13.4 Biodegradable and Non-biodegradable Polymers

Polymers are large molecules composed of repeating structural units. Their interaction with the environment, particularly regarding their degradation, is a critical aspect of modern chemistry and environmental science. Polymers can be broadly categorized into biodegradable and non-biodegradable types based on their ability to decompose.

1. Biodegradable Polymers

Definition: These are polymers that can be decomposed by the action of microorganisms (e.g., bacteria, fungi) in the environment.

Chemical Characteristics:

• They typically contain hydrolysable functional groups, such as amino (in polyamides) or ester (in polyesters) groups.
• These groups can be easily broken down by enzymes produced by microorganisms, as well as by acids and alkalis.

Examples:

• Polyamides (e.g., Nylon-2-Nylon-6)
• Polyesters (e.g., PHBV - Polyhydroxybutyrate-co-hydroxyvalerate, PLA - Polylactic acid, PGA - Polyglycolic acid)

2. Non-biodegradable Polymers

Definition: These are polymers that cannot be decomposed by the action of microorganisms and remain intact in the environment for extended periods.

Chemical Characteristics:

• Often formed from addition polymerization.
• Characterized by being unreactive or inert, largely due to their non-polar and saturated nature.
• They possess long chains of carbon atoms linked by non-polar C-C bonds, which are chemically very stable and difficult for biological systems to break down.

Examples:

• Polyethylene (PE)
• Polypropylene (PP)
• Polyvinyl chloride (PVC)
• Polyethylene terephthalate (PET)

Some non-biodegradable polymers can be recycled to form new polymers for different purposes, offering an alternative to direct disposal. This relates to the Ethical Considerations In The Production And Use Of Chemical Substances→ regarding waste management.

3. UV Degradation

Some non-biodegradable polymers, despite resisting microbial action, can be degraded by ultraviolet (UV) light.

Mechanism: UV light can break down the polymer chains (photodegradation), leading to the weakening and eventual disintegration of the material.

Examples: Polyethylene, polypropylene, and polystyrene.

4. Long-Term Effects of Non-biodegradable Polymers

Non-biodegradable polymers pose significant environmental challenges due to their persistence:

• Environmental Accumulation: They accumulate in landfills, oceans, and natural habitats because they do not decompose naturally.
• Pollutant Production: In the presence of sunlight, water, and air, these materials can produce highly toxic pollutants.
• Water Pollution: These pollutants can leach into water bodies, causing severe water pollution. This can be monitored using techniques like the Winkler Method For Biological Oxygen Demand→.
• Food Chain Entry: Microplastics (small fragments of non-biodegradable polymers) can enter the food chain, potentially impacting ecosystems and human health.

Comparison of Biodegradable and Non-biodegradable Polymers