When a polypropylene chair fades or a greenhouse film cracks, the instinctive question is 'which UV stabilizer should we add?' — as if HALS and UV absorbers were substitutes. They are not: the two families attack photo-degradation at entirely different points, and the commercial difference shows up in longevity data.

UV Absorbers Work Optically

UV absorbers such as UV-326 and UV-531 absorb photons in the 300–380 nm band and dissipate the energy as heat before it cleaves polymer bonds. But they are never perfect shields — typically absorbing 90–97% of incident UV — and they do nothing about the radicals that form anyway, nor about visible-light or thermal oxidation.

HALS Work Chemically

HALS such as UV-770 and UV-944 do not absorb UV at all; instead they scavenge the radicals created once degradation starts, and — uniquely — they regenerate themselves in the process. One HALS molecule can neutralize thousands of radicals over its service life, which is why loadings of 0.2% can multiply outdoor life five-fold.

The Systems View: Florida Panel Data

The absorber reduces the radical population generated; the HALS cleans up whatever radicals remain. In our Florida-exposure panels, PP reached 50% elongation retention after:

  • 0.3% UV-770 alone — 14 months
  • 0.3% UV-326 alone — 16 months
  • both together — beyond 30 months

Neither substitution reproduces that curve.

Practical Selection

  • Thin films and fibers — where extraction matters — favor oligomeric HALS like UV-622/UV-944 with food-contact absorbers like UV-326.
  • Thick moldings tolerate the cheaper UV-770.
  • Pigmented systems should bias HALS (absorbers compete with pigment for photons); unpigmented systems benefit more from absorbers protecting the substrate beneath.

Color belongs to the same formulation conversation: pigmented polyolefins face the identical UV exposure that degrades the polymer, and outdoor fastness starts with the colorant itself. Our group's colorants portal maintains an organic pigment catalog at Aolong Chemical with grades rated for outdoor polyolefin and masterbatch use — worth selecting together with the stabilizer package.

Send us your resin, geography and warranty target — we will size the package and supply trial quantities.