There is a growing interest in low monomer systems due to improvements in industrial hygiene practices and the pending restriction of diisocyanates. Progress has been made in developing low free monomer urethane prepolymers, below 0.1%, which have been commercialised for use in automotive (hot melt) and construction (OCF) applications. This low monomer technology offers excellent performance, superior processing and productivity, as well as environmental, health and safety advantages.
Further development work showed that low monomer systems are quite different from conventional systems. This presentation is focused on addressing these differences.
The removal of diisocyanate monomer can present challenges in the final adhesive formulation such as different reactivity, amount of prepolymer needed and overall different adhesive properties. These challenges can be overcome by exploring additional chemistries based on increased polyol functionality and optimisation of molecular weight and structure. In addition, unique morphologies due to a combination approach of crystalline and amorphous polyols are explored.
These developments lead to a broad formulation platform that enables design of prepolymers with a tailored balance between reactivity (different isomer ratio of 2,4 and 4,4 MDI) and processability in different adhesive formulations. In addition to 2,4 and 4,4 MDI a broad range of isocyanate chemistries is available.