UNIT 3: Plastics and textiles.

PLASTIC MATERIALS.

▪ Plastics consist of long chains of atoms which are mostly composed of carbon.
▪ Plastics can be classified into natural and synthetic plastics.
▪ The process of manufacturing plastic is called polymerisation.
▪ Plastic materials are resistant, insulating (against electricity, heat and sound) , ductile, maleable, impermeable and light.
▪ There are three types of plastic recycling processes: chemical and mechanical recycling and energy recovery.

THE CLASSIFICATION OF PLASTICS.

▪ Thermoplastics are ussually made from petroleum products. The most common thermoplastics are:

∙ Polyethylene terephthalate (PET)
∙ High- density polyethylene.
∙ Polyvinyl chloride (PVC)
∙ Low density polyethylene.
∙ Polypropylene.
∙ Moulded polystyrene.
∙ Expanded polystyrene or Styrofoam.

▪ Thermosetting plastics are made from petroleum products. They include:

∙ Polyurethane.
∙ Bakelite.
∙ Melamine.
∙ Polyester resins.

▪ Typical elastomers include rubber and neoprene.

PLASTIC FORMING TECHNIQUES.

▪ Various industrial techniques can be used to manufacture plastic, products, such as: extrusión , calendering, vacuum forming and moulding.
▪ The main techniques for using moulds are as follows: blow moulding, injection moulding and compression moulding.



MODIFICATION TECHNIQUES.

▪ Modification techniques use tolos and machines to make changes to prefabricated materials, such as sheets, bars or mouldings.
▪ Examples of these techniques include: measuring➡ drawing marks and lines ➡ cutting ➡ drilling ➡ filling and sanding ➡ joining.
▪ You must always pay special attention to health and safety rules.

TEXTILES.

▪ Both natural and synthetic fibres can be woven to make a variety of textiles.
▪ Natural fibres may come from animal sources (wool, silk), plant sources (cotton, linen, esparto, bamboo) and mineral sources ( gold, silver and cooper fibres).
▪ Synthetic fibres, such as nylon, polyester, rayon and Lycra, are plastic materials.

Basic devices made with electronic components.

Electronic components are usually used to build devices:

TIMERS.

It is a device that operates for a period of time and shuts itself off automatically. A timer works in a circuit by that way:

∎At first, when we push the button, a current flows and pass through the base of the transistor, and then the LED turns on. The capacitor begins to store electric current.
∎When we reléase the button, the LED stills on for a period of time, using current from the capacitor. Finally, when there isn´t more current in the capacitor, the transistor cuts off and the LED turns off.

INTEGRATED CIRCUITS.

They consist of miniature electronic components, for example capacitors, transistors and resistors.

Transistors.

They are made from semiconductor materials and have three electrodes caled the base, the collector and the emitter. There are two types:

Each electrode is connected to a semiconductor material which releases electrons or acceps electrons.
I'm going to explain how transistors work:

⇒When there aren't electrons through the base, electrons cant pass from the collector to the emitter. This phase is called cut off.

⇒When electrons are passing through the base, electrons can pass from the collector and the emitter.
This phase is called saturation.

⇒When the flow of electrons is between cut off and saturation, the flow of electrons between the collector and the emitter is proportional. This phase is called active región.

Transistors are the basisc components of the microprocessors and memory circuits that are used in computers. This is called a transistor gain.