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Quang-Vu Bach, Cuong Manh Vu, Dinh Duc Nguyen, Bui XuanKien
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.
SEM Hitachi SU-3800