MICROSTRUCTURE AND MECHANICAL … AND MECHANICAL PROPERTIES OF EPOX ... labouratory using hounsfield (monsanto) tensometer, ... 3.3.1 Tensile Testing of Composite Samples - - -

1

MICROSTRUCTURE AND MECHANICAL

PROPERTIES OF EPOXY – RICE HUSK ASH

COMPOSITE

BY

NNAJI, NDUBUISI BENNERTH

REG NO:PG/M.ENG/08/49185

DEPARTMENT OF MECHANICAL

ENGINEERING

UNIVERSITY OF NIGERIA, NSUKKA

SEPTEMBER, 2012.

i

TITLE PAGE

MICROSTRUCTURE AND MECHANICAL PROPERTIES OF EPOX

Y- RICE HUSK ASH COMPOSITE

BY

NNAJI, NDUBUISI BENNERTH.

REG NO:PG/M.ENG/08/49185

A PROJECT REPORT SUBMITTED TO THE DEPARTMENT OF

MECHANICAL ENGINEERING, FACULTY OF ENGINEERING,

UNIVERSITY OF NIGERIA, NSUKKA IN PARTIAL FULFILMENT

OF THE REQUIREMENTS FOR THE AWARD OF MASTER OF

ENGINEERING (M.ENG) DEGREE IN MECHANICAL

ENGINEERING WITH SPECIALIZATION IN MATERIALS

TECHNOLOGY AND MECHANICS.

SEPTEMBER, 2012.

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APPROVAL PAGE

This project report has been approved as meeting the requirements for

the award of Master of Engineering (M.Eng) Degree in Mechanical

Engineering with Specialization in Materials Technology and Mechanics,

University Of Nigeria, Nsukka.

By

. . . . . . . . .. . . . . . . . .. . . . . . .. . ….

Engr. Prof. D.O.N. Obikwelu Date

(Supervisor)

. . . . . . . . . . . . . . . . . . . . . . . . …..

Date

(Head of Department)

. . . . . . . . . . . . . . . . . . . . .

Dean of Faculty Date

. . . . . . . . . . . . . . . . . . . . . . . . ….

External Examiner Date

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CERTIFICATION

This is to certify that this project is an original work carried out by

Nnaji, Ndubuisi Bennerth with Registration No: PG/M.ENG/08/49185 in

partial fulfillment of the requirements for the award of Master of

Engineering degree in Mechanical Engineering with specialization in

Materials Technology and Mechanics.

………………………………

Engr. Prof. D.O.N Obikwelu

Project Supervisor

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DEDICATION

This project is dedicated to my late father.

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ACKNOWLEDGMENT

My profound gratitude is expressed to the Almighty God for giving me life,

knowledge and resources to complete this study.

I express my unalloyed regards, indebtedness and deep appreciation to my

project supervisor and all the lecturers in Mechanical Engineering Department

University of Nigeria Nsukka, for scholarly criticisms, meticulous teachings and

sagacious advice throughout the study.

The fervent support of my mother, brothers, sister and brother-in-law is

highly appreciated.

Thanks to the management of the following establishments; Sheda Science

and Technology Complex, Abuja; Standards Organization of Nigeria, Enugu;

National Root Crops Research Institute, Umudike; Strength of Materials

Laboratory, University of Nigeria, Nsukka and Polymer and Textile Engineering

Laboratory, Federal University of Technology, Owerri. The technical staff of the

establishments listed above provided the professional advice and characterization

machines that helped me to finish this research. I acknowledge the assistance

rendered to me by my friends and course mates.

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ABSTRACT

This study is about the production and characterization of epoxy-rice husk

ash composite. Composites were produced at 10%,20%,30%,40% and 50%

volume fraction of Rice Husk Ash(RHA) fillers and the epoxy was cast neat at

0%RHA which served as the control .The microstructure of the composites were

studied with Scanning Electron Microscopy(SEM) and Energy Dispersive X-ray

Spectroscopy(EDX).Mechanical properties of the composites such as tensile

properties(tensile stress, tensile strain, Young’s modulus, tensile strength and

percentage elongation at fracture),compressive strength, toughness, flexural

strength and hardness were experimentally determined in the engineering

labouratory using hounsfield (monsanto) tensometer, charpy v-notch impact

testing machine, flexural testing machine and Rockwell hardness testing machine.

The Scanning Electron Microscopy (SEM) analysis showed that interfacial

interactions existed between the rice husk ash particles and the epoxy matrix.

Energy Dispersive X-ray Spectroscopy (EDX) analysis indicated that interfacial

reactions existed between the epoxy matrix and the rice husk ash particles

because the composites did not contain homogenous elements. However each of

the composites contained C,O,Si and Cl while the cast neat epoxy(control)

contained C,O and Cl. Results of the mechanical property tests showed low gain

in hardness, toughness, flexural strength and Young’s modulus. The tensile

properties showed: that at 40%RHA the highest tensile strength of 37.006MPa was

obtained, the cast neat epoxy (control 0%RHA) had the best Young’s modulus of

356.538MPa and percentage elongation at fracture improved from 1.3% to 2.0%

as volume fraction of rice husk ash increased from 0% to 10%,20%,30%,40% and

50%.Increasing the volume fraction of rice husk ash from 0% to 10%,

20%,30%,40% and 50% led to decrease of these mechanical properties: toughness

from 2.0J to 0.3J,hardness from 344hardness value to 144 hardness value and

flexural strength from 6.0Mpa to 1.50Mpa.There was significant improvement in

the compressive strength of the composites from 15.75MPa to 18.75MPa as the

volume fraction of rice husk ash increased from 0% to 10%,20%,30%,40% and

50%.It was deduced from the study that epoxy-rice husk ash composite is

suitable for engineering applications subjected to compression. Surface coating of

rice husk ash could be used to improve its adhesion to the epoxy matrix in order

to enhance the mechanical properties of the composites for other engineering

applications.

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TABLE OF CONTENTS

Title Page - - - - - - - - - - i

Approval Page- - - - - - - - - ii

Certification - - - - - - - - - iii

Dedication - - - - - - - - - - iv

Acknowledgement - - - - - - - - - v

Abstract - - - - - - - - - vi

Table of Content - - - - - - - - vii

List of Figures - - - - - - - - x

List of Tables - - - - - - - - xiii

List of Plates - - - - - - - - - xv

CHAPTER ONE: INTRODUCTION

1.1 Background Information - - - - - - 1

1.2 Statement of the Problem - - - - - - 5

1.3 Objectives of the Study - - - - - - 6

1.4 Justification of the Study - - - - - - 7

1.5 Scope and Limitations of the Study - - - - - 7

CHAPTER TWO: LITERATURE REVIEW

2.1 Overview of Composites - - - - - - 9

2.2 Rice Husk Ash - - - - - - - - 14

2. 2.1 Industrial Applications of Rice Husk Ash - - - - 15

2.3 Epoxy - - - - - - - - - 16

2.3.1 Curing of Epoxy Resins - - - - - - 17

2.5.2 Engineering Applications of Epoxy - - - - 17

2.4 Compressive Strength - - - - - - 18

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2.5 Toughness - - - - - - - - 19

2.6 Flexural Strength - - - - - - - 19

2.7 Hardness - - - - - - - - 19

2.8 Tensile Properties - - - - - - - 20

2.8.1 Stress - - - - - - - - - 20

2.8.2 Strain - - - - - - - - - 20

2.8.3 Tensile Strength - - - - - - - 21

2.8.4 Young’s Modulus - - - - - - - 22

2.8.5 Elongation at Fracture - - - - - - 22

2.9 Scanning Electron Microscopy - - - - - 23

2.9.1 Components of a Scanning Electron Microscope - - 25

2.10 Energy Dispersive X-Ray Spectroscopy - - - - 26

2.10.1 Applications of Scanning Electron Microscopy – Energy Dispersive

X-Ray Spectroscopy Analysis - - - - - 29

2.11 Microstructure - - - - - - - - 30

2.12 Adhesion and Cohesion - - - - - - 31

2.13 Calculation of Fiber Volume Fraction - - - - 32

CHAPTER THREE: MATERIALS AND METHODS

3.1 Materials - - - - - - - - - 33

3.1.1 Matrix Material - - - - - - - 33

3.1.2 Filler Material - - - - - - - - 33

3.2.0 Methods - - - - - - - - 34

3.2.1 Preparation of Composite Mould - - - - - 34

3.2.2 Composite Fabrication - - - - - - 35

3.3 Mechanical Property Tests - - - - - - 37

3.3.1 Tensile Testing of Composite Samples - - - - 37

3.3.2 Compressive Strength Test - - - - - - 38

3.3.3 Toughness Test - - - - - - - 38

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3.3.4 Hardness Test - - - - - - - - 39

3.3.5 Flexural Strength Test - - - - - - 39

3.4 Scanning Electron Microscopy and Energy Dispersive X- Ray

Spectroscopy Analysis - - - - - 40

CHAPTER FOUR: RESULTS AND DISCUSSION

4.1 Results - - - - - - - - - 42

4.1a Results for Mechanical Properties - - - - - 43

4.1b Results of Scanning Electron Microscopy Analysis - - 53

4.1c Results of the Energy Dispersive X-Ray Spectroscopy Analysis 61

4.2 Discussion of Results - - - - - - - 70

4.2.1 Mechanical Properties - - - - - - 70

4.2.1a Tensile Properties - - - - - - - 70

4.2.1b Toughness - - - - - - -- - 72

4.2.1c Hardness - - - - - - - - 73

4.2.1d Flexural Strength - - - - - - - 73

4.2.1e Compressive Strength - - - - - - 73

4.2.2 Scanning Electron Microscopy Analysis - - - - 74

4.2.3 Energy Dispersive X-Ray Spectroscopy Analysis - - 76

CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion - - - - - - - 78

5.2 Recommendations - - - - - - - 79

References - - - - - - - - - 80

Appendix I- - - - - - - - - - 85

Appendix II - - - - - - - - - 86

Appendix III - - - - - - - - - 87

Appendix IV - - - - - - - - - 88

Appendix V - - - - - - - - - - 91

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LIST OF FIGURES

Figure 2.1: Reaction and structure of a typical epoxy resin - - 17

Figure. 2.2 Stress and strain curve - - - - - 21

Figure 2.3: SEM column and specimen chamber - - - 25

Figure 2.4: EDS spectrum of the mineral crust of Rimicaris exoculta 28

Figure 2.5: Energy transitions during EDX analysis - - - 28

Figure 3.1 Mold - - - - - - - - 34

Figure 4.1 Stress- strain graph for cast neat epoxy - - - 48

Figure 4.2 Stress-strain graph for epoxy – rice

husk ash composite (90%epoxy 10%rice husk ash) - - - 48

Figure 4.3 Stress-strain graph for epoxy-rice husk ash composite

(80%epoxy 20%rice husk ash) - - - - - 49

Figure 4.4 Stress-strain graph for epoxy – rice husk ash composite

(70%epoxy 30% rice husk ash) - - - - - 49

Figure 4.5 Stress-strain graph for epoxy- rice husk ash composite

(60%epoxy 40% rice husk ash) - - - - - 50

Figure 4.6 Stress-strain graph for epoxy- rice husk ash composite

(50% epoxy 50% rice husk ash) - - - - - 50

Figure 4.7 Tensile strength - %RHA graph - - - - 50

Figure 4.8 Young’s modulus - %RHA graph - - - - 51

Figure 4.9 Elongation at fracture - %RHA graph - - - 51

Figure 4.10 Energy absorbed (toughness) - %RHA graph - - 51

Figure 4.11 Hardness value - %RHA graph - - - - 52

Figure 4. 12 Flexural strength - %RHA graph - - - - 52

Figure 4.13 Compressive strength - %RHA graph - - - 52

Figure 4.14 Scanning electron micrograph of Adani rice husk ash at

200x magnification - - - - - - - 53

Figure 4.15 Scanning electron micrograph of Adani rice husk ash at

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2000x magnification - - - - - - 54

Figure 4.16 Scanning electron micrograph of cast neat epoxy at 200x

magnification - - - - - - - 54

Figure 4.17 Scanning electron micrograph of cast neat epoxy at

2000x magnification - - - - - - - 55

Figure 4.18 Scanning electron micrograph of epoxy –rice husk ash composite

containing 10% rice husk ash at 200x magnification - - - 55

Figure 4.19 Scanning electron micrograph of epoxy- rice husk ash composite

containing 10% rice husk ash at 2000x magnification. - - - 56

Figure 4.20 Scanning electron micrograph of epoxy – rice husk ash composite







containing 30% rice husk ash at 2000x magnification - - 58

Figure 4.24 Scanning electron micrograph of epoxy-rice husk ash composite



containing 40% rice husk ash composite at 2000x magnification - 59





Figure 4.28 EDX spectrum of cast neat epoxy - - - - 61

Fig 4.29 Quantitative results for cast neat epoxy - - - 62

Figure 4.30 EDX spectrum of epoxy- rice husk ash composite (90% Epoxy,

10% RHA) - - - - - - - - 63

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Figure 4.31 Quantitative results for epoxy – rice husk ash composite

(90% Epoxy 10% RHA) - - - - - - - 64

Figure 4.32 EDX spectrum of epoxy- rice husk ash composite

(80% Epoxy, 20% RHA) - - - - - - - 64


(80%Epoxy 20%RHA) - - - - - - - 65

Figure 4.34 EDX spectrum of epoxy – rice husk ash composite (70%

Epoxy, 30% RHA) - - - - - - - - 66

Figure 4.35 Quantitative results for epoxy –rice husk ash composite

(70%Epoxy 30%RHA) - - - - - - - 67

Figure 4.36 EDX spectrum of epoxy rice husk ash composite

(60% Epoxy, 40% RHA) - - - - - - - 67

Figure 4.37 Quantitative results of epoxy –rice husk ash composite

(60%Epoxy 40%RHA) - - - - - - - 68

Figure 4.38 EDX spectrum of epoxy- rice husk ash composite (50% Epoxy,

50% RHA) - - - - - - - - - 69


(50%Epoxy 50%RHA) - - - - - - - 70

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LIST OF TABLES

Table 3.1a Chemical com position of the rice husk ash used for the study. 34

Table 3.1b Composition of the composites - - - 36

Table 3.1c Dimensions of specimen for different mechanical property

tests - - - - - - - - - 36

Table 4.1: Load, Extension, Stress, Strain Values For Cast Neat Epoxy

(100% Epoxy 0% RHA,) - - - - - - 43

Table 4.2: Load, Extension, Stress, Strain Values For

Epoxy-Rice Husk Ash Composite (90% Epoxy 10% RHA) - - 43


Epoxy-Rice Husk Ash Composite (80% Epoxy 20% RHA ) - - 44


Epoxy-Rice Husk Ash Composite (70% Epoxy 30% RHA) - 44


Epoxy-Rice Husk Ash Composite ( 60% Epoxy 40% RHA) - - 45


Epoxy-Rice Husk Ash Composite (50% Epoxy 50% RHA) - - 45

Table 4.7 Tensile Strength - - - - - - 45

Table 4.8: Young’s Modulus - - - - - - 46

Table 4.9: % Elongation at Fracture - - - - - 46

Table 4.10: Toughness Test Result - - - - - 46

Table 4.11: Hardness Test Result (Rockwell) - - - - 46

Table 4.12: Flexural Strength Test Result - - - - 47

Table 4.13: Compressive Strength Test Result - - - - 47

Table 4.14 Elemental composition of cast neat epoxy - - - 61

Table 4.15 Elemental composition of epoxy- rice husk ash composite

(90% epoxy 10% RHA) - - - - - - - 63

Table 4.16 Elemental composition epoxy-rice husk ash composite

(80%Epoxy 20%RHA) - - - - - - - 65

xiv

Table 4.17: Elemental composition of epoxy –rice husk ash

composite (70%Epoxy30% RHA) - - - - - 66

Table 4.18 Elemental composition of epoxy –rice husk ash composite

(60%Epoxy 30%RHA) - - - - - - - 68

Table 4.19 Elemental composition of epoxy – rice husk ash composite

(50%Epoxy 50%RHA) - - - - - - - 69

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LIST OF PLATES

Plate 1: Rice husks piles being burnt in rice Mills - - - 87

Plate 2: Close-up of burning rice husk - - - - - 87

Plate 3: Rice husk ash - - - - - - - 87

Plate 4 Mixing of the epoxy - - - - - - 88

Plate 5: Curing of the composites- - - - - - 88

Plate 6: Hardness test specimen - - - - - - 89

Plate 7 Tensile test specimen - - - - - - 89

Plate 8: Cast composites. - - - - - - - 90

Plate 9: Compressive test specimen - - - - - 90

Plate 10: Hounsfield Tensometer - - - - - - 91

Plate11: Charpy impact testing machine - - - - - 92

Plate 12: Rockwell hardness tester - - - - - - 94

Plate 13: Flexural testing machine - - - - - 94

Plate 14: Carl Zee’s Scanning electron microscope - - - 95

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1

CHAPTER ONE

INTRODUCTION

1.1 Background Information

Most times engineers are faced with the task of developing a new material that

has light weight, low cost and good mechanical properties. A promising option to

this task is to use a low density particulate material like rice husk ash in a polymer

matrix to form a polymer composite. Rice husk ash is a by-product of combustion

of rice husk at rice mills (Zemke and Woods, 2008). Researchers are currently

investigating the use of ash for composite production since ash is an abundant

agricultural waste, is renewable and has low bulk density. Rice husk ash had

been applied in other areas like manufacturing insulating powder, production of

refractory bricks, cement production and sandcrete block production. However

there are limited applications of rice husk ash in composite production.

A composite material is a microscopic or macroscopic combination of two

or more distinct materials with a recognizable interface between them. In a

composite material the constituents do not dissolve or merge completely in one

another. Normally the components in a composite material can be physically

identified and they exhibit interface between one another. A particulate composite

consists of a matrix reinforced with a dispersed phase in form of particles. Soft

particles like coir dust, rice husk flour, baggase ash, sawdust and rice husk ash can

be dispersed in a harder matrix to improve machinability and reduce coefficient of

friction (Lake,2002;Jiquao et al, 2010)

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2

One advantage of a composite is that two or more materials could be combined to

take advantage of the good characteristics of each of them.

Composites are gaining a wide range of applications in engineering because of the

following advantages: weight savings, corrosion resistance, easy manufacturing,

low temperature processing, possibility of producing novel shapes, reduced parts

and long fatigue life (Nowosielki et al, 2006;Ranganathatiah,2010).

Composites can be made of two or more components, the matrix and the

dispersed phase. The properties of a composite material depend on the following :

properties of the matrix; properties and distribution of reinforcement, nature of

bonding at the interface and volume fractions occupied by the constituents (Lake,

2002).

A matrix is a material in which the reinforcements or other components of a

composite system are embedded. It can be made of metal, ceramic or polymer

(Askeland, 1994). The purpose of the matrix is to bind the reinforcements together

by virtue of its cohesive and adhesive characteristics, to transfer load to and

between the reinforcements and to protect the reinforcements from environment

and handling. The matrix is often the weak link in a composite when viewed from

a structural perspective. Chemical treatment of reinforcement materials or filler

increase interfacial adhesion between the matrix and fillers leading to better

mechanical properties of the composites (Gauthier et al, 1998). It is in view of

these expected roles of matrix materials that epoxy resin was used in this study.

3

A polymer matrix composite is a composite formed by the combination of a

polymer (resin) matrix and a fibrous reinforcing phase (Ezuanmustapha et al,

2005). Polymer composites are gaining importance as substitute for metals in

applications in the aerospace, automotive, marine, sporting goods and electronics

industries due to their light weight and corrosion resistance. Polymer matrix can

be classified as thermoplastics and thermo set. Thermoplastics include low density

polyethylene, high density polyethylene, nylon, polypropylene and polyester while

epoxy resin is an example of a thermo set.

Epoxy resin is currently of much research interest due to its superior properties

over polyester resin. Some of the properties of the epoxy resin identified by

researchers are low cure shrinkage, better resistance to moisture, better

mechanical properties, processing flexibility and better handling.

Epoxy resins are presently used more than all other matrices in advanced

composite materials for structural applications in the United States of

America(USA) Air Force and Navy. The dispersed phase of a composite refers to

the reinforcement or fillers added in the matrix and the role of reinforcement in

a composite material is to increase the mechanical properties of the neat resin

system (Askeland, 1994).

Filler materials are generally the inert materials which are used in composite

materials to reduce cost, absorb thermal stresses, improve mechanical properties

to some extent and in some cases to improve processing (Singla and Chawla,

2010). Fillers which increase bulk volume and hence reduce cost are known as

4

extender fillers while those that improve mechanical properties particularly tensile

strength are termed reinforcing fillers (Igwe and Onuegbu, 2010).

Many researchers like Suwanprateeb and Hathapamit(2002), Zemke and

Woods(2009) are optimistic to find out whether rice husk ash is a reinforcing

filler or an extender filler. The current challenge is to make composite production

cost effective and this has resulted to high filler loadings. An interface is the

boundary between the individual, physically distinguishable constituents of a

composite. It is the bonding surface or zone where discontinuity occurs. Interface

must be large and exhibit strong adhesion between the fibers and the matrix.

Wetting occurs at the interface and its failure at the interface is called debonding

which may or may not be desirable. Interfacial bonding is a bonding type in

which the surfaces of two bodies in contact with one another are held together by

intermolecular forces like covalent, ionic, vanderwaals and hydrogen bonds.

Interfaces have been identified as zones where compositional, structural and

mechanical properties are altered in composites. Mechanical properties are

properties of a material that are associated with elastic and inelastic reaction when

force is applied or the properties involving relationship between stress and

strain(Royalance, 2008).

Microstructure is the microscopic description of individual constituents of

a material. Microstructure studies of composites show what happens at the atomic

and microscopic levels of the interface.

5

Electron microscopy analysis is used to characterize the microstructure of

composites. Scanning electron microscopy shows the morphology and topography

of the composites while compositional analysis is conducted using energy

dispersive x-ray spectroscopy. Energy dispersive x-ray spectroscopy is a chemical

microanalytical technique used in conjunction with scanning electron microscopy

to determine the elements in the microstructure of a material.

1.2 Statement of the Problem

Most developing countries like Nigeria are not yet properly utilizing

agricultural wastes such as rice husk ash for gainful engineering production. Rice

husk ash constitutes environmental pollution and causes health hazards like

silicosis, cancer, tuberculosis, chronic cough and sight disorder in areas where it is

dumped. Therefore there is need to develop more ways of reducing the amount of

the waste in the environment. One of the easiest ways of solving the problem is to

rice husk ash as filler in epoxy matrix to form epoxy-rice husk ash composite.

Epoxy based composites can be used in producing sole of shoes, side stools ,slabs,

industrial flooring and other components for electrical and industrial engineering.

Material engineers are facing the problem of developing materials that have

low cost, light weight and enhanced mechanical properties for executing

construction works. Metals which have good strength are insidiously affected by

corrosion and heavy weight making the search for alternative materials like epoxy

based composites that can be substituted for metals in some engineering

6

applications inevitable. Particle filled composites are gaining wide research

interest due to the problem of delamination and fiber pullout associated with

fibrous composites. The behavior of epoxy resins have not been fully understood

by researchers especially its slow curing character. Microstructural study of the

effect of interfacial adhesions between particle and matrix is fundamental in

understanding mechanical behavior of polymer composites.

1.3 Objectives of the Study

The general objective of this project is to characterize composite materials

produced from different compositions of epoxy and rice husk ash. The specific

objectives of the study are:

1. To produce epoxy-rice husk ash composite using rice husk ash considered as

an agricultural waste as a filler.

2. To conduct scanning electron microscopy and energy dispersive x-ray

spectroscopy analysis on epoxy –rice husk ash composite and study the

effect of variation of rice husk ash volume fractions on the microstructure.

3. To carry out scanning electron microscopy on Adani Rice husk ash.

4. To examine the effect of rice husk ash volume fraction on some mechanical

properties of epoxy- rice husk ash composite and ascertain the suitability of

the composite for engineering applications.

1.4 Justification of the Study

7

This study is valuable in understanding the potentials of rice husk ash as

filler in composite production and the behavior of Epoxy resins. The study is

useful to engineers and researchers in the composite industry because it will help

to suggest ways of improving the mechanical properties of the epoxy-rice husk ash

composite. Composite production can offer employment opportunity to

unemployed youths due to low energy and machinery requirements for

production. The knowledge of microstructure and mechanical properties of

particle filled composites is vital in describing the behaviours at the interface and

the effect of forces on the composites. Proper understanding of the microstructure

and mechanical properties of composites will help to ascertain the engineering

application of composite in structures, industries, electronics, oil and gas, and

other industrial production.

1.5 Scope and Limitations of the Study

Experimental approach was used in this study involving composite

production, microstructural analysis using scanning electron microscopy and

energy dispersive x-ray spectroscopy as well as the determination of the

mechanical properties of the composite material. The composites were produced at

0%, 10%, 20%, 30% 40% and 50% volume fraction of rice husk ash fillers. The

rice husk used in the study was sourced from Adani rice mill, Enugu State,

Nigeria. Apart from production of the amorphous rice husk ash at 550oC

all other

experiments were done at room temperature. In order to adequately view the

8

particle and matrix interfacial interactions two magnifications of 200x and 2000x

were used for the scanning electron microscopy analysis. Lack of accessibility to

transmission electron microscope hindered possibility of investigating other

microstructural features. Other limitations faced in the research were sourcing the

epoxy resin and getting the characterization equipment.

9

CHAPTER TWO

LITERATURE REVIEW

2.1 Overview of Composites

The encyclopedia of life support defined composite material as a

multiphase material in which the phase distribution and geometry have been

controlled in order to optimize one or more properties. The intention of producing

a composite material is to make a material that combines the best properties of the

components whilst eliminating any poor properties. Composites are also materials

that comprise strong load carrying materials known as reinforcement embedded in

a weaker material known as matrix (Askeland, 1994).

Reinforcement provides strength and rigidity, helping to support structural

load. The matrix or binder (organic or inorganic) maintains the position and

orientation of the reinforcement.

The use of composites started many centuries ago. The Book of Exodus in

the Christian Bible recorded that straws were used to produce rigidity and strength

in mud walls. Historical examples include the use of bamboos as a reinforcing

material in mud walls in houses by Egyptians (15000BC) and laminated metals in

the forging of swords (1800AD). In the 20th

century, modern composites were

used in the 1930’s, where glass fibers reinforced resins. Boats and aircrafts were

built out of these glass composites commonly called fiberglass (wikipedia.org.

composite materials).

9

10

Since the 1970’s the application of composite materials has widely

increased due to development of new fibers such as carbon, boron and aramids and

new composite systems with matrices made of metal and ceramics.

Singla and Chawla (2010) produced epoxy-fly ash composites at high filler

loading using fly wheel ash particles. They found that as the Fly wheel ash

particles loading increased the compressive strength of the composites increased

while the impact strength reduced. Kulkurni and Krishore (2003) studied the

mechanical properties of fiber epoxy composites. The result of the study showed

that the addition of fly ash particles to epoxy matrix led to reduction of the density

and increase in the modulus of the composites. According to Cattaleeya et al

(2008) rice husk ash is not considered good reinforcing filler in rubber composites

due to the large particle size and low reactive functional group at the filler surface.

The reinforcing effect of rice husk ash is not as good as silica and carbon black,

but is only comparable to calcium carbonate (CaCO3). Cattaleeya et al were of the

view that chemical surface treatment of rice husk ash prepared under special

condition is effective in reinforcement only at low filler loading.

Hathapamit (2003) compared the suitability of silica particles and rice husk

ash particles for embedding composites in electronic devices. In his study he

found that silica filled epoxy composites had better tensile strength than the rice

husk ash filled epoxy composites but the mixing viscosity, water absorption and

coefficient of thermal expansion were better than the silica filled composites.

Osureminda and Abode (2010) reinforced rubber products with baggase ash fillers

11

and succeeded in improving the tensile strength, abrasion resistance and hardness

of rubber composites with increasing filler loading while the elongation at break

and compressive strength decreased.

According to Hanseung et al (2008) rice husk floor is not good reinforcing

filler for polymer composites but can be utilized as biodegradable filler in

polymeric materials to minimize environmental pollution. They found from the

study of mechanical properties of polypropylene composites that addition of rice

husk flour decreased the mechanical properties of the composites due to poor

interfacial bonding between the matrix and the filler and holes formed in the

microstructures because of pulling of filler particles in the matrix.

Ahmadi et al (2007) found that replacement of cement with rice husk ash

up to 20% volume in the matrix will improve the mechanical properties of the

concrete. The researchers posited that using pozzolans like rice husk ash will

reduce the utilization of cement and lower the cost of buildings.

Yunfu et al (2008) were of the view that particle size, particle matrix

interface adhesion and particle loading affect mechanical properties of

composites. They found that introduction of rigid fillers like Al2O3, glass, CaCo3

into epoxy matrix normally result to decrease in mechanical properties. Yunfu et

al further stated that coupling agents should be used in filler composites to

improve adhesion and that tensile modulus is not affected by adhesion but by

filler loading. The researchers found that using nano fillers increased the stiffness

of composites.

12

The findings of Sapuan et al (2005) showed that fiber treatment improved

interfacial bonding between fiber and epoxy matrix and led to better mechanical

properties of the spathe-fibre reinforced composite laminates.

Arukalam and Madufor (2011) studied the effect of filler loading on some

mechanical properties of calcite-filled low density polyethylene composite. They

found that as the filler loading increased tensile strength, tensile modulus and

elongation at break (ductility) of the composites reduced. There were gains in

hardness of the composites because calcite obtained from snail shell is harder than

the low density polyethylene matrix. Srinavasa and Bharath (2011) investigated

the hardness and impact properties of Areca fiber epoxy-reinforced composites.

They treated areca fibers extracted from areca husk with potassium hydroxide to

get better interfacial bonding between the fiber and the epoxy matrix. Mechanical

properties of the composites increased as the fiber volume fraction and composite

post curing time increased. They concluded that mechanical properties of fiber

reinforced composites depend on the nature of matrix material, the distribution and

orientation of reinforcing fibers and the nature of the fiber matrix interfaces and

interphase region.

According to Srinavasa and Bharath, Arecafiber – epoxy reinforced

composite is a good material in fabrication of lightweight materials used in

automobile body building, office furniture, packaging industry and partition panel.

Egwaikhade et al (2007) developed rubber composites using palm kernel

shell husk. The study proved that palm kernel husk is a potential filler for natural

13

rubber compounds because addition of palm kernel shell husk fillers improved

some mechanical properties.

Due to the continuous decrease of mechanical properties at higher filler

loadings associated with untreated fibers and fillers most researchers have

advocated the coating of fillers with coupling agents. According to the report from

handbook of USA Department of Defense (2002) coupling agents are substances

that are used in small quantities to treat a surface so that bonding occurs between it

and other surfaces. Coupling agents include bonding agents and surfactants

(surface reactive agents), compatibilizers and dispersing agents. Organic coupling

agents produce stronger adhesion and include isocyanides, anhydrides, silanes

and anhydride modified co-polymers.

Gauthier et al (1998) reported that adhesion can be improved using

coupling agents like maleic anhydride to incorporate hydroxyl groups on the

matrix through hydrophilization and consequently enhancing wetting effect of the

resin on the fillers.

Ranganathatiah(2010) did a comparative study of mechanical properties of

composites formed from epoxy matrix modified with amine containing silicone

and unmodified epoxy matrix using fly ash and calcium aluminosilicate as fillers.

He discovered that the fillers interacted favorably with the modified matrix and

mechanical properties were improved at higher loads.

Ezuanmustapha et al (2005) incorporated 4wt% of a coupling agent matrix

anhydride modified polypropylene into composites prepared with rice husk and

14

polypropylene matrix. It was observed that the addition of MAPP coupling agent

increased the flexural strength of the composites but decreased the flexural

modulus and impact strength. Razman etal(2003) studied the effect of chemical

modification of rice husk and reports that with chemical modification the

reinforcing effect can be increased to an acceptable limit.

2.2 Rice Husk Ash

Rice husk is an agricultural by product from the rice mill. It constitutes

about 20% of the weight of rice. Rice husk contains about 50% cellulose, 25%-30

lignin and 15-20% silica (Abubaker et al, 2010). Rice husk ash is the general term

used to describe all the types of ash produced from burning rice husk (Zemke,

2009). If the burning process is incomplete carbonized rice husk is produced. At a

burning temperature range of 550oC to 800

oC armorphous ash that is black in

colour is produced while at higher temperatures crystalline ash having grey to

white colour is produced (Bronzeoak limited, 2003). The nature and composition

of the ash produced by burning rice husk depend on the burning temperature, the

soil chemistry, paddy variety, climatic conditions and the type of fertilizer used in

growing the rice (Bronzeoak, 2003: Abubaker et al, 2010). The properties of rice

husk ash are low bulk density, porous morphology, good insulator, high meeting

point, light weight and high pozzolannic activity (Basha et al, 2005; Della et al,

2002). Major compounds from rice husk ash are silica and cellulose which yield

carbon when thermally decomposed (Omatora et al, 2009). Rice husk ash has

15

constituted serious environmental pollution in growing countries like India,

Thailand, Malaysia, Argentina (Bronzeoak, 2003).

2. 2.1 Industrial Applications of Rice Husk Ash

1. Rice husk ash is used as a suitable additive in foundry sands for mold

production and as a binder due to its high melting point and good compressive

strength (Aigbodion et al, 2005).

2. Idenyi and Ani (2005) found that Abakaliki rice husk ash is suitable for

making cement and as an additive in clays for refractory bricks production.

3. Rice husk ash can is used for making low sandcrete blocks applied in building

houses (Oyetola and Abdullahi, 2010).

4. The Indian space research organization has successfully developed a

technology for producing high purity precipitated silica from rice husk ash and

this has a potential use in the computer industry (Omatora and Onoja, 2009).

Many American and British scientists have also developed ways to extract and

purify silicon from rice husk ash with the aim of using it in semi conductor

manufacture (Omatora and Onojah, 2009).

The silica from rice husk ash can is used for silicon chip manufacture used

in electronics (Bronzeoak, 2003).

5. Other useful applications of rice husk ash are: as a filler in rubber industry,

cleansing agent in toothpaste, building materials, in stabilization of soil for

farming, controlling insects and pest in farm, in steel industry, as an oil spill

absorbent, in making activated carbon used for water purification and in

16

improving corrosion resistance of steel pipes and concrete (Basha et al, 2005;

Bronzeoak, 2003 and Zemke, 2009).

2.3 Epoxy

Epoxy is also known as polyepoxide. It is a thermosetting polymer formed

from the reaction of an epoxide resin with a polyamine hardener. Epoxy is a

copolymer because it is formed from two different chemicals referred to as resin

and hardener (wikipedia.org.epoxy).

An epoxy resin contains oxirane or ethoxyline groups. Epoxy resins are

mostly produced by the reaction between bisphenol A with epichlorohydrin in the

presence of a basic catalyst (Sunilbhangle.tripod.com).

Examples of commercial epoxy resins are diglycidylether of bisphenol A

(DGEBA),glycidylethers of novolac resins and phenoxy epoxy resin. Properties of

epoxy resins are: low viscousity, low shrinkage, low glass transition temperature,

low shrinkage ,good adhesion to other materials ,good chemical and

environmental resistance, good insulating properties, ability to be processed under

variety conditions and good mechanical properties(May ,1988;Singla and

Chawla;2010 and Turner,2007). The structure and reaction of a typical epoxy

resin is shown in figure 2.1.

17

Figure 2.1: Reaction and structure of a typical epoxy resin diglycidylether of

bisphenol A, n is the degree of polymerization and ranges from 0 to 25.

2.3.1 Curing of Epoxy Resins

Curing process is a chemical reaction in which the epoxide groups in epoxy

resins react with curing hardener in order to convert epoxy resin into a hard,

infusible and rigid material (sunizbhangle.tripod.com).

Curing process normally involves an exothermic reaction. Epoxy resin cure

quickly and easily at practically any temperature from 5 – 150oC depending on the

choice of curing agent. Curing agents are amines, polyamides, phenolic resins,

anhydrides and isocyanates (pascault and Williams, 2010).

2.3.2 Engineering Applications of Epoxy

Epoxy resins were first commercialized in 1946 and are widely used in

industry in the following areas:

1) Protective coatings: Epoxy resins can be applied in corrosion protection of

steel pipes and fittings used in oil and gas industry (wikipedia.org.Epoxy).

18

2) Structural applications: Epoxy has been applied in the production of

composites, molds, industrial tools, laminates, casings, fixtures, automobile

bumper and other industrial production aids (wikipedia.org.Epoxy).

3) Electrical systems and electronics: Epoxy has excellent insulating abilities

that protect electrical components from short circuiting, dust and moisture.

This has resulted to usage in motors, generators, transformers, switch gear

and insulators. It is equally used in making integrated circuits, hybrid

circuits and printed circuit boards (wikipedia.org.Epoxy).

4) Singla and Chawla (2009) reported that epoxy can be applied in production

of military aircraft and commercial aircraft.

5) Consumer and Marine Applications: Epoxy is suitable for production of

shoe, furniture, boats and ship component. (wikipedia.org.Epoxy).

6) Adhesives: Epoxy adhesives are used for construction of aircrafts, bicycles,

golf clubs, snow board and other applications were high strength bond is

required (sunilbhangle tripod.com: wikipedia.org.Epoxy).

2.4 Compressive Strength (MPa)

Compressive strength is the capacity of a material or structure to withstand

axially directed pushing forces (wikipedia.org.compressive strength).

Compressive test determines the behaviour of materials under crushing loads.

When the limit of compressive strength is reached the materials fail completely. In

19

compression the molecules of atoms are forced together. Brittle materials are

stronger in compression than in tension (Onwuka, 2001).

Maximum Compressive Force (2.1)

Area

2.5 Toughness (J)

According to Roylance (2008), toughness is the ability of a material to

absorb energy before actual failure or fracture occurs. The higher the energy

absorbed by a material the higher the toughness of the material. Toughness can be

determined by performing an impact test with Charpy or Izod impact testing

machine or calculating the area under the stress/strain curve. Toughness indicates

how much energy a material can absorb before rupturing.

2.6 Flexural Strength (MPa)

Flexural strength is the ability of an engineering material to resist bending

or twisting under load (wikipedia.org.flexural strength). It is known as modulus of

rupture, bend strength or fracture strength.

Flexural strength is a mechanical parameter for brittle materials. Flexural

strength represents the highest stress experienced within the material at its moment

of rupture (Hogkinson, 2000).

2.7 Hardness

Hardness is the resistance of a material to localized plastic deformation; it

indicates wear resistance and resistance to scratching, abrasion and indentation

Compressive strength =

20

(Askeland, 1994). Hardness testing can be done with Rockwell, Vickers, Brinell

sclerescope, durometer, rebound and barcol hardness tester.

2.8 Tensile Properties

According to Liu (1999) tensile properties indicate how materials will react

to forces applied on tension. Tensile properties are determined by performing a

tensile test. Tensile test is a simple uniaxial test that consists of slowly pulling a

sample of material in tension until it breaks. These properties can be found from a

tensile test: modulus of elasticity, elongation at break, tensile strength, tensile

stress and tensile strain.

2.8.1 Stress (MPa)

Tensile stress of the material is defined as the force per unit area as the

material is stretched (Liu, 1999). The area used in finding tensile stress is the

original under formed cross sectional area because the cross sectional area of a

material may change if the material deforms on stretching.

Tensile stress (δ) = A

P=

Area nalcrossectio Original

forceor Load (2.2)

2.8.2 Strain

According to Onwuka (2001) Strain is the non dimensional measure of

deformation of a material with respect to a given length dimension of that

material. Tensile strain or engineering strain is the change in length of a sample of

material divided by the original length or gauge length of the sample. Strain can be

represented thus,

21

Strain = lengthGuage

lengthinChange

lengthOriginal

lengthinChange=

= 000

0

65.5 A

L

A

L

L

LLf ∆=

∆=

− (2.3)

Were L0 = Original length

∆ L = Axial deformation or change in length, Lf = final length, A . = Original

cross sectional area

2.8.3 Tensile Strength (MPa)

According to Askeland (1994) Tensile strength or ultimate strength is the

maximum amount of tensile stress that a material can absorb before breaking. It is

the maximum tensile stress reached on a stress-strain diagram. Tensile strength of

a material is affected by the preparation of the test specimen, the presence of

surface defects (voids, porosity and inclusions), the temperature of the test

environment and the nature of the material.

Tensile strength = Area. nalCrossectio Original

Applied Force Tensile Maximum (2.4)

Figure 2.2: Stress- strain curve

22

2.8.4 Young’s Modulus (MPa)

Young’s modulus or modulus of elasticity (E) is the slope of the stress-

strain curve (Askeland, 1994). According to Hooke’s law it is a measure of the

stiffness of the material. Stiffness is the property of a material to resist

deformation in the elastic range or within the proportional limit. Young’s modulus

(E) = Strain

Stress (2.5)

2.8.5 Elongation at Fracture (%)

Elongation at fracture is the strain on a sample when it fractures. It is

usually expressed in percentage and is a measure of the ductility of the material

.Elongation at fracture is the amount of uniaxial strain at fracture and is depicted

as strain. Elongation at fracture is mostly calculated by removing fractured

specimen from the grips, fitting the broken ends together and measuring the

distance between gauge marks. % Elongation at fracture = 1000

0×

−

L

LL f

Or 100length Original

Extension × (2.6)

Lf = final length of tensile test specimen at rupture. L0 = initial length of test

specimen.

23

2.9 Scanning Electron Microscopy

Scanning electron microscope is a microscope that uses electrons rather

than light to form an image. (Dunlap and Adaskareg, 2000). Since the

development of scanning electron microscope in the early 1950’s, new areas of

study in the medical and physical science communities have been developed.

Scanning electron microscope has allowed researchers to examine much bigger

variety of specimens because of the large depth of field which allows large

particle of the sample to be in focus at one time (Boyde, 1994). Scanning electron

microscope also produces images of high resolution which means that closely

spaced features can be examined at a higher magnification

(wikipedia.org.scanning electron microscopy). Preparation of sample is easy in

scanning electron microscopy and most scanning electron microscopes require the

sample to be conductive. These properties have made the scanning electron

microscope inevitable in the study of morphology of materials by researchers.

Sivasprasad and Krishnia (2011) analyzed the microstructure of A356.21 RHA

composite using scanning electron microscope. Their microstructure analysis

showed uniform distribution of rice husk ash particles in the aluminum alloy and

good retention of rice husk ash particles in the matrix.

Rajendran et al (2010) used scanning electron microscope to study the

topography of zinc oxide particles used for the production of antimicrobial textiles

and found that zinc oxide particles were embedded in the treated fabrics.

24

Nowosielski et al (2006) characterized the microstructure of composite materials

with powders of barium ferrite with x-ray diffractometer and scanning electron

microscopy. The result of the scanning electron microscopy analysis made it

possible to understand that the distribution of powders of barium ferrite in the

polymer matrix was irregular and the powder particles had irregular shapes and

dimensions.

Singla and Chawla (2010) applied scanning electron microscopy in the

study of mechanical properties of epoxy-fly ash composites. The scanning electron

microscope observations showed uniform distribution of fly ash in the matrix and

good adhesion.

Castejon (1998) used scanning electron microscope to study the cerebella

golgi cells of mouse, telecast fish, primate and human species and the scanning

electron microscopy analysis showed three dimensional neuronal geometry and

smooth outer surfaces of the organisms. The University of Tennessee equally

reported in 2000 that scanning electron microscope can be used in the following

areas:

1) Analysis of the surface features of materials,

2) Obtaining the crystallographic information of the materials,

3) Analysis of the microstructural features of materials, that is, grain size, grain

shapes, distribution of various phase and defects such as cracks and voids.

3) To determine the chemical composition of materials when used in

conjunction with energy dispersive x-ray spectrophotometry

25

2.9.1 Components of a Scanning Electron Microscope (SEM)

Figure 2.3 below shows the major components of a scanning electron.

microscope.(Dunlap and Adaskareg 2000).

Figure 2.3: SEM column and specimen chamber

Some of the components of SEM are the vacuum, beam generation, beam

manipulation, beam interaction, detection, signal processing, and display and

recording units.

These systems function together to determine the results and qualities of a

micrograph such as magnification, resolution, depth of field, contrast and

brightness. The functions are as follows: vacuum system: This system is required

26

when using an electron beam because electrons will quickly disperse or scatter due

to collision with other particles.

Electron beam generation system: This system is found at the top of the

microscope column. It generates the illuminating beam of electrons known as

primary electrons.

Electron beam manipulation system: This system consist of electromagnetic

lenses and coils located in the microscope column and control the size, shape and

position of the electron beam on the specimen surface.

Beam specimen interaction system: This system involves the interaction of the

electron beam with the specimen and the types of signals that can be detected.

Detection System: This system can consist of several different detectors each

sensitive to different energy/particle emission that occurs in the sample.

Signal processing system: This system is an electronic system that processes the

signal generated by the detection system and allows additional electronic

manipulation of the image.

Display and recording system: This system allows visualization of an electronic

signal using cathode ray tube and permits recording of the results using

photographic or magnetic media.

2.10 Energy Dispersive X-Ray Spectroscopy

Energy dispersive x-ray spectroscopy (EDS or EDX) is an analytical

technique used for elemental analysis or chemical characterization of a sample

27

(wikipedia.org.energy dispersive x-ray spectroscopy). Since the 1960’s EDS is

attached to scanning electron microscope. (SEM – EDX)

During energy dispersive X-ray spectroscopy analysis, a sample is exposed

to an electron beam inside a scanning electron microscope (SEM). The electrons

collide with the electrons within the sample causing some of them to be knocked

out of their orbits. The vacated positions are filled by higher energy electrons

which emit x-rays in the process. By analyzing the emitted x-rays the elemental

composition of the sample can be determined. Energy dispersive x-ray

spectroscopy is a powerful tool for micro analysis of elemental constituents.

(Ronjenkins, 2011). Accuracy of energy dispersive X-ray spectrum can be affected

by many factors namely

1) Windows in front of the detector can absorb low energy X-rays (EDS

detectors cannot detect elements with atomic number less than 4 that is H,

He, L)

2) Nature of samples, there is reduced accuracy in homogenous and rough

samples.

3) Elements that have overlapping peak.

Figure 2.4 shows the EDS spectrum of the mineral crust of Rimicaris exoculta.The

elements identified are C,Ca,Cl,S,Mg,Fe,P and O.

The energy transitions during EDS analysis is also shown in figure 2.5.

28

Figure 2.4

EDS spectrum of the mineral crust of Rimicaris exoculta (source

wikipedia.org.energy dispersive x-ray spectroscopy)

Figure 2.5 Energy transitions during EDX analysis

29

2.10.1 Applications of Scanning Electron Microscopy – Energy Dispersive X-

Ray Analysis (SEM-EDX)

Areekijsere (2009) used SEM-EDX to study the structure Spectroscopy

and elemental composition of soils from different agricultural areas in the western

region of Thailand. The SEM result showed that the soils were spherical in shape

while the EDX analysis revealed that the soils contained oxygen, magnesium,

aluminum, potassium, silicon, calcium, titanium and iron.

According to Andrews (2007) EDX can be used in electron beam analysis

of metallurgical samples in the areas of pyrometallurgy, mineral processing,

hydrometallurgy, physical metallurgy, corrosion and forensic analysis. Andrews

further opined that limitations of EDX are poor spectral resolution and high

detection limits while it has the advantage of speed especially for quick phase

transformations.

Atuanya et al (2011) studied the microstructure of wood composites using

SEM-EDX. It was found that there were no chemical interfacial reactions between

the wood particles and the recycled low density polyethylene matrix (LDPE). This

was because the EDX analysis gave carbon and oxygen as the major elements in

wood composites. Observations from the SEM analysis showed uniform

distribution of wood particles in the LDPE.

Asaka et al (2004) analyzed resin composites with EDX and SEM and

discovered that the main element in the resin composite was silicon. The SEM

30

observations showed three different types of filler morphology:- splintered,

splintered and prepolymerized and spherical.

2.11 Microstructure

Microstructure is defined as the structure of a prepared surface of thin foil

of a material as revealed by a microscope above 25x magnification

(wikipedia.org.microstructure).

According to Slouf( 2010) microstructures are structures of dimension 1um

to 1000um.The microstructure of a material can be analyzed with the optical

microscope, scanning electron microscope, X-ray diffractometer and scanning

transmission electron microscope (wikipedia.org.electron microscope). According

to the report from Lancaster State University handout (2010) microstructure is the

microscopic description of the individual constituents of a material. Microstructure

is equally the study of the crystal structure of a material, its size, chemical

composition, phases, defects, orientation and interaction and their effect on the

macroscopic behaviour in terms of physical properties and mechanical properties

such as strength, toughness, ductility, hardness, corrosion resistance, low and high

temperature behaviour, wearability and so on. These properties govern the

application of materials in industry. The basis of materials science involves

relating the desired properties to the structure of atoms and phases.

31

2.12 Adhesion and Cohesion

Adhesion is an attraction process between dissimilar molecular species

which have been brought into direct contact such that the adhesive (binder or

matrix) binds to the applied surface.

Cohesion is an attraction process that occurs between similar molecules,

primarily as the result of chemical bonds that have been formed between the

individual components of the adhesive or bonding agent for example curing of cast

neat epoxy.

Cohesion may be defined as the internal strength of an adhesive due to

various interactions within that adhesive or binder that binds the mass together

whereas adhesion is the bonding of one material to another namely an adhesive to

a substrate, due to a number of different possible interactions at the adhesive

substrate interface. The strength of adhesion between two materials depends on the

interactions between the two materials and the surface area which the materials are

in contact. (Fraunhofer, 2010). Adhesion is necessary for achieving high level of

mechanical properties.

The various types of adhesion are:

chemical adhesion: It is a type of adhesion in which the cohesive strength of a

matrix material is determined by chemical bonds within the matrix material,

chemical bonds due to cross linking of polymer(s) within a resin based material,

inter molecular interactions between adhesive (binder) molecules and mechanical

bonds and interactions between the molecules in the adhesive (resin, binder).

32

Wetting is the ability of a liquid to form an interface with a solid surface

(Fraunhofer, 2011). The two materials form a compound at the interface by Ionic

or covalent bonds that results in strong bond between them. Such bonds are

usually brittle except with nano particles.

Dispersive adhesion: This type of adhesion involves holding the surfaces of two

materials together by Vander walls forces.

Diffusive adhesion involves merging or intermingling of the materials at

the bonding interface by diffusion typically when the molecules of both materials

are mobile and soluble. Example includes sintering of ceramics or powder

metallurgy.

The types of adhesion explained above are the ones that affect mechanical

properties of composites. Interfacial region is known as the adhesion region.

2.13 Calculation of Fiber Volume Fraction

The fiber volume fraction is mostly calculated using this formula

Vf = fmmf

fm

WPWP

WP

+ (2.7)

Where Vf = volume fraction of fibers.

Wf = weight of fibers

Wm = weight of matrix

Pf = density of fibers

Pm = density of matrix

33

CHAPTER THREE

MATERIALS AND METHODS

3.1 Materials

3.1.1 Matrix Material

A standard epoxy resin of grade 3554A, chemically belonging to the

epoxide family and curing hardener of grade 3554B were used as the matrix

material. The resin and hardener were supplied by De Paragon Chuks Ventures

(NIG) LTD, 195 Faulks Rd, chemical Zone Ariaria, Aba, Abia State. The epoxy

resin has a density of 1.15g/cm3.

3.1.2 Filler Material

Rice husk ash

The filler material used in this study is rice husk ash which was produced

from rice husk waste sourced from Adani Rice Mill, Enugu State. The finely

milled rice husk fillers were collected in large quantity and washed with water to

remove impurities like dust, small rice particles and fine sand particles. After

washing, drying followed in the oven at a temperature of 70oC

for 24 hours in

order to remove moisture from it. The dried rice husk was taken to the Soil

Science Laboratory, National Root Crops Research Institute Umudike where it

was burnt in a furnace at 550oC

for 6 hours to produce the rice husk ash used for

the study. The rice husk ash was characterized using Atomic Absorption

Spectrophotometer (AAS) and the chemical compositions of the major compounds

33

34

were determined. Table 3.1(a) shows the chemical composition. Trace elements

and unburnt carbon (LOI) were not determined.

Table 3.1 (a) Chemical composition of the rice husk ash used for the study.

3.2.0 Methods

3.2.1 Preparation of Composite Mould

Mild steel sheets were cut and formed into different sizes that served as molds for

the test samples. The testing techniques for the composite required that five sets of

pattern (tensile, compressive, hardness, flexural and toughness) should be

produced. The patterns were made according to the required dimensions of the test

samples. Flat wooden bars were used and served as mould control volume for

other test piece samples. The molds were constructed to within ± Imm to give

allowance for machining, and the surfaces were rubbed with wax releaser to

ensure easy removal of the composite. Figure 3.I below shows the mold used for

composite production.

Chemical

compound 32OAl 2SiO MgO ONa2 ZnO K20 MnO4 PO4 Fe2O3 CaO

Composition

(%)

13.5 26.5 4.8 8.9 3.07 9.4 4.2 10.3 2.9 8.0

35

3.2.2 Composite Fabrication

The composites were produced using facilities at the Centre for Composite

Research and Development, Juneng Nigeria Limited, Nsukka. Manual mixing

method and hand lay up technique were used for the composite production. The

composites were prepared using 10%, 20%, 30%, 40% and 50% volume fraction

of rice husk ash.

The matrix material (epoxy resin, grade 3554A and hardener grade 3554B)

were prepared in the ratio of 2 parts of epoxy resin to 1 part of hardener (2:1). The

measured volume of resin and hardener were mixed in a container and stirred at

low speed for 10 minutes until the mixture became uniform, tacky and exothermic

reaction occurred. The mixture of the matrix material was poured into the mold.

Rice husk ash fillers were uniformly and evenly spread in the mold and adequately

impregnated into the matrix and allowed to cure. For the cast neat epoxy samples,

the epoxy resin and hardener were poured into the mold and allowed to cure. The

Figure 3.1: Mold

36

curing time was 24 hours at room temperature. Finally the composite plates were

demolded and cut into different dimensions for mechanical property tests.

Tables 3.1 (b) and 3. 1 (c) give the composition of the composites and dimensions

for different mechanical property test.

Table 3.1. (b) Composition of the composites.

S/NO Volume of RHA

filler (VF)

Volume of epoxy

matrix (VM)

Sample 1 0% 100%

Sample 2 10% 90%

Sample 3 20% 80%

Sample 4 30% 70%

Sample 5 40% 60%

Sample 6 50% 50%

VF = 100 - VM (3.1)

VC = VF +VM (3.2)

where VC is the volume of composite

Table 3.1 (c) Dimensions of specimen for different mechanical property tests

S/NO Test Length (mm) Breadth (mm) Thickness (mm)

1 Hardness 40 40 40

2 Tensile 300 19 3.2

3 Compressive 20 20 20

4 Toughness 55 10 10

5 Flexural 240 40 40

37

3.3 Mechanical Property Tests

3.3.1 Tensile Testing of Composite Samples

Tensile testing of the samples was done at the Strength of Materials

Laboratory, University of Nigeria, Nsukka.

Hounsfield (Monsanto) tensometer was used in performing the tensile test.

The tensometer was manually operated. The cured epoxy-rice husk ash composite

and the cast neat epoxy were cut into tensile test samples in accordance with the

ASTM standard D638. The cut tensile test samples were of dimension 300mm

long by 19mm by 3.2mm.Prior to the test the cross sectional area of the samples

was calculated. The steps followed before carrying out the test were: loading the

correct beam in the hounsfield, attaching the movable and fixed jaws, setting the

mercury indicator, attaching a graph paper to the rotating drum and ensuring that

the ends of the test piece were fitted into the grip of the tensometer. Tensile forces

were applied gradually by turning the hand wheel of the rotating drum. Turning of

the hand wheel of the rotating drum pulled the samples until fracture occurred.

The deformations were obtained from the load-extension curve. The traced load-

extension curve was converted to stress-strain values. Other tensile properties like

elongation at fracture, tensile strength and young modulus were determined from

this stress- strain curve.

38

3.3.2 Compressive Strength Test

The compressive strength test was done at strength of materials engineering

laboratory, University of Nigeria, Nsukka. Hounsfield (Monsanto) tensometer

universal testing machine was used in carrying out the test.

A compressive test rig was used for the compressive test. Compressive test

specimen of dimension 20mm by 20mm by 20mm were loaded to fracture by

applying uniaxial compressive force. The maximum compressive force that

crushed the specimen were read from graph paper attached to the tensometer. The

compressive strength was calculated using equation 2.1 which is:

Compressive strength = Maximum Compressive Force

Area

3.3.3 Toughness Test

The toughness test was performed at Engineering Laboratory, Standards

Organization of Nigeria, Emene Enugu. The test was carried out according to the

recommended standard charpy V- notched method. Impact specimen 55mm by

10mm by 10mm were notched at the middle to a depth of 2mm to create an area of

stress concentration for initiating fracture. Each of them were fixed on a charpy

impact testing machine to receive a blow from the fast moving hammer released

from a fixed height on the machine. The reading on a dial gauge on the machine

showed the energy absorbed (toughness) by the respective specimen.

39

3.3.4 Hardness Test

The hardness test was done at the Engineering Laboratory, Standards

Organization of Nigeria, Emene Enugu. An automatic electric powered Rockwell

hardness testing machine was used to determine the hardness value of the cast neat

epoxy and the composites. The procedure followed in performing the test were:

switching on the machine, selecting the desired

load of 30kgf, placing the surface of the specimen to be tested on the anvil of the

machine and releasing the indenter of the machine from the lever until it touched

the specimen making a green to be shown to indicate test zone specimen. The

next thing done was pressing the test button and there was automatic indentation

of the specimen by the conical shaped indenter of the Rockwell tester. At the end

of the indentation a red light showed “read” and instantly reading was directly

done from the dial indicator. The value was reported as Rockwell hardness value

{689HRD30}.

3.3.5 Flexural Strength Test

The flexural strength test was done at Engineering Laboratory of Standards

Organization of Nigeria, Emene Enugu. Each specimen of dimension 240mm by

40mm by 40mm was placed in the flexural testing machine. The three point

flexing and loading arrangement was used in which fracture occured at the middle.

40

The specimen was flexed and flexural force that fractured the specimen at the

middle was read from the scale of the machine. The flexural strength was

calculated using equation 3.3.

Fs = 2

bd

FL (3.3)

Where F= flexural force (KN)

L = length in (mm)

B = breadth (mm)

D = thickness (mm)

Fs = flexural strength.

3.4 Scanning Electron Microscopy and Energy Dispersive X-Ray

Spectroscopy Analysis.

The SEM & EDX analysis was done at the Advanced Physics Laboratory,

Sheda Science and Technology Complex, (SHETSCO) Abuja. The Carle Zees

scanning electron microscope with an attached INCA energy dispersive x-ray

microanalysis system was used for the analysis. The scanning electron microscope

has the microscope column, specimen chamber and vacuum system on the left

with the computer monitor and many other instrument controls on the right. The

energy dispersive x- ray spectrophotometer attached to the scanning electron

microscope has four set ups which are: the beam source, the x- ray detector made

of lithium drifted silicon, the pulse processor and the analyzer. The five composite

samples of different composition of rice husk ash particle, the cast neat epoxy and

41

the sample of rice husk ash were loaded in the specimen chamber. Conductive

double sided carbon tape was used to hold the specimens in order to make them

conductive. The cathode and magnetic lenses in the scanning electron microscope

created and focused a beam of electrons on each of the specimen. The

bombardment of the specimen with scanning beam of electrons generated

backscattered electrons and secondary electrons due to beam specimen interaction.

The backscattered electrons and secondary electrons were collected, amplified and

displayed on a cathode ray tube. The backscattered electrons and cathode ray tube

scanned synchronously to produce an image of the surface of the specimen

formed. The analytical lithium drifted silicon detector in the energy dispersive X-

ray spectrophotometer meter converted x- ray energy into voltage signals which

measure the signal and passed them onto the analyzer for elemental analysis and

data display. The morphology and elemental composition of the samples were

displayed on the computer screen sequentially with the help of the software.

42

CHAPTER FOUR

RESULTS AND DISCUSSION

4.1 Results

The results of the study are presented in three main headings, namely

mechanical properties, scanning electron microscopy and energy dispersive x-ray

spectroscopy analyses. Result of mechanical properties shows the behaviour of the

composites and cast neat epoxy to different kinds of forces. Scanning electron

photomicrographs showed the microstructure of the composites, the rice husk ash

and cast neat epoxy. The photomicrographs are shown in figures

4.14,4.15,4.16,4.17,4.18,4.19,4.20,4.21,4.22,4.23,4.24,4.25,4.26 and 4.27. The

energy dispersive X-ray spectroscopy results were presented with the EDX

spectrum in figures 4.28,4.30,4.32,4.34,4.36 and 4.38 and tables

4.14,4.15,4.16,4.17,4.18 and 4.19 showing elemental composition and

concentration of elements in the microstructure of the composites and statistical

bar charts in figures 4.29,4.31,4.33,4.35,4.37 and 4.39 illustrating the quantitative

results of each element.

42

43

4.1a Results for Mechanical Properties are shown as Follows:

Tensile properties are shown in tables 4.1 to 4.9

Table 4.1: Load, Extension, Stress, Strain values for Cast neat Epoxy (100% Epoxy

0% RHA,)

S/N Load (N) Extension

(mm)

Strain (ε) Stress (MPa)

1 0 0.0000 0.0000 0.0000

2 200 0.5000 0.0114 3.2894

3 400 0.8125 0.0184 6.1678

4 550 1.1250 0.0255 9.0460

5 1050 2.0000 0.0454 17.2697

6 1250 2.5000 0.0568 20.5592

7 1600 3.0000 0.0681 26.3158

8 2000 4.0000 0.0908 32.89471

Table 4.2: Load, Extension, Stress, Strain Values for Epoxy-Rice Husk Ash

Composite (90% Epoxy 10% RHA)


(mm) Strain (ε) Stress (MPa)

1 0 0.0000 0.0000 0.0000

2 250 0.5000 0.0114 4.1118

3 350 1.1250 0.0255 5.7566

4 550 1.7500 0.0397 9.0462

5 740 2.3750 0.0539 12.1710

6 970 2.7500 0.0624 15.9539

7 1150 3.5000 0.0795 18.9145

44





1 0 0.0000 0.0000 0.0000

2 200 0.7500 0.0170 3.2895

3 400 2.0000 0.0454 6.5789

4 650 3.2500 0.0738 10.6908

5 750 3.5000 0.0795 12.3355

6 900 4.2500 0.0965 14.8026

7 1100 4.7500 0.1078 18.0921

8 1500 6.0000 0.1362 24.6710





1 0 0.0000 0.0000 0.0000

2 300 1.2500 0.0284 4.9342

3 500 2.0000 0.0454 8.2236

4 850 2.5000 0.0568 13.9803

5 950 2.6250 0.0596 15.6250

6 1050 3.2500 0.0738 17.2697

7 1500 4.2500 0.0965 24.6710

8 1600 4.7500 0.1078 26.3157

45





1 0 0.0000 0.0000 0.0000

2 150 1.0000 0.0227 2.4672

3 450 1.7500 0.0397 7.4013

4 800 2.7500 0.0624 13.1578

5 1000 3.2500 0.0738 16.4473

6 1250 3.7500 0.8510 20.5592

7 1650 4.5000 0.1022 27.1381

8 1850 5.0000 0.1135 30.4276

9 2000 5.5000 0.1249 32.8940

10 2250 6.0000 0.1362 37.0065





1 0 0.0000 0.0000 0.0000

2 150 0.7500 0.0170 2.4671

3 300 1.2500 0.0284 4.9342

4 500 2.0000 0.0454 8.2237

5 800 2.8750 0.0653 13.1579

6 1000 3.3750 0.0766 16.4474

7 1300 3.7500 0.0851 21.3815

8 1500 4.2500 0.0965 23.8488.

Table 4.7: Tensile Strength

S/N Material Tensile Strength (MPa)

1 100% Epoxy 0% RHA 32.894

2 90% Epoxy 10% RHA 18.915

3 80% Epoxy 20% RHA 24.671

4 70% Epoxy 30% RHA 26.317

5 60% Epoxy 40% RHA 37.006

6 50% Epoxy 50% RHA 23.848

46

Table 4.8: Young’s Modulus

S/N Material Young’s modulus (MPa)

1 100% Epoxy 0% RHA 356.5380

2 90% Epoxy 10% RHA 234.9442

3 80% Epoxy 20% RHA 167.8115

4 70% Epoxy 30% RHA 245.4050

5 60% Epoxy 40% RHA 276.9320

6 50% Epoxy 50% RHA 285.729

Table 4.9: % Elongation at Fracture

S/N Material Elongation at fracture (%)

1 100% Epoxy 0% RHA 1.30

2 90% Epoxy 10% RHA 1.36

3 80% Epoxy 20% RHA 1.40

4 70% Epoxy 30% RHA 1.58

5 60% Epoxy 40% RHA 2.00

6 50% Epoxy 50% RHA 2.00

S/N Material Energy Absorbed (J)

1 100% Epoxy 0% RHA 2.0

2 90% Epoxy 10% RHA 1.6

3 80% Epoxy 20% RHA 0.9

4 70% Epoxy 30% RHA 0.7

5 60% Epoxy 40% RHA 0.5

6 50% Epoxy 50% RHA 0.3

Table 4.11: Hardness Test Result (Rockwell)

S/N Material Hardness value

1 100% Epoxy 0% RHA 344

2 90% Epoxy 10% RHA 219

3 80% Epoxy 20% RHA 202

4 70% Epoxy 30% RHA 190

5 60% Epoxy 40% RHA 150

6 50% Epoxy 50% RHA 144

Table 4.10: Toughness Test Result

47

Table 4.12: Flexural Strength Test Result

S/N Material Flexural

force(KN)

Flexural strength (MPa)

1 100% Epoxy 0% RHA 1.600 6.00

2 90% Epoxy 10% RHA 1.200 4.50

3 80% Epoxy 20% RHA 0.800 3.00

4 70% Epoxy 30% RHA 0.600 2.25

5 60% Epoxy 40% RHA 0.500 1.88

6 50% Epoxy 50% RHA 0.400 1.50

Table 4.13: Compressive Strength Test Result

S/N Material Maximum

compressive force

(N)

Compressive

strength (MPa)

1 100% Epoxy 0% RHA 6300 15.75

2 90% Epoxy 10% RHA 6400 16.00

3 80% Epoxy 20% RHA 6800 17.00

4 70% Epoxy 30% RHA 7100 17.75

5 60% Epoxy 40% RHA 7450 18.63

6 50% Epoxy 50% RHA

7500 18.75

48

Figure 4.1 Stress - Strain relationship for cast neat epoxy.

Figure 4.2 Stress – Strain relationship for epoxy – rice husk ash composite

(90%epoxy 10%rice husk ash)

Stress

Stress 90% Epoxy 10% RHA



Str

ess

(MP

A)

Str

ess

(MP

A)

49

Figure 4.3 Stress- Strain relationship for epoxy-rice husk ash

Composite (80%epoxy 20%rice husk ash)

Figure 4.4 Stress – Strain relationship for epoxy – rice husk ash composite

(70%epoxy 30% rice husk ash)


Str

ess

(MP

A)

Strain

Stress 70% Epoxy 30%RHA

Str

ess

(MP

A)

50

Figure 4.5 Stress – Strain relationship for epoxy- rice husk ash composite

(60%epoxy 40% rice husk ash)

Figure 4.6 Stress – Strain relationship for epoxy- rice husk ash composite

(50% epoxy 50% rice husk ash)

Figure 4.7 Tensile strength - %RHA graph


Str

ess

(MP

A)


Str

ess

(MP

A)

51

Figure 4.8 Young’s modulus - %RHA graph

Figure 4.9 Elongation at fracture - %RHA graph

Figure 4.10 Energy absorbed (toughness) - %RHA graph

Yo

un

g’s

Mod

ulu

s

(MP

A)

Young’s Modulus

(MPa)

Elo

ng

atio

n a

t fr

actu

re (

%)

(MP

A) Elongation at

fracture (%)

52

Figure 4.11 Hardness value - %RHA graph

Figure 4. 12 Flexural strength - %RHA graph

Figure 4.13 Compressive strength - %RHA graph

53

Results of scanning electron microscopy are presented in figures 4.14 to 4.27.

Figure 4.14 Scanning electron micrograph of epoxy – rice of Adani rice husk

ash x200.

4.1b Results of Scanning Electron Microscopy (SEM).

54

Figure 4.15 Scanning electron micrograph of Adani rice husk ash x2000.

Figure 4.16 Scanning electron micrograph of cast neat epoxy x200.

55

Figure 4.17 Scanning electron micrograph of cast neat epoxy x2000.


containing 10% rice husk ash x200.

56





57

Figure 4.21 Scanning electron micrograph of epoxy – rice husk ash

composite containing 20% rice husk ash x2000.



58





59


containing 40% rice husk ash composite x2000.



60



61

The results of energy dispersive x-ray spectroscopy are presented in figures

4.28 to 4.39 and on tables 4.14 to 4.19.

Element App Intensity Weight% Weight% Atomic%

Conc. Corrn. Sigma

C K 342.57 1.5885 81.35 0.39 85.46

O K 16.44 0.3395 18.27 0.39 14.41

Cl K 0.86 0.8356 0.39 0.04 0.14

Totals 100.00

Table 4.14: Elemental composition of cast neat epoxy.

Figure 4.28 EDX spectrum of cast neat epoxy

4.1c Results of the Energy Dispersive X-ray Spectroscopy Analysis (EDX).

62

Quantitative resultsW

eig

ht%

020406080

100

Fig 4.29 Quantitative results for cast neat epoxy showing

weight% of elements.

C O Cl

63


Conc. Corrn. Sigma

C K 112.01 0.7330 64.95 0.72 75.96

O K 19.53 0.3915 21.21 0.57 18.62

Al K 1.08 0.8643 0.53 0.04 0.28

Si K 13.56 0.9253 6.23 0.14 3.12

P K 0.52 1.2301 0.18 0.05 0.08

Cl K 1.51 0.8015 0.80 0.06 0.32

K K 3.08 1.0299 1.27 0.07 0.46

Ca K 1.46 0.9646 0.64 0.06 0.22

Fe K 2.26 0.8001 1.20 0.12 0.30

Zn K 5.26 0.7465 2.99 0.23 0.64

Totals 100.00

Table 4.15 Elemental composition of epoxy- rice husk ash composite (90%

epoxy 10% RHA)

Figure 4.30 EDX spectrum of epoxy- rice husk ash composite (90%

Epoxy, 10% RHA)

64

Quantitative resultsW

eig

ht%

020406080

Figure 4.31 Quantitative results for epoxy – rice

husk ash composite (90% Epoxy 10% RHA)

showing weight % of elements.

C P Cl Ca O Al Si K Fe Zn

Figure 4.32 EDX spectrum of epoxy- rice husk ash composite

(80% Epoxy, 20% RHA)

65

Table 4.16: Elemental composition epoxy-rice husk ash composite(80%Epoxy

20%RHA)


Conc. Corrn. Sigma

C K 226.60 1.2025 71.37 1.51 77.97

O K 25.90 0.3866 25.37 1.48 20.80

Si K 3.83 0.9459 1.53 0.16 0.72

Cl K 1.28 0.8261 0.59 0.14 0.22

K K 0.73 1.0381 0.27 0.13 0.09

Fe K 1.79 0.7767 0.88 0.26 0.21

Totals 100.00

Quantitative results

We

igh

t%

020406080

Figure 4.33 Quantitative results for epoxy – rice husk ash composite(80%Epoxy

20%RHA) showing weight% of elements.

C O Si Cl K Fe

66

Table 4.17: Elemental composition of epoxy –rice husk ash composite

(70%Epoxy30% RHA)


Conc. Corrn. Sigma

C K 286.07 1.5090 80.07 0.41 84.57

O K 15.43 0.3442 18.93 0.40 15.01

Al K 0.75 0.9089 0.35 0.03 0.16

Si K 0.45 0.9585 0.20 0.03 0.09

Cl K 0.72 0.8334 0.37 0.04 0.13

K K 0.21 1.0399 0.09 0.03 0.03

Totals 100.00

Figure 4.34 EDX spectrum of epoxy – rice husk ash composite

(70% Epoxy, 30% RHA)

67


We

igh

t%

020406080

100

Figure 4.35 Quantitative results for epoxy –rice husk ash composite

(70%Epoxy 30%RHA) showing weight % of elements.

Figure 4.36 EDX spectrum of epoxy rice husk ash composite (60% Epoxy, 40%

RHA)

C O Al Si Cl K

68

Table 4.18 Elemental composition of epoxy –rice husk ash

composite(60%Epoxy 30%RHA)


Conc. Corrn. Sigma

C K 307.99 1.5354 78.77 0.29 83.37

O K 18.48 0.3519 20.63 0.29 16.39

Si K 0.76 0.9588 0.31 0.02 0.14

Cl K 0.51 0.8331 0.24 0.02 0.09

K K 0.13 1.0406 0.05 0.02 0.02

Totals 100.00


We

igh

t%

020406080

Figure 4.37 Quantitative results of epoxy –rice husk ash composite

(60%Epoxy 40%RHA) showing weight % of elements.

C O Si Cl K

69

Table 4.19: Elemental composition of epoxy – rice husk ash composite (50%Epoxy

50%RHA)


Conc. Corrn. Sigma

C K 291.96 1.5144 79.69 0.32 84.22

O K 16.29 0.3464 19.43 0.32 15.42

Al K 0.21 0.9071 0.09 0.02 0.04

Si K 1.03 0.9609 0.44 0.03 0.20

Cl K 0.57 0.8328 0.28 0.03 0.10

K K 0.17 1.0400 0.07 0.02 0.02

Totals 100.00

Figure 4.38 EDX spectrum of epoxy rice husk ash composite (50% Epoxy,

50% RHA)

70

Figure 4.39 Quantitative results for epoxy – rice husk ash

composite (50%Epoxy 50%RHA)

4.2 Discussion of results

4.2.1 Mechanical properties

The mechanical properties of the composites did not improve with

increasing filler content as expected. Based on observations from labouratory

tests conducted on the composites and the rice husk ash in Standards Organization

Of Nigeria and Sheda Science and Technology Complex, Abuja the decrease in

mechanical properties could be attributed to the non coating of the surface of the

rice husk ash fillers with coupling agents, manual mixing method used for

composite production and the porous structure of rice husk ash.

4.2.1a Tensile Properties

Tensile properties showed how the cast neat epoxy and the composites

reacted to tensile forces. Figures 4.1 to 4.6 showed stress versus strain graphs of

the materials. From these graphs it can be seen that the materials were brittle. The

reason for the brittleness is because the composites did not sustain large

C O Al Si Cl K


We

igh

t%

020406080

71

deformations before fracture and the stress-strain diagrams had no yield point.

Figure 4.7 shows the tensile strengths of the composites. The tensile strengths of

the composites with 10%, 20%, 30% and 50% volume of RHA were lower than

the cast neat epoxy while the highest tensile strength of 37.006MPa was recorded

at 40% volume of RHA. The reasons for this result are: tensile strength are

affected by volume fractions, degree of adhesion between the filler and the matrix,

level of dispersion of the filler and matrix and surface related defects. Tensile

strength can decrease with increasing filler content if the filler matrix adhesion is

weak and this accounts for the reason why the tensile strength of 10%, 20%, 30%,

40% and 50% volume fraction of RHA were lower than the cast neat epoxy. The

increase in rice husk ash content led to greater possibility of weak locations in the

composites which caused easy debonding at the interface when tensile forces were

applied. However the reasons for the higher tensile strength of the 40% RHA

could be because there were strong interfacial adhesions between the rice husk ash

fillers and epoxy matrix or better stirring during the production process. The

swingling of the graph is because manual mixing was used which caused irregular

dispersion of the fillers on the matrix.

Fig 4.8 shows the Young’s modulus of the composites at different composition of

rice husk ash. It can be seen that the cast neat epoxy had the highest tensile

modulus of 356.538MPa. The addition of rice husk ash fillers caused loss of

tensile modulus because the manual mixing method used in the composite

preparation caused some rice husk ash fillers to be poorly dispersed and this

72

poorly dispersed fillers formed agglomerates. These agglomerated fillers acted as

stress concentration sites due to their porous nature and weakened the composite

stiffness on tension.

Fig 4.9 shows the graph of elongation at fracture versus % RHA. There was

gain in elongation at fracture from 1.30% to 2.0% as the percentage of rice husk

ash fillers increased. The improvement in elongation at fracture of the composites

could be attributed to the interfacial interactions between the rice husk ash

particles and the epoxy matrix. These interfacial interactions induced lattice strains

in the composites that led to higher strains.

4.2.1b Toughness

Figure 4.10 showed that the toughness of the composites decreased from

2.0J to 0.3J as percentage of rice husk ash increased. This decrease could be

because of poor wettability of rice husk ash which led to poor interfacial adhesion

between the hydrophobic epoxy matrix and hydrophilic rice husk ash fillers. Poor

interfacial adhesion (bonding) led to formation voids in the composites. These

voids acted as sites for crack nucleation and propagation upon impact. Hence as

the percent of rice husk ash increased the number of voids in the composites

increased amounting to lower energy absorbed before fracture. Similar works by

Singla and Chawla (2010), Arukalam and Madufor (2011) and Onuegbu and Igwe

(2010) equally showed that increase in filler content led to decrease in toughness.

73

4.2.1c Hardness

The hardness value of the composites decreased from 344 to 144 with

increase in percentage of rice husk ash as can be seen in figure 4.11. This decrease

is due to the soft nature of the rice husk ash fillers. The softness and lightness of

the rice husk ash allowed quick penetration of the indenter on indentation. Soft

material embedded in a harder material most times result in reduction of hardness.

4.2.1d Flexural Strength

The graph of flexural strength versus %RHA in figure 4.12 shows that

flexural strength decreased from 6.0 MPa to 1.5MPa as the percentage of rice husk

ash increased. Flexural strength is the ability of material to resist bending, twisting

and deformation under load. The reasons for the decrease in flexural strength were

poor interfacial adhesion (bonding) between the rice husk ash and the epoxy

matrix, distortion in the microstructure caused by addition of rice husk ash and

porous morphology of the rice husk ash. These defects accounted for lower

resistance of epoxy-rice husk ash composites to flexural force leading to quick

rupture.

4.2.1e Compressive Strength

From the graph of compressive strength versus % RHA in figure 4.12, the

compressive strength of the composites increased from 15.75MPa to 18.75MPa as

the % RHA increased. The increased resistance of the composites to crushing

loads could be attributed to the hollowness of the rice husk ash particles as shown

in figure 4.15 and the strong interfacial energy between the rich husk ash particles

74

and the epoxy matrix. Brittle materials have better resistance to compression; since

the composites were brittle in tension it is expected that they will have improved

compressive strength.

Another reason for the increase in compressive strength is that during

compression the molecules of the composites were forced together and cracks are

closed up.

4.2.2 Scanning Electron Microscopy Analysis

Scanning Electron microscopy analyses was done to observe the

distribution and interaction of rice husk ash fillers in the epoxy matrix and to

determine the morphology of the cast neat epoxy and Adani rice husk ash. Two

magnifications of 200x and 2000x were used in order to adequately view the

specimens. The explanations of the scanning microscopy analysis are given thus:

Figures 4.14 and 4.15 show the photomicrographs of Adani rice husk ash at 200x

and 2000x magnifications. At 200x magnification the rice husk ash had a porous

structure with the particles looking a bit rough and dispersed. The increase in

magnification to 2000x gave a hollow structure of the rice husk ash.

Figures 4.16 and 4.17 showed that the cast neat epoxy had a rough surface and

there were poor cohesion between the hardener and the resin in some regions in

the microstructure. An observation of the composite with 10% RHA in figures

4.18 and 4.19 showed that the surface of the composite was rough and the rice

husk ash particles were fairly distributed in the matrix. The rice husk ash particles

were interacting at the interface.

75

Figures 4.20 and 4.21 showed the scanning electron microscopy analysis of the

composite containing 20%RHA. It can be deduced from the photomicrographs

that the composite had a smooth surface with the particles of rice husk ash evenly

distributed and there were interactions at the interface. However the particles did

not bond well with the matrix. Looking at the microstructure of the composite

containing 30% RHA in figures 4.22 and 4.23. It can be seen that interfacial

interactions existed between the rice husk ash particles and the epoxy matrix. At

2000x magnification the particles formed a cluster at the edge and the particles did

not bond well with the matrix. The microstructure appeared strained at 2000x

magnification while at 200x magnification a smooth surface was observed.

From figures 4.24 and 4.25 the composite containing 40% RHA had a smooth

surface at 200x and fairly strained surface at 2000x. The rice husk ash particles

were uniformly distributed. Figures 4.26 and 4 .27 showed the microstructure of

the composite containing 50% RHA. It was observed that the rice husk ash was

not well distributed in the matrix. At 200x magnification a smooth surface was

noticed with clusters of rice husk ash while at 2000x magnification the surface

looked a bit strained.

Conclusively it was observed in the scanning electron microscopy analyses

that interfacial interactions existed between rice husk ash particles and epoxy

matrix. Scanning electron microscopy analysis equally showed that there was poor

interfacial adhesion (bonding) between the rice husk ash particles and the epoxy

76

matrix in the microstructure and poor dispersion of rice husk ash particles in the

epoxy matrix.

4.2.3 Energy Dispersive X-Ray Spectroscopy Analysis

Energy dispersive x-ray spectroscopy analysis showed the elements in the

microstructure of the composites and the cast neat epoxy .The elements and their

composition were found from the EDX attached to the SEM with the help of a

software. The EDX results showed that interfacial reactions existed between the

rice husk ash particles and the epoxy matrix because the composites did not

contain homogenous elements in their microstructure. In an EDX result, the EDX

spectrum showed the elements and their peaks with corresponding energy on the

horizontal line of the spectrum. The elemental composition was shown in the

tables. The elemental composition was given in atomic%, weight%, approximate

concentration and intensity. The results of the energy dispersive x-ray

spectroscopy analysis for the cast neat epoxy and the composites are explained as

follows:

Table 4.14 and figure 4. 28 show the elemental composition and the EDX

spectrum of the cast neat epoxy respectively It showed that the cast neat epoxy

contained these elements C, O,Cl. Table 4.15 and figure.4.30 gave the elemental

composition of the composite with 10% RHA as C,O, Al, Si, P, Cl,K, Ca, Fe, Zn.

The surface of this composite allowed more reactions between the epoxy matrix

and rice husk ash particles which accounted for the highest elements in its

77

microstructure than other composites. Table 4.16 and figure 4.32 showed that the

composite with 20% RHA contained C, O, Si, Cl, K and Fe.

From table 4.17 and figure 4.34 the composite with 30% RHA was found to

contain C, O, Al, Si, Cl and K.

Table 4.18 and figure 4.36 showed that the elemental composition of the

composite with 40% RHA is C, O, Si, Cl and K.

Table 4.19 and figure 4.38 showed that the elements in the microstructure of the

composites with 50% RHA are C,O,Al, Si, Cl and K.

It became evident from the analysis that all the composites had C, O, Cl and Si in

their microstructure. All the composites had higher composition of carbon in them

and their peaks overlapped.

78

CHAPTER FIVE

CONCLUSION AND RECOMMENDATIONS

5.1 Conclusion

This study showed from the scanning electron microscopy and energy

dispersive x-ray spectroscopy microstructural analysis that the microstructure and

elemental composition of the composites varied at the interface of the epoxy

matrix and rice husk ash particles.

It was found from the study that porous structure of rice husk ash, poor

dispersion and poor interfacial adhesion (bonding) between the rice husk ash and

the epoxy matrix caused decrease in flexural strength, toughness and hardness as

percentage of rice husk ash fillers increased. Due to these findings rice husk ash

could be utilized for composite production in areas subjected to tension and

abrasion as an extender filler to reduce cost and minimize environmental pollution.

Rice husk ash is not a good reinforcement material

The only remarkable reinforcing effect of rice husk ash fillers were on

compression because the compressive strengths of the epoxy-rice husk ash

composites were higher than the cast neat epoxy. Hence epoxy-rice husk ash

composite could be used in engineering applications in areas where light weight

and resistance to compression are required such as in producing sole of shoes,

industrial floors, tiles, coating of pipelines, grain storage silos, tanks, tables and

slabs.

78

79

5.2 Recommendations

1. The government should assist engineering research in universities through

the provision of some characterization equipment like Atomic Absorption

Spectrophotometer, X-ray Diffractormeter, Scanning Electron Microscope,

Transmission Electron Microscope, Scanning Transmission Electron

microscope, Instron Universal Testing Machine and Durometer.

2. The use of low volume fractions of rice husk ash for composite production

should be investigated.

3. Coating of the surface of rice husk ash with coupling agents should be done

to improve interfacial adhesion.

4. The particle size of rice husk ash should be reduced to a nano particle to

improve the mechanical properties.

5. Mechanized stirring and dispersants should be used in the mixing of rice

husk ash and epoxy to improve dispersion and prevent agglomeration of

fillers.

6. In order to increase the hardness of the composite harder reinforcing

materials like snail shell, Iron fillings, carbon fibers, periwinkle shell and

palm kernel shell should be used together with rice husk ash.

7. The rheological properties of epoxy should be studied.

80

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85

APPENDIX I

EDX Analysis of Adani Rice Husk Ash

86

APPENDIX II

Structures of different types of composites

a. Random fiber (short fiber) reinforced composites

c. Particles as the reinforcement (Particulate composites):

d. Flat flakes as the reinforcement (Flake composites):

b. Continuous fiber (long fiber) reinforced composites

e. Fillers as the reinforcement (Filler composites):

87

APPENDIX III

Rice Husk Ash Production Process

Plate1 : Rice husks piles being burnt in rice mills: Plate 2: Close-up of burning rice husk

Plate 3: Adani rice husk and Adani rice husk ash

88

APPENDIX IV

Composite Fabrication Procedures

Plate 5: Curing of the composites

Plate 4: Mixing of the epoxy.

89

Plate 6: Hardness test specimen.

Plate 7: Tensile test specimen.

90

Plate 8: Cast composites.

Plate 9: Compressive test specimen

91

APPENDIX V

Testing of Composites

ASTM D638 Tensile test specimen size

Plate 10: Hounsfield Tensometer

92

:

Plate 11: Charpy impact testing machine

Test specimen size for compressive test

93

Unotched specimen

Notched test specimen for toughness test

Test specimen size for hardness test

94

.

Plate 12: Rockwell hardness tester

Test specimen size for Flexural strength test

Plate 13: Flexural testing machine

95

Plate 14: Carl Zees Scanning electron microscope

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