Borates have made their debut in various materials (timber, cellulose insulation, PVC and textiles) for flame retardancy. Boron suppresses combustion by sealing the surface of the burning material and blocking its contact with oxygen. Zinc borate is used in plastic materials while soluble borates such as boric acid, borax pentahydrate and borax decahydrate are used in cellulosic agents. These agents are natural fibres such as wood, plywood, wood fibre, paper and cotton.
Borax pentahydrate and boric acid are employed for cellulosic insulation. These products are used for improving energy efficiency, preventing the growth of fungi and other microorganisms and enhancing flame-proof character of the material.
Zinc borate, barium metaborate, boron phosphate and ammonium fluoborate constitute the main boron compounds employed as flame-retardants for PVCs. HCl is released during PVC combustion. When zinc borate is doped as flame retardant to PVC, the gas reacts with non-volatile zinc and boron compounds, preventing the release of hazardous gases.
Though borax and boric acid are useful flame retardants in textile, washing-off from the product is a problem as they are soluble in water.
Disodium octaborate tetrahydrate is a successful solution for the long-term protection of wood from fungi and pests. This agent can conveniently be applied to timber by spraying, painting or pressure without any special measure.