chapter 3$4

Chapter three

Materials and methodology

3.1 materials

A low cost manufacturing process using simple experimental design

methodology has been developed for this study, and no expensive machinery was

required for processing. Locally evaluable raw materials were used in this work.

The agro-waste material (cassava cortex) was obtained from local markets in

Nsukka in Enugu state. Simple molding process was used in the sample fabrication. After

the fabrication of the samples, they were subjected to series of tests such as dielectric

test and mechanical tests. The description of the process is shown below.

3.2 Experimental Materials

I. Cassava cortex

II. Epoxy resin

III. Hardener

Cassava cortex: cassava cortex is the raw material that constitutes the particulate of the

composite. It is gotten by peeling off the back of a cassava and allowing it to dry in the

sun. This material forms a composite with good dielectric property when mixed with

epoxy.

Epoxy resin: Epoxy belongs to a class of polymer called thermoset. It is hard, tough,

insoluble and infusible when cured. Its property of infusibility differentiates thermoset

from thermoplastics. Epoxy cure at room temperature. During curing, it undergo

exothermic reaction. Epoxy is the most widely used polymer because of its exceptional

properties. Below are the advantages one can gain from using epoxy resin:

1. Good handling characteristic.

2. Low shrinkage.

3. Excellent adhesive property.

4. Flame resistance.

5. Good chemical resistance.

6. No by-product form during curing.

7. Good mechanical properties.

8. Good electrical resistivity.

9. Good dielectric constant.

Hardener: these are comprehensive line of anhydride based hardeners designed for

indoor/outdoor electrical application and composites. When paired with a compactible

epoxy resin, anhydride based polymers offers low viscosity, UV stability, high

temperature performance and good electrical insulation properties.

3.2.1 Preparation of cassava cortex

The cassava peels used was sourced locally from markets in Nsukka in Enugu

state. The cassava peels was sun dried after which, the brown exterior of the cassava

peel was easily removed with hand. Part of the cassava cortex was carbonized and some

of them was left uncarbonized. For the carbonized cassava cortex, the carbonization was

done at a temperature of 300 degree Celsius. The cortex was ground into powder using

grinding machine. After the grinding, sieve analysis was carried out on the particle. This

is where different particle size of the powder was separated using sieve. Particle size of

150microns, 300microns and 600microns where used. The cassava cortex powder which

is now the reinforcement was mixed with epoxy gum which is the matrix in certain ratio

that will be later specified and stirred, after which, the mixture will now be cast into the

mold for the fabrication into any desired shape. After the casting, the specimen was

allowed to dry and solidify.

3.3 fabrication process

A relatively low cost polymer composite manufacturing process using simple

experimental design methodology was employed for this study. The activities involved

are classified into three steps, which include:

Molding making

Preparation of the composition for the samples

Casting

3.3.1 Molding making

The materials used for the preparation of the molds is an embossed paper. This

embossed paper is cut into different sizes and shapes for the fabrication of the mold.

After the mold has been fabricated, they were placed on a flat metal sheet and with

masking tape, these molds where held in place. For the cylindrical molds, it was ensured

that the base of the mold was firmly held to avoid leakage during pouring.

3.3.2 Preparation of the composite for the samples

S/N Designation Composition

1 150 microns cassava

cortex particulate

40% epoxy + 20% hardener + 40% particulate

33% epoxy + 17% hardener + 50% particulate

27% epoxy + 13% hardener + 60% particulate

2 300 microns cassava

cortex particulate

40% epoxy + 20% hardener + 40% particulate

33% epoxy + 17% hardener + 50% particulate

27% epoxy + 13% hardener + 60% particulate

3 600 microns cassava

cortex particulate

40% epoxy + 20% hardener + 40% particulate

33% epoxy + 17% hardener + 50% particulate

27% epoxy + 13% hardener + 60% particulate

From the table above, samples were produced for each particulate size.

3.3.3 Casting of the samples

The casting process is the last stage of fabrication of the sample. After the

equivalent volume is known for each sample, releasing agent was properly applied in

the mold for easy removal of the sample after curing. The resin (epoxy) is then mixed

with the hardener in the ratio of 2:1 in a glass beaker and stirred properly. The

particulate was then measured and poured into the mixture, it was stirred to ensure a

homogeneous mixture. After the stirring, it was poured into the mold and allowed to

cure. After curing, the samples were removed from the mold and were taken to the next

procedure which involved testing.

3.4 Testing of fabricated samples

The tests that were carried out on these samples are for the determination of

the breakdown voltage, dielectric test, water absorption capacity test, moisture content

test, surface resistivity and volume resistivity, mechanical testing which include tensile

test, compressive test, flexural test, impact test, hardness test and wear test.

3.4.1 Breakdown voltage

The cylindrical sample of 25mm diameter and thickness of 5mm was placed

between two sphere-type electrodes of 20mm diameter and an impulse voltage was

gradually applied to the sample from the control desk. The value at which the insulator

failed is recorded and the breakdown voltage of all the specimen is recorded via the same

procedure.

3.4.2 Dielectric test

To determine the dielectric constant, the composite samples were molded into

rectangular plates of length 50mm, width 30mm and thickness 2mm. the figure below

shows the plan for the experimental setup used for the determination of the dielectric

constant. It comprises of two parallel plate capacitors, DC battery, and a digital

multimeter for measuring the applied voltage across the samples. An air gap was

created between two parallel plate capacitors which has the same thickness with the

sample. The parallel plate capacitors were connected to the battery and the voltage

across was measured (Vo). The samples were then inserted between this air gap and the

different voltage was taken for the different samples.

Given below is the relationship between the Vo (voltage between the capacitor with an

air gap between them) and V (voltage across the capacitor with the sample between

them).

Below is the diagram of the dielectric test being perform.

3.4.3 Water absorption capacity test

The water absorbed by the material is specified as the percentage weight gained

by the material. With the cylindrical sample of length 30mm and diameter 15mm, the

samples were weight to the nearest 0.01g (M1) and immersed in the water for a period

of one month (30 days) after which, it was removed from the water and allowed to

drain in the ambient, then the sample was weighed again the second time (M2). The

water absorbed was calculated as percentage weight gain using the following formula:

Wa=( M 2−M 1 )

M 1∗100

3.4.4 Moisture content

The moisture present in the samples has samples has significant effects on the dielectric

strength and resistivity of the materials. Therefore, the moisture content at the time of

measurement is needed to be specified. The sample with length 5mm and diameter 15mm was

taken and each of them was weighed to the nearest 0.01g (M3), the samples were then placed

in an oven for 3 hours at 90 degree Celsius. After proper drying, the samples were weighed to

obtain the value (M4). The moisture content was calculated as percentage of the dry sample

using the following equation:

Wc=( M 3−M 4 )

M 3×100

3.4.5 Tensile test

The strength of the insulators was investigated by determining their tensile strength

according to (ASTM, 1985b). A Universal tensile testing machine was used to carry out

the failing load of the samples. The insulators were coupled on the tensile machine and

allowed to be loaded up to until failure was experienced.

3.4.6 Impact test

3.4.7 Linear Shrinkage

The dimensional changes in length were taken and the results were used to determine the

linear shrinkage after firing at 105C. The linear shrinkage was determined using

equations (1) to (3) below.

Drying shrinkage = Lw−Ld

Ld∗100 % - - (1)

Fired shrinkage = Lw−Lf

Ld∗100 % - - (2)

Total shrinkage = Lw−Lf

Lw∗100 % - - (3)

Where Ld = Dry length, Lw = Wet length, Lf = Fired length

3.4.8 Density

Density was calculated using a direct volume measurement method. This method

involves the use of water displacement method and the mass of the samples. The mass of

the sample divided by the volume of the displaced water will give the density of the

samples

Density = Mv

=mass/volume (g/cm3)

Chapter 4

Data, analysis and interpretation

This chapter is centered on the explanation of all the results of the tests that has been

carried out on the fabricated sample. Some of these tests are destructive (damaging the

specimen after the test) while some of them are non-destructive (the specimen still intact after

the test was conducted)

Below are the data generated for the various tests and the possible explanations to the nature

of the prevailing values

4.1 breakdown voltage.

Below is the breakdown voltage value of the composite with different volume fraction of

particles and epoxy

S/N Sample Breakdown voltage (V)

1 40% 150U 30

2 50% 150U 37

3 60% 150U 36

4 40% 300U 25

5 50% 300U 35

6 60% 300U 25

7 40% 600U 40

8 50% 600U 38

9 60% 600U 40

10 CONTROL

4.2 dielectric test

Below is the values gotten for the dielectric test conducted on the samples

S/N Sample Vo = voltage across

with an air gap

V = voltage across with

the sampleυ=Vo

V

1 40% 150U 1.00059 1.02V 0.9810

2 50% 150U 1.00059 0.06V 16.6765

3 60% 150U 1.00059 0.10V 10.0059

4 40% 300U 1.00059 0.65V 1.5394

5 50% 300U 1.00059 1.15V 0.8701

6 60% 300U 1.00059 0.20V 5.0030

7 40% 600U 1.00059 0.10V 10.0059

8 50% 600U 1.00059 0.21V 4.7647

9 60% 600U 1.00059 0.20V 5.0030

10 control 1.00059

4.3 water absorption capacity test

Below are the values gotten form the test conducted on water absorption capacity of the

samples

S/N Samples Initial weight

before immersion

in water = M1(g)

Final weight after

removal from water =

M2(g)

Water absorption rate (%)

WA=(M2-M1)/M1 X 100

(percentage)

1 40% 150U 36 36 0

2 50% 150U 34 34 0

3 60% 150U 36 36 0

4 40% 300U 37 37 0

5 50% 300U 35 35 0

6 60% 300U 38 38 0

7 40% 600U 35 35 0

8 50% 600U 33 33 0

9 60% 600U 30 31 3.33

10 control 37 37 0

From the table above, it can be observed that the composite has a zero moisture absorption

content. That is, the weight of the material before the absorption is the weight of the material

after the absorption.

4.4 moisture content

Below are the value gotten from the different samples based on the moisture content test

S/N Samples Initial weight with

moisture content =

M3(g)

Final weight after

drying in the oven =

M4(g)

Moisture content (%)

MC=(M3-M4)/M3 X 100

1 40% 150U 36 35 2.86

2 50% 150U 34 33 2.94

3 60% 150U 36 35 2.86

4 40% 300U 37 35 2.70

5 50% 300U 35 33 5.71

6 60% 300U 38 35 7.89

7 40% 600U 35 32 8.57

8 50% 600U 33 30 9.09

9 60% 600U 30 27 10.00

10 control 37 38 2.70

4.5 tensile test

The strength of the insulators was investigated with the help of the result. It was observed that the sample with higher percentage composition of cassava has lower strength compared to the ones with high epoxy content. This shows that the strength of the composite insulator are enhanced by the presence of the epoxy matrix.

4.6 impact test

These are the values gotten from the impact test

S/N Samples Energy(J)

1 40% 150U 5.10

2 50% 150U 5.00

3 60% 150U 5.00

4 40% 300U 3.45

5 50% 300U 3.50

6 60% 300U 3.40

7 40% 600U 3.35

8 50% 600U 3.75

9 60% 600U 2.95

10 CONTROL 5.50

4.7 Linear Shrinkage

The total linear shrinkage percentage of insulators were found to increase with increasing cassava cortex content and reduction of epoxy as indicated by Tables

S/N Sample Dry

length

Wet

length

Fired

length

Dry

shrinkage

Fired

shrinkage

Total

shrinkage

1 40% 150U 12 12 11.5 0 4.17 4.17

2 50% 150U 12 12 11.1 0 7.50 7.50

3 60% 150U 12 12 10.9 0 9.16 9.17

4 40% 300U 12 12 10.4 0 13.33 13.33

5 50% 300U 12 12 10.5 0 12.50 12.50

6 60% 300U 12 12 10.0 0 16.67 16.67

7 40% 600U 12 12 9.80 0 18.33 18.33

8 50% 600U 12 12 9.80 0 18.33 18.33

9 60% 600U 12 12 9.70 0 19.67 19.17

10 CONTROL 12 12 11.5 0 4.17 4.17

4.8 Density

These are the values of density of the different samples of the composite.

S/N Sample Mass(g) Volume(cm3) Density(g/cm3)

1 40% 150U 36 25 1.44

2 50% 150U 34 25 1.36

3 60% 150U 36 27 1.33

4 40% 300U 37 24 1.54

5 50% 300U 35 28 1.25

6 60% 300U 38 29 1.31

7 40% 600U 35 30 1.17

8 50% 600U 33 26 1.27

9 60% 600U 30 27 1.11

10 CONTROL 37 27 1.37