PLASTICS

we also use plastics in
many economic and industnal
sectors

Origin and transformation of plastics

Depending on their origin, we can describe plastics as natural or
synthetic

Natural plastics

Synthetic plastic

are obtained directly from raw vegetable matenals

are made from compounds extracted from
petroleum, natural gas and carbon

The majority of plastics belong
to this group

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

During the manufacturing process, we can add materials such as fibreglass, textile fibres, paper, silica and sawdust to reduce production costs, and to develop certain characteristics

We can incorporate chemrcal additives to increase flexibility and to strengthen the polymers, and we can add pigments to give colour to the plastics

Properties of plastics

The properties of plastics depend on their type and on their composition

Strength, elasticity, rigidity and flexibility are characteristics of many plastics, although they vary from one type to another

There are other properties that are common to the majority of plastics

Mechanichal

Acoustic

Electrical

Thermal

Other properties

Impermeability

Low density

Ductility

Malleability

Mechanical resistance

Acoustic insulation

Electrical insulation

Thermal insulation

Ecological properties

We can recycle plastics. There are three recycling processes

Chemical recycling

We apply chemical processes to make new
materials from the original components of plasutic residues

Mechanical Recycling

We make new products from plastic
granules

Agglutination

Extursion

Floating

Pelletising

Separation and crushing

We separate the plastics according to
type and then they' re crushed

The filaments are then reduced to granules that we call pellets

We melt the material, and then it's extruded into long
filaments

The material is compacted and then incorporated
into other materials

We wash the plastics and then dry them by centrifugal
force

Energetic Recycling

We can incinerate plastics and the energy that
is produced is used tn industry, for heating or producing electricity

The majority of plastics are not yet biodegradable, but thanks to new technologies, we' re increasingly able to produce biodegradable materials

plastics that decompose on contact with certain bacteria and
biological agents

plastics that dissolve on hot or cold water

CLASSIFICATION OF PLASTICS

Thermoplastics

We manufacture thermoplastics from compounds adquired from petroleum

They' re made up of weakly formed molecular chains

When we heat them they become soft, wich allows them to be formed into different shapes

Thermostableplastics

These plastics are made from compounds derived from petroleum

They`re formed by strongly-linked chains running in different directions

When heated, they become soft and can be shaped.When cooled, they cannot be remoulded by applying heat

Elastomers

Made by vulcanisation: mixing sulphur and rubber, and heating to 160ºC

They are hard, resistant and very elastic —stretching easily under force

They' re formed by chains linked laterally and then folded over themselves, like a ball of wool or string

FORMATION TECHNIQUES

Extrusion

Lamination

Vacuum forming

1.We put thermoplastic, in granural form, into a previously heated cylinder

2.We apply pressure by means of a large, rotating screw, which forces the melted material out, through a nuzzle

3.We cool the shaped material slowly in a refrigerated water bath until it's solid

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

Thermoplastic produced by the extrusion method is passed through a series 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.

1.We put thermoplastic into a mould

2.We then use a heater to heat the mould and soften the plastic

3.We extract the air below the sheet so that the plastic is pulled against the inside walls of the shaped mould, and the desired form is created

4.We leave the mould to cool, then remove the object

Moulding

Injection

1.We inject melted thermoplastic into a mould

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

Blow

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

2.We close the mould and blow pressurised air into it, so that the plastic adheres to the sides of the mould and takes its shape

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

Compression

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

  1. 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
  1. The plastic adapts to the shape of the cavity between the two parts of the mould

4.We extract the object when the plastic has cooled and solidified

SHAPING AND FINISHING TECHNIQUES

We can use dtfferent tools and machines to finish the plastic objects that we have made

Cutting

Cutter

Scissors

Steel bit

Frestsaw

Jig saw

To cut sheets of different thickness, depending on their hardness

To cut soft, thin flexible sheets

To cut sheets less than 1mm in thickness

To cut soft, low density plastic

Cann make straight, slanting and curved cuts

To cut very large sheets of plastic, and rigid plastics in general

Cann make straight, slanting and
curved cuts

Power press

To cut flat sheets of low density plastic

Makes simple objects by
applying pressure

Hot metal thread thimmer

To cut sheets of soft thermoplastic

Perforating

Tool that makes holes in plastics

Consits of inserting a long, thin round and threaded piece of metal into the head of the machine thaqt revolves at high speed for cutting holes

Trimming and filing

A file has a rough surface

Used to finish the surfaces and edges of hard materials

A rasp has an even rougher surface, covered with 'teeth'

Used to finish the surfaces and edges of soft materials

Joining plastics

When plastics have been formed, shaped and finished, we can join pieces each to other

Temporary joints

Permanent joints

We can join and then separate objects with mechanical fasteners

Nut and bolt

Standard screw

Double ended screw

Used to fasten two objects together

Nut used to tighten the bolt

Used to fasten two objects

Holes must bne drilled first before the screw in inserted

Each end of the screw can be inserted into one of a pair of objects

We use this type of joint when we don't want to separate or dismantle the pieces

Adhesives

Soldering

Joining two surfaces permanently

Resins with two components: liquid, high water resistance

Acrylic cement: liquid, used mainly with PVC and polystirene

Joining thermoplastics using heat and pressure

Textiles and leather

We use textiles in the form of threads to produce cloth

Natural fibres and leather

Synthetic fibres

We get natural fibres from raw materials

Vegetable origin

Animal origin

Mineral origin

Cotton

Linen

Hemp

From the plant of the same name

Naturally white; can be dyed

Elastic and flexible

Light and absorbs moisture

Good thermal insulator

Resistant to acids

From the flax plant

Naturally white or beige

Elastic and flexible

Good thermal productor

Resistant to chlorinee and bleach

Extracted from a herbaceous plant

very strong

Used in shoemaking, crafts and decorations

Wool

Silk

From sheep

Various natural colors, but easily died

Very elastic

Excellent thermal insulator

Resistant to acids

Made from a material secreted by a worm called a silkworm, which forms extremely fine threads

Highly resistant and elastic

Good thermal and electrical insulator

Asbestos

Metals

Fibrous minerals

Fireproof

Used for fire-resistant roofs

A health risk to use aqnd inhale

Threads of gold, silver and copper

Used to make cloth

Synthetic fibres such as nylon, polyester, rayon and Lycra' are plastics

They are long-lasting, resistant and waterproof

A mixture of natural and synthetic fibres is often used to make textiles

STONE AND CERAMICS

Stone

These are materials found in nature as large blocks of rock within the Earth

Marble and granit

high density, cold to the touch, hard, high resistance to environmental conditions

widely varied natural colour

brilliant sheen when polished

used on floors and walls, in architecture and in sculpture

Slate

hard, dense and compact, making it waterproof

extracted from the Eanh in smooth, flat pieces that are cut and pressed

used mainly to cover roofs and as paving stones

Stone binders

Sand and gravel are used directly to make asphalt and also for binders, which are used to 'bind' or join other materials together

Plaster

Cement

Mortar

Concrete

processed from crushed gypsum that is dehydrated

then mixed with water to make a paste that hardens rapidly

water-soluble adhesive when first mixed that is resistant to pressure and to fire

used to make archways, partitions, and as a rovening for walls and paving, etc.

grey powder made from a mixture of crushed and heated limestone, clay and gypsum

mixed with water to make a soft paste

very strong and resistant

used to make mortar and other binders for construction materials like bricks

binder made from cement and sand, hardens when mixed with water

used to hold together construction materials like brick, cement block and
paving stone, and to make artifinal stone

mixture of gravel, sand, water and cement that dries and hardens

strong resistance to pressure

adheres to steel, used to makereinforced concrete

used to make foundations for buildings, bridges, etc.

Ceramics

Physical and chemical propertie

Clay is a fine-grained earth composed of aluminium silicates and other substances. We can mould it easily when it's wet.

It's soft, porous, resistant to high temperatures and chemically inert

It has many different. colours; it's abundant in nature and very versatile

Making ceramics

1.Preparating the clay

We clean the clay to remove traces of vegetable
matter, then apply a breakdown process using rollers

2.Mixing

We add water, anti-grease agents, fluxes and colouring

3.Modelling

We shape the clay in the form of the oblect we want to
make

4.Drying

To allow all water to evaporate

5.Baking

in an industnal oven called a kiln at temperatures between
700ºC and 1700ºC

  1. Glazing and enamelling

Clasification of ceramic materials

There are two large groups: structural ceramics and whiteware ceramics

Structural ceramics are permeable; whiteware ceramics are impermeable

Glass

Glass is a transparent or translucent material that can have different textures and colours

It's waterproof, smooth and hard, but fragile

It's resistant to environmental conditions and to chemical compounds

It's a good thermal, electncal and acoustic insulator

Shaping techniques

We make glass by mixing sand, soda (which acts as a flux) and limestone

We heat this mixture to 1400'C; it then melts tn form a paste

Mould blowing

We put the paste into a hollow mould which has the shape of the object we want to make

We close the mould and inject
compressed air, causing the paste to adhere
to the sides of the mould

When the mould is completely cooled, iyig
we remove the obiect

Float glass making

We float molten glass on top of a layer of molten tin

The glass spreads to form a sheet that we pass through a system of rollers

Weleave it cool

Lamination

We pass the soft material through a system of rollers The roflers can be smooth, or engraved to create a design on the glas