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Property Improvements of an Epoxy Resin by Nanosilica

Particle Reinforcement for Tribological Applications

SUBMISSION OF MINOR PROJECT FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY

in

Mechanical Engineering

By

SACHIN CHAINTHA (06305) AMAN CHANDEL (06318) SAURABH GUPTA (06315) ASHWANI THAKUR (06317)

Under the Guidance of

Dr. AMAR PATNAIK

Department of Mechanical Engineering

Department of Mechanical Engineering National Institute of Technology

Hamirpur April. 2009

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Property Improvements of an Epoxy Resin by Nanosilica Particle

Reinforcement for Tribological Applications

1. Introduction

Fibre reinforced polymer composites have many applications as a class of structural

materials because of their ease of fabrication, relatively low cost and superior mechanical

properties compared to polymer resins. A pre-requisite of most structural/engineering

materials is that they have good stiffness and strength along with adequate toughness.

Composites reinforced with man-made fibers like glass fibers usually fulfill this

requirement, especially since they exhibit crack-stopping capability which makes them

very attractive for structural or semi-structural applications. However, natural fiber

reinforced materials have inferior mechanical and wear-resistance properties than

conventional glass-fibre reinforced composites. In order to overcome these

disadvantages, several treatments have been proposed in the literature [1–4]. In spite of

this, in recent years, there is an increasing interest in natural fibers as substitutes for glass

fibers mainly because of their low specific gravity, low cost, as well as their renewable

and biodegradable nature [5]. Among the naturally available fibers again, there has been

a growing demand, more specifically, for the use of ligno-cellulosic fibers (derived from

plant leaf or bark) as reinforcing elements in polymeric matrix [6-10]. Several types of

natural fibres which are abundantly available like sisal, jute, coir, oil palm, bamboo,

wheat and flax straw, waste silk, banana have proved to be good and effective

reinforcement in the thermoset and thermoplastic matrices [11-19]. Sugarcane fibres are

long plant fibres, like hemp, flax [20-22], and bamboo [16,17] that have considerable

potential in the manufacture of composite materials. Natural fibre-reinforced polymers

exhibit very different wear properties, mechanical performances and environmental aging

resistances depending on their inter-phase properties, but most studies available in the

existing literature have been dedicated to fibre surface treatment [1-5]. And although

reinforcement of these natural fibers has long been an attractive option in composite

making, the potential of pine bark, as a reinforcing fiber has not been explored so far.

Hence the present work is undertaken to investigate exclusively the tensile, flexural as

well as the wear behaviour of this plant fibre (pine bark) reinforced composite. The

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Himalayan subtropical pine forests are renowned for being the largest in the whole of

Indo-Pacific areas. Various types of pine trees are found in this region; especially in

Himachal Pradesh, wide ranging tracts of Chir Pine are seen. The scientific name of Chir

Pine is Pinus roxburghii. Over the years these forests have faced several threats from the

modern day society. Overgrazing, cultivation, exploitation for fuel woods etc have

brought about degradation of this eco region. Hence, there is an urgent need for

plantation, preservation of this natural wealth and its utilization with great care and

sensibility.

Surprisingly, publications concerning the tribological behaviour of natural fiber

reinforced polymers are rare in the tribology literature. Only few articles were

concentrated on the use of sugarcane bagasse to reinforce low cost composites [23], and

to reinforce cement composite [24]. Furthermore, a series of researches was focused on

the study of abrasive wear behaviour of bamboo fibres [16-17, 25-28]. The work by El-

Tayeb [29] reports the adhesive behaviour of sugarcane reinforced polymer composites

as compared to that of glass reinforced polymer composites. It is strange that despite the

interest and environmental appeal of plant fibres, their use has been limited mostly to

non-tribological applications. It may be due to their lower strength and stiffness

compared with synthetic fiber reinforced polymer composites. However, the stiffness and

strength shortcomings of bio-composites can be overcome by structural configurations

and better arrangement in a sense of placing fibers in specific locations for highest

strength performance and also by hybridization of the composites. Composites having

two or more fillers contained in the same matrix are called hybrid composites [30,31].

Recently there is a growing interest in hybridizing different natural fibers in order to

produce high performance composite materials.

Against this background, the present investigation is undertaken to develop a new kind of

hybrid composite consisting of pine-bark fibers as the reinforcement, cement-kiln-dust as

the particulate filler and polyester as the matrix. Short fibers in the form of flakes of pine

tree barks, which are abundantly available in the Himalayan valley in northern India are

reinforced in polyester resin filled with a fixed quantity of cement kiln dust to prepare the

composites. The cement kiln dust is a by-product of the manufacture of Portland cement.

It is generated during the calcining process in the kiln. Apart from CaO, that constitutes

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roughly 60 % of the dust, other compounds present in it include SiO2, Al2O3, Fe2O3, K2O,

Na2O, Cl–, etc. The present work thus involves the development of this new class of

particle filled plant fiber reinforced composites and reports on their sliding wear

characteristics. Such multi-component hybrid composites form complex systems and

there is inadequate research reported on their wear characteristics. To study the

correlation between the wear properties and the characteristic parameters, e.g., the

composition of the composite and the operating conditions is of prime importance for

designing proper composites in order to satisfy various functional requirements. But

visualization of impact of any individual control factor in an interacting environment

really becomes difficult. To this end, an attempt has been made in this study to analyze

the impact of more than one parameter on abrasive wear behavior of the epoxy based

nanosilica filled composites. It is important as in actual practice the resultant wear rate is

the combined effect of more than one interacting variable. An inexpensive and easy-to-

operate experimental strategy based on Taguchi’s parameter design has been adopted to

study the effect of various parameters and their interactions. This experimental procedure

has been successfully applied for parametric appraisal in the wire electrical discharge

machining (WEDM) process, drilling of metal matrix composites, and erosion behavior

of polymer–matrix composites [32-37].

2. Identified Research Gaps

At present, the incorporation of the SiO2, particles in a polymer matrix on a nanoscale

level is a major challenge in this field. The formation of agglomerates which is observed

in composites prepared by conventional techniques can deteriorate the final properties of

the product. To overcome this problem, the sol-gel process for incorporating nanosilica

particles into a reactive epoxy resin may try in the works presented here. By this process,

inorganic or inorganic-organic materials can be produced from liquid starting materials

via a low temperature process. By employing chemical methods, nanoparticles can be

produced elegantly and free of agglomerates.

The major challenge is to transfer these nanosilica particles from the aqueous medium

into the prepolymer of a reactive epoxy resin without affecting the particle distribution. In

the liquid process, toxicological problems during handling of the pure nanoparticle

substances do not exist or can be eliminated at the initial stage. The incorporation of

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nanosilica particles also aims at a low shrinkage upon curing because this improves the

toughness and ductility of the cured products and also prevents debonding of the casting

compound from the matrix. The special nano-scaled design of the particles is the key to a

property enhancement. The silica phase consists of surface-modified, synthetic SiO2,

nanospheres with diameter of less than 50 nm and extremely narrow size distribution.

3. Specific objectives of this project work up to eight semesters

Keeping in view of the magnitude of the problem, current status of research and

preliminary findings based on some of the commercial composites the following

objectives are set in the scope of the present project work.

• Development of methods for the efficient fabrication of the SiO2 particles in a

polymer matrix on a nanoscale level.

• The formation of agglomerates which is observed in composites prepared by

conventional techniques can deteriorate the final properties of the product or not.

• To overcome this problem, the sol-gel process for incorporating nanosilica particles

into a reactive epoxy resin may try in the works presented here.

• By this process, inorganic or inorganic-organic materials can be produced from

liquid starting materials via a low temperature process. By employing chemical

methods, nanoparticles can be produced elegantly and free of agglomerates.

• Study on Structural and Mechanical Analysis of the composites. Structural

properties such as: Microstructure, Viscosity Studies of the Unfilled and Filled

Resin and Mechanical Properties like Three-Point Bending, Micro-hardness,

Fracture Toughness.

• Study on the tribological properties of the prepared composites and their failure

analysis (fracture surface).

4. Proposed Methodology

1. The raw materials needed for this work are epoxy resin, E-glass fibers and

incorporation of SiO2 particle under different weight percentage. These are to be

procured from different firms.

2. Composite slabs will be fabricated using injection molding technique following

prescribed norms for loading and curing. Specimens for various characterization

tests will be made as per required dimensions using a diamond cutter.

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3. Friction and dry wear test will be carried out using abrasive wear test rig. Wear rate

will be calculated on ‘mass loss’ basis under different operating conditions. Real

time wear situations will be simulated by varying the control factors such as: sliding

velocity, normal load, erodent size, sliding distance etc. The influence of each

factor on the material loss will be studied in an interacting environment. For this,

the experimental schedule will be designed as per Taguchi’s methodology. This will

lead to identify significant factors and the relative significance of their interactions.

4. The eroded samples will be examined under scanning electron microscope to get an

insight to the damage mechanism as a result of solid particle impact.

5. Experimental details

5.1. Specimen preparation

Glass fiber are reinforced epoxy resin composite mixed with nano-silica powder with

different weight percentage. The composites are cast by conventional hand-lay-up

technique so as to get square specimens (120x120 mm2). Composites of five different

compositions (0 wt%, 4 wt%, 8 wt% and 12 wt% of nanoSiO2) are made with the weight

fraction of glass fiber kept fixed (50 wt%) for all samples. Its common name is

Bisphenol-A-Diglycidyl-Ether and it chemically belongs to the ‘epoxide’ family. The

epoxy resin and the hardener are supplied by Ciba Geigy India Ltd. E-glass fiber and

epoxy resin have modulus of 72.5 GPa and 3.42GPa respectively and possess density of

2590 kg/m3 and 1100 kg/m3 respectively. The composite slabs are made by conventional

hand-lay-up technique followed by light compression moulding technique. A stainless

steel mould having dimensions of 210 × 210 × 40 mm3 is used. A releasing agent (Silicon

spray) is used to facilitate easy removal of the composite from the mould after curing.

The low temperature curing epoxy resin and corresponding hardener (HY951) are mixed

in a ratio of 10:1 by weight as recommended. The mix is stirred manually to disperse the

fibres in the matrix. Care is taken to ensure a uniform sample since fibres have a

tendency to clump and tangle together when mixed. The cast of each composite is cured

under a load of about 50kg for 24 h before it removed from the mould. Then this cast is

post cured in the air for another 24 h after removing out of the mould. Specimens of

suitable dimension are cut using a diamond cutter for physical characterization and

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mechanical testing. Utmost care has been taken to maintain uniformity and homogeneity

of the composite.

5.2. Abrasive wear test

The schematic representation of rubber wheel test set up is shown in Figure 1. In the

present study, silica sand (density 2.6 g/cm3) is used as the abrasive. The abrasive

particles of AFS 60 grade silica sand were angular in shape with sharp edges. The shape

of the silica sand used for abrasive wear study is shown in Figure 2. The abrasive is fed at

the contacting face between the rotating rubber wheel and the test sample. The tests were

conducted at a rotational speed of 100 rpm. The rate of feeding the abrasive is 255±5

g/min. The sample is cleaned with acetone and then dried. Its initial weight is determined

in a high precision digital balance (0.1mg accuracy) before it is mounted in the sample

holder. The abrasives were introduced between the test specimen and rotating abrasive

wheel composed of chlorobutyl rubber tyre (hardness: Durometer-A 58-62). The

diameter of the rubber wheel used is 228 mm. The test specimen is pressed against the

rotating wheel at a specified force by means of lever arm while a controlled flow of

abrasives abrades the test surface. The rotation of the abrasive wheel is such that its

contacting face moves in the direction of sand flow. The pivot axis of the lever arm lies

within a plane, which is approximately tangent to the rubber wheel surface and normal to

the horizontal diameter along which the load is applied. At the end of a set test duration,

the specimen is removed, thoroughly cleaned and again weighed (final weight). The

difference in weight before and after abrasion is determined. At least three tests were

performed and the average values so obtained were used in this study. The wear rate is

measured by the loss in weight, which is then converted into specific wear rate using the

measured density data. The specific wear rate (WS) is calculated from the equation:

WS = Δm/ρt VS.FN (1)

where

Δm is the mass loss in the test duration (gm)

ρ is the density of the composite (gm/mm3)

t is the test duration (sec).

Vs is the sliding velocity (m/sec)

FN is the average normal load (N).

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The specific wear rate is defined as the volume loss of the specimen per unit sliding

distance per unit applied normal load.

Figure 1. Schematic diagram of abrasive jet machine

5.3. Experimental design

Taguchi experimental design is a powerful analysis tool for modeling and analyzing the

influence of control factors on performance output. This method achieves the integration

of design of experiments (DOE) with the parametric optimization of the process yielding

the desired results. The orthogonal array (OA) requires a set of well-balanced (minimum

experimental runs) experiments. Taguchi’s method uses a statistical measure of

performance called signal-to-noise ratio (S/N), which is logarithmic function of desired

output to serve as objective functions for optimization. The S/N ratio considers both the

mean and the variability into account. It is defined as the ratio of the mean (signal) to the

standard deviation (noise). The ratio depends on the quality characteristics of the

product/process to be optimized. The three categories of S/N ratios are used: lower the-

better (LB), higher-the-better (HB) and nominal-the best (NB). The experimental

observations are transformed into a signal-to-noise (S/N) ratio. There are several S/N

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Abrasive hopper

Abrasive particles

Normal load

Composite sample

Nozzle

Rubber wheel

Steel disc

Sample holder

Particle collecting bag

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ratios available depending on the type of characteristics. The S/N ratio for minimum

erosion rate coming under smaller is better characteristic can be calculated as logarithmic

transformation of the loss function as shown below

Smaller is the better characteristic: (2)

where ‘n’ the number of observations, and y the observed data.

The most important stage in the design of experiment lies in the selection of the control

factors. Exhaustive literature review on erosion behavior of polymer composites reveal

that factors viz., impact velocity, filler content, erodent temperature, impingement angle,

stand-off distance and erodent size etc largely influence the erosion rate of polymer

composites [18]. Hence in the present work the impact of these five parameters are

studied using L16 (45) orthogonal design. In conventional full factorial experiment design,

it would require 45 = 1024 runs to study five factors each at four levels whereas,

Taguchi’s factorial experiment approach reduces it to only 16 runs offering a great

advantage in terms of experimental time and cost. The operating conditions under which

erosion tests are carried out are given in Table 1. The tests are conducted as per

experimental design given in Table 2 in which each column represents a test parameter

whereas a row stands for a treatment or test condition which is nothing but combination

of parameter levels [19].

The plan of the experiments is as follows: the first column is assigned to sliding velocity

(A), the second column to normal load (B), the third column to nano-silica content (C),

the fourth column to sliding distance (D) and the fifth column to erodent size (E),

respectively to estimate specific wear rate. Table 1. Levels of the variables used in the experiment

Level Control factor I II III IV Units A: Sliding velocity 60 120 180 240 cm/sec B: Normal load 10 20 30 40 N C: Fly ash content 75 70 65 60 % D: Sliding distance 500 1000 1500 2000 m E: Erodent size 200 300 400 500 µm

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Table 2. Orthogonal array for L16 (45) Taguchi Design Expt. No. A B C D E

1 1 1 1 1 1 2 1 2 2 2 2 3 1 3 3 3 3 4 1 4 4 4 4 5 2 1 2 3 4 6 2 2 1 4 3 7 2 3 4 1 2 8 2 4 3 2 1 9 3 1 3 4 2 10 3 2 4 3 1 11 3 3 1 2 4 12 3 4 2 1 3 13 4 1 4 2 3 14 4 2 3 1 4 15 4 3 2 4 1 16 4 4 1 3 2

6. Expected out come of this project work as:

The most important benefits expected from the nanosilica reinforcement are the

following: (i) lower viscosity of the resin formulation compared to common reinforcing

fillers and a complete suppression of sedimentation, (ii) increased fracture toughness,

impact strength, and modulus, (iii) improved scratch- and abrasion-resistance, (iv)

reduced shrinkage upon curing and reduction of the coefficient of thermal expansion, (v)

improved dielectric properties, (vi) improvement of heat distortion, chemical resistance,

glass transition temperature, durability and weathering stability, (vii) no adverse

influence on the processing characteristics of the basic resin The following section deals

with the exact description of the preparation of nanosilica-reinforced epoxies by the sol-

gel technique, and of the relation of their structure to various rheological, mechanical,

and tribological properties.

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7. Road Map for project Work: Time period Up-to Sixth Sem. Up-to Seventh Sem. Up-to Eight Sem. Jan-Mar-2009 May-2009 Jun-sept-09 Oct-09 Nov-Dec-09 Jan-Mar-09 Up to end

Sem Literature Survey: Sample preparation Results and Analysis: Calculation of erosion rate and exposure towards SEM.

Microstructure Observations/Aspects: will be done for all the three samples in order to asses the rate of erosion and type of fracture.

Mechanical Properties study Computer Simulation of thermal properties by Ansys-8 software and compare with experimental results.

Report writing and presentation

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