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Polymers

Leaving cert Engineering HL Q6

QuestionAnswer
What is natural rubber? Natural rubber is the sap from the rubber tree. It has folded polymer chains which are bonded by weak Van der Waals forces. It is both plastic and elastic.
What is synthetic rubber? Synthetic rubber is rubber processed with sulphur to give cross-links between the folded chains, this is vulcanisation. A stronger bond which is more durable and less flexible than natural rubber is developed.
What are foaming agents? Foaming agents are substances which add bubbles to a polymer. They increase the bulk of the polymer making it lighter. Examples include sponges and buoyancy aids.
What are fillers? These additives control the mechanical properties, such as material strength, of the polymer. They reduce the amount of expensive polymer used. Fillers such as chalk, wood flour and glass fibre can be used.
What is a catalyst? This will speed up or slow down a chemical reaction. Catalysts are used to initiate the polymerisation process.
What is an inhibitor? This prevent certain chemical combinations from happening or slow down a reaction.
What is an amorphous polymer? Amorphous polymers do not have a pattern in the arrangement of their atoms but are a more random structure.
What is a crystalline polymer? Crystalline polymers have atoms that are bonded together in a pattern that is repeated.
Discuss the main properties and the internal structures of Thermoplastics Can have linear or branched structure. Properties: Low melting point >Allows for easy moulding >Easily disrupted by heat >Low tensile strength >Branched structures have higher tensile strength than linear >Ideal for recycling.
Discuss the main properties and the internal structures of Thermosetting plastics Have a cross-linked structure. Properties: High melting point >High tensile strength >Good thermal insulation >Can withstand high temperatures without losing rigidity >Stiff and less flexible.
Discuss the main properties and the internal structures of Elastomers Linear chains that are coiled, entangled & subject to minimal cross-linking. Properties: >Elastic at room temperature >Soft & deformable >Return to shape when forces of tension, torsion or compression are removed >Low permeability to air >Good insulation.
What are Plasticisers? Plasticisers are added to polymers to improve their flexibility. They achieve this by altering the forces of attraction between molecules of the polymer.
What are Stabilisers? Stabilisers help prevent the degradation effects that heat, ultra-violet light and other environmental conditions place on the polymer.
How do glass or carbon fibers improve polymer properties? Glass or carbon fibre: The addition of glass or carbon fibre greatly increases the strength of plastic, commonly polyester resins are used. Boats and storage tanks are commonly made from these materials.
What is Lamination? Lamination: Thin layers of materials bonded together. High strength plastics can be produced by layers of paper or cloth coated with resin being bonded together. Heat and pressure can be used.
Name some Thermoplastic materials Acrylic, PVC, Polythene, Polystyrene, Nylon
Name some Thermosetting materials Phenol-formaldehyde resin, Polyester resin, Epoxy resin, Urea-formaldehyde
Describe how to use a strip heater Electric current is passed through a wire which heats it, the work piece is placed along the wire, A strip of the thermoplastic work piece becomes soft and flexible, it is bent to the required angle and held in this position until it cools.
Explain vacuum forming Thermoplastic sheet is clamped in the machine, a heated softens the sheet, a mould is raised up under the sheet, a vacuum sucks the plastic sheet down around the mould, the plastic sheet cools and holds it shape, the mould is removed.
Name some products produced by vacuum forming Biscuit tin inserts, shower tray
Explain Blow moulding Parison extruded down into a mould, mould closes in, air is pumped in, the parison blows up like a balloon and fills the mould, the plastic cools and holds its shape, the mould opens and the product is taken out.
Name some products produced by Blow moulding Plastic bottles
Explain extrusion granules fed from hopper into machine, auger pushes granules along barrell, heaters melt the granules into a plastic paste, plastic paste forced through a die, extruded plastic is cooled with water so it holds it shape, cut when it reaches certain length.
Name some products produced by extrusion Plastic pipes, PVC window frames, electrical condute, anything with a consistent cross section
Explain injection moulding granules fed from hopper into machine, auger pushes granules along barrell, heaters melt the granules into a plastic paste, auger moved forward like a syringe and forces plastic through a sprue into a mould, plastic cools, mould opens, product is ejected.
Name some products produced by injection moulding Toys, lunch boxes, door handles, jugs, xbox controllers, playstation casing, plastic chair, TV remote control (you can see the end of the sprue on any product that has been injection moulded)
Explain callendering Plastic paste is run through a series of rollers, each pair of rollers get tighter until the plastic is squeezed into a thin sheet, the plastic sheet is gathered onto a roll
Name some products produced by callendering Silage wrap, cling film,
Explain compression moulding It uses a split mould. A measured amount of polymer powder is put in the mould. The mould is closed under huge pressure. Heat triggers the chemical reaction of ‘cross-linking’ and the object sets (curing). The mould is opened and the object is removed.
Name some products produced by compression moulding This is suitable for thermosetting polymers and are ideal for electric insulators such as plug tops, socket covers and light switches
Explain transfer moulding The moulding powder is placed in a compartment above the mould where it is heated. The plunger forces the molten polymer into a cooled mould cavity. The polymer solidifies in the mould which is then opened and the product is removed.
Name some products produced by transfer moulding This is suitable for thermosetting polymer products with metal inserts such as a phase tester screwdriver.
Explain rotational moulding Split mould. Polymer powder put inside. Mould rotates & is heated. Polymer melts and sticks to the inside of the mould. When it has all melted, the mpuld is cooled while still rotating. When cooled fully the mould is opened & the product is ejected.
Name some products produced by rotational moulding Oil tanks, Plastic balls, Childrens peddal toy tractors
Describe the Addition Polymerisation process Polyethylene. Long chainlike molecules. Strong & a weak bond between the carbon atoms. Free radical added. The weak bond is broken. Ethylene molecule behaves like a radical. Chain reaction. Another radical added at the end. Weak van der Waals forces.
What types of polymers are produced from Addition polymerisation Thermoplastic polymers like polyethylene, acrylic and PVC
Describe the Condensation Polymerisation process Two monomers react chemically to form a new molecule with water eliminated as a by-product. Produces a cross-linked structure with strong primary bonds. The polymer produced cannot be re-softened, has a high tensile strength and a high melting point.
What types of polymers are produced from Condensation polymerisation Thermosetting polymers like Phenol-formaldehyde, Urea-formaldehyde and Polyester resin
Created by: todd.ciaran