The tennis player wipes the sweat from her forehead and shakes it from the back of her hand. She bounces the tennis ball once, twice, three times, before tossing it up, squinting, and thwack. The ball is propelled forward at 130 miles per hour.
Her high-speed serve is made possible by a fiber-reinforced polymer (FRP) – the tennis racket. Strong, yet lightweight and maneuverable, it has a frame of graphite and a string grid pattern of plastic resin.
The racket will serve the tennis player well, but when the paint has chipped off the frame, and it has been strung and re-strung, it will become just another dingy piece of garbage in another landfill.
Prof. Anil Netravali, fiber science & apparel design, wants to keep the growing amount of FRPs, also known as fiber reinforced plastics or composites, out of landfills because “that landfill is essentially useless for any other application or use,” Netravali said.
FRPs are non-biodegradable, and by definition, they consist of two or more dissimilar materials and are thus difficult to reuse or recycle. Exacerbating their environmental impact is the fact that conventional FRPs are manufactured using petroleum-derived fibers and resins.
As an alternative, Netravali has been working since the mid-1990s to develop fully biodegradable green composites using fibers and resins derived from annual (yearly renewable) plants –– as opposed to petroleum, a non-renewable resource.
His goal is for the manufacturing process to be carbon neutral and for the composite to be composted, producing nutrient-rich soils to grow the very plants that are the sources of the fibers and resins. Netravali’s process is also strictly water-based, using water as the solvent rather than any toxic or carcinogenic chemicals, which pollute the water supply and air (when trash is burned).
Annual plants, unlike wood, are continually available. Oak trees, or any other large plant, need to grow for 25 years before they can be harvested to manufacture products such as furniture. Wood furniture is commonly a piece of particle board –– wood flour blended into a formaldehyde-based resin –– with a veneer coating.
The formaldehyde is a known carcinogen and non-biodegradable, and even the wood takes a long time to biodegrade in the anaerobic conditions of a landfill. Although reuse is an option, it is not as cost-effective as simply purchasing a new piece of furniture. According to Netravali, 94 percent of composites end up in landfills. His green composite alternative to particle board uses fiber from annual plants instead of wood, and soybean or starch resin instead of formaldehyde resin.
Soybeans, like many other plants, are primarily harvested for food. When the lipids have been extracted from the soybeans to produce oil, a defatted soy flour containing proteins and sugars is left. The proteins can be used to make green composites and nanofibers, while the sugars are fed to the Acetobacter bacteria, which excrete cellulose fibers.
Nanofibers filters have personal, residential, and automotive applications, and the meshlike bacterial cellulose has a variety of biomedical applications. It can be used as temporary skin for burn victims, in wound healing, and for tissue scaffolding. The treatment process is pain-free, eliminates dressing changes, and is “almost natural, almost original,” Netravali said.
Currently, FRPs are used in the civil and structural, transportation, medical, aerospace, sports, and electronics sectors, all of which can be greenified. Green composites are already in use in the areas of green building, medical treatments and ballistics.