The choice of polyurethane catalyst affects the reactivity of the entire foaming system and some of the individual factors described above. Reaction selectivity. The reactivity of a foaming system is expressed by the system’s activation time, curing process, demoulding or curing time.
Changes in reaction selectivity as a function of changes in catalyst selection affect the equilibrium of the reactions that occur, the type and sequence of polymer chains formed, and foaming The fluidity of the system, and thus the processing and physical properties of the final foam.
The most commonly used catalysts for urethane foaming are tertiary amines, quaternary amines, amine salts and metal nucleic acid salts (usually SnII, SnIV or K+). Tertiary amines are used to promote gelling. Foaming and cross-linking reactions. Limb salts and heat-sensitive amines, such as diazobicycloundecane, are used to provide delayed action. Metal acid salts strongly influence the gelling reaction.
Stannous compounds (SnⅡ) are low in cost, but are easily hydrolyzed and unstable. Its typical use is where individual streams can be metered, such as soft blocks.
Tin compounds (SnIV) are not easily hydrolyzed and can be incorporated into systems such as soft molding and rigid foaming. For example, a specific class of compounds such as quaternary ammonium, potassium nucleic acid, tris(dimethylaminomethyl)phenol and 2,4,6-tris[3-(dimethylamino)n-propyl]hexahydrogenated Trimerization is highly selective.
Polyurethane foam is characterized by its variable polymer structure, which can meet a wide range of application needs. This structural difference is not only caused by the different isocyanates and polyols used as raw materials, but also related to the different reactions carried out by these raw materials. These reactions are strongly influenced by the type and amount of polyurethane catalyst used.
