The Role of Foam Stabilizers

Oct 26, 2020

In the formulation, the main functions of surfactants are: one is to improve the emulsifying ability between the components, so that they can be more effectively mixed with each other; the other is to control the system to have proper surface tension during the foaming process to produce good Bubble network structure, therefore, can also be called foam stabilizer. Polyester and polyether flexible foam have different raw material bases and different properties. Therefore, the selection and dosage of surfactants are also different. The amount of surfactant commonly used in the formulation of polyester polyurethane flexible foam is 1.0~2.5 parts per 100 parts of polyol polymer. Its blending can effectively improve the emulsification ability between the raw material components, promote the stable growth of foam and prevent shrinkage. However, various surfactants have different effects. For example, A-3 can prevent the foam from shrinking, while A-7 and A-9 can delay the gel time of the foam surface and prevent the foam from cracking.
In recent years, in the production of polyurethane products, stabilizers have been proven to be one of the key components in foam production. They make the pores fine and uniform. When the system is in the low viscosity stage, it stabilizes the pore wall/the pores can grow to a thickness suitable for opening, creating conditions for the final opening. The type of foam is different, and the type of stabilizer used is also; at the same time, its main function is to nucleate and emulsify each component in the formula. The compatibility of the various components in the foam formulation is not good, so a stabilizer with strong emulsifying ability is needed to emulsify and mix them. The soft foam is made of water as a blowing agent, which accounts for 3% to 5% of the weight of the polyether in the formula. The reaction rate of water and isocyanate is higher than that of isocyanate and polyol, so there are a lot of solids in the initial stage of foaming. Polyurea is formed, which is a defoaming agent that can help open and blast holes. Opening and popping are the stages when soft foam foaming must occur, otherwise, closed cells will occur and the foam performance will decrease. However, the opening and popping must occur when the foaming reaction and the gel reaction are basically completed and reach equilibrium. That is, when the foam rises to the highest point and the strength of the foam can support its own weight, otherwise it will cause the foam to collapse. Therefore, another important function of the soft steam foam stabilizer is that it can dissolve the polyurea formed by the reaction in the early stage of foaming and can help open and burst holes in the late stage of foaming. According to this principle, the following aspects should be considered when choosing a soft foam stabilizer. ①The activity of the stabilizer;   ②The relationship between the operating range of the stabilizer and the range of tin dosage ③The influence of various raw materials constituting the stabilizer on the operating range. Stabilizers with high activity are generally less used in the formulation and are economically cost-effective. Nephew is that the operating range of the high-activity stabilizer is narrow, which is likely to cause foam quality problems, so special attention should be paid when choosing. Generally speaking, if the polyether has low activity, or propylene oxide polyether, a high-activity stabilizer can be used to extend the time for dissolving polyurea. If the polyether is a copolymer of propylene oxide and ethylene oxide, the polyether has a strong ability to dissolve polyurea due to the presence of ethoxy groups, so it is appropriate to use a stabilizer of medium activity. In some special high-density foams, such as 40-50kg/cm3, low-activity stabilizers are required. The situation of hard foam is different from that of soft foam. It has a higher degree of cross-linking and the bubbles are easy to stabilize. Rigid foam is mostly used for molded products or foaming in a restricted cavity, so the fluidity of the material is an extremely important process parameter. Poor fluidity will cause vacancies and affect the insulation performance. Therefore, the rigid foam stabilizer The requirements are as follows. ①Strong ability to emulsify raw material components;   ②Strongly control the cell size;   ③make the material have better fluidity and uniform density distribution.