Clear PET Box Yellowing From China: UV Inhibitor and Material Grade

Short answer: a clear PET box that arrives crystal-clear from China can yellow in 6 months under warehouse lighting. The cause is almost always UV inhibitor omission or a downshift from virgin PET to recycled PET without disclosure. The factory is not lying; you asked for clear PET, and clear PET includes rPET. Here is how to lock the grade and the additive before deposit.

ChinaSecurely clear PET box yellowing prevention checklist for small importers sourcing from China

Why clear PET boxes yellow on the shelf

Two forces drive yellowing. The first is photo-oxidative degradation: UV light breaks the polymer chain, generating chromophores that absorb in the blue range and turn the box amber. Virgin PET is intrinsically more photo-stable than recycled PET because the polymer chain is shorter and more uniform. The second force is UV-inhibitor omission: most clear PET boxes are sold without a UV stabilizer package because the additive is not visible, not testable by the buyer, and adds 2 to 4 percent to the resin cost. The factory can save the 2 to 4 percent and the buyer will not see the difference until the box is on the shelf for 6 months.

The China-side explanation is straightforward. PET resin pricing moves with paraxylene spot prices, and rPET pricing follows the recycled-bottle market. A factory that quotes a 30 percent lower price on a 10,000-piece clear box order is almost certainly using rPET, not virgin PET. The visual appearance at delivery is identical; the photo-oxidative stability is not. A small importer who orders by price-per-box and inspects by visual clarity will accept the cheaper quote and discover the yellowing six months later, when the customer reviews turn against the listing.

What to lock on the PO

Resin grade: virgin PET (intrinsic viscosity 0.80 to 0.85 dL/g) or rPET (intrinsic viscosity 0.70 to 0.80 dL/g), with the IV number in writing.
UV inhibitor: benzotriazole or HALS package at 0.1 to 0.5 percent loading, with the additive name.
Haze rating: maximum 1.0 percent per ASTM D1003 on a 1 mm plaque.
Yellowness index: maximum 2.0 per ASTM D1925 on a 1 mm plaque at delivery.
Aging test: 500 hours per ASTM G154 cycle 2 (UVA-340), with haze and YI re-measured.
Storage clause: warehouse exposure maximum 30 days before shipment.

Buyer must verify before deposit

Ask the supplier for the PET resin grade name (e.g., SK Chemicals SKYPET, Sinopec Yuhuang, or equivalent).
Ask the supplier for the UV additive name and the loading percentage.
Request a 5-piece pre-production sample for accelerated aging per ASTM G154.
Inspect the warehouse lighting at the factory: direct sunlight, fluorescent, or LED.
Test the sample haze on a hazemeter per ASTM D1003 at delivery.
Test the sample yellowness on a spectrophotometer per ASTM D1925 at delivery and after G154 aging.

China-side explanation

PET resin spot prices in China have ranged from RMB 6,500 to RMB 10,000 per ton in the last three years. Virgin PET typically costs 15 to 25 percent more than rPET of the same IV. A factory that quotes aggressively will downshift to rPET without disclosure, and the visual difference at delivery is hard to detect. The photo-oxidative stability difference is real but takes 3 to 12 months to manifest under warehouse lighting. By the time the buyer sees the yellowing, the production run is long shipped and the factory’s deposit is spent. The cheapest insurance is to lock the resin grade and UV additive in writing on the PO, and to require a sample retention clause plus an accelerated aging test on a 5-piece pre-production run.

Step-by-step solution

Send the supplier a written spec: resin grade (virgin PET or rPET), UV inhibitor name and loading, haze rating, YI rating, and aging test clause.
Order a 5-piece pre-production sample from the real production line.
Test the sample haze and YI at delivery with a hazemeter and a spectrophotometer.
Run an accelerated aging test per ASTM G154 cycle 2 on 2 of the 5 samples.
Re-test haze and YI after 500 hours of G154 aging and compare to the at-delivery baseline.
Add a sample retention clause and a 12-month yellowing warranty to the PO.

Quick checklist

Resin grade locked: virgin PET with IV 0.80 to 0.85 dL/g.
UV inhibitor locked: 0.1 to 0.5 percent benzotriazole or HALS.
Haze rating locked: max 1.0 percent per ASTM D1003.
Yellowness index locked: max 2.0 per ASTM D1925 at delivery.
Aging test: 500 hours per ASTM G154 cycle 2.
Sample retention clause added to the PO.

ChinaSecurely Clear PET Box Yellowing: Process & Buyer Verify sourcing verification flow and buyer checks

Sources

This article is for sourcing verification, not for polymer engineering. Confirm your final PET grade and UV additive selection with a qualified materials engineer before bulk production.

Clear PET Boxes From China Yellow After 6 Months: UV Inhibitor and Material Grade Checks