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A study of the crystallization process in oriented amorphous polyethyleneterephthalate
Crystallization process in oriented amorphous polyethyleneterephthalate
423
(7) It has been established that the principal factor favouring the amorphous state in non-crystallizing polycarbonates is not the rigidity of the polymer chain, but rather the impossibility of achieving the required packing density, that is, the effect of a steric (conformational) factor. Translated by G. F. MODLEN REFERENCES 1. P.V. KOZLOV, G.I. BRAG]NSKII, Khimia i tekhnologiya polimernykh plenok (Chemistry and Technology of Polymer Films). Izd. "Iskusstvo", 1965 2. H. SCHNELL, Angew. Chemie 68: 633, 1965 3. V. A. KARGIN, N. F. BAKEYEV and Kh. VERGIN, Dokl. Akad. Nauk SSSR, 122, 97, 1958 4. V. A. KARGIN, A. A. EFENDIYEV and Z. Ya. BERESTNEVA, Tezisy X V I I Vsesoyuznoi konferentsii po polimeram (Preceedings of XVIIth All-union Conference on Polymers). Leningrad, 1964 5. N. F. B,AI~EYEV, ZhVKhO im. D. I. Mendeleyev 6: 630, 1964 6. A. I. KITAIGORODSI~H, Bold. Akad. Nauk SSSR, 124, 861, 1959 7. A. N. PEREPE1LKIN and P. V. KOZLOV, Vysokomol. soyed. 8: 51, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 1, 57, 1966) 8. L. MANDEL'KERN, Uspekhi khimii, 27, 193, 1958 9. A. PRIETZSCHK, Kolloid.-Z, 156: 8, 1958
A STUDY OF THE CRYSTALLIZATION PROCESS IN ORIENTED AMORPHOUS POLYETHYLENETEREPHTHALATE* L. G. K ~ x R x ~
and D. YA. TSV~XKZN
Institute for Elementary Organic Compounds, U.S.S.R. Academy of Sciences (Received 19 March 1966)
POLYETHYLEI~1"ETEREPHTHALATE(PETP) is a very suitable material for studying the process of crystallization, since the glass temperature of P E T P is approximately 80°C, and specimens may easily be obtained at room temperature with different degrees of crystallinity, including oriented films, ranging from textured amorphous films to films having a crystalline texture [1]. This gives rise to the possibility of studying the crystallization process in oriented specimens, in which the starting point is a structure of a type of amorphous texture, in which a three-dimensional lattice is completely absent but the molecules are, nevertheless, parallel one to another. The character of the positioning * Vysokomol. soyed. A9: No 2. 377-384, 1967.
424
L. (3. KA~RYAN and D. YA. TSVANKIN
o f the chains in t h e a m o r p h o u s oriented film h a s b e e n studied p r e v i o u s l y [2] b y m e a n s of X - r a y diffraction a t large angles. F u r t h e r , t h e b r e a k d o w n o f ordering in the a m o r p h o u s t e x t u r e a n d t h e kinetics of t h e crystallization processes in various P E T P specimens h a v e been i n v e s t i g a t e d b y m e a n s o f nuclear m a g n e t i c r e s o n a n c e [3, 4]. The principal a i m of t h e p r e s e n t work, which is a direct c o n t i n u a t i o n o f these investigations, is t h e s t u d y o f s t r u c t u r a l changes during t h e process of c h a n g i n g o v e r f r o m t h e a m o r p h o u s t e x t u r e to a crystalline axial t e x t u r e . S o m e papers, in w h i c h v a r i o u s m e t h o d s o f i n v e s t i g a t i o n h a v e b e e n u s e d [5-9] h a v e b e e n d e v o t e d to the s t u d y of t h e crystallization process in P E T P . H o w e v e r , in these p a p e r s o n l y t h e crystallization o f u n o r i e n t e d specimens h a s b e e n studied, whereas t h e process o f crystallization in a n a m o r p h o u s t e x t u r e h a s n o t b e e n s t u d i e d in detail u p to now. Low-angle diffraction o f X - r a y r a d i a t i o n w a s u s e d p r i n c i p a l l y in s t u d y i n g t h e crystallization process in the oriented condition; b y this means, changes in large i d e n t i t y periods were s t u d i e d during crystallization. I n i n t e r p r e t i n g t h e large i d e n t i t y periods a n d in t h e d e t e r m i n a t i o n o f crystallite dimensions a n d degree of c r y s t a l l i n i t y b y m e a n s of t h e m , use was m a d e o f t h e o r e t i c a l i n t e n s i t y d i s t r i b u t i o n curves a n d of the corresponding calibration g r a p h s [10].
EXPERIMENTAL Film of amorphous oriented P E T P was obtained from a film of amorphous unoriented P E T P by 700~/o stretching in a thermostat at 70°C. Further, to study the crystallization process in an amorphous oriented film, three series of films were prepared, which were crystallized at 140, 180 and 220°C with different times at those temperatures. The crystallization of the oriented films was carried out in the unrestrained condition. The temperature in the thermostat was held with an accuracy of ± 2°C. After annealing, the specimens were cooled to room temperature. A camera with a Kratki type collimator and ionization recording (Geiger counter) was used to study the low-angle scattering of the X-ray radiation. The distribution of intensity along the texture axis was studied. Therefore, in all cases the incident beam was positioned perpendicular to the texture axis of the specimen. The specimens for the low-angle exposures took the form of packs made up of piled-up individual films. In order that one could compare the scattered intensity curves for the various specimens with each other, the scattering mass for all the specimens was approximately the same, this being checked from the absorption of the X-ray radiation in the specimens, To calculate the lattice parameters of crystallized specimens, an X-ray exposure was made at large angles in a RKU-I14 camera, the specimen being rotated about its texture axis. Interplanar spacings were measured on a comparator. In the calculation of the interplanar spacings, corrections were introduced in the camera radius and for the specimen absorption by the method described in reference [11]. Three diffraction photographs were taken for each specimen, the adjustment of the specimen being carried out anew each time. The average scatter in the parameter values is :t:0"015 ~. All the X-ray exposures were made with copper radiation and a nickel filter. The intensity curves and the low-angle diffraction photographs showed that in all cases there is a low-angle reflection in the form of a stripe along the meridian of the X-ray photograph. To treat the scattering curves and to determine the crystallite dimensions
Crystallization process in oriented amorphous polyethyleneterephthalato
425
a n d the dimensions of the amorphous regions, a method based on theroretical scattering curves was used [ 10]. The treatment of the low-angie curves, the separation of the background, the calculation of the true width of the scattering m a x i m u m and the calculation of the parameters kl, c, a, l were carried out b y use of the method described in references [10, 12] (a is the average dimension of the crystalline regions; 1 is the average dimension of the amorphous regions; c-~a-}-l is the identity period along the axis of the fibrils; k ~ a / c is the crystallinity (%)). The q u a n t i t y d~-2/20 (the large identity period) is determined directly from the position of_the m a x i m u m on the scattering curve. The value of the intensity at the m a x i m u m after its separation from the background was taken as the value typifying the intensity of the large identity period (1 in Tables 1 and 4). The density of the specimens was measured by the hydrostatic weighing method with an accuracy of ~=0.001 g/cm 3 at 20°C.
INTENSITY OF LOW ANGLE SCATTERING Before going on to discuss the results, we shall derive a formula by moans of which one m a y assess the intensity of a low-anglo reflection. Since the m a x i m u m in the low-angle scattering, corresponding to the largo identity period, arises because of interference of waves scattered b y the individual crystaUites in the fibril, the intensity I ought to be written in the following way I=Nn*~ (sin 0/2), (1) whore N is the n u m b e r of crystallites in the specimen; n is the excess of electrons in the crystallito as compared with the amorphous part; ~ ((sin 0/2) is a scattering function, calculated for a single crystallite; 0 is the diffraction angle; 2 is the wavelength. The function ¢ ( s i n 0/2) depends on the degree of erystaUinity [10]. I f the erystallinity changes from 60 to 65%, the form of the function hardly changes at all. TABLE 1.
T, °C
QUANTITIES
Duration of crystallization, m i n
140
180
200
5 15 30 60 240 5 15 30 60 240 360 5 15 30 60 240
OBTAINED
g POX " - cm $
FROM
THE
LOW-ANGLE
SCATTERING
CURVES
Ij
d,A
c,A
a,A
1, A
kl, %
impulse sec
1.367 1.370 1.375 1.380 1.385 1-386 1-385 1.378 1.383 1.391
1.393 1.396 1.401 1.405 1.406 1.408 1-408 1.409
101 98
m
120 112.5 114 110 108,5 111 109 113 125 126 125.5 125 150 150 145.5 145 152
66.0 67.5 69.5 71.5 69"5 72.5 67.0 73.0 81.0 84.0 83.5 82.0 95.0 96.0 96-0 95.0 102.0
54'0 45.0 44.5 38.5 39.0 39.0 42.0 40.0 44.0 42.0 43.0 43.0 55.0 55.0 49.5 50-0 50.0
55 60 61 65 64 65 61 65 65 67 67 66 63 63 66 66 67
1.5 2.2 3.5 6.5 7.0 7"0 7"5 5.8 8.5 11.5 16.0 17.5 17.5 28 29 3O 32 32
426
L.G. KAz~Y~
and D. YA. TSVA~Xn¢
The n u m b e r of crystallites in a substance m a y be expressed as a ratio of the volume of the entire crystalline phase (Vcr.ph) to the volume of a single erystallite (Vcr)
N = Vcr.ph/Ve,:=k V,p/V~,:
(2)
where Vsp is the volume of the entire specimen mad /c is the degree of crystallinity. The excess of electrons (n) is equal to the product of the erystallite volume and the difference between the densities of the ez.ystalline (Per) and amorphous (Pa) regions
n = Ver(pcr- pa).
(3)
By substituting equation (2) and (3) in equation (1), we obtain
I=kVspVcr(Pcr--Pa)2q~(sin 0/2) .
(4)
Since Vsp=M/p where M is the mass of the entire specimen and p its density, then
I = (KM/p) Ver(Per-- pa)2~ (sin 0/2) .
(5)
Since we have determined intensities only in relative and not in absolute units, we have calculated a ratio of intensities; it was thus assumed that both M and also ~(sin 0/2) remain constant. It
I2
kxP=Va'cr (Pl'cr-- Pa)2 k=PlV=,cr(P2,cr-- Pa) 2
(6)
I n calculating the ratio (6), it m a y be assumed that Vcr~aS, whore a is the crystallito size; hence the ratio of the intensities m a y be written in the following form:
11 kxp=aSt(pl,cr-- pa) 2 1--~= k,,pla~ (p2.er--ps) 2
(7)
DISCUSSION OF RESULTS
No maximum is observable on the low-angle scattering curve of the initial oriented amorphous P E T P film, and consequently this film does not have a large identity period. As the duration of annealing increases, the corresponding maxim u m on the curve appears and gradually increases. Low angle scattering curves along the texture axis are shown in Figs. 1, 2 and 3 for specimens of oriented PETP, crystallized under different conditions. The results of the measurements together with all the quantities obtained by treatment of the low angle scattering curves are shown in Table 1. The intensity of the scattering depends strongly on the density of the specimen. A specimen with a density of 1.367 g/cm 3 gives such a weak maximum that it is difficult to distinguish it from the background (Fig. 1), whereas the X-ray diffraction photograph of this specimen (crystallization temperature 140°C, time of crystallization 2 min) at large angles points to the presence of a complete three-dimensional ordering. A detailed study of the scattering curves and the determination of the quantities a, l, k z was carried out for specimens crystallized at 140, 180 and 220°C, having a density of not less than 1.370 g/cm 3.
Crystallization process in oriented amorphous polyethyleneterophthalate
427
The specimens crystallized at 140°C (Fig. 1) all have the same large identity period d, approximately equal to 100 A (Table 1). The quantity c=a+l is always somewhat larger than d [10, 12]. I t is also roughly constant and equal to 110 A. With an increase in the crystallization time, an increase in the density of the sample occurs, this being accompanied by an increase in intensity by a factor of 5, by an increase in the dimensions of the crystalline regions from 66 to 71 A, and by a reduction in the dimensions of the amorphous regions from 54 to 39/~. This leads to an increase in crystallinity from 55 to 65%. Annealing the specimens for 30 min, 1 hr and 4 hr at 140°C leads to the same density, to the same crystallinity, and to the same intensity of reflections.
!
10
I
,30
I
I
50
t
I
70
I
1
I
8g 20,mia
FIe. 1. Low-angle scattering curves for PETP specimens, annealed at 140°C for: 1--2 rain, 2--4 min, 3--5 min, 6--30 min, 7--1 hr, 8--4 hr. As the recrystallization temperature is raised, the large identity period increases. At 180°C (Table 1, Fig. 2) the large identity period reaches 120 A, and the dimensions of the crystalline regions become 85 A. With an increase in the duration of crystallization, the same changes are observed as were observed at 140°C. The density of the specimens increases, the scattered intensity increases, and the degree of crystallinity rises from 61 to 67%. Crystallization of specimens at 220°C (Fig. 3) leads to a further increase in d to 140 A (Table 1). The average dimensions of the crystalline and amorphous regions increase to approximately 95 and 50 /~ respectively. Thus the crystallinity k 1 hardly changes at all. However, at 220°C the intensity of the reflection rises by a factor of 4 as compared with 140°C, and by a factor of 1.5 as compaxed with 180°C. During annealing at 220°C, the density of the specimens depends little on the time of annealing, changing from 1.405 g/cm a at 5 min annealing to 1.408 g/cm a at 6 hr annealing. In this way, with an increase in crystallization temperature both the large identity period and also the dimensions of the crystalline and amorphous regions increase. Such a phenomenon is similar to the changes during the an-
L. G. KAZARYAN and D. YA. TSVANKIN
428
nealing of specimens previously crystallized [12]. As m a y be seen from Table 1, the crystallite dimensions depend principally on the crystallization temperature, whereas the intensity of the low-angle reflection depends both on temperature and on the time of crystallization to the same extent. Thus the typical crystal-
30
25
4
2O
15 3 75 10 10
5
5
I0
I
I
I
I
I
I
JO
50
70
SO 28,mZa
10
30
FlO. 2
I
50
I
70
,9020,m/n
FIG. 3
FIG. 2. Low-angle scattering curves for PETP specimens, annealod at 180°C for: 1--5 rain, 2--15 rain, 3--30 min, 4--1 hr, 5--6 hr. FIG. 3. Low-angle scattering curves for PETP specimens, annealed at 220°C for: 1 - - 5 rain, 2 - - 1 5 rain, 3 - - 3 0 rain, 4--1 hr, 5--4 hr. lite dimension obtained at 140°C is 70 -~, at 180°C, 80A; and at 220°C, 95 A. This phenomenon is especially clearly seen from the data for crystallization at 140 and 220°C. During crystallization at 180°C, the crystallites grew from 70 to 80 _~, that is, b y a factor of 1.14. However, the scattered intensity thus rose much more rapidly, increasing b y a factor of 2.66. With a change in the crystallization time and temperature, an increase takes place in the density of the entire specimen (Pex) from 1.370 to 1-408 g/cm s. Know-
Crystallization process in oriented amorphous polyethyleneterephthalate
429
ing the dimensions of the crystalline and amorphous regions and the density of the entire specimen, we calculated the density of the crystallites from the formula f l : (flex ( a - - ~) - - fla ~) c~-1
(S)
with the supposition that the density of the amorphous regions was equal to the density of amorphous P E T P in the initial (1.336 g/cm a) or in the oriented (1.360 g/cm 3) P E T P . The values of the densities calculated, Pl with pa=1"336 g/cm a and p~ with p a = l ' 3 6 0 g/cm a, which are shown in Table 3, indicate that an increase in the density of the crystallites takes place at the same time as the increase in the density of the entire specimen Pex" The density of the crystallites m a y be calculated from the parameters of the unit cell, which m a y be determined by means of the diffraction photographs taken at large angles. The parameters a and b were determined from the interplanar spacings dl0o and do10. Oblique X-ray diffraction photographs were taken to determine the identity period along the axis of the molecule; from these it was seen that the parameter c does not change during crystallization (c= 10.75 •). The change in the parameters a and b during the crystallization of P E T P leads to a shift in the intensity maximum of the equatorial reflections in the direction of larger angles. It has however been shown [13], that a shift in the positions of individual interferences m a y also take place because of a structural factor if the number of cells in the crystallite parallel to a particular axis is small. With an increase in the number of cells, the maximum is shifted in the direction of larger angles. We calculated the intensity of the 100 P E T P reflection for a crystallite with a number of chains ranging from 2 to 16. The calculation showed that the maximum in the intensity of the 100 reflection is only shifted if the crystallite has a small number of chains. I f the number of chains or cells in one direction is greater than 8, then this shift disappears. The smallest erystallite dimension which we had obtained (Table 1), is 68 A. The crystallite dimensions obtained from the width of the 100 reflection by means of the Seherrer formula without taking imperfections into account, is 64 A. I f the interplanar spacing for the 100 reflection is equal to 3-5 A, then the number of chains in this direction will be equal to 18. Consequently, even in the case of the most poorly ordered crystallite no shift in the reflection ought to take place as a result of erystallite dimensions, and the observed shift in the equatorial reflections in the direction of larger angles can take place only as a result of a reduction in the dimensions of the unit cell. The lattice parameters a and b, and the volume of the unit cell calculated from them and the crystallite density given by the X-ray measurements (Px-ray) are shown in Table 2. The change in the lattice parameters of unoriented P E T P as a function of annealing temperature has also been studied by Kilian et al. [14], who obtained very low values for the parameters of highly crystalline PETP;
430
L . G . KAZARYAIqand D. YA. TSVANKIIV
this leads to a the P E T P cell of 1.455 g/cm a 1.454 g/cm a, in
m a x i m u m density value of 1.495 g/cm a whereas, according to parameters calculated b y D a u b e n y a n d B u n n [15], a density is obtained. The m a x i m u m density according to our d a t a is satisfactory agreement w i t h the results of reference [15]. TABLE 2. CELL PARAMETERS
Crystallization conditions T, °C
time, min
140
5 15 60 240 5 15 60 360 60
180
220
dloo,/~.
3"53 3"48 3"46 3"47 3"49 3"49 3"48 3"47 3"45
dolo,
5'13 5"12 5"10 5"10 5"10 5"09 5"09 5"08 5.07
d11o,
a,A
b,A
V, ~8
g PX-ray cm s
3.98 3-98 3.94 3.95
4"62 4"58 4"56 4"57 4"60 4"60 4"58 4"57 4"55
6.04 6.02 6.00 6-00 6.00 5.99 5.99 5.98 5.96
225.6 222.9 221.2 221.7 223.1 222.7 221.8 220-4 219.2
1.410 1.430 1.441 1.438 1.429 1.431 1.437 1.446 1.454
3-98 3-96 3.95 3-95 3.95
The d a t a of Table 2 indicate t h a t in all cases an increase in the density of the entire specimen Pex is accompanied b y an increase in the density of the crystallite. L e t us now compare the densities Pl a n d p~, calculated b y means of formula (8), with Px-ray" I t is clear t h a t the results for Pl, obtained with pa=1"336 g/cm a, are in the closer agreement, which is evidence in favour of the density of the amorphous portions being equal to 1.336 g/cm a. B y means of PX-ray, o n e m a y determine the crystallinity k s from the following formula: /C2~ [(Pex--,Oa)/(PX.ray--,Oa)]" 100% (9) with the assumption t h a t pa--1"336 g/cm a. Usually, the determination of the crystallinity from densities is also m a d e from formula (9), but, in place of the different values of Px-ray, the value for the density calculated from the lattice parameters of the most highly crystallized specimen is adopted. The crystallinity lca calculated in this w a y is also shown w i t h k 1 a n d k 2 i.n Table 3. F r o m Table 3, it m a y be seen t h a t the values of k s are closer t h a n those of/c a to the values of k 1 . The differences in the crystallinity values k s and/Cz m a y n a t u r a l l y be explained b y the fact t h a t in the calculation of kl using reference [10], it was assumed t h a t the specimen consists of amorphous-crystalline fibrils, w i t h o u t a n y intermediate a n d transitional zones; an additional explanation is t h a t the density of the crystallites m a y be •considerably less t h a n PX-rar, because of the presence of p a r t l y ordered interm e d i a t e regions, a n d also because of the presence of pores of various sizes.
431
Crystallization process in oriented amorphous polyethyloneterophthalate TABLV.3. DENSITY OF CRYSTALLITESAND DEGREE OF CRYSTALT.,INITY Crystallization conditions T, °C 140
180
220
time, rain 5 15 60 240 5 15 60 360 60
g g g Pl,cm~ P~,c-~7 PX-ray, g Pex, cm 3 with with cm a pa= 1"336 pa= 1.360
kl, %
1.401 1'408 1.414 1.411 1.403 1.408 1.426 1.435 1.445
i
1.387 1.393 1.401 1.394 1.391 1.401 1.416 1.426 1.431
ks, %
50 47 48 48 45 50 56 59 61
32"5 37 42 41 35 39 48 54"5 60"4
t
I
1.375 1.380 1.386 1.385 1.378 1"383 1-393 1.401 1.408
k2, %
60 61 64 65 61 65 67 66 66
1.410 1-430 1.441 1.438 1.429 1.431 1.437 1.446 1.454
T h e change in the density o f the crystallites is also a reason for t h e change in the i n t e n s i t y of the low-angle scattering (Table 1). W e carried out a calculation of t h e ratio of t h e intensity, using f o r m u l a (7), w i t h the help of the d a t a o b t a i n e d from the diffraction p h o t o g r a p h s a t low a n d large angles. Since the c r y s t a l l i n i t y (kl) of our specimens varies f r o m 60 to 65%, a n d the density of t h e specimens varies f r o m 1.380 t o 1.408 g/cm 3, t h u s t h e smallest change in the q u a n t i t y is klpflk2pI = 1.05. Consequently, the r a t i o o f the intensities m a y be calculated f r o m t h e f o r m u l a
II112---- aa~(Pl.cr-- Pa)2/a32(Pi,cr - - Pa) 2
(10)
I n calculating the i n t e n s i t y o f the low-angle s c a t t e r i n g b y m e a n s of f o r m u l a (10) we assumed t h a t the density of t h e a m o r p h o u s p a r t s was equal to t h e density of the initial a m o r p h o u s P E T P (1.336 g/cma). TABLE
4. RATIO
Specimen
I(220 °, I(220 °, I(220 °, I(180 °,
i hr)/I(180 o, 6 hr) 1 hr)/I(180 °, 6 hr) 1 hr)/I(180 °, 5 min) 6 hr)/I(140 °, 5 min)
OF THE LOW-ANGLE I 1 --9
REFLEXION
INTENSITIES
I 1
Specimen
I2 '
exp.
calc.
1"86 3"75 5"2 5"3
1"63 3"55 4"8 5"0
1(220 °, I(220 °, I(180 °, 1(140 °,
1 hr)/I(140 °, 5 rain) 1 hr)/I(140 °, 4 hr) 6 hr)/I(140 °, 4 hr) 4 hr)/I(140 °, 5 min)
IL 12 '
K'
oxp,
ealc.
9.4 4.5 2.4 2-1
8.5 3.4 2.0 2.3
I1
T h e satisfactory a g r e e m e n t b e t w e e n t h e calculated a n d m e a s u r e d ratios o f the intensity, as shown in Table 4, is also s u p p o r t for t h e fact t h a t the crystallite sizes d e t e r m i n e d b y means of small angles, a n d t h e a s s u m p t i o n a d o p t e d b y us t h a t pa=1"336 g/cm 3, are correct.
432
L.G. KAZAt(YANand D. YA. TSVANKIIV
Usually, the overall process of crystallization of polyethyleneterephthalate is divided into two stages [5-7]. In the first stage, crystallization proceeds comparatively rapidly, and the change in crystallinity and density follow an exponential law (the Avrami equation). In the second stage (post-crystallization) the changes in crystallinity and density proceed much more slowly. It follows from a comparison of our data for the density with other results [5] that the post-crystallization process is typical of the majority of our specimens. As m a y be seen from the data presented, the principal process taking place in this period of crystallization is an increase in the ordering within the crystallites, and, because of this, an increase in the density of the entire specimens. It should be borne in mind that, although the density of the crystallites changes during the crystallization process only by 0.05 g/cm 3, this change is very substantial, in so far as the greatest difference between the density of an amorphous specimen and the density of a specimen crystallized to the maximum extent is equal to 0.12 g/cm 8. The crystallite dimensions are clearly established in the first stage, during the crystallization process itself, and depend principally on the temperature of crystallization. CONCLUSIONS
(l) A study has been made of the large identity periods during the crystallization process for oriented amorphous films of PETP, and the specimen densities and the unit cell parameters have been determined. (2) The size of the large identity period, and also the crystallite dimensions and the dimensions of the amorphous regions depend principally on the crystallization temperature. (3) With an increase in the crystallization time, an increase in the density of the entire specimen takes place; this is accompanied by a rise in the crystallite density and by a rise in the intensity of low-angle scattering. (4) Crystallization of oriented amorphous P E T P proceeds in two stages. In the first stage, poorly ordered crystallites are formed with dimensions typical of the given temperature and changing little with time. In the second stage, an improvement in the ordering within the crystallites chiefly takes place. Translated by G. F. MODLEN REFERENCES
1. P. V. KOZLOV and G. L. BERESTNEVA, Vysokomol. soyed. 2: 590, 1960 (Not translated in Polymer Sci. U.S.S.R.) 2. L. G. KAZARYAN and L. Ya. TSVANKIN, Vysokomol. soyed. 7: 80, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 1, 84, 1965) 3. L. G. KAZARYAN and Ya. (L URMAN, Zh. strukt, khimii 5: 534, 1964 4. L. (L KAZARYAN and Ya. G. UR~AN, Zh. strukt, khimii 7: 44, 1966 5. H. {L ZAgHMAN and H. A. STUART, Macromol. Chem. 41: 131, 148, 1960 6. F. RYRNIKAR, J. Polymer Sci AI: 2031, 1963 7. F. RYBNIKAR, Collect. Czechosl. Chem. Com. 25: 1529, 1960
Relaxation properties of crystalline and amorphous polymers
433
8. Yu. A. ZUBOV, G. S. MARKOVA and V. A. KARCIN, Vysokomol. soyed. 5: 1171, 1963 (Translated in Polymer Sci. U.S.S.R, 5: No. 2, 1961) 9. G. FARROX, Polymer 1: 518, 1960 10. D. Ya. TSVANKIN, Vysokomol. soyed. 6: 2078, 2083, 1964 (Translated in P o l y m e r Sci. U.S.S.R. 6: 11, 2304; 2310, 1964) 11. A. TAYLOR and H. SINCLAIR, Proc. Phys. Soc. A57: 108, 1945 12. Yu. A. ZUBOV and D. Ya. TSVANKIN, Vysokomol. soyed. 6: 2131, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 12, 2358, 1964) 13. Ch. RUSCHER and V. SCHRODER, Faserforseh und Textiltechn. 11: 165, 1960 14, H. C. KILIAN, H. HALROTH and E. JENKEL, Kolloid.-Z., 172: 166, 1960 15, R. P. I)AUBENY, C. W. BUNN and C. J. BROWN, Proc Roy, Soc, A226: 531, 1954
INVESTIGATION OF THE EFFECT OF SUPERMOLECULAR STRUCTURE ON THE RELAXATION PROPERTIES OF CRYSTALLINE AND AMORPHOUS POLYMERS* V. I. PAVLOV, A. A. ASKADSKIIand G. L. SLOI~'IMSKII Institute for Elementary Organic Compounds, U.S.S.R. Academy of Sciences I n s t i t u t e for the Chemistry of High Molecular Compounds, Ukrainian S.S.R. A c a d e m y of Sciences
(Received 25 May 1966) THE objective of the present work was a structural and mechanical investigation of monolithic crystalline and solid amorphous polymers, with the aim of establishing quantitative connections between the characteristics of their supermolecular structures and the parameters of their relaxation properties. EXPERIMENTAL Two polymers, which m a y exist in different phase states, were selected as the experimental materials; crystalline isotactic polypropylene, in which different supermolecular structures m a y be obtained comparatively easily [1-8], and amorphous polyarylates, which are exceptionally interesting new glassy polymers with rigid macromolecules [9-11]. The different supermolecular structures in the bulk polypropylene specimens were obtained from the melt b y the method of changing the cooling rate during pressing. F o r the investigation, a highly crystalline isotactic polypropylene "Moplen" was used in t h e form of granules with an intrinsic viscosity [F/]=3.83, as measured in tetralin at 135°C. A pressing regime was selected for the preparation of the specimens which m a d e it possible to obtain a structure, the elements of which were individual spherulites; the regime eliminated the appearance of various supra-spherulitic formations which are known [3, 12] to exert an effect on t h e mechanical properties of the polymer body. The specimens were * Vysokomol. soyod. A9: :No. 2, 385-392, 1967.
423
(7) It has been established that the principal factor favouring the amorphous state in non-crystallizing polycarbonates is not the rigidity of the polymer chain, but rather the impossibility of achieving the required packing density, that is, the effect of a steric (conformational) factor. Translated by G. F. MODLEN REFERENCES 1. P.V. KOZLOV, G.I. BRAG]NSKII, Khimia i tekhnologiya polimernykh plenok (Chemistry and Technology of Polymer Films). Izd. "Iskusstvo", 1965 2. H. SCHNELL, Angew. Chemie 68: 633, 1965 3. V. A. KARGIN, N. F. BAKEYEV and Kh. VERGIN, Dokl. Akad. Nauk SSSR, 122, 97, 1958 4. V. A. KARGIN, A. A. EFENDIYEV and Z. Ya. BERESTNEVA, Tezisy X V I I Vsesoyuznoi konferentsii po polimeram (Preceedings of XVIIth All-union Conference on Polymers). Leningrad, 1964 5. N. F. B,AI~EYEV, ZhVKhO im. D. I. Mendeleyev 6: 630, 1964 6. A. I. KITAIGORODSI~H, Bold. Akad. Nauk SSSR, 124, 861, 1959 7. A. N. PEREPE1LKIN and P. V. KOZLOV, Vysokomol. soyed. 8: 51, 1966 (Translated in Polymer Sci. U.S.S.R. 8: 1, 57, 1966) 8. L. MANDEL'KERN, Uspekhi khimii, 27, 193, 1958 9. A. PRIETZSCHK, Kolloid.-Z, 156: 8, 1958
A STUDY OF THE CRYSTALLIZATION PROCESS IN ORIENTED AMORPHOUS POLYETHYLENETEREPHTHALATE* L. G. K ~ x R x ~
and D. YA. TSV~XKZN
Institute for Elementary Organic Compounds, U.S.S.R. Academy of Sciences (Received 19 March 1966)
POLYETHYLEI~1"ETEREPHTHALATE(PETP) is a very suitable material for studying the process of crystallization, since the glass temperature of P E T P is approximately 80°C, and specimens may easily be obtained at room temperature with different degrees of crystallinity, including oriented films, ranging from textured amorphous films to films having a crystalline texture [1]. This gives rise to the possibility of studying the crystallization process in oriented specimens, in which the starting point is a structure of a type of amorphous texture, in which a three-dimensional lattice is completely absent but the molecules are, nevertheless, parallel one to another. The character of the positioning * Vysokomol. soyed. A9: No 2. 377-384, 1967.
424
L. (3. KA~RYAN and D. YA. TSVANKIN
o f the chains in t h e a m o r p h o u s oriented film h a s b e e n studied p r e v i o u s l y [2] b y m e a n s of X - r a y diffraction a t large angles. F u r t h e r , t h e b r e a k d o w n o f ordering in the a m o r p h o u s t e x t u r e a n d t h e kinetics of t h e crystallization processes in various P E T P specimens h a v e been i n v e s t i g a t e d b y m e a n s o f nuclear m a g n e t i c r e s o n a n c e [3, 4]. The principal a i m of t h e p r e s e n t work, which is a direct c o n t i n u a t i o n o f these investigations, is t h e s t u d y o f s t r u c t u r a l changes during t h e process of c h a n g i n g o v e r f r o m t h e a m o r p h o u s t e x t u r e to a crystalline axial t e x t u r e . S o m e papers, in w h i c h v a r i o u s m e t h o d s o f i n v e s t i g a t i o n h a v e b e e n u s e d [5-9] h a v e b e e n d e v o t e d to the s t u d y of t h e crystallization process in P E T P . H o w e v e r , in these p a p e r s o n l y t h e crystallization o f u n o r i e n t e d specimens h a s b e e n studied, whereas t h e process o f crystallization in a n a m o r p h o u s t e x t u r e h a s n o t b e e n s t u d i e d in detail u p to now. Low-angle diffraction o f X - r a y r a d i a t i o n w a s u s e d p r i n c i p a l l y in s t u d y i n g t h e crystallization process in the oriented condition; b y this means, changes in large i d e n t i t y periods were s t u d i e d during crystallization. I n i n t e r p r e t i n g t h e large i d e n t i t y periods a n d in t h e d e t e r m i n a t i o n o f crystallite dimensions a n d degree of c r y s t a l l i n i t y b y m e a n s of t h e m , use was m a d e o f t h e o r e t i c a l i n t e n s i t y d i s t r i b u t i o n curves a n d of the corresponding calibration g r a p h s [10].
EXPERIMENTAL Film of amorphous oriented P E T P was obtained from a film of amorphous unoriented P E T P by 700~/o stretching in a thermostat at 70°C. Further, to study the crystallization process in an amorphous oriented film, three series of films were prepared, which were crystallized at 140, 180 and 220°C with different times at those temperatures. The crystallization of the oriented films was carried out in the unrestrained condition. The temperature in the thermostat was held with an accuracy of ± 2°C. After annealing, the specimens were cooled to room temperature. A camera with a Kratki type collimator and ionization recording (Geiger counter) was used to study the low-angle scattering of the X-ray radiation. The distribution of intensity along the texture axis was studied. Therefore, in all cases the incident beam was positioned perpendicular to the texture axis of the specimen. The specimens for the low-angle exposures took the form of packs made up of piled-up individual films. In order that one could compare the scattered intensity curves for the various specimens with each other, the scattering mass for all the specimens was approximately the same, this being checked from the absorption of the X-ray radiation in the specimens, To calculate the lattice parameters of crystallized specimens, an X-ray exposure was made at large angles in a RKU-I14 camera, the specimen being rotated about its texture axis. Interplanar spacings were measured on a comparator. In the calculation of the interplanar spacings, corrections were introduced in the camera radius and for the specimen absorption by the method described in reference [11]. Three diffraction photographs were taken for each specimen, the adjustment of the specimen being carried out anew each time. The average scatter in the parameter values is :t:0"015 ~. All the X-ray exposures were made with copper radiation and a nickel filter. The intensity curves and the low-angle diffraction photographs showed that in all cases there is a low-angle reflection in the form of a stripe along the meridian of the X-ray photograph. To treat the scattering curves and to determine the crystallite dimensions
Crystallization process in oriented amorphous polyethyleneterephthalato
425
a n d the dimensions of the amorphous regions, a method based on theroretical scattering curves was used [ 10]. The treatment of the low-angie curves, the separation of the background, the calculation of the true width of the scattering m a x i m u m and the calculation of the parameters kl, c, a, l were carried out b y use of the method described in references [10, 12] (a is the average dimension of the crystalline regions; 1 is the average dimension of the amorphous regions; c-~a-}-l is the identity period along the axis of the fibrils; k ~ a / c is the crystallinity (%)). The q u a n t i t y d~-2/20 (the large identity period) is determined directly from the position of_the m a x i m u m on the scattering curve. The value of the intensity at the m a x i m u m after its separation from the background was taken as the value typifying the intensity of the large identity period (1 in Tables 1 and 4). The density of the specimens was measured by the hydrostatic weighing method with an accuracy of ~=0.001 g/cm 3 at 20°C.
INTENSITY OF LOW ANGLE SCATTERING Before going on to discuss the results, we shall derive a formula by moans of which one m a y assess the intensity of a low-anglo reflection. Since the m a x i m u m in the low-angle scattering, corresponding to the largo identity period, arises because of interference of waves scattered b y the individual crystaUites in the fibril, the intensity I ought to be written in the following way I=Nn*~ (sin 0/2), (1) whore N is the n u m b e r of crystallites in the specimen; n is the excess of electrons in the crystallito as compared with the amorphous part; ~ ((sin 0/2) is a scattering function, calculated for a single crystallite; 0 is the diffraction angle; 2 is the wavelength. The function ¢ ( s i n 0/2) depends on the degree of erystaUinity [10]. I f the erystallinity changes from 60 to 65%, the form of the function hardly changes at all. TABLE 1.
T, °C
QUANTITIES
Duration of crystallization, m i n
140
180
200
5 15 30 60 240 5 15 30 60 240 360 5 15 30 60 240
OBTAINED
g POX " - cm $
FROM
THE
LOW-ANGLE
SCATTERING
CURVES
Ij
d,A
c,A
a,A
1, A
kl, %
impulse sec
1.367 1.370 1.375 1.380 1.385 1-386 1-385 1.378 1.383 1.391
1.393 1.396 1.401 1.405 1.406 1.408 1-408 1.409
101 98
m
120 112.5 114 110 108,5 111 109 113 125 126 125.5 125 150 150 145.5 145 152
66.0 67.5 69.5 71.5 69"5 72.5 67.0 73.0 81.0 84.0 83.5 82.0 95.0 96.0 96-0 95.0 102.0
54'0 45.0 44.5 38.5 39.0 39.0 42.0 40.0 44.0 42.0 43.0 43.0 55.0 55.0 49.5 50-0 50.0
55 60 61 65 64 65 61 65 65 67 67 66 63 63 66 66 67
1.5 2.2 3.5 6.5 7.0 7"0 7"5 5.8 8.5 11.5 16.0 17.5 17.5 28 29 3O 32 32
426
L.G. KAz~Y~
and D. YA. TSVA~Xn¢
The n u m b e r of crystallites in a substance m a y be expressed as a ratio of the volume of the entire crystalline phase (Vcr.ph) to the volume of a single erystallite (Vcr)
N = Vcr.ph/Ve,:=k V,p/V~,:
(2)
where Vsp is the volume of the entire specimen mad /c is the degree of crystallinity. The excess of electrons (n) is equal to the product of the erystallite volume and the difference between the densities of the ez.ystalline (Per) and amorphous (Pa) regions
n = Ver(pcr- pa).
(3)
By substituting equation (2) and (3) in equation (1), we obtain
I=kVspVcr(Pcr--Pa)2q~(sin 0/2) .
(4)
Since Vsp=M/p where M is the mass of the entire specimen and p its density, then
I = (KM/p) Ver(Per-- pa)2~ (sin 0/2) .
(5)
Since we have determined intensities only in relative and not in absolute units, we have calculated a ratio of intensities; it was thus assumed that both M and also ~(sin 0/2) remain constant. It
I2
kxP=Va'cr (Pl'cr-- Pa)2 k=PlV=,cr(P2,cr-- Pa) 2
(6)
I n calculating the ratio (6), it m a y be assumed that Vcr~aS, whore a is the crystallito size; hence the ratio of the intensities m a y be written in the following form:
11 kxp=aSt(pl,cr-- pa) 2 1--~= k,,pla~ (p2.er--ps) 2
(7)
DISCUSSION OF RESULTS
No maximum is observable on the low-angle scattering curve of the initial oriented amorphous P E T P film, and consequently this film does not have a large identity period. As the duration of annealing increases, the corresponding maxim u m on the curve appears and gradually increases. Low angle scattering curves along the texture axis are shown in Figs. 1, 2 and 3 for specimens of oriented PETP, crystallized under different conditions. The results of the measurements together with all the quantities obtained by treatment of the low angle scattering curves are shown in Table 1. The intensity of the scattering depends strongly on the density of the specimen. A specimen with a density of 1.367 g/cm 3 gives such a weak maximum that it is difficult to distinguish it from the background (Fig. 1), whereas the X-ray diffraction photograph of this specimen (crystallization temperature 140°C, time of crystallization 2 min) at large angles points to the presence of a complete three-dimensional ordering. A detailed study of the scattering curves and the determination of the quantities a, l, k z was carried out for specimens crystallized at 140, 180 and 220°C, having a density of not less than 1.370 g/cm 3.
Crystallization process in oriented amorphous polyethyleneterophthalate
427
The specimens crystallized at 140°C (Fig. 1) all have the same large identity period d, approximately equal to 100 A (Table 1). The quantity c=a+l is always somewhat larger than d [10, 12]. I t is also roughly constant and equal to 110 A. With an increase in the crystallization time, an increase in the density of the sample occurs, this being accompanied by an increase in intensity by a factor of 5, by an increase in the dimensions of the crystalline regions from 66 to 71 A, and by a reduction in the dimensions of the amorphous regions from 54 to 39/~. This leads to an increase in crystallinity from 55 to 65%. Annealing the specimens for 30 min, 1 hr and 4 hr at 140°C leads to the same density, to the same crystallinity, and to the same intensity of reflections.
!
10
I
,30
I
I
50
t
I
70
I
1
I
8g 20,mia
FIe. 1. Low-angle scattering curves for PETP specimens, annealed at 140°C for: 1--2 rain, 2--4 min, 3--5 min, 6--30 min, 7--1 hr, 8--4 hr. As the recrystallization temperature is raised, the large identity period increases. At 180°C (Table 1, Fig. 2) the large identity period reaches 120 A, and the dimensions of the crystalline regions become 85 A. With an increase in the duration of crystallization, the same changes are observed as were observed at 140°C. The density of the specimens increases, the scattered intensity increases, and the degree of crystallinity rises from 61 to 67%. Crystallization of specimens at 220°C (Fig. 3) leads to a further increase in d to 140 A (Table 1). The average dimensions of the crystalline and amorphous regions increase to approximately 95 and 50 /~ respectively. Thus the crystallinity k 1 hardly changes at all. However, at 220°C the intensity of the reflection rises by a factor of 4 as compared with 140°C, and by a factor of 1.5 as compaxed with 180°C. During annealing at 220°C, the density of the specimens depends little on the time of annealing, changing from 1.405 g/cm a at 5 min annealing to 1.408 g/cm a at 6 hr annealing. In this way, with an increase in crystallization temperature both the large identity period and also the dimensions of the crystalline and amorphous regions increase. Such a phenomenon is similar to the changes during the an-
L. G. KAZARYAN and D. YA. TSVANKIN
428
nealing of specimens previously crystallized [12]. As m a y be seen from Table 1, the crystallite dimensions depend principally on the crystallization temperature, whereas the intensity of the low-angle reflection depends both on temperature and on the time of crystallization to the same extent. Thus the typical crystal-
30
25
4
2O
15 3 75 10 10
5
5
I0
I
I
I
I
I
I
JO
50
70
SO 28,mZa
10
30
FlO. 2
I
50
I
70
,9020,m/n
FIG. 3
FIG. 2. Low-angle scattering curves for PETP specimens, annealod at 180°C for: 1--5 rain, 2--15 rain, 3--30 min, 4--1 hr, 5--6 hr. FIG. 3. Low-angle scattering curves for PETP specimens, annealed at 220°C for: 1 - - 5 rain, 2 - - 1 5 rain, 3 - - 3 0 rain, 4--1 hr, 5--4 hr. lite dimension obtained at 140°C is 70 -~, at 180°C, 80A; and at 220°C, 95 A. This phenomenon is especially clearly seen from the data for crystallization at 140 and 220°C. During crystallization at 180°C, the crystallites grew from 70 to 80 _~, that is, b y a factor of 1.14. However, the scattered intensity thus rose much more rapidly, increasing b y a factor of 2.66. With a change in the crystallization time and temperature, an increase takes place in the density of the entire specimen (Pex) from 1.370 to 1-408 g/cm s. Know-
Crystallization process in oriented amorphous polyethyleneterephthalate
429
ing the dimensions of the crystalline and amorphous regions and the density of the entire specimen, we calculated the density of the crystallites from the formula f l : (flex ( a - - ~) - - fla ~) c~-1
(S)
with the supposition that the density of the amorphous regions was equal to the density of amorphous P E T P in the initial (1.336 g/cm a) or in the oriented (1.360 g/cm 3) P E T P . The values of the densities calculated, Pl with pa=1"336 g/cm a and p~ with p a = l ' 3 6 0 g/cm a, which are shown in Table 3, indicate that an increase in the density of the crystallites takes place at the same time as the increase in the density of the entire specimen Pex" The density of the crystallites m a y be calculated from the parameters of the unit cell, which m a y be determined by means of the diffraction photographs taken at large angles. The parameters a and b were determined from the interplanar spacings dl0o and do10. Oblique X-ray diffraction photographs were taken to determine the identity period along the axis of the molecule; from these it was seen that the parameter c does not change during crystallization (c= 10.75 •). The change in the parameters a and b during the crystallization of P E T P leads to a shift in the intensity maximum of the equatorial reflections in the direction of larger angles. It has however been shown [13], that a shift in the positions of individual interferences m a y also take place because of a structural factor if the number of cells in the crystallite parallel to a particular axis is small. With an increase in the number of cells, the maximum is shifted in the direction of larger angles. We calculated the intensity of the 100 P E T P reflection for a crystallite with a number of chains ranging from 2 to 16. The calculation showed that the maximum in the intensity of the 100 reflection is only shifted if the crystallite has a small number of chains. I f the number of chains or cells in one direction is greater than 8, then this shift disappears. The smallest erystallite dimension which we had obtained (Table 1), is 68 A. The crystallite dimensions obtained from the width of the 100 reflection by means of the Seherrer formula without taking imperfections into account, is 64 A. I f the interplanar spacing for the 100 reflection is equal to 3-5 A, then the number of chains in this direction will be equal to 18. Consequently, even in the case of the most poorly ordered crystallite no shift in the reflection ought to take place as a result of erystallite dimensions, and the observed shift in the equatorial reflections in the direction of larger angles can take place only as a result of a reduction in the dimensions of the unit cell. The lattice parameters a and b, and the volume of the unit cell calculated from them and the crystallite density given by the X-ray measurements (Px-ray) are shown in Table 2. The change in the lattice parameters of unoriented P E T P as a function of annealing temperature has also been studied by Kilian et al. [14], who obtained very low values for the parameters of highly crystalline PETP;
430
L . G . KAZARYAIqand D. YA. TSVANKIIV
this leads to a the P E T P cell of 1.455 g/cm a 1.454 g/cm a, in
m a x i m u m density value of 1.495 g/cm a whereas, according to parameters calculated b y D a u b e n y a n d B u n n [15], a density is obtained. The m a x i m u m density according to our d a t a is satisfactory agreement w i t h the results of reference [15]. TABLE 2. CELL PARAMETERS
Crystallization conditions T, °C
time, min
140
5 15 60 240 5 15 60 360 60
180
220
dloo,/~.
3"53 3"48 3"46 3"47 3"49 3"49 3"48 3"47 3"45
dolo,
5'13 5"12 5"10 5"10 5"10 5"09 5"09 5"08 5.07
d11o,
a,A
b,A
V, ~8
g PX-ray cm s
3.98 3-98 3.94 3.95
4"62 4"58 4"56 4"57 4"60 4"60 4"58 4"57 4"55
6.04 6.02 6.00 6-00 6.00 5.99 5.99 5.98 5.96
225.6 222.9 221.2 221.7 223.1 222.7 221.8 220-4 219.2
1.410 1.430 1.441 1.438 1.429 1.431 1.437 1.446 1.454
3-98 3-96 3.95 3-95 3.95
The d a t a of Table 2 indicate t h a t in all cases an increase in the density of the entire specimen Pex is accompanied b y an increase in the density of the crystallite. L e t us now compare the densities Pl a n d p~, calculated b y means of formula (8), with Px-ray" I t is clear t h a t the results for Pl, obtained with pa=1"336 g/cm a, are in the closer agreement, which is evidence in favour of the density of the amorphous portions being equal to 1.336 g/cm a. B y means of PX-ray, o n e m a y determine the crystallinity k s from the following formula: /C2~ [(Pex--,Oa)/(PX.ray--,Oa)]" 100% (9) with the assumption t h a t pa--1"336 g/cm a. Usually, the determination of the crystallinity from densities is also m a d e from formula (9), but, in place of the different values of Px-ray, the value for the density calculated from the lattice parameters of the most highly crystallized specimen is adopted. The crystallinity lca calculated in this w a y is also shown w i t h k 1 a n d k 2 i.n Table 3. F r o m Table 3, it m a y be seen t h a t the values of k s are closer t h a n those of/c a to the values of k 1 . The differences in the crystallinity values k s and/Cz m a y n a t u r a l l y be explained b y the fact t h a t in the calculation of kl using reference [10], it was assumed t h a t the specimen consists of amorphous-crystalline fibrils, w i t h o u t a n y intermediate a n d transitional zones; an additional explanation is t h a t the density of the crystallites m a y be •considerably less t h a n PX-rar, because of the presence of p a r t l y ordered interm e d i a t e regions, a n d also because of the presence of pores of various sizes.
431
Crystallization process in oriented amorphous polyethyloneterophthalate TABLV.3. DENSITY OF CRYSTALLITESAND DEGREE OF CRYSTALT.,INITY Crystallization conditions T, °C 140
180
220
time, rain 5 15 60 240 5 15 60 360 60
g g g Pl,cm~ P~,c-~7 PX-ray, g Pex, cm 3 with with cm a pa= 1"336 pa= 1.360
kl, %
1.401 1'408 1.414 1.411 1.403 1.408 1.426 1.435 1.445
i
1.387 1.393 1.401 1.394 1.391 1.401 1.416 1.426 1.431
ks, %
50 47 48 48 45 50 56 59 61
32"5 37 42 41 35 39 48 54"5 60"4
t
I
1.375 1.380 1.386 1.385 1.378 1"383 1-393 1.401 1.408
k2, %
60 61 64 65 61 65 67 66 66
1.410 1-430 1.441 1.438 1.429 1.431 1.437 1.446 1.454
T h e change in the density o f the crystallites is also a reason for t h e change in the i n t e n s i t y of the low-angle scattering (Table 1). W e carried out a calculation of t h e ratio of t h e intensity, using f o r m u l a (7), w i t h the help of the d a t a o b t a i n e d from the diffraction p h o t o g r a p h s a t low a n d large angles. Since the c r y s t a l l i n i t y (kl) of our specimens varies f r o m 60 to 65%, a n d the density of t h e specimens varies f r o m 1.380 t o 1.408 g/cm 3, t h u s t h e smallest change in the q u a n t i t y is klpflk2pI = 1.05. Consequently, the r a t i o o f the intensities m a y be calculated f r o m t h e f o r m u l a
II112---- aa~(Pl.cr-- Pa)2/a32(Pi,cr - - Pa) 2
(10)
I n calculating the i n t e n s i t y o f the low-angle s c a t t e r i n g b y m e a n s of f o r m u l a (10) we assumed t h a t the density of t h e a m o r p h o u s p a r t s was equal to t h e density of the initial a m o r p h o u s P E T P (1.336 g/cma). TABLE
4. RATIO
Specimen
I(220 °, I(220 °, I(220 °, I(180 °,
i hr)/I(180 o, 6 hr) 1 hr)/I(180 °, 6 hr) 1 hr)/I(180 °, 5 min) 6 hr)/I(140 °, 5 min)
OF THE LOW-ANGLE I 1 --9
REFLEXION
INTENSITIES
I 1
Specimen
I2 '
exp.
calc.
1"86 3"75 5"2 5"3
1"63 3"55 4"8 5"0
1(220 °, I(220 °, I(180 °, 1(140 °,
1 hr)/I(140 °, 5 rain) 1 hr)/I(140 °, 4 hr) 6 hr)/I(140 °, 4 hr) 4 hr)/I(140 °, 5 min)
IL 12 '
K'
oxp,
ealc.
9.4 4.5 2.4 2-1
8.5 3.4 2.0 2.3
I1
T h e satisfactory a g r e e m e n t b e t w e e n t h e calculated a n d m e a s u r e d ratios o f the intensity, as shown in Table 4, is also s u p p o r t for t h e fact t h a t the crystallite sizes d e t e r m i n e d b y means of small angles, a n d t h e a s s u m p t i o n a d o p t e d b y us t h a t pa=1"336 g/cm 3, are correct.
432
L.G. KAZAt(YANand D. YA. TSVANKIIV
Usually, the overall process of crystallization of polyethyleneterephthalate is divided into two stages [5-7]. In the first stage, crystallization proceeds comparatively rapidly, and the change in crystallinity and density follow an exponential law (the Avrami equation). In the second stage (post-crystallization) the changes in crystallinity and density proceed much more slowly. It follows from a comparison of our data for the density with other results [5] that the post-crystallization process is typical of the majority of our specimens. As m a y be seen from the data presented, the principal process taking place in this period of crystallization is an increase in the ordering within the crystallites, and, because of this, an increase in the density of the entire specimens. It should be borne in mind that, although the density of the crystallites changes during the crystallization process only by 0.05 g/cm 3, this change is very substantial, in so far as the greatest difference between the density of an amorphous specimen and the density of a specimen crystallized to the maximum extent is equal to 0.12 g/cm 8. The crystallite dimensions are clearly established in the first stage, during the crystallization process itself, and depend principally on the temperature of crystallization. CONCLUSIONS
(l) A study has been made of the large identity periods during the crystallization process for oriented amorphous films of PETP, and the specimen densities and the unit cell parameters have been determined. (2) The size of the large identity period, and also the crystallite dimensions and the dimensions of the amorphous regions depend principally on the crystallization temperature. (3) With an increase in the crystallization time, an increase in the density of the entire specimen takes place; this is accompanied by a rise in the crystallite density and by a rise in the intensity of low-angle scattering. (4) Crystallization of oriented amorphous P E T P proceeds in two stages. In the first stage, poorly ordered crystallites are formed with dimensions typical of the given temperature and changing little with time. In the second stage, an improvement in the ordering within the crystallites chiefly takes place. Translated by G. F. MODLEN REFERENCES
1. P. V. KOZLOV and G. L. BERESTNEVA, Vysokomol. soyed. 2: 590, 1960 (Not translated in Polymer Sci. U.S.S.R.) 2. L. G. KAZARYAN and L. Ya. TSVANKIN, Vysokomol. soyed. 7: 80, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 1, 84, 1965) 3. L. G. KAZARYAN and Ya. (L URMAN, Zh. strukt, khimii 5: 534, 1964 4. L. (L KAZARYAN and Ya. G. UR~AN, Zh. strukt, khimii 7: 44, 1966 5. H. {L ZAgHMAN and H. A. STUART, Macromol. Chem. 41: 131, 148, 1960 6. F. RYRNIKAR, J. Polymer Sci AI: 2031, 1963 7. F. RYBNIKAR, Collect. Czechosl. Chem. Com. 25: 1529, 1960
Relaxation properties of crystalline and amorphous polymers
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8. Yu. A. ZUBOV, G. S. MARKOVA and V. A. KARCIN, Vysokomol. soyed. 5: 1171, 1963 (Translated in Polymer Sci. U.S.S.R, 5: No. 2, 1961) 9. G. FARROX, Polymer 1: 518, 1960 10. D. Ya. TSVANKIN, Vysokomol. soyed. 6: 2078, 2083, 1964 (Translated in P o l y m e r Sci. U.S.S.R. 6: 11, 2304; 2310, 1964) 11. A. TAYLOR and H. SINCLAIR, Proc. Phys. Soc. A57: 108, 1945 12. Yu. A. ZUBOV and D. Ya. TSVANKIN, Vysokomol. soyed. 6: 2131, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 12, 2358, 1964) 13. Ch. RUSCHER and V. SCHRODER, Faserforseh und Textiltechn. 11: 165, 1960 14, H. C. KILIAN, H. HALROTH and E. JENKEL, Kolloid.-Z., 172: 166, 1960 15, R. P. I)AUBENY, C. W. BUNN and C. J. BROWN, Proc Roy, Soc, A226: 531, 1954
INVESTIGATION OF THE EFFECT OF SUPERMOLECULAR STRUCTURE ON THE RELAXATION PROPERTIES OF CRYSTALLINE AND AMORPHOUS POLYMERS* V. I. PAVLOV, A. A. ASKADSKIIand G. L. SLOI~'IMSKII Institute for Elementary Organic Compounds, U.S.S.R. Academy of Sciences I n s t i t u t e for the Chemistry of High Molecular Compounds, Ukrainian S.S.R. A c a d e m y of Sciences
(Received 25 May 1966) THE objective of the present work was a structural and mechanical investigation of monolithic crystalline and solid amorphous polymers, with the aim of establishing quantitative connections between the characteristics of their supermolecular structures and the parameters of their relaxation properties. EXPERIMENTAL Two polymers, which m a y exist in different phase states, were selected as the experimental materials; crystalline isotactic polypropylene, in which different supermolecular structures m a y be obtained comparatively easily [1-8], and amorphous polyarylates, which are exceptionally interesting new glassy polymers with rigid macromolecules [9-11]. The different supermolecular structures in the bulk polypropylene specimens were obtained from the melt b y the method of changing the cooling rate during pressing. F o r the investigation, a highly crystalline isotactic polypropylene "Moplen" was used in t h e form of granules with an intrinsic viscosity [F/]=3.83, as measured in tetralin at 135°C. A pressing regime was selected for the preparation of the specimens which m a d e it possible to obtain a structure, the elements of which were individual spherulites; the regime eliminated the appearance of various supra-spherulitic formations which are known [3, 12] to exert an effect on t h e mechanical properties of the polymer body. The specimens were * Vysokomol. soyod. A9: :No. 2, 385-392, 1967.