Controllable fabrication of zinc borate hierarchical nanostructure on brucite surface for enhanced mechanical properties and flame retardant behaviors.
A novel and efficient halogen-free composite flame retardant (CFR) consisting of a brucite core and a fine zinc borate [Zn6O(OH)(BO3)3] hierarchical nanostructure shell was designed and synthesized via a facile nanoengineering route. It had been demonstrated that this unique hybrid structure possessed a high BET specific surface area (65 m(2)/g) and could significantly enhance the interfacial interaction when mixing with ethylene-vinyl acetate (EVA). This improved the transfer of stress between CFR particles and EVA matrix and increased the viscosity of EVA/EVA blends, which was beneficial for droplet inhibition and char forming. The mechanical properties and flammability behaviors of the EVA/CFR blends had been compared with the EVA/physical mixture (PM, with the given proportion of brucite and Zn6O(OH)(BO3)3). The mechanical properties of EVA/CFR blends, especially the tensile strength (TS), presented a remarkable increase reaching at least a 20% increment. Meanwhile, with the same 45 wt % of fillers, the EVA/CFR formulation could achieve a limiting oxygen index (LOI) value of 33 (37.5 % higher than that of EVA/PM blends) and UL-94 V-0 rating. Moreover, the heat release rate (HRR), peak heat release rate (PHRR), total heat released (THR), smoke production rate (SPR) and mass loss rate (MLR) were considerably reduced, especially PHRR and SPR for EVA/CFR blends were reduced to 32%. According to this study, the design of fine structure might pave the way for the future development of halogen-free flame retardants combining both enhanced mechanical properties and excellent flame retardant behaviors.
Preparation of 2MgO·B2O3·1.5H2O nanomaterials and evaluation of their flame retardant properties by a thermal decomposition kinetic method
Two morphologies of magnesium borate 2MgO·B2O3·1.5H2O, nanorod and nanowire, have been controllably prepared by hydrothermal method through changing the amount of H2O. All samples were characterized by XRD, FT-IR, SEM, TG and chemical analysis. Their flame retardant properties were investigated by thermal analysis method (including TG, DSC and non-isothermal decomposition kinetics) and oxygen index method. With the decrease in TG mass loss, the decrease in heat release for DSC, the increase in LOI values and the increase in apparent activation energy Ea, the flame retardant properties of prepared 2MgO·B2O3·1.5H2O samples are increased gradually from non-nanostructure to nanorods then to nanowires, which may be ascribed to their sizes being decreased accordingly. The possible flame retarding mechanism has been proposed. It can be predicted that 2MgO·B2O3·1.5H2O nanowire could serve as a potential flame retardant.
Oxidation of carbon fibers coated with pyrolytic silicon carbide
Conclusions1.Determinations were made of the rates of oxidation of carbon fibers with pyrolytic silicon carbide coatings of various thicknesses in atmospheric oxygen and carbon dioxide.2.It has been found that at all temperatures the rate of oxidation of coated carbon fibers decreases with increase in coating thickness irrespective of the nature of the oxidizing agent.3.It is shown that the energies of activation for the reactions C+O2 and C+CO2 on uncoated fibers and fibers with pyrolytic silicon carbide coatings are practically identical and equal to 37 and 58 kcal/mole, respectively.4.X-ray structural analyses of starting and oxidized fibers with coatings have demonstrated that starting fibers contain graphite and silicon carbide phases, while in oxidized fibers there is, in addition to silicon carbide, another phase, probably silica.