Polymers Flashcards
What are Thermoforming Polymers (Thermoplastics)?
These plastics can be re-heated and therefore shaped in various ways. They become mouldable after reheating as they do not undergo significant chemical change. Reheating and the pastic makes the bonds between the molecules weaker, and weaker, so the molecules are now free to move, and therefore be reshaped. These types of plastics can be recycled.
What are Thermosetting Polymers (Thermosetting Plastics)?
Once ‘set’ these plastics cannot be reheated to soften, shape and mould. The molecules of these plastics are cross linked in three dimentions and this is ehy they cannot be reshaped or recycled. The bond between the molecules is very strong.
How does ‘Plastic Memory’ work in Thermoplastics and how can you test it
Thermoplastics have what is termed ‘plastic memory’; that is when they are heated they soften and return to their original shape (usually a flat sheet). This can be tested by bending an old phone card or bank card in half, placing it in a bowl and poring boiling water over it: it will return to its flat shape.
What is the big downside with Thermoplastics
Thermoplastics generally soften at low temperatures (as low as 100 °C). This makes them inappropriate for products that involve relatively high temperatures. However, thermoplastics are the most common type of plastic and are widely used for everyday products.
What makes Thermosetting Plastic so different to Thermoforming Plastic
These are very different from thermoplastics. When they are being formed a chemical reaction occurs causing them to create strong links or cross chains in their structure, which means that when they are permanently formed, they can not be softened by reheating.
Because they do not soften when heated they can take very high temperatures, often in excess of 400°C.
What are Elastomers
These are polymers that have good elasticity, i.e. They can be distorted under pressure but will return to their original shape when the pressure is removed. Elastomers have long-chain molecules that can be considered to be coils (similar to springs); when the material is distorted (compressed or stretched) the molecules distort, and then released they return to their original shape. These coiled molecules give the Elastomers their elastic properties.
What 2 categories do Elastomers fall under
- Thermosetting – natural or synthetic rubbers, cannot be recycled or reshaped, ex. Liquid silicon rubber
- Thermoplastic - can be reheated and reshaped therefore recycled, can be manufactured using conventional equipment such as injection moulding or blow moulding.
Examples of Thermoplastics
- Nylon
- High Impact Polystyrene (HIPS)
- High Density Polyethylene (HDPE)
- Acrylic (PMMA)
- Polypropylene (PP)
- Polyvinyl Chloride (PVC)
- Unplasticised Polyvinyl Chloride
- Low-Density Polyethylene (LDPE)
- Acrylonitrile Butadiene Styrene (ABS)
Examples of Thermosetting Plastics
- Polyester Resin
- Melamine Formaldehyde
- Epoxy Resin
- Urea Formaldehyde
Examples of Elastomers
- Natural Rubber (Polyisoprene)
- Buradiene Rubber (BR)
- Silicone
- Neoprene (Polychloroprene Rubber)
What Polymer Enhancements used for
Enhancing a polymers properties by using additives (added to the polymer stock form for a variety of reasons).
It is a way of improving a materials properties to better suit the requirements of the final product.
Examples of Polymer Enhancements
- Lubricants
- Thermal Antioxidants
- Pigments
- Antistatics
- Flame Retardants
- Plasticisers
- Fillers
- Biodegradable Plasticisers
- Antioxidants
- UV Light Stabilisers
What are some Performance Characteristics of Polymer
- Toughness
- Elasticity
- Insulation (thermal and electrical)
- UV Resistance
- Ability to be moulded
- Resistance to chemicals and liquids
- Melting points
- Suitability for food packaging applications
- Biodegradability
- Recyclability
- Self finishing
- Ability to be combined with other polymers and/or additives
What are Biodegradable Polymers (Biopolymers) designed to do
Bio-polymers can be designed to degrade in as little time as a few months to a couple of years.
What caused Biodegradable Polymers (Biopolymers) to degrade
Degradation occurs in the presence of:
- Light (photodegradable)
- Oxygen (oxy-degradable)
- Water (hydro-degradable)
