Lesson3 plastics

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Learn about plastics

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Lesson3 plastics

  1. 1. Technical Materials: plastics Lesson 3 1st term
  2. 2. Introduction • Plastics are a subgroup of materials within the group of polymers composed of huge organic molecules which we call polymers and a group of additives which help them achieve their properties. • Polymers are huge organic molecules formed by the union of many molecules called monomers. They are chains Polymerization is the proccess of bonding monomers. • The process of artificial polimerization is called synthesis • If the monomers are all the same, we talk about homopolymers. If they are different, we call them oligopolymers
  3. 3. Properties of plastics • Properties of plastics vary between the huge variety of them. In general terms they are • Ligth • Good insulators • Resistant to corrosion • Mouldable • Low melting point • Degradable under UV • Pollutant
  4. 4. Types of plastics • There are three different kind of plastics, according with the way in which their chains are bound, and so their properties differ: • Thermoplastics • Thermosets • Elastomers
  5. 5. Thermoplastics • Thermoplastics are relatively flexible • Low melting point • The bonds between chains are weaker than the bonds beteween monomers: they are easy to recycle • The most usual thermoplastics are: polyetilene, PVC, PS, PP
  6. 6. thermosets • Thermosets are stronger than thermoplastics and better for higher temperatures • They melt at about 250ºC (bonds beetween chain) but bonds between monomers break at about 200ºC. There is a chemical change when we melt them, so they are nonrecyclable. • The most important thermosets are polyurethane, polyesther, epoxi resin and phenolic resin
  7. 7. Elastomers • • • • Elastomers are very flexible The links between chains don´t break under an effort, they widen. After the effort they return to this original position The bonds between chain brak after some bonds between monomers when we heat the plastic: they are non-recyclable The most important elastomers are polyisoprene and polyvynilidene chloride
  8. 8. Manufacturing plastics • As a material, plastics are sampled in the form ofdust, or small particles. • Most techniques start by introducing these particles an extrusion machine, where they are heated to the melting point and pushed out trough a mouth. Plastic objects can adquire shape through this mouth or be reinjected in other machine

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