Three Stages of the Curing Process: Transformation from Liquid to Elastomer

Three Stages of the Curing Process: Transformation from Liquid to Elastomer
The curing of MS sealant is a gradual process, typically divided into three phases, with distinct changes in morphology and properties at each stage:
1. Induction Period (0.5-2 hours after application, depending on the formulation)
Reaction Characteristics: The accelerator and initiator begin to react, with the initiator slowly decomposing to produce a small amount of free radicals, but no distinct polymer chains have yet formed;
Appearance and Performance: The colloid remains liquid or semi-liquid, exhibiting a certain degree of fluidity and unable to withstand external forces (e.g., deformation upon pressure);
Core Function: This is the free radical “accumulation” phase, preparing for subsequent rapid polymerization. 2. Rapid Polymerization Phase (1-6 hours after the induction phase)
Reaction Characteristics: The free radical concentration reaches a critical value, triggering a chain polymerization reaction—a large number of monomer double bonds break, combining with the prepolymer to form linear polymers. Crosslinkers (such as monomers with multiple double bonds) then form a preliminary network structure.
Appearance and Performance: The colloid gradually loses fluidity, the surface begins to solidify (not sticky to the touch), while the interior remains semi-cured, with initial elasticity emerging.
Note: This stage is accompanied by a slight exotherm (polymerization heat), but because the monomer content is controllable, the exotherm temperature is typically < 40°C, posing no safety risks. 3. Full Curing Period (24-72 hours, subject to significant environmental impact)
Reaction Characteristics: Linear polymers further crosslink to form a dense three-dimensional network structure. Small amounts of unreacted monomer continue to polymerize until the reaction reaches equilibrium.
Appearance and Performance: The colloid fully cures into an elastomer with a smooth, non-sticky surface. It exhibits the designed tensile strength (typically 0.5-2 MPa), elongation at break (200%-500%), and weather resistance.
Key Performance Indicators: After full curing, the colloid maintains a relatively stable volume with no noticeable shrinkage, and can withstand long-term environmental stresses such as vibration and temperature fluctuations.