Key Factors Affecting Curing Speed-MS
Key Factors Affecting Curing Speed
The curing speed of MS sealants is not fixed but is controlled by the following four key factors. These conditions can be adjusted to optimize curing efficiency in practice:
Temperature:
Temperature is the key factor affecting the rate of free radical generation. As the temperature increases (e.g., from 25°C to 40°C), the initiator decomposition rate accelerates, shortening the curing time by 30%-50%.
Low temperatures (<5°C) significantly slow curing. In these conditions, slow initiator decomposition leads to insufficient free radical concentration, potentially resulting in only surface cure within 24 hours, with full cure requiring more than 7 days. Therefore, for low-temperature environments, it is recommended to use a “low-temperature, fast-curing” MS sealant.
Humidity:
MS sealants do not rely on moisture for curing (unlike silicone and polyurethane sealants), so humidity has little effect on curing speed.
However, high humidity (>85%) may cause moisture to adsorb onto the surface of the sealant, slightly affecting the surface drying time (extending 1-2 hours) without affecting the internal cure quality. Adhesive Thickness:
The thicker the adhesive layer, the slower the heat dissipation from the interior. Slight heat release can accelerate internal curing. However, excessive thickness (>10mm) may cause the surface to cure first, hindering internal monomer volatilization and prolonging the full cure time.
Recommended adhesive layer thickness: 1-5mm (balancing cure speed and sealing performance).
Formulation Design:
Initiator/Accelerator Ratio: A higher ratio (e.g., increasing the initiator content from 1% to 2%) results in faster cure. However, a higher ratio may cause “implosion” (rapid curing but brittle curing).
Prepolymer Molecular Weight: Low molecular weight prepolymers (better flowability) cure faster than high molecular weight prepolymers (higher viscosity). Therefore, “fast-drying” MS adhesives often use low molecular weight prepolymers.