ISSN 0036�0244, Russian Journal of Physical Chemistry A, 2011, Vol. 85, No. 4, pp. 617–620. © Pleiades Publishing, Ltd., 2011.

617

INTRODUCTION

Polymer blending is one of the most importantcontemporary ways for the development of new poly�meric materials, because of the preparation of poly�meric materials with superior properties, low basiccost and improved process ability. However, the mani�festation of superior properties depends upon the mis�cibility of two polymers on the molecular scale. Sev�eral techniques have been used to investigate the poly�mer–polymer miscibility, for instance, Fouriertransform infrared [1, 2], atomic force microscopy [3],thermal analysis [4, 5], dynamic mechanical studies[6, 7] and viscosity techniques [8–10]. Some of thesetechniques may be complicated costly and time con�suming. Hence, viscosity method is a simple, low costand rapid technique and has been extensively used tostudy the polymer–polymer miscibility.

In this work, the miscibility of ethyl cellu�lose/copolyamide6/66/1010 (EC/PA�130) blends hasbeen studied using viscometry and refractive indexmethod at 25°C. Viscosity and refractive index mea�surements were conducted for EC/PA�130 blend solu�tions of different composition (100/0, 90/10, 80/20,50/50, 20/80, 10/90, 0/100) using formic acid as sol�vent. Various criteria and parameters were calculatedto discuss the miscibility of these blends in differentcomposition. The results show the existence of misci�bility window.

EXPERIMENTAL

Materials. Copolyamide6/66/1010 (PA�130, Copo�lymerization Moore ratio equal 20/10/70) and ethyl

cellulose (EC, η = 8~10 mPa s, DS = 2.13), formicacid (AR Grade, 88 wt %) were purchased fromShanghai Reagent Company of China and used forthis work.

The preparation of pure polymers and blends ofEC/PA�130. For viscosity studies, stock solutions ofpure polymers and the blends of EC/PA�130 of differ�ent compositions, 10/90, 20/80, 30/70, 40/60, 50/50,60/40, 70/30, 80/20, and 90/10 were prepared in for�mic acid, and the total polymer concentration wasalways maintained at 0.4 g/dl.

Instruments and methods. The viscosity of polymersolutions in formic acid was measured using the Ubbe�lohde’s capillary viscometer immersed in a constanttemperature water bath at 25.0 ± 0.1°C. The stocksolutions of each system were prepared and diluted toyield four lower concentrations made by adding theappropriate amount of formic acid to the stock solu�tions. The relative viscosities of blends were calculatedby dividing the flow times of solutions by that of thepure solvent. The refractive indices of the EC/PA�130blend solutions were measured using a WZS�I Abberefractometer.

THEORETICAL

In dilute solution, the intrinsic viscosity [η],reflecting the interaction between polymer and solu�tion, was determined by plotting against the solutionconcentration, c, for each blend composition, accord�ing to Huggins’s equation:

, (1)

where b = k[η]2, ηsp denotes specific viscosity, c is themass concentration of solution. b is related to the

η = η +[ ]c bcsp/

Miscibility of Ethyl Cellulose/Copolyamide6/66/1010 Blends by Viscometry and Refractive Index Method1

Xiuzhen Zhang, Yuhua Shen, Anjian Xie, Sulian Gao, and Zhiying XingSchool of Chemistry & Chemical Engineering, Anhui University, Hefei, Anhui, 230039, People’s Republic of China

e�mail: s_yuhua@163.comReceived April 15, 2010

Abstract—The miscibility of ethyl cellulose (EC)/copolyamide6/66/1010 (PA�130) in formic acid is studiedby viscometry and refractive index techniques at 25°C. Using viscosity data, the criteria Δb, Δb', Δ[η]m, inter�action parameter μ, β and thermodynamic parameter α are calculated. These investigations indicate thatblend of EC/PA�130 is miscible when the ethyl cellulose content is more than 50 wt % in the blend. Furtherthe result was also confirmed by refractive index measurements.

Keywords: blends, EC, PA�130, miscibility, viscometry, refractive index.

DOI: 10.1134/S0036024411040297

PHYSICAL CHEMISTRY OF SOLUTIONS

1The article is published in the original.

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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 85 No. 4 2011

XIUZHEN ZHANG et al.

Huggins coefficient k, which reflects the binary inter�actions between polymer segments.

In polymer (1)/polymer (2)/solvent system, Chee[11] suggests

(2)

where bm = km , c = c1 + c2. Subscripts 1, 2, and mcorrespond to polymer 1, 2 and their blends, respec�tively.

As described by Aroguz and Baaysal [8], the infor�mation on the intermolecular interaction in binarypolymer blends, (polymer 1 and polymer 2) can beobtained from a comparison of experimental interac�

tion coefficient and theoretical value .

(3)

η + = η + +1 2 1 2( ) [ ] ( ),c c b c cspm m m/

η[ ]m2

exp12b id

12b

Δ = − = −idexp exp 1/2

12 12 12 11 22( ) .b b b b b b

There, the values of b11, b22, and are obtained fromthe slope of Eq. (2) for the pure polymer 1, polymer 2,and blends, respectively. The experimental value of

is estimated by the following equation:

(4)

There, w1 and w2 indicate the weight fraction of poly�mer 1 and 2.

According to the ideal blends behavior supposed byCatsiff and Hewett [12]:

(5)

Δb > 0 or Δb' > 0 signifies miscibility, whereas Δb < 0 orΔb' < 0, indicates immiscibility.

Using the value of Δb' given in Eq. (5), a moreeffective parameter μ is obtained to predict polymer–polymer miscibility as follow:

(6)

If μ > 0, the system is miscible, and if μ < 0, the systemis miscible.

According to the considerations of Sun et al. [13],α is a parameter for polymer–polymer miscibility interms of a thermodynamic parameter. If α ≥ 0, attrac�tive forces between polymers occur, and miscibility isfound. If α < 0, repulsive forces will prevail and misci�bility should not be expected:

(7)

where

(8)

By substituting Eq. (8) into Eq. (7), this criterion βcan be written in the following from [9]:

(9)

expbm

exp12b

= + +

exp 2 2 exp1 11 1 22 1 2 122 .b w b w b w w bm

Δ = − = − +id /exp exp

12 12 12 11 22'' ( ) 2,b b b b b b

μ = Δ η − η2

1 2' ([ ] [ ] ) .b /

α =

η + η η + η−

η + η

m

2 2 1/2 2 21 1 1 1 2 1 2 1 2 2 2 2

21 1 2 2

[ ] 2( ) [ ] [ ] [ ],

( [ ] [ ] )

K

k w k k w w k w

w w

η + η η + η=

η + η

2 2 2 21 1 1 12 1 2 1 2 2 2 2

21 1 2 2

[ ] 2 [ ] [ ] [ ] .( [ ] [ ] )

k w k w w k wKw w

m

β = Δ η η η + η2

1 2 1 2 1 1 2 22 [ ] [ ] ( [ ] [ ] ) ,kw w w w/

0.40 0.1 0.2 0.3 0.4

c, g/dl

0.5

0.6

0.7

0.8ηsp/c, dl/g

PA�130

10/90

80/20

50/50

80/20

90/10

EC

Fig. 1. Reduced viscosity values of the pure polymer of EC,PA�130 and their mixtures (EC/PA�130 = 10/90, 20/80,50/50, 80/20, 90/10 as labeled in the figure) as the func�tion of concentrations (c).

Table 1. Experimental and calculated polymer–polymer interaction coefficient and parameters Δb, Δb', and μ for EC/PA�130 blends

EC/PA�130 Δb Δb' μ Miscibility

100/0 0.09599 – – – –

90/10 0.16571 0.483703 0.391193 0.39112778 5.519536 Miscible

80/20 0.26227 0.616469 0.523959 0.52389375 7.393109 Miscible

50/50 0.20865 0.324725 0.232215 0.23215 3.276066 Miscible

20/80 0.10845 0.148588 0.056078 0.0560125 0.79044 Miscible

10/90 0.10423 0.172503 0.079993 0.07992778 1.127929 Miscible

0/100 0.08916 – – – –

bmexp

b12exp

RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 85 No. 4 2011

MISCIBILITY OF ETHYL CELLULOSE/COPOLYAMIDE6/66/1010 BLENDS 619

where

(10)

and

(11)

A blend will be miscible when β ≥ 0 and immisciblewhen β < 0.

Additionally, another miscibility criterion Δ[η]m

was proposed by Garcia [14], which is base on the dif�

ference between the experimental and ideal values:

(12)

(13)

Δ[η]m < 0 and Δ[η]m > 0 show miscibility and immis�cibility, respectively.

Δ = −1/2

12 1 2( )k k k k

m m/ / /2 2 21 11 1 2 22 2 12[ ] , [ ] , [ ] .k b k b k b= η = η = η

ηexp[ ]m η

idm[ ]

Δ η = η − η[ ] [ ] [ ] ,exp idm m m

η = η + η1 1 2 2[ ] [ ] [ ] ,w widm

RESULTS AND DISCUSSION

The Huggin’s polts for the pure components (ECand PA�130) and their blends in different weight frac�tions at 25°C are shown in Fig. 1. The points can befitted to be linear very well for the EC, PA�130 and allof mixtures (EC/PA�130) over a whole composition

range. The values of are obtained from the slops ofthe experimental lines in Fig. 1. Values of the parame�

ters , , Δb, Δb', and μ calculated using Eqs. (3)–(6) are tabulated in Table 1. As can be seen from Table 1,three criteria values for all of EC/PA�130 mixtures areposition. According to these criteria this system is mis�cible for these compositions.

The experimental values of intrinsic viscosity were determined from the intercept of these plots

using linear fit. The ideal and the compatibilitycriterion Δ[η]m values were computed using Eqs. (12)and (13) and given in Table 2, Figs. 2 and 3. For allcases, the experimental intrinsic viscosities are some�what smaller than ideal values as indicated by Fig. 2. Itcan be seen from Fig. 3 that the values of Δ[η]m for all

expbm

expbmexp12b

ηexp[ ]m

η[ ]idm

Table 2. A comparison of the experimental and ideal intrin�sic viscosity of EC/PA�130 blends

EC/PA�130 –Δ[η]m Miscibility

100/0 0.4798 – –

90/10 0.4932 0.50642 0.01322 Miscible

80/20 0.494 0.53304 0.03904 Miscible

50/50 0.5813 0.6129 0.0316 Miscible

20/80 0.6844 0.69276 0.00836 Miscible

10/90 0.7033 0.71938 0.01608 Miscible

0/100 0.746 – –

η[ ]mexp

η[ ]mid

0 0.2 0.4 0.6 1.0w

0.5

0.6

0.7

[η], dl/g

0.8

Fig. 2. Plot of experimental intrinsic viscosity ( ) vs.weight fraction of EC (w) in EC/PA�130 blends. Dotted

line indicates the ideal values of which follow theweight additive rule.

η mexp[ ]

ηidm[ ]

0.2 0.4 0.6 1.0w

0

0.02

−Δ[η], dl/g

0.8

0.04

Fig. 3. Plot of criterion of Δ[η]m vs. EC weight fraction inthe blend.

Table 3. The numerical values of polymer–polymer inter�action parameters for EC/PA�130 blends

EC/PA�130 α ΔK β Miscibility

90/10 0.04128 0.422781 0.422781 Miscible

80/20 0.224855 0.816255 0.816255 Miscible

50/50 0.047902 0.35901 0.35901 Miscible

20/80 –0.06811 –0.02693 –0.02693 Immiscible

10/90 –0.03812 –0.04774 –0.04774 Immiscible

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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 85 No. 4 2011

XIUZHEN ZHANG et al.

compositions of EC/PA�130 blends are negative.Then, from this point of view, these blends may be mis�cible in this formic acid.

The values of the parameters α, ΔK, and β are cal�culated using Eqs. (7), (10), and (9), respectively andpresent in Table 3. The curves of interaction parame�ters α and β against weight fraction of EC in the mix�tures are shown in Fig. 4. It can be seen that α and βare positive values for the EC/PA�130 blends for theweight fraction (EC) 0.5 and above and negative forthe weight fraction (EC) below 0.5. These parametersplotted as a function of weight fraction of EC acrossthe concentration axis at around 0.25–0.45. Figure 4indicates that the EC/PA�130 blends are miscible onlyfor the weight fractions (EC) no smaller than 0.45.

Rajulu et al. [15] have suggested that the variationof refractive index with blend composition is linear formiscible blend and non�linear for immiscible blend.Figure 5 shows the plot of refractive index as a functionof weight fraction of EC for the system EC/PA�130 inthe formic acid. Obviously, the variation of the refrac�tion index with EC wt. fraction of blend is linear,exhibiting this system miscible for these compositions.

CONCLUSIONS

In this work, blends of EC/PA�130 have been stud�ied. Using viscosity and refractive index methods, it isconcluded that the blend of EC/PA�130 is found to bemiscible, when EC content is greater than 50% in theblend. Below this EC concentration, the EC/PA�130system is found to be immiscible. Results from refrac�tive index measurement match very well those of vis�cometry. Thus afore mentioned techniques are simple,low cost, rapid and efficient methods in exploring themiscibility windows of EC/PA�130 blend in solution.

ACKNOWLEDGMENTS

This work is supported by the National ScienceFoundation of China (20871001, 20671001, and50973001), the Research Foundation for the DoctoralProgram of Higher Education of China(20070357002), the Important Project of Anhui Pro�vincial Education Department (ZD2007004�1), andthe Foundation of Key Laboratory of Environment�friendly Polymer Materials.

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0 0.2 0.4 0.6 1.0w

0

0.4

0.8

Criterion

0.8

β

α

Fig. 4. Plot of criterion α and β vs. EC weight fraction inEC/PA�130 blends.

0 0.2 0.4 0.6 1.0w

1.3690

1.3698

1.3702

0.8

1.3706

1.3694

Refractive index

Fig. 5. Plot of refractive index vs. EC weight fraction inEC/PA�130 blends at 25°C.