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4.5.1 Describe a covalent bond.

In a covalent bond the outer electrons of some atoms come close enough to overlap and are shared between the nuclei, forming a covalent bond. Each pair of electrons is called a covalent bond. Mention of sigma (σ), pi (π), double or triple bonds is not required. Covalent bonds are strong bonds and examples of primary bonds (as are metallic and ionic bonds).

4.5.2 Describe secondary bonds as weak forces of attraction between molecules.

Kevlar atomic Structure

Hydrogen is positively charged and the Oxygen (one side) is negatively charged.

An interesting link on cross-linking.

4.5.3 Describe the structure and bonding of a thermoplastic.

Thermoplastics are linear chain molecules with weak secondary bonds between the chains.

Types of Plastics

4.5.4 Describe the effect of load on a thermoplastic with reference to orientation of the polymer chains.

Deformation occurs in two ways:

elastic, in which initially coiled chains are stretched and the material returns to its original size and shape when the load is removed
plastic, when at higher loads the secondary bonds between the chains weaken and allow the molecular chains to slide over each other, and the material does not return to its original size and shape when the load is removed. Creep and flow are important.
No quantitative details are required.

4.5.5 Explain the reversible effect of temperature on a thermoplastic, with reference to orientation of the polymer chains.

Increase in temperature causes plastic deformation.

The weak secondary bonds
That can easily broken by heat
Thus the long chains can slide over each other.
When plastically deformed and cooled at the same time new secondary bonds are made.

4.5.6 Explain how the reversible effect of temperature on a thermoplastic contributes to the ease of recycling of thermoplastics.

The Increase in temperature causes the weak secondary bonds to break (The heat is sufficient enough to break the secondary bonds but not the primary, covalent, bonds)
allows the long molecular chains to slide over each other, i.e. be reshaped into a new product.
when a plastically deformed and allowed to cool it will remain in the new shape
due to new secondary bonds being formed
recycling of plastic

Activity: Make a spinning wind twirler.

4.5.7 Draw and describe the structure and bonding of a thermoset.

Thermosets are linear chain molecules with strong primary bonds between adjacent polymer chains. This gives thermosets a rigid 3D structure.

4.5.8 Explain the non-reversible effect of temperature on a thermoset.

The heating process increases the number of permanent cross links
and so hardens the thermoset plastic
this cross linking is permanent

4.5.9 Discuss the properties and uses of polypropene and polyethene thermoplastic materials.

Polypropene

Properties
- is resistant to fatigue
- durable
- higher melting point than other thermoplastics (160 Celsius)
- high impact strength or toughness
- high tensile strength
- low density
- corrosion resistant
- retains stiffness at very high temperatures
- can be easily coloured
Uses
- in carpeting
- ropes
- dishwasher safe housewares
- plastic containers that have hinges
- bumpers on cars

Websites

wisegeek.com on Polypropylene
more
and still more

Polyethene (Polyethylene)

Properties
- high hardness
- high stiffness
- strong
- corrosion resistant
- high transparency and colourless
Uses
- footwear
- houseware
- insulation
- luggage

Websites

An incredibly long http://www.ides.com/generics/PE/PE_applications.htm \ list or applications
polyethene
polyethene
An in-depth look at polyethene


polypropylene	Polyethene from science museum

4.5.10 Discuss the properties and uses of polyurethane and urea�formaldehyde (methanal) thermoset materials.

Polyurethane.

Properties
- "Polyurethanes can be manufactured in an extremely wide range of grades, in densities from 6kg/m3 to 1220kg/m3 and polymer stiffnesses from very flexible elastomers to rigid, hard plastics." from Huntsman.com

Look closely and you will see a wide range of applications according to the way it was manufactured

Uses
- Note above

Websites

List of applications
overview
Properties and uses

Urea�formaldehyde

Wikipeadia reference
Methanal in-depth

4.5.11 Discuss the issues associated with the disposal of plastics, for example, polyvinyl chloride (PVC).

Although PVC disposal is problematic, PVC is still widely used as a structural material, for example, in windows and for guttering and drainpipes

PVC Free campaign from the Centre for Health, Environment and Justice NY
Wikipeadia on PVC
Greenpeace campaign
toxic plastic


PVC Products	Greenpeace Campaign

Courtesy of Center for Health, Environment and Justice

References

Bulleted list and italicised paragraphs are excerpted from Design Technology: guide. Cardiff Wales, UK: International Baccalaureate Organization, 2007.

Images are clickable links to its location.

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Plastics New

4.5.1 Describe a covalent bond.

4.5.2 Describe secondary bonds as weak forces of attraction between molecules.

4.5.3 Describe the structure and bonding of a thermoplastic.

4.5.4 Describe the effect of load on a thermoplastic with reference to orientation of the polymer chains.

4.5.5 Explain the reversible effect of temperature on a thermoplastic, with reference to orientation of the polymer chains.

4.5.6 Explain how the reversible effect of temperature on a thermoplastic contributes to the ease of recycling of thermoplastics.

4.5.7 Draw and describe the structure and bonding of a thermoset.

4.5.8 Explain the non-reversible effect of temperature on a thermoset.

4.5.9 Discuss the properties and uses of polypropene and polyethene thermoplastic materials.

4.5.10 Discuss the properties and uses of polyurethane and urea�formaldehyde (methanal) thermoset materials.

4.5.11 Discuss the issues associated with the disposal of plastics, for example, polyvinyl chloride (PVC).

References