3.12 Polymers

• • Poly(alkenes) are chemically inert due to the strong C-C and C-H bonds and non-polar nature of the bonds and therefore are non-biodegradable.
• The repeating units in polyesters (eg Terylene)

  • Benzene 1,4 dicarboxylic acid (dicarboxylic acid)
  • Ethane -1,2- diol (diol)
  • Terylene fabric is used in clothing, tire cords
• Nylon 6,6 - a common polyamide

  • Hexanedioic acid
  • Hexane -1,6- diamine
• Kevlar- a common polyamide

  • Used in bulletproof vests
  • benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene
• 3.3.12.2 Biodegradability and disposal of polymers

  • Polyesters and polyamides can be broken down by hydrolysis and are, therefore, biodegradable
  • The reactivity can be explained by the presence of polar bonds which can attract attacking species such as nucleophiles and acids
• The manufacturers of PLA claim that the material will break down to compost in just 12 weeks. Suggest one reason why PLA in landfill may take longer than 12 weeks to break down.

  • In landfill, no air or UV, to assist decay OR not enough water or moisture (to hydrolyse polyester)
  • Allow landfill has / contains: no or few bacteria / micro-organisms / enzymes compared with compost heap
  • OR less oxygen OR lower temperature.
• Name the type of reaction that occurred between the polyester and the aqueous sodium hydroxide. Explain why the aqueous sodium hydroxide reacted with the polyester. [3 marks]

  • Type of reaction = (base or alkaline) Hydrolysis // Nucleophilic addition-elimination
  • Explanation:
  • δ+ C in polyester
  • reacts with OH– or hydroxide ion
• Although Terylene is biodegradeable, it is preferable to recycle objects made from Terylene. Give one advantage and one disadvantage of recycling objects made from Terylene. [4]

  Advantages:

  • reduces landfill
  • saves raw materials
  • lower cost for recycling than making from scratch
  • reduces CO2 emissions by not being incinerated

  Disadvantages

  • difficulty/cost of collecting/sorting/processing product not suitable for original purpose, easily contaminated
• State the difference in the biodegradability of Kevlar compared to that of rubber made of polymerised alkenes.

  Use your knowledge of the bonding in these polymer molecules to explain this difference.

  • M1 Kevlar is biodegradeable but polyalkenes not allow Kevlar is more biodegradeable 1
  • M2 Kevlar has polar bonds/is a (poly) amide/has peptide link comment on structure of Kevlar 1
  • M3 can be hydrolysed/attacked by nucleophiles/acids/ bases/enzymes 1
  • M4 polyalkenes non polar/has non-polar bonds
  • comment on structure of polyalkenes but not just strong bonds
• The advantages and disadvantages of different methods of disposal of polymers, including recycling.

  Advantages

  • Saves raw materials- nearly all polymers are formed from compounds sourced/produced from crude oil.
  • Saves precious resources.
  • Disadvantages
  • Polymers need collecting/ sorting- expensive process in terms of energy and manpower.
  • Polymers can only be recycled into the same type – so careful separation needs to be done.
  • Thermoplastic polymers can be melted down and reshaped
• Landfill

  Advantages - The most common method of disposal of waste

  • Most polymers (polyalkenes) are non-biodegradable and take many years to break down.
  • Could use more biodegradable plastics, e.g. Polyamides and cellulose and starch based polymers to improve rates of decomposition