PLASTIC

What is plasticsAre materials which can be shaped or moulded under appropriate conditions of temperature and pressure, and then hold their shape.

IntroductionPlastic has become increasingly important in our every day lives.

For the most part, plastics are organic high polymers, which means they are made of large chain that contain carbon.

These polymers are changed into a plastic state either as they transition from a small-molecule chemical to a solid.

Types of Plastics

Thermoplastic Thermosetting

i. Thermoplastic Become soft when heated and harden when cool and the process can be repeated is called thermo-softening plastic or simply thermoplastics.

Is like wax

Thermoplastics are linear with no crosslinks between the polymeric chains.

Can be recycling because can be melted and re-molded.1st

Structure of thermoplastic Thermoplastic Have linear structures and soften when heated hence it can be reshaped and recycled.Monomer- linear

Conc thermoplasticThe bonds holding the polymer chains together are usually the weak Van der Waals force.

When heated, the distance between the chain increases and the polymer becomes soft.

Allow the polymer chains to slide past one another.

On cooling, the chains come closer and the polymer becomes hard.

Picture of thermoplasticsPE Plastics

Picture of thermoplasticsPP Plastics

Picture of thermoplasticsPVC Plastics

Picture of thermoplasticsPET Plastics

Picture of thermoplasticsPolyamides Plastics

Examples of Thermoplastic

TypesUsesPolyethene (PE)Wide range of inexpensive uses including supermarket bags, plastic bottles.Polypropene (PP)Food containers, appliances, car fenders (bumpers). Nylon (Polyamide)Synthetic fiber, substituted for silk ( in silk stockings), tufted carpet, machine gear wheelsPolyvinylchloride(PVC)Plumbing pipes and guttering, shower curtains, window frames, flooring, erotic clothing.PETCarbonated drinks bottles, jars, plastic film, microwavable packaging.

Properties and Uses of Thermoplastics

ii. Thermosetting Plastics

Is like concrete.

Highly cross-linked chains and hence usually are rigid and brittle.

They must be given their shape before their final chemical structure is produced. 2nd

Structure ofthermosetting plasticsCross-linkedCross-linked:More tougherMore elasticMore heat resistantLess soluble in organic solvent

Concthermosetting plastics They cannot be molten, but will decompose at high temperatures.

They are entirely insoluble and will not swell when treated with solvents. They do not lend themselves to recycling. ( like with eggs, once hard boiled, they cannot be softened ).

Picture of Thermosetting plastics

Picture of Thermosetting plastics

Properties and Uses of Thermosetting Plastics

Examples of Thermosetting plastics

TypesUsesVulcanized rubber Tyres, gloves and tubingBakelitElectrical insulators and plastic wearPolyester Glass-reinforced plastics / fibreglass (GRP)Epoxy Adhesive and in fibre reinforced plastic such as glass reinforced plastic and graphite-reinforced plastic.Acrylonitrile butadiene styrene (ABS)Electronic equipment cases (e.g., computer monitors, printers, keyboards).

Processing of plastic

Processing of thermosetting plastic

Processing of thermosetting plasticsThermosetting plastics are plastics that cannot be remelted once they have hardened. Compression molding forms thermosetting plastic objects in a steel mold. When heat and pressure are applied, the softened plastic squeezes into all parts of the mold to form the desired shape. Laminating binds layers of materials together in a plastic matrix. The layers are fused when heated plates melt the plastic and squeeze the material together.

Processing of thermoplastic

Processing of ThermoplasticsThermoplastics are plastics that can be hardened and melted more than once. In the calendering process, continuous plastic sheets are formed by forcing hot plastic between successive sets of heated rollers. Injection molding uses a screw to push plastic through a heated tube into a mold. Extrusion is a continuous process that heats plastic pellets in a long barrel. A screw pushes the heated plastic through a die opening to form objects such as garden hose and piping. In thermoforming a hot plastic sheet is draped over a mold and a vacuum draws the plastic down into the mold. Blow molding forms containers from soft, hollow plastic tubes that have a mold fitted around the outside. The tube is heated, and air injected into the heated tube expands the plastic against the walls of the mold.

Additives are used in both forms of plasticThese can include: Stabilisers to prevent degradation due to moisture or UV light. Lubricants such as sulphides and waxes to make the polymer easier to form and self lubricating in use. Pigments - often referred to as 'master batch' adding colours to the plastic. Plasticisers - added to make the plastic les hard or brittle.

Fillers - these can be added to enhance properties such as wear/strength/toughness/durability and talc and clay may be used to bulk out the plastic reducing costs.

Flame retardants - to prevent combustion in materials such as domestic foams. Blowing agents - to permit foams to be blown. Anti-static agents - used to prevent the build up of electrical charge.

Common properties of plasticsRigidSolidHardTransparentResistant to stainNon- biodegradableResistant to chemicalsResistant to oxidation agent

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