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Antibacterial activated carbon fiber derived from phenolic resin containing silver nitrate
Curhon. Vol. 3 I. No. I. pp. 7 l-73. Pnnted I” Great Britain.
1993 Copynghi
0008-6223193 $6.00 + .oO (0 I993 Pergamon Press Ltd.
ANTIBACTERIAL ACTIVATED CARBON FIBER DERIVED FROM PHENOLIC RESIN CONTAINING SILVER NITRATE A. OYA* and S. YOSHIDA Faculty of Engineering, Gunma University. Kiryu, Gunma 376, Japan and Y. ABE, T. IIZUKA and N. MAKIYAMA Gun-ei Chemical Industry Co., Ltd., Oyagi, Takasaki, Gunma 370, Japan (Received 6 April 1992; accepled in revisedjbrm 2 June 1992) Abstract-A
novolactype phenolic resin including I wt% of AgN03 was spun, hardened, carbonized at 900°C under nitrogen and finally activated at 900°C for 10 and 60 min under steam. The resulting fibers showed specific Nl-BET surface areas of 280 and 1,940 m*/g, respectively. The latter contained 2.2 wt% ofthe silver particles ofwhich the largest size was several 100 nm and showed antibacterial activity against Staphyk~coccus aureus and Escherichia co/i. After soaking in the flowing tap water for 20 days, this fiber lost one third of silver but kept the antibacterial activity.
Key Words-Antibacterial
1.
ability, activated carbon fiber, water purifier, silver.
uum evaporator at room temperature, was spun using a spinning apparatus with a nozzle diameter of 1.5 mm, described earlier[ lo]. The spinning temper-
INTRODUaION
Activated carbon fiber has now some applications, one of which is as a water purifier[ 1,2,3]. Since the
ature was controlled over a relatively wide range between 100 and 145°C because of poor spinnability of the resulting resin. The resulting resin fiber including AgN03 (abbreviation: KF) was soaked in the hardner at 20 min at room temperature, heated up to 95°C at O.S”C/min and kept for 8 h at this temperature.The hardened fiber (abbreviation: HF) was neutralized by treatment with aqueous ammonia (1 mol/dm’), followed by drying under vacuum after extensive washing in the flowing water. Next the fiber was carbonized at 900°C for 30 min under a nitrogen stream. The resulting carbonized fiber (abbreviation: CF) was activated at 900°C for 10 min (abbreviation: ACF- 10) and 60 min (abbreviation: ACF-60) under a stream of steam (partial pressure of steam: ca.30%).
carbon material is known to have a high affinity for bacteria[4], however, bacteria may breed on this fiber during the purification process, becoming itself a pollutant. In order to avoid such a disadvantage, an an-
tibacterial activated carbon fiber is required. It is well known that silver ion and fine silver particle have strong antibacterial activity[5,6]. Therefore, an antibacterial activated carbon fiber may be prepared by dispersing fine silver particles in it. The present work was undertaken to develop an antibacterial activated carbon fiber derived from a phenolic resin which included silver nitrate. 2. EXPERIMENTAL
2.1 Materials Silver nitrate (AgNO,) used was reagent grade. A novolactype phenolic resin with a softening point of I 15- 120°C was supplied by the Gun-ei Chemical Co. Ltd. This resin is a raw material for the flame resistance “Kynol” fiber, which is described elsewhere[791. The hardener supplied by same company contains formaldehyde as a cross-linking agent and hydrochloric acid as a catalyst. Details are described elsewhere[7-91.
2.3 Measurements The fibers were subjected to the following measurements. The powder X-ray diffraction patterns were obtained using Ni-filtered CuKol-radiation. Transmission electron microscopy (TEM) was used to observe the physical state of the silver in the fiber. The silver content in the fiber was measured by ICP emission spectroscopy. BET specific surface area was determined from the adsorption isotherm of Nz at 77K (one-point method). Mechanical testing of the fibers was performed on an Instron testing machine using a cross-head speed of 0.2 cm/min and a gauge length of 2.5 cm. Antibacterial tests against St~phylo~o~cus utueus and Eschcrichia coli were carried out by the halo method, as reported elsewhere[5,6]. Finally the fiber was subjected to an effusion test; that
2.2 Preparation procedures The phenolic resin and AgNOx (100: 1 by wt ratio) were dissolved in methanol, followed by blending. The resin, after removal of methanol by using a vac-
*Author to whom all correspondence dressed.
should be ad-
is, antibacterial 71
activity
and silver content
of the fi-
A. OYA et al.
72
Table I. Properties of the fibers
Yield (wt%)
Ag content (w+%)
Surface area (m2/g)
Antibacterial activity E. coli
S. aureus
inactive active active
inactive active active
0.31
KF E
ACF- 10
ACF-60
100 56
0.67 0.38
16
53
0.69
280
21
2.20
1940
bers were examined after soaking in the flowing tap water for 10 and 20 days. 3. RESULTS AND DISCUSSION
3.1 Carbonization and activation yields, Ag content and surface area Carbonization and activation yields, Ag content and surface area of the fibers at various stages are shown in Table 1. The carbon yield of the CF based on the HF was 56 wt%. The ACF- 10 and the ACF-60 yields were 53 and 21 wt%, respectively. If the amount of silver in the fiber is assumed to remain unchanged after carbonization and activation, the calculated Ag contents are 0.68,0.72, and 1.8 1 wt% for the CF, the ACF-10 and the ACF-60. There are no big differences between the observed and calculated values of Ag contents. The surface areas of the CF in-
creased remarkably reach 1,940 m’/g.
after activation
for 60 min to
3.2 X-ray dljiiaction Figure 1 shows X-ray diffraction profiles of the fibers together with the resin fiber without AgNOx prepared in the same way for a reference (abbreviation: SKF). The addition of AgNO, gave no difference between the profiles of the resin fibers KF and SISF. Since any XRD peaks relating to silver and its compounds were not observed, silver (particles or other states) must be dispersed finely throughout the RF. The carbon structure created in the CF is shown by the shifting ofthe broad peak in the HF to somewhat higher diffraction angle than 20”. The peaks from Ag metal appeared in the CF and strengthened with proceeding of activation. The mean crystallite sizes of Ag metal in the CF, the ACF-10 and the ACF-60 were 38, 5 1, and 52 nm based on the half width of the peaks (Sherrer’s equation using 111 diffraction peak of silver around 38”). When the CF was carbonized for additional 60 min at 900°C in nitrogen, the crystalline size of silver did not change. 3.3 Mechanical properties Figure 2 shows relationship between diameter and tensile strength of the fibers at various stages. That strength increased with decreasing of the fiber diameter is well known. There appears to be no difference between strength ofthe CF and the carbon fiber with-
20
60 40 20 (CUKa)
80
Fig. 1. X-ray diffraction profiles ofthe fibers, with and without AgNO,, at various stages.
Diameter
(pm)
Fig. 2. Relationship between diameter and tensile strength of the fibers at various stages.
73
Antibacterial activated carbon fiber
Table 2. Ag content and antibacterial activity before and after effusion test Soaking time (day)
Ag content (wt%)
inactive
inactive active inactive
active
active
20
0.69 0.67 0.71
active active
active active
20 0
ACF-IO
IO 0
2.20
IO
I .oo
active active
active active
20
0.79
active
active
ACF-60
out AgNO, (abbreviation:
SCF), although there is a large scatter in the data. The activation lowered the strength of the fiber slightly.
3.4 TEA4 observation Figure 3 shows TEM photographs of the AgNOjadded fibers at various stages, As shown in X-ray analysis, various sizes of silver particles (as arrowed) are formed after carbonization and grew with proceeding of activation. A large silver particle of several 100 nm was observed in the ACF-60 the photograph. Ways of suppressing
as indicated the growth
S. uureus
active active
10
Fig. 3. TEM photographs of the fibers at various stages
E. coii
0.67 0.72 0.12
0
CF
ACF-10
Antibacterial activity
however, Ag content decreased remarkably with soaking time. As stated above, the antibacterial activated carbon fiber with a specific surface area of ca.2,000 m’/g was prepared by dispersing fine silver particles. This surface area is sufficient to use as a water purifier. When this fiber is used practically as a water purifier, however, other problems remain to be solved. The first is the pore size distribution which is not discussed here. The second is how to suppress the removal of silver from the fiber duringsoakingin the flowing tap water. The third is to determine the lowest Ag content in the ACF required for the antibacterial activity.Thebe studies are now in progress and will be reported later. authors thank Daiwa Chemical for antibacterial test.
Ackno,l,/~~d~~~rnent-The
co. Ltd.
in
of silver particle at activation stage should be studied, because the finer particle exhibits stronger antibacterial activity.
REFERENCES
1. A. Sakoda, M. Suzuki. and K. Kawazoe. Uhl. Res. 21, 717 (1987).
3.5 Antibacterial activity Antibacterial activity of the fibers before and after activation is shown in Table 1. The CF has no activity to both bacteria but both ACFs showed activity to both bacteria clearly.
3.6 .Efkion
test
Table 2 shows Ag content and antibacterial activity before and after the effusion test. The CF showed activity after the test except for no activity of the CF after 20 days soaking to S. aureus. Both ACFs had strong activity to both bacteria before and after the effusion test. The effusion test gave no effect on Ag content for the CF and the ACF-10. In the ACF-20,
2. A. Sakoda. M. Suzuki. R. Hirai, and K. Kawazoe, U’ut. Rcs. 25,219(1991). 3. Toho Rayon Co. Ltd., Catalogue on the activated carbon fiber “Finegard”. 4. M. Kuroda. M. Yuzawa, Y. Sakakibara. and M. Okamura. I+‘ut.Rev. 22, 653 (I 988). 5. A. Oya. T. Banse, F. Ohashi, and S. Otani. .Ipp/. Cluy Ser.6, 135 (1991). 6. A. Oya, T. Banse, and F. Ohashi, &v/. C/u~~Sci. 6. 3 1 1 (1992). 7. F. S. Hayes, Jr.. in Kirk-Othmcr: Encyclopc>diu q/ Chemicul Twhnologj,, Vol. 16. Third Ed.. pp. 125. John Wiley & Sons, Inc. (198 I). 8. Y. Arita, D. Arita, R. Fujii, F. Ogata, and M. Irisawa, Chrmtech, 424
( 1989).
9. Jupunesr Putent Publication 1978-439 I I IO. S. Otani, Curbon 3, 3 1 (I 965).
1993 Copynghi
0008-6223193 $6.00 + .oO (0 I993 Pergamon Press Ltd.
ANTIBACTERIAL ACTIVATED CARBON FIBER DERIVED FROM PHENOLIC RESIN CONTAINING SILVER NITRATE A. OYA* and S. YOSHIDA Faculty of Engineering, Gunma University. Kiryu, Gunma 376, Japan and Y. ABE, T. IIZUKA and N. MAKIYAMA Gun-ei Chemical Industry Co., Ltd., Oyagi, Takasaki, Gunma 370, Japan (Received 6 April 1992; accepled in revisedjbrm 2 June 1992) Abstract-A
novolactype phenolic resin including I wt% of AgN03 was spun, hardened, carbonized at 900°C under nitrogen and finally activated at 900°C for 10 and 60 min under steam. The resulting fibers showed specific Nl-BET surface areas of 280 and 1,940 m*/g, respectively. The latter contained 2.2 wt% ofthe silver particles ofwhich the largest size was several 100 nm and showed antibacterial activity against Staphyk~coccus aureus and Escherichia co/i. After soaking in the flowing tap water for 20 days, this fiber lost one third of silver but kept the antibacterial activity.
Key Words-Antibacterial
1.
ability, activated carbon fiber, water purifier, silver.
uum evaporator at room temperature, was spun using a spinning apparatus with a nozzle diameter of 1.5 mm, described earlier[ lo]. The spinning temper-
INTRODUaION
Activated carbon fiber has now some applications, one of which is as a water purifier[ 1,2,3]. Since the
ature was controlled over a relatively wide range between 100 and 145°C because of poor spinnability of the resulting resin. The resulting resin fiber including AgN03 (abbreviation: KF) was soaked in the hardner at 20 min at room temperature, heated up to 95°C at O.S”C/min and kept for 8 h at this temperature.The hardened fiber (abbreviation: HF) was neutralized by treatment with aqueous ammonia (1 mol/dm’), followed by drying under vacuum after extensive washing in the flowing water. Next the fiber was carbonized at 900°C for 30 min under a nitrogen stream. The resulting carbonized fiber (abbreviation: CF) was activated at 900°C for 10 min (abbreviation: ACF- 10) and 60 min (abbreviation: ACF-60) under a stream of steam (partial pressure of steam: ca.30%).
carbon material is known to have a high affinity for bacteria[4], however, bacteria may breed on this fiber during the purification process, becoming itself a pollutant. In order to avoid such a disadvantage, an an-
tibacterial activated carbon fiber is required. It is well known that silver ion and fine silver particle have strong antibacterial activity[5,6]. Therefore, an antibacterial activated carbon fiber may be prepared by dispersing fine silver particles in it. The present work was undertaken to develop an antibacterial activated carbon fiber derived from a phenolic resin which included silver nitrate. 2. EXPERIMENTAL
2.1 Materials Silver nitrate (AgNO,) used was reagent grade. A novolactype phenolic resin with a softening point of I 15- 120°C was supplied by the Gun-ei Chemical Co. Ltd. This resin is a raw material for the flame resistance “Kynol” fiber, which is described elsewhere[791. The hardener supplied by same company contains formaldehyde as a cross-linking agent and hydrochloric acid as a catalyst. Details are described elsewhere[7-91.
2.3 Measurements The fibers were subjected to the following measurements. The powder X-ray diffraction patterns were obtained using Ni-filtered CuKol-radiation. Transmission electron microscopy (TEM) was used to observe the physical state of the silver in the fiber. The silver content in the fiber was measured by ICP emission spectroscopy. BET specific surface area was determined from the adsorption isotherm of Nz at 77K (one-point method). Mechanical testing of the fibers was performed on an Instron testing machine using a cross-head speed of 0.2 cm/min and a gauge length of 2.5 cm. Antibacterial tests against St~phylo~o~cus utueus and Eschcrichia coli were carried out by the halo method, as reported elsewhere[5,6]. Finally the fiber was subjected to an effusion test; that
2.2 Preparation procedures The phenolic resin and AgNOx (100: 1 by wt ratio) were dissolved in methanol, followed by blending. The resin, after removal of methanol by using a vac-
*Author to whom all correspondence dressed.
should be ad-
is, antibacterial 71
activity
and silver content
of the fi-
A. OYA et al.
72
Table I. Properties of the fibers
Yield (wt%)
Ag content (w+%)
Surface area (m2/g)
Antibacterial activity E. coli
S. aureus
inactive active active
inactive active active
0.31
KF E
ACF- 10
ACF-60
100 56
0.67 0.38
16
53
0.69
280
21
2.20
1940
bers were examined after soaking in the flowing tap water for 10 and 20 days. 3. RESULTS AND DISCUSSION
3.1 Carbonization and activation yields, Ag content and surface area Carbonization and activation yields, Ag content and surface area of the fibers at various stages are shown in Table 1. The carbon yield of the CF based on the HF was 56 wt%. The ACF- 10 and the ACF-60 yields were 53 and 21 wt%, respectively. If the amount of silver in the fiber is assumed to remain unchanged after carbonization and activation, the calculated Ag contents are 0.68,0.72, and 1.8 1 wt% for the CF, the ACF-10 and the ACF-60. There are no big differences between the observed and calculated values of Ag contents. The surface areas of the CF in-
creased remarkably reach 1,940 m’/g.
after activation
for 60 min to
3.2 X-ray dljiiaction Figure 1 shows X-ray diffraction profiles of the fibers together with the resin fiber without AgNOx prepared in the same way for a reference (abbreviation: SKF). The addition of AgNO, gave no difference between the profiles of the resin fibers KF and SISF. Since any XRD peaks relating to silver and its compounds were not observed, silver (particles or other states) must be dispersed finely throughout the RF. The carbon structure created in the CF is shown by the shifting ofthe broad peak in the HF to somewhat higher diffraction angle than 20”. The peaks from Ag metal appeared in the CF and strengthened with proceeding of activation. The mean crystallite sizes of Ag metal in the CF, the ACF-10 and the ACF-60 were 38, 5 1, and 52 nm based on the half width of the peaks (Sherrer’s equation using 111 diffraction peak of silver around 38”). When the CF was carbonized for additional 60 min at 900°C in nitrogen, the crystalline size of silver did not change. 3.3 Mechanical properties Figure 2 shows relationship between diameter and tensile strength of the fibers at various stages. That strength increased with decreasing of the fiber diameter is well known. There appears to be no difference between strength ofthe CF and the carbon fiber with-
20
60 40 20 (CUKa)
80
Fig. 1. X-ray diffraction profiles ofthe fibers, with and without AgNO,, at various stages.
Diameter
(pm)
Fig. 2. Relationship between diameter and tensile strength of the fibers at various stages.
73
Antibacterial activated carbon fiber
Table 2. Ag content and antibacterial activity before and after effusion test Soaking time (day)
Ag content (wt%)
inactive
inactive active inactive
active
active
20
0.69 0.67 0.71
active active
active active
20 0
ACF-IO
IO 0
2.20
IO
I .oo
active active
active active
20
0.79
active
active
ACF-60
out AgNO, (abbreviation:
SCF), although there is a large scatter in the data. The activation lowered the strength of the fiber slightly.
3.4 TEA4 observation Figure 3 shows TEM photographs of the AgNOjadded fibers at various stages, As shown in X-ray analysis, various sizes of silver particles (as arrowed) are formed after carbonization and grew with proceeding of activation. A large silver particle of several 100 nm was observed in the ACF-60 the photograph. Ways of suppressing
as indicated the growth
S. uureus
active active
10
Fig. 3. TEM photographs of the fibers at various stages
E. coii
0.67 0.72 0.12
0
CF
ACF-10
Antibacterial activity
however, Ag content decreased remarkably with soaking time. As stated above, the antibacterial activated carbon fiber with a specific surface area of ca.2,000 m’/g was prepared by dispersing fine silver particles. This surface area is sufficient to use as a water purifier. When this fiber is used practically as a water purifier, however, other problems remain to be solved. The first is the pore size distribution which is not discussed here. The second is how to suppress the removal of silver from the fiber duringsoakingin the flowing tap water. The third is to determine the lowest Ag content in the ACF required for the antibacterial activity.Thebe studies are now in progress and will be reported later. authors thank Daiwa Chemical for antibacterial test.
Ackno,l,/~~d~~~rnent-The
co. Ltd.
in
of silver particle at activation stage should be studied, because the finer particle exhibits stronger antibacterial activity.
REFERENCES
1. A. Sakoda, M. Suzuki. and K. Kawazoe. Uhl. Res. 21, 717 (1987).
3.5 Antibacterial activity Antibacterial activity of the fibers before and after activation is shown in Table 1. The CF has no activity to both bacteria but both ACFs showed activity to both bacteria clearly.
3.6 .Efkion
test
Table 2 shows Ag content and antibacterial activity before and after the effusion test. The CF showed activity after the test except for no activity of the CF after 20 days soaking to S. aureus. Both ACFs had strong activity to both bacteria before and after the effusion test. The effusion test gave no effect on Ag content for the CF and the ACF-10. In the ACF-20,
2. A. Sakoda. M. Suzuki. R. Hirai, and K. Kawazoe, U’ut. Rcs. 25,219(1991). 3. Toho Rayon Co. Ltd., Catalogue on the activated carbon fiber “Finegard”. 4. M. Kuroda. M. Yuzawa, Y. Sakakibara. and M. Okamura. I+‘ut.Rev. 22, 653 (I 988). 5. A. Oya. T. Banse, F. Ohashi, and S. Otani. .Ipp/. Cluy Ser.6, 135 (1991). 6. A. Oya, T. Banse, and F. Ohashi, &v/. C/u~~Sci. 6. 3 1 1 (1992). 7. F. S. Hayes, Jr.. in Kirk-Othmcr: Encyclopc>diu q/ Chemicul Twhnologj,, Vol. 16. Third Ed.. pp. 125. John Wiley & Sons, Inc. (198 I). 8. Y. Arita, D. Arita, R. Fujii, F. Ogata, and M. Irisawa, Chrmtech, 424
( 1989).
9. Jupunesr Putent Publication 1978-439 I I IO. S. Otani, Curbon 3, 3 1 (I 965).