Study On The Effect Of The Silicon-boron Flame Retardant On The Wood Plastics Composites

The wood plastic composites (WPC) have been applied in many field, but the flammability of WPC limits its application in daily life. Therefore, the study on flame retardancy of WPC is particularly important. Depending on the requirement of the flame retardant, we focus on the high efficiency, economical and environmental flame retardant. The silicone flame-retardant and boron flame-retardant as the leader of these flame retardants, we could study on the synergistic effect of coordinated flame retardant for WPC. Nano silica, polysiloxane and zinc borate all have flame-retardant effect in wood flour polypropylene composites. A series of tests could help us study the influence on WPC.When the mass ratio of nano silica and zinc borate was 2:3, adding 20%flame retardant, the limiting oxygen index (LOI) of the material reached 32.1%, the maximum value of heat release rate(HRR) is 175.34 kW·m2, the maximum value of total heat release(THR) was 51.57 MJ·m-2, the peak value of the smoke release rate(SPR) decreased to 2.98 X 10-2m2·s-1, the total amount of smoke release(TSP) decreased to 7.89 m2·s-1.The tensile strength of the material was 18.0 MPa, the bending strength was 37.2 MPa, the impact strength was 3.84kJ·m-2. Nano silica could improve the impact strength of the material, played the role of flame retardant mainly in solid phase. Zinc borate provided two ways of flame retardant:taking off the crystallization water to absorb the heat of the combustion zone and the condensation-phase flame retardant. Zinc borate also had the best smoke suppressing effect.When the mass ratio of polysiloxane and zinc borate was 1:4, the maximum value of HRR is 181.34 kW·m-2, the maximum value of THR was 45.42 MJ·m-2, the peak value of the SPR decreased to 2.60X 10-2 m2·s-1, the TSP decreased to 5.98 m2·s-1.The tensile strength of the material was 22.3 MPa, the bending strength was 42.0 MPa, the impact strength was 3.45 kJ·m-2. Polysiloxane could improve the mechanical properties of WPC, the main flame retardant mechanism was crosslinking with polypropylene to inhibit the pyrolysis of PP. Meanwhile, polysiloxane with low molecular weight could generate fused silica.When the mass ratio of nano silica, polysiloxane and zinc borate was 3:1:6, the LOI of the materials was rising to 32.3%, the impact strength was the maximum, the maximum value of HRR was 148.52 kW·m-2, the maximum value of THR was 38.92 MJ·m2, the peak value of the SPR decreased to 1.97X 10-2 m2·s-1, the TSP decreased to 5.23 m2·s-1. At this point, the SEM image of the material was dense and homogeneous. Silicon-boron flame retardantof WPC could be exerted both in gas-phase and condensation-phase.