Light Stabilizer & UV Absorber Selection Guide

Light Stabilizer and UV Absorber Selection Guide

1. The short answer

Film and fibre: HS-950. Thick mouldings: T-78. Water extraction: BW-10LD. Complex formulation: HS-362.

The numbers in brackets are industry designations, so you can map them onto the formulation you already run: HS-950 corresponds to 944, T-78 covers the moulding duties of 770, HS-362 corresponds to 783, and BW-10LD is 622. That covers most routine cases. The rest — acidic systems, food contact, very thin parts, formulations that also carry flame retardants — are looked up by condition in section 4. If all you need is a grade to start a trial with, this is enough.

Beijing Tiangang Auxiliary has worked in polymer anti-ageing for over three decades. The Tiangang® range covers hindered-amine light stabilizers, UV absorbers, synergistic blends, antioxidants and application-specific one-packs, with an annual capacity above 30,000 tonnes. Every selection rule on this page is traceable to a grade's specification or its confirmed substrate list; nothing here is an unverified recommendation.

2. Selection by substrate

2.1 Polypropylene (PP)

PP is the largest volume user of light stabilizers. Under UV it undergoes photo-oxidation, losing mechanical strength and chalking at the surface. The range below covers injection moulding and extrusion through to films and long-life outdoor parts.

2.2 Polyethylene (PE)

PE covers blown and cast film, pipe, rotational moulding and cable. The grade choice is driven mainly by wall thickness: thin film cannot afford a volatile HALS, while pipe needs extraction resistance against water.

2.3 ABS and ABS alloys

ABS and its alloys (PC/ABS, PA/ABS) are usually painted or used indoors, but the unpainted grades and light-coloured parts still yellow. Low-basicity grades matter here because ABS carries acidic residues from polymerisation.

2.4 Polycarbonate (PC) and polyester

PC and polyester (PBT/PET) are processed above 250 °C, so volatility and thermal stability decide the grade. Triazine-type UV absorbers are the usual starting point for PC sheet and profile.

2.5 Polyamide (nylon)

Nylon needs care: glass-fibre sizing agents and some pigments are acidic, and a high-basicity HALS is protonated and lost. Low-basicity grades, or a UV absorber used alone, are the practical options.

2.6 Polyurethane (PU)

PU spans coatings, foam and elastomers. Coatings are usually liquid systems where a liquid stabilizer saves a milling step; foam and elastomer are dosed as solids and need to stay dispersed without affecting cell structure.

3. Comparing the four main HALS grades

944, 622, 770 and 783 account for most enquiries. All four are hindered-amine light stabilizers and all work the same way: in service they convert to a nitroxyl radical that traps alkyl radicals and is then regenerated, so the mechanism is catalytic rather than consumptive. What separates them is two attributes — molecular weight, which decides whether the additive stays in the part, and basicity, which decides whether it still works in an acidic formulation.

How to read it: the molecular-weight ranges are from the product specifications. The 480.7 figure for 770 is calculated from the formula C₂₈H₅₂O₄N₂ and is theoretical, not a measured value. Volatility and basicity are assigned from chemical structure for qualitative comparison, not measured parameters. Suitability and substrate lists come from each grade's stated use. Request the certificate of analysis for the values that matter.

The table reduces to one trade-off: the lower the molecular weight, the faster the additive diffuses and the sooner it acts — and the more it is lost to volatilisation and migration. The lower the basicity, the better it survives acidic co-additives, at some cost in radical-trapping efficiency. Selection means picking a position between those two ends for a given wall thickness and service environment.

4. Reverse lookup by application

The hard part of selection is usually not picking a grade but deciding which category your part belongs to. The table below works backwards from the part.

Loading follows wall thickness and design life. Film 0.1–0.5%, injection moulding 0.3–1.0% and fibre 0.3–0.8% are common industry ranges, not guarantees; the formulation trial decides the actual figure. More is not better — past the compatibility limit the additive blooms to the surface, which costs money and spoils appearance without improving protection.

Two mistakes worth avoiding. First, acidic components are not only flame retardants: certain pigments, sulphur-bearing additives and acid-catalysed coating residues all count, so run a small trial before committing. Second, do not swap grades at equal loading — molecular weight and basicity both change, and the loading has to be re-verified.

5. Selection FAQ

Q1: What is the difference between a HALS and a UV absorber?

UV absorbers screen UV light before it reaches the polymer. HALS act afterwards: they trap the radicals that photo-oxidation produces and regenerate in the process. Absorbers protect the surface, HALS protect the bulk. Many outdoor formulations use both.

Q2: When is a low-molecular-weight HALS the right choice over a polymeric one?

Low-molecular-weight grades such as 770 diffuse quickly and reach thick-section interiors, at the cost of volatilisation. Above roughly 2 mm wall thickness that trade is usually worth it. Below 50 μm, loss dominates and a polymeric grade is needed.

Q3: Why do coatings often use liquid light stabilizers?

A liquid disperses without a milling step, which matters in solvent-borne coatings where pigment loading is already high. It also avoids the dust and dosing problems that powders create in a paint plant.

Q4: The part must survive both high temperature and low volatility. Which grade?

Read the 10% weight-loss temperature and the molecular weight together. A polymeric triazine HALS such as HS-950 or HS-362 covers both. Monomeric grades such as 770 do not: they volatilise during high-temperature processing.

Q5: How do I stop agrochemicals from deactivating the HALS in agricultural film?

Sulphur- and chlorine-containing agrochemicals release acidic species that protonate the amine. Use a lower-basicity grade such as HS-625, raise the loading, or add a UV absorber so the surface is protected by a second mechanism.

Q6: What is a typical loading, and does more always help?

Film 0.1–0.5%, injection moulding 0.3–1.0% and fibre 0.3–0.8% are common industry ranges, not guarantees. Above the compatibility limit the additive blooms to the surface: cost rises, appearance suffers, and protection stops improving.

Q7: Does Tiangang supply masterbatch instead of powder?

Yes. Masterbatch avoids dust and dosing errors on lines that run many small batches. Divide the target loading by the active content to get the let-down ratio: a 20% masterbatch at a 0.3% target is 1.5%.

Q8: How do I get a sample and run an application trial?

Send a request through the contact page with the resin, the process, the target service life and any co-additives that could interact. We reply with a grade recommendation and a starting loading; the trial result decides the final formulation.