I hereby certify that this material, which I now submit for assessment on the program of study leading to the award of BACHELOR OF ENGINEERING HONOURS (MANUFACTURING AND DESIGN ENGINEERING) is entirely my own work and has not been submitted for assessment for any academic purpose other than in partial fulfillment for that stated above.
Signed
Hussein Al-Tuhoo
ACKNOWLEDGEMENTS
I have been indebted in the preparation of this thesis to my supervisor, Dr Maura Kelleher of Dublin Institute of Technology College, whose patience and kindness, as well as her academic experience, have been invaluable to me. I am extremely grateful to Mr. Neill Branigan and Ms Anna Reid for helping me with the lab process and the use of lab machines and instruments to carry out necessary tests. The help of the staff of the Dublin Institute of Technology Bolton Street Library and the encouragement of Professor Dr Maura Kelleher, and the procedural guidance of Dr Maura Kelleher and Natalia Pawlak in the Dublin Institute of Technology lab, have also been most helpful. The informal support and encouragement of many friends has been indispensable, and I would like particularly to acknowledge the contribution of Esther Manuel Oni, Omolola Ojewunmi, Femi Cole, Sony Skaria and latterly Michael Jacob, Dayo Olowoniyi, Herman Kinito, Kenny Ibrahim and Tobi Akande, Abiodun Onasanya. My sincere thanks go to Mr. Sean Kean for his support with designing the moulds that were used for this project.
My parent, brothers and sisters, Tolani Oladunjoye, Kazeem, Ayobami, Shubomi, Busayo, have been a constant source of support emotionally and moral during my undergraduate years, and this thesis would certainly not have existed without them.
Chapter 1 - Introduction 4
1.1 Aim 6
1.2 Objectives 6
1.3 Justification 6
Chapter 2- Literature review 7
2.1 Introduction 7
2.2 Bio-polymers
2.2.1 Bio-polymers as Medical devices 13
2.3 PMMA (Poly-Methyl Methacrylate) 16
2.3.1 Definition and the properties for PMMA 16
2.3.2 General properties of PMMA 17
2.3.3 Biocompatible and biodegradable 14
2.3.4 Applications of PMMA 19
2.3.5 Polymerization processing of PMMA 20
2.3.5 Polymer tests 24
2.4 Bone Cement 25
2.3.1 PMMA properties as a bone cement
2.3.2 Processing of PMMA in bone cement 28
2.3.3 Polymerization process in bone cement 29
2.3.4 Compare to n-butylmethacrylate
2.3.5 Conclusion
Chapter 3- Experimental 30
3.1 Materials 30
3.1.1 Costs
3.2 Design of the material 30
3.3.1 Bending test Design
3.3.2 Tensile test Design 31
Dimensions in mm 31
3.3.2 Compressive test Design 32
3.3 Equipment 33
3.3.1 Ohaus Pioneer 33
3.3.2 Oven 34
3.3.3 Steel container 34
3.3.4 Water bath 35
3.4 Methodology 36
4.0 Discussion 43
5.0 Conclusion and Recommendations 66
6.0 References 67
Table1. Typical physical properties of poly (methyl methacrylate)
Chapter 1 - Introduction
1.1 Aim
The aim of the project is to determine the optimum processing conditions to produce high mechanical properties of PMMA.
1.2 Objectives
These are the objectives that are needed to be achieved for this project:
The source of the material
Design of the material
Processing and the equipment
The manufacturing process of the material
Testing of the material
Interpreting analysis data
Justification
PMMA (Polymethyl Methacrylate) is a biopolymer material which has great mechanical properties for use in medical fields. There are various kinds of processing of PMMA such as cast and extruded acrylic which produces a variation in properties depending upon the conditions and equipments being used. So ensuring the optimum processing of MMA to produces the PMMA with optimum properties which is already being used in general areas such as; Rear Lights, Windows, LCD screens, etc. PMMA is also used in medical and dental fields such as; bone cement, lens, artificial teeth, etc.
Additionally, the use of PMMA as a bone cement is facing big challenges nowadays. The loosening of the femoral component is the primary contributor to failure of cemented total hip replacements, as breakdowns of the cement can cause the artificial joint to come loose. So by improving the mechanical properties of PMMA, the loosening of the material can be reduced. However, PMMA may be replaced with other materials such as Polycarbonate. Investigating the properties of each material, the material best fit for use in general and medical fields could be verified.
Chapter 2- Literature review
Introduction
This project aims to study the behavior of different plastic materials for different applications with special attention to Poly Methyl Methacrylate (PMMA). This project will study in depth, the possibility of the use of PMMA against different other plastic materials for different purposes with the medical field in particular focus. We will study the production steps of PMMA and try to optimize the production of PMMA and the steps involved, so as to optimize the mechanical and physical properties of PMMA.
Polymers
Polymer is a Greek word, meaning 'many' (poly) 'parts' (meros). Polymer is a long or larger molecule consisting of a chain or network of many repeating units, formed by chemically bonding together many identical or similar small molecules called monomers. A polymer is formed by polymerization, the joining of many monomer molecules. Examples of natural polymers are cellulose, shellac and amber. Biopolymers such as proteins and nucleic acids play crucial roles in biological processes.
Common synthetic polymers are Bakelite, neoprene, nylon, PVC (polyvinyl chloride), polystyrene, PMMA (Polymethyl Methacrylate) and Polycarbonate.
2.3 Bio-materials
A biomaterial may be defined as any material device which may replace a part or used to make a function of the body in a safe, reliable, economic, and physiologically acceptable manner. A variety of devices and materials are used in the treatment of disease or injury. Commonplace examples include sutures, tooth fillings, needles, catheters, bone plates, etc. A biomaterial is a synthesis material used to replace part of a living system or a function in intimate contact with living tissue.
Since the ultimate goal of using biomaterials is to improve human health by restoring the function of natural living tissues and organs in the body, it is essential to understand relationships among the properties, functions, and structures of biological materials. Thus, three aspects of study on the subject of biomaterials can be envisioned: biological materials implant materials, and interaction between the two in the body.
Figure1. Schematic illustration of biocompatibility.
The success of a biomaterial or an implant is highly dependent on three major factors: the properties and biocompatibility of the implant (Figure 1), the health condition of the recipient, and the competency of the surgeon who implants and monitors it progress. It is easy to understand the requirements for an implant by examining the characteristics that bone plate must satisfy for stabilizing a fractured femur after an accident, these are:
Acceptance of the plate to the tissue surface, i.e., biocompatibility (this is a broad term and includes points 2 and 3)
Pharmacological acceptability (nontoxic, non-allergenic, non-immunogenic, non-carcinogenic, etc.)
Chemically inert and stable (no time-dependent degradation)
Adequate mechanical strength
Adequate fatigue life
Sound engineering design
Proper weight and density
Relatively inexpensive, reproducible, and easy to fabricate and process for large-scale production.
The list in Table 1illustrates some of the advantages, disadvantages, and applications of four groups of synthetic (manmade) materials used for implantation. Reconstituted (natural) materials such as collagen have been used for replacements (e.g., arterial wall, heart valve, and skin).
2.4 Synthetic Polymers
Synthetic polymers are polymers that are man-made. Most synthetic polymers are manufactured from petroleum.
Some examples of synthetic polymers include:
Polystyrene is the polymer found in Styrofoam, used for everything from packing materials and insulation to drinking cups.
Polyvinyl chloride, widely known by its abbreviation PVC, is used in a lot of building material (and is well-known as being ubiquitous in piping).
Poly (Methyl Methacrylate) (PMMA) is a transparent thermoplastic often used as a lightweight or shatter-resistant alternative to soda-lime glass
These materials are generally not biodegradable, and because they are made from petroleum, once the basic materials for creating them are used up, we cannot produce them anymore.
2.5 Radical Polymerization
The most common type of addition polymerization is free radical polymerization. A free radical is simply a molecule with an unpaired electron. The tendency for this free radical to gain an additional electron in order to form a pair makes it highly reactive so that it breaks the bond on another molecule by stealing an electron, leaving that molecule with an unpaired election (which is another free radical). Free radicals are often created by the division of a molecule (known as an initiator) into two fragments along a single bond. The following diagram shows the formation of a radical from its initiator, in this case benzoyl peroxide.
Figure2. Free radical polymerization
The stability of a radical refers to the molecule's tendency to react with other compounds. An unstable radical will readily combine with many different molecules. However a stable radical will not easily interact with other chemical substances. The stability of free radicals can vary widely depending on the properties of the molecule. The active center is the location of the unpaired electron on the radical because this is where the reaction takes place. In free radical polymerization, the radical attacks one monomer, and the electron migrates to another part of the molecule. This newly formed radical attacks another monomer and the process is repeated. Thus the active center moves down the chain as the polymerization occurs.
There are three significant reactions that take place in addition polymerization: initiation (birth), propagation (growth), and termination (death). These separate steps are explained below.
2.5.1 Initiation Reaction
The first step in producing polymers by free radical polymerization is initiation. This step begins when an initiator decomposes into free radicals in the presence of monomers. The instability of carbon-carbon double bonds in the monomer makes them susceptible to reaction with the unpaired electrons in the radical. In this reaction, the active center of the radical "grabs" one of the electrons from the double bond of the monomer, leaving an unpaired electron to appear as a new active center at the end of the chain. Addition can occur at either end of the monomer. This process is illustrated in the following animation in which a chlorine atom possessing an unpaired electron (often indicated as cl-) initiates the reaction. As it collides with an ethylene molecule, it attracts one of the ethylene's pair of pi bonded electrons in forming a bond with one of the carbons. The other pi electron becomes the active center able to repeat this process with another ethylene molecule. The sigma bond between the carbons of the ethylene is not disturbed.
In a typical synthesis, between 60% and 100% of the free radicals undergo an initiation reaction with a monomer. The remaining radicals may join with each other or with an impurity instead of with a monomer. "Self destruction" of free radicals is a major hindrance to the initiation reaction. By controlling the monomer to radical ratio, this problem can be reduced.
2.5.2 Propagation Reaction
After a synthesis reaction has been initiated, the propagation reaction takes over. In the propagation stage, the process of electron transfer and consequent motion of the active center down the chain proceeds. In this diagram, (chain) refers to a chain of connected monomers, and X refers to a substituent group (a molecular fragment) specific to the monomer. For example, if X were a methyl group, the monomer would be propylene and the polymer, polypropylene.
In free radical polymerization, the entire propagation reaction usually takes place within a fraction of a second. Thousands of monomers are added to the chain within this time. The entire process stops when the termination reaction occurs.
2.5.3 Termination Reaction
In theory, the propagation reaction could continue until the supply of monomers is exhausted. However, this outcome is very unlikely. Most often the growth of a polymer chain is halted by the termination reaction. Termination typically occurs in two ways: Combination and disproportionation.
Combination occurs when the polymer's growth is stopped by free electrons from two growing chains that join and form a single chain. The following diagram depicts combination, with the symbol (R) representing the rest of the chain.
Disproportionation halts the propagation reaction when a free radical strips a hydrogen atom from an active chain. A carbon-carbon double bond takes the place of the missing hydrogen. Termination by disproportionation is shown in the diagram.
Disproportionation can also occur when the radical reacts with an impurity. This is why it is so important that polymerization be carried out under very clean conditions.
2.6 Bio-polymers as Medical devices
Biopolymers have been widely utilized in medicine. The biopolymers have potential uses in virtually every section of the medicine sector. The principle of biopolymer applications is majorly perceived in medical devices and drugs. For instance, they are used in making implants. The implants have been credited for safety and effectiveness on producing medical devices. The manufacture of medical devices while utilizing with the polymers have improved the bio-absorption effect in these devices thus making them efficient. In addition, drugs development while interacting with polymers validates the dosage as well as elution rates. Biopolymer knowledge is the best way to address global economic and environmental concerns in healthcare, agriculture, water and energy efficiency.
The durability of biopolymers makes them ideal for medical practices. Examples of polymers used in medical arena include; heparin, used in anti-thrombotic effect as coating, polysaccharides are used in oral health care as tartar agents, Chitosan made from crustacean shells and applied to wounds for quick healing. Other polymers include alginate chitin, starch, hyaluronic and biosynthesized cellulose that are applied in plastic surgery procedures. Creative use of biopolymers has helped to empower many countries in the way they are utilizing resources and moving towards green technological revolution.
Similarly, the health care has also embraced biodegradable polymers as a way of maintaining and protecting environmental and physical health. Although the polymers are widely utilized, their challenges are also experienced. Some of the polymers have shown issues adverse immune reactions and cultural sensitivities. In the recent past great concerns have also been expressed on how medical devices are approved by Food and Drugs Administration. This calls for medical manufacturers to continue focusing on biopolymers, but they should be aware that not everything is good for implants they ought to be selective.
2.7 Biocompatible and biodegradable
During the past few years, the biocompatibility of biomaterials (non-vital material intended to interact with biological systems within or on the human body) has evolved into a comprehensive, complex, and independent discipline of biomaterials science. Consequently, a number of terms have been developed or were adopted from toxicology. Some of these terms may be familiar to patients and clinicians from daily life – for example, the term “safety”. Safety in relation to the evaluation of biomaterials means freedom from unacceptable risks. Thus, safety does not stand for a complete lack of risks.
2.7.1 Definition of Biocompatibility
Biocompatibility is a word that is extensively used within biomaterials science, but there still exists a great deal of uncertainty about what it actually means and about the mechanisms that are subsumed within the phenomena that collectively constitute biocompatibility.
During the 2nd Consensus Conference in Liverpool, biocompatibility was defined as “the ability of a material to perform with an appropriate host response in a specific application”. A biocompatible material may not be completely “inert”; in fact, the appropriateness of the host response is decisive. Previously, the selection criteria for implantable biomaterials evolved as a list of events that had to be avoided, most of these originating from those events associated with the release of some products of corrosion or degradation, or additives to or contaminants of the main constituents of the biomaterial, and their subsequent biological activity, either locally or systemically. Materials were therefore selected, or occasionally developed, on the basis that they would be non-toxic, non-immunogenic, non-thrombogenic, non-carcinogenic, non-irritant and so on, such a list of negatives becoming, by default, the definition of biocompatibility. A re-evaluation of this position was initiated by two important factors. Firstly, an increasing number of applications required that the material should specifically react with the tissues rather than be ignored by them, as required in the case of an inert material. Secondly, and in a similar context, some applications required that the material should degrade over time in the body rather than remain indefinitely. It was therefore considered that the very basic edict that biocompatibility, which was equated with biological safety, meant that the material should do no harm to the patient, was no longer a sufficient pre-requisite. Accordingly, biocompatibility was redefined in 2008 as “the ability of a material to perform its desired function with respect to a medical therapy, without eliciting any undesirable local or systemic effects in the recipient or beneficiary of that therapy, but generating the most appropriate beneficial cellular or tissue response in that specific situation, and optimizing the clinically relevant performance of that therapy”.
2.7.1 Definition of Biodegradability
Biodegradation is the chemical dissolution of materials by bacteria, fungi or other biological means. Although often conflated, biodegradable is distinct in meaning from compostable. While biodegradable simply means to be consumed by microorganisms and return to compounds found in nature, "compostable" makes the specific demand that the object break down under composting conditions. The term is often used in relation to ecology, waste management, biomedicine, and the natural environment (bioremediation) and is now commonly associated with environmentally friendly products that are capable of decomposing back into natural elements. Organic material can be degraded aerobically with oxygen, or an aerobically, without oxygen. Bio-surfactant, an extracellular surfactant secreted by microorganisms, enhances the biodegradation process.
Biodegradable matter is generally organic material such as plant and animal matter and other substances originating from living organisms, or artificial materials that are similar enough to plant and animal matter to be put to use by microorganisms. Some microorganisms have a naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a huge range of compounds including hydrocarbons (e.g. oil), polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), pharmaceutical substances, radio nuclides, pesticides, and metals. Decomposition of biodegradable substances may include both biological and abiotic steps. Products that contain biodegradable matter and non-biodegradable matter are often marketed as biodegradable.
2.8 PMMA (Polymethyl Methacrylate)
Polymethyl Methacrylate (PMMA) is a chemical and synthetic transparent thermoplastic material serves as an alternative for glass formed from the Methyl Methacrylate polymerization. The transparent plastic material from the acrylic resin family manufacturing and processing improvement employ scientific polymerization principles and mechanisms for the productivity and quality improvements. Thus, the processing and manufacturing process does not only focus on the industry or market needs but also health, environment and the social effects. PMMA is a compatible material (not biodegradable).
It has since been sold under many different names, including Acrylic, Lucite, and Perspex.
2.8.1 Definition and the properties for PMMA
PMMA is a rigid, tough and transparent of the resin family found in paint and glasses. On the synthesis of the material, the polymer produced by bulk, solution and emulsion polymerization processes by the initiation of the radiations that aids in its extraction from its primary source. The polymer material is cut and joining properties by the application of solvents or welding that dissolves the plastic joints. The PMMA material dissolves in organic solvents, transmit visible light, allowing both refractions of light and blockage of the infrared light. On a different point of view, the polymer burns in air to form carbon (IV) and water. The polymer has a good environmental stability and a poor resistance to many chemicals as it readily hydrolyzes forming esters.
On a broad front, further analysis on the properties modification reveals, addition of acrylates co monomers in small proportions to improve grades and additional of butyl acrylates to improve the product's strength. In addition, methacrylic acids are added to increase transition temperature where the glass material qualities improved. An impact property is improved during processing by the addition of the plasticizers as the glass transition temperature is lowered. The cost effectiveness of the polymer is added by incorporating filters during the production process as well as adding dyes to produce a decorative color application.
2.8.2 General properties of PMMA
PMMA is a linear thermoplastic polymer. Main physical characteristics of PMMA are shown in Table 2.
Table2. Typical physical properties of poly (methyl methacrylate)
PMMA has high mechanical strength, high Young's modulus and low elongation at break. It does not shatter on rapture. It is one of the hardest thermoplastics and is also highly scratch resistant. It exhibits low moisture and water absorbing capacity, due to which products made have good dimensional stability. Both of these characteristics increase as the temperature rises. Table 2 shows some of mechanical characteristics of PMMA.
Table3. Typical mechanical properties of poly (methyl methacrylate)
The low water absorption capacity of PMMA makes it very suitable for electrical engineering purposes. It dielectric properties are very good, but polystyrene and LDPE are superior to it. Its resistivity depends on the ambient temperature and relative humidity. The dielectric constant, as well as the loss tangent, depends on the temperature, the relative humidity of air and the frequency.
Table4. Typical electrical properties of poly (methyl methacrylate)
The thermal stability of standard PMMA is only 65 °C. Heat-stabilized types can withstand temperatures of up to 100 °C. PMMA can withstand temperatures as low as - 70 °C. Its resistance to temperature changes is very good.
PMMA is a combustible material, which continues burning even after the flame is removed.
PMMA’s physical and chemical properties make it suitable for various applications.
The properties such as its being transparent strong, durable and transparent make it suitable in the manufacture of rear-lights and lenses for glasses. The versatility of PMMA also makes the material applied in the production of various instrument clusters for the motor-vehicles.
The strength of the material combined with its water absorption capacity make the material to useful in the manufacture of windows, sanitary ware, furniture, and LCD screens, among others (Bronzino, 2000). The material’s resistance to the exposure of sunlight and the effects of UV rays has made it useful in the coating of polymers. The above is due to its stability when exposed to various environmental situations such as moisture and sunlight.
Figure4. Dental restorations made of PMMA
In addition, PMMA stability and purity have also been used in dental and medical fields. Its compatibility with the human tissue has also been exploited in the manufacture of intraocular lenses. Further, it is applied in the bone cement to fix implants. The transparent appearance of PMM makes is suitable for its use in patient’s teeth and production of ocular prostheses. Therefore, the physical and mechanical properties PPMA combined with the properties of other polymers enhance the manufacture of better materials with maximum mechanical properties.
2.9 Polymerization processing of PMMA
In general, Polymerization processing of PMMA depends on two factors:
Amount of initiator per grams of monomer are being used (For every 20 cm3 of MMA 0.1-0.3 g of initiator must be used).
The reaction starts at 100 °C and above.
However, there are some other factors that would depends on the type of processing are being used during polymerization. Cast acrylic and Extruded acrylic would be the most common types of processes that have been used in industrial. Extruded acrylic mostly used in the high production mass industries.
2.9.1 Cast processing [Used as experimentally]
Cast acrylic, as the name suggests, is manufactured by a process whereby MMA (Methyl Methacrylate monomer) liquid and amount of initiator is pumped into a mould made from two sheets of glass. The mould or monomer is then submerged in warm water and the process of polymerization takes place as shown in Figure 5.
Figure5. Processing of cast acrylic
In addition to the above cast acrylic sheets lend themselves to ease of fabrication. Moreover, cast acrylic when laser cut produce a highly polished edge, thus reducing finishing times when fabricating. Furthermore, when hot wire line bending, drape or vacuum forming cast acrylic sheets are more malleable / pliable than extruded acrylic sheet.
2.9.2 Extruded processing [High production mass industries]
Extruded Acrylic sheets are manufactured by a continuous production process. Acrylic or PMMA pellets are fed from a containment silo to a feed hopper above an extruder line. The pellets are fed into the extrusion barrel and are driven through the barrel by a single or twin screw auger system.
Figure6. Processing of extruded acrylic
As the pellets progress through the heated zones of the extruder barrel the heat increases until the pellets melt into a molten mass.
This molten mass is pushed forward into a conical / cone shaped die which then widens out into the die lips. The molten mass, under pressure from the screw-drive, reaches the die lips and pushes outwards along the die lips to produce a molten sheet. The height / gap of the die lips is set slightly larger than the thickness required for the finished sheet. This continuous band of molten acrylic sheet is then passed through sets of cooling rollers, which may emboss a pattern / finish onto the sheet as it cools or may just produce a standard gloss / smooth finish.
As the sheet progresses down the haul-off line it has cooled sufficiently to be edge trimmed, cut to the final finished length required and a protective P/E film is applied. Finally, the sheets are palletized and wrapped for dispatch.
Extruded acrylic VS Cast Acrylic
The comparison between two methods of acrylic processing is as follows.
Chemical Resistance
Cast acrylic is more resistant to the same solvents.
Laser cutting
When laser cutting extruded acrylic, there will be a burr on one side of the part. On the cast acrylic there are almost no burrs. The edges on extruded acrylic parts can look a bit different depending on the direction of the acrylic extrusion.
Laser engraving
The Laser engraving will be seen on extruded acrylic which looks matt gray. On the cast acrylic, it will look matt white.
Heat bending and thermoforming
A sheet of extruded acrylic can, because of the acrylic extrusion direction, behave differently depending on the bending direction relatively to the extrusion. With cast acrylic, it makes no difference.
When cast colored acrylic is heated for thermoforming or heat bending the color can change. Matt-colored surfaces can become clear and clear surfaces can become matt. In addition, the shade of color can change. Cast acrylic is harder to bend / shape.
Thickness tolerance
Sheets of cast acrylic vary more in thickness. A cast 3 mm acrylic sheet varies +/- 15%, while an extruded sheet only varies +/- 5%. The dispersion within the tolerance also seems to be less on extruded sheets.
Scratch-resistant
Cast acrylic it more scratch resistant than extruded acrylic.
Flame polishing
Cast acrylic is harder to flame polish.
Colors
Cast acrylic is produced in a many different color and thicknesses. The color selection is more limited for extruded acrylic. If one orders a special color from a supplier, it will in most cases be cast acrylic.
Tension
There is more tension in extruded acrylic.
2.10 PMMA challenges with Polycarbonate
Acrylic has a big challenges with Polycarbonate (Lexan) and glasses in Lenses and other fields in industrial and that kind of comparison was taken out from:
Strength (Acrylic and Polycarbonate are both half the weight of glass and yet both of these plastics are much stronger than glass).
Light & Clarity (Acrylic also has better clarity than glass, with a light transmittance of 92 percent “Not yellowing”. Where Polycarbonate has a light transmittance of 88 percent.
Durability (Acrylic is more likely to chip than polycarbonate because it is less impact-resistant).
Cost (Polycarbonate is more expensive than acrylic. It tends to cost about 35% more).
Laser cutting (Polycarbonate becomes yellow and burnt when laser cut. Foils up to 0.5 mm can be laser cut to produces overlays. Laser cutting sheets is not recommended).
Colors (Color selection of polycarbonate sheets is limited).
Scratch robustness (Polycarbonate is easier to scratch, but can as with acrylic be delivered with a hard-coated surface).
Strength (Polycarbonate has a higher tensile strength).
2.10 Bone Cement
Bone cement has been attributed as a successful anchor to repair joints such as hip, knee, and shoulder joints. The chemical combination of bone cement is Polymethyl Methacrylate (PMMA). The excellent compatibility of bone cement to the body tissue made it possible for the component to be used for anchorage. Bone cement is considered reliable for clinical practices and has proven long survival rate for artificial hip and knee joints. PMMA material in the bone cement is the most enduring material during the orthopaedic surgery process. However, there is a great concern to revitalize its mechanical and chemical properties in order to enhance the clinical performance.
Figure7. Artificial hip joint replacement [22]
Figure8. Artificial knee joint replacement [20]
PMMA cement has recorded potential pitfall thus the need for changing its mechanical properties. The major failure recorded is the loosening and shrinkage that results from damage to the monomer-mediated bone. The shrinkage is results from the end-polymerization process that compromises the bone and cement interface. These failures are attributed to the disregarding of crucial elements when working with PMMA. In order to attain strong bone cement, methyl Methacrylate monomer should be allowed to polymerize at room temperature. Most clinicians are tempted to alter the mix constituents when preparing the bone cement that increases the maximum setting temperature thus reducing the comprehensive strength. Altering the mix content reduces the polymer chain concentration and introducing multiple stress risers.
It is advisable for clinicians to take care when performing unpredictable alteration since they distort the mechanical properties of the bone cement. In addition, the role of nano hydroxyapatite particles on mechanical properties of PMMA should be considered since they contribute to the comprehensive strength of the bone cement. Addition of 2.5% of HA nano-composites increases the elongation break of PMMA as well as enhancing the maximum bending strength value. These HA nano-composites enhance the biocompatibility of the cement since they have a higher tensile and toughness when they reinforce methyl Methacrylate polymers. Polymethyl Methacrylate is brittle and notch sensitive especially when utilized for total hip replacement. The modulus of elasticity is tested with the tension the bone can withhold.
Materials required for fixation should not degrade when responding to corrosive conditions. The manufacturing of PMMA cement should contain properties that permit fabrication in optimum design. Clinicians should note that polymers have poor adhesive properties, for this reason, when using PMMA cement for total hip replacement; they should safeguard the patient from the deleterious effect of the exothermic polymerization process on the surrounding tissues. Implanted PMMA ought to be minimal in volume in a bid to have a proper structural configuration that can withstand intrinsic and extrinsic forces during heat dissipation. In addition, the PMMA should have enhanced fibres that will control its elasticity structure.
Figure.9 Difference between unloosening and loosening bone cement
The drawback to using bone cement is that it may degrade over time and bits of cement can break off, potentially causing problems such as a breakdown of the cement can cause the artificial joint to come loose, which may prompt the need for another joint replacement surgery (revision surgery). In that case from that project based on trying to reduce the amount of loosening that causes by the time. That could be solved by increase the strength and young's modulus of PMMA in the side of trying to get the maximum mechanical properties by approving the best condition of processing polymers.
Hip replacement is an operational process in which the hip joint substituted by a prosthetic implant. Its surgery performed as a hemi (half) replacement or a total replacement (THR). Hip and knee joint substitution orthopaedic surgery is implemented to alleviate arthritis ache or in a number of hip fractures. The total hip replacement (THR) comprises of substituting both the femoral and acetabulum head while hemiarthroplasty substitutes the femoral head.
Figure 10. sample of cementing
Polymethyl Methacrylate (PMMA) bone cement is a medical appliance, projected for implant purposes constituted from Polymethyl Methacrylate, methyl Methacrylate, copolymers with Polymethyl Methacrylate, or esters of methacrylic acid and polystyrene. PMMA intended for utilization in arthroplastic processes of the knee, hip and extra joints for the fixation of polymer prosthetic implants to an active bone.
2.11.1 Processing of PMMA as a bone cement
The process of PMMA bone cement is a self-curative, two constituent mechanisms consisting of powder and liquid constitutes. The liquid part contains the accelerator, the inhibitor, and the monomer. The powder part has the polymer, initiator, and radio-pacifier. PMMA is a brittle, notch responsive substance. In the circumstance of THR, PMMA relative features are essential. The feature of modulus of elasticity is tested in tension and estimate 2400 MPa. The amount is approximately ten folds lesser than that of the adjacent cortical bone and 100 folds below that of the metal trunk. For this reason, it acts as an elastic interface between two inflexible layers. In addition, cement is less fragile in vivo compared to laboratory testing results, turning more elastic when heated. The process occurs at the glass changeover temperature (Tg) that ranges with structure of the monomer and the molecular weight. Cement saturated with liquid in vivo, which minimizes the Tg and, for this reason, has a plasticizing property. Polymers show properties of both viscous liquids and elastic solids under circumstances of low strain and for this reason illustrated as visco-elastic. At a molecular stage, comparatively weak non-covalent interfaces exist between neighboring polymer side-chains, and they breached, consequence in visco-elastic properties.
The process of PMMA bone cements leads to the polymerization process. Polymerization process of the bone cement involves an exothermic effect, which happens as the cement hardens in situ. The discharged heat may break bone or tissues neighboring the implant. Insufficient fixation or unexpected postoperative incidents may distress the cement-bone bond and result to micro motion of cement touching bone facade. A fibrous tissue section may expand between the bone and the cement, and loosening of a part of the bone occurs leading to implant malfunction. Long-term monitoring advised for every patient on a recurrently scheduled condition. The surgeon must be acquainted with the features, handling distinctiveness, and usage of bone cements. The knowledge is essential because the handling and curative properties of this bone cement differ with humidity, temperature, and mixing method, they are best resolution by the surgeon's tangible experience.
2.11.2 Polymerization process in bone cement
The polymerization process starts by the interaction between the initiator and the activator, providing a free element that react with the monomer. On the other hand, the solidified polymer can protect a firm fixation of the cemented bones. Even though acrylic bone cements extensively applicable in orthopedics, a number of drawbacks associated with their utilization. The residual monomer accumulates on the body and results in fat embolism. The exothermic property of the polymerization procedure leads to a potential consequence of neurosis of the neighboring tissue. The most significant shortcoming is aseptic loosening such as aseptic loosening implant during the cementing process. The basis of aseptic loosening could be biochemical or mechanical. Biochemically, torn debris of the polyethylene constituent could transfer to the bone cement boundary and cause an inflammatory reaction, resulting to osteolysis and deteriorating the implant edge. Mechanically, cyclic weight of the implant result to fatigue crack of the cement. In order to enhance PMMA fixation, a potential approach is to avoid cement crack by increasing the mechanical elasticity of the cement. Researchers have engineered bone cement with advanced bonding power and compressive modulus than usual PMMA, combining a bisphenol-A-glycidyl dimethacrylate (Bis-GMA)-based adhesive impregment with glass bioactive ceramics. Another strategy takes advantage of composite by strengthening PMMA using bioactive glass and hydroxyapatite (HA), which incorporates strengths and elasticity with bioactivity.
2.12 Polymers tests
Tensile, compression, density and melting temperature test are the standard tests that determine the quality of the polymer materials. Tensile test measures breakability properties such as modulus, strength, elongation and strain quality of the polymers. Compression test determines ultimate compressive strength and deflection and density test determine the density of the material. Melting temperature test determines thermal behavior of the material.
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.
3.3.2 Tensile test mould Design
According to ISO 527-2-2012
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)
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
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
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
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
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
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.
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)
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.
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.
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.
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.
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.
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
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
Chapter 4 - Results
4.1 Tests and analysis
Tensile, compression, density and melting temperature test are the kinds of test that would use to do a comparison between parts of Acrylic. Tensile test measures breakability properties such as modulus, strength, elongation and strain quality of the polymers. Compression test determines ultimate compressive strength and deflection and density test determine the density of the material. Melting temperature test determines thermal behavior of the material.
Kind of Tests:
Density Test
Compression Test
Tensile Test
Melting Temperature Test
Parts to be in the tests:
Extruded Acrylic [Thickness= 4mm Height= 230mm Width= 9mm] available in materials lab.
Cast Acrylic (Laser Cut) part [Thickness= 3mm Height= 168mm Width= 8mm].
Experimental Cast Acrylic [Thickness= 4mm].
4.2 Density test
Density is a measurement of the amount of matter in a given volume of a substance or material. Density is a physical characteristic, and it is a measure of mass per unit of volume of a particular substance or material. Density is an important property which can be used to identify a substance.
For the density test, the following process had to be carried out.
Measure the samples that will be used for the density test by using the weighing device that is provided in the lab.
Figure39. Samples measurement
Fill the graduated cylinder with desired amount of water but make sure the sample can be immersed.
Measure the amount of water in the graduated cylinder and record the value.
Drop the sample in to the graduated cylinder; also make sure the sample gets immersed.
Measure the increase in level of water while the sample is in the graduated cylinder.
4.2.1 Extruded acrylic sample
Using a 10cm3 graduated cylinder, pour some amount of water in the graduated cylinder while making sure that the amount of water poured into the graduated cylinder is more than the length of the sample. This was done because the sample will be immersed into the water. If the sample is not immersed, it would be no good. The change in water volume would be the volume of the part.
Figure40. Extruded acrylic part immersed in water
The sample was then thrown into the graduated cylinder. While the samples was immersed in the graduated cylinder, the water level increased by 5.3 cm3.
4.2.2 Cast acrylic (Laser Cut) sample
The exact process that was carried out for the first sample was also carried out for the second sample.
Figure41. Cast acrylic (Laser Cut) part immersed in water
The sample was then thrown into the graduated cylinder. While the samples was immersed in the graduated cylinder, the water level increased by 3 cm3.
4.2.3 Cast acrylic (Experimental) sample
The exact process that was carried out for the first and second sample was also carried out for the third sample.
Figure42. Cast acrylic (experimental) part immersed in water
The sample was then thrown into the graduated cylinder. While the samples was immersed in the graduated cylinder, the water level increased by 9.2 cm3.
4.3 Compression test
Compressive test of a material is the force per unit area that it can withstand during compression test. A compression test determines the behavior of a material under crushing load. The sample is compressed and deformation and various loads will be recorded. Compressive stress and deflection are calculated and plotted as a stress deflection diagram, which is used to determine ultimate compressive strength.
4.3.1 Extruded acrylic sample
For the first sample, the sample was placed under load for the compression test and the Lloyd instrument machine was used to compress the sample. About 50% of compression was applied according into the thickness of the part which was 4 mm so 2 mm of compression would be applied. The diameter area of compression should be 12 mm.
Figure43. Compression test of extruded acrylic part
As shown in Figure 44, which describes the compression behavior of the material where that's would help to figure out the ultimate compressive strength.
Force VS Deflection
14000
12000
10000
8000
6000
4000
2000
0 0.5 1 1.5 2
Deflection (mm)
Figure44. Compression Test graph of extruded acrylic sample
Sample Calculations
Compressive strength (σ) = (Maximum Load / Cross sectional area of the specimen)
d:Diameter of specimen.
Cross sectional area of the specimen that would be in compression =
d=12 mm (Diameter of the compressive circle that used in Lloyd instruments)
Maximum load = 13122 N
RESULT
Compressive strength of specimen = 116 MPa
Deflection VS Compressive Strength
140
120
100
80
60
40
20
0 0.5 1 1.5 2
Deflection (mm)
Figure45. Compressive strength VS Deflection graph of extruded acrylic
4.3.2 Cast acrylic (Laser cut) sample
For the second sample, the sample was placed under load for the compression test and the Lloyd instrument machine was used to compress the sample. About 50% of compression was applied according into the thickness of the part which was 3 mm so 1.5 mm of compression would be applied. The diameter area of compression should be 12 mm.
Figure46. Compression test of extruded acrylic part
As shown in Figure 47, which describes the compression behavior of the material where that's would help to figure out the ultimate compressive strength.
Force VS Deflection
-0.5
16000
14000
12000
10000
8000
6000
4000
2000
0 0.5 1 1.5 2
Deflection (mm)
Figure47. Compression Test graph of cast acrylic (Laser Cut) sample
Sample Calculations
Compressive strength (σ) = (Maximum Load / Cross sectional area of the specimen) d:Diameter of specimen.
Cross sectional area of the specimen that would be in compression =
d=12 mm (Diameter of the compressive circle that used in Lloyd instruments) Maximum load = 13684.64 N
RESULT
Compressive strength of specimen = 121 MPa
Deflection VS Compressive Strength
-0.2
140
120
100
80
60
40
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Deflection (mm)
Figure48. Compressive strength VS Deflection graph of cast acrylic(Laser Cut)
4.3.2 Cast acrylic (Experimental) sample
For the third sample, the sample was placed under load for the compression test and the Lloyd instrument machine was used to compress the sample. The cylindrical shape of acrylic (test tube sample) was cutting in 4mm circle thickness to be compatible with compression test. About 50% of compression was applied according into the thickness of the part which was 3 mm so 1.5 mm of compression would be applied. The diameter area of compression should be 12 mm.
Figure49. Compression test of cast acrylic (Experimental) part
As shown in Figure 50, which describes the compression behavior of the material where that's would help to figure out the ultimate compressive strength.
Force VS Deflection
16000
14000
12000
10000
8000
6000
4000
2000
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Deflection (mm)
Figure50. Compression Test graph of cast acrylic(Experimental) sample
Sample Calculations
Compressive strength (σ) = (Maximum Load / Cross sectional area of the specimen) d:Diameter of specimen.
Cross sectional area of the specimen that would be in compress =
d=12 mm (Diameter of the compressive circle that used in Lloyd instruments) Maximum load = 13478.57N
RESULT
Compressive strength of specimen = 119.17 MPa
Deflection VS Compressive Strength
140
120
100
80
60
40
20
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6
Deflection (mm)
Figure51. Compressive strength VS Deflection graph of cast acrylic (Experimental)
4.4 Melting Temperature Test
Melting temperature test is used to determine the thermal stability of each part of the sample. In this test, hot plate is used to heat up the pieces until they would melt. Thermocouple was used to measure and notify the temperature on the hot plate.
Figure51. Melting temperature test
Values of melting temperature measurement were:
Extruded acrylic melts at 150 °C.
Experimental and commercial cast acrylic melts at 160 °C.
4.5 Tensile Test
Tensile test of a material is the force per unit area that it can withstand during tension test. A tension test determines the behavior of a material under elongation. Tensile test measures breakability properties such as modulus, strength, elongation and strain quality of the polymers. Tensile stress and strain are calculated and plotted as a stress strain diagram, which is used to determine elastic limits, yield point and ultimate tensile strength. In that test experimental part was not able to be used because of its circular shape so as we verified in density compression and melting temperature tests that the experimental part exist the same properties of commercial laser cut one because both of them were made by cast processing. So in that reason we could compare cast acrylic using commercial part (Laser Cut) with extruded acrylic that's available in the lab.
4.5.1 Extruded acrylic sample
For the first sample, the sample was placed under tension load for the tensile test and the Lloyd instrument machine was used to elongate the sample.
Figure53. Tensile test of extruded acrylic
Force VS Extension
3000
2500
2000
1500
1000
500
0 1 2 3 4 5 6 7
Extension (mm)
Figure54. Tensile Test graph of Extruded acrylic sample
Sample Calculations
Ultimate Tensile stress (σ) = (Maximum Load / Cross sectional area of the specimen) By given data:
Try to pick a point in Maximum load = 2737.1 N
@ point of maximum load the Extension ΔL = 6.6554 mm
So the stress would be,
and the strain,
So the percentage of elongation at the break point would be 3%
RESULT
Ultimate tensile strength of specimen = 72 MPa
Percentage of elongation of specimen at the break point = 3% Tensile Modulus (E) = 2.4 GPa
Stress VS Strain
80
70
60
50
40
30
20
10
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035
Strain ε
Figure55. Tensile strength VS Strain graph of Extruded acrylic
4.5.1 Cast acrylic sample
For the first sample, the sample was placed under tension load for the tensile test and the Lloyd instrument machine was used to elongate the sample.
Figure56. Tensile test of extruded acrylic
Force VS Extension
-0.5
1400
1200
1000
800
600
400
200
0 0.5 1 1.5 2 2.5 3 3.5
Extension (mm)
Figure57. Tensile Test graph of Cast acrylic sample
Sample Calculations
Ultimate Tensile stress (σ) = (Maximum Load / Cross sectional area of the specimen)
Try to pick a point in Maximum load = 1261.8N
@ point of maximum load the Extension ΔL = 3.2876 mm So the stress would be,
and the strain,
So the percentage of elongation at the break point would be 1.9%
RESULT
Ultimate tensile strength of specimen = 52.575 MPa Percentage of elongation of specimen at the break point = 1.9% Tensile Modulus (E) = 2.7 GPa
Stress VS Strain
60
50
40
30
20
10
-0.005 0 0.005 0.01 0.015 0.02 0.025
Strain ε
Figure58. Tensile strength VS Strain graph of Cast acrylic
Chapter 5 - Discussion
Using Lauroyl Peroxide initiator could get much better results and it is getting the reaction to be much quicker with lower temperature than using AIBN.
Bubbles that form during the time for the reaction to get to the glycerine stage affected the shape of the specimen, so bubbles need to be prevented.
It was observed that the use of aluminum foil allowed the reaction solution to leak a much lesser amount of MMA during the reaction as compared to the fourth stage in which the temperature was higher than the third stage.
Observing after introducing a larger amount of initiator gives quicker reaction times even when lesser heat was supplied to the solution. About 1g of initiator was used for every 100g of MMA.
It was observed that the cast acrylic sample displaced 5 cm3 of water, while extruded sample displaced 3 cm3 and the experimental sample displaced 9.2 cm3. This signifies that the experimental sample had the least density among the three.
The extruded sample had a compressive strength of 116 MPa, cast acrylic laser cut sample had 121 MPa and Experimental sample had 119 MPa. So, Laser cut sample had the highest compressive strength.
Extruded acrylic melts and 150 °C while experimental and commercial melt at 160 °C. So, extruded acrylic has the lowest melting point.
Extruded acrylic sample has a higher tensile strength of 72 MPa while the cast acrylic has a lower tensile strength of 52 MPa.
Chapter 6 – Conclusion and Recommendations
According to the results that we have obtained during the experiment and the observations, aluminum foil is preferable to be used to prevent the evaporation of MMA during the reaction. We would try to cool the reaction solution rapidly to the glycerin stage so that bubble formation could be avoided. We also might contact the organic chemistry lecturer Dr. Colleran to take some guidance about the processing of PMMA. However, after approving the optimum condition of processing PMMA, moulds in accordance with the ISO standards of polymers specimen for each different test wo
