II. Synthesis Principles of Sponge
During the synthesis process of sponge, there are mainly chain growth reactions, foaming, and cross-linking processes, which are related to the molecular structure, functionality, and molecular weight of the raw materials.
2.1 Chain Extension Reaction
The chain extension reaction between isocyanate and di-functional polyether polyol occurs. Due to the excess of isocyanate by about 5%, the final product of the chain extension is isocyanate groups. This repeated process promotes the rapid growth of the chain.
2.2 Foaming Reaction Accompanied by Chain Growth
During the production of sponge, the foaming gas mainly comes from the reaction of TDI with water, which generates a large amount of CO2 gas. At the same time, the newly generated amine reacts with isocyanate to form urea bond compounds. This repeated process is accompanied by chain growth.
2.3 Crosslinking Reaction
The crosslinking reaction is crucial for the preparation of the sponge. If it occurs too early or too late, it will lead to a decline in the quality of the sponge or even its destruction.
2.3.1 Crosslinking of Polyfunctional Compounds
The reaction between polyether polyols and isocyanates directly affects the density of the sponge. The molecular weight of the crosslinking points is 2000-20000. The smaller the molecular weight, the greater the crosslinking density, and the higher the hardness of the foam, while the softness and elasticity will decrease relatively.
2.3.2 Diurea Crosslinking
Water reacts with isocyanates to form urea bond compounds, which further react with isocyanates to form three-dimensional structure diurea crosslinking compounds.
2.3.3 Ureaformate Crosslinking
The hydrogen on the nitrogen atom in the aminoformate group reacts with isocyanates to form a three-dimensional crosslinking structure of ureaformate.
III. Production Process and Flow
At present, the majority of sponge production adopts the one-step box-type foaming method. Various raw materials are rapidly added to the forming box under high-speed stirring, and the chain growth, foaming, cross-linking, and curing reactions are completed in the forming box, thereby completing the sponge production. The advantages of this process are a short process flow, low material viscosity, easy control, energy saving, small equipment investment, and wide applicability in density range.
3.1 Process
It is divided into two components: Component A, polyether polyol, water, amine catalyst, silicone oil, is mixed for 20 seconds under high-speed stirring. Component B, TDI, flame retardant, organic tin, is stirred for 10 seconds. Component A and Component B are mixed and stirred at high speed for 10 seconds, then quickly poured into the forming box. The mold holding time is 6-8 seconds, and the foaming time is about 1 minute. After aging for 2 hours, it can be cut into the required size after 24 hours. Sponge production technology process