Researchers at the SUNY College of Environmental Science and Forestry (ESF) in Syracuse, N.Y. are using cellulose from wood to strengthen plastics. An ounce of cellulose nanocrystal from wood and other biologically derived materials added to a pound of plastic can reportedly increase strength by a factor of 3,000. The process will provide another use for the one billion tons of biomass (biologically derived material) produced annually in the U.S., according to an estimate from the U.S. Departments of Energy and Agriculture. "All plant materials ranging from trees and willow shrubs to orange pulp and pomace left behind during apple cider production contain at least 25% cellulose," explains William T. Winter, ESF chemistry professor and director of the Cellulose Research Institute. "Wood from trees is a little higher, between 40 and 50%."
The key is to pull nanocrystals of cellulose from the biomass, Winter says. "An ounce of such crystals added to a pound of plastic can increase its strength by a factor of 3,000. And in the end, the biodegradable cellulose particles take less than 90 days to break down into carbon dioxide and water in the landfill."
The process first purifies the cellulose by removing substances such as wax and gluey lignin from the biomass. The cellulose then goes through a homogenizing process, similar that used for dairy products. The cellulose is shredded into nanocrystals under high pressure, producing a viscous, white liquid. This liquid goes into a microcompounder, where it mixes with plastic under high pressure. The unit produces a cord or ribbon, depending on the die being used to shape it, of crystal-reinforced plastic.
Additionally, the nanocrystals can be used in ceramics and biomedical applications such as artificial joints and disposable medical equipment. Using cellulosic nanocrystals to strengthen plastics has advantages over conventional glass reinforcement: Glass is heavier, harder on processing machinery and therefore more expensive to work with, and it stays in the ground for centuries.
Current work is on refining the nanocrystal surfaces so they adhere better to the plastic and disburse more easily. In the future, Winter says, the process could be tied to the production of cellulosic ethanol. When hemicellulose is removed from wood for fermentation into ethanol, it leaves behind cellulose. This byproduct can in turn be treated with enzymes and reduced to the nanocrystals and thus would significantly reduce the cost of producing ethanol.
The Departments of Agriculture and Energy and Environmental Protection Agency, and Eastman Chemical Co. supplied funding for this research.This article appeared in the December issue of the Materials Monthly e-mail newsletter. If you enjoyed this article and would like to read similar articles sign up today for our free e-mail newsletters!