35.3 Degradable polymers

In a poly(alkene), the original C=C bonds have become strong C–C single bonds in a saturated carbon backbone. With no easily attacked functional group, the material is relatively chemically inert.

This stability gives useful durability but also makes many poly(alkenes) difficult for organisms and ordinary conditions to biodegrade.

Poly(ethene) packaging can remain for long periods because hydrolysis has no ester or amide link to attack; fragmentation by sunlight is not the same as complete biodegradation.

“Inert” does not mean indestructible or non-reactive under every extreme condition; it means resistant under ordinary biological/environmental conditions.

Ultraviolet light can supply enough energy to break polymer bonds or create reactive radicals, causing chains to fragment. This is photodegradation, not necessarily complete biodegradation.

The rate depends on the polymer, light intensity, oxygen and stabilising additives. Fragmentation may produce smaller pieces without converting them fully to CO₂ and water.

A poly(alkene) exposed to sunlight can become brittle as chains break, yet the resulting microfragments can persist.

“Breaks into pieces” does not mean “biodegradable”; physical fragmentation and biological mineralisation are different endpoints.

Polyesters contain ester bonds and polyamides contain amide bonds. Water, acid or alkali can hydrolyse these polar links, so such polymers can be more biodegradable than poly(alkenes) under suitable conditions.

Hydrolysis rate depends on accessibility, temperature, pH and polymer structure. “Biodegradable” is a conditions-dependent claim, not an instant disappearance label.

An ester link can split into an alcohol and carboxylic acid (or carboxylate in alkali); an amide link gives an amine/ammonium product plus acid/carboxylate.

The presence of an ester or amide makes hydrolysis possible, not automatically rapid in every environment.