Synthesis and characterization of melamine-formaldehyde rigid foams for vacuum thermal insulation

摘要

A novel core material for vacuum thermal insulation, the melamine-formaldehyde (MF) rigid foam was processed from an emulsion of the melamine-formaldehyde resin at temperatures between 130℃ and 150 ℃, using pentane as the blowing agent. The achieved porosity was between 92% and 98%. Open pore structure with desired mechanical properties was achieved by variations of the initial chemical composition of liquid reactants and controlled foaming and hardening, employing classical heating. The average pore size was determined directly by SEM and indirectly by measuring the thermal conductivity in a wide pressure range from 10~(-3) mbar to the atmosphere. Optimization of the synthesis resulted in the base thermal conductivity equal to only 0.006 Wm~(-1) K~(-1) and an extremely low outgassing rate. The long-term pressure-rise measurements indicate that these MF rigid foams could be the first organic candidates applied as the core material in Vacuum Insulating Panels (VIPs) whose performance may be comparable to selected inorganic core materials. Their further advantages compared to conventional organic foams are their stability, as they can withstand a temperature in excess of 200 ℃, and good fire resistance.