DOC

PLASTICS - Qld Science Teachers

By Corey Morris,2014-03-17 22:09
7 views 0
PLASTICS - Qld Science TeachersQld,QLD

    ADVANTAGES AND DISADVANTAGES OF PLASTICS

    NAME OF USE ADVANTAGES DISADVAN-PLASTIC TAGES Polyester Clothing Light, cheap, Flammable,

     flexible easily melted,

     polluting due to

     slow

    decomposition Polystyrene Packaging

    foam,

    insulation in

    eskies

    Polythene Plastic

     shopping

     bag

PVC Plumbing

    (polyvinyl pipe

    chloride)

Perspex Glass

     alternative

Epoxy resin Glue

Bakelite Saucepan

     handle, light

     switch

    WHAT ARE POLYMERS AND PLASTICS?

    ; Polymers are long-chain molecules. They may be natural (e.g.

    silk, wool, protein) or synthetic (e.g. polyester). ; Plastics are flexible synthetic long chain molecules (polymers).

    They are made from joining many smaller molecules

    (monomers) together. The raw materials for making plastics

    come from crude oil and the petrochemical industry. ; Examples of Plastics include bakelite, nylon, polyester and PVC

    (polyvinyl chloride).

    HOW ARE PLASTICS MADE?

    ; Polymerisation is the chemical reaction that joins repeating

    units called monomers together to form polymers. There are

    two types of polymerisation reactions.

    ; Two Polymerisation Reactions:

    1. Addition Polymerisation occurs when the double bonds of

    hydrocarbons called alkenes are broken, and then joined

    into a long chain molecule (e.g. Many ethene molecules

    join to form polyethene in plastic bags).

    2. Condensation Polymerisation occurs when two types of

    monomers join to form a long chain polymer and water

    is given off (e.g. Many molecules of urea and

    formaldehyde are joined to form glue).

    QUESTIONS

1. What are 2 natural polymers?

    2. What are 2 synthetic or man-made polymers?

    3. Proteins are made of smaller units called amino acids. Which is

    the monomer and which is the polymer?

    4. Polythene (actually it is polyethene) is made of many ethene

    molecules. Which is the monomer and which is the polymer?

    5. Of what smaller monomers is PVC (polyvinyl chloride) made?

    6. In addition polymerisation, alkenes such as ethene are joined.

    First, the double bonds are broken and then all the ethene

    molecules are joined into a very long chain. Using the

    monomers of ethene as a guide, draw a portion of the long-

    chain polymer called polythene.

    H H H H H H

     C C C C C C

    H H H H H H

SOME PLASTICS MELT AND SOME DON’T –

    WHAT ARE THE TWO TYPES OF PLASTICS ?

; Thermoplastics consist of long chains with no cross links that

    allow the molecules to slide over each other when heated. This

    allows them to be moulded into new shapes. Common

    examples are polyethene in plastic bags, nylon, polyvinyl

    chloride (PVC), perspex and polystyrene.

    ; Thermosetting Plastics have cross-linking between many

    molecules and they cannot slide over each other. Once they are

    first set into a certain shape, they cannot be remoulded. If they

    are heated, they will not melt but will eventually burn. Common

    examples are bakelite in light switches and saucepan handles,

    polyurethanes and epoxy resins.

    WHAT ARE THE 3 WAYS OF SHAPING PLASTICS ?

    Plastics can be moulded into objects in 3 main ways: 1. Injection moulding

    2. Extrusion

    3. Blow moulding

Injection Moulding

    ; Injection moulding consists of heating a thermoplastic and

    injecting it into a mould where it cools and hardens into the new

    object.

    ; This process is fast and economical for producing large

    numbers of objects.

    ; Injection moulding leaves a small line on the object where the

    mould splits to allow the object to be taken out. ; Examples: cups, bottle caps, dessert bowls

Extrusion

    ; Softened thermoplastics are forced through an opening in a

    piece of metal called a die. Once through the die, the plastic

    cools and hardens.

    ; The shape of the die determines the cross-section of the object. ; Examples: pipes, tubes, straws and plastic rods

Blow Moulding

    ; A small amount of thermoplastic is softened by heating, and

    then expanded by compressed air to fill the walls of a mould. ; Blow moulding is fast and economical for making hollow items. ; Examples: softdrink bottles

    QUESTIONS

    7. What type of plastic melts when heated and can be reshaped?

    8. What type of plastic does not melt but will eventually burn if

    heated sufficiently?

    9. Which plastic type thermoplastic or thermosetting plastic is

    best for plumbing pipe, the plastic of an electric hairdryer, a

    haircomb and a drinking straw?

10. Match the following:

    A. extrusion X. plastic milk bottle

    B. injection moulding Y. bathroom pipes

    C. blow moulding Z. drinking cup

    11. At ‘Fast Fred’s Fabulous Feast’ takeaway shop, you buy a

    hamburger in an enclosed polystyrene container and a Coke in

    polyethene plastic cup with a lid and a straw. Describe how

    these packaging products are made.

Report this document

For any questions or suggestions please email
cust-service@docsford.com