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Potential of palm kernel activated carbon epoxy (PKAC-E) composite as solid
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lubricant: Effect of load on friction and wear properties
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K.W. Chuaa, M.F.B. Abdollaha,b,*, N.A. Mat Tahira, H. Amiruddina,b
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a
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Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka,
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Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
b
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Centre for Advanced Research on Energy, Universiti Teknikal Malaysia Melaka,
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Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
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*
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Corresponding author: mohdfadzli@utem.edu.my
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HIGHLIGHT
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Wear rate and friction coefficient of PKAC-E composite decreases with applied load.
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However, at higher load, friction coefficient increases slightly and remains almost invariant
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with applied load.
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Palm kernel activated carbon epoxy composite (PKAC-E) has a potential to act as a selflubricating material at low load under unlubricated conditions.
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ABSTRACTS
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The aim of this study is to investigate the effect of load on the friction and wear properties of palm
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kernel activated carbon epoxy (PKAC-E) composite. The PKAC-E composite specimen was
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fabricated by hot compression molding method. Dry sliding test was performed by using a pin-on-
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disc tribometer at various load conditions with constant sliding speed and distance. The experimental
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results show that wear rate and friction coefficient of PKAC-E composite decreases with applied
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load. However, at higher load, friction coefficient increases slightly and remains almost invariant
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with applied load. In addition, some adhesive and abrasive wear types were identified on the worn
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surfaces. The main conclusion of this work is that PKAC-E composite show unique properties as
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solid lubricant at low load under unlubricated conditions.
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Keywords: Palm kernel activated carbon, wear, coefficient of friction
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1.0
INTRODUCTION
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For a decade, many researchers have investigated different types of solid lubricants as
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reinforcement or coating materials for tribological applications (Erdemir et al., 2000; Heimberg et al.,
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2001; Tokoroyama et al., 2006; Liu et al., 2009; Baradeswaran, 2011; Abdollah et al., 2012;
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Masripan et al., 2013).
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Recently, the potential of local waste materials as substitute reinforcement in fabrication of
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lightweight materials, such as metal matrix composites and polymer matrix composites has attracted
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lots of attentions due to its self-lubricating properties and adopt zero waste strategy at affordable cost
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(Zamri et al., 2010; Zamri et al., 2011; Aigbodion et al., 2011; Bakry et al., 2013;).
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A few researcher found out that porous carbon also known as activated carbon, such as palm
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shell activated carbon (PSAC), exhibited its potential to act as a self-lubricating material when
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reinforced in aluminium alloy, which significantly improved wear resistance by increasing PSAC
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content up to 10 wt.% (Zamri et al., 2010; Zamri et al., 2011). Gomes et. al., 2001 stated in his study
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of carbon-carbon composites, the friction coefficient is almost independent in sliding speed but
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highly affected by test temperature.
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In general, as observed from prior studies, there are a limited number of studies to investigate
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the potential of activated carbon materials as solid lubricants in polymer matrix composites. Hence,
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the goal of this paper is to study the effect of applied load on the friction and wear properties of palm
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kernel activated carbon epoxy (PKAC-E) composite.
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2.0
METHODOLOGY
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2.1
Specimen Preparation
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In this study, the materials used are palm kernel activated carbon (PKAC), West System 105
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Epoxy Resin (105-B) and West System 206 Slow Hardener (206-B). All specimens were fabricated
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by hot compression molding method. The PKAC particulate was ground into smaller particle and
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mixed with epoxy resin (E) and hardener at a composition ratio of 70 wt.% PKAC and 30 wt.% E.
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The compression process was conducted using hot press machine at 80oC and 2.5 MPa of
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compression pressure. The green specimen was then cured under room temperature for 2 - 3 days.
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The length and diameter of the specimen was 30 mm and 10 mm, respectively, as shown in
Figure 1.
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Figure 1 PKAC-E specimen
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2.2
Dry sliding test
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The dry sliding testing was performed to determine the friction coefficient and wear rate
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between the contact surfaces using a pin-on-disc tribometer. The testing procedure followed the
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ASTM standard G99-95a (Standard Test Method for Wear Testing with a Pin-on-Disk Apparatus).
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All tests were performed at room temperature with a constant sliding speed and distance at 200 rpm
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and 3770 m, respectively. Prior to the sliding test, pin was ground by sliding against 600grit silicon
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carbide (SiC) paper at one end. Then, both pin and disc were cleaned using acetone in an ultrasonic
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bath. As illustrated in Figure 2, The pin was then mounted vertically on the tester arm at one end and
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the other pin surface was hold against the rotating EN-31 carbon alloy steel disc (hardened to HRC
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62; ground to Ra = 0.8µm) with a diameter and thickness of 16.5 mm and 8 mm, respectively.
A coefficient of friction and frictional force encounter by the ball in sliding were measured by
a PC based data logging system. The coefficient of friction is then being determined as follows:
F W
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(1)
Where F is the frictional force in N and W is the applied load in N.
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The wear at the pin was recorded by measuring the mass of the pin before and after the wear
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test. The mass loss in mass unit is converted to the volume loss by dividing with bulk density of
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material. The specific wear rate is then being determined as follows:
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Vloss  mloss 
(2)
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k  Vloss WL
(3)
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Where Vloss is the volume loss in mm3, mloss is the mass loss in g,  is the bulk density of material in
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g/mm3, k is the specific wear rate of material in mm3/Nmm, W is the applied load in N and L is the
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sliding distance in mm.
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The worn surfaces morphology was observed using a digital microscope and profilometer.
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Load
Rotating
EN-31 steel
disc
Stationary
PKAC-E
composite
PSAC-Al
composite
Wear track
(a)
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(b)
Figure 2 (a) Illustration and (b) schematic diagram of the sliding test using a pin-on-disc tribometer
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3.0
RESULTS AND DISCUSSION
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Figure 3 indicates the friction coefficient decreases with the increase of applied load within
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the observed range though from 60 N, it increases slightly and remains almost invariant with applied
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load (Figure 4). The frictional heating, which will induce tribofilm formation, is believed to be
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responsible for the decrease of friction with the increase of applied load. There was a strong
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dependence of tribofilm formation on temperature (Komvopoulos et al., 2002). The tribofilm
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generated from the preferential wear of the soft carbon material results in a carbon based tribofilm
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adhering on the worn surface which breaks the adhesive joints between the asperities and thereafter
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leads to low friction (Luo, 2013). However, as stated by Bakry et al. 2013, at higher load, the
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tribofilm was broken and carbon shows a drastic reduction in lubricity; consequently increases
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friction coefficient.
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Average coefficient of friction
0.10
Low load
Medium load
0.08
0.06
0.04
0.02
0.00
0
20
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60
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Normal load [N]
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Figure 3 Relationship between applied loads and average friction coefficient of PKAC-E composite
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Coefficient of friction
0.10
0.08
5N
0.06
60N
0.04
100N
80N
0.02
20N
40N
0.00
0
1000
2000
Time [secs]
3000
4000
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Figure 4 Comparison of friction coefficient as a function of time at different load
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As regard to the wear, Table 1 shows the distribution of calculated wear rate with applied
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load. As shown in Figure 5, the wear rate of PKAC-E composite decreased significantly with applied
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load. From Figure 6, worn surfaces of the material were characterized by some adhesion wear and
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abrasive wear. However, at higher load, adhesion wear was slightly reduced with smoother surfaces
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and show signs of fine scratches. A reduction in adhesion is directly responsible for the reduction in
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friction and wears (Zhao et al., 2014). These results agree with the calculated wear rate values as in
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Figure 5. Among the experiments conducted there was no seizure condition noticed.
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Table 1 Weight of specimen before and after tribo testing with calculated wear rate
Sample
Load [N]
m1 [g]
m2 [g]
mloss [g]
k [mm3/Nmm]
A
5
3.3483
3.3443
0.0040
0.7800
B
20
3.1647
3.1643
0.0004
0.0780
C
40
3.0090
3.0073
0.0017
0.3315
D
60
3.4947
3.4943
0.0004
0.0780
E
80
3.5783
3.5767
0.0016
0.3120
F
100
3.3530
3.3513
0.0017
0.3315
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Specific wear rate, k [mm3/Nmm]
x 10-7
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
20
40
60
80
Normal load [N]
100
120
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Figure 5 Relationship between applied loads and wear rate of PKAC-E composite
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Figure 6 Digital microscope image of worn surfaces of PKAC-E composite testing at (a) 5N,
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(b) 20N, (c) 40N, (d) 60N, (e) 80N and (f) 100N
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4.0
CONCLUSIONS
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As a conclusion, it was found that the wear rate and friction coefficient of PKAC-E
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composite was decreasing with the increasing in applied load. However, at higher load, friction
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coefficient increases slightly and remains almost invariant with applied load. In addition, some
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adhesive and abrasive wear types were identified on the worn surfaces. From the overall findings,
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PKAC-E composite show unique properties as solid lubricant at low load under unlubricated
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conditions.
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ACKNWLEDGEMENTS
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The authors gratefully acknowledge contributions from the members of the Green Tribology
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and Engine Performance (G-TriboE) research group. This research was supported by the grant from
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the Ministry of Education Malaysia (Grant No.: ERGS/2013/FKM/TK01/UTEM/02/04/E00016).
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