Biodegradable polyesters
3 marks · EasyLactic acid is a monomer that can be used to make the biodegradable polyester polylactic acid (PLA). The data table below shows three monomers, the type of polymerisation they can undergo, and whether the resulting polymer is biodegradable.
| Monomer | Type of polymerisation | Is the polymer biodegradable? |
|---|---|---|
| Lactic acid | Condensation | Yes |
| Ethene | Addition | No |
| Hexanedioic acid and ethane-1,2-diol | Condensation | Yes |
Analyse the table and answer the following parts:
State which monomer from the table is used to make PLA.
Based on the table, what type of polymerisation is used to make PLA?
Use the data to give one reason why polylactic acid (PLA) is considered environmentally friendly.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Lactic acid
(b) Condensation polymerisation
(c) PLA is biodegradable (it breaks down naturally in the environment).
Common mistakes: Mixing up addition and condensation polymerisation; Calling ethene biodegradable; Confusing which monomer makes PLA
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States lactic acid as the monomer for PLA.
B1 (b) · 1 mark · Identifies condensation polymerisation for PLA.
B1 (c) · 1 mark · Gives a valid environmental reason using data (e.g., PLA is biodegradable or will break down).
Worked solution
a) Lactic acid is the monomer used to make PLA, as shown in the table.
b) The table says PLA is made by condensation polymerisation.
c) PLA is environmentally friendly because it is biodegradable, which means it will break down naturally rather than persist in the environment.