Thermal Expansion Properties of '
PLASTIC MATERIALS R. 4.e&,
ab.,d
~ M. R-.
CARBIDE A N D C A R B O N CHEMICALS C O R P O R A T I O N , N E W YORK,
N. Y .
The test specimens were rods approximately 15 em. X 6 mm. X 6 mm., with rounded edges. They were weighed and sealed into the bulb (Figure lB), which was then weighed and filled with mercury by a simple vacuum technique. The level of the mercury in the capillary was adjusted to a convenient height (usually about 20 cm. on the scale a t room temperature) by introducing a clean piano wire to remove excess mercury. The tube was then reweighed and the scale attached, as in Figure 1C. The length, LO,of the capillary between the stem mark (which fixes the depth of immersion) and the scale zero was measured to *0.5 mm. Two procedures were followed. I n the first, the bath temperature was held constant, the apparatus immersed to the stem mark, and the level of the mercury meniscus. X . read a t 5-minute intervals until it had remained constant for 10 minutes. The bath temperature was then adjusted to the next desired value and the X reading taken. I n this type of run, readings were usually taken a t intervals of 10" C. I n the second type, the bath temperature was continuously varied a t a maximum rate of 0.5' C. per minute and X readings wereo taken at intervals of 5 . Except a t temperatures fairly near ( * 10' to 20" C.) the transition interval, the readings obtained by the two methods did not differ significantly, regardless of the direction of temperature change. Since the latter method is usually more rapid, it was employed in all recent work.
A simple dilatometer technique for determining the volume-temperature relations of plastics is described, and data are reported for a number of thermoplastic materials. Cubical expansion coefficients have been calculated below and above the observed transition temperatures, and the effect of plasticizer addition on these properties is reported. Polyethylene shows expansion characteristics similar to those of paraffin wax but appreciably different from those observed for the other thermoplastics studied.
HE object of this investigation was to determine the volumetemperature relations of a number of commercial and experimentally compounded plastic samples, in order to extend the scope of knowledge of their thermal behavior and of the effects of certain compounding ingredients on that behavior. When a liquid is cooled to and below its freezing temperature, one of two things may occur. There may be a separation into a solid and a liquid phase which coexist at the freeaing point, or there may be, without the appearance of any second phase, an increasingly rapid rise in viscosity (8) which continues until the liquid becomes so rigid that for most purposes it behaves as a solid. Crystalline materials exhibit the former behavior, amorphous materials the latter. Many properties (such as volume, dielectric constant, index of refraction, and others) often show an approximately linear dependence on temperature for the liquid, for the crystalline solid, and for the amorphous solid. During the transition from liquid to solid, these properties behave in a characteristic way for each of the two types of transformation. If a crystalline solid is formed, two phases are present and the properties change discontinuously; in the formation of an amorphous solid where only one phase is present, the properties change rapidly but continuously from those of the liquid to those of the solid. The first differentials with respect to temperature of such properties, constant for the liquid and for the solid, also change continuously during the transition. It has been suggested that such a transition may correspond to the acquisition by the molecules of a new degree of freedom, probably a vibrational or rotational one. According to Ueberreiter (S), a macromolecule whose links are rigid can be softened in two ways. Inner softening involves substituting highly mobile links for some of the rigid ones, as in the copolymerization of vinyl chloride and vinyl acetate. Outer softening is effected by solvents and plasticizers, whose molecules penetrate the macromolecule, form solvate casings around active parts of the chain links, and increase mobility by saturating internal chemical forces. He suggests the use Qf volume-temperature curves for evaluating softening agents.
T
EXPERIMENTAL PROCEDURE
The apparatus used was a glass dilatometer (Figure 1). The capillary part is approximately 1 meter long X 6 mm. 0.d. X 0.7 mm. bore; the bulb member is approximately 20 om. long x 9 mm. 0.d. X 1 mm. wall. I n use, the bulb and lower part of the capillary were immersed to a h e d depth in a bath (dry iceacetone below 10' C., water between 10" and 95' C., and oil, above 95' C.) whose temperature was regulated to * 0.1' C. 279
In the transition interval (except for paraffin and polyethylene, where the interval was much longer than the region of varying X A B c values), equilibrium was not attained and the Figure I. Glass Dilatometer values of X for a run inwhich the temperature was dropping were generally somewhat higher than those obtained when the temperature was rising. Since these X values were not involved in the determination of expansion coefficient and transition temperature, it was not thought profitable to attempt determination of the equilibrium values. Knowing the mass and density of the sample, the mass of mercury in the system, and the cross section area, A , of the caoillarv, - . the volume of the system below the stem mark at any temperature, t , was readily calculated.
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
280
Vol. 36, No. 3
*-DIOCTYL PHTHALATE o -T RI C R ESY L PH0 SP HAT
I"
? Q o
IO 20 PER C E N T ADDITION AGENT
0
Figure 2.
u, =
mass of sample mass Hg density of sample + density Hg
IO 20 PER C E N T ADDITION AGENT
Transition Temperature VI. Percentage Addition Agent
- A(Lo
+
X)
The change in volume of the system, Au,, over any temperature interval At, is equal to
where 0% V
Avs = Avo A u ~= Avm -I- A V = volume of mercury = =
30
which is roughly proportional to the weight percentage of addition agent. It was suggested that this lowering might be analo-
TABLE I. EFFECTOF ADDITION AGENTSON CUBICAL EXPANSIO~ COEFFICIENTS AXD TRSXSITION TEMPERATURES
- A(Xt, - XI,)
volume of glass bulb volume of plastic sample
( S o emergent stem correction was made. Runs made with systems containing only mercury shovied a straight-line X US. i function.) Then
- Xil) - (t, - t i ) ( a m ~ m -LY~u,) cubical expansion coefficient of mercury 0 1 ~ = cubical expansion coefficient of glass VI* Vci 4- AV
Addition Agent
CY,,,
None Dioctyl phthalate
=
For ready comparison between different samples of the same material, we have chosen t o use the relative volume of the sample; that is, Brat. = VtPO where V o = volume of sample a t 0" C. Vrel,ws. t was graphed. The slope of this curve at any point is the cubical coefficient of expansion of the sample at that temperature; its value for straight-line portions of the curve was determined by applying the method of least squares. ta, the transition temperature, was defined as the temperature intersection of two such adjacent portions. RESULTS AND DISCUSSION
Table I gives cubical expansion coefficients, 011 and 012 (respectively, below and above transition temperature ta), for a series of VYNS vinyl chloride-acetate resin compounds of varying plasticizer content. 6 is the difference between the transition temperature of the base compound (no plasticizer) and that of the compound in question. Figure 2 shows a plot of transition temperature against percentage plasticizer for this series. Table I also gives the effect of plasticizer additioh on V Y S W vinyl chloride-acetate and XYSG polyvinyl partial butyral resins. The influence of plasticizer content on transition temperature for these compounds is also illuatrated in Figure 2. As Table I and Figure 2 show, all addition agents except aluminum hydroxide cause a lowering of transition temperature
4o' r
("
C.)-i
a2
("
VYNS Vinyl Chloride-Acetate Resin Lubricant and Stabilizer Addition Agent Total
AV = A ( X t ,
where
Wt.
Aluminum hydroxide AlzOa.3HzO Dibutyl sebacate Butyl Cellosolve phthalate Tricresyl phosphate Dow KO.7
0 5 10
15 20 25 10 20 30 5
5
5 5
10
207 215 198 227 239 259 206 171 177 199
x
108
C.)-i 100
La,
- 2.5
Butyl Cellosolve phthalate Trioresyl phosphate Dibutyl sebacate Triglycol di-(Z-ethylhexoate)
C.
Y (by wt.) Y
100
58.7 0 47.3 11.4 30.3 28.4 21.8 36 9 10.2 48.5 -1.9 60.6 506;523a 5 7 . 5 ; 6 2 . 0 1 . 2 ; - 3 . 8 520;576a 5 3 . 4 ; 5 7 . 7 5 . 3 ; 1 . 0 454;49Ba 54.6;fiO.Q 4 . 1 ; - 2 . 2 567 39.2 19.5
181 196 191 216
584 607 560 583
46.8 49.2 52.2 53.1
11.9 9.5 6.5 5 6
-
100 - 2 2
Y
Y
100
0 10 20 30
194 267 252 339
511 562 581 632
63.2 39.3 10.4 -3.7
0 23.9 52.8 66 9
10
237 221 329 223 210 282 277 31:
612 600 648 581 582 658 662 620 642
42 .O 7.8 -2.8 44.2 20.1 6.3 39.1 2.1 -24b
21.2 55 4 65.0 19.0 43.1 56.9 24.1 61.1
282
579
41.7
20 30 10 20 30 10 20 30 10
XYSG Polyvinyl Butyral Resin Lubricant and Stabilizer Addition Agent Total None Triglycol di-(g-ethyl butyrate)
-
6,
557 633 596 610 570 642
VYKW Vinyl Chloride-Acetrtte Resin Lubricant and Stabilizer Addition Agent Total None Dioctyl phthalate
2.5
C.
0
236
100
- 44
.
87 b
21.5
- Y Y
100 692
50.1
0
20 328 720 14.5 35.6 31 519 712 -3.9 54.0 a Unlike the others, alu,m,inum hydroxide compounds show markedly different values of OL for the initial and second runs. Transition temperature was so low t h a t not enough points were obtained to determine (11. la w m estimated from the graph a n d i s only approximate.
March, 1944
-40
Figure 3.
-20
INDUSTRIAL AND ENGINEERING CHEMISTRY
0 20 40 60 80 100 TEMPERATURE, DEGREES CENTIGRADE
120
Relative Volume vs. Temperature for Resins AYAT, VYCF, and QYNA
281
solution is not usually considered dilute. Also, the amounts of lubricant and stabilizer added were of the same order of magnitude as those of plasticizer, and the effect of this addition on the transition temperature is unknown. It may be as great as that of the plasticizer. For these reasons the effect of plasticizer addition cannot be examined on a quantitative basis until further data have been obtained. Qualitatively it appears t o be of the same nature as the lowering of the freezing point. If plasticizer addition has any simple effect on expansion coefficient, the data fail to make it evident. It may be that a1 is raised by addition of plasticizer; but the 011 values at 10% plasticizer content with VYNS resin and a t 20y0 with VYNW must then be assumed t o be far in error. Again, the effects of lubricant and stabilizer were not evaluated. 012 appears to be insensitive to plasticizer addition. Table 111 gives a ~ a2, , and t, for a number of different resins. Figure 3 shows Vrez. us. t for three of them; these VTez.values were displaced by the amounts indicated in order t o prevent the three curves from overlapping,
gous to the lowering of the freezing point observed with solutions. Accordingly, a comparison of 8, the depression of the transition temperature, with the molecular weight of addition agent at a fixed weight percehtage was made (Table 11). e increases as the molecular weight decreases for 5% by weight plasticizer addition in VYNS resin. The relation is less clear for the case of 10% plasticizer in VYNW resin. However, the equation e = Kjm where e = depression of freezing point KJ = constant characteristic of solvent m = total solute molality applies strictly only to solutions which are both ideal and dilute.
Figure 5.
Relative Volume vs. Temperature for Polyethylene and Paraffin Wax
Table I11 also gives al,CYZ, and ta for the compounds (A.S.T.M.) whose Vret, vs. t curves appear in Figure 4. A number of them show protracted transition intervals which could be interpreted as intermediate linear segments of the VTct.us. t curve, According to this interpretation which was originally adopted, these materials ’would show two transitions. However, Carswell ( 1 ) pointed out that the interpretation shown graphically was equally logical and corresponded much better to that used for other similar plastics,
TABLE 11. CHANGEIN TRANSITION TEMPERATURE FOR DIFFERENT ADDITION AGENTS 7
‘46
-!20
Figure 4.
2b 4b 6b
’
TEMPERATURE 20 100 120 140 TEMPERATURE, DEGREES CENTIGRADE ’
’’
Relative Volume vs. Temperature for A.S.T.M. Samples
Base Resin VYNS
%
VYNW
10
5
Addition Agent Name Mol. wt. 314 Dibutyl sebacate Butyl Cellosolve phthalate 366 Dioctyl hthalate 391 Trior esyr phosphate 400 Dow No. 7 495 Dibutyl sebacate 314 Butyl Cellosolve phthalate 366 Dioctyl hthalate 391 Tricreey? phosphate 400 Triglycol di-(2-ethyl hexoate) 403
C. 19.5 11.9 11.4 9.5 6.5 24.1 21.2 23.9 19.0 21.5
6,
The latter part of Table I11 and Figure 4 cover a set of A.S. T.M. “round robin” samples which were also reported by Wiley (4), who used a gravitometric method. Agreement between the two methods on these samples was poor. To some extent this may result from the fact that his samples were conditioned to remove water, whereas ours were run “as received”.
INDUSTRIAL AND ENGINEERING CHEMISTRY
282
TABLE 111. CUBICALEXPANSION COEFFICIENTS AND TRANSITION TEMPEIZATURES OF VARIOUS RESINS (I1 x 106, (I2 x 106
Resin AYAT polyvinyl acetate XYSG polyvinyl partial butyral F C F Vinyon C F Y N A polyvinyl chloride MS-A-85 polystyrene
( 0
C.) - 1
(0
232 236 206 202 211
A.S.T.M. Samples Cellulose acetate, B-96 326 Cellulose acetate C-23 325 Cellulose acetate broDionate. CP-I 3 57 Cellulose apetate-butyrate, AA-5 419 Cellulose nitrate F-2 265 206 Methacrylate, K-24 207 Methaor late, Y-6 Vinyl chibride-aoetate L-9 171
C.) 694 692 562 670 589
696 677 569 708 514 593 767 590
-:
ta,
O
c.
24.9
50.1
64.6 75.0 78.0 68.6 49.2 38.8 49.9 52.6 55.0 94.9 48.2
Figure 5 shows Vre~. os. 1 curves for polyethylene resin and paraffin wax. Expansion coefficient values were not determined for the paraffin, which was run only for comparison. For the resin above 115" and at least t o 150" C., Vfilei. us. tis a straight-line function corresponding t o an expansion coefficient value of 012 = 762 X 1 0 - 6 ( " C.)-1. Below 110" C. the curve was found t o fit an equation of the form:
v,.i.l. = 0.9773 where T = temperature,
e3.664
' K.
(T -
186)2
X
Vol. 36, No. 3
Differentiating this equation with respect to T yields a, Values for polyethylene resin as calculated from the above equation, for temperatures below 115' C., follow: CI x 106, a x 106, a x 106, t , c. -35 -20 0
( 0
t,
C.) - 1 302 413 563
c.
20 40 60
80
C . )-1 719 88 1 1020 1230
t,
(0
c.
100 110 115' and above
(0
C.)-1
1420 1550 762
Polyethylene and paraffin behave very differently from all other plastics so far tested in this laboratory. The width of the transition interval appears t o be greatly increased until, for polyethylene, it extends over the greater part of the measured temperature range (from -35" to 115' C.). Over an appreciable portion of the transition interval the expansion coefficient is much higher than it is immediately above the interval. So far as has been determined, the drop in a appears t o be nearly discontinuous. Both paraffm and polyethylene soften so sharply that the softening temperature is frequently referred t o as a melting point. For samples tested in this laboratory, this temperature corresponds wit,hin 1" or 2' t o the upper end of the transition interval. LITERATURE CITED
(1) (2)
Carswell, T. S., private communication. Tamman, Gustav, "Der Glaszustand", Leipzig, Leopold Voss, (1933).
(3) Ueberreiter, Kurt, Angew. Chem., 53,247 (1940). (4) Wiley, F. E., IND.ENG.CREM., 34,1052 (1943).
VOLUMETRIC BEHAVIOR OF 'n-BUTANE R. H. OLDS, H. H. REAMER, B. H. SAGE, AND W. N. LACEY California Institute of Technology, Pasadena, Calif.
M
ODERN developments in petroleum production and processinghave directed interest ' to the behavior of hydrocarbons and their mixtures at somewhat higher pressures than were covered in earlier investigations. As a component of hydrocarbon fluids, n-butane has sufficient industrial importance to justify volumetric measurements in an increased pressure range. The vapor pressure of n-butane at several temperatures between 160" and 300" F. was accurately measured by Beattie, Simard, and Su ( I ) , who determined the critical constants and the volumetric behavior at pressures up to 5000 pounds per square inch in the temperature interval from 300" to 600" F. (8). Later Kay (3) studied in detail the volumetric and phase behavior of n-butane at pressures up to V
V
V
(Left) Figure 1. Isochoric Pressure-Temperature Diagram for Liquid n-Butane
