Polyurethane | A brief analysis of the classification of polyurethane catalysts and the selection of catalysts for different polyurethane products

1. Introduction

Catalyst is a chemical substance that can change the rate of chemical reaction. Catalysts used in the polyurethane synthesis process can be roughly divided into tertiary amine catalysts, organotin compounds, non-tin organometallic compounds, and other new catalysts.

2. Characteristics of various catalysts

Amine catalysts are good catalysts for the reaction of NCO and water; organotin and organic mercury have high selectivity for the reaction of NCO and OH, and are insensitive to the reaction of water and NCO; some new catalysts such as temperature-sensitive catalysts, at different temperatures It has different catalytic efficiencies and is widely used in some two-component polyurethane products.

3. Purpose of using catalyst

Usually we use catalysts for two main purposes: 1. To make the reaction proceed in the direction we expect; 2. To adjust the reaction rate, shorten the reaction time, and improve production efficiency.

4. Principles for selecting catalysts for different polyurethane products

Polyurethane products can be roughly divided into foam, elastomer, and polyurethane resin. Below we briefly analyze the selection of catalysts used for these three types of products.

4.1 Polyurethane foam catalyst selection

Polyurethane foam products are mainly synthesized from polyether, isocyanate, foaming agent, catalyst, etc. The main process of foam formation is generally considered as follows: 1. Foam is generated in the polyurethane reaction system through physical and chemical methods, and the foam is evenly dispersed in the reaction system. The main foaming method is to use water and isocyanate to produce carbon dioxide. Bubble. 2. The foam generation process requires the viscosity of the reaction system to increase in order to stabilize the foam and prevent it 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-linked system to stabilize the foam and shape it into a product.

In this case, we need at least two catalysts to regulate the progress of the reaction. One catalyst promotes the reaction between isocyanate and water, that is, promotes the foaming reaction. Usually, an amine catalyst is selected; the other The first is to promote the reaction between isocyanate and polyether or alcohol, which is the reaction of polyurethane molecular chain growth and cross-linking. Generally, metal catalysts are used. Therefore, in the polyurethane foam synthesis process, we generally use amine catalysts and organometallic catalysts to produce synergistic effects to achieve the best results. The specific types and proportions of amine catalysts and organometallic catalysts require experimentation or experience to adjust and select based on different products, and will not be elaborated here.

4.2 Polyurethane elastomer catalyst selection

The reaction of polyurethane elastomers with NCO and water must be strictly avoided, so metal catalysts are generally used at this time, such as organic tin, organic bismuth, and even eliminated organic mercury.

4.3 Polyurethane resin catalyst selection

During the polyurethane resin synthesis process, the reaction between NCO and water must be avoided as much as possible, so organic bismuth and organic tin are generally used.

5. Follow-up

In the actual application process, literature, experience and specific experiments should be combined to select the catalyst suitable for the system