Polyethylene reinforced by biomimetic (polydopamine, tannic acid) modified magnesium oxysulfate whisker: Mechanical properties, thermal properties and flame retardancy

Two-dimensional magnesium oxysulfate whisker (MOSw) was modified by polydopamine (PDA) and tannic acid (TA) instead of the traditional inorganic flame retardants activated by silane coupling agent ( γ -methacryloxypropyltrimethoxy silane, KH570) such as Mg(OH) 2 and Al(OH) 3 . Differential scanning calorimeter (DSC) results showed that MOSw could act as heterogeneous nucleation for crystallization of HDPE, and further increased the initial crystallization temperatures of composites treated with PDA and TA. Dynamic mechanical thermal analysis (DMTA) showed that both the storage modules and loss modules of the composites with modified MOSw were significantly increased, which suggested the improved compatibility and dispersion between the modified MOSw and matrix. The tensile strengths of HDPE/MOSw@PDA composite and HDPE/MOSw@TA composite could be 118.0% and 121.2% higher than that of HDPE/MOSw@KH570 composite, and the corresponding impact strengths could be 124.0% and 111.2% higher, respectively. Compared to HDPE, the synergistic effect of PDA- MOSw and TA- MOSw (combustion heat through the dehydration of MOSw, gas-phase flame-retarded effect of MOSw, scavenging of active free radicals) increased the limit oxygen index (LOI) of composites from 19.4% to 23.4% and 23.8%, respectively, which were higher than 20.6% of traditional HDPE/Al(OH) 3 @KH570 composite with the same 30 wt.% filler. Schematic of self-polymerization of dopamine, and chelation of tannic acid with metal ions • MOSw covered with PDA and TA substituted for the traditional inorganic flame retardants activated by silane coupling agent. • Different from traditional inorganic flame retardants such as Mg (OH) 2 and Al (OH) 3 , MOSw modified by PDA and TA could not only improved the flame retardancy of HDPE, but also improved the tensile strength to a certain extent. • The composites with MOSw modified by PDA and TA showed good thermal stability.