In place of polyester, vinylester and epoxy used in resin transfer molding (RTM), the use of polyurethane resin is being introduced. RTM technology process has been a preferred method for manufacturing composite parts. Bayer MaterialScience LLC is pioneering the use of polyurethane resin in the RTM technology process. In the RTM process, a fiberglass mat is placed in a two-sided mold. The mold is closed, and polyurethane resin is injected into it. Once the part cures, the mold is opened and the finished part removed.
A new variation of resin transfer molding technology is vacuum-assisted resin transfer molding (VARTM), a process in which the resin is "pulled" by vacuum into the mold - rather than injected - as a means of fiber wetting. The VARTM process ensures complete wetout of the fiberglass mat, infusing it with the polyurethane resin to eliminate dry spots that can cause defects.
One major advantage of using polyurethane resin in the RTM and VARTM processes is that it offers improved physical properties compared with other resins such as unsaturated polyester or vinylester. In fact, the strength and stiffness properties of polyurethane are greater than those of polyester resins. Polyurethane resin is also a more environmentally friendly alternative to other types of resins such as polyester, which contains VOC-emitting styrene as well as peroxide catalysts that require energy-consuming refrigeration.
The superior toughness of composite parts manufactured using polyurethane in the RTM and VARTM processes has opened the technology up to completely new markets, including ballistics and sporting goods applications.