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UV effect on the alkaline dissolution of γ-irradiated polyvinylidene fluoride film
Radiat. Phys. Chem. Vol. 27. No. 5, pp. 399--405, 1986 Int, Jnl. Radiat. Applic, lnstrum., Part C
0146-5724/86 $3.00 + .00 © 1986 Pergamon Press Ltd.
Printed in Great Britain.
UV EFFECT ON THE ALKALINE DISSOLUTION OF 'y-IRRADIATED POLYVINYLIDENE FLUORIDE FILM YOSHIHIDEKOMAKI Department of Chemistry, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, Japan (Received 30 December 1983; in revised form 15 February 1984)'t
Abstract--The exposure of T-irradiated polyvinylidene fluoride to UV in oxygen was found to change the dissolution characteristics in an alkaline solution. The UV and IR spectra, the gel fraction, and the elongation at the break of the film were measured to understand the experiment. The UV exposure decreased the intensity of absorption in the UV spectrum and caused the changes in the IR spectrum. The gel fraction and the elongation were changed in relation to the dose of ~t radiation and the UV exposure. At the higher dose of ~t radiation the dissolution increases with the UV exposure, but at the lower dose it decreases. In the latter photocrosslinking is available for strengthening of the binding among the polymer and in the former the formation of the oxygenated species which was formed through the violent T-irradiation leads to the ready dissolution. INTRODUCTION THE AUTHOR has studied the nuclear pore filter of polyvinylidene' fluoride (PVDF) by the chemical etching o f the tracks formed by fission fragments (FF). O-3) In this case, it is chemically important for the track etching that the dissolution along the track core is larger than that of the bulk in polymer. The exposure to UV in the gaseous atmosphere has been known to be effective on the subsequent alkaline development of the fission tracks in polycarbonate and in cellulose esters. Especially in polycarbonate, the exposure to UV in oxygen successfully developed the fission tracks within far shorter period. ¢4.s~ Contrary to expectation, the time taken for the development of F F tracks in P V D F film was found to be longer after the UV exposure. Polycarbonate and cellulose nitrate are defined to be polymers of the degrading type with radiation. The author feels that the degraded products may not form photo-crosslinking but react with oxygen under the UV exposure, leading to more rapid dissolution in the alkaline solution. Then, the dissolution of v-irradiated P V D F film in the alkaline solution was examined with the UV exposure. Since the dissolution was found to be affected with the radiation dose and the UV exposure, the UV and IR spectra, the gel fraction, and the elongation o f P V D F film were examined subsequently. The main chain scission and crosslinking of poly m e r was known to occur by v-irradiation or electron beam and sometimes ultraviolet radiation (UV), such as in polyethylene, ~6~ polypropylene, ~ polyvinyl chloride cs~ and others. ~9'~°J But it has not 5"Publication was delayed due to a fire at the typesetting facility. The publisher regrets any inconvenience to the author and readers.
been known that the polymer irradiated in advance by v-ray was exposed to UV in order to change the characteristics. EXPERIMENTAL A P V D F fdm (Kureha K F Polymer, a biaxially stretched 50 ttm film, d = 1.76 at 250C) was irradiated 1 x 104 to 2 x 106 G y of V radiation at dose rate o f 1.3 × 106 R/hr. Irradiation were carried out in vacuum and in oxygen or in nitrogen at 6.6 x 104 Pa, the specimen in a glass ampoule. After irradiation a part of the specimens was stored in air, as a reference in order to see the effect o f storage, and another was exposed to UV under the flow of oxygen o r nitrogen at the flow rate of 1.2 m/min. The UV lamp used is a high pressure mercury lamp with main emission lines at 254, 313, 366 and 435 nm, respectively. (SHL-100 UV-2, Toshiba Electric Co. Ltd.) The film was horizontally rotated so as to minimize the irregular irradiation and absorbed UV through a convex quartz lens without any filter. The UV intensity at the position of f'dm was measured to be about 3 mW/cm 2 over the whole wavelengths from 200 to 320 nm using UV radiometer (Topcon, UVR-254). The IR and UV spectra were measured instantly after the UV exposure. The rate of dissolution of P V D F ftlm was measured every constant time for the specimen exposed to U V from the weight decrease in a 10N N a O H solution at 85°C. The measurement of the gel fraction of P V D F followed the method b y Makuuchi et al.
399
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Y. KOMAK[
RESULTS Dissolution in the alkaline solution The dissolution of PVDF fdm in the alkaline solution was found to change in relation to the dose of ~/-irradiation and the UV exposure. The rates of dissolution of v-irradiated PVDF were examined after the period of 22, 50, 100 and 150 hrs of the UV exposure [UV(t)] and the ratios of these to that without the UV exposure [UV(0)] were obtained. When the ratio is 1, the dissolution is not affected with the UV exposure. The ratio more than 1 indicates the increase of dissolution with the UV exposure and the ratio less than 1 contrarily the decrease. Figure 1 shows the ratios against the dose of radiation. Effects of the UV exposure are summarized as follows. First, in the specimen irradiated by v-ray up to the dose of 105 Gy, a tendency of rather difficult dissolution appears with the UV exposure. Secondarily, up to the dose of los Gy, the ratio increases with the UV exposure and goes up to as high as 3 times compared with that without the UV exposure. Finally, over l0 s Gy, a), the dissolution shows a tendency to decrease for the short UV exposure, and b), that again increases for the longer UV exposure. The UV exposure reduced also the color of PVDF film which colored yellow to brown with the dose of radiation. Figure 2 shows the absorbance ratio at 600 nm against the UV exposure time as the degree of discoloration of ~-irradiated film. The absorbance ratio was defined as the value equal to [Abs(0) - Abs(U)]/Abs(0), × 100%, where the abbreviation, Abs(0,U) indicates the absorbances in the absence of UV exposure, UV(0), or in the presence, UV(U). The UV exposure showed 27% fading I
'
l
of color on the v-irradiated P V D F film. In the immersion of alkaline solution, the v-irradiated P V D F film colored further brownish to black, but the film which was in advance exposed to U V merely colored pale brown. In order to examine the changes of characteristicsof P V D F in relationto the dose of ~/irradiation and the U V exposure, U V and IR spectra were measured, and the gel fraction and the elongation at break were also measured to discuss the crosslinking. UV spectrum Figure 3(a) is the UV spectrum of PVDF film virradiated to 5 x 10~ Gy in vacuum. The similar curves were obtained by the v-irradiation in oxygen, but the intensity was larger in vacuum than in oxygen. The peaks of absorptions were observed at 227 nm, 274 nm and 315 nm which were assigned to diene, triene and tetraene, respectively} TM The spectrum was stable in air for a long period. The exposure to UV reduced the intensity of the UV spectrum as in Fig. 3(b) after 100 hrs exposure. Figtire 3(c) is the spectrum of a virgin film. Figure 4 shows the differences of absorption from 200 to 500 nm between the -/-irradiated PVDF and the UV exposure in oxygen after v-irradiation. The difference of absorbance increases with the UV exposure time. Long storage of the fdm in air shows the same tendency of UV absorption to an extent. In order to see the effects of atmospheres, the films were exposed to UV in the absence of oxygen, that is, in nitrogen. The UV exposure effect appeared only in the presence of oxygen and not in nitrogen. When the fdm was first exposed to UV in oxygen for a certain period and subsequently in '
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RADIATION DOSE (Gy)
Fig. I. The ratio o f dissolution rates vs 3, radiation dose. The dissolution rate means the weight dissolved
from a single face of the film per hour. The dissolution rates, UV(t, 0), indicate the one after UV exposure for some periods and the one without UV exposure, respectively.
Alkaline dissolution of V-irradiated polyvinylidene fluoride film '1
i
401
nitrogen, the decrease o f the absorptions at 227 nm were compared with each time as shown in Fig. 5. A f i ~ !($i~1~U V eXposUre ih nitrogen, re-exposure to UV in the presence of oxygen decreased surely the absorption.
30 7 O
IR spectrum
2o
There were slight changes in the IR spectrum of P V D F before and after the v-irradiation. Absorpt,J,J tions in the neighborhood of 1850, 1830, 1760, 1720 Z and 1600 cm - j are observed in the range of 1900(Z:) 0:: 1600 c m - i in wave number. ° t> Figure 6 shows that o ~0 r~ the UV exposure induced the relative intensities of IR transmittances against the UV exposure time for the frequencies at 1850, 1760 and 1720 c m - I . The intensities of absorptions at 1850 and 1760 c m increased with the UV exposure, but the absorption t I l 50 10o 150 at 1720 cm-m decreased. Absorptions at 1850 and 1760 cm -m had been assigned to - C O O H and HOURS EXPOSED - C O F , respectively, (~H3) and at 1830 cm - I the Fig. 2. The discoloration of brownish color in v-irradiated binding o f oxygen. ( ' ) The assignment of 1720 c m PVDF film to yellowish by UV exposure was examined of the absorption intensity in the wavelength of 600 nm was not clear to be an isolated or a conjugated douwhich was assigned yellow to brown in color region of the ble bond (t3) and 1600 cm-* has been left unvague. spectrum. The 50 p,m thick film was irradiated to the dose of 5 x 105 Gy. Gel fraction Figure 7 shows the gel fraction of P V D F film irradiated by ~,-ray. F o r the 9 ~m thick P V D F film
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WAVELENGTH (nm) Fig. 3. The UV absorption spectrum ofv-in'adiated PVDF film (a), the one of V-irradiated PVDF film after UV exposure, and the one of a virgin PVDF film, vs wavelength. (a) 3' radiation (5 x 105 Gy) induced absorbance. (b) The absorbance after UV exposure for 100 h. (c) The absorbance in the virgin PVDF t'dm.
WAVE LENGTH (nm) Fig. 4. The difference of the absorbances of 3'-irradiated PVDF film after UV exposure and the one without UV exposure in the range of 200-500 nm. The numerals on the curves show the time exposed to UV(min).
402
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STORAGE TIME 50
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HOURS EXPOSED Fig. 5. The change of the absorptions after alternate UV exposures in oxygen and in nitrogen vs UV exposure time. The curve at the top of the figure shows the absorption of 3,-irradiated PVDF film without UV exposure, but stored in air, and the one at the bottom of "~-irradiated PVDF film after alternate UV exposures in oxygen and in nitrogen for some periods.
I .
0.05~
~--~
(o)
-
0.15 L.U Z
Mechanical property The results of elongation at break of the PVDF films irradiated by w-ray and the UV exposure were
(b)
133 re-
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irradiated by ~/-ray in oxygen, the gel was not detected until the dose up to ca. 106 Gy. The gel fraction showed to be smaller in oxygen than that in vacuum, as Makuuchi et al. pointed out that oxygen hindered the formation of crosslinking.(Iw) Figure 8 shows the gel fraction of 50 ~m thick PVDF films ~t-irradiated up to 4 × 105 and 106 Gy against the UV exposure. This indicates the effect of UV exposure after the ~/-irradiation. On the exposure to UV, the gel fraction decreased for short time of UV exposure and shows the almost constant for further UV exposure.
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HOURS EXPOSED Fig. 6. The UV exposure induced relative intensities of the IR transmittances for frequencies at (a) 1850, (b) 1760 and (c) 1720 cm-t vs UV exposure time.
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106
107
RADIATION DOSE (Gy) Fig. 7. The gel fractions of-v-irradiated PVDF film in vacuum or in oxygen, vs ~ radiation dose. PVDF film; 50 p.m thick.
Alkaline dissolution of ~/-irradiated:,polyvinylidene fluoride film
. . . .
403
were assigned already to the oxygenated species which were formed from the scissions of main chains in PVDF, that is, -COOH and -COF, reo (o) o_ spectively.(, :.m On the contrary, the absorption at 1720 c m - ' has been observed both in the thermal decomposition"3) and in the ~/-irradiation, "l) but {b) .,., 5 0 has been left undetermined, although it had merely been assigned to a double bond. In this experiment, LIthe absorption at 1720 cm- : may be assigned to the _.I l.IJ stretching band of the conjugated double bond, because the double bond absorption due to the polyenes decreases by the UV exposure as shown in 0(~ I I I I I I I I I I I Fig. 3. 50 I00 A detailed interpretation of the UV effect upon HOURS EXPOSED the dissolution of v-irradiated PVDF film in the alFig. 8. The gel fractions of v-irradiated PVDF film (50 p.m) kaline solution is difficult directly at this time. in vacuum after UV exposure, vs UV exposure time. (a) Using Seguchi and Makuuchi's interpretations of The PVDF film was irradiated to the dose of I x 106 Gy. Co) The PVDF film was irradiated to the dose of 4 x 105 the changes of characteristics in the v-irradiated PVDF and in addition, using these experimental reGy. sults, the dissolution behaviors with the UV exposure in Fig. 1 may be explained as follows. S T E P I: On radiation dose up to ca. 105 Gy. TABLE1. THE ELONGATIONATBB.EAK OF THE"~-IRRADIATEDPVDF From(50 1) Effect of ~/-irradiation: The main chain scis~m) EXPOSEDTOUV FORSOME sion and crosslinking increase progressively, but PERIODS.THE RATEOFELONGATION: give only insignificant effect. There are the release 20 cm/min AT 20°C. of hydrogen fluoride and the formation of the oxi" IJ.V. Bongoygenated species with the isolated and the conjurodiation tion gated double bonds. Ix, 2) Effect of the UV exposure: The UV expoI 0 42O sure ruptures mainly the conjugated double bonds to form the photo-crosslinking. The photo-crossA 2 0 20 400 linking serves to strengthen the bindings of the pol3 160 570 ymer molecules, leading to the difficult dissolution 1 0 410 of film to an extent. The conjugated double bonds e 2 ix104 20 360 serve to form the oxygenated species, too.
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310 60
20
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160
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indicated in Table 1. For PVDF v-irradiated to 104 Gy, there appears no significant changes of the elongation for the period of 20-160 hrs of UV exposure, but at 5 × 105 Gy, the elongation at break decreases abruptly for the long UV exposure. DISCUSSION Although the commercial PVDF films have no absorptions of wavelength longer than ca. 220 nm, the distinct absorptions reveal at 227, 274, 315 nm after v-irradiation. It was found that the UV exposure reduced clearly the intensities of these absorptions only in the presence of oxygen as shown in Fig. 3. On the other hand, the IR spectrum showed that the absorptions at 1850 and 1760 cm- J increased a little, but that at 1720 c m - : decreased as shown in Fig. 6. The former two absorptions
RPC
27/5-F
S T E P H: On the dose more than ca. 105 Gy.
1) Effect of ~/-irradiation: The main chain scissions and crosslinkings become to give some significant effects increasingly. ('4) Since the G-value, G(s), of scission is roughly the same with that of crosslinking, G(x), G(s) = G(x) - 0.6":) the polymer becomes to be readily soluble through the subsequent formation of the micro-cracking like a spongeCm by the violent release of the gaseous products, and colors appreciably in an immersion of the alkaline solution to show the vigorous formation of double bonds. 2) Effect of the UV exposure: To the film irradiated significantly by ",/-ray, the UV exposure can fasten no longer the networks of the individual polymeric molecules by photo-crosslinking, but increase the formation of oxygenated species through the double bonds followed by the ready dissolution of polymer. The fading of coloration and the increase of pliancy of the film with the UV exposure suggest the change of characteristics. Reaching the dose of 2 x 106 Gy, the effect of UV exposure on the dissolution decreases. This indicates that the dissolution in highly -t-irradiated film occurs in small correlation with the UV exposure. But the long UV exposure may show the effect yet.
404
Y. KOMAKI
Now, the reaction of a virgin PVDF film with the mixture of oxygen and fluorine was found to form new bond in PVDF having oxygen. ('2) Such a compound becomes to be readily soluble in the alkaline solution. The following scheme has been proposed to the ready dissolution, ~COF
+H20
) --COOH
+NaOH> --:COONa.
The author believes that the increasing dissolution rate of the v-irradiated PVDF film in the alkaline solution is primarily based upon the formation of oxygenated PVDF. It is reasonable from the photochemical considerations for the reaction of polydiene with oxygen, beside the present experimentals, that the conjugated double bonds produced by ~/ radiation are concerned with the formation of carbonyls and photo-crosslinking. When cis and trans 1,4 polybutadiene which have the conjugated double bonds in the main chains were exposed to UV in the presence of oxygen, for instance, the formation of carbonyls were reported, followed by photo-crosslinking, H6) ( CH~-CH~---CH--CH~ )
"~-O ' z , h v
....
the slight dissolution of the film in the alkaline solution. Table 1 indicates the changes of elongation at break of the films against the dose of ~/radiation and the time of the UV exposure. The elongation of film decreases generally with the increasing crosslinking. The table showed the elongation in relation to photo-crosslinking and the radiation induced crosslinking, although there were some scatters. For the films T-irradiated up to the dose of 104 Gy, it is shown that the change of elongation is small, but for the dose more than that, it appears to increase appreciably and that the UV exposure gives effect upon the elongation, that is, the formation of photo-crosslinking. This tends to show appreciably in the dose of 5 x l(f Gy. Such an inclination corresponds to the dose of ~/radiation which the gel fraction was detected in Fig. 7 showing the relation between the ~/radiation and the gel fractions. It is also inferred in Fig. 8 that a constant value of the gel fraction with increasing the UV exposure is concerned with the increase of the formarion of photo-crosslinking.
) ( CH2-'-CH~-~CH--C~H
hv
II
)
O
(. C H z - - C H - - - C H ~ C m H
II
O On adopting this scheme to the v-irradiated PVDF, the following mechanism may be presumed on the UV exposure, for instance,
-(---CH=~---CF-------CF---CH~ )
+o2.h~
The results of elongation of the film irradiated by ~/-ray does not give the undoubted evidence in support of the dissolution of the v-irradiated PVDF
( CHr--CH~---CH-- C - - H
hv
)
II
O CH~CF---CF--C--H
I
'o'
( CF2--CH---CH~C--F or
CH2---CF--CF~ C--H
tl
O on the UV exposure the reaction of oxygen with the degraded products in the v-irradiated PVDF occurred initially at the surface of the film and the oxygenated products produced, primarily carbonyls, tended to be attacked by the alkaline solution. On the contrary, in the inside of the thick film the poor diffusion of oxygen results in the small amounts of formation of oxygenated products and
I I 'o'
( CF2--CH---CHm C - - F
II
O on the UV exposure, but are believed to be consistent with such a presumption. CONCLUSIONS The conclusions summarized are as follows. The alkaline dissolution of the T-irradiated PVDF film are affected with the UV exposure. For
Alkaline dissolution of v-irradiated polyvinylidene fluoride film the dose less than ca. 105 Gy, the longer the time for the exposure to UV is, the less Soluble the film is. F o r the dose up to 2 x 106 Gy, the film becomes more soluble with the exposure to UV. F o r more than that, the dissolution o f films change with the exposure to UV. The UV absorptions in the y-irradiated P V D F film reduced progressively with the e x p o s u r e - t o UV. The IR spectrum o f the f'dm indicated the formation o f oxygenated species after the UV exposure. The UV exposure formed also the photo-crosslinking, leading the f'dm to the difficult dissolution in the alkaline solution. Acknowledgments--Grateful acknowledgment is made to Dr T. Seguchi for his valuable discussions from a view point of radiation chemistry of PVDF and especially for the measurement of elongation of the films. The author thanks also Dr S. Tsujimura for his sincere encouragement during this work. REFERENCES 1. Y. KOMAKI and S. TSUJIMURA, Science. 1978, 199, 421. 2. Y. KOMAKI,Nucl. Tracks. 1979, 3, 33.
405
3. Y. KOlVlAKiand H. OHTSU, J. Electr. Microscopy. 1981, ~ , 292. 4. W. T. CRAWFORD,W. DESoRsoand J. S. HUMPHREY, JR. Nature. 1968, 220, 1313. 5. R. P. HENKE, E. V. BENTONand H. H. HECKMAN, Radiat. Effects. 1970, 3, 43. 6. M. Hums, J. Appl. Polym. Sci. 1972, 16, 2397. 7. C. KUJIRAI,S. HASHIYA,H. FURUNOand N. TERADA, J. Polym. Sci. Part A-I. 1968, 6, 589. 8. H. SoeuE, Y. TABATAand Y. TAJIMA,J. Polym. Sci. Polym. Chem. Edn. 1958, 27, 596. 9. J. F. McKELLARand N. S. ALLEN, Photochemistry of Manmade Polymers. Applied Science Publishers Ltd, London, 1979. 10. B. RANBYand J. F. RAnEK.Photodegradation, Photooxidation, and Photostabilization of Polymers. John Wiley & Sons, London, 1975. 11. K. MAKUUCHI,Y. SEGUCm, T. Suw^, T. ABE, N. TAMURA and M. TAKEHISA, Nippon Kagaku Kaishi. 1973, 1574. 12. H. SmNOHA~.A,J. Polym. Sci. Polym. Chem. Edn. 1979, 17, 1543. 13. T. WE~rn~a, JR., L. J. WILLWERTHand J. P. PHANEUF, J. Polym. Sci. 1961, $$, 551. 14. T. SF~ucm, K. MAKUUCHI,T. Suw^, T. AEE, N. T^MURA and M. TAKEHISA, Nippon Kagaku Kaishi. 1974, 1309. 15. A. C. OU^NO, Polymer Eng. Sci. 1978, 18, 306. 16. S. W. BEAVANand D. PmLLWS, Eur. Polym. J. 1973, 10, 593.
0146-5724/86 $3.00 + .00 © 1986 Pergamon Press Ltd.
Printed in Great Britain.
UV EFFECT ON THE ALKALINE DISSOLUTION OF 'y-IRRADIATED POLYVINYLIDENE FLUORIDE FILM YOSHIHIDEKOMAKI Department of Chemistry, Japan Atomic Energy Research Institute, Tokai-mura, Naka-gun, Ibaraki-ken, Japan (Received 30 December 1983; in revised form 15 February 1984)'t
Abstract--The exposure of T-irradiated polyvinylidene fluoride to UV in oxygen was found to change the dissolution characteristics in an alkaline solution. The UV and IR spectra, the gel fraction, and the elongation at the break of the film were measured to understand the experiment. The UV exposure decreased the intensity of absorption in the UV spectrum and caused the changes in the IR spectrum. The gel fraction and the elongation were changed in relation to the dose of ~t radiation and the UV exposure. At the higher dose of ~t radiation the dissolution increases with the UV exposure, but at the lower dose it decreases. In the latter photocrosslinking is available for strengthening of the binding among the polymer and in the former the formation of the oxygenated species which was formed through the violent T-irradiation leads to the ready dissolution. INTRODUCTION THE AUTHOR has studied the nuclear pore filter of polyvinylidene' fluoride (PVDF) by the chemical etching o f the tracks formed by fission fragments (FF). O-3) In this case, it is chemically important for the track etching that the dissolution along the track core is larger than that of the bulk in polymer. The exposure to UV in the gaseous atmosphere has been known to be effective on the subsequent alkaline development of the fission tracks in polycarbonate and in cellulose esters. Especially in polycarbonate, the exposure to UV in oxygen successfully developed the fission tracks within far shorter period. ¢4.s~ Contrary to expectation, the time taken for the development of F F tracks in P V D F film was found to be longer after the UV exposure. Polycarbonate and cellulose nitrate are defined to be polymers of the degrading type with radiation. The author feels that the degraded products may not form photo-crosslinking but react with oxygen under the UV exposure, leading to more rapid dissolution in the alkaline solution. Then, the dissolution of v-irradiated P V D F film in the alkaline solution was examined with the UV exposure. Since the dissolution was found to be affected with the radiation dose and the UV exposure, the UV and IR spectra, the gel fraction, and the elongation o f P V D F film were examined subsequently. The main chain scission and crosslinking of poly m e r was known to occur by v-irradiation or electron beam and sometimes ultraviolet radiation (UV), such as in polyethylene, ~6~ polypropylene, ~ polyvinyl chloride cs~ and others. ~9'~°J But it has not 5"Publication was delayed due to a fire at the typesetting facility. The publisher regrets any inconvenience to the author and readers.
been known that the polymer irradiated in advance by v-ray was exposed to UV in order to change the characteristics. EXPERIMENTAL A P V D F fdm (Kureha K F Polymer, a biaxially stretched 50 ttm film, d = 1.76 at 250C) was irradiated 1 x 104 to 2 x 106 G y of V radiation at dose rate o f 1.3 × 106 R/hr. Irradiation were carried out in vacuum and in oxygen or in nitrogen at 6.6 x 104 Pa, the specimen in a glass ampoule. After irradiation a part of the specimens was stored in air, as a reference in order to see the effect o f storage, and another was exposed to UV under the flow of oxygen o r nitrogen at the flow rate of 1.2 m/min. The UV lamp used is a high pressure mercury lamp with main emission lines at 254, 313, 366 and 435 nm, respectively. (SHL-100 UV-2, Toshiba Electric Co. Ltd.) The film was horizontally rotated so as to minimize the irregular irradiation and absorbed UV through a convex quartz lens without any filter. The UV intensity at the position of f'dm was measured to be about 3 mW/cm 2 over the whole wavelengths from 200 to 320 nm using UV radiometer (Topcon, UVR-254). The IR and UV spectra were measured instantly after the UV exposure. The rate of dissolution of P V D F ftlm was measured every constant time for the specimen exposed to U V from the weight decrease in a 10N N a O H solution at 85°C. The measurement of the gel fraction of P V D F followed the method b y Makuuchi et al.
399
4OO
Y. KOMAK[
RESULTS Dissolution in the alkaline solution The dissolution of PVDF fdm in the alkaline solution was found to change in relation to the dose of ~/-irradiation and the UV exposure. The rates of dissolution of v-irradiated PVDF were examined after the period of 22, 50, 100 and 150 hrs of the UV exposure [UV(t)] and the ratios of these to that without the UV exposure [UV(0)] were obtained. When the ratio is 1, the dissolution is not affected with the UV exposure. The ratio more than 1 indicates the increase of dissolution with the UV exposure and the ratio less than 1 contrarily the decrease. Figure 1 shows the ratios against the dose of radiation. Effects of the UV exposure are summarized as follows. First, in the specimen irradiated by v-ray up to the dose of 105 Gy, a tendency of rather difficult dissolution appears with the UV exposure. Secondarily, up to the dose of los Gy, the ratio increases with the UV exposure and goes up to as high as 3 times compared with that without the UV exposure. Finally, over l0 s Gy, a), the dissolution shows a tendency to decrease for the short UV exposure, and b), that again increases for the longer UV exposure. The UV exposure reduced also the color of PVDF film which colored yellow to brown with the dose of radiation. Figure 2 shows the absorbance ratio at 600 nm against the UV exposure time as the degree of discoloration of ~-irradiated film. The absorbance ratio was defined as the value equal to [Abs(0) - Abs(U)]/Abs(0), × 100%, where the abbreviation, Abs(0,U) indicates the absorbances in the absence of UV exposure, UV(0), or in the presence, UV(U). The UV exposure showed 27% fading I
'
l
of color on the v-irradiated P V D F film. In the immersion of alkaline solution, the v-irradiated P V D F film colored further brownish to black, but the film which was in advance exposed to U V merely colored pale brown. In order to examine the changes of characteristicsof P V D F in relationto the dose of ~/irradiation and the U V exposure, U V and IR spectra were measured, and the gel fraction and the elongation at break were also measured to discuss the crosslinking. UV spectrum Figure 3(a) is the UV spectrum of PVDF film virradiated to 5 x 10~ Gy in vacuum. The similar curves were obtained by the v-irradiation in oxygen, but the intensity was larger in vacuum than in oxygen. The peaks of absorptions were observed at 227 nm, 274 nm and 315 nm which were assigned to diene, triene and tetraene, respectively} TM The spectrum was stable in air for a long period. The exposure to UV reduced the intensity of the UV spectrum as in Fig. 3(b) after 100 hrs exposure. Figtire 3(c) is the spectrum of a virgin film. Figure 4 shows the differences of absorption from 200 to 500 nm between the -/-irradiated PVDF and the UV exposure in oxygen after v-irradiation. The difference of absorbance increases with the UV exposure time. Long storage of the fdm in air shows the same tendency of UV absorption to an extent. In order to see the effects of atmospheres, the films were exposed to UV in the absence of oxygen, that is, in nitrogen. The UV exposure effect appeared only in the presence of oxygen and not in nitrogen. When the fdm was first exposed to UV in oxygen for a certain period and subsequently in '
I
l
3 "' z ~
~ 150 hr __ No 100 2
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1
...........
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0
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t
1o'
[
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I
50 ,i
1o6
RADIATION DOSE (Gy)
Fig. I. The ratio o f dissolution rates vs 3, radiation dose. The dissolution rate means the weight dissolved
from a single face of the film per hour. The dissolution rates, UV(t, 0), indicate the one after UV exposure for some periods and the one without UV exposure, respectively.
Alkaline dissolution of V-irradiated polyvinylidene fluoride film '1
i
401
nitrogen, the decrease o f the absorptions at 227 nm were compared with each time as shown in Fig. 5. A f i ~ !($i~1~U V eXposUre ih nitrogen, re-exposure to UV in the presence of oxygen decreased surely the absorption.
30 7 O
IR spectrum
2o
There were slight changes in the IR spectrum of P V D F before and after the v-irradiation. Absorpt,J,J tions in the neighborhood of 1850, 1830, 1760, 1720 Z and 1600 cm - j are observed in the range of 1900(Z:) 0:: 1600 c m - i in wave number. ° t> Figure 6 shows that o ~0 r~ the UV exposure induced the relative intensities of IR transmittances against the UV exposure time for the frequencies at 1850, 1760 and 1720 c m - I . The intensities of absorptions at 1850 and 1760 c m increased with the UV exposure, but the absorption t I l 50 10o 150 at 1720 cm-m decreased. Absorptions at 1850 and 1760 cm -m had been assigned to - C O O H and HOURS EXPOSED - C O F , respectively, (~H3) and at 1830 cm - I the Fig. 2. The discoloration of brownish color in v-irradiated binding o f oxygen. ( ' ) The assignment of 1720 c m PVDF film to yellowish by UV exposure was examined of the absorption intensity in the wavelength of 600 nm was not clear to be an isolated or a conjugated douwhich was assigned yellow to brown in color region of the ble bond (t3) and 1600 cm-* has been left unvague. spectrum. The 50 p,m thick film was irradiated to the dose of 5 x 105 Gy. Gel fraction Figure 7 shows the gel fraction of P V D F film irradiated by ~,-ray. F o r the 9 ~m thick P V D F film
I
'
1
~
I-01 '
I
A 1700
1300
3.0
(o) 2.0 tJ, J
0.~ rP"
m
(b)
(:3¢1
1.0
-
I
C :200
L
I,
3OO
i
I
400
WAVELENGTH (nm) Fig. 3. The UV absorption spectrum ofv-in'adiated PVDF film (a), the one of V-irradiated PVDF film after UV exposure, and the one of a virgin PVDF film, vs wavelength. (a) 3' radiation (5 x 105 Gy) induced absorbance. (b) The absorbance after UV exposure for 100 h. (c) The absorbance in the virgin PVDF t'dm.
WAVE LENGTH (nm) Fig. 4. The difference of the absorbances of 3'-irradiated PVDF film after UV exposure and the one without UV exposure in the range of 200-500 nm. The numerals on the curves show the time exposed to UV(min).
402
Y.
KOMAKI
STORAGE TIME 50
3.°i
'
( DAYS) 100 I
I
non UV. exposure, in air
2.o1-,, ` z
o
I--
in 02 -
0"-- ......................
~
1.01-
~
"0
in N2
"1 I I00
I
O01
I
200
HOURS EXPOSED Fig. 5. The change of the absorptions after alternate UV exposures in oxygen and in nitrogen vs UV exposure time. The curve at the top of the figure shows the absorption of 3,-irradiated PVDF film without UV exposure, but stored in air, and the one at the bottom of "~-irradiated PVDF film after alternate UV exposures in oxygen and in nitrogen for some periods.
I .
0.05~
~--~
(o)
-
0.15 L.U Z
Mechanical property The results of elongation at break of the PVDF films irradiated by w-ray and the UV exposure were
(b)
133 re-
o
irradiated by ~/-ray in oxygen, the gel was not detected until the dose up to ca. 106 Gy. The gel fraction showed to be smaller in oxygen than that in vacuum, as Makuuchi et al. pointed out that oxygen hindered the formation of crosslinking.(Iw) Figure 8 shows the gel fraction of 50 ~m thick PVDF films ~t-irradiated up to 4 × 105 and 106 Gy against the UV exposure. This indicates the effect of UV exposure after the ~/-irradiation. On the exposure to UV, the gel fraction decreased for short time of UV exposure and shows the almost constant for further UV exposure.
0.1 100
025 -
rJ ,
in VOC
Z 0
in 02 50
r~ I,
o
,,--I lad
(c)
0.2
,l 0
50
"1"
100
HOURS EXPOSED Fig. 6. The UV exposure induced relative intensities of the IR transmittances for frequencies at (a) 1850, (b) 1760 and (c) 1720 cm-t vs UV exposure time.
tO5
106
107
RADIATION DOSE (Gy) Fig. 7. The gel fractions of-v-irradiated PVDF film in vacuum or in oxygen, vs ~ radiation dose. PVDF film; 50 p.m thick.
Alkaline dissolution of ~/-irradiated:,polyvinylidene fluoride film
. . . .
403
were assigned already to the oxygenated species which were formed from the scissions of main chains in PVDF, that is, -COOH and -COF, reo (o) o_ spectively.(, :.m On the contrary, the absorption at 1720 c m - ' has been observed both in the thermal decomposition"3) and in the ~/-irradiation, "l) but {b) .,., 5 0 has been left undetermined, although it had merely been assigned to a double bond. In this experiment, LIthe absorption at 1720 cm- : may be assigned to the _.I l.IJ stretching band of the conjugated double bond, because the double bond absorption due to the polyenes decreases by the UV exposure as shown in 0(~ I I I I I I I I I I I Fig. 3. 50 I00 A detailed interpretation of the UV effect upon HOURS EXPOSED the dissolution of v-irradiated PVDF film in the alFig. 8. The gel fractions of v-irradiated PVDF film (50 p.m) kaline solution is difficult directly at this time. in vacuum after UV exposure, vs UV exposure time. (a) Using Seguchi and Makuuchi's interpretations of The PVDF film was irradiated to the dose of I x 106 Gy. Co) The PVDF film was irradiated to the dose of 4 x 105 the changes of characteristics in the v-irradiated PVDF and in addition, using these experimental reGy. sults, the dissolution behaviors with the UV exposure in Fig. 1 may be explained as follows. S T E P I: On radiation dose up to ca. 105 Gy. TABLE1. THE ELONGATIONATBB.EAK OF THE"~-IRRADIATEDPVDF From(50 1) Effect of ~/-irradiation: The main chain scis~m) EXPOSEDTOUV FORSOME sion and crosslinking increase progressively, but PERIODS.THE RATEOFELONGATION: give only insignificant effect. There are the release 20 cm/min AT 20°C. of hydrogen fluoride and the formation of the oxi" IJ.V. Bongoygenated species with the isolated and the conjurodiation tion gated double bonds. Ix, 2) Effect of the UV exposure: The UV expoI 0 42O sure ruptures mainly the conjugated double bonds to form the photo-crosslinking. The photo-crossA 2 0 20 400 linking serves to strengthen the bindings of the pol3 160 570 ymer molecules, leading to the difficult dissolution 1 0 410 of film to an extent. The conjugated double bonds e 2 ix104 20 360 serve to form the oxygenated species, too.
100[
I
'
'
'
'
I
cGy) 'Wf'
3 1
C 2 5xI05 3
160 0
310 60
20
90
160
3
indicated in Table 1. For PVDF v-irradiated to 104 Gy, there appears no significant changes of the elongation for the period of 20-160 hrs of UV exposure, but at 5 × 105 Gy, the elongation at break decreases abruptly for the long UV exposure. DISCUSSION Although the commercial PVDF films have no absorptions of wavelength longer than ca. 220 nm, the distinct absorptions reveal at 227, 274, 315 nm after v-irradiation. It was found that the UV exposure reduced clearly the intensities of these absorptions only in the presence of oxygen as shown in Fig. 3. On the other hand, the IR spectrum showed that the absorptions at 1850 and 1760 cm- J increased a little, but that at 1720 c m - : decreased as shown in Fig. 6. The former two absorptions
RPC
27/5-F
S T E P H: On the dose more than ca. 105 Gy.
1) Effect of ~/-irradiation: The main chain scissions and crosslinkings become to give some significant effects increasingly. ('4) Since the G-value, G(s), of scission is roughly the same with that of crosslinking, G(x), G(s) = G(x) - 0.6":) the polymer becomes to be readily soluble through the subsequent formation of the micro-cracking like a spongeCm by the violent release of the gaseous products, and colors appreciably in an immersion of the alkaline solution to show the vigorous formation of double bonds. 2) Effect of the UV exposure: To the film irradiated significantly by ",/-ray, the UV exposure can fasten no longer the networks of the individual polymeric molecules by photo-crosslinking, but increase the formation of oxygenated species through the double bonds followed by the ready dissolution of polymer. The fading of coloration and the increase of pliancy of the film with the UV exposure suggest the change of characteristics. Reaching the dose of 2 x 106 Gy, the effect of UV exposure on the dissolution decreases. This indicates that the dissolution in highly -t-irradiated film occurs in small correlation with the UV exposure. But the long UV exposure may show the effect yet.
404
Y. KOMAKI
Now, the reaction of a virgin PVDF film with the mixture of oxygen and fluorine was found to form new bond in PVDF having oxygen. ('2) Such a compound becomes to be readily soluble in the alkaline solution. The following scheme has been proposed to the ready dissolution, ~COF
+H20
) --COOH
+NaOH> --:COONa.
The author believes that the increasing dissolution rate of the v-irradiated PVDF film in the alkaline solution is primarily based upon the formation of oxygenated PVDF. It is reasonable from the photochemical considerations for the reaction of polydiene with oxygen, beside the present experimentals, that the conjugated double bonds produced by ~/ radiation are concerned with the formation of carbonyls and photo-crosslinking. When cis and trans 1,4 polybutadiene which have the conjugated double bonds in the main chains were exposed to UV in the presence of oxygen, for instance, the formation of carbonyls were reported, followed by photo-crosslinking, H6) ( CH~-CH~---CH--CH~ )
"~-O ' z , h v
....
the slight dissolution of the film in the alkaline solution. Table 1 indicates the changes of elongation at break of the films against the dose of ~/radiation and the time of the UV exposure. The elongation of film decreases generally with the increasing crosslinking. The table showed the elongation in relation to photo-crosslinking and the radiation induced crosslinking, although there were some scatters. For the films T-irradiated up to the dose of 104 Gy, it is shown that the change of elongation is small, but for the dose more than that, it appears to increase appreciably and that the UV exposure gives effect upon the elongation, that is, the formation of photo-crosslinking. This tends to show appreciably in the dose of 5 x l(f Gy. Such an inclination corresponds to the dose of ~/radiation which the gel fraction was detected in Fig. 7 showing the relation between the ~/radiation and the gel fractions. It is also inferred in Fig. 8 that a constant value of the gel fraction with increasing the UV exposure is concerned with the increase of the formarion of photo-crosslinking.
) ( CH2-'-CH~-~CH--C~H
hv
II
)
O
(. C H z - - C H - - - C H ~ C m H
II
O On adopting this scheme to the v-irradiated PVDF, the following mechanism may be presumed on the UV exposure, for instance,
-(---CH=~---CF-------CF---CH~ )
+o2.h~
The results of elongation of the film irradiated by ~/-ray does not give the undoubted evidence in support of the dissolution of the v-irradiated PVDF
( CHr--CH~---CH-- C - - H
hv
)
II
O CH~CF---CF--C--H
I
'o'
( CF2--CH---CH~C--F or
CH2---CF--CF~ C--H
tl
O on the UV exposure the reaction of oxygen with the degraded products in the v-irradiated PVDF occurred initially at the surface of the film and the oxygenated products produced, primarily carbonyls, tended to be attacked by the alkaline solution. On the contrary, in the inside of the thick film the poor diffusion of oxygen results in the small amounts of formation of oxygenated products and
I I 'o'
( CF2--CH---CHm C - - F
II
O on the UV exposure, but are believed to be consistent with such a presumption. CONCLUSIONS The conclusions summarized are as follows. The alkaline dissolution of the T-irradiated PVDF film are affected with the UV exposure. For
Alkaline dissolution of v-irradiated polyvinylidene fluoride film the dose less than ca. 105 Gy, the longer the time for the exposure to UV is, the less Soluble the film is. F o r the dose up to 2 x 106 Gy, the film becomes more soluble with the exposure to UV. F o r more than that, the dissolution o f films change with the exposure to UV. The UV absorptions in the y-irradiated P V D F film reduced progressively with the e x p o s u r e - t o UV. The IR spectrum o f the f'dm indicated the formation o f oxygenated species after the UV exposure. The UV exposure formed also the photo-crosslinking, leading the f'dm to the difficult dissolution in the alkaline solution. Acknowledgments--Grateful acknowledgment is made to Dr T. Seguchi for his valuable discussions from a view point of radiation chemistry of PVDF and especially for the measurement of elongation of the films. The author thanks also Dr S. Tsujimura for his sincere encouragement during this work. REFERENCES 1. Y. KOMAKI and S. TSUJIMURA, Science. 1978, 199, 421. 2. Y. KOMAKI,Nucl. Tracks. 1979, 3, 33.
405
3. Y. KOlVlAKiand H. OHTSU, J. Electr. Microscopy. 1981, ~ , 292. 4. W. T. CRAWFORD,W. DESoRsoand J. S. HUMPHREY, JR. Nature. 1968, 220, 1313. 5. R. P. HENKE, E. V. BENTONand H. H. HECKMAN, Radiat. Effects. 1970, 3, 43. 6. M. Hums, J. Appl. Polym. Sci. 1972, 16, 2397. 7. C. KUJIRAI,S. HASHIYA,H. FURUNOand N. TERADA, J. Polym. Sci. Part A-I. 1968, 6, 589. 8. H. SoeuE, Y. TABATAand Y. TAJIMA,J. Polym. Sci. Polym. Chem. Edn. 1958, 27, 596. 9. J. F. McKELLARand N. S. ALLEN, Photochemistry of Manmade Polymers. Applied Science Publishers Ltd, London, 1979. 10. B. RANBYand J. F. RAnEK.Photodegradation, Photooxidation, and Photostabilization of Polymers. John Wiley & Sons, London, 1975. 11. K. MAKUUCHI,Y. SEGUCm, T. Suw^, T. ABE, N. TAMURA and M. TAKEHISA, Nippon Kagaku Kaishi. 1973, 1574. 12. H. SmNOHA~.A,J. Polym. Sci. Polym. Chem. Edn. 1979, 17, 1543. 13. T. WE~rn~a, JR., L. J. WILLWERTHand J. P. PHANEUF, J. Polym. Sci. 1961, $$, 551. 14. T. SF~ucm, K. MAKUUCHI,T. Suw^, T. AEE, N. T^MURA and M. TAKEHISA, Nippon Kagaku Kaishi. 1974, 1309. 15. A. C. OU^NO, Polymer Eng. Sci. 1978, 18, 306. 16. S. W. BEAVANand D. PmLLWS, Eur. Polym. J. 1973, 10, 593.