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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
Give two reasons why the thermosetting polymer phenol formaldehyde resin is suitable for the manufacture of pool balls Phenol formaldehyde resin is used for the pool balls because of its ability to absorb impact when the balls collide and when the cue hits the balls. It is also used because of its hardness and ability to withstand chipping and cracking
Describe, with the aid of a diagram, a suitable process to manufacture thermoset products Phenol formaldehyde pool balls can be resin cast. A common method of manufacturing thermosetting products is compression moulding
State two reasons why injection moulding is suitable for the manufacture of a kicking tee. Injection moulding allows objects of various shapes and cross-sections to be manufactured. It also facilitates mass production of thermoplastic objects. The kicking tee could be manufactured in just two parts.
Describe briefly how the flexibility of a kicking tee can be improved during the moulding process The addition of plasticisers will improve flexibility. In the design of kicking tees, the wall thickness could be reduced to make the product more flexible (and weaker).
The Formula 1 race tyre shown is manufactured from the synthetic rubber elastomer polybutadiene. Explain the term synthetic rubber. 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
Describe the basic properties of elastomer materials. Elastic at room temperature Soft, deformable and flexible Resilience to return to shape when forces are removed Low permeability to air, gases, water and steam Low tensile strength Recyclability Good electrical and thermal insulation.
Describe the internal structure of elastomer materials. Internal structure - Linear chains that are coiled, entangled and subject to minimal cross-linking.
Name a process used to manufacture the thermoplastic tubes used in the frame of a tent Extrusion
Select a suitable thermoplastic for the frame tubing used in a camping tent and give one reason for your selection Nylon is strong, difficult to break and lightweight
Many toys, including Lego® bricks, are manufactured from the copolymer Acrylonitrile Butadiene Styrene (ABS). Copolymer is a polymer formed when two different mers are linked together in the same polymer chain. This new polymer may have a mixture of new improved properties, it is similar to alloying in metals
Outline two reasons for the use of ABS in the manufacture of toys • Light weight copolymer. • It has the ability to be injection moulded which makes it useful in manufacturing toys, including Lego. • Polymers such as ABS have excellent impact resistance. • It also facilitates mass production of thermoplastic objects
Describe Plastic pultrusion; similar to extrusion,used with thermosetting polymers.fibers are impregnated with resin, pulled through a heated stationary die where the resin undergoes polymerization. impregnation is done by pulling through a bath or by injecting into a chamber
Describe the term Monomer Monomer a molecule of a compound which can react with other molecules to form a polymer.
Outline a suitable polymer additive which is used to improve the roof box of a car for each of the following: • to increase flexibility • to provide greater resistance to UV rays Plasticisers make products softer and more flexible. the "new car smell" is caused by plasticisers evaporating from the car interior. UV stabilizers: Used to protect the polymers mechanical properties by absorbing UV rays resulting in less degradation.
Explain the term Glass transition temperature Glass transition temperature describes the temperature at which a solid glassy amorphous polymer changes to a rubbery, viscous polymer. It is engineered by altering the degree of branching or cross-linking in the polymer by the addition of plasticisers.
Describe Van der Waal forces Van der waal forces: These are the bonding forces between polymer chains produced by addition polymerisation. They are weak, secondary covalent bonds that may be disrupted by heat or pressure
Explain two reasons why elastomer seals are used to hold glass panels in frames Two reasons for using elastomer seals: • Flexibility/softness • Easy to fit • Dampening effect on vibrations • Cushion between two hard surfaces.
Describe elastic memory Elastic memory is the ability of a thermoplastic to return to its original state from a deformed state caused by heat. If a thermoplastic has been bent to a specific shape using the strip heater, when reheated it will return to its original shape.
Describe elasticity Elasticity is displayed when a load is applied to a polymer, that is flexible at room temperature, to cause the object to change shape. When the load is removed, the polymer will return to its original shape
Discuss the use of lubricants in polymer manufacturing processes Lubricants make the polymer easier to mould. Various types of waxes are used in small amounts for this purpose.
Outline the negative effects on the environment of the continuous use of polymer materials. Won't degrade, sent to landfill, using up earths resources to manufacture plastics, wildlife can get caught in waste plastic objects
Describe the term Lamination related to polymers 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.
Describe carbon fibre Carbon fibre: The addition of glass or carbon fibre greatly increases the strength of plastic materials, commonly polyester resins are used. Boats and storage tanks are commonly made from these materials
Created by: todd.ciaran