Preparation of Carbon Nano Composite Fibre Using Electro-spinning Method

8/19/2019 Preparation of Carbon Nano Composite Fibre Using Electro-spinning Method

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PREPARATION AND CHARACTERIZATION OF CARBON FIBER NANO-COMPOSITE BY

ELECTROSPINNING METHOD INFLUENCED BY CONCENTRATION OF ACTIVATED

CARBON, VOLTAGE AND COLLECTOR

MUHAMMAD ARIFF ASRAF BIN ZAINAL

PROGRAM KIMIA INDUSTRI

SEKOLAH SAINS DAN TEKNOLOGI

UNIVERSITI MALAYSIA SABAH

2011


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Chapter 1

Introduction

1.1 Research Background

Activated carbon is an amorphous solid that has an extremely large surface area and

pore volume. These properties along with high degree of surface reactivity, porosity

and thermal stability make it an excellent form of adsorbent. Since it was discovered

a century ago, various materials have been used to synthesize this unique

compound. The raw material used includes bones, coconut shell (Daud et al ., 2004),

peat, woods, fruit stones and nut shells (Lua & Yang, 2000).

Polyacrylonitrile (PAN) exhibits good mechanical properties and has beenwidely used as separation membrane materials. However, due to some inherent

disadvantages, such as brittleness, relatively low hydrophilicity and poor

biocompatibility, modifications on PAN or PAN-based membranes must be made to

meet the requirements of the increasingly extended applications (Wan et al ., 2006).


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1.2 Application of Activated Carbon

Activated carbon is known to have commercial value mainly as adsorbent. Because of

its porous surface, activated carbons are able to absorb unwanted molecules from a

medium such as heavy metals, dyes, and dangerous inorganic and organic

compound. The application of activated carbon as absorbent can further be divided

into two categories which are the liquid-phase application and the gas-phase

application.

The liquid phase application involves the application of activated carbon in a

liquid-phase medium such as waste water treatment (Dinesh et al ., 2006), portable

water treatment (Muhamed et al ., 2004), oil and sugar purification (Kawashima et

al ., 2009), groundwater remediation (Wang et al ., 2003) and food related application

(Raquel et al ., 2010)

While gas phase application involves application of activated carbon in gasphase medium such as air purification, solvent vapour recovery (Yun et al ., 2000),

emission control (Giorgos et al ., 2006) and gas filters. Besides that, activated carbons

are also used in chemical processes as catalyst support. Recently, activated carbon

has also been used on the electronic field to make double layer capacitor (Wang et

al ., 2010)

The application is now broaden with the intense research on composite and

polymers. Polyacrilonitrile (PAN) is widely used as the basic of a polymer composite

(Wan et al., 2006). It is used to produce various kinds of applications which range

from clothing to pharmaceuticals. PAN is also known to have some disadvantages

that made the application of PAN alone inconvenient. The application of activated

carbon in this polymer will produce a composite with improved properties compared

to PAN alone.


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1.3 Scope of Study

This study will concentrate on the application of activated carbon in polymer

composite. Activated carbon is used as additive in the preparation of carbon

fiber nano-composite while polyacrylonitrile (PAN) is used as the base

polymer for the fiber nano-composite. Solution of PAN and dimetyl formide

(DMF) is prepared by heating and stirring of the mixture at 70oC for six hours.

The solution is then added with two different concentration of activated

carbon before being heated for another hour. Carbon fiber nano-composite is

obtained from the solution using electro-spinning process. Parameters

involved during the process are concentration of activated carbon, voltagesupply and collector’s condition. The concentration of activated carbon used

are 2 wt% and 5 wt%, the voltage supply used are 15kV and 20kV and the

collector’s condition are alternate between dry and wet. The distance from

the tip of the syringe and the flow rate of the syringe pump on the other hand

is kept constant. The fiber collected from the electro-spinning will be

characterize using Differential Scanning Calorimetry (DSC) and Fourier

Transform Infra Red (FT-IR) machine.


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1.4 Objectives

The objective of the study are:

a) To prepare polyacrylonitrile (PAN) carbon fiber nano-composite reinforced

with activated carbon using electro-spinning method and

b) To characterize the properties of the carbon fiber nao-composite using

Diffrential Scanning Calorimeter (DSC) and Fourier Transform Infra Red (FT-

IR) machine and

c) To study the different parameters in the preparation of carbon fiber nano-

composite such as concentration of activated carbon, voltage supply andcollection method.


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Chapter 2

Literature Review

2.1 History of activated carbon

Activated carbon or activated coal is a porous material with an extraordinary

excellent surface property which enables it to be a superior adsorbent and catalytic

support (Khalili et al., 2002 ). The structure of activated carbon is best described as a

twisted network of defective carbon layer planes, cross-linked by aliphatic bridging

groups as shown in Figure 2.1 (McEnany et al., 2004). The race for modern industrial

production of activated carbon was established in 1900-1901 to replace bone chars in

the sugar refining process. In 1900, two very important processes in the

development and manufacturing of activated carbon was founded and patented. Not

very long after that, the first commercial product was produced in Europe.

The precursors at that time are mainly wood which was called Eponite, year

1909, peat which was called Norit, year 1913 and by product of papermaking

process. During World War 1, further developments were achieved. Granular

activated carbon was synthesized from coconut shells in response to the demand of

protective gas mask. Following the war, large-scale commercial use of activated

carbon was extended to refining of beet sugar and corn syrup and to purification.


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1940, the termination of the supply of coconut char from the Philippines and India

during World War II forced the development of granular activated carbon products

from coal. More recent innovations in the manufacture and use of activated carbon

products have been driven by the need to recycle resources and to prevent

environmental pollution.

Figure 2.1 Chemical structure of activated carbon

2.2 Physical and Chemical properties

According to McEnany et al (2004), the structure of activated carbon is best

described as a twisted network of defective carbon layer planes, cross linked by

aliphatic bridging group. Under X-ray diffraction, activated carbon reveals that it is

non graphitic. It remains amorphous because of the randomly cross linked network

that inhibits reordering of the structure.

The International Union of Pure and Applied Chemistry or IUPAC classes the

pore sizes of the activated carbon in three categories as shown in the cross section

view of activated carbon particle. Table 2.1 shows the types of pores that can befound on activated carbon particles and its pore width range. Micropores has pores


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with width less than 2nm, mesopores has pores with width from 2-50nm and

macropores has pores with width of 50nm. The surface area on the other hand is

determined by the application of the Brunauer-Emmet-Teller or BET model of

physical adsorbtion which uses nitrogen as the adsoptive. Commercially produced

activated carbon has specific surface area in the range of 500-2000 m2 /g to 3500-

5000 m2 /g.

For the microporous activated carbon, the actual effective surface areas are

often smaller if not far smaller because the effective adsorbtion of nitrogen does not

follow the BET model. This results in the extremely high values for surface area.These properties and dimensions of the activated carbon often depend on the

precursor and the parameters used during the manufacturing process. Picture 2.1

shows the surface structure of activated carbon generated by SEM. The development

of carbon materials with controlled micro- and mesoporosity is of paramount

importance in order to achieve a high adsorption capacity together with fast

adsorption kinetics for processes involving large molecules (Juárez et al ., 2009)

Besides the physical characteristics stated above, the surface chemistry plays

an equal role for the effectiveness in chosen application. The interaction of the free

radicals on the carbon surface with atoms such as oxygen and nitrogen in the

precursor and atmosphere forms functional groups. These functional groups render

the surface of the activated carbon thus influencing its adsorbative properties.

Although activated carbon is known to exhibit a low affinity for water, the functional

groups on it can, making the carbon surface to be more hydrophilic (Salame et al .,2003).

Other than surface area, pore size distribution and surface chemistry, other

important properties of activated carbon especially commercialized activated carbon

includes pore volume, particle size distribution, apparent density, particle density,

abrasion resistance, hardness and ash content. An example of commercial activated

carbon properties is given in table 2.2.


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Table 2.1 Pore types and width range in nanometres

Pore types Pore Width Range

Micropores < 2nm

Mesopores 2-50nm

Macropores >50nm

Figure 2.2 Cross section view of activated carbon particle

Picture 2.1 SEM image of the surface of activated carbon


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Table 2.2 Properties of three types of activated carbon

2.3 Economic value of activated carbon

World demand for activated carbon is forecast to expand 9.9 percent per year

through 2014 to 1.7 million metric tons. As for 2010, world demand has reached 1.2

million metric tons. Most of the activated carbons are marketed to the mature

markets in North America, Western Europe and Japan. Besides the mature market,

Asia and Middle East region has increased its share of the global activated carbon

market as most of the nations in the regions are experiencing rapid economic growth

(Boyce, 2006)

In the developed and developing countries, the strongest growth prospects

for activated carbons are in pharmaceutical and medical sectors besides industry use

and environmental. Developing countries market are more to environment such as

wastewater treatment application. Other environment application such as hazardous

Property Gas phase carbon Liquid phase carbon

Calgon Coal Norit Peat Westvacowood

CalgonCoal

Norit Peat Westvacowood

Particle size, US

Mesh

12x30 3.8mm 10x27 8x30 64% 65-85%

Apparent density,

g/cm3

>0.48 0.43 0.27 0.52 0.46 0.34-0.37

Particle density,

g/cm3

0.80 - 0.50 0.80 - -

Hardness number, >90 99 - - - -

Abrasion number >75 - -

Ash content, % 6 6 3-5BET surface area,

m2 /g

1050-1150 1100-1200 1750 900-1000 750 1400-1800

Total pore volume,

cm3 /g

0.8 0.9 1.2 0.85 - 2.2-2.5

Heat capacity,

J/(g.K)d

1.05 - - 1.05 - -


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waste remediation and flue gas treatment continues to boost in demand of activated

carbon worldwide. The manufactures of activated carbon are mainly from America,

China and Japan.

2.4 Preparation of activated carbon

The synthesis of activated carbon involves two steps which are preparation of

precursor and activation. The activation processes are then divided into two

methods, thermal or physical activation and chemical activation.

2.4.1 Precursors

Activated carbon requires material with high content of carbon in it. Activated carbon

was originally synthesized from bone chars for the refining process of sugar around

1900-1901. After that, various raw materials have been used to produce this unique

structured material. The materials used includes bark, beat sugar sludge, coal, coffeebeans, coconut shell, lignite, lignin, nut shells, olive stones, wood, rice hulls, rubber

waste, petroleum coke, graphite, municipal waste, molasses, news paper, oil shake,

leather waste, lampblack, refinery waste, jute stick, fruit pits, corn cobs, cottonseed

hulls, carbohydrates, bagasse, palm tree cobs and wheat straw. The preparation of

precursor is fairly simple. The raw material being used will be grinded and sieved

before advancing to activation. More precursors to activated carbon are being

developed and most of them are mainly from organic waste as the awareness to

environment is rising (Mohan et al ., 2006). Some of the commonly used raw

materials for the precursors of activated carbons are wood, coconut shell, coal and

petroleum coke.

a. Woods

The wood based activated carbon has high porosity and purity. Majority is

being used in the water and wastewater treatment, decolourization and


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vapour phase injection systems (Celis et al ., 2008). Table 2.3 shows the

properties for the common wood based activated carbon produced.

Table 2.3 properties of a commercial wood based activated carbon

Product unit descriptions Product Range available

Mesh Size (US sieve) Passing 100 (99%)

Passing 200 (95%)

Passing 300 (90%)

Surface area (minimum) 1000 m2 /g

Moisture 10%

Iron content

Chlorine content

0.07-0.1%

0.1%

b. Coconut shells

Coconut shells have been used as a precursor to activated carbon since theWorld War I to produce face mask. Since then, it has been a favourite

precursor among the manufacturer. Coconut shells contain high halocellulose

content and low on lignin. The high content of halocellulose results in a hard

carbon (Daud et al ., 2004). This means it can maintain its shape during

carbonization process making it easy to handle. Coconut shells activated

carbon have been used in various application such as gas storage (Azevedo et

al., 2007), and other liquid phase and gas phase application. Table 2.4 shows

the properties of a commercial granular coconut shell activated carbon.


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Table 2.4 properties of a commercial coconut shell based activated carbon

Product unit descriptions Product range available

Mesh size (US sieve) 4x8 / 6x12 / 8x16 / 8x30 / 12x40 /

20x50

Surface area (minimum) 850-1350 m2 /g

Apparent density 0.40-0.54 g/cc

Hardness (minimum) 95-99%

Ash content (maximum) 5%

Moisture content (maximum) 5%

c. Coal

Coal based activated carbon originates from coal that has undergone steam

activation process to create its activated carbon form. Coal based carbon has

mainly meso-pores and macro-pores and due to its unique distribution of

pores diameter, coal based activated carbon are very popular in the gas

phase purification, potable water purification industries, wastewater

purification industries and aquarium/pond water purification industries. Table2.5 shows the properties for the commercial coal based activated carbon.

Table 2.5 properties of a commercial coal based activated carbon

Product unit descriptions Product range available

Mesh size (US sieve) 4x6/4x8/4x10/5x7/6x12/8x16/8x20/8x30/

10x30/10x40/12x40/20x50

Surface area (minimum) -

Apparent density 0.35 - 0.60 g/cc

Hardness (minimum) 80 / 85 / 90 / 95%

Ash content (maximum) 8/9/10/11/12/13/14/15/16/17/18%

Moisture content (maximum) 2-5%


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d. Palm kernel shell

As a leading palm oil producer of the world, Malaysia produces a tremendous

amount of palm kernel shell as a by-product of the edible oil industries. Forthe past decades, research conduction by various universities concludes that

palm kernel shell produces good quality activated carbon (Jumarial et al .,

2004). Palm kernel shells have a higher lignin and lower halocellulose content

as compared to its direct rival which is the coconut shell. This means that the

carbon produced are softer compared to coconut shell carbon. For pore

volume, it is known that palm kernel shell produces activated carbon in the

micropore and mesopore range (Daud et al ., 2003) which means palm kernel

activated carbon can be used in both gas phase application and liquid phase

application. Picture 2.3 shows a cross section of a palm fruit showing its hard

kernel shell or mesocarp.

Picture 2.2 Cross section of a palm fruit showing the hard shell or mesocarp


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2.4.2 Activation Process

The word activated suggests that the physical and chemical properties of the carbon

are enhanced by chemical and physical treatment. During the activation process, less

organized loosely bound carbonaceous material in the material are removed. This

clears the spaces between elementary crystalline. The clear spaces together with the

fissure within and parallel to the graphite planes constitute to the porous structure of

activated carbon. The activation processes are normally divided into two categories;

physical or thermal activation and chemical activation. The basic differences between

physical and chemical activation is the number of stages required for activation andthe activation temperature. Chemical activation occurs in one step while physical

activation employs two steps, carbonization and activation. Physical activation

requires temperatures between 800 –1000 ◦C are higher than those of chemical

activation which only require temperature in the range of 200 –800 ◦C (Mohan et

al ., 2006

a. Physical or thermal activation

Physical activation involves the carbonization of the precursor at high

temperature (400-600oC). The carbonization process eliminates any form of

volatile matter that may exist forming a carbon skeleton possessing a latent

pore structure. It is then normally followed by partial gasification using mild

oxidizing agent such as carbon dioxide, steam or fuel at 800-1000 oC that

greatly increases the pore volume and surface area of the sample. This is the

step where the porosity and the high surface area are achieved (Dinesh et al .,

2006).

Figure 2.3 shows the process and steps of thermal activation of bituminous

coal taken from Study of Chemical Process by Kirk et al ., 2004. Bituminous

coal is pulverized and passed to a briquette press. Binders may be added at

this stage before compression of the coal into briquettes. The briquetted coalis then crushed and passed through a screen, from which the on size material


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passes to an oxidizing kiln. Here, the coking properties of the coal particles

are destroyed by oxidation at moderate temperatures in air. The oxidized coal

is then devolatilized in a second rotary kiln at higher temperatures under

steam.

To comply with environmental pollution regulations, the kiln off gases

containing dust and volatile matter pass through an incinerator before

discharge to the atmosphere. The devolatilized coal particles are transported

to a direct-fired multihearth furnace where they are activated by holding the

temperature of the furnace at about 1000

o

C. Product quality is maintained bycontrolling coal feed rate and bed temperature. As before, dust particles in

the furnace off-gas are combusted in an afterburner before discharge of the

gas to the atmosphere. Finally, the granular product is screened to provide

the desired particle size. A typical yield of activated carbon is about 30 –35%

by weight based on the raw coal.

Physical activation process is widely adopted industrially for commercial

production owing to the simplicity of process and the ability to produceactivated carbons with well developed micro porosity and desirable physical

characteristics such as the good physical strength (Yang et al ., 2010)

Figure 2.3 Thermal activation process of bituminous coal


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b. Chemical activation

Chemical activation on the other hand uses chemicals as the name suggests

developing the porosity. Inorganic additives, metallic chlorides, phosphoric

acid, and potassium hydroxide are impregnated into the precursor before the

carbonization process. Carbons with well-developed meso- and microporous

structure can be produced by ZnCl2 incorporation. KOH activation successfully

increased active carbon surface area and pore volume. Ammonium salts,

borates, calcium oxide, ferric and ferrous compound, manganese dioxide,

nickel salts, hydrochloric acid, nitric acid and sulphuric acid have also been

used for activation. Unlike physical activation, chemical activation requires

less temperature which is around 200-800 oC (Dinesh et al ., 2006).

Figure 2.4 shows the steps in chemical activation from The Study of Chemical

Process by Kirk et al ., 2004. In the first step, sawdust is impregnated with

concentrated phosphoric acid and fed to a rotary kiln, where it is dried,

carbonized, and activated at a moderate temperature. To comply with

environmental pollution regulations, the kiln off-gases are treated beforedischarge to the atmosphere. The char is washed with water to remove the

acid from the carbon, and the carbon is separated from the slurry. The filtrate

is then passed to an acid recovery unit. Some manufacturing plants do not

recycle all the acid but use a part of it to manufacture fertilizer in an allied

plant. If necessary, the pH of the activated carbon is adjusted, and the

product is dried. The dry product is screened and classified into the size range

required for specific granular carbon applications.

Chemical activation offers several advantages which include single step

activation, low activation temperatures, low activation time, higher yields and

better porous structure. However the process involves a complex recovery

and recycle of the activating agent, which generates liquid discharge that

demands effluent treatment (Yang et al ., 2010).


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Figure 2.4 Chemical activation of wood

2.5 Application of activated carbon

Nowadays, activated carbon has been widely used as adsorbent and the purification

and separation of gas and liquid stream. Recent studies have also shown that

activated carbon can be used successfully in solvent recovery, gas refining, and airpurification, exhaust desulfurization and deodorization processes (Yun et al., 2000).

Application of these carbons has been considered a major unit operation in the

chemical and petrochemical industries. In addition to serving as an adsorbent, high-

porosity carbons have recently been used in the manufacture of high-performance

double-layer capacitors (Wang et al ., 2010).

Activated carbon are normally produced and classified as granular, powdered,

shaped and pelletized products. Granular activated carbons are produced directly

from its granular precursor such as crushed coal while powdered activated carbons

are obtained by grinding the granular activated carbon products. Shaped and

pelletized activated carbons are the same thing as shaped activated carbon is

produced as cylindrical pellets by extrusion of the precursor with binders. The

different classification enables activated carbon to be applied to various applications

that needs specific requirement. Picture 2.2 shows the different physical

characteristic of the activated carbon.


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Picture 2.3 Classification of activated carbon

2.5.1 Liquid Phase Application

Application of activated carbon in the liquid phase related industry accounts for

approximately 82% of the total activated carbon. They include portable water (Cheng

et al ., 2010), industrial and municipal wastewater (Mohan et al ., 2006)., sweetener

decolourization, groundwater, household uses, food and beverages (Raquel et al .,

2010), mining, pharmaceutical (Rivera et al ., 2009) and chemical processing. Thedifference between activated carbon for liquid phase application is their pore volumes

which are higher in the macropore and mesopore range. This characteristic allows

the liquid to diffuse more rapidly into the meso and macropores. The form of liquid

phase activated carbon used depends strongly on its application. Granular and

shaped carbons are usually applied when there is a continuous flow through deep

bed involved and when a large carbon buffer is needed in order to withstand

variations in adsorbtion variations (Joana et al ., 2007).

Powdered carbons on the other hand are preferred when a wider range of

impurity removal is required. This can be attained by batch application of powdered

activated carbon with controlled dose until the degree of purification desired is

achieved.


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a. Potable Water Treatment

Treatment for drinking water accounts for about 30% of the total activated

carbon used in liquid-phase application. Most of the common water sources

are often contaminated by bacteria, viruses, pesticide residue, halogenated

materials, organic compound, heavy metals such as zinc, lead and copper and

vegetation decay product (Muhamed et al ., 2004). Although most of the

contaminants can be removed by filtration and normal disinfection, some toxic

compound may still be there. Treatment by activated carbon removes these

toxic materials from the water making it safe for consumption at a low price

compared to other complex/ hybrid filtration system. For portable water

treatment, activated carbon that is normally used is the granular type.

Recent studies by Kim et al, (2005) combines powdered activated carbon with

microfiltration system to enhance the result of treatment. By using this hybrid

method to purify portable water from rivers containing secondary effluent, the

removal rates were increased to almost 100 percent. Another research

focuses on the removal of arsenic from portable water. Arsenic is a toxic

material that can be highly harmful to living organisms. It can cause various

dangerous deceases including skin, kidney, lung and bladder cancer.

Treatment with granular activated carbon impregnated with iron removes

arsenic from portable and drinking water effectively (Cheng et al ., 2010)

b. Industrial water Treatment

Wastewater from industries has always had a large potential to cause water

pollution. Unlike the domestic waste, it is sometimes very difficult to

generalize wastewater from the industries as it varies from plant to plant.

Wastewater contains suspended solids, toxic organic material, inorganic

contaminants and hazardous microorganisms. The conventional methods for

removing these impurities are expensive to build, maintain and operate.

These contaminants must be removed before the water can be rereleased to

the environment. Granular and shaped carbon removes this contaminants

efficiently especially the residual toxic waste (Mohan et al ., 2006)


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Hybrid technology in the filtration filed has shown significant result recently.

Taraj Mohammadi et al . (2004) showed that when activated carbon is coupled

with ultra-filtration unit to produce a hybrid ultra-filtration, the results

obtained are more promising with more advantages. Conventional system can

sometimes be difficult to control and operate. The hybrid technology

developed on other hand is more operator friendly as it is easier to control

and operate. The hybrid system is also more efficient compared to the

conventional result.

c.

Groundwater Remediation

Groundwater contamination has been recognised since the early 80’s.

Pollution of groundwater with nitrate is an increasing problem. Water

contaminated with this substance causes various diseases (Wang et al.,

2003). There are basically two ways for treating groundwater. The first one is

the conventional method using granular, powdered and shaped carbon. The

second method uses air stripping to transfer the volatile compounds from

water to air. The compound can be recovered by passing the contaminant airthrough a bed of activated carbon (Bayer et al ., 2005)

d. Decolourization of commercial sweetener

Activated carbons are originally used for one sole purpose which is purification

of corn syrup and sugar. It is the sweetener industries that jumpstarts the

activated carbon research race. The sugars produced from sugar canes arenormally brown in colour because of the impurities content. By applying

activated carbon, the sugar or sweetener is decolorized producing white

product. Besides normal sugar, high fructose corn sweeteners are also

produced in the same manner. The activated carbon eliminates undesirable

taste and odour in the compound. (Kuhn et al ., 2010)


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e. Foods

Activated carbons are one of the used in the food purification process. In the

production of alcoholic beverages for instance, activated carbon is used to

remove the haze causing compound from beer, taste and odour from vodka

and fusel oil from whiskey. Edible oil such as animal fat and vegetable oils

uses activated carbon to eliminate contaminants (Kawashima et al ., 2009).

While feed water for soft drink production is often treated with carbon in

order to capture the undesirable taste and odour compounds and also to

remove free chlorine radical that got through the disinfection treatment.

2.5.2 Gas phase Application

Gas-phase applications of activated carbon include separation, gas storage, and

catalysis. Although only 20% of activated carbon production is used for gas-phase

applications, these products are generally more expensive than liquid-phase carbons

and account for about 40% of the total dollar value of shipments. Most of theactivated carbon used in gas-phase applications is granular or shaped. Gas phase

applications account for 18% of total activated carbon. They include air purification,

42%; automotive emission control, 21%; solvent vapour recovery, 14%; cigarette

filters medium, 2% and miscellaneous, 21%. Separation processes comprise the

main gas-phase applications of activated carbon. These usually exploit the

differences in the adsorptive behaviour of gases and vapours on activated carbon on

the basis of molecular weight and size. For example, organic molecules with a

molecular weight greater than about 40 are readily removed from air by activated

carbon. (Guo et al., 2000 )

a. Emission control

Petroleum based fuel has always caused emission that are dangerous to

human and living things. These emission that escape from vents in


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automotive fuels system can be controlled with proper method (Ho et al .,

2008). One of the methods used is absorption by activated carbon (Giorgos et

al ., 2006). Fuel vapours vented when the fuel tank or engine are heated are

captured in a canister containing 0.5 to 2 L of activated carbon. Regeneration

of the carbon is then accomplished by using intake manifold vacuum to draw

air through the canister. The air carries desorbed vapour into the engine

where it is burned during normal operation. Typically, the adsorption vessels

contain around 15 m3 of activated carbon and are regenerated by application

of a vacuum. Regeneration for the condition is normally quite mild. The most

suitable type of pore size would be the mesopores (Kirk et al ., 2004)

b. Solvent vapour recovery

Activated carbon with micropores has a very strong adsorbtion forces. These

forces enable the activated carbon to capture small vapour molecules such as

acetone. Larger and heavier vapour molecules such as cyclohexanone and

cumene adsorbed better by mesopores activated carbon. Because of these

interesting properties, activated carbon is used to prevent the release of

organic compounds that are harmful into the atmosphere which are often

used as solvent in the industries. Application of activated carbon gave a huge

impact in the industries as the solvent adsorbed by activated carbon are able

to be recovered to its usable stage (Yun et al ., 2000).

c.

Cigarette filter medium

Cigarette smoke has been known to contain various chemicals that are

harmful to one’s health. These colloidal particles and vapours of chemical

compound can somehow be removed without affecting the taste of the

tobacco. One of the promising methods for removing these undesired

compounds is the incorporation of activated carbon into the picture (Sasaki et

al., 2008). The reason behind this is because activated carbon adsorbs

volatile compounds effectively in the smoke and from other source.


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Out of all the form of nano-composite developed, carbon fiber has shown to have a

very bright future as commercial product.

Carbon fibers are prepared from a solution of carbon source, polymer and

solvent. The solution is either extruded directly into a coagulation bath or extruded

through an electric field onto a collector (Chae et al ., 2009). The later process is also

known as electro-spinning method. Electro-spinning has gained the world’s attention

for its versatility in producing a wide variety of polymeric fibers and also consistently

producing fibers in the submicron range which is very difficult to achieve with other

method (Bhardway & Kundu, 2010).

The fundamentals of electro-spinning dates more than 60 years earlier when

Formalas published a method describing the process (Huang et al ., 2003). In the

process, polymer filament was produced by introducing a polymer solution into an

electric field between two oppositely charged electrodes. One electrode was placed

into the solution while the other was placed on the collector. The polymer solution

was then ejected through a metal spinnerets and collected on the collector (Huang et

al., 2003)


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Figure 2.5 Electro-spinning apparatus setup

Figure 2.5 shows the typical apparatus setup for electro-spinning process.

During the electro-spinning process, the electrostatic force from the electric field

created is more than the surface tension of the viscoelastic region of the polymer.

This results in the dispersion of the polymer onto the collector creating fine

nanofibers (Fenot et al ., 2003).

Like any other process, electro-spinning process is affected by various

parameters. Besides the polymer used, other parameters that affect the properties of

the carbon fiber nano-composite includes the solvent, the concentration of carbon

source, voltage of power supply, the distance between the tip of the syringe and the

collector and collector (Duan et al ., 2006). The concentration of the reinforcement for

instance will affect the thermal behaviour, and surface chemistry of the fiber nano-

composite produced. It can also affect the morphologies of the fiber nano-composite.

While the voltage, collector, syringe distance, flow rate of polymer and other


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parameter might only affect the morphology of the fiber nano-composite prepared.

Good fiber nano-composite can be prepared by the clever manipulation of the

parameters.


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Chapter 3

Methodology

3.1 Chemicals and Apparatus

The chemicals and apparatus used in this research are shown in the table 3.1 and

table 3.2.

Table 3.1 List of chemicals

Chemical Brand Purity

Acetone QRec 99.5%

Dimethyl formide (DMF) J.T. Baker 99%

Activated carbon Sigma aldrich 99%

Nitrogen gas (N2) MOX 99.999%

Oxygen gas (O2) MOX 98%

Polyacrylonitrile (PAN) SIGMA-ALDRICH -


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Table 3.2 List of apparatus

Apparatus Brand

High voltage power supply GlassmanSyringe pump TERUMO

Differential Scanning Calorimetry (DSC) PerkinElmer

Glass syringe (10,15,20cm) TERUMO

Trineck flask Quickfit

Syringe needle TERUMO

Rotary evaporator FAVORIT

3.2 Raw Material

Raw material in this study is granulated activated carbon from Norit which was

imported from Sigma Aldrich. The activated carbon is from peat origin that was

steam activated. The detailed information about raw material in this study is shown

in Table 3.3

Table 3.3 The name, purity, brand, diameter and functional group of raw material.

Raw Material Purity Brand Size

Granulated activated

carbon (AC)

99% Sigma Aldrich 3.8nm


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Figure 3.1 Diagram of electro-spinning station

Table 3.4 Summary of the parameters and naming of each sample

Sample

Description

Concentration of AC Collector Voltage Supply, kV

AD15KV 2 wt% Dry 15

AD20KV 2 wt% Dry 20

AW15KV 2 wt% Wet 15

AW20KV 2 wt% Wet 20

BD15KV 5 wt% Dry 15

BD20KV 5 wt% Dry 20

BW15KV 5 wt% Wet 15

BW20KV 5 wt% Wet 20


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In the parameter studied, the voltage supplies used were 15kV and 20kV. The

solution with 2 wt% and 5 wt% activated carbon undergoes the electro-spinning with

both voltage supplies. The other parameter studied was the collector. Two collectors

were used in the process, a dry collector and a wet collector. The dry collector uses a

cardboard wrapped with an aluminium foil while the wet collector uses a basin filled

with tap water. The spun collected was dried and kept in plastic container.

3.4 Characterization

The carbon fiber nano-composite produced is characterized using two instruments. A

Differential Scanning Calorimetri (DSC) is used to obtain the samples thermal profile

such as its melting point and heat enthalpies while a Fourier Transform Infra Red

(FT-IR) machine is used to detect the functional group present in the samples.

3.4.1 Differential Scanning Calorimetri (DSC)

Picture 3.1 shows a picture of a DSC machine. DSC reads the thermal profile of a

sample when exposed to a long range of temperature. The thermal profile obtained

can be used to determine a sample’s melting point, crystallization point, heat

enthalpies and stability. Small amount of product would be placed in the machine

and setting 30 minutes of time with the presence of nitrogen gas. The changes of

sample’s weight in relation to change in temperature would be observed in a graphform. The temperature range set is until 4500C (Hohne et al ., 1996)


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Picture 3.1 Perkin Elmer Differential Scanning Calorimetri (DSC)

3.4.2 Fourier Transform Infrared Spectroscopy (FT-IR)

Fourier Transform-Infrared Spectroscopy (FTIR) is an analytical technique used to

identify organic and in some cases inorganic materials by detecting the functional

groupe present in the compound. This technique measures the absorption of infrared

radiation by the sample material versus wavelength. The infrared absorption bandsidentify molecular components and structures. When a material is irradiated with

infrared radiation, absorbed IR radiation usually excites molecules into a higher

vibrational state. The wavelength of light absorbed by a particular molecule is a

function of the energy difference between the at-rest and excited vibrational states.

The wavelengths that are absorbed by the sample are characteristic of its molecular

structure.

Picture 3.4 Perkin-Elmer FT-IR

http://en.wikipedia.org/wiki/Fourier_transformhttp://en.wikipedia.org/wiki/Fourier_transform


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3.5 Flow Chart

3.5.1 Preparation of polyacrilonitrile (PAN)/DMF/ activated carbon

solution

The solution was separated into two portion, one for 2 wt% activated carbon and

one for 5 wt%

10.00g PAN was dissolved in 100mL of DMF

PAN/DMF mixture was heated, stirred at 70oC in an oil bath for 6 hours.

The mixture of PAN/DMF/AC were heated and stirred at 70o

C in an oil bath for 1hour

Homogenous solution obtained transferred into a syringe for electro-spinning

process


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3.5.2 Preparation of carbon fiber nano-composite using electro-spinning

method

Flow rate of syringe pump set to 2mL/min

Voltage of 15kV was applied

Polymer composite solution transferred to syringe

Distance from the tip of syringe to collector was set to 15cm

Electro-spinning process starts

Carbon fiber nano-composite obtained dried and stored

Steps repeated using 20kV of voltage supply


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CHAPTER 4

RESULTS AND DISCUSSION

In this study, carbon fiber nanocomposite was prepared by electro-spinning method.

Poly-acrylonitrile (PAN) was used as the polymer base with dimethylformide (DMF) asthe solvent. The weight ratio of Poly-acrilonitrile to volume of DMF used was 1:10

while granulated activated carbon was used as the carbon source. The weight

percent of activated carbon used was 2 wt% and 5 wt%. Besides the weight percent

of activated carbon, other parameters include amount of voltage used and collecting

method. The distance from the tip of the needle to the collector and flow rate of the

syringe pump was kept constant for the entire sample.

The properties of the carbon fiber nano-composite prepared were then

characterized using two instruments. A Differential Scanning Calorimeter (DSC) was

used to identify the thermal behavior of the carbon fiber nano-composite prepared

while the functional group present was determined by a FT-IR machine. Table 4.1

shows the list of sample prepared with descriptions and coding.


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These values might lessen than the original PAN range as the cyclization is

initiated easily at lower temperature in electro-spun fibers, that low cyclization

temperature is mainly due to the improvement in the orientation of molecular chains

in the fibers (Han et al ., 2010), where molecular chains were oriented within the

electrospun fibers during the electrospinning process.

Figure 4.1 Thermal profile of activated carbon (Yellow), electrospun PAN fiber with

DMF and (Red) and eletrospun carbon fiber from AD20KV ( Black)

Table 4.2 Summary of the thermal profile of activated carbon, elecrospun PAN fiber

with DMF and sample AD20KV

Sample Melting point (oC) Heat enthalpy (J/g)

Activated carbon - -

PAN + DMF 301.27 -205.2378

AD20KV 309.73 -292.8354

This theory was proved by the thermal profile obtained; the controlled groupwhich was the PAN with DMF, has a melting point of 300oC, lower than the PAN in


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powdered form while the activated carbon produces an endothermic peak around

100oC and no exothermic peak. When these two compounds are combined together

in the activated carbon fiber composite, it gives a slightly higher melting point which

was 318oC which was higher than the controlled group than the controlled group.

The thermal profile obtained from DSC for PAN with DMF shows an

exothermic peak at 120oC. This exothermic behavior is the result of crystallization of

the PAN polymer. In this crystalline state, the molecules in the polymer are arranged

in a more ordered manner, the process gives up heat. Next on the curve is a peak at

300

o

C which represent its melting point. During the melting of the polymer, theearlier arranged crystalline structure of the molecules began to fall apart and come

out from their ordered arrangement leaving them freely moving. This process uses

heat thus creating an endothermic peak in the DSC curve (M. Naffakh et al ., 2011).

The activated carbon curve has no endothermic peak as it has been stabilize during

the activation process.

The thermal profiling data obtained from the DSC for all of the samples are

listed in table 4.1. The entire sample shows an endothermic peak in their curve with

weak exothermic peak in some of the samples. The temperature for the melting point

ranges from 304oC to 334oC. This thermal behavior differences are due to the

parameters incorporated in the procedure which are the concentration of activated

carbon used, voltage supply and collector condition. The effect of each parameter on

the thermal behavior of each sample is discussed by comparing the samples.


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Table 4.3 Thermal profiles for all the samples and controlled groups


PAN + DMF 301.27 -205.2378

AD15KV 334.87 -322.9976

AD20KV 309.73 -292.8354

AW15KV 316.14 -300.0930

AW20KV 304.39 -419.8985

BD15KV 303.41 -343.5365

BD20KV 316.65 -246.9860BW15KV 316.57 -223.9124

BW20KV 318.31 -263.7909

4.1.1 Concentration of activated carbon

The first parameter that will be evaluated is the weight percent of the

activated carbon used. Figure 4.2 and table 4.4 shows the thermal profile for the first

batch, which was the one prepared with 2 wt% of activated carbon; the melting

point of the four samples ranges from as low as 304.39oC to as high as 334.00oC.

The incorporation of activated carbon in the composite resulted in a higher melting

point than the controlled group, PAN and DMF.

There are also noticeable exothermic peaks at the beginning of the heating

process for all the four samples, which are around 70oC; this may be attributed by

the presence of water in the sample which was evaporated at that particular

temperature. This exothermic peak normally appears around 0oC but in this case, the

heating process was started at around 25.0oC, so the exothermic shifts to a slightly

higher temperature (M. Naffakh et al ., 2011). The shift may also be contributed by

the presence of impurities either in the water present or in the sample itself. Besides


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the ability to shift the baseline, impurities can also act as plasticizers and disrupts the

transition temperature of the fiber composite prepared.

After the melting peak, a weak exothermic signal can be seen in all of the

samples with 2wt% activated carbon. This is caused by the baseline shift which

happens as a result of changes in the sample weight, heating rate or the specific

heat of the sample (M. Naffakh et al ., 2011) A change in specific heat might occur as

the sample has gone through melting transition while the weight of the sample often

changes after the decomposition of the sample.

Figure 4.2 Thermal profile sample AD15KV (red line), AD20KV (blue line), AW15KV

(black line), AW20KV (yellow line)


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Table 4.4 Thermal profile of carbon fiber nanocomposite prepared with 2 wt%

activated carbon


AD15KV 334.87 -322.9976

AD20KV 309.73 -292.8354

AW15KV 316.14 -300.0930

AW20KV 304.39 -419.8985

The second batch was prepared with 5 wt% of activated carbon. Figure 4.3

and table 4.5 shows the thermal profile for the carbon fiber nanocomposite prepared

with 5 wt% activated carbon. The melting point of the carbon fiber prepared varies

from 303.41oC to 318.31oC. Similar to the fiber with 2 wt% activated carbon, fiber

with 5 wt% activated carbon also shows the exothermic peak created by the

presence of impurities such as water. The exothermic peak was expected as the

samples was not stored in a dry and air tight environment. Besides, other impurities

can also be the cause of the exothermic peak as the electro-spun fibers were nottreated before the analysis took place. The treatment was not carried out because

the process was difficult to set up besides the unavailability of some apparatus. The

temperature regimes for the two concentration of activated carbon are also different.

The fibers prepared with 2 wt% activated carbon in average have a higher initial

temperature, which caused a broader temperature regime and greater heat energies.

In comparison to the electro-spun fibers prepared with 5 wt% activated

carbon, the main peak in average displays higher temperature in the initial state and

broader regime but with smaller heat energies. This results indicate that the fiber

prepared with the higher concentration of activated carbon has relatively high

thermal stability than the one prepared with 2wt% activated carbon which was

expected because of the properties of the activated carbon used. The differences is

due to the cross linking which favors the higher concentration activated carbon which

limit the segment mobility in amorphous area and reduce the cyclization in the

molecule, giving it a better thermal stability (Han et al., 2007)


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Figure 4.3 Thermal profile sample BD15KV (red line), BD20KV (blue line), BW15KV

(black line), BW20KV (yellow line)

Table 4.5 Thermal profile of carbon fiber nanocomposite prepared with 5 wt%activated carbon


BD15KV 303.41 -343.5365

BD20KV 316.65 -246.9860

BW15KV 316.57 -223.9124

BW20KV 318.31 -263.7909

The best sample from each concentration was then compared with activated

carbon and PAN fiber with DMF solvent. Figure 4.4 and table 4.6 show the thermal

profile of activated carbon, PAN fiber, AD20KV and BD20KV. The sample prepared

with dry collector with 20KV power supply was chosen because the sample shows

better thermal stability than the other sample. The thermal stability was measured by


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the melting point and the heat enthalpies of the sample, higher melting point and

lower heat enthalpies results in improved thermal stability.

Based on figure 4.4, the PAN fiber prepared with DMF has a melting point of

301.27oC with an enthalpy of -205.2378 J/g. The improved nano-composite fibers on

the other hand has higher melting point than the controlled group. This indicates that

the addition of activated carbon into the PAN fiber nano-composite successfully

improved the melting point of the compound. The heat enthalpies of samples

increased slightly than the controlled group. BD20KV has a higher heat enthalpy

compared to the AD20KV sample, thus giving the BD20KV better thermal stabilitythan AD20KV.

Figure 4.4 Thermal profile of activated carbon (Blue), PAN fiber (Red), AD20KV

(Black) and BD20KV (Green)


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Table 4.6 Thermal profile of activated carbon, PAN fiber, AD20KV and BD20KV


PAN + DMF 301.27 -205.2378 AD20KV 309.73 -292.8354

BD20KV 316.65 -246.9860

4.1.2 Voltage

The second parameter is the voltage used which are 15KV and 20KV for creating the

electric field in the electro-spinning method. The differences between the two voltage

used affects mainly the melting point and the heat energies of the fiber. In the 2

wt% activated carbon fiber for instance, the fiber prepared by using 20KV as the

power supply produces lower temperature regime than the 15KV. The heat enthalpy

is also lower in the 20KV fiber.

Figure 4.5 Thermal profile of activated carbon (Black), PAN fiber (Red), BD20KV

(Blue), BD15KV (Green)


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Table 4.7 Thermal profile of activated carbon, PAN with DMF fiber, BD15KV and

BD20KV


PAN + DMF 301.27 -205.2378

BD15KV 303.41 -343.5365

BD20KV 316.65 -246.9860

From the concentration of activated carbon used, it is known that 5 wt%

activated carbon produce carbon fiber nano-composite with better thermal properties

than 2 wt% activated carbon. So, only the carbon fiber nano-composite prepared

with 5 wt% activated carbon with voltage 15KV and 20KV will be compared with the

activated carbon and controlled group.

The carbon fiber prepared with 15KV shows a melting point of 303.41oC with

a heat enthalpy of -343.5365 J/g while the carbon fiber prepared with 20KV produces

a melting point of 316.65oC with a heat enthalpy of -246.9860 J/g. Both sample

shows higher melting point than the controlled group but sample BD20KV proves to

be far superior to the controlled group and BD15KV.

Greater voltage also causes greater stretching of the solution as the result ofthe greater columbic forces in the jet which affects the reduction of fiber diameter

and evaporation of solvent from the fiber (Bhardwaj & Kundu, 2010). The heat

enthalpy for BD20KV are also smaller than sample BD15KV, this means that it has a

better thermal stability. Besides that, the applied voltage does not really affect the

thermal properties of the fiber produced. The effect of voltage can mainly be seen in

the fiber morphology and physical characteristics such as its diameter, presence of

beads and etc.


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4.1.3 Collection method

The collection methods used in this study are wet and dry collector. The dry collector

incorporate a piece of cardboard wrapped with aluminum foil while the wet collector

uses a basin filled with tap water. Theoretically, wet collector will produce a more

better fiber composite as the electrons from tap water help attracts the positively

charged fibers but it appears to be quite an unconventional method as the fibers

tend to fall into the water and agglomerate and produce wet fibers.

Figure 4.6 Thermal profile of activated carbon (Black), PAN fiber (Red), BD20KV

(Blue) and BW20KV (Green)

Table 4.8 Thermal profile of activated carbon, Pan fiber, BD20KV and BW20KV


PAN + DMF 301.27 -205.2378

BW20KV 318.31 -263.7909

BD20KV 316.65 -246.9860


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Figure 4.6 shows the thermal profile of activated carbon, PAN fiber, BW20KV

and BD20KV while table 4.8 show the summary of the thermal profile obtained.

These two samples were chosen for comparisons because the previous parameters

which are concentrations of activated carbon and voltage supply concludes that the

carbon fiber produced with 5 wt% activated carbon 20kV power supply has the most

outstanding thermal properties among the other samples.

Sample BW20KV shows the highest melting point among the three fibers but

it also shows a high heat enthalpy. BD20KV on the other hand has a lower melting

point than sample BW20KV but with a smaller heat enthalpy. Small heat enthalpyresults in better thermal stability of the carbon fiber nano-composite. The differences

are relatively low as the collector’s condition affects mainly the morphology of the

carbon fiber nano-composite produced.

Besides the thermal profile, it was found that the carbon fiber collected with

wet collector tends to agglomerate the PAN, activated carbon and DMF solution, thus

producing beads. The dry collector on the other hand produces fine fibers with no

beads. As mentioned earlier, the wet collector should produce better result as the

positively charged solution is attracted to the negative charge of the water molecules

but the result show the opposite. This is due to the pH of the solution which are

around which is more basic than normal. The pH of the solution was in the 7.6 to 7.6

range. Basic solution is attracted to positively charged compound; in this case it is

the aluminum foil used.


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4.2 Study of functional group of carbon fiber nano-composite

The significance of this study is to identify the functional group present in the carbon

fiber nano-composite. The chemical structure and properties of the fiber prepared

was analyzed with a FT-IR machine which provides useful information regarding its

functional group content. The entire fiber sample was prepared by the same solvent

and activated carbon, so they all have the same chemical structure which includes

the functional group. Instead of comparing the spectra of all the samples, only one

sample, controlled group and activated carbon spectra were compared. Based on the

thermal behavior of the fiber, it is known that the fiber composite containingactivated carbon have a higher thermal resistance than the controlled group. The

thermal resistance may also be attributed by the combination of functional group

present in the sample.

Figure 4.7 is an FT-IR spectra obtained from the activated carbon fiber

composite with 5 wt% activated carbon in dry condition. As can be seen, the signals

are quite weak but most of the important functional groups can be identified. For

instance, the C=N stretch vibration from the polyacrylonitrile used can be seen at

around 2200 cm-1.There are also some overlapping peaks at 1800 to 1100 cm-1 which

indicates the presence of conjugated C=C, C=N, C=O, C-O and –OH group which

results from the combination of the PAN and activated carbon. This overlapping peak

proves that the combination of these two compounds was close to successful. The

major functional groups for AD20KV had to be estimated as the signal is very low.

Table 4.9 shows the major peaks present in the spectra and their wavelength.


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CHAPTER 5

CONCLUSION

An activated carbon fiber composite was prepared by electro-spinning method where

two concentration of activated carbon were used, 2 wt% and 5wt%. Other

parameters include voltage used for the electric field and collection methods which

are wet and dry while the syringe flow rate and distance from the tip of the needle to

the collector was kept constant for the whole experiment. From the thermal analysis

conducted with DSC machine, the fiber composite produced was found to have

higher melting point than the PAN DMF group. Comparison of the sample prepared

with the three parameters found that the fiber composite with 5wt% activated

carbon has higher thermal stability than the fiber composite with 2wt% activated

carbon. The differences in thermal stability are due to the cross linking which favors

the higher concentration activated carbon which limit the segment mobility inamorphous area and reduce the cyclization in the molecule. As for the voltage and

collection method, these parameters did not affect the thermal behavior and

functional group of the fiber composite much. The effects are more pronounce in the

morphology of the fiber composite produced. Higher voltage produced a more fine

fiber composite than the lower 15KV. Wet collection method proves to be

inconvenience as wet fibers was produced. The wet collection method also makes the

polymer solution agglomerate faster resulting in bead formation on the fibers. The


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study of functional group proves that the composite was successfully produced with

the presence of overlapping functional groups.


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APPENDIX

Picture of the electro-spun carbon fiber nano-composite.

Top left: AD15KV, AD20KV, AW15KV, AW20KV

Bottom left: BD15KV, BD20KV, BW15KV, BW20KV


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Picture of electrospun carbon fiber nano-composite collected with dry (left) and wet

collector (right) with 20kV and 5 wt% activated carbon

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Preparation of Carbon Nano Composite Fibre Using Electro-spinning Method

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