Chapter 2 - Effect of Carboxymethyl Cellulose Sodium Salt (CMC-Na ...

Chapter2–EffectofCMC‐NaontheRheologicalPropertiesofAlmondO/WEmulsions.

StudiesinMixedSurfactantSystemsandVegetableOilEmulsions 72

Chapter 2 -

Effect of Carboxymethyl Cellulose Sodium Salt

(CMC-Na) on the Rheological Properties of

Almond Oil in Water Emulsions Obtained by

Required HLB Method



2.1 Introduction

Emulsions are thermodynamically unstable systems which form the basis for

many commercially important foods, cosmetic and healthcare products. The desired self

life stability and aesthetic properties such as texture and flow characteristics are achieved

by careful selection of emulsion constituents such as emulsifiers, rheological additives,

texture enhancers and polymeric additives. The composition as well as aesthetic

properties of emulsions plays a decisive role in deciding feel and activity of every

emulsion system.

In many commercial applications such as, health care, food industry, etc. oil in

water (O/W) emulsions are preferred over the water in oil (W/O) emulsion. O/W

emulsions has several advantages such as, less expensive, lower viscosity and consistency

indices due to the minimal internal oil phase incorporation as oil phase in the cost

controlling parameter in such application. The emulsion framework disruption due to

rancidity as well as chemical alternations in oil phase can be prevented by blending

minimal oil phase in excess external aqueous phase allowing better encapsulation of oil.

O/W emulsions show a better skin application property and skin feel. The O/W

type of emulsion gets converted to the W/O type of emulsion upon rubbing due to partial

evaporation of external water phase, keeping the requisite constituents on the applied

area. Here, the external phase effectively contributes to easy spreading of emulsion and

minimal oil phase gives least feeling of oiliness. On the other hand in the process of

removing O/W emulsion from applied surface the gentle washing with water brings the

W/O emulsion to its original O/W in the presence of emulsifier which can be easily taken

off from the applied surface. 224-226

However, due to the minimal internal oil phase incorporation, most of the O/W

emulsions show lower consistency indices i.e. high fluidity. One of the best options to

achieve the desired consistency and texture to the emulsion system is to incorporate

polymeric thickener for enhancing the viscosity. The incorporation of highly hydrophilic

polymeric thickener considerably increases the viscosity of the external aqueous phase in

case of O/W emulsions thereby retarding the probability of collisions and subsequent

merging of dispersed internal phase globules.227, 228 Such polymeric additives have shown

an excellent potential in terms of sustained release of incorporated oil phase and also the

sustained release of pharmaceutically active excipient in dispersed oil phase. 229

It has been observed that the emulsion stability and its rheological properties are a

complex function of large number of interactions among the emulsion constituents. Each



of the emulsion constituent alters the stability as well as rheological properties of the

emulsion by its own way. The synergistic enhancement in emulsion stability by the

addition of common emulsion ingredients such as salt, 230-233 sugar, 234 etc. for vegetable

oils such as soyabean and safflower oil is shown by many researchers. It is possible to

achieve almost 50% increase in O/W emulsion viscosity with ~ 0.5% level of starch based

polymeric thickener.235 The use of non gelling polymer such as xanthan gum and locust

bean gum has shown improvement on the emulsion stability. These emulsions are

intended to be used as model sauce 236 and traditional wax based formulation for easy

peelers. 237 The most desired properties of the hydrocolloid are to act as an emulsifying

agent as well as emulsion stabilizing agent. Their effectiveness is measured in terms of

ability to protect the newly formed oil droplets from flocculation and coalescence to

impart long term stability against droplet aggregation, creaming and Ostwald ripening. 238

– 241 Incorporation of hydroxyl propyl cellulose in O/W emulsions obtained by using

lecithin as an amphoteric emulsifier has shown considerable facilitation in emulsion

formation and excellent emulsion stability against creaming. 242

Carboxymethyl Cellulose – Sodium Salt (CMC-Na) being non-toxic and non-

irritant it is widely used in oral and topical formulations primarily for stabilizing,

viscosity building and controlled release purposes. 243 The CMC obtained by

etherification of the sugar beet pulp cellulose was used as a hydrophilic polymer with

different compositions of emulsions to extend shelf-life of fruit products and to maintain

the quality. The coating of peach and pear surfaces with emulsions containing CMC from

sugar beet pulp cellulose as a hydrophilic polymer extended the shelf-lives of peach and

pear to 12 and 16 days, respectively. 244 CMC-Na has played a decisive role in deciding

stability of veegum / mucuna gum emulsions, 245 aqueous white phosphorus emulsions, 246 edible emulsified films of glycerol and oleic acid, 247 high-fat coconut milk emulsion. 248 CMC-Na has shown improvement in emulsifying properties of soybean protein isolate. 249 Droplet characteristics, flow properties and stability of egg yolk-stabilized oil-in-water

(O/W) emulsions as affected by the presence of carboxymethyl cellulose (CMC), guar

gum (GG), locust bean gum (LBG) and gum Arabic (AG) were studied. The results

supported the ability of CMC, GG and LBG in reducing partial coalescence by providing

sufficiently thick continuous phase or by acting as a protective coating for oil droplets. 250

CMC-Na triggers the controlled release of theophylline by forming semi-interpenetrating

polymer network hydrogel blend microspheres. 251, 252



The extensive literature review shows the importance of O/W emulsions and

incorporation of CMC-Na in deciding texture, flow, sensory properties of many emulsion

based products. Addition of CMC-Na has also contributed in controlling release of

pharmaceutically active ingredient. However, despite of all these important

characteristics, the influence of CMC-Na on O/W emulsions is not extensively expressed

in terms of its role in deciding emulsion stability, increasing consistency indices, etc.

The present research work is focused on finding the influence of CMC-Na

concentration on vegetable oil based O/W emulsions intended to be used as health care as

well as food supplement and to develop a mathematical model providing direct

relationship between the concentration of CMC-Na and O/W emulsion parameters such

as, consistency index, activation energy and pre-exponential factor in “Arrhenius type”

equation correlating emulsion consistency indices with temperature.



2.2 Experimental

2.2.1 Materials:

Almond oil was procured from M/s. Ashwin Pharma. Ltd. Mumbai, India.

Carboxymethyl cellulose sodium salt was purchased from M/s. Sigma Aldrich GmbH,

Germany. Surfactants (Span 80 and Tween 80) were purchased from M/s. S. D. Fine

Chemicals Ltd. India. Deionized water was used for emulsion preparation.

2.2.2 Methods

2.2.2.1 Emulsion preparation

All emulsions were prepared with varying Carboxymethyl cellulose sodium salt

(CMC-Na) concentration from 0.0 to 2.0% keeping almond oil and surfactant blend

concentrations fixed at 20 and 2 % respectively. Hydrophilic lipophilic balance (HLB)

number of almond oil was calculated by preparing a series of emulsions with varying

HLB number of surfactant blend comprised of Tween 80 and Span 80. HLB number of

Tween 80 and Span 80 were and 15 and 4.5 respectively. Out of the series of emulsions

prepared the most stable emulsion was having an HLB number of 6.5 which is the HLB

number of almond oil.

Emulsions were prepared by the addition of emulsifiable concentrate (EC)

comprising of almond oil with dissolved surfactant blend to the aqueous solution of

CMC-Na in water phase under gentle stirring. After the complete addition of EC the

resultant emulsion was homogenized at preoptimized speed of agitation of 10000 rpm

(Remi Motor Model) for 10 minutes at 30°C. Air trapped in the emulsion framework was

evacuated at 100 mm of Hg pressure (Lab India) till bubbling ceases. Table 2.1 shows the

composition of emulsions.

Table 2.1 – Composition of almond oil in water emulsions*

Entry Almond oil$ (g) Surfactant blend† (g) Water (g) CMC-Na (g)

1 20 2 78 0.0 2 20 2 77.5 0.5 3 20 2 77 1.0 4 20 2 76.5 1.5 5 20 2 76 2.0

* Each 100 g emulsion, $ Estimated HLB is 6.5, † Comprising of Span 80 : Tween 80 – 80:20



2.2.2.2 Rheological measurements

Viscosity measurements were performed for emulsions with varying CMC-Na

concentration and at controlled temperatures of 20°C, 30°C, 40°C and 50°C using a

digital rotational Haake VT 500 Viscometer operated by “Thermo Rheowin 2.97

software” equipped with DC-5 cooling system. Each viscometric measurement was

performed in five independent replications and average values were plotted. 50 mL of

each emulsion was exposed to shearing force in terms of rpm values ranging from 2 to

500 rpm at desired temperatures.

2.2.2.3 Storage stability (Oiling)

In order to study the effect of concentration of rheological additive on emulsion

stability each 100 mL of emulsion with varying CMC-Na concentration was stored in a

graduated glass cylinders at 60°C for 30 days. The height of clear oil layer separated at

the top of the cylinder was considered as the extent of emulsion instability. On the other

hand in order to know the extent of influence of temperature on emulsion stability the

almond oil in water having 0.5% of CMC-Na concentration was stored at different

temperatures of 20°C, 30°C, 40°C, 50°C, 60°C for 30 days in thermo stated cabinet

(Labindia)

2.2.2.4 Statistical Analysis

An analysis of variance i. e. two way anova was used for statistical analysis of

obtained data (POLYMATH Version 5 Software Package) at a confidence limit of 95 %.

Regression analysis was performed by the method of least square.



2.3 Results and discussion

2.3.1 Screening of rheological additives for emulsification

In emulsion pre-optimization studies the CMC-Na was found to be a better

rheological additive as compared to guar gum (GG), xanthan gum (XG) and sodium

alginate (SA). 100% emulsion stability is achieved just by adding 0.5% CMC-Na. This

may be due to the enhancement in hydrophilic character of CMC-Na, which built-up the

consistency index (an indication of apparent viscosity) of external aqueous phase and

thereby prevents the successive inter-globule collisions responsible for creaming and

subsequently for emulsion oiling. The effect is shown in figure 2.1.

Figure 2.1 – Screening of different rheological additives for almond oil in water

emulsion. (at 30,000 rpm, for 60 sec at 30°C)

2.3.2 Effect of concentration of rheological additive on emulsion stability

The emulsion stability was found to be influenced by the CMC-Na concentration.

An increase in CMC-Na concentration simultaneously increased the emulsion stability. In

case of CMC-Na deficient emulsions during storage at elevated temperatures the oil

globule coalesced to form a bigger oil droplet having tendency to migrate towards the top

of the container due to the differences in the gravitational forces as well as specific

gravity of oil phase incorporated and continuous aqueous phase. The emulsion stability of

96.8, 97.8, 98.5, 99.2 and 99.8% were obtained for the CMC-Na concentration of 0, 0.5,



1, 1.5 and 2% respectively. This indicated that the CMC-Na dramatically increased the

long term shelf life stability of emulsion even at elevated temperatures. (Figure 2.2)

Figure 2.2 – Effect of CMC-Na concentration on O/W emulsion stability. (At 60°C

for 30 days)

2.3.3 Effect of temperature of rheological additive on emulsion stability

Similarly, the rise in emulsion temperature linearly destabilized them during

storage. In case of almond oil emulsions having 0.5% CMC-Na concentration an

emulsion stability of 100%, 99.6%, 98.5%, 98.1% and 97.8% were observed for

temperatures of 20°C, 30°C, 40°C, 50°C and 60°C respectively. (Figure 2.3)



Figure 2.3 – Effect of temperature on O/W emulsion stability. (Almond oil 20%,

Surfactant blend 2%, CMC-Na 0.5% for 30 days)

2.3.4 Rheological characterization

The relationship between the apparent viscosity of emulsion and the rotational

speed of spindle at temperatures of 293 K, 303 K, 313 K and 323 K is shown in figure

2.4, 2.5, 2.6 and 2.7 respectively. A steady increase in emulsion viscosity with increase in

CMC-Na concentration was observed in case of all formulated emulsions. The increase in

emulsion viscosity with increases in CMC-Na concentration is attributed to the formation

of rigid interfacial films, molecular movements within the emulsion framework and

formation of physical barriers by means of the added ingredients. All formulated

emulsions showed a non Newtonian type behavior i. e. shear thinning flow behavior for

CMC-Na concentration ranging from 0.5 to 2.0 and also at all temperatures from 293 K to

323 K.

Increase in rotational speed of spindle decreased apparent viscosity of O/W

emulsions in two parts. Initially a rapid and sharp decrease in apparent viscosity was

observed for spindle speed of 2 to approximately 20 rpm which further decreased slowly

and exponentially after spindle speed of 20 rpm. This decrease in emulsion apparent

viscosity was a result of breakdown of emulsion aggregates as well as structural

breakdown of emulsion framework. On overlaying figure 2.4, 2.5, 2.6 and 2.7 it was

observed that the each 10°C rise in emulsion temperature has dominated the 0.5%



increase in CMC-Na concentration as the viscosity curve was remained lower for every

O/W emulsion having same CMC-Na concentration but differing in temperature by at

least 10°C. The decrease in apparent viscosity with increase in temperature for the

emulsions with 0% and 2% CMC-Na concentration is shown in figure 2.8 and 2.9

respectively. A power law type relationship between the rotational speed and apparent

viscosity was given by equation (1),234

η kγ (1)

Where,

ηapp is apparent viscosity (m Pa s)

k is consistency index (m Pa sn)

n is flow behavior index (Non-dimensional)

γ is rotational speed (s-1)



Figure 2.4 – The relationship between the apparent viscosity and rotational speed of

O/W emulsions at 293 K.




O/W emulsions without CMC-Na at varying temperature.




O/W emulsions at 2% CMC-Na concentration at varying temperature.

The two way ANOVA based analysis of variance revealed the significant

influence of CMC-Na concentration as well as temperature on the apparent viscosity of

almond O/W emulsions with p < 0.05. However, the multiple range analysis denoted that

there is no significant difference in the viscosity of almond O/W emulsions containing 1.5

% and 2 % CMC-Na concentration.



Table 2.2 - Rheological parameters.

Temperature (K) CMC-Na (%) K n r2

293

0 2697 0.48 ± 2.3×10-2 0.985

0.5 3326 0.50 ± 1.3×10-3 0.997

1 3552 0.44 ± 8.7×10-3 0.999

1.5 4280 0.57 ± 3.1×10-2 0.975

2 4623 0.51 ± 5.1×10-2 0.999

303

0 2128 0.44 ± 2.1×10-2 0.997

0.5 2751 0.45 ± 1.5×10-2 0.998

1 2875 0.47 ± 8.1×10-3 0.999

1.5 3538 0.49 ± 7.1×10-3 0.995

2 3856 0.51 ± 1.2×10-2 0.998

313

0 1812 0.51 ± 7.7×10-3 0.992

0.5 2067 0.50 ± 6.2×10-3 0.991

1 2622 0.51 ± 5.1×10-3 0.994

1.5 3045 0.51 ± 1.5×10-2 0.992

2 3416 0.52 ± 8.3×10-3 0.991

323

0 1486 0.48 ± 2.2×10-2 0.982

0.5 1877 0.46 ± 1.3×10-2 0.977

1 2007 0.43 ± 2.5×10-2 0.989

1.5 2508 0.50 ± 3.1×10-2 0.991

2 2684 0.51 ± 5.3×10-2 0.989

Table 2.2 contains the rheological parameters such as consistency indices and

flow behavior indices at different CMC-Na concentration and temperature. The model

suitably explained the experimental data by means of the correlation coefficient (r2)

values from 0.977 to 0.999. The pseudoplastic flow behavior of all formulated O/W

emulsions at all tested temperatures and CMC-Na concentrations were revealed by the

consistent below unity flow behavior indices.

However, no concrete relationship between the flow behavior indices (n) and

CMC-Na concentration and temperature is observed. The increase in temperature resulted

in stepwise and consistent decrease in the consistency indices (k) which is an indication



of viscous nature of the system. On the contrary, an increase in CMC-Na concentration

increased the consistency indices at respective temperature.

The mean values of emulsion flow behavior indices (n) were found to be not

significantly different from each other by the “t-test”. An average flow behavior value

was calculated by combining all 20 mean values form table 2.2 and used to define the

empirical flow behavior index of almond O/W emulsion.

The Arrehenius type relationship was developed considering the consistency

indices (k) as an indication of apparent viscosity of emulsions from the figure 2.10 whose

output parameters are depicted in table 2.3 as follows,

Figure 2.10 – The plot of ln (k) verses 1/T (K) at varying CMC-Na concentrations.

Table 2.3 - Estimated parameters of the Arrhenius type equation

CMC-Na (%) k0 (mPasn) Ea (kJ/kg mol) r2

0 1.644 15197.992 0.997

0.5 2.211 14308.394 0.945

1 2.373 14125.486 0.963

1.5 2.649 13917.636 0.995

2 2.834 13651.588 0.978



Figure 2.11 – The plot of “Ea” verses CMC-Na concentration.

The increase in CMC-Na concentration from 0 to 2 % resulted in decrease in “Ea”

values from 15,197 to 13,651 kJ/kg mol as shown in figure 2.11 which is given by

equation (2) as

Ea = (-696.7) C + 14937 (2)

Figure 2.12 – The Plot of ln (k0) verses CMC-Na concentration.



The dependency of pre-exponential factor in Arrehenius equation on CMC-Na

concentration is graphically depicted in figure 2.12 and equation is as follows,

k0 = 0.254 (C) + 0.580 (3)

The dependency of O/W emulsion consistency indices on temperature (T) and

CMC-Na concentration (C) is calculated by multiple regression with a correlation

coefficient of 0.943 and as shown in equation (4)

k 6.29e . (4)

Substituting value of consistency indices (k) from equation (4) in equation (1) an

empirical equation for predicting apparent viscosity (ηapp) at varying concentration of

CMC-Na (C), temperature (T) and rotational speed (γ) is given by equation (5) as follows,

η 6.29e . γ . (5)

The figure 2.13 graphically depicts the validity of developed empirical equation

(5) as follows,



Figure 2.13 – Validation of developed empirical equation.

2.4 Conclusion

Carboxymethyl cellulose sodium salt (CMC-Na) was efficiently used as

hydrophilic rheological thickener in preparation and stabilization of almond oil in water

emulsions using a blend of non-ionic surfactants having hydrophilic lipophilic balance

number of 6.5. Carboxymethyl cellulose sodium salt has synergistically increased the

O/W emulsion stability than sugar and salt. All formulated emulsions behaved as a

pseudoplastic fluids and the common rheological model was effectively applied to these

emulsion systems. The emulsion activation energies were found to be varied from 13651

to 15197 kJ/kg mol and decreased with increase in concentration of CMC-Na in

emulsion. The value of pre-exponential factor in “Arrhenius type” was increased with

increase in concentration of CMC-Na. The empirical equation correlating concentration

of CMC-Na and Apparent viscosity of O/W emulsion is successfully developed.



2.5 Nomenclature

R Universal gas constant (8.314 kJ/kg mol K)

T Temperature (K)

γ Rotational speed (s-1)

ηapp Apparent viscosity (m Pa s)

C Concentration of CMC-Na (g/100 g)

Ea Emulsion activation energy (kJ/kg mol)

k Consistency index (m Pa sn)

n Flow behavior index (Non-dimensional)

r Correlation coefficient (Non-dimensional)

k0 Pre-exponential factor in Arrhenius equation (m Pa sn)

Chapter 2 - Effect of Carboxymethyl Cellulose Sodium Salt (CMC-Na ...

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