1. Unit 2: Plastics

2. Index
1. What Are Plastics?
8. Elastomers.
2. What Are Plastics Made Of?
9. Textile Fibers.
3. Obtaining Plastics.
10. Fabrication of Plastics:
Techniques.
4. Properties Of Plastics.
11. Polymerization &
Recycling.
5. Types of Plastics.
6. Thermoplastics.
7. Thermosettings.

12.Work With Plastics In
The Workshop.

3. What Are Plastics?



The term plastic is used to
designate some synthetic materials
obtained from fossil fuels, which,
in general, are flexible, resistant,
light and insulators.
The plastics are also called
polymers and they are mainly
compound by oxigen, hydrogen,
carbon, nitrogen and sulfur.
Plastics are malleable and ductile,
and they have a great plasticity
which gives them their name.

4. What Are Plastics Made Of?


The fossil fuels (oil, coal
and natural gas) are
formed in a period of
millions of years, by the
accumulation of the
remains of living beings
under the Earth's crust.
Polymers are obtained
from the multiple addition
of the molecules from the
fossil fuels.

5. Obtaining Plastics
1.Obtainig the raw materials.
2.Synthesizing the monomers.
3.Linking the monomers to
obtain the polymers
(polymerization).
·

6. Obtaining Plastics: Polymerization
In this process a
monomer is
introduced in a
machine called
reactor with a
solvent and a
catalyst, at a
specific pressure
and temperature.

During the
chemical reaction,
the monomers are
linked forming
macro-molecules,
the polymers.

7. Obtaining Plastics
4. Making the pellets.
5. Adding the polymers some
additives to modify their
properties.
6. Heating them to get the form
desired. (conformation).

8. Properties Of Plastics (I)
1. Plastics are very bad
conductors of electricity and
heat. They're insulators.
2. They are combustible i.e.
They can burn easily.
3. They can be combined with
other materials and sustances,
for example pigments.
4. Plastics are non-toxic and
non-corrosive.

9. Properties Of Plastics (II)
5. Plastics have a high
mechanical strength in relation
to its extreme lightness.
6. They have, in general, a
great elasticity.
7. They can be moulded when
you heat them, so they have
plasticity.
8. Plastics are versatile
materials and can be processed
easily.
9. They are relatively cheap

10. Types of Plastics
The plastics can be
clasified in three main
groups:
·Thermoplastics.
·Thermosettings.
·Elastomers.

11. Thermoplastics
Thermoplastics can be heated,
moulded and shaped various
ways, lots of times.
They are softer and less
resistant than thermosettings.
Thermoplastics are, for example,
PET (water bottles), PVC (pipes) &
Polyethene (plastic bags).

12. Thermosettings



They are harder and resist
higher temperatures than
thermoplastics.
They're not recyclable
heating them again.
Thermosetting plastics are,
for example, Amines (boat
hulls), Polyester Resins (ski)
& Phenols (cookware
handles).

13. Elastomers




Elastomers are
characterized by their
elasticity.
They can't be recycled.
They don't resist high
temperatures.
Elastomers are, for
example, Synthetic Rubber
(ballons) & Neoprene
(wetsuits).

14. Textile Fibers


Textile fibers are threads which
can twisted, stained and weaved
to make fabrics.
They are divided into two groups:
1 Synthetic (or man-made)
Fibers: they are obtain by a
chemestry reaction. F.e.:
Naylon, Polyester, Elastane, …
2 Natural Fibers: they are
obtained from animals, like the
Silk and the Wool, or vegetables,
like Cotton or Flax.

15. Fabrication of Plastics: Techniques
Extrusion: It is used to produce a wide range of different forms of
plastic, such as tubes, sheets and films, structural parts, etc.
Plastic pellets are placed in a feed hopper which feeds into the
system. A turning screw pushes the plastic into the barrel where
heaters increase the temperature and a melted polymer is obtained.
The melted plastic is forced through a shaping die. Depending on the
particular shape of this element, a continuous shape is formed and
pulled out of the extrusion machine.

16. Fabrication of Plastics: Techniques
Injection: Plastics pellets flows, from the feed hopper onto a turning
screw. It is converted into a melted plastic by the action of heaters
situated along the barrel. The screw moves the molten plastic forward,
forcing the plastic through a gate into the cooled mould. The mould is
opened once the plastic has solidified and the piece is pushed from the
mould. After we get the manufactured piece, the mould is closed and
the process begins again.

17. Fabrication of Plastics: Techniques
Compression molding: This is a similar process to extrusion. In
compression moulding, plastics pellets, sometimes called moulding
powder, are placed in the feed hopper and pushed to the gate by
the action of the turning screw. It is heated and compressed while it
passes through the barrel. After the gate, the molten charge is
quickly transferred to a press where it is moulded while still hot.
The part is removed after sufficient cooling.

18. Fabrication of Plastics: Techniques
Blow molding: Plastic grocery bags, bottles and similar items are made
using this processing. As in compression processing, plastic pellets are
melted and the plastic is forced through a gate into the blow pin
camera. The plastic substance is expanded and cooled by being made to
flow around a massive air bubble. After a few seconds, the mould is
opened and the manufactured product is ready.

19. Fabrication of Plastics: Techniques
Vacuum forming: Vacuum forming works by removing air, thereby
creating a partial vacuum underneath a soft and flexible
thermoplastic sheet and allowing atmospheric pressure to push the
plastic down onto a mould. The vacuum forming process may start
with a ‘blow’ that stretches the plastic.

20. Fabrication of Plastics: Techniques

Laminated: in this process
the pellets go througth a
series of heated roller,
making a sheet.

Spinning: in this tecnique the
pellets are heated above a
kind of colander. Then it is
pushed to make threads.
When they are falling they
must be dried. Spinning is
used to make synthetic
textile fibers.

21. Work With Plastics In The Workshop
You must follow these eight steps:
1. Marking. Before cutting we need to
mark the plastics with a soft pencil or
a permanent marker.
2. Holding. To hold plastics we use
the jack.
3. Cutting.
- if the sheet are thin and soft we
use scissors.
-if they're thick we use a metal bow
saw.
-if they're expanded (plastics) we use
a heated metal wire.

22. Work With Plastics In The Workshop 2
4. Drilling. To make holes we use an
electric drill.
5. Smoothing down. To sand them
down we use a sandpaper.
6. Folding. To do this we use piece
of wood and heat the plastic to
bend it.
7. Finishing. To get a good finished
we can use a paint compresson or
paint the plastic after give it a glue
layer.
8. Joining. To join plastics we use
different glues depending on the
type of plastic.

23. Recycling plastics


We can recycle plastics
by heating them again
when they have no longer
use. But we can only
recycle thermoplastics.
To recycle thermosettings
we need to use another
process more complex.

24. The End