Polyurethane Chemistry An Attractive Alternative To Traditional Materials For RTM, VARTM Processes
Vacuum infusion and Vacuum Assisted Resin Transfer Molding (VARTM) are fast-growing composite molding technologies. Recent advancements in polyurethane chemistry for VARTM and Resin Transfer Molding (RTM) processes have resulted in a dramatic increase in commercial interest for producing a wide range of products, including those utilized in wind energy production.
Dr. Usama Younes, principal scientist, Bayer MaterialScience LLC, presented his paper, Development of PU-based RTM and VARTM Technology, at COMPOSITES 2010 in Las Vegas. 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 demold. 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 allows long gel times, ranging from 5 minutes to 60 minutes, with corresponding demold times of 15 minutes to 7 hours at room temperature. The resin 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."
About Bayer MaterialScience LLC
Bayer MaterialScience LLC is one of the leading producers of polymers and high-performance plastics in North America and is part of the global Bayer MaterialScience business with nearly 15,100 employees at 30 sites around the world and 2008 sales of 9.7 billion euros. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction, medical, and sports and leisure industries.
SOURCE: Bayer MaterialScience LLC