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Thermoluminescence of polymers irradiated at room temperature and at high pressure
PolymerScienceVoi.33, No. 3, pp. 422-428,1991
0032-3950/91$15.00+ .00 ~ 1992PergamonPressplc
Printed in GreatBritain.
THERMOLUMINESCENCE OF POLYMERS IRRADIATED AT ROOM TEMPERATURE AND AT HIGH PRESSURE* V. A . AULOV Karpov PhysicochemicalResearch Institute (Received 2 October 1989)
The influence of pressure to 2.3 GPa on the thermoluminescence of PE, PP and FFFE irradiated at room temperature has been studied. Thermoluminescence of the polymers irradiated without pressure is represented by a weak glow above 300 K with a maximum at 333-350 K. Irradiation under pressure raises the intensity and lowers the temperature of this maximum. Shift of the maximum continues until it reaches the position of the phase or relaxationai transition (-300 K for PTFE, 255 K for PP and 225 K for PE) after which the temperature of the maximum does not change but its intensity begins to drop. With rise in pressure the initial portion of the thermoluminescence curve continues to shift to low temperatures leading to the formation of a further two to three maxima in the interval 150-200 K at a pressure >1.7 GPa. The appearance of the thermoluminescence maxima after irradiation at room temperature under pressure signifies that during irradiation the temperature of the relaxational transition of the polymer is higher than the temperature of irradiation, the molecular mobility characteristic of it is inhibted by pressure and the charges are able to stabilize. The differences between the polymers in the number of thermoluminescence maxima and the rate of shift of the initial portion of the curve with rise in pressure are connected with the difference in the values of free volume and compressibility.
THERMOLUMINESCENCE (TL) of polymers is usually observed after irradiation at low temperature. Most investigators consider that charge recombination leading to luminscence is stimulated by acceleration of diffusion of the charges in the intervals of the relaxational transitions to which is also related the correlation between the positions of the maxima of T L and the relaxational transitions. Yet it is well known that the position of the relaxational transitions depends on the pressure applied since by reducing the size of the free volume the molecular mobility is arrested. In this connection it was of interest to investigate the effect of pressure on the T L of polymers, it being desirable to alter only one p a r a m e t e r - - p r e s s u r e , leaving unchanged the temperature of irradiation since change both in temperature and pressure [1-3] complicates the analysis and interpretation of the experimental results. To establish the effect of pressure on the form of the TL curve and determine the baric coefficients of the position of the relaxational transitions we, in the present work, investigated the T L of some polymers after irradiation at room temperature and at high pressure. We used linear P E with Mw = 3 x 105, polydispersity 3.5 and number of branchings < 1 per 1000 C atoms, H D P E of grade Marlex 5005, commercial high and low density P E samples, PP and PTFE. Irradiation was carried out at r o o m temperature in a device of the piston-cylinder type with the pressure fixed with a nut. The pressure value was determined from the exertion produced on the piston with a diameter 4 and 10 mm. The friction between piston and cylinder was disregarded. The polymers under pressure were held for I h, irradiated to a dose 15 kGr with a y source with a power 12 kGr/h, cooled immediately after irradiation in liquid nitrogen, the pressure dropped and the
*Vysokomol. soyed. A33: No. 3, 501-507, 1991. 422
Thermoluminescence of polymers
100
TM, K
300
(~)
Q O Q
2501
423
I. e=
• q
•
I~ t
I
ZM 8
-
~/
-
•
•
J 1
2
P, GPa
FIG. 1. TL curves on irradiation of PP at room temperature and a pressure 0 (1); 0.25 (2); 1.0 (3); 1.5 (4); 1.7 (5) 2.3 GPa (6) (a) and dependence of TMand 1Mon pressure on irradiation (b). samples r e m o v e d f r o m t h e d e v i c e . The samples were stored in this form up to heating which was carried out at the rate 10 K/min. Figure 1 presents the results obtained for PP. It will be seen that irradiation at r o o m t e m p e r a t u r e without pressure leads, on heating, to the appearance of weak luminescence above 300 K with a m a x i m u m at - 3 5 0 K. Increase in pressure on irradiation raises the intensity of luminescence IM and lowers the t e m p e r a t u r e of the m a x i m u m TM. These changes continue to --1.0 GPa. With further increase in pressure the position of the m a x i m u m does not change but its intensity diminishes. H o w e v e r , the initial portion of the T L curve as pressure rises continues to shift to low t e m p e r a t u r e s leading to the formation of a further two T L m a x i m a (~200 and --150 K). Thus, irradiation of PP at r o o m t e m p e r a t u r e and a pressure > 1 . 7 G P a leads to the appearance of T L in the interval 100-300 K
424
V . A . AuLov
with three maxima. We would emphasize a characteristic feature of all the TL maxima and of all the polymers studied---after reaching the highest value the intensity begins to drop with increase in pressure with no change in its position. A similar picture was also observed for PTFE (Fig. 2). Admittedly, the intensity of its TL is much less and, therefore, it is hard to monitor in detail all the changes in the form of the TL curve. Nevertheless, it is quite clear that, in the pressure interval used, three TL maxima can be obtained (~300 K, in the interval 215-230 K and ~150 K). As in the case of PP, the maxima at 300 K does not change its position, while its intensity begins to drop with rise in pressure after 0.6--0.7 GPa. As Fig. 3 shows, the behaviour of the TL curve of polyethylene in the initial portion of change in pressure on irradiation differs little from that of the PP curve: the maximum grows in intensity but its temperature falls. This portion ends at 1.3-1.5 GPa after which the position of the maximum remains unchanged (225 K) but the intensity begins to drop. With further rise in pressure the initial
l / I
200
I00
soo
~K
o,e
jIo t T= , K O
2gO
o
o
~" f'l 0 O 0
I
u C ~
I !
I
o
0
I 2
I P, GPa
F~o. 2. TL curves on irradiation of PTFE at room temperature and different pressures (numbering o f curves as in Fig. 1) (a) and dependence of TM and IM on pressure on irradiation (b).
Thermoluminescence of polymers
• /0
425
2
q
I
f~O
I r,K
250
270 _ ~ ( b )
o
o
- 3O
.
230
/
2
P, GPa
FIG. 3. TL curves on irradiation of PE at room temperature and different pressures (numbering of curves as in Fig. 1) (a) and dependence of TM (1) and IM (2) on pressure on irradiation.
portion of the TL curve continues to shift to low temperatures leading to the appearance of a further maximum, true, in the form of a shoulder about 180 K which even for the highest pressure used does not stand out as an independent maximum. Figure 4 presents the dependences of the position of the initial portion of the TL curve, (Ii,it = 0.1 IM) on pressure on irradiation. Despite the fairly heavy scatter, at least two portions of the dependence may be isolated with different slopes both for PE and PP. The numerical values of the slope of the high temperature straight line portions (0.094+0.007 and 0.08+0.01 K/MPa respectively for PP and PE) are close for the two polymers although at lower temperatures (higher pressures) they strongly differ (0.05 + 0.01 and 0.020 + 0.006 K/MPa for PP and PE, respectively). Analysis of the results shows that all the TL maxima which appear after irradiation of the polymers at room temperature and at raised pressures are located in the intervals of the known PS $$:3-@
426
V . A . AULOV 1 I
I
2 I
I
P, GPa ~,K
20O
200
150
2
%
100
I
I
I
I 2
P, GPa
FIG. 4. Position of the initial portion of the T L curve as a function of pressure on irradiation at room t e m p e r a t u r e for P E (1) and PP (2).
phase and relaxational transitions in polymers. Thus, the maximum at 300 K for F r F E is close to the known (4) phase transitions for this polymer (294 and 303 K). The maxima at 225 K for PE and 225 K for PP are close to the known relaxational transitions for these polymers (the glass transition temperature of the amorphous regions [5, 6]). The other maxima are associated with secondary relaxational transitions observed by different methods [5-7]. The appearance of the luminescence maximum at the temperature of the transition means that during irradiation the temperature of this transition was higher than that of irradiation, the molecular mobility characteristic of this transition is arrested by pressure and the charges become able to stabilize at the temperature of irradiation (at room temperature in the given case). Since restriction of motion occurs only through pressure, i.e. through reduction in the free volume, it is natural to assume that the differences in behaviour between the polymers are associated with differences in compressibility. In fact, the compressibility is minimal in PE and maximal in PTFE with PP occupying a midway position [8]. In addition, the glass transition temperatures increase in the series PE < PP < PTFE which also results in a different value of free volume in the glassy state
Thermoluminescence of polymers
427
[9] (minimal in PE and maximal in PTFE). The differences in the free volumes in the glassy state of the polymers studied lead to differences in compressibility and then to a difference in the baric coefficients of shift of luminescence to low temperatures and, finally, to a different form of the TL curves after irradiation at high pressures. Increase in pressure leads to restriction of the movement of a particular portion in the spectrum of the molecular motions of the given relaxational transition. In other words, there is mechanical vitrification of a certain portion in the spectrum of molecular motions. With rise in pressure the width of this portion increases. This explains the rise in intensity and the fall in the temperature of the TL maximum. However, as soon as the portion of restricted motion reaches a maximum in the spectrum, fall in the temperature of the TL maximum ceases. As follows from the results, all the relaxational transitions show similar behaviour. As for the fall in the intensity of the TL maximum after a certain pressure level, here one may advance the assumption that it is linked with increase in the density of the polymer, i.e. with decrease in the distance between neighbouring molecules, which facilitates intermolecular charge transfer (both of the electron and hole), i.e. accelerates diffusion of the charges with subsequent recombination. Thus, the application of pressure during irradiation results in two competing processes: on the one hand, the number of stabilized charges grows through restriction of the molecular motions and, on the other, the effectiveness of stabilization drops through increase in the mobility of the charges due to increase in the probability of intermolecular charge transfer which subsequent recombination. As soon as the first of these processes rapidly slow after reaching a maximum in the relaxation time spectrum, a second process immediately appears and the intensity of the TL maximum begins to drop. With such an interpretation it is clear why arrest of shift of the TL maximum and the attainment of its highest intensity depending on pressure match. As Fig. 2b shows, the intensity of the TL maximum at 300 K for PTFE begins to fall at a pressure >0.6-0.7 GPa which corresponds to the pressure of the transition at room temperature to a denser phase [10]. Incidentally, this transition is also reflected in stabilization of the radicals [11]: the radiation-chemical yield of the radicals under pressure above 0.7 GPa drops rapidly. It may also be assumed that TL recorded in the present work is entirely due to the charges stabilized in the amorphous regions of the polymer since the whole impact on the crystalline regions elastically disappears on removing the pressure in liquid nitrogen. Thus, the pressure applied at room temperature leads to arresting of the movements of the segments in polymers the smaller the higher the pressure. Physically this means that the glass transition temperature of the polymer either of another relaxational or phase transition has become higher than the temperature of irradiation and the charges are able to stabilize on irradiation. Subsequent cooling in liquid nitrogen of the polymer irradiated under pressure and removal of pressure do not lead to decay of the stabilized charges since now the molecular mobility is frozen out. The decay of charges occurs on heating in the intervals of the relaxational and phasic transitions. It should be particularly emphasized that the release and recombination of charges results from the unfreezing of the diffusion of charges (limiting stage). The direct heat expulsion of an electron from the trap is excluded since on irradiation the polymer was at room temperature, i.e. above the temperature of all the TL maxima appearing. The small traps from which expulsion of electrons would be normally possible are simply empty. In other words, the technique proposed in the work allows one to record the TL due to recombination of stabilized electrons in traps with a depth above a certain value which depends on the temperature of irradiation.
Translated by A. CRozv
428
S.N. CHVALUN
REFERENCES 1. E. R. KLINSHPONT, V. P. KIRYUKHIN and V. K. MILINCHUK, Dokl. Akad. Nauk SSSR 279: 924, 1983. 2. V. K. MILINCHUK, E. R. KLINSHPONT and V. P. KIRYUKHIN, Radiat. Phys. Chem. 28: 331, 1986. 3. Ye. Yu, ASTAKHOV, E. R. KLINSHPONT and V. K. MILINCHUK, Vysokomol. soyed. A30: 702, 1988 (translated in Polymer Sci. U.S.S.R. A30: 4, 699, 1988). 4. E. L. RODRIGUEZ, J. Appl. Polymer Sci. 32: 4049, 1986. 5. Perekhody i relaksatsionnye yavleniya v polimerakh (Transitions and Relaxational Phenomena in Polymers) (Edited by R. F. Boyer). P. 384, Moscow, 1968. 6. R.F. BOYER, Rubber Chem. Technol. 36: 1303, 1963. 7. V. P. PRIVALKO, Spravochnik po fizicheskoi khimii polimerov (Guide to Polymer Physical Chemistry). Vol. 2, p. 156, Kiev, 1984. 8. I. I. PEREPECHKO, Svoistva polimerov pri nizkoi temperature (Properties of Polymers at Low Temperature). P. 180, Moscow, 1977. 9. Yu. P. YEMPOL'SKII and S. M. SHISHATSKII, Dokl. Akad. Nauk SSSR 304: 1191, 1989. 10. S. K. BHATEJA and K. D. PAE, J. Macromolec. Sci. C13: 77, 1975. 11. V. K. MILINCHUK, V. P. KIRYUKHIN and E. R. KLINSPONT, Dokl. Akad. Nauk SSSR 227: 149, 1976.
0032-3950/91$15.00+ .00 (~)1992PergamonPressplc
PolymerScienceVol. 33, No. 3, pp. 428-436,1991 Printed in GreatBritain.
CALCULATION OF X-RAY DIFFRACTION IN THE STRUCTURE OF HIGHLY ORIENTED POLYETHYLENE* S. N. CHVALUN Karpov PhysicochemicalResearch Institute (Received 25 December 1989)
The intensity of scatter in a system of crystallites and the amorphous region between them modelling the structure of highly oriented polyethylene has been calculated. The increase observed on orientational stretching of PE in the longitudinal size of the crystallite and the integral intensity of the reflection 002 is linked with the formation of extended linear systemsof several crystallites and straightened communicating chains between them. An explanation for the existence of X-ray scattering on the meridian of the first layer line is proposed.
THE FACT, established in highly oriented PE, that the longitudinal size of the crystallite exceeds the length of the large period has led to the appearance of various models of the structure of such specimens. This is also the model of the advent in oriented polymers of fibrillar or acicular crystallites [1, 2], the model of the three-dimensionally ordered crystallite bridges [3], the formation of linear systems including chains in the neighbouring crystallites and straightened communicating chains in the amorphous regions [4]. In reference [5] this was explained with the coherent
* Vysokomol. soyed. A33: No. 3,508-515, 1991.
0032-3950/91$15.00+ .00 ~ 1992PergamonPressplc
Printed in GreatBritain.
THERMOLUMINESCENCE OF POLYMERS IRRADIATED AT ROOM TEMPERATURE AND AT HIGH PRESSURE* V. A . AULOV Karpov PhysicochemicalResearch Institute (Received 2 October 1989)
The influence of pressure to 2.3 GPa on the thermoluminescence of PE, PP and FFFE irradiated at room temperature has been studied. Thermoluminescence of the polymers irradiated without pressure is represented by a weak glow above 300 K with a maximum at 333-350 K. Irradiation under pressure raises the intensity and lowers the temperature of this maximum. Shift of the maximum continues until it reaches the position of the phase or relaxationai transition (-300 K for PTFE, 255 K for PP and 225 K for PE) after which the temperature of the maximum does not change but its intensity begins to drop. With rise in pressure the initial portion of the thermoluminescence curve continues to shift to low temperatures leading to the formation of a further two to three maxima in the interval 150-200 K at a pressure >1.7 GPa. The appearance of the thermoluminescence maxima after irradiation at room temperature under pressure signifies that during irradiation the temperature of the relaxational transition of the polymer is higher than the temperature of irradiation, the molecular mobility characteristic of it is inhibted by pressure and the charges are able to stabilize. The differences between the polymers in the number of thermoluminescence maxima and the rate of shift of the initial portion of the curve with rise in pressure are connected with the difference in the values of free volume and compressibility.
THERMOLUMINESCENCE (TL) of polymers is usually observed after irradiation at low temperature. Most investigators consider that charge recombination leading to luminscence is stimulated by acceleration of diffusion of the charges in the intervals of the relaxational transitions to which is also related the correlation between the positions of the maxima of T L and the relaxational transitions. Yet it is well known that the position of the relaxational transitions depends on the pressure applied since by reducing the size of the free volume the molecular mobility is arrested. In this connection it was of interest to investigate the effect of pressure on the T L of polymers, it being desirable to alter only one p a r a m e t e r - - p r e s s u r e , leaving unchanged the temperature of irradiation since change both in temperature and pressure [1-3] complicates the analysis and interpretation of the experimental results. To establish the effect of pressure on the form of the TL curve and determine the baric coefficients of the position of the relaxational transitions we, in the present work, investigated the T L of some polymers after irradiation at room temperature and at high pressure. We used linear P E with Mw = 3 x 105, polydispersity 3.5 and number of branchings < 1 per 1000 C atoms, H D P E of grade Marlex 5005, commercial high and low density P E samples, PP and PTFE. Irradiation was carried out at r o o m temperature in a device of the piston-cylinder type with the pressure fixed with a nut. The pressure value was determined from the exertion produced on the piston with a diameter 4 and 10 mm. The friction between piston and cylinder was disregarded. The polymers under pressure were held for I h, irradiated to a dose 15 kGr with a y source with a power 12 kGr/h, cooled immediately after irradiation in liquid nitrogen, the pressure dropped and the
*Vysokomol. soyed. A33: No. 3, 501-507, 1991. 422
Thermoluminescence of polymers
100
TM, K
300
(~)
Q O Q
2501
423
I. e=
• q
•
I~ t
I
ZM 8
-
~/
-
•
•
J 1
2
P, GPa
FIG. 1. TL curves on irradiation of PP at room temperature and a pressure 0 (1); 0.25 (2); 1.0 (3); 1.5 (4); 1.7 (5) 2.3 GPa (6) (a) and dependence of TMand 1Mon pressure on irradiation (b). samples r e m o v e d f r o m t h e d e v i c e . The samples were stored in this form up to heating which was carried out at the rate 10 K/min. Figure 1 presents the results obtained for PP. It will be seen that irradiation at r o o m t e m p e r a t u r e without pressure leads, on heating, to the appearance of weak luminescence above 300 K with a m a x i m u m at - 3 5 0 K. Increase in pressure on irradiation raises the intensity of luminescence IM and lowers the t e m p e r a t u r e of the m a x i m u m TM. These changes continue to --1.0 GPa. With further increase in pressure the position of the m a x i m u m does not change but its intensity diminishes. H o w e v e r , the initial portion of the T L curve as pressure rises continues to shift to low t e m p e r a t u r e s leading to the formation of a further two T L m a x i m a (~200 and --150 K). Thus, irradiation of PP at r o o m t e m p e r a t u r e and a pressure > 1 . 7 G P a leads to the appearance of T L in the interval 100-300 K
424
V . A . AuLov
with three maxima. We would emphasize a characteristic feature of all the TL maxima and of all the polymers studied---after reaching the highest value the intensity begins to drop with increase in pressure with no change in its position. A similar picture was also observed for PTFE (Fig. 2). Admittedly, the intensity of its TL is much less and, therefore, it is hard to monitor in detail all the changes in the form of the TL curve. Nevertheless, it is quite clear that, in the pressure interval used, three TL maxima can be obtained (~300 K, in the interval 215-230 K and ~150 K). As in the case of PP, the maxima at 300 K does not change its position, while its intensity begins to drop with rise in pressure after 0.6--0.7 GPa. As Fig. 3 shows, the behaviour of the TL curve of polyethylene in the initial portion of change in pressure on irradiation differs little from that of the PP curve: the maximum grows in intensity but its temperature falls. This portion ends at 1.3-1.5 GPa after which the position of the maximum remains unchanged (225 K) but the intensity begins to drop. With further rise in pressure the initial
l / I
200
I00
soo
~K
o,e
jIo t T= , K O
2gO
o
o
~" f'l 0 O 0
I
u C ~
I !
I
o
0
I 2
I P, GPa
F~o. 2. TL curves on irradiation of PTFE at room temperature and different pressures (numbering o f curves as in Fig. 1) (a) and dependence of TM and IM on pressure on irradiation (b).
Thermoluminescence of polymers
• /0
425
2
q
I
f~O
I r,K
250
270 _ ~ ( b )
o
o
- 3O
.
230
/
2
P, GPa
FIG. 3. TL curves on irradiation of PE at room temperature and different pressures (numbering of curves as in Fig. 1) (a) and dependence of TM (1) and IM (2) on pressure on irradiation.
portion of the TL curve continues to shift to low temperatures leading to the appearance of a further maximum, true, in the form of a shoulder about 180 K which even for the highest pressure used does not stand out as an independent maximum. Figure 4 presents the dependences of the position of the initial portion of the TL curve, (Ii,it = 0.1 IM) on pressure on irradiation. Despite the fairly heavy scatter, at least two portions of the dependence may be isolated with different slopes both for PE and PP. The numerical values of the slope of the high temperature straight line portions (0.094+0.007 and 0.08+0.01 K/MPa respectively for PP and PE) are close for the two polymers although at lower temperatures (higher pressures) they strongly differ (0.05 + 0.01 and 0.020 + 0.006 K/MPa for PP and PE, respectively). Analysis of the results shows that all the TL maxima which appear after irradiation of the polymers at room temperature and at raised pressures are located in the intervals of the known PS $$:3-@
426
V . A . AULOV 1 I
I
2 I
I
P, GPa ~,K
20O
200
150
2
%
100
I
I
I
I 2
P, GPa
FIG. 4. Position of the initial portion of the T L curve as a function of pressure on irradiation at room t e m p e r a t u r e for P E (1) and PP (2).
phase and relaxational transitions in polymers. Thus, the maximum at 300 K for F r F E is close to the known (4) phase transitions for this polymer (294 and 303 K). The maxima at 225 K for PE and 225 K for PP are close to the known relaxational transitions for these polymers (the glass transition temperature of the amorphous regions [5, 6]). The other maxima are associated with secondary relaxational transitions observed by different methods [5-7]. The appearance of the luminescence maximum at the temperature of the transition means that during irradiation the temperature of this transition was higher than that of irradiation, the molecular mobility characteristic of this transition is arrested by pressure and the charges become able to stabilize at the temperature of irradiation (at room temperature in the given case). Since restriction of motion occurs only through pressure, i.e. through reduction in the free volume, it is natural to assume that the differences in behaviour between the polymers are associated with differences in compressibility. In fact, the compressibility is minimal in PE and maximal in PTFE with PP occupying a midway position [8]. In addition, the glass transition temperatures increase in the series PE < PP < PTFE which also results in a different value of free volume in the glassy state
Thermoluminescence of polymers
427
[9] (minimal in PE and maximal in PTFE). The differences in the free volumes in the glassy state of the polymers studied lead to differences in compressibility and then to a difference in the baric coefficients of shift of luminescence to low temperatures and, finally, to a different form of the TL curves after irradiation at high pressures. Increase in pressure leads to restriction of the movement of a particular portion in the spectrum of the molecular motions of the given relaxational transition. In other words, there is mechanical vitrification of a certain portion in the spectrum of molecular motions. With rise in pressure the width of this portion increases. This explains the rise in intensity and the fall in the temperature of the TL maximum. However, as soon as the portion of restricted motion reaches a maximum in the spectrum, fall in the temperature of the TL maximum ceases. As follows from the results, all the relaxational transitions show similar behaviour. As for the fall in the intensity of the TL maximum after a certain pressure level, here one may advance the assumption that it is linked with increase in the density of the polymer, i.e. with decrease in the distance between neighbouring molecules, which facilitates intermolecular charge transfer (both of the electron and hole), i.e. accelerates diffusion of the charges with subsequent recombination. Thus, the application of pressure during irradiation results in two competing processes: on the one hand, the number of stabilized charges grows through restriction of the molecular motions and, on the other, the effectiveness of stabilization drops through increase in the mobility of the charges due to increase in the probability of intermolecular charge transfer which subsequent recombination. As soon as the first of these processes rapidly slow after reaching a maximum in the relaxation time spectrum, a second process immediately appears and the intensity of the TL maximum begins to drop. With such an interpretation it is clear why arrest of shift of the TL maximum and the attainment of its highest intensity depending on pressure match. As Fig. 2b shows, the intensity of the TL maximum at 300 K for PTFE begins to fall at a pressure >0.6-0.7 GPa which corresponds to the pressure of the transition at room temperature to a denser phase [10]. Incidentally, this transition is also reflected in stabilization of the radicals [11]: the radiation-chemical yield of the radicals under pressure above 0.7 GPa drops rapidly. It may also be assumed that TL recorded in the present work is entirely due to the charges stabilized in the amorphous regions of the polymer since the whole impact on the crystalline regions elastically disappears on removing the pressure in liquid nitrogen. Thus, the pressure applied at room temperature leads to arresting of the movements of the segments in polymers the smaller the higher the pressure. Physically this means that the glass transition temperature of the polymer either of another relaxational or phase transition has become higher than the temperature of irradiation and the charges are able to stabilize on irradiation. Subsequent cooling in liquid nitrogen of the polymer irradiated under pressure and removal of pressure do not lead to decay of the stabilized charges since now the molecular mobility is frozen out. The decay of charges occurs on heating in the intervals of the relaxational and phasic transitions. It should be particularly emphasized that the release and recombination of charges results from the unfreezing of the diffusion of charges (limiting stage). The direct heat expulsion of an electron from the trap is excluded since on irradiation the polymer was at room temperature, i.e. above the temperature of all the TL maxima appearing. The small traps from which expulsion of electrons would be normally possible are simply empty. In other words, the technique proposed in the work allows one to record the TL due to recombination of stabilized electrons in traps with a depth above a certain value which depends on the temperature of irradiation.
Translated by A. CRozv
428
S.N. CHVALUN
REFERENCES 1. E. R. KLINSHPONT, V. P. KIRYUKHIN and V. K. MILINCHUK, Dokl. Akad. Nauk SSSR 279: 924, 1983. 2. V. K. MILINCHUK, E. R. KLINSHPONT and V. P. KIRYUKHIN, Radiat. Phys. Chem. 28: 331, 1986. 3. Ye. Yu, ASTAKHOV, E. R. KLINSHPONT and V. K. MILINCHUK, Vysokomol. soyed. A30: 702, 1988 (translated in Polymer Sci. U.S.S.R. A30: 4, 699, 1988). 4. E. L. RODRIGUEZ, J. Appl. Polymer Sci. 32: 4049, 1986. 5. Perekhody i relaksatsionnye yavleniya v polimerakh (Transitions and Relaxational Phenomena in Polymers) (Edited by R. F. Boyer). P. 384, Moscow, 1968. 6. R.F. BOYER, Rubber Chem. Technol. 36: 1303, 1963. 7. V. P. PRIVALKO, Spravochnik po fizicheskoi khimii polimerov (Guide to Polymer Physical Chemistry). Vol. 2, p. 156, Kiev, 1984. 8. I. I. PEREPECHKO, Svoistva polimerov pri nizkoi temperature (Properties of Polymers at Low Temperature). P. 180, Moscow, 1977. 9. Yu. P. YEMPOL'SKII and S. M. SHISHATSKII, Dokl. Akad. Nauk SSSR 304: 1191, 1989. 10. S. K. BHATEJA and K. D. PAE, J. Macromolec. Sci. C13: 77, 1975. 11. V. K. MILINCHUK, V. P. KIRYUKHIN and E. R. KLINSPONT, Dokl. Akad. Nauk SSSR 227: 149, 1976.
0032-3950/91$15.00+ .00 (~)1992PergamonPressplc
PolymerScienceVol. 33, No. 3, pp. 428-436,1991 Printed in GreatBritain.
CALCULATION OF X-RAY DIFFRACTION IN THE STRUCTURE OF HIGHLY ORIENTED POLYETHYLENE* S. N. CHVALUN Karpov PhysicochemicalResearch Institute (Received 25 December 1989)
The intensity of scatter in a system of crystallites and the amorphous region between them modelling the structure of highly oriented polyethylene has been calculated. The increase observed on orientational stretching of PE in the longitudinal size of the crystallite and the integral intensity of the reflection 002 is linked with the formation of extended linear systemsof several crystallites and straightened communicating chains between them. An explanation for the existence of X-ray scattering on the meridian of the first layer line is proposed.
THE FACT, established in highly oriented PE, that the longitudinal size of the crystallite exceeds the length of the large period has led to the appearance of various models of the structure of such specimens. This is also the model of the advent in oriented polymers of fibrillar or acicular crystallites [1, 2], the model of the three-dimensionally ordered crystallite bridges [3], the formation of linear systems including chains in the neighbouring crystallites and straightened communicating chains in the amorphous regions [4]. In reference [5] this was explained with the coherent
* Vysokomol. soyed. A33: No. 3,508-515, 1991.