Last year, as a junior mechanical engineering student at Brigham Young University (BYU), Alex Stiles, and two of his classmates, Steve Gardner and Roger Smith, took home second prize in the Society for the Advancement of Material and Process Engineering (SAMPE) Bridge Contest. This March, Stiles, who has since transferred to the Illinois Institute of Technology, was also honored with Cali Bamboo’s Project of the Month prize.
Before the competition, Stiles had worked with bamboo to build a laminate cardboard desk. He was impressed by its strength and began investigating its use for other applications. He applied for a university research grant to research creating a commercially viable natural fiber composite, which he received.
According to Stiles, bamboo is a promising material for a number of reasons. It’s plentiful and easy to grow. It’s also strong, recognizable to consumers as “green” and at $0.25 to $1 a pound, the raw material is competitive with fiberglass and much cheaper than carbon.
Bamboo hasn’t been researched as much as other natural fibers for composites, in part because its fibers are difficult to extract, Stiles says. That was one of the biggest challenges his team faced in creating the bamboo composite for its bridge. The strongest parts of any plant are its cellulose fibers he explains, and it was those fibers the team extracted to create its composite.
Stiles started with bamboo matting made by Cali Bamboo, which he tore apart and processed with an alkaline treatment. He machine-rolled the strips using a rolling mill, then washed them to separate them into fiber bundles.
“That’s really as far treated as I wanted to get them,” Stiles says. “There’s some research that shows that if you chemically process bamboo to the point where you end up with just pure cellulose, the fibers are actually weaker.”
To maximize the strength of the beams for the bridge, he used a hand roller to align the fibers unidirectionally in aluminum sheet-metal molds, a process he describes as very time consuming and labor-intensive.
Stiles mixed the unidirectional mats with an epoxy resin the lab kept in stock, but found the mats would break apart in a traditional wet layup. Most unidirectional mats come pre-impregnated, but because Stiles had fashioned his own, he had to improvise. To make his own prepreg, he mixed a slow cure resin with the unidirectional mats and stuck the mixture in a compression molder at 180° F for five minutes.