How does the molecular structure of thermoplastic elastomer evolve during repeated melt-reprocessing, affecting its final performance stability?
Publish Time: 2026-06-29
With the increasing emphasis on the circular economy and sustainable material utilization, thermoplastic elastomer (TPE) is widely used in automotive, electronics, consumer goods, and medical fields due to its reusable melt-reprocessing properties. However, during repeated melt-reprocessing, its molecular structure is not completely stable but undergoes a certain degree of evolution. This change directly affects the material's mechanical properties, appearance, and long-term stability.1. Molecular Chain Breaking and Decrease in Relative Molecular MassUnder repeated heating and shearing, the polymer chains in thermoplastic elastomer may break, leading to a gradual decrease in the average relative molecular mass. As the molecular chains shorten, the tensile strength and resilience of the material often decrease, and tear resistance may also weaken. This chain breakage phenomenon is more pronounced under high-temperature or high-shear processing conditions, thus affecting the structural stability of the final product.2. Microscopic Rearrangement of Hard and Soft Phase StructuresThermoplastic elastomers typically consist of a microphase-separated structure of hard and soft segments to achieve a balance between elasticity and processability. During repeated melting, this microphase structure may rearrange or be locally disrupted, leading to an uneven distribution of the original phases. Hard segment crystalline regions may undergo reorganization or size changes, while soft segment fluidity may increase, resulting in fluctuations in overall material hardness and affecting the consistency of feel and rebound stability.3. Performance Degradation Caused by Thermo-Oxidative AgingDuring repeated processing, if the antioxidant system is insufficient, high-temperature oxidation reactions may continue, generating free radicals and triggering further chain degradation. This not only accelerates molecular chain breakage but may also cause the material to yellow, become sticky, or exhibit slight powdering. With increasing processing cycles, this cumulative effect of thermo-oxidative aging gradually amplifies, reducing the long-term stability of the material.4. Migration and Interfacial Imbalance in Additive SystemsTPE systems typically contain additives such as plasticizers, lubricants, and stabilizers. During repeated melting, these small molecule components may migrate or volatilize, leading to an imbalance in the formulation ratio. Reducing the amount of additives can affect the material's flexibility and processing flowability, while also weakening the overall stable structure of the system, leading to fluctuating performance of the final product.Overall, the molecular chain structure, microphase morphology, and additive system of thermoplastic elastomer undergo varying degrees of evolution during repeated melt-reprocessing. These changes work together to cause a gradual decline in material properties after repeated processing. Therefore, in practical applications, it is usually necessary to optimize formulation design, incorporate anti-aging systems, and control processing conditions to maintain its long-term performance stability and recyclability as much as possible.
