Flame retardancy, photostability, and thermal properties of vanillin-epoxidized soybean oil composites reinforced with walnut shell

Abstract

Vanillin produced from lignin is an environmentally friendly compound having various active structures that can be crosslinked with hexanediamine and epoxidized soybean oil (ESO) to form water resistant composite. Inclusion of ammonium dihydrogen phosphate (ADP) could render the composite flame retardant, but its mechanical properties could be influenced. Therefore, walnut shell powder (WSP), as a common biomass waste, can be incorporated to improve its hardness and compressive strength. A matrix named VHEA was prepared by the condensation of vanillin, hexanediamine, ESO, and ADP. WSP was used as the skeleton for blending with VHEA to create VHEAW composite. Mechanical properties, dimensional stability, UV-resistance, thermal conductivity and flame retardancy of the composites were evaluated. The inclusion of WSP at a ratio of 1:1 to VHEA improved the compressive strength, Brinell hardness and flexural strength of the composite. Meanwhile, its water contact angle reaches 131.48 °, indicates its superior hydrophobicity. It also has high UV resistance and good flame retardancy as the LOI value is as high as 35.1 %, and its peak heat release rate is as low as 123.19 kW/m2. Its outstanding thermal insulation and flame retardancy, combined with excellent UV-resistance, render it suitable for various building components, including roofing, exterior siding, windows, and doors.