Degradable Polymers
Quick Notes
- Polyalkenes (e.g. poly(ethene), poly(propene)) are chemically inert and non-biodegradable.
- Some polymers contain additives that enable degradation by light (photodegradable).
- Polyesters and polyamides can biodegrade via hydrolysis in acidic or alkaline conditions.
- Biodegradable polymers break down more easily in the environment, helping reduce pollution.
Full Notes
Poly(alkenes) and Biodegradability
Poly(alkenes), such as poly(ethene) and poly(propene), are made by addition polymerisation of alkenes.
These polymers have only strong C–C and C–H bonds, with no polar or reactive functional groups.
As a result, they are:
- Chemically inert meaning they don’t easily react with substances in the environment.
- Non-biodegradable meaning microorganisms cannot break them down.
- Environmental Impact: Their durability leads to long-term accumulation in landfills and oceans, contributing to plastic pollution.
Photodegradable Polymers
Some synthetic polymers are made to be photodegradable, meaning they break down under UV light or sunlight.
This is achieved by adding light-sensitive groups to the polymer chain or incorporating metal-based additives that catalyse degradation when exposed to light.
A possible limitation is that photodegradation only occurs in environments with sufficient light exposure meaning it isn't effective in buried landfills.
Biodegradable Condensation Polymers
Unlike poly(alkenes), polyesters and polyamides contain functional groups (–COO– and –CONH–) that are susceptible to hydrolysis.
These polymers can be broken down:
- By acidic hydrolysis with dilute acids.
- By alkaline hydrolysis with bases like NaOH.
- By enzymes and microorganisms in the environment.
Polyesters (e.g. PLA – polylactic acid) and polyamides (e.g. nylon, proteins) are therefore biodegradable and suitable for eco-friendly uses.
For Example
Polyesters can be broken down into diocarboxylic acids and diols.
Summary
| Polymer Type | Key Bonds | Biodegradability | Degradation Method |
|---|---|---|---|
| Poly(alkenes) | C–C, C–H | Non-biodegradable | Very resistant, only photodegradable with additives |
| Polyesters | Ester (–COO–) | Biodegradable | Hydrolysis (acid/alkali), microorganisms |
| Polyamides | Amide (–CONH–) | Biodegradable | Hydrolysis (acid/alkali), enzymes |
- Polyalkenes are non-biodegradable due to inert C–C and C–H bonds.
- Photodegradable polymers contain light-sensitive additives to break down under UV light.
- Polyesters and polyamides are biodegradable because their ester and amide bonds can hydrolyse.
- Biodegradable polymers reduce environmental impact compared to non-biodegradable plastics.