Open Journal of Applied Sciences, 2012, 2, 277-282
doi:10.4236/ojapps.2012.24041 Published Online December 2012 (
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: *
Received October 1, 2012; revised November 2, 2012; accepted November 12, 2012
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.
Copyright © 2012 SciRes. OJAppS
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-
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
Copyright © 2012 SciRes. OJAppS
Copyright © 2012 SciRes. OJAppS
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,
where Ia and Ic are the integrated intensity of the amor-
phous and crystalline region respectively.
3.3. Scanning Electron Microscopy (SEM)
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
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)
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
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.
Copyright © 2012 SciRes. OJAppS
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.
Table 1. Tensile strength and hardness value of blend and
Sample Code Tensile Strength (MPa) Hardness Value
S 32.4 18.05
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-
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