Krasnov et al. 2010 studies different processes having
polymers and polymer based materials running in contact. The studies related to
systems and regularities of friction and wear of such materials covers under
polymer tribology. However Mitrus,
Wojtowicz&Moscicki, (2009) explained that a single layer molecule developed by
joining the chain of small molecules in
a repeated manner is named as polymer. Moreover
the main purpose behind the development of polymers is to have a product having
unique physical and chemical properties. Chemists manipulate large, complex
molecules and capitalize on the connections between their molecular structure
and properties that make them light weight, hard strong and flexible with
distinct thermal, electrical and optical properties, thus making them useful in
major industries as packaging, transportation, fiber and communication
industries. Harsha &Tewari, (2003) emphasize that the polymer composites are developed
to enhance the wear resistance capability and also to minimize the coefficient
of friction. It concludes that polymer composites thus developed are for
tribological applications. Furthermore
they also studies the five types of wear observed in the practical scenarios.
These wear are abrasive, adhesive, fretting, erosion and fatigue wear. Chiu
et al. (2012) explained that the thermoplastics as polyaryletherketone (PEEK) and polyimides when blend
with solid lubricants results in reducing the coefficient of friction. Unal,
Sen & Mimaroglu, (2005) defined wear as loss of material when two material
are placed in contact with each other and there exist a relative motion between
the contact surfaces, thus wear is a damage to a solid surface.
Myshkin, Petrokovets&Kovalev(2006) explained that
a polymer surface which is under elastic, plastic and viscos-elastic
deformation depends upon material characteristics. The properties of polymers
like wear, friction resistance can be used with high effectiveness. This
effectiveness was explained by Sinha&
Briscoe (2009) with the
explanation that the polymers like films, bulk and composites are being used in
shoes, tires, brakes, bearings, MEMS, hair products and artificial human
joints. Wegner (2000) develop the
understanding about the importance of polymer surface properties particularly
in paints and thin coatings. These coatings are extensively used for corrosion
protection as adhesive or anti reflection layers. The best example is the
wetting behavior change of the film with respect to water from hydrophilic to
hydrophobic. This behavioral change is carried out by the addition of small
amount of a surface active component to a polymer material. Shalwan & Yousif(2012) discussed the
significance change in the tribological properties of polymer composites when
glass fiber is added. The common forms
of glass fiber produced in the industry are woven or chopped strand mats. However
Parallel (P-O), Anit-Parallel (AP-O), Normal (N-O) are the three
principle orientations of composites with respect to sliding directions. Also there are several studies have been investigated
the tribological behaviour of glass/polymer composites considering one
orientation (Normal, N-O). Chiu et al(2012) concluded by simulation investigation that the
highest friction corresponding gross
interfacial chain rearrangement is on the perpendicular sliding direction and
this is independent of the polymer type. Baldan. A, (2004) suggested that performance of the adhesive bond, the
adhered surface (metallic or non metallic) can be improved by using some pre
treatment. This pretreatment may be either by using the physical, mechanical,
chemical, photochemical, and thermal, or plasma method. However Zhou & Yan (2004) revealed that although the adhesion of the transfer
film to the counter face may be enhanced by the fillers which is an attribute
of wear reduction. However, the friction reducing and wear resistant mechanisms
of various fillers in different polymer matrices are not well understood. According to Zhou & Yan, (2004), it is feasible to improve the dispersion of fillers
by incorporating the compatibilizers in the composites. This will also increase
the adhesive ability between the polymers and the fillers. Interfacial adhesion canbe enhanced and the
depressed phase size can be reduced by some copolymers or graft
polymers with reactive groups and similar chemical structures. For example, polyethylene-graft-maleic anhydride
(PE-g-MAH) has been used as a compatibilizing agent in many polymer–polymer
alloys. Yan, Xue& Wang (2002)& Lai, Yue& Li (2007) introduced that preferential load of fillers also
help to enhance the wear reducing ability of fillers. This method was proposed
by Lancaster and further theoretically by Tanaka and Kawakami. Yan, Xue &
Wang (2002) divided the actions of metallic fillers on transfer
film in to two aspects. The hard filler exposed on the wear surface of the
composite can scrape the polymer transfer film on the counterpart surface; and
the transfer film composed of metallic filler can mechanically hold the polymer
forming the composite transfer film, because its mechanical strength is higher
than that of the polymer matrix. A steady state model of wear of polymer
composite material was explained by Blanchet & SUNG (1998). This model also includes the effects of preferential
load support by and surface accumulation of wear-resistant filler particles.
This theory was further developed by Han and Blanchet both experimentally and
theoretically. Yan,
Xue& Wang (2002) studied the transfer process and preferential
load support of hard fillers. The study was conducted to understand the
characteristics of metallic fillers under a type of extreme friction condition
as high load and reciprocating motion and the influence on the tribological
behavior and transfer of polymer composite was recorded. Moreover, Chiu et al (2012) developed the
hypothesis that the transfer film in the
polymer/polymer composites during sliding provide the protective and low shear
interfaces due to which the wear resistance is increased and friction
coefficient is reduced. Yousif
& Ku (2012) suggested that
natural fiber due to low density, high strength, high flexural modulus and high
impact strength are more preferable for developing polymer composites.
Furthermore the polymeric composites can be found in housing construction material, industrial and automotive
parts. Suresha et al. (2010) explained that by adding the fillers or reinforced
fibres, the mechanical properties of the
polymers are improved at higher rate as compared to the effect in the wear rate
which do not invariably beneficent. Also, Suresha et al, (2013) added the extensive applications of high strength and
stiffness polymers and its composites like epoxy, vinyl ester, polyamide (PA),
polyetheretherketone (PEEK), and polyphenylenesulfide (PPS). These polymers can
be manufactured by compression moulding/injection moulding with ease and
economics.
Skeist&Miron, (1990) reported adhesive cure is necessary to join together the
small resin molecules (mers) so that large molecules known as polymers could be
formed. For example, one of some adhesives, such as this wood adhesive, is used
only with specific substrates because of the cure time needed to allow for good
bonding. Although
Adhesion is considered as friction impact and Johnson- Kendal-Roberts model
theory used small and big sizes having the properties of polymers (Myshkin et
al. 2005). They also explained the way
the special instruments can be used to measure the molecular forces acting
between the solids. According to Deryagin et al. (cited in Myshkin et al. 2005,
p. 911), molecular attraction forces can be measured by applying the concept of
feedback balance. However these molecular forces are now being measured by
using atomic force microscopy. Also the mechanical energy dissipates when
deformation occurs between the two sliding surfaces. The deformation may be
elastic deformation, plastic deformation and visco-elastic deformation. Thus
this concludes that the adhesion and deformation is the source of fractional
forces (Myshkin et al. 2005, p. 913). Load, velocity and the temperature has the
direct effect on the friction. Firstly, friction force is proportional to the
applied load and coefficient of friction staying constant at load between
10-100 Newton. Secondly, sliding velocity has a relationship with friction. By
increasing velocity, viscous resistance will increase and at high velocity,
friction force will reduce due to short duration of contact. Thirdly,
temperature resulted from friction by converting mechanical energy to heat and
this heat is generated from friction and the source of this heat is deformation
of materials.
Yousif (2008) explained the performance
evaluation of polyester in terms of frictional and wear performance using dry
sliding contact against the smooth stainless steel using block-on-disk
(BOD) machine. The polyester is reinforced by the
multilayered (mainly three or four layers) of coir fiber. The results were the
worn surface analyzed on scanning electronic microscope and
wear rate and friction coefficient were calculated in different aspects
including;
·
Different
applied load between 10N to 30N.
·
Different
sliding distance between, (0km) to (4.2km).
This experiment
concluded that the coir
fibre-reinforced polyester (CFRP) composites with three layers are better than
four layers with better frictional and wear performance. Moreover, CFRP
composites with four layers gave a high friction coefficient (Yousif 2008).
Yousif (2008) concludes with some outcomes as follows:
·
Strong
interfacial adhesion between the polyester and the coir fibres which overcome
the pull out of fibres at the interface.
·
High coefficient
of friction was observed.
·
Reinforced
polyester with coir fibres has improved adhesive wear characteristic of (NP).
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