Development of High Strength Microcellular

DEVELOPMENT OF HIGH STRENGTH MICROCELLULAR

FOAMS USING POLYETHER BLOCK AMIDE

…………………..

KUN LIN

…………………..

M.Eng. PROJECT REPORT

DEPARTMENT OF MECHANICAL AND INDUSTRIAL ENGINEERING

UNIVERSITY OF TORONTO

2010

DEVELOPMENT OF HIGH STRENGTH MICROCELLULAR

FOAMS USING POLYETHER BLOCK AMIDE

KUN LIN

A thesis submitted in conformity with the requirements for the degree

of Masters of Engineering Graduate Department of Mechanical and

Industrial Engineering University of Toronto

Development of High Strength Microcellular Foams Using Polyether Block Amide

M.Eng. 2010-09-15

Kun Lin

Department of Mechanical & Industrial Engineering

University of Toronto

Abstract

This report presents a successful development of batch foaming techniques of the engineering elastomer. The polyether block amide (PEBAX) was investigated as an engineering elastomer by using batch foaming techniques. The Pebax provide a unique combination of mechanical and chemical properties. Understanding the effect of the different parameter in batch foaming process allows obtaining the high quality foamed product of the engineering elastomer.

Temperature has been considered as an important parameter in the batch foaming process.

It was shown that the density of foamed product was decreasing by the temperature increasing under its melting temperature. Both temperature and pressure have to reach the minimum requirement to obtain the fine foamed product. As an experiment result, it indicates that there is an optimal portfolio of foaming parameter for the different Pebax resin.

Acknowledgements

I would like to thank my supervisor Professor Chul B. Park, who provided me this

opportunity and resources to complete this research project. I would like to thank my co-

supervisor Nan Chen for his guidance, supports and encouragements during my research.

I would also like to thank my colleagues, Anson Wang, Hasan, Hongtao Zhang, Jing

Wang, Raymond Chu, Wentao Zhai, in the Microcellular Plastic Manufacturing

Laboratory and Reza Rizvi in the SAPL Laboratory.

Moreover, my thanks also to Donna Liu for her assistance with departmental regulations and report format.

Finally, I would also like to thank my family for giving me their love, patience, support and encouragement throughout the project. It would not have been possible to finish my study. To all people mentioned above and those I have not acknowledged, thank you.

Table of Contents

1. Introduction ...... 1

1.1 Purpose of Project ...... 1

1.2 Technology of Foaming ...... 2

1.3 Microcellular Foaming ...... 2

1.4 Batch Foaming Process ...... 3

2. Literature review ...... 5

2.1 Blowing Agents ...... 5

2.2 Cell Nucleation ...... 6

2.3 Cell growth and stabilization ...... 9

2.4 Density and Cell Density ...... 9

2.5 Engineering Thermoplastic Elastomers ...... 10

2.5.1 The Pebax Polymer (ether-block-amide) ...... 10

2.5.2 The Mechanical Properties of Pebax ...... 11

2.5.3 Elastic Properties ...... 13

2.5.4 Fatigue Resistance ...... 14

2.5.5 Resistance of the Chemicals ...... 14

2.6 The Application of Pebax ...... 14

3. Experimental Equipment ...... 15

3.1 DSM Compounder ...... 15

3.2 Carver Bench Press Model 2697 ...... 16

3.3 Drying Oven ...... 16

3.4 Coating Equipment ...... 17

3.5 Rheometric Scientific Rheometer ...... 17

3.6 Softness Tester ...... 17

3.7 Scanning Electron Microscope (SEM) ...... 17

4 Experiments and Results ...... 19

4.1 Materials ...... 19

4.2 Experimental Process ...... 19

4.3 Experimental Results and Discussion ...... 20

5. Summary and Conclusion ...... 51

6. Recommendations for Future Work: ...... 53

List of Tables

Table 4.10: The basic information of raw Pebax materials ...... 19

Table 4.30: Softness of the foamed Pebax at its best foaming temperature ...... 22

Table 5.10 Foaming behaviour of experiment materials at given temperature ...... 51

List of Figures

Figure 3.10: DSM Compounder ...... 15

Figure 3.20: Carver Bench Press Model 2697 ...... 16

Figure 3.80: Schematic of batch foaming simulation system ...... 18

Figure 4.30: the Density of Pebax 3533, 4033 and 7233 ...... 23

Figure 4.31: The Expansion Ratio of Pebax 3533, 4033 and 7233 ...... 24

Figure 4.32: Pebax 3533 Cell Density ...... 25

Figure 4.33: Pebax 4033 Cell Density ...... 25

Figure 4.34: Pebax 7233 Cell Density ...... 26

Figure 4.35: the Density of 30%, 50%, 70%Pebax 7233 ...... 27

Figure 4.36: the Expansion Ratio of 30%, 50%, 70%Pebax 7233 ...... 28

Figure 4.37: the Cell Density of 30%, 50%, 70% Pebax 7233 ...... 28

Figure 4.38: Pebax 3533 Viscosity Feature ...... 29

Figure 4.39: Pebax 4033 Viscosity Feature ...... 29

Figure 4.40: Pebax 7233 Viscosity Feature ...... 30

Figure 4.41: Pebax 3533 Extensional Viscosity at 130 oC ...... 31

Figure 4.42: Pebax 4033 Extensional Viscosity at 160 °C ...... 31

Figure 4.43: Pebax 7233 Extensional Viscosity at 160 °C ...... 32

Figure 4.44: 30% Pebax 7233, 70% Pebax 3533 Extensional Viscosity at 130 °C ...... 32

Figure 4.45: 50% Pebax 7233, 50%Pebax 3533 Extensional Viscosity at 130 °C ...... 33

Figure 4.46: 70% Pebax 7233, 30% Pebax 3533 Extensional Viscosity at 130 °C ...... 33

Figure 4.47: SEM (Pebax 3533 at 80 °C, 2500PSI, 2hours) ...... 34

Figure 4.48: SEM (Pebax 3533 at 100 °C, 2500PSI, 2hours) ...... 34

Figure 4.49: SEM (Pebax 3533 at 120 °C, 2500PSI, 2hours) ...... 35

Figure 4.50: SEM (Pebax 3533 at 140 °C, 2500PSI, 2hours) ...... 35

Figure 4.51: SEM (30%,70% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours) ...... 36

Figure 4.52: SEM (50%,50% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours) ...... 36

Figure 4.53: SEM (70%, 30% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours) ...... 37

Figure 4.54: SEM (Pebax 4033 at 60 °C, 2500PSI, 2hours) ...... 37

Figure 4.55: SEM (30%, 70% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours) ...... 38

Figure 4.56: SEM (50%, 50% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours) ...... 38

Figure 4.57: SEM (70%, 30% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours) ...... 39

Figure 4.58: SEM (Pebax 4033 at 80 °C, 2500PSI, 2hours) ...... 39

Figure 4.59: SEM (30%, 70% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours) ...... 40

Figure 4.60: SEM (50%, 50% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours) ...... 40

Figure 4.61: SEM (70%, 30% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours) ...... 41

Figure 4.62: SEM (Pebax 4033 at 100 °C, 2500PSI, 2hours) ...... 41

Figure 4.63: SEM (30%, 70% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours) ...... 42

Figure 4.64: SEM (50%, 50% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours) ...... 42

Figure 4.65: SEM (70%, 30% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours) ...... 43

Figure 4.66: SEM (Pebax 4033 at 120 °C, 2500PSI, 2hours) ...... 43

Figure 4.67: SEM (Pebax 4033 at 120 °C, 2500PSI, 2hours, 2000X) ...... 44

Figure 4.68: SEM (30%, 70% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours) ...... 44

Figure 4.69: SEM (50%, 50% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours) ...... 45

Figure 4.70: SEM (70%, 30% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours) ...... 45

Figure 4.71: SEM (Pebax 4033 at 140 °C, 2500PSI, 2hours) ...... 46

Figure 4.72: SEM (Pebax 4033 at 140 °C, 2500PSI, 2hours, 1000X) ...... 46

Figure 4.73: SEM (70%, 30% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours) ...... 47

Figure 4.74: SEM (50%, 50% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours) ...... 47

Figure 4.75: SEM (50%, 50% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours, 1000X) ... 48

Figure 4.76: SEM (Pebax 4033 at 160 °C, 2500PSI, 2hours) ...... 48

Figure 4.87: Pebax 3533 Foaming Video Image (At 120 °C) ...... 49

Figure 4.88: Pebax 4033 Foaming Video Image (At 120°C) ...... 50

Development of High Strength Microcellular Foams Using Polyether

Block Amide

1. Introduction

1.1 Purpose of Project

The thermoplastic elastomers (TPE) have become a commercial product 50 years ago.

During the past half century, they are widely used in industry for many purposes. The demands of TPEs keep growing at about 9% per year because TPEs show both advantages of elastic materials and plastic materials. Polyether block amide is a type of thermoplastic elastomer. It also has been known as the trade name of PEBAX. It is a block copolymer which offers the widest range of performances among the thermoplastic elastomers.

The remarkable performances of PEBAX make them become an ideal material for the sports equipment and many mechanical parts. However, there is no any foamed PEBAX available commercially. It is believe that the high strength microcellular foams of

PEBAX will decrease the density without corresponding loss of properties, so that it can expect to reduce the weight and save the raw materials for the product. This provides the basic motivation of this project, which is to develop a technology for producing the foamed PEBAX.

The objective of this project is to develop a fundamental understanding of the foaming for the 33 series PEBAX.

1.2 Technology of Foaming

Foam is a material, and foaming is a phenomenon. [1] The foamed materials can be

converted from the raw materials by the foaming phenomenon. The foamed product

contains porous structures as a gas-solid composite.

Foamed product provides many advantages over the traditional materials. Foams are very cost effective and among other attributes have unique insulating properties, impact resistance characteristics, buoyancy, and outstanding strength to weight ratio [2].

Therefore, the foamed polymers are widely used in the industry field today.

In general, there are two main foaming technologies: physical foaming and chemical foaming. For both foaming method, they include three steps within the polymer: implementation of gas, expansion of gas, and stabilization of the polymer. Competing mechanisms appear to make the kinetic process more complex when surrounding conditions change [1].

1.3 Microcellular Foaming

The technology of microcellular structure in a polymer was invented by Suh et al at the

MIT (Massachusetts Institute of Technology in the early 1980’s [3]. This concept of the

Microcellular structure is developed from the idea that a large number micro bubbles can reduce the weight and the consumption of the raw materials without the mechanical properties losing.

Microcellular foams provide more benefits than the conventional foams since they have higher cell density and uniform cell size distribution. The mechanism for producing a very fine cell structure is that a gas has dissolved into the polymer matrix and then

2 inducing a thermodynamic instability nucleates a large number of bubbles. This instability can be created by rapidly dropping the pressures. Finally, the growth of the nucleated bubbles is controlled and bubbles are ultimately stabilized [3,4].

The microcellular foamed product was initially created in the batch foaming process. And then, it has been developed to the extrusion and injection molding system.

1.4 Batch Foaming Process

Microcellular polymers were first produced in a batch process [5]. In this process, a polymer sample is placed in a high pressure chamber connected to a gas reservoir. The gas can be either nitrogen (N2) or carbon dioxide (CO2). The polymer sample absorbs the gas and, after a sufficient time, reaches a saturation state. The amount of gas dissolved in the polymer plays an important role in the final foam quality. The Flory-Huggins equation is a good guideline for determining how much gas can be implemented in the polymer [1]. When the sample is fully saturated with the gas, the pressure is rapidly decreased to cause a sudden drop in the solubility of the gas in the polymer. This initiates a thermodynamic instability, which drives nucleation of billions of microcells. These microcells cannot expand significantly, as a large amount of gas is lost during cell growth.

The foaming of the sample in the batch process is initiated by heating through the surface of the sample. Since the temperature of the foam skin is always the highest during the foaming process, the gas can easily escape through the hot skin to the atmosphere.

Therefore, the sample expands to the presence of a large number of nuclei generated in the polymer matrix.

In a batch process, cell nucleation is governed mainly by the saturation pressure (or pressure drop rate), and cell growth is governed by the heating temperature and time.

Therefore, the number of nucleated cells and the amount of expansion can be independently controlled. It must be noted that in a batch process, the foaming temperature is in general chosen to be the lowest to make the cell growth step easily controllable [6]. When the nuclei are generated, their growth is retarded due to the high stiffness of the polymer matrix at the low temperature. However, this prevents the degradation of the foam product due to coalescence of the cells. Modulating the temperature and the time of exposure to heat can control growth of cells.

The major drawback of the batch foaming process is that a very long time has been required for saturation of gas in the polymer. This is the limit of the low rate gas diffusion into the polymer at room temperature. In some cases, the rate of gas diffusion can be increased at higher temperature. For example, the diffusivity of CO2 in polystyrene at room temperature is 6x10-8 cm2/s [7].

2. Literature review

2.1 Blowing Agents

The blowing agent is a substance which produces a cellular structure in the polymer materials. Generally, the gaseous phase of the foamed composites derives from the blowing agents in the foam manufacturing process. The blowing agent can be a gas, liquid, or some chemical compound. All types of the blowing agent will expand or release the gas when the environment changing. For instance, as the blowing agent, gases will expand when pressure is released, liquid develops cells when it changes to gases, and chemical agents will decompose or react to generate the gases.

Besides the polymer materials, the blowing agent plays another important role in the polymer foaming industry. The blowing agent is the core factor controlling the density of the foamed polymer. And also, the microstructure and morphology of the foamed polymer will be affected by the factor of the blowing agent. In some cases, they decide the commercial performance in the foamed product. In many others, such as packaging the cushioning, the cellular structure of the foam is such that the blowing agent escapes almost immediately after the foam is formed. In such cases, referred to as open cell foam, though the cellular structure and morphology imprint of the blowing agent impact of the performance of the foam [8].

Generally, the blowing agent (BA) includes the physical blowing agent (PBA) and chemical blowing agent (CBA). The CBA is normally a powder or solid at room environment and pressure and undergo a chemical transformation when generating gases.

The PBA is generally a liquid or gas at room environment; undergo either a reversible change of state or expansion.

The physical blowing agent provides gas for the expansion of polymers by undergoing a

physical environment changing. These changes may include volatilization of the liquid or

the release of the compressed gas to the standard pressure after it has been dissolved into

the polymer. As the gaseous blowing agents, the common gases include carbon dioxide and nitrogen. The gaseous blowing agent can be used in the generation of all types of foamed polymer, such as thermoplastics. The PBA is almost the only blowing agent used

when the foam density is very low. And comparing chemical blowing agent, the physical

blowing agent has lower cost and environment friendly, but in some cases, it may need

special equipment.

Many factors have to be considered to select the correct physical blowing agent. For

instance, solubility in raw material, compatibility with materials of construction, boiling

point, molecular weight, vapour pressure in the temperature range, heat of vaporization,

pricing and environmental concern, etc..

2.2 Cell Nucleation

The generation of tiny bubbles in a polymer system is called nucleation of bubbles and is

part of the process used to make polymeric foams. There are several different nucleation

mechanisms, such as homogeneous, heterogeneous, mixed-mode, shear-induced, and

void nucleation theories [1]. After cell nucleation, they grow due to the diffusion of

excess gas. The viscosity of the polymer, the gas concentration, the foaming temperature,

and the amount of nucleating agent and its nature are some of the variables that control

the foam growth process. And foaming dynamics are very complicated [1].

In the homogeneous nucleation process, the bubbles are generated from a single

homogeneous phase containing no impurity or dirt. However, this process is rare since

the additives have been added to the resins for various reasons in most cases. If tiny

particles are present in the liquid, and if they assist in the formation of cells, then the

process is called heterogeneous nucleation. In this process, the nucleation takes place at a solid and liquid interface [1].

Microcellular nucleation can be easily promoted in a rapid-pressure-drop nucleation nozzle [9, 10]. The rapid drop in pressure causes a rapid drop in the solubility of gas in the polymer melt. This induces a thermodynamic instability, as in the case of batch process which drives nucleation of a large number of microcells. The generated cells continue to grow at the die exit. The final foam structure is determined by the conditions under which the three steps of the process are performed and the condition of the extrusion in terms of its melt temperature and surface temperature [11].

In microcellular processing, nucleation is induced by a thermodynamic instability, which

is achieved by using a rapid pressure drop device. Colton and Suh [12, 13] developed a

model of bubble nucleation rate:

Δ = 0 0 − 𝐺𝐺 𝑘𝑘𝑘𝑘 Where = rate of nucleation, #/cm3s,𝑁𝑁 ̇ 𝑓𝑓 𝐶𝐶 𝑒𝑒 ̇ 𝑁𝑁0 = frequency factor of gas molecules joining the nucleus, 1/s,

3 𝑓𝑓0 = concentration of gas molecules in solution, #/m ,

Δ𝐶𝐶 = Gibbs free energy of bubble nucleation, J,

k𝐺𝐺 = Boltzman constant, J/K, and

T = temperature, K.

Therefore, increasing the amount of gases in the polymer can generate more cells. When the saturation pressure increases, the nucleation rate will be higher. In addition, another key factor which affects the nucleation rate is the pressure drop rate. The investigation of

Park explained the pressure drop rate effect by “nucleation/cell growth competition” model for the dissolved gas [10, 14]. If the pressure drop rate is high, there is relatively less time for the gas to diffuse into the already nucleated cells, and the gas tends to nucleate an additional cell. Therefore, a greater number of nuclei can be obtained by inducing a higher-pressure drop rate. Under the higher pressure drop rate, the nucleated cells do not have a chance to grow. Therefore, more gases are utilized for cell nucleation and less are used for cell growing. As this result, the foams with high cell density or microcellular foams can be generated by high pressure drop rate. In addition, Chen et al

[15, 16] investigated the effect of shear stress on cell nucleation density: the amount of gases required for sufficient nucleation is significantly reduced by introducing shear stress.

In the heterogeneous nucleation process, it was found that foams with some additives have higher cell density [17, 18]. Chen et al [19] investigated the mechanism of heterogeneous nucleation with filled polymers. The hypothesis of this process is that the un-dissolve gas between the polymer and additives creates cells when the system pressure drops during the foaming process. In addition, during mixing the polymer may not be able to fill the cracks or defects on the additive surface and gaps between two phases due to completely the surface tension.

2.3 Cell growth and stabilization

Cell growth is next important step after cells are nucleated in the formation of

microcellular foams. Since the pressure inside the cells is greater than the surrounding

pressure, cells tend to grow in order to decrease the pressure difference between the

inside and outside [34]. The cell growth process can be affected by viscosity, the diffusion coefficient, the gas concentration and the number of nucleated cells, etc. The factor of temperature is an important factor which can affect the amount of growth.

2.4 Density and Cell Density

The density of a foamed material is an important characteristic parameter for the foamed

polymers. It can be measured in accordance with ISO 1183-1987. The weight of the

sample was measured in the atmosphere and distilled water by using an analytical

balance (METTLER TOLEDO AB204) with an accuracy of 0.1 mg.

The density (D) of the given sample was calculated by the following formula:

D= (Mgas/Mwater)*ρwater

Where, ρwater is the density of the distilled water at room temperature; Mgas and Mwater

represent the mass of sample in atmosphere and in the distilled water. The Expansion

Ratio can be calculated by the density of the raw (un-foamed) sample and the density of

the foamed sample.

E.R. = ρ/ρf

The cell density is evaluated by the sample surface morphology which can be obtained with a scanning electron microscope (SEM). The foamed sample needs to be prepared well for the SEM image. The foamed samples were fractured in the liquid nitrogen, coated with an approximately 10 nm thick layer of gold on the fractured surface, and then, observed the morphology of the fractured surface with the scanning electron microscope

(SEM, JEOL JSM-6060).

The cell diameters and cell density were characterized using the method of Kumar and

Suh. [35]. Cell diameter is the average of all the cells in the SEM micrograph. The cell density (Nf), which is the number of the cells per cubic centimetre of the foam, can be

calculated as,

2 3/2 Nf = (nM /A)

Where, n is the number of the cells that can be seen on the SEM micrograph, A is the

area of the micrograph in unit cm2, and M is the magnification factor.

2.5 Engineering Thermoplastic Elastomers

Foamed thermoplastic elastomers have been employed in the auto industry. The

application includes exterior and interior assembly of the car, wires, cables, film products,

medical products, adhesives and sport relative product. The engineering thermoplastic

elastomers have a unique combination of the flexibility and toughness of synthetic rubber

with the process ability of the plastics [21-23]

2.5.1 The Pebax Polymer (ether-block-amide)

Polyether block amide is a type of thermoplastic elastomer. It also has been known as the trade name of PEBAX. It is a block copolymer which offers the widest range of

performances among the thermoplastic elastomers. Pebax is plasticize-free thermoplastic

elastomers belonging to the engineering polymer family. It is easy to process by injection

molding and profile or film extrusion. Pebax can be easily melt blended with other

polymers. The unique chemistry allows Pebax to achieve a wide range of physical and

mechanical properties by varying the monomeric block types and ratios.

The Pebax is a new member of the engineering thermoplastic elastomers family [24-26].

The normal formula is (A-B)n, and it combines linear chains of rigid polyamide segments

interspaced with flexible polyether segments [27]. The hard amide block provides the

strong mechanical strength and the soft ether block is shown the rubbery properties [28].

The Pebax, as one of the engineering thermoplastic elastomers, is featured with the edge

advantages in better mechanical properties and wider application temperature than the

normal thermoplastic elastomers [20].

2.5.2 The Mechanical Properties of Pebax

The grades 33 series of Pebax are composed of polyamide 12 segments (PA12) and polytetramethylene glycol segments (PTMG), leading to a very low material density when compared to the other thermoplastic elastomers. Generally, the density of grade 33 series Pebax is around 1.01g/cm3 by ISO 1183.

The basic mechanical properties have been described on the Pebax website [29]. The raw

Pebax materials have been shown as the good mechanical properties and also in the large

temperature range. It includes the range of hardness, range of flexural modulus and the

tensile strength.

Firstly, hardness can be defined as the resistance of a material to an indentation deformation. The materials have better resistance of deformation if they have the higher

hardness. For the thermoplastic materials, the hardness is defined as the Shore D

reference. The maximum hardness of Pebax Grade 33 Series is 69 Shore D Hardness

(Pebax 7233) [29].

The Shore A reference is used for elastomers and low modulus materials. The test can determine the penetration depth in the sample under the standard load and fixed time. For the Pebax materials, the 15 seconds is the typical time lap. The standard procedure is ISO

868 which is equivalent to ASTM standard D2240 in this measurement.

Secondly, the flexural resistance can be measured by the three point method. A force is applied in the middle of the sample which is supported on the two ends. The force will lead the three point loading. This experiment combines compression, tensile and shear solicitations in the sample material. The flexural stress versus strain curve will be plotted to determine the flexural modulus. The flexural curve will be obtained per standard ISO

178. For the Pebax grade 33 series resin, the constraint (MPa) will increase by the deformation rising.

The flexural modulus value test is normally performed by using the standard ISO 178 or

the standard ASTM-D-790. All the value is expressed in MPa. The sample geometries are

80x10x4 mm3 bars by using the standard ISO 178 [29]. The value of the Pebax 7233 is

greater than other Grade 33 series Pebax resin in Flexural Modulus.

FLEXURAL MODULUS (MPa)

Materials ASTM-D-790 ISO 178

Pebax 3533 20 21

Pebax 4033 81 77

Pebax 7233 518 513

Table 2.52 Flexural Modulus of Pebax grade 33 series resin

These values indicate the flexural modulus range which offered by the Pebax 33 series.

Another important property is tensile strength. The tensile stress-strain curves can be

obtained in the below by using the standard ASTM-D-638, after a standard conditioning of 14 days at 23oC and 50% relative humidity. The break values of stress and strain can

be obtained from the tensile tests by using standard ISO 527-1-BA (using a strain rate of

200 mm/min) or the standard ASTM-D-638 (using a strain rate of 500 mm/min). The constraint value of Pebax 7233 is higher than Pebax 4033 which is higher than the Pebax

3533.

Tensile Strength

ASTM-D-638 type IV ISO 527 1 BA Materials Strain % Stress (Mpa) Strain % Stress (MPa)

Pebax 3533 692 27 615 26

Pebax 4033 466 30 408 26

Pebax 7233 357 45 319 54

Table 2.53 Tensile Strength of Pebax grade 33 series

2.5.3 Elastic Properties

The elastic behaviour can be defined as the ability of the material recovering its initial shape after the deformation. The remanent deformation can be measured under tensile solicitation. It is typically performed at 23oC under ASTM-D-412 standard, and the

samples have been conditioned for 15 days at 23oC and 50% relative humidity. For the

Pebax grade 33 series, the Pebax 7233 has the best Elastic Properties, and Pebax 4033 is

better than Pebax 3533.

2.5.4 Fatigue Resistance

The fatigue property can be defined as the behaviour of the material under cyclic or

repeated solicitation with the random intensity. As a result, the Pebax is poorly sensitive to degradation under the fatigue tests [29]. The Ross Flex test has been used to determine

the fatigue resistance for the Pebax materials. The test can be performed at various

temperatures. Generally, the Pebax materials offer an excellent resistance to alternate

flexural solicitations at room temperature. The standard ASTM-D-1052 can be used to guide this test.

2.5.5 Resistance of the Chemicals

The unique chemistry of Pebax provides its excellent properties. In general, the Pebax product has a good resistance to the chemicals. The relative information of chemical resistance to the common solvents can be reached at the company website [29].

2.6 The Application of Pebax

The Pebax is widely used in the industry, such as medical product, sport equipment, power transmission and film product, etc. The Grade 33 series Pebax can be used in many places in sport equipment and power transmission field due to the excellent combination with maximum strength and flexibility.

For the hydrophilic grades of Pebax, a thin film on the substrate can provide an excellent permeability to the moisture vapour with barrier layer to water and bacteria. Many paper investigated in PEBA membranes in gas sweetening or separation [30, 31]. As an experiment result, the PEBA film on the porous ceramic has a good performance for the separation of CO2/N2 binary gas mixture.

3. Experimental Equipment

3.1 DSM Compounder

The DSM compounder as shown in Figure 3.10 consists of a twin screw compounder

with a few grams of material. This DSM compounder can only process batch volumes up

to 15 ml. Maximum axial force is up to 8000N; the screw speed is continuously variable

1-250 RPM. Overall dimensions are 103x73x42 cm, weight is about 150Kg, and the drive is DC control with 900 Watt. The dedicated software enables the operator to control the instrument the parameters and to collect the data to analyse a processing cycle.

Figure 3.10: DSM Compounder

3.2 Carver Bench Press Model 2697

High temperature Carver bench press, model 2697 as shown in Figure 3.20 consists of

two flat heating plates (one fixed and one moveable with a hydraulic pump) with attached

thermocouples, one hydraulic pump, a pressure measuring gauge and a manual lever to

operate the hydraulic pump.

Figure 3.20: Carver Bench Press Model 2697

3.3 Drying Oven

Oven drying of the Pebax material is the most common used method for preparation of

Pebax in laboratory, since its water absorption is around 1.2% in 24 hours period. Napco

E series, model 5851 vacuum oven was used for these experiments. For most Pebax materials, drying has been performed at 75oC in 6 hours.

3.4 Coating Equipment

Mini Sputter Coater model SC7620 was used to perform coating on the sample before

taking SEM photos. This equipment includes: basic unit, Gold/Palladium target and a

start-up kit. A vacuum pump and an argon gas cylinder are attached to this equipment for

supplements.

3.5 Rheometric Scientific Rheometer

The Rheometer has been used to measure the liquid, suspension or slurry flows in

response to the given forces. It is generally a laboratory device, and used for some fluids which cannot be defined by a single value of the viscosity. Therefore, more parameters are required to measure these fluids. The results are called the rheology of the fluid.

3.6 Softness Tester

The indentation resistance of elastomeric or soft plastic materials are based on the depth of penetration of a conical indenter. The standard ASTM-D-2240 can be used to guide this test. The range of hardness values is from 0 (full penetration) to 100 (no penetration).

3.7 Scanning Electron Microscope (SEM)

The scanning electron microscope is one of the electron microscopes that can show the morphology of the sample surface. The SEM can image the sample surface by scanning it with a high energy beam of electrons in a raster scan pattern. The sample will generate the signals while the electrons interact with the atoms. These signals include secondary electrons, back-scattered electrons, characteristic X-rays, light, specimen current and transmitted electrons. The certain equipment, however, cannot detect all above signals.

Normally, the detectors collect the signal which is from the interactions of the electron

beam with atoms near the sample surface. The SEM can provide the high-resolution

images of the sample surface in the most standard detection mode.

3.8 Batch Foaming Simulation system

The batch foaming simulation system can be established based on the combination of the high-pressure chamber and the solenoid valve. The simulation system consists of a high- pressure, high-temperature chamber, a pressure-drop rate-control system, a data acquisition system for pressure measurement, a gas supplier (Gas tank, syringe pump, and valves), an objective lens, a light source, and a high-speed CMOS camera. The schematic of the equipment is shown in Figure 3.80 [36].

Figure 3.80: Schematic of batch foaming simulation system

4 Experiments and Results

4.1 Materials

The following experiments have been carried out by using Pebax 3533, Pebax 4033,

Pebax 7233 and Carbon Dioxide.

Name Materials Melting Temperature Density

Raw Material 1 Pebax 3533 SA01 109-154 °C 1.01 g/cm3

Raw Material 2 Pebax 4033 SN01 160°C 1.01 g/cm3

Raw Material 3 Pebax 7233 SN01 176°C 1.02 g/cm3

Table 4.10: The basic information of raw Pebax materials

4.2 Experimental Process

The overall experimental process is quite detailed. Firstly, the Pebax resin is dried in an

oven at 75oC for more than 6 hours to remove the moisture contents. Secondly, the Pebax

resin has been put into the DSM compounder to mix and blend over its melting

temperature. After 10 minutes the whole blend is taken out of the DSM compounder.

Thirdly, the pre-mixed Pebax resin has been shaped in the cavity of the mold by using

Carver Bench Press Model. The sample needs to be hold in the Carver Bench Press for at

least 10 minutes at 10 degree above its melting temperature.

The Pebax resin is tested in DSC to verify the application temperature range. A

Rheometer is applied to measure the viscosity and extensional viscosity of the certain

Pebax. The Figure 4.20 is a detailed description for the batch foaming procedure. The

shaped sample has been put into a closed space at given temperature and pressure, and

then hold for 2 hours. After 2 hours, the space has been opened quickly, which triggers the foaming. A foamed product is obtained and cooled in the room environment.

4.3 Experimental Results and Discussion

By the above experimental steps, the foamed Pebax samples have been obtained. For each raw material (Pebax 3533, Pebax 4033 or Pebax 7233), the best foam can be only obtained at a certain temperature when the pressure and time is fixed. In general, it is easy to obtain a fine-foamed sample by increasing the holding and foaming temperature.

In this experiment, the testing pressure and time period have been fixed to 2500PSI and 2 hours.

There is a maximum foaming temperature for each Pebax material in the batch foaming procedure. The maximum temperature has to below its melting temperature.

At the beginning of this experiment, the pressure has been hold at room temperature, and then foamed at the different temperature. It is shown that the fine-foam is hard to obtain even if the pressure has been hold for 24 hours. As this result, the above three raw materials (Pebax 3533, Pebax 4033 and Pebax 7233) have a very low penetration rate at the room temperature. It is not good enough to do the batch foaming test at room temperature.

By the following experiment, the temperature control has been added into the pressure holding period. The fine-foamed samples were obtained when the holding and foaming temperature was increased to 60oC for both Pebax 3533 and Pebax 4033. For the Pebax

7233, the penetration rate is too low to obtain a fine-foamed sample until 140oC.

Finally, the Pebax 3533 and Pebax 7233 have been mixed at three different ratios. The

first mixed ratio is 30% Pebax 3533 with 70% Pebax 7233. The second mixed ratio is 70%

Pebax 3533 with 30% Pebax 7233. The third one is 50% for each. Each of them shows

the mixed feature. For example, all three mixed sample can obtain the foam from 60oC.

The foamed samples were characterized by using a scanning electron microscope (SEM,

JEOL JSM-6060) to evaluate the morphology. The samples were dipped in liquid

nitrogen and then fractured to expose the cellular morphology and then the fractured surface was sputter-coated with gold. The microstructure was investigated by SEM.

v The expansion ratio ( e ) was calculated as the ratio of the bulk density of pure polymer

ρ ρ ( p ) to the bulk density of foamed sample ( f ) as shown in Equation 1 [32].

ρ v = p e ρ f (1)

× The number of cells (nc) could be defined in the SEM pictures in an area (l l ). Cell

density Nf was calculated as the number of cells per unit volume with respect to the un-

foamed polymer (Eq. 2) [33].

n = c 3/ 2 × 12 × n ( 2 ) 10 ve l (2)

Cell Density Nf was calculated as the number of cells per unit volume with respect to the

un-foamed polymer (Eq. 2) [33].

The softness of the foamed Pebax product is below:

Softness of the foamed Pebax at its best foaming temperature

Materials Foaming Temperature Softness

Pebax 3533 100oC 89

Pebax 4033 120oC 95

Pebax 7233 160oC 97

30% Pebax 7233 120°C 92

70% Pebax 7233 140°C 98

50% Pebax 7233 120°C 96

Table 4.30: Softness of the foamed Pebax at its best foaming temperature

Softness

Softness 40

0 Pebax 3533 Pebax 4033 Pebax 7233 30% Pebax 7233 50% Pebax 7233 70% Pebax 7233 Materials

Figure 4.29 Softness of the foamed Pebax

Pebax 3533 1.5 Pebax 4033 Pebax 7233

1.2 ) 3 0.9

0.6 Density (g/cm

0.3

0.0 40 80 120 160 Temperature(oC)

Figure 4.30: the Density of Pebax 3533, 4033 and 7233

The above graph shows the density change by the temperature increasing. For the Pebax

3533 and Pebax 4033, the optimal batch foaming temperature was found. The Pebax

7233 was hard to get fine foam at batch foaming condition since it is harder than other

Pebax Grade 33 series resin. The foamed Pebax 7233 can be obtained at 160°C, and this temperature is close to its melting temperature.

Pebax 3533 5 Pebax 4033 Pebax 7233

2 Expansion ratio

40 80 120 160 Temperature(oC)

Figure 4.31: The Expansion Ratio of Pebax 3533, 4033 and 7233

Pebax 3533

108 ) 3

107 Cell Density( /cm

106

80 120 160 Temperature(oC)

Figure 4.32: Pebax 3533 Cell Density

Pebax 4033

1012

1011 ) 3

1010

109 Cell Density ( /cm 108

107

80 120 160 Temperature(oC)

Figure 4.33: Pebax 4033 Cell Density

Pebax 7233

3.6x106

3.5x106

) 6 3 3.4x10

3.3x106

3.2x106 Cell Density ( /cm

3.1x106

3x106 150 160 170 Temperature(oC)

Figure 4.34: Pebax 7233 Cell Density

Figure 4.34 shows the cell density of Pebax 7233 at 160°C. There was only one value from the experiment since the fine foamed Pebax 7233 can be only obtained at 160°C in the batch foaming experiment.

After the experiment of the pure Pebax Grade 33 series, another batch foaming experiment has been establish by using the mixture of Pebax 7233 and 3533. (30%, 70%

Pebax 7233 and 3533; 50%, 50% Pebax 7233 and 3533; 70%, 30% Pebax 7233 and 3533)

30% Pebax 7233 50% Pebax 7233 70% Pebax 7233

1.0 ) 3 0.8

Density (g/cm 0.6

0.4 80 120 160 Temperature(oC)

Figure 4.35: the Density of 30%, 50%, 70%Pebax 7233

30% Pebax 7233 5.0 50% Pebax 7233 70% Pebax 7233 4.5

4.0

3.5

3.0

2.5

Expansion ratio 2.0

1.5

1.0

40 80 120 160 Temperature(oC)

Figure 4.36: the Expansion Ratio of 30%, 50%, 70%Pebax 7233

30% Pebax 7233 50% Pebax 7233 10 10 70% Pebax 7233

) 9 3 10

108 Cell Density( /cm

80 120 160 Temperature(oC)

Figure 4.37: the Cell Density of 30%, 50%, 70% Pebax 7233

140oC o 5x103 150 C 160oC 170oC 4x103 180oC

3x103

2x103 Eta (Pa-S)

1x103

10-1 100 101 Freq (Hz)

Figure 4.38: Pebax 3533 Viscosity Feature

140oC 150oC 160oC 170oC 104 180oC 190oC

103 Eta (Pa-S)

102

10-1 100 101 Freq (Hz)

Figure 4.39: Pebax 4033 Viscosity Feature

160oC 170oC 180oC 190oC 200oC

104

3 Eta (Pa-S) 10

102 100 101 Freq (Hz)

Figure 4.40: Pebax 7233 Viscosity Feature

Pebax 3533

107

106 Elongation Viscosity(Pa-S)

105 10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.41: Pebax 3533 Extensional Viscosity at 130°C

Pebax 4033

106

105 Elongation Viscosity (Pa-S)

104

10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.42: Pebax 4033 Extensional Viscosity at 160 °C

Pebax 7233 106

8x105

6x105

4x105

2x105 Elongation Viscosity (Pa-S)

10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.43: Pebax 7233 Extensional Viscosity at 160 °C

30% Pebax7233

106

105

Elongation Viscosity (Pa-S) 10

10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.44: 30% Pebax 7233, 70% Pebax 3533 Extensional Viscosity at 130 °C

50% Pebax 7233 107

106

105 Elongation Viscosity (Pa-S)

104 10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.45: 50% Pebax 7233, 50%Pebax 3533 Extensional Viscosity at 130 °C

70% Pebax 7233

107

106

105 Elongation Viscosity (Pa-S)

10-2 10-1 100 101 102 Elongation Time (s)

Figure 4.46: 70% Pebax 7233, 30% Pebax 3533 Extensional Viscosity at 130 °C

Figure 4.47: SEM (Pebax 3533 at 80 °C, 2500PSI, 2hours)

Figure 4.48: SEM (Pebax 3533 at 100 °C, 2500PSI, 2hours)

Figure 4.49: SEM (Pebax 3533 at 120 °C, 2500PSI, 2hours)

Figure 4.50: SEM (Pebax 3533 at 140 °C, 2500PSI, 2hours)

Figure 4.51: SEM (30%,70% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours)

Figure 4.52: SEM (50%,50% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours)

Figure 4.53: SEM (70%, 30% Pebax 7233,3533 at 60 °C, 2500PSI, 2hours)

Figure 4.54: SEM (Pebax 4033 at 60 °C, 2500PSI, 2hours)

Figure 4.55: SEM (30%, 70% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours)

Figure 4.56: SEM (50%, 50% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours)

Figure 4.57: SEM (70%, 30% Pebax 7233, 3533 at 80 °C, 2500PSI, 2hours)

Figure 4.58: SEM (Pebax 4033 at 80 °C, 2500PSI, 2hours)

Figure 4.59: SEM (30%, 70% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours)

Figure 4.60: SEM (50%, 50% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours)

Figure 4.61: SEM (70%, 30% Pebax 7233, 3533 at 100 °C, 2500PSI, 2hours)

Figure 4.62: SEM (Pebax 4033 at 100 °C, 2500PSI, 2hours)

Figure 4.63: SEM (30%, 70% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours)

Figure 4.64: SEM (50%, 50% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours)

Figure 4.65: SEM (70%, 30% Pebax 7233, 3533 at 120 °C, 2500PSI, 2hours)

Figure 4.66: SEM (Pebax 4033 at 120 °C, 2500PSI, 2hours)

Figure 4.67: SEM (Pebax 4033 at 120 °C, 2500PSI, 2hours, 2000X)

Figure 4.68: SEM (30%, 70% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours)

Figure 4.69: SEM (50%, 50% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours)

Figure 4.70: SEM (70%, 30% Pebax 7233, 3533 at 140 °C, 2500PSI, 2hours)

Figure 4.71: SEM (Pebax 4033 at 140 °C, 2500PSI, 2hours)

Figure 4.72: SEM (Pebax 4033 at 140 °C, 2500PSI, 2hours, 1000X)

Figure 4.73: SEM (70%, 30% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours)

Figure 4.74: SEM (50%, 50% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours)

Figure 4.75: SEM (50%, 50% Pebax 7233, 3533 at 160 °C, 2500PSI, 2hours, 1000X)

Figure 4.76: SEM (Pebax 4033 at 160 °C, 2500PSI, 2hours)

Pebax 3533 Foaming Video Image (At 120oC)

0 (S) 0.02 (S) 0.04 (S) 0.06 (S)

0.08 (S) 0.10 (S) 0.12 (S) 0.14 (S)

0.16 (S) 0.18 (S) 0.20 (S) 0.22 (S)

0.24 (S) 0.26 (S) 0.28 (S) 0.30 (S)

Figure 4.87: Pebax 3533 Foaming Video Image (At 120 °C)

Pebax 4033 Foaming Video Image (At 120oC)

0 (S) 0.2 (S) 0.4 (S) 0.6 (S)

0.8 (S) 1.0 (S) 1.2 (S) 1.4 (S)

1.6 (S) 1.8 (S) 2.0 (S) 2.2 (S)

2.4 (S) 2.6 (S) 2.8 (S) 3.0 (S)

3.2 (S) 3.4 (S) Figure 4.88: Pebax 4033 Foaming Video Image (At 120°C)

5. Summary and Conclusion

In this project, six different kinds of polymers or polymer blends have been investigated.

The foamed Pebax Grade 33 series material was developed successfully by using the

carbon dioxide as a physical blowing agent on the fixed temperature. The Pebax 3533

and Pebax 7233 exhibited a good compatibility on the three different ratios. Foaming

behaviour of these polymers or polymer blends has been shown in Table 5.10.

Materials Compatibility Foaming behaviour of the experiment materials

Pebax 3533 N/A Good foaming at low temperature (around 80°C)

Good foaming at medium temperature (around Pebax 4033 N/A 120°C), and has high cell density

Cannot foam at low temperature. It has only fine Pebax 7233 N/A foam near the melting temperature

30% Pebax 7233 Good Good foaming at low temperature 70% Pebax 3533

50% Pebax 7233 Good Good foaming at low temperature 50% Pebax 3533

70% Pebax 7233 Good Good foaming at high temperature 30% Pebax 3533

Table 5.10 Foaming behaviour of experiment materials at given temperature

The Pebax 7233 cannot be foamed at the low temperature since it has highest strength in

the Grade 33 series Pebax materials. The cell density of Pebax 4033 was greater than

others (1012level) in the batch foaming around foaming temperature100°C. The Pebax

3533 can be foamed from the low temperature; however, the foamed product is soft.

The mixture property of the foamed product can be obtained when the Pebax 3533 (the pure soft material) and Pebax 7233 (the hard one) was blended in this experiment. The mixed Pebax material shows a greater range of foaming temperature and a higher strength of the foamed product.

6. Recommendations for Future Work:

The development of foamed Pebax materials has been investigated. There are some issues to be studied in order to produce a high quality product. Therefore, the following four aspects are recommended to carry out.

1. In the batch foaming experiment, some parameters can be changed to get the high

quality foam, such as pressure and holding time.

2. Other blowing agents should be considered as an alternative agent.

3. The effects of pressure drop rate should be studied in the future experiment.

4. The use of an extrusion puller should be used in conjunction with the experiment

in order to obtain a better sample for the analysis.

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