Design of an Anti-Aging System

BASIC · FORMULATION

Design of an Anti-Aging System

Putting three additives into one formulation looks simple, but it is actually the step in material development that most demands experience and is most easily done wrong. This article explains the method.

The question customers ask us most often is not "which additive to use," but "how should these be combined." The same batch of additives works at factory A but fails at factory B - the difference is usually not the additives themselves, but the system design.

Every principle of system design must ultimately be verified on the test bench, not assumed from experience.

I. Four Basic Principles

Start at step 1, define the failure mode, then pair a primary phenol with a phosphite and set dose from target life.

II. What Each of the Three Components Does

Typical ratio: primary to secondary antioxidant by mass 1:1 to 3:1.

Antioxidant: handles "heat" and "oxygen"

Polymers undergo chain oxidation during processing, hot processing and service, forming hydroperoxides (ROOH). Free radicals from hydroperoxide decomposition accelerate the next oxidation round, creating an autocatalytic cycle.

• Primary antioxidant (phenolic, e.g. 1010 / 1076): interrupts the oxidative chain, traps alkylperoxy radicals. 1076 has lower migration and better extraction resistance than 1010, suitable for bleed-sensitive scenarios.
• Secondary antioxidant (phosphite, e.g. 168): decomposes hydroperoxides, chelates metal ions, blocks catalytic degradation. Phosphites hydrolyze easily and need extra evaluation in damp environments or with alkaline fillers.
• Pre-blended (e.g. 215 / 225): pre-mixed products of 1010 and 168 that turn "combined synergy" into a commercial action, avoiding customer ratio mistakes.

In flame-retardant PP systems, typical antioxidant dosage is 0.1-0.8 phr (preferably 0.3-0.5 phr).

UV absorber: handles "light"

Benzotriazole UVAs work by capturing UV and converting it to heat - but this is a sacrificial mechanism: one molecule can only "sacrifice" once, forming a quinone-type intermediate.

This leads to an important corollary: under long-term outdoor exposure, relying solely on an absorber produces an "early effective, late failure" cliff-like decay. So UVA must be used with the regenerative HALS.

Compliance note: the four common benzotriazole products UV-326 / 327 / 328 / 329 have all entered EU restriction lists - UV-328 is on the POPs regulation (limit 1 mg/kg), UV-327 is on the authorization list, and UV-326 / 329 are on the SVHC candidate list. For formulations with export business, UVA selection must consider compliance from the very beginning.

Hindered-amine light stabilizer (HALS): handles the autocatalysis of photo-oxidation

HALS works through excited-state quenching and a hydrogen-donor regeneration cycle. The key feature: it does not consume itself, but regenerates within the reaction cycle, theoretically enabling durable protection.

But this advantage has a precondition: the nitrogen atom must remain basic. Once protonated by an acid, the cycle stops immediately - which is precisely why acid from flame retardants is the industry's biggest difficulty.

The synergy among the three

On "synergy factor": the "synergy factor" is not a simple addition of absorber and HALS. After adding the same level of UVA to the base formulation, if the light-stability efficiency improvement of HALS exceeds the corresponding baseline, synergy exists; if it is below baseline, the formulation itself is unstable and the antioxidant/HALS ratio needs rebalancing. When formulating for customers, Tiangang follows this judgment logic rather than giving a fixed "synergy multiplier" number - a fixed multiplier is technically not rigorous.

III. Dosage and Addition Order: the Most Easily Overlooked Part

A common industry rule of thumb: in agricultural film, 0.25% addition corresponds to about 5 years of life, 0.5% to over 5 years.

The boundary of dosage

Too little dosage, weather resistance fails; beyond the compatibility critical value, blooming, haze, ink migration/peeling, and heat-seal strength drop appear. Under the thinning trend of film products, this window is often only a few tenths of a percent wide.

But this is only a starting point - the specific dosage must be determined by combining the base-resin grade, processing temperature, product thickness and service environment (latitude, irradiation intensity).

Addition order: in acidic systems, this step decides success or failure

During high-shear extrusion, the flame retardant may slightly decompose and release acidic by-products. A conventional COA only controls purity - the melt-phase acid-value drift is a hidden variable outside the COA, continuously consuming HALS until the part turns white.

• Add the acid scavenger first (hydrotalcite, epoxy-functional polymer) - neutralize the acid already in the melt.
• Then add the flame retardant and ensure full dispersion - let the retardant release acidic by-products after it is dispersed in place.
• Finally add the light stabilizer - avoid the acid produced in the first two steps consuming HALS on the spot.
• Monitor the melt-temperature ceiling throughout - the higher the temperature, the faster the retardant decomposes and the more violent the acid-value drift.

IV. Five Most Common Mistakes

Mistake 1 is adding antioxidant without pairing a primary phenol with a phosphite, so hydroperoxides keep accumulating.

V. System Design Must Be Verified, Not Believed

On life conversion: please do not use single-value conversions like "1000 hours of xenon = 5 years outdoors" as acceptance criteria.

After the formulation is designed, the next step is always verification. Tiangang's approach runs three tracks in parallel:

• Accelerated aging: xenon-arc (WOM) and fluorescent UV (QUV) per GB/T 16422.2-2022, ASTM G154 and other standards, combined with thermo-oxidative aging; track Delta E, tensile retention, gloss loss, grey-scale rating.
• Outdoor measurement: samples sent to Beijing and Guangzhou exposure bases, building correlation between accelerated data and real climate.
• Baseline control: same-condition comparison with the customer's existing formulation, not absolute numbers - weather resistance depends heavily on substrate and working conditions, and absolute values divorced from premises are meaningless.

Xenon-arc is an accelerated simulation suitable for horizontal relative comparison, not a precise replication of all real outdoor environmental factors; the year-to-year variation of natural exposure can exceed +/-30%. Tiangang does not use single-value conversions in external statements, but gives conclusions through the "accelerated test + outdoor measurement" dual track.

Want to re-examine your formulation from scratch? Tell us the base-resin grade, processing conditions, service life and environment, and the technical team will first do a failure diagnosis, then give a compatibility plan, dosage and process-order advice, and run a same-condition comparison verification in the lab.

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