Abstract
Composite insulators with metal oxides are widely used in overhead transmission. While synthesized metal oxides are often used in polymer composites, efforts are on to develop metal oxide micro/nanoparticles from naturally occurring materials. The consumption of periwinkles, a species of small edible sea snail produces residual shells that aredisposed of. The shell, a natural ceramics containing several metal oxides is used in material application such as concrete. This research report the characteristics of a powder produced from the periwinkleshell (PWS) and its effect on the mechanical and dielectric behaviour of epoxy-based polymer composite. The sizes of the particles of the prepared shell fine powder were estimated using the Scanning Electron Microscopy and the image revealed that the sizes of the PWS powder range from 4.39 to 100μm. The chemical composition, thermal conductivity, anddielectric properties were studied using the X-ray Fluorescence (XRF), Thermal conductivity setup, and programmable LCR Bridge respectively. Polymer composite was produced from epoxy resin and the prepared PWS as filler with a composition ranging from 0.5 – 1%. The dielectric and mechanical properties of the produced epoxy composite samples were studied using the programmable LCR Bridge, Monsanto tensometer, Vickers harder tester, and Charpy impact testing machine. The XRF result revealed a powder with over 80% CaO. The thermal and electrical conducting properties of the powder were superior compared with that of pure CaO. The dielectric constant and the electrical conductivity of the powder were determined to be 12.15 and 1.6876 × 10-8 S/m respectively, at the frequency of 200 Hz. Improved properties of epoxy composites were achieved using PWS as reinforcement up to a maximum of 1wt%. The dispersion of the powder up to 1wt% results in a decrease in the dielectric loss and an increase in the dielectric constant of the epoxy polymer. The mechanical properties have optimum improvement of up to 68% with the dispersion of 0.9wt% of PWS into the epoxy polymer. Periwinkle shell powder, if properly processed to micro and even nano-sized particles, can be good candidate filler in polymer composites. The waste periwinkle shell can serve as a cheap resource to produce low-cost polymer composite with improved insulation properties for use in high voltage application and encapsulation power electronic modules.
Table of Contents
Title page
Declaration i
Certification ii
Dedication iii
Acknowledgement iv
Abstract v
Table of contents vi
List of table x
List of figures xi
List of appendices xiii
List of plates xiv
Abbreviations xv
CHAPTER ONE: INTRODUCTION
1.0 Background to study 1
1.1 Periwinkle shell… 4
1.2 Epoxy Resin… 5
1.2.1 Component of Epoxy resin… 7
1.3 Composite 8
1.4 Statement of research problem 9
1.5 Aim and Objective 9
1.6 Scope of the work 10
1.7 Justification 10
CHAPTER TWO: LITERATURE REVIEW
2.0 Introduction… 11
2.1 Review of previous work 11
2.2 Dielectric theory 15
2.2.1 Electric susceptibility and electrical constant 15
2.2.2 Dielectric polarization 16
2.3 Frequency dependence of permittivity 18
2.3.1 Debye relaxation 19
2.3.2 Capacitors… 20
2.4 High voltage insulation 20
2.4.1 Conduction in solids 21
2.4.2 Thermal conductivity 21
2.4.3 Breakdown and high voltage 22
CHAPTER THREE: MATERIALS AND METHODS
3.0 Materials and Equipment 24
3.0.1 Materials 24
3.0.2 Equipment 24
3.1 Methods… 24
3.1.1 Sample preparation 24
3.1.1.1 Sample preparation of periwinkle shell powder… 24
3.1.1.2 Preparation of polymeric composite 25
3.1.1.3 Molding of the polymer composite material 25
3.1.2 Characterization 29
3.1.2.1 Elemental Composition 29
3.1.2.2 Morphology analysis 30
3.1.3 Thermal properties 30
3.1.3.1 Thermal conductivity 30
3.1.4 Mechanical properties… 32
3.1.4.1 Tensile strength test 32
3.1.4.2 Compressive strength test 33
3.1.4.3 Hardness test 33
3.1.4.4 Impact test 33
3.1.5 Electrical properties 34
3.1.5.1 Real and imaginary part of the complex permittivity 34
3.1.5.2 Resistivity and electrical conductivity 35
CHAPTER FOUR: RESULTS AND DISCUSSION
4.0 Introduction 36
4.1 Elemental analysis of the periwinkle shell powder by X-ray fluorescent 36
4.2 Thermal conductivity result 38
4.3 Micro structural result 39
4.4 Mechanical properties 43
4.5 Electrical properties 48
4.5.1 Electrical properties of periwinkle shell powder 48
4.5.2 Electrical properties of polymeric composite samples 53
CHAPTER FIVE: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
5.0 Summary 59
5.1 Conclusions 59
5.2 Recommendations… 61
Reference 62
Appendices 67
List of Tables
Table 3.1: Sample identification numbers of compositions and their percentages 27
Table 4.1: Chemical composition of periwinkle shell powder XRF 37
Table 4,2: Tensile, Compressive, Hardness and Impact test result 45
Table A1: Real permittivity of the polymer microcomposite result 67
Table A2: Imaginary permittivity of the polymer microcomposite result 68
Table A3: Tan Delta (δ) of the polymer microcomposite result 69
Table A4: Electrical Conductivity of the polymer microcomposite result 70
List of Figures
Figure 1.1: Structure of Epoxy resin 6
Figure 1.2: Structure of composite in different constituent materials 9
Figure 2.1: An electric field in positive and negative point charges 17
Figure 3.1: Searle’s Experimental setup for measuring the thermal conductivity of a Pelletized periwinkle shell powder 32
Figure 3.2: A piece of resistive material with electrical contacts on both end 35
Figure 4.1: XRF spectra of periwinkle shell powder 36
Figure 4.2: Profile of Tensile strength of the samples composition in different percentage powder addition 44
Figure 4.3: Profile of compressive strength of the samples composition in different percentage powder addition… 45
Figure 4.4: Profile of Hardness values of the samples composition in different percentage powder addition 46
Figure 4.5: Profile of impact strength of the samples composition in different percentage powder addition 46
Figure 4.6: Variation of real part of the periwinkle shell powder pelletized sample for different temperature as a function of frequency 49
Figure 4.7: Variation of imaginary part of the periwinkle shell powder pelletized sample for different temperature as a function of frequency 49
Figure 4.8: Variation of Tan δ of the periwinkle shell powder pelletized sample as a function of frequency for different temperature 50
Figure 4.9: Variation of electrical conductivity of the periwinkle shell powder pelletized sample as a function of frequency for different temperature 51
Figure 4.10: Variation of real permittivity of the polymer microcomposite sample as a function of frequency 53
Figure 4.11: Variation of imaginary permittivity of the polymer microcomposite sample as a function of frequency 53
Figure 4.12: Variation of Tan δ of the polymer microcomposite sample for different percentage of periwinkle shell powder as a function of frequency 54
Figure 4.13: Variation of electrical conductivity of the polymer microcomposite sample for different percentage of periwinkle shell powder as a function of frequency 54
List of Plates
Plate I: Periwinkle shells 5
Plate II. Mould with sample 26
Plate III. Sample A with different percentage of the powder for hardness and dielectric properties test 28
Plate IV. Sample B with different percentage of the powder for tensile strength… 28
Plate V. Sample C with different percentage of the powder for compressive and Impact strength test… 29
Plate VI. A pelletized periwinkle shell powder using a hydraulic press… 31
Plate VII: The SEM Micrograph of periwinkle shell powder 39
Plate VIII: The SEM Micrograph of reinforced epoxy resin without periwinkle shell powder…40
Plate IX: The SEM Micrograph of reinforced epoxy resin with 0.5% of periwinkle shell powder 40
Plate X: The SEM Micrograph of reinforced epoxy resin with 0.7% of periwinkle shell powder 41
Plate XI: The SEM Micrograph of reinforced epoxy resin with 0.9% of periwinkle shell powder… 41
Plate XII: The SEM Micrograph of reinforced epoxy resin with 1% of periwinkle shell powder… 42
Abbreviation
PWS - Periwinkle Shell
% - Percentage
δ - Delta
μm- Micrometer
Kgm-3 - Kilogram per Meter Cubic
SEM - Scanning Electron Microscope
LCR - Inductance Capacitance Resistance
XRF - X-ray Fluorescence
Kv - Kilovolt
mm - Millimeter
mA - Miliampere
J - Joule
Kev - Kilo Electron Volt
Wm-1k-1 - Watt per Meter per Kelvin Mpa - Mega Pascal
KHz - Kilo Hertz
Sm-1 - Siemens per Meter
0C - Degree Celsius
DC - Direct Current
AC - Alternative Current
Pb - Lead
CaO - Calcium Oxide
SiO2 - Silicon Oxide
MgO - Magnesium Oxide
Cr2O3 - Chromium Oxide
Fe2O3 - Iron Oxide
K2O - Potassium Oxide
Na2O - Sodium Oxide
MnO - Manganese Oxide
ZnO - Zinc Oxide
CuO - Copper Oxide
Al2O3 - Aluminum Oxide
P2O5 - Phosphorus Oxide
SO3 - Sulfur Oxide
Cl - Chlorine
SrO - Strontium Oxide
CHAPTER ONE
INTRODUCTION
1.0 BACKGROUND OFTHE STUDY
The need for improved polymeric insulation brings about the idea of composite dielectrics. This involved the addition of micro/nano-additives in dielectric materials to create composite materials. Composite materials are multiphase materials in which the phase distribution and geometry have been controlled in order to optimize one or more properties. The intent of producing composite material is to make a material that combines the best properties. Several papers have reported progress made in the dispersion of additives in polymers to produce the composite dielectric materials (Singha and Thomas, 2008). Polymeric materials are important components of electrical insulation and epoxy family occupies a very important position in polymeric materials.
Epoxies are class of thermostat materials used extensively in structural and specialty composite applications because they offer a unique combination of properties that are unattainable with other thermoset resins. Available in a wide variety of physical forms, from low viscosity liquid to high melting solids, they are amendable to a wide range of processes and applications. Epoxies offer high strength, low shrinkage, excellent adhesion to various substrates, effective electrical insulation, chemical and solvent resistance, low cost and low toxicity.
They are easily cured without the evolution of volatiles or byproducts by a broad range of chemical species. Epoxy resins are also chemically compatible with most substrates and tend to wet surfaces easily making them especially well-suited to the composite application (Boyle and Martin, 2001). In an attempt to improve the mechanical properties of the epoxy polymer, the effect of different fillers dispersed in the polymer was investigated by various researchers. The effect of periwinkle shell powder on the mechanical properties of polypropylene and polyester composites was studied at high filler content (10-50 wt %) (Onueghu and Igwe, 2011). It was reported that the addition of the filler in the polypropylene matrix led to an improvement in the mechanical properties of the polypropylene composite and that the composite can broaden the application scope of polypropylene. The addition of 30 wt% periwinkle shell in polyester was reported to have produced a polyester composite with the highest tensile and flexural strength (Onyechi and Asiegbu, 2015). For polymer composite used as polymeric insulation, oxides of metals are often used as fillers at low filler content. Aside from acting as insulators, polymers serve as a mechanical support in the power system.
Polymer nanocomposites were found to have improved the dielectric loss and breakdown strength at certain filler content. Some of the common metal oxides used to modify the structure of the polymer matrix include SiO2, TiO2 and Al3O2(Liang and Wong, 2017). While the microparticles of these metal oxides produced materials with increased dielectric loss, the nanoparticles were found to produce polymer composites with decreasing dielectric loss at lower filler loading. This was attributed to the morphology of the nano-materials (Singha and Thomas, 2008).
Calcium oxide as an alkaline earth metal oxide is known to have many applications. This includes its use as catalyst (Ngamcharussrivichai and Meechan, 2011), toxic-waste remediation agent, an additive in refractory (Tang and Claveau, 2008),and a crucial factor for CO2 capture (Park and Bae, 2013). Calcium oxidealso been used as an additive to modify the electrical and dielectric properties of materialscomposite (Alavi and Morsali, 2010).Report on the electrical properties of calcium oxide shows that, it has electrical conductivity of 1 × 10−6 S m−1 (Surplice, 1966). The electrical conductivity of polyaniline (PANI) nanofibers was studied by systematically varying the addition of CaO in the range from 0.005 to 1.00 g. Increase in CaO loadings was reported to have resulted in a decrease in the electrical conductivity of the composite material (Rahman and Wee, 2014).
Animal shells are known to be composed of several metal oxides that are being exploited for numerous industrial applications. Instead of producing micro- or nanoparticle through chemical methods, can the micro- or nanoparticles produced from such waste sea animal shells serve the same purpose? Periwinkle is another type of seashell animal. It is a species of small edible sea snail that is consumed in large quantity in Nigeria. Its consumption produces residual shells which posed an environmental hazard. The shell is a natural ceramics which contained several metal oxides used in material applications such as filler in concrete production. The shell ash was investigated as a replacement for cement in concrete. These shells are used as a mechanical re- enforcement (Raju, 2012). It was utilized as coarse aggregate in concrete in areas where there are neither stones nor granite for purposes such as paving of water logged areas. The large amount of these shells are still disposed off as waste and with disposal already constituting a problem in areas where they cannot find any use for it, and large deposits have accumulated in many places over the years (Raju, 2012).
It was a reported that there are about 40.3 tones of Periwinkle per year being harvested from 35 mangrove communities of Delta and River states of Nigeria (Jamabo and Chinda, 2010). Massive periwinkle harvesting is also reported from some communities in Bayelsa, Cross Rivers and Edo States of Nigeria (Jamabo and Chinda, 2010). According to Aku (2012), Periwinkle shell particle exhibited a density of 1.24g/cm . Structurally, the periwinkle shell has several layers and is typically made of an organic matrix (Conchiolin) which is bonded with calcium carbonate precipitate, carbonate-filled organic matrix shells are resistant to water and this property makes it possible for periwinkle shells and their derivatives to have very wide applications such as, it is used in enhancing microbial breakdown of spilled oil and also as coarse aggregates in concrete (Painter and Hemmer, 1979).It can be used for removal of Pb and Cu from industrial waste and loss control agent in water-based drilling mud (Powell and Hart, 1985). In this work, microparticles prepared from waste periwinkle shells are characterized for its possible use in polymer composite for mechanical properties and high-voltage electrical insulation application.
1.1 PERIWINKLE SHELL
Periwinkle is a species of small edible whelk or sea snail, a marinegastropodmollusc that hasgills and an operculum, and is classified within the family of Littorinidae, Periwinkles are robust intertidal species with a dark and sometimes banded shell. It is native to the rocky shores of the Northeastern coasts of the Atlantic Ocean (Welch, 2010).
The periwinkle shell (PWS) is broadly ovate, thick, and sharply pointed except when eroded. The periwinkle shell contains six to seven whorls with some fine threads and wrinkles; the color is variable from grayish to gray-brown, often with dark spiral bands. The base of the columella is white, the periwinkle shell lacks an umbilicus, the white outer lip is sometimes checkered with brown patches and the inside of the shell has a chocolate-brown color (David and Gofas, 2011). Benson (2008), reported that, the width of the periwinkle shell ranges from 10 to 12 mm at maturity, with an average length of 16–38 mm and height can reach up to 30 mm, 43 mm or 52 mm. Periwinkles shell is used as bait for catching small fish, it is usually crushed and the soft parts extracted and put on a hook (Painter and Hemmer, 1979). A sample picture of these Periwinkle shells (PWS) is shown in PlateI
Plate I. Periwinkle shells
1.2 EPOXY RESIN
Epoxy is a term used for both the basic components and the cured end products of epoxy resins, as well as a colloquial name for the epoxide functional group. Epoxy has a wide range of applications, including metal coatings (Hakiki,2015), used in electronics and electrical components and high tension electrical insulators (Clayton, 1987), fiber-reinforced plastic materials and structural adhesives (Hakiki, 2015).
Epoxy resins (polyepoxides) are a class of reactive pre-polymers and polymers which contain epoxide groups. Epoxy resins may be reacted either with themselves through catalytic homopolymerization or with a wide range of co-reactants including poly-functional amines, acids, phenols, alcohols and thiols. These co-reactants are referred to as hardeners or curatives and the cross-linking reaction is commonly referred to as curing. Reaction of epoxy resin with themselves or with poly-functional hardeners forms a thermosettingpolymer, with high mechanical properties, temperature and chemical resistance (Farizal, 2015). TheStructure of a cured Epoxy resin is shown in Figure 1.1.
Figure 1.1. Structure of Epoxy resin (Farizal, 2015)
The triamine hardener is shown in yellow, the resin in white, the resin's epoxide groups have reacted with the hardener and are not present anymore. The material is highly cross-linked and contains many OH groups, which confer adhesive properties. Epoxy resins are low molecular weight pre-polymers or higher molecular weight polymers which normally contain at least two epoxide groups; common types of epoxy resin are bisphenol A, bisphenol F, Novolae, Aliphatic and Glycdylamine. A wide range of epoxy resins are produced industrially, the raw materials for epoxy resin production are today largely petroleum derived, although some plant derived sources are now becoming commercially available and epoxy resins are polymeric or semi-polymeric materials (Hakiki, 2015).
An important criterion for epoxy resins is the epoxide content, the epoxide number, which is the number of epoxide equivalents in 1 kg of resin or as the equivalent weight, which is the weight in grammes of resin containing 1 mole equivalent of epoxide (g/mol).
The equivalent weight or epoxide number is used to calculate the amount of co-reactant (hardener) to use when curing epoxy resins. As with other classes of thermoset polymer materials, blending different grades of epoxy resin, as well as use of additives, plasticizers or fillers is common to achieve the desired processing, final properties and to reduce cost (Staubli, 1963).
1.2.1 COMPONENT OF EPOXY RESIN
Uncured epoxy resins have poor mechanical, chemical and heat resistance properties,good properties are obtained by reacting the linear epoxy resin with suitable curatives to form three- dimensional cross-linked thermoset structures. This process is commonly referred to as curing or gelation process, Curing of epoxy resins is an exothermic reaction and in some cases produces sufficient heat to cause thermal degradation, if not controlled. The resin and hardener are supplied pre-mixed to the end user and only require heat to initiate curing. There are two basic components of the epoxy resin namely;
i. Resin: the resin component is usually light, sometimes almost clear colored and odorless. Examples are diepoxide and polyepoxide.
ii. Hardener: the hardener component is usually dark and has slight odor. Examples are Polyamides, mercaptans, phenolic.
When these two components are mixed, they chemically bond together and once the chemical reaction has finished, it is strong and rigid plastic material. Epoxy resins are used because of their outstanding chemical resistance, durability, low porosity and strong bond (Farizal, 2015).
1.3 COMPOSITE
A composite material is a material made from two or more constituent materials with significantly different physical or chemical properties that, when combined, produce a material with characteristics different from the individual components. Composites are made up of individual materials referred to as constituent materials. There are two main categories of constituent materials: matrix and reinforcement.
The matrix material surrounds and supports the reinforcement materials by maintaining their relative positions. The reinforcements impart their special mechanical and physical properties to enhance the matrix properties (Waterman, 2007). More recently, researchers have also begun to actively include sensing, actuation, computation and communication into composites, which are known as Robotic Materials.
Composite materials are generally used for buildings, bridges, and structures such as boat hulls, swimming pool panels, race car bodies, shower stalls, bathtubs, storage tanks, imitation granite, and cultured marble sinks and countertops. The most advanced examples perform routinely on spacecraft and aircraft in demanding environments (Waterman, 2007). Sample pictures of these composite are shown in Figure 1.2.
Figure 1.2. Structure of composite in different constituent materials (Waterman, 2007).
1.4 STATEMENT OF RESEARCH PROBLEM
Some natural ceramic sources such as clays, animal shells etc, for a long period of time have been used for industrial polymeric insulation in some part of the world. In Nigeria, these natural ceramic sources are in abundance and these shells are still disposed off as waste and with disposal already constituting a problem in areas where they cannot find any use for it. However, the application of these shells has not been explored in industry for high voltage insulation. In line with this, this research work intended to examine the feasibility of using periwinkle shells powder to enable waste to be converted to wealth.
1.5 AIM AND OBJECTIVES
The aim of this research is to investigate assessment of the influence of periwinkle shell powder on the mechanical and dielectric properties of Epoxy resin. The objectives of the research are to:
i. Produce powder from properly cleaned periwinkle shell; perform the morphology, electrical and thermal characterization of the powder to understand the properties of the particles.
ii. Prepare an epoxy resin based micro polymer using the powder obtained from periwinkle shell.
iii. Examine the impact of the powder on the mechanical strength of the micro-polymer.
iv. Evaluate the dielectric properties of the prepared micro-polymeric insulation.
v. Compare the measured properties of the polymer samples with dispersed periwinkle shell powder.
1.6 SCOPE OF THE WORK
In this research work, microparticles powder was produced from periwinkle shell with particle sizes ranging from 4.39 μm to 100 μm size. Polymer composite was successfully prepared from epoxy resin and the periwinkle shell powder with enhanced properties. The prepared samples were subjected to morphology, elemental analysis and thermal conductivity, mechanical and dielectric characterization.
1.7 JUSTIFICATION
Periwinkles which are naturally found at the coasts of Atlantic Ocean are a species of small edible sea animal. Periwinkles are used as good seafood. The natural ceramic sources are of recent considered as valuable sources for numerous industrial applications. Sequel to this proper utilization of these natural ceramic sources as polymeric will add economical value and at same reduce disposal challenges in the environment.
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