Chapter 3- Experimental
3.1 Methodology
In order to produce PMMA, some steps need to be followed.
PMMA is generally made by mixing 20 cm3 of Methyl Methacrylate monomer with 0.1-0.3 g of Lauroyl peroxide initiator. It needs to be poured into a steel or glass mould and heated up by submerging the mould into a water or oil bath at 100 °C. Once the glycerine stage has been shaped, the mould is put into a cold water bath.
3.2 Source of the material
The types of material that would be used for this project is Methyl Methacrylate [monomer] and 1, 1’-AZOBIS (CYCLOHEXANECARBONITRILE) [Initiator] and Lauroyl peroxide (Luperox) [Initiator]. The materials are not available in Dublin Institute of Technology, so they would be purchased from SIGMA-ALDRICH.
3.3 Design of the material
The design of the material depends upon the type of the test, because each test has a unique set of standard specifications that they need to follow in accordance with the ISO standards of polymer specimen tests. The ISO standards may be found in DIT Bolton street library. The library staff knows how to get to each specific ISO standard. The design would be made by SOLIDWORKS then saved as STL file and uploaded into the Shapeways company website so that it would be shipped in approximately 10-15 business days.
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3.3.2 Tensile test mould Design
Figure11. Tensile test specimen [ISO 527-2-2012]
Dimensions in mm
According to ISO 604-2010 The preferred dimensions are:
According to IS0 60-1977 (E) the design of the mould would be according to the dimensions shown below. All dimensions are in mm unless otherwise stated.
Figure14. Density test mould design by solid works (mm)
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3.4 Manufacture process equipment
3.4.1 Ohaus Pioneer
The Ohaus pioneer is designed for basic routine weighing of a variety of laboratory, educational and industrial applications. It has the right combination of performance and features.
Density test using Archimedes principle.
Figure15. Density measuring equipment
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3.4.2 Hot plate
Hot plate is used to heat up the solution to about 100 °C to start the reaction.
Figure16. Oven (Heat up the temperature)
3.4.3 Steel container
Steel mould is used as an initial mould for this project by submerging the reaction solution into a water bath. As the reaction proceeds and the surface starts to solidify, the solid surface is taken out of the mould.
Figure17. Steel Mould
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3.4.4 Water bath
Water bath is used to heat up the reaction solution to such a temperature so as to start the reaction. The reaction usually starts at about 100 °C.
Figure18. Water bath
3.4.5 Ultrasonic
A high frequency generator produces around 35000 oscillations per second which are transferred into the cleaning solution and made to vibrate. The energy density of the sound is so high that cavitation starts to take place. Innumerous tiny vacuum bubbles develop and burst in microseconds due to pressure and suction.
Advantages
The machine is easy to use.
It saves time and cost.
Universal and compact.
Low maintenance.
Fast and highly efficient in cleaning.
Figure19. Ultrasonic
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3.4.6 Oil bath
Oil bath is the equipment used to heat up the reaction solution to a temperature of about 100 °C to start the reaction. The difference between a water bath and an oil bath is that the oil bath can get the temperature to rise instantly above 100 °C and the reaction starts to occur.
Figure20. Oil bath
3.4.7 Lloyd instrument
The Lloyd instrument machine is used for multiple purposes. It may be used to determine tensile strength, compression, flexure, friction, tear, ductility, shear strength, etc. Lloyd instrument is an established manufacturer of material testing machines, software, polymer testing instruments and texture analyzers.
Material testing machines up to 150 kN
Material testing analysis and control software
Grips and fixtures
Safety shields
Software customization service
Figure21. Lloyd instrument
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3.5 Experimental processes
The experiments were performed in room 391 (Chemistry Lab) with Lab technical assistant Anna Reid.
3.5.1 Initial Process
The beaker was
submerged into the water bath at 100°C (1.5hrs)
The solution was left at room temperature (48 hrs)
Figure22. Initial process
In this experiment, a huge amount of initiator was used because 0.08 g of AIBN initiator did not initiate the reaction, and an unknown amount of Lauroyl peroxide was added. After 48 hours, a nice solid PMMA plastic was formed at the bottom of the beaker, but it was not perfectly transparent. Otherwise, most of the MMA evaporated during the heating of the reaction solution.
Figure23. First part of PMMA obtained experimentally
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As the first sample was successfully obtained, melting point temperature was tested to check whether it was lying in the theoretical range.
Figure24 . Melting point temperature testing
The first PMMA sample melted around 125 °C which was within the expected theoretical range (about 135 °C from Table4). So the thermal properties of the first sample were acceptable.
3.5.2 Second Process
100g of MMA was poured into a steel container
The steel container was
submerged in the water bath at 90°C (1.5hrs)
The solution was left at room temperature (48 hrs)
0.08g of Lauroyl peroxide initiator was added into the solution
Figure25. Second process
In the process, measurable amount of Lauroyl peroxide initiator was used to see if it kick-started the reaction. Also the solution heated up with a lower temperature of less than 100°C to prevent the solution from being evaporated. At the end of the experiment, most of the MMA monomer evaporated and a film of PMMA was formed which was not solidifying.
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3.5.3 Third Process
200g of MMA was poured into a steel container
The steel container was put at
hot plate 70°C the water bath in about 70°C (4.5 hrs)
0.08g of Lauroyl peroxide initiator was added into the solution
The solution was left at room temperature (48 hrs)
In this process, much of MMA was used to reduce the amount of MMA evaporation. The reaction was carried out at a lower temperature to prevent MMA from being evaporated. However, the result was pretty much the same, and the specimen still looked to be the same as the previous one, although a much more increased amount of MMA was used with lesser heating.
Figure26. Second process specimen (Left) and Third process specimen (Right)
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3.5.4 Fourth Process
2g of Lauroyl peroxide
250g of MMA was poured into
a steel container and Initiator was added into solution covered by Aluminum foil
The steel container was put into
oven at 70°C the water bath in about 80°C (2 hrs)
The solution was left at room temperature (48 hrs)
Figure27. Two solutions from the fourth process
The same procedure was used for AIBN initiator to check if different initiators gave different results. The point of using Aluminum foils was to prevent the escape of the evaporated MMA and to be sure that the temperature remains uniform throughout the reaction solution. This experiment produced a perfectly solidified PMMA. But this time, bubbles developed during heating of the solution and were trapped the solid product.
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Figure28. Two Parts Prototype of the fourth process
Figure 28 shows two different specimens with the usage of Lauroyl peroxide initiator (Left) and AIBN initiator (Right) respectively.
3.5.5 Dr. John Colleran interview
An interview with Dr. John Colleran, an organic chemistry lecturer from D.I.T, at Kevin Street was organized. The objective of the interview was to investigate the methodology of processing so that the unwanted results could be fixed.
The suggestions that Dr. Colleran had were:
Try to find an initiator that does not release gases (O2 or N2).
For every 20 cm3 of MMA, 0.1-0.3g of initiator must be used.
Remove dissolved O2 in monomer before the reaction.
Use a closed mould.
Use an oil bath on the hot plate.
Immerse beaker in oil bath at 100 °C.
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Point 1 could not be attempted because of the initiators being used. AIBN or Lauroyl peroxide would always release gases during the polymerization reaction. So, unfortunately, no initiator could be found that did not release gases.
Point 2 was taken care of, and the recommended amount of initiator was used with every 20 cm3 of the monomer.
Point 3 was taken care of, and an Ultra-Sonic device was used to remove the dissolved O2 out of the monomer before the reaction was started.
Point 4 was partially implemented by using an aluminum foil which served the purpose of using a fully closed mould.
Point 5 and 6 was implemented by using a water bath in place of an oil bath because of the fact that water boils at 100 °C and it could not take the reaction solution to a temperature near 100 °C, whereas, the oil bath made sure that there was a homogenous heating of the reaction solution and it took the solution to a temperature of above 100 °C so the monomer and initiator could react easily.
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3.5.6 Fifth process
This process was carried out after implementing the findings from the interview with Dr. Colleran.
The sample of PMMA was formed in the bottom of the test tube and it looked clear with good transparency and surface finish as shown in Figure 29. The part would then be used for some tests to figure out the general properties of the part.
Figure29. Fifth process sample
3.5.7 Sixth process
Figure30. Stainless steel moulds according to ISO specifications
In this process, the moulds that were designed according to the ISO standard specifications were used as shown in Figure 30. The same methodology was used in the Fifth process, but instead of leaving the solution to solidify in the test tube, it was immediately poured into the moulds as it got to the glycerine stage. Otherwise, the moulds could not be submerged into the oil bath because the oil would flow past the aluminum foil into the PMMA solution. That's why, test tube was used until the glycerine stage.
As the moulds were left in hot plate for about 2 hrs at below 100 °C, the sample was getting the same results as in the second and the third process where the sample of film at the bottom of the mould was mostly evaporated.
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3.5.8 Seventh process
This process was used to verify the methodology used in the fifth process in which test tube was used as a mould instead of a stainless steel mould which did not give a satisfying surface finish of PMMA.
Figure31. Seventh process part
As you see in Figure 31 above, the sample got very good surface finish. The sample would be cut into 4mm thickness to perform some tests on it and compare it with other commercial samples which are processed in a different way such as Extruded process of acrylic.
3.6 Laser cut part
A plate of cast Acrylic (100 * 60) cm2 and 3 mm thickness was ordered from CENTRAL TECHNOLOGY SUPPLIES LTD. The reason for ordering was to verify the properties of our experimental cast acrylic specimen with that of the commercial one. So, it would be compared with the extruded part which is available in materials lab. The reason was the inability to acquire PMMA with stainless steel moulds because the solution was easily evaporating from the moulds. The use of glass test tube produced a very useful specimen but the problem was the spherical shape of the final specimen and the specimen could not be used as a cast acrylic specimen in the tensile test, so the cast acrylic commercial product was ordered.
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The specimen was cut into pieces by plastic cutter to fit in [Zing Laser Cut] machine as shown in Figure 32 which has the ability to accept the maximum dimensions of (60 * 40) cm2. So, the specimen was cut into two halves by plastic cutter as shown in Figure 33 with approximately (50 * 40) dimensions for each piece.
Figure 32. Zing Laser Cut machine
Figure33. Cast acrylic commercial part with cutter
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The part was designed according to ISO 527-1:2012 by SOLID WORKS in DWG file format as shown in Figure 34.
Figure34. SOLID WORKS design of commercial part for tensile test
After sending the SOLID WORKS DWG file into the Zing Laser Cut machine, the specimen begins to take the shape as shown in Figure 35 which was expected and it could be compared with extruded acrylic specimen available in materials lab for tests.
Figure 35. Laser cut (cast acrylic) part
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