Materials Sciences and Applications, 2011, 2, 481-485
doi:10.4236/msa.2011.25065 Published Online May 2011 (
Copyright © 2011 SciRes. MSA
The Potential of Silane Coated Calcium Carbonate
on Mechanical Properties of Rigid PVC
Composites for Pipe Manufacturing
Amin Al Robaidi1, Ahmad Mousa1*, Sami Massade h 1, Ibrahim Al Rawabdeh2, Nabil Anagreh1
1Materials Department, Al-Balq'a Applied University, Salt, Jordan; 2Industrial Engineering Department, University of Jordan, Am-
man, Jordan.
Received July 7th, 2010; revised November 3rd 2010; accepted May 12th, 2011.
The inclusion of CaCO3 and kaolin in polyvinyl chloride (PVC) polymer matrices greatly enhances the physical and
mechanical properties of the composite. In this study, the effects of kaolin and surface treatment of CaCO3 and kaolin
particles on the microstructure and mechanical properties of PVC composites filled with kaolin particles via melt
blending method were studied by means of SEM, tensile, Charpy impact testin g. Treated and un treated kaolin particles
were dispersed in matrices of PVC resin at different conc entrations up to 30wt percentage. The tens ile strength, elastic
modulus, strain to failure and morphology of the resulting composites were measured for various filler loadings. Uni-
form dispersion of the fillers into the matrix proved to be a critical factor. SEM images revealed that small sized par-
ticles were more agglomerated than micron-sized particles and the amount of agglomerates increased with increasing
particle content. Silane treated Kaolin-CaCO3/PVC composites had superior tensile and impact strengths to untreated
kaolin-CaCO3/PVC composites. The Youngs modulus of all composites increased with increasing particle content up to
maximum a t 10% filler loading followed by gradually decreasing as content increased.
Keywords: Polyvinyl Chloride)/Calcium Carbonate (PVC/) Nano-Composite, Particle Size, Melt Blending, Tensile
Testing, Charpy Impact
1. Introduction
Kaolin and calcium carbonate has long been recognized
as useful additives for thermoplastics and particularly in
PVC for many applications. Ground kaolin and calcium
carbonate are generally used as filler with an interesting
ratio performance/price. The specific structure allows this
material to fulfill additional functions like Processing aid,
impact modification and better weather ability. Its regular
and controlled crystalline shape and ultra fine particle size
together with the hydrophobic surface coating combine to
the benefit of both polymer processing and subsequent
physical properties. PVC is the second most consumed
polymer right after PE. This low-cost material has nu-
merous advantages, such as a high modulus, excellent
chemical resistance and easy conversion. The addition of
low-cost fillers such as calcium carbonate or talc was his-
torically justified by the cost reduction; however, perfor-
mance improvements and other benefits brought by the
use of these materials are the cause of its increasing use in
PVC systems [1-5]. The major challenge in plastic rein-
forcement is to reach an optimal balance between Young
Modulus and Impact resistance [6-9]. The most favorable
balance could be obtained by a good control of dispersion
and adhesion between the filler and polymer matrix as
shown in Figure 1. Increasing filler percentages after
exceeding a certain concentration will significantly affects
impact resistance and modulus of elasticity [4,9]. There-
fore treating of the filler to achieve a better dispersion and
increase filler matrix compatibility is targeted. Silane is a
material of choice due to its ability to form grafting spe-
cies with the polymer matrix and its availability as a
commercial product.
2. Experimental
Sample Preparation:
Different PVC samples were prepared using brabender
plastograh. Batches were produced by the addition of one
pack stabilizer system in the mixing station followed by
The Potential of Silane Coated Calcium Carbonate on Mechanical Properties of Rigid PVC Composites
for Pipe Manufacturing
Copyright © 2011 SciRes. MSA
Figure 1. Balanced conditions in PVC systems between
Charpy Impact and Young modulus (schematic).
adding different percentages of kaoline and CaCO3 un-
treated and with silane treated, as listed in Table 1 be-
low. One pack stabilizer system manufactured by DSM
was used and kept constant by 3% concentration through
out all formulations. During the mixing step torque and
fusion time were measured, that reflects rheological be-
haviour of the compound. Compounding temperature
was kept const at 190˚C for all samples prepared. All
ingredients were added to the PVC matrix in accordance
to their weight percentage to the Brabender Sigma mixer
and were mixed for (4) minutes at 100 rpm and 140˚C,
the samples weights were measured using SCALTEC
accurate balance. When mixing was completed, 2 mm
thickness sheets were made using a hot press. Tensile
samples according to ASTM 3039 were cut from the
sheets for mechanical testing. The probes were subjected
to mechanical testing using Ektron tensile testing ma-
chine and to charpy impact test using a Ciest im-
pact-testing machine. It is will none that particle size has
a significant impact on the mechanical properties. Choos-
ing CaCO3 small particle size was selected to reach good
mechanical performances. The CaCO3 particle size, com-
mercial grade with an average particle size of 5 micron
was used. Kaolin particle size was around 0.2 - 0.5 mi-
crons. Disadvantage of fine particle, is its ability to ag-
glomerate during the manufacturing process. However,
to get that total benefit, care must be taken to disperse
them correctly in the polymer matrix.
Dispersion quality affects the final agglomerate size in
the polymer: an optimal dispersion is one that evenly
distributes throughout a polymer down to the smallest
units, the aggregates, a poorer dispersion results in larger
agglomerates (Figure 2), moreover, affects finally the
mechanical properties.
To have improved and more homogenous distribution,
the filler particles were treated with silane. Moreover,
Table 1. Formulation prepared in this study.
weight % % CaCO3 Impact
modifier %
treated with
100 ref ref - -
97 3 0 0 no
97 3 0 0 yes
95 5 0 0 no
95 5 0 0 yes
90 10 0 0 no
90 10 0 0 yes
87 10 3 3 no
80 20 0 0 yes
80 20 0 0 no
77 20 3 3 no
70 30 0 0 no
70 30 0 0 yes
Figure 2. Primary particles fuse together in the reactor and
form aggregates and agglomerates.
treating of the particles with silane was aimed to im-
proved compatibility with the PVC matrix. SEM photo-
graphs in Figure 3 shows CaCO3 particle agglomeration;
when the CaCO3 was treated with silane (Figure 3), a
homogenous distribution was achieved. The treatment of
the filler was conducted by placing 250 g in the oven at
90˚C, for 15 minutes, then the addition of silane using
micropipette at weight percentages of 2.5% and letting
the mix in the oven at 90˚C, for 30 minutes. Every 5 mi-
nutes the mix were taken out from the oven and shacked
3. Results and Discussion
3.1. Mechanical Testing
Determination of tensile strength, elongation and impact
strength are essential in examining the materials behavior
The Potential of Silane Coated Calcium Carbonate on Mechanical Properties of Rigid PVC Composites
for Pipe Manufacturing
Copyright © 2011 SciRes. MSA
Figure 3. Show the distribution after CaCO 3 was treated with silane and particle agglomeration before silane treating.
under engineering conditions. As indicated in Figure 4
below, the Impact strength did increase significantly with
CaCO3 content up to approximately 10%, followed be a
sharp decrease of Impact resistance. It should be noticed
that because of influence of filler effect, impact strength
did increase slightly, but there was a considerable de-
crease of elongation at break. The explanation of this
positive behaviour can be found in both the processing
improvements that synthetic calcium carbonate provides
along with its ability to improve the dispersibility of oth-
er components of the formulation i.e. organic impact
modifiers.UTS and elongation changed as the percentag-
es of calcium carbonate changes as well. That change
was negligible for UTS but more severe in elongation as
it could bee seen in Figures 5 and 6.
3.2. Rheological Behaviour of Dispersion
Fusion test were carried out using Brabender plastograph.
Some results are shown in the plots below. The degree of
Figure 4. Impact strength versus Calcium Carbonate for
rigid PVC designated for electrical pipe extrusion.
gelation is a measure of the breakdown of the PVC grain
structure and its transformation into a homogenous ma-
trix. If the PVC is under gelled or over gelled, poor
physical properties will result. Kaolin and CaCO3, be-
cause of its very small particle size and surface coating
generates fast, efficient fusion in PVC formulations. The
Figure 5. Ultimate Tensile Strength versus content for rigid
PVC designated for electric al pipe ex tr usion.
Figure 6. Elongation at break versus content for rigid PVC
designated for electrical pipe extrusion.
The Potential of Silane Coated Calcium Carbonate on Mechanical Properties of Rigid PVC Composites
for Pipe Manufacturing
Copyright © 2011 SciRes. MSA
more complete gelation that results from the inclusion of
calcium carbonate provides a matrix that in comparison
to natural PVC has fewer defect sites and opportunities
for a crack propagation process leading to reduced me-
chanical properties.
The fusion time measured for untreated samples was
around 24 minutes (Figure 7), whereby a 36 minutes
fusion time for the silane treated samples as shown in
Figure 8, showing different rheological behaviour, was
obtained. Increasing fusion time indicates more stabile
compounds. This is an indication for more stable com-
pound and longer resident time in polymer extrusion.
Further, it is an indication to obtain ductile failures with
reduced impact modifier levels.
4. Conclusions
Filler treatment with silane resulted in a better dispersion
of the filler particles in PVC matrix and had a good in-
terfacial cohesion. A little amount of particles agglome-
ration and some cavities were found after treatment,
while a lot of agglomeration and cavities occurred when
filled with untreated particles. Treated samples had lower
equilibrium torque, higher tensile strength and bet-
ter-notched impact strength. The notched impact strength
of tested samples reached 26.5 kJ/m2, which was about
4 times as high as that of neat PVC, by 10/100 mass ratio
of /PVC. Kaolin particles stiffen and toughen PVC si-
multaneously, and optimal properties were achieved at
Figure 7. Fusion time of 10% content for rigid PVC designated for electrical pipe extrusion.
Figure 8. Fusion time of silane coated 15% content for rigid PVC designated for electrical pipe extrusion.
The Potential of Silane Coated Calcium Carbonate on Mechanical Properties of Rigid PVC Composites
for Pipe Manufacturing
Copyright © 2011 SciRes. MSA
10-wt% of CaCO3 particles in Young’s modulus, tensile
yield strength, elongation at break and Charpy notched
impact energy. Detailed examinations of micro-failure
micro mechanisms of impact and tensile specimens
showed that the CaCO3 particles acted as stress raisers
leading to debonding/voiding and deformation of the
matrix material around the particles. These mechanisms
also lead to impact toughening of the composites.
The tensile and impact strengths of CaCO3/PVC greatly
increased with decreasing CaCO3 particle size, which
was attributed to increased interfacial contact area and
enhanced interfacial adhesion between filler particles and
PVC matrix. Silane kaolin-CaCO3/PVC composites had
superior tensile and impact strengths to untreated ones.
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