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Fly-ash-filled PU beats wood

By David Reed, UT EditorAnaheim, California-Rigid polyurethane foams with high loadings of fly ash are being touted as high-performance lumber for use in outdoor applications including decking, where they are claimed to offer benefits over existing products-including systems based on other plastics and treated wood itself.Dubbed LifeTime by its developers, a plant to make boards based on the technology has been brought on stream by Century Products llc in Anaheim. This uses proprietary water-blown formulations based on conventional polyether polyols and MDI (methylene diphenyl diisocyanate) in a continuous conveyor-type process capable of making porous boards with cross-sections of 2 x 6 in (50.8 x 152 mm) and lengths of 16 ft (4.9 m), according to information supplied by Fyodor Shutov, senior vice president of research and development with Century. Water-blown foam system are used because “the amount of moisture in fly ash is normally too small to provide us the densities we need to manufacture, and [so] we add some more water to generate more carbon dioxide,” he explained. Although fly-ash loadings as high as 80 percent weight filler are possible, the typical ash content is around 65%w, Shutov continued. The fly ash used is a byproduct of power generation from pulverized fuels and often has to be disposed of into landfill or as an inert filler in concrete and other products.In addition, he claimed that the process can be adjusted so that “we can easily produce commercial materials in a wide range of densities, say between 30-65 pounds per cubic foot (500-1000 kg/m3), depending on application.”A mixer has been developed to handle the fly ash which is used as supplied, without any pretreatment or sorting by particle size, according to information supplied by Shutov, who is technical supervisor and developer of the product and its manufacturing process. The mix is then dispensed into a mould on a conveyor system where it is foamed, shaped, textured and cured, followed by cutting to length.The LifeTime product has a typical density of 45 pcf (720 kg/m3), a high ratio of modulus of elasticity/density (around 60), low water absorption (0.41 percent), a low coefficient of thermal expansion (1.07×10-5), and high screw-withdrawal parameter (926#/in), data from Century indicated. In addition, the company claims, the boards have extremely high fire- and weather-resistance, and high thermal oxidative aging performance, as well as good stain, slip, mould and termite resistance.The Century Products unit is already on stream, but the company is also considering the possibility of licensing the use of the process to interested parties in other companies and countries. The typical investment cost for an industrial plant with three continuous lines, having an output of 5000 lbs (2250 kg) per hour each, is around $6 million, according to Shutov.”

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