Sunlight degrades plastics through photo-oxidation — causing chalking, cracking, loss of gloss, colour fade and embrittlement. Two families of light stabiliser prevent this, and they work in completely different ways.
UV absorbers (UVA)
UV absorbers such as benzotriazoles (Tinuvin 326/327/1130) and hydroxyphenyl-triazines (Tinuvin 1577/1600) work by absorbing harmful UV light and dissipating it as heat before it damages the polymer. They need sufficient part thickness to be effective and are gradually consumed over time.
HALS (hindered amine light stabilisers)
HALS such as Tinuvin 770/765/292 and Chimassorb 944/2020 do not absorb UV. Instead they scavenge the free radicals formed during photo-oxidation, through a regenerative (Denisov) cycle — so a little goes a long way, and they remain effective even in thin sections and films.
Which should you use?
- Thin films / fibres → HALS are especially effective; UVAs need thickness.
- Thick, transparent parts → UVA + HALS together.
- Best overall durability → combine a UV absorber with a HALS — they act synergistically.
- Acidic environments (e.g. certain pesticides, coatings) → choose the HALS type carefully, as basic HALS can be deactivated.