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Department of Mechanical Engineering

Assamawal Al-Hinai 0705137

BEng in Mechanical Design Engineering

Final Year Project 2011

(Design and Manufacture of Smart Materials 2)

Shape Memory Polymers

Supervised By: Dr Philip Harrison

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Table of Contents 1.1 Abstract ........................................................................................................................... 2

2.1 Acknowledgments ............................................................................................................................ 5

3.1 Executive summary ............................................................................................................. 6

4.1 Objectives .......................................................................................................................... 8

5.1 Introduction .................................................................................................................................. 9

6.1 Literature review……………………………………………………………………………………………………………………11

7.1 Introduction to Shape Memory Polymers…………………………………………………………………………………13

7.2 How Do SMP’s Function……………………………………………………………………………………………………………15

7.3 Applications of Shape Memory Polymers…………………………………………………………………………………16

7.31 Bionic Muscles ………………………………………………………………………………………………………………………16

7.32 biodegradable SMP’s……………………………………………………………………………………………………………..17

7.33 Braided shape memory Stents……………………………………………………………………………………………….18

7.4 Characterization of Shape Memory Polymers………………………………………………………………………….19

8.1 Experiments…………………………………………………………………………………………………………………………….21

9.1 1st set of experiments……………………………………………………………………………………………………………21

10.1 1st part of the 1st set of experiments……………………………………………………………………………………..22

10.11 Discussion…………………………………………………………………………………………………………………………….24

10.2 2nd part of the 1st set of experiments…………………………………………………………………………………….25

11.1 1st part of the 2nd set of experiments…………………………………………………………………………………….28

11.11 Discussion…………………………………………………………………………………………………………………………..30

11.2 2nd part of the 2nd set of experiments……………………………………………………………………………………31

11.21 Discussion and Conclusion………………………………………………………………………………………………….33

12.1 1st part of the 3rd set of experiments……………………………………………………………………………………36

12.11 Discussion and Conclusion………………………………………………………………………………………………….37

12.2 2nd part of the 3rd set of experiments…………………………………………………………………………………..38

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12.21 Experiment method……………………………………………………………………………………………………………39

12.22 Experiment results………………………………………………………………………………………………………………40

13.1 Final Conclusion……………………………………………………………………………………………………………….…...42

Appendix A………………………………………………………………………………………………………………………………..….44

Appendix B………………………………………………………………………………………………………………………………...…45

Appendix C……………………………………………………………………………………………………………………………………46

Appendix D……………………………………………………………………………………………………………………………………47

Appendix E……………………………………………………………………………………………………………………….……………48

References …………………………………………………………………………………………………….………………..…………..55

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1.1 Abstract:

Shape memory polymers are smart materials that are capable of recalling its original shape

via the application of an external stimulus such as temperature. Its distinctive properties

allow it to achieve such a unique behaviour. The report explains the uniqueness of this type

of polymers and explains the concept behind them. SMPs are of a great importance and

increasingly becoming used in many applications in many fields such as medicine and

engineering. The report gives some examples of these applications. 3 set experiments have

been carried out to assess the properties of shape memory polymers. The first set of

experiments‟ was intended to assess the feasibility of manufacturing a SMP infused with

glass fibre. The second experiment involved the application of tensile cyclic loading to both:

SMP and SMP infused with glass fibre. This was undertaken to examine the durability and

recovery precision properties of pure and impure (infused) shape memory polymers. The

third and final set of experiments entailed the creation of a new material combination which

consists of a shape memory polymer combined with composite twintex. When this new type

of material was subjected to bending, it demonstrated excellent recovery properties as it

recalled its original shape when heated above the first transition temperature.

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2.1 Acknowledgments:

I would like to thank a few people for the help they offered throughout this project.

I would like to thank mostly and show my appreciation to my advisor Dr Philip Harrison of the

department of mechanical engineering for his support and guidance and keeping me up to

pace with this project when things got difficult, and being generous with his time and the

knowledge he gave me.

I would like to also thank Mr Headong Park a PhD student, for shearing his information about

shape memory polymers and helping obtain the chemicals needed for the project.

Also i like to thank Miss Zaleha Mustafa and Mr John Davidson for the training to use the lab

equipment‟s and offering their time for helping make the experiments work.

Lastly I would like to thank the University of Glasgow for giving me the opportunity and the

resources to start a research programme that is knowledgably valuable to me.

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3.1 Executive summary:

Over the past few year increased interest towards developing new advanced smart materials

to be used in moderns applications to minimise product complexity that has a benefit of

decreasing weight cost and labour intensiveness in a specific area where manual human

work is scarce.

With limited laboratory equipment recourses this report will be following gradually steady

steps into developing a new product material that has many benefits in modern industry from

the space industry to robotics where the end material fabric that those experiments produced

in this project would make it simpler for innovations to work and even decrease costs and

complexity.

Starting from the beginning, shape memory polymers are a type of plastics that have the

ability to be modelled into a certain shape and then the shape would be deformed stretched

or twisted, with an external stimulus like heat the material would have the ability to recover

the shape it was previously programmed to and modelled. Using the ability of this polymer, it

has been infused with a piece of glass fibre to give it extra strength by using the process of

vacuum infusion. The result material combination is then put into several tests to test its

ability to retain its programmed shape. These include some mistakes and how we overcame

them to produce a more efficient material with limited lab resources.

For the first experiment the fibre was put into a tensile test to deform it while under heat, it

would be expected for the material to remain in its temporary shape after being cooled but

the experiment and more literature review showed that there was a small mistake of

predicting the wrong glass transition temperature of the polymer.

A set of new experiment were later designed to test the durability and precision of the shape

memory polymer alone, and to an outstanding performance the polymer proved to be very

precise and durable, even when the sample polymer was later found out to contain air voids

that should affect its performance.

A similar test was also devised to test the combination of shape memory polymer that was

infused with glass fibre; the tensile test proved that stretching this material combination

would result in a failing material that was not durable enough for modern industry.

After learning from previous experiments it was then concluded that for the most effective

and efficient polymer fibre material to retain its shape, it has to be bent and not stretched as

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updated experiments like moulding fibre polymer into a helix shape around a tube would had

impressive outcome results, proved.

For the last part of this project report, a new product material that utilises a modern

composite material called twintex that has the ability to simply melt in a certain temperature

and then after being cooled it produces a very strong and rigid material structure. The

twintex was sandwiched between 2 polymer fibre mats that wore programmed to memorise

a “C” shape, after this new material system combination was put in an oven, it proved to

work to a very impressive standard which later, this report will discuss ways to improving the

outcomes of the new system and how it could be made to give more precise and accurate

results.

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4.1 Objectives:

1- To define SMP polymers and give a brief explanation of its salient properties.

2- To discuss the recent and beneficial applications that use shape memory

polymers.

3- To assess using laboratory methods the feasibility of manufacturing of shape

memory polymer infused with glass fibre.

4- To compare the recovery properties of a pure shape memory polymer with a

shape memory polymer infused with glass fibre.

5- To determine the variation in durability between pure shape memory polymers

with the durability of a shape memory polymer infused in glass fibre.

6- To create a new material combination which consists of materials used in the

composite industries and advanced shape memory materials.

7- To examine the recovery properties of a shape memory polymer combined with

composite twintex when bending is applied from the polymer onto the twintex.

It is important to note here that all of the intended objectives have been fully attempted

with varying level of success being attained. In the first set of experiments, the

manufactured SMP failed to exhibit the expected properties. However, this has been fully

researched and discussed and the reasons for this failure have been provided in the

relevant section.

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5.1 Introduction:

One of the new topics in materials that was given great attention, devoted and increasing

research is Shape Memory Polymers. Shape memory polymers (SMPs) are compound

plastic smart polymers of a unique chemical structure that enables it to recall its original

shape and return back from the temporary deformed shape to the desired application shape

via the application of an external stimulus such as heat. SMPs are capable of achieving so

due to their unique chemical structure. Polymers are molecules that are made up of large

number of repeating structural sub-units which are connected together by chemical bonds.

Distinctively, shape memory polymers are found to occur in two states, Crystalline state and

an Amorphous state where when in a crystalline state it is organised uniformly and can be

characterised as a rigid and stronger structure, and when in the amorphous state the

polymers sub-units are randomly scattered and are softer and more flexible to move around

relatively freely. Shape memory polymers have two transition temperatures (i.e. the

temperature at which the polymer is transformed from Crystalline region to the amorphous

region). The first one is responsible for the temporary change in the polymer shape and the

second being the limit which if exceeded the polymer will be deformed permanently and will

lose the unique capacity of recalling its original shape. In practise, the SMP is typically

heated to a temperature above the first glass transition temperature and a stress is applied

to it so that it deforms to the desired temporary shape. Then it is cooled down to maintain its

new temporary shape. When the material is heated up again to the first glass transition

temperature, it goes back to the original shape. This autonomous movement of the polymer

can be alternatively expressed as a self-provocked energy/force that, if exploited adaptively

and suitably, can save considerable amount of energy. The wide range of sizes the into

which shape memory polymers can be manipulated, gives it an additional advantage over

classical machineries. It enables the polymer to reach locations that are never accessible by

using usual equipments. For instance it can be used for locking pipes in deeper layers. The

increasing focused research in this area can be attributed to the many useful applications

this material offers. These applications include; Biodegradable shape memory polymers,

braided shape memory polymers‟ stents and bionic muscles. The latter being only enhanced

by the inclusion of shape memory polymers in the artificial Mckibben Muscles as a

replacement to the old and more expensive control system that is needed to hold the joint in

position (see more details on this on the applications‟ section under the bionic muscle sub-

section). In this project report, three sets of experiments to SMP infused with a composite

were undertaken. The experiments‟ main objective was to examine the functionality,

durability and recovery of the SMPs if they are combined or infused with other non SMP

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materials. The first set of experiment aimed to test the functionality of a vacuum infused

SMP with glass fibre through tensile testing. The material failed to behave as expected.

Therefore, it was necessary to investigate the reasons behind the test failure by carrying out

some further research and undertaking another simple test to confirm the test failure. The

second test of experiments apply cyclic tensile loading on both SMP and SMP infused with

glass fibre to examine the discrepancies and assess the durability and precision of the

recovery for each. The third and last experiment assessed the application of bending to a

different combination of materials. This combination consists of 3 layers; one twintex-fibre

layer in between two outer layers that are made of SMPs infused with glass fibre. The

second and third set of experiments demonstrated impressive precision in the recovery

properties of SMPs in their different materials combination. Furthermore, it showed the

variation in durability properties between the different materials‟ combinations.

This report will first explain the basic properties and definition of shape memory polymers. It

will then discuss some SMP applications and explain the significance of such. After that, a

description of the three experiments will be detailed together with discussions and analyses

on them. Finally, a conclusion of the main outcomes of the experiments will be drawn.

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6.1 Literature review:

Being under increased focus, shape memory polymers are being researched on and

developed by many institutes around the world. This is mainly due to shape memory

polymers giving a wide range of possible applications, from space programs to aerospace

and the automotive industry. A lot of the main focuses of the researched done only in the

recent past few year, may researches are just to understand more about the molecular

functions of SMP‟s and their characteristic of basically how they work and what affects them.

J.Diani, C.fredy, P.Gilormini[11] have devised a new torsion device that was designed and

built for testing the shape fixity and shape recovery of shape memory polymers at large

deformations. The torsion testing system provided a quantitative estimate of the kinematics

and kinetics of shape recovery for sample subjected to very large deformations at moderate

strains that are more likely to be expected in actual shape memory industry applications. The

recovery was observed and recorded under varying deformation magnitudes, heating rates

and tests the best recovery temperatures. Two SMPs were investigated, a thermoset shape

memory epoxy and a thermoplastic shape memory polyurethane. Each type of polymer

expresses a specific characteristic unique to its chemical formation with various ranges of

recovery precision and time.

M.John and G.Li[5] have investigated the possibilities of creating a self-healing shape

memory polymer based on a foam structure where micro glass beads are mixed with the

compound to make it less dense and therefore foam like. To heal the composite, simple

heating is required which reverse transforms the polymer edges and brings the crack faces

back into contact.

Q.Meng, J. Hu[15] have looked into blends to create an improved shape memory polymer.

The preparation of SMP blends is mainly for specific aims. Improving shape recovery stress

and mechanical properties as usually shape memory alloys are better in this but are more

expensive and harder to work with, a slight drawback of shape memory polymers is their

time which they take to recover to recover, this is improved by increasing thermal

conductivity simple solution to this is to produce a conductive polymers fill them with

conductive powders, this is all to help in fabricating shape memory materials sensitive to

electricity, magnetic, light and moisture.

B.Yang, W.M.Huang[9] have investigated the effect of moisture on the glass transition

temperature of a polyurethane shape memory polymers. It is found that the SMP composites

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before immersion in water have a slightly lower glass transition temperature. On the other

hand, the moisture can remarkably reduce the glass transition temperature of the

composites. Heating to over 180 degrees Celsius can be an effective way to remove the

moisture, which also results in the glass transition temperature back to the original.

To a more closer research to what this report will be investigating Kazuto Takashima[10] have

infused shape memory polyurethane polymer into carbon fibre to create a Mckibben muscle

actuator. It is a concept based on pressurised air and shape memory effect where since the

memory polymer has a one way effect where air is pumped to a sealed cylindrical polymer

infused fibre and contracts, later the valve is opened and the effect of the shape memory

polymer will re-expand the muscle where it was programmed to memorise that shape. They

had similar problems that this report will discuss where uneven spreading of the polymer into

the mesh (i.e. glass fibre) has an effect on the performance.

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7.1 Introduction to SMP:

SMP are compound plastics polymers that have a special chemical structure that gives

the ability to return from a deformed shape (temporary state) to their original

(programmed) state induced by an external stimulus in the form of heat, light, electricity

or magnetism, usually all these stimuli generate heat with in the polymer to activate.

Shape Memory Polymers usually retain two shapes, (the deformed shape and the

original programmed shape) but recently more complex shape structures are achievable.

(Figure 1: showing a recovery process of a SMP[7]

) (Figure 2: showing a polymer sub-unit[16]

)

(Figure 3: organised strong crystalline structure and a weak amorphous structure[16]

)

Polymers are molecules that are made up of large number of repeating structural

subunits which are connected together by chemical bonds either covalent or ionic and, in

shape memory polymers covalent bonds are found. Polymers are found to occur in two

states, a Crystalline state and an Amorphous state (Figure1) where when in a crystalline

state it is organised uniformly and becomes a rigid and stronger structure, and when in

the amorphous state the polymers subunits are randomly scattered and are soft and

flexible and able to move around relatively freely. A shape memory polymer has a semi-

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crystalline structure where both states occur at the same time within a specific

temperature, usually room temperature.

(Figure 4: The Crystalline state at A and at B Tg:A is 170°C lower than Tg:B 200°C [7]

)

A “Glass Transition Temperature (Tg)” is when the polymer changes from one state to

the other i.e. from crystalline state to amorphous due to the increase in heat energy.

SMP‟s have two glass transition temperatures A and B. With reference to figure (4), area

A has a lower glass transition temperature than area B. In the crystalline state all

movements of the polymer segments are frozen. The increase of temperature means

that the rotation around the segment bonds becomes increasingly unimpeded. After

heating, internal stresses (strain storage) inside the polymers react elastically causing

the polymer to recover to its original (programmed) state (Figure 4). SMP‟s have an

elongation capabilities of over 400% to its size and with an accuracy when reforming of

99%.

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7.2 How do SMP’s function:

(Figure 5: microstructure faze change during heating and elongation[7]

)

When a shape memory polymer is heated above the first glass transition temperature

(Tg) the crystalline region is transformed to the amorphous state and becomes flexible

and extendable (show in a). A load is then applied and the specimen of SMP extends,

while it‟s under heat (path a-b). The specimen is then cooled when it‟s deformed to a

temperature under its first glass transition temperature (path b-c) and the amorphous

region then changes back to the crystalline state. The specimen will be fixed to its new

deformed state, but due to internal stresses of the uncrystallized amorphous region the

specimen will contract to a small extent (path c-d).

If the specimen is then heated again to a temperature above its first Tg with no load on,

the specimen will then return to is original shape (programmed state). The speed in

which this polymer returns to its programmed structure is limited by the friction generated

within the molecular structure.

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7.3 Applications of Shape Memory Polymers:

(Figure 6 clockwise from top: SMP stitching, an Artery stent, Bionic muscle[7][10]

)

Shape memory polymers (SMPs) have been studied and developed since the 1980s

because of their feature of being able to change their shape to a useful predefined one, in

the response to a stimulus. This feature can be exploited to design components that are

used to enhance product performance and quality under changeable environments.

Due to some of the unique thermo mechanical properties, shape memory polymers have

found numerous applications.

8.31 Bionic Muscles:

One of the important applications of shape memory polymers (SMP) is its use in the creation

of bionic muscles. In countries that have high percentage of elderly people such as Japan,

there is a growing attention to improve the lives of aging people by manufacturing new

technologies that can assist elderly people to carry out their daily life activities with optimum

comfort and practicality. The natural and unavoidable physical degradation of muscles as a

result of aging is normally overcome by the use electric motors. Clearly, these machines are

heavy and difficult to use due to their lack of flexibility. A new and alternative technology

employs shape memory polymers to manufacture artificial muscles. This new technology is

favored over the electric motors due to many reasons:

1- They are light in weight.

2- They enjoy much higher flexibility than electric motors.

3- They produce large energy output and allow back drivability.

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The concept of Mckibben artificial muscles: Mckibben robotic muscles are usually used

to drive robotic joints. „‟they are typically configured in pairs which act antagonistically to

increase joint stiffness‟‟ (Takashima, 2010). However, in order for the configuration to uphold

a fixed position, constant control is required. Thankfully, the inherent properties in shape

memory polymers assist in the development of artificial muscles that can maintain a firm

shape without the need of continuous control. SMP can be manipulated into a different

shape if it is heated above its glass transition temperature upon the application of a small

load. They can remain deformed if they are cooled to below Tg. If they are reheated, they go

back to their original shape. Using these unique characteristics, and by the infusion of a

SMP into braided mesh shell of an artificial Mckibben muscle, it becomes possible to

maintain a rigid shape joint without the need for any air or control system. When the new

actuator (the one infused with SMP) is warmed above the first glass transmission

temperature, the artificial muscle behaves conventionally. When it reaches the required

length, it can be cooled to below the first transition temperature and the SMP will hold the

actuator in place without the need for any air or control system (Takashima, 2010).

8.32 Biodegradable shape memory polymers:

Biodegradable shape memory polymers prove to have promising applications in the medical

field. Biodegradability and shape memory capacity of a material offers multifunctional

properties that are of great importance in the medical field. A number of beneficial

applications are being researched. An example of which is the use of biodegradable shape

memory polymers in minimal invasive surgery. The polymer‟s properties enables „‟the

insertion of bulky implants in a compressed shape into the human body through a small

incision‟‟. When they are entered in the body they return to their application purpose shape.

Another example of medical applications is its use as a smart suture for wound closure.

Once the impact of the shape memory polymer is actuated, it applies a pressure (stress) to

the wound lips to help it heal and close with time. It is very important to note here that shape

memory polymers used in medical applications must have a low first transition temperature.

This is because the body temperature of humans is around 37 degrees. Therefore, the

polymer first transition temperature has to be close to this range so that it returns to its

original or application shape when it enters the body. The image (below) illustrates the

progressive increase of the stress applied to the wound as the temperature increases

resulting in the shrinkage of the wound. Another worth mentioning advantage of shape

memory sutures is its biodegradability property, which avoids the necessity of removing the

suture after the wound closes up.

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(Figure 7: self tightening SMP stitching)

7.33 Braided Shape Memory Polymers’ Stents

One very beneficial application of shape memory polymers is its use as braided stents in the

medical field. According to (Kim, 2009), a stent is a metallic or plastic tube inserted into

abnormally narrowed or closed vessel such as an artery or duct in the human body to open it

mechanically and maintain the blood flow inside it. In terms of the stents‟ deployment

method, they are categorised into two groups; self expandable and balloon expandable

stents. Shape memory alloys SPA (self expandable) are becoming increasingly more

popular than balloon expandable stents due to their „‟high radial and bending compliance

and the prevention of balloon trauma‟‟. However, shape memory polymers are a recently

discovered technology that is favoured over shape memory alloys due to many reasons:

1- Low cost.

2- Light weight.

3- Excellent Process ability.

4- Large recoverable strains that reaches 400% of strain recovery.

The shape memory polymer used in this technology is polyurethanes. The basic idea behind

this technology is to manufacture a tube made of shape memory polyurethanes with a

diameter that is relatively large enough to expand the vessel in question to allow the

passage of blood through it. Then a stress and heat is applied to the tube to minimise its size

(diameter) so that it can enter the abnormally narrow vessel. It is important to note here that

the heat applied should be higher than the first transition temperature of the polymer. After

that, the SMP tube should be cooled down before removing the stress applied to it so that it

maintains the deformed shape. Now the tube is ready to be inserted to vessel in question.

The temperature of the SMP tube increases when it enters the human body. By the time it

reaches the vessel in question, the temperature of the tube exceeds the shape memory

polyurethanes‟ first transition temperature, which results in the tube recalling its original

shape, thus, expands causing the vessel increase in diameter and allows blood flow. Again,

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It is crucial that the polymer used in such an application has a first transition temperature of

around 37 degrees so that it recalls its original shape when heated to body temperature.

See the figure (below) for an illustration of stents.

Geometric models of braided stents (a) with free ends and (b) with welded ends.

7.4 Characterization of SMP’s:

Shape memory polymers are modelled using the theory of springs and dash pots

“viscoelastic models” to establish a mechanical model with a similar response of the SMP

when heated frozen then heated again. The models, which include the Maxwell model, the

Kelvin-Voigt model, and the Standard Linear Solid Model, are used to predict a material's

response under different loading conditions. Some SMP‟s models:

(E is the elastic modulus and η is the material coefficient of viscosity)

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(Graph 1: showing strain curve of an elongated SMP to 50% of its size then stopped)

From (graph 1) we can see that characterising shape memory polymers by modelling them to

dash pots and springs work. It is estimated that roughly 50% of the mixture has a glass transition

temperature of A and the other 50% has a Tg of B. if we assumingly heat the material over its

first Tg then half of the spring force would be gone as shown in the figure above. This also

should mean that if the sample is heated above its second Tg then as soon as the elongation

stops, stress would drop to about 0N. Modelling SMP‟s is more complex, the more different

elements combined to give it a better resemblance the more complicated it gets and in reality

behaviour of SMP‟s is too complicated to be described accurately using dashpots and springs.

The more elements combined in the model the more it accurately models the flow.

(Below showing a proposed model for polyurethane SMP)

Tg :A Tg :B

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8.1 Experiments:

Thesis:

Since SMP‟s would contract or return to their original upon inducing external inputs like

heat, it would be theoretically functional to infuse the memory polymer with composite fabrics

like glass-fibre[A] using different approaches like hand laminating, or vacuum infusion to give

the polymer extra shearing strength along the axis. It would also theoretically be a fully

functional SMP infused fabric with the same specification properties and abilities of shape

memorising as a normal SMP would have and thus deform and return to the programmed

shape initiated by an external energy input.

9.1 1st set of experiments:

Experiment preparation:

A solution of shape memory polymer[E] has been prepared previously and while it was still in

the liquid state the solution was vacuum infused[B] to 4 different glass fibre configurations.1-

1 layer normal GF 2- 1 layer pre-sheared GF 3- 3 layered normal GF 4- 3 layered pre-

sheared GF. Vacuum infusion has been chosen as Voids are reduced to the minimum, pulse

since the liquid is very thick and viscous it will be very difficult to diffuse the polymer into the

fibre itself through and in between the yearns. However this is not the best way and will be

discussed later.

(Figure 8: Vacuum infusion and heat pressing)

After the infusion the samples were left at room temperature for about 3 days for the solution

to fully evaporate and cure. Due to imperfections during the process, the result SMP fabrics

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were not completely flat, therefore the sample fabrics have been heat pressed at 200°C

(above the second glass transition temperature to permanently programme it as a flat shape)

at a pressure of 5 bar. The result was a perfectly flat SMP infused composite that the

experiment will be recorded fairly to all four samples.

10.1 1st part of the 1st set of experiments:

For the first experiment it was decided to start with the single layer un-sheared SMP infused

composite. The sample was placed in a picture frame for a tensile test and the two end

corners of the frame will be pulled apart 10mm while length extension (in mm) and extension

force (in Newton‟s) is recorded.

(Figure 9: SMP infused fibre being put in a picture frame then put in a special oven to stretch it, last picture

showing quenching process)

The whole picture frame was put in a special oven to confine and heat the SMP infused

composite.

The experiment process went as follow:-

1- Heat the sample fabric to 55°C (80°C was chosen to be on the safe side).

2- The sample fabric is then stretched under heat.

3- The sample was cooled (quenched) by ice spray to temporary hold its deformed

shape.

4- The picture frame is then contracted until the total force the fabric is generating is

zero.

5- The fabric is then heated again to 80°C and observed.

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The results however were unexpected and the experiment did not perform as previously

anticipated.

(Graph 2: stress graph of first try of the experiment)

Since the sample fabric was extended (deformed) under heat then cooled while it is in the

deformed state, the material was more or less supposed to withhold and retain that shape

after cooling and maybe contract a small amount just to relieve some internal stresses but

mostly hold that Form.

Step 3 did not behave as expected and affected step 4. It is possible to see from graph.2

that the polymer fabric almost fully returned to its original shape like any rubber material

would.

The experiment was repeated with that same steps and the same material but this time the

polymer fabric will be extended to 40mm instead of 10mm.

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(Graph 3: showing second try of the experiment)

Unexpectedly the results were similar as the first experiment, and the polymer fabric did not

act as a shape memory polymer but rather acted as a rubber or as any normal elastic

polymer. Another surprising result was the large amount of stress generated, 450N for a

single layer SMP fabric was very large and it was obviously not a practical material to work

with since a big amount of force was needed to deform the material.

10.11 Discussion:

From the results graphs it is possible to see that the experiment has failed and infusing SMP

into a composite will only have a strength benefit while the SMP will lose its shape

memorising capability. Also noting that the polymer fabric had been permanently damaged

due to extensive stretching. From the second experiment it is possible to see in (Graph 3)

that the polymer fabric was damaged internally and therefore would return to zero mm when

contracting if it has not been affected.

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However doing extensive literature review and reading experimental articles and contacting

other researchers {Mr haydong park} there are several important conclusion points to be

noted as to why this experiment was a failure.

Previous literature readings that were done stated that while using their own

“specific” Polyurethane shape memory polymer, they had 55°C as their first glass

transition temperature. Through extensive reading, It was figured out that there were

several different types of (polyurethane) shape memory polymer and not only one,

and each with a different specification to the two glass transition temperature and

each PU-SMP has a different chemical name with different external stimuli.

Contacting a PhD researcher this specific shape memory polymer that is used in the

two previous experiments had an unknown but estimated first glass transition

temperature of somewhere between 80-140°C while previously thought before the

experiments to be at 55°C. That was why the polymer fabric acted as a spring rather

than a dashpot when heated in experiment 1 and 2 and why it did not retain its

deformed shape when cooled. It has also been brought into attention that the second

glass transition temperature which if exceeded would permanently deform the

polymer is anywhere above 190°C. A differential scanning caliometry test (DSC) [D] is

planned to be used to find the exact glass transition temperatures of this type of

polyurethane shape memory polymer.

Sometimes external environments have an affect of the properties of shape memory

polymers, taking into account that an ice water was used to quench and cool the

polymer fabric this might have an affect on the properties of that polymer.

Experiments have been done to prove that sometimes moisture has and effect on

glass transition temperature, though being uncertain that moisture has any affect on

this type of polyurethane it should be taken in consideration.

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10.2 2nd part of the 1st set of experiments:

As it is possible to see from (graph 3) the polymer fabric was deform to an extent of 10mm

since theoretically this could mean either that the polymer was damaged internally with micro

cracks or that the material was partially temporarily deformed so a simple test was devised

to see exactly what happened to the fabric.

(Figure 10: showing small shear in the SMP fabric then placed in an oven)

(Figure 11: showing recovery of sheared sample)

The SMP infused composite was laid on a sheet of paper and with a pen outlining its edges,

after that the polymer fabric was then placed inside an oven for 15 minutes to a temperature

of 170°C, the polymer fabric was removed from the oven and on the same sheet of paper

27

the same corner had been placed on top of the previous drawing and again the edges have

been outlined with a pen. The result from (figure11), it is possible to see that the polymer

infused fabric, has returned to its original shape upon inducing it with an external heat

source and the theory behind this composite-polymer combination would work. The reason

why it has not worked in the first two experiments was due to the fact that the heat used was

not sufficient enough to transform the first set of crystalline region to the amorphous state

due to the temperature being lower than the glass transition temperature.

28

11.1 1st part of the 2nd set of experiments:

Learning from the 1st set of experiments and what had happened, a few tests have been

designed to test the shape memory polymer and understand more about its characteristics

on how well it would perform and to roughly estimate the two glass transition temperatures

for the shape memory polymer used in this experiments series.

A cyclic loading test has been set to test several aspects together at once. First of all an

estimated temperature of 170°C for the first glass transition temperature and a 200°C for the

second glass transition temperature(permanent deforming temperature). A smaller side test

was done with a small sample just to test these temperatures of heating programming, then

heating deforming, then heating and returning to original shape. As expected the small side

experiment worked.

For the 1st part of the 2nd set of experiments a flat piece of Shape Memory Polymer only

plastic was cut into a rectangular piece (permanently programmed) to dimensions of

25mmx50mm and the second piece of dimensions 45mmx90mm, and under cyclic loading ,

the two pieces are subjected to a tensile stress when being clamped by both ends while one

end is attached to a secure object while the other end is attached to a weight of 50N and the

whole sample is placed inside an oven to heat it repeatedly. The experiment goes as

follows:-

1. A weight clamped to the polymer end and the system is subjected to a heat of 170°C

and left for 15 minutes.

2. Cool spray (quench) the polymer and unclamp the weight, and then record the

elongation (ΔL).

3. The polymer is reheated again to 170°C for 15 minutes while weight is unclamped.

Length is then recorded.

4. Steps 1-3 are repeated as many times as possible while recording length after every

step.

29

(Figure 12: weight attached to SM polymer and measured after cyclic loading test)

(Graph 2 above: thin sample tested) (Graph 3 below: thick sample tested)

(Graph 1) (graph 2)

25x50mm SMP Load Unload Cycle

0

20

40

60

80

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120

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1HUL

UL

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45x90mm SMP Load Unload Cycle

0

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30

11.11 Discussion:

From the graphs recorded it is possible to see how well the specimens preformed. Its was

also possible to see that 170°C and 200°C for the two glass transition temperatures (Tg) are

very good estimations as they worked perfectly well through out the cycles.

The sample showed extreme precision its shape recovery while strain was over 130%. Due

to imperfections during manufacturing of the polymer piece, there happens to be a fair

amount of bubbles or air voids inside the specimen and due to these voids, they were crack

initiators. In cycle 6 at (graph2) it is possible to see a small amount of fatigue due to internal

cracking as cycles progressed, if however more care was taken during manufacturing to

avoid air bubbles the specimen would perform perfectly with extreme precision especially in

the very first cycles of its life. This experiment however was too time-consuming to continue

with more cycles as they would show more accurately how the sample specimen would

perform.

31

11.2 2nd part of the 2nd set of experiments:

For this second part of this set, the experiment was exactly the same as the previous

experiment in this set, except that the specimen that was tested had been vacuum infused

polyurethane SMP composite fibre. The specimens had to be twice the length on one side

compared to the other.

(Figure 13: a sample of SMP fabric) (Figure 14: fabric being clamped to a weight and shearing)

32

(Graph 4: showing fatigue through the cycle)

(Graph 5: showing fatigue through the cycle)

3 Layer Pre-Sheared SMP+Composite Load Unload cycle

0

5

10

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40

45

1HUL

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0

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33

11.21 Discussion and conclusion:

(Figure 14: showing dislocations and distortions in the twills)

This experiment showed that cyclic loading of the combination of SMP+ composite fibre was

failing. From (Figure14) it is possible to see that the reason why the material fatigued in both

experiments was due to the twills and fibres inside the material being dislocated and

distorted from their positions due to the edges not being secure. This mean that loading

force was acting directly along the twill fibres rather than the polymer plastic, which means

that there is no deformation of the polymer for it to recover by heating as the cycles

progress, Another reason was due to the fact that vacuum infusion is a very effective and

efficient way designed by the composite industries to infuse resins with fibres. Vacuum

infusion gives the final product a ratio of 60% fibre to 40% resin or polymer content, while

hand lay-up gives the opposite result of 60% resin or polymer and 40% fibre content,

vacuum infusion may be very desirable in the composite industries, but not in this

experiment. This means that maybe for this type of materials combination, a hand lay-up is

desired, as the main player in this combination is the matrix it‟s self and not the fibre rigidity

or strength that is wanted by the composite industries, a larger matrix ratio here is what is

aimed for by this experiment.

34

(Figure 15: left locating air voids, right showing places of elongation and contraction of SMP in the twills)

However on the other side, there is a big advantage vacuum infusion provides, from the 1st

part of the 2nd set of experiments, it was concluded that air voids are crack initiators and

fatigue the polymer, plus from (figure15) it is possible to see the main areas that stress is

generating on the polymer matrix are anywhere between the twill and its neighbour twill and

where twills cross each other, vacuum infusion has the advantage of filling up these spaces

by force and therefore increasing the amount of polymer matrix within the neighbouring twills

only.

(Figure 16: vacuum infusion forcing air bubbles out of the fibres)

This could be concluded that for best possible results vacuum infusion would be used to

clear air voids, yet also hand lay-up an extra layer of shape memory polymer on the surface

to increase the ratio of polymer to fabric and thus giving the fabric some more recovery

Usual air voids

locations

35

force. Edges should also be secured to avoid dislocations of the twills, this could be done by

gluing or clamping the edges not to allow the twills to move and thus keep their positions,

noting also that gluing or clamping should not hinder elongation or contraction of the

specimen, this is very difficult to do and not a very practical system to design.

36

12.1 1st part 3rd set of experiments:

Since from the experiments in the 2nd set, it could be learned that polymer infused composite

fibres have a tendency to fail when stretched due to various reasons like lack of polymer,

dislocations of the twills, and fatigue due to air voids, or even imperfections during

manufacturing. Therefore this experiment is made to test the ability of the polymer fibre to

shape memorise and its accuracy to return to its original state when bent and not stretched.

The sample is prepared by a simple single layer glass fibre composite is infused with the

shape memory polymer, and then another layer of the polymer was hand laid-up of both

sides of the fabric to give it an extra layer of polymer for more recovery force and precision

reasons as to what was learned and concluded from the previous set of experiments.

The new polymer fabric was then cut to the dimension of roughly 10mm by 140mm as

cutting this fabric was a difficult process, accuracy in this experiment was not a big concern.

The ribbon of polymer fabric was then wrapped around a cylindrical tube and formed into a

helix shape, the piece was then taped into its position and inserted into an oven at 200°C

(above its estimated second glass transition temperature) to give it that permanent shape.

The polymer fabric ribbon had successfully remained at its programmed shape after the

tapes and the cylindrical tube were removed.

37

(Figure 17: the process of polymer composite ribbon recovery)

After the polymer ribbon was formed to its helix shape, it was placed in a heat press at a

temperature of 170°C under 5 bar of pressure for about 3 minutes, and again the polymer

fabric ribbon was temporarily deformed and held its deformed shape after it was removed

from the heat press and rapidly cooled, though from (figure17) the ribbon piece did don‟t fully

flatten, this is thought to happen due to the thin and long area the ribbon had as previous

experiments that used larger areas of similar material combination had completely flattened

the samples. The polymer composite ribbon was then left in an oven at 170°C, Pictures 1, 2,

and 3 of (figure17) show the process of recovery until the end product (C) after 15 minutes.

12.11 Discussion and conclusion:

From the results produced from this experiment it could be argued that bending the polymer

composite fabric results in a better forming ability compared to stretching the sample, though

bending actually means stretching in the outer radius, it is less aggressive to the fabric twills

as no extensive force is used. The precision of the recovery was also very impressive,

thought the radius of the helix shape was not actually measured at the start of the

experiment the length of the helix shaped ribbon was calculated roughly. It was

38

approximately 50mm long but when gone through the experiment process the final recovery

length was around 58mm, 84% was the recovery precision of the final product, it

demonstrates a very impressive result for a shape memory fabric that is not made from

100% of shape memorising material.

12.2 2nd part of the 3rd set of experiments:

After concluding all the past experiments, it was thought to be a creative idea to use the

ability of this material combination to create a product that would simplify a lot of advance

products and minimise complexity.

Since it was found out that bending the shape memory polymer composite fabric has a

better advantage regarding shape recovery, a twintex[C] layer had been sandwiched between

two shape memory fabrics as shown in (figure18)

(Figure 18: the three layer sandwich inside a steel mould)

the purpose of this experiment is to produce a product that would be in a certain shape at

first but when heated above a certain temperature the material would form into a

programmed shape and when it cools down it would create a very strong and rigid material

specifically designed into a certain desired shape, and would therefore utilise the ability of

the product developed in the previous experiments.

SMP+Composite

Twintex layer

SMP+Composite

Steel mould

39

12.21 Experiment method:

A shape memory polymer fabric would be manufactured using optimum methods discussed

in the previous experiments, two samples of the polymer fabric of dimensions 50mmx70mm

will sandwich a piece of the twintex layer.(figure17)

The sandwich combination would then be put into a mould (a “C” shape in this case) and

inserted in the oven a 200°C to permanently program the shape memory polyurethane

infused with the fibre to remember the could shape (“C” shape) and cool it after removing it

from the oven. Noting at temperatures above 170°C the twintex contains polypropylene

which melts over the fibres within the twintex creating a rigid structure after being cooled, it is

also possible to say that the polypropylene within the twintex fibres could be melted

repeatedly to a reasonable extent.

After that the material combination is the placed in a heat press at 170°C at 5 bars for the

shape memory polymer material combination to temporary memories the new flat shape

after it being cooled bellow 170°C.

(Figure 19:1-moulded hard part, 2- heat pressed at 170°C, 3-final flat piece)

The theory now predicts that if the system is heated again to 170°C using an external heat

source (e.g. oven) the polypropylene will melt and become flexible and at that temperature

the shape memory polymer will take effect and return to its programmed “C” shape.

40

12.22 Results:

(Figure 20: material system combination recovery being compared with the mould shape)

From (figure20) it is possible to see that the experiment was a success in to what the theory

predicted, there are some small errors done in this experiment the would also give the final

outcome a better result. Although the materials system combination did not return 100% to

its original programmed shape it could be concluded that to create a better final product it is

necessary to design for compensation of the spring back rate. The small errors done in this

experiment if prevented, the final product would have a more shape memorising precision.

One error was the mistake of assuming that the melting temperature of polypropylene was

170°C, manufacturers recommend the used of temperatures between 180-230°C, though

however the polypropylene did melt, it was probably too viscous for the shape memory to

over come the force needed, and therefore it was not able to retain fully its programmed

shape, and especially in the last few millimetres.

41

Another error was due to the use of too much pressure force from the heat press. 5 bars of

pressure have made the melted the polypropylene diffuse in other places other than its own

fibres, it has diffused to the shape memory polymers that sandwiched on both sides, it has

creating a black product and probably hindered the work of the polyurethane memory

polymer.

Two layers of shape memory fabric probably was not enough to overcome the force needed

to reshape the polypropylene and fibre in the middle, it would therefore be a better idea to

use more layers to give a better overcoming force. So to be on the safer side, the material

system should of had been heated to a temperature of somewhere between 180-190°C.

The last error was probably using a too difficult shape, or to put it in a better phrase, a shape

that was too demanding, using a more lenient shape with no hard angels would give the

recovery a better precision. A problem that is also related to this was probably it the system

was given more time inside the oven it would produce better results, longer than 15 minutes

is long for a small product and is not cost effective companied to its size in what ever aspect

it is looked on, therefore accuracy and time rate is heavily dependant if the shape and size

factor of the programmed shape.

42

13.0 Conclusion and further research:

There is more work to be done with this research to improve the performance of the material

Combination, but it could be concluded in the main points that had been discoveries and

developments to increase the efficiency of the end product.

The combination of smart materials and composite fibres will result in a high strength

material durable to go through high percentage of strains with no shearing or breakage.

Vacuum infusion will work best if used with hand lamination process afterwards, as vacuum

infusion is a very efficient method of infusing a fabric with a viscous liquid material, it does

how ever result in a high ratio of fabric to polymer and this is disadvantageous in this

composite polymer system. On the other hand vacuum infusion eliminates voids or air

bubbles between the fibre twills. Air bubbles are crack initiators therefore eliminating them

will decrease fatigue within the material assuming is goes through any form of cyclic loading.

Another point is that air bubbles are more present between the neighbouring twills and the

areas where twill fibres cross each other, specifically those locations are the areas that go

through the majority of the deformation and stresses exerted when the fibre is put under

strain, vacuum infusion fills up these locations by force. Therefore for the best possible result

vacuum infusion is to be done first to infuse the shape memory polymer into the composite

fibre, after that a hand lay-up process is best done on both sides to give the material system

a higher ration of polymer to fibre.

SMP+ Composite work better in bending rather than stretching. Stretching will work the

composite twills and result in dislocations and distortion except when the edges of the fibre

are well secured E.g. with a clamp or glued. The problem here is to make sure that the glue

or the clamp does not affect the elongation or contraction of the polymer fabric, this is a

difficult system to do and will not prove efficient. Therefore bending the material is more

efficient and effective for this system combination not to destroy it but again to a lesser

extent too much bending will result in fibres breakage.

The introduction of composite fibres to SMP will affects the accuracy of the shape memory

effect as not 100% of the material is shape memorising. Therefore it is important to

compensate this accuracy loss in the design of the mould where spring back rate should be

predicted prior to choosing the mould specifications to allow for some spring back loss. For

best possible and accurate results keeping the design as simple as possible and avoiding

demanding shapes is critical. Also keeping the ratio of SMP to fibre high will give the end

product better spring back rate.

43

Shape memory polyurethane polymers could be made different with different characteristics

and specifications of each, custom polymers can be designed to suit different glass transition

temperatures needed, therefore the optimum specification needed for the last system

created of the two SMP fabrics sandwiching a twintex layers, is to have a memory polymer

with a slightly lower 1st glass transition temperature and a very high 2nd glass transition

temperature around 230°C. Preferably the larger the gap difference between the 1st and the

2nd Tg‟s , and where the melting point of the polypropylene sits in the middle, the narrower

the margin of error would be.

Further future research:

Characterise the new combination of materials using dashpots and springs theory.

Find the optimum design for recovery of the material as each specific design has its

drawbacks.

Find the exact glass transition temperature of this type of polyurethane SMP using a

DSC test.

Design new shapes and ideas of new SMP and Twintex combinations.

Find the spring back force of the SMP and how strong the recovery force is to the

ratio of size and volume.

Simulation of the viscoelastic behaviour using Matlab.

44

Appendix A:

Glass fibre:-

Glass fibre is a type of composite fabric that was developed in the 1940’s being first used in the aircraft

industry. It is made from fine strings of glass fibres and woven into various textile like crosslink roving’s.

It has many advantages over metals and plastics as it provides very strong structures compared to

plastics with lower weights when matched to steel sheets and other types of metals sheets. It usually

comes as a white collared textile supplied in rolls.

(Figure showing unidirectional glass fibres)

Composites like glass fibre are usually infused with thermoplastics resins which is called the matrix the

composite fibres are stiffer and stronger than the polymer matrix;

glass fibres have good surface character for them to effectively mechanically couple to the matrix. They

have low thermal conductivity making them good insulators.

Tensile strength for two types of fibre glass:

Fiber type Tensile strength (MPa) Density (g/cm^3)

E-Glass 3,450 2.57

S-Glass 4,710 2.48

Glass fibre is dimensional stable when infused with a matrix. It has the ability to be heat resistant and

have good chemical resistance, glass fibres durably form around complex surface shapes, as this gives it

an advantage in this project as some complex shapes are demanded.

45

Appendix B:

Vacuum infusion:-

Vacuum infusion is a process largely used in the composite industries to infused matrix solutions like

resins, glues or any type of liquid materials that would harden after curing.

The main advantage of vacuum infusion it to eliminate air voids that if left untreated it would result

in a weaker material susceptible to fatigue and cracking.

(Figure showing the process of vacuum infusion)

Instead of the resin this project used the shape memory polymer that is being developed. The

process starts with the piece of fabric (i.e. glass fibre being) placed on the mould and covered with a

plastic bag called the vacuum bag. This bag will seal shut the mould with the glass fibre all air intake.

Two pips will be inserted through the vacuum bag, the inlet which will allow only the matrix in (i.e.

shape memory polymer) and the outlet which will be connected to a vacuum pump which will be

sucking all the air out of the vacuum back and air bubbles from the glass fibre matt. While the

vacuum pump is sucking air from the vacuum inside the vacuum bag, the atmospheric pressure will

be forcing the matrix solution to travel to the inlet of the vacuum bag, and thus impregnating the

glass fibre mat.

The resign trap of the matrix trap has a propos of stopping the resin of the polymer from going to

the vacuum pump and destroying it.

46

Appendix C:

Twintex:-

Twintex is a commingled glass fibre that has polypropylene filaments woven through.

Twintex is sometimes referred to PEP or PET, it is glass fiber reinforced plastic but instead of using

some resin in the matrix like normal glass fiber products would use it has a thermoplastic plastic like

polyethylene or polypropylene it has the durability of plastics and the strength of Glass fiber.

It has many advantages due to its practicality:

It has fast processing time.

the process is done by heating material above melting temperature of the polypropylene

matrix (180 C – 230 C) and applying a low pressure of (1-30) before cooling under pressure

No solvent emission

Easy to store and safe to work with.

High structural rigidity with weight saving advantages.

(Figure showing a sample of twintex, the sample is darker than normal GF due to PP filaments being

present)

47

Appendix D:

Differential Scanning Caliometry:-

A DSC test is a thermo analytical technique used to predict a materials’ glass transition temperature

and its melting temperature.

It work by calculation the difference of the energy required to increase a samples temperature

compared to a reference sample, noting that both the material being tested and the reference

sample should be with extreme precision exactly the same temperature while they are being heated

up.

The reference sample should have a well-defined heat capacity over the range of temperatures to be

scanned.

(A sample of a DCS graph)

In the above sample graph, it could be seen that the graph changes in the energy requirement, the

large jumps indicate a change in faze for the material sample. Glass transition temperature,

Crystallization, and the melting temperature are indicated by large dips or jumps abnormal to the

graph line.

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Appendix E:

Making shape memory polymer:-

Note: all experiment descriptions bellow are courtesy of Mr. Headong Park

1. Materials ① Polyurethane pellets ② DMF(Dimethylformamide)

I. puriss., absolute, over molecular sieve (H2O≤0.005%), ≥99.5% (GC) II. Product code – 40228 in Sigma-Aldrich III. Amount : at least 1L IV. Cost [£] : 61.50 (estimated in April, 2010)

③ THF(Tetrahydrofuran) I. ReagentPlus®, ≥99.0%, contains 250 ppm BHT as inhibitor II. Product code – 178810 in Sigma-Aldrich III. Amount : at least 1L IV. Cost [£] : 20.90 (estimated in April, 2010)

④ Acetone I. CHROMASOLV®, for HPLC, ≥99.8% II. Product code – 34850 in Sigma-Aldrich III. Amount : at least 1L IV. Cost [£] : 9.90 (estimated in April, 2010)

⑤ Teflon film for cooking I. POUNDLAND II. Amount : 10ea III. Cost [£] : 1.00

⑥ Cotton work gloves I. POUNDLAND II. Amount : 1pr III. Cost [£] : 1.00

⑦ Glove I. Microflex Micro One Latex Gloves; size, medium, 100ea/bx II. Product code - WZ-86231-51 in Cole-Parmer III. Amount : 1bx IV. Cost [£] : 7.28 (estimated in April, 2010)

⑧ Half Mask I. 3M® 5000 Series Maintenance-Free Respirator, Multigas vapor, L II. Product code - WZ-40112-25 in Cole-Parmer III. Amount : 1ea IV. Cost [£] : 18.27 (estimated in April, 2010)

⑨ Bottles I. 100mL Media Storage Bottles, 10qty/cs II. Product code - WZ-34523-00 in Cole-Parmer III. Amount : 1cs IV. Cost [£] : 62.00 (estimated in April, 2010)

⑩ Silicone Tape I. Silicone Tape, Orange II. Product code - WZ-08280-00 in Cole-Parmer III. Amount : 1rl IV. Cost [£] : 17.03 (estimated in April, 2010)

49

⑪ Stir Bar I. Micro Stir Bar, 12.7mm L x 3mm dia, 3.32£/ea II. Product code - WZ-08545-03 in Cole-Parmer III. Amount : 3ea IV. Cost [£] : 9.96 (estimated in April, 2010)

⑫ Pipettes I. Kontes(R) Disposable Pasteur Pipettes, Borosilicate Glass, 5 3/4", 250ea/cs II. Product code - WZ-16603-02 in Cole-Parmer III. Amount : 1cs IV. Cost [£] : 10.41 (estimated in April, 2010)

⑬ Spatula I. Nickel/stainless steel laboratory spatula, with 3/4"L spooned end and 1 1/2"L

plastisol handle, 3ea/pk II. Product code - WZ-06369-03 in Cole-Parmer III. Amount : 1pk IV. Cost [£] : 12.23 (estimated in April, 2010)

2. Manual of making polyurethane composite with randomly distributed iron particles ① First, 20wt% of polyurethane solution has to be made. Pour 40ml of DMF, 40ml of THF

into the sample bottle. Put a magnetic bar into the bottle.(in the following picture, you can see small magnetic bar. But I recommend using larger magnetic bar) Put them onto stirring machine and turn on the stirring function. Then, input 20g of polyurethane pellets. (Very slowly)

② The entrance of bottle has to be closed by silicone tape or other appropriate experimental tape to avoid spilling out of solution. Keep the stirring continuing 24hr.

50

③ Pour the solution into aluminum bowl. This aluminum bowl can be made of aluminum foil.

④ After 3~4 days, hardened rectangular sample can be obtained. But some part of its color is white because some solvent or water remains.

⑤ Collect three or more samples.

51

⑥ Prepare PTFE film (Teflon film). It can be bought in Poundland.

⑦ Preheat hot press machine up to 200℃. First, press PG button. Then, by using two arrow buttons, set the number as 200. Finally, press enter button. It takes about 1 hour to heat it up from room temperature.

52

⑧ Do hot press for each sample. First, put one PTFE film. Second, put one sample and 2 hard materials with thickness 2mm. Then, cover them with other PTFE film. Finally, do hot press them with 5 bar of pressure for 2.5~3 minutes.

53

⑨ One hot pressed sample can be obtained. But it has many pores.

⑩ So, hot press for collected samples (3 samples) has to be done for 3~4 minutes. Even after this, if the sample has many pores, more hot press has to be done.(I folded the

54

sample then I did hot press again.) But because hot press for too much time makes brittle sample, total process time must not exceed 15 minutes.

⑪ Finally, clear sample can be obtained. You may cut this into the specimens manually or by cutting machine.

55

Refrences:

[1] Sheng Zhang, Zhijun Yu, Thirumala Govender, Haiya Luo, Bangjing Li (May 2008)“A

novel supramolecular shape memory material based on partial

a-CD–PEG inclusion complex” Research Institute of Sichuan University,

[2] Heng Zhang, Haitao Wang, Wei Zhong*, Qiangguo Du*(jan 2009) “A novel type of shape

memory polymer blend and the shape

memory mechanism”. Department of Macromolecular Science, Fudan University

[3] G.J. Monkman (October 2000) “Advances in shape memory polymer actuation”,

Regensburg, Germany

[4] Nikhil Gupta (2007) “A Functionally Graded Syntactic Foam Material for High Energy

Absorption under Compression” , Mechanical, Aerospace and Manufacturing Engineering

Department Polytechnic University.

[5] Manu John and Guoqiang Li1 (2010) “Self-healing of sandwich structures with a

grid stiffened shape memory polymer

syntactic foam core”, Department of Mechanical Engineering, Louisiana State University.

[6] Fred L. Cook1, Karl I. Jacob1, Malcolm Polk1, Behnam Pourdeyhimi “Shape Memory

Polymer Fibers for Comfort Wear” Georgia Institute of Technology

2College of Textiles

[7] Marc Behl and Andreas Lendlein (2009) “Shape Memory Polymers” Center for

Biomaterial Development, Institute of Polymer Research

[8] Takeru Ohki, Qing-Qing Ni*, Norihito Ohsako, Masaharu Iwamoto (March 2004)

“Mechanical and shape memory behavior of composites

with shape memory polymer” Division of Advanced Fibro-Science, Kyoto Institute of

Technology.

[9] Bin Yang, Wei Min Huang *, Chuan Li, Jun Hoe Chor (November 2004)“ Effects of

moisture on the glass transition temperature

of polyurethane shape memory polymer filled

with nano-carbon powder” School of MPE, Nanyang Technological University.

56

[10] Kazuto Takashima, Jonathan Rossiter, Toshiharu Mukai (September 2010) “McKibben

artificial muscle using shape-memory polymer” Center for Human-Interactive Robot

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