Introduction to Polyurethane Foaming Agents – Other Introduction to Polyurethane Foaming Agents – Other Foaming Agents

Dichloromethane (MC):

Dichloromethane is a low-boiling-point (40°C) halogenated hydrocarbon with a relative molecular mass of 85, commonly used as a solvent. It is primarily used as a CFC replacement foaming agent in low-density polyurethane flexible foam. In flexible foam systems, water acts as the primary foaming agent, while physical foaming agents like MC serve as auxiliaries. Since MC has a higher boiling point (40°C) than CFC-11, it vaporizes later and has a certain dissolving and swelling effect on the polyurethane resin matrix. Therefore, it is essential to select suitable catalysts and additives. Due to its non-zero ODP (Ozone Depletion Potential) and certain toxicity, MC is restricted by environmental regulations and is considered only a transitional foaming agent.

Liquid Carbon Dioxide:

Liquid carbon dioxide has become a specialized foaming agent. It is a high-pressure liquefied gas that can be mixed into the polyurethane reaction mixture under appropriate pressure reduction using special equipment. It primarily serves as a foaming agent for low-density block soft foam. Industrial installations for this application already exist abroad, and several units have been introduced domestically. In specific processes, liquid carbon dioxide can also be used as a foaming agent for polyurethane rigid foam.

Acetone and Other Low-Boiling Organic Compounds:

Low-boiling-point organic compounds such as acetone can also be used as foaming agents for polyurethane foam plastics. However, due to their strong dissolving effect on the polyurethane matrix, they cannot be used independently and are now rarely seen in industrial applications.

Fluorinated Ether Compounds:

Fluorinated ether compounds, such as HFE-245mf (chemical formula CF₃CH₂OCHF₂) and HFE-347mcf (chemical formula CF₃CF₃CH₂OCHF₂), are characterized by low thermal conductivity, safety in use, and minimal environmental impact. These have also been studied as potential foaming agents.

Perfluoroalkanes (PFA):

In the early 1990s, perfluoroalkanes were studied as foaming agents for polyurethane rigid foam. Usable perfluoroalkanes include perfluoropentane (boiling point 30°C) and perfluorohexane (boiling point 57°C). These compounds feature zero ODP, appropriate boiling points, non-flammability, non-toxicity, and low thermal conductivity. However, they have drawbacks such as low solubility in polyurethane raw materials (polyols and isocyanates), high cost, low foaming efficiency, and significant greenhouse effects.