Why does TPU turn yellow?

Why does TPU turn yellow? TPU is a polymer material formed by the reaction and polymerization of diisocyanate molecules such as diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI), macromolecular polyols, and low-molecular polyols (chain extenders)
.
As the main raw material of synthetic polyurethane materials-diphenylmethane diisocyanate (MDI) or toluene diisocyanate (TDI) and other diisocyanates will turn yellow under ultraviolet light, so yellowing is an attribute of TPU
.
How to prevent TPU from yellowing? Because TPU is a kind of yellowing resin, yellowing is a problem that TPU materials cannot avoid.
How to prevent or delay the yellowing of TPU is the problem we have to face
.
To prevent the yellowing of TPU materials, if there is no cost limitation, the preferred material must be aliphatic polyurethane (Aliphatic Polyurethane) TPU
.
Aliphatic polyurethane has excellent chemical resistance and excellent aging resistance, and is suitable for long-term use under harsh conditions
.
If there are cost considerations, we choose non-aliphatic economical TPU materials with anti-aging agents
.
However, the yellowing of TPU with anti-aging agents will happen sooner or later
.
Therefore, we have to find a way to delay the yellowing time of TPU
.
How to delay the yellowing time of TPU? 1.
TPU materials should be stored in a cool and well-ventilated area, without sunlight
.
2.
Add anti-aging agent (anti-yellowing) 3.
Spray anti-yellowing paint on the surface of TPU products
.
The spraying of anti-yellowing paint will form a protective layer on the surface of the TPU product to avoid yellowing of the TPU surface in contact with the atmosphere
.
4.
Avoid pollution during manual operation
.
Many TPU products are contaminated during the finishing or salvage process, resulting in yellowing such as human sweat and organic solvents.
Therefore, TPU products should pay special attention to the cleanness of the contact body and reduce the finishing process as much as possible
.