Lesson 12 of 12
Materials after use
Chemical resistance helps in service but can become a disposal problem.
A-Level 8873, revised syllabus (2026-2027)
I can relate polyalkene inertness to difficult biodegradation.Syllabus
Syllabus 8873, 9(r). Relate polyalkene inertness to difficult biodegradation.
I can recognise hydrolysis as a biodegradation route for polyesters and polyamides.Syllabus
Syllabus 8873, 9(s). Recognise hydrolysis as a biodegradation route for polyesters and polyamides.
I can evaluate recycling in the context of finite material resources.Syllabus
Syllabus 8873, 9(t). Evaluate recycling in the context of finite material resources.
Follow a plastic beyond its first use
Chemical resistance helps in service but can become a disposal problem.
Poly(alkenes) have strong C-C backbones with mostly C-H bonds. Being so unreactive makes them useful for containers and waterproof materials. But it also makes many of them hard to biodegrade, because water and living things cannot easily cut those chains into small molecules. Breaking into small pieces is not the same as biodegrading completely.
Polyesters and polyamides have ester or amide links that can be hydrolysed. So they usually biodegrade more easily than poly(alkenes). Cutting these links shortens the chains and can give small molecules that living things can use. A link that can be hydrolysed does not guarantee fast breakdown everywhere. Temperature, water, how crystalline the polymer is, the chain structure and suitable microorganisms all affect the rate. A long-lasting PET bottle and a fast-degrading polyester both contain ester links.
| Process | What changes | Limit to remember |
|---|---|---|
| Reuse | The same object serves again with little chemical change. | Suitability depends on its condition, cleaning and intended use. |
| Mechanical recycling | Material is collected, sorted and processed into new items, commonly by remelting suitable thermoplastics. | Mixed polymers, contamination and repeated degradation can reduce useful quality. |
| Chemical recycling or controlled hydrolysis | Chemical bonds are broken to recover smaller molecules or feedstock. | Reagents, separation and energy are still needed; a chemically possible route is not automatically economical. |
| Biodegradation | Biological activity contributes to conversion into simpler substances under suitable conditions. | Do not assume an item will biodegrade quickly in ordinary soil, seawater or a landfill merely from a broad material label. |
Materials and the resources used to make them are limited. Recycling can reduce the need for new raw materials and cut waste, but judge the whole process. A good comparison follows the material and the energy through collection, sorting, transport, cleaning, processing and its next use. Do not stop at the recycling symbol.
| Dimension | Benefits to examine | Costs or constraints to examine |
|---|---|---|
| Economic | Recover usable material; reduce purchase of some fresh feedstock; support useful collection and processing work. | Collection, transport, sorting, cleaning, processing energy and demand for the recovered material affect viability. |
| Environmental | Reduce extraction of resources, waste accumulation and potentially the energy or emissions of making new material. | Washing uses water; transport and processing use energy; rejected contaminated material still needs treatment. Compare like-for-like outcomes. |
| Social | Cleaner surroundings, access to durable useful products, and opportunities for responsible collection and employment. | Convenience and affordability influence participation; workers and communities share the burdens of collection and waste handling. Clear instructions and suitable infrastructure matter. |
Worked exampleMake a balanced recommendation from data
A supplied study says process A recovers 80% of a sorted plastic stream, while process B recovers 95% but uses substantially more energy. Is B automatically better?
Try it first. Then show the worked stepsHide the worked steps
- The higher recovery fraction is a benefit: more material is retained per initial batch.
- Compare the quantity and quality of usable product, energy source, total energy, transport, cost and the fate of residues. A percentage alone omits these consequences.
- Consider whether collection and sorting are practical for users and workers. State which evidence supports the recommendation and which missing data could change it.
No. The decision must combine economic, environmental and social factors for the same functional outcome.
Check your understanding
"PET has ester links, so it will quickly disappear if thrown away." Why is this not justified?
Show the answer
Ester links can be hydrolysed, but in tightly packed PET this is very slow.
A possible reaction is not a fast one. The rate depends on conditions and on water reaching the links, and a dense, durable bottle can last a long time.
Exam-style question
Paper 2 Section B styleThis question draws on Chemical Bonding and Polymers and Organic Chemistry.
Poly(ethene) is made from ethene, CH2=CH2. Nylon 6,6 is made from hexane-1,6-diamine, H2N(CH2)6NH2, and hexanedioic acid, HOOC(CH2)4COOH. Both are used to make fibres and packaging.
- (a) Describe the bonding in the carbon-carbon double bond of ethene in terms of orbital overlap. State the shape around each carbon atom and the H-C-H bond angle. [3]
- (b) Draw the repeat unit of poly(ethene) and name the type of polymerisation. [2]
- (c) Explain why poly(ethene) is hardly broken down in the environment. [1]
- (d) Draw the link that joins the monomers in nylon 6,6. Name the link, the type of polymerisation and the small molecule that is lost. [3]
- (e) Nylon 6,6 has a higher melting point than poly(ethene) with chains of a similar length. Explain this in terms of the forces between the chains. [3]
- (f) Nylon 6,6 can be broken down by heating with dilute hydrochloric acid. Name this type of reaction and give the two organic products. [3]
- (g) Poly(ethene) softens when heated and can be remoulded, but some polymers char instead of softening. Explain this difference in terms of structure. [2]
- (h) Give one advantage and two limitations of recycling poly(ethene) bags into new plastic. [3]
[20]
Saved on this browser only. Anyone using this browser can see it.