Reactive hot-melt (RHM or HMPUR) adhesives are solid prepolymers terminated in reactive groups (-NCO-) manufactured from mixtures of solid and liquid polyester/ether polyols with isocyanates, which are very low in free isocyanates. These solid prepolymers have a lower melting point than conventional hot-melt (HM) adhesives but show final strength and mechanical performance similar to a reactive system. Each of the raw materials can be appropriately adjusted to obtain required pot life, open time, and green strength.
The application temperature and viscosity of RHMs are significantly lower than standard thermoplastic HM adhesives (90-120°C), and time is needed to attain maximum bond strength. It is also important to keep in mind that the system needs protection against external moisture in the atmosphere before application.