Wood can be hewn, sawed, bored, and planed. It can also be fractionated – which means splitting it into its chemical components of lignin, cellulose, and hemicellulose.
These compounds are tightly locked together. Together, they give trees the strength to stand tall. Separately, some of them are used to make:
- Paper, rayon, and cellophane;
- Food additives, including emulsifiers, stabilizers, and binders;
- Industrial chemicals;
- Cellulosic nanocrystals, transparent wood composites, and other materials of the future.
Before any of these products can be made, the bonds between the lignin and the other compounds must be broken. Breaking these bonds – dissolving a tree trunk, essentially – is not easy.
USDA Forest Service emeritus researcher Chung-Yun Hse has dedicated his career to developing new fractionation methods and other processes. Hse researches numerous aspects of materials science, a discipline that uses forestry, physics, chemistry, and engineering. He has contributed to more than a hundred research papers.
Hse’s research is an important step towards identifying new industrial processes that produce less waste, use fewer chemicals, and can add value to small trees that have few commercial uses. Thinning small trees to reduce fire risk or to restore open forests is a common management goal.
“Currently, pre-commercial thinning is just an expense to landowners,” says Dana Mitchell, SRS scientist and project leader. “Sometimes small trees and unmarketable biomass are just piled and burned.” Hse’s research is helping to develop commercial uses for this supply of wood.
Breaking the bonds between and within the chemical components of wood has many steps. The wood is usually chipped and treated with acid and heat. Hse and his colleagues are developing a process that does not require acid. They are also experimenting with different types of acid catalysts and with acids that can be captured and re-crystallized to use again and again.
Developing methods that do not yield harmful waste products is one of Hse’s goals. He is constantly seeking to improve older processes. For example, the Kraft process that is used to produce paper requires a lot of water, and the waste can be smelly. Hse has published numerous papers on using microwave digesters – which are very energy efficient – to break wood down.
Much of Hse’s work involves extracting useful substances from wood, like cellulose nanocrystals. Methyl levulinate is a compound that can be used in medicine, as a fuel additive, and for many other purposes. Hse and his colleagues showed how methyl levulinate can be produced with bamboo and other woody species. Methyl levulinate can also be produced from poplar wood, as Hse and his colleagues showed.
Hse’s research takes place at small scales. For example, the methyl levulinate study used 10 grams (less than the weight of a toothbrush) of poplar sawdust in each run. “This research focuses more on knowledge discovery,” says Mitchell. Scaling up the research will be someone else’s project. However, Hse’s contributions are making future changes to industrial processes possible.
Hse has also researched composite products such as plywood. Wood composites are often stronger than natural wood. Composites can be made from small trees, invasive species, overgrown forests that need to be thinned, or other biomass.
Hse has conducted research at SRS for more than 50 years. During his time with SRS, Hse has won many awards, successfully filed for patents, maintained scholarly international collaborations, and worked with more than 50 international students.