Innovations

Traditional Polyurethane Technologies

The demands of the marketplace to meet ever higher end-use application requirements are driving the development of new material formulations and process technologies. As a result, use of reaction injection molding is growing rapidly, particularly in the composites market.

Rigid Polyurethane Structural Foams
An OEM’s desire to utilize renewable resources in the production of body panels was made possible with a polyurethane structural foam from Bayer MaterialScience. The polyurethane is made with a polyol produced partly from soybeans rather than entirely from oil and natural gas. John Deere used the soybean-based polyurethane RIM material to mold the roof, rear shield and door of its STS harvester combines. Expanded use of soybean-based polyurethanes is expected in other applications.
Solid Elastomer Systems
High-heat polyurea systems have been developed that offer typical performance characteristics of polyurethane but with the added capability to handle higher-heat requirements. These new polyurea systems can easily withstand 400¡F. These new high-heat systems have been used with short mineral fillers to make large automotive body panels that are assembled to the metal chassis of vehicles and go through the E-coat painting lines. Body panels of the GMC Denali pickup truck have used high-heat polyurea RIM systems from Bayer MaterialScience. High-heat polyurea systems have also been used to produce engine enclosures and hoods for non-automotive vehicles.
Structural RIM (SRIM) Composites
Often, SRIM is called a two-step process: the operator places a preformed glass fiber mat into the open mold the mold is closed and the polyurethane resin is injected into the mold, where it permeates and surrounds the glass fiber mat to form the part The traditional SRIM process uses either fiberglass preforms or directional or non-directional mats as inserts in the mold cavity through which the polyurethane is injected. Recent developments in foamed polyurethane SRIM systems include lower-viscosity, better-flowing polyurethane systems that allow processors to make larger, lighter composite parts for applications varying from automotive door liners to marine plywood replacement products to heavy-duty truck interiors. Vinyl and fabric outer skins are often vacuum-formed into the mold cavity prior to inserting the glass mat and injecting or open-pouring the SRIM system into the mold. The result is a highly aesthetic, lightweight, structural part ready for the assembly line after a trimming operation. Foamed polyurethane SRIM is also moving into new applications based on the development of new, longer gel time and better flowing polyurethanes. An HVAC enclosure for a Caterpillar front loader used a vinyl outer skin that was vacuum-formed in the mold cavity prior to inserting the glass mat and injecting the polyurethane SRIM system. The final part was 50 percent lighter than an RTM composite part and provides significant cost savings. Foamed polyurethane SRIM opens up new possibilities for designers and composite fabricators. The chart below shows a plot of flexural modulus versus density for polyurethane SRIM and traditional plastics and composites. The foamed SRIM composites offer the same stiffness with a 20-40 percent lower density. Foamed polyurethane SRIM is being used for applications such as automotive door liners, furniture and marine plywood replacement.