Foaming agents are materials that help to create foam in plywood glue. Foam can reduce the density and cost of plywood, and improve its properties and performance. There are two main types of foaming agents: physical and chemical.
Physical foaming agents are gases or liquids that form bubbles in the glue. They can be injected into the glue or dissolved in the glue and released by heating or pressure reduction. Some examples of physical foaming agents are carbon dioxide, pentane, water, argon, nitrogen, and air. Physical foaming agents have the advantages of low toxicity, high efficiency, and easy control. However, they also have the disadvantages of high cost, high gas diffusion, and low foam stability.
Chemical foaming agents are compounds that release gases when they decompose. They can be organic or inorganic, and they can be mixed with the glue or added as a masterbatch. Some examples of chemical foaming agents are azodicarbonamide, sodium bicarbonate, baking powder, and hydrazine. Chemical foaming agents have the advantages of low cost, low gas diffusion, and high foam stability. However, they also have the disadvantages of high toxicity, low efficiency, and difficult control.
Different types of plywood require different types of foaming agents. For example, interior plywood can use urea formaldehyde resin with a chemical foaming agent, while exterior plywood can use phenol formaldehyde resin with a physical foaming agent. The choice of foaming agent depends on the desired properties and performance of the plywood.