4.4 Materials

• The advantages of synthetic polymers are…

  • Plasticity - easily shaped through moulding
  • Lightweight eases transportation and use less fossil fuels 
  • Requires less energy to make compared to other materials (metal)
  • Better thermal and electrical insulators than metals
• The disadvantages of synthetic polymers are…

  • Difficulty disposing as they derive from fossil fuels, in which microorganisms cannot break down
  • If exposed to UV, it will break in small pieces and produce smoke, toxic gases and ash
  • Made from finite sources/non-renewable resources
  • Wasteful attitudes towards them due to the cheap production
• Thermoplastic polymers have no covalent bonding of cross links between them, and hence are only held together by secondary intermolecular forces of H bonding or dispersion forces. Hence, they can be softened when heated and reshape, thus, be recycled and used again.

  Thermoset polymers have cross links between them, in which when heated, they will char due to the strong covalent bonding of cross links.
• If a polymer contains only non-polar side chains, with only dispersion force, they are soft, flexible and not elastic

  If a polymer contains polar NH, OH, C=O groups, with hydrogen bonding, then they are stronger, rigid and elastic. 

  If a polymer has cross-links of covalent bonding, they have the highest rigidity, elasticity, hardness and durability 
• Vulcanisation is to introduce these covalent bonds to form cross links by breaking the double bonds of a polymer. S2 is added as a common cross link 
• The advantages of biodegradable polymers are…

  • Reduces the accumulation of waste in landfills and oceans
  • Many are made from renewable resources, reducing fossil fuel dependency 
  • Less likely to released harmful chemicals into the environment despite being exposed to UV
• A polymer is biodegradable if they have functional groups in their chains that can be hydrolysed by some enzymes/microorganisms to break the polymer down in the environment such as ester or amide groups.
• 1. Concentration of the mineral: involves crushing of the ore (deposits of minerals) before the removal of waste. It also increases the surface area which increases the rate of reaction of froth flotation.
• Froth Flotation:

  • The powdered ore is mixed with water in tanks. Surfactants of xanthates are added and air is blown into the mixture. 
  • The negatively charged xanthate ions attract to the positively charged zinc (or metal) ion in the solution, encapsulating the metal ion inside. Considering its non-polar tail is hydrophobic, its tail sticks into the bubbles of air, where no water is present, forming reverse micelles. Since bubbles naturally rise to the surface, the micelles travel with it, in which the metal ions are collected.
• 2. Conversion of the concentration: converting the mineral into a different compound/form before reduction
• 3. Reduction: turns the metal ion into metal,

  1. Metals above Zn must use electrolysis of molten salt or molten oxide because high reactivity forms very stable compounds. Cannot be reduced with an aqueous solution though because H2O could be reduced in preference to the metal. Additionally, it cannot be chemically reduced with CO as it is not a strong enough reducing agent to reduce reduce the ions to metal
• 1. Zn below can use reduction through carbon monoxide to gain the metal because carbon monoxide can be easily oxidised 
  2. Cu and Hg can be roasted with oxygen where its sulphides are converted to an oxide. This metal oxide can be easily reduced to the metal
• 4. Refining the metal: increases the purity due to its usage in circuits, which involves more electrolytic cells 
• There is a finite amount of materials on earth. Recycling the materials reduces the amount of new materials that need to be produced, prolonging the availability of the materials. It also decreases energy costs to make completely new materials.
• As composite materials have different unique properties, they offer a broad range of applications such as concrete, fibreglass.

  However, if the material is composite, each component of the composite material has different properties and so must be treated for recycling in different ways.
• Each monomer must contain 2 functional groups of hydroxyl and carboxyl groups to form the ester functional groups for condensation polymerisation
• Mining is required to obtain fossil fuels and this requires lots of energy, releasing CO2 emissions. If the hydrolysis of water is powered by renewable electricity, then there are no co2 emissions