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UPDATE “Architectures are becoming

increasingly more intricate and delicate. At the same time, buildings still need to meet all specified safety standards,” says Dr Wilfried Huster, head of Application Technology for Dispersions in Europe at WACKER’s polymers division. This applies especially to those relating to fire. True, the steel columns

themselves are not flammable, but this otherwise highly stable material has an Achilles heel – intense heat. When the temperature reaches 500°C, steel frames soften rapidly, and buildings are in danger of collapse. “Basically, the steel just ‘floats’ away,” says Dr. Niels Friede, process engineer and head of Emergency Services/ Fire Safety at WACKER in Burghausen. Not only that, steel expands extensively in heat. “Unlike stone and even

wooden walls, which undergo little dimensional change, steel columns lengthen and widen. In so doing, they force other components apart, thereby further weakening the structural stability,” adds Friede. That is why fire safety is so crucial in steel-frame structures.

GREATER STAYING POWER One solution here is to boost the resistance of the columns by painting them with so-called intumescent coatings, which swell in the event of a fire and confer greater “staying power” to the metal columns. The coatings are applied like paints in thicknesses ranging from just 300 micrometers to several millimetres, the precise thickness depending on the application. Even though these heat shields are fairly thin, they nonetheless afford substantial protection. “When a fire breaks out, the coatings swell by 10 to 100 times their original thickness to form a thermally insulating foam jacket around the steel column,” says Huster. The thermal insulation properties stem from the foam’s high density and very fine pores. The foam slows the rate at which the steel heats up, greatly delaying the time taken to reach the critical 500°C. “The buildings can thus resist a fire for much longer, and that gives the rescue teams more precious time to save lives,” adds Friede, a fire expert.

ESSENTIAL INGREDIENTS If the intumescent coatings are to generate the insulating foam in a fire, certain ingredients are essential. Alongside “reactive” components such as melamine, pentaerythritol and ammonium polyphosphate (such as Clariant’s Exolit® AP), they also

contain organic binders made by WACKER. “The binder in a fire protection coating has far more jobs to do than simply hold the filler particles together, as it does in conventional wall paint,” stresses Huster. When the temperature

reaches 250°C, the binder fuses to form a matrix in which subsequent thermochemical reactions can take place. The first reaction is decomposition of the ammonium polyphosphate, which constitutes one quarter and thus the major ingredient of the intumescent coating. The resultant phosphoric acid reacts with the pentaerythritol to form phosphoric acid esters. If the temperature keeps rising, the esters themselves start to decompose, forming residues that contain carbon and phosphorus. Meanwhile the melamine also decomposes, emitting ammonia and nitrogen gases. These act as a blowing agent that gradually expands the carbon and phosphorus ester residues into a layer of insulating foam. “Extensive studies have

shown that special copolymers based on vinyl acetate and ethylene – in other words, our VAE dispersions – and terpolymers based on vinyl acetate, ethylene and vinyl ester are particularly effective in promoting the formation of a stable matrix,” explains Huster. Without the binder, the



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