Effect of Coupling Agents on Mechanical Properties and Morphology ...

Journal <strong>of</strong> Metals, Materials and Minerals, Vol.18 No.2 pp.131-135, 2008
<strong>Effect</strong> <strong>of</strong> <strong>Coupling</strong> <strong>Agents</strong> on Mechanical Properties and Morphology
<strong>of</strong> CaCO 3 -filled Recycled High Density Polyethylene
Nilubol PHUEAKBUAKHAO 1* , Walaiporn PRISSANAROON-OUAJAI 1
and Narumol KREUA-ONGARJNUKOOL 1
Department <strong>of</strong> Industrial Chemistry, Faculty <strong>of</strong> Applied Science,
King Mongkut’s University <strong>of</strong> Technology North Bangkok
Abstract
Received Nov. 24, 2008
Accepted Feb. 11, 2009
This research presents mechanical properties and morphology <strong>of</strong> recycled high density polyethylene
(r-HDPE) filled with 10 wt.% CaCO 3 . The influence <strong>of</strong> treatment <strong>of</strong> CaCO 3 with various coupling agents,
including stearic acid (SA), aminopropyltriethoxy silane (AMPTES), glycidoxypropyltrimethoxy silane
(GPTMS) and maleic anhydride grafted HDPE (MA-g-HDPE), was investigated. This study clearly
demonstrated that the addition <strong>of</strong> coupling agent to CaCO 3 modifies the mechanical properties <strong>of</strong> the r-
HDPE/CaCO 3 composites. It was also found that each coupling agent gives rise to increases in a particular
mechanical properties due to its characteristics. In the case <strong>of</strong> AMPTES, the best mechanical properties was
observed at 2 wt.% whereas GPTMS and MA-g-HDPE showed the best performance at 3 wt.% and 4 wt.%,
respectively. SEM micrographs <strong>of</strong> the fractured surfaces <strong>of</strong> the composites revealed a strong interfacial
interaction between r-HDPE and CaCO 3 , resulting in improvement <strong>of</strong> the fracture toughness.
Key words : <strong>Coupling</strong> <strong>Agents</strong>, Calcium Carbonate, Polyethylene/CaCo 3 Composite
Introduction
The
High density polyethylene (HDPE) is one
<strong>of</strong> the most widely used polymers, having a broad
amount <strong>of</strong> applications such as bottles, containers
and consumer goods, due to its superior stiffness, yield
strength and toughness and excellent environmental
stress cracking resistance. Post-consumer HDPE is
an interesting source <strong>of</strong> recycled materials and has
potential in a number <strong>of</strong> applications (Albano, et
al. 2000) however, the mechanical and impact
properties <strong>of</strong> the recycled HDPE (r-HDPE)
significantly decrease compared to the virgin
HDPE. Introduction <strong>of</strong> particulate inorganic fillers
generally enhances some mechanical properties,
such as Young’s modulus or yield strength, and
reduces the cost. The most common filler for
HDPE is CaCO 3 because <strong>of</strong> its stability, high
whiteness and low cost. (5) Although CaCO 3 improves
some mechanical properties mentioned above,
other important properties like toughness and
impact strength are usually degraded. (3, 7) Several
researches have reported that promotion <strong>of</strong> CaCO 3 -
polymer interaction would improve the tensile and
impact properties and has been achieved by surface
(10, 6, 4)
treatment <strong>of</strong> CaCO 3 with coupling agents.
purpose <strong>of</strong> this study was to investigate
the effect <strong>of</strong> adding CaCO 3 , treated with
various coupling agents, including stearic acid
(SA), 3-aminopropyltriethoxysilane (AMPTES),
3-glycidoxy propyltrimethoxy silane (GPTMS) and
maleic anhydride grafted HDPE (MA-g-HDPE), on
the mechanical behavior <strong>of</strong> the r-HDPE/CaCO 3
composites. The impact behavior in relation to the
morphology <strong>of</strong> the fractured surfaces <strong>of</strong> the r-
HDPE/CaCO 3 composites was also studied.
Materials and Experimental Procedures
Materials
r-HDPE (MFI: 7.92 g/10 min; 190 °C and
2.16 load) was supplied by S.D.C. Plastic Co., Ltd.
Two commercial CaCO 3 grades, untreated and SAtreated
forms, with particle size <strong>of</strong> 2 µm were
obtained from Surint Omya Chemicals Co., Ltd.
AMPTES and GPTMS, silane coupling agents,
were purchased from Italmar (Thailand) Co., Ltd.
MA-g-HDPE was provided by Dupont (Thailand)
Co., Ltd. The chemical structure <strong>of</strong> the coupling
agents are given in Table 1.
*Corresponding author : Nilubol Phueakbuakhao Tel. 02-9132500-24 ext. 4808,
Fax. 02-9132500-24 ext.4816 E-mail : pnilubol @ yahoo.com

132
PHUEAKBUAKHAO, N. et al.
Table 1. Chemical structure <strong>of</strong> the selected coupling agents.
Abbreviation Name Chemical structure
SA
AMPTES
GPTMS
Stearic acid
3-Aminopropyltriethoxy silane
3-Glycidoxypropyltrimethoxy silane
CH 3 -(CH 2 ) 15 -CH 2 -COOH
NH 2 -CH 2 -CH 2 -CH 2 -Si-(O-CH 2 -CH 3 ) 3
CH 2 -CH-CH 2 -O-CH 2 -CH 2 -CH 2 -Si-(O-CH 3 ) 3
O
MA-g-HDPE
Maleic anhydride grafted HDPE
CHCH 2
n
O
O
O
Surface Treatment <strong>of</strong> CaCO 3 with Silane <strong>Coupling</strong>
<strong>Agents</strong>. (2) Surface treatment <strong>of</strong> CaCO 3 was carried
out in the suspension containing 30 g CaCO 3 and
30 ml n-butanol. The desired volume <strong>of</strong> the silane
coupling agent, either AMPTES or GPTMS, to
reach 1, 2, 3, 4 and 5 wt.% compositions which
respect to CaCO 3 was added to the stirred
suspension. After being stirred for 3 h, the slurry
was left standing for 3 days. The solvent was
removed by vacuum evaporating and dried. The
treated CaCO 3 was put into saturated water vapor
atmosphere for 10
Preparation <strong>of</strong> r-HDPE/CaCO 3 Composites
The r-HDPE was blended with 10 wt.%
silane-treated CaCO 3 in a twin screw extruder at
190 °C. The composite pellets were compressionmolded
into specimens according to ASTM D256,
ASTMD638 and ISO 178.
In the case <strong>of</strong> using MA-g-HDPE as a
coupling agent, the required amount <strong>of</strong> MA-g-
HDPE to reach 1, 2, 3, 4 and 5 wt.% compositions
which respect to CaCO 3 was added to the mixture
<strong>of</strong> r-HDPE and untreated CaCO 3 before blending
in a twin screw extruder.
Characterization <strong>of</strong> r-HDPE/CaCO 3 Composites
The tensile and flexural properties were
determined using an Universal Test Machine
(LLOYD Instruments; LR 10 K). The tensile tests
were performed at a crosshead speed <strong>of</strong> 50
mm/min with a fixed gauge length <strong>of</strong> 50 mm. For
the flexural testing, a three point loading system
with a span <strong>of</strong> 64 mm was used and the crosshead
speed was set at 50 mm/min. The notched Izod
Impact strength was determined using a pendulum
energy <strong>of</strong> 10.96 J. The analysis <strong>of</strong> the fractured
surface <strong>of</strong> the specimens after the impact test was
carried out a using scanning electron microscope
(JEOL; JSM 5410 LV). Before observation, the
fractured surfaces <strong>of</strong> the tested specimens were
vacuum coated with a thin layer <strong>of</strong> gold to make
them electrically conductive.
Results and Discussion
Characterization <strong>of</strong> CaCO 3 Treated with AMPTES
and GPTMS
The characteristic spectra <strong>of</strong> CaCO 3 before and
after treatment with AMPTES and GPTMS are
presented in Figure 1 and Figure 2, respectively.
Table 2 presents the selected peals assignment. As
can be seen in Figure 1, the absorptions at 2926 cm -
1 and 2853 cm -1 attributed to the alkyl chains <strong>of</strong>
AMPTES are observed. In addition, there is an
increase in absorbance in these bands with the
increment <strong>of</strong> AMPTES content, suggesting more
coupling level. The peaks in the range <strong>of</strong> 1250-950
cm -1 assigned to Si-O-Si stretching vibration <strong>of</strong> the
polysiloxane structure, indicating the incorporation
<strong>of</strong> the silane coupling agent into CaCO 3 particles. (8)
The similar results are observed for GPTMStreated
CaCO 3 as shown in Figure 2.

<strong>Effect</strong> <strong>of</strong> <strong>Coupling</strong> <strong>Agents</strong> on
Mechanical Properties and Morphology
<strong>of</strong> CaCO
3 -filled Recycled High Density Polyethylene
133
untreated
1 wt.%
2 wt.%
3 wt.%
4 wt.%
5 wt.%
treatment <strong>of</strong> CaCO 3 improves the mechanical
properties, including tensile strength, flexurall
strength, impact strength and elongation at break,
<strong>of</strong> the r-HDPE/CaCO 3 composites, compared to
untreatment. By treatment with 1 wt.%
<strong>of</strong> different
coupling agents, SA-treated CaCO3 appears to
exhibit the greatest improvement in the
mechanical
properties <strong>of</strong> the r-HDPE/CaCO 3 composites,
particularly impact strength
are shown in Figure 3.
Table 3 Mechanical properties <strong>of</strong> r-HDPE/10
wt.% CaCO 3
composi ites. (CaCO 3 treated with 1 wt.% coupling
agents)
Figure 1. Infrared spectra <strong>of</strong> CaCO 3 treated with different
content <strong>of</strong> AMPTES.
untreated
1 wt.%
2 wt.%
3 wt.%
<strong>Coupling</strong>
agent
Tensile
strength
Flexural
strength
Impact
strength
(MPa)
(MPa)
(kJ/m 2 )
Untreated Stearic
acid
AMPTES GPTMS MA-g-
HDPE
14. .01
15. .68
15. .16
14. .98
15. .27
19.87 24.93 23.80 23.73 22.75 10.28
13.23
12.03
11.11
11.96
Elongationn
at Break
(%)
18.77
21.65
21.08
19.52
20.19
4 wt.%
5 wt.%
Figure 2. Infrared spectra <strong>of</strong> CaCO 3 treated with different
content <strong>of</strong> GPTMS.
Table 2. Assignment <strong>of</strong> characteristic bands in the FTIR
spec ctra <strong>of</strong> CaCO 3 treated with silane coupling agents
Wavelength
(cm -1 )
Functional group
2926 - CH 2 Strertching (Asymmetric Vibration)
- CH
2853
3 and
- CH 2 -C-H Strertching
(Symmetric Vibration)
1250-950 Si-O-Si (Polysiloxane) Si-O-Si Strertching
Mechanical
Properties <strong>of</strong>
r-HDPE/CaCO 3 Composites
Mechanical properties <strong>of</strong> r-HDPE/untreated
CaCO 3 and
r-HDPE/treated CaCO 3 compositess are
shown in Table 3. In this case, CaCO 3 was treated
with the fixed 1 wt.% <strong>of</strong> different coupling agents
and the amount <strong>of</strong> CaCO 3 blended to r-HDPE
matrix weighed <strong>of</strong> 10% %. It can be seen that surface
Figure 3. <strong>Effect</strong> <strong>of</strong> CaCO 3 treated with 1% different coupling
agents on the impact strength <strong>of</strong> r-HDPE/CaCO 3
composites.
This results may be expounded that a
strong chemical bonding between the polar group
<strong>of</strong> the stearic acid and CaCO 3 to form calcium
stearate enhances the compatibility <strong>of</strong> the polymer
matrix and CaCO 3 particles
resulting improvement
the
mechanical properties <strong>of</strong> composites can be
achieved, by changes hydrophilic <strong>of</strong> CaCO 3 to
hydrophobic. In
the case <strong>of</strong> other coupling agents
including AMPTES, GPTMS and MA-g-HDPE,
the
interactionn at interface areas between the
polymer matrix and CaCO 3 particles can be
achieved by van der waals forces, which are
relatively weak
compared to chemical bonds. Thus,
using a few concentrations <strong>of</strong> coupling agent,

134
PHUEAKBUAKHAO, N. et al.
chemical bonding can be improved the interaction
at interface areas between the polymer matrix and
CaCO 3 particles more than physical bonding or van
der waals forces.
Using other coupling agents at concentrations
<strong>of</strong> 2, 3, 4 and 5 wt.% to study the possibility <strong>of</strong>
increasing the polymer-CaCO 3 interaction. It was
found that the mechanical properties <strong>of</strong> composite
can be improved, especially impact resistance when
increase the concentrations <strong>of</strong> coupling agents.
Table 4 summarizes the mechanical properties
<strong>of</strong> the r-HDPE filled CaCO 3 treated with the
optimum concentrations <strong>of</strong> each coupling agent.
The results show that each coupling agent gives
rise to increase in a particular mechanical properties
due to its characteristics. The r-HDPE/treated-
CaCO 3 composites show the best mechanical
properties when CaCO 3 were treated with SA,
AMPTES, GPTMS and MA-g-HDPE at 1, 2, 3 and
4 wt.%, respectively. This behavior can be
explained based on the fact that increasing the
concentrations <strong>of</strong> coupling agents can improve the
interaction between the polymer matrix and CaCO 3
particle, which are physical forces or van der waals
forces as well as chemical forces but have to use
more concentrations. This indicates that selection
the type and quantity <strong>of</strong> coupling agents for the
composites is important to gets the optimum
property <strong>of</strong> final products.
and the surface was rather smooth. This shows that
the polymer matrix and CaCO 3 particles didn’t
restrain together. On the other hand, the rough
surfaces are observed for the r-HDPE/treated
CaCO 3 composites, as presented in Figure 4(b) -
Figure 4(e). This indicates the ductile fracture. The
morphologies <strong>of</strong> the fractured surfaces were
consistent with the impact strength listed in Table 2
and Table 3. High magnified SEM micrographs
(x3500) <strong>of</strong> the r-HDPE/CaCO 3 composites are
illustrated in Figure 5. Phase separation can be
seen when the untreated CaCO 3 was incorporated
in the r-HDPE matrix (Figure 5(a)). This
phenomenon is not visible when the treated CaCO 3
was used (Figure 5(b) - Figure 5(e)). The interfacial
interaction between the r-HDPE matrix and CaCO 3
particles was stronger, resulted from the
pretreatment <strong>of</strong> CaCO 3 particles. This would be
another reason for the improvement in the
mechanical properties, particularly impact strength,
<strong>of</strong> the r-HDPE/CaCO 3 composites. (9)
(a) untreated
Table 4. Mechanical properties <strong>of</strong> r-HDPE/CaCO 3
composites (CaCO 3 treated with optimum
content <strong>of</strong> coupling agents)
<strong>Coupling</strong>
Agent
Tensile
strength
(MPa)
Flexural
strength
(MPa)
Impact
strength
(kJ/m 2 )
Elongation
at Break
(%)
Untreated 14.01 19.87 10.28 18.77
1. wt%
Stearic acid
2. wt%
AMPTES
3. wt%
GPTMS
4. wt%
MA-g-HDPE
15.68 24.93 13.23 21.65
16.17 25.54 15.00 22.32
15.87 25.28 14.67 21.95
16.03 25.84 14.89 23.24
(b) 1 wt.% SA
(c) 2 wt.% AMPTES
Morphology <strong>of</strong> r-HDPE/CaCO 3 Composites
The fractured surfaces <strong>of</strong> the r-HDPE/CaCO 3
composites after the impact test were examined by
SEM. Figure 4(a) shows that the r-HDPE filled
with the untreated CaCO 3 exhibits brittle fracture
(d) 3 wt.% GPTMS
(e) 4 wt.% MA-g-HDPE
Figure 4. SEM micrographs (x500) <strong>of</strong> r-HDPE/CaCO 3
composites when CaCO 3 treated with different
coupling agents

<strong>Effect</strong> <strong>of</strong> <strong>Coupling</strong> <strong>Agents</strong> on Mechanical Properties and Morphology
<strong>of</strong> CaCO 3 -filled Recycled High Density Polyethylene
135
Bangkok is also thanks for partial financial
supports for this research.
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Conclusions
This study obviously demonstrated that the
pretreatment <strong>of</strong> CaCO 3 with the coupling agent
improved the mechanical properties <strong>of</strong> the r-
HDPE/CaCO 3 composites. Due to the particular
characteristics <strong>of</strong> the coupling agents, each one
showed rise to increases in a specific mechanical
property. In this study, the r-HDPE/treated-CaCO 3
composites exhibited the best mechanical properties
when CaCO 3 was treated with SA, AMPTES, GPTMS
and MA-g-HDPE at 1, 2, 3 and 4 wt.%, respectively.
SEM micrographs confirmed a strong interfacial
interaction between r-HDPE matrix and CaCO 3 ,
resulting in improvement <strong>of</strong> the fracture toughness.
Acknowledgment
(e) 4 wt.% MA-g-HDPE
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