A curing agent, also known as a hardener, is a substance that is added to plywood glue to accelerate its curing process and improve its bonding strength. Curing agents can have different chemical compositions and properties depending on the type of glue and the intended use of the plywood.
Some common types of curing agents used in plywood manufacturing are:
Ammonium salts: These are inorganic salts that act as acid catalysts for urea formaldehyde resin, which is a common glue for interior plywood. Ammonium salts can reduce the pH of the glue and speed up its curing time. However, they can also increase the formaldehyde emission and toxicity of the plywood.
Phenolic resin: This is a synthetic resin that acts as a cross-linking agent for phenol formaldehyde resin, which is a common glue for exterior plywood, structural plywood, or marine plywood. Phenolic resin can increase the water resistance and durability of the glue. However, it also requires high temperature and pressure to cure, and it can be toxic if not used in a well-ventilated area.
Citric acid: This is an organic acid that acts as a modifier-curing agent for urea formaldehyde resin, which is a common glue for interior plywood. Citric acid can reduce the pH of the glue and speed up its curing time. It can also increase the hydrolytic stability and reduce the formaldehyde emission and toxicity of the plywood.