What is tertiary amine catalyst
For the preparation of polyurethane foam, there are generally three reactions: isocyanate hydroxyl reaction, isocyanate water reaction, isocyanate isocyanate reaction. Therefore, catalysts of different types and functions are needed to meet different needs.
Polyurethane catalyst is generally divided into tertiary amine catalyst and metal catalyst. Tertiary amine catalyst is widely used in the manufacture of polyurethane foam. According to the structure, it can be divided into aliphatic tertiary amines, such as bis (dimethylaminoether) BDMAEE, aromatic/alicyclic tertiary amines, such as n-methylmorpholine NEM and heterocyclic tertiary amines, such as triethylenediamine TEDA.
Tertiary amine catalyst has reaction selectivity: it promotes the reaction between isocyanate and water, and is usually considered as foaming catalyst; Tertiary amine can promote the reaction between isocyanate and polyol, and is usually considered as gel catalyst. However, most foaming tertiary amine catalysts also contribute to gel reaction, and gel tertiary amine catalysts also contribute to foaming reaction.
In the polyurethane foam system, various amine combinations are used to balance the gel and foaming reaction, so that the foaming process can be properly controlled. One or more types of tertiary amine catalysts can be selected to meet the process requirements through dosage, such as milking time, rising curve, gel time and even skin ripening.
Standard tertiary amine catalyst
Gel catalyst: TEDA
In the two-step process (prepolymer process) for the early production of flexible polyurethane foam, it was difficult to control the process because the end isocyanate polyurethane prepolymer was prepared first, and then reacted with water for foaming. Since the invention of DABCO 1,4-diazobicyclo [2,2,2] octane (also known as triethylenediamine TEDA), it has been used as a unique catalyst to cooperate with silicone surfactant and replace the prepolymer process in one step. The appearance of these raw materials makes the polyurethane foam industry develop rapidly.
TEDA has accelerated the reaction of secondary OH group and NCO group, accelerated the chain growth and carbon dioxide release under the appropriate balance of the reaction, eliminated time-consuming prepolymer preparation, and entered the one-step method era.
Due to the high initial cost of TEDA, other catalyst combinations, such as amine tin composite catalyst, have been developed. However, due to technical progress and localization, TEDA has become the standard product of polyurethane industry standard gel catalyst.
Foaming catalyst: bis (dimethylaminoethyl) ether BDMAEE
Bis (dimethylaminoether) ether BDMAEE is commonly used as a foaming catalyst for high resilience and soft molding formulations. Because of its highly alkaline chemical structure, it can complexe with water, strongly promote the reaction of isocyanate with water, generate a large amount of carbon dioxide gas, and reduce the density of foam.
Bis (dimethylaminoethyl) ether BDMAEE has high foaming catalytic activity, which can prolong the pre reaction time of polyurethane foaming and improve the fluidity. The control effect of bis (dimethylamino ether) BDMAEE on gas production reaction (foaming reaction) accounts for about 80%, and on gel reaction (gel reaction) accounts for about 20%.
Most foam formulations use BDMAEE in combination with gel catalyst TEDA to balance the foaming reaction.
Low odor demand:
Some tertiary amine catalysts will leave residual odor to the foam, which is due to the evaporation of tertiary amine catalysts left in the foam structure and the release of amine odor, which may limit their use in automotive interior, bedding, upholstered furniture and other applications. Many catalyst suppliers have introduced catalysts containing isocyanate reaction groups to help molecules bind to the polymer network, but this usually reduces the catalytic efficiency of tertiary amine catalysts.
Delayed catalyst:
The need for better mold fluidity and faster curing, as well as the need to balance the reactivity of foam in the dual hardness foaming process, led to the development of delayed action catalysts.
Tertiary amine catalyst is widely used to prepare polyurethane foam, and its catalytic activity depends on its structure and alkalinity.
The selection of tertiary amine will affect the performance of foam, such as physical parameters, resilience, opening and closing of pores, surface curing, etc. If the foaming catalyst is too strong/the amount of foaming catalyst is too high, the foam will burst. If the gel catalyst is too strong/the amount of gel catalyst is too high, the closed cell foam will be caused, which will lead to the shrinkage of foam. Only when the gel and foaming reaction reach a good balance, can a foam with open pores and good performance be formed.
