Analysis of catalysts for polyurethane foaming
The choice of polyurethane catalyst affects the reactivity of the whole foaming system and the selectivity of some individual reactions described above. The reactivity of the foaming system is expressed by the activation time, curing process, demoulding or curing time of the system。
The change of selectivity, as a function of catalyst selection and change, affects the balance of reaction, the type and order of polymer chain formed and the fluidity of foaming system, thereby affecting the final foam processing and physical properties.
he most commonly used catalysts for urethane foaming are tertiary amine, quaternary amine, amine salt and metal nucleic acid salt (usually Sn Ⅱ, sniv or K +). Tertiary amines are used to promote gelation. Foaming and crosslinking reaction. Limb salts and heat sensitive amines, such as diazodicycloundecanone, are used to provide delayed action. Metal acid salts strongly affect the gelation reaction.
Stannous compound (SN Ⅱ) has low cost, but is easy to hydrolyze and unstable. Its typical use is for occasions where separate logistics can be measured, such as soft blocks.
Tin compounds (SN Ⅳ) are not easy to hydrolyze and can be incorporated into systems, such as soft molding and hard foaming. For example, specific compounds such as quaternary amine, potassium nucleic acid, tris (Dimethylaminomethyl) phenol and 2,4,6-tris [3 - (dimethylamino) n-propyl] hexahydrohomotriad have strong selectivity for trimerization.
Polyurethane foam is characterized by a variety of polymer structures that can meet the needs of a wide range of applications. This structural difference is not only caused by the different isocyanates and polyols used as raw materials, but also related to the different reactions of these raw materials. These reactions are deeply affected by the type and amount of polyurethane catalyst used.
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