Phenyl silicone, a high-performance silicone rubber material, is widely used in medical, electronics, automotive, and other fields. Secondary vulcanization, as a key post-treatment process, can significantly enhance material performance. The following provides a comprehensive analysis of the process principles, performance improvement mechanisms, process parameter optimization, and practical applications.

1. Secondary Vulcanization Process Principles
Secondary vulcanization refers to the process of heating a silicone product that has undergone primary vulcanization. Its core principle is based on the thermal crosslinking reaction of the silicone material:

Molecular Crosslinking Mechanism: After primary vulcanization, the silicone molecular chains have formed a preliminary crosslinked network, but unreacted reactive groups (such as silanol groups) remain. During secondary vulcanization (180-250°C), these groups further form Si-O-Si bonds through dehydration condensation, further completing the three-dimensional network structure.

Removal of Low-Molecular-Weight Compounds: Peroxide vulcanization systems decompose to produce low-molecular-weight compounds such as benzene and benzoic acid. Secondary vulcanization can volatilize these compounds, preventing them from affecting mechanical properties.

Increased Crosslink Density: By extending the crosslinking reaction time (typically 2-4 hours), more crosslinks are formed between the molecular chains, increasing the material's density.

II. Improved Physical Properties
Post-vulcanization significantly improves the physical properties of phenyl silicone, as shown below:
Performance Parameters Improvement Mechanism of Action
Tensile Strength 30%-50% Increased molecular crosslink density, resulting in a more complete network structure
Shore Hardness 2-5°C Increased crosslinks restrict molecular chain movement
Rebound Resilience Significantly Improved A more homogenized crosslinked network reduces energy dissipation
Temperature Resistance -40 to 230°C Phenyl structure enhances thermal stability, while the crosslinked network inhibits thermal degradation
Compression Set 20-30% Reduced The cross-linked structure enhances deformation resistance.

III. Improved Chemical Properties
Enhanced Chemical Stability: Removes residual low-molecular compounds, reducing the risk of chemical corrosion.
Improved Radiation Resistance: The phenyl structure and improved cross-linking network work together to enhance resistance to radiation degradation.
Improved Media Resistance: Increased cross-linking density reduces solvent permeability, improving oil, acid, and alkali resistance.
Long-Term Stability: Reduces performance degradation caused by thermal oxidative aging, extending service life.

IV. Influence of Key Process Parameters: The secondary vulcanization effect is significantly affected by process parameters. Optimal conditions are:
Temperature Control: 180-250°C, with a 10°C increase in temperature for each reaction. Increase the rate by 1.5-2 times.
Time setting: 2-4 hours. Too short a time will result in incomplete crosslinking, while too long a time will cause material degradation.
Pressure adjustment: 0.1-0.3 MPa, which helps reduce internal defects.
Atmosphere: Hot air flow rate of 0.5-1.5 m/s ensures uniform heating.

V. Typical Applications
Medical microseals: Post-curing improves biocompatibility and is FDA-certified.
Automotive sensor seals: Temperature resistance up to 230°C, meeting engine compartment environmental requirements.
Electronic waterproof seals: Improved hardness stability ensures long-term waterproof performance.
Aerospace components: Radiation resistance meets space environmental requirements.