Name and quickly explain three methods to separate different polymer fragments
Sink float density separation is a commonly used sorting method. Polymer fragments are fed into a flotation bath in which they either float or sink, depending on their densities.
Triboelectric separation is based on the differences in electrostatic properties between polymers.
Near infrared spectroscopy is an optical sorting method that is based on how different polymers reflect light of different wavelengths.
How can the properties of recycled plastics be improved?
The properties of recycled plastics can be improved through compounding: i.e. blending in addditives or virgin polymers.
Which properties are typically affected when comparing recycled to virgin plastics?
The following properties might be influenced:
Density
Tensile strength
elasticity
brittleness
viscosity when moulding
aesthetic properties ( colour, odour, surface finish)
Properties of recycled plastics can be improved by blending in fillers and additives such as thermal stabilisers, UV absorbers and impact modifiers. What is the downside of these additives?
The additives may themselves make the material more difficult to recycle in the future. Therefore, their use has to be limited whenever possible.
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