How do ambient temperature and humidity affect the curing time of MS sealant?

How do ambient temperature and humidity affect the curing time of MS sealant?
Ambient temperature and humidity are important external factors affecting the curing time of MS sealant. Their mechanisms of action and degree of influence on the curing process differ significantly, as follows:
1. Ambient temperature: The decisive influence on curing time
Temperature directly regulates the curing speed of MS sealant by changing the rate of molecular movement and chemical reactivity, making it the most significant factor.

High temperature accelerates curing
MS sealant curing relies on a polymerization reaction initiated by free radicals. Increased temperature significantly accelerates the decomposition rate of the initiator, promoting the rapid generation of free radicals and thus accelerating the cross-linking of the molecular chains.
For example, an MS sealant that fully cures in 48 hours at 25°C (room temperature) can be cured in 24-30 hours at 35-40°C. If the temperature is raised to 50°C (within a short-term controllable range), the surface curing time can be reduced from 1-2 hours to less than 30 minutes, and the full cure time can be further compressed to 12-18 hours. Principle: For every 10°C increase in temperature, the chemical reaction rate typically increases by 1-2 times (Arrhenius’s law), accelerating the crosslinking reaction of the active ingredients within the colloid.

Low temperatures delay curing.

When temperatures fall below 15°C, the decomposition of the initiator slows, resulting in insufficient free radical generation and a significant slowdown in the curing process.

For example, at 10°C, a surface cure time of 24 hours may take 36-48 hours, and the full cure time may extend from 48 hours to over 72 hours.

If the temperature falls below 5°C, the curing reaction of some formulations may nearly stall, leaving the surface sticky for extended periods and requiring 1-2 weeks for full cure. Extremely low temperatures (below 0°C) may terminate the cure, preventing the colloid from developing effective strength and losing its sealing properties. 2. Ambient Humidity: A Minor and Indirect Effect on Curing Time
Unlike silicone sealants (which rely on moisture absorption for curing) and polyurethane sealants (which are sensitive to humidity), MS sealants cure through free radical polymerization and do not rely on moisture. Therefore, humidity has a minimal effect on curing time, primarily manifesting as indirect effects:

Normal Humidity (30%-70%): Essentially No Effect
In normal humidity environments, moisture neither participates in the curing reaction nor significantly interferes with free radical activity. Curing times are generally consistent with those in dry environments (with deviations typically within 1-2 hours and are negligible).

High Humidity (>80%): Slightly Delays Surface Curing
When ambient humidity is extremely high (such as on rainy days or in humid workshops), a thin film of water vapor may adsorb onto the adhesive surface. This film can slightly hinder oxygen diffusion (oxygen has a slight inhibitory effect on surface free radicals, but this effect is far less pronounced than temperature), or delay the evaporation of surface solvents (if the formulation contains a small amount of volatile ingredients), resulting in a 10%-20% increase in surface curing time (for example, from 1 hour to 1.2 hours). Note: This effect only affects the surface and has little effect on the internal curing of the adhesive layer. The deviation in full cure time typically does not exceed 5%.
Low humidity (<30%): No significant effect
In a dry environment, a water film is less likely to form on the adhesive surface, allowing for more oxygen exposure. However, since MS adhesive cures independently of moisture, low humidity does not accelerate the cure time, leaving the overall cure time essentially the same as in normal temperature and humidity environments.
Summary: Temperature is the key variable; the effect of humidity can be ignored.
Temperature: The core factor in controlling the cure time of MS sealant. High temperatures significantly accelerate the cure time, while low temperatures significantly delay it. In actual application, the ambient temperature should be controlled between 15-35°C (the optimal curing range) to ensure efficiency and quality.
Humidity: Extremely high humidity only slightly delays surface cure and has minimal impact on the overall full cure time, so it does not need to be a primary control factor.

Therefore, in practical applications, controlling the temperature is the primary method for adjusting the cure time. The only requirement is to avoid prolonged application in extreme humidity environments exceeding 90%.