Mechanical and Crystalline Behavior of Polymeric Nanocomposites in Presence of Natural Clay

doi:10.4236/ojapps.2012.24041

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Open Journal of Applied Sciences, 2012, 2, 277-282

doi:10.4236/ojapps.2012.24041 Published Online December 2012 (http://www.SciRP.org/journal/ojapps)

Mechanical and Crystalline Behavior of Polymeric

Nanocomposites in Presence of Natural Clay

Parthajit Pal1, Mrinal Kanti Kundu1, Swinderjeetsingh Kalra2, Chapal Kumar Das1*

1Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur, India

2Department of Chemistry, Dayanand Anglo-Vedic (D. A.-V.) College, Kanpur, India

Email: *[email protected]

Received October 1, 2012; revised November 2, 2012; accepted November 12, 2012

ABSTRACT

Fabrication of nanocomposites from immiscible polymer blend system has been represented in this work. A new type of

natural clay named Halloysite Nanotubes (HNTs) are modified by Polyethyleneimine (PEI) and these PEI grafted HNTs

are incorporated into the immiscible blend system during melt mixing process to prepare halloysite based nanocompo-

sites. Fourier Transform Infrared Spectroscopy (FTIR) study confirms the formation of PEI grafted HNTs. The nano-

composites are characterized by SEM for morphological study and, the dispersion manners of nanoclays by Transmis-

sion Electron Microscopy (TEM). Storage modulus is studied by Dynamic Mechanical Thermal Analysis (DMTA) in-

strument. The tensile measurement explored better tensile property of nanocomposites as compared to the virgin blend.

XRD is performed to determine the crystalline behavior of the nanocomposites as well as for blend. The above investi-

gations reveal that the HNTs act as reinforcing as well as nucleating agent in the blend system.

Keywords: Nanocomposite; Mechanical; Crystallinity; Halloysite; Polyethyleneimine

1. Introduction

Naturally occurring tubular halloysite clay has attracted

considerable interest of the researches due to its multi-

purpose features. This nanomaterial may be utilized as

nanofiller for polymers. Reinforcement of thermoplastic

matrices with HNTs has been studied extensively by dif-

ferent research groups. HNTs are used in polymeric

nanocomposites to develop the mechanical strength,

thermal stability, crystalline behavior etc of the polymers.

Generally, layered halloysite are obtained in two poly-

morphs: the hydrated form with 10 Å basal distances and

the anhydrous one with 7 Å basal distances. Halloysite

comprised of Al and Si at 1:1 ratio with molecular for-

mula of Al2Si2O5(OH)4·nH 2O, where “n” equals to 2 and

0, corresponding hydrated and dehydrated HNTs [1,2].

Kaolin has almost similar chemical composition to HNTs

but presence of interlayer water in HNTs makes it dis-

tinguishable from kaolin. Weakly bonded intercalated

water can be readily removed irreversibly. Halloysite has

high aspect ratio (L/D ratio). Its length and diameter varies

from 500 - 1000 nm and 15 - 100 nm respectively. Arti-

ficially, HNTs have not been synthesized yet. At the in-

ternal surface it contains gibbsite octahedral Al-OH

groups, and the outer surface contains SiO4 tetrahedra.

This difference results in acid-base properties for both

surfaces. At pH range 2 - 8, outer surface gets negatively

charged and inner lumen gets positively charged [3,4].

Grafting of HNTs can be done via covalent or non cova-

lent approaches [5]. Polypropylene (PP) is widely used

polymer worldwide due to its easy processibility and

relatively low cost. It has good mechanical and physical

properties, but its inferior properties (e.g. impact strength,

low UV resistance, brittle at lower temperatures etc.)

restrict its engineering applications. Many researchers

have paid their attention on properties of PP/HNT com-

posite [6-9]. Polyoxymethylene (POM), is also called

acetal or polyacetal or polyformaldehyde etc. It consists

of C-O backbone in main polymer chain [10]. This engi-

neering thermoplastic have good toughness, excellent fa-

tigue and creep resistance, high resistance to oxidative

degradation and susceptible to UV degradation [11].

Polyethyleneimine (PEI), is a cationic hydrophilic poly-

mer with amine groups [12]. Grafting of PEI had been

done in case of carbon nanotubes (CNTs) [13]. It can also

be used as a surface modifier for halloysites.

In the present work we have chosen PP and POM be-

cause both the polymers have comparable melting point

leading to almost similar processing temperature [7,10].

In order to have the reasonable properties we have melt

blended those polymers by melt mixing process in inter-

nal melt mixer. To gain better properties, raw HNTs have

been incorporated and nanocomposite prepared. Misci-

*Corresponding author.

P. PAL ET AL.

278

bility of this blend is not favorable so to overcome it,

surface treatment of HNTs were done with PEI, and PEI

grafted HNTs (gHNTs) are then melt mixed with the

blend system and hence modified nanocomposites fabri-

cated. We are mainly focusing on the mechanical prop-

erty and crystallinity of nanocomposites after addition of

raw HNTs/gHNTs.

2. Experimental

2.1. Materials

The PP of grade H030SG purchased from Reliance in-

dustries limited (India) and POM of the grade H2320 004

was received from BASF (Germany). HNTs were ob-

tained from Sigma-Aldrich (Germany) as nanopowder

and 50 wt% aqueous solution of PEI (Mn = 70,000) from

Aldrich, USA.

2.2. Surface Treatment of HNTs

At first 500 mg of HNTs were taken in 200 ml distilled

water and the suspension was dispersed in an ultrasoni-

cator for 20 min at room temperature. The solution pH

was then adjusted to 8 - 9 by adding NaOH solution. 2 ml

PEI solution was added to it and the whole solution was

heated at 60˚C under constant stirring for 24 h. Then the

reaction mixture was centrifuged for 20 minutes at an

rpm of 4000. After centrifugation, the obtained particu-

lates were washed with distilled water. The obtained

product were kept overnight for drying in vacuum at

80˚C and named as PEI grafted HNTs (gHNTs). Scheme

1 shows the schematic representation of the reaction.

2.3. Preparation of Blend and Nanocomposites

At first one batch of PP/POM at 80/20 w/w pure blend

was prepared (coded as S) by melt mixing process using

internal melt mixer at 190˚C and 40 rpm. Then unmodi-

fied nanocomposites (S-HNT) and modified nanocompo-

site (S-gHNT) were prepared via same way by incorpo-

rating raw HNTs and gHNTs. In the entire cases 80/20

w/w PP/POM ratio was maintained and HNTs/gHNTs

were taken only 1 wt% in each case for respective nano-

composite fabrication.

3. Results and Discussion

3.1. Fourier Transform Infrared Spectroscopy

(FTIR) Study

FTIR of the HNTs/gHNTs and nanocomposite were per-

formed using a Tensor 27 (Bruker, Germany) FTIR

equipment. FTIR graphs are shown in Figure 1, of which

(a) for raw HNTs (b) for gHNTs and (c) for S-HNT

nanocomposite. In this figure peaks come at 3692 and

3620 cm–1 in all of the three cases (a) - (c) due to OH

Scheme 1. Schematic representation of the surface treat-

ment of HNTs.

Figure 1. FTIR graphs of (a) raw HNTs; (b) PEI grafted

HNTs (gHNTs); and (c) HNTs filled nanocomposite (S-

HNT).

groups of HNTs, but peak intensities were not same for

all three, which indicates OH groups were engaged in

interaction between the modifier as well as blend matri-

ces to different extent. Interlayer H2O peak of HNTs was

observed at around 3482 cm–1. Beside these, gHNTs ac-

quired some additional peaks e.g. 3358 cm–1 which be-

longs to N-H stretching; 2933 and 2882 cm–1 attributed

to C-H asymmetric and symmetric stretching respec-

tively. Peaks due to N-H and C-H bonds were present in

case of PEI grafted HNTs but it was totally absent in case

of raw HNTs. This IR result gives such a hint that PEI

attached with HNTs. It was believed that negatively

charged OH groups of HNTs had a noncovalent physical

interaction with the H of NH2 group of PEI. But it was

very difficult to differentiate that peak because the peak

raised due to the interlayer water molecules of HNTs

(3482 cm–1) might suppress the peak accession due to the

interaction between HNTs and PEI. So from the above

results it can be said that PEI was grafted on the surface

of the HNTs [14]. Peak at around 2985 cm–1 at (c) for

S-HNT nanocomposite was due to C-H stretching vibra-

tion. Due to similarity with S-HNT curve, S-gHNT nano-

composite curve was not entrained in this figure.

3.2. XRD Analysis

XRD of the pure blend and nanocomposites were done

P. PAL ET AL.

279

SEM images of pure blend, composites and raw HNTs

are shown in Figures 3(a)-(e). The micrograph states

about the immiscibility of those two polymers. Certain

changes were found in those micrographs, Figure 3(a)

represents the pure blend where POM got dispersed in PP

matrix. Similar trend was also found in case of S-HNT

and S-gHNT nanocomposite (Figures 3(c) and (d)), as

the corresponding polymer ratio was constant.

with X-ray diffractometer (Rigaku XRD, Ultima-III, Ja-

pan). It was operated at 40 kV and 100 mA with nickel-

filtered CuKα line (λ = 0.15404 nm). Figure 2 shows the

XRD curves. It can be said that after addition of raw

HNTs % of crystallinity (χc) increases but further in-

crease on addition of gHNTs. Prashantha et al. [7] re-

ported on increase in crystallinity with incorporation of

modified HNTs. As per the previous researchers, addi-

tion of very low percentage (1 wt%) of HNTs do not

make any significant changes on peak positions [8]. The

highest intense peak (near at 23˚) and peak at its extreme

right (near at 34˚) appeared due to presence of POM [15];

and other peaks were due to PP [8]. It was clear that

HNTs behaved as nucleating agent and enhanced the

crystallinity of the nanocomposites. The percent of crys-

tallinity was calculated by using the Scherer’s equation.

Percent of crystallinity,



100

ccac

II I





(1)

where Ia and Ic are the integrated intensity of the amor-

phous and crystalline region respectively.

3.3. Scanning Electron Microscopy (SEM)

Analysis

The surface morphology of our prepared samples was

analyzed by JEOL SEM (JSM-5900 LV) with an ace-

lerating voltage of 20 kV. For conductivity, the fractured

surfaces of the samples were coated with thin layer of gold.

Figure 2. XRD curves of pure blend, HNTs filled nanocom-

posite and gHNTs filled nanocomposite (percent of crystal-

linity shown inset).

Figure 3. SEM micrograph of (a) Pure polymer blend of PP/POM 80/20 w/w (b) Raw HNTs (c) 1 wt% raw HNTs loaded

nanocomposite (d) 1 wt% gHNTs loaded nanocomposite and (e) High magnified micrograph of 1 wt% gHNTs loaded nano-

omposite. c

P. PAL ET AL.

280

After addition of raw HNTs few fibrillation was found

TEMf our samples were carried out by using

Around more than 4% nitrogen inclusion occurred. This

DMTas carried out by TA Instrument (DMA

the micrograph 3c. G. V. Vinogradov et al. showed the

fibrillation of POM [16]. Also after incorporation of

gHNTs, droplet sizes of POM reduced in S-gHNT nano-

composite which imply about the compatibility of

gHNTs. Micrograph 3e of S-gHNT was taken at high

magnification to have better idea about the morphology.

This micrograph stated the grafted HNTs were remaining

in between two polymer phases.

3.4. Transmission Electron Microscopy (TEM)

Analysis

analyses o

JEOL TEM (JEM-2100) at 200 kV. Nanocomposites

were cryogenically ultramicrotomed and taking the

thickness of about 300 nm, the powdered samples were

dispersed ultrasonically before the TEM analysis. In

Figure 4, TEM micrographs along with one EDAX are

shown. Figure 4(a) was for raw HNTs, Figure 4(b) for

PEI grafted HNTs. From Figure 4(b) micrograph it can

be seen that PEI was coated on the surface of HNTs.

Figure 4(c) was the TEM-EDAX for PEI grafted HNTs.

EDAX values gestured that nitrogen assimilation oc-

curred during the surface treatment of HNTs by PEI.

value was also in support of the FTIR results, i.e. grafting

by PEI modifier on HNTs surface. Figures 4(d) and (e)

represents the S-HNT and S-gHNT nanocomposites re-

spectively. It can be said from those micrographs that

agglomeration of raw HNTs were present in S-HNT

nanocomposite but this agglomeration disappears for

gHNTs in S-gHNT nanocomposite. This indicates the

dispersion of gHNTs were better as compared to the raw

HNTs of their respective nanocomposites.

3.5. Dynamic Mechanical Thermal Analysis

(DMTA)

A study w

2980) at single cantilever bending mode vibration. The

storage modulus (E′) was recorded at 1 Hz frequency at

temperature range –80˚C to 140˚C at the heating rate of 5˚C/

min. Experiment was conducted under purging of nitrogen.

Data on viscoelastic property of our prepared samples

are recorded and plotted, which are shown in Figure 5.

Graph stated that virgin blend had lowest storage modu-

lus and gHNTs filled nanocomposite had the highest one.

Reason behind this could be the dispersion of HNTs and

gHNTs. We noticed that (from TEM micrograph) raw

Figure 4. TEM micrograph of (a) raw HNTs (b) PEI grafted HNTs (c) TEM-EDAX of PEI grafted HNTs (d) raw HNTs filled

nanocomposite and (e) gHNTs filled nanocomposite.

P. PAL ET AL. 281

HNTs dispersion was poorer in comparison with gHNTs.

igher the agglomerations lower the surface areHa and

re performed by Houns-

g machine) tensile testing

ller distribution helps to im-

nanocomposites were fabricated via

vice versa, so better dispersion gives enough surface area

for load transfer to the halloysite. As dispersion of fillers

is a vital factor for the physical performances of the nano-

composites, S-gHNT showed the highest storage modu-

lus value among the others.

3.6. Mechanical Properti

Tensile test of the specimens we

field HS 10 KS (universal testin

machine maintaining ASTM standard D638, with cross-

head speed of 1 mm/min at room temperature (25˚C).

Micro hardness of the specimens were performed using

UHL VMHT (VH001), maintaining the load 25 gf (gram

force) and time 12 s. Tensile strength and hardness values

are summarized in Table 1.

Gradual increase in tensile strength as well as hardness

had been observed. In fact fi

ove mechanical properties. Consequently nanocompo-

sites can sustain maximum load. Load transfer was best

for S-gHNT nanocomposite thus it showed the highest

values in respective fields.

4. Conclusion

Virgin blend and

Figure 5. Storage modulus of (a) pure blend (b) raw HNTs

filled nanocomposites and (c) gHNTs filled nanocomposite.

anocomposites.

Table 1. Tensile strength and hardness value of blend and

Sample Code Tensile Strength (MPa) Hardness Value

S 32.4 18.05

S-T

S-gHNT 36.9 19.09

HN35.3 18.40

melt mixing technique. Mechanical properties and crys-

tallinity of these nanocomposites were investigated.

HNT as nucleatingt and therefore crys-

tallieases. It wasn that, HNTs after surface

“Structural, Electronic, and Mechanical Proper-

ties of Single-Walled Halloysite Nanotube Models,”

Journal of Phy 114, No. 26, 2010,

pp. 11358-1132e

s acted agen % of

nity incr show

treatment uniformly dispersed in blend matrices and re-

mains mainly in between two phases. Better dispersion of

gHNTs improves the ultimate performance of the nano-

composite.

REFERENCES

[1] L. Guimaraes, A. N. Enyashin, G. Seifert and H. A.

Duarte,

sical Chemistry C, Vol.

63. doi:10.1021/jp10090

[2] M. Du, B. Guo and D. Jia, “Newly Emerging Applica-

tions of Halloysite Nanotubes: A Review,” Polymer In-

ternational, Vol. 59, No. 5, 2010, pp. 574-582.

doi:10.1002/pi.2754

[3] R. D. White, D. V. Bavykin and F. C. Walsh, “The Sta-

4/23/6/065705

bility of Halloysite Nanotubes in Acidic and Alkaline

Aqueous Suspensions,” Nanotechnology, Vol. 23, No. 6,

2012, Article ID: 065705.

doi:10.1088/0957-448

, Vol. 134, No. 3, 2012, pp.

[4] W. O. Yah, A. Takahara and Y. M. Lvov, “Selective Mo-

dification of Halloysite Lumen with Octadecylphospho-

nic Acid: New Inorganic Tubular Micelle,” Journal of the

American Chemical Society

1853-1859. doi:10.1021/ja210258y

[5] C. Wan, M. Li, X. Bai and Y. Zhang, “Synthesis and

Characterization of Photoluminescent Eu(III) Coordina-

tion Halloysite Nanotube-Based Nanohybrids,” Journal

of Physical Chemistry C, Vol. 113, No. 36, 2009, pp.

16238-16246. doi:10.1021/jp9051648

[6] Z. H. Lin, M. Peng and Q. Zheng, “Isothermal Crystalli-

zation Behavior of Polypropylene Catalloys,” Journal of

Applied Polymer Science, Vol. 93, No. 2, 2004, pp. 877-

882. doi:10.1002/app.20501

[7] K. Prashantha, M. F. Lacrampe and P. Krawczak, “Pro-

ies,” eXPRESS Polymer Let-

cessing and Characterization of Halloysite Nanotubes

Filled Polypropylene Nanocomposites Based on a Mas-

terbatch Route: Effect of Halloysites Treatment on Struc-

tural and Mechanical Propert

ters, Vol. 5, No. 4, 2011, pp. 295-307.

doi:10.3144/expresspolymlett.2011.30

[8] N. Ning, Q. Yin, F. Luo, Q. Zhang, R. Du and Q. Fu,

“Crystallization Behavior and Mechanical Properties of

Polypropylene/Halloysite Composites,” Polymer, Vol. 48,

No. 25, 2007, pp. 7374-7384.

doi:10.1016/j.polymer.2007.10.005

[9] M. Du, B. Guo and D. Jia, “Thermal Stability and Flame

Retardant Effects of Halloysite Nanotubes on Poly (Pro-

pylene),” European Polymer Journal, Vol. 42, No. 6,

2006, pp. 1362-1369.

doi:10.1016/j.eurpolymj.2005.12.006

mine-Formaldehyde Polycondensate and Its Thermal Sta-

[10] Y. Hu, L. Ye and X. Zhao, “Synthesis of the Mela-

P. PAL ET AL.

282

bilization Effect on Polyoxymethylene,” Polymer, Vol. 47,

No. 8, 2006, pp. 2649-2659.

doi:10.1016/j.polymer.2006.02.050

ChemTec Publish-

r the Dehydration of

mparison with Glu-

logy, Vol. 48, No. 3, 2006, pp. 244-

[11] G. Wypych, “Handbook of Polymers,”

ing, Toronto, 2012.

[12] P. S. Rao, B. Smitha, S. Sridhar and A. Krishnaiah, “Pre-

paration and Performance of Poly(vinyl Alcohol)/Poly-

ethyleneimine Blend Membranes fo

1,4-Dioxane by Pervaporation: Co

taraldehyde Cross-Linked Membranes,” Separation and

Purification Techno

254. doi:10.1016/j.seppur.2005.07.031

[13] E. J. Petersen, R. A. Pinto, D. J. Mai, P. F. Landrum and

W. J. Weber Jr., “Influence of Polyethyleneimine Graft-

ings of Multi-Walled Carbon Nanotubes on Their Accu-

mulation and Elimination by and Toxicity to Daphnia

magna,” Environmental Science & Technology, Vol. 45,

No. 3, 2011, pp. 1133-1138. doi:10.1021/es1030239

[14] B. Gao, P. Jiang and H. Lei, “Studies on Adsorption

Property of Novel Composite Adsorption Material PEI/

SiO for Uric Acid,” Materials Letters, Vol. 60, No

200

. 28,

6, pp. 3398-3404. doi:10.1016/j.matlet.2006.03.086

[15] J. Wang, K. H. Hu, Y. F. Xu and X. G. Hu, “Structural,

Thermal, and Tribological Properties of Intercalated Poly-

oxymethylene/Molybdenum Disulfide Nanocomposites,”

Journal of Applied Polymer Science, Vol. 110, No. 1,

2008, pp. 91-96. doi:10.1002/app.28519

[16] G. V. Vinogradov and B. V. Yarlykov, “Fibrillation in the

Flow of Polyoxymethylene Melts,” Polymer, Vol. 16, No.

8, 1975, pp. 609-614. doi:10.1016/0032-3861(75)90156-1