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Composites 2010 gave a stage for Dr. Usama Younes, principal scientist, Bayer MaterialScience LLC, to present his latest paper, Development of PU-based RTM and Vacuum Assisted Resin Transfer Moulding (VARTM) Technology.
The paper focused on the chemistry and properties of polyurethane materials, with emphasis on structure/property relationship and the development of high surface quality (Class A) VARTM composites. Younes also discussed the advantages of polyurethane resins including room temperature cure, no volatile organic compounds (VOCs) and high impact properties.
According to Younes, until now, there has been a two-fold challenge to using polyurethane resin in vacuum infusion processes. One challenge is reacting components to maintain a relatively constant and low viscosity over a long period of time, yet provide a short demould. The second challenge is moisture sensitivity, as the isocyanate portion of the reacting components tends to react with water to produce carbon dioxide, which causes foaming. These issues are not common in materials used in vacuum infusion, such as epoxy, vinyl ester and unsaturated polyester.
These challenges have been overcome by the development of polyurethane resin chemistry that is said to allow long gel times, ranging from 5 minutes to 60 minutes, with corresponding demould times of 15 minutes to 7 hours at room temperature. The resin has reported viscosities of 250 cps (centipoises) at 25° C and 90 cps at 40° C allow easy wet out of high levels of glass.
“Polyurethane chemistry is an attractive alternative to traditional materials for use in RTM and vacuum infusion applications,” said Younes, who also discussed a technology developed by Bayer MaterialScience LLC that uses a polyurethane gel coat for painted VARTM surfaces. “Because of its combination of mechanical and environmental benefits, we expect interest in polyurethanes for RTM and VARTM to continue to grow.”
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