From: Associated Press
Published October 23, 2006 12:00 AM

Scientists Say Wood Makes Plastic Stronger

SYRACUSE, N.Y. -- Scientists at the State University of New York's College of Environmental Science and Forestry are developing a way to add wood fiber to plastic to make it stronger.


The process focuses on extracting nanocrystals of cellulose out of woody materials, like trees and willow shrubs, and mixing them with the plastic.


The eventual result will be strong, lightweight plastics that would degrade in a landfill, said William Winter, a chemistry professor and director of the college's Cellulose Research Institute, where the process is being developed.


"By adding an ounce of crystals to a pound of plastic, you can increase the strength of the plastic by a factor of 3,000," Winter said. "And in the end, in a landfill, it's just carbon dioxide and water, which can be taken up and made into more biomass."


In addition their use as strengtheners in plastics, the nanocrystals can be used in ceramics and in biomedical applications such as artificial joints and disposable medical equipment, Winter said.


"All plant materials contain a minimum of 25 percent cellulose," Winter said. "Wood from trees is a little higher, between 40 percent and 50 percent."


Using cellulosic nanocrystals to strengthen plastics has advantages over the glass that is often used. Glass is heavier, harder on processing machinery and therefore more expensive to work with, and it stays in the ground for centuries.


The cellulose nanocrystals will break down in a landfill in less than 90 days, he said.


Winter and his team work with a reactor that can process up to 500 grams _ about a pound _ of material at a time. That is a significant increase over the 5-gram quantities that are typically used in laboratory settings.


First, the scientists purify the cellulose to remove substances such as wax and gluey lignin. The cellulose then goes through a homogenizing process, similar to the one used with dairy products. The cellulose is shredded into tiny particles under high pressure, producing nanocrystals _ which are measured in billionths of a meter.


A viscous, white liquid is produced that goes into a microcompounder, where it is mixed with plastic under high pressure.


Winter's team is currently working on refining the surface of the crystals so they adhere better to the plastic and disbursing the crystals throughout the material to achieve the best results.


The next step will be to scale the process up to a commercial level, he said.


Source: Associated Press


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