How to improve the quality and anlti-yellowing of TPU shoe elastomer?

Thermoplastic polyurethane (TPU) combines the elasticity of rubber and the processing performance of plastic. Characterized by high abrasion resistance, low density and high elasticity, it is an ideal material for producing lightweight and thin soles, and plays an increasingly important role in the field of sport shoes.

※ Advantages of TPU shoe elastomers：

TPU material has excellent elastic recovery performance, elongation at break can reach more than 600%, which can provide good cushioning effect for sports shoes, and is the most common shoe material.

In terms of hardness, the Shore hardness of TPU ranges from 60A-95A, which can be adjusted by formula to meet the needs of different shoe types.

In the abrasion resistance test, the TPU has a Taber abrasion value of 30-50mg, showing better abrasion resistance.

※ How to improve the quality and yellowing resistance of TPU shoe elastomer?

(1) Add suitable UV absorber/HALS/ANTIOXIDANT

Degradation occurs during temperature change or UV irradiation, weakening its physical and mechanical properties and making it more susceptible to discoloration.

UV absorbers: e.g. Benzotriazoles (OMNISTAB UV360), Benzophenones (OMNISTAB UV531), Benzylmidazoles (OMNISTAB UV1) absorb UV light and are converted it into harmless heat.

Light stabilizers (HALS): e.g. OMNISTAB LS622/LS770,  inhibit photo-oxidation by trapping free radicals. Recommended for use in combination: UV+HALS synergistic effect (0.5-1.0% of each additive).

Antioxidants: such as phosphite (OMNISTAB AN626) or hindered phenolic antioxidants (OMNISTAB AN245), to inhibit thermo-oxidative degradation, enhance the long-term weathering and anti-yellowing properties of TPU.

(2) Select raw materials with good yellowing resistance

Aliphatic TPU is more recommended, which is more resistant to yellowing than aromatic TPU (containing benzene ring), but the cost is higher.

(3) Selection of pigments  

Avoid the use of organic pigments that contain heavy metals or are prone to migration, and give preference to pigments with good weathering properties.

(4) Processing control

Strict drying of raw materials: TPU is easy to absorb moisture, it needs to be dried at 80~100℃ for 4~6 hours to avoid hydrolytic degradation caused by moisture.

Ø OMNISTAB ADDITIVES FOR TPU SHOE ELASTOMER 

UV ABSORBER

OMNISTAB UV360 (Eco-friendly alternative for UV328)

OMNISTAB UV531

OMNISTAB UV1

HALS

OMNISTAB LS622

OMNISTAB LS770

ANTIOXIDANT

OMNISTAB AN245

OMNISTAB AN626

OMNISTAB HN130