1. Formation and characteristics of phase separation structure
Thermoplastic polyurethanes (TPU) is a block copolymer composed of soft segments and hard segments. At the microscopic level, phase separation occurs due to the thermodynamic incompatibility between the soft and hard segments. The soft segment is usually composed of long-chain polyester or polyether, which has good flexibility and elasticity; the hard segment is generated by the reaction of isocyanate and small molecule chain extender, which has high rigidity. This phase separation structure forms micro-regions of soft phase and hard phase inside TPU. The soft phase provides elasticity and flexibility, while the hard phase plays a role of reinforcement and physical cross-linking, just like embedding rigid nodes in the elastic network to limit the excessive movement of the molecular chain.
2. Influence on elasticity and flexibility
The microscopic phase separation structure directly affects the elasticity and flexibility of TPU. The presence of the soft phase gives TPU good elastic recovery ability. When stretched by external force, the soft segment molecular chain can stretch and store elastic potential energy; when the external force is removed, the soft segment can quickly return to its original state under the restriction of the hard segment, giving TPU excellent elasticity. The higher the degree of phase separation, the better the continuity of the soft phase, and the better the elasticity and flexibility of the material. For example, in the application of sole materials, TPU with a good phase separation structure can effectively buffer the impact of the ground during walking, and quickly restore its shape after the pressure disappears, providing a comfortable wearing experience.
3. Effect on mechanical strength
The hard phase plays a key role in the mechanical strength of the microscopic phase separation structure of TPU. Physical crosslinking points are formed between the hard segments through interactions such as hydrogen bonds. These crosslinking points connect the soft segments to form an overall three-dimensional network structure. When subjected to external forces, the hard phase can effectively resist deformation, transfer stress, and prevent excessive stretching and rupture of the material. Factors such as the content and distribution of the hard phase in the phase separation structure and the chemical structure of the hard segment will affect the mechanical strength of TPU. Appropriately increasing the proportion of the hard phase or optimizing the structure of the hard segment can improve the mechanical properties of TPU such as tensile strength and tear strength, so that it can perform well in application scenarios that need to withstand large external forces, such as industrial conveyor belts and automotive interior parts.
4. Correlation with temperature resistance and stability
The microscopic phase separation structure is also related to the temperature resistance and stability of TPU. The presence of the hard phase of thermoplastic polyurethanes increases the glass transition temperature and melting point of the material, allowing TPU to maintain certain physical properties at higher temperatures. In the phase separation structure, the hard phase can limit the molecular chain movement of the soft segment at high temperatures, preventing the material from softening and deforming. At the same time, this structure also helps to improve the chemical stability of TPU, because the hard phase can act as a barrier to reduce the erosion of the soft segment by external chemicals. For example, in TPU products used outdoors, the microscopic phase separation structure can enable it to maintain good performance under different temperature environments, resist the influence of environmental factors such as ultraviolet rays and rain, and extend the service life of the product.
