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Polymer Testing 31 (2012) 171–175

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Polymer Testing

journal homepage: www.elsevier .com/locate/polytest

Material properties

Miscibility and interfacial property studies of the blends of ethyl cellulosewith copolyamide6/66/1010

Xiuzhen Zhang, Yuhua Shen*, Anjian Xie, Sulian GaoSchool of Chemistry & Chemical Engineering, Anhui University, Hefei, Anhui 230039, People’s Republic of China

a r t i c l e i n f o

Article history:Received 10 September 2011Accepted 23 October 2011

Keywords:Ethyl celluloseCopolyamide6/66/1010BlendsMiscibilityInterfacial property

* Corresponding author. Tel./fax: þ86 551 510870E-mail address: s_yuhua@163.com (Y. Shen).

0142-9418/$ – see front matter � 2011 Elsevier Ltddoi:10.1016/j.polymertesting.2011.10.008

a b s t r a c t

Interfacial properties governing reverse osmosis separations were studied by using liquidchromatography data with respect to ethyl cellulose/copolyamide6/66/1010 (EC/PA-130)blends. The miscibility of ethyl cellulose/copolyamide6/66/1010 (EC/PA-130) blends wasinvestigated by using differential scanning calorimetry (DSC) and Fourier transforminfrared, while the interfacial properties of the blends, including the interfacial adsorption,hydrophobicity, polar and non-polar parameters and b-parameters, were studied by usingliquid chromatography. The results show that EC and PA-130 are miscible at compositionsof (80/20), (70/30) and (50/50). The hydrophobicity of EC/PA-130 increases with the of PA-130 content. The EC/PA-130(70/30) is superior to the other blends for separating non-dissociable polar organic solute and is more suitable for use as desalting membranematerial. It seems that liquid chromatography is an effective tool for studying the inter-facial properties of polymer blend materials and selecting high performance of membranematerials.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, study of polymer blend has attractedmany researchers because the blends often exhibit prop-erties that are superior to any one of the componentpolymers alone. However, the final properties of the poly-mer blends are determined by the miscibility of itscomponents at the molecular scale. Methods for theexperimental study of polymer miscibility are numerousand very diverse. The most often used experimentalmethod to investigate polymer–polymer miscibility in thesolid state is differential scanning calorimetry (DSC) [1–7].

At present, the reverse osmosis (RO) membrane sepa-ration technology is widely used in the chemical industry.The more effective utilization of this technology requiresa better understanding of its mechanism and of the inter-facial properties of polymer blend membrane material

2.

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used. The mechanism of the RO separation process,expounded by Sourirajan S. [8,9], is very similar to that ofliquid chromatography (LC). Therefore, LC experiment canmimic interfacial equilibrium conditions of the RO processin which polymer material is taken as the column packingto measure several interfacial parameters [10,11].

Cellulose is one of the abundant natural polymers withrenewable and biodegradable characteristics. Cellulosemembranes are widely used for reverse osmosis and ultrafiltration. As a derivative of cellulose, ethyl cellulose (EC)has some attractive physical and chemical properties, forexample excellent membrane-forming ability, durabilityand low cost. Previous studies [12–15] show that EC hasbeen used to blend with poly(3-hydroxybutyrate), poly-vinyl pyridine and poly(propylene carbonate), and thethermal stability, miscibility and rest properties of blendhave been studied. We have previously studied the misci-bility of ethyl cellulose/copolyamide6/66/1010 by usingviscometry and refractive index methods [16].

In the present work, LC experiments that mimicinterfacial equilibrium conditions of polymer blend in

X. Zhang et al. / Polymer Testing 31 (2012) 171–175172

reverse osmosis separation were used to measure severalinterfacial parameters. Ethyl cellulose/copolyamide6/66/1010 (EC/) blends were prepared by means of solutionblending and liquid–solid phase inversion. The miscibilityof the blends was investigated and the interfacial prop-erties, including the interfacial adsorption, hydrophobicity,polar and non-polar parameters and b-parameters, wassubsequently studied. This work should be a useful refer-ence in choosing the polymer membrane material forreverse osmosis and the process of orientation membranefabrication.

2. Materials and methods

2.1. Materials

Copolyamide6/66/1010 (PA-130, copolymerizationMoore ratio is equal 20/10/70), ethyl cellulose (EC,h ¼ 8w10 mPa$s, DS ¼ 2.13), and all the reagents withanalytical-reagent grade were purchased from ShanghaiReagent Company of China.

2.2. Preparation of blends and the analytical column of liquidchromatography

EC/PA-130 blends of variable weight fraction (80/20, 70/30 and 50/50) were prepared by means of solutionblending and liquid–solid phase transformation, formicacid being selected as the common solvent, 1.0 mol/Lsodium hydroxide solution was used as precipitator. Theblends were ground, screened and floated with redistilledwater. Then, the analytical column (stainless steel tube,150 mm � 4 mm i.d.) was packed using the wet method.The weighst of EC, EC/PA-130(80/20, 70/30, 50/50) in thecolumn was 0.6281 g, 0.4122 g, 0.4829 g and 0.5293 g,respectively.

EC/PA-130 80/20

2.3. Preparation of sample solutions

Except for deuterium-oxide, sample solutions wereprepared in redistilled water; concentrations were 10.0mg/mL for inorganic solutes, xylose and rhamnose, and 5.0%volumetric concentration for other organic solutes used forliquid chromatography.

30 60 90 120 150 180

70/30 50/50

0

TmTg

En

do

H

ea

t F

lo

w

Temperature(°C)

Fig. 1. DSC thermogram for EC/PA-130 blends.

2.4. Characterizations

Differential scanning calorimetry (DSC) was carried outwith a PE Pyres-1 DSC apparatus at a heating rate of 10 �C/min and in nitrogen atmosphere. The thermal analysisexperiments were conducted using a PE Pyres-1 thermalgravimetric analyzer (TGA) in the temperature range of25w500 �C at a heating rate of 10 �C min in nitrogenatmosphere. Liquid chromatography (LC) was carried outwith a Varian Prostar-210 high-performance liquid chro-matograph equipped with a refractive index (RI) detector(5.12 � 10�4 RI unit full scale). The mobile phase wasredistilled water, at a flow rate (F) of 0.5 mL/min. Thesample injection volume was 10 mL.

3. Result and discussion

Generally, polymer–polymer miscibility is commonlyestimated by the determination of the glass transitiontemperature (Tg) of the blends. If a blend exhibits a singleglass transition temperature between the Tg values of bothcomponents, the blend can be regarded as a miscible one.Fig. 1 shows DSC curves of EC/PA-130 blends. All the blendsin this work exhibit a single Tg, indicating that they aremiscible. This conclusion matches with those of viscometryand refractive index results [18]. In the case where onecomponent is crystalline, observation of a melting pointdepression of this polymer also supports the miscibility ofthe blend. From Fig. 1, the melting temperature (Tm) valuesof EC/PA-130 (80/20, 70/30, 50/50) blends are 117 �C, 123 �Cand 126 �C, respectively. Obviously, the melting tempera-ture of blends increases with the PA-130 content.

Fig. 2 shows the TGA/DTG curves of different composi-tions of EC/PA-130. Initial weight loss of each sample wasfound to be very small, whichmay correspond to the loss ofadsorbed and bound water and the residue of formic acid.Pure EC thermal degradation consists of two stages and thefirst thermal event is a weight loss of about 3% withmaximum rate at 232 �C, which is related to dehydration ofEC. The second thermal event starts at 280 �C, with themaximum at 382 �C and is related to degradation of ethylcellulose. For the pure PA-130, only one decompositionstage starts at 400 �Cwith themaximum at 482 �C. Then, allthe blends start degrading at 320 �C, with the major peaksat 385 �C and 475 �C. The absence of the first thermal eventfor pure EC at 210w250 �C in the blends indicates someinteractions between the polymers and may be consideredas further proof of their miscibility.

Each sample solution was tested by HPLC with thechromatographic conditions given above. The retentionvolume (VR) of each solute was calculated from the reten-tion time (tR) and carrier flow rate (F), and are listed in Table1. Quantitatively, interaction force at the polymer-solutioninterface depends on the value of equilibrium distributioncoefficient (K) of the solute. The lower the value of K is, thegreater is the repulsive force between solute and polymerinterface, whereas the larger the value of K, the greater is

0 100 200 300 400 500 6000

20

40

60

80

100

We

ig

ht(%

)

Temperature(°C)

EC/PA-130 100/0 80/20 70/30 50/50 0/100

100 200 300 400 500 600Temperature(°C)

EC/PA-130 100/0 80/20 70/30 50/50 0/100

Fig. 2. TGA/DTG thermogram for pure PA-130 and EC/PA-130 blends.

X. Zhang et al. / Polymer Testing 31 (2012) 171–175 173

the adsorption force between them. According to liquidchromatographic theory, K is given by

K ¼ �VR � ðVRÞmin

���ðVRÞwater�ðVRÞmin

�(1)

where VR, (VR)water and (VR)min represent retention volumesfor solute, deuterated water and lactose, respectively. The Kvalues were calculated and listed in Table 2. Obviously,solutes of aromatic compounds such as phenol andbenzene are strongly adsorbed on the polymer surfacewhen their corresponding values of K [ 1. Single func-tional nonionized polar organic solutes, such as ethylacetate and methanol, are also adsorbed, whereas carbo-hydrate solutes such as xylose, rhamnose, and inorganicsolutes are strongly repulsed on the polymer surface whenK < 1. Comparing EC with EC/PA-130 blends in the sepa-ration, EC/PA-130 (70/30) is most suitable to be used asdesalination membrane material because the K value ofsodium chloride is the lowest.

As proposed by Matsuura et al. [9], hydrophobicity of theblendscanbecharacterizedby thevolumeof interfacialwaterper unit weight of polymer (Vs/m) in the LC column. Thehydrophobicity of polymer increases with a decrease in thevalue of Vs/m, which is expressed by the following formula:

Table 1Date of HPLC experiments with EC and its blends as column-packing material.

solute EC/PA-130

100/0 80/20

tR/min VR/mL tR/min VR/

NaCl 2.822 1.411 2.549 1.CaCl2 2.782 1.391 2.517 1.FeCl3 2.744 1.372 2.509 1.phenol 56.884 28.443 54.683 27.benzene 9.588 4.794 9.500 4.n-butanol 3.982 1.991 5.766 2.n-propanol 3.842 1.921 3.637 1.ethanol 3.382 1.651 3.097 1.methanol 3.242 1.621 2.990 1.ethyl acetate 4.376 2.188 4.139 2.glycol 2.978 1.489 2.959 1.isopropanol 3.164 1.582 3.082 1.D2O 2.882 1.441 2.647 1.formaldehyde 3.064 1.532 2.574 1.D(þ)-xylose 2.722 1.361 2.436 1.rhamnose 2.684 1.342 2.409 1.sucrose 2.508 1.254 2.408 1.

VS=m ¼ �ðVRÞwater�ðVRÞmin

��m (2)

Thus, the Vs/m values of EC and EC/PA-130 blends wereobtained and listed in Table 3. Obviously, the hydropho-bicity of EC/PA-130 improves with the percent of PA-130increasing.

The interfacial polar (ap) and non-polar (an) parametersare used to characterize the polarity and the non-polarity ofpolymer at polymer-solute-solution interface, respectively.The increasing of ap and an values can improve reverseosmosis separations for non ionized polar organic solutes.In previous work [10,17], the following formula have beenobtained:

g ¼ Ks1=Ks2 (3)

lng1 ¼ ap þ an (4)

lng2 ¼ xap þ an (5)

where g is the ratio of the equilibrium distribution coeffi-cient K of two solutes, and the value of x assessed frompolymer solubility parameters is approximately �0.232

70/30 50/50

mL tR/min VR/mL tR/min VR/mL

275 2.431 1.216 2.589 1.294259 2.394 1.197 2.546 1.273255 2.358 1.179 2.563 1.282342 51.912 25.956 46.878 23.439750 6.278 3.139 7.554 3.777883 4.278 2.139 3.615 1.808819 3.852 1.926 3.486 1.743549 3.334 1.667 3.423 1.712495 3.130 1.565 3.353 1.676070 2.478 1.239 3.322 1.661480 2.476 1.238 3.101 1.550541 3.197 1.599 2.967 1.484324 2.562 1.281 2.420 1.210287 2.506 1.253 2.413 1.206218 2.408 1.204 2.255 1.128205 2.380 1.190 2.229 1.114204 2.352 1.176 2.217 1.108

Table 2Equilibrium distribution coefficient of EC and its blends.

solute EC/PA-130

100/0 80/20 70/30 50/50

KA KA KA KA

NaCl 0.840 0.592 0.381 1.824CaCl2 0.733 0.458 0.200 1.618FeCl3 0.631 0.425 0.028 1.706phenol 145.396 217.817 236.000 218.931benzene 18.930 29.55 18.695 26.1667n-butanol 3.941 13.992 9.171 6.863n-propanol 3.567 5.125 7.143 6.225ethanol 2.123 2.875 4.676 5.922methanol 1.962 2.425 3.705 5.569ethyl acetate 4.995 7.217 0.600 5.422glycol 1.257 2.300 0.590 4.333isopropanol 1.754 2.808 4.028 3.686formaldehyde 1.487 0.692 0.733 0.961D(þ)-xylose 0.572 0.117 0.267 0.196rhamnose 0.470 0.008 0.133 0.059

X. Zhang et al. / Polymer Testing 31 (2012) 171–175174

[18]. Methanol, ethanol and isopropanol were selected asthe reference solutes in the present experiment, theng1 ¼ Kethanol/Kmethanol and g2 ¼ Kisopropanol/Kethanol. Thevalues of g1, g2, ap, and an were finally calculated andsummarized in Table 3. The EC/PA-130(80/20, 70/30)blends have greater separation efficiency than EC.

Parameter b that is represented by LC data characterizesthe difference between the affinity of polymer for non-ionized polar organic compounds and that for dissociableinorganic compounds. Polymerwith larger b parameter hashigher affinity for organic solute than inorganic solute. Thevalue of b is in the range from 1.37 to 0.50, the lower itsvalue the greater is the separation efficiency for organicsolute. By the selective rule of reference solute expoundedin Ref. [18], we chose sodium chloride, formaldehyde andethyl acetate as the reference solutes to determine the b-parameter. Therefore, the following equations have beenobtained:

gs1 ¼ Kethyl acetate=KNaCl (6)

gs2 ¼ Kformaldehyde=KNaCl (7)

b ¼ ðlngs1 þ lngs2Þ=2 (8)

The values of gs1, gs2 and b can be calculated by using Eqs.(6)–(8) and are listed in Table 3. They indicate that EC/PA-130(70/30) blends have greater separation efficiency fornonionized polar organic solute than the other materials.

Table 3Parameters of EC and its blends.

EC/PA-130

VS/m(mL/g)

g1 g2 ap an gs1 gs2 b

100/0 0.298 1.082 0.826 0.219 �0.140 5.946 1.77 1.17780/20 0.291 1.186 0.977 0.157 �0.014 12.191 1.169 1.32870/30 0.217 1.262 0.861 0.310 �0.077 1.575 1.924 0.55450/50 0.193 1.063 0.622 0.435 �0.374 2.972 0.527 0.224

4. Conclusions

The miscibility and interfacial properties of EC/PA-130blends have been investigated by means of DSC, TGA andHPLC. EC/PA-130 blend is found to be miscible at compo-sitions of (80/20), (70/30) and (50/50). LC data can reflectquantitatively the interaction force between solute andinterface of polymer blends. The hydrophobicity of EC/PA-130 blend improves with increase of PA-130 content. EC/PA-170 (70/30) is suitable to be used as desalinationmembrane material and is superior to EC and the otherblends for separation efficiency for nonionized polarorganic solute. Therefore, HPLC seems to be a very effectivetool for study the interfacial properties of polymer blendmaterial. Interfacial properties for polymer blend material-solution systems have contributed significantly to ourunderstanding of the physicochemical basis of reverseosmosis separations.

Acknowledgements

This work is supported by the National Science Foun-dation of China (20871001, 20671001 and 50973001), theResearch Foundation for the Doctoral Program of HigherEducation of China (20070357002), the Important Projectof Anhui Provincial Education Department (ZD2007004-1),the Foundation of Key Laboratory of Environment-friendlyPolymer Materials and the Foundation of the 211 Project ofAnhui University (KJQN1021).

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