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Why transparent TPU products turn yellow over time and how to deal with it
November 26 , 2021

Most of the transparent products on the market are made from a material known as thermoplastic polyurethane, or TPU. TPU is widely used in daily necessities, sporting goods, toys, decorative materials and other fields. TPU products are durable and flexible thanks to the good elasticity, abrasion resistance and oil resistance features of TPU material. Divided by the difference material, there are mainly two types: Aromatic TPU and Aliphatic TPU. Transparent TPU products may turn yellowish due to exposure to sunlight, sweat, or smudges after using it for a period of time.

Why do TPU turn yellow over time?

Aromatic TPU can easily react with negative ions in the air and will cause the product to age and discolor when it processed at high temperature. Plus, MDI molecular structure in TPU is easy to yellow under ultraviolet light. methylene bridge between two phenyl groups in MDI molecular structure of aromatic TPU is easily oxidized under ultraviolet light. Thereby, a conjugated system formed between two aromatic rings and cause irreversible yellowing. HDI molecular structure of aliphatic TPU does not contain benzene ring and is stable. Therefore aliphatic TPU is resistant to yellowing.

How to reduce the yellowish of TPU products?

1.Add anti-yellowing agent to the raw materials during TPU polymerization

2.Sprayed with a yellowing-resistant coating on the surface of the TPU product to protect the TPU product from yellowing. The anti-yellowing coating will form a protective layer on the surface of the TPU finished product.

2 Keep your TPU products out of direct sunlight. The storage environment for TPU should be cool and ventilated, and avoid direct sunlight.

3 Avoid any other direct visible light exposure, such as harsh lights or lamps

4 Avoid exposing your products to extreme climate conditions such as high temperatures and high humidity

5 choose aliphatic TPU instead of Aromatic TPU

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