Learn about plastics

1. Technical Materials:
plastics
Lesson 3 1st term

2. Introduction
• Plastics are a subgroup of materials within the group of
polymers composed of huge organic molecules which we call
polymers and a group of additives which help them achieve
their properties.
• Polymers are huge organic molecules formed by the union of
many molecules called monomers. They are chains
Polymerization is the proccess of bonding monomers.
• The process of artificial polimerization is called synthesis
• If the monomers are all the same, we talk about
homopolymers. If they are different, we call them
oligopolymers

3. Properties of plastics
• Properties of plastics vary
between the huge variety
of them. In general terms
they are
• Ligth
• Good insulators
• Resistant to corrosion
• Mouldable
• Low melting point
• Degradable under UV
• Pollutant

4. Types of plastics
• There are three different kind of plastics,
according with the way in which their
chains are bound, and so their properties
differ:
• Thermoplastics
• Thermosets
•
Elastomers

5. Thermoplastics
• Thermoplastics are
relatively flexible
• Low melting point
• The bonds between chains
are weaker than the bonds
beteween monomers: they
are easy to recycle
• The most usual
thermoplastics are:
polyetilene, PVC, PS, PP

6. thermosets
• Thermosets are stronger than
thermoplastics and better for
higher temperatures
• They melt at about 250ºC
(bonds beetween chain) but
bonds between monomers
break at about 200ºC. There
is a chemical change when we
melt them, so they are nonrecyclable.
• The most important
thermosets are polyurethane,
polyesther, epoxi resin and
phenolic resin

7. Elastomers
•
•
•
•
Elastomers are very flexible
The links between chains don´t break under an effort, they widen. After
the effort they return to this original position
The bonds between chain brak after some bonds between monomers when
we heat the plastic: they are non-recyclable
The most important elastomers are polyisoprene and polyvynilidene chloride

8. Manufacturing plastics
• As a material, plastics are sampled in the form ofdust, or small
particles.
• Most techniques start by introducing these particles an extrusion
machine, where they are heated to the melting point and pushed out
trough a mouth. Plastic objects can adquire shape through this mouth
or be reinjected in other machine