Reactive hot melts are based on moisture curing polyurethane technology and how you use them differs from normal hot melt adhesives. 

The typical recommended operating temperature is 120°C-130°C and an application system designed for reactive melts must used. In general the viscosity of a reactive hot melt will rise on prolonged heating even in the absence of moisture. Therefore, if the application equipment is left for more than 30 minutes it is recommended that the temperatures on the equipment be reduced by 20°C.

If the nozzle is left unused for more that 2 hours then the reactive hot melt may skin on the surface. In this case the system should be purged with a suitable cleaner such as Pur-Fect Purge or a barrier of high temperature grease be applied to the end of the nozzle to prevent moisture coming into contact with the exposed adhesive.

Typically, the full cure of the adhesive will take 3-7 days dependent on the ambient conditions and substrates. The bond will not be a full strength until fully cured. If bonding takes place under dry conditions (relative humidity below 50%) the coated adhesive surface may be misted with water to ensure the cure takes place at a reasonable speed.

When heated, all reactive hot melt give off fumes that contain MDI. There should be forced air extraction around the premelter and application area to remove these fumes from the workplace.

If someone is burned by the adhesive, full first aid advice can be found in the Hot Melt Adhesives trouble shooting section.