ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE, September 2019. Vol. 15(3):510-518

Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.
Print ISSN: 1596-2490, Electronic ISSN: 2545-5818

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ORIGINAL RESEARCH ARTICLE

EVALUATION OF SHEANUT SHELL-REINFORCED AUTOMOTIVE BRAKE PAD

V. N. Haruna1*, A. S. Abdulrahman2, M. S. Abolarin1 and R. A. Muriana2
(1Department of Mechanical Engineering, Federal University of Technology, Minna, Niger State, Nigeria

2Department of Material and Metallurgical Engineering, Federal University of Technology, Minna, Niger State, Nigeria)
* Corresponding author’s email address: ndarabaharuna@gmail.com

ARTICLE INFORMATION

Submitted 19 December, 2018
Revised 15 April, 2019
Accepted 19 April, 2019

Keywords:
Epoxy
Sheanut Shell
Asbestos
Brake Pad
Development

ABSTRACT
For over a century now, asbestos has been used as friction material in
the manufacture of brake pads but its use is currently been avoided
due to its carcinogenic nature and potential to cause cancer. This study
is focused on development of a new brake pad using sheanut shell
(SNS) which is an eco-friendly material as the reinforcement and epoxy
resin as the binder. Other constituents used are calcium carbonate
(CaCO3), graphite and aluminium oxide (Al2O3). Five compositions were
formulated with the epoxy resin and reinforcement varied at interval of
5 wt% while CaCO3, graphite and Al2O3 remain constant at 30, 10 and
10 wt% respectively. The developed brake pads were subjected to
compressive, abrasive and water absorption tests while their densities
were also measured. The results showed that the compressive strength,
abrasive strength and the density of the samples decreased as the
reinforcement content increased while the water absorption rate
increased as the reinforcement content increased. The value of the
compressive strength ranged from 64.88 – 93.04Mpa, wear rate from
3.13 – 6.25mg/m, water absorption from 0.899 – 2.722% and density
from 0.764 – 1.487g/m3. The result of this research indicates that SNS
particles can be used as a replacement for asbestos in brake pad
production.

© 2019 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

1.0 Introduction
Brake pads are important parts of braking system for all types of vehicles using disc brake. The
importance of brake pad is to convert the dynamic energy of the vehicle to heat energy by
means of friction and dissipating the heat to the surrounding environment (Maleque et al., 2012).
Different types of brake materials are used in different machines. They are usually classified into
four components namely binders, fillers, modifiers and reinforcements (Dagwa and Ibhadode,
2006; Blau, 2001; Maleque et al., 2012; Umamaheswara, 2015). The brake pads generally consist
of asbestos fibres embedded in polymeric matrix along with several other components. The use
of asbestos fibers is being avoided due to its carcinogenic nature (Yuvaraj and Jeyanthi, 2015).
Despite its good properties, asbestos is being withdrawn from all the applications, where there is
a possibility of alternate material for making brake pad that will not pose health risks leading to
diseases like asbestosis, mesothelioma, lung cancer and other cancers (Dagwa and Ibhadode,
2006; Mathur et al., 2004; Anon, 2004; Norton, 2001; Rinek and Cowen, 1995). Although the use
of asbestos for brake pads has not been banned, much of the brake pad industry is moving away

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from asbestos brake pads because of concerns regarding airborne particles in the factories and
disposal of wastes containing asbestos (Aigbodion et al., 2010).

Several researches have been carried out in the area of development of asbestos-free brake
pads. The use of coconut shell, palm kernel shell (PKS) have been investigated (Dagwa and
Ibhadodo, 2006; Dagwa and Ibhadode, 2005). Researches all over the world are focusing on
ways of utilizing either industrial or agricultural wastes as a source of raw materials for
composite development (Lemon et al., 2008). These wastes utilization will not only provide more
economic benefit, but may also result to foreign exchange earnings and environmental
sanitation (Yuvaraj and Jeyanthi, 2015). Sheanut shells are wastes resulting from Shea nut
consumption were collected from the refuse dumped cite in Kodan village, Niger State. The
presence of hard elements like silicon, calcium, iron, carbon and magnesium which are equally
found in asbestos suggests that sheanut shell can be used as a reinforcement material for brake
pad production as similarly observed in the work of Ikpambese et al., 2014. The application of
sheanut shell as a reinforcement material will not only eradicate the health risk posed by using
asbestos but also move Nigeria ahead towards realization of her dream of increasing local
content in automobile industry.

2. Materials and Methods
2.1 Materials
Materials used in this study consist of the main components of the brake pad namely: Sheanut
Shells (SNS) as the reinforcement and epoxy as binder, CaCO3 as filler and graphite (Figure 1B)
and Al2O3 as the frictional additives. The reinforcement is to improve the mechanical properties
of the composites, the binder maintains the pad’s structural integrity under mechanical and
thermal stresses, the filler material improves the manufacturability of the brake pad while the
frictional additives modify the coefficient of friction and the wear rate. Other materials used
include sodium hydroxide and distilled water. These materials were almost the same with the
materials used by Bala et al. (2016).

2.2 Methods
2.2.1 Preparation of the Raw Material (Reinforcement)
The SNS were collected and soaked in a solution of water and sunlight detergent for 30 minutes
for easy removal of dirt and other contaminants. The SNS were thereafter washed properly and
sun dried to constant weight after which it was ground using milling machine. This method is in
line with the one adopted by Bala et al. (2016). The ground SNS (Figure 1A) was treated with
10% Sodium Hydroxide (NaOH) and sun dried to constant weight. This treatment is to increase
the bonding ability of the reinforcement with the resin (Pujari et al., 2014). The treated
reinforcement was then sieved using 150µm mesh.

Figure 1: Ground SNS (A), Ground graphite (B)

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Haruna, et al: Evaluation of sheanut shell-reinforced automotive brake pad. AZOJETE, 15(3):510-518. ISSN 1596-2490;
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2.2.2 Formulation of the Brake Pad Compositions
The formulation of the brake pad compositions which is in line with the approach of Bala et al.
(2016) is shown in Table 1.

Table 1: Weight Percent Compositions of the Brake Pad
Sample No 1 2 3 4 5
Resin 40 35 30 25 20
SNS 10 15 20 25 30
CaCO3 30 30 30 30 30
Graphite 10 10 10 10 10
Al2O3 10 10 10 10 10
Total 100 100 100 100 100

2.2.3. Production of the Brake Pad Samples
Production of automotive brake pad consists of a number of unit operations including mixing of
its components, hot pressing, cooling, post curing and finishing (Gurunath and Bijwe, 2008; Koya
and Fono, 2009).
Different samples of ground SNS, calcium carbonate, graphite and aluminium oxide were
thoroughly mixed in a container to obtain the percentages indicated in Table 1, following the
method of Abutu et al., 2018. The epoxy resin + triethylenetetramine hardener was properly
mixed in a separate container, poured into the first mixture and then mixed thoroughly for five
minutes to obtain a homogenous mixture (Yawas et al., 2016). This homogenous mixture was
then charged into a metallic mould lined with aluminium foil for easy removal of the cast. The
samples were kept under the hydraulic press at a pressure of 11 N/mm2 and temperature of
120°C for 10 min. The cast samples were post cured in an electric oven at 150°C for 2 h. This was
similar to the method adopted by Yawas et al. (2016) and Mathur et al. (2004). Figure 2A, B and
C shows the mixing of the constituents, the samples produced and the sheanut shells
respectively.

A B C
Figure 2: Mixing of the constituents (A), Produced Samples (B), Sheanut Shells (C)

2.2.4 Characterization of the Produced Brake Pads
The produced brake pads were characterized by subjecting them to density measurement,
compressive, absorption, abrasive and thermal conductivity tests using standard methods and
procedures.

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2.2.4.1 Density
Density depends on the constituents of the brake materials formulation (Talib 2007; Nirmal et al.,
2011). The true densities of the specimens were determined using Archimedes’s principles. The
volumes of water in the cylinder before and after immersion of the specimens were taken and
their difference gives the volume of the specimen. The densities of the specimens were
determined by dividing the mass of the specimen before the immersion by the difference in the
volumes of the water (Egeonu et al., 2015). That is, by weighing them on a digital weighing
machine and measuring their volumes by liquid displacement method (Aigbodion and Akadike,
2010). The density was calculated using the formula given by Cracium et al., (2017):

v
mP  (1)

where:
Ρ = Density in g/cm3
m = Mass in g
v = Volume of liquid displaced in cm3

2.2.4.2 Compressive Strength
Specimens were subjected to compressive test using Enerpac Universal Hydraulic Digital Material
Testing Machine 100KN, Norwood Instrument Ltd, New Mill Road Houley, Hundersfield, Great
Britain HD9 6QD shown in Figure 3(A) in accordance with ASTM D3410/D3410M. The specimens
were cut to a dimension of 20 × 20 × 10 mm in order to conform to the specification of the
instrument used. These specimens were loaded manually continuously until failure occurred. The
load at failure was digitally displayed and recorded. This was in accordance with the method
adopted by Aigbodion and Akadike (2010). The compressive strength was calculated using the
formula:

A
Pc  (2)

where:
σc = Compressive Strength in MPa
P = Applied Load in N
A = Cross Sectional Area in mm2

2.2.4.3 Water Absorption Test
The 24-h water soak test was carried out to determine the water absorption behaviour of the
brake pads produced. The samples were oven dried at 70°C for 1 h and their weights measured.
After 24 h of submersion in water at 30°C according to Idris et al. (2015), the specimens were
weighed after the excess water had drained off. The absorption was calculated using the given
formula (Smales, 1995; Talib, 2007; Edokpia et al., 2014):

(3)
where:

W1= weight after immersion in g ; Wo = weight before immersion in g

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Haruna, et al: Evaluation of sheanut shell-reinforced automotive brake pad. AZOJETE, 15(3):510-518. ISSN 1596-2490;
e-ISSN 2545-5818, www.azojete.com.ng

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2.2.4.4 Wear Rate
An apparatus known as “Tribometer”, Anton Paar, Switzerland shown in Figure 3(B)was used to
investigate the dry sliding wear rate of the sample in accordance with ASTM: G99 – 05 standards
(Idris et al., 2015). This equipment and methods used to examine the worn surface include
optical microscopes, scanning electron microscopes, optical interferometry and mechanical
roughness testers. The result of the wear test using this apparatus is always displayed on the
screen of the computer attached to it.The samples dimensions were 25 mm in diameter and 5
mm in thickness. The difference in weights of the samples before and after test gives the wear of
the samples. Loss in weight was converted to wear rate using the formula given by Aigbodion
and Akadike (2010):

s
wrateWear 

 (4)

where
ΔW = difference in weight before and after test in mg
s = sliding distance in m.

A B
Figure 3: Compression tester (A), Tribometer (B)

3. Results and Discussion
3.1 Characterization of the Produced Brake Pads
3.1.1 Density
Figure 1 shows the variation of density with reinforcement content in the composite samples. It
was observed from the result that the density of the composite decreased as the reinforcement
content increased. This according to Idris et al., (2015) may be attributed to the reduction in the
interfacial bonding between the reinforcement and the resin. This result was in agreement with
the previous study of Bala et al. (2016). The values obtained were between 0.764 – 1.487 g/cm3
which are within the recommended values for the application of brake pad given by Kim et al.
(2003).

Figure 4: Variation of Density with Reinforcement Content

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3.1.2 Compressive Strength
Figure 2 shows the effect of the reinforcement content on the compressive strength of the
composite. It was observed from the result that the compressive strength decreased with
increase in reinforcement content. This gradual decrease may be attributed to the decreasing
surface area and pore packaging capability of the reinforcement in the resin as the
reinforcement content is increasing (Aigbodion et al., 2010). The values of the compressive
strength obtained are between 64.88 and 93.04 MPa. These values are within the range of the
values obtained in the work reported by Idris et al. (2015).

Figure 5: Variation of Compressive Strength with Reinforcement Content

3.1.3 Water Absorption
Figure 3 depicts the variation of the absorption rate with the reinforcement content in the
composite. It can be seen from the result that the absorption rate increased as the reinforcement
content increased. This may be attributed to the increase in pores as the reinforcement content
increased which could be due to reduction in interfacial bonding between the reinforcement and
the matrix. This result is in agreement with that of Bala et al., (2016). The values obtained were
within the range of 0.899 – 2.722 %. These values are also within the range of the values
obtained in the work of Bala et al., (2016).The less the value of the absorption rate, the better the
material for brake pad production under study.

Figure 6: Variation of Water Absorption Rate with Reinforcement Content

3.1.4 Material Wear
The variation of wear rate with reinforcement content of the composite is shown in Figure 4. It is
observed from the result that the wear rate reduced as the reinforcement content increased. This
may be due to better interfacial bonding between the reinforcement and the matrix causing
good surface property. This result is in agreement with the research work of Idris et al. (2015).
The values of the wear rate of this work ranges from 3.13 – 6.25 mg/m.

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Haruna, et al: Evaluation of sheanut shell-reinforced automotive brake pad. AZOJETE, 15(3):510-518. ISSN 1596-2490;
e-ISSN 2545-5818, www.azojete.com.ng

Corresponding author’s e-mail address: ndarabaharuna@gmail.com 516

Figure 7: Variation of Wear Rate with Reinforcement Content

3.2 Comparison of SNS Based Brake Pad with other Experimental Brake Pads
Table 2 below shows the comparison between the SNS based brake pad and other experimental
brake pads.
Table 2: Comparison of SNS Based Brake Pad with other Experimental Brake Pads
Properties Commercial

Asbestos
Based
Brake Pad

Palm Kernel
Based
Formulation

Bagasse
Based
Formulation

Carbonized
Banana Peels
Based
Formulation

SNS Based
Formulation

Density (g/cm3) 1.89 1.65 1.43 1.20 0.764-1.487
Water Absorption (%) 0.9 5.03 3.48 3.0 0.899-2.722

Compressive Strength
(MPa)

110 103.5 105.6 61.20 64.88-93.04

Wear Rate (mg/m) 3.8 4.40 4.20 4.67 3.13-6.25

Table 2 shows the density, water absorption, compressive strength and wear rate values for
asbestos, palm kernel, bagasse, carbonized banana peels and SNS based brake pads (Ibhadode
and Dagwa, 2008; Aigbodion et al., 2010; Idris et al., 2015). Though the values for commercial
asbestos based are taken as the standard, other brake pad formulations shown in the table
cannot be out of place since they also have some properties that are better than that of asbestos
based. For example, the density of the SNS based (1.487g/cm3) is less than that of the asbestos
based (0.9g/cm3) while other properties are in close agreement.

4. Conclusion
From the results obtained, the values of the compressive strength, wear rate and the density
were observed to be decreasing with the increase in reinforcement content while the water
absorption rate was increasing with the increase in reinforcement content. However, the values
obtained for all the tests carried out can be comparable to the values of the commercial
asbestos based and other experimental brake pads. Hence, the shea nut shell can be used as a
replacement for asbestos in the production of brake pads.

Acknowledgement
The authors are grateful to the Tertiary Education Trust Fund (TETFund) and Management of
Federal University of Technology, Minna, Niger State, Nigeria for the grant
(TETFUND/FUTMINNA/2016-2017/B/19) allocated to this research work.

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