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Chapter 6 P a g e | 113

Effect of Barium Sulphate Nanofiller on the Properties of PP/LDH Nanocomposites

ABSTRACT

Poly(propylene) (PP)/layered double hydroxide (LDH) composites with

addition of barium sulphate (BaSO4) nanoparticles were prepared by melt

compounding with Brabender Plastograph EC. The effect of incorporation of barium

sulphate nanoparticles on PP/LDH composites was studied with respect to

mechanical, thermal and morphological properties. Nano barium sulphate particles

were synthesized by in situ precipitation method. Universal testing machine (UTM),

Izod impact tester and hardness tester were used to test mechanical performance of

composites and it was compared with pristine poly(propylene) matrix. Flammability

study of the prepared nanocomposites was carried out using UL-94 method.

Thermogravimetric analyzer (TGA) was used to asses thermal stability of the

nanocomposites. The morphology of bare nanoparticles and nanocomposites was

studied using Scanning Electron Microscopy (SEM). In the conclusion, the

incorporation of barium sulphate (BaSO4) nanoparticles at 3 phr modified the

mechanical properties of nanocomposites.



6.1 INTRODUCTION

Addition of nanofillers as strengthening agent in polymer matrix has played an

important role in the past few years because of their considerable improvement in

physical, mechanical and thermal properties compared to their quantity[1-3]. The

assimilation of inorganic fillers into organic binding matrix resulted into high stiff and

strength which is one of the important classes of polymer composites[4]. Sometimes

conventional fillers are necessary to add in order to increase volume and reduce cost

of final polymeric products[5]. To enhance specific properties of composites,

conventional fillers require high filler loading which may affects on other mechanical

performance of composites. On the contrary, nanofillers at lower loading are able to

improve performance than conventional fillers[6-8]. This is because small size of

filler provides more surface area available for interfacial interactions of it with

polymer matrix resulting into improvement in performance of subsequent

composites[9, 10]. Properties of composites depend on the size, shape, content and

type of fillers used[11, 12]. As per the definition, fillers having at least one dimension

in the range of 1–100 nm are considered as nanofillers[13]. It has been observed that

enhancement in stress transfer between materials with complementary properties, or

an increase in the density of shear deformation event may be due to the nano effect

over microstructure materials[14]. Conventionally, micro sized natural fibers and

glass fibers have been used for the preparation of polymer composites because of their

low cost, high tensile strength, high chemical resistance, low density and insulating

properties. However, they have limitations in processing due to abrasion, thermal

stability and moisture sensitivity.

Poly(propylene) is one of the most useful commodity polymers because of its

property profile suitable for applications in diverse fields such as automotive, home



appliances, fibres, electronics and construction[15-17]. Another reason behind its

suitability over expanded applications may be its flexibility towards properties and

applications[18]. Easy processing, high softening point, low cost as compare to its

weight, easy availability and low density made it more favourable engineering

material in commercial aspects and research fields[19-23].

Nanoclay has been used as a reinforcing agent in polymer matrix because of

low abrasion, high strength and thermal stability. It has advantages of melt mixing

with polymer matrix i.e. addition of such filler do not require organic solvents, hence

melt compounding is eco-friendly and mostly adopted for preparation of

composites[24, 25]. In recent years, use of LDH in polymer composites has attracted

more attention of researchers due to their high versatility, easy tailorable properties

and low cost[26]. The presence of unique physical, thermal and chemical properties

of LDH has enlarged claims of polymer composites in many applications[27].

Moreover, LDH reinforced polymer composites deserve good thermal, mechanical

and flame retardant properties[28-30].

In our previous work, effect of nano zinc phosphate as synergist filler in

PP/LDH nanocomposites has been studied to improve flame retardancy, mechanical

and thermal properties of pristine poly(propylene)[31]. Positive effect of nano zinc

phosphate as a synergistic filler and many advantages of barium sulphate over other

conventional fillers, inspired us to study effect of barium sulphate as a synergistic

filler in a poly(propylene) composites. Hence, in the present report, nano zinc

phosphate has been replaced by barium sulphate nanofiller. Barium sulphate is one of

the mineral fillers having commercial potential due to good whiteness, reasonable

price and excellent chemical resistance[32-34]. However, the use of nanofiller suffers



from agglomeration that can break and well dispersed by applying high shear force

during melt mixing of them with polymer matrix[35, 36].

6.2 EXPERIMENTAL

6.2.1 Materials

Poly(propylene) (Repol D120MA) was obtained from Reliance Industries Ltd., India.

Barium chloride and ammonium sulphate (Analytical grade) were purchased from

Loba Chemicals Pvt. Ltd., India. LDH was purchased from Sigma Aldrich.

Poly(ethylene glycol) [PEG] with a molecular weight of 6000 g/mol was purchased

from S. D. Fine Chemicals, India.

6.2.2 Synthesis of Nano Barium Sulphate

Nano size barium sulphate was synthesised by an in situ precipitation technique with

some modifications as per the previous reports[37, 38].

The general reaction for synthesis of BaSO4 and actual process used are given below.

BaCl2 + (NH4)2 SO4 BaSO4 (Nano size) + 2NH4Cl.

Barium chloride (BaCl2, 208 g) was dissolved in distilled water (100 mL).

Similarly PEG, (372 g) was dissolved separately in water (200 mL). Both BaCl2 and

PEG solutions were mixed in 1:6 ratio with constant stirring and kept for 12 h for

digestion. A solution of ammonium sulphate (132 g) was prepared by dissolving in

distilled water (100 mL). The first complex was then added slowly to the ammonium

sulphate solution under constant stirring and the reaction mixture was kept as such for

12 h. The BaSO4 nanoparticles obtained in the form of precipitate were separated by

filtration and washed number of times with water. The nanoparticles were finally

washed with acetone to remove the water and to disperse the nano BaSO4 particles.

Dispersion was subjected to ultra-sonication for one hour in order to break



agglomerates present in BaSO4. After breaking agglomerates of BaSO4, dispersion

was filtered and dried again.

6.2.3 Melt Compounding of PP/LDH/BaSO4 Nanocomposites

Melt compounding of the PP/LDH/nano barium sulphate composites was performed

by means of a Brabender Plastograph EC, Germany. The Plastograph used has an

electrically heated mixing head with two non-interchangeable rotors and it is fully

computerised controlled. Processing conditions like temperature, rotor speed and

blending time were selected as 1900C, 60 rpm and 10 min respectively for all samples

and all these parameters were controlled through software provided by the

manufacturer. Maximum 90% (55 cm3) capacity of hopper was used to fill up the

mixing chamber with components of the nanocomposites to be prepared[39]. Initially

PP was melted and then other ingredients were homogeneously mixed into it. After

mixing components for 10 min, the mixing chamber was allowed to cool to room

temperature and output was removed from it.

Table 6.1: Compositions of prepared nanocomposites

Sample Code Component Composition

(phr)

B1 PP 100

B2 PP + LDH 100+2

B3 PP + LDH +BaSO4 100+2+1

B4 PP + LDH +BaSO4 100+2+3

B5 PP + LDH +BaSO4 100+2+5

The output (in the form of lumps) of all compositions was coarsely grinded

using a laboratory grinder. These samples were then injection molded into dumb-bell

shaped specimens of uniform size and thickness using a Joy Baby Injection Moulding,



Ahmedabad, India, which were further used to check performance of nanocomposites.

The compositions of samples are given in the Table 6.1.

6.3 CHARACTERIZATION

6.3.1 Mechanical Strength and Flammability

Mechanical properties tested for composites are tensile strength, impact strength,

hardness and flammability test was carried out as described in Chapter 5.

6.3.2 Thermogravimetric Analysis (TGA)

The thermal analysis of composites was performed by a thermogravimetric analyser

(TGA-4000, Perkin Elmer, USA) as described in Chapter 2.

6.3.3 Dynamic Mechanical Analysis (DMA)

Dynamic mechanical analysis of PP/LDH/barium sulphate nanocomposites was

carried out as described in Chapter 4.

6.3.4 Scanning Electron Microscopy (SEM)

The surface morphology of tensile fractured samples from pull out test was tested as

discussed in Chapter 2 for studying size of nanoparticles and morphologies of

nanoparticles as well as nanocomposites. The nanoparticles of BaSO4 were dispersed

in acetone and ultrasonicated before characterization by SEM.

6.4 RESULTS AND DISCUSSION

6.4.1 Scanning Electron Microscopy of Nano Barium Sulphate

The scanning electron microscopic image of barium sulphate is shown in the Fig. 6.1.

From the image, it was observed that barium sulphate has rod shape morphology.

These rods had size in the range of 50-200 nm.



Fig. 6.1: SEM image of barium sulphate

6.4.2 Tensile Strength

Table 6.2: Properties of nanocomposites

Sample

Code

Tensile Strength

(MPa)

Impact Strength

(KJ/m2)

Hardness

(Shore-D)

Flammability

(mm/min)

B1 30 3.86 55 43.0

B2 40 6.67 57 38.0

B3 42 6.75 58 37.5

B4 43 7.37 59 35.7

B5 41 6.28 59 36.5

The Figure 6.2 is a graphical representation of tensile strength of nano BaSO4

filled PP/LDH nanocomposites and numerical values of the same are given in the

Table 6.2. The results showed that addition of LDH enhances tensile strength of PP

composites as compared to pristine PP matrix. This may be attributed to reinforcing

effect of LDH on PP matrix. This enhancement was more noticeable when nano

barium sulphate was used in PP/LDH composites from 1 to 3 phr or in some cases 1

to 4 phr. The presence of BaSO4 in PP/LDH composites has increased the tensile



strength of composites because enough amount of stress could have been transferred

throughout the sample instead of concentrating at particular point as stress can be

transferred from the matrix to inorganic nanoparticles and vice-versa. The reduction

of tensile property was detected with addition of 5 phr barium sulphate that may be

caused by aggregation of nanoparticles which provides less surface area for the

interacting particles of filler with polymer matrix than under separated condition.

Fig. 6.2: Tensile strength of nano BaSO4 filled PP/LDH nanocomposites

6.4.3 Impact Strength

Impact strength of nano BaSO4 filled PP nanocomposites is given in the Table 6.2 and

graphically represented in the Fig. 6.3. Impact strength of PP nanocomposites was

varied with change in filler content i.e. LDH with nano BaSO4. Results showed that

the impact strength of the PP nanocomposites was higher than pristine PP matrix in

the case of LDH and it was further increased with an increase in nano BaSO4 up to 3

phr. This may be due to impact energy applied can be well distributed throughout the

polymer matrix and it is not concentrated at particular area which can result into

formation of localized weak spots that decrease impact strength. At higher loading of

0

5

10

15

20

25

30

35

40

45

B1 B2 B3 B4 B5

Ten

sile

Str

ength

(M

Pa)

Sample Code

Tensile Strength



nanofiller i.e. for 5 phr the agglomeration of nanofillers might be responsible behind

deviating from linear increase in the properties of PP nanocomposites.

Fig. 6.3: Impact strength of nano BaSO4 filled PP nanocomposites

6.4.4 Hardness

Fig. 6.4: Hardness of nano BaSO4 filled PP nanocomposites

Graphical and numerical values for hardness of PP nanocomposites are given in the

Table 6.2 and Fig. 6.4 respectively. From the results, it can be concluded that the

0

1

2

3

4

5

6

7

8

B1 B2 B3 B4 B5

Imp

act

Str

ength

(K

J/m

2)

Sample Code

Impact Strength

53

54

55

56

57

58

59

B1 B2 B3 B4 B5

Samples

Hardness Shore-D



hardness of all compositions of PP nanocomposites was increased with addition of

both LDH individually and LDH with nano BaSO4. This change was significant when

LDH was added with nano BaSO4. The increase in hardness may be due to presence

of hard discontinuous phase i.e. LDH and BaSO4 as well as proper dispersion of

nanofillers in PP matrix.

6.4.5 Flammability by UL-94

Fig. 6.5: Flammability of PP/LDH/Barium sulphate nanocomposites

The graphical representation of flammability studied by UL-94 method of

PP/LDH/barium sulphate nanocomposites is shown in the Fig. 6.5. From the results it

was observed that the pristine PP showed fast burning nature than PP

nanocomposites. LDH loading resists burning speed of composites because water

molecules generated from LDH at elevated temperature achieved by burning of PP.

Synergism observed when LDH was added with barium sulphate, where the flame

retardant property was further improved. This may be due to addition of inorganic

nanoparticles into polymer matrix. However, at higher phr loading the difference was

almost same as that of 3 phr filler.

0

10

20

30

40

50

B1 B2 B3 B4 B5

Fla

mm

ab

ilit

y (

mm

/min

)

Sample Code

Flammability



6.4.6 Dynamical Mechanical Analysis (DMA)

Graphical presentation (Fig. 6.6) of storage modulus of nanocomposites showed that

it was lowest for pristine polymer among all nanocomposites. Enhancement in storage

moduli was observed when 2 phr LDH were incorporated into polymer. Enhancement

in storage modulus of nanocomposites was significantly increased after addition of

barium sulphate as secondary filler than LDH filled and pristine composites. This

shows synergistic effect in case of storage modulus when both fillers were

incorporated into polymer. Enhancement in storage modulus was continued upto 3 phr

loading of barium sulphate and at 5 phr the storage modulus was decreased, further

decrease in storage modulus may be due to formation of agglomeration; which is a

tendency of nanoparticles at higher concentrations.

Fig. 6.6: Storage modulus of PP nanocomposites

0 100 200 300 400 500 600 700

0

20000

40000

60000

80000

100000

Sto

rage

Mod

ulus

, G'M

Pa

Frequency cm-1

B1

B2

B3

B4

B5



6.4.7 Thermogravimetric Analysis (TGA)

Fig. 6.7: Thermogravimetric analyses of PP nanocomposites

The Fig. 6.7 demonstrates thermal behavior of representative samples containing

pristine PP, PP/LDH and PP/LDH/BaSO4 nano-composites. All three composites

showed single stage degradation. Pristine PP showed least thermal stability among

them, while thermal stability has increased with the addition of nano LDH.

Difference was also slightly high when nano BaSO4 was added into the composites.

Eventhough, the difference was not that much high but it was noticeable when

composites were incorporated with nano BaSO4. It was concluded that thermal

stability of nano-composites was increased with addition of LDH because the

presence of LDH has tendency to delay degradation.



6.4.8 Scanning Electron Microscopy (SEM)

The Fig. 6.8 contains representative SEM images of 1 phr and 5 phr nano BaSO4

reinforced PP nano-composites.

Fig. 6.8: SEM of PP/LDH nanocomposites containing a) 1 phr and b) 5 phr nano

BaSO4.

Although it has been mentioned in number of reports, that presence of small

amount of filler is able to improve the performance of composites and well dispersed

nanoparticles can only be able to give higher performance. The micrograph of 1 phr

barium sulphate loaded nano-composites showed smooth surface of the composites

and uniform dispersion of the nanoparticles in the composites. When concentration of

barium sulphate has increased, nanoparticles were sometimes aggregated and pull out

from the matrix surface due to poor dispersion. Hence, it can be concluded that

uniform dispersion of BaSO4 at lower amount was obtained and it decreased for 5 phr

filler. This may be one of the reason for not increasing the tensile strength at high

loading of filler.



CONCLUSION

PP nanocomposites were prepared by reinforcing LDH and nano BaSO4 by melt

mixing on the Brabender Plastograph EC. The results showed that mechanical

properties and thermal properties of nanocomposites were increased by addition of

nanoparticles. However, these results were more significant when they were added

combinely and acted cooperatively on the performance. The synergism in flame

retardant property was observed with addition of LDH and barium sulphate

nanofillers. Flame retardancy was not much more affected at high phr loading of

barium sulphate. PP/LDH nanocomposites improved mechanical performance up to 3

phr and decreased at 5 phr nano BaSO4 filler loading may be due to aggregation.



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