LAUSR

Abstract Although widely used in industrial applications, epoxy resins generally display low toughness and high flammability. The use of phosphorus compounds can improve flame-retardant capabilities along with reducing mechanical properties. Herein, the novel flame-retardant additive of phosphorous-linked epoxidized vegetable oil (P-L-EVO) was fabricated from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and epoxidized vegetable oil through a ring opening reaction before applying it as additive for an epoxy/silica system. The silica was extracted from a rice husk using a combined approach of acid treatment and thermal treatment. Successful grafting and extraction reactions were confirmed using Fourier transform infrared analysis (FTIR) and nuclear magnetic resonace (NMR). The epoxy resin-based samples were cured with diethylenetriamine (DETA) hardener at ambient conditions. The influences of additives on the mechanical properties and flame-retardant capabilities were examined via tensile strength, impact strength, critical stress intensity (KIC), a cone calorimeter, the limited oxygen index (LOI), and the UL 94 vertical test. The epoxy sample with 20 wt.% silica and 10 wt.% of P-L-EVO (S20.10) reached the LOI value of 35.89 % and a V0 rating of UL94. Moreover, this combination improved the impact strength, tensile strength, and KIC by up to 90.16 %, 20.28 %, and 73.84 %, respectively in comparison with pristine epoxy sample (S00.00). The formation of a non-thermal decomposition char layer along with a release of flame-retardant radicals was considered the novel flame-retardant mechanism.