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Sep 18, 2020
Foam stabilizer is a kind of surfactant, and its functions in the production process of polyurethane rigid foam plastics are as follows:
(1) Emulsification
The surface tension of raw material system is reduced and the miscibility of raw material components is improved.
(2) Nucleation
Promote the formation and stabilization of bubble core in the early foaming stage, regulate the structure, diameter and distribution of bubble hole.
(3) Stabilizing effect
Improve the stability and fluidity of the expanded foamed plastic raw material system, make the foamed plastic product density distribution uniform, no cavity.
Therefore, the surfactant not only plays a role in the processing performance of rigid foamed plastics, but also has a great impact on the physical properties of foamed plastics, such as density, compression strength, thermal conductivity, dimensional stability.
The foam stabilizer used in rigid polyurethane foam plastics emphasizes nucleation emulsification and homogenization. Foam stabilizers containing sulfonic acid are good foam stabilizers for making polyester foams, typically represented by sulfonated sodium ricinolate. Twain 80 (JuAnYiXi sorbitol glycerate) and ester soft foam foam stabilizer in common use.
The foam stabilizer used in all polyether foams is water-soluble polyether siloxane, which is the reaction product of polydimethylsiloxane with copolymer of ethylene oxide and propylene oxide.
Polyether siloxane is also known as polysilamino-oxyalkyl block copolymer. One of the differences between these products is that some are hydrolyzable and some are non-hydrolyzable. This is due to the different bonds between the polysiloxane and polyether parts of the molecule.
The Si - C bond is non-hydrolytic, while the Si - O - C bond is hydrolytic, which is not important in terms of foam stabilization per se, but can have an indirect effect. For example, when a mixture of foam stabilizer, tertiary amine catalyst and water is stored for a period of time, the SI-O-C bond hydrolyzes and the product loses its foam properties. At present, most of these water - able silicon foam stabilizer have been replaced by non - hydrolytic silicon foam stabilizer.