Why a Plastic Garden Chair Turns Chalky: The Chemistry That Buys Outdoor Products More Time
Published on 10/04/2026 at 10:50 | Editorial boerse-global.de
Leave a polyethylene crate on a patio for a few summers and it will tell you everything: the colour fades, the surface powders, and one day a corner snaps off in your hand. That slow unravelling is photo-oxidation, and the plastics industry spends a great deal of effort slowing it down.
Technical reviews of the field lay out how ultraviolet absorbers extend the working life of polymer products, and what criteria should guide the selection of a weather-resistant material. The core problem is simple. Polymers left unprotected outdoors face continuous solar exposure, and the damage that follows is neither cosmetic nor trivial.
Sunlight triggers photo-oxidative reactions that, over time, discolour plastics, make them brittle and measurably reduce their mechanical strength. To hold that decay at bay, processors rely on carefully matched stabiliser systems.
Two mechanisms, one goal
Protection rests on combining different chemical additives. Conventional UV absorbers take in high-energy radiation and release the energy harmlessly as heat. Hindered amine light stabilisers, known as HALS, work differently — they intercept the free radicals generated during photo-oxidation. Pairing the two approaches is intended to reinforce the material's defences synergistically.
Octabenzone, also called UV absorber 531, is a textbook illustration. It dissipates absorbed UV energy as heat and is used chiefly in polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS) and polycarbonate (PC).
Recommended loading runs from 0.1 to 0.5 percent by weight, depending on the polymer, the intended application and the expected stress — and adding HALS alongside can deliver synergistic protection. Triazine absorbers such as UV-1164 also soak up radiation across a broad spectrum, particularly in the UV-B range, and release it as heat.
Their low volatility and compatibility with PE, PP, PC, polyethylene terephthalate (PET) and polyamide (PA) make them a fixture in automotive parts, agricultural films, coatings, textiles and synthetic fibres.
Other additives answer specific thermal demands. UV absorber 3035 (ethyl 2-cyano-3,3-diphenylacrylate) does not discolour plastics, resists heat, and is applied at 0.1 to 0.5 percent of polymer weight. Its territory covers ABS, ASA, HIPS, rigid and flexible PVC, polyesters, polyamides, polyurethanes and acrylates.
For materials exposed to high thermal loads, such as PC and PET, UV absorber 3030 is the option of choice. It is reported to hold US Food and Drug Administration and EU clearances for indirect food contact and is used in vehicle components, electronics and packaging.
The intermediate 2,4'-dichlorobenzophenone likewise shields polymers against photo-oxidative ageing, embrittlement, loss of strength and chalking, while in coatings it guards against cracking.
Keeping the shield in place
Because additives that wash out or evaporate early stop protecting anything, high-molecular-weight HALS compounds are drawing growing attention. The high-molecular HALS with CAS number 106990-43-6 is distinguished by low migration and volatility and can be processed with polyolefins, styrenic plastics and engineering polymers.
Alongside it, bis(1,2,2,6,6-pentamethyl-4-piperidyl) sebacate (CAS 41556-26-7) scavenges free radicals and protects formulations in polyurethanes and acrylates destined for consumer goods, construction materials and automotive parts.
The company NINGBO INNO PHARMCHEM points to its LS-2020 product in this connection. The high-molecular stabiliser, it says, captures radicals, neutralises photolytic oxidation and, thanks to low volatility, stays anchored in the polymer network over the long term — in agricultural, construction and vehicle applications, for instance.
The related UV stabiliser 944 reduces extraction in PP and PE and shields greenhouse films, mulch films, food packaging and fibres from loss of strength, yellowing and deterioration of barrier properties. HALS 622, combined with benzotriazole or benzophenone absorbers, keeps agricultural films, garden furniture and automotive components from breaking down.
Outdoor PVC — window profiles, siding, fencing, roofing membranes, decking — is commonly protected with calcium-zinc stabilisers. The calcium compounds absorb UV radiation and trap radicals, while the zinc fraction neutralises the hydrogen chloride produced under thermal stress.
Testing what the weather really does
Judging how well any of this works requires standardised testing. One of the signature failure modes in under-protected materials is chalking, which occurs when weathering and UV break down the binder near the surface, leaving pigments and fillers exposed.
The phenomenon depends on pigmentation, binder, weathering exposure and pigment volume concentration, among other factors, and has links to wet-scrub resistance under DIN EN 13300.
Established standards cover the measurement of chalking, among them the Kempf stamp method under DIN 53159 and the adhesive tape method under DIN EN ISO 4628-6, supplemented by colorimetric measurement or visual comparison against reference samples.
Specialists caution that purely artificial short-term weathering in the laboratory can overstress a material. Reliable predictions of long-term durability therefore depend on systematic comparison with real outdoor exposure data.
