Effect of Cenosphere Concentration on the Mechanical, Thermal, Rheological and Morphological Properties of Nylon 6

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 807-812

Published Online August 2012 (http://www.SciRP.org/journal/jmmce)

Effect of Cenosphere Conc entration on the Mechanical,

Thermal, Rheological and Morphologica l P ropert i e s of

Nylon 6

Parag A. Wasekar, Pravin G. Kadam, Shashank T. Mhaske*

Department of Polymer and Surface Engineering, Institute of Chemical Technology, Mumbai, India

Email: *[email protected]

Received April 14, 2012; revised May 28, 2012; accepted June 17, 2012

ABSTRACT

Cenospheres are widely used as filler in thermoset plastics and concrete mainly for density reduction of the material.

But there is no work noted of using cenosphere as filler in thermoplastics. In this paper cenosphere concentration was

varied from 0 to 10 phr of nylon 6 and the effect of the same on the mechanical, thermal, rheological and morphological

properties of the composite were studied. Elongation was found to have increased by 83% and impact strength by 44%

at 2.5 phr loading of cenosphere. Flexural strength increased upto 25% at 10 phr content of cenosphere.

Keywords: Nylon 6; Cenosphere; Crystallinity; Reinforcing Agent

1. Introduction

In the previous studies use of cenosphere is noted to de-

crease the density of the material, due to its micro-

spherical nature. Cenosphere is a hydrophilic material

and found in fly ash [1]. So, for its use as filler in poly-

mers like PP, HDPE, PS, it is surface treated to induce

hydrophobicity gi ving bet ter com patibil ity wit h the matri x.

Abdullah et al. utilized amine containing silicone as

toughening agent and hollow cenosphere as filler in ep-

oxy resin. Their study was to understand the microstruc-

ture formed and its influence on mechanical properties

and free volume measurements of the composite. Tensile

strength increased and tensile modulus decreased with

increase in cenosphere content up to 30%, due to low

density of the filler [2]. Gu et al. studied epoxy filled

with cenosphere surface treated with different chemicals.

Surface modified cenosphere were observed to have dis-

tributed uniformerly into the epoxy matrix. Surface

modified cenosphere had a wider glass transition tem-

perature region and a higher loss factor, and had rela-

tively higher impact toughness [3]. Deepthi et al. studied

the mechanical and thermal properties of high density

polyethylene filled with cenosphere. They used ceno-

sphere as filler after silane treatment, and also with a

compatibilizer [4]. Cardoso et al. studied the effect of

particle size and surface treatment o f cenosphere as filler

on the properties of polyester resin [5]. Huo et al. studied

the preparation of poly-o-phenylenediamine (POPD)/

TiO2/fly ash cenosphere composite and its photo-degra-

dation properties [6]. Chaliven dra et al. studied the proc-

essing and mechanical characterization of lightweight

polyurethane composites using cenosphere. Polyurethane

was loaded with cenosphere upto 40% and was tested for

mechanical properties to estimate the fracture toughness

of the material. Cenosphere decreased the density of the

composite. The high strain rate constitutive behavior of

100% polyurethane showed monotonic stiffening whereas

the composite at higher cenosphere volume fractions (40%)

exhibited a stiffening-softening-stiffening behavior, due to

easy flowability induced by cenosphere micros pheres [7].

In this paper, cenosphere was used as reinforcing agent

in nylon 6 matrix. Cenosphere and nylon 6 both are hy-

drophilic materials, so they possessed good compatibilit y

requiring no use of compatibilizer or surface treatment of

cenosphere. Cenosphere obtained was used as such and

loaded as 2.5 phr, 5 phr, 7.5 phr and 10 phr in the nylon

matrix, and tested for mechanical, thermal, rheological

and morphological properties. As cenosphere was used in

very low concentration to affect the density of the matrix

material, density measurement was not done.

2. Experimental

2.1. Materials

Nylon 6 for was obtained from Next Polymers Ltd.,

Mumbai, India. Cenosphere was procured from Nasik

thermal power plant (India) having chemical composition

as shown in the Table 1. Cenosphere was used as ob-

*Corresponding author.

P. A. WASEKAR ET AL.

808

tained without any purification or chemical modification

or surface treatment. Finalux G3 (wetting agent) was

obtained fr o m Fine Organics Ltd., M umbai, India.

2.2. Preparation of Composite

Concentration of cenosphere was varied upto 10 phr into

the nylon matrix. Firstly, dry blending of cenosphere and

nylon 6 was done in tumbler mixer for 15 - 20 min, using

finalux G3 as the wetting agent. Then the mix was melt

blended in a twin screw co-rotating extruder (Lab Tech

Engineering Co. Ltd., Germany) having L/D ratio of 32:1

and temperature profile from the hopper to the die as

170˚C, 190˚C, 200˚C, 210˚C, 220˚C, 230˚C, 240˚C and

250˚C. Extruded strands were water cooled at 30˚C and

pelettized. Pellets obtained were used for injection mold-

ing after pre-drying at 80˚C for 8 - 10 hrs. Injection

molding (Boolani machineries India ltd, Mumbai, India)

was done maintaining temperature profile as 210˚C,

230˚C and 250˚C from the hopper to the ejection nozzle.

Standard ASTM based samples for tensile, flexural and

impact testing were obtained from injection molding.

Samples for impact testing were notch cut before testing.

2.3. Characterization and Testing

2.3.1. Mechanica l Pro p e rties

Tensile properties; tensile strength and elongation at

break and flexural properties; flexural strength and flex-

ural modulus, were measured at ambient condition using

a universal testing machine (LR-50K, Lloyds Instrument,

UK), according to ASTM procedures D638 and D790; at

a crosshead speed of 50 mm/min and 2.8 mm/min re-

spectively. The notch for impact test was made using a

motorized notch-cutting machine (Polytest model 1, Ray

Ran, UK). Notched Izod impact strength was determined

at ambient condition according to ASTM D256 standard,

using impact tester (Avery Denison, UK) having striking

velocity of 3.46 m/s employing a 2.7 J striker.

2.3.2. Thermal Properties

Differential scanning calorimetry (Q 100 DSC, TA in-

struments Ltd., India) characterization was done to in-

vestigate the crystallization and melting behaviour of the

composite. Two consecutive heating scans were found to

minimize the influence of possible residual stresses in the

material due to any specific thermal history. Scanning

rate of 10˚C/min was maintained for both heating and

cooling cycle; whereas nitrogen gas purge rate main-

tained at 50 ml/min. Melting temperature was determined

from the second heating scan while the crystallization

temperature (Tc) from cooling scan.

2.3.3. Rheological Properties

The melt viscosity was measured using rotational rheometer

(MCR101, Anton Paar, India) with parallel plate assem-

bly having diameter of 35 mm. Samples were predried

before analysis. Viscosity was determined for sh ear rates

from 0.01 s–1 to 100 s–1 at the constant temperature of

250˚C.

2.3.4. M orp hologica l Properties

Scanning electron microscope (SEM) analysis was per-

formed with JEOL 6380 LA (Japan). Samples were frac-

tured under liquid nitrogen to avoid any disturbance to

the molecular structure and then coated with gold before

imaging.

2.3.5. X-Ray Diffr ac tion

The XRD analysis was carried out to determine the per-

centage crystallinity of the prepared co mposite. A normal

focus copper X-ray tube was operated at 30 kV and 15

mA. Sample scanning was done from 2.00˚ to 80.00˚ at

the rate of 3.00˚/min. The data processing was done us-

ing Jade 6.0 software.

2.4. Formulation

The formulations prepared are as shown in the Table 2.

Concentration of cenosphere was varied from 0 to 10 phr

of nylon 6, while concentration of wetting agent was

maintained constan t at 5 phr of nylon 6.

Table 1. Chemical composition of cenosphere obtained from Nasik thermal power plant.

Components Al2O3 SiO2 P

2O5 SO3 K

2O CaO TiO2 V

2O5 Fe2O3

wt% 24.559 50.300 0.409 0.060 6.765 1.109 5.129 0.102 11.566

Table 2. Formulation of cenosphere/nylon 6 composites.

Sr. No. Sample Name Nylon 6 (gm) Cenosphere (phr, gm) Wetting Agent (phr, gm)

1 VNY 500 0.0, 0.0 5, 25

2 NC 2.5 500 2.5, 12.5 5, 25

3 NC 5 500 5.0, 25.0 5, 25

4 NC 7.5 500 7.5, 37.5 5, 25

5 NC 10 500 10.0, 50.0 5, 25

P. A. WASEKAR ET AL. 809

3. Results and Discussion

3.1. X-Ray Diffrac tio n

X-ray diffraction pattern of the composites are shown in

the Figure 1; whereas percentage crystallinity of the

composites are noted in Table 3. It was found that per-

centage crystallinity was least for 2.5 phr cenosphere

loaded nylon 6; and increased with increase in ceno-

sphere concentration. But, percentage crystallinity re-

mained lower than the base polymer even for 10 phr

cenosphere loaded nylon 6.

Cenosphere and nylon 6 both are hydrophilic material,

providing better compatib ility between the two materials.

But, the intermolecular forces of attraction between the

nylon 6 polymer chains are better than that between ny-

lon 6 and cenosphere. Due to the micro-spherical nature

of cenosphere, nylon 6 polymer chains come in contact

with cenosphere only at a single tangential point or may

be a little more, depending on the molecular arrange ment.

But, the chance of nylon 6 chains to completely cover the

surface of cenosphere is negligible.

At 2.5 phr concentration of cenosphere, particles are

uniformly dispersed in the nylon 6 matrix. So, the num-

ber of nylon 6 polymer chains contacting cenosphere

tangentially at one point is more. Also, the spherical na-

ture of the cenosphere remained intact at lower concen-

tration, increasing flowability of nylon 6 polymer chains

onto each other. As the concentration of cenosphere in-

creased, it started forming agglomerates, decreasing the

spherical nature of the cenosphere. This decreases the

flowability of nylon 6 molecular chains over it, increas-

ing crystallinity. Due to agglomerate formation, the con-

tact area between cenosphere and nylon 6 also increases,

making nylon 6 polymer chains to align more properly

increasing crystallinity.

3.2. Mechanical Properties

Mechanical properties; tensile, flexural and impact strengths,

are reported in Table 4. Tensile strength remained nearly

constant with incre ase in ceno sph ere con cen tr ation, where as

tensile modulus, elongation at break, impact strength,

flexural strength and flexural modulus increased.

Elongation at break was highest for 2.5 phr cenosphere/

nylon 6 composites and started decreasing with increase

in concentration. But, even for maximum cenosphere

content, elongation is still higher than virgin nylon 6.

Impact strength was also highest for 2.5 phr cenosphere.

Impact strength is proportional to elongation property of

the material. At 2.5 phr cenosphere content elongation at

break increased by 83% and impact strength by 44%.

Impact strength decreased with increase in cenosphere

content. But, even for maximum cenosphere content, it

was still higher than virgin nylon 6. X-ray diffraction

showed lowest crystallinity for 2.5 phr cenosphere/nylon

6 composites. This correlated with the increase in elon-

gation at break and impact strength of the material.

Figure 1. X-r ay differaction pattern of nylon 6 and nylon 6/

cenosphere composites.

Table 3. Percentage crystallinity of the ny lon 6 a nd nyl on 6/

cenosphere composites.

Sr. No. Sample Name Crystallinity (%)

1 VNY 5.15

2 NC 2.5 4.49

3 NC 5 4.58

4 NC 7.5 4.83

5 NC 10 4.99

Table 4. Mechanical properties of nylon 6 and nylon 6/cenosphere composites.

Sr. No. Sample

Name Tensile Strength

(MPa) Tensile Modulus

(MPa) % E @ BreakImpact Strength

(J/m) Flexural Strength

(MPa) Flexural Modulus

(MPa)

1 VNY 51.25 1937.8 90.94 56.46 70.66 2455.4

2 NC 2.5 57.93 2061.8 165.71 81.17 72.88 2521.7

3 NC 5 53.29 2277.1 119.57 70.83 87.32 3020.5

4 NC 7.5 49.59 2303.0 119.13 68.33 88.88 3121.3

5 NC 10 50.35 2330.8 79.53 71.50 88.37 3123.3

P. A. WASEKAR ET AL.

810

More amorphous the material b ecomes, better it is able

to transfer the impact force, without undergoing cracking.

This increases the impact strength of the material. The

spherical nature of the cenosphere was thus best utilized

for increasing amorphous characteristic of the nylon 6.

Flexural strength increased with increase in cenosphere

content. For 10 phr cenosphere/nylon 6 composite, flex-

ural strength was found to have increased by about 25%.

3.3. Thermal Properties

Heating and cooling scans of the nylon 6 and nylon 6/

cenosphere composites are shown in Figures 2 and 3

respectively. Table 5 reports enthalpy of melting, melt-

ing temperature, enthalpy of crystallization and crystalliza-

tion temperature of nylon 6 and nylon 6/cenosphere com-

posites.

Enthaply of heating was found to be least for 2.5 phr

cenosphere/nylon 6 composites, and started increasing

with increase in cenosphere content. But, enthalpy of

composite containing highest cenosphere content was

still less than that of the virgin nylon 6. Even en thalpy of

crystallization gave the same trend. Melting temperature

and crystallization temperature didn’t change appreciably

with change in cenosphere content. Enthalpy of the mate-

rial is proportional to the crystallinity, thus 2.5 phr ceno-

sphere/nylon 6 showed lowest enthalpy of melting, which

increased with cenosphere concentration. While enthalpy

of crystallization increased with increase in cenosphere

content.

3.4. Rheological Properties

Figure 4 shows the rheological properties of nylon 6 and

nylon 6/cenosphere composites. It was found that, at

lower shear rate viscosity of nylon 6 and nylon 6/ceno-

sphere composites is same, but at higher shear rate differ-

ence becomes prominent. Viscosity of nylon 6 was found

to be highest, while that of 2.5 phr cenosphere loaded ny-

lon 6 composites was found to be lowest. Viscosity in-

creased with increase in cenosphere content, but even at

maximum loading it was lower than the base polymer.

Lowest viscosity at 2.5 phr loaded cenosphere is due

to maximum amorphicity and flowability th at it posseses.

Viscosity increased with increase in cenosphere concen-

tration. This correlates with the increase in crystallinity

as shown by X-ray diffraction, mechanical properties and

thermal properties. Also as cen osph ere con tent in crea sed,

it started forming agglomerate, decreasing the spherical

nature of the material. This decreased the flowability of

the composite material, increasing viscosity. All samples

showed drastic shear thinning after the shear rate of 10.

Zero shear viscosity of all the sample was also found to

be nearly same, i.e. at 1000 Pa·s.

Figure 2. Heating scan of vergin nylon 6/cenosphere com-

posites.

Figure 3. Cooling scan of virgin nylon 6/cenosphere com-

posites.

Table 5. Thermal properties of nylon 6 and nylon 6/cenosphere composites.

Sr. No. Sample Name Enthalpy of

melting (J/g) Melting temperature

(˚C) Enthalpy of

crystallization (J/g) Crystallization

temperature (˚C)

1 VNY 69.16 221.23 82.92 192.65

2 NC 2.5 46.68 222.26 48.43 193.50

3 NC 5 59.64 223.24 61.04 191.02

4 NC 7.5 65.61 221.81 65.02 191.16

5 NC 10 66.13 223.24 80.32 191.71

P. A. WASEKAR ET AL. 811

Figure 4. Viscosity vs shear rate graph of nylon 6/ceno-

sphere composites.

Figure 5. SEM image of 2.5 phr cenosphere loaded nylon 6

at 5000× showing particle size distribution.

(a) (b)

Figure 6. Showing particle size of (a) SEM image of 2.5 phr cenosphere loaded nylon 6 at 20000×; (b) SEM image of 5 phr

cenosphere loaded nylon 6 at 5000×; (c) SEM image of 7.5 phr cenosphere loaded nylon 6 at 5000×; (d) SEM image of 10 phr

cenosphere loaded nylon 6 at 5000×.

3.5. Morphological Properties

Morphological properties of the cenosphere/nylon 6

composites were found using scanning electron micros-

copy (SEM). SEM images of 2.5 phr cenosphere/nylon 6

lon 6 composites showing cenosphere particle size, 5 phr

composites showing dispersion, 2.5 phr cenosphere/

r cenosphere/ny-

here/nylon 6 com-

pectively.

3.9 to 4.2 µm, as

nosphere content, ny-

cenosphere/nylon 6 composites, 7.5 ph

lon 6 composites and 10 phr cenosp

posites are show n in Figures 5 and 6 res

Particle size of cenosphere is about

evident from Figure 6. At 2.5 phr ce

P. A. WASEKAR ET AL.

812

cenosphere are un iformly distributed in th e nylon matrix,

giving better flowability to the nylon 6 matrix. As the

cenosphere content increases in the nylon 6 matrix, it

forms agglomerate, increasing particle size. Increase in

agent in nylon 6. By use of cenosphere as

n nylon 6 matrix, elongation at break

pact strength by 44%; at 2.5 phr

NCES

Materials Charing, Vol. 1, No. 1,

rticle size is gradual with increase in cenosphere con-

centration.

4. Conclusion

Cenosphere has always been used as a material to reduce

the density of the material due to its micro-spherical na-

ture. However, cenosphere can be effectively used as

reinforcing

reinforcing agent i

increased by 83%, im

content. Flexural strength increased with increase in

cenosphere content. Flexural strength increased by 25%

at 10 phr cenosphere content. Cenosphere decreased crys-

tallinity and also increased flowability of nylon 6. No

change in tensile strength of the composites was ob-

served with change in cenosphere content.

5. Acknowledgements

The authors gratefully acknowledge the financial support

from The University Grant Commission under the SAP

scheme for their financial support.

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