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.
Charring of fire retarded ethylene vinyl acetate copolymer — magnesium hydroxide/zinc borate formulations
Abstract Zinc borate has been used as a synergistic agent in EVA-Mg(OH)2 flame retardant (FR) formulations. Solid state NMR of carbon in the residues collected after thermal treatment allows the study of the charring of the flame retardant system. The study has shown that polymer fragments are in the char layer. It is suggested that zinc borate slows the degradation of the polymer, creating a vitreous protective residual layer which could act as a physical barrier and a glassy cage for polyethylene chains.
11B NMR in Polycrystalline Calcium Metaborate
Boron‐11 nuclear magnetic resonance has been observed in polycrystalline calcium metaborate doped with paramagnetic Mn2+. The spectrum arises from the m = 12↔m= − 12 transition broadened in second order by a quadrupole interaction having a nonzero asymmetry parameter. The quadrupole coupling constant of 2.58 ± 0.02 MHz is consistent with previously published values for three‐coordinated boron. However, the electric field gradient asymmetry parameter of 0.55 ± 0.01 is several times greater than expected, and this large value is attributed to the presence of a nonbridging oxygen in the boron coordination shell. The possibility of using this result for the study of noncrystalline solids is discussed.