chapter 7 influence of filler loading, blend composition...

Chapter 7

Influence of Filler Loading, Blend Composition and Organic Modification on the Gas Barrier Properties

of NR/NBR Blend Nanocomposites - Permeation of O2 and CO2

Abstract

In this chapter the gas permeability studies done on NR/NBR/O1Mt

nanocomposites are given. The studies have been done by referring mainly to

the blend composition, filler loading, preparation method etc. The barrier

properties have been studied using two different gases O2 and CO2 and it was

found that the permeation of CO2 was higher. The permeability of gas

transport was affected profoundly by blend composition and it was found that

an increase in NBR component decreased the permeability to an appreciable

level. The permeability was also found to decrease with the filler loading. The

preparation method also influenced the gas transport behaviour. The

modelling of the gas transport behaviour of the blend composites was also

done using parallel mode, series model, Maxwell model and Brugmann model

to permeability properties of gases on the basis of blend morphology. While

Nielson model and Baradwaj model was applied to compare the experimental

value based on the dispersion of the nanoclay.1

1 The results of this chapter has been submitted for publication in Soft Matter.

222 Chapter 7

7.1 Introduction

Combining an elastomer of poor barrier properties with a highly impermeable

elastomer, which can be produced by an industrially viable method has

significant applications in packaging industries or coating industries.

Improvement in barrier properties of polymer blends will be beneficial for

applications in pharmaceuticals, packaging of electronic items and particularly

packaging of food products, which are sensitive to gaseous molecules. On

blending together incompatible polymers results in poor dispersion, in which

the dispersed phase is very large and there is a weak adhesion between the two

polymers. The morphological development of the blend nanocomposites

influences the transport properties of polymer blends to a great extent.

Zemboua et al.1 studied the barrier properties of poly(3-hydroxybutyrate-Co-

3-hydroxyvalerate)/polylactide blends prepared by melt mixing. They

reported that PHBV imparted better water and oxygen barrier properties to

PHBV/PLA blends by acting as an efficient barrier promoter for PLA, even at

quite low ratio. Lafitte et al.2 have studied the influence of the blend

composition and morphology on the barrier properties of polyamide 11/ poly

(hydroxy amino ether) blend and found that the improvement of hydrogen

barrier properties was mainly related to the blend composition whereas a

significant effect of the blend morphology was observed on mechanical

properties in the rubbery state. Subramanian et al.3,4 have studied the barrier

properties of polymer blends and reported on the influence of morphology of

the blend on the barrier property.

However, in many cases the required property cannot be reached due toweak

adhesion and presence of voids or free volume. This adversity of the

incompatible polymers can be reduced to a great extent by incorporating a

compatibilizer which can improve the interface and modify the dispersion.

Gas barrier properties of….. 223

In immiscible polymer blends, these compatibilizers can reduce the

interfacial tension or influence other parameters like viscosity ratio which

influence the homogenous dispersion of the dispersed domains. Thus

carefully controlling the morphology, the gas transport through polymer

blends can be modified. This is mainly influenced by blend composition,

nature of blends, preparation of the blends and the presence of other

materials in the blend. The introduction of nanoparticles can impart some

significant effect in tuning up the blend morphology. Recently, a lot of work

have been reported5-8which have made use of nanoparticles as property

enhancer or compatibilizer in immiscible polymer blends. Frounchi et al.9,

have studied the gas barrier properties of PP/EPDM blend nanocomposites

and found that the oxygen and carbon dioxide permeability of the

nanocomposite reduced twice by adding only 1.5 vol% of nanoclay. Yeh et

al.10 have investigated the oxygen barrier properties of clay mineral

nanocomposites prepared from modified polyamide (MPA) and nylon-6

clay (NYC) blends and found that at 20 wt.% optimum content of NYC, the

oxygen barrier improvement of nanocomposites reached the maximum.11 All

films have been shown to possess superior oxygen barrier properties

compared to the plain PE films. Ghanbari et al12. studied the O2 barrier

properties of polymer/organoclay nanocomposites based on poly(ethylene

terephthalate) and sulfo polyester blendsand reported that for all the

nanocomposite films, the permeability is decreased in comparison to neat

PET due to both the presence of clay particles and a higher crystallinity. This

proved the strong influence of the nanoclay distribution on the barrier

properties. Bitinis13 et al. have studied the barrier properties of organoclay

filled polylactic acid/natural rubber blend bionanocomposites and observed

that organoclays were preferentially located at the interface and acted as

224 Chapter 7

compatibiliser between both polymer phases and resulted in a marked

improvement of the physical and mechanical properties of the system.

Here, this chapter reports the analysis of gas transport behaviour through

NR/NBR blend nanocomposites with reference to the blend composition, filler

loading, nature of permeant and preparation type. The purpose of the study in

discussed in this chapter is to know the effect of nanoclay in enhancing the gas

barrier properties of immiscible and incompatible NR/NBR blends. The study

also aimed in knowing the relationship between barrier properties and

morphological development of the blend nanocomposite system.

7.2 Results and discussion

7.2.1 Effect of blend composition

Barrier properties of oxygen through NR/NBR blends show improvement on

increasing the NBR content. The gas permeability values shown in Fig.7.1 shows

the extent of improvement compared to gum NR. It can be noted that for 30/70

composition 94% of improvement in gas permeability was observed (improved

about 16-fold) by adding only 30 parts, while for 70/30 and 50/50, an 84% and

82% of reduced permeability was observed. This can be attributed to the

homogenous dispersion of NR domains in the NBR matrix for 30/70 composition

although the NBR content is increased which should have contributed to the

reduction in permeation for 50/50. The SEM micrographs show that the blends

are heterogeneous in nature and that NR exists as domains in the continuous NBR

matrix. The dispersed/matrix morphology of blend offers a more tortuous path

for the penetrant14, thereby reducing the diffusivity through the membrane, which

in turn results in the reduction in permeability. For pure NR the chain flexibility

is very high due to the low glass transition temperature of NR. So NR becomes

the continuous phase for 50/50 and 70/30 composition and offers a comparatively

better permeation of O2 thereby increasing the permeability value. The


continuous morphology of 50/50 blend composites (Fig.7.2) also contributes to

the higher permeability15. Also the permeability of a gas molecule through a

polymeric membrane can be determined from the relationship between cohesive

energy density and activation energy given by the equation developed by Meares

(Eq.7.1)16

�� = �/(� �� (�� ………… (7.1)

Where �� is the cross section of the penetrant molecule, � �� the jump length

and NA is the Avogadro’s’ number and CED the cohesive enrgy density. The

polarity of NBR makes the cohesive energy density of NBR high and hence

results in low permeability. The reason for the decrease in permeability on

adding NBR can thus be clearly explained.

100/0 70/30 50/50 30/70 0/1000

2000

4000

6000

8000

10000

Per

mea

bilit

y g/

cm2

Blend composition (NR/NBR)

Figure 7.1: Oxygen permeability of different NR/ NBR nanocomposites with varying

blend composition

226 Chapter 7

Figure 7.2: SEM of 50/50 NR/NBR blend

7.2.2 Effect of filler loading

Incorporating nanoclay into the NR/NBR polymer blend system has reduced the

gas permeability of the elastomer films (Fig 7.3 to Fig. 7.5, & Fig.7.7). The

inorganic nature of nanoclay makes it impermeable to gases. The large aspect

ratio and nano scale dimensions either in exfoliated stage or intercalated stage

present large surface area even at low concentration of nanoclay, and there by

reduces the area of cross section available for permeation. The tortuosity also is

increased in the blend and hence increases the path length of diffusing molecules.

This can be observed from the morphological data of TEM given in Fig.7.3 and

Fig. 7.4 (inset), Fig.7.6, & Fig.7.8 where the images for different filler loading

is given. The decrease in the free volume due to the densely packed polymer

chains 17 as a result of interaction between nanoclay with NR and NBR can also

be the contributing factor in decreasing the permeability.


0phr 1phr 2phr 5phr 10phr0

100

200

300

400

500

600P

erm

eabi

lity

(g/c

m2 )

Filler loading (phr)

Figure 7.3 Oxygen permeability of NBR nanocomposites with varying filler loading. (inset)the TEM image of NBR nanomposite at 5 phr loading.


2000

4000

6000

8000

10000


Per

mea

bilit

y (g

m/c

m2 )

Figure 7.4 Oxygen permeability of NR nanocomposites with varying filler loading (inset) the TEM image of NR nancomposite at 5 phr loading.

228 Chapter 7


500

1000

1500

2000P

erm

eabi

lity

(g/c

m2 )


Figure 7.5 Oxygen permeability of 50/50 NR/NBR blend with varying filler loading.

Figure 7.6 TEM images showing of 50/50 NR/NBR blend with 2,5 and 10phr nanoclay.



100

200

300

400

500P

erm

eabi

lity

(g/c

m2 )

Filler Loading (phr)


Figure 7.8 TEM images showing of 30/70 NR/NBR blend with 2,5 and 10phr nanoclay

Increasing the clay content to 10% reduced the permeability for all the blend

composite although the extent of decrease is different for different blend

composite. While for NR nanocomposite a 8 fold improvement in barrier

properties was shown the barrier property improvement was only 4 fold for

the NBR nanocomposite. While the extent of barrier property improvement

was 2 fold, for 50/50 blend nancomposites (Fig 7.7), For 30/70 (Fig 7.7) and

70/30 (Fig 7.8) blend nanocomposites showed a 2.8 fold and 1.5 fold increase

230 Chapter 7

at higher clay loading (Fig. 7.9). This shows the difference in dispersion of

the nanoclay in these blends which influence the barrier properties. It was

interesting to note that all the composites showed a levelling off at higher

concentration. It can be considered to be due to the multilayer localization or

interfacial saturation as explained in chapter 6. The stacks of nanoclay at the

interface or the NBR domains doesn’t contribute further in increasing the

barrier properties. The low degree of dispersion of clay platelets which gets

stacked together can also be another reason and can be further observed from

the TEM images. (Fig 7.10).


500

1000

1500

2000

2500

3000

Per

mea

bilit

y (g

/cm

2 )




Figure 7.10 TEM images showing 70/30 NR/NBR blend with a)2 b)5 and c)10phr nanoclay

7.2.3 Effect of gas type

The effect of size of gas molecules on the permeability property of NR/NBR

blend were also observed and is given in Fig. 7.11. The influence of penetrant

size clearly contributes to the diffusion of gas molecules. It can be observed

that for all the composition the permeability of O2 is very low compared to

CO2. It is interesting to find that the CO2 which posses a higher molecular

weight is showing higher permeability. One reason for this behaviour is the

higher solubility of C02 with rubber. Yet another reason can be explained

using Stokes–Einstein equation which explains that, diffusion of gas

molecules is inversely related to the friction exerted. The eq. (7.2) is given by

D = K�. T/f ………..(7.2)

Where KB is the Boltzmann constant, T is the absolute temperature, and f is

the friction factor which is given by eq (7.3).

f = 6πμR� .……….(7.3)

The increase in radius of the gas molecule the friction factor also increases by

the relation and there is a corresponding decrease of permeability. Also on

considering the kinetic diameter of the two gas molecules also explains this

232 Chapter 7

reduction of permeability for O2. It is reported that among the various

descriptions of the sizes of molecules, that most applicable to transport

phenomena is called the "kinetic diameter" of molecules. The kinetic diameter

is a reflection of the smallest effective dimension of a given molecule. It is

given that for O2 the kinetic diameter is 3.4X 10-10m while for CO2 it is 3.3

x10-10 m.This shows that C02 is having lower kinetic diameter than O2 and

therefore C02 shows higher permeability than C02. This point is included in

the revised thesis.

50/50(1) 50/50(2) 50/50(5) 50/50(10)0

2000

4000

6000

8000

10000

Per

mea

bilit

y (g

/cm

2 )

Blend composition (NR/NBR/01Mt)

Oxygen Carbon dioxide

Figure 7.11 Comparison of oxygen permeability and carbon dioxide permeability of 50/50 NR/NBR blend with varying filler loading

7.3 Models for permeation

7.3.1 Theoretical prediction of polymer blends

Models such as Parallel model, Series model, Maxwell model and Brugmann

model have been applied to the blend system to predict the permeability

properties of gases in homogeneous and heterogeneous blends, on the basis of


blend morphology. Equation 7.4 represents the series model where the

components are considered to be arranged series to each other and equation

(7.5) represents the parallel model

= !"! + �"� .………. (7.4)

1 % = "! !% + "� �.% … … … … … . (7.5� .……….(7.5)

where P is the permeability of the blend, P1 and P2 are the permeabilities of

components 1 and 2, and φ1 and φ2 are the volume fractions of components 1

and 2, respectively.

Two theoretically based models, the Maxwell model and Bruggeman model

that were developed to describe transport properties in micro particulate

dispersion of one component in a continuous matrix of a second component

are also applied to fit the permeation data. The Maxwell model and

Bruggeman model given in equation (7.6) and (7.7) respectively corresponds

to a morphology with continuous and dispersed phase structure.

)*+,-. = )/ 011123 + 4∅.

6). )/7 8). )/7 93:;∅. <===> .……….(7.6)

)*+,-. = )/ ? ). )/% ;)*+,-. )/%(3;∅.�@ ). )/% ;3 AB4 .………. (7.7)

where Pblend is the blend permeability, Pc, is the permeability of the continuous

phase, Pd is the permeability of the dispersed phase, and φd is the volume

234 Chapter 7

fraction of the dispersed phase. Using pure component permeability values

for each penetrant in NR and NBR, the Maxwell and Bruggeman models

predict the dependence of permeability on blend composition. A comparison

of blend permeability for O2 values predicted by these models and

experimental data is shown in Fig 7.12. Maxwell Model is valid when the

dispersion of dispersed phase are uniformly maximised. The Bruggeman

model corresponds to a random packing of dispersed phases. The Maxwell

model fits quite well with the experimental value when both the phases are

continuous. For 50/50 and 30/70 blends the Maxwell model deviates from the

experimental data while the Bruggeman model fits well with the experimental

value at all other blend composition, predicting the random arrangement of

dispersed phase.

100/0 70/30 50/50 30/70 0/100

0

2000

4000

6000

8000

10000

Per

mea

bilit

y (g

/cm

2 /day

)

Blend composition (NR/NBR)

Experimental Series Parallel Maxwell Brugmann

Figure 7.12 Theoretical fiittng of the permeability values for different blends


7.3.2 Theoretical prediction of permeation for polymer blend nanocomposites

Now, to account for the polymer nanocomposite properties, there are several

models reported for predicting the properties of composite materials based on

the properties of the pure components and the morphology of the composite.

They all describe the decrease in permeability in polymer composite, based on

different aspects like tortuosity, orientation etc. Although several factors like

component properties, such as matrix type, volume fraction, filler aspect ratio,

filler orientation, and filler distribution determines the impermeability in the

case of filled system, it is the dispersion18 and distribution of nanoparticles in

the polymer matrix that influences the most in barrier properties. However,

the main factors behind the improvement in gas barrier properties are not yet

fully understood. The reason for the decrease in permeability is affected by

different factors. The factors which have decreased the permeablitiy can be

found out based on the theoretical equations predicted, based on different

factors.

One model for polymer filled system which describes the maximum decrease

in permeability is Nielsen model19. According to this theory, if the fillers are

impenetrable to a diffusing gas or liquid molecule, then the diffusing molecule

should follow a tortuous path, which is the ratio of the actual distance that a

penetrant must travel to the shortest distance that it would have travelled in the

absence of the layered silicate. It was predicted by Nielson that fillers with

large aspect ratio plate - like filler can dramatically reduce the permeability.

If the filler particles are substantially impenetrable to a diffusing gas or liquid

molecule, then the diffusing molecules must go around the filler particles. As

clays are crystalline materials, they are believed to increase the barrier

properties by creating a maze or “tortuous path” that restricts the progress of

236 Chapter 7

the gas molecules to pass through the polymer matrices19. According to this

theory, the addition of fillers reduce the gas permeability of polymers as per

eq. (7.8).

………..(7.8)

Where "s is the volume fraction of filler and L/2W is the aspect ratio of filler

particles, Ps and Pp represent the permeabilities of the nanocomposite and neat

polymer respectively.

Later Bharadwaj20 modified the model by correlating the sheet length,

concentration, relative orientation, and state of aggregation of the filler in the

polymer matrix. This model could thus give further direction in the design of

better barrier materials for nanocomposites. Bharadwaj predicted, using

equation 7.9 that the relative permeability (Ps/Pp) is a function of the silicate

sheet length. Bharadwaj modified the tortuosity factor to include the

orientational order (S), writing the relative permeability using equation (7.9)

………..(7.9)

According to Gulsev and Lusti 21the permeablility levels that can be obtained

with nanocomposites are dependent on two factors viz. a geometric factor that

reduces the permeability by increasing the diffusion pathways around the

platelets and changes in the local permeability due to molecular-level

transformations in the polymer matrix. Bhatia et al.22have reported the

increase of oxygen barrier properties of styrene-butadiene co-polymer

montmorillonite based nanocomposites, and attributed it to the increase of the

nanoclay/polymer interactions. These interactions would lead to a decrease of


the free volume and of the chain segment mobility. This decreases the mobility

of each polymer, forming a more compact structure with a smaller free volume

than normal polymeric membranes. Yang, et. al17 in their studies on super gas

barrier of all-polymer multilayer thin films, further reports that the interaction

between polymers will decrease the mobility of each polymer23, forming a

more compact structure with a smaller free volume, than normal polymeric

membranes. In these models, different parameters are considered viz. the

aspect ratio, the volume fraction of the impermeable phases, and the

orientation of the nanoclay platelets.

In the present study, of NR/NBR nanocomposites, the Bhardwaj model and

Nielsen model are considered to be more appropriate as it includes the

influence of parameters like aspect ratio, the volume fraction of the

impermeable phases and the orientation of the nanoclay platelets, according to

the equation (7.8) and (7.9) respectively.

The fitting of the experimental permeation data for both, the Neilson model

and Bhardwaj model is presented in Figure 7.13 and 7.14 respectively. The

two equations differ as explained earlier. For Bharadwaj the orientation of the

clay layers also is included in the tortuosity factor. Here, the orientation

represented as ‘S’ reduces to Neilson equation when the value of S= 1 i.e.

when there is a planar arrangement. An orthogonal arrangement is expected

when the value of S = -1/2 i.e. when there is negligible increase in the

tortuosity, the permeability will be almost similar to that of neat polymer24.

According to equation (7.9), the tortuosity factor (P1m=P1c) can be as high as

3–29-fold for impermeable platelets with fully dispersed aspect ratios of

100–300, at low mineral loadings25. While Bharadwaj concluded that if the

length (L) of the sheet like filler is >500 nm it will be orientated randomly

inside the matrix, it was more beneficial for the barrier properties than the case

238 Chapter 7

where the sheets were aligned perpendicular to the diffusing path. The two

models and their theoretical assumption are given in table 7.1.

Table 7.1:- The theoretical assumption of two models used.

The experimental data fitted to Nielson model is shown in Fig. 7.13(inset).

The fitted aspect ratio is found to be 138nm, which is appreciable compared

to the aspect ratio of montmorillonite clay which is reported as approx.

200nm26. Also it is reported that, for cloiste 10A, aspect ratio is 177.7 nm,

when a high degree of clay dispersion occurs and of approximately 300nm

when the clay is exfoliated in the polymer nanocomposite27-29. Comparing this

with the obtained value, it is suggested that the clay layers have dispersed to a

good extent, and have a high intercalation rate although it is not completely

exfoliated. Other parameters such as the interactions between polymer and

nanoclays and the stiffness of the polymer chain at the vicinity of the

nanoclays also should have influenced this factor. Based on the Bhardwaj

model (equation 7.9), it is observed that the aspect ratio is found to be 189nm

and the calculated order parameter is approximately equal to 0.5

(Fig. 7.14) (Inset). The obtained value of S suggests that the orientation of

clay platelets should have existed in between parallel and orthogonal

arrangement as it lies in between the two values viz 1 and -0.5. Both the data

fit reasonably well with the experimental results which proves that both


tortuosity and orientation of the clay platelets have influenced the permeability

of gas molecules through the NR/NBR clay nanocomposites. The TEM images

given in Fig. (7.15) also shows aspect ratio to be near to the calculated value

based on the Bharadwaj model.

0.000 0.005 0.010 0.015 0.020 0.0250.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 Model: Neilson Chi^2/DoF = 0.0032R^2 = 0.94092L/2W = 68.98 ±9.82

Rel

ativ

e pe

rmea

bilit

y of

O2

Volume fraction of nanoclay ( φ)

Figure 7.13 The experimental data fitted to Nielson model for 50/50 NR/NBR/O1Mt naocomposites with different clay loading

240 Chapter 7

0.000 0.005 0.010 0.015 0.020 0.0250.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0 Model: Bharadwaj

Chi^2/DoF = 0.00384R^2 = 0.94687L/2W = 63.12±13.9S = 0.47 ±0.05

Rel

ativ

e pe

rmea

bilit

y of

O2

Volume raction of nanoclay ( φ)

Figure 7.14 The experimental data fitted to Bharadwaj model for 50/50 NR/NBR/O1Mt naocomposiutes with different clay loading

Figure 7.15 TEM micrograph of 50/50(5) NR/NBR/O1Mt nanocomposites

Fig. 7.15 shows the aspect ratio of the nanoclay found from the TEM

micrographs using image j software. Both models could not be validated well

as there were changes in aspect ratio compared to theoretical prediction

although the experimental value could follow the same trend.


7.4 Conclusion

NR/NBR/cloisite 10A nanocomposite with 2,5, and 10 wt% of nanoclay were

prepared for different blend composition. Using TEM and SEM their

morphology was examined. Improvement in oxygen permeability was

significantly noticed for NR/NBR/Cloisite 10A nano composites with the

addition of O1Mt. However, the permeability was found to depend on the

blend composition, and permeation rate showed varied improvement with

different NR/NBR composition. Although, the stacks of clay and non-

uniform dispersion of clay particle was shown in the TEM micrographs, the

tortuosity path for the gas molecules was increased sufficiently to make a

significant improvement in gas barrier properties. The models for blends like

Maxwell model and Bruggemann model l were found to fit well with the

experimental values.of NR/NBR/cloisite 10A nanocomposites, and could

validate the Bharadwaj model and Nielson's model up to 5wt% of clay content.

For higher nanoclay loading, deviation from both was observed due to the

presence of clusters and agglomerates.

242 Chapter 7

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