Short and Long Fibers
Access to short fiber biobased byproducts for non-structural or semi-structural components is commercially plentiful, coming from leafy plants such as sisal, abaca, sunflower hull, rice hull, coconut husk and more. A ready, affordable supply of long fiber byproduct or “bast” for structural composites is less so. “These materials, which are derived from the stalk or bark of a plant, provide the reinforcing fiber characteristics that are valuable for structural composites,” says Ulven.
Jute, flax and, in Europe, hemp, are the dominant long fiber sources currently in play. Growing hemp has long been banned in the U.S., but the USDA’s 2014 farm bill allows state agriculture departments, colleges and universities to grow hemp for academic or agricultural research purposes in states where industrial hemp farming is legal. “The future may open up for hemp, but right now there is only one U.S. approved vendor,” says Gradient Engineering’s Riddle. For commercial applications, hemp must currently be sourced from Canada or overseas.
RheTech Inc. in Whitmore Lake, Mich., began compounding and distributing its RheVision® line of bio-fiber reinforced polypropylene in 2006. “We quickly branched into a range of natural fibers for a more complete product line, including agave fiber, ground coconut shell, rice hull and husk, flax fiber and wood fiber,” says Jim Preston, vice president of business development. “We’re supplying the Ford Motor Co. with a combination of ground rice hulls and polypropylene. When we’re replacing a glass-filled polypropylene, we are primarily using flax filler, substituting a non-renewable with a renewable resource.”
RheTech is also starting to work with hemp. “In the long term, it will help us be more competitive with glass fiber systems,” says Preston. “Right now, we’re importing hemp from Saskatchewan for research purposes, but transportation costs are an obstacle to commercialization.”
Earlier this year, Gradient Engineering established a spin-off company, SunStrand, to develop and distribute bamboo fiber reinforcing products for polymer composites. When planted in the proper environment, Riddle says, bamboo requires almost no pesticides, fertilizers or additional watering. He adds it can sequester up to 70 percent more carbon per year than hardwood forest and can be harvested without the need to replant. “Bamboo fibers have been underrepresented in this market,” says Riddle. “It has antimicrobial properties which will make it a good fit for medical and sanitary applications. Plus, there is an infrastructure already in place to support it so that there are minimal sourcing issues.”