Fire resistant plastics

The use of halogenated flame retardants in plastics is steadily declining because they are volatile, pose an environmental risk and are difficult to recycle. Microcapsules, fibers and melamine resin foams represent some of the chief alternatives.

As successfully as the endless variety of plastics have established themselves on the market, these multifaceted materials show another face when it comes to fire. They melt and feed the flames like the petroleum from which they were ultimately produced. As a preventative measure, a variety of flame retardants are added to plastics, yet this introduces a number of problems. Additives often alter the mechanical properties and electrical insulating effect of plastics. Especially brominated and chlorinated additives migrate through the material and can damage metal and electronic components. Moreover, they represent a health risk and interfere with the recycling process. Yet fire safety regulations require the use of flame retardants.

The Fraunhofer Institute for Applied Polymer Research IAP is developing combustion-resistant and self-extinguishing plastics. Last November members of the working group, directed by Dr. Gerald Rafler, received the Friedrichs Prize for new technologies, along with 15,000 Euro in prize money, for their innovations and development of new materials. The prize is awarded by the German Federation of Industrial Cooperative Research Associations “Otto von Guericke” AiF. The new materials are already being tested and prepared for market introduction by the Austrian company Agrolinz Melamin GmbH.

“The microencapsulation of flame retardants is one of three strategies we are currently pursuing,” explains Rafler. “The outer shell of the microscopic capsules is made of nonfusable, flame-resistant melamine resin like that used for frying pan handles or power plugs. The flame retardants remain enclosed in the capsules and are only released in the event of fire.” Even substances incompatible with the base plastic material can be used if encapsulated. Nitrogen, carbon dioxide and compounds designed to produce extinguishing gases in reaction to heat are some examples. Gas-filled microcapsules are pressure-resistant and withstand plastics processing procedures such as extrusion, granulation and injection molding without rupturing.

The IAP research team has developed two further concepts to replace halogenated flame retardants. They manufacture fiber-reinforced polymers made of melt-spun melamine fibers. Such composite materials are easier to process and recycle than those reinforced with glass fiber. Finally, they manufacture high tenacity melamine foams that begin to slowly decompose at temperatures above 360 °C.

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Dr. Johannes Ehrlenspiel Fraunhofer-Gesellschaft

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