In silicone product manufacturing, there is one core question you cannot avoid: Which curing system should you use?

Curing is the process of "cross-linking" linear silicone molecular chains into a three-dimensional network structure, transforming silicone from a flowing liquid into an elastic solid. Different curing systems determine the upper limit of product quality, production efficiency, and regulatory compliance.

Currently, there are three mainstream silicone curing systems in the industry: Platinum Catalysis (Addition Cure), Peroxide Cure (Free Radical Cross-linking), and Tin Catalysis (Condensation Cure). Their principles are completely different, and their application scenarios vary accordingly. Today, we will systematically compare these three systems from principle to practice.

1. Differences in Principles of the Three Major Curing Systems

1. Platinum Catalysis – Addition Reaction, No By-products
Platinum catalysis belongs to addition-cure vulcanization. The core reaction involves the C=C double bonds in vinyl silicone oil and the Si-H bonds in hydrogen silicone oil undergoing an addition reaction under the action of a platinum catalyst, directly forming Si-C cross-links.
The biggest feature of this reaction is that it produces no small-molecule by-products. The entire cross-linking process is clean, with no gas release and no volatiles like acids or alcohols.

2. Peroxide Cure – Free Radical Reaction, With Decomposition Products
Peroxide cure belongs to free radical cross-linking. Common peroxides include DCBP (Dicumyl Peroxide, often referred to as "Double 2-4" in industry) and DBPMH (2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane, often referred to as "Double 2-5"). At high temperatures, peroxides decompose to generate free radicals, which attack silicone molecular chains, creating radicals that cross-link with each other.
The problem is: Peroxide decomposition produces small-molecule by-products such as ketones, alcohols, and benzoic acid. These residues remain in the product, causing odor and potentially leading to micropores in insulation layers. Therefore, high-temperature post-curing (baking at over 200°C for 2 to 4 hours) is required to remove residues.

3. Tin Catalysis – Condensation Reaction, Requires Moisture
Tin catalysis belongs to condensation cure, mainly used for Room Temperature Vulcanization (RTV) silicone. The base polymer is hydroxyl-terminated polysiloxane, the cross-linker is silicate compounds like tetraethyl orthosilicate, and the catalyst is an organotin compound (such as Dibutyltin Dilaurate or Stannous Octoate).
The condensation reaction requires moisture (H₂O) from the air to initiate, releasing small-molecule by-products like ethanol during the process. Since it relies on moisture penetration, the deep curing of thick-walled products is very slow, and the shrinkage rate is much higher than that of addition-cure systems.

2. Comprehensive Comparison Across Seven Dimensions

1. By-products and Odor

• Platinum Cure: No by-products | Odorless
• Peroxide Cure: Ketones, alcohols, benzoic acid, etc. | Distinct "rubber smell"
• Tin Cure: Ethanol and other small molecules | Alcohol smell

Platinum curing crushes the other two in terms of "cleanliness." This is why food-grade and medical-grade silicones almost exclusively use platinum curing—residual by-products from peroxide curing cannot pass FDA or ISO 10993 biocompatibility tests.

2. Transparency and Yellowing Resistance

• Platinum Cure: Extremely high (Transmittance >95%) | Excellent, does not yellow over long-term use
• Peroxide Cure: Average | Poor, tends to yellow after high-temperature vulcanization
• Tin Cure: Medium | Medium, may darken after long-term aging

Platinum-cured products offer far superior transparency, making them ideal for products requiring high-clarity aesthetics (e.g., optical device encapsulation, transparent seals).

3. Shrinkage Rate

• Platinum Cure: ≤0.01%
• Peroxide Cure: 0.1% ~ 0.5%
• Tin Cure: 0.1% ~ 1.0%

Since the addition reaction involves no escape of small molecules, volume remains virtually unchanged, giving platinum curing the lowest shrinkage. This difference is critical for scenarios requiring high dimensional precision, such as precision mold replication and electronic potting.

4. Curing Speed and Efficiency

• Platinum Cure: Fast (seconds to minutes at 120~200°C) | No post-curing required
• Peroxide Cure: Medium (2~10 minutes) | Mandatory (baking at 200°C for 2~4 hours)
• Tin Cure: Slow (hours to days at room temperature) | No post-curing, but deep curing is extremely slow

Platinum curing eliminates the post-curing step, offering a significant efficiency advantage on continuous production lines. For example, in silicone tube extrusion, platinum curing line speeds can be 30% to 50% faster than traditional peroxide systems.

5. Mechanical Properties

• Platinum Cure: Uniform cross-linking | High Tensile Strength | High Tear Strength | Low Compression Set (Excellent)
• Peroxide Cure: Random cross-linking | Medium Tensile Strength | Medium Tear Strength | Higher Compression Set
• Tin Cure: Medium cross-linking | Medium Tensile Strength | Medium Tear Strength | Medium Compression Set

Platinum curing creates a more uniform and dense cross-linking network, with cross-link points precisely controlled by the formulation. In contrast, peroxide curing generates cross-link points randomly via free radicals, resulting in much poorer uniformity. In practical performance, platinum-cured products have a compression set 30% to 50% lower than peroxide systems, offering a higher level of long-term sealing reliability.

6. Safety and Compliance

• Platinum Cure: Easily passes FDA Food Grade | Can pass full ISO 10993 Medical Grade | Compliant with RoHS
• Peroxide Cure: Difficult (due to residual by-products) | Some indicators hard to meet | Partially non-compliant
• Tin Cure: Restricted (organotin toxicity) | Not applicable | Restricted

Residual by-products are the biggest obstacle for peroxide curing to pass food-grade and medical-grade certifications. Organotin catalysts (like Dibutyltin) are moderately toxic substances; they are being gradually replaced by lower-toxicity Octyltin in the EU and are banned in food bags and blood bags.

7. Cost

• Platinum Cure: Catalyst is expensive, but dosage is minimal (ppm level) | Medium overall cost (saves post-curing energy, high efficiency)
• Peroxide Cure: Cheap | Low overall cost (but gap narrows when adding post-curing energy consumption)
• Tin Cure: Cheap | Low overall cost (but low efficiency, slow deep curing)

Although platinum catalysts are pricey, the minimal dosage (only a few grams of platinum per ton of rubber) and the elimination of post-curing energy/time mean the overall cost gap is not as large as imagined. For high-end products (food, medical, electronics), platinum curing is almost the only choice.

3. Summary Table

4. How to Choose?

• Making food-grade, medical-grade, baby products, or electronic potting? Choose Platinum Curing. There is no alternative.
• Making general industrial seals, shock pads, without food-grade requirements? Peroxide Cure offers the best cost-performance ratio.
• Making mold replication, room-temperature potting, or scenarios where heating is inconvenient? Tin Catalysis (Condensation RTV) remains a convenient choice.