Polyurethane products can be roughly divided into foams, elastomers, and polyurethane resins. Below, WHAMINE will analyze the selection of polyurethane catalysts for these three types of products.
Foamed polyurethane catalyst products are mainly synthesized from polyethers, isocyanates, foaming agents, catalysts, etc. The main process of foam formation is generally considered as follows:
(1) Foam is generated in the polyurethane reaction system by physical and chemical methods, and the foam is uniformly dispersed in the reaction system. The main foaming method is to use water and isocyanate to produce carbon dioxide for foaming.
(2) The foam generation process requires the viscosity of the reaction system to increase accordingly so as to stabilize the foam from escaping.
(3) When the foam formation reaches the required number and size, the viscosity of the reaction system needs to continue to increase or even form a cross-linking system to stabilize the foam and shape it into a product.
In this case, we need at least two catalysts to adjust the progress of the reaction. One catalyst is to promote the reaction between isocyanate and water, that is, to promote the foaming reaction. Usually, an amine catalyst is selected; To promote the reaction of isocyanate and polyether or alcohol, that is, the reaction of polyurethane molecular chain growth and cross-linking, metal catalysts are generally used.
Therefore, in the synthesis process of polyurethane catalyst, we generally use amine catalysts and organometallic catalysts to produce synergistic effects to achieve the best results. The specific types and ratios of amine catalysts and organometallic catalysts need to be adjusted and selected according to different products through experiments or experience.
The reaction of elastomer polyurethane catalysts to isocyanate (NCO) and water should be strictly avoided, so metal catalysts are generally used at this time, such as organic tin, organic bismuth, and even eliminated organic mercury.
In the synthesis process of resin polyurethane catalyst, the reaction of NCO and water should be avoided as much as possible, so organic bismuth and organic tin are generally used.