Cellulose derivative and liquid crystal blend membranes for oxygen enrichment

Cellulose derivative and liquid crystal blend membranes foroxygen enrichment

Xin-Gui Li a, *, Mei-Rong Huanga, Ling Hub, Gang Linb, Pu-Chen Yangb

aDepartment of Polymer Materials Science Engineering, College of Materials Science Engineering, Tongji University, 1239 Siping

Road, Shanghai 200092, People's Republic of ChinabTianjin Institute of Textile Science and Technology, Tianjin 300160, People's Republic of China

Received 3 June 1997; accepted 22 January 1998

Abstract

Oxygen enriching property and stability of the blend membranes, 10±45 mm thick, fabricated from ethyl cellulose,cellulose nitrate, cellulose diacetate, and cellulose triacetate, with thermotropic cholesteric or nematic liquid crystals(LC), such as cholesteryl oleyl carbonate, p-heptyl-p'-cyanobiphenyl, p-pentylphenol-p'-methoxybenzoate, benzoate-

containing liquid crystal mixture, and triheptyl cellulose, were studied by a variable volume method. Themembranes with 1.5±4 wt% LCs showed the maximum oxygen-enriching ability in the temperature range of theirLC phase. The oxygen-enriched air ¯ux QOEA and the oxygen concentration YO2

increased simultaneously as theoperating pressure increased. The 30 mm-thick triheptyl cellulose/ethyl cellulose (8/92) homogeneous membrane

exhibited almost constant oxygen- enriching e�ciencies of QOEA 1.0 � 10ÿ4 ml(STP)/s �cm2 and YO240% at 308C

and 0.41 MPa in a single step for a 35 day operating time. # 1998 Elsevier Science Ltd. All rights reserved.

1. Introduction

The liquid crystal (LC)-containing membranes which

are simple in structure and are easy to work with [1±

4], can result in much lower capital cost of enriching

oxygen directly from air than the carrier facilitated

transport membranes and immobilized molten salt

membranes which are believed to be highly oxygen-

enriching membranes [5, 6]. Previously prepared

nematic LC membranes containing 40±60 wt% low

molecular LC might have a short lifetime due to the

loss of LC materials, especially when the membrane

thickness is less than 45 mm under a high operating

pressure [1]. One way of getting around this problem is

by blending a small amount of higher viscosity choles-

teric LC with the membrane matrix. Our recent investi-

gations have demonstrated that cholesteric LC

membranes show not only higher oxygen enrichment

but also higher stability [1, 2, 7±12]. The purpose of

this paper is to further illustrate the enhancement ofoxygen enrichment through the blend membranes of

the four cellulose derivatives with ®ve types of liquidcrystals.

2. Experimental

2.1. Materials

Cholesteryl oleyl carbonate (COC) and the benzo-ate-containing liquid crystal mixture DYC were pur-chased from the 2nd Chemical Reagent Factory of

Tianjin China. p-Heptyl-p'-cyanobiphenyl (7CB) and p-pentylphenol-p'-methoxybenzoate (5PMB) wereobtained from the Jinghua Special Materials Institute

of Shijiazhuang China. The above mentioned fourkinds of low molecular weight LCs have the purity ofhigher than 99%. A polymer liquid crystal, i.e. trihep-

tyl cellulose (THC), was synthesized in ourlaboratory [13]. The ®ve LCs were selected for this in-vestigation because they are thermotropic and their

European Polymer Journal 35 (1999) 157±166

0014-3057/98/$ - see front matter # 1998 Elsevier Science Ltd. All rights reserved.

PII: S0014-3057(98 )00088-3

PERGAMON

* Corresponding author.

solid±liquid crystalline phase transition temperaturesapproach room temperature. The cholesteric LC phase

temperature range of the COC, DYC and THC are25±398C, 29±328C and 20±1008C, while the nematicLC phase temperature ranges of 7CB and 5PMB are

28.5±408C and 30±438C, respectively.Four cellulose derivatives, ethyl cellulose (EC), cellu-

lose nitrate (CN) made in China, cellulose diacetate

(CDA) and cellulose triacetate (CTA) obtained fromDaicel Chemical Company in Japan, were used. The 5wt% EC solution viscosity in ethanol/toluene (1/1) is

ca. 0.06 Pa.s. The falling sphere viscosity of the CN is25 sec and its nitrogen content is 12%. The intrinsicviscosity of the CDA in chloroform is 28 dl/g. Thedegree of substitution and the number-average molecu-

lar weight of the CTA are 2.7 and 86751, respectively.

2.2. Membrane preparation

The blend membranes were prepared by a solution

casting method of LC and a cellulose derivatives blendsolution. A ¯at and uniform blend membrane, with athickness ranging between 10 and 45 mm was obtained

through casting the tetrahydrofuran or dichloro-methane solution of EC and CDA or CTA blend withLCs on a glass plate.

2.3. Oxygen-enrichment evaluation

The measurements of the oxygen-enriching perform-ance through the membranes were performed using apermeability stainless-steel cell of the variable volume

type [12]. The permeate pressure was atmospheric and

the feed pressure was 0.06±0.48 MPa. In order to pro-vide more signi®cant information guiding membrane-

based oxygen enrichment, the air from the air com-pressor was directly used as the test gas. The oxygenconcentration in the oxygen-enriched air (OEA)

through the membranes was measured using anIndustrial Gas Analyzer, Model 491, manufactured byTianjin Factory of Glass Instrument of China. The

membrane e�ective area was 50 cm2. A detailedmethod for the calculation of oxygen-enrichment par-ameters, including the OEA ¯ux QOEA, the OEA per-

meability POEA, the oxygen permeability PO2, the

oxygen concentration YO2, the actual separation factor

ASF, is given in our earlier papers [1, 8, 12].

3. Results and discussion

3.1. Dependence of oxygen enrichment on LC content

The e�ects of the LC content in the homongeneousdense blend membranes on the oxygen enrichments

were examined by increasing LC content from zero to45 wt% at 308C and an operating pressure 0.43 MPa.The relationship between the LC content and the oxy-

gen enrichment is shown in Table 1 and Fig. 1. Boththe ¯ux QOEA, the permeability POEA and oxygen con-centration YO2

of the oxygen-enriched air through themembranes increase ®rst and then decrease slowly as

the LC content increases from zero to 45 wt%. Whenthe LC content ranges between 1.5 and 12 wt%, theQOEA and YO2

values appear to reach the maxima of

1.59 � 10ÿ4 ml(STP)/s cm2 and 41%, respectively.

Table 1

E�ect of LC content in the dense blend membranes on oxygen enriching properties at 308C under operating pressure 0.43 MPa

COC/CN (wt/wt) 0/100 4/96 10/90

Membrane thickness (mm) 30 25 30

QOEA�105 (cm3(STP)/s cm2) 0.81 1.25 2.06

PO2�1010 (cm3(STP) cm/cm2 s cmHg) 1.98 3.32 5.39

YO2(%) 34.5 40.3 36.0

THC/EC (wt/wt) 0/100 1.5/98.5 4/96 10/90 20/80 30/70

Membrane thickness (mm) 18 17 20 20 36a 35a

QOEA�105 (cm3(STP)/s cm2) 5.91 7.22 10.1 11.4 6.41 6.05

PO2�1010 (cm3(STP) cm/cm2 s cmHg) 9.90 13.43 20.59 21.12 21.40 18.96

YO2(%) 37.4 41.0 39.4 37.3 37.2 36.5

7CB/EC (wt/wt) 0/100 4/96 9/91 12/88 16/84 38/62 45/55

Membrane thickness (mm) 18 17 22 25 27 35a 40a

QOEA�105 (cm3(STP)/s cm2) 6.42 8.70 8.01 6.47 6.10 5.60 6.99

PO2�1010 (cm3(STP) cm/cm2 s cmHg) 10.65 16.18 18.33 16.48 17.16 19.19 27.47

YO2(%) 37.2 41.0 39.9 40.3 39.9 38.0 38.6

a These may be the thinnest membranes which are pinhole-free under an operating pressure 0.43 MPa.

Xin-Gui Li et al. / European Polymer Journal 35 (1999) 157±166158

Fig. 1(b) suggests that the YO2values through all ®ve

7CB/EC membranes seem to go through a maximum

close to a particular temperature range from 27.8±308C, which partially overlaps the temperature region(28.5±408C) of the liquid crystalline phase of the 7CB

liquid crystal. These indicate that the introduction ofthe LCs can enhance the oxygen-enriching capacity ofthe cellulose derivatives [11±14]. It must be noticedthat QOEA decreases as a result of the increase in the

thickness of the membranes containing more than 20wt% LCs. A larger thickness for the membranes con-taining 20 wt% LCs are necessary to prevent the for-

mation of the pinholes in the membranes under ahigher operating pressure.

3.2. Dependence of oxygen enrichment on LC variety

The oxygen-enriching properties of the blend mem-branes prepared from cellulose triacetate (CTA), cellu-lose diacetate (CDA) and four di�erent LCs of 9 wt%

are presented in Table 2. It is found that all of theseLCs can e�ectively improve the oxygen-enriching prop-erties of the CTA and CDA membranes, though their

molecular structures, liquid crystalline phases, and LCtransition temperatures are di�erent from one another.

The oxygen-enriching properties through the ethyl cel-lulose (EC) and cellulose nitrate (CN) membranes arealso improved by the four kinds of LCs [1]. It is well

known that the viscosity of LCs will rapidly decreaseupon transforming into the anisotropic phase state.This will lead the cellulose derivative and LC mol-

ecules in the blend membranes to move and rotateeasily, therefore the membranes possess more freevolume which bene®ts the oxygen permeation. A small

amount of LC-enriched domain dispersed in the mem-branes might be the main path of oxygen in the LCtemperature range. Furthermore, the mechanism ofoxygen transport may change from di�usion to sol-

ution control. In the eight types of membranes, theCDA/cholesteryl oleyl carbonate (COC) membraneshows the highest QOEA (1.0 � 10ÿ4 ml(STP)/s cm2)

and POEA (3.3 � 10ÿ10 ml(STP) cm/cm2 s cmHg) whichare nearly double that of the pure CDA membrane,and the CTA/p-pentylphenol-p'-methoxybenzoate

(5PMB) membrane displays the highest YO2(40.5%)

and actual separation factor (ASF) (2.56). The formermight be attributed to both the higher oxygen per-

meability of CDA than CTA and the lower LC phasetemperature of COC which is responsible for higher¯owing ability and lower viscosity at the same tem-perature 278C. The latter may be caused by the chemi-

cal in®nities of oxygen towards the ester groups in theCTA and 5PMB. The YO2

through the 5PMB/CTAmembrane is as large as 40.3%, indicative that the

membrane has the potential to approach the limitingYO2

of 47% in a single stage if the operating pressureincreased [1]. It might be predicted that the OEA con-

taining 97.6% oxygen could be produced in a simple®ve-step enriching operation.

3.3. Dependence of oxygen enrichment on cellulosederivative variety

The oxygen-enriching properties across the fourkinds of cellulose derivative membranes containing 9wt% p-heptyl-p'-cyanobiphenyl (7CB), benzoate-con-

taining liquid crystal mixture DYC, and COC, areshown in Table 3. The 7CB/EC membrane in themidst of the membranes exhibits the highest QOEA

(1.43 � 10ÿ4 ml(STP)/s cm2) and POEA (9.52 � 10ÿ10

ml(STP) cm/cm2 s cmHg) regardless of their similarpolymeric skeletons. This may be related to the largeamount of random structures of EC with ethyl side-

groups, and to the low density which is responsible forthe larger free volume. As seen in Table 3, the 7CB/CTA membrane shows the highest YO2

(40.5%) and

ASF (2.56) which is attributed to the high oxygen overnitrogen selectivity of the CTA among the four cellu-lose derivatives.

Fig. 1. Plots of POEA (a) and YO2(b) vs temperatures through

the blend membranes with six 7CB/EC ratios at the trans-

membrane pressure di�erence of 0.4 MPa.

Xin-Gui Li et al. / European Polymer Journal 35 (1999) 157±166 159

3.4. Dependence of oxygen enrichment on operatingpressure

Figs. 2, 3 and 4 show the plots of QOEA and YO2

versus pressure di�erence across the cellulose deriva-tive/LC membranes. There are concurrent increases in

QOEA and YO2for the membranes when increasing the

operating pressure from 0.1 to 0.45 MPa. The depen-

dency of QOEA on the operating pressure is nearly lin-ear whereas the enhancement of the YO2

is exponential

with the operating pressure, which is in agreement

with that of ordinary membranes. Note that the largestQOEA and YO2

values produced simultaneously for the

DYC/EC(9/91) membrane are 1.0 � 10ÿ4 ml(STP)/scm2 and 39.9%, respectively. It could be estimated

that the QOEA through the DYC/EC(9/91) membranemight reach 2.0 � 10ÿ4 ml(STP)/s cm2 under the oper-

ating pressure of 1.0 MPa.

3.5. Dependence of oxygen enrichment on operatingtemperature

The plots of QOEA, POEA and YO2vs, temperature

shown in Figs. 5, 6, 7, 8, 9 and 10 indicate that thePOEA and YO2

values through the LC/cellulose deriva-

tive (9/91) membranes depend strongly on the tempera-ture ranging from 10±708C. It is interesting that more

rapid QOEA and POEA increases and a maximum YO2

value were observed in the LC state temperature range

of the LCs. This phenomenon might result from the

strong sensitivity of the LC viscosity in the ordered LCstate to the temperature change. Above the isotropic

temperature (T1), the LCs will transform into a dis-order isotropic phase, resulting in a further increase in

QOEA and POEA but a decrease in YO2. The permeation

activation energy of the OEA across the LC mem-

branes are higher in the liquid crystalline state tem-

Table 2

The oxygen-enriching properties through the LC/CTA or CDA(9/91) blend membranes at 278C under 0.44 MPa operating pressure

Membranes

Membrane

thickness (mm)

QOEA�105(cm3(STP)/s cm2)

(POEA/PO2) � 1010

(cm3(STP) cm/cm2 s cmHg) YO2(%) ASF

Pure CTA 18 2.69 1.45 4.12 36.1 2.13

COC/CTA 13 5.67 2.20 7.53 40.2 2.53

DYC/CTA 12 5.81 2.08 7.12 40.2 2.53

7CB/CTA 11 5.45 1.80 6.16 40.3 2.54

5PMB/CTA 14 4.91 2.06 7.12 40.5 2.56

Pure CDA 11 6.01 1.97 5.36 35.1 2.04

COC/CDA 12 10.0 3.58 9.13 33.7 1.91

DYC/CDA 11 9.46 3.11 7.52 32.6 1.82

7CB/CDA 12 6.05 2.17 7.07 39.1 2.42

5PMB/CDA 15 5.53 2.48 7.45 37.3 2.24

Table 3

The oxygen-enriching properties through the LC/cellulose derivatives(9/91) blend membranes at 308C under 0.47 MPa operating

pressure

Membranes

Membrane

thickness (mm)

QOEA�105(cm3(STP)/s cm2)

(POEA/PO2) � 1010

(cm3(STP) cm/cm2 s cmHg) YO2(%) ASF

7CB/EC 16 14.3 6.41 19.4 38.5 2.36

7CB/CDA 12 6.86 2.30 7.19 39.2 2.44

7CB/CTA 11 6.14 1.89 6.24 40.5 2.56

DYC/EC 20 10.3 7.51 18.5 39.9 2.50

DYC/CDA 11 10.7 3.30 9.00 36.1 2.13

DYC/CTA 12 6.57 2.21 7.05 40.0 2.51

COC/EC 18 12.8 6.45 19.9 38.9 2.40

COC/CDA 12 11.6 3.90 9.27 33.0 1.86

COC/CTA 13 6.38 2.32 7.43 39.8 2.50

COC/CN 30 2.41 2.02 6.37 39.5 2.47


Fig. 2. Plots of QOEA and YO2versus operating pressure for

the LC/EC(9/91) blend membranes containing the LC: (w) no

LC, (.) 7CB, (r) 5PMB, (R) COC, (t) DYC.


the LC/CDA(9/91) blend membranes containing the LC: (w)

no LC, (.) 7CB, (r) 5PMB, (R) COC, (t) DYC.


the LC/CTA(9/91) blend membranes containing the LC: (w)

no LC, (.) 7CB, (r) 5PMB, (R) COC.

Fig. 5. Plots of QOEA versus operating temperature for the

LC/EC(9/91) blend membranes containing the LC: (w) no

LC, (.) 7CB, (r) 5PMB, (R) COC, (t) DYC.


perature range than in the solid LC or isotropic states

since the viscosity of liquid-crystalline state reduces

more rapidly as the temperature increases, as seen inTable 4. The slight uncertainties in permeation acti-

vation energy in Table 4 might be related to distinctlynon-linear behaviour of some plots shown in Fig. 8(a),

9(a) and 10(a). It is noted from Figs. 1 and 8±10 and

Table 5 that the LC blend membranes exhibit the

maximum oxygen-enriching ability at the transitiontemperature (TKN or TKCh) from crystalline solid to

liquid crystalline phase of the LC components regard-

less of cellulose derivative matrix and their LC contentto a certain extent. The three pure cellulose derivate

membranes containing no LC hardly ever show the

maximal YO2value with the variation of temperature.

The maximum oxygen-enriching ability of the LC

membranes might result from the more free volume,¯owing ordered phase and higher thermal-expansion

coe�cient of the LCs [7]. The ordering phase structure

within the liquid crystal system might be due to a uni-form and dense anisotropic structure having fewer

defect-like solid crystals than the isotropic non-liquid

crystalline phase, resulting in larger YO2values.

Note that an obvious sudden jump of OEA per-meability through the blend membranes containing

7CB and COC liquid crystals was sometimes seen in

the temperature ranging from 26±308C, as shown inFig. 1(a), 6, 7, 9(a) and 10(a). This temperature range


LC/CDA(9/91) blend membranes containing the LC (w) no

LC (.) 7CB, (r) 5PMB, (R) COC, (t) DYC.


LC/CTA(9/91) blend membranes containing the LC (w) no

LC (.) 7CB, (r) 5PMB, (R) COC, (t) DYC.

Fig. 8. Plots of POEA (a) and YO2(b) versus operating tem-

perature for the LC/EC(9/91) blend membranes containing

the LC (w) no LC, (r) 7CB, (t) 5PMB, (r) COC, (+)

DYC.



perature for the LC/CDA(9/91) blend membranes containing


DYC.


perature for the LC/CTA(9/91) blend membranes containing


DYC.

Table 4

Permeation activation energy of the oxygen-enriched air containing 36±40% oxygen across the LC/cellulose(9/91) derivative mem-

brane under operating pressure 0.44 MPa

Permeation activation energy (kJ/mol) at the temperature T

Membrane T< TKN or TKCh TKN or TKCh<T< T1 T>T1

COC/EC 14.4 27.4 12.0

5PMB/EC 25.5 28.9 8.50

7CB/EC 25.5 34.2 18.2

DYC/EC 29.5 38.3 16.6

5PMB/CDA 17.7 26.9 16.5

DYC/CDA 20.3 31.9 21.1

7CB/CDA 25.5 33.5 15.3

COC/CDA 10.0 49.6 17.3

COC/CTA 16.0 25.6 23.0

7CB/CTA 23.9 25.6 21.5

5PMB/CTA 19.2 28.7 23.9

DYC/CTA 26.8 31.9 25.5


overlaps the liquid crystalline phase temperature of the

7CB and COC.

3.6. Dependence of oxygen enrichment on operating time

Generally, the more the LC content, the thinner theLC/cellulose derivative blend membrane, and the lower

the stability of the membranes [1, 14, 15], especially atan elevated operating temperature and pressure. Thevariation of the QOEA and YO2

of the OEA enriched

by four homogeneous dense blend membranes withhigh LC content are evaluated as the operating time,as shown in Fig. 11. It is apparent that the 7CB/

EC(38/62) blend membrane whose QOEA declines sig-ni®cantly after 120 h operation exhibits the loweststability because of the high 7CB content. The 7CB/EC(12/88) and THC/EC(20/80) membranes have

higher stability of performance. The THC/EC(8/92)membrane shows the highest stability because of thelow THC content in the membrane and also because

THC has much higher molecular weight than otherLCs. There is no signi®cant variation in the OEA ¯uxand oxygen concentration with the operating time ran-

ging from 0 to 35 days. After the operating time of 35days, the YO2

decreases dramatically from 39 to 36%which is higher than the YO2

in the OEA enriched byTable

5

Thetemperature

ofmaxim

allyconcentratingoxygen

from

airbytheLC/cellulose

derivativemem

branes

Liquid

crystal

7CB

7CB

7CB

5PMB

5PMB

5PMB

COC

COC

COC

DYC

DYC

DYC

Cellulose

derivative

EC

CDA

CTA

EC

CDA

CTA

EC

CDA

CTA

EC

CDA

CTA

Tem

perature

(8C)

29±30

30

30

30

31

28

26

26

28

29

30

28

Maxim

um

YO

2(%

)40.3

38.3

39.6

35.3

37.5

40.0

38.9

33.0

39.6

39.5

33.7

39.5

Fig. 11. Plots of QOEA (a) and YO2(b) versus operating time

at 0.4 MPa for (w) 30 mm-thick THC/EC(8/92) membrane at

408C; (r) 45 mm-thick THC/EC(20/80) blend membrane at

408C; (t) 25 mm-thick 7CB/EC(12/88) membrane at 308C;and (r) 36 mm-thick 7CB/EC(38/62) at 308C.


poly(1-(trimethylsilyl)-1-propyne) membrane but lowerthan the YO2

in the OEA enriched through the polycar-

bonate, polysulfone, and poly(4-methylpentene-1)membranes [16±18]. But the QOEA increases from

1.15 � 10ÿ4 to 1.35 � 10ÿ4 ml(STP)/s cm2 which mightresult from some pinhole formed during the continu-

ous operation at the higher pressure. It is believed thatthe less LC-containing homogeneous blend membranes

can maintain their defect-free feature over a workinglife of at least 45 days in the presence of long-term

pressurization [17].

3.7. Distribution of LC components in the matrix

The LC/CDA(9/91) blend membrane appears toexhibit phase separation, to a certain extent, because

Fig. 12. Dynamic mechanical loss Tan d at 11 Hz and 28C/min (a) and wide-angle X-ray di�ractograms (CuKa) (b) of the virgin

membranes for THC/EC(40/60), COC/EC(9/91) and EC.


there are many small adhesive and visible LC regionsto the naked eye, resulting in lower air-separation per-

formance. As shown in Tables 2, 3 and 5, the averageYO2

values through LC/CDA(9/91) membranes areindeed lower than those of the LC/EC and LC/CTA

membranes. Fig. 12(a) plots the dynamic mechanicalloss with rising temperature for pure EC, COC/EC(9/91), and THC/EC(40/60) membranes. Apparently, the

two blend membranes are similar to pure EC indynamic mechanical behaviour. Only the COC/ECblend membranes exhibited broader loss peak in a tem-

perature range of 110±1508C than the EC membrane.But when the LC content is lower than 20 wt%, LC/EC, LC/CTA and LC/CN membranes are transparentby visual observation and have no adhesive touch. A

dark ®eld in the view of the membranes was observedunder polarized microscopy, indicating no assemblingLC phase. The virgin LC/EC membranes exhibit simi-

lar wide-angle X-ray di�ractograms to the EC mem-brane, as shown in Fig. 12(b) and Ref. [7]. Theaddition of 40 wt% THC to EC caused the peak at

the spacing of 0.46 nm to become lower and wider, in-dicating interaction between the THC and EC, i.e., theTHC could be compatible with EC. These all suggest

that the LC components might be essentially uniformlydistributed in the cellulose derivative matrix except forCDA. The LCs may play a plasticizing role in the LCblend membranes and enable the membranes to exhibit

higher gas permeability.

4. Conclusions

Liquid crystal/cellulose derivative blends have been

successfully cast into homogeneous dense blend mem-branes with the thickness ranging between 10 and45 mm using a solution casting technique. The oxygen-enriching performance of the blend membranes is sig-

ni®cantly enhanced compared to that of the pure cellu-lose derivative membranes. This is veri®ed by theincrease in PO2

and YO2of the LC blend membranes in

nearly the entire temperature range examined in thisstudy. The oxygen enrichment of the blend membranesdepends strongly on the membrane composition; LC/

cellulose derivative ratio and operating temperatureand pressure, but the oxygen enrichment through theless LC-containing blend membranes are slightly

dependent of operating time after 35 days. The oxygenenrichment of the LC blend membranes exhibits aunique dependency on temperature with a similardependency on transmembrane pressure di�erence to

ordinary LC-free membranes. The blend membranescan give the highest oxygen-enriching capability of an

OEA ¯ux of 1.0 � 10ÿ4 ml(STP)/s cm2 with an oxygenconcentration of 40±41% under the transmembranepressure di�erence of 0.41±0.43 MPa and 308C in a

single step. The thick, self-supporting membranes showhigher oxygen concentration than the composite mem-branes fabricated by laminating the blend thin-®lm

with the same composition. These membranes may beapplicable for breathing systems in medical ®elds.

Acknowledgements

This investigation was supported by the NationalNatural Science Foundation of P.R. China andScience Technology Development Foundation ofTongji University in Shanghai China.

References

[1] Huang M-R, Li X-G. Gas Sep. Purif. 1995;9:87.

[2] Li X-G, Huang M-R. Sep. Sci. Technol. 1994;29:1905.

[3] Li X-G, Yang P-C. Polym. Bull. (Beijing) 1990;3:142.

[4] Li X-G, Huang M-R, Yang P-C. Chem. Ind. Eng.

(China) 1991;8(1):16.

[5] Li X-G, Huang M-R, Technol. Water Treatment,

1994;20:99; Chem. Abst., 1995;122:1076992.

[6] Huang M-R, Li X-G. Chem. Ind. Eng. (China)

1994;11(4):15.

[7] Huang M-R, Li X-G, Lin G. Sep. Sci. Technol.

1995;30:449.

[8] Li X-G, Huang M-R, Lin G. J. Membrane Sci.

1996;116:143.

[9] Li X-G, Huang M-R, Lin G, Yang P-C. Colloid Polym.

Sci. 1995;273:772.

[10] Li X-G, Huang M-R, Lin G, Yang P-C. J. Appl. Polym.

Sci. 1994;51:743.

[11] Chen L, Li X-G, Wang N-C, Polym. Mater. Sci. Eng.

(China), 1993;9(4):103; Chem. Abst., 1994;121:1809236;

Engineering Index, 1994;32:M007281, 1994:A091493.

[12] Huang M-R, Li X-G. Plastics Ind. (China) 1993;2:49.

[13] Huang M-R, Li X-G. J. Appl. Polym. Sci. 1994;54:463.

[14] Li X-G, Huang M-R. Angew. Makromol. Chem.

1994;220:151.

[15] Li X-G, Huang M-R, Lin G, Yang P-C. Sep. Sci.

Technol. 1994;29:671.

[16] Li X-G, Huang M-R, Lin G, Chen L, Yang P-C.

Proceedings of 34th IUPAC Congress. Beijing, China,

1993. p. 645.

[17] Li X-G, Huang M-R. Sep. Sci. Technol. 1996;31:579.

[18] Li X-G, Huang M-R. J. Appl. Polym. Sci. 1997;66:2139.


Cellulose derivative and liquid crystal blend membranes for oxygen enrichment

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