the lowest loss in heating of the three. These are balanced by diethyl phthalate plastics having the lowest impact strength, especially a t low tempcrature. I t is somewhat surprising t h a t diethyl pht,halitte having the highest vapor pressure and .ivat,er solubility of the -threr% sbould have such excellent permanence properties. In the concent,rat#ion studied, this probably can be attribut,ed to the high clegree of plasticizer-polymer interaction. A t concentrations oi higher than 20%, the plasticizer leaching and loss on heating rise rapidly. This tends to confirm the v i m that excess plasticiacr is more than sufficient, t o cover all active ccnters on the polymer arid be only held by plasticizer-plasticizer interaction. The di-2-et)hylhexyl adipate has the lowest vapor pressure arid least solvent power of the three. While the other two are unlimitedly compatible with cellulose acetate butyrate, this plasticizer is difficult' to incorporate beyond 30% plasticizer. Such a plasiicizer gives the lowest tensile and flexural strengths a t 77" F. and lowest surface hardness but best impact strength a t both 77 F. and -40' F. Over-all permanence properties are the best of the+ three; its low vapor pressure and high resistance to water hydrolysis make it quite permanent. These physical properties show. that this plasticizer is the best of the three in resisting temperature change. The loss in tensile or flexural strength by going from 77 to 160 O E'. is the least of the three. Jn a similar manner, the impact strengt,h is lowered the least, of the three in going froni 77" to.-40" F. Dibutyl aebacato plastics, in general, fall between plastics from the ot,her two plasticizers in physical properties. Its propertic,!: tend t o be closer to those of di-2-ethyl hexyl adipate plastics. T w o somewhat anomalous results may be noted. I n going fxoiii 77O t o 160" F., the tensile and flexural strengths have the greatest, percentage loss of the three. This correlates with the surfaclci hardness being equivalent instead of higher than the adipaic. plastics. The other fact is that dibutyl sebacate, in spite of it?, fairly low vapor pressure, has a. higher loss in heating than thc. ot,her two. In comparing thesc plasticizers, all those in concentrations b(.-low 8% give similar properties, well wit,hin the error of the test conducted. Variations in properties in this range may he attrihnt,ed to variation in molecular weight of the base polymer. ,\I ihc beginning of this study, it was hoped that>some COIW-
54
-I
52
a so V Y
e
I
2- 46 0
a:
44
W
Z 42
W
z
40
0 %
t-
Q 36
PERCENT
PLASTICIZER
Figure 11. Activation Energy of Flow Per Cent Plasticizer
Vol. 41, No. 4
vs.
energy of the diethyl phthalate is open to some doubt. These BCtivation energies are of the order of half t h a t associated with the principal viscosity of the base ester and are less than those of the highly plasticized esters. The implication is that, as temperature increases, the principal viscosity decreases more rapidly than does the viscoe1asticit.y. In each individual experiment,, it was found that the four constants of the four-element model were adequate to describe the experimental data. I t would not improve the fit to assume a distribution of retardation times, as is often proposed to account for the viscoelast'ic properties a t room temperatures. There is no test of the degree of Kewtonian character of the viscositics 112 and 73, inasmuch as the stress and, therefore, the rate of shear, is so low. For example, if following Eyring's theories, a hyperbolic sine form of dependence of q on the stress were assumed, at the low stresses in the present experiments, the non-n'ewtonian expression approaches the Ncwt:onian fo1.m asymptotically.
M E C H A N I C A L PROPERTIES O F CELLULOSE ACETATE BUTYRATE PLASTICIZER C O M P O S I T I O N S As was shown by Meyer and Gearhart ( 5 ) measurements of solvent power will correlate with the usual measures of mechanical physical properties. The cellulose ester is dissolved in 50:50 acetone-plasticizer solutions a t concentrations up to 1%. The intrinsic viscosity of these solutions (plotted as v., against concentrations in grams per liter) gives a more precise measurement, of the solvent power than is obtained by the test tube test previously described. The diethyl phthalate data give a line of the stcepest slope, and the dibutyl sebacate of a flatter slope; the 50: 50 di-2-ethyl hexyl adipateacetone solution will not dissolve the cellulose acetate butyrate. Physical tests were run by the usual A.S.T.M. methods. Examination of these properties for each of the plasticizers studied sho\+s that diethyl
* '"0
2
4
6
8
IO
I2 14
16
18 20 22 24 26
PERCENT PLASTICIZER
Figure 12.
0
2
4
6
8
IO I2
PERCENT
14 I6
I S 2 0 2 2 24 26
PLASTICIZER
Reciprocal of Absolute Temperature vs. Per Cent Plasticize1
Constant value of GIand Gz equal to 10' d y n e s per square centimeter
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1949
701
energies of flow in the increasing order: phthalate, sebacate, adipate, indicating as they do, increasing temperature variation of properties in the same order, seem t o be the reverse of the order of temperature dependence of the physical properties a t lower temperatures. This may be a consequence of marked differences in t h e course of polymer-plasticizer interaction in the transition region. Since such physical properties are usually measured at 25' C., little correlation might have been expected between them and plastometer data taken at temperatures ranging from 120" t o 195' C. At these high temperatures the plasticizers would undergo changes in solvent power. Since diethyl phthalate has high solvent power a t 25" C., the higher temperatures would not be expected t o increase this power t o any great extent. Dibutyl sebacate would be enabled t o increase its solvent power to become a good solvent. Di-2-ethyl hexyl adipate, especially in the higher temperatures above 170"C., becomes a rather good solvent.
ACKNOWLEDGMENT The authors wish to express their appreciation for the assistance of James Stranch, who carried out t h e experiments and many of the calculations. PERCENT
Figure 13.
Log
72
PLASTICIZER
vs. Per Cent Plasticizer at Constant, 162" C.
T
LITERATURE CITED =
lation between the plasticizing efficiency of the three plasticizers and these physical properties might be found. Whereas, at a fixed percentage of plasticizer, the diethyl phthalate was found to give viscosities generally higher than those of the other two, a t corresponding temperatures, the flow temperatures indicate the reverse is true as was pointed out above. The greater activation
(1) Dienes, G. J., J . Colloid Sci., 2,131 (1947). (2) Dienes, G. J., and Dexter, F. D., IND.ENQ.CHDM.,40, 2319 (1948). (3) Dienes, G. J., and Dexter, F. D., J . Colloid Sci., 3, 181 (1948). (4) Dienes, G. J., and Klemm, H. F., J . Applied Phue., 17,458(1946). (5) Meyer, L. W. A., and Gearhart, W. M., IND.ENO.CHEM.,40, 1478 (1948). (6) Piech, F.E.,and Gloor, W. E., A.S.T.M. Bull. 151 (Maroh 1948). (7) Spencer, R.9.. and Dillon, R. E., J. Colloid Sci., 3, 163 (1948). R E C E I ~ EFebruary D 2, 1949.
PLASTICIZED POLYVINYL CHLORIDE Structure and Mechanical Behavior TURNER ALFREY, JR., A N D N O R M A N WIEDERHORN, Polytechnic Institute of Brooklyn, Brooklyn, N. Y. R I C H A R D STEIN
AND
A R T H U R TOBOLSKY, Princeton University, Princeton, N. J.
The existence of a three-dimensional network system in plasticized polyvinyl chIoride and Vinylite VYNW compositions has been established on the basis of creep, stress relaxation, dilatometry, birefringence, and x-ray measurements. X-ray diffraction diagrams of unoriented, plasticized VYNW and Geon 101 films yield patterns which are crystalline in nature. The mechanical properties of a given formulation can be altered by recrystallization procedures.
N A previous publication ( 1 ) the creep behavior of plasticized Vinylite VYNW was described. At that time a n attempt was
I
made t o relate this behavior to the structure of plasticized polymer compositions. One of the conclusions arrived at was t h a t a three-dimensional gel network of great permanence must be present. This was necessary t o explain the combination of the small amount of long-time creep, associated wilh large short-time compliance and the essentially compIete recovery of films which had been subjected to stresses for weeks.
The nature of the gel structure now has been studied more thoroughly with the aid of numerous experimental techniques. The results of this work not only confirm the existence of a threedimensional network system in plasticized polyvinyl chloride and W N W compositions, b u t also lead t o a fairly definite picture of its details. It has been established on the basis of creep, stress r e laxation, dilatometry, birefringence, and x-ray measurements, that these materials are partially crystalline in nature. The relative amounts of crystalline and amorphous polymer in any one composition has not been established, but there is no doubt that the crystalline regions comprise but a small fraction of the total composition.
X - R A Y DIFFRACTION STUDIES The most direct evidence for the existence of crystallization in plastic polyvinyl chloride is probably supplied by the x-ray diffraction results. These results may be summarized as follows: 1.
Unoriented, plasticized VYNW and Geon 101 films yield
