Halogen free flame retardants
Flame retardants are substances or compounds that are added to other materials, such as plastics, coatings and textiles to prevent or delat the the spread of fire. The first applications of flame retardants predate the Gregorian calendar. Egyptians soaked wood in alum (potassium aluminium sulphate) around 450 B.C. and timbers were painted with vinegar arounsd 360 B.C. to increase their resistance to fire. Since then, many other materials have been used as flame retardants including clay, hair and gypsum. In 1735, Obadiah Wilde received British patent 551 for his mixture of alum, borax (sodium borate) and ferrous sulphate, which he used to improve the flame retardancy of paper and textile. His invention was first applied to improve safety of canvas used in theatres and public buildings.
Today, global demand for flame retardants has exceeded 2 million tons per year. A major part of this demand comes from the global plastic industries. Since all carbon-based materials are combustible, and the use of plastics is so widespread, there is a need to decrease the risk of fire related accidents. If it is not possible to select a polymer that is inherently flame retardant (e.g. polyamide), adding a flame retardant is a solution. The flame retardant can be mixed with the base material or chemically bonded to it. Broadly speaking, flame retardants can be devided in three groups, (1) inorganic or mineral flame retardants and (2) halogenated compounds. While the performance of halogenated flame retardance is excellent, many of these chemicals are associated with health and environmental problems. As a result, several brominated and chlorinated flame retardants have been banned in the past. Examples of banned compounds include polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and Decabromodiphenyl ether (DecaBDE).
Companies looking for less toxic products, often try to make changes to the articles materials and design or to select safer (inorganic) chemicals. Examples of such chemicals include aluminium trihydroxide (ATH), a mixture of huntitite and hydromagnesite and magnesium (di)hydroxide (MDH). These mineral flame retardants are non-toxic and work by decomposing endothermically. This means that at a certain temperature, the compounds fall apart thereby adsorbing heat and releasing water vapor. The oxides that are formed results in a protective layer that provides a smoke suppressing effect. Despite the obvious advantages of mineral flame retardants, it is not always possible to replace halogenated flame retadants. To reach flammability standards in demanding applications, mineral flame retardants need to be added in very high dosage levels (up to 80 w/w%).
If the use of mineral flame retardants is feasible, the most suitable compound is often selected based on its decomposition temperature. Aluminum Trioxide is generally cheaper than Magnesium Hydroxide, but starts to decompose at 180 oC making it unsuitable for thermoplastics like polypropylene which are molded at 200 oC. For these materials, magnesium hydroxide is often selected based on its stability up to 340 oC. Kisuma Chemicals is a renowned supplier of magnesium hydroxide products, which are marketed under the brandname Kisuma 5®.
For more information about the use of magnesium hydroxide products to improve flame retardancy of your products, contact our Marketing and Sales department today.