Hatano Y., Katsumura Y., Mozumder A. (Eds.) Charged Particle and Photon Interactions with Matter - Recent Advances, Applications, and Interfaces

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740 Charged Particle and Photon Interactions with Matter

Chitin is poly-β-(1-4)-N-acetyl-d-glucosamine, which is the main component of the external

skeleton in Arthropoda and the periostracum in Mollusca. Its deacetylated derivative is chitosan.

Chitin and chitosan are not soluble in water. After carboxymethylation, the resulting carboxymethyl

chitin, CMCht, and carboxymethyl chitosan, CMChts, become soluble in water. Their chemical

structures are shown in Figure 27.3. The chemically modied CMCht and CMChts can be cross-

linked in these paste-like states (Wasikiewicz et al., 2006), though intrinsic chitin and chitosan are

decomposed by high energy irradiation. Figure 27.4 shows the effect of concentration on gel frac-

tion. EB irradiation of 50kGy gave gel fractions of 65% and 40% for CMCht and CMChts, respec-

tively, in the 30%–40% concentration range. At lower and higher concentrations, the gel fraction

went

down.

the swelling, the correlations were divided into two categories. In both the cases of CMCht

and CMChts, the hydrogels show similar tendencies. There are linear relationships between the

gel fraction and swelling of CMCht and CMChts. Though the swelling decreased with an increase

of the gel fraction, CMChts hydrogels show lower swelling than CMCht hydrogels at the same gel

fraction.

27.2.1.1 applications

of p

olymer

els

Polysaccharides are well-known biodegradable materials. This feature is maintained even after

cross-linking with high energy radiation. The obtained gel can be degraded by microorganisms after

disposal. This characteristic is useful for environment-friendly products such as bedsore prevention

mats

(Chmielewski, 2006), coolants, and water absorbents for livestock excrement treatment.

0 20 40 60 80

100

(a)

(b)

(c)

Dose (kGy)

Gel fraction (%)

Figure 27.2 Gel fraction of cross-linked CMC having different degrees of substitution (DS) at concentra-

tion of 20%; (a) DS = 2.2, (b) DS = 1.3, and (c) DS = 0.86. (From Fei, B. et al., J. App. Polym. Science, 278,

2000.

With permission.)

NHR

Figure 27.3 Chemical structures of carboxymethyl chitin and chitosan; R

= H or COCH

and R

COONa or H.

Radiation Processing of Polymers and Its Applications 741

Bedsore prevention requires the bedsore prevention mat to be suitably elastic for promoting

blood circulation. CMC hydrogel was applied as bedsore prevention mat, which is used as bed mats

during the surgical operation procedures (Figure 27.5). Before the operation is conducted, the mat is

pre-heated to body temperature (37°C) using an oven heater. Temperature could be maintained dur-

ing operation. Clinical tests proved that CMC mat was very effective in the prevention of bedsores.

The comparison of blood ow with CMC mat, with those of other mats such as board and general

mattress revealed that CMC hydrogel mat reached the highest value. The hydrogel can disperse the

body pressure and improve circulation of blood during operation. Thus, it could prevent bedsores

patients.

CMC

hydrogel has also been applied as a coolant. This hydrogel coolant has a high capacity to

retain low temperatures longer than general liquid coolants. Fish and vegetables could be trans-

ported from the production district to distant markets using a hydrogel coolant. This product uses

swollen

CMC dry gel.

CMC

dry gel can absorb water, several hundreds times its own weight. The addition of CMC

dry gel controls the water content in livestock excreta and accelerates its composting process. Field

heaping and open storage of livestock excreta have been legally prohibited in Japan, since the

release of excrement and urine contaminates groundwater and river water. The high water content

of around 90% in excrement retards its fermentation to fertilizer. The addition of 0.2% CMC dry gel

to the excrement as a water absorbent can reduce the water content by up to 70% and can enhance

Concentration (%)

Gel fraction (%)

Degradation

100

0 20 40 60 80 100

Cross-linking

CM-chitin

CM-

chitosan

Figure 27.4 Effect of concentration on gel fraction in cross-linked CM-chitin and CM-chitosan; CM-chitin

and

CM-chitosan were irradiated with 50

kGy

at 30% aqua paste-like state.

Hydrogel

Figure 27.5 Bedsore prevention mat composed of hydrogel obtained by cross-linking of CMC.

742 Charged Particle and Photon Interactions with Matter

the fermentation. Previously, saw dust was used for this purpose. Usage of CMC dry gel minimized

the consumption of saw dust to one-sixth. The advantages of this novel technology are to reduce

storage

area for saw dust, heavy work, and odor diffusion to environment.

CMCht

and CMChts are considered to be the most abundant natural amino polysaccharide and

have versatile applications in cosmetics, food, and medical materials (Kumar, 2000). They were

used as metal-ion adsorbents as they carry an amine group that has afnity toward metal ions

such as copper, zinc, and mercury (Benavente, 2008). Such commercialized, adsorbent resins were

generally synthesized by copolymerizing the precursor monomer, chloromethylstyrene, and cross-

linker, divinylbenzene. The resulting cross-linked resin has the convertible site of –CH

Cl in the

chloromethylstyrene moiety to the functional group having afnity toward metal ions. This precur-

sor resin can be chemically modied to a metal-ion adsorbent having –SO

, –COOH, and –NH

groups. However, these resins are derived from petroleum products. To secure petroleum resources

and decrease environmental burdens, the naturally occurring polymers such as CMCht and CMChts

should

be used as raw materials for synthesizing metal-ion adsorbents.

The

metal adsorption of CMCht and CMChts hydrogels shows the adsorption of various metal

ions as shown in Figure 27.6 (Wasikiewicz et al., 2005a). The CMCht hydrogel adsorbed Pd, Au,

Cd, V, and Pt in 60min. In the case of CMChts, Au and Pt were preferentially adsorbed in 120min.

Adsorbed metals on CMCht and CMChts hydrogels can be eluted by dilute hydrochloric acid solu-

tion. After disposal of CMCht and CMChts, the size and thickness of the lms in soil become

smaller. Figure 27.7 shows CMCht and CMChts hydrogel lms, 1mm thick, before and after keeping

100

Adsorption (%)

Adsorption time (min)

0 120 240 360 480

Adsorption time (min)

100

Adsorption (%)

(b)(a)

Figure 27.6 Metal adsorption of CM-chitin and chitosan gels at pH 3.9; (a) CM-chitin hydrogel and

(b)CM-chitosan hydrogel. (Modied from Wasikiewicz, J.M. et al., Nucl. Instrum. Methods Phys. Res.Sect.B,

236,

617, 2005a.)

(b)

(a)

Figure 27.7 Degradation of CM-chitin and chitosan gels kept in soil for 10 weeks; (a) CM-chitin hydrogel and

(b) CM-chitosan hydrogel. (From Wasikiewick, J.M. et al., J. Appl. Polym. Sci., 102, 758, 2006. With permission.)

Radiation Processing of Polymers and Its Applications 743

in soil for 10 weeks from October to December in Japan. In the case of CMChts, a number of small

holes are noticeable. It can be concluded that prolonged storing of these lms in the ground would

cause their complete disintegration as a result of bacterial activity. Natural polymers including chi-

tin and chitosan are renewable resources and are spontaneously degraded by naturally occurring

microorganisms. Such polymers do not increase the burden to the natural environment since they

do not produce any toxic waste products during the degradation process.

27.2.2 biodegradable plaSticS

Poly(l-lactic acid), PLA, is a transparent and hard plastic and is produced by condensation polymer-

ization of lactic acid obtained by fermentation of starch (Reddy et al., 2008). In this regard, PLA is a

typical renewable plastic. In the near future, nonbiodegradable engineering plastics will be replaced

by PLA on the viewpoint of environmental preservation. One of the promising applications of PLA

is in thermally molded products such as those used in food packaging, bottles, medical, and phar-

maceutical products, which require high thermal stability. However, PLA is thermally deformed at

temperatures higher than its glass transition temperature of 60°C, though it has a high melting point

175°C.

PLA

is not cross-linked by irradiation without a certain cross-linker, since PLA is degraded

by ionizing radiation. It was found that the addition of polyfunctional monomers (PFM) as cross-

linkers to PLA could induce cross-linking (Charlesby, 1981). PFM such as triallyl isocyanurate

(TAIC), trimethallyl isocyanurate (TMAIC), trimethylolpropane triacrylate (TMPTA), trimethy-

lolpropane trimethacrylate (TMPTMA), 1,6-hexanediol diacrylate (HDDA), and ethylene glycol

bis[pentakis(glycidyl allyl ether)] ether (EG) have been widely used as cross-linkers for polyolens,

owing

to their high reactivity against polymer chains.

After

screening of various PFM, it was found that TAIC is a suitable cross-linker for PLA. Figure

27.8 shows the effect of dose on the gel fraction of irradiated PLA with 1% and 3% TAIC. The gel

fraction of the cross-linked PLA was estimated by the weight of its insoluble part after immersion

in chloroform for 48h. The gel fraction reached 83.3% for 3% of TAIC after irradiation of 50kGy.

TMAIC gave a slightly lower gel fraction. In the cases of TMAPT, TMPTMA, HDDA, and EG,

the gel fractions did not reach 30%. TAIC was the most effective cross-linker for PLA since it has

three functional groups of C=C and an isocyanuric ring that achieves a greater three-dimensional

network

by irradiation than that achieved by acrylate-type PFM.

100

0 20 40 60

Dose (kGy)

Gel fraction (%)

Figure 27.8 Effect of dose on cross-linking of PLA with TAIC; (○) 1% TAIC and (●) 3% TAIC. (Modied

from

Nagasawa, N. et al., Nucl. Instrum. Methods Phys. Res. Sect. B, 236, 611, 2005.)

744 Charged Particle and Photon Interactions with Matter

Figure 27.9 shows the thermal deformation of cross-linked PLA with 3% TAIC and PLA without

cross-linking (Nagasawa et al., 2005). The thermal deformation was evaluated on PLA lms heated

from room temperature up to 200°C in a nitrogen atmosphere under a constant load of 0.5g at a

heating rate of 10°C/min. Under thermal stretching, the PLA started to elongate at the glass transi-

tion

temperature of 60°C, and then thermal stretching reached 60% at 100°C. The cross-linked PLA

showed no elongation at glass transition temperature and has low elongation of thermal stretching

less than 10% even at 200°C. This result revealed that radiation-induced cross-linking induced the

thermal resistance of PLA, high enough for versatile applications. Enzymatic degradation of PLA was

evaluated by degradation using proteinase K enzyme from Tritirachium album. The weight loss of

PLA was 60% after 140h incubation, whereas the cross-linked PLA with TAIC were degraded 30%

in weight losses. After cross-linking, the diffusion of the enzyme is considered to be disturbed by the

network structure of PLA. However, enzyme degradability was still maintained at half of intrinsic

PLA. This result implies that PLA is an environmentally acceptable material, even after cross-linking.

Cross-linked PLA can be applied to tableware such as cups and plates. PLA containing 3% TAIC

was molded to cups and plates by an extruder and then irradiated with 50kGy to induce cross-

linking. The obtained tableware were transparent since PLA is an intrinsically colorless polymer.

When boiling water was poured into cups with and without cross-linked PLA, the cup without PLA

cross-linking deformed and changed to white as shown in Figure 27.10. But the cross-linked PLA

Temperature (°C)

0 50 100 150 200

ermal stretching (%)

Figure 27.9 Thermal deformation of PLA and cross-linked PLA; PLA was kneaded with 3% of TAIC

and then irradiated with 50kGy; broken line is for PLA and dotted line cross-linked PLA. (Modied from

Nagasawa,

N. et al., Nucl. Instrum. Methods Phys. Res. Sect. B, 236, 611, 2005.)

(a)

(b)

Figure 27.10 Effect of cross-linking on thermal property of PLA; (a) PLA and (b) cross-linked PLA.

(Modied

from Nagasawa, N. et al., Nucl. Instrum. Methods Phys. Res. Sect. B, 236, 611, 2005.)

Radiation Processing of Polymers and Its Applications 745

cup maintained its original transparency and shape. The color change from transparent to milky

was caused by the crystallization of PLA. After cross-linking, the movement of PLA molecules was

restricted by the cross-linking point. Due to this reason, the cross-linked PLA cup could maintain

transparency

when it was heated close to 100°C.

Cross-linked

PLA can be used in heat-shrinkable tubes. The resulting cross-linked PLA tube is

expanded diametrically to double its size at 200°C and then holds the expanded shape when it cools

down to room temperature. This is a heat-shrinkable tube that thermally shrinks to unexpanded

tube size. PLA without cross-linking cannot be expanded at the temperature over its melting point

of 160°C. Such heat-shrinkable polyethylene tube have already been commercialized. However,

PLA heat-shrinkable tubes have several advantages such as biodegradability, high heat resistance,

and transparency.

If the elastic property can be imparted into PLA, new applications such as renewable lapping

lms and impact absorbing liners can be realized. Plasticizers are used to induce the elastic property

into hard plastics like PLA. When PLA is simply mixed with plasticizer, PLA temporarily becomes

elastic. However, the plasticizer is gradually expelled from the PLA. In the case of PLA without

cross-linking, the plasticizer is not maintained in the PLA for 30min at 100°C. This is because the

PLA crystallizes at this temperate and simultaneously the plasticizer is expelled from PLA. After

cross-linking, PLA can contain the plasticizer up to the concentration of 35% and obtains stable

elasticity

as shown in Figure 27.11.

27.3 new material produCtion using radiation-induCed graFting

27.3.1 general application

The membranes prepared by radiation-induced graft polymerization (radiation-grafted membranes)

have been widely applied to separation processes (pervaporation, reverse osmosis, and electrodi-

alysis), electrochemical processes (bottom battery and fuel cells), and adsorbents for metal ions

(Figure 27.12) (Saito and Sugo, 2001; Gupta et al., 2004; Nasef and Hegazy, 2004). These mem-

branes, in general, consist of similar components, hydrophilic grafted polymers (grafts) attached

into hydrophobic trunk polymers (substrates), namely, the so-called anion-exchange membrane

structures. The membranes containing the grafts with acids such as carboxylic, phosphoric, and

sulfonic acids and those with bases such as amino groups and ammonium salts are called “cation-

and anion-exchange membranes,” respectively. Hydrophobic polymer substrates can be classied as

Figure 27.11 Elasticity appeared by holding plasticizer in cross-linked PLA. (From Nagasawa, N. et al.,

High Functionalization and Recycling Technology for Bioplastic NTS Inc.pp. 162–169, 2008. With permission.)

746 Charged Particle and Photon Interactions with Matter

conventional polyolen lms (polyethylene (PE) and polypropylene (PP)), peruoro- and partially

uorinated-polymer lms (poly(tetrauoroethylene)) (PTFE), poly(tetrauoroethylene-co-hexau-

oropropylene) (FEP), poly(tetrauoroethylene-co-peruorovinyl ether) (PFA), poly(vinylidene uo-

ride) (PVDF) and poly(ethylene-co-tetrauoroethylene) (ETFE), and natural polymer resins (wool,

cotton, and paper), as shown in Figure 27.13. To the above substrates, acrylic acid (AAc), methyl

methacrylate (MMA), styrene derivatives, vinyl pyridine, and the corresponding salts are intro-

duced as hydrophilic graft polymers (grafts), and subsequent chemical transformation results in

radiation-grafted

membranes.

The

grafting of poly(copper acrylate), poly(vinylpyridinium salts), and phosphonium salts gave

antibacterial natural polymers. The grafted membranes, consisting of poly(AAc) incorporated into

Hydrocarbon polymers

Perfluorocarbon polymers

Partially fluorinated carbon polymers

Polyethylene

Polypropylene

Poly(tetrafluoroethylene)

Poly(tetrafluoroethylene-

co-hexafluoroethylene)

Poly(tetrafluoroethylene-

co-perfluorovinyl ether)

Poly(vinylidene fluoride)

Poly(ethylene-

co-tetrafluoroethylene)

Monomers

Styrene

O OH

O O

O OH

Acrylic acid

(AAc)

Methyl methacrylate

(MMA)

PTFE

FEP

PFA

PVDF

ETFE

Figure 27.13 Structures of polymer substrates and monomers constituting grafted membranes.

Separation process

• Pervaporation

(alcohol, organic chemicals from water)

•

Reverse

osmosis

•

Metal adsorbents (hazardous metal separation or precious metal correction)

Electrochemical

processes

•

Electrodialysis

(production of water, NaCl)

•

Chloroalkali

(production of NaOH, Cl

)

Battery/energy

system

•

Bottom

battery

•

Polymer

electrolytes for fuel cell

Figure 27.12 Application elds of radiation-grafted membranes.

Radiation Processing of Polymers and Its Applications 747

PE, can be applied to pervaporation membranes to remove only water from aqueous alcohol solutions

owing to higher afnity of the poly(AAc) grafts to water than alcohols (Gupta et al., 2004). The mem-

branes having carboxylic, sulfonic, and phosphoric acids in the grafts into PE can act as metal-ion

adsorbents owing to the high afnity of the grafts to the metal ions in aqueous solutions (Saito and

Sugo, 2001). Furthermore, the radiation-grafted membranes, possessing poly(AAc) grafts into PE can

be commercialized as a battery separator of bottom cells because only hydroxide ions, but not metal

ions (Ag(OH)

−

) can pass through the membranes (Ishigaki et al., 1982a,b; Hsiue and Huang, 1985).

After the successful utilization of radiation-grafted membranes in battery cells, the grafted

membranes consisting of uorinated-polymer substrates, having higher mechanical and thermal

strengths, and the grafts, having more acidic sulfonic acid groups, have been developed for polymer

electrolyte membranes (PEM) for fuel cells, which require higher conductivity and durability at

higher temperatures. Sections 27.3.2 and 27.3.3 focus on recent advancements of radiation-grafted

membranes as metal adsorbents to recover precious metal ions and in battery applications such as

bottom cells and fuel cells.

27.3.2 fibrouS Metal-ion adSorbentS

To synthesize the metal adsorbent, the functional groups having strong afnity toward metal ions

should be imparted into these trunk polymers by grafting, as shown in Figure 27.14. Other func-

tional groups were reviewed by Smith and Alexangratos (2000). When a monomer has a chelating

group in its side chain, the metal adsorbent is directly synthesized only by grafting. In the case of a

monomer having a precursor for coordination, chemical modication is necessary after its grafting

(Seko et al., 2005). Table 27.1 lists the representative functional group for metal adsorption, cor-

responding

grafting monomer, and chemical reagent (Basuki et al., 2003).

GMA

is a useful monomer for the precursor of metal adsorbents. The grafting of GMA generally

is carried out using organic solvents such as methanol (Kavalla et al., 2004) and dimethyl sulfoxide

(Aoki et al., 2001). It was found that grafting yield was dramatically enhanced when GMA was

emulsied by surfactants in water instead of organic solvents (Seko et al., 2007). This aqueous

GMA emulsion grafting on PE bers gave a degree of grafting of 130% in preirradiation conditions

kGy,

grafting temperature of 40°C, and grafting time of 2

Nonwoven fabric made of polyethylene is used as a trunk polymer. This is because the resulting

fabric adsorbent causes swift adsorption of metal ions and ensures easy handling in the adsorption

process. For example, the metal adsorbed in the fabric adsorbent can be picked up from the solution by

forceps after it is dipped into the metal solution for a few minutes. Additionally, a conventional adsor-

bent resin is used in a volume-normalized ow rate, namely space velocity, around 10h

−1

. At ow rates

far more than 10h

−1

, the adsorption capacity dramatically decreases in a column mode adsorption.

However, the adsorbent fabric can be used in the space velocity more than 1000h

−1

(Jyo et al., 2003).

As applications of metal adsorbents, toxic and rare metals were attempted to be collected for envi-

ronmental preservation and metal resource security, respectively. During scallop processing, the mid-

gut gland is discarded since this part contains 20–40ppm of cadmium. The discarded mid-gut gland

Graft chains

Graft polymerization

Monomer

Addition of

monomer

Radicals

Creation of

active species

Irradiation

(EB and γ-ray)

Trunk

polymer

Figure 27.14 Schematic diagram of radiation-induced graft polymerization.

748 Charged Particle and Photon Interactions with Matter

is incinerated even though it contains a large amount of nutrients such as straight-chain fatty acids

and fat. The mid-gut gland is treated with amidoxime adsorbent (Shiraishi et al., 2003). The bench

scale plants for removal of cadmium from mid-gut glands was operated using iminodiacetic acid

adsorbent and cadmium-free mid-gut gland could be used as fertilizer and animal feed. Iminodiacetic

acid adsorbent was used in the bench scale plant because the pH of the eluent was3. In this pH range,

the iminodiacetic acid adsorbent has a higher selectivity to cadmium than the amidoxime adsorbent.

Uranium collection from seawater has been researched from the viewpoint of resource security

of atomic power generation. Amidoxime-type adsorbents synthesized by graft polymerization can

adsorb uranium occurring in an extremely low concentration, 3 ppb, in seawater with the coexis-

tence

of sodium and magnesium ions.

The

performance of uranium adsorbent fabrics was evaluated using 350kg adsorbent stacks

by soaking in the ocean in the ofng of Mutsu-Sekine, Aomori, Japan, as shown in Figure 27.15.

Figure 27.15 Collection process of uranium adsorbent stacks at marine experiment. (From Seko, N. et al.,

Nucl. Technol.,

144, 274, 2003. With permission.)

table 27.1

Functional

roups

mparted

by g

raft

olymerization,

rafting

onomer

and

Chemical r

eagents

for s

ynthesis

of m

etal

dsorbents

Functional group grafting monomer Chemical reagent references

Amidoxime Acrylonitrile Hydoxylamine Seko

et al. (2005)

Amines Glycidyl

methacrylate Diethylamine Kabay et al. (1993)

N-Vinyl

formamide Sodium hydroxide Abrol et al. (2007)

Iminodiethanol Glycidyl

methacrylate

2,2′-Iminodiethanol

Awual et al. (2008)

Iminodiacetic

acid Glycidyl methacrylate Sodium iminodiacetate Ozawa et al. (2000)

Glucamine Glycidyl methacrylate N-Methyl glucamine Choi and Nho (1999)

Sulfonic acid Styrene Sulfuric acid Hoshina et al. (2007)

Glycidyl methacrylate Sodium sulte Vahdat et al. (2007)

Phosphoric acid Glycidyl methacrylate Phosphoric acid Kim and Saito (2000)

2-Hydroxyethyl

methacrylate

phosphoric

acid

Lee et al. (2002)

Source:

Tamada,

M. K., Kobunshi (High Polymers), 58, 397, 2009.

Radiation Processing of Polymers and Its Applications 749

One kilogram of uranium was successfully collected in 3 years’ marine experiment in the form of

a yellow cake (Seko et al., 2003). To make uranium collection from seawater cost effective, a braid-

type adsorbent was developed. The mooring system for the braid-type adsorbent does not need the

oat on the sea surface and a heavy adsorbent bed. The braid-type adsorbent is fabricated by braid-

ing the amidoxime adsorbent bers. The recovery cost of uranium from seawater was evaluated

on the basis of the recovery system of the braid-type adsorbent. Figure 27.16 shows the assembly

of braid-type adsorbent for a supposed annual collection of 1200 t uranium. When a performance

of 4g of uranium/kg of adsorbent, which can be reused 18 or more times is achieved, the uranium

cost reduces to 25,000 ¥/kg of uranium (96 $/lb-U

) (Tamada et al., 2006). The 4g uranium/kg of

adsorbent

is the most promising performance of uranium adsorbent in marine experiments.

27.3.3 polyMer electrolyte MeMbraneS for battery and fuel cellS

27.3.3.1 aac-grafted pe: bottom battery

The separator membranes in compact-bottom-type silver oxide cells were previously made of regen-

erated cellulose and porous PP lms. However, the conventional silver oxide cells had drawbacks, so

that silver hydroxide ion (Ag(OH)

−

) generated as a by-product on anode passes through the separa-

tor and was reduced to precipitated metal Ag, resulting in self-discharge and power deterioration.

To solve the above problems, radiation grafting was applied to the separation membranes; here,

poly(acrylic acid) (poly(AAc)) was grafted onto PE, which is very cheap, good lm forming, and

chemically

stable (Ishigaki et al., 1982a,b; Hsiue and Huang, 1985).

Hsiue

et al. reported that the specic resistivity of the lms rapidly decreased with increasing

grafting degrees up to 20% and reached 50 Ω cm (σ = 0.02 S/cm) (Hsiue and Huang, 1985). In

real production processes, PE roll lms are irradiated with an EB accelerator to generate radicals

and subsequently immersed in an aqueous AAc monomer solution to introduce poly(AAc) grafts

homogeneously through the PE lms (Figure 27.17). The obtained membranes act as high perfor-

mance battery separators because only hydroxide ions (OH

−

) but not by-product Ag(OH)

−

can pass

through the grafted membranes, which suppress self-discharge, resulting in the higher shelf life.

To develop the radiation-grafting technique, the bottom-type battery cells prepared using radiation

grafting can be used for a long time and in a stable manner, and the above problem can be solved.

Thus,

the AAc-grafted PE achieved 100% of market share in Japan.

27.3.3.2 Fluoropolymers for Fuel Cell pem

As a result of the successful application of the poly(AAc)-grafted PE to bottom cells, radiation

grafting has been applied to the preparation of PEM for hydrogen type (polymer electrolyte fuel

cell (PEFC)) and direct methanol type fuel cell (DMFC) in the last 10–15 years (Table 27.2).

Sea

surface

Bottom

Braid type

adsorbent

More than

40 m

100–200 m

60 m

Chain

8 m

Figure 27.16 Mooringstateof braid adsorbent forpractical systemof uranium collection. (FromTamada,M.

al., Trans. At. Energy Soc. Jpn., 5, 358, 2006. With permission.)