The stubborn polymer assortment of aromatic alcohols known as lignin continues to be a key factor limiting the efficiency of pulp and paper production. Although it gives physical strength to wood at the cellular level, lignin must be removed to produce secondary products such as paper or biofuel. The necessary processes demand harsh solvents and chemicals and yield a great deal of waste, which is good for little more than burning.
Shawn Mansfield, a professor of wood science at the University of British Columbia, has spent most of his academic career looking at ways of tackling this problem. Rather than trying to develop more sophisticated enzymes to break down the lignin with less waste, he has considered an even more fundamental approach — modify it in plants. So Mansfield and his colleagues are looking at ways of building better trees to reduce lignin, which would decrease chemical use.
The poplar tree’s relative strength and fast growth make it a key commodity for the pulp and paper industry. Photo credit: Crusier.
A potential solution, Mansfield says, lies with manipulating trees so that they create ester rather than ether molecular bonds, which form the complex linkages that create the backbone of lignin molecules. “Ester linkages are much more chemically labile than the ether linkages. It requires only a mild chemical treatment to get the lignin to fall apart.” Some plants have genes that naturally produce ester-linked conjugates that could act as monolignols, the building blocks of the lignin polymer, during Making short work of long lignin molecules in pulp Na tural Resources lignin polymerization. “So now we’re trying to use biotechnology to overcome the yield penalties with some of the natural varieties that exist,” Mansfield says.
The focal point for this work is poplar trees — widely used for paper production — which grow quickly and thrive in Canada. More importantly, this tree’s genome has been fully sequenced, offering many unique insights into its biology. Mansfield has been collaborating on this work with members of the University of Wisconsin-Madison and Michigan State University through the Great Lakes Bioenergy Research Center. In a recent Science article, the group outlined how they engineered poplar trees with the altered lignin backbone for easier processing.
Mansfield acknowledges that these transgenic products may be unsettling to people who are suspicious of genetically modified crops (GMOs) but adds that the economic and environmental benefits associated with these products are hard to ignore. Moreover, competitors in several other countries, most notably Brazil, have already embraced genetic and advanced breeding strategies for identifying the best trees to meet the short fibre needs of paper production. “They have genotypes that go into toilet paper or fine paper,” says Mansfield. Such advanced strategies will impact the future of the short-fibre industry in Canada and “ultimately influence any competitive advantages we have,” he adds.