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

Abstract

Abstract 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.