Physical properties and energy absorption of epoxidized natural rubber/reclaimed rubber foam.

PHYSICAL PROPERTIES AND ENERGY ABSORPTION

OF EPOXIDIZED NATURAL RUBBER/RECLAIMED

RUBBER FOAM

AMIRUL HAKIMI BIN MOHD ZAIN

B051010064

UNIVERSITI TEKNIKAL MALAYSIA MELAKA 2014

UNIVERSITI TEKNIKAL MALAYSIA MELAKA (UTeM)

PHYSICAL PROPERTIES AND ENERGY ABSORPTION OF

EPOXIDIZED NATURAL RUBBER/RECLAIMED RUBBER

(ENR/RR) FOAM

This report is submitted with requirement of the Universiti Teknikal Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering (Engineering Materials)

(Hons.)

by

AMIRUL HAKIMI BIN MOHD ZAIN

B051010064

880504-11-5425

FACULTY OF MANUFACTURING ENGINEERING 2014

UN

BORANG PENG

TAJUK: PHYSICAL PR

NARUTAL RUBBER/RE

SESI PENGAJIAN: 2013 Saya AMIRUL HAKIMI mengaku membenarkan Malaysia Melaka (UTeM 1. Laporan PSM adala 2. Perpustakaan Unive

tujuan pengajian sah 3. Perpustakaan diben

antara institusi peng 4. **Sila tandakan (

SULIT

TERHAD

TIDAK TERH

AlamatTetap:

1348 PJALAN KENANG BATU BUROK, 20400 K TERENGGANU

TERENGGANU DARUL

UNIVERSITI TEKNIKAL MALAYS

NGESAHAN STATUS LAPORAN PROJEK S

PROERTIES AND ENERGY ABSORPTION O /RECLAIMED RUBBER (ENR/RR) FOAM 013/14 Semester2

I BIN MOHD ZIAN

anLaporan PSM ini disimpan di Perpustakaan eM) dengan syarat-syarat kegunaan seperti be

lah hak milik Universiti Teknikal Malaysia Mela iversiti Teknikal Malaysia Melaka dibenarkan m

ahaja dengan izin penulis.

enarkan membuat salinan laporan PSM ini seb ngajian tinggi.

)

RHAD

(Mengandungi maklumat yang berdarja kepentingan Malaysia sebagaimana ya AKTA RAHSIA RASMI 1972)

(Mengandungi maklumat TERHAD yang organisasi/badan di mana penyelidikan

NGA 0 KUALA UL IMAN Dis Cop Rasmi:

AYSIA MELAKA

SARJANA MUDA OF EPOXIDIZED

an Universiti Teknikal berikut:

elaka dan penulis. membuat salinan untuk ebagai bahan pertukaran

arjah keselamatan atau yang termaktub dalam

ng telah ditentukan oleh dijalankan)

DECLARATION

I hereby, declared this report entitled ‘physical properties and energy absorption in ENR/RR pore’ is the results of my own research except as cited in references.

Signature : ……… Author’s Name : Amirul Hakimi Bin Mohd Zain Date : 23th JUNE 2014

APPROVAL

This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a partial fulfilment to the requirements for the degree of Bachelor of Manufacturing Engineering (Engineering Materials) (Hons.). The member of the supervisory is as follow:

……….. (Dr Noraiham Binti Mohamad)

ABSTRAK

Objektif untuk kajian ini adalah untuk menentukan kesan jenis busa terhasil terhadap tenaga serapan. Bahan yang telah dipilih untuk kajian ini ENR/RR, dan nisbah untuk setiap sampel telah ditetapkan untuk menghasilkan busa yang berlainan. Untuk proses yang pertama, ENR/RR akan dimasukkan kedalam mesin pencampuran dalaman bagi mengisar bahan tersebut sehingga sebati. Selepas itu, bahan yang telah siap diadun akan dikisar menjadi hancur. Tujuan adalah untuk dimasukan kedalam proses mampatan.Ini adalah untuk menghasikan bahan dalam bentuk lapisanuntuk dijadikan sampel. Proses seterusnya, adalah proses penghasilan busa didalam sampel. Setiap proses yang dialankan mempunyai parameter yang tersendiri mengikut keadaan bahan yang digunakan. Sampel yang telah siap diproses akan dijalani eksperimen untuk melihat daya serapan yang dapat dihasilkan. Eksperimen yang dijalankan berdasar tajuk ini adalah eksperimen jatuhkan bola. Tujuan eksperimen ini adalah untuk megkaji daya serapan tenaga yang boleh diserapkan oleh sampel. eksperimen jatuhkan bola ini dijalankan 3 kali bagi mendapatkan bacaan purata dan mengelakkan berlaku ralat. Manakala saiz busa didalam sampel pula telah ditentukan oleh mikroskop optik. Dengan mikroskop optik, busa apat dilihat dengan lebih jelas dan setiap gambaran telah direkod untuk dianalisiskan. Saiz busa yang terhasil berbeza dalam setiap sampel dan tenanga serapan juga menunjukkan perbezaan. Ini menunjukkan saiz busa yang optimum menghasilkan kadar serapan tenaga yang tinggi.

ABSTRACT

The objective of this study is to determine the effect of pore type on energy absorption. The material used for this study is the blend of ENR and RR. The ratio is varied in order to produce different types of pore. Initially, ENR and RR are inserted into the internal mixing for compounding. The blend is crushed into small aggregates before hot compressed using hot press to form ENR/RR sheet. Then, foaming process is performed on the ENR/RR blend. Sample were perform under experiments in which, the experiment were conducted for this study is the ball drop test. The purpose of this experiment was to observe the effects of pore against energy absorption. With this test, it was observed that the pore reduce the impact. Each of these samples was conducted 3 times and done in accordance with the parameters of the resulting ratio. To get the size of the pore in the sample, an optical microscope was used and the pore can be clearly seen. The results of each experiment and were recorded in the optical microscope and draw conclusions about the study. The size of pore that produces shows different in every sample. Pore that have optimum size also produce more pore unit in volume show the energy absorption high compare to the other sample.

DEDICATION

This report is dedicated to my parents (En Mohd Zain bin Shamsuddin and Puan

Rohani binti Ismail).

ACKNOWLEDGEMENT

I would like to gratitude to Allah S.W.T for His generous blessing and undying strength bestowed upon me during the course of this research.

Firstly, I would like to extend my heartiest gratitude to Dr Noraiham Mohamad as my supervisor who had given me guidance and support me during the research. And not to be forgotten to other lecturers, my friends and other person whose name is not mentioned here.

Secondly, I want to thank my lovely mother and father because they support me to conduct this study. With prayers and moral support from both of them, I have gained strength to endure in this study. Thank you very much also to my mentor, Nor Nadiah binti Abdul Hamid for help. I also want thank to UTeM management especially from faculty of manufacturing because giving me opportunity to get more experiences and knowledge during the research.

TABLE OF CONTENT

ABSTRAK i

ABSTRACT ii

DEDICATION iii

ACKNOWLEDGEMENT iv

LIST OF FIGURE ix

CHAPTER 1 1

INTRODUCTION 1

1.1 Background 1

1.2 Problem statement 2

1.3 Objective 4

1.4 Scope 4

CHAPTER 2 5

LITERATURE REVIEW 5

2.1 Solid Foam 5

2.2.1 Classification Material of Solid Foam 7

2.2 Classification of Polymer Foam 11

2.3 Type of Rubber Blend 14

2.3.1 Natural Rubber Based Blends 15

2.3.2 Reclaimed Rubber Based Blend 16

2.3.3 Epoxidized Natural Rubber Based Blends 19

2.4 Processing Method 22

2.4.1 Liquid 22

2.4.2 Solid Melt 23

2.4.3 Foaming 25

2.5 Properties 26

2.5.1 Physical Properties under Impact 26

2.5.2 Mechanical Properties under Impact 27

2.5.3 Energy Absorption 31

CHAPTER 3 34

METHODOLOGY 34

3.1 Methodology 34

3.2 Characteristic of Raw Material 36

3.2.1 Epoxidized Natural Rubber 36

3.2.2 Reclaimed Rubber Glove 36

3.2.3 Sodium bicarbonate 37

3.3 Preparation of the Sample and Process 38

3.3.1 Blending of ENR/RR blends in Internal Mixer 38

3.4 Hot pressing 42

3.4.1 Compression Moulding Process 42

3.5 Foaming process 43

3.6 Testing and Analysis 44

3.6.1 Physical Test 44

3.6.2 Physical Test 47

3.6.3 Morphological Study 48

CHAPTER 4 51

RESULT AND DISCUSSION 51

4.1 Introduction 51

4.2 Physical properties of rubber foam 52

4.2.1 Density of solid rubber and rubber foam 52

4.2.2 Relative Density 53

4.2.3 Expansion Ratio 54

4.2.4 Water absorption 58

4.3 Physical Properties of Rubber Pore 59

4.3.1 Drop Ball Testing 59

4.4 Morphological Analysis 63

4.4.1 Digital Camera 63

4.4.2 Optical Microscope 66

CHAPTER 5 70

CONCLUSION AND FUTURE WORKS 70

5.1 Conclusion 70

LIST OF TABLE

2.1 Technical specification of reclaimed rubber 18

3.1 Rubplas Reclaim Grades G 37

3.2 Physical properties and chemical properties of 38

Sodium bicarbonate

3.3 Formulation of natural rubber compounds 40

3.4 Ratio of Rubber 40

4.1 Density of solid rubber and rubber foam 52

4.2 Relative Density 53

4.3 Expansion ratio 55

4.4 Water absorption rate of rubber foam 58

4.5 Drop Ball Testing 60

4.6 Average of diameter and unit cell/volume every sample 67 4.7 Correlation between pore characteristic with energy absorption 68

LIST OF FIGURE

2.1 The bee's honeycomb is a two-dimensional cellular 6

structure

2.2 Open-cell Structure in Ceramic Foam 6

2.3 Example of Closed-Cell Structure in aluminium foam 7

2.4 Porous ceramic 8

2.5 A type of polymer foam 8

2.6 Rigid foam aluminium type between plates 9

2.7 The microstructure of the carbon foam used in this 10 Investigation showing an open cell structure and fiber-

like ligaments

2.8 Polyurethane Chain 11

2.9 The modern motorcycle helmet delivers its life-saving 13 protection via the use of expanded polystyrene (EPS)

foam, which dissipates the energy of high-impact trauma

2.10 This diagram schematically shows the stress strain curve 14 of rubber

2.11 Schematic illustration of the reactor for the product of 17 reclaimed rubber

2.12 Continuous recycling process for the product of reclaimed 18 rubber.

2.13 Stress-strain curves of crosslinked rubbers. 19

2.14 (a) Structure of natural rubber, cis-1, 4-polyisoprene, 20 (b) Formation of peroxy formic acid and

(c) The production of ENR

2.15 Epoxidized Natural Rubber (ENR) Flow Process 21

2.16 Flexible natural rubber foam at 100 magnification 27

2.17 Example of stress strain curve 28

2.18 Drop ball test technique 30

3.1 The flowchart of overall processing method, testing and 35 analysis of rubber foam

3.2 HAAKE RHEOMIX OS Internal Mixer 39

3.3 Reclaimed rubber 41

3.4 Additives in rubber formulation (a) Zinc Oxide 41

(b) Stearic acid (c) Cut with scissor

3.5 (a) Rubber compound (b) Rubber compound cut with scissor 42

3.6 (a) Hot moulding machines (b) Mould of rubber foam 43

3.7 Air circulating oven 43

3.8 Rubber foam 44

3.9 Electronic densimeter 46

3.10 Impact Test Ball Drop 48

3.11 Digital camera 49

3.12 Optical microscope 50

4.1 Increase percentage of foam (%) 53

4.2 Graph relative density 54

4.3 Height of sample after baked oven for every sample 56

4.4 Expansion ratio graph 57

4.5 Water absorption rate of sample 59

4.6 Height of impact drop ball test 61

4.7 Energy of absorption of the foam sample 63

4.8 (a) Micrograph of 90:10. (b) Micrograph of 70:30. 65

(c) Micrograph of 50:50. (d) Micrograph of 30:70. (e) Micrograph of 0:100.

4.9 (a) Optical micrograph of 90:10 at magnification of 2x. 66 (b) Optical micrograph of 70:30 at magnification of 2x.

(c) Optical micrograph of 50:50 at magnification of 2x. (d) Optical micrograph of 30:70 at magnification of 2x. (e) Optical micrograph of 0:100 at magnification of 2x

LIST OF ABBREVIATIONS, SYMBOLS AND

NOMENCLATURES

0 -

Degree

C - Celcius

CO2 - Carbon Dioxide

CS - Benzothiazyl-2-cyclohexyl-sulphenamide

EMI - _{Electromagnetic Interference}

ENR - Epoxidized Natural Rubber

EPS - _{Expanded Polystyrene}

EPDM - Ethylene Propylene Dience Monomer Rubber HRSI - _{High-Temperature Reusable Surface Insulation}

J - Joule (N.m)

MM - Milimeter

MPa - Mega Pascal

NaHCO3 - Sodium Bicarbonate

NR - Natural Rubber

PSI - Pressure

RR - Reclaimed Rubber

SEM - Scanning Electron Microscopy

SBR - Styrene Butadiene Rubber

TMTD - Tetramethylthiuram-disulfenamide XSBR - _{Carboxylated Styrene-Butadiene Rubber}

CHAPTER 1

INTRODUCTION

1.1 Background

In industrialized countries, rubber products are everywhere to be found, though few people recognize rubber in all of its applications. Since 1920, demand for rubber manufacturing has been largely dependent on the automobile industry, the biggest consumer of rubber products. Rubber forms a part of many mechanical devices in the kitchen, helps to exclude draughts and to insulate against noise. Sofas and chairs may be upholstered with foam rubber cushions, and beds may have natural rubber pillows and mattresses. Clothing and footwear may contain rubber for example elasticized threads in undergarments or shoe soles. Still other applications have been developed due to special properties of certain types of synthetic rubber, and there are now more than 100,000 types of articles in which rubber are used as a raw material (Pothen 2011).

The use of rubber in so many applications results in a growing volume of rubber waste. With the increase in demands, the manufacturing and use of rubber and the rubber products has increased tremendously both in the developed and less

developed countries. By the middle of 1980s less than 1% of the worldwide polymer consumption was in the form of reclaim. At the beginning of 20th century half of the rubber consumed was in the form of reclaim. It is expected that in 21st century most of the scrap rubber will be recycled in the form of reclaim because of day to day increase in environmental awareness. One of the various problems which mankind faces as it enters into the 21st century is the problem of waste disposal management.

Although reclaim rubber is a product of discarded rubber articles it has gained much importance as additive in various rubber article formulations. It is true that mechanical properties like tensile strength, modulus, resilience and tear resistances are all reduced with the increasing amounts of reclaim rubber in fresh rubber formulation. But at the same time the reclaim rubber provides many advantages if incorporated in fresh rubber. The increase in the awareness of waste management and environment related issues has led to substantial progress in the utilization of rubber waste. Recycling materials back into its initial use often are more sustainable rather than finding new applications.

1.2 Problem statement

Since polymeric materials do not decompose easily, disposal of waste polymers is a serious environmental problem. Large amounts of rubbers are used as glove and tires for airplanes, trucks and car. Reclaimed rubber is the product resulting when waste vulcanized scrap rubber is treated to produce a plastic material which can be easily processed, compounded and vulcanized with or without the addition of either natural or synthetic rubbers. Reclaiming of the waste rubber can cost half than that of natural or synthetic rubber, some properties that are better than those of virgin rubber, requires less energy in the total production process than does virgin material and it is an excellent way to dispose of unwanted rubber products, which is often difficult.

Although reclaim rubber is a product of discarded rubber articles it has gained much importance as additive in various rubber article formulations. It is true that mechanical properties like tensile strength, modulus, resilience and tear resistances

are all reduced with the increasing amounts of reclaim rubber in fresh rubber formulation. But at the same time the reclaim rubber provides many advantages if incorporated in fresh rubber. The increase in the awareness of waste management and environment related issues has led to substantial progress in the utilization of rubber waste. Recycling materials back into its initial use often are more sustainable rather than finding new applications.

Epoxidized natural rubber (ENR) is a versatile material due to its unique properties. It shows combination properties of natural rubber and durability of selected for its ability to be combined with other material with different mixture ratios. Furthermore, the research about ENR/RR blend still not wide this used and need more information will be required in this research. To understand concept of ENR blend, need a few sample of rubber blend that related with ENR blends. Pore that related with rubber is hard to understand because not much research about that can be found. All the research about ENR or RR must be related with pore in rubber, because in this topic we focusing in pore type as an energy absorption in pore under impact. There have many of pore type; it is because for the shock absorption application, it needs optimum size of pore to make it perfect absorption.

Energy absorption can also be applied in various fields. For example, they could be put to reduce the rate of injury in an accident such as in a car bumper, safety helmet, and others. Moreover, energy absorption can also be used by athletes in sports in which to reduce the shock foot in the shoe or insole. Sometimes, the human body also requires a cushion from damaging shockwave, especially during your strenuous activity. This means, we can apply to energy absorption in many applications.

1.3 Objective

The main objectives on this research are:

i. To prepare epoxidized natural rubber/reclaimed rubber blend though melt compounding using internal mixer.

ii. To introduce pores in epoxidized natural rubber/reclaimed rubber by adding blowing agent though two step of heat transfer.

iii. To correlate energy absorption with dimension pore epoxidized natural rubber/reclaimed rubber pore.

1.4 Scope

This research is to study the compounding pore in epoxidized natural rubber/reclaimed rubber by preparing different ratio of epoxidized natural rubber/reclaimed rubber blend though melt compounding using internal mechanical testing. Then, introduce compounding pore in epoxidized natural rubber/reclaimed rubber by adding blowing agent, though two steps of heat transfer. The prepared machines that were used internal mixer for blending all the material and additive together. For the secondary process is compounded moulding that used to compact the material to be a sample. This process involves heating and cold working. Some analysis, such as morphology was performed to support the data. This analysis is for to correlate absorption with ENR/RR ratio.

CHAPTER 2

LITERATURE REVIEW

2.1 Solid Foam

Solid foams form an important class of lightweight cellular engineering materials. These foams can be divided into two types based on their pore, open-cell-structured foams and closed cell foams. Solid foams are cellular materials, materials which are made up from a framework of solid material surrounding gas-filled voids (bubbles). Solid foams can be 100 times lighter than the equivalent solid material (Julia et al., 2006). Figure 2.1 show the honeycomb that easily seen their cellular structure. This structure allow the minimization of the amount of used material to reach minimal weight and minimal material cost.

Figure 2.1: The bee's honeycomb is a two-dimensional cellular structure (Source: Waynesword)

Recent developments in metal foams, especially aluminium, have produced a new class of lightweight materials, which are excellent energy absorbers. This property is useful in reducing the impact of a car crash.

Figure 2.2 show an open cell structure of ceramic that have low density materials has developed to produce lightweight porous structures for aerospace and industrial applications. Open cell structured foams contain pores that are connected to each other and form an interconnected network that is relatively soft. Open cell foams will fill with whatever they are surrounded with. If filled with air, it will give good insulation, but, if the open cells filled with water, the insulation properties would be reduced. Foam rubber is a type of open-cell foam (Sivertsen, 2007).

Closed-cell foams do not have interconnected pores. The closed-cell foams normally have higher compressive strength due to their structures. However, closed-cell foams are also in general denser, require more material, and as a consequence are more expensive to produce. The closed cells can be filled with a specialized gas to provide improved insulation. The closed-cell structure foams have higher dimensional stability, low moisture absorption coefficients, and higher strength compared to open-cell-structured foams. All types of foam are widely used as core material in sandwich-structured composite materials (Sivertsen, 2007).

Figure2.3 : Example of Closed-Cell Structure in Alminium Foam (Source: invention high strength)

2.2.1 Classification Material of Solid Foam

Solid foam can be classified based on type of its basic material whether polymers, composites, steel, ceramic and so on.

Ceramic foams made from a wide range of ceramic materials, both oxide and nonoxide, are being considered for a whole range of potential applications. These include hot gas filters, interpenetrating composites and biomedical applications as well as thermal insulation, kiln furniture and catalyst supports amongst others. Three of these are described briefly below as well as a new processing route based on gel casting (Biastto, 2006). Ceramic materials with controlled porous microstructures can be produced using particle stabilised foams, freeze casting, sacrificial templates

and partial sintering. The structure can be characterised with micro computed tomography as shown in Figure 2.4.

Figure2.4: Porous Ceramic (source: CeramicEngineering)

There's a polymer that's soft (or in solution), and a lot of gas (usually not air) that's blown in to make a whole bunch of tiny little bubbles (foam). The big difference is that the polymer bubbles will stay. The gas that's blown in to make the foam is called a "blowing agent" or "foaming agent''. The best kind of gas to use is one that will not react with anything, especially with the polymer, will be fire-resistant, and will be nontoxic. Nontoxic is important not only for the folks who make these foams, but for whoever buys them. The amount of gas or foaming agent, used controls the size and the number of the bubbles, known as "foam cells" after it hardens.

are all reduced with the increasing amounts of reclaim rubber in fresh rubber formulation. But at the same time the reclaim rubber provides many advantages if incorporated in fresh rubber. The increase in the awareness of waste management and environment related issues has led to substantial progress in the utilization of rubber waste. Recycling materials back into its initial use often are more sustainable rather than finding new applications.

Epoxidized natural rubber (ENR) is a versatile material due to its unique properties. It shows combination properties of natural rubber and durability of selected for its ability to be combined with other material with different mixture ratios. Furthermore, the research about ENR/RR blend still not wide this used and need more information will be required in this research. To understand concept of ENR blend, need a few sample of rubber blend that related with ENR blends. Pore that related with rubber is hard to understand because not much research about that can be found. All the research about ENR or RR must be related with pore in rubber, because in this topic we focusing in pore type as an energy absorption in pore under impact. There have many of pore type; it is because for the shock absorption application, it needs optimum size of pore to make it perfect absorption.

Energy absorption can also be applied in various fields. For example, they could be put to reduce the rate of injury in an accident such as in a car bumper, safety helmet, and others. Moreover, energy absorption can also be used by athletes in sports in which to reduce the shock foot in the shoe or insole. Sometimes, the human body also requires a cushion from damaging shockwave, especially during your strenuous activity. This means, we can apply to energy absorption in many applications.

1.3 Objective

The main objectives on this research are:

i. To prepare epoxidized natural rubber/reclaimed rubber blend though melt compounding using internal mixer.

ii. To introduce pores in epoxidized natural rubber/reclaimed rubber by adding blowing agent though two step of heat transfer.

iii. To correlate energy absorption with dimension pore epoxidized natural rubber/reclaimed rubber pore.

1.4 Scope

This research is to study the compounding pore in epoxidized natural rubber/reclaimed rubber by preparing different ratio of epoxidized natural rubber/reclaimed rubber blend though melt compounding using internal mechanical testing. Then, introduce compounding pore in epoxidized natural rubber/reclaimed rubber by adding blowing agent, though two steps of heat transfer. The prepared machines that were used internal mixer for blending all the material and additive together. For the secondary process is compounded moulding that used to compact the material to be a sample. This process involves heating and cold working. Some analysis, such as morphology was performed to support the data. This analysis is for to correlate absorption with ENR/RR ratio.

CHAPTER 2

LITERATURE REVIEW

2.1 Solid Foam

Solid foams form an important class of lightweight cellular engineering materials. These foams can be divided into two types based on their pore, open-cell-structured foams and closed cell foams. Solid foams are cellular materials, materials which are made up from a framework of solid material surrounding gas-filled voids (bubbles). Solid foams can be 100 times lighter than the equivalent solid material (Julia et al., 2006). Figure 2.1 show the honeycomb that easily seen their cellular structure. This structure allow the minimization of the amount of used material to reach minimal weight and minimal material cost.

Figure 2.1: The bee's honeycomb is a two-dimensional cellular structure (Source: Waynesword)

Recent developments in metal foams, especially aluminium, have produced a new class of lightweight materials, which are excellent energy absorbers. This property is useful in reducing the impact of a car crash.

Figure 2.2 show an open cell structure of ceramic that have low density materials has developed to produce lightweight porous structures for aerospace and industrial applications. Open cell structured foams contain pores that are connected to each other and form an interconnected network that is relatively soft. Open cell foams will fill with whatever they are surrounded with. If filled with air, it will give good insulation, but, if the open cells filled with water, the insulation properties would be reduced. Foam rubber is a type of open-cell foam (Sivertsen, 2007).

Closed-cell foams do not have interconnected pores. The closed-cell foams normally have higher compressive strength due to their structures. However, closed-cell foams are also in general denser, require more material, and as a consequence are more expensive to produce. The closed cells can be filled with a specialized gas to provide improved insulation. The closed-cell structure foams have higher dimensional stability, low moisture absorption coefficients, and higher strength compared to open-cell-structured foams. All types of foam are widely used as core material in sandwich-structured composite materials (Sivertsen, 2007).

Figure2.3 : Example of Closed-Cell Structure in Alminium Foam (Source: invention high strength)

2.2.1 Classification Material of Solid Foam

Solid foam can be classified based on type of its basic material whether polymers, composites, steel, ceramic and so on.

Ceramic foams made from a wide range of ceramic materials, both oxide and nonoxide, are being considered for a whole range of potential applications. These include hot gas filters, interpenetrating composites and biomedical applications as well as thermal insulation, kiln furniture and catalyst supports amongst others. Three of these are described briefly below as well as a new processing route based on gel casting (Biastto, 2006). Ceramic materials with controlled porous microstructures can be produced using particle stabilised foams, freeze casting, sacrificial templates

and partial sintering. The structure can be characterised with micro computed tomography as shown in Figure 2.4.

Figure2.4: Porous Ceramic (source: CeramicEngineering)

There's a polymer that's soft (or in solution), and a lot of gas (usually not air) that's blown in to make a whole bunch of tiny little bubbles (foam). The big difference is that the polymer bubbles will stay. The gas that's blown in to make the foam is called a "blowing agent" or "foaming agent''. The best kind of gas to use is one that will not react with anything, especially with the polymer, will be fire-resistant, and will be nontoxic. Nontoxic is important not only for the folks who make these foams, but for whoever buys them. The amount of gas or foaming agent, used controls the size and the number of the bubbles, known as "foam cells" after it hardens.