Topic 12 of 12
Materials after use
Chemical resistance helps in service but can become a disposal problem.
A-Level 8873, revised syllabus (2026-2027)
Follow a plastic beyond its first use
Chemical resistance helps in service but can become a disposal problem.
Poly(alkenes) have robust C-C backbones and mostly C-H bonds. Their relative chemical inertness is useful for containers and waterproof materials, but it makes many of them difficult to biodegrade: ordinary aqueous conditions and biological processes do not readily cleave those backbones into small usable molecules. Fragmenting into smaller pieces is not the same as complete biodegradation.
Polyesters and polyamides contain hydrolysable ester or amide links, so they are generally more susceptible to biodegradation through hydrolysis than comparable poly(alkenes). Cutting these links reduces chain length and can produce smaller molecules that further biological processes may use. A hydrolysable link does not guarantee rapid breakdown in every environment. Temperature, water access, crystallinity, chain structure and suitable biological activity affect the rate. A durable PET bottle and a readily degradable polyester can 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 produce them are finite. Recycling can reduce demand for fresh feedstock and reduce waste, but it should be evaluated across the whole process. A persuasive comparison follows the material and energy through collection, sorting, transport, cleaning, processing and its next useful life, rather than stopping 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 example
Make 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?
- 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.