To make silicone more resilient, comprehensive optimization is required from multiple aspects such as material formulation, processing technology, structural design and post-processing. The following are specific measures and principle analysis:
1. Material formulation optimization
Adjust the cross-linking density
Reduce the amount of cross-linking agent: Appropriately reducing the amount of vulcanizer (such as peroxide, platinum catalyst) added can reduce the cross-linking density, so that more activity space is retained between molecular chains, thereby improving resilience. However, it is necessary to avoid insufficient cross-linking that causes the material to become sticky or the strength to decrease.
Choose a highly active vulcanizer: such as a platinum vulcanization system, which can form a more uniform cross-linking network, reduce local stress concentration, and improve resilience.
Optimize the filler system
Reduce reinforcing fillers: Although fillers such as white carbon black can enhance mechanical properties, excessive addition will increase rigidity and reduce resilience. It is recommended to control the amount of filler according to the hardness requirements (such as the amount of fumed white carbon black added ≤30phr).
Use spherical fillers: Spherical fillers (such as nano-silica) have less hindrance to the movement of molecular chains than needle-shaped or flake fillers, which helps to maintain resilience.
Adding elastomer modifiers: For example, blending silicone rubber with ethylene-acrylate rubber can introduce flexible segments to improve resilience.
Select low-viscosity silicone oil
Using low molecular weight, low-viscosity silicone oil as the base polymer can reduce the friction between molecular chains, making it easier for the material to recover after being stressed.
2. Processing control
Vulcanization process optimization
Control the vulcanization temperature and time: Insufficient vulcanization will lead to low crosslinking density and poor resilience; excessive vulcanization may cause molecular chain breakage. The optimal vulcanization conditions need to be determined experimentally (such as platinum vulcanization systems are usually vulcanized at 120-150°C for 10-20 minutes).
Using two-stage vulcanization: one stage vulcanization (high temperature rapid prototyping) followed by two-stage vulcanization (low temperature long-term treatment) can eliminate internal stress and improve resilience.
Mixing uniformity
Ensure that fillers, vulcanizers and other additives are evenly dispersed in the silicone to avoid local performance differences. Internal mixer or open mixer can be used for multiple mixing, and the mixing temperature should be controlled (to avoid excessive temperature causing volatilization of silicone oil or premature reaction of cross-linking agent).
Demolding and post-processing
Use high-efficiency demoulding agent to reduce demoulding resistance and avoid internal stress accumulation of materials.
Heat treatment of vulcanized silicone (such as baking at 150℃ for 2 hours) can further release internal stress and improve resilience.
III. Structural design improvement
Optimize product shape
Avoid sharp corners or thin-walled structures to reduce stress concentration points. For example, changing right angles to rounded corners can reduce local deformation when subjected to force and improve rebound uniformity.
Design hollow structures or honeycomb structures to reduce rigidity by reducing material usage while maintaining overall rebound resilience.
Add buffer layer
Adding a flexible buffer layer (such as foam, spring) on the surface or inside of silicone products can absorb part of the impact energy, reduce the deformation of the silicone body, and thus indirectly improve the rebound force.
IV. Post-processing and surface modification
Surface coating
Applying silicone oil or fluorine coating can reduce the surface friction coefficient, reduce energy loss when subjected to force, and improve rebound efficiency.
Physical modification
By forming a dense layer on the surface of silicone through irradiation cross-linking (such as electron beam irradiation), the surface resilience can be improved while maintaining internal flexibility.
5. Application scenario adaptation
Temperature control
Avoid using silicone in low temperature environments (such as below -40°C), because low temperature will hinder the movement of molecular chains and significantly reduce the resilience. If low temperature applications are required, cold-resistant silicone (such as phenyl silicone rubber) can be selected.
Medium isolation
If silicone needs to contact oil, acid, alkali and other media, chemically resistant silicone (such as fluorosilicone rubber) must be selected, or the medium must be isolated through surface coating to prevent loss of resilience due to swelling or degradation.
6. Experimental verification and iteration
Resilience test
Use a rebound tester (such as Shaw's rebound tester) or a falling ball rebound tester to quantitatively test the rebound rate of silicone (the ratio of rebound height to falling height).
Compare the rebound rates under different formulas or processes to select the best solution.
Long-term performance evaluation
Evaluate the attenuation of the resilience of silicone through fatigue tests (such as repeated compression 100,000 times) to ensure that the material maintains stable performance in long-term use.
Example formula and process
High resilience silicone formula:
Base polymer: 100phr low viscosity dimethyl silicone oil (molecular weight 50,000-100,000)
Filler: 20phr fumed silica (surface treated with silane coupling agent)
Vulcanizer: 0.5phr platinum catalyst (including inhibitor)
Auxiliary agent: 1phr hydroxy silicone oil (to adjust fluidity)
Processing technology:
Mixing: Mixing in an internal mixer at 120℃ for 10 minutes, and thinning in an open mixer 3 times.
Vulcanization: 150℃ molded vulcanization for 15 minutes, and second-stage vulcanization baking at 180℃ for 4 hours.
Post-treatment: Apply fluorine coating on the surface to reduce the friction coefficient.
Through the above measures, the rebound rate of silicone can be increased to 60%-80% (ordinary silicone is usually 40%-60%), which is suitable for scenarios with high requirements for rebound resilience, such as sports equipment, automobile shock absorption, and medical catheters.