What's the Properties of TPU 2?
Hardness
Hardness, a material's resistance to deformation or indentation, is largely determined by the hard segment content in TPU. Shore A and Shore D tests (ASTM D2240 or ISO 868) are commonly used. TPU hardness can be tuned across a wide range-from Shore A70 to Shore D80-by adjusting segment composition.
Stiffness
Stiffness, measured by flexural modulus (ASTM D790), is not directly indicated by Shore hardness but is influenced by the segment structure. TPU stiffness increases with hard segment content but still retains good flexibility.
Dynamic Properties
TPU performs well under dynamic loading, cyclic stress, and high-frequency vibrations. Key dynamic metrics include:
Storage Modulus (E'): Represents the elastic component; varies significantly with temperature and frequency.
Loss Modulus (E''): Indicates energy dissipation capacity; peaks near the glass transition temperature (Tg).
Loss Factor (tanδ = E''/E'): Reflects damping performance. A higher tanδ is ideal for shock absorption (e.g., shoe soles), while lower values are better for rebound-focused applications (e.g., sports equipment).
Thermal Properties
TPUs are generally suitable for long-term use between -40°C and 80°C, with some grades tolerating short-term exposure to 120°C. Higher usage temperatures can be achieved by increasing hard segment content or selecting specific chain extenders or diisocyanates. Decomposition typically begins slowly at 150–200°C, accelerating at 200–250°C. Polyester-based TPUs generally offer better thermal and oxidative stability than ether-based versions.
Hydrolysis Resistance
Due to their ester or ether urethane linkages, TPUs are susceptible to hydrolysis to some extent. Their resistance depends on chemical structure, with the order of stability being: polyether > polycaprolactone-based > polyester. Polyester-based TPUs degrade mainly through ester hydrolysis, which is catalyzed by acids; this can be mitigated using carbodiimide additives. Ether-based TPUs primarily degrade via urethane bond hydrolysis.
Environmental factors such as humidity, temperature, and pH, along with the presence of stabilizers and antioxidants, significantly influence hydrolysis resistance.