Degradable Polymers
This lesson covers:
- Why many synthetic polymers are non-biodegradable
- Developments in biodegradable and photodegradable polymers
Polymers are useful but difficult to dispose of
Synthetic polymers are highly valued for their numerous benefits and wide range of uses. However, a significant challenge associated with them is that many are non-biodegradable, meaning they do not naturally break down over time.
Polyalkenes:
- These polymers are chemically inert and non-biodegradable because they are composed of long-chain, saturated alkane molecules containing strong, non-polar C-H and C-C bonds.
- These bonds do not readily react with other substances in the natural environment, making polyalkenes resistant to breakdown.
Polyesters and polyamides:
- These polymers have polar bonds within their chains, such as ester links (-COO-) in polyesters and amide links (-CONH-) in polyamides, which can undergo hydrolysis.
- Hydrolysis is a process that breaks down the polymer chains, making these polymers biodegradable, although the process is very slow.
- Under acidic or alkaline conditions, the amide links in polyamides can be hydrolysed, breaking the polymer chain into the original dicarboxylic acid and diamine monomers.
- Similarly, the ester links in polyesters can be hydrolysed under acidic or alkaline conditions, breaking the polymer chain into the original dicarboxylic acid and diol monomers.
Developments in degradable polymers
To address the challenges posed by non-biodegradable polymers, researchers have developed degradable polymers that decompose more quickly, offering environmental benefits by reducing the accumulation of persistent plastic waste.
Biodegradable polymers:
- Incorporate starch granules or are derived from plant-based monomers, making them more susceptible to digestion by microorganisms.
- Polyamides and polyesters can decompose through acid hydrolysis under the hot, acidic conditions often found in landfills.
Photodegradable polymers:
- Contain light-sensitive carbonyl groups that absorb UV light, weakening nearby bonds and causing the polymer to fragment into smaller pieces.
- Fragmentation accelerates the biodegradation process.
- Have limited effectiveness in landfill environments where waste is typically buried, blocking light and preventing photodegradation.