Printer Friendly

Oxygen-enriching properties of a new hybrid membrane cross-linked from PDMS and fluorine-containing silicone resin.

INTRODUCTION

Polydimethylsiloxane (PDMS) is one of the most important polymeric membrane materials For oxygen/nitrogen separation from air due to its high intrinsic permeability. PDMS membranes possess excellent oxygen permeability (about 600 Barrer) and have quickly obtained commercial applications. This is attributed to its large free volume formed from the flexibility of the siloxane linkages (-Si-O-). However, its oxygen/nitrogen separation factor is only about 2.0 and the membrane-forming ability is also unsatisfied to limit its further effective applications in a way. Therefore, various modification studies on PDMS membranes have focused on enhancing both permselectivity and membrane-forming ability. For this purpose, different functional groups and chemical components have been introduced into backbone or side chains of PDMS by blocking, grafting, and alternating copolymerization as well as macromolecular reactions. Stern systematically investigated the substitution effects of bulkier functional groups led in the backbone chains or side chains of PDMS (l-4). However, there is an inverse relationship between gas permeability and selectivity in the performance changes with the chemical structures.

Organic-inorganic hybrid membranes have attracted considerable attention as potential "next generation" membrane materials because such hybrid materials have the potential to combine the desired properties of organic and inorganic systems, e.g., improving the thermal properties of inorganic ones with the flexibility and selectivity of organic ones (5-12). However, some organic-inorganic membranes which are by simply incorporating inorganic particles such as silica into dense polymeric membranes failed to cross the Robeson's upper-bound tradeoff curve due to the following disadvantages: agglomeration of inorganic particles and formation of nonselective voids (6), (13).

To improve oxygen/nitrogen separation factor of polymeric membranes with high oxygen permeability coefficient but low oxygen/nitrogen separation factor, some attempts to introduce fluorine-containing groups have been reported (14), (15). For example, when trifluoro-propyl groups or heptadecafluorodecyl groups were introduced into the side chains of the block copolymer of poly(tetramethyl-p-silphenylenesiloxane) and PDMS, oxygen permeability coefficient and oxygen/nitrogen separation factor simultaneously increased (16). In ethylcellulose with PDMS grafts, the methyl groups were substituted by several fluorine-containing groups to result in a good improvement of oxygen permeability coefficient and oxygen/nitrogen separation factor (17). However, many reports on the introduction of only one or two CF3 groups showed that oxygen permeability coefficient increased while oxygen/nitrogen separation factor decreased. Hence, it is necessary that higher contents of fluorine-containing components are introduced without crystallization.

Gas permselectivity for a polymeric membrane is closely concerned with several factors such as the chemical structure and the aggregation structure of the membrane, as well as penetrating gas species and transport mechanism. In all modified methods, cross-linking is a simple and effective way to change-the membrane structure and to improve selectivity (18-20). Unnikrishnan et al. (19) had investigated the effects of cross-linking on the diffusion and transport of aromatic hydrocarbons through natural rubber membranes. Stern et al. (20) suggested that a potential method for increasing the gas selectivity of silicone rubber polymers, without significantly decreasing their permeability, was to incorporate functional groups that induce specific interactions with the desired gases.

In this study, a fluorine-containing silicone resin substituent group, vinyl group, and inorganic framework (SR-FVI) was synthesized through hydrolytic condensation. A new cross-linked hybrid membrane (CHM) was prepared with the hydrogen-containing silicone oil (HSO) as a cross-linking agent, PDMS containing vinyl group and the SR-FVI as matrix materials to enhance its membrane-forming ability and permselectivity.

EXPERIMENTAL

Materials

PDMS (vinyl group content of 10 mol% and a number-average molecular weight of 500,000 g/mol) and a chloroplatinic acid solution (as a catalyst) were obtained from the Research Center of Organic Silicone of Chengdu, China. Tetraethoxysi lane, 13-fluorooctyltrie-thoxysilane, tetramethyldivinyldisiloxane, and hydrogen-containing silicone oil (number-average molecular weight of 7000 g/mol and hydrogen-containing content of 1.6 wt%) were obtained from Fine Chemical Institute of Silicone and Fluoride of Guangzhou, China. All other chemical agents are analytical grade and used without further purification. Pure gases ([0.sub.2] and [N.sub.2]) with a minimum purity of 99.9% were purchased from Guangzhou Gas Ltd., China.

Synthesis of SR-FVI

Tetramethyldivinyldisiloxane (1.86 g, 0.01 mol), concentrated hydrochloric acid (0.61 g), water (1.2 g), and ethanol (0.72 g) were mixed to form a mixture solution. The solution was added dropwise into a solution composed of tetraethoxysilane (2.35 g, 0.011 mop, vinyltrie-thoxysilane (1.50 g, 0.012 mol), and 13-fluorooctyltrie-thoxysilane (5.10 g, 0.01 mol) under stirring at room temperature. The resulting mixture was maintained for 1 h at 90[degrees]C. Subsequently, the organic layer was separated from the mixture and washed by water, and then was heated with toluene in reflux to remove water azeotropic mixture. Finally, the toluene and the low-boiling components were removed in vacuum at 110[degrees]C and 3 mm Hg for 2 h to obtain a transparent viscosity silicone resin.

Preparation of CHM

PDMS with a vinyl content of 10 mol% (1.0 g) was dissolved in 10 mL of THF to form a solution. HSO (0.06 g) and chloroplatinic acid solution (0.006 g) as well as different weight contents of the above SR-FVI (designated 0, 10, 20, 30, 40, and 50 wt%, respectively) were added into the above solution and stirred to form a uniform solution. The CHMs were prepared by casting from the solution on a PET sheet at room temperature. The membrane-forming process by volatilizing solvent and cross-linking reactions between the silicon-hydrogen bond and the vinyl group were carried out simultaneously under the catalytic action of chloroplatinic acid. The resulting membranes were easily stripped and then dried in a vacuum. Transparent and flexible CHMs with different weight contents of the SR-FYI were obtained. The thicknesses of the membranes were ~100 pm, which average calculated by determining the thickness of more than five locations on any membranes.

Measurement of Gas Permselectivity

Oxygen and nitrogen permeability coefficients [[cm.sup.2] (STP) cm/([cm.sup.2] s cm Hg)] of the membranes were measured according to the variable volume method of Stern (21). Oxygen permeability coefficient ([P.sub.02]), nitrogen permeability coefficient ([P.sub.N2]), and oxygen/nitrogen separation factor ([P.sub.02/N2]) are calculated by the previous report (22). Each value of permeability coefficients and separation factions is obtained by determining at least five times. The standard deviation was within ca. -[+ or -]5%. Pressure is usually corrected to standard conditions (STP) of temperature (273[degrees]C) and pressure (76 cm Hg).

Characterizations

Fourier Transform Infrared Spectroscopy Measurement. Fourier transform infrared (FTIR) spectra of the CHMs and the cross-linked PDMS membrane without the SR-FVI as well as other materials were measured by using a Bruker EQUINX 55 spectrometer. Except the membrane samples, other KBr tabletting specimens were prepared by using KBr and the materials, respectively.

Scanning Electron Microscopy Observation. The substrate-facing surface and the fracture surface of the hybrid membranes and the cross-linked PDMS membrane without the silicone resin were coated with gold and observed by using a German Scanning Electro Microscope of JEOL JSM-T300.

Swelling Testing. To attain the physical performance and the degree of chemical cross-linking, the swelling behavior of the hybrid membranes and the cross-linked PDMS membrane without the silicone resin were studied. The swell coefficients were measured according to the literature (23). The membranes were dipped in THF, xylene, toluene, and chloroform for 4 h at room temperature, respectively.

RESULTS AND DISCUSSION

Synthesis of SR-FVI and Preparation of CUM

The SR-FVI was synthesized by using several organic silicon monomers with different functionalities such as tetraethoxysilicone, vinyltriethoxysilane, 13-fluorooctyl-triethoxysilane, and tetramethyldivinylsilane. The obtained SR-FVI is a viscous liquid and can be soluble in organic solvents (such as xylene) by controlling molar ratio of the alkoxyl groups in the monomers and extent of reaction of the functional groups. It is miscible in xylene with the PDMS containing vinyl group of 10 mol% and the HSO to prepare easily the CHM by silicon-hydrogen addition reaction at room temperature by means of casting solution method. The synthesis reaction of the SR-FVI and the cross-linking reaction of the CHM are shown in Scheme 1. For the structure of the resulting SR-FVI, the silicon oxide framework component can also be formed besides pendent fluorine substituent groups and vinyl groups. For the cross-linking reactions, addition reactions between silicon-hydrogen and vinyl group are carried out among the SR-FVI, the PDMS, and the HSO under the catalytic effect of chloroplatinic acid. A cross-linked hybrid network structure had been formed during membrane-forming process.

The hybrid membranes have a transparent appearance and are in a rubbery state at room temperature. Their cross-linking densities increased and flexibilities decreased with increasing the SR-FVI content in the CHMs. Additionally, the hybrid membrane shows certain obvious brittleness when the SR-FVI content in the CHMs is up to 50 wt%, but it has still fairly good strength which is needed to determine the permeability.

Characterizotion of SR-FVI and CHM

FTIR Analysis. The chemical structures of the SR-FVI and the CHM were measured by FTIR spectroscopy and their spectrograms are shown in Fig. 1. These spectrogram curves include the SR-FVI (Fig. 1a), the HSO (Fig. 1b), the PDMS (Fig. 1c), the cross-linked PDMS membrane without the SR-FVI (Fig. 1d), and the CHM (Fig. 1e), respectively. As shown in Fig. 1a, there are two characteristic absorption peaks: C--F bonds at 1205 [cm.sup.-1] and 936 [cm.sup.-1]; C=C bonds at 1597 [cm.sup.-1], which show that the fluorine substituent groups and the vinyl groups have been successfully introduced into the structure of the SR-FVI. In addition, the characteristic peaks of silicon-hydrogen bonds (Si--H) for the HSO (Fig. 1b) and C=C bonds for the PDMS (Fig. 1c) present at 2156 [cm.sup.-1] and 1597 [cm.sup.-1], respectively. When the cross-linking reactions completed, the above two characteristic absorptions disappear; however, C--F bonds at 1205 [cm.sup.-1] still existed despite they display a weaker characteristic absorption in the CHM curve (Fig. 1e). This indicates that the fluorine substituent groups have been introduced into the structure of the CHM.

Morphology Observation. The CHMs are transparent to indicate a completely amorphous morphology because both the SR-FVI and PDMS are no-crystalline polymers. The samples for the CHM and the cross-linked PDMS membrane without the SR-FVI were observed by scanning electron microscopy (SEM). Figure 2 shows the SEM photographs of the substrate-facing surface (SFS) and the fracture surface (FS) for the cross-linked PDMS membrane without the SR-FVI (Fig. 2a-c) and the CHM containing the SR-FVI of 50 wt% (Fig. 2d-f). It can be seen that the membranes show dense, sleek and even appearances either SFS or FS. However, there is still a difference between the membranes for FS. FS of the CHM is coarser and more asymmetric than that of the cross-linked PDMS membrane without the SR-FVI. There are some blocky-shaped particles and scraggly chases as well as ridges which are mainly attributed to the occurrence of rigid inorganic framework network phase formed from tetraethoxysilane in the SR-FVI. In addition, much denser cross-linked morphology in their inside could also be observed.

Swelling Properties of the Membranes. Since the cross-linked polymers can only swell but not dissolve in the organic solvents, the swelling degrees of the cross-linked membranes reflect their cross-linking degree chemically. Hence, the swelling degrees of the membranes for some typical solvents such as xylene, toluene, tetrahydrofuran, and chloroform were measured at room temperature to estimate their cross-linking behaviors. The swelling test was obtained by making a membrane immerge into a solvent at 30[degrees]C for 4 h. The swelling coefficients of the membranes for different solvents calculated according to the testing results are listed in Table 1. It can be seen that coefficients of the CHM are smaller than those of the cross-linked PDMS membrane without the SR-FVI for the same solvents, suggesting that the CHMs have larger cross-linking degree.

TABLE 1, Swelling coefficients of the cross-linked PDMS membrane
without the SR-FVI and the CHMs for several different solvents.

Membrane                   Xylene  Toluene    THF  Chloroform

Cross-linked PDMS membrane  1.395    1.400  1.432       1.289
CHM                         1.262    1.241  1.321       1.148


Oxygen-Enriching Properties of the CHM. Effect of the SR-FVI Content. Oxygen-enriching properties of the CHM were measured according to the variable volume method. Oxygen permeability coefficient, nitrogen permeability coefficient, and oxygen/nitrogen separation factor of the CHMs with several different weight contents of the SR-FVI (designated 10, 20, 30, 40, and 50 wt%, respectively) are listed in Table 2 at 30[degrees]C and pressure difference of 0.10 MPa. Clearly, oxygen permeability coefficients of the CHM decrease slightly with an increase of the SR-FVI content, but [[alpha].sub.O2]/N2] increase obviously. The oxygen/nitrogen separation factor values are greater than 3.0 while [P.sub.02] values still maintain over 600 Barrer when the SR-FVI contents in the CHMs are 40 wt% or over 40 wt%. Especially, oxygen permeability coefficient and oxygen/nitrogen separation factor of the CHM containing the SR-FVI of 50 wt% are 628 Barrer and 3.36, respectively. The value of the CHM is distinctly larger than that (oxygen/nitrogen separation factor is 2.75) of the cross-linked PDMS membrane without the SR-FVI as a control. The good oxygen-enriching property is attributed to the fluorine-containing component in the CHM due to its excellent solubility for oxygen. But the property is not obtained as the SR-FVI content is less than 40 wt%. By calculating in theory, the fluorine-containing component in the SR-FVI is about 33 wt%. Thus, for the CHMs containing the SR-FVI of 30 wt% and 50 wt%, the proportions of the fluorine-containing component probably are 10 wt% and 16 wt%, respectively. In the CHMs, fluorine components are introduced by firstly forming the SR-FVI and then concerning with cross-linking reactions. According to some literature, the cross-linking mode that is a simple and effective way is beneficial to form a more uniform cross-linking network structure, which can change the membrane structure and improve selectivity in all modified methods for polymeric membranes (18-20). Therefore, the fluorine-containing component in the CHMs can be up to 16 wt% in the work. The cross-linking network structure and introduction of the fluorine-containing component in the hybrid membrane can improve permselectivities of some polymeric membranes.

TABLE 2. Oxygen-enriching properties of the CHMs at
30[degrees]C and 0.10 MPa.

CHM no.   SR-FVI   permeability  permeability  Oxygen/nitrogen
         content    coefficient   coefficient       separation
           (wt%)       (Barrer)      (Barrer)           factor

Control        0            745           271             2.75

1             10            672           284             2.36

2             20            689           295             2.37

3             30            620           286             2.32

4             40            637           211             3.01


The introduction of the fluorine-containing component enhances affinity of the membrane to oxygen and results in an increase in selectivity for [0.sub.2]/[N.sub.2]. However, the SR-FV1 content in the membrane cannot be further increased because the CHM containing the SR-FVI of 50 wt% has displayed certain obvious brittleness, but it still has fair strength which needs to determine the permeability. The CHMs were in a transparent and flexible rubbery state at room temperature and possessed reproducibility.

The data of oxygen-enriching properties for various modified PDMS membranes reported by the literatures and our works are listed in Table 3. It can be seen that the oxygen permselectivities of the fluorine-containing CHMs show better balanceable performances for various modified PDMS membranes. Therefore, according to these results, we can think the fluorine component can enhance selectivity of the PDMS hybrid membrane. Some researchers had reported that the introduction of fluorine atom into side chains of polymeric membranes could enhance permselectivity (14), (15), (24).

TABLE 3. Oxygen-enriching properties of various modification
silicone rubber membranes.

No.  Modified PDMS            Temperature        Oxygen
     membranes              ([degrees] C)  permeability
                                            coefficient
                                               (Barrer)

1    PDMS                                           605

2    PDMS-b-PC                                      200

3    PDMS-b-PU                                       43

4    Poly(viny/phcnol)                              340
     cross-linked by PDMS

5    Triblock copolymer of                           23
     PDMS and poly (amino
     acid) (DMS contents
     54 mol%)

6    Comb-shaped polymer                         10-100
     with
     oligodimelhyloxane
     (DMS content:
     60-70%)

7    I'DMS-g-Polysulfone                            115
     (DMS content:
     60-65%)

8    PDMS-g-Polyimide (DMS                          163
     content: 60-65%)

9    PPO-g-PDMS                                     340

10   PPS-g-PDMS                                     480

11   PAA-g-PDMS                                     239

12   PDMS                              20           593

 Oxygen/nitrogen  Membrane  Reference
               s  forming
eparation factor  ability

            2.00  Bad             [1]

            2.00  Good            [2]

            4.10  Good           [18]

            2.10  Good            [3]

            3.00  Good            [4]

       2.40-4.40  Good         [5, 6]

            2.66  Good            [7]

            2.45  Good            [8]

             2.5  Good            [9]

             3.1  Good           [19]

            1.75  -               [9]

            3.50  Good              -


Pressure Difference Effect. Generally, pressure difference does not influence [P.sub.O2] and [P.sub.N2] of polymeric membrane through which the gases penetrate according to the solution--diffusion mechanism. Stern et al. (1) proved such opinion by studying the modified PDMS membranes of which the bulkier functional groups substituted in the backbone chains or side chains. For the CHM containing the SR-FVI of 50 wt%, as an example, the correlations between oxygen permeability coefficient, nitrogen permeability coefficient, oxygen/nitrogen separation factor, and pressure difference at 20[degrees]C are shown in Fig. 3. Obviously, slight increase in oxygen permeability coefficient and slight decrease in nitrogen permeability coefficient are obtained to exhibit two lines with decreasing pressure difference. For example, when gas pressure decreased from 0.40 to 0.10 MPa, oxygen permeability coefficient and oxygen/nitrogen separation factor of the CHM increased from 547 Barrer and 2.91 to 594 Barrer and 3.50, respectively. Thus, both the higher oxygen permeability coefficient and the higher oxygen/nitrogen separation factor value only occur at lower pressure difference of 0.10 MPa.

Temperature Effect. Effects of temperature on oxygen permeability coefficient, nitrogen permeability coefficient, and oxygen/nitrogen separation factor of the CHM containing the SR-FVI of 50 wt% at pressure difference of 0.10 MPa are shown in Fig. 4. It shows that a usual "inverse" permeability/selectivity behavior occurred, that is, both oxygen permeability coefficient and nitrogen permeability coefficient increase and oxygen/nitrogen separation factor decrease with an increase in the testing temperature. The behavior is in accord with the general role of gas separation membranes. It should be pointed out that the CHM exhibits excellent permselectivity at 20[degrees]C, for instance, oxygen permeability coefficient and oxygen/nitrogen separation factor are 594 Barrer and 3.50, respectively. When the temperature rose from 20[degrees]C to 50[degrees]C, oxygen permeability coefficient increased to 836 Barrer and oxygen/nitrogen separation factor decreased to 3.04. Even if at high temperature of 50[degrees]C, oxygen/nitrogen separation factor is still above 3.0, which undoubtedly is a quite good permselectivity performance. Stern et al. (1) investigated structure--permeability relationships of the silicone membranes to prove that the effect of temperature on gas permeability coefficient depended on changes in its diffusion coefficient and solubility coefficient. The diffusion coefficient always increased with increasing temperature, whereas the opposite tendency was generally observed in the solubility coefficient. In other words, the gas permeability enhancement was basically a result of the increase in the diffusion ability of the gases in the membrane when the temperature was raised. Hence, the solubility behavior of the gas for the membrane became an important control factor for the gas permeation process here. In fact, the higher [[alpha].sub.02]/[N.sub.2] value is precisely benefit from the enhancement of solution property for oxygen caused by the fluorine-containing component in the CHM.

The activation energies of oxygen and nitrogen permeating through the membrane can be obtained according to the Arrhenius equation. The Arrhenius diagrams of the CHM containing the SR-FVI of 50 wt% at pressure difference of 0.10 MPa is shown in Fig. 5. Both oxygen permeability coefficient and nitrogen permeability coefficient exhibit two straight lines. The slopes measured by the lines and the activation energies calculated from these slopes are collected in Table 4. The activation energies of oxygen permeability and nitrogen permeability are 9.06 and 12.64 kJ/mol, respectively. The results suggest that not only the potential energy barriers for oxygen and nitrogen permeate through the CHM are different but also those of oxygen are always lower.

TABLE 4. Activation energies calculated from line slopes of oxygen
and nitrogen for the CHM. containing SR-FYI of 50 wt% at pressure
difference of 0.10 MPa.

                    [E.sub.02]  [E.sub.N2]  [E.sub.N2]/   Reference
Membrane              (kJ/mol)    (kJ/mol)   [E.sub.02]

Cross-linked PDMS         7.90        9.20         1.16        1201
membrane

CHM containing SR-FV1     9.06       12.64         1.40           -
of 50 wt%


CONCLUSIONS

To improve permselectivity and membrane-forming ability of PDMS, we have prepared a new cross-linked hybrid membrane containing fluorine resulted from a fluorine-containing silicone resin substituent group, vinyl group, and inorganic framework. The matrix membrane materials involved PDMS containing high vinyl group of 10 mol% and the silicone resin. The membrane-forming process and the cross-linking reactions consisted of the addition reaction between the silicon-hydrogen bond and the vinyl group can carry out together at room temperature. Both the membrane-forming ability and oxygen-enriching properties of the cross-linked hybrid membrane have been enhanced simultaneously. The silicon resin content in the cross-linked hybrid membrane significantly affected the morphology and the permselectivity of the membranes. Only the silicone resin content is over 30 wt%, oxygen-enriching properties of the cross-linked hybrid membrane can exhibit obvious enhancement. On the one hand, the oxygen-enriching properties benefit from enhancement in cross-linking degree; on the other hand, they are attributed mainly to the fluorine-containing component in the membrane due to its good affinity for oxygen.

Correspondence to: H.X. Rao; e-mail: traohx@jnu.edu.cn

Contract grant sponsor: National Natural Science Foundation of China; contract grant numbers: 30971915, 31000446; contract grant sponsor: Guangdong Province Science Foundation of China; contract grant number: 8151063201000055.

DOI 10.1002/pen.23486

Published online in Wiley Online Library (wileyonlinelibrary.com).

[c] 2013 Society of Plastics Engineers

REFERENCES

(1.) S.A. Stern, V.M. Shan, and B. Hardy, J. Polym Sci. Part B: Polym. Phys., 25, 1263 (1987).

(2.) S.P. Shi, Z.J. Du, H. Ye, C. Zhang, and 1-1.Q. Li, Polym. J., 38, 949 (2006).

(3.) M.P. Achalpurkar, U.K. Kharul, H.R. Lohokare, and P.B. Karadkar, Sep. Purif Technol., 57, 304 (2007).

(4.) M.M. Dal-Cin, K. Darcovich, and S.A. Saimani, J. Membr. Sci., 361, 176 (2010).

(5.) S.H. Zhong, H.W. Sun, X.T. Wang, H.Q. Shao, and J.B. Guo, J. Membr. Sci., 278, 212 (2006).

(6.) T.C. Merkel, B.D. Freeman, R.J. Spontak, Z. He, I. Pinnau, P. Meakin, and A.J. Hill, Science, 296, 519 (2002).

(7.) S.H. Ycon, K.S. Lee, B. Sea, Y.I. Park, and K.H. Lee, J. Membr. Sci., 257, 156 (2005).

(8.) T. Uragami, K. Okazaki, H. Matsugi, and T. Miyata, Macm-molecules, 35, 9156 (2002).

(9.) H.B. Park, J.K. Kim, S.Y. Natn, and Y.M. Lee, .J. Membr. Sci., 220, 59 (2003).

(10.) G. Monscrrat, B. Jonathan, E.G. Ramon, C. Daniele, G.T. Javier, E.Z. Werner, V. Henk, and H.A.B. Dave, Polym. Eng. Sci., 44, 1240 (2004).

(11.) M. Lavorgna, L. Fusco, F. Piscitelli, G. Mensitieri, P. Agoretti, A. Borriello, and L. Mascia, Polym. Eng. Sci., 48, 2389 (2008).

(12.) J.S. Liu, Y. Ma, K.Y. Hu, H.M. He, and G.Q. Shao, .1. Appl. Polym. Sci., 117, 2464 (2010).

(13.) T.H. Kim, W.J. Koros, and G.R. Husk, J. Membr. Sci., 46, 43 (1989).

(14.) M. Srividhya and B.S.R. Reddy, J. Membr. Sci., 296, 65 (2007).

(15.) Y. Nagase, J. Ochiai, K. Matsui, and M. Uchikura, Polymer, 29, 740 (1988).

(16.) Y. Nagase, J. Ochiai, K. Matsui, and M. Uchikura, Polyin. Coninnin., 129, 10 (1988).

(17.) S. Keleser, Y. Salt. A. Hasanoglu, S. Ozkan, and S. Dincer, Desalination, 200, 44 (2006).

(18.) C.H. Xu and S.Y. Feng, React. Fund. Polymer, 47, 141 (2001).

(19.) G. Unnikrishnan and S. Thomas. Polymer, 35, 5504 (1994).

(20.) S.A. Stern, T.F. Sinclair, and P. Gareis, J. Mod. Plast., 42, 154 (1964).

(21.) H.X. Rao, Z.Y. Zhang, C. Song, T. Qiao, and S.B. Xu, Sep. Purtf. Technol., 78, 132 (2011).

(22.) Y.P. Yampolskii, N.B. Bespalova, E.S. Finkel'shtein, V. Bondar, and A.V. Popov, Macromolecules, 27, 2872 (1994).

(23.) R. Prabhakar and B. Freeman, Desalination, 144, 79 (2002).

(24.) L. Mathew, K.U. Joseph, and R. Joseph, Bull. Mater. Sci., 29, 91 (2006).

Ziyong Zhang, Jianheng Huang, Yi Lin, Huaxin Rao

Department of Materials Science and Engineering, Jinan University, Guangzhou 570632, China
COPYRIGHT 2013 Society of Plastics Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Zhang, Ziyong; Huang, Jianheng; Lin, Yi; Rao, Huaxin
Publication:Polymer Engineering and Science
Article Type:Report
Geographic Code:9CHIN
Date:Nov 1, 2013
Words:4076
Previous Article:Irradiation effects in poly(ethylene oxide)/silica nanocomposite films and gels.
Next Article:Effect of molecular weight and molecular weight distribution on weld-line interface in injection-molded polypropylene.
Topics:

Terms of use | Privacy policy | Copyright © 2022 Farlex, Inc. | Feedback | For webmasters |