What is the synergistic flame retardancy of aluminum hypophosphite and zinc borate?

When used together, aluminum hypophosphite (AHP) and zinc borate (ZB) create a synergistic effect, greatly enhancing the flame retardant properties of the system. The aluminum hypophosphite synergistic zinc borate flame retardant system is commonly used in various applications, including plastics, textiles, paints, and coatings. It provides an effective and environmentally-friendly solution for improving the fire safety of these materials.

In the current study, it was thought that ZB might exhibit adjuvant and/or synergistic interactions with AHP through different mechanisms. For example, the phosphorus-containing gas released from AHP reacts with the borate ions of ZB to form a stable boron-phosphorus layer on the surface of the material. The layer also acts as a barrier to heat, oxygen and volatile gases, effectively inhibiting flame spread and reducing smoke production.

AHP/ZB Flame Retardant System for Polyamide

The flame retardant effect of AHP/ZB flame retardant system in polyamide 6 was studied. The results show that ZB can improve the thermal stability of AHP. In the presence of ZB, the char yield increased slightly. The existence of chemical interaction between AHP and ZB can be verified by XRD results. Due to this interaction, the formation of an almost amorphous structure and some minor crystalline products (boron phosphate and zinc pyrophosphate) was observed. In summary, in the polyamide 6 matrix, the AHP/ZB flame retardant system caused a decrease in pHRR, aHRR, pMLR and THE values. The auxiliary effect of ZB mainly comes from increasing the density, quantity and height of coke in the condensed phase.

XRD patterns of AlHP, ZnB and their mixture. [1]

AHP/ZB Flame Retardant System for Polyethylene (PE)

PE/AHP/ZB flame retardant composite materials can be prepared by melt blending method. AHP and ZB have good dispersion in the PE matrix without obvious agglomeration. When m(AHP):m(ZB)=21:4, the material LOI can increase to 27.4% (the LOI of pure PE is 18%), passing the UL94 (3.2mm) V-1 level.

AHP/ZB Flame Retardant System for Silicone Foam

A flame-retardant microcapsule (MAHP) with an aluminum hypophosphite (AHP) core was first prepared. Then the effect of MAHP/ZB composite flame retardant on the mechanical properties, flame retardancy and smoke suppression performance of silicone foam (SiF) materials was tested. Possible flame retardant mechanisms of MAHP/ZB in SiF include:

• MAHP burns and decomposes to produce CO₂, H₂O, NH₃, PH₃ and AlPO₄. These gases can significantly reduce the oxygen concentration around SiF and exhibit a gas-phase flame retardant mechanism.
• AlPO₄ melts when heated and forms a glass body, thereby protecting the substrate from burning.
• The SiO₂ residue acts as a "thermal barrier", acting as a mass transfer barrier and delaying the volatilization of decomposition products.
• Zinc borate will decompose during combustion to form ZnO, B₂O₃ and water vapor. B₂O₃ will participate in the formation of a cross-linked network in the formed char residue, thereby enhancing the density of the char residue.