富山大学水素同位体科学研究センター研究報告29 ･ 30 : 61‑64, 2010.

Permeation of Tritiated Water throughPolypropylene
Masanori Haral) and Ⅵlka Tbgashi2)

1) Hydrogen Isotope Research Cente7; UniversiO, ofToyama, Toyama 930‑8555, LIapan
2) Faculo, of Science, UniversiO) ofToyama, Toyama 930‑8555, Japan

The permeability of water through the polypropylene film was studied using tritiatedwater･ Experiments were carried out in aflOw type vessel designed for the determination of
the permeability or water. All permeated water was captured by a water bubbler. The
permeability was evaluated from the amount of tritiated water permeated through thepolymer･ The obtained apparent pe‑eability increased with increasing temperature. The
temperature dependence was governed by the water vapor pressure･ The pemeability orwater through polypropylene no‑alized by water vapor pressure was fわund to bel･9xl0113gcm cm‑2 S‑1 Torr‑1 at 296 K･

Keywords: tritiated water, permeation, polypropylene

Ⅰ. Imtroductiom

Hydrophobic polymers are used to package

tritiated water through polypropylene wasmeasured at ambient near temperatures.

fわods and medicines in order to isolate themfrom air and moisture･ However, Polymers may

ⅠⅠ. Experimental

II.A. Theory
absorb and permeate some water. It causes todamp the packed material and reduction or theirln general, the amount of the water

quality･ Therefore, the barrier properties of

pemeated through hydrophobic polymers, likepolymer films agamSt Water Vapor are apolyethylene or polypropylene, lS glVen by theparticularly important criterion in theexpression

development of package material.

D(Cup,H20 ‑ Cd,,wn,H2,, )Hydrophobic polymers are widely used as aq=barrier material for handling radioactivea･t,(1)materials･ In case of tritium handling thepossible conversion of molecular HT into HTO
demands special precautions. For instance, HTO

where D denotes the diffusion coefficient of water
through the polymer, Cup,H2() and Cd,,wn,H,0 are

absorbed in polymer gloves constitutes anenhanced radiologlCal hazard due to thethe surface concentrations of water at the upstream

associated proximlty tO the skin of workers andand downstream sides respectively, α is thethe more prolonged exposure time.

permeation area of the polymer, L is the thicknessTo understand the barrier properties ofofthepolymerand∫thetime.

Thewaterpolymer materials agalnSt Water, the permeation

concentration at the surface of the polymer can beof tritiated water needs to be accurately

considered proportional to the product of theevaluated. 1n this works the permeation ofsolubility constant and the vapor pressure. Hence,61

M. Hara and Y. Togashi
equation can be rewritten as

D ･ S(1?,p,H2(, ‑ PdL,wn,H2,,)
a･t, (2)q=where g stands fわr the solubility constant andI:LP,H2,, and Pd(,wn,H20 are the water vapor

Tritiated water:4.10

pressures of the upstream and downstream sides,
respectively.

げitisassumed

MBq/cm3, 10cm3

thatPup,FIB() ‑ COnSt･ and Pd,,wn,H,()彩0 , the amount

Fig･ 1 ･ Schematic diagram orexperimental setup･

ofpemeated water is glVen by

D･S ･ Pup,H2()
q=α･才.

(3)

series of bubblers, the upper volume was swept byargon gas. Permeated water, i･e･ H20 and HTO,The D･S term is actually the permeability
coefficient of water through the hydrophobic

was mainly captured by the first bubbler.

Consequently, the tritium concentration in the firstbubbler increased with time.

polymer. Equation 3 indicates that the pemeability(D ･S ) is evaluated from the cumulative amountof water permeated (q).

II. C. Procedures
The plastic cup was filled with 10 cm3

II. B. Apparatus
The experimental apparatus wasdesigned following Eq. 3 and it was assumed thatsome of radiologlCal isotope exchange reactions ortritiated water and placed into the lower vessel.
The concentration of the tritiated water wasassayedtobe

4･10±0･09

MBq/cm3･ HTO/H20‑6･91xlOL8 ,with a liquid

HTO absorbed in polymer with structural C‑Hbonds in the polymer can be ignore. Figure 1
shows a simple schematic diagram of theexperimental setup. The measurement vessel
consists of an upper and a lower vessel separated

by the sample polymer film. Both the upper andthe lower vessel are made of stainless steel where

inside surface are coated by gold. The size of thevessels determine the permeation area or 28･3 cm2･

The lower vessel stored tritiated water (10 cm3). To
estimate the humidity of the lower vessel, thedummy vessel equlpped a hygrometer was also

scintillation counter. Polypropylene film (Omegadata systems in the Netherlands) was selected as
sample, its thickness was 6m. Viton 0‑rings

were used to fix the polypropylene film between

the lower and the upper vessel. During anexperiment the vessels were kept on a thermostat
at a glVen temperature. Temperature wereselected in the range or278 K ‑ 413 K･ The gas
inlet and outlet of the upper vessel wereconnected with the carrier gas supplier and thewater bubblers, respectively. The water bubblers

contained 100 cm3 0f Millipore water･ The highplaced. Since the humidity in the dummy vessel

was close to 100 % at the various temperature of
the experiments, the humidity in the lower vessel
was considered achieving saturation. To transport

the water pemeated through the polymer to the62purityargon as the carrier gas mowed throughthe upper vessel to carry tritiated water

permeated to the water bubbler. The now rate ofargon gas was maintained constant at 30 sccm･Permeation of Tritiated Water through Polypropylene

The dew polnt Of argon gas was detemined tobe less than223K. It is mentioned that theatmosphere or both lower and upper vessel

C. uJ3b皿PJ aleきPalel uこOlunOuJea^l elnuJnU
niiI

should beair and argon, respectively. The tritium

5050

000

00 0 0 0 0

concentration in the bubbler was routinely
308K.さ迷

ｸ8

ﾃB

34ｲ

assayed with a liquid scintillation counter todetemine the cumulative amount of tritiatedメ:塘ｲ+water. On this study, the same film was used for

ヤｲ

all permeability measurements withoutreplacement.

200400III. Results and Discussion
Figure

2600

800

1000

1200Tlme,…OっSshows the increase in tritium

concentration of the water in the bubbler as afunction of time at fわur temperature. The amountFig. 2. Time‑dependence of the amount ortritiatedof tritium in the bubbler increased linearly withwater pemeated through polypropylene.

time, which should be expected from Eq. 3.
However, the slopes would be the apparentpermeability(D'S'Pup,H2,, 'a'X) except

Temperature, T/KsL｣Ebg/JV.^雲qeauJ aduJn萱)uaJed l310
00300

290

2800

when it is normalized from the water vapor
pressure of the lower vessel and the permeation

area. As apparent permeability from Fig. 2 theslopes increase with increaslng temperature. The1

apparent permeability plotted as a function ofthe reciprocal temperature in Fig. 3, follows anA汀henius type line. The pemeability at 308 K
is 5 times larger than that at 288 K. Therefわre, a3.2

3.3

3.4

3.5

3.6

Reciprocal temperature, Tl/1 0･3Kl1

reduction of permeabilitycan effectively be
accomplished by decreaslng the ambient
temperature･Fig. 3. Apparent pemeability oftritiated water.
The apparent permeability contains a vapor
pressure or water term, which depends onambient temperature. To obtain the permeability( D･S ), the apparent permeability

wasno‑alized by the vapor pressure of water, thepolypropylene obeys van't Hofflaw and then thedimlSion fわllows Arrhenius law. Therefわre, thethickness of the polymer and the effective area

temperature dependence or the permeability atof the polymer. The result is shown in Fig. 4.
thena汀OW

temperature

rangeOf

thisThe obtained permeability fわllowed aninvestigation can be represented by an A汀henius

Arrhenius type equation. It is assumed that thetemperature dependence on water solubility into

type equation ll].

63

M. Hara and Y. Togashi

IV. Summary
L･ J OiL･ SN･ uJU∈06/aJL^1 ‑l E28∈LaJ00

The pemeability of water throughpolypropylene was measured uslng tritiatedwater･ The pe‑eability of water nomalized by●watervapor

pressurewas

fわundtobe

l･9×10‑lュg cm cm‑2 S‑I Torr‑1 at 296 K･0 0032

0 00330 00340 00350 0036FtecIPrOCal temperature. Tl I K 1

Acknowledgments

This research was supported by the Ministry
Fig･ 4･ Permeability of tritiated water throughof Education, Science, Sports and Culture,polypropylene.

Grant‑in‑Aid for Scientific Research on Priority
Area, 19055009.

The slope f♭r the temperature dependence

in Fig. 4 was reduced by the normalization ofwater vapor pressure. It means that theReferences

temperature dependence of the apparent

pe‑eability (see Fig. 3) was govemed by thewater vapor pressure on the experimentalconditions.

[1] M. A. Bertuzzi, E. F. Castro Vidaurre, M.

Armada and J. C. Gottifredi, "Water vapor

permeabilityofedible starch based films", J.
Food Engineering, 80 (2007)972‑978.

The pe‑eability of water throughpolypropylene was fわund to be l･9×10 13g cm

cmI2 sll Tor,ll at 296 K (see Fig. 4). The
pemeability cited in the literature is 3.7×10 13g cm cm 2 S l To汀 ‑ al 296 良 [2]. Possible

reasons for this difference are (1) the degree ofpolymerization of the sample l3], (2) the historyof the polymer or (3) the different atmosphere.

Additional work is necessary to clarifythis
discrepancy.

64[2]N. S. Sangaj and V. C. Malshe,"Pemeability of polymers in protective
organic coatlngS'', Prog. Org. Coat.,50(2004)28‑39.
[3] A. 良. Coulter, 良. A. Deeken and G. M.

Zentner, "Water permeability in poly (Orthoester)S",J.

65(1992)269‑275.

MembraneS°i.,