Journal of Minerals & Materials Characterization & Engineering, Vol. 5, No.1, pp 1-19, 2006
jmmce.org Printed in the USA. All rights reserved
1
Utilization of Granite Powder as a Filler for Polybutylene
Terepthalate Toughened Epoxy Resin
H. V. Ramakrishna and S. K Rai*
Department of Polymer Science, Sir M.V.P.G Center, University of Mysore
Tubinakere Industrial area, Mandya, Karnataka, INDIA 571402
*Correspondence Author’s Email: [e-mail]
Abstract:
Granite powder filled epoxy and polybutylene terephthalate (PBT) toughened epoxy
composites were prepared. The variation of the mechanical properties such as tensile, flexural,
compressive strengths and impact with filler content was evaluated. The effect of the silane
coupling agent on the properties of these composites and the chemical resistance and water
absorption of these composites was studied. The composites with 50% granite powder showed
better properties.
Keywords: Granite powder, PBT, toughening, tensile, flexural, compression,
Impact, chemical resistance, composites
INTRODUCTION
Epoxy is widely used as a matrix material for making many composites.
However, it is brittle in nature and has poor resistance to crack propagation [1].
Many investigators have used various toughening agents with epoxy, such as liquid
amine terminated [2], carboxyl terminated [3] and hydroxyl terminated [4]
copolymers of butadiene and acryloitrile. Recently many investigators are using
thermoplastics as toughening agents for epoxy. Among them, polybutylene
terephthalate (PBT) is found to be effective due to its phase transformation
toughening mechanism [5].
In order to reduce the cost of the composites, cheaper, naturally occurring
fillers such as CaCO
3
, silica, talc, clay [6], flyash [7], cellulose based fillers [8],
and kaolin [9,10] have been widely used. Utilizing locally available resources is a
cost effective source of filler material. For example, granite powder is generated in
large quantities during the sizing of granite slabs. The authors used this waste
granite powder generated by the local industries as filler in epoxy and PBT
toughened epoxy. The authors determined the mechanical properties of these
composites and studied their variation with filler content. The authors also studied
the chemical resistance and water absorption of these composites to assess their
performance.

2 H. V. Ramakrishna and S. K Rai Vol.5, No.1
EXPERIMENTAL
Materials
In the present work, a commercially available epoxy resin DGEBA procured
from M/s Vantico Ltd. Bombay was used as the polymer matrix. Triethylene
tetramine was used as the hardener. The coupling agent triethoxy methyl silane, for
modifying the granite powder, was procured from E Merck. Commercially
available PBT was obtained from local suppliers. Granite powder was collected
from local granite industries. The particle size of the granite powder ranged from 1
to 100 micrometers and the chemical composition is given in Table 1.
Preparation of the Composites
The granite powder was washed thoroughly with water then dried in an oven
at 120
o
C for 2h to remove any moisture before using it as filler for epoxy resin. A
1% solution of the silane coupling agent in acetone was used with 100gm of filler.
The granite powder was mixed with the coupling agent solution for 30 minutes to
ensure uniform distribution of the coupling agent. The treated granite powder was
then dried at 60
o
C in an oven for about 1 h to allow complete evaporation of the
acetone. The density of the granite powder was found to be 2.19 as determined by
ASTM standard.
For blending of PBT and epoxies, the PBT pellets were dissolved in
dichloromethane and the solution was poured to the beaker containing epoxy resin.
The amount of PBT in epoxy resin was varied from 1 to 4 % by weight. Above this
content, the epoxy resin became highly viscous. The resin to hardener ratio was
maintained at 100:10 parts by weight as suggested by the manufacturer. The
dichloromethane was evaporated by heating resin mixture at 80
o
C. After complete
evaporation of the dichloromethane, the mixture of PBT and epoxy resin was
stirred at 150
o
C continuously for 1h and then cooled to room temperature. Before
curing, the mixtures were degassed and poured into moulds. The epoxy and
hardener system was cured at room temperature for 24 h and then post cured at 100
o
C for 2 h to ensure complete curing.
Testing of Composites
Laminates of the composites under study were made by room temperature
curing for 24 hours in a 260x130x3 mm Teflon mould. The laminates were cut to
the required specimen size as per the ASTM standards for mechanical testing. All
the samples were post cured at 100
0
C in an oven for 2h to ensure complete curing
before subjecting them to mechanical testing. The specimens were also made in
the presence of the coupling agent.

Vol.5, No.1 Utilization of Granite Powder as a Filler 3
The tensile, compressive and flexural modulus and strength were
determined using a Lloyd’s LR 100 KN type universal testing machine. The impact
tests of the un-notched specimens were carried out using an Izod impact tester. For
each test, ten specimens of each type were used and the average value is reported.
The chemical resistance of the blend matrix and the composites was studied
as per ASTM D 543 method. For this purpose, two strong acids (conc. HCl and
conc. HNO
3
), lactic acid, and glacial acetic acid; aqueous solutions of 40% NaOH,
and 20% of Na
2
CO
3
; and three organic solvents (benzene, carbon tetrachloride, and
toluene) were selected. The pre-weighed samples were dipped in chemicals for
24h, removed, washed thoroughly with distilled water and dried immediately by
pressing them on both sides by filter paper. The final weight of the samples and
percentage weight loss/gain was determined. The chemical test was repeated for
ten samples in each case and the average value was reported.
For the water absorption test, rectangular specimens with dimensions of
25.4mm x 76.2 mm were cut from the laminates. Three replicate specimens were
tested and the results are presented as average. The samples were dried in an oven
at 50
o
C for 24 h, cooled in a decicator and immediately weighed to the nearest
0.001gm. In order to measure the water absorption of the composites, all samples
were immersed in water for about 24 h at room temperature as described in ASTM
D 570 – 99 (ASTM 1999) procedure. Excess water on the surface of the samples
was removed before weighing. The percentage increase in weight during
immersion was calculated to the nearest 0.01% as follows.
Wet Wt. – Reconditioned Wt.
Increase in weight % = X 100
Reconditioned Wt.
RESULTS AND DISCUSSION
In order to optimize the content of PBT in toughening the epoxy, blends with
different percentages of PBT were prepared and their mechanical properties
determined. These values are presented in Table 2. From this data it is evident
that the tensile, flexural, compressive and impact strength are maximum when the
PBT content is 2% in the blend. At 2% PBT content, the increment in tensile,
flexural, compressive and impact strength over the pure epoxy matrix are found to
be 51.7%, 17.5%, 53.7% and 33.3% respectively. When the PBT content was
increased above 2%, the mechanical parameters decreased. This behavior may be
due to the fact that as the fraction of PBT in epoxy increases, the dispersing phase
of PBT in the epoxy rich matrix increases, which hinders the cross linking of

4 H. V. Ramakrishna and S. K Rai Vol.5, No.1
epoxy with amine hardener thereby decreasing the total strength of the system.
Thus 2% PBT is found to be optimum for effective toughening of epoxy.
The variation of tensile strength, modulus and % elongation at break of the
composites with untreated and coupling agent treated granite in epoxy and with
coupling agent treated granite powder in 2% PBT toughened epoxy is shown in
Figs. 1-3 respectively. From these figures, it is evident that in all these cases, the
tensile properties are found to increase with filler content up to 50 % and decreased
beyond this content. The increase in the tensile properties with filler content (up to
50%) may be due to the restriction of the mobility and deformability of the matrix
with the introduction of mechanical restraint, and the filler particle size. Most
investigators have enumerated that particle size is inversely related to reinforcing
character and that an increase in surface area (as a consequence of reduced particle
size) increases the composite mechanical properties [11,12]. Simultaneously, the
higher stiffness of granite powder as compared to the epoxy matrix in which the
filler is dispersed may also contribute to the above enhancement. The decrease in
the tensile properties beyond 50% filler content may be due to the non-wetting of
the filler particles with the matrix and the non-uniform distribution of filler
particles in the cured matrix. Further, it is observed that the coupling agent on the
filler and PBT in the matrix improved the tensile strength and modulus. Besides,
from Fig.3, it is found that the % elongation at break decreased with filler content.
This is understandable as the filler is stiffer than the matrix.
The variation of flexural strength, flexural modulus, compressive strength,
and compressive modulus for the composites under study with filler content are
presented in Figs 4, 5, 6, and 7 respectively. From these figures it is evident that
the flexural and compressive properties are higher when coupling agent and PBT
were used in the composites. The coupling agent is expected to improve the stress
transfer between the matrix and the filler by the formation of a stronger
filler/matrix interface. A similar observation was made by Wong et.al [13] in the
case of flyash/polypropylene composites.
The trend of the variation of flexural and
compressive properties with filler is similar to that of the variation of tensile
properties. Further, the enhanced compressive strength properties of the
composites over that of the matrix may be due to the stiff nature of the filler. In
addition, the presence of PBT and platelet shape of granite powder might have also
contributed to such an increase [6]. It was assumed that the space between the
granite powder particles was filled with the blend matrix, thus minimizing the
presence of voids and bubbles and leading consequently to an increase in both
strength and modulus.
Incorporation of a rigid filler may enhance or deteriorate the impact
properties of composites [14,15]. Impact strength is an indication of tolerability for
a sudden impact. When a composite is subjected to an impact, rapid crack

Vol.5, No.1 Utilization of Granite Powder as a Filler 5
propagation is initiated through the material. When such crack propagation
encounters a filler particle in the filled composite, the filler can absorb the energy
and stop the crack propagation if the filler-matrix interaction is strong. On the
other hand, if the interfacial adhesion is poor, the filler particle cannot resist crack
propagation as effectively as the polymer alone and consequently a catastrophic
crack propagates, lowering the impact strength of the composite as loading
increases. In the filled composites, as the filler loading increases the tendency for
agglomeration also increases. As filler agglomeration increases, interfacial
adhesion becomes weaker leading to weaker interfacial regions. These
agglomerates act as stress concentration points or crack initiation sites. Therefore
reduction in impact strength with increasing filler content is expected.
The variation of the impact strength of the untreated and coupling agent
treated granite in epoxy and the coupling agent treated granite in 2% PBT
toughened epoxy is shown in Fig. 8. Here also it is observed that the impact
strength is higher when the filler was treated with the coupling agent and the
matrix was toughened with PBT. It is also observed that in all cases the impact
strength increased up to 50% filler loading and decreased with further increment in
the filler content. This is due to the fact that the 50% filler content is the maximum
filler content and, as said earlier, for further increments the impact strength
decreased. The increased impact strength in the case of 2% PBT toughened epoxy
treated granite powder composite is due to increased toughness from introducing
PBT into the epoxy matrix, thereby reducing the brittleness of the epoxy resin. The
increase in toughness of PBT toughened epoxy seems to arise from a combination
of processes that include primary crack bridging, crack bifurcation, crack path
alteration, formation of steps and welts and secondary crack bridging. Other factors
include ductile fracture of the dispersed PBT particles in epoxy rich matrix and
phase transformation mechanisms [16]. According to Griffth’s theory, a large
aggregate is a weak point, which lowers the stress required for the composite to
fracture. As Nakagawa and Sano [17] have shown, the presence of fine particles
dispersed with in the matrix make plastic deformation easier. So, during the
fracture of a composite in which the mineral filler is fine and well dispersed, i.e., in
which the material is more homogeneous, the stress will have to be bigger to start a
micro crack on a particle and impact energy will largely be absorbed by plastic
deformation. Hence, good filler dispersion resulting from the coupling agent
treatment leads to better impact strength of the composites. This observation
clearly suggests that 2% PBT toughened epoxy treated granite powder composites
have better toughness characteristics over untreated and coupling agent treated
granite powder/epoxy composites.
The percent weight gain (+) or weight loss (-) data for untreated and
coupling agent treated granite powder/epoxy composites immersed in various

6 H. V. Ramakrishna and S. K Rai Vol.5, No.1
chemical are presented in Table 3. These values for coupling agent treated granite
powder/PBT toughened epoxy composites are presented in Table 4. From Table 3,
it is clearly evident that weight gain is observed in both the untreated and coupling
agent treated granite powder composites. In the case of coupling agent treated
granite powder composites, less weight gain is observed when compared to
untreated granite powder composites. These results indicate that the addition of the
coupling agent is bringing the components closer; as a result, close packing is
ensured in the composites. Generally, close packing enhances the chemical
resistance of the materials. From Table 4, it is evident that when epoxy was
toughened with 2% PBT weight gain is observed when composites were immersed
in acetic acid, hydrochloric acid, nitric acid and lactic acid whereas weight loss
was observed when composites were immersed in solvents and alkalis. This weight
loss may be due to the slight removal of PBT, which is slightly soluble in organic
solvents. The weight gain is understandable as cross-linked systems form three-
dimensional networks that are chemically more stable.
Water absorption behavior of polymer-filler composites in a particular
environment is determined by factors such as processing techniques, matrix and
filler characteristics, polymer: filler ratio, and duration of immersion in water. The
variation of water absorption by untreated and coupling agent treated granite
powder/epoxy and coupling agent treated granite powder/PBT toughened epoxy is
presented in Fig. 9. From the figure, it is evident that the water absorption is lower
when epoxy was toughened with PBT. Further, the presence of the coupling agent
also decreased water absorption. The lower water absorption results indicate that
the added coupling agent is bringing the components closer. As a result, close
packing of filler and matrix is ensured and the presence of the thermoplastic PBT
results in lower water absorption of these composites.
CONCLUSSION
Toughening epoxy resin with 2wt% PBT enhanced tensile, flexural,
compression and impact properties. The enhancement was prominent in strength of
all the composites, which showed improved matrix filler adhesion by the coupling
agent. The mechanical properties of the composites under study were maximized at
50% granite powder filler content. The composites prepared had good chemical
resistance and lower water absorption.
REFERENCES
1. H.Lee and K. Neville, Hand book of Epoxy resins, Newyork; McGraw-
Hill, 1967
2. G.Levita, A.Marchelli and Bertha E , Polymer, 26 (1985) 1110
3. S.C.Kunz, J.A.Sayre and R.A. Assink, (1982), Polymer, 23 (1982) 1897

Vol.5, No.1 Utilization of Granite Powder as a Filler 7
4. S.J.Sankaran, J. Appl.Polym.Sci., 39 (1090) 1635
5. Sangcheol Kim, Won Ho Jo, J. Mater.Sci, 34 (1999) 161
6. H.S.Katz and J.V. Milewski, Hand Book of Fillers and Reinforcements for
Plastics, Vannostrand Reinhold, 1978
7. M.Sarojadevi,V.Murugesan,K.Rengaraj,PAnand,Appl.Polym.Sci,69 (1998)
1385
8. R.G.Raj, B.V.Kokta, D.Maldas and C.Daneult, J. Appl.Polym.Sci, 37
(1989)1089
9. M.Paaw and M. Lurius, J. Appl.Polym.Sci., 51 (1994) 127
10. S.Fellahi, N.Chikhi, M. Baker, J. Appl.Polym.Sci, 82 (2001)861
11. C. Hepburn, Plast. Rubber. Int, 9(1984)11
12. B.Pukanszki, E.Fekete, Poly.Compos,6(1998)313
13. K.W.Y Wong, R.W. Truss, Comp.Sci and Tech, 52(1994)361
14. A.M.Riley, C.D.Paynter, P.M.McGenity and J.M.Adams, Plast and
Rubb.Process and Applications, 14(2) (1990) 85
15. L.Jilken, G.Malhmmar and R.Selden, Polym. Testing,
10 (1991) 329
16. Jun Kyung Kim, R.E. Robertson, J.Mater.Sci 27(1992)161
17. H.Nakagawa, H.Sano, Polym. Prepr.,26(1982)249

8 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Table 1. Chemical composition of Granite powder.
Compound Wt.%
Silica 70-77
Alumina 11-13
Potassium oxide 3-5
Soda 3-5
Lime 1
Iron 2-3
Magnesia & Titania Less than 1
Table 2. Tensile, Flexural, Compression and Impact properties of epoxy
toughened with PBT blend matrix.
Tensile properties Flexural properties Compression properties
% of PBT
content in
epoxy
Tensile
strength
MPa
Tensile
modulus
MPa
%
elongation
at break
Flexural
strength
MPa
Flexural
modulus
Mpa
Compression
strength MPa
Compression
modulus
Mpa
Impact
strength
J/m
0 18.6 525 4.0 45.9 640 48.4 2931 30
1 27.5 563 7.0 50.0 1064 93.0 3663 40
2 38.5 606 6.4 55.6 1143 104.4 3730 45
3 35.0 523 5.4 54.2 1138 96.0 3867 36
4 30.4 493 4.5 49.6 905 89.3 4744 28

Vol.5, No.1 Utilization of Granite Powder as a Filler 9
Table 3.Chemical resistance properties of Untreated, coupling agent treated and
epoxy/granite powder composites.
(Percentage of filler content in matrix by wt.)
30 40 50 60
Chemicals
Untreated Treated Untreated Treated Untreated Treated Untreated Treated
Acetic acid 0.60 0.59 0.54 0.53 0.52 0.51 0.51 0.49
Hydrochloric
acid
1.29 1.11 1.18 1.17 101.7 1.16 1.16 1.15
Nitric acid
Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved Dissolved
Sodium
hydroxide
0.17 0.16 0.12 0.11 0.10 0.09 0.09 0.08
Sodium
carbonate
0.39 0.30 0.31 0.30 0.21 0.19 0.19 0.18
Benzene 0.07 0.07 0.06 0.06 0.01 No
change
No
change
No
change
Carbon tetra
chloride
No change No
change
No
change
No
change
No
change
No
change
No
change
No
change
Toluene 0.08 0.07 0.06 0.06 0.05 0.04 0.05 0.05
Lactic acid 0.39 0.31 0.23 0.20 0.11 0.96 0.10 0.09

10 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Table 4.Chemical resistance properties of 2% PBT toughened epoxy/granite
powder composites.
Percentage of filler content in the matrix by wt
C
HEMICALS
2% PBT in
Epoxy Blend
30 40 50 60
Acetic acid 2.09 0.55 0.30 0.17 0.05
Hydrochloric
acid
0.34 0.49 0.37 0.30 0.30
Nitric acid -6.64 30.47 21.59 14.62 9.91
Sodium
hydroxide
-0.14 -0.13 -0.07 -0.13 -0.02
Sodium
carbonate
0.02 No Change 0.01 0.02 0.04
Benzene 0.01 -0.16 -0.05 No Change -0.09
Carbon tetra
chloride
-0.07 -0.28 -0.10 -0.01 -0.02
Toluene -0.05 -0.20 -0.07 -0.02 -0.08
Lactic acid 0.06 0.16 0.39 0.01 -0.04

Journal of Minerals & Materials Characterization & Engineering, Vol. 5, No.1, pp 1-19, 2006
jmmce.org Printed in the USA. All rights reserved
11
Fig. 1. Variation of tensile strength of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
15
20
25
30
35
40
45
Tensile strength in MPa
Percentage of filler content in the matrix

12 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Fig. 2. Variation of tensile Modulus of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
Tensile modulus in Mpa
Percentage of filler content in matrix

Vol.5, No.1 Utilization of Granite Powder as a Filler 13
Fig. 3. Variation of tensile elongation of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
% Elongation at break
Percentage of filler content in matrix

14 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Fig. 4. Variation of flexural strength of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
45
50
55
60
65
70
75
80
85
Flexural strength in MPa
Percentage of filler content in matrix

Vol.5, No.1 Utilization of Granite Powder as a Filler 15
Fig. 5. Variation of flexural modulus of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
Flexural modulus in MPa
Percentage of filler content in matrix

16 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Fig. 6.Variation of compression strength of untreated (■), coupling agent treated (●) and 2
wt% PBT toughened epoxy (▲) with filler content.
0102030405060
45
50
55
60
65
70
75
80
85
90
95
100
105
110
115
120
125
130
135
140
Compression strength in MPa
Percentage of filler content in matrix

Vol.5, No.1 Utilization of Granite Powder as a Filler 17
Fig. 7. Variation of compression modulus of untreated (■), coupling agent treated (●) and 2
wt% PBT toughened epoxy (▲) with filler content.
0102030405060
3000
4000
5000
6000
7000
8000
Compression modulus in MPa
Percentage of filler content in matrix

18 H. V. Ramakrishna and S. K Rai Vol.5, No.1
Fig. 8.Variation of impact strength of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
0102030405060
20
40
60
80
100
120
140
Impact strength in J/m
Percentage of filler content in matrix

Vol.5, No.1 Utilization of Granite Powder as a Filler 19
Fig. 9.Variation of water absorption of untreated (■), coupling agent treated (●) and 2 wt%
PBT toughened epoxy (▲) with filler content.
30354045505560
0.160
0.165
0.170
0.175
0.180
0.185
0.190
0.195
0.200
0.205
0.210
Water absorption in %
Percentage of filler content in matrix