A furfural-based DOPO-containing flame retardant, 6,6′-(((methylenebis(4,1-phenylene))bis(azanediyl))bis(furan-2-ylmethylene))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (MBF-DOPO), was synthesized and utilized as a co-curing agent of 4,4′-diaminodiphenyl methane (DDM) for fire-safe epoxy thermosets. For the cured epoxy resin containing 4.0% MBF-DOPO, the limiting oxygen index (LOI) reached 32.9% (with the V-0 rating in UL-94 test), and the peak heat release rate and total smoke production values were respectively decreased by 29.3% and 33.6%, compared to pure epoxy resin. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) results confirmed that the furfural-based flame retardant MBF-DOPO promoted the charring formation of the epoxy matrix, which effectively isolated the gas and heat transfer during combustion and thus enhanced the fire-safety performance of the epoxy thermosets. This work provides an effective route for synthesizing a furfural-based flame retardant, which possesses great potential for application in fire-safe epoxy thermosets.

Herein, a new renewable Schiff base flame retardant 4,4′-((1E,1′E)-((oxybis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(benzene-1,2-diol) (PH-ODA) was prepared by the reaction of protocatechualdehyde with 4,4′-diaminodiphenyl ether (ODA). PH-ODA (acting as a carbonization agent) combined with ammonium polyphosphate (APP) were used as intumescent flame retardants for commercial bisphenol A epoxy resin (DGEBA). For the cured epoxy resin containing 7.5% APP and 2.5% PH-ODA, the limiting oxygen index (LOI) reached 29.9% (with the V-0 rating in UL-94 test), and the peak heat release rate and total smoke production were respectively decreased by 88.1% and 68.3%, compared with pure epoxy resin. The enhancement of fire-safety performance was due to PH-ODA/APP promoting the formation of a compact intumescent char structure. It was also found that the synergism between PH-ODA and APP was helpful to enhance the fire resistance of the epoxy matrix. This work provides a facile and sustainable route for synthesizing Schiff base compounds from biomass-derived resources, possessing great potential for application in highly-effective intumescent flame retardants.

Metal-organic frameworks (MOFs) hold great promise for diverse applications when combined with polymers. However, a persistent challenge lies in the susceptibility of exposed MOF pores to molecule and polymer penetration, compromising the porosity and overall performance. Here, we design a molecular-caged MOF (MC-MOF) to achieve contracted window without sacrificing the MOF porosity by torsional conjugated ligands. These molecular cages effectively shield against the undesired molecule penetration during polymerization, thereby preserving the pristine porosity of MC-MOF and providing outstanding light and thermal management to the composites. The polymer containing 0.5 wt % MC-MOF achieves an 83% transmittance and an exceptional haze of 93% at 550 nanometers, coupled with remarkable thermal insulation. These MC-MOF/polymer composites offer the potential for more uniform daylighting and reduced energy consumption in sustainable buildings when compared to traditional glass materials. This work delivers a general method to uphold MOF porosity in polymers through molecular cage design, advancing MOF-polymer applications in energy and sustainability.