PLASTICS

ORIGIN

Natural plastics: are obtained directly from raw vegetable materials
— for example, cellulose or latex, or from animal proteins.

Synthetic Plastics : are made from compounds extracted from petroleum , naturla gas and carbon


The transformation of these raw matenals and compounds into plastics
is called polymerisation.

Properties of Plastics

Strength, elasticity, rigidity and flexibtflty are charecteristics of many plastics

• electrical: electrical insulation

• thermaL thermal insulation

• acoustic: acoustic insulation

• mechanical: malleabrlity, ductility, mechanical resistence

• other properties: low density, impermeability

ecogolical properties

• Chemical recycling. We apply chemical processes to make new
materials from the original components of plastic residues.

• Mechanical recycling. We make new products from plastic
granules The process has five stages

  1. Floating. TVe wash the plastics and then dry them by centrtfugal
    force
  1. Agglutination. The matenal is compacted and then incorporated
    into other matenals
  1. Extrusion. tve melt the matenal, and then tt's extruded into long
    filaments
  1. Pelletising. The filaments are then reduced to granules that we Plastic waste should be put tnto yellow
    call pellets.

En ergetic recycling. We can incinerate plastics and the energy that
is produced is used tn industry, for heating or producing electnctty.

  1. Separation and crushing. We separate the plastics according to
    type and then they' re crushed.

plastics that decompose on contact with certain bacteria and
biological agents

• plastics that dissolve tn hot or cold water.

Classification of plastics

Elastomers
(60'C.
Made by vulcanisationi mixing sulphur and rubber, and heating to

Thermostable plastics :these plastics are made from compounds derived

Thermoplastics : we manufacture thermoplastics from compounds acquired from petroleum

Formation techniques

Extrusion

We apply pressure by means of a large, rotattng screw, whtch forces
the melted matenal out, through a nuzzle.

We cool the shaped material slowly In a refngerated water bath until
lt's solid.

we put thermostatic, in granular form , into a previusly heated cylender

Finally, we collect the pieces of plastic through a feeder system

Lamination

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Thermoplastic produced by the extrusion method ls passed through a

senes of hot cylinders to produce sheets of varying thtckness

With this technique, we can produce different finishes, for example,

glossy, matt or textured. This depends on the outer coating applied by the final cylinder

. Vacuum forming

We extract the air below the sheet so that the plastic ts pulled against
the instde walls of the shaped mould, and the desired form ts created

We then use a heater to heat the mould and soften the plasuc

We leave the mould to cool, then remove the obiec

We put thermoplasttc into a mould.

Moulding

blow moulding

compression

injection

We inject melted thermoplastic into a mould

When the material has cooled and solidified, we extract it from the mould

we put a tubular-shaped piece of plastic into a hollow mould wich has the same shape as the object that we want to make

  1. We close the mould and blow pressurised air into it, so that the plastics adheres to the sides of mould and take its shape

When the object is cold, we remove it from the mould

We put thermostable plastic, which can be in granular form, into the base of a cavity mould

the outer part of the cavity
mould, shaped the same, is closed to compress the material inside . We then heat it and it
becomes soft and malleable

The plastic adapts to the shape of the cavity between the two parts of
the mould

We extract the oblect when the plastic has cooled and solidified

finishing techniques : Principal techniques are cutting, perforating, trimming and filing

cutting

scissors

steel bit

cutter

fretsaw

jig saw

power press

hot metal thread trimmer

perforting

drill bit

Trimming and filing

Joining plastics

Temporary joints

Standard screw

Double ended screw

Nut and bolt

nut used to tighten the bolt

used to fasten two objects together

used to fasten two objects

holes must be drilled first before the screw is enserted

each end pf screw can be inserted into a one of a pair of objects

permanent joints

Soldering

Adhesives

Joining thermoplastics using heat and pressure

Joining two surfaces permanently

resins with two components: liquid, high water resistance

acrylic cement: hquid, used mainly with PVC and sheets polystyrene

contact adhesives: liquid, work instantly after applymg to
both surfaces, used with all types of plastics