Biodegradability of Polymers

What is a biodegradable polymer?

• A polymer that can be broken down by the action of microorganisms in the environment.

Are addition polymers (like poly(ethene)) biodegradable? Why?

• No. They are chemically inert and non-biodegradable. Reason: Their backbone consists of strong, non-polar C-C bonds, which are not susceptible to attack by microorganisms.

Are condensation polymers (like polyesters and polyamides) biodegradable? Why?

• Yes.

• Reason: The polar ester (–COO–) or amide (–CONH–) linkages in the chain can be broken down by hydrolysis. This process is much faster in a compost heap than in a landfill.

What are the main advantages of landfills for polymer disposal?

• Cost-effective methods of disposal, polyesters and polyamides can decompose slowly

• Less need for sorting or separation of plastics

State three disadvantages of disposing of polymer waste in landfill sites.

• Wastes large areas of land and sites are often an eyesore.

• Non-biodegradable polymers (like polyalkenes) persist for hundreds of years, causing long-term land pollution.

• Harmful substances can leach from the plastics into the soil.

• Anaerobic decomposition of waste releases methane, a potent greenhouse gas.

(any three)

State two advantages of disposing of polymer waste by incineration.

• It massively reduces the volume of waste (by up to 90%), so less landfill space is needed for the remaining ash.

• The heat released can be used in energy recovery to generate electricity. (Also: can be done locally, saving transport costs; prevents unsightly landfill sites ).

State two disadvantages of disposing of polymer waste by incineration.

• Combustion releases CO₂, a greenhouse gas.

• Polymers containing chlorine (like PVC) produce toxic HCl gas, which contributes to acid rain and must be neutralised ('scrubbed'). (Also: it is more expensive than landfill and wastes a non-renewable resource ).

State two key advantages of recycling polymers.

• It conserves finite resources, as most polymers are derived from non-renewable crude oil .

• It reduces the amount of waste sent to landfill, making landfill sites last longer and reducing land pollution.

State a major disadvantage or difficulty associated with recycling polymers.

• Mechanical recycling (melting and remoulding) is difficult because different types of polymers must be sorted before processing, which is a complex and expensive task.

• Feedstock recycling (breaking polymers back into monomers) is a complex chemical process, though it does produce a higher-quality product .

Explain why poly(ethene) and Terylene (a polyester) differ in their biodegradability.

• Poly(ethene) is non-biodegradable because it is a saturated molecule with strong, non-polar C-C and C-H bonds that are chemically inert.

• Terylene is biodegradable because it contains polar ester linkages (–COO–). These can be attacked and broken down by nucleophiles, allowing the polymer to be hydrolysed.

A T-shirt is made from a polyester. What are the products of acidic hydrolysis of this T-shirt?

(The repeating unit is shown below). –[–O–(CH₂)₂–O–CO–(C₆H₄)–CO–]–n

• Ethane-1,2-diol: HO–(CH₂)₂–OH

• Benzene-1,4-dicarboxylic acid: HOOC–(C₆H₄)–COOH

(Self-marking note: Acid hydrolysis (H⁺/H₂O) breaks the ester bonds and re-forms the original diol and dicarboxylic acid monomers).

State two advantages of recycling polymers over disposing of them by landfill or incineration.

1. Conserves finite resources: Polymers are made from crude oil, which is non-renewable. Recycling reduces the amount of crude oil needed.

2. Reduces waste: It decreases the volume of waste going to landfill, so sites last longer and less land is used for waste. (Other valid answers: Reduces CO₂ emissions compared to incineration; reduces toxic gas release).