How to Choose HALS Stabilizers for Plastics
How HALS Work
HALS contain a 2,2,6,6-tetramethylpiperidine ring system. Under UV exposure, the amine nitrogen forms a nitroxyl radical that scavenges carbon-centred radicals from photo-oxidation. The HALS species is then regenerated — allowing a single molecule to interrupt multiple oxidative events. This catalytic mechanism delivers far better long-term UV protection than stoichiometric absorbers.
Low vs High Molecular Weight HALS
- LMW HALS (300–500 g/mol): Higher mobility, faster initial activity, suitable for thick sections (>3 mm)
- HMW HALS (1000–3000+ g/mol): Lower volatility, better permanence — preferred for thin films, fibres, automotive exterior, wire/cable
NOR-HALS
N-alkoxyamine HALS with improved performance in acidic environments. Recommended for formulations with halogenated flame retardants, where conventional HALS are deactivated by acid.
Application Recommendations
- Thin films (<0.5 mm): HMW HALS required
- Agricultural film: Must use pesticide-resistant grade
- Automotive exterior: HMW HALS + UV absorber combination
- Outdoor pipe and profile: UV absorber + HMW HALS system
- Wire and cable: HMW HALS for permanence under long-term exposure
Compatibility Notes
- Conventional HALS are sensitive to acid deactivation by halogenated flame retardants — use NOR-HALS
- Some HALS interact with carbon black at high loadings — confirm in pigmented systems
- Combined UV absorber + HALS system consistently outperforms either alone
Typical Dosage
0.1–1.0% by weight. Confirm through accelerated weathering testing (QUV, Xenon arc) for your target service life.
Contact SUNCHEM
SUNCHEM supplies standard and specialty HALS grades with technical selection support. Contactez-nous for samples and documentation.