UV Stabilizer Selection — HALS, Absorbers and the Difference That Matters

Direct answer

A UV absorber and a hindered amine light stabilizer do different jobs. The absorber intercepts UV photons before they reach the polymer backbone and works best in thicker sections where there is enough path length to absorb in. HALS does not absorb UV at all: it scavenges the radicals that photo-oxidation generates, regenerating itself as it does so, which is why it dominates thin sections such as film and fibre where an absorber has nowhere to work. Most serious outdoor packages use both, and the correct question at RFQ is not "which stabilizer" but "what service life, in what section thickness, at what latitude, with what pigment".

Why the failure mode tells you the package

• Chalking and surface powdering — the polymer surface has oxidised and the filler or pigment is exposed. Radical control, so HALS-led.
• Yellowing without loss of strength — often chromophore formation from thermal history rather than UV. Look at the antioxidant package before adding more light stabilizer.
• Tensile or elongation loss after one season — insufficient total UV package for the exposure, not the wrong type.
• Cracking at stress points only — environmental stress cracking amplified by photo-oxidation; the part geometry contributes as much as the additive.

Constraints that quietly kill a HALS package

HALS is basic. Acidic species deactivate it. That includes residues from halogenated flame retardants, certain acidic pigments, some agricultural pesticide contact on greenhouse film, and sulphur-containing secondary antioxidants in specific combinations. This is the single most common reason a correctly specified HALS loading underperforms in service. Where the compound also carries an acid source, an acid scavenger — or a low-basicity HALS grade — belongs in the same conversation.

Carbon black changes the calculation entirely: at 2 to 2.5 % of a well-dispersed fine-particle grade it is itself a highly effective UV screen, and the light stabilizer package can usually be reduced. A titanium dioxide white does the opposite in some grades: photoactive TiO₂ catalyses surface degradation unless a surface-treated, weather-grade pigment is used.

What to send with the enquiry

Section thickness, required service life in years, geography and exposure angle, host polymer and grade, pigment or filler system already fixed, whether the part sees agrochemicals or disinfectants, and any flame retardant already in the formulation. Those seven lines let a supplier quote a package instead of a generic additive.

What we supply

Allzone supplies UV stabilizer masterbatch for polyolefins as a pre-dispersed concentrate. Loading, dosage range and service-life expectation are confirmed against the current supplier technical data sheet at quotation — never inferred from a general recommendation.