APPROVED:

Witold Brostow, Major Professor Richard F. Reidy, Committee Member Samir Aouadi, Committee Member Sundeep Mukherjee, Committtee Member Nigel Shepherd, Chair of the Department of

Materials Science and Engineering Costas Tsatsoulis, Interim Dean of the

Toulouse Graduate School

NANOHYBRIDS BASED ON SOLID AND FOAM POLYURETHANES

Chong Bo, B.E.

Thesis Prepared for the Degree of

MASTER OF SCIENCE

UNIVERSITY OF NORTH TEXAS

May 2015

Bo, Chong. Nanohybrids Based on Solid and Foam Polyurethanes. Master of Science

(Materials Science and Engineering), May 2015, 52 pp., 4 tables, 26 figures, references, 40

numbered titles.

Polymer nanocomposites are a going part of Materials Science and Engineering. These new

composite materials exhibit dimensional and thermal stability of inorganic materials and

toughness and dielectric properties of polymers. Development of nanocomposites become an

important approach to create high-performance composite materials.

In this study silica, fly ash, silica nanotubes and carbon black particles have been added to

modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition

of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material,

increase of the compressive strength, and greater resistance to deformation. However, the

uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to

the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material

stiffness and compressive strength, resistance to deformation, and has little impact on the

dynamic friction of the material. Adding nanotubes make bubble size unequal, and the

arrangement of the bubble uneven, resulting in decreased strength of the material, while the

friction increases. After the addition of carbon black to the polyurethane foam, due to the special

surface structure of the carbon black, the foam generates more bubbles during the foaming

process changing the foam structure. Therefore, the material becomes soft, we obtain a flexible

polyurethane foam.

The results of mechanical properties determination of the thermoplastic polyurethane show

that adding particles may increase the stiffness and wear resistance of the thermoplastic

polyurethane, while the tensile properties of the material are reduced. This phenomenon may be

due to agglomeration of particles during the mixing process. Possibly the particles cannot be

uniformly dispersed in the thermoplastic polyurethane.

Copyright 2015

by

Chong Bo

ii

ACKNOWLEDGEMENTS

This thesis was prepared, under the distinguished Dr. Witold Brostow careful supervision.

I thank Dr. Witold Brostow for offering to me the opportunity to work and study in the LAPOM.

Dr. Witold Brostow rigorous scholarship, profound theoretical knowledge, excellent research

skills, a wealth of practical experience, also generous character, positive style of work that I will

never forget. I heartfeltly thank Dr. Witold Brostow for his care and guidance.

I thank my partner Yingji Wu for her help to me in this work. I am very honored to be

working with her. I also would like to thank the lab manager Nathalie Hnatchuk and my entire lab

including colleagues Gregory, Zachary and Thomas for their support and help during the work. In

interaction with them, I acquired much valuable knowledge, what is important for my research and

future work.

I want to thank my parents for their concern, encouragement and support over the years.

Thanks to my husband for staying with me. Family support has been my power source in my

progress.

iii

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENT ............................................................................................................. iii

LIST OF TABLES ........................................................................................................................ vii

LIST OF FIGURES ..................................................................................................................... viii

CHAPTER 1 INTRODUCTION .....................................................................................................1

1.1 Purpose .....................................................................................................................1

1.2 Polymer Nanocomposites ........................................................................................2

1.2.1 Mixed Method ..............................................................................................3

1.2.2 Sol-Gel Method ............................................................................................3

1.2.3 Intercalation Method ....................................................................................4

1.2.4 In Situ Polymerization .................................................................................5

1.3 Rigid Polyurethane Foams .......................................................................................5

1.4 Polyurethane Foam + Inorganic Nanocomposites ...................................................6

1.4.1 Polyurethane Foam + Calcium Carbonate Nanocomposites .......................6

1.4.2 Polyurethane Foam / Silicate Nanocomposites............................................7

1.5 Application of Polyurethane Foam ..........................................................................7

1.6 Description of Thermoplastic Polyurethanes ...........................................................8

1.6.1 Thermoplastic Polyurethanes .......................................................................8

1.6.2 Classification of Thermoplastic Polyurethanes ...........................................8

1.7 Thermoplastic Polyurethane + Inorganic Nanocomposites .....................................9

1.7.1 Thermoplastic Polyurethane + Carbon Matrix Composites ........................9

1.7.2 Thermoplastic Polyurethane + Layered Silicate Nanocomposites ............10

iv

CHAPTER 2 SAMPLE PREPARATION .....................................................................................12

2.1 Material ..................................................................................................................12

2.1.1 Polyurethane Foam ....................................................................................12

2.1.2 Thermoplastic Polyurethanes .....................................................................12

2.1.3 Filler Particles ............................................................................................13

2.2 Polyurethane Foam Sample Preparation ................................................................13

2.2.1 Principle of Foaming Polyurethane Foam .................................................13

2.2.2 Polyurethane Foam Sample Preparation ....................................................14

2.3 Thermoplastic Polyurethane Sample Preparation ..................................................15

2.3.1 Structure and Principles of Thermoplastic Polyurethanes .........................15

2.3.2 Thermoplastic Polyurethanes Sample Preparation ....................................16

CHAPTER 3 EXPERIMENTAL TECHNIQUES.........................................................................18

3.1 Compression Testing .............................................................................................18

3.1.1 Compression Testing Procedure ................................................................18

3.1.2 Compression Testing Details .....................................................................19

3.2 Three Points Bending Testing ................................................................................19

3.2.1 Three Points Bending Test Principle .........................................................19

3.2.2 Three Points Bending Testing Details .......................................................21

3.3 Pin-on-Disk Tribometry .........................................................................................21

3.3.1 Pin-on-Disk Tribometry Principle .............................................................21

3.3.2 Pin-on-Disk Tribometry Details ................................................................21

3.4 Thermal Conductivity Test ....................................................................................22

3.4.1 Thermal Conductivity Test Principle .........................................................22

v

3.4.2 Thermal Conductivity Test Details ............................................................23

3.5 SEM .......................................................................................................................23

3.5.1 SEM Principle ............................................................................................23

3.5.2 SEM Detail.................................................................................................25

3.6 Tensile Testing .......................................................................................................25

3.6.1 Tensile Testing Principle ...........................................................................25

CHAPTER 4 RESULTS AND DISCUSSION ..............................................................................27

4.1 Testing of Polyurethane Foam ...............................................................................27

4.1.1 Volume Testing ..........................................................................................27

4.1.2 Compression Testing .................................................................................28

4.1.3 Three Points Bending .................................................................................35

4.1.4 SEM ...........................................................................................................38

4.1.5 Pin-on-Disk Tribometry .............................................................................40

4.1.6 Thermal Conductivity Results ...................................................................41

4.2 Thermoplastic Polyurethanes .................................................................................42

4.2.1 Tensile Testing ...........................................................................................42

4.2.2 Pin-on-Disk Tribometry .............................................................................45

CHAPTER 5 CONCLUSIONS .....................................................................................................47

REFERENCES ..............................................................................................................................48

vi

LIST OF TABLES

Page

Table 1 Properties of Polyurethane Foam ...........................................................................12

Table 2 Properties of Estane® CP80AS2 TPU ...................................................................13

Table 3 Particle Size of Four Types of Fly Ash ..................................................................30

Table 4 Components of the Four Types of Fly Ash ............................................................31

vii

LIST OF FIGURES

Page

Figure 1 Thermoplastic polyurethanes sample preparation .................................................15

Figure 2 Thermoplastic polyurethanes structure ..................................................................16

Figure 3 MTS Qtest/5 ...........................................................................................................19

Figure 4 Three points bending test .......................................................................................20

Figure 5 TPS 1500 Thermal Conductivity System ..............................................................23

Figure 6 Structural diagram of the scanning electron microscope (SEM) ...........................24

Figure 7 Tensile testing of thermoplastic polyurethane .......................................................26

Figure 8 Volume test result of polyurethane foams .............................................................27

Figure 9 Silica compression modulus ..................................................................................28

Figure 10 Fly ash compression modulus ................................................................................29

Figure 11 Monticello fly ash compression modulus ..............................................................32

Figure 12 Compression modulus of silica nanotubes and carbon black ................................33

Figure 13 Compression test result for 20% filler concentrations ...........................................34

Figure 14 Compression strength of polyurethane foam mix with 20 wt.% filler ...................34

Figure 16 Flexural modulus values from the three points bending tests ................................36

Figure 17 Break strain and break stress of three points bending test .....................................37

Figure 18 Maximum stress of three points bending test ........................................................38

Figure 19 Polyurethane rigid foam microstructure obtained by scanning electron microscopy (SEM) analysis at 50 times magnification .........................................39

Figure 20 Dynamic friction of polyurethane foam .................................................................40

Figure 21 Thermal conductivity of polyurethane foam..........................................................41

Figure 22 Tensile testing result for thermoplastic polyurethanes with 20% filler .................43

viii

Figure 23 Tensile modulus of thermoplastic polyurethane ....................................................43

Figure 24 Maximum stress of thermoplastic polyurethane ....................................................44

Figure 25 Break strain of thermoplastic polyurethane ...........................................................44

Figure 26 Dynamic friction of thermoplastic polyurethane ...................................................46

ix

1

CHAPTER 1

INTRODUCTION

1.1 Purpose

Polyurethanes are a class of large molecular compounds containing repeat carbamate group

in the main chain. They are composed of an organic diisocyanate or multi isocyanate with two

hydroxyl or polyhydroxy compounds.

Based on the variations of polyurethane components, polyurethanes (PUs) can have a wide

range of properties. Therefore, polyurethanes can be used in a wide range of applications.

Polyurethanes can be foams, coatings, adhesives, elastomers, and fibers. Rigid polyurethane

foams have good heat insulating properties, light weight, high specific strength, provide sound

insulation, are shockproof, provide electric insulation and more. Consequently, rigid PU foams

have applications in the freezer, piping, building, refrigerators, and transportation 1.

Thermoplastic polyurethanes (TPUs) are elastomers. They are different from rubbers

because TPUs do not have crosslinks. Therefore TPUs can change shape at high temperatures. As

elastomers, TPUs have significant advantages. They have a wide range of hardness, high

mechanical strength, cold resistance, oil resistance, and solvent resistance. TPUs main

applications include auto parts, cables, footwear, bags and more.

Although polyurethanes foams and TPUs have very good properties for many applications,

they also have some shortcomings in performance. For example,

2

PU foams do not have good mechanical properties. TPUs lack mechanical strength.

Therefore, there is a need to enhance their mechanical properties. Nanohybrids particles have

small sizes and large surface areas. When the particle sizes decrease, the surface energy and

surface tension increase. When the PU materials are modified by nanohybrids, the resulting

composites not only maintain the advantageous properties of polymeric materials but also can

have many beneficial properties of nanohybrids.

This thesis is focused on the polyurethanes modified by different types of nanohybrids

particles, enabling comparisons the several nanohybrids influence the rigid polyurethane foams

and TPUs.

1.2 Polymer Nanocomposites

Work on polymer nanocomposites has grown in recent years. In general, we are dealing less

than 100 nm particles of a dispersed phase in a composite material 2,3. Such composite materials

can well combine rigidity, dimensional and thermal stability of inorganic material and polymer

materials toughness and dielectric behavior. Preparation of nanocomposites has become an

important way to acquire high-performance composites. There are several ways to prepare

nanocomposites, including four commonly used methods 30.

3

1.2.1 Mixed Method

Mixed method refers to the preparation of various forms of nanoparticles first, and then the

nanoparticles are dispersed into the polymer matrix. An advantage of this method is stepwise

controlled morphology and size of nanoparticles. However, because the surface activity of nano

powders, and their strong tendency to self-aggregation when blending it, is difficult to ensure

uniform dispersion of nanoparticles in the matrix, so as to obtain the nano-composite material in

true sense. Thus, typically prior to mixing, a surface treatment of the nanoparticles or the

dispersant is preformed, in order to facilitate the particle dispersion in the matrix as uniform as

possible.

1.2.2 Sol-Gel Method

Using water-soluble salts or alcohol-soluble salt, the polymer is dissolved in water or in an

organic solvent to form a homogeneous solution. Hydrolysis or alcoholysis material reacts to

form nanoscale particles of an inorganic oxide, and a sol system. This is followed by conversion

of the sol into a gel by evaporation to dryness, with the inorganic nanoparticles uniformly

dispersed therein. Sol-gel prepared nanocomposites have the advantages of a low temperature

process, high purity, while high uniformity material can be prepared in large quantities. The

features can be controlled from the initial stage of the process to the material structure at the

nanometer scale, achieving good binding between the inorganic and the organic phases. The

biggest problem of the method is at the stage of the gel drying process, since volatilization of

4

solvent or water may result in material shrinkage or embrittlement. Further, the number of types

of nanocomposites can be prepared in this manner is limited 31.

1.2.3 Intercalation Method

Many inorganic compounds, such as clays silicates, phosphates, graphite, some metal

oxides, disulfides, trisulfide phosphorus complexes, have a typical layered structure. Polymer

monomers can be deposited into the inorganic material layer by in situ polymerization otherwise

polymer is directly deposited into the inorganic layer, thus obtaining organic or inorganic

nanocomposites. Depending on the specific implementation method, intercalation method can be

divided further into three methods:

(a) Intercalation polymerization: The organic monomer is deposited into the layer of

inorganic material with a layered structure, what leads to in situ polymerization of monomer in

the interlayer. During the polymerization, the inorganic layer spacing increases, becomes

independent of the thickness of the sheet-like nanoscale, and is uniformly dispersed in the

continuous phase polymer, thus obtaining organic - inorganic nanocomposites 32.

(b) Solution intercalation: The co-polymer and layered inorganic compounds are dispersed

in a solvent. Then the polymer in solution goes directly into the inorganic layer 33,34.

(c) Melt intercalation: The layered inorganic compounds with molten polymer blend.

Polymer is inserted directly into the inorganic layer to obtain polymers intercalated inorganic

nanocomposites 34.

5

1.2.4 In Situ Polymerization

In situ polymerization is performed so that nanoparticles are uniformly dispersed in a

polymer after polymerization under certain conditions, to directly obtain nano-composites 35.

This approach provides a polymer nano-template with a molecular structure containing to

polar groups, one of them a sulfonic acid group, plus an acid group shuttle. The polar groups can

strong bind with ionic bonds and coordination bond which are formed between metal ions of

strongly polar inorganic nanoparticles, thereby reducing the probability of collisions between

particles. While the polymer chains can prevent excessive accumulation of particles, at certain

location. These polar polymers containing an ionic group include ionomers, ion exchange resins,

the polar group-containing homopolymers, copolymers and more.

1.3 Rigid Polyurethane Foams

A porous polyurethane material contains a large number of fine pores forming main and

collateral channels. The resulting material is commonly known as "polyurethane foam".

According to the ratio of soft and hard PU constituents, we can have three types of foam: soft,

rigid and semi-hard 36.

Rigid polyurethane foams, are referred to as the PURFs, PURFs are a solid phase and gas

phase composite materials, wherein the solid phase is the continuous one providing, the main

mechanical structure in a closed cell structure gas container. The mechanical properties depend

mainly on the foam morphology. Pure PURFs show relatively low tensile and compression

6

strength. Value to further enhance the mechanical properties, commonly used are inorganic

particles, glass fiber and other material 4.

Rigid polyurethane foams form closed cell structures, have good heat insulation properties,

light weight, high specific strength, and other excellent characteristics. They provide sound

insulation, are shockproof, give electric insulation, heat resistance, cold resistance, and solvent

resistance 5. Such foams are widely used in refrigerators, freezers, cold storage box adiabatic

layers, refrigerated trucks and other insulation structures. Smaller amounts are used for

non-adiabatic applications, such as imitation wood packing materials, etc. In general, a

polyurethane hard bubble of low density is mainly used for thermal insulation materials; high

density polyurethane rigid foams can be used as structural materials.

Rigid polyurethane foams are generally at room temperature; the molding process is

relatively simple. According to the degree of construction mechanization, the processes can be

divided into manual and mechanical foaming. Foaming pressure can be either high or low. Press

molding can be divided into pouring foaming and spraying foaming 6.

1.4 Polyurethane Foam + Inorganic Nanocomposites

1.4.1 Polyurethane Foam + Calcium Carbonate Nanocomposites

Calcium carbonate is the filler often used in polymer modification, a cheap material 7.

Calcium carbonate surface hydroxyl groups can react with isocyanates. Thus the calcium

carbonate particles can be uniformly dispersed in the isocyanate, making it easier to play a

7

reinforcing role 8.

1.4.2 Polyurethane Foam / Silicate Nanocomposites

Add a small amount of dispersed nano-scale layered nano silicate, can significantly improve

the PURF foam heat resistance, strength, modulus and gas barrier properties. Montmorillonite,

garnet, rectories, meerschaum, talc and other nano-layered silicate are used. Silicates may be

well dispersed in the isocyanate and polyol, improving the mechanical properties of the PU

foams7.

1.5 Application of Polyurethane Foam

A rigid polyurethane foam, is composed of a rigid foam polyether polyol, and aggregation

of MDI (also known as black material). Such foams are widely used in refrigerators, spraying,

solar energy, devices heat pipelines, construction and other fields.

1．Freezing equipment and food industry: such as refrigerator, cold storage, refrigerated

trucks.

2．Industrial equipment such as tanks, pipelines and other industrial equipment that require

insulation.

3．Building materials: in developed countries in Europe and America, rigid polyurethane

foams account for about half of total consumption of hard foams.

4．Transportation: such as automobile roofs, interior decorations etc.

8

5．Imitation wood: high density (density 300-700kg/m3) rigid polyurethane foam or glass

fiber reinforced rigid foams also called imitation wood, have high strength, good toughness, and

easy formation by a simple process. One achieves a higher, strength than the natural wood.

6．Potting materials.

1.6 Description of Thermoplastic Polyurethanes

1.6.1 Thermoplastic Polyurethanes

Thermoplastic polyurethanes (TPUs) are elastomers different from other elastomers. TPUs

are elastic and melt-processable. TPUs can be processed by extrusion, injection molding, blow

molding, die-casting method 9, can be coated and colored and are suitable for a variety of

manufacturing methods. The process can be repeated without losing structural integrity after

processing. Moreover, TPUs have good mechanical properties, such as high tensile strength, high

elongation and resistance to oil, grease, solvent, abrasion. Since TPU has many excellent

properties, it has been applied in a variety of fields 10.

1.6.2 Classification of Thermoplastic Polyurethanes

There are three main chemical classes of TPU: polyester, polyether and polycaprolactone 11.

Polyester TPUs: they are compatible with PVC or other polar plastics materials, added in

order to increase the performance of the material. Such TPUs are oil resistant and abrasion

resistant 37.

9

Polyether TPUs: they are slightly lower in specific gravity than polyester and

polycaprolactone grades. This PU have good abrasion resistance, tear resistance and toughness at

low temperatures. Because they can resist microbes and also exhibit water resistance, Polyether

TPUs can be widely used in underwater environments 38.

Polycaprolactone TPUs: they exhibit high toughness and a relatively high resistance to

hydrolysis. They are an ideal raw material for hydraulic and pneumatic seals19.

1.7 Thermoplastic Polyurethane + Inorganic Nanocomposites

1.7.1 Thermoplastic Polyurethane + Carbon Matrix Composites

Currently in the preparation of thermoplastic polyurethane + carbon nanotube composites, a

common method is to use a strong acid for the surface modification of carbon-based materials 39.

Typically one applies nitric acid or mixed acid with carbon nanotubes subjected to oxidation

treatment to modify the surface properties. One so improves compatibility of the carbon

nanotubes and the polyurethane, and increases the filler dispersibility in the polymer matrix.

Meanwhile, after the acid treatment of carbon-based material, its surface may be added carboxyl

and hydroxyl reactive groups. These reactive groups can not only improve the interface

compatibility between the substrate, it can also participate in the reaction to form a chemical

bond composite 12.

10

1.7.2 Thermoplastic Polyurethane + Layered Silicate Nanocomposites

Layered silicates can be relatively easily dispersed in the TPUs. According to the study of

Bradley Finnigan 14, the layered silicate can enhance the rigidity of the thermoplastic

polyurethane, but decreases the tensile strength of the material. Asim Pattanayak 29. reported that

the layered silicate clay may enhance the thermal stability of the material, and to increase the

mechanical strength 40.

Rectories are an inter-layer structure of non-metallic minerals. They are layered silicates.

The inter-layer contains switchable hydrated cations. Rectories are one of the few natural mineral

materials with easy separation into nanometer microchips. After appropriate processing, rectories

interlayer structure can be separated into Nanoparticles of mica and montmorillonite 13. Rectories

enhancing the mechanical properties of the material, can keep the toughness of polymer

materials.

1.8 Application of Thermoplastic Polyurethanes

1．Footwear: shoes, sports shoes, air cushions, mountaineering shoes, snow shoes, golf

shoes, skating shoes, fabrics and lining joint material.

2．Apparel: snow clothes, windbreaker, jacket, cold proof raincoat, field service, paper

diapers, fabric composite materials (such as waterproof and moisture permeable).

3．medicine: operation clothes, hat, shoes, hospital mattresses, ice bags, bandages, plasma

bags, surgical dressing cloth, masks, the fabric and lining material, operation bed bags.

4．Military uses: the aircraft fuel tanks, weapons, tents, protection window sealed film bags,

11

life jackets and inflatable boats.

5．Sports: football surfaces and inner linings, inflatable beds, water bags, ski gloves

(waterproof bag), diving suits, ski jackets, swimwear, skis, trademarks, air bag, sport shirts, thin

clothing such as fabric and lining materials.

6．Industrial supplies: loudspeaker drum paper rubber edges, sound insulation materials,

fire-proof materials, fireproof clothes, fire service products, fireproof cloth and other fabrics and

lining composite material.

7．Other applications: mobile phone keys, the plastic inflatable toys, bed sheets, tablecloths,

shower curtains, furniture, cloth, aprons, pianos, keyboards, coated fabric and lining materials

and more.

12

CHAPTER 2

SAMPLE PREPARATION

2.1 Material

2.1.1 Polyurethane Foam

Polyurethane foam used was ‘Polyurethane Mix and Pour Foam’ purchased from Fibre

Glast. It has two liquid parts: #625（Diphenylmethane diisocyanate）and #624 (Polyol). Table I

shows their properties. After mixing two liquids for 60 seconds, the material will begin to react

and expand for several minutes. Before cure, the foam is expanded for 10 minutes. It can fill any

shape.

Table 1 Properties of Polyurethane Foam

2.1.2 Thermoplastic Polyurethanes

Estane® CP80AS2 TPU was used, and also Estane® CP80AS2 TPU which is a polyester

TPU. Both are compatible with PVC, oil resistant, abrasion resistant and are well suited for

blending process.

13

Table 2 Properties of Estane® CP80AS2 TPU

2.1.3 Filler Particles

In this study, I used several types of particles, including silica, silica nanotubes, carbon

black and fly ash. Silica used was MIN-U-SIL Fine Ground Silica, 10 micron maximum size,

purchased from US SILICA. Carbon black (surface area 350 m2/g) was purchased from

COLUMBIAN CHEMICALS COMPANY. Silica nanotubes, 30-70nm×1-3μm, was purchased

from SIGMA-ALDRICH. There are four types of fly ash: Rockdale Fly Ash, Monticello Fly Ash,

San Miguel Fly Ash, and Wansley Fly Ash.

2.2 Polyurethane Foam Sample Preparation

2.2.1 Principle of Foaming Polyurethane Foam

Rigid polyurethane foams are made by mixing two liquid parts, one is polyol and the other

one is isocyanate. Polyurethane foam rise is obtained by combining polyol component,

14

isocyanate component, water and foaming agent in two processes, foaming reaction and curing

reaction 15. In the foaming reaction, isocyanate component reacts with water and generates gas

by chemical reaction, thus achieving the foaming effect. The chemical reaction can be written as:

222 CONHOHNCO

The second process is the curing reaction, involving the amine group and isocyanate

component producing resin. The chemical reaction can be written as:

NHCONHNCONH2

OCONHNCOOH

From the above we can see the increase of water contents increase the carbon dioxide

production. Thus, we can obtain the polyurethane foam of different densities by adjusting the

dosage of water.

2.2.2 Polyurethane Foam Sample Preparation

In situ polymerization was used to modify the polyurethane foam. The polymerization

operation is very simple and easy to control. Preparation of polyurethane foams should follow

these steps:

1.Taking #625 mixed with particles in a cup, and putting #624.

2.Pouring the mixed solution into a mold, the mold is rectangular mold with width 2.6 inch,

length 2.6 inch and height of 3 inch.

3.Foaming. Let the solution foam for half an hour, until the foam has solidified and cooled

15

down.

4.Cutting into various shapes for various tests.

Figure 1 Thermoplastic polyurethanes sample preparation

2.3 Thermoplastic Polyurethane Sample Preparation

2.3.1 Structure and Principles of Thermoplastic Polyurethanes

A TPU is a multi-phase block copolymer that is created when three basic raw materials are

combined together in a specific way:

A polyol or long-chain diol;

A chain extender or short-chain diol;

A diisocyanate.

16

Figure 2 Thermoplastic polyurethanes structure

The polyols and the chain extender react with the diisocyanates through polyaddition to

form linear polyurethane. Flexible segments are created by the reaction of the polyol with the

diisocyanate. The combination of diisocyanate with short-chain diol produces the rigid

component 19.

Due to the structure of TPU, it is made up of block copolymer molecules with alternating

rigid and flexible segments. We have combination of flexible, elastic segments with a high

extensibility and low glass transition temperature.

2.3.2 Thermoplastic Polyurethanes Sample Preparation

Before making samples, thermoplastic polyurethanes should dry one night at 60°C in the

oven. After the drying, mixing into the cup and put them into a Brabender machine. The mixing

temperature is 200°C; one turns on rotors for 2 minutes. The speed is 50 RPM. The material

should be put into the machine slowly, and not put in too much at one time. After the mixing, one

17

closes the cover and keeps 200°C for 4 minutes. When the mixing process is finished, one turns

off the rotors, opens the cover and uses a small spade to take down the material before it

becomes cold. Since the mixed material is a big block, it needs to be cut to small pieces.

Then one put the small pieces of the material into the mold and uses compression molding

to form desired shapes. First, the mold is placed in the compression molding machine preheated

10 minutes; the preheating temperature is 200°C; Then 10 tons pressure is applied to the mold.

Second, the residual gas in the material is discharged by decreasing the pressure to 0 tons and

then increasing it again to 10 tons, repeated three times. After the gas has been discharge, the

mold is cooled down by water.

18

CHAPTER 3

EXPERIMENTAL TECHNIQUES

In the study of polymer modification by add particles, the range of applications of the

material and the mechanical properties required for the focus needs to be considered.

Characterizations of the compressive strength, flexural modulus, thermal conductivity, tensile

modulus, frictional behavior, and surface morphology, have to be taken into account.

Compression testing, three points bending testing, tensile testing and thermal conductivity

determination have been performed together with pin-on-disk tribometry. SEM was used to

observe surface morphology.

3.1 Compression Testing

3.1.1 Compression Testing Procedure

Compressive strength is a very important value for the materials. In the study of strength of

materials, the compressive strength correspond to the maximum pressure of the capacity of the

material withstand, when the material is unconfined. Compression test can provide the values for

the modulus of the compressive strength, compressive stress, and compressive strain. When

some materials withstand their compressive strength limit, they will fracture. Because some

materials deform irreversibly, in those cases, a given amount of deformation may be considered

as the compressive strength 16.

19

Figure 3 MTS Qtest/5

3.1.2 Compression Testing Details

MTS Qtest/5 machine be used for several types of testing. For example, three points

bending, compression test, tensile test and more. In the compression test, the sample size is:

width 2.6 inch, length 2.6 inch and height 1.0 inch. The specimen is put on the test table which is

the lower plate of the machine. The upper plate moves down until it touches the sample.

Compression continues until the sample is compressed by thirty percent.

3.2 Three Points Bending Testing

3.2.1 Three Points Bending Test Principle

With the demand for high-quality material continues to increase, three points bending test

20

has become an important test method in the production and research. Three points bending test is

used to define the material ability to resist17.

The three point bending test provides values for the modulus of elasticity, in bending fE ,

flexural stress f , flexural strain f and the flexural stress-strain response of the material.

Advantages of three-point bending test are easy prototyping and testing method is simple.

Disadvantages of three-point bending test are the results of the testing method are sensitive to

sample and loading geometry and strain rate.

Figure 4 Three points bending test

Flexural stress is used to measures the maximum force that a material with withstand before

it breaks 26. Calculation of the flexural stress f :

223bdFL

f

Flexural strain represents material unit deformation when subjected to bending moment.

Calculation of the flexural strain f :

26LDd

f

Flexural Modulus represents the slope of a stress vs. strain curve and is an indication of

material’s stiffness 18. Calculation of flexural modulus fE :

21

3

3

4bdmLE

f

ff

3.2.2 Three Points Bending Testing Details

In the three points banding test, the sample size is: width 2.0 cm, thickness 0.5 cm, length

10.0 cm.

3.3 Pin-on-Disk Tribometry

3.3.1 Pin-on-Disk Tribometry Principle

I used a NANOVEA pin-on-disk tribometer which performs rotational friction experiments,

the test reproduces the rotational motion found in many real-world tribology mechanisms. A pin

or ball tip is loaded onto a test sample with a precisely known weight and at a specific position

from the center of rotation. As the sample starts rotating, the tip creates a rotational wear track.

Dynamic friction is accurately measured during the test by the deflection of a load cell which is

precisely calibrated. Wear rates for the tip and the sample are calculated from the volume of

material lost during the test. Depth can be recorded during the test using an accurate LVDT or an

optical pen sensor attached to the loading arm. A wide variety of testing procedures included

varying radius and speeds 20.

3.3.2 Pin-on-Disk Tribometry Details

Polyurethane foams and polyurethane solid plastics have different properties. In order to

22

compare the particle impact for the two different species, the friction tests use same load weights

and same friction speeds for the foams and polyurethane plastics. The foam samples were cut to

width 2.0 cm, 2.0 cm length and 0.5 cm thickness Square sheet of (2.0×2.0 cm) of the plastics

sample were made width, thickness of 0.2 cm. Each sample was placed on the stand, a pin loaded

under the force of 2.0 N. The rotation speed was 500 revs/minute, the radius is 4mm, distance is

12.6 m, and the test time is 5 minutes.

3.4 Thermal Conductivity Test

3.4.1 Thermal Conductivity Test Principle

Needless to say, heat transfer occurs at a higher rate across materials of high thermal

conductivity than across materials of low thermal conductivity. Correspondingly, materials of

high thermal conductivity are widely used in heat sink applications while materials of low

thermal conductivity are used as thermal insulation. The thermal conductivity of a material

typically depends on temperature. The reciprocal of thermal conductivity is called thermal

resistivity 27.

23

Figure 5 TPS 1500 Thermal Conductivity System: (a) TPS 1500 Thermal Conductivity System;

(b) TPS high pressure compression stand; (c) HTK TPS Sensor 5501.

3.4.2 Thermal Conductivity Test Details

The thermal conductivity was measured using TPS 1500 Thermal Conductivity System 28.

The polyurethane foams were cut into two 4 cm diameter, 0.5 cm thick round slices. As shown

above, the two samples were placed in TPS high pressure compression stand with a clamp

sensor.

3.5 SEM

3.5.1 SEM Principle

Scanning electron microscope operates on the basis of the interactions of electrons with

matter. A very thin electron beam is focused with high energy to scan the samples, providing a

24

variety of physical information. Processing this information, the image is enlarged and displayed

to show the appearance of the surface of the sample 21.

When a bunch of very thin and high energy incident electron is scanning the sample surface,

the area will be excited to produce secondary electrons, Auger electrons, characteristic X-ray and

X-ray continuum, backscattered electrons, transmission electrons, as well as in the visible,

ultraviolet, infrared light regions. At the same time, the beam can also produce electron-hole

pairs, lattice vibrations, and electronic oscillations 22.

Figure 6 Structural diagram of the scanning electron microscope (SEM)

In general, because metals are conductive and can provide their own pathway to the ground,

they do not require coatings before imaging in the SEM. However polymeric materials are not

conductive, hence they usually are coated with metals, to provide a pathway to the ground.

25

3.5.2 SEM Detail

In this situation, coating the polymeric sample is the first step for the imaging in the SEM.

The SEM Coating Unit E5100 is used to coat gold-platinum plasma to the surface of samples.

The samples are cut into 1.0 cm wide, 1.0 cm long and 0.5 cm thick specimens. After coating, the

sample surface will be conductive. Then the sample is placed in the SEM, the surface

morphology of the sample observed and imaged for enlargement of 50 times or 150 times.

3.6 Tensile Testing

3.6.1 Tensile Testing Principle

One measures material properties under tensile loads. It is one of the basic mechanical

properties of materials testing methods, mainly used to determine whether the material meets the

required standards or for research purposes 23. The sample is placed in a tensile tester; a pulling

force is applied to the sample ends, and deformation occurs until fracture. During this process,

the instrument records the elongation and force. The results include file material elastic limit,

elongation at break, modulus of elasticity, tensile strength, yield point and the tensile yield

strength 24.

26

Figure 7 Tensile testing of thermoplastic polyurethane: (a) thermoplastic polyurethane sample

change in the testing process; (b) a flat shoulder is used with serrated grips.

The elongation measurement is used to calculate the engineering strain, ε, using the

following equation:

0

0

0 LLL

LL

Here ΔL is the change in the length of the sample, L0 is the initial length, and L is the final

length, as seen in figure 7(a).

The force measurement is used to calculate the engineering stress, σ, defined by the

following equation:

0AFn

Here F is the tensile force and A0 is the nominal cross-section of the specimen. The speed

applied was 30 mm/min.

27

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Testing of Polyurethane Foam

4.1.1 Volume Testing

The impact of particles on the polyurethane foam volume is an important factor affecting

the mechanical properties of the foam. Thus, the volume test is the first test for polyurethane

foam.

Figure 8 Volume test result of polyurethane foams; volume factor of the PU liquid before

foaming is 1.0.

We observe two kinds of behavior. Silica and fly ash added produce no significant changes

in the volume. Only when the concentration of silica is 20%, the volume of the foam decreased

slightly. This result can be explained as follows. The volume does not change with low

concentration of filler particles because they fill in the foam bubbles. This is how the particle

does not affect the volume of the foam.

28

By contrast, carbon black and silica nanotubes have a large impact on the volume of the

foams. With the increase of concentration of these fillers, we can see a rapid rise in the volume of

the foam. Apparently these two filler particles have an impact on the foam foaming process.

Because the size and nature of the carbon black particles surfaces, carbon black takes the

role of foaming agent in the foaming process. Addition of carbon black increases the generation

of air bubbles in the polyurethane foam. Possibly gases absorbed in PU contribute fine air

bubbles 25. With increasing carbon black concentration, the bubble generation during the reaction

increases, hence an increase in the volume of polyurethane foam.

4.1.2 Compression Testing

4.1.2.1 Effects of Silica on the Compression Modulus of Polyurethane Foam

The results are displayed in figure 9.

Figure 9 Silica compression modulus

29

Inspection of Figure 9 shows that offer initial addition of silica particles to polyurethane

foam, the compression modulus of the material decreases. However, when exceeding the silica

concentration of 5%, the compression modulus starts to increase. When the concentration of the

silica is 25%, the compression modulus decreases again. Thus, apparently first the silica perturbs

the cohesion in the polymer. Then silica particle provide reinforcement. At still higher

concentration, these particles agglomerate, hence the compression modulus decrease.

4.1.2.2 Effects of Fly Ash on the Compression Modulus of Polyurethane Foam

The results are presented in figure 10.

Figure 10 Fly ash compression modulus

We see in Figure 10 that, among the four types of fly ash, Monticello fly ash provides

highest compression modulus; in addition that strength increases with the increase of fly ash

concentration. For Rockdale Fly Ash and Wansley Fly Ash, the compression modulus of the

30

foam first decrease low concentration of fly ash. However, continued addition of fly ash, results

in increasing compression modulus. For the San Miguel Fly Ash, this has the lowest compression

modulus among the four of the fly ashes, the compressive modulus of the material first decreases

with the increase of filler concentration up to 5%, and then starts to increase up to 10%. A further

increase of the fly ash concentration seems to have a very small effect.

Fly ash is pulverized coal burning at high temperatures (1300 ~ 1500℃), then cooled,

providing spherical smooth surface particles. Depending on combustion conditions, fuel type,

and the way of ash collection, its chemical composition varies greatly. It is for this reason that

four types of fly ash have been investigated.

In Table 3 particle size of fly ash are listed.

Table 3 Particle Size of Four Types of Fly Ash

Sample d10 (um) d50 (um) d90 (um)BET Surface

Area (m2/g)

Monticello Fly Ash 4.1 60.4 212 5.4

Rockdale Fly Ash 0.8 2.1 4.7 2.7

San Miguel Fly Ash 13.9 96.9 249.6 0.8

Wansley Fly Ash 2.2 14.7 64.4 1.1

We recall that Monticello Fly Ash provides the highest compression modulus to PU foam.

Table III tell us that Monticello Fly Ash has the largest surface area of the four. Further,

Monticello Fly Ash particle size is smaller than Rockdale Fly Ash and Wansley Fly Ash. In

31

general, the size of the particle directly affects the size of the surface area. As in our materials,

the smaller the particle diameter has the greater the surface area. Monticello Fly Ash has a

relatively large particle diameter, but it has a relatively large surface area of the particles. The

main reason is that the particles contain voids, while voids increase the surface areas of the

particles. As for the San Miguel Fly Ash, it has the lowest compression modulus. Also, it has the

biggest particle size and the smallest surface area.

We see how the size of the particle surface area is one of the main factors affecting of the

compression modulus. As the filler surface area increases, the foam compression modulus also

increases. This is due to the relatively large surface area of the filler can be better combined with

the foam during the foaming process.

In Table 4 the compositions of fly ashes studied is provided.

Table 4 Components of the Four Types of Fly Ash

Content %

Fly Ashes Al2O3 SiO2 CaO Total

Monticello 19.3 66.1 14.5 100

Rockdale 26.6 61.7 11.7 100

San Miguel 18.9 74.4 6.7 100

Wansley 31.2 66.2 2.7 100

For the components of the fly ashes providing high compression modulus, namely

32

Monticello and Rockdale fly ashes, CaO content is higher than in other types of fly ash. We see

that Al2O3 and SiO2 contents are similar in the four type fly ashes, and there is not much

difference. Therefore, one cannot judge the impact on the compression modulus of these two

components.

Given the results reported above Monticello fly ash as the only one studied into the

following experiments.

Due to compression modulus of the addition of Monticello fly ash polyurethane foam

continues to grow. Therefore, subsequent experiments carried out for the foam. Increasing the

percentage of fly ash in the foam, and the production of the fly ash content of 25%, 30%, 40%,

and 60% of the samples for tested, results were as follows.

Figure 11 Monticello fly ash compression modulus

As shown, the increase in the percentage of fly ash, the compression modulus of the foam

continued to increase. When the concentration of the fly ash is increased to 40%, the pressure

33

measurement needed is more than the testing ability of the instrument, thus testing could not

continue.

4.1.2.3 Effects of Silica Nanotube or Carbon Black on the Compression Modulus of Polyurethane

Foams

Figure 12 Compression modulus of silica nanotubes and carbon black

After adding silica nanotubes and carbon black into the polyurethane foam, the foam

compression strength rapidly decline with increasing particle content.

4.1.2.3 Compression Modulus of Added 20% Particles Polyurethane Foam

In turn, result of adding 20 wt.% of several fillers, were studied. The results are displayed in

Figure 13. In the form of stress vs. Stain diagrams.

34

Figure 13 Compression test result for 20% filler concentrations

From Figure 14 we present compression modulus values for the same material as in figure

13.

Figure 14 Compression strength of polyurethane foam mix with 20 wt.% filler

We see in Figure 14 show that addition of fly ash provided the maximum compression

modulus. In other words, fly ash increases the rigidity of the polyurethane foam the most;

35

provide the highest resistance to deformation. Carbon black provides the lowest. Thus carbon

black is appropriate when soft and easily deformable foams are needed.

4.1.3 Three Points Bending

Figure 15 show the three points bending test results for 20 wt.% of particle concentration of

adding filler. Bending modulus, stress at break, strain at break and maximum stress value can be

obtained from these figure.

Figure 15 Three points bending test result of added 20% particles

The results in Figure 15 have been used to calculate the bending modulus values. The

results are displayed in Figure 16.

36

Figure 16 Flexural modulus values from the three points bending tests

Figure 16 we can see in that adding fly ash or silica particles to the foam results in higher

modulus than that of the pure polyurethane foam. In contrast, adding carbon black or silica

nanotube particles to the foam lowers the modulus. Fly ash provides the highest modulus, carbon

black the lowest.

Qualitatively flexural modulus reflects the material’s stiffness. Adding fly ash or silica

increase foam stiffness, and the foam texture becomes hard. Conversely, nanotubes or carbon

black added reduce the stiffness of the foam, and the texture becomes soft. In the case of the

addition of carbon black, the modulus is approaching 0 MPa, the foam texture becomes

extremely soft.

From Figure 17 we provide strain at break and stress at break values form bending tests.

37

Figure 17 Break strain and break stress of three points bending test

Consider Figure 17 of stress at break 20% fly ash and 20% silica does not differ much from

pure PU. The value for 20% fly ash is slightly higher than pure polyurethane; the value for silica

added is slightly lower. However, the stress at break for 20% silica nanotubes is lower.

In turn, considering the strain at break, all composites have lower value than the pure foam.

The largest decrease strain at break is by fly ash and silica. Therefore, addition of the filler

particles lowers deformation possible before material fracture.

Figure 16 shows no value for the strain at break of the carbon black. There was no fracture

during testing. Added carbon black not only increases the volume of the foam, but the texture

becomes very soft. Foam could not be broken during the test; it was not possible to obtain

quantitative data.

In Figure 18 we provide maximum stress values.

38

Figure 18 Maximum stress of three points bending test

We see in Figure 18 that maximum stress values are smaller than stress at break value. 20%

fly ash foam has a value slightly higher than pure PU foam, and 20% silica foam has slightly

lower maximum stress than the pure PU foam.

4.1.4 SEM

SEM results are presented in Figure 19.

39

Figure 19 Polyurethane rigid foam microstructure obtained by scanning electron microscopy

(SEM) analysis at 50 times magnification: (a) pure polyurethane rigid foam; (b) 20% silica; (c)

20% fly ash; (d) 20% silica nanotubes; (e) 20% carbon black;

Consider first pure PU. We see large bubbles while the distribution is very uniform. After

the addition of silica particles, bubbles become smaller but the shape becomes irregular. Adding

fly ash results in the bubbles, the bubble becomes smaller than in PU but larger than for silica,

relatively uniform. Silica nanotubes make bubbles somewhat smaller than in PU and varying

sizes, unevenly distributed. After the addition of carbon black, the foam structure has undergone

some changes. There are large bubbles, small bubble, bubbles joining to form ‘passages’, so that

40

the foam structure becomes loose.

4.1.5 Pin-on-Disk Tribometry

In Figure 20 dynamic friction values are displayed.

Figure 20 Dynamic friction of polyurethane foam

Figure 20 show that particles added result in dynamic friction increases. Silica nanotubes

provide the largest dynamic friction increase, up to about 0.65. Also, addition of silica and fly

ash fillers results in a dynamic friction increase, but compared to the silica nanotubes, the effect

is much smaller. Fly ash has little effect on the dynamic friction. Unfortunately, because carbon

black in polyurethane foam result in soft texture, it is not possible to determine the dynamic

friction.

We recall the SEM result; one sees a connection. Silica nanotubes cause the foam bubbles to

be unevenly distributed which corresponds to the highest dynamic friction. Fly ash has the

41

smaller bubbles than pure PU, and comparable dynamic friction. Thus the size of the bubble and

the size distribution are related to the dynamic friction. Smaller bubble sizes and uniform

distribution of the bubbles results in smaller dynamic friction values.

4.1.6 Thermal Conductivity Results.

Results are presented in Figure 21.

Figure 21 Thermal conductivity of polyurethane foam

In general, conductivity of the same material is related to the material structure, density,

also to external parameter such as humidity, temperature and pressure. With low moisture

content and at lower temperatures, the thermal conductivity is small. In general, the thermal

conductivity of solids is larger than for liquid, and for the liquid it is larger than for gases.

Because polyurethane rigid foam structure is closed-cell, it has good insulation properties.

As can be seen from the diagram, particles are added to increase the thermal conductivity of the

42

foam, in other words, filler particles reduce the thermal insulation properties of the foam. One

notes the larger impact of carbon black and silica on the thermal conductivity, while fly ash and

silica nanotubes provider smaller effects.

Carbon black and silica have higher thermal conductivities, while fly ash and the silica

nanotubes have relatively low conductivity values, but SNTs have a large effect on PU foams.

Due to closed-cell structure PU foams have good thermal insulators. The fillers change the

structure of the foams thus a cause for the increase in thermal conductivity. However, even with

filler particles in the sample, the thermal conductivities are still relatively low. Since the foam is

a good insulator, the thermal conductivity of the foam with added particles does not make much

impact

4.2 Thermoplastic Polyurethanes

4.2.1 Tensile Testing

The Stress vs. Strain are displayed in figure 22.

43

Figure 22 Tensile testing result for thermoplastic polyurethanes with 20% filler.

From Figure 22 one can be obtain tensile modulus, strain at break, and maximum stress

values. We will consider these parameters in turn. Tensile modulus values are presented in Figure

23.

Figure 23 Tensile modulus of thermoplastic polyurethane

Tensile modulus, also called Young's modulus, represent resistance of the material to tensile

deformation. Thus the larger the Young modulus the less easily is the material deformed.

Form the Figure 23, we see that fly ash does not change significantly. However with silica

and silica nanotubes, significant increases are seen. Carbon black provides a dramatic increase.

In Figure 24 the maximum stress values are shown with stress at break values.

44

Figure 24 Maximum stress of thermoplastic polyurethane

We see in Figure 24 that all fillers cause a decrease in the stress at break values. Apparently

the internal cohesion of the polymer is reduced.

Figure 25 Break strain of thermoplastic polyurethane

Addition of 20% fly ash, silica, silica nanotubes and carbon black cause a decrease in

elongation. Among them, the maximum impact on the elongation is carbon black; the elongation

drops to 400% from 1600%.

45

According to analysis of the polyurethane tensile test, added particles into the polyurethane

can increase the hardness of the polyurethane, but with the increase in material hardness, tensile

stretch properties of the polyurethane is gradually decreased. For example, after adding carbon

black polyurethane, which stretch the modulus increased significantly, which also shows an

increase in hardness of the material. However, the tensile stress and strain decreased, reflecting

the tensile properties of the material becomes low, and material is more easily broken.

When the filler particles are added into polyurethane, the reason of its tensile properties

deterioration may be related to the compatibility of interface between the particles and

polyurethane. Because the particles have not been surface-treated, interface compatibility

between particles is poor. In the mixing process, the particles tend to aggregate and cannot be

uniformly mixed with the polyurethane.

Interface compatibility of particles is one of the reasons than can cause tensile performance

degradation. The material mixing and molding are performed at high temperatures, what might

cause structural change.

4.2.2 Pin-on-Disk Tribometry

Dynamic friction values are presented in Figure 26

46

Figure 26 Dynamic friction of thermoplastic polyurethane

Dynamic friction is related to the surface roughness. The lower the dynamic friction of the

material implies in a lower surface roughness.

According to Figure 26, the dynamic friction of thermoplastic PU with added particles is

lower than the pure thermoplastic polyurethane sample. This apparently shows that the particles

reduce the surface roughness of the polyurethane.

In conjunction with Figure 23, the tensile modulus values are approximately, inversely

proportional to the tensile modulus and the dynamic friction. The larger the tensile modulus of

the material, the dynamic friction will be smaller. The carbon black containing thermoplastic

polyurethane has the maximum tensile modulus. Its dynamic friction is also the smallest. We

know that the tensile modulus relates to the stiffness of the material, so there is a relation

between stiffness and dynamic friction. The higher the dynamic friction is, the smaller the

stiffness.

47

CHAPTER 5

CONCLUSIONS

In this study, the use of silica, fly ash, silica nanotubes and carbon black were used to

modify polyurethane foams and thermoplastic polyurethane. In situ polymerization was used for

polyurethane foams, and blending method was used for thermoplastic polyurethane. Mechanical

properties of the samples were determined and surface morphologies observed. The following

conclusions can be formulated:

(1) Effects of filler particles: mechanical tests, and surface morphology observations show

that the addition of silica makes foam bubbles smaller, resulting in an increase in stiffness of the

material; the compression modulus increases, deformation is more difficult. However, since the

uniformity of the bubbles is reduced, the result is increased dynamic friction of the material. Fly

ash added to the foam makes bubbles smaller providing good uniformity of cells sizes. Effects of

adding silica nanotubes are: unequal bubble sizes and uneven spatial distribution of bubbles,

resulting in decreased strength of the material, thus the dynamic friction increases. As for carbon

black, there is a generation of more bubbles during the foaming process affecting the foam

structure. Therefore, the material becomes soft; one obtains flexible polyurethane foam.

(2) Effects of filler particles on thermoplastic polyurethane: the tensile properties are

reduced. This phenomenon may be due to agglomeration of particles occurs during the mixing

process, the particles cannot be uniformly dispersed in the thermoplastic polyurethane.

48

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