As the catalyst concentration of polyurethane rigid foam increases, the tensile strength, shear strength and compressive strength of the foam increase, while the curing time decreases. However, there is an upper limit to the catalyst concentration. Beyond this upper limit, the foam will crack. Increasing catalyst concentration usually results in a decrease in the K factor. This phenomenon can be explained by the fact that only a small amount of fluorocarbon blowing agent leaks through the foam cell wall, so the fluorocarbon blowing agent is well retained, thereby reducing the K factor value. Increasing catalyst concentration results in a tighter cross-linked structure of the polymer, thereby reducing the diffusion constant and the solubility of the fluorocarbon blowing agent.
In the prepolymer system, the main reaction is the formation of gas, so the catalyst must be able to control the formation of CO2 well. As the amount of catalyst increases, the compressive strength of foam materials generally decreases, while the compression deformation increases. Supporting properties are also affected by the amount and relative proportions of catalysts. In general, increasing the amount of catalyst will result in softer foam materials.
For CO2 foam, tertiary amine is sufficient as the only catalyst. However, for solvent-blown foams, a more active catalyst is required due to the cooling effect of the solvent. There is a synergistic effect between tin catalysts and tertiary amines. For rigid foams of one-time molding systems and polyether or polyester prepolymer systems, due to their large degree of cross-linking and rapid gel reaction, only tertiary amine catalysts are sufficient. The structure of the tertiary amine has a considerable impact on its own catalytic effect and also on the practicality of foam production. The catalytic activity of the catalyst increases as the basicity of the amine increases and as the steric hindrance of the amino nitrogen decreases.
For polyester-type one-shot molding systems or polyether-type prepolymer systems with relatively high initial viscosity, tertiary amine catalysts can provide good foaming performance. Due to the influence of the catalyst on the foaming rate, the selection of the catalyst system and concentration will greatly affect the density and processing of the foam.
The choice of catalyst in flexible foam formulations is determined by the type of polyol used. For some polyether systems with low viscosity and low activity, a very effective polymerization catalyst must be used. For such a system, the best catalyst is a tin dicarboxylate salt (such as stannous octoate). If the tertiary amine catalyst is used alone, the process of one-step polyether system foam materials is difficult to control. Therefore, tertiary amines are often used in combination with tin compounds. Generally speaking, polyester-based systems work best with catalysts with low activity. Tertiary amines, such as methyl, ethyl, cocomorpholine, and dialkyl amines, can be used alone.
Shanghai New Material Technology Co., Ltd. focuses on the R&D and production of polyurethane catalysts and polyurethane rigid foam catalysts. Everyone is welcome to pay attention. If you want to know more about catalysts, please call 4000808689.
