Silicone (typically referring to silicone rubber) is a polymer elastic material with a silicon-oxygen (Si-O) backbone and organic groups on side chains. Its form can be diversified through formulation design and processing techniques to meet various engineering requirements. This article systematically outlines the preparation principles, performance characteristics, and application areas of major forms such as solid silicone, foamed silicone, and sponge silicone.
I. Solid Silicone Rubber
Preparation and Structure
Solid silicone is produced by mixing raw polysiloxane gum with reinforcing fillers (e.g., fumed silica), structure control agents, cross-linking agents, and additives, followed by compounding, molding, and vulcanization. Vulcanization methods include peroxide curing and addition curing (platinum-catalyzed), forming a dense three-dimensional network structure.
Performance Characteristics
- Thermal Stability: Long-term service temperature -60°C ~ 250°C, short-term resistance above 300°C.
- Chemical Inertia: Resistant to ozone, UV radiation, various chemical media, and physiologically inert for medical/food-grade standards.
- Mechanical Properties: Hardness range 10~80 Shore A, tensile strength 4~12 MPa, tear strength 10~50 kN/m.
- Electrical Insulation: Volume resistivity >10¹⁵ Ω·cm, dielectric strength 15~30 kV/mm.
- Gas Permeability: Significantly higher permeability to gases like O₂ and CO₂ compared to organic rubbers.
Typical Applications
Sealing rings, medical catheters, keyboard conductive pads, high-temperature wire insulation, baby bottle nipples.
II. Foamed Silicone Rubber
Preparation and Structure
Produced via chemical blowing agents (e.g., azodicarbonamide) decomposing to generate gas or physical foaming (supercritical CO₂ foaming), forming closed-cell/open-cell mixed structures during vulcanization. Density can be reduced to 0.25~0.60 g/cm³.
Performance Characteristics
- Density and Cushioning: Density reduced by 40%~70%, compression set <10% (50% compression, 22h).
- Thermal and Acoustic Insulation: Thermal conductivity 0.08~0.12 W/(m·K), sound absorption coefficient 0.6~0.9 (500 Hz).
- Flame Retardancy: UL94 V-0 rating, limiting oxygen index >30%.
- Compressibility: Compression rate up to 80%+, rebound time <0.5 s.
Typical Applications
Aerospace sealing gaskets, firefighting thermal barriers, electronic device shock pads, sports equipment grips.
III. Sponge Silicone Rubber
Preparation and Structure
Utilizes low-temperature vulcanization and efficient foaming processes to form highly open-cell (>90%) interconnected networks. Pore size 100~500 μm, density as low as 0.15 g/cm³.
Performance Characteristics
- Permeability: Air permeability 5~20 L/(dm²·min) (100 Pa pressure difference), moisture permeability >2000 g/(m²·24h).
- Flexibility: Stress required for 50% compression 0.01~0.05 MPa, fatigue life >10⁵ cycles.
- Liquid Absorption: Can absorb 5~10 times its weight in liquid, releasable under pressure.
- Biocompatibility: Passes cytotoxicity tests (ISO 10993-5).
Typical Applications
Wound dressing carriers, fuel cell gas diffusion layers, precision instrument shockproof packaging, filtration materials.
IV. Other Silicone Forms
1. Liquid Silicone Rubber (LSR)
- Characteristics: Viscosity 5000~10000 mPa·s, injection molding cycle <30 s, linear shrinkage 0.2%~0.3%.
- Applications: Infant products, optical lens encapsulation, microfluidic chips.
2. Silicone Gel
- Characteristics: Penetration 100~300 (0.1 mm), self-healing properties, dielectric constant 2.8~3.2.
- Applications: Electronic device potting, medical ultrasound coupling agents, pressure sensing media.
3. Thermally Conductive Silicone
- Characteristics: Thermal conductivity 1.5~6.0 W/(m·K), breakdown voltage >5 kV/mm, viscosity 500~2000 Pa·s.
- Applications: CPU thermal pads, power module interface materials, LED heat dissipation.
V. Form-Performance Comparison
| Form | Density (g/cm³) | Porosity | Compression Rebound Rate | Max. Temp. Resistance | Typical Hardness |
|---|---|---|---|---|---|
| Solid Silicone | 1.10~1.30 | <5% | 40%~60% | 250°C | 20~80 Shore A |
| Foamed Silicone | 0.25~0.60 | 40%~70% | 70%~85% | 200°C | 5~30 Asker C |
| Sponge Silicone | 0.15~0.40 | >90% | 85%~95% | 180°C | 3~15 Asker C |
| Liquid Silicone | 1.10~1.15 | 0% | 30%~50% | 200°C | 10~60 Shore A |
VI. Technological Trends
- Functional Integration: Dual-functional foams (e.g., conductive-thermal), shape-memory sponges.
- Microcellular Foaming: Supercritical fluid foaming for sub-10 μm pores, enhancing acoustic insulation/filtration efficiency.
- Biodegradability: Incorporation of degradable segments (e.g., polylactic acid) for absorbable medical devices.
- 4D Printing Applications: Utilizing silicone shape-memory effects for printable deformable structures.
Conclusion
The multi-form versatility of silicone expands its applications from structural materials to functional media. Form design essentially involves precise control of pore structure, cross-linking density, and filler distribution, tailored to core requirements such as sealing, cushioning, breathability, and thermal insulation. With demands for advanced manufacturing and green transformation, silicone form engineering will continue evolving toward ultra-performance, intelligence, and sustainability.
Post time: Feb-26-2026