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MUHAMMAD ABDULLAH ADIL
Reg. number: 1426-111001
Following are the objectives of this experiment
To synthesize Thermo set and Thermo plastic composites.
Polymers are large molecules composed of many similar smaller molecules linked together. The individual smaller molecules are called monomers. When small organic molecules are joined together, giant molecules are produced. These giant molecules are known as macromolecules.
Generally speaking, all macromolecules are produced from a small set of about 50 monomers. Different macromolecules vary because of the arrangement of these monomers. By varying the sequence, an incredibly large variety of macromolecules can be produced. The term polymer encompasses a very large, broad classes of compounds, both natural and synthetic, with a wide variety of properties.
Thermoplastics, in basic terms, are melt-processable plastics (materials that are processed with heat). When enough heat is added to bring the temperature of the plastic above its melt point, the plastic liquefies (softens enough to be processed). When the heat source is removed and the temperature of the plastic drops below its melt point, the plastic solidifies (or freezes) back into a glass-like solid. This process can be repeated, with the plastic melting and solidifying as the temperature climbs above and drops below the melt temperature, respectively. However, the material can be increasingly subject to deterioration in its molten state, so there is a practical limit to the number of times that this reprocessing can take place before material properties begin to suffer. Many thermoplastic polymers are addition-type, capable of yielding very long molecular chain lengths (very high molecular weights)
Thermosets, again in basic terms, are materials that undergo a chemical reaction (cure) and transform from a liquid to a solid. In its uncured form, the material has very small, unlinked molecules (known as monomers). The addition of a second material (catalyst) and/or heat or some other activating influence will initiate the chemical reaction. During this reaction the molecules cross-link and form significantly longer molecular chains, causing the material to solidify. This change is permanent and irreversible. Subsequently, exposure to high heat will cause the material to degrade, not melt. This is because these materials typically degrade at a temperature below where it would be able to melt.
Polymer Matrix Composites:
Composite materials (also called composition materials or shortened to composites) are materials made from two or more constituent materials with significantly different physical or chemical properties, that when combined, produce a material with characteristics different from the individual components. The individual components remain separate and distinct within the finished structure.
Most commercially produced composites use a polymer matrix material often called a resin solution. There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyether ether ketone (PEEK), and others. The reinforcement materials are often bers but can also be common ground minerals . The various methods described below have been developed to reduce the resin content of the nal product. As a rule of thumb, hand lay up results in a product containing 60% resin and 40% ber, whereas vacuum infusion gives a nal product with 40% resin and 60% ber content. The strength of the product is greatly dependent on this ratio.PMCs are very popular due to their low cost and simple fabrication methods. Use of nonreinforced polymers as structure materials is limited by low level of their mechanical properties, namely strength, modulus, and impact resistance. Reinforcement of polymers by strong brous network permits fabrication of PMCs, which is characterized by the following:
a) High speci c strength
b) High speci c stiffness
c) High fracture resistance
d) Good abrasion resistance
e) Good impact resistance
f) Good corrosion resistance
g) Good fatigue resistance
h) Low cost
These are unsaturated resins formed by the reaction of dibasic organic acids and polyhydric alcohols. Unsaturated polyesters are condensation polymers formed by the reaction of polyols (also known as polyhydric alcohols), organic compounds with multiple alcohol or hydroxy functional groups, with saturated or unsaturated dibasic acids. The use of unsaturated polyesters and additives such as styrene lowers the viscosity of the resin. The initially liquid resin is converted to a solid by cross-linking chains. This is done by creating free radicals at unsaturated bonds, which propagate in a chain reaction to other unsaturated bonds in adjacent molecules, linking them in the process. The initial free radicals are induced by adding a compound that easily decomposes into free radicals. This compound is usually and incorrectly known as the catalyst. Substances used are generally organic peroxides such as benzoyl peroxide or methyl ethyl ketone peroxide.
Polyester resins are thermosetting and, as with other resins, cure exothermically. The use of excessive catalyst can, therefore, cause charring or even ignition during the curing process. Excessive catalyst may also cause the product to fracture or form a rubbery material. Polyester resins such as these are of the 'unsaturated' type. Unsaturated polyester resin is a thermoset, capable of being cured from a liquid or solid state when subject to the right conditions. It is usual to refer to unsaturated polyester resins as 'polyester resins', or simply as 'polyesters'. There is a whole range of polyesters made from different acids, glycols and monomers, all having varying properties.
Methyl ethyl ketone peroxide
(MEKP) is an organic peroxide, a high explosive similar to acetone peroxide. MEKP is a colorless, oily liquid whereas acetone peroxide is a white powder at STP; MEKP is slightly less sensitive to shock and temperature, and more stable in storage. Depending on the experimental conditions, several different adducts of methyl ethyl ketone and hydrogen peroxide are known. The first to be reported was a cyclic dimer, C8H16O4, in 1906. Later studies found that a linear dimer is the most prevalent in the mixture of products typically obtained, and this is the form that is typically quoted in the commercially available material from chemical supply companies.
Dilute solutions of 30 to 60% MEKP are used in industry and by hobbyists as the catalyst which initiates the Crosslinking of unsaturated polyester resins used in glass-reinforced plastic, and casting. For this application, MEKP is dissolved in dimethyl phthalate, cyclohexane peroxide, or diallyl phthalate to reduce sensitivity to shock. Benzoyl peroxide can be used for the same purpose.
A cross-link is a bond that links one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers (such as proteins). When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of cross-links to promote a difference in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions, as well as other creative cross-linking methodologies.
Mixing in a mixture:
First the matrix powder is added and then after its melting we add reinforcement or filler powder,and allow it to mix thoroughly,when once complete we can either connect it with injection moulding machine,extruder or take it out directly and form thin sheets by applying load.
Injection molding utilizes a ram or screw-type plunger to force molten plastic material into a mold cavity; this solidifies into a shape that has conformed to the contour of the mold. It is most commonly used to process both thermoplastic and thermosetting polymers, with the former being considerably more prolific in terms of annual material volumes processed. Thermoplastics are prevalent due to characteristics which make them highly suitable for injection molding, such as the ease with which they may be recycled, their versatility allowing them to be used in a wide variety of applications, and their ability to soften and flow upon heating. Thermoplastics also have an element of safety over thermosets; if a thermosetting polymer is not ejected from the injection barrel in a timely manner, chemical crosslinking may occur causing the screw and check valves to seize and potentially damaging the injection molding machine.
Injection molding consists of high pressure injection of the raw material into a mold which shapes the polymer into the desired shape. Molds can be of a single cavity or multiple cavities. In multiple cavity molds, each cavity can be identical and form the same parts or can be unique and form multiple different geometries during a single cycle. Molds are generally made from tool steels, but stainless steels and aluminum molds are suitable for certain applications. Aluminum molds typically are ill-suited for high volume production or parts with narrow dimensional tolerances, as they have inferior mechanical properties and are more prone to wear, damage, and deformation during the injection and clamping cycles; but are cost effective in low volume applications as mold fabrication costs and time are considerably reduced. Many steel molds are designed to process well over a million parts during their lifetime and can cost hundreds of thousands of dollars to fabricate.
Melt intercalation: no solvent is required. A popular method for thermoplastic nanocomposites. Layered silicate is mixed within polymer matrix in the molten state. A thermoplastic polymer is mechanically mixed by conventional methods such as extrusion and injection molding with organophillic clay at an elevated temperature. Polymer chains are intercalated or exfoliated to form nanocomposites. Polymers, not suitable for adsorption or in situ polymerization, can be processed using this technique.
Extrusion is a process used to create objects of a fixed, cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections and work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish.
Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold.
Polymer Resin - 50 ml, Activator – 2 to 3 drops, Initiator (Methyl ethyl ketone peroxide – MEKP) – 1% of the double bond in the system, Cross linking agent (styrene), Release Agent (Poly Vinyl Alcohol), Random fibre glass sheet, a mold.
We started by pouring the release agent (PVA) on the mold and spreading it evenly everywhere on the mold surface.
After that, we mix the polymer resin, the activator, the cross linking agent and the initiator together, making a viscous solution. We did this in an empty container and with the help of a stirrer we constantly stirred the solution to stop it from getting hard inside the container and settling down there.
Then we poured this 'Resin + Activator + Cross linking agent + Initiator' solution over the release agent containing mold surface, a little at a time to avoid the formation of air bubbles.
Then with the help of a brush, we applied the solution evenly over the surface of the mold.
After this we placed the fibre glass sheet over the viscous solution coating mold surface.
With the help of a brush we again poured the remaining of the viscous solution over the fibre glass sheet, to bind it with the mold.
We also placed a colored piece of clothing over the fibre glass surface, just to make it look good.
After that we poured all of the remaining viscous solution of the polymer resin over the (fibre glass and cloth) surface of the mold.
In this system, the polymer resin is the matrix and the fibre glass sheet is the reinforcement.
After completely covering the fibre glass sheet with the polymer resin, we allowed the system to dry and form into a Polymer Composite.
Use gloves while handling the chemicals.
While making the viscous solution of Polymer resin + activator + initiator + Cross linking agent, don't add too much of the cross linking agent or the solution will get too hard and will stuck inside the container.
Avoid rapid pouring of the viscous solution over the mold surface or else air bubbles will be created
Always pour the release agent over the mold surface before pouring the polymer solution.
While applying the polymer solution, the mold should be placed at a stable surface and its position should not be frequently disturbed/changed.
Polymer – High Density Polymer Ethylene (HDPE), Magnesium Hydroxide (Mg (OH)2), Steric acid (Lubricant), Mixer.
We started here by pre heating the Rotor Mixer till a temperature of 180°C, the melting temperature for the polymer used here (HDPE).
On reaching this temperature, we added the HDPE in the mixer and allowed the polymer to melt.
After the melting of the polymer is completed, we add the steric acid to the mixer which acts as a lubricant here.
After that we added Mg (OH)2 to the mixer and allowed the polymer and the Mg (OH)2 to get thoroughly mixed with each other.
We allowed the mixing of the HDPE and Mg (OH)2 for 9 minutes and 25 seconds and at the melting temperature of the polymer i.e. @180°C.
In this system, the Polymer act as the Matrix where as Mg (OH)2 acts as the reinforcement.
After mixing the matrix and reinforcement for 9 minutes and 25 seconds and at 180°C, we got a whitish viscous material. This is our Polymer Composite.
In order to characterize this Polymer composite, we can make sheets of the viscous (composite) material in a hot press.
Compression molding is done in the hot press at the same temperature as the processing temperature. i.e. 180 °C
Once these sheets are made, we can cut down strips from them and then tensile properties can be tested.
Allow the polymer to completely melt before adding the reinforcement material.
While extracting the polymer from the mixer, always wear heat resistant gloves.
As the mixer operates at high temperatures, don't tounch any of its components without gloves.