The first step is finding the right fibers. For composites taking on structural loads, “we want fibers on the longer side (i.e. high aspect ratio of fiber length to diameter) with good chemical properties and tensile strength,” says Choo-Smith. “We tend to focus on flax and hemp because they fit these requirements, grow well in our prairie regions, and we have a good amount of it.”
In choosing a fiber, CIC staff look at how well a plant goes through the decortication process, which separates the fibers from the hurd (the woody or pulpy matter of the plant). Fibers with more hurd can’t be used for higher end applications like textiles. CIC tests the fiber’s tensile strength, its moisture uptake and its behavior with various resins. “If there is a nice affinity between resin and fiber, then there is a good chance that it will stick well to the fiber, which is known as wet-out,” says Choo-Smith. “If it doesn’t, we may need to treat the fiber with chemicals to change the surface properties.”
One benefit of biofibers is that they come from a renewable resource, but that also makes them more heterogeneous in the way that they behave. Synthetic fibers produced in a factory are very consistent. But bio-based fibers may change with growing conditions; if there’s more or less rain in the summer, what happens to the quality of the product? Choo-Smith notes that winemakers have overcome a similar dilemma by blending various harvests, and the same could be done with biofibers.
CIC staff hope to provide an economic boost to rural communities by making better use of the parts of crops that are otherwise composted or burned. But the conditions ideal for food production may not be the best for producing composite fibers. For example, spacing flax plants close together results in narrower stems and finer fibers, which is ideal for some end-use applications in composites. But farmers prefer wider spacing, since they produce more seed that way. If the demand for biocomposites grows and the economics are right, farmers may be willing to adjust their growing patterns to the industry’s needs.
Resins from Plants
Dixie Chemical of Pasadena, Texas, has been working with bio-based materials for their resins since 2011. Alejandrina Campanella, the company’s thermoset and bio-based material platform leader, says it’s easier to work with plant oils, which are fairly consistent in their performance, than with biofibers, which can vary with environmental conditions.