Effects of Mg(OH)₂ on flame retardant of benzoxazine epoxy composites

Mg(OH)₂-glass fiber fabric/benzoxazine (BZ)-epoxy (EP) laminate was prepared by thermo-compression formation using Mg(OH)₂ as the flame retardant, BZ-EP as the matrix.The flame retardant of the laminate was tested by the vertical flame and the limited oxygen index method.The effects of Mg(OH)₂ powder amount, particle size and compound addition of powder with different sizes on flame retardant of composites were analyzed.SEM was used to characterize the dispersion structure of Mg(OH)₂ powder in impregnation resin.The results indicate that the flame retardant of the laminates is influenced by the particle size and the amount of Mg(OH)₂ powder.The compound addition of powders with different particle sizes makes a flame-retardant net in composites, leading to the best flame retardant effect.And the negative impact of inorganic particle on the mechanical and electrical properties of the laminates is reduced.When the content of Mg(OH)₂ is 30wt% of total mass of BZ-EP and the mass ratio of Mg(OH)₂ powder with 2 μm (YX-105) and 4 μm (YX-110) is 1:2, the limited oxygen index of the laminates is 34%.The shortest self-extinguishing time of single sample in vertical burning test is 7.52 s, and the total self-extinguishing time of the five samples is 49.81 s, which reaches the ranking of UL-94V-0.The bending strength and the relative dielectric constant of the composite is 399.84 MPa and 3.848, respectively.