Researcher looks

Erin Ghere

The newsprint on which these words appear will not survive the recycling process well. But thanks to the research of one former University student, someday it might.
Bangji Cao, who earned his Ph.D. at the University two years ago in paper science, concluded that paper’s chemical makeup determines its ability to sustain the recycling process.
Cao’s research, which he completed as he was finishing his degree, was published in the December 1998 issue of the Technical Association of the Pulp and Paper Industry Journal. Cao now works for Voith Sulzer Paper Technology in Appleton, Wis.
“We asked the question of what part of the paper is more important in recycling,” said Ulrike Tschirner, co-adviser of the project and an associate professor in the Department of Wood and Paper Science.
Cao experimented by changing in paper pulp the amounts of substances that naturally occur in wood. He then subjected the altered paper to the recycling process as many as five times.
His conclusion: Paper which contains more hemicellulose — a small molecule that is contained in natural wood fibers but is vulnerable to the recycling process — is stronger and longer lasting through repeated recycling.
“He correlated recycling properties with chemical properties,” said Shri Ramaswamy, co-adviser of the project and an associate professor in the Department of Wood and Paper Science.
Wood contains two naturally occurring substances important to the pulping process: lignin and hemicellulose.
Lignin, an organic substance that binds wood fibers and causes its brown color, is removed from the wood in chemical pulping as it causes paper to yellow. In mechanical pulping it is left in the mix.
But as lignin is removed, amounts of hemicellulose are significantly reduced — a process that eventually weakens paper as it is recycled.
Hemicellulose is essential for strength, but it also allows the fibers to retain their flexibility. This allows the paper to withstand the recycling process while better retaining its properties.
“If paper is recycled several times, you lose quality,” Tschirner said.
With higher levels of hemicellulose in paper, the paper would be more durable through numerous recycling processes, according to Cao’s research.
Although this research is new, Tschirner said she does not think the development will change the paper recycling industry immediately.
“It has helped to understand the (paper’s) mechanisms better,” she said.
Follow-up research needs to determine what can be done with the new knowledge, she added.
Changes in the pulping process to better retain hemicellulose and discovering ways to create it chemically are all possible future developments, Ramaswamy said.