Using Methyl Silicone Oil for Release Agents? Beware of Carbonization at High Temperature-Iota

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News > Dynamic industry > Using Methyl Silicone Oil for Release Agents? Beware of Carbonization at High Temperature

Using Methyl Silicone Oil for Release Agents? Beware of Carbonization at High Temperature

“The mold surface turned black, and the parts started sticking!”
An industrial rubber manufacturer encountered severe demolding failure while producing vulcanized products above 180°C. After investigation, the root cause was traced to the release agent base oil: standard methyl silicone oil lacked sufficient thermal stability. Under high temperature, it oxidized, degraded, and even carbonized — forming stubborn residues instead of a clean release layer.

This is not an isolated case.

In high-temperature compression molding applications such as automotive seals, railway vibration pads, and industrial rubber rollers, many users still formulate release agents with low-cost methyl silicone oil, overlooking its thermal decomposition threshold — typically around 200°C.

When mold temperatures continuously exceed 180°C, the silicone molecular chains begin to break down, generating low-molecular-weight volatiles and carbonaceous residues. The result: mold contamination, surface defects on molded parts, and difficulties in secondary processing.

By contrast, phenyl-modified silicone oils or high-phenyl-content silicone resins benefit from the conjugation stability of phenyl groups. Their thermal decomposition temperature can increase to 250–300°C. Even under prolonged high heat, they maintain a dense, smooth release film — enabling truly clean, residue-free demolding.

Test comparison (simulated 200°C × 4h thermal aging):

Standard methyl silicone oil: noticeable black carbonized layer on mold surface; adhesive residue remained even after wiping.
Phenyl-modified silicone oil: transparent, intact film layer; mold surface remained smooth after release; no transfer or contamination on molded parts.

“Not every silicone oil qualifies as a ‘high-temperature release agent,’” an application engineer emphasized. “The key lies in whether the polymer backbone incorporates thermally stable groups such as phenyl or vinyl — and whether it has been validated through high-temperature film-forming tests.”

We recommend upgrading the release agent base oil under the following conditions:

Vulcanization temperature ≥ 180°C
Precision steel or mirror-finish molds
Products requiring secondary processing such as painting, printing, or bonding

As a professional silicone oil supplier, we offer a range of high-temperature release-grade silicone oils and provide thermogravimetric analysis (TGA), high-temperature film evaluation, and on-site trial support to help eliminate carbonization risks at the source.

Demolding is not just about applying a layer of oil —
Choosing the right base oil ensures every high-temperature release is clean and efficient.

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