The resilience of silicone is closely related to multiple factors, which together determine the ability of silicone to restore its original shape after being stressed. The following are the main influencing factors and their mechanisms of action:
1. Molecular structure and crosslinking density of silicone
Crosslinking density: Silicone is a three-dimensional network structure formed by siloxane chains through crosslinking agents. The higher the crosslinking density (that is, the more crosslinking points), the stronger the constraints between molecular chains, and the higher the resilience is usually. However, excessive crosslinking may cause the material to become brittle, which in turn reduces the resilience performance.
Molecular chain length: Silicone with long molecular chains (such as high molecular weight silicone) can absorb energy through chain segment sliding when subjected to force, and the rebound process is smoother; silicone with short molecular chains rebounds faster but may be accompanied by energy loss.
2. Vulcanization system and process
Vulcanizing agent type: Different vulcanizing agents (such as peroxides, platinum catalysts) will affect the crosslinking structure and efficiency. For example, platinum vulcanization systems usually form a more uniform crosslinking network and improve resilience.
Vulcanization temperature and time: Insufficient vulcanization will lead to low crosslinking density and poor resilience; excessive vulcanization may cause molecular chain breakage and reduce resilience. The degree of crosslinking needs to be balanced through process optimization.
3. Fillers and additives
Reinforcing fillers: such as fumed silica and precipitated silica, can enhance the mechanical properties of silicone, but excessive addition may increase rigidity and reduce resilience. The amount and dispersibility of fillers need to be controlled.
Plasticizers: Adding plasticizers can reduce the hardness of silicone, but may weaken the intermolecular forces, resulting in reduced resilience. Flexibility and resilience need to be weighed according to the application scenario.
Other additives: such as antioxidants, flame retardants, etc., may indirectly affect resilience by affecting molecular structure or crosslinking density.
4. Hardness and formula design of silicone
Hardness range: Silicone with lower hardness (such as Shore A 20-40) usually has better resilience because the molecular chain has more room for activity; too high hardness (such as Shore A 70 or above) may have limited rebound due to excessive crosslinking density.
Formula balance: By adjusting the proportion of silicone oil, filler, vulcanizer, etc., the balance between resilience and hardness, tensile strength and other properties can be optimized.
5. Use environment and conditions
Temperature: At low temperatures, the movement of silicone molecular chains is hindered, and the resilience is reduced; high temperatures may cause the cross-linked structure to be destroyed, and the resilience performance will decrease after long-term use.
Stress frequency and amplitude: Under high frequency or high stress, the resilience of silicone may decrease due to excessive energy dissipation; long-term fatigue loading may also cause permanent deformation.
Medium contact: Contact with oil, acid, alkali and other media may cause swelling or degradation, affecting the resilience. Chemically resistant silicone should be selected according to the type of medium.
6. Processing technology and post-treatment
Mixing uniformity: Uneven dispersion of fillers or additives will lead to local performance differences and affect the overall resilience.
Demolding and post-vulcanization: Residual release agent or insufficient post-vulcanization may cause internal stress and reduce the resilience performance.
7. Silicone type and use
General silicone: moderate resilience, suitable for sealing, shock absorption and other scenarios.
High resilience silicone: Through special formula design (such as low cross-linking density, high molecular weight silicone oil), the resilience can reach 60%-80%, suitable for sports equipment, automotive parts, etc.
Fumed silicone: Due to the high fineness of the filler, excellent resilience and transparency, it is often used in medical and food contact fields.
Optimization suggestions
Improve resilience: Choose a low hardness formula, optimize the vulcanization process, reduce the amount of filler or use a highly active vulcanizer.
Balanced performance: According to the application scenario (such as high resilience and high temperature resistance at the same time), the formula and process parameters need to be adjusted through experiments.
Environmental adaptability: For specific use environments (such as low temperature or chemical media), choose weather-resistant or chemical-resistant silicone materials.