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The Effect of Treatment on Tribo-Performance of CFRP Composites

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The aim of this project is to study the effects of chemical treatment on the tribo-performance of coir reinforced polyester (CFRP) composite. Alkaline treatment and bleaching method were used to perform the surface modification on the coir fibre. In order to investigate the wear performance of treated and untreated CFRP composites, the experimental works were conducted using Pin On Disc (POD) machine at different applied loads (10N, 20N, 30N) and constant rotational speed (2.8m/s). Debonding gap between the untreated coir fibre and matrix resulted in higher weight loss due to lack of protection from the fibres. The results revealed that tribo-performance of the CFRP composite depend on the test parameter and condition. Treated coir fibre exhibited better interfacial adhesion and improved the wear characteristic of the composites. Worn surfaces were observed by Scanning Electron Microscopy (SEM) and optical microscopy. The development of friction layer at the rubbing surface enhanced the interaction between the counterface and specimen. The present article discusses some important patents related to Tribo performance of CFRP Composites.
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Recent Patents on Materials Science 2009, 2, 67-74 67
1874-4656/09 $100.00+.00 © 2009 Bentham Science Publishers Ltd.
The Effect of Treatment on Tribo-Performance of CFRP Composites
Belal. F. Yousif*, Ong B. Leong, Low K. Ong and Wong K. Jye
Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450, Melaka, Malaysia
Received: August 11, 2008; Accepted: September 9, 2008; Revised: November 3, 2008
Abstract: The aim of this project is to study the effects of chemical treatment on the tribo-performance of coir reinforced
polyester (CFRP) composite. Alkaline treatment and bleaching method were used to perform the surface modification on
the coir fibre. In order to investigate the wear performance of treated and untreated CFRP composites, the experimental
works were conducted using Pin On Disc (POD) machine at different applied loads (10N, 20N, 30N) and constant
rotational speed (2.8m/s). Debonding gap between the untreated coir fibre and matrix resulted in higher weight loss due to
lack of protection from the fibres. The results revealed that tribo-performance of the CFRP composite depend on the test
parameter and condition. Treated coir fibre exhibited better interfacial adhesion and improved the wear characteristic of
the composites. Worn surfaces were observed by Scanning Electron Microscopy (SEM) and optical microscopy. The
development of friction layer at the rubbing surface enhanced the interaction between the counterface and specimen. The
present article discusses some important patents related to Tribo performance of CFRP Composites.
Keywords: Coir fibre, polyester, chemical treatment, wear, friction layer.
1. INTRODUCTION
Polymers have emerged as the material used for wide
range of applications nowadays due to their unique and
attractive properties. They possess excellent impact and
abrasion resistance, high strength-to-weight ratio and high
durability which fulfill the requirement for many designs in
manufacturing components [1-3]. For instance, the bearing
components used in automobile industry such as gears,
bushes, cams, wheels, and etc. require high quality and
durability during their life span [4]. In fabrication of polymer
composites, natural fibres have good potential to replace
synthetic fibres as the reinforcement agent. Handa et al.
dicussed the structure and properties of the composites in EP
patent 1950330 [5]. This is because natural fibres are
abundantly available, low cost, biodegradable, and possess
attractive physical and mechanical properties [6-11].
Most of the natural fibres in this country such as coconut,
oil palm, bamboo, and sugarcane fibres are discarded as
wastage. However, much attention has been drawn to take
advantage of their attractive characteristics. Therefore, the
usage of natural fibres to reinforce polymer have increased
dramatically. For example, polyester was strengthened with
oil palm fibres and showed an improvement in wear
resistance [7]. This could be due to the protection offered by
the oil palm fibres on the exposed rubbing layer of the
composite along sliding distance. Meanwhile, the fibres were
pulled out from the matrix at higher sliding velocity due to
poor interfacial adhesion.
Although coir fibre possesses numerous advantages,
unsatisfactory performance in coir fibre reinforced polymer
(CFRP) composites has limited the application of coir. The
large amount of hydroxyl exists in the cellulose chains, high
level of moisture absorption, low cellulose content and high
*Address correspondence to this author at the Faculty of Engineering and
Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450,
Melaka, Malaysia; Tel: +606 252 3339; Fax: +606 231 6552;
E-mail: belal.f.yousif@mmu.edu.my
lignin are the main factors which lead to debonding of coir
fibres from the matrix [8-13]. To overcome such effect,
surface treatment of coir using chemical has been reported to
have a long lasting effect on the mechanical behavior of coir,
and can be used optimize the interfacial adhesion between
the coir and the matrix [8-11]. One of the most common
chemical used in alkaline treatment is Sodium Hydroxide
(NaOH), which has been found to treat surface imperfection
such as lignin, wax, oils that covered the outer surface of the
coir [8]. The removal of such impurities from the outer layer
of the fibre results in higher surface roughness of the fibre.
In addition, alkaline treatment also changed the crystal
structure in the cellulose chain. The combined effect of both
factors improved the mechanical interlocking and adhesion
bonding between the matrix and fibre [9].
2. EXPERIMENTAL DETAILS
2.1. Fibers Preparation
The coconuts were obtained from a wet market in Negeri
Sembilan, Malaysia. The steps to extract the coir fibre are
shown in Fig. (1). The coconuts were firstly crushed into
smaller fibrous pieces. In order to extract the fibers easily,
the fibrous pieces were then soaked into water and dried
under the sun for 24 hours. During the extraction process,
short branches along the fibers were cut to ensure that the
fibers have a smooth, long and hair-like geometry. In
addition, the selected fibres must meet the requirement of (1)
length longer than 10cm, and (2) approximately constant
diameter of 1mm. The untreated coir fibres have impurities
(or waxy layer) covering the bundle of fibres, which can be
seen from the SEM micrograph in Fig. (2).
2.2. Surface Treatment
For alkaline treatment, NaOH concentration of 5% was
used as it has been reported improve the tensile strength and
the flexural strength of the fibres [11]. The coir fibres were
soaked in 5% of NaOH for 24 hours at room temperature.
After that, the coir fibres were rinsed and dried under the sun
68 Recent Patents on Materials Science 2009, Vol. 2, No. 1 Yousif et al.
Fig. (1). Fibre preparation.
Fig. (2). SEM micrograph of untreated coir fibre.
for another 24 hours. Another surface treatment method used
to enhance the adhesion bonding of the coir fibres is the by
bleaching. Bleach ed detergent (contains 5% of sodium
hypochlorite) was used to remove the impurities on the
surfaces. Coir fibres were soaked in the mixture of water and
5% of bleached detergent for 24 hours. Then, coir fibres
were rinsed with water and dried under the sun for another
24 hours.
2.3. Composites Fabrication
A U-shaped aluminium frame was used as an open mould
with an inert cross section area of 10x10mm2 and a length of
100mm. The mould was coated with wax (maximu m release)
as release agent. The fibre mats were prepared by attaching
both ends of fibres on adhesive tapes and arranging them
parallel to each other to form a layer consisting of 10 fibres.
During the arrangement, the mats were stretched to ensure
that the fibres were straight with no slacking, thus preventing
intersection of fibres within the matrix. The mats were then
placed in the mould. Unsaturated polyester, which served as
a matrix medium, was mixed with 1.5% hardener and poured
into the mould. After being cured for 48 hours, the CFRP
composites were removed from the mould and cut into
pieces of 20 mm lengths each. The preparation process of the
composite is shown in Fig. (3). Wlach et al. discuss the fibre
composite material join ing to thermoplastic Material in WO
patent 2008087194 [12].
Fig. (3). CFRP composite preparation.
2.4. Tribo-Tests Procedure
Tribo-tests were conducted on a pin-on-disk (POD)
testing machine as illustrated in Fig. (4). The counterface
was made of stainless steel (1250 HB). Before each test,
abrasive paper (Sic G2000) was used to polish the
counterface surface and the composite samples. The average
roughness of the counterface and the samples were about
0.25 and 1.88 μm, respectively. The initial weights of the
specimens were measured using Setra precision balance. The
friction force was measured by the load cell. An infrared
thermometer (Extech 42580) was used to measure the
interface temperature. The composite surface morphology
was examined using SEM (JEOL, JSM 840). Before using
the SEM machine, the composite surfaces were gold coated
using ion sputtering device (JEOL, JFC-1600).
3. RESULTS AND DISCUSSION
3.1. Interfacial Adhesion
For untreated condition, poor adhesion bonding between
the coir fibre and polyester matrix leads to existence of
debonding gap around the fibre. However, significant
improvement of wetting was observed after the fibre was
subjected to surface treatment. This can be confirmed with
the SEM micrograph of the surface in Fig. (5).
Treated Tribo-Polymeric Composites Recent Patents on Materials Science 2009, Vol. 2, No. 1 69
Fig. (4). Pin-on-disc machine.
Fig. (5). SEM micrographs (a) untreated fibre; (b) treated fibre.
3.2. Untreated CFRP Composites
The friction coefficient of untreated CFRP composites in
three different applied loads (10N, 20N, 30N) are shown as a
function of sliding distance in Fig. (6). Generally, an
increase in the applied load shows gradual increase in the
friction coefficient. This was due to high real contact
pressure between the specimen and the counterface. The
interface temperature for different applied load is presented
in Fig. (7). The composites showed a steady increase in
temperature for the three applied loads. It was observed that
the highest temperature occurred at 30N, which could be due
high contact pressure and long sliding distance. The high
temperature leads to severe decomposition of the material
due to softening and development of large scale cracks. It
was found that the weight loss depends on the applied load
and interfacial temperature of the specimen. This can be
explained in Fig. (8) where higher weight loss happened at
30N due to the combined effects of high applied load and
interfacial temperature. Untreated CFRP composites showed
better wear resistance compared to the neat polyester due to
the load carrying capacity of the coir fibres [13]. At the
beginning, the specific wear rate is relatively high as the
Fig. (6). Friction coefficient of untreated CFRP composites vs.
sliding distance at different applied loads.
Fig. (7). Interface temperature of untreated CFRP composites vs.
sliding distance at different applied loads.
Infrared Thermometer
Specimen
Speed
Controller
Counterface Motor
Normal Load
Friction
Indicator
Load Cell
Friction Coefficient vs. Sliding Distance
(Untreated Fibre)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0.00 0.67 1.34 2.02 2.69 3.36 4.03
Sliding Distance, km
Friction Coefficient
10N 20N 30N
Interface Temperature vs. Sliding Distance
(Untreated Fibre)
0.0
10.0
20.0
30.0
40.0
50.0
60.0
0.000 0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
Temperature,
10N 20N 30N
70 Recent Patents on Materials Science 2009, Vol. 2, No. 1 Yousif et al.
Fig. (8). Weight loss of untreated CFRP composites vs. sliding
distance at different applied loads.
surface of the specimen was in direct contact with the rough
counterface. The specific wear rate started to decrease after
0.84km sliding distance and almost achieved steady state
between 3.36km and 4.2km. A possible reason for this trend
was the formation of a thin polymeric layer (or friction layer)
against the counterface, which in turn protects the rubbing
surface from worn. Thus, the volume loss of the specimen
was minimized because the friction layer acted as a solid
lubricant that separated the two surfaces as shown in Fig. (9).
Fig. (9). SEM micrograph of the worn surface of CFRP Untreated
composite after testing at 20N applied load, 2.8m/s sliding velocity
after 3.36km sliding distance.
3.3. Treated CFRP Composites
Untreated coir fibre reinforced polyester composites
showed unsatisfactory wear performance due to poor
adhesion of the coir fibre. The outer layer was found to
contain impurities (or waxy layer), and globular particle was
embedded in the untreated coir fibre surface. The removal of
the waxy layer gave a better interfacial bonding with the
polymeric matrix. Therefore, surface treatment was used to
enhance the performance of coir fibre embedded in
polymeric matrix. Figure (10) shows the effect of sliding
Fig. (10). Friction Coefficient of treated and untreated CFRP com-
posites vs. Sliding Distance for different applied loads.
distance on the friction coefficient of untreated and treated
(bleaching method and alkaline treatment) CFRP composites
at different applied loads. The friction coefficient of the
untreated CFRP composites was found to be higher at each
applied load. In addition, the friction coefficient of CFRP
composite treated by bleaching method was nearly similar
with the untreated CFRP composites and no improvement
was observed. In contrast, the alkaline treated CFRP com-
posite exhibited lower and steady friction coefficient than the
others. This is probably, because the surface modification by
the bleaching method was not effective as the impurities
were still present on the surface of the fibres. On the other
hand, steady state began at 3.36km onward for the alkaline
treated CFRP composite due to the formation of wear debris
on the rubbing surface.
Weight Loss vs. Sliding Distance
(Untreated Fibre)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
Weight Loss, g
10N 20N 30N
c.) Frcition Coefficient vs. Sliding Distance
(30N Load Applied)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0 0.84 1.68 2.52 3.36 4.2
Sliding Distance, km
Frcition Coefficient
Untreated Bl eachi ng NaOH
a.) Frcition Coefficient vs. Sliding Distance
(10N Load Applied)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0 0.84 1.68 2.52 3.36 4.2
Sliding Distance, km
Friction Coefficient
Unt reat ed Bl eachi ng NaO
H
b.) Frcition Coefficient vs. Sliding Distance
(20N Load Applied)
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0 0.84 1.68 2.52 3.36 4.2
Sliding Distance, km
Frcition Coefficient
Untreated Bl eachi ng NaO
H
Treated Tribo-Polymeric Composites Recent Patents on Materials Science 2009, Vol. 2, No. 1 71
The weight loss of the untreated, bleach treated and alkali
treated CFRP are presented in Fig. (11). Increasing the
applied load resulted in higher weight loss due to high
pressure and friction at the interface. A constant weight loss
was observed at 10N as the applied load to the specimen was
low. Meanwhile, alkaline treated CFRP composites showed
lower weight loss compared to untreated and bleached CFRP
composite for all test loads. The reduction in the weight loss
was caused by the strong adhesion between the fibres and
polymeric matrix which helped to protect the rubbing surface
from worn. Besides, no cracks were formed around the
Fig. (11). Weight Loss of treated and untreated CFRP composites
vs. sliding distance for different applied loads.
embedded fibre and this minimized the weight loss for the
alkali treated CFRP composites. The interface temperature of
the bleached treated and alkaline treated CFRP composites
increased along the sliding distance and high temperature
was achieved at higher applied load. This can be observed in
Fig. (12) and Fig. (13). In previous study [14], the rubbing
surface of the polyester became brittle due to rise in
temperature. Higher temperature caused the surface contact
area to soften, resulting in burnt surface and micro crack
which consequently lead to greater material removal.
Fig. (12). Interface temperature of bleached-treated CFRP com-
posites vs. sliding distance for different applied loads.
Fig. (13). Interface temperature of alkaline-treated CFRP com-
posites vs. sliding distance for different applied loads.
Figure 14 presents the specific wear rate (SWR) of
treated and untreated CFRP composites as a function of
sliding distance for different applied loads. The alkaline
treated CFRP composite exhibited lower specific wear rate
compared to the others. The removal of the waxy layer by
alkaline treatment increased the mechanical interlocking
between the coir fibre and polyester resin. In addition, some
of the load was shared by the strong fibres assists in reducing
the wear rate. Furthermore, there was no sign of fibre pull-
out from the matrix after sliding motion because the high
a.) Weight Loss vs. Sliding Distance
(10N Applied Load)
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
Weight Loss, g
Untreated Bleaching NaOH
b.) Weight Loss vs. Sliding Distance
(20N Applied Load)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
Weight Loss, g
U
n
t
r
eat ed
Bl
eac
hi n
g
N
H
c.) Weight Loss vs. Sliding Distance
(30N Applied Load)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
Weight Loss, g
Unt r ea t ed Bl eachi n
g
NaOH
72 Recent Patents on Materials Science 2009, Vol. 2, No. 1 Yousif et al.
Fig. (14). Specific wear rate of treated and untreated CFRP
composites vs. sliding distance for different applied loads.
amount of exposed cellulose on the treated coir fibre resulted
in high interfacial adhesion. Therefore, alkaline surface
treatment improved the interfacial bonding and the strength
of the coir fibre. In contrast, higher specific wear rate
occurred for the untreated fibre CFRP composite. The
debonded coir fibre attributed to high friction and wear since
coir fibres do not play its role to protect the rubbing surface.
The worn surface of bleached treated CFRP and alkaline
treated CFRP composite tested at 30N applied load and
2.8m/s sliding velocity is presented in Fig. (15) and Fig. (16)
a.) 30N 2.8m/s after 1.68km
b.) 30N 2.8m/s after 2.52km
c.) 30N 2.8m/s after 3.36km
Fig. (15). Micrograph of worn surface of bleached-treated CFRP
composite at 30N applied load.
a.) SWR vs. Sliding Distance
(10N Applied Load)
0.000
5.000
10.000
15.000
20.000
25.000
30.000
35.000
40.000
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
SWR, mm3/Nm E-5
Unt r eat ed Bl eachi ng Na OH
b.) SWR vs. Sliding Distance
(20N Applied Load)
0.000
5.000
10.000
15.000
20.000
25.000
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
SWR, mm3/Nm E-5
Untreated Bl eac hi ng Na O
H
c.) SWR vs. Sliding Distance
(30N Load Applied)
0.000
2.000
4.000
6.000
8.000
10.000
12.000
14.000
16.000
18.000
20.000
0.840 1.680 2.520 3.360 4.200
Sliding Distance, km
SWR, mm3/Nm E-5
Unt r eat ed Bl eachi ng Na OH
Treated Tribo-Polymeric Composites Recent Patents on Materials Science 2009, Vol. 2, No. 1 73
a.) 30N 2.8m/s after 1.68km
b.) 30N 2.8m/s after 2.52km
c.) 30N 2.8m/s after 3.36km
Fig. (16). Micrograph of worn surface of alkaline-treated CFRP
composite at 30N applied load.
respectively. The development of wear debris was distri-
buted on the rubbing surface and treated coir fibres were
adhered well after 3.36km.
4. CURRENT & FUTURE DEVELOPMENTS
From the experimental observations, it can be concluded
that:
1. Tribological performance strongly depends on the test
parameter (applied load, sliding distance and interfacial
temperature).
2. Untreated CFRP composites have higher wear rate for
different applied load. This is due to the debonding of
the coir fibre embedded in the matrix. Micro crack at the
untreated CFRP surface attributed to the removal of
material.
3. Surface modification (either bleached or alkaline
treated) on coir fibres exhibits good interfacial adhesion
when used as a reinforcement in polyester composites.
4. Alkaline treated CFRP composites have better wear
resistance compared to the bleached treated and
untreated CFRP composites. The high adhesion bonding
between the matrix and the coir fibre assists in
protecting the rubbing surface from worn.
5. Due to the fact that wear performance of such materials
are not universal at all test configurations and
conditions, abrasive wear performance of such materials
is recommended for the future work.
ACKNOWLEDGMENT
The participant authors would also like to acknowledge
financial support provided by Multimedia University.
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Chapter
In the course of the development of green products for automotive application, minimizing/eliminating the environmental impacts caused by polymer-based products is most important. Therefore, tribologists have been looking for the most attractive and alternative materials to polymer-based products. Natural fiber-reinforced polymer composites have emerged as a potential environment-friendly, eco-friendly, and cost-effective option to synthetic fiber-reinforced composites. Natural fiber-based composites with superior mechanical properties have attracted tribologists, as natural fibers are environment and eco-friendly, fully biodegradable, abundantly available, renewable and cheap, and have low density. The present review article emphasizes on tribological properties of natural fiber-based composites and the factors such as adhesiveness, volume fraction, and orientation of fiber influencing friction and wear behavior of the natural fiber-based composites. In this study, a review on the tribological behavior of natural fiber-reinforced composites is made to understand the effectiveness of treatment and hybridization on influencing factors of friction and wear.
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Mechanical properties of the regulator multifaceted schemes additional well than outmoded approaches Fuzzy logic in this research manufacture contracts around the construction procedure than spare coir sheath reinforced polymer composite material. The scheme of fuzzy logic organizer has three efforts to prosper accurate coir casing armored polymer composite lasciviously. It stood established to incomes for indicator lay-up distance to ethyl methyl ketone peroxide catalyst, cobalt naphthalene as an accelerator. Action of coir to NaOH at dissimilar reach retro is achieved in a oversight of advance fuzzy logic to attachment asset amongst fibres of environment resources and alignments upheld to coir fibres. To decompound breadth is invented secure at 3mm.Flexural asset to a fibres is enhanced afterwards benefaction the fibres for 10 hours of alkali operation. Established on the possessions dirty for choir, imagine fibres should be peculiar to using Fuzzy logic equally to support of green composites.
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Mechanical properties of the regulator multifaceted schemes additional well than outmoded approaches Fuzzy logic in this research manufacture contracts around the construction procedure than spare coir sheath reinforced polymer composite material. The scheme of fuzzy logic organizer has three efforts to prosper accurate coir casing armored polymer composite lasciviously. It stood established to incomes for indicator lay-up distance to ethyl methyl ketone peroxide catalyst, cobalt naphthalene as an accelerator. Action of coir to NaOH at dissimilar reach retro is achieved in a oversight of advance fuzzy logic to attachment asset amongst fibres of environment resources and alignments upheld to coir fibres. To decompound breadth is invented secure at 3mm.Flexural asset to a fibres is enhanced afterwards benefaction the fibres for 10 hours of alkali operation. Established on the possessions dirty for choir, imagine fibres should be peculiar to using Fuzzy logic equally to support of green composites.
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Mechanical properties of the regulator multifaceted schemes additional well than outmoded approaches Fuzzy logic in this research manufacture contracts around the construction procedure than spare coir sheath reinforced polymer composite material. The scheme of fuzzy logic organizer has three efforts to prosper accurate coir casing armored polymer composite lasciviously. It stood established to incomes for indicator lay-up distance to ethyl methyl ketone peroxide catalyst, cobalt naphthalene as an accelerator. Action of coir to NaOH at dissimilar reach retro is achieved in a oversight of advance fuzzy logic to attachment asset amongst fibres of environment resources and alignments upheld to coir fibres. To decompound breadth is invented secure at 3mm.Flexural asset to a fibres is enhanced afterwards benefaction the fibres for 10 hours of alkali operation. Established on the possessions dirty for choir, imagine fibres should be peculiar to using Fuzzy logic equally to support of green composites.
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Surface modifications of coir fibres involving alkali treatment, bleaching, and vinyl grafting are made in view of their use as reinforcing agents in general-purpose polyester resin matrix. The mechanical properties of composites like tensile, flexural and impact strength increase as a result of surface modification. Among all modifications, bleached (65°C) coir-polyester composites show better flexural strength (61.6 MPa) whereas 2% alkali-treated coir/polyester composites show significant improvement in tensile strength (26.80 MPa). Hybrid composites comprising glass fibre mat (7 wt.%), coir fibre mat (13 wt.%) and polyester resin matrix are prepared. Hybrid composites containing surface modified coir fibres show significant improvement in flexural strength. Water absorption studies of coir/polyester and hybrid composites show significant reduction in water absorption due to surface modifications of coir fibres. Scanning electron microscopy (SEM) investigations show that surface modifications improve the fibre/matrix adhesion.
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The tribo-potential of sugarcane fibre reinforcement in the thermoset polymers for enhancing the adhesive wear resistance has not been explored so far. Hence, the present work aims to explore the possibility of using this natural fibre to reinforce polyester and thus opens a new way to implement locally available inexpensive fibres and produce a new candidate tribo-material for bearing applications. Sugarcane fibre/polyester (SCRP) and glass fibre/polyester (GRP) composites (with chopped fibres of 1, 5, 10 mm length randomly distributed and unidirectional mat fibres) were prepared using compression mould and hand-lay-up techniques. Friction coefficients and wear rates of SCRP and GRP composites were determined under dry sliding contact conditions in parallel and anti-parallel orientations and subjected to different operating parameters such as load, speed and test duration.
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Coconut fibre has been used as reinforcement in low-density polyethylene. The effect of natural waxy surface layer of the fibre on fibre/matrix interfacial bonding and composite properties has been studied by single fibre pullout test and evaluating the tensile properties of oriented discontinuous fibre composites. The waxy layer provided good fibre–matrix bond such that removal of the layer resulted in drastic decrease of the fibre pullout stress, increase of the critical fibre length and corresponding decrease in tensile strength and modulus of the composites. The waxy layer of polymeric nature also exhibited a stronger effect on interfacial bonding than by grafted layer of a C15 long-chain alkyl molecule onto the wax-free fibre. The morphological features of the fibre along with its surface compatibility with the matrix favours oriented flow of relatively long fibres along with the molten matrix during extrusion.
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The aim of this paper is the improvement of the mechanical properties of natural-fibre-reinforced thermosets, as a result of optimization of the properties of tossa jute fibres by the use of an NaOH treatment process. By this process shrinkage of the fibres during treatment had significant effects on fibre structure and, as a result, on the mechanical properties of the fibres. The highest fibre strength and stiffness were reached by using isometric conditions (shrinkage=0%). The fracture mechanism of the fibre was also affected by the shrinkage state. Regarding fibre/matrix adhesion, the rougher surface morphology after NaOH treatment did not lead to any improvement. Composite strength and stiffness generally increased as a consequence of the improved mechanical properties of the fibres by NaOH treatment under isometric conditions. The Young's modulus of the composites was linearly dependent on fibre content for both untreated and treated fibre composites. The Young's moduli of composites with treated and untreated fibres were approximately 30% and 50%, respectively, lower than for comparable glass-fibre/epoxy composites. The improvement in dynamic modulus (measured in an increasing-load test) of the composites as a result of the use of treated fibres was similar to that observed for Young's modulus. Furthermore, the use of treated fibres and of higher fibre contents, both led to a decrease in fatigue behaviour and progress in damage in the composites. Impact damping was distinctly affected by the shrinkage state of the fibres during the NaOH treatment because of its influence on yarn toughness. A good correlation was found between composite impact damping and yarn toughness for the jute/epoxy composites investigated.