Plastics Different Types

1

• Plastics
• They can be split into two main types
• Thermoplastics describe those that when they are
  heated can be shaped and reformed any number of
  times.
• Thermosetting plastics can be heated and shaped
  only once.
• So, how does this affect what we use the plastic
  for?
• If we want to make plastic drinks bottles we want
  them to be recyclable,
• so they must be able to be heated up again and
  have their shape changed
• into something different - hence they are
  thermoplastics.
• Plastic saucepan handles can get very hot when
  they are on a gas or electric
• cooker ring, so the plastic handles must stay in
  the same shape when they
• get hot - hence they are thermosets.

Plastics - Different Types
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• Some common thermoplastics are
• Acrylic - available in a wide range of colours
  and thicknesses (from 2mm to 15mm or more) but is
  brittle,
• i.e. tends to crack more easily when dropped.
• HIPS - High Impact Polystyrene Sheet, available
  in a wide range of colours but tends to be quite
  thin
• (1mm to 3mm or so) but is quite tough, hence
  its name High Impact.
• PET - This plastic is used to make all the fizzy
  drinks bottles as it creates a superb gas
  barrier, hence
• the fizz cannot get out and your drink stays
  fizzy for longer.

Not just for making simple objects. Being thin
HIPS is great for making complex curved shapes.
Plastics - Thermoplastics
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• Some common thermosets are
• Urea-formaldehyde is used commonly on kitchen
  worktops (i.e Formica) where it is applied as a
  thin
• sheet on top of another material, for example
  chipboard or mdf.
• Glass Reinforced Plastic (GRP) - as its name
  describes this is a plastic which has had its
  strength
• increased by reinforcing it with fibres of
  glass. Car bodies and canoes are both sometimes
  made
• from GRP.

Why do you think plastic light bulb fittings need
to be made from a thermoset?
Plastics - Thermosets
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As the picture above shows a piece of plastic is
held in the FRAME and then HEATED. This causes
the plastic to go soft. The soft plastic is then
automatically moved to the MOLD where pressure is
used to PRESS it into the right shape. The
plastic then cools and the piece removed.
Plastics - Press Forming