What are the polyurethane foaming aids?
Foaming aids are essential in the manufacture of polyurethane foam plastics, including catalysts, foam stabilizers, foaming agents, etc. Some additives are optional and are used when necessary, such as flame retardants, chain extenders/cross-linking agents, antioxidants, light stabilizers, foam softeners, cell openers, fillers, color pastes, antistatic agents, hydrolysis stabilizers, foam combination material storage stabilizers, etc.
1. Foaming agent
Water is an important foaming agent in the production of polyurethane materials. It belongs to a chemical foaming agent. It reacts with isocyanate to generate carbon dioxide gas to expand, foam, and solidify viscoelastic foam materials, various polyurethane foam plastics.
In the production of polyurethane soft foam, in order to obtain low-density soft foam plastics, and at the same time avoid causing foam stiffness due to excessive water, it is generally necessary to control the amount of water and add an appropriate amount of physical foaming agent as an auxiliary foaming agent.
2. Foam stabilizer
When producing polyurethane foam plastics, foam stabilizer (or foam leveler) is an indispensable component. It can increase the mutual solubility of each component, play the role of emulsifying foam materials, stabilizing foam and regulating foam cells. Foam stabilizer belongs to surfactants, which are divided into two categories: non-silicon compounds and organosilicon compounds.
Most of the foam stabilizers currently used are polysiloxane oxidized olefin block copolymers, which belong to polyether modified silicone surfactants, and are sometimes commonly known as "silicone oil" in the industry. Because this type of surfactant has a wide range of structural composition variations and good use effects, polyether modified silicone surfactants have been widely used as foam stabilizers in the polyurethane foam plastics industry.
3. Cell openers
Cell openers are a special type of surfactants, generally containing hydrophobic and hydrophilic segments or groups. Their function is to reduce the surface tension of the foam, promote the rupture of the pores, increase the open porosity of polyurethane foam, and improve the shrinkage of soft, semi-rigid, and rigid foam products caused by closed cells.
In the early days, hydrophobic liquid paraffin, polybutadiene, dimethyl polysiloxane, etc. can be used as foam stabilizers and cell openers. Paraffin dispersions and polyethylene oxide can also be used as cell openers. Currently, polyoxypropylene-ethylene oxide copolyethers and polyoxyolefin-polysiloxane copolymers with special chemical compositions are mostly used as cell openers.
4. Softeners
The use of softeners in the production of high-water-content polyurethane soft foams can suppress the problem of foam stiffness caused by excessive urea groups. Foam softening modifiers have a softening effect. The use of softeners can reduce the amount of isocyanate used and thus reduce the hardness of the foam, and are used in the production of soft polyurethane foams. Commercial softeners generally contain special polyethers, special polyols, and water.