How to Increase the Elasticity of Liquid Silicone Rubber (LSR)?
To enhance the elasticity of Liquid Silicone Rubber (LSR), optimization is required in formulation design, processing techniques, and post-treatment. The following are specific methods:
1. Adjust the Base Formulation
(1) Choose Silicone with Low Crosslink Density
Base Polymer: Select polydimethylsiloxane (PDMS) with lower vinyl content for more flexible molecular chains.
Crosslinking Agent Ratio: Reduce the amount of platinum catalysts (e.g., Pt-based) or peroxide crosslinkers to lower crosslink density. Excessive crosslinking can make the material harder and less elastic.
(2) Incorporate Flexible Chain Segments
Modified Silicones: Introduce long-chain alkyl groups (e.g., phenyl silicone oils) or polyether-modified silicones to increase molecular flexibility.
Blend with Elastomers: Mix with compatible elastomers like TPU or SEBS to improve elasticity (compatibility must be ensured).
2. Optimize the Filler System
(1) Use Nano-Reinforcing Fillers
Fumed Silica: Select hydrophobic fumed silica with low surface hydroxyl content (e.g., HDK® H18) to reduce hindrance to molecular mobility.
Carbon Nanotubes/Graphene: Add in trace amounts (<1%) to enhance the elastic modulus without significantly reducing rebound performance.
(2) Control Filler Loading
Excess filler (>30%) restricts chain movement. A balanced amount (recommended: 10–20%) provides reinforcement while maintaining elasticity.
3. Adjust the Curing Process
(1) Low-Temperature, Slow Curing
Cure at lower temperatures (e.g., 110–130°C) for extended times to form a more uniform crosslink network and reduce internal stress.
(2) Secondary Cure (Post-Curing)
Bake at 150–200°C for 2–4 hours to remove residual volatiles and stabilize the crosslink network, reducing permanent deformation.
4. Add Elasticity-Enhancing Additives
Plasticizers: Add silicone oils (e.g., dimethyl silicone oil) or phosphate-based plasticizers (watch for potential migration).
Dynamic Crosslinkers: Use crosslinking agents with flexible segments (e.g., long-chain alkyl silanes).
Elastic Microspheres: Incorporate hollow glass microspheres or elastic microbeads to improve compression rebound rate.
5. Optimize Structural Design
Porous Structure: Use chemical or physical foaming processes to create microcellular silicone, improving compressive elasticity.
Nonlinear Geometry: Design spring-like or wave-shaped structures to enhance macroscopic elasticity through geometry.
6. Testing and Validation
Rebound Rate: Test according to ISO 4662 or ASTM D2632.
Compression Set: Compress 50% and measure recovery after 24 hours (ASTM D395).
Dynamic Mechanical Analysis (DMA): Analyze storage modulus (G') and loss factor (tanδ).
Key Considerations
Performance Balance: Enhancing elasticity may reduce tensile strength or oil resistance-balance according to application needs.
Processing Stability: Modified LSR must maintain flowability and cure time suitable for injection molding or casting.
Biocompatibility: For medical applications, raw materials must be FDA-approved or certified to ISO 10993.
By applying these methods, the elasticity of LSR can be significantly improved-for example, rebound rate can be increased from 70% to over 90% (exact values require experimental validation).