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By Nancy B. Solomon, AIA

Case study: biobased components

The University of Delaware’s Affordable Composites from Renewable Sources (ACRES) Group, led by Chemical Engineering Professor Richard P. Wool, has been experimenting with biobased structural composites to address an eclectic mixture of political, environmental, and construction concerns. The multidisciplinary program, a collaborative effort among the university’s Center for Composite Materials, Department of Chemical Engineering, and College of Agriculture, has been supported by grants from a variety of sources—including the National Science Foundation, the Environmental Protection Agency, and the U.S. Department of Energy.

 

An All-Natural Roof The University of Delaware’s Affordable Composites from Renewable Sources Group asked industrial designer Elizabeth Linstrom to design a prototype for a nonrectilinear roof, using a composite material made of polymer resin and fiber. Not yet all-natural, engineers are developing a biobased foam from soy oil to replace the commercially available foam. Image: Courtesy Elizabeth Linstrom/ACRES

A composite material consists, essentially, of polymer resin and fiber. The resin is the “glue” that holds the reinforcing fiber together. Most composite structures contain phenolic, epoxy, or polyester resins reinforced with glass, carbon, or aramid fibers. Although these formulations can be very strong, they are also expensive and rely heavily on nonrenewable resources: petroleum is a major component of the resins, and lots of energy is consumed in the production of the fibers.

The ACRES Group (www.ccm.udel.edu/research/acres/) has experimented with different types of resins and fibers that are formulated largely from plant sources. Such renewable raw ingredients are readily available and affordable—they reduce our dependency on fossil fuels, they are often obtained from materials that would otherwise be discarded as waste, and depending on the particular application, they are potentially recyclable or biodegradable.

While the initial ingredients sound low-tech, the science is not: “We are combining advances in biotechnology with polymer science to come up with remarkable materials,” says Wool. And the steps required to move from material formulation to commercially available building component are lengthy and complex. Wool and his colleagues initially developed a resin based on soybean oil. Although the polymer is not completely petroleum-free—it includes styrene, which is derived from the fossil fuel—the researchers determined the optimum amount of styrene for this application. And other research is now looking for a biomaterial substitute for the styrene. The team then studied different fibers—including flax, recycled paper, jute, hemp, and even chicken feathers. Fiber mats were infused with the soybean resin using vacuum-molding technology. The resulting composite sheets underwent further testing.

Subsequently, prototypical composite structures were fabricated and tested. The inner core of each beam consisted of commercially available closed-cell polyisocyanurate foam. Although not a biobased material, the foam is lightweight and provides excellent thermal insulation. The ACRES group is carrying out research on developing biobased foam from soy oil to replace the current commercially available foam. The component skin of each beam varied: Some relied on a single type of fiber, others on two fibers in combination. All were infused with the soybean resin and affixed to the foam with the same vacuum process.