Biomass-derived Schiff base compound enabled fire-safe epoxy thermoset with excellent mechanical properties and high glass transition temperature

[Display omitted] •A novel biomass-derived epoxy thermoset was synthesized from Schiff base compound.•Schiff base structure promotes char formation and reduces the fire hazards of epoxy thermoset.•The new epoxy thermoset exhibits superior mechanical properties and high glass transition temperature.•This paper provides a new strategy for simultaneously enhancing the mechanical properties and fire-safety performance. Recently, biomass-derived fire-safe epoxy thermosets have been developed for the substitute of petroleum-derived bisphenol A epoxy thermosets due to the shortage of petroleum resources and the negative health impacts of petroleum-derived products. However, the synthesis of bio-based epoxy thermosets combining excellent mechanical properties and fire-safety performance is still a great challenge. In this paper, a novel Schiff base compound 4,4′-((1E,1′E)-((oxybis(4,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(benzene-1,2-diol) (PH-ODA) was efficiently synthesized from bio-based protocatechualdehyde. PH-ODA was subsequently reacted with epichlorohydrin to obtain the epoxy monomer (1E,1′E)-N,N′-(oxybis(4,1-phenylene))bis(1-(3,4-bis(oxiran-2-ylmethoxy)phenyl)methanimine) (PH-ODA-EP). After curing PH-ODA-EP with 4,4′-diaminodiphenylmethane (DDM), the cured resin PH-ODA-EP/DDM network possessed a high glass transition temperature (Tg) of 204.9 °C and showed a 181.8%, 105.8% and 87.0% increase in char yield (in N2) (41.7% vs. 14.8%), storage modulus (at 30 °C) (6.01 GPa vs. 2.92 GPa) and tensile modulus (6.21 GPa vs. 3.32 GPa), respectively, compared with the cured bisphenol A epoxy resin (DGEBA)/DDM. Moreover, PH-ODA-EP/DDM possessed excellent fire-safety properties (limited oxygen index (LOI) value = 40.5%) due to the introduction of Schiff base structure, showing a 90.9% and 72.0% reduction (compared with DGEBA/DDM) in peak heat release rate and total heat release value. This work provided a facile and sustainable route for synthesizing Schiff base compounds using biomass-derived resources, exhibiting great potential for the application in high-performance fire-safe epoxy thermosets.