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

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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