- Email: [email protected]
Accelerated radiation-induced degradation of polystyrene containing flame-retardant agents
PolymerDegradationand Stability45 (1994) 155-157 1994 ElsevierScienceLimited Printed in Northern Ireland. All rights reserved 0141-3910/94/$7.00
ELSEVIER
NOTE
Accelerated radiation-induced degradation of polystyrene containing flame-retardant agents Ayako Torikai, Hitoshi Kato Department of Applied Chemistry, School of Engineering, Nagoya University, Nagoya, 464-01 Japan
&
Yuji Suzuki* Chemical Research Laboratory, Tosoh Corporation, Kaisei-cho, Shin-nanyo, Yamaguchi, 746 Japan (Received 23 December 1993; accepted 8 January 1994)
Radiation-induced degradation of incombustible polystyrene (PSt) was studied by optical absorption and viscosity measurements. It was found that y-ray induced degradation of PSt was accelerated by the addition of flame-retardant agent containing bromine atoms in the molecule. This acceleration is dependent on the concentration of additive in PSt.
INTRODUCTION
radiation-induced degradation of PSt takes place on addition of D B D E or TBA, then we can study the fundamental role of halogen-containing molecules in accelerated degradation, and answer the practical problem of finding a method of degradation of the waste material. We have already reported that the accelerated photodegradation of PSt in the solid phase can take place by doping with EEl43 o r at a higher temperature than the Tg. 4 Although the radiation-induced degradation of PSt has been studied extensively, little is known about the accelerated degradation in the solid phase. The effect of flame-retardant agents has not yet been studied. In the present work we have attempted to study the accelerated radiation-induced degradation of PSt in the presence of D B D E or TBA.
Polystyrene (PSt) is used widely in various industrial fields due to its mouldability, transparency, high refractive index, low density, low price and other favorable characteristics. Recently, we have investigated the photodegradation of polypropylene (PP) and PSt containing flame-retardant agents which have bromine atoms in their molecules, and have found that the photodegradation of PP and PSt is accelerated by the addition of decabromodiphenyl oxide(DBDE) or tetrabromobisphenol A(TBA) as an additive, t This acceleration was found to be dependent on the wavelength of the radiation. PSt is known to be one of the most stable polymers to ionizing radiation. It has been reported that G-values for main-chain scission and crosslinking of PSt are 0-02 and 0.03, respectively, which is very low compared with other polymeric materials. 2 If accelerated
EXPERIMENTAL Polystyrene (GPPS HF-55) was supplied by Mitsui Monsanto Chemicals, as pellets. Two
* Present address: Research Laboratory, PLAS-TECH Corporation, 1-10, Shin-machi, Hiratsuka, 254 Japan. 155
156
Ayako Torikai, Hitoshi Kato, Yuji Suzuki
flame-retardant agents were used, namely decabromodiphenyl oxide ( D B D E ) 0.2 o ¢q
r~
Br
Br
Br
0.1
Br
tetrabromobisphenol-A(TBA) Br,
CH3/Br
0 2
0
4
6
Dose ( x I 0 - 4 G y )
Br /
CH3
Br
Details of film preparation were given in a previous paper.~ The thickness of the films was c. 0-05 ram. The concentration of additives was 2, 5 and 10 %wt for D B D E and TBA. Spectro-grade toluene was used as received. Films of PSt and PSt containing D B D E or TBA were irradiated with ),-rays from a ~Co source in air at room temperature at a dose rate of 8.5 x liP Gy/h. UV spectra were observed using a Hitachi 323 spectrophotometer. The viscosity average molecular weight, Mv, was calculated using the equation: 5 [r/] = 1.1 x 10-4Mv °72
(1)
The intrinsic viscosity, [r/], was obtained in toluene solution, at 25 +0.1°C using an Ubbelohde viscometer. The number of main chain scissions (Cs) per molecule, which is a measure of degradation, was estimated from the equation: Cs = 1/Mv
-
1/Mv0
Fig. 1. Changes in the optical density at 320 nm with the irradiation dose: x, PSt; O, PSt-DBDE (2%); A, PSt-DBDE (5%); D, PSt-DBDE (10%); Q, PSt-TBA (2%); A, PSt-TBA 5%; I , PSt-TBA (10%).
irradiation dose in Fig. 1. It clearly increases with increase of irradiation dose and the concentration of the additives. AOD32o at constant irradiation dose is plotted against the additive concentration in Fig. 2. AOO32o increases with the concentration of D B D E or TBA in PSt, but the nature of the increase is different for each additive. In the P S t - T B A system, AOD32o begins to increase at a low concentration of the additive and then levels off at a concentration higher than 5%. For the P S t - D B D E system, AODa2o increases sharply at concentrations higher than 5%. These different behaviors may be due to their distributions in PSt. It has been observed that
(2)
where, Mvo and Mv are the viscosity average molecular weights of polymers before and after y-ray irradiation.
0.2 O
r~
RESULTS AND DISCUSSION
0.1
U-V spectral change U V spectra were obtained of ),-irradiated PSt and PSt containing additive. In each case, an increase occurs in the intensity of the absorption band in the 210 to 360 nm region. The increase in absorbance at 320 nm of ),-irradiated PSt samples (AOD32o) was chosen as a measure of the degradation of PSt. ~ AOD32o is plotted against
0
0
I
I
i
i
2
4
6
8
Additives
10
(wt%)
Fig. 2. Changes in the optical density at 320 nm (AOD32o) of PSt and PSt containing flame-retardant agents: ©, PSt-DBDE; Q, PSt-TBA. Dose, 7.7 x 104 Gy.
Accelerated radiation-induced degradation of polystyrene
o
u
0
t
t
i
t
2
4
6
8
Additives
0
( w t %)
Fig. 3. Number of chain scission of y-ray irradiated PSt and PSt containing flame-retardant agents: O, PSt-DBDE; 0, PSt-TBA. Dose, 7.7 x 104Gy. T B A is distributed homogeneously in PSt film, while D B D E is distributed inhomogeneously (Suzuki, Y., unpublished), so that the accelerated degradation is favored by the h o m o g e n e o u s system.
Molecular weight change Figure 3 shows the n u m b e r of chain scissions, calculated from eqn (2). y-Ray induced degradation of PSt (main chain scission) occurs only to a very limited extent at an irradiation dose of 7.7 x 104 Gy. On addition of D B D E or T B A , the degradation of PSt is accelerated. PSt is one of the most radiationresistant of polymeric materials, and the G-value of main chain scission has been reported to be very small, as we have already m e n t i o n e d in the first part of this section. The Cs of PSt does not
157
reach a plateau value on addition of 10%wt of D B D E . However, 10%wt of additive is a limit value for PSt, because larger amounts change the characteristic useful properties. In any case, the accelerated degradation by D B D E or T B A is clearly observed in these samples and T B A seems to be a more efficient additive than D B D E for y-ray induced degradation of PSt. These results are consistent with those from UV-spectral analysis (compare Fig. 2 with Fig. 3). This consistency shows that we can use the AOD326 value as a measure of y-ray induced degradation of PSt. Although the reaction mechanism of y-ray induced degradation of PSt containing D B D E or T B A as additive has not been fully elucidated, it is evident that the bromine-containing flameretardant agents play an important role in the accelerated y-ray induced degradation of PSt.
ACKNOWLEDGMENT This study was partially supported by a Grant-in-Aid for Scientific Research No. 04650807 from the Ministry of Education, Science and Culture.
REFERENCES 1. Torikai, A., Kato, H., Fueki, K., Suzuki, Y., Okisaki, F. & Nagata, M., J. Appl. Polym. Sci., 50 (1993) 2185. 2. Schnabel, W., Polymer Degradation, Hanser International, Miinchen, 1981, p. 139. 3. Torikai, A., Kato, S. & Fueki, K., Polym. Deg. and Stab., 17 (1987) 21. 4. Torikai, A., Takeuchi, A. & Fueki, K., Polym. Deg. and Stab., 14 (1986) 367. 5. Busfield, W. K. & O'Donnell, H., J. Polym. Sci., Polym. Syrup., 49 (1975) 22.
ELSEVIER
NOTE
Accelerated radiation-induced degradation of polystyrene containing flame-retardant agents Ayako Torikai, Hitoshi Kato Department of Applied Chemistry, School of Engineering, Nagoya University, Nagoya, 464-01 Japan
&
Yuji Suzuki* Chemical Research Laboratory, Tosoh Corporation, Kaisei-cho, Shin-nanyo, Yamaguchi, 746 Japan (Received 23 December 1993; accepted 8 January 1994)
Radiation-induced degradation of incombustible polystyrene (PSt) was studied by optical absorption and viscosity measurements. It was found that y-ray induced degradation of PSt was accelerated by the addition of flame-retardant agent containing bromine atoms in the molecule. This acceleration is dependent on the concentration of additive in PSt.
INTRODUCTION
radiation-induced degradation of PSt takes place on addition of D B D E or TBA, then we can study the fundamental role of halogen-containing molecules in accelerated degradation, and answer the practical problem of finding a method of degradation of the waste material. We have already reported that the accelerated photodegradation of PSt in the solid phase can take place by doping with EEl43 o r at a higher temperature than the Tg. 4 Although the radiation-induced degradation of PSt has been studied extensively, little is known about the accelerated degradation in the solid phase. The effect of flame-retardant agents has not yet been studied. In the present work we have attempted to study the accelerated radiation-induced degradation of PSt in the presence of D B D E or TBA.
Polystyrene (PSt) is used widely in various industrial fields due to its mouldability, transparency, high refractive index, low density, low price and other favorable characteristics. Recently, we have investigated the photodegradation of polypropylene (PP) and PSt containing flame-retardant agents which have bromine atoms in their molecules, and have found that the photodegradation of PP and PSt is accelerated by the addition of decabromodiphenyl oxide(DBDE) or tetrabromobisphenol A(TBA) as an additive, t This acceleration was found to be dependent on the wavelength of the radiation. PSt is known to be one of the most stable polymers to ionizing radiation. It has been reported that G-values for main-chain scission and crosslinking of PSt are 0-02 and 0.03, respectively, which is very low compared with other polymeric materials. 2 If accelerated
EXPERIMENTAL Polystyrene (GPPS HF-55) was supplied by Mitsui Monsanto Chemicals, as pellets. Two
* Present address: Research Laboratory, PLAS-TECH Corporation, 1-10, Shin-machi, Hiratsuka, 254 Japan. 155
156
Ayako Torikai, Hitoshi Kato, Yuji Suzuki
flame-retardant agents were used, namely decabromodiphenyl oxide ( D B D E ) 0.2 o ¢q
r~
Br
Br
Br
0.1
Br
tetrabromobisphenol-A(TBA) Br,
CH3/Br
0 2
0
4
6
Dose ( x I 0 - 4 G y )
Br /
CH3
Br
Details of film preparation were given in a previous paper.~ The thickness of the films was c. 0-05 ram. The concentration of additives was 2, 5 and 10 %wt for D B D E and TBA. Spectro-grade toluene was used as received. Films of PSt and PSt containing D B D E or TBA were irradiated with ),-rays from a ~Co source in air at room temperature at a dose rate of 8.5 x liP Gy/h. UV spectra were observed using a Hitachi 323 spectrophotometer. The viscosity average molecular weight, Mv, was calculated using the equation: 5 [r/] = 1.1 x 10-4Mv °72
(1)
The intrinsic viscosity, [r/], was obtained in toluene solution, at 25 +0.1°C using an Ubbelohde viscometer. The number of main chain scissions (Cs) per molecule, which is a measure of degradation, was estimated from the equation: Cs = 1/Mv
-
1/Mv0
Fig. 1. Changes in the optical density at 320 nm with the irradiation dose: x, PSt; O, PSt-DBDE (2%); A, PSt-DBDE (5%); D, PSt-DBDE (10%); Q, PSt-TBA (2%); A, PSt-TBA 5%; I , PSt-TBA (10%).
irradiation dose in Fig. 1. It clearly increases with increase of irradiation dose and the concentration of the additives. AOD32o at constant irradiation dose is plotted against the additive concentration in Fig. 2. AOO32o increases with the concentration of D B D E or TBA in PSt, but the nature of the increase is different for each additive. In the P S t - T B A system, AOD32o begins to increase at a low concentration of the additive and then levels off at a concentration higher than 5%. For the P S t - D B D E system, AODa2o increases sharply at concentrations higher than 5%. These different behaviors may be due to their distributions in PSt. It has been observed that
(2)
where, Mvo and Mv are the viscosity average molecular weights of polymers before and after y-ray irradiation.
0.2 O
r~
RESULTS AND DISCUSSION
0.1
U-V spectral change U V spectra were obtained of ),-irradiated PSt and PSt containing additive. In each case, an increase occurs in the intensity of the absorption band in the 210 to 360 nm region. The increase in absorbance at 320 nm of ),-irradiated PSt samples (AOD32o) was chosen as a measure of the degradation of PSt. ~ AOD32o is plotted against
0
0
I
I
i
i
2
4
6
8
Additives
10
(wt%)
Fig. 2. Changes in the optical density at 320 nm (AOD32o) of PSt and PSt containing flame-retardant agents: ©, PSt-DBDE; Q, PSt-TBA. Dose, 7.7 x 104 Gy.
Accelerated radiation-induced degradation of polystyrene
o
u
0
t
t
i
t
2
4
6
8
Additives
0
( w t %)
Fig. 3. Number of chain scission of y-ray irradiated PSt and PSt containing flame-retardant agents: O, PSt-DBDE; 0, PSt-TBA. Dose, 7.7 x 104Gy. T B A is distributed homogeneously in PSt film, while D B D E is distributed inhomogeneously (Suzuki, Y., unpublished), so that the accelerated degradation is favored by the h o m o g e n e o u s system.
Molecular weight change Figure 3 shows the n u m b e r of chain scissions, calculated from eqn (2). y-Ray induced degradation of PSt (main chain scission) occurs only to a very limited extent at an irradiation dose of 7.7 x 104 Gy. On addition of D B D E or T B A , the degradation of PSt is accelerated. PSt is one of the most radiationresistant of polymeric materials, and the G-value of main chain scission has been reported to be very small, as we have already m e n t i o n e d in the first part of this section. The Cs of PSt does not
157
reach a plateau value on addition of 10%wt of D B D E . However, 10%wt of additive is a limit value for PSt, because larger amounts change the characteristic useful properties. In any case, the accelerated degradation by D B D E or T B A is clearly observed in these samples and T B A seems to be a more efficient additive than D B D E for y-ray induced degradation of PSt. These results are consistent with those from UV-spectral analysis (compare Fig. 2 with Fig. 3). This consistency shows that we can use the AOD326 value as a measure of y-ray induced degradation of PSt. Although the reaction mechanism of y-ray induced degradation of PSt containing D B D E or T B A as additive has not been fully elucidated, it is evident that the bromine-containing flameretardant agents play an important role in the accelerated y-ray induced degradation of PSt.
ACKNOWLEDGMENT This study was partially supported by a Grant-in-Aid for Scientific Research No. 04650807 from the Ministry of Education, Science and Culture.
REFERENCES 1. Torikai, A., Kato, H., Fueki, K., Suzuki, Y., Okisaki, F. & Nagata, M., J. Appl. Polym. Sci., 50 (1993) 2185. 2. Schnabel, W., Polymer Degradation, Hanser International, Miinchen, 1981, p. 139. 3. Torikai, A., Kato, S. & Fueki, K., Polym. Deg. and Stab., 17 (1987) 21. 4. Torikai, A., Takeuchi, A. & Fueki, K., Polym. Deg. and Stab., 14 (1986) 367. 5. Busfield, W. K. & O'Donnell, H., J. Polym. Sci., Polym. Syrup., 49 (1975) 22.