'We have 6 guest/s online'
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.
4.5.4 Describe the effect of load on a thermoplastic with reference to orientation of the polymer chains.
Deformation occurs in two ways:
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.
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.
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.
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).
Although PVC disposal is problematic, PVC is still widely used as a structural material, for example, in windows and for guttering and drainpipes
Courtesy of Center for Health, Environment and Justice
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.