LESSON 79: common causes of early polymerization.

Early polymerization during polyurethane (PU) foam production happens when the gelling or curing reaction becomes too fast compared to foam expansion. This is commonly caused by excessive tin catalyst, overly active amine catalysts, high isocyanate index, low water level, high chemical or ambient temperature, and poor formulation balance. Strong silicone stabilization or highly reactive raw materials can also accelerate polymer formation too quickly. In practice, early polymerization causes restricted foam rise, high density, tight or closed cells, poor flow, internal stress, scorching, and surface cracking because the foam structure hardens before full gas expansion is completed.