Gas permeability of a novel cellulose membrane

Journal of Membrane Science 204 (2002) 185–194

Gas permeability of a novel cellulose membrane

Jiang Wu, Quan Yuan∗Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, PR China

Accepted 29 January 2002

Abstract

A novel cellulose membrane was prepared by using amine oxides as the solvent and its mechanical performance wasmeasured. Steady-state permeation rates of carbon dioxide, hydrogen, methane, nitrogen, oxygen, argon and helium in thehomogeneous dense cellulose membrane were measured in the temperature range of 298–353 K and under gas pressures up to1 MPa. The effect of swelling on hydrophilic membrane permeability was studied in some detail on the cellulose membrane.The difference in gas permeability between the “dry” cellulose membrane and the “water-swollen” cellulose membrane wasinvestigated, and the gas permeability between the cellulose membrane and the Cellophane was compared. In this paper,the separation performance of CO2 over H2 in a “water-swollen” cellulose membrane is reported for the first time and theseparation factor of CO2/H2 can be up to 15. © 2002 Elsevier Science B.V. All rights reserved.

Keywords: N-MethylmorpholineN-oxide; Gas permeability; “Dry” cellulose membrane; “Water-swollen” cellulose membrane; Cellophane

1. Introduction

In spite of the rapid development in synthetic poly-mer industries, cellulose and its derivatives are stillholding an important position. As a kind of renewableand in-exhaustible resources, cellulose, a naturallyoccurring polysaccharide, has been re-evaluated re-cently. In order to develop further new, functionaland high-performance materials, blend films preparedfrom cellulose and new solvents have been intensivelystudied [1–6].

Because of the strong hydrogen bonds that occurbetween cellulose chains, cellulose does not melt ordissolve in ordinary solvents. Thus, cellulose mem-brane is made by converting purified cellulose to asoluble derivative, such as xanthate or cuprammo-nium cellulose complex, and then precipitating from

∗ Corresponding author. Tel.:+86-411-4687994;fax: +86-411-4687994.E-mail address: [email protected] (Q. Yuan).

its coagulation bath. Usually, the resulting mem-brane is given the name of Cellophane membraneor regenerated cuprammonium cellulose membrane[7]. However, conventional membrane preparationtechniques have various shortcomings, such as un-satisfactory cellulose native structural characteristics,low cellulose solubilities (<10%) and low degreesof polymerization(DP< 800) [8,9]. In this work,a novel cellulose membrane has been developed,which was prepared by using amine oxides, par-ticularly N-methylmorpholineN-oxide (abbreviatedto MMNO) as the organic solvent. The membrane,prepared by directly dissolving pure cellulose, is ca-pable of keeping the cellulose native characteristics,and has comparatively higher cellulose solubility andpolymerization degree.

On the other hand, as a kind of hydrophilic mem-brane, the state and behavior of water in the membraneare crucial for the physical properties and separationperformance of the membrane. For researches of dial-ysis [10], liquid permeation [11,12], gas separation

0376-7388/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.PII: S0376-7388(02)00037-6

186 J. Wu, Q. Yuan / Journal of Membrane Science 204 (2002) 185–194

Nomenclature

A membrane area (cm2)D diffusion coefficient (cm2 s−1)ED diffusion active energy (kJ mol−1)Ep permeation active energy (kJ mol−1)E′ Young’s moduli (dyne cm−2)Jw flow rate of water (ml cm−2 s−1)l thickness of the membrane (cm)P permeability coefficient

(ml(STP) cm cm−2 s−1 cmHg−1)p pressure (Pa)R universal gas constant (J mol−1 K−1)S solubility coefficient (cmHg−1)t time (s)T temperature (K)Vc measured gas volume (ml)Vl measured liquid permeation volume (ml)Vm gas mol volume at standard status

(ml mol−1)W1 weight of the dry membrane (kg)W2 weight of the wet membrane (kg)

Greek lettersα separation factor�HS solution heat (kJ mol−1)εb breaking elongation (%)σ b tensile strength, (kg cm−2)

Subscripts0 reference statusf feed sidei one componentp permeation side

[13–15,23,26] and pervaporation [16], the liquid con-tent in the membranes is an important parameter con-cerning permeability. The state of water in cellulosicmembranes has been a subject of interest for manyyears [17–19]. For example, Kuznetsov and Malyusov[20] reported that pretreatment of Cellophane filmsby boiling in water increased the permeability anddecreased the selectivity for a series of water–alcoholsolutions. Carter and Jagannadhaswamy [21] inves-tigated the separation of water–alcohol mixtures byusing a Cellophane membrane. They suggested that

selective permeation of a liquid mixture involvesboth preferential absorption at the upstream surfaceof the membrane and diffusion rates of transportthrough the film. They also discussed the effect offilm swelling and hydrogen bonding between waterand Cellophane on the separation efficiency. Peter[22] postulated the existence of extensive solvatedshells around the polymer molecules for the per-meation of water–sugar solutions through swollenhydrophilic membranes. The investigation of in-tramembrane transport properties of sugar–watersolutions in Cellophane by Kaufmann and Leonard[23] revealed the importance of solute–polymer inter-actions.

In this paper, the gas permeability of cellulose mem-branes was investigated. In view of the importance ofthe water–polymer interactions, the permeation andseparation characteristics of a gas through “dry” cellu-lose membranes and “water-swollen” cellulose mem-branes were examined, and a comparative study withrespect to Cellophane was also performed.

2. Experimental

2.1. Materials

The cellulose used in this study was a wood pulpwith degree of polymerization of 1000, and was kindlysupplied by The Dalian Institute of Light Industry.Cellophane membrane was purchased from Aldrich.

Aqueous MMNO solvent was a highly hydratedproduct (50 wt.%) purchased from Tokyo ChemicalCo., Japan. In this form, its good stability preventsstoring problems.

MMNO monohydrate was obtained via vacuumsublimation of the MMNO solvent as the temperaturewas slowly increased from 40 to 80◦C. The productcontained 13.3 wt.% water, i.e. one molecule of waterper molecule of MMNO and melted at 72◦C. Whenassociating with one water molecule (monohydrate),MMNO constitutes a system with high dissolvingpower.

2.2. Preparation of membranes

Cellulose was dissolved with mechanical stir-ring in the aqueous MMNO monohydrate solution

J. Wu, Q. Yuan / Journal of Membrane Science 204 (2002) 185–194 187

Fig. 1. Schematic diagram of liquid permeation apparatus: (1) feedtank; (2) feed pump; (3) buffer tank; (4) exit valve; (5) permeationcell; (6) membrane; and (7) permeation liquid.

at a cellulose concentration of 10–15 wt.% and inthe temperature range of 110–130◦C. The cellulosemembranes were prepared by casting the aqueoussolution on a glass plate and coagulated in water bathat 25◦C. And after drying, the membranes were keptin a desiccator for further use.

2.3. Apparatus and measurements

The effective area of the permeation cell was16 cm2, and the cell was set in a water bath the tem-perature of which was controlled to within±0.5◦C.

A schematic diagram of the water permeability ap-paratus used in our experiments is shown in Fig. 1. Theoperation pressure was in the range of (1–3)× 105 Pa,and the flow rate of water was determined by weighing

Fig. 2. Schematic of the experimental setup used for measuring single gas permeation, properties of membranes: (1) thermostatic container;(2) permeation cell; (3) vacuum gauge; (4) vacuum pump; (5) membrane; (6) porous metal disk; (7) filter paper; and (8) rubber gasket.

the amount of water passed through the membrane ata given time intervals as following equation:

Jw = Vl

A × �t(1)

The schematic diagram of the gas permeability ap-paratus is shown in Fig. 2. Steady-state gas perme-ation rateP at various operating pressures was mea-sured with a soap–film meter in the temperature rangeof 298–353 K as following equation:

P = pp

�t(pf − pp)

Vc

RT

l

AVm (2)

X-ray diffractograms were obtained by placing themembranes on a glass support, adapting them to thehorizontal goniometer and using nickel-filtered Cu K�radiation (D/MAX-RB X-ray generator) operating at40 kV and 50 mA at a rate of 2◦ per minute. The degreeof crystallinity was calculated according to a generalmethod [24].

13CP/MAS NMR spectra were obtained froma Bruker DRX-400 spectrometer operating at100.62 MHz.

Tensile strength (σ b), breaking elongation(εb) andYoung’s moduli (E′) of the membranes were measuredon a Shimadzu AG-2000 according to the Chinesestandard method (China National Bureau of Standards,GB 13022-91).


2.4. Swelling degree

The membranes were immersed in water in flasks,and the vessels were placed in a bath at 25◦C. Af-ter 2 days, the membranes were removed, pressed be-tween a tissue paper and weighed. The membraneswere dried under reduced pressure at 60◦C for 24 hand weighed again. The swelling degree was expressedas a relative weight increase. The swelling ratio wasalso defined as the water content of the membrane byfollowing equation:

Swelling degree= W2 − W1

W1× 100 (3)

3. Results and discussion

3.1. Mechanical performance of the cellulosemembranes

Fig. 3 shows scanning electron micrographs of thecellulose membrane prepared from MMNO solvent.The membrane is homogeneous. It presents smoothsurfaces with transparent appearance. The thicknessof membrane is about 18�m. Table 1 compared themechanical performance of the cellulose membraneprepared from MMNO with the cellulose membranesprepared by other methods. It can be seen that dueto the higher cellulose solution concentration and de-gree of polymerization, the tensile strength (σ b) andYoung’s moduli (E′) of the cellulose membrane of thiswork have all been improved. Usually, materials with

Fig. 3. SEM micrographs of the cellulose membrane: (a) cross-section; (b) surface.

higher strengths will have comparatively lower break-ing elongation (εb). The breaking elongation (εb) ofthe cellulose membrane of this work is no more than6% and far less than that of the cellulose membranesprepared by other methods.

3.2. Gas permeability of the cellulose membrane

In view of the hydrophilic character of cellulose,gas permeability from two different parts of “dry”and “wet” states was investigated. In the “dry” state,the permeation rates of CO2, H2, N2, CH4, O2, Heand Ar in the cellulose membranes of this workwere measured by the variable volume method be-tween 25 and 80◦C and at gas pressures up to 1 MPa[26]. The “dry” cellulose membrane shows very lowabsolute permeability, which is similar to that ofCellophane membrane [7,27]. The gas permeabilitycoefficient, in particular for He and H2, is less than10−12 ml(STP) cm cm−2 s−1 cmHg−1.

But in the “wet” state, the cellulose membranegave excellent gas permeability. After it was made toswollen, three pieces of cellulose membrane were usedfor determinations. The water content of the cellulosemembrane was 48 wt.%. The reproducibility of thedata was checked. The pressure and temperature de-pendence on gas permeability of the “water-swollen”cellulose membranes are shown in Figs. 4 and 5. FromFig. 4, it can be seen that the various gas permeabili-ties changed slightly under different pressures. More-over, the “water-swollen” cellulose membrane showeda high permeation rate for CO2. The separation


Table 1Comparison of the mechanical performance of various cellulose membranes

Membrane Solvent Solutionconcentration(wt.%)

DP σ b (kg cm−2) εb (%) E′ × 10−10 (dyne cm−2)

Dry Wet Dry Wet Dry Wet

Cellulosemembranea

Cuoxam/zincoxene

6 685 465–831 80–178 30–52 98–147 2.7–4.2 –

Cellophane – – 600 631–758 200–304 12.4–15.3 65.7–76.3 0.77–0.80 0.055–0.061This work MMNO 15 870 1197–1333 446–512 4.3–5.4 37.9–55.1 1.41–1.50 1.01–1.34

a Data comes from [25].

factors of CO2 over N2, CH4 and H2 are 50, 30, and 15,respectively. Especially, the “water-swollen” cellulosemembrane gave a separation factor of CO2 over H2 of15. From Fig. 5, it can be seen that the values ofP forthe “water-swollen” cellulose membrane as a functionof temperature are conforming to the Arrhenius-typeplots.

Pi = DiSi (4)

Pi = P0, i exp

(−Ep, i

RT

)

Ep, i = ED, i + �Hs, i (6)

Various gas permeation activation energies (Ep) arelisted in Table 2. According to the “solution–diffusion”mechanism, the permeation activation energy is com-prised of heat of solution and activation energy ofdiffusion. The heat of gas solution in the membraneis generally from−10 to +10 kJ mol−1, and the dif-fusion rate of a gas with a lower molecular weight

Fig. 4. Pressure dependence of permeation rates of various gasesfor the “water-swollen” cellulose membrane.

Fig. 5. Temperature dependence of various gases for the “water-swollen” cellulose membrane.

in the membrane is far quicker than that of a gaswith higher molecular weight. So, macroscopically,the gas with lower molecular weight will have highergas permeation activation energy. It can be seenfrom Table 2 that the gas transport process in the“water-swollen” cellulose membrane can be explainedby the “solution–diffusion” model.

There are differences in transport properties be-tween the “dry” and the “water-swollen” cellulose

Table 2Temperature dependence of permeability coefficients for the“water-swollen” cellulose membranea

Gases P0×107

(ml(STP) cm cm−2 s−1 cmHg−1)Ep (kJ mol−1)

H2 5.24 17.48N2 1.06 16.04O2 0.50 12.58CH4 1.0 15.01CO2 1.28 7.34

a P = P0 exp(−Ep/RT).


Table 3Comparison of gas permeability in the membrane and in water

P × 1010 (ml(STP) cm cm−2 s−1 cmHg−1) Separation factorα

T (◦C) CO2 H2 O2 N2 CO2/H2 CO2/O2 CO2/N2 O2/N2 H2/O2 H2/N2

Cellulose membrane25 127.74 9.14 6.28 2.58 13.99 20.34 49.51 2.43 1.45 3.5440 163.84 12.74 8.16 3.86 12.86 20.09 42.45 2.11 1.56 3.3060 173.8 19.62 9.92 6.98 8.86 17.52 24.88 1.42 1.98 2.8180 213.52 27.18 13.84 8.36 7.85 15.44 25.53 1.65 1.97 3.25

Gas permeability coefficients in water:P = DS25a 1957.42 134.70 93.42 37.13 14.53 20.95 52.72 2.52 1.44 3.6340b 1435.60 132.58 80.15 31.90 10.82 17.91 45.00 2.51 1.60 4.0160b 1051.81 137.61 71.67 27.93 7.64 14.67 37.65 2.56 1.65 4.1680b 763.67 145.87 68.57 28.42 5.24 11.13 26.86 2.41 1.92 4.93

a Data of D come from [20], and data ofS come from [30].b Data of D refer to the calculation method of Wike-Chang in [29], and data ofS come from [30].

membranes. It is water in the membrane that playsan important role in the process. Therefore, the gastransport mechanism in the “water-swollen” cellu-lose membrane should be further studied. Table 3compares the gas permeability coefficients in the“water-swollen” cellulose membrane and in water atvarious temperatures. It shows that the gas perme-ability coefficients in the “water-swollen” cellulosemembrane decrease approximately as that in water.Furthermore, it can be seen that the gas permselec-tivities of the “water-swollen” cellulose membranechange equally with that in water. It is convincing thatthe permeation rate of a gas through a “water-swollen”cellulose membrane depends on both the solubilityand diffusivity of the gas in the water which existsin the membrane. As for the gas transport propertiesof a “dry” cellulose membrane, they are related toprocesses of dissolving and diffusing in the cellulosemolecules. Moreover, from the relationship betweenthe temperature and permeation rate of a gas througha membrane, it may be concluded that the permeationrates of gases in water decrease with the increasingof the temperature, but the permeation rates of gasesin the “water-swollen” cellulose membrane increasewith the increasing of the temperature. It may be alsoconcluded that the state of water molecules whichexists in the membrane is different from the free statein bulk water, so that the interaction between thecellulose membrane and the water molecules has aneffect on the gas permeation in the membrane and hasa primary influence on the permeance diffusivity.

3.3. Comparative studies on permeationperformances of cellulose membranes

Cellulose membranes prepared by our lab andCellophane membranes purchased from Aldrichwere used in this study. Fig. 6 presents their X-ray

Fig. 6. X-ray diagrams of: (A) Cellophane in this experiment;(B) Cellophane from [8]; (C) Cuprophan membrane from [8]; and(D) cellulose membrane in this work.


Fig. 7. 13C-NMR spectra of Cellophane and cellulose membranesprepared in this work.

diagrams. It can be seen that Cellophane has an amor-phous structure and the cellulose membrane preparedby our lab has a high crystallization structure. Thehighly crystalline structure may be one reason thatcan explain the excellent mechanical performance ofthe cellulose membrane prepared by our lab. Fig. 7shows the relevant portions of the13C-NMR spectraof the ring carbons of the two membranes. It can benoted that the two membranes have the same num-bering of the carbons in anhydroglucose (AHG) unitsas follows:

But Cellophane and the cellulose membrane havedifferent spatial structure. The assignment of the peaksindicates that greater extents of interaction occurredbetween the molecules of Cellophane than in the caseof the cellulose membrane. On the other hand, the factthat the carbons which bear a hydroxyl group (C2,

C3, C5) have a broader peak in Cellophane suggeststhat cellulose membranes made by us possess a higherdegree of ordered spatial structure.

3.3.1. Hydraulic permeabilityThe swelling degree and the hydraulic permeabil-

ity between the cellulose membranes prepared by ourlab and the commercial Cellophane membranes werecompared, and the results are summarized in Table 4.As shown in Table 4, the cellulose membranes, usingMMNO as the solvent, can keep a larger amount ofnative characteristics of the raw cellulose and containmore hydroxyls. They can also keep more water aswell as allow more water to pass through.

3.3.2. Gas permeability of “water-swollen” cellulosemembranes

The relationship between the water content of themembrane and the permeation rates of the gases N2,CO2 and H2 was investigated. Figs. 8–10 comparethe permeation rates of the gases of the cellulosemembranes made by us with that of the Cellophane.Fig. 8 shows a plot of N2 permeance as a functionof the water content of the membrane. It appears thatN2 permeation is not strongly affected by the amountof the water content, and there is no much differencebetween the Cellophane and the cellulose membranein N2 permeance. From Figs. 9 and 10, it can be notedthat if the membrane contains more than 50 wt.%of water, the permeation rates of the gases decrease

Fig. 8. N2 permeability as a function of water content of themembrane.


Table 4Degree of swelling and flow rate of water for the membranes

No. Manufacturer Type Thickness of swollenmembrane,l (�m)

Degree ofswelling(wt.%)

JW × l (×10−8 ml cm−2 s−1)a

pre = 1 × 105 Pa pre = 2 × 105 Pa pre = 3 × 105 Pa

1b Union Carbide Co. 36/32 36.2 51 4.78 9.52 13.542b Visking Co. 36/32 33.2 60 5.28 10.76 15.973 Cellophane 60 68 5.10 10.50 15.724 This work 26–30 82.5 8.26 16.91 24.98

a Data come from the literature [28].b The flow rate of water,Jw, was measured at 20◦C.

gradually as water content is decreased. However,when the membrane contains less than 45 wt.% ofwater, the permeation rates of the gases, especiallythat of CO2, fall off rapidly as the water contentis lowered. It can also be seen that at higher watercontent of the membrane, cellulose membranes havegreater permeation rate for CO2 than for the Cello-phane, while Cellophane has greater H2 permeationrate. So obviously, the CO2/H2 separation factor ofcellulose membranes is almost two times higher thanthat of Cellophane, and can be as high as 15.

Referring to the conclusion of Filho et al. [10] whoqualitatively studied the state of water in some kindof cellulosic membranes, as well as from the factthat the cellulose membrane made by us (line D inFig. 6) have a certain degree of molecular ordering(57% crystallinity) which almost equals to that ofCuprophan membrane (line C in Fig. 6) and greaterthan that of Cellophane (line A in Fig. 6), we canconclude that the process of water penetrating into the

Fig. 9. The effect of water content of the membrane on gaspermeability for the cellulose membranes prepared in this work.

two membranes is different. The amorphous regionsof our cellulose membrane are more ordered and itsH bonds in the amorphous region are stronger, sothey cannot arrange themselves freely as those of theCellophane. In other words, as water penetrates intothe membrane, the liquid water in our cellulose mem-brane is existing in a more free state. With the samewater content, Cellophane has more areas for keepingthe more dispersed water, while the high crystallinityof our cellulose membrane results in extensive waterclusters in comparatively small amorphous regions.The results are well in accordance with the analysisof the 13C-NMR spectra. And this also explains thephenomena of the differing gas permeabilities be-tween Cellophane and our cellulose membrane whenthe water content in the membranes is changed. Be-cause the different distribution states of water in thetwo membranes, the extensive water clusters in our

Fig. 10. The effect of water content of the membrane on gaspermeability for Cellophane.


cellulose membrane is in favor of permeation forlarger diameter molecules such as CO2, and Cello-phane for its larger gas permeation region avails insmaller gas molecule permeation such as H2, whileN2 is no obvious difference in the two membranes.

4. Conclusion

New cellulose membranes with excellent mechan-ical performance were prepared by using NMNO asthe organic solvent, and the gas permeabilites of “dry”and “water-swollen” cellulose membranes were in-vestigated. The “water-swollen” cellulose membraneshowed a high permeation rate to CO2. The separationfactors of CO2 over N2, CH4 and H2 are 50, 30, and 15,respectively. There are differences in transport proper-ties between the “dry” and “water-swollen” cellulosemembranes of this work. The effects of swelling onthe membrane permeability were examined in somedetail by carrying out a comparison study with Cel-lophane. The difference in gas permeability betweenCellophane and cellulose membranes of this work isdue to the different distribution states of water in thetwo membranes. And it is the crystallininty and spatialstructure that induce the different distribution statesof water in the two membranes. A significant phe-nomenon is that cellulose membrane may have theproperties of a gate membrane owing to the water con-tent of the membrane. It is useful for separating CO2from other gases, and the gas permeation rate andpermselectivity can be controlled by the water contentof the membrane.

Acknowledgements

We are grateful for the help given us by Dr. W.PBan and his colleagues of The Dalian Institute of LightIndustry at supplying material and measuring materialpolymerization degree.

References

[1] K. Patel, R.St.J. Manley, Carbon dioxide sorption andtransport in miscible cellulose/poly (vinyl alcohol) blend,Macromolecules 28 (1995) 5793.

[2] J.F. Masson, R.St.J. Manley, Solid-state NMR of somecellulose/synthetic polymer blends, Macromolecules 25(1992) 589.

[3] X. Liang, Y. Guo, L. Gu, E. Ding, Crystalline-amorphousphase transition of a poly(ethylene glycol)/cellulose blend,Macromolecules 28 (1995) 6551.

[4] M. Dube, Spherulitic precipitation of cellulose from amine-oxide solutions, J. Polym. Sci. 22 (1984) 163–171.

[5] E. Maia, S. Pérez, Cellulose organic solvents. Part II.The structure ofN-methylmorpholineN-oxide 2.5H2O, ActaCryst. B 38 (1982) 849–852.

[6] L. Zhang, G. Yang, L. Xiao, Blend membranes of cellulosecuoxam/casein, J. Membr. Sci. 103 (1995) 65–71.

[7] K. Kamide, H. Iijima, Recent advances in cellulosicmembranes, Cellulosic Polymer, Blends and Composites,Hanser, Munich, 1994, Chapter 10, p. 189.

[8] R.A. Penque, US Patent 3,850,771 (1971).[9] A.T. Serkov, US Patent 4,159,299 (1979).

[10] G.R. Filho, W.A. Bueno, Water state of Cuprophan(hemodialysis membrane), J. Membr. Sci. 74 (1992) 19–27.

[11] T. Uragami, Y. Sugitani, M. Sugihara, Studies onsyntheses and permeabilities of special polymer membranes:33. Permeation behaviour of aqueous alcohol solutionthrough cellulose membranes, Polymer 23 (1982) 192–196.

[12] V. Shantora, R.Y.M. Huang, Separation of liquid mixturesby using polymer membranes. Part III. Grafted poly (vinylalcohol) membranes in vacuum permeation and dialysis, J.Appl. Polym. Sci. 26 (1981) 3223–3243.

[13] V.N. Buchner, Gas permeability at various relative humiditiesof Cellophane foils of Cellophane combined with othercomponents, Papier 14 (1960) 123–130.

[14] J.S. Cha, R. Li, K.K. Sirkar, Removal of water vaporand VOCs from nitrogen in a hydrophic hollow fiber gelmembrane permeator, J. Membr. Sci. 119 (1996) 139–153.

[15] K. Petrak, E. Pitts, Permeability of oxygen through polymers.Part II. The effect of humidity and film thickness on thepermeation and diffusion coefficients, J. Appl. Polym. Sci.25 (1980) 879–886.

[16] E. Nagy, O. Borlai, A. Ujhidy, Membrane permeation ofwater–alcohol binary mixtures, J. Membr. Sci. 7 (1980) 109–118.

[17] J. Tai, F. Franks, Water in biological systems, Nature 30(1971) 91.

[18] H. Susi, J.S. Ard, R.J. Carrol, The infrared spectrum andwater binding of collagen as a function of relative humidity,Biopolymers 10 (1971) 1597.

[19] A. Higuchi, T. Lijima, D.S.C. investigation of the states ofwater in poly (vinyl alcohol) membranes, Polymer 26 (1985)1207–1211.

[20] V.V. Kuznetsov, V.A. Malyusov, Khim. Prom. 8 (1963) 622.[21] J.W. Carter, B. Jagannadhaswamy, Symposium on the less

common means of separation, Inst. Chem. Eng. (1963) 35–42.[22] S. Peter, Mechanism of water transport through semiperme-

able poly (vinyl alcohol) membranes, Naturwissenschaften52 (5) (1965) 106.


[23] T.G. Kaufmann, E.F. Leonard, Intramembrane transport.Phenomenological approach, A.I.Ch.E.J. 14 (1968) 110.

[24] J.F. Rabek, Experimental methods in polymer chemistry:X-ray diffraction analysis, Wiley, Chichester, 1980, p. 488.

[25] L. Zhang, G. Yang, W. Fang, Regenerated cellulose membranefrom cuoxam/zincoxene blend, J. Membr. Sci. 56 (1991) 207–215.

[26] S.A. Stern, S.K. Sen, A.K. Rao, The permeation of gasesthrough symmetric and asymmetric (Loeb-Type) celluloseacetate membranes, J. Macromol. Sci. Phys. B 10 (3) (1974)507–541.

[27] S. Weller, W.A. Steiner, Separation of gases by fractionalpermeation through membranes, J. Appl. Phys. 21 (1950)279–283.

[28] Z. Morita, H. Ishida, H. Shimamoto, Anion permeabilityof cellulosic membranes. Part 1. Porosity of water-swollenmembranes, J. Membr. Sci. 46 (1989) 283–298.

[29] R.H. Perry, Perry’s chemical engineer’s handbook, 6thedition, McGraw Hill, New York, 1984.

[30] W.F. Linke, Solubilities—inorganic and metal-organic com-pounds, Vol. 1, 4th Edition, American Chemical Society,Washington, DC, 1967.

Documents

Gas permeability of a novel cellulose membrane