Understanding the principles of foam reactions is critically important. To master foaming, we must strive to establish a foam reaction model in our minds using the following four reaction equations. Familiarity with these variations will help us develop a comprehensive understanding of the foam reaction process, enhancing our polyurethane soft foam knowledge and foaming skills. Whether actively studying foam reaction principles or passively exploring them during foaming, this understanding is essential for deepening our knowledge of formulations and improving our skills.
Reaction 1
TDI + Polyether → Urethane
Reaction 2
TDI + Urethane → Urethane Carbamate
Reaction 3
TDI + Water → Urea + Carbon Dioxide
Reaction 4
TDI + Urea → Biuret (Polyurea)
01: Reactions 1 and 2 are chain-growth reactions, forming the main chain of the foam. Before the foam reaches two-thirds of its maximum height, the main chain rapidly elongates, with chain-growth reactions predominating inside the foam. At this stage, due to relatively low internal temperatures, reactions 3 and 4 are not prominent.
02: Reactions 3 and 4 are cross-linking reactions, forming the branches of the foam. Once the foam reaches two-thirds of its maximum height, the internal temperature rises, and reactions 3 and 4 intensify rapidly. During this stage, reactions 1 to 4 are vigorous, marking a critical period for the formation of foam properties. Reactions 3 and 4 provide stability and support to the foam system. Reaction 1 contributes to foam elasticity, while reactions 3 and 4 contribute to foam tensile strength and hardness.
03: Gas-producing reactions are termed foaming reactions. The generation of carbon dioxide is a foaming reaction and the primary exothermic reaction in polyurethane foam. In reaction systems containing methane, the vaporization of methane constitutes a foaming reaction and an endothermic process.
04: Reactions leading to the formation of foam constituents are known as gelation reactions, encompassing all reactions except for gas-producing reactions. This includes the formation of urethane, urea, urethane carbamate, and biuret (polyurea) from reactions 1 to 4.
