ORNL’s tough new plastic is made with 50 percent renewable content from biomass.
OAK RIDGE, US: Your car’s bumper is probably made of a mouldable thermoplastic polymer called ABS, shorthand for its acrylonitrile, butadiene and styrene components. Light, strong and tough, it is also the stuff of ventilation pipes, protective headgear, kitchen appliances, Lego bricks and many other consumer products. Useful as it is, one of its drawbacks is that it is made using chemicals derived from petroleum.
Now, researchers at the Department of Energy’s Oak Ridge National Laboratory (ORNL) have made a better thermoplastic by replacing styrene with lignin, a brittle, rigid polymer that, with cellulose, forms the woody cell walls of plants. In doing so, they have invented a solvent-free production process that interconnects equal parts of nanoscale lignin dispersed in a synthetic rubber matrix to produce a meltable, mouldable, ductile material that’s at least ten times tougher than ABS. The resulting thermoplastic—called ABL for acrylonitrile, butadiene, lignin—is recyclable, as it can be melted three times and still perform well.
This research is published in the journal Advanced Functional Materials.
“The new thermoplastic has better performance than commodity
plastics like ABS,” said senior author Amit Naskar in ORNL’s materials science and technology division, who along with co-inventor Chau Tran has filed a patent application for the process to make the new material. “We can call it a green product because 50 percent of its content is renewable and technology to enable its commercial exploitation would reduce the need for petrochemicals.”
The technology could make use of the lignin-rich biomass byproduct stream from biorefineries and pulp and paper mills. With the prices of natural gas and oil dropping, renewable fuels can’t compete with fossil fuels, so biorefineries are exploring options for developing other economically viable products. Among cellulose, hemicellulose and lignin, the major structural constituents of plants, lignin is the most commercially underutilized. The study aimed to use it to produce, with an eye toward commercialization, a renewable thermoplastic with properties rivaling those of current petroleum-derived alternatives.
To produce an energy-efficient method of synthesizing and extruding high-performance thermoplastic elastomers based on lignin, the ORNL team needed to answer several questions.
“Lignin is a brittle natural polymer, so it needs to be toughened,” said Naskar, leader of ORNL’s Carbon and Composites group. A major goal of the group is producing industrial polymers that are strong and tough enough to be deformed without fracturing. “We need to chemically combine soft matter with lignin. That soft matrix would be ductile so that it can be malleable or stretchable. Very rigid lignin segments would offer resistance to deformation and thus provide stiffness.”
All lignins are not equal in terms of heat stability. To determine what type would make the best thermoplastic feedstock, the scientists evaluated lignin from wheat straw, softwoods like pine and hardwoods like oak. They found hardwood lignin is the most thermally stable, and some types of softwood lignins are also melt-stable.
Next, the researchers needed to couple the lignin with soft matter. Chemists typically accomplish this by synthesizing polymers in the presence of solvents. Because lignin and a synthetic rubber containing acrylonitrile and butadiene, called nitrile rubber, both have chemical groups in which electrons are unequally distributed and therefore likely to interact, Naskar and Chau Tran (who performed melt-mixing and characterization experiments) instead tried to couple the two in a melted phase without solvents.
Future studies will explore different feedstocks, particularly those from biorefineries, and correlations among processing conditions, material structure and performance. Investigations are also planned to study the performance of ORNL’s new thermoplastic in carbon-fibre-reinforced composites.
“More renewable materials will probably be used in the future,” Naskar said. “I’m glad that we could continue work in renewable materials, not only for automotive applications but even for commodity usage.”
© ORNL News
Read more on Plastics:
Scientists make renewable plastic from carbon dioxide, plants