Abstract
Biobased flame retardants have attracted great attention owing to their environmental friendliness and easy availability. Urushiol, extracted from natural resin-raw lacquer, has been capped with diphenylphosphoryl chloride to afford a biobased flame retardant, namely urushiol-based phosphonate (U-DC). As an additive this material is effective in reducing flammability while maintaining good mechanical strength for epoxy resins (EP). Impressively, an EP/9 %U-DC blend exhibits a UL-94 V-0 rating, and an LOI of 37.1 % for combustion. Further, compared to that for EP, the peak heat release rate (pHRR) and total heat release (THR) for the EP/9 %U-DC blend was lower by 40.5 % and 26.6 %. Through analysis of volatile products formed and char residue produced during polymer degradation, a mode of flame retardant action for U-DC has been proposed. Further, EP/U-DC blends display better mechanical properties than those of unmodified EP. Tensile strength of EP containing 7 wt% U-DC (81.6 MPa) is greater than that for unmodified EP (64.4 MPa). This may be ascribed to the presence of abundant rigid benzene units in U-DC and chain entanglement between the long side chain of U-DC and the epoxy macromolecular chain. These observations provide a basis for the utilization of new urushiol derivatives in the production of high-performance EP.
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