In the vulcanization process of silicone rubber, there are significant differences in the influence of different oxide vulcanizing agents on the vulcanization reaction and product properties, which are mainly reflected in the vulcanization activity, crosslinking efficiency, physical and mechanical properties of the product and process applicability.Starting from the typical types of oxide vulcanizing agents, combined with their mechanism of action and practical application cases, the following systematically analyzes their influence on the vulcanization of silicone rubber.


1. Organic peroxides: the core choice of mainstream vulcanization systems
Organic peroxides are the most commonly used oxide vulcanizing agents for the vulcanization of silicone rubber. Their mechanism of action is based on free radical reaction: they decompose at high temperatures to produce free radicals, capture hydrogen atoms or vinyl on the molecular chain of silicone rubber, and form macromolecular free radicals. After the coupling reaction, a crosslinking bond is formed.According to the difference in activity, organic peroxides can be divided into two categories：


Highly active type (such as benzoylbenzyl peroxide BP, 2,4-dichlorobenzoylbenzyl peroxide DCBP)：
Advantages: Low vulcanization temperature, short vulcanization time, and high production efficiency.For example, BP can be quickly vulcanized at 160℃, which is suitable for molded products.
Limitations: It is easy to cause scorching (the rubber is cross-linked in advance if it is not vulcanized), and the decomposition product contains acidic substances (such as benzoic acid), which may degrade the main chain of silicone rubber, resulting in uneven vulcanization of thick products.Although the decomposition product of DCBP is low in volatility, the tendency to scorch is more serious, and the dosage needs to be strictly controlled.
Application scenario: The continuous vulcanization of thin-walled products and pressed-out products needs to be combined with silicone oil ointment preparations to improve dispersion.
Low-activity type (such as di-tert-butyl peroxide DTBP, 2,5-dimethyl-2,5-di-tert-butyl hexane peroxide DBPMH)：
Advantages: High vulcanization temperature, good scorching safety, decomposition products are neutral substances such as ketones and aldehydes, and have no degradation effect on silicone rubber. It is suitable for thick products and carbon black rubber.For example, DBPMH is vulcanized at 170℃, which can produce model products with high compression and permanent deformation.
Limitations: The vulcanization time is long, and the two-stage vulcanization process needs to be optimized.
Application scenarios: molded thick products, products bonded to metal, and injection products.
2. Metal oxides: auxiliary selection of special rubber systems
Metal oxides (such as zinc oxide and magnesium oxide) are less used in the vulcanization of silicone rubber, but they play a key role in specific systems.：


Zinc oxide：
Function: It is used as the main vulcanizing agent in halogen-containing rubbers such as neoprene rubber and chlorosulfonated polyethylene to form a crosslinking bond by reacting with the halogen in the rubber molecule.In silicone rubber, zinc oxide is usually used as an active agent or reinforcing agent in an amount of 5-10 parts, which can improve the heat resistance and UV resistance of the product.
Limitations: Silicone rubber cannot be vulcanized independently, and needs to be used in conjunction with other vulcanizing agents.
Magnesium oxide：
Function: It is used as a secondary vulcanizing agent in neoprene rubber to prevent early vulcanization (scorching), and at the same time neutralize the hydrogen sulfide generated during the vulcanization process.In silicone rubber, magnesium oxide can improve the hardness and tensile strength of the product, but the water resistance is poor.
Application scenario: Oil-resistant and chemical-resistant silicone rubber products.
3. The differentiated influence of oxide vulcanizing agent on product performance
Physical and mechanical properties：
High-activity peroxide vulcanized products have high tensile strength, but their tear resistance decreases; low-activity peroxide vulcanized products have small compression permanent deformation and balanced physical and mechanical properties.
Metal oxides can improve the hardness and heat resistance of products, but the amount needs to be controlled to avoid increased brittleness.
Process adaptability：
High-activity peroxides are preferred for thin-walled products, and low-activity peroxides or segmented vulcanization processes are required for thick products.
Carbon black-containing rubber should avoid the use of aromatic acyl peroxides (such as BP) to prevent carbon black from interfering with the vulcanization reaction.
Environmental protection and safety：
Peroxide vulcanizing agents may produce volatile decomposition products (such as benzene and carbon dioxide), and ventilation conditions need to be optimized; metal oxides are non-volatile, but magnesium oxide is easy to absorb moisture and agglomeration, and it needs to be sealed and stored.
4. Future development trends
With the expansion of the application field of silicone rubber, oxide vulcanizing agents are developing in the direction of high efficiency, safety and environmental protection.：


Compound vulcanizing agent: By combining high-activity and low-activity peroxides, the vulcanization efficiency and scorching safety are taken into account.
Nano-oxides: Nano-zinc oxide and magnesium oxide are used to enhance vulcanization activity, reduce dosage and improve dispersion.
Green alternative: Develop peroxides without acidic decomposition products to reduce the degradation of the main chain of silicone rubber.