Category: Macromolecules

Describe depolymerisation as a process in which polymers are broken down into their monomers, exemplified by hydrolysis of polyesters using acid as a catalyst.

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Depolymerisation is a process which involves breaking down the plastic polymer into its monomer units. The monomers can then be purified and used to create new plastics.

An example is the hydrolysis of polyesters using acid as a catalyst.

In the hydrolysis process, the ester linkages that hold the polymer chains together are broken. The polyesters will be broken down to form a large number of dicarboxylic acid monomers and diol monomers.

Conditions for hydrolysis of polyesters:
– An acid catalyst, usually sulfuric acid or hydrochloric acid
– Water as a reactant
– High temperature of between 80 deg C to 150 deg C

Describe two methods of recycling plastics.

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1. Physical Method
The physical method used in recycling plastics involves physically breaking down the plastics into very small pieces. The plastics are physically crushed into smaller pieces and blended to form a mixture of uniform homogenous quality. The blended mixture is melted and passed through a screen to form strands. This is known as extrusion. After cooling, the plastic strands are cut into pellets to be used as materials for new products.

2. Chemical Method
The chemical methods used in recycling plastics involve chemically breaking down the long-chain molecular structure in plastics into smaller molecules.
Cracking of plastics and depolymerisation of plastics are the two common chemical methods of recycling plastics.
i. Cracking of plastics
Cracking of plastics involves heating the plastic waste to high temperatures in the presence of a catalyst. The long-chain molecules are broken down into smaller molecules. This process transformed the plastic waste into a mixture of gases, liquids and solids. This mixture is then separated and processed to create new raw materials or fuels.
ii. Depolymerisation of plastics
This process involves breaking down the plastic polymer into its monomer units. The monomers can then be purified and used to create new plastics.

Describe the pollution problems caused by the disposal of non-biodegradable plastics.

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– Plastics are flammable.
In the event of a fire, plastic materials burn readily, causing the fire to spread quickly.

– Burning of plastics gives off toxic gases.
Many plastics produce poisonous gases upon incineration, causing air pollution.

– Plastics are non-biodegradable.
By “non-biodegradable”, it means that plastics cannot be decomposed by bacteria in the soil. Improper disposal of plastics can cause land and water pollution.