Green fabrication of starch-based epoxy thermosets towards the excellent intrinsic fire safety and smoke suppression properties

A new intrinsically flame-retardant starch-based epoxy resin (OS-DDM-EP) was successfully fabricated from a green and facile process using resource-rich and low-cost starch as raw materials. The molecule structure of OS-DDM-EP was verified by infrared spectrum and nuclear magnetic resonance. TGA results revealed a much higher than residual char rate for OS-DDM-EP/DDM (22.3 %) compared to DGEBA/DDM (15.1 %) at 800 °C. Starch-based epoxy thermoset achieved a limited oxygen index of 34.5 % and passed V-0 rating of UL-94 vertical burning test. In comparison to the DGEBA/DDM thermosets, starch-based epoxy thermosets showcased a notably enhanced flame retardancy and smoke suppression. The peak heat release rate and total heat release were respectively dropped by 62.2 % and 53.4 %. Similarly, the peak smoke production rate and total smoke production were respectively reduced by 33.5 % and 57.8 %. Schiff base and polysaccharide structures of starch-based epoxy thermoset played a pivotal role in the formation of a consistent and dense char. Interestingly, the flexural modulus and flexural strength of starch-based epoxy thermosets were 3.26 GPa and 156.1 MPa, much higher than those of the commercial epoxy thermosets (2.23 GPa, 113.5 MPa). Furthermore, the flame retardancy improvement was attributed to the synergistic impact of gas and condensed phases. This research presents a simple and eco-friendly method for large-scale producing fire safety bio-based epoxy thermosets.